Copyright 2014, Ruvini Mathangadeera

EVALUATING THE IMPACT OF FIBER PROCESSING ON COTTON FIBER

TENSILE PROPERTIES

by

Ruvini Mathangadeera, B. Sc.

A Thesis

In

PLANT AND SOIL SCIENCE

Submitted to the Graduate Faculty

of Texas Tech University in

Partial Fulfillment of

the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

Dr. Eric Hequet

Chair of Committee

Dr. Noureddine Abidi

Dr. John Wanjura

Mark Sheridan

Dean of the Graduate School

December, 2014

Copyright 2014, Ruvini Mathangadeera

Texas Tech University, Ruvini Mathangadeera, December 2014

ii

ACKNOWLEDGEMENTS

First and foremost I wish to express my most sincere gratitude to my advisor, Dr. Eric

Hequet, for his inspiring supervision and untiring guidance throughout the research study

and the graduate program. I am also greatly indebted to the members of my advisory

committee, Dr. Noureddine Abidi and Dr. John Wanjura for their support and guidance.

I would also like to thank the entire staff at the Fiber and Biopolymer Research Institute

for their kind assistance throughout my research study. Special thanks go to Brendan

Kelly, who is always willing to share his valuable ideas and knowledge with his

colleagues. I gratefully acknowledge all my friends at the Fiber and Biopolymer Research

Institute, Addissu Ayele, Kolby Mccormick, Suman Lamichhane, Roji Manandhar,

Deepika Mishra and all the friends at the Biopolymer lab for their help and friendship.

I am grateful to Cotton Incorporated for providing financial support for this research.

My sincere thanks also go to Sankalya Ambagaspitiya and all the Sri Lankan friends at

Lubbock for their invaluable assistance during my stay here. Finally, a warm and special

word of thanks goes to my parents and my brother for their unconditional encouragement

and emotional support.


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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ................................................................................................ ii

ABSTRACT……………………………………………………………………………….v

LIST OF TABLES……………………………………………………………………….vii

LIST OF FIGURES……………………………………………………………………..viii

1. LITERATURE REVIEW ............................................................................................... 1

1.1 Tensile Properties of Cotton Fibers ........................................................................... 1

1.2 Relationship between Single Fiber and Fiber Bundle Tensile Properties

of Cotton ................................................................................................................... 7

1.3 Impact of Fiber Processing on Cotton Fiber Tensile Properties ............................. 10

1.4 Cotton Fiber Elongation and its Importance ........................................................... 13

2. EVALUATING THE RELATIONSHIPS BETWEEN TENSILE PROPERTIES

OF SINGLE FIBERS AND FIBER BUNDLES OF COTTON .................................. 24

2.1 Introduction ............................................................................................................. 24

2.2 Objectives ................................................................................................................ 31

2.3 Materials and Methods ............................................................................................ 31

2.4 Results and Discussion ............................................................................................ 33

2.5 Conclusion ............................................................................................................... 46

3. EVALUATING THE IMPACT OF FIBER PROCESSING ON TENSILE

PROPERTIES OF COTTON FIBERS......................................................................... 49

3.1 Introduction ............................................................................................................. 49


iv

3.2 Objectives ................................................................................................................ 53



3.5 Conclusion ............................................................................................................... 72

4. EVALUATING THE IMPORTANCE OF COTTON FIBER ELONGATION IN

TERMS OF FIBER PROCESSING ............................................................................. 74

4.1 Introduction ............................................................................................................. 74

4.2 Hypotheses .............................................................................................................. 77

4.3 Objectives ................................................................................................................ 79



4.6 Conclusion ............................................................................................................. 106

5. SUMMARY AND CONCLUSION………………………………………………....109

REFERENCES ............................................................................................................... 112


v

ABSTRACT

Cotton fiber tensile properties impact the processing performance of the fibers and the

quality of the final product. Among the main tensile properties, fiber strength is

considered as the dominant tensile property while fiber elongation has generally been

neglected. The presence of a negative correlation between bundle tenacity and elongation

is a main reason for the lack of interest in elongation. In this study, a positive correlation

was detected between individual fiber strength and elongation measured by FAVIMAT,

whereas negative correlations were observed between bundle tenacity and elongation

measured by both Stelometer and HVI. The negative relationship between bundle

tenacity and elongation can be explained by the variation in individual fiber elongation of

the constituent fibers of a bundle.

Impact of fiber processing on the tensile properties was assessed employing two levels of

processing, namely light processing and aggressive processing. Light processing does not

cause enough fiber breakage to reveal an impact of processing. Yet, during aggressive

processing higher elongation fibers tend to show better performance. Therefore, with the

increasing processing speeds in the textile industry, the importance of elongation will be

more prominent.

The importance of elongation suggested at the earlier stages of the study, was further

assessed employing samples which represented a wide range in elongation. All other

fiber properties except elongation were constant within a family. The results indicated the

better performance of higher elongation fibers. Thus, in order to achieve better processing


vi

performance of fibers, elongation should be given more consideration in the breeding

programs.


vii

LIST OF TABLES

2.1 Descriptive statistics of the FAVIMAT and HVI tensile measurements of

the 30 samples selected for the experiment……………………………………….32

2.2 Average tensile property measurements of the three calibration cottons

used in the Stelometer……………………………………………………………..33

2.3 Descriptive statistics of the Stelometer tensile measurements of the

30 samples…………………………………………………………………………34

3.1 Mean tensile property measurements of the selected samples for stage I

(measured by FAVIMAT)……………………………………...………………….54

3.2 Mean AFIS fiber properties of the selected samples for stage I…………………..54

4.1 Mean tensile property measurements of each group for the raw stage…………....81

4.2 Student’s t-test ranking of difference between raw and processed cotton in

mean elongation-at-break of the 32 samples………………………………………86

4.3 Mean separation of difference between raw and processed cotton in

mean elongation-at-break of the two families……………………………………..87


mean force-to-break of the 32 samples…………………………………………….89


mean work-to-break of the 32 samples…………………………………………….91


viii

LIST OF FIGURES

1.1 Cotton fiber force-elongation curve………………………………………………...2

1.2 Relationships between crystallinity and tensile properties of native

Egyptian cotton (Hindeleh, 1980)………………………………………………….21

2.1 Stelometer………………………………………………………………………….26

2.2 Components of the Stelometer……………………………………………………..27

2.3 High Volume Instrument (HVI)…………………………………………………...29

2.4 FAVIMAT…………………………………………………………………………30

2.5 Relationship between tenacity and elongation determined by Stelometer………...35

2.6 Relationship between strength and elongation determined by HVI……………….36

2.7 Relationship between force-to-break and elongation-at-break determined

by FAVIMAT……………………………………………………………………...37

2.8 Relationship between FAVIMAT elongation and the standard deviation of

FAVIMAT elongation……………………………………………………………..40

2.9 Relationship between Stelometer elongation and FAVIMAT elongation………….41

2.10 Relationship between HVI elongation and FAVIMAT elongation………………...42

2.11 Relationship between Stelometer elongation and HVI elongation…………………43

2.12 Relationship between Stelometer tenacity and FAVIMAT force-to-break………...44

2.13 Relationship between HVI strength and FAVIMAT force-to-break……………….45

2.14 Relationship between Stelometer tenacity and HVI strength………………………46

3.1 Advanced Fiber Information System (AFIS)……………………………………….51


ix

3.2 AFIS fiber individualizer………………………………………………………….52

3.3 Microdust and Trash Monitor (MTM)…………………………………………….53

3.4 Procedure for evaluating the impact of less aggressive (AFIS) processing……….56

3.5 Procedure for evaluating the impact of very aggressive (MTM) processing……...57

3.6 AFIS length distribution of sample 3643 in the 3 stages………………………….58

3.7 Mean elongation-at-break values of the 5 samples across the 3 stages…………...59

3.8 Mean force-to-break values of the 5 samples across the 3 stages………………....60

3.9 Mean work-to-break values of the 5 samples across the 3 stages…………………61

3.10 AFIS length distribution of sample 25 in the 3 stages……………………………..64

3.11 AFIS length distribution of sample 3552 in the 3 stages…………………………..64

3.12 AFIS length distribution of sample 3653 in the 3 stages…………………………..65

3.13 AFIS length distribution of sample 8 in the 3 stages………………………………66

3.14 AFIS length distribution of sample 25 at light and aggressive

processing stages…………………………………………......................................67

3.15 Mean force-to-break values of the 5 samples at the 2 processing stages…………..68

3.16 Mean elongation-at-break values of the 5 samples at the 2 processing stages…….69

3.17 Mean work-to-break values of the 5 samples at the 2 processing stages………….71

4.1 Micro Dust and Trash Analyzer 3 (MDTA 3)……………………………………..76

4.2 Cottonscope………………………………………………………………………..77

4.3 Hypothesized elongation-at-break distributions of the raw and

processed stages……………………………………………………………………78


x

4.4 The cotton samples selected for the experiment………………………………....80

4.5 AFIS length distributions of lower elongation group of family 1 in raw

and processed stages…………………………………………………………….83

4.6 Mean elongation-at-break values of the 8 groups for the two stages……………84

4.7 Mean force-to-break values of the 8 groups for the two stages………………….88

4.8 Mean work-to-break values of the 8 groups for the two stages………………….90

4.9 Elongation-at-break distributions of the 4 field replications of location A

of higher elongation group of family 1 at the raw stage…………………………..93

4.10 Elongation-at-break distributions of the two elongation groups of family 1

for both raw and processed stages………………………………………………..94

4.11 Elongation-at-break distributions of the two elongation groups of family 2


4.12 Force-to-break distributions of the two elongation groups of family 1


4.13 Force-to-break distributions of the two elongation groups of family 2


4.14 Work-to-break distributions of the two elongation groups of family 1


4.15 Work-to-break distributions of the two elongation groups of family 2

for both raw and processed stages……………………………………………….100

4.16 AFIS length distributions of the two elongation groups of family 1

at the raw stage…………………………………………………………………..101

4.17 AFIS length distributions of the two elongation groups of family 1

at the processed stage……………………………………………………………102


xi

4.18 Individual fiber force-elongation scatter plot of location A of higher

elongation group of family 1……………………………………………………104

4.19 Individual fiber force-elongation scatter plot of location A of lower

elongation group of family 1…………………………………………………….105

4.20 Individual fiber force-elongation scatter plot of location A of higher

elongation group of family 2…………………………………………………….105


1

CHAPTER I

LITERATURE REVIEW

1.1 Tensile Properties of Cotton Fibers

The mechanical properties of textile fibers describe the behavior of the fibers under

applied forces and deformations (Collier & Tortora, 2001). Tensile properties of textile

fibers are the most widely studied mechanical properties which define the responses of

the fibers to forces and deformations applied along the fiber axis. In addition, the tensile

properties of textile fibers are probably the most important properties, which contribute to

the performance of fibers during processing and the quality of the final product (Morton

& Hearle, 1993). Therefore, cotton fiber tensile properties are considered to be the

indicators of the tensile properties of the yarn and fabric.

Tensile strength is a measure of the tensile force required to break a fiber, which is

known as tenacity when it is expressed with respect to linear density. Tenacity is usually

measured in grams per tex (g/tex). Tenacity can be used for appropriately comparing

different types of fiber since linear density is used in its calculation. For instance, when

nylon and polyester fibers of the same diameter break under identical tensile forces, the

nylon fiber will have a higher tenacity because of its lower density (Collier & Tortora,

2001).

The primary constituent of cotton fibers is the natural polymer cellulose. It is known that

the rigidity of the cellulosic chains, the highly fibrillar and crystalline structure of

cellulose, and the extensive intermolecular and intramolecular hydrogen bonding are the

factors which contribute to the strength of cotton fibers. In addition, the molecular weight


2

of cellulose, the molecular weight distributions, and the reversal and convolution

structure of fibers also act as indicators of cotton fiber tensile properties. An increase in

average molecular weight usually results in an increase in tensile strength of cotton fibers

(Timpa & Ramey, 1994).

Elongation is the degree of stretching or lengthening of a fiber under a tensile force. Fiber

elongation is commonly measured as “elongation-at-break”, which is the amount of

stretch that can be endured by the fiber before it breaks. A fiber that will stretch or

elongate more prior to breakage will show greater “toughness”, or durability, than a

stiffer fiber which breaks at the same breaking load but at a lower elongation (Collier &

Tortora, 2001). Work of rupture or toughness is the energy needed to break the fiber. It is

equal to the area under the load-elongation curve, which displays the behavior of an

individual fiber under a gradually increasing applied force (Morton & Hearle, 1993).

Figure 1.1 Cotton fiber force-elongation curve


3

Both load-elongation and stress-strain curves possess the same shape while load-

elongation curves can be converted into stress-strain curves by changing units of the

tensile properties. Fiber modulus which is the ratio of stress to strain is defined by the

slope of the initial linear portion of the stress-strain or the load elongation curve. This

initial modulus represents the stiffness of a fiber. A stiffer fiber is characterized by a

higher initial modulus whereas a more flexible fiber is characterized by a lower initial

modulus.

As stated by Morton and Hearle (1993), the results of tensile experiments will be

impacted by the condition of the fibers, the arrangement and dimensions of the specimen,

and the nature and duration of the experiment. The history of the fiber, such as the

processes the fiber has undergone previously, its moisture content and temperature, are

factors which contribute to the condition of the fiber. All the above conditions must be

specified for the results of the tests to be of worth. When considering the dimensions of

the specimen, length and area of cross-section are important. In a variable material like

cotton fiber, there is a greater chance of presence of a very weak place in a long length

compared to a short length. As a fiber breaks at the weakest place, mean breaking load of

long lengths will be less than that of short ones. Therefore, it is necessary to state the

length of the tested specimen.

The elongation of a textile fiber is not just a function of the applied load. It also depends

on the length of time for which the present load and any previous loads have been

applied. The load required for fiber breakage will be different depending on the speed of

the tensile test. A higher breaking load will be required for a rapid test compared to a


4

slow one. Since the load is applied for a short period of time in a rapid test, it needs to be

higher to be great enough to cause fiber breakage. The nature of the experiment means

the manner in which the load is applied. The load can be applied by means of constant

rate of elongation, constant rate of loading, reduction from a higher load, or any other

sequence of events (Morton & Hearle, 1993).

Properties of a fiber, including strength and elongation, are affected by the arrangement

of its constituent polymer chains within the fiber. A random, disordered arrangement of

polymer chains gives rise to an amorphous region while ordered, parallel arrangement of

polymer chains results in a crystalline region within the fiber. The amorphous regions are

weaker than the crystalline regions (Collier & Tortora, 2001). Thus, crystalline regions

are known to be important for fiber strength whereas amorphous regions are known to be

important for fiber elongation.

Several different methods are used for measuring tensile properties of textile fibers

depending upon the end-use of the textile fabric to be evaluated (Grant et al., 1952).

Tensile properties of cotton fibers can be determined from single fiber tests or fiber

bundle tests. Single fiber tensile tests are time consuming and tedious. Thus, these are

considered to be unrealistic for large scale and industrial applications related to cotton,

and are widely being used for research purposes. Bundle tests are usually faster, and are

known to better predict yarn tensile properties since fiber bundle simulates the yarn.

Therefore, bundle tests are usually preferred over single fiber tensile tests. Yet, as stated

by Hsieh (1999) bundle strength measurement is not sensitive to strength variability.

Hence the measurement of single fiber strength is also necessary.


5

Another drawback associated with bundle tensile tests is that bundle tensile properties do

not always correlate well with individual fiber tensile properties. A fiber bundle

consisting of fine immature fibers could have higher bundle strength merely due to the

fact that it contains more fibers for a given weight. Accordingly a fiber bundle consisting

of coarse and mature fibers could have lower bundle strength as it contains fewer fibers

in a given weight. Therefore, fibers that may have been regarded as weak by individual

fiber tests have a probability of being considered as strong when subjected to bundle

tensile tests, except in extreme scenarios where fibers are extremely immature or mature.

Mantis and FAVIMAT are the main instruments used for individual fiber tensile property

testing. FAVIMAT has been primarily developed for man-made fiber testing. Unlike

man-made fibers cotton fibers possess higher within sample variability. Therefore, when

cotton fiber properties are determined with FAVIMAT a higher amount of fibers need to

be tested.

Both FAVIMAT and Mantis operate according to the principle of constant rate of

elongation. In general both instruments employ similar techniques to obtain

measurements. A single fiber is clamped at both ends between two sets of jaws. Then a

computer system controls fiber breakage and provides tensile property measurements and

force elongation curves. In Mantis, fibers are manually placed between clamps while this

process is automated in FAVIMAT. However, it can also be performed manually if

necessary. FAVIMAT also differs from Mantis by providing a linear density

measurement which is determined using vibroscopic technique. Even though FAVIMAT

fiber testing can be done at any gauge length from 2mm to 100mm, linear density can be


6

determined only at the 10mm gauge or higher gauge lengths. Furthermore, FAVIMAT

also measures fiber crimp which is not measured by Mantis.

Pressley and Stelometer are the conventional fiber strength testers used for the bundle

measurements. Stelometer is much preferred over Pressley since it provides an elongation

measurement in addition to strength. Gauge lengths of zero and 3.2 mm can be used with

Pressley while 3.2 mm gauge length is used with Stelometer. In both instruments linear

density is measured by weighing fiber bundles of known length. Nevertheless, use of

Pressley and Stelometer has become limited due to two main reasons; both testing

procedures are very slow owing to the time consuming sample preparation process and

the results could be influenced by the technique of the operator (Taylor, 1982).

Development of HVI has made it possible to perform bundle tensile tests more rapidly.

HVI provides both bundle strength and elongation measurements though it is not

currently calibrated for elongation. HVI as well as the Stelometer follows the same

principle of constant rate of elongation. The gauge length used in HVI is also 3.2mm. In

order to be tested with HVI, cotton samples need to be in their raw or unprocessed form.

In HVI, mass of the testing fiber specimen is not directly determined. It is indirectly

estimated with optical density and micronaire which is a time saving approach compared

to weighing the specimen. In contrast, when using the Stelometer and Pressley

instruments mass of the tested fiber bundle is also measured.


7

1.2 Relationship between Single Fiber and Fiber Bundle Tensile

Properties of Cotton

The relationships between tensile properties of single fibers and fiber bundles have been

widely studied which is clearly evident from the availability of numerous research

articles on that subject.

As stated by Orr et al. (1955) good correlations between single fiber and fiber bundle

measurements for tenacity and elongation might exist when the measurements are made

at the same gauge length. In fact, results obtained by the authors demonstrated that single

fiber tenacities were more than double the corresponding measured flat bundle tenacities.

Sasser et al. (1991) convey the idea that the average single fiber breaking strength sets an

upper limit for the fiber bundle breaking strength. The results also indicate the possibility

of obtaining improved correlations between fiber strength and yarn strength by using

average single fiber strength instead of HVI or Stelometer bundle strength. Cui et al.

(2003) report that in many cases results of single fiber tensile property tests are

considered to be more desirable than results of bundle tests.

Rebenfeld (1958) has experimented on the degree of transmission of single cotton fiber

properties to the properties of cotton fiber bundles, yarns and fabrics. As observed by

Rebenfeld, single fiber strength is not fully transferred to bundle strength and the degree

of strength transmission is not constant for all cottons. Furthermore, the degree of

transmission seems to be a function of fiber breaking tenacity where the weaker cottons

exhibit a higher transmission of fiber strength. In addition, degree of transmission of


8

single fiber breaking elongation to fiber bundles appears to be inversely proportional to

the single fiber breaking elongation. Therefore, cottons with a low breaking elongation

would more efficiently transfer the property to fiber bundles than cottons with a high

breaking elongation.

Warrier and Munshi (1982) report that irrespective of the employed fiber testing

instrument, on an average nearly 50% of the strength of single fibers is realized when

fiber bundles are tested. As mentioned by Cui et al. (2003) these differences between the

results of single fiber and fiber bundle tensile tests might be due to variations in fiber

breaking elongation, breaking strength and fiber crimp. Very good correlations between

elongations of single fibers and fiber bundles have also been reported several times

(Hertel & Craven (1956); Warrier & Munshi (1982)).

Dhavan et al. (1984) state that in a practical sense there are various confounding factors

which affect the bundle strength tests. Namely the uncertainty in test specimen length and

the fibers within the testing bundle not being parallel which might be due to fiber crimp

might complicate the bundle measurements. Inter fiber interactions can disrupt stress

transmission from individual fiber to fiber bundles. In addition, the non-linear nature of

the individual fiber load-elongation curves might also cause confusion.

Over the years researchers have come up with a considerable number of mathematical

models which relate single fiber and fiber bundle tensile properties of cotton. These

models constitute of methods used for predicting bundle tensile properties from single

fiber tensile properties as well as the reverse approach of predicting single fiber


9

properties when bundle properties are available. Nachane and Iyer (1980) developed a

model to predict bundle tenacity with the use of mean single fiber strength and breaking

elongation distribution.

Dhavan et al. (1984) have introduced a mathematical model to predict single cotton fiber

tensile properties from bundle load-elongation curves assuming that the fiber bundles are

parallel. Nevertheless, cotton fibers are crimped and the crimps can be reduced by

combing and brushing performed during specimen preparation of fiber bundle. Yet, it is

not possible to completely get rid of these crimps without causing excessive fiber damage

(Cui et al., 2003). Since the presence of fiber crimps in a bundle could significantly

influence results of bundle tests, the model proposed by Dhavan et al. (1984) cannot be

used for accurate estimation of bundles which are not parallel.

A bundle which consists of fibers with unequal lengths between the jaws of a tensile

tester is referred to as a slack bundle by Cui et al. (2003). They have tried to develop a

method to estimate single cotton fiber tensile properties from load-elongation curves of

HVI bundles which are referred to as slack bundles. However, the estimates were less

reliable and their use has not been recommended for applications which require accurate

single fiber tensile properties.


10

1.3 Impact of Fiber Processing on Cotton Fiber Tensile Properties

Cotton fibers need to go through a series of mechanical processes from being harvested in

field to reaching the textile mill, following which they undergo a number of different

textile processing steps. The textile processing steps such as carding, spinning, weaving

and mercerizing are expected to affect the cotton fibers. Whether they are mechanical or

chemical, during these processes stresses are applied on the fibers correspondingly

altering their properties. While many of those changes that occur in fiber properties

enhance fiber performance, some of them could adversely influence fiber quality

(Rebenfeld, 1957).

Effects caused by chemical processing like mercerizing and resin-finishing on fiber

properties are most likely favorable, whereas mechanical processing, in general, causes

fiber property alterations which are not usually beneficial (Rebenfeld, 1957). Mechanical

processing, especially cleaning cotton and maintaining good fiber quality is known to be

a compromise at the gin and textile mill. There is evidence of the nature of gin treatment

affecting fiber length and strength. Short fiber content and neps are increased with

additional lint cleaners used at the gin which in turn would be detrimental to yarn quality

(Bel et al., 1991). The extent of fiber damage caused in the ginning process is also variety

dependent. Fiber damage occurred at the gin would be greater as the longer and finer a

cotton is (Sui et al., 2010).

The process of fiber to yarn conversion consists of two basic stages, namely spinning

preparation and yarn formation. Spinning preparation consists of opening and cleaning,

carding, drawing and combing. An additional step, roving, is required if ring spinning is


11

to be performed. During opening, the compressed fiber bales are separated into smaller

masses. It also results in removal of trash, dust, foreign material and other impurities.

Usually during carding and spinning fibers are extended and the fiber crimp is removed

to some extent. Basically carding is known to individualize, parallelize and blend the

fibers. It might also remove short fibers and cause some fiber breakage. Drawing

straightens the fibers and provides additional fiber blending. During combing short fibers,

fiber neps, seed coat fragments and trash are removed. Spinning might also cause fiber

breakage of some of the weaker fibers.

Rebenfeld (1957) has conducted a study aimed at determining how cotton fiber properties

are altered during different mechanical and chemical processing operations. Opening,

picking, carding, drawing, roving, spinning, weaving, singeing, desizing, scouring,

bleaching, mercerizing and resin treatment were the processes which were monitored. As

stated by the author, magnitude of fiber property alterations due to processing is not

constant for all cottons and mostly the changes in fiber properties are functions of the

original fiber properties. The results indicate that the change in fiber breaking stress due

to processing is a function of the original breaking stress. In the study conducted using six

cottons, weaker cottons have increased in breaking stress whereas stronger cottons have

decreased in breaking stress after being subjected to processing. Similarly, the decrease in

breaking elongation due to processing is also a function of the original fiber breaking

elongation. Cottons with a high breaking elongation exhibited a greater decrease in

elongation than cottons with a low breaking elongation. These facts were observed for all

processing steps up to and including mercerization. The resin treatment, unlike the other


12

stages, has caused a decrease in both breaking stress and breaking elongation. In addition,

the magnitude of fiber property changes resulted by this treatment was nearly constant for

the six cottons suggesting that it is not a function of the fiber property prior to the

treatment. However, it is important to note that these findings were based on mechanical

properties determined on minute samples which seem to be inadequate, i.e. only 50 fibers

from each cotton representing each stage.

In the same study (Rebenfeld, 1957), property changes due to processing exhibited

similar trends between fiber and fabric breaking strength as well as fiber and fabric

breaking elongation. Thus, the author concludes that the fiber property changes caused by

a particular treatment are reflected as changes in the fabric characteristics. This indicates

the impact of cotton fiber properties on the fabric performance. Grant et al. (1952) has

also mentioned that any damage that befalls cotton fibers during mechanical processing

will be transferred to the textile products and might affect their overall quality.

Since the changes in fiber properties which occur due to processing are not constant

across different cottons, it is less reliable to predict fabric characteristics from properties

of the unprocessed fiber. Thus, processed fibers should more closely represent the

characteristics of fibers in the fabric than unprocessed fibers (Grant et al., 1952).

Grant et al. (1952) have conducted a study assessing the effects of mechanical processing

on physical properties of cotton fibers. Ginned cotton was considered as unprocessed

cotton while fibers obtained from untwisted yarns were used for the measurements of

processed cotton. Bundle tenacity and single fiber breaking load and tenacity were not


13

significantly different between the unprocessed and processed fiber samples, whereas

single fiber breaking elongation was significantly lower in the processed cottons.

Farag and Elmogahzy (2009) have commented on the effect of mechanical ginning on

cotton fibers. From the widely used two types of mechanical ginning, saw ginning which

is used for medium and short staple cottons apply more stress on fibers than roller

ginning which is used for long and extra-long staple cottons.

Salhotra and Chattopadhyay (1984) indicate a significant loss in cotton fiber bundle

tenacity and elongation due to the opening process. Opening is a spinning preparation

process. The opening roller system which is used for fiber separation in rotor spinning

causes substantial amount of fiber breakage. The authors have attributed the reduction in

fiber tenacity upon opening to the action caused by teeth or pins on the fibers which

causes surface damage by forming minuscule cuts. Consequently, weak spots are created

along the length of the fiber resulting in loss of fiber tenacity.

Rebenfeld (1958) has brought up a different idea that textile processing operations have a

tendency to reduce differences among cottons. Even though the differences among

cottons are not entirely eliminated, the main differences present in the single fiber state

tend to be balanced out by textile processing.

1.4 Cotton Fiber Elongation and its Importance

Cotton fiber elongation is an important tensile property which plays a significant role in

textile manufacturing. Yet, it has been largely neglected while strength, length and

micronaire were considered to be the only properties which determine the spinning


14

performance and yarn quality. It is strange that cotton fiber elongation has never really

turned up as one of the properties that should be considered when purchasing cotton raw

stock or putting together mix laydowns (Backe, 1996).

Elongation becomes a key property in cotton preparation procedures like ginning. During

ginning, excessive lint cleaning can result in fiber breakage and increased short fiber

content if the fibers lack sufficient tenacity and elongation to withstand the stresses

(Benzina et al., 2007).

Elongation plays an important role in almost all of the textile manufacturing procedures.

Cotton fibers with high elongation will perform better in spinning. The spinning

efficiency of cotton is usually decided by end breakage rate during the process which can

significantly impact the production cost and product quality. As cotton fibers are

subjected to a variety of external stresses in the spinning mill during the processes such

as opening, cleaning, carding and drafting, having more flexibility or being less stiff is

important to endure these stresses (Mogahzy & Chewning, 2001).

As mentioned by Benzina et al. (2007), the fibers which do not possess adequate

elongation as well as tenacity fail to withstand these stresses and result in fiber breakage.

Therefore, the short fiber content generated by opening, carding and other mechanical

processes is negatively correlated with fiber tenacity and elongation. Fiori et al. (1956)

have stated that fibers with higher elongation and lower modulus would be expected to

spin more efficiently as it might tend to deform more easily during spinning and

subsequent processes. It is essential to note that the significance of elongation is


15

gradually becoming prominent with the increasing spinning speeds and dynamic forces

connected to recent advancements in processing.

Waters et al. (1966) have investigated on the effect of fiber elongation on end breakage of

yarns spun at varying twists, spindle speeds and spinning drafts. Eighteen cotton bales of

medium staple lengths which were used in the experiment varied widely in bundle

elongation while all other fiber properties were nearly equal. Each group of low, medium

and high bundle elongation cottons was represented by six bales. The results indicated

that the high elongation cotton demonstrated better spinning performance than the low

elongation cotton irrespective of spindle speed, twist, draft, or yarn number. James S.

Parker (1963) has also reported that high elongation cotton has produced a better yarn

with fewer ends down than low elongation cotton.

Yarn with good elongation will perform better in weaving than a yarn with poor

elongation. Since yarn is subjected to abrupt forces during weaving preparation steps

such as winding and warping, and the weaving process itself, good elongations are

necessary in order to have better weaving efficiency. Toughness, or the ability of a fiber,

yarn, or fabric to withstand large deformations, is the product of the breaking strength

times the elongation value at break. Therefore, a yarn that has a low breaking strength

and a high elongation value might probably be tougher than a yarn with a high breaking

strength and a low elongation value. Thus the lower strength yarn could possibly weave

better than the higher strength yarn, as it is tougher and can stand the rigors of weaving

better (Backe, 1996).


16

Sizing process, which is also a weaving preparation step, causes reduction in yarn

elongation due to the application of size material on yarn. This gives rise to stiffness in

the yarn rendering it undesirable for weaving. Thus, in order to compensate for this loss

of elasticity it is better to use cotton fibers with high elongation in weaving. In knitting

yarn elongation is not as important as that is in weaving. Yet, it is a vital characteristic

which is important in providing the required flexibility and easy bending of yarn around

the different knitting components (Farag & Elmogahzy, 2009).

To determine the effect of cotton fiber elongation on yarn quality and weaving

performance, Backe (1996) has conducted a study using three cotton mixes representing

three different levels of fiber elongation, namely high, medium and low elongation. HVI,

AFIS, Stelometer and Uster Evenness Tester 3 data of the card and drawing slivers

showed that except for elongation all other fiber properties were relatively constant

between the three elongation levels. The results indicated that cotton fiber elongation

significantly contributed to yarn qualities of the open-end spun yarn, such as evenness

and defect levels, strength and elongation, work to rupture, hairiness and weaving

performance. For instance, the higher the elongation of the raw cotton, the higher the

skein strength and the single-end strength were. Unsurprisingly, higher fiber elongation

also resulted in higher yarn elongation. Especially there was deterioration in yarn

evenness and an increase in imperfection count as fiber elongation became less. In

addition, higher fiber elongation also yielded fewer hairs per meter in yarn.

In a study aimed to determine the effect of fiber bundle elongation on processing

performance and yarn properties, Waters et al. (1966) have also concluded that the


17

single-strand yarn strength, skein strength and yarn elongation were linearly related to

fiber bundle elongation. Accordingly, increased fiber bundle elongation has resulted in

increased yarn strength and elongation in this experiment. Results obtained by Louis et

al. (1961a) also indicate that the tenacity and elongation of single yarns are directly

related to the fiber elongation of the cottons from which the yarns are spun.

Fiber elongation is also a significant decisive factor of the fiber bundle strength value.

The maximum fiber bundle strength of a given set of fibers can be obtained when all the

fibers in the bundle break at the same elongation. Consequently, the bundle strength

increases with decreasing standard deviation of single fiber elongation (Fryer et al.,

1996). A study done by Coleman (1958) has concluded that the tensile strength of a fiber

bundle is always less than the average tensile strength of its individual components.

Nachane and Iyer (1980) also state a concept similar to Fryer et al. (1996) by mentioning

that poor bundle strength can arise from the unequal extensibility of individual fibers in

the bundle.

Standard deviation of single fiber elongation is likely to be higher for a fiber bundle

formed from a cotton blend than for a fiber bundle formed form one of the constituent

cottons. And the high standard deviation can result in lower bundle strength of the blend

despite the mean single fiber elongation values of the bundles being equal for the blends

and the constituent cottons. In contrast to elongation, merely an increase in single fiber

strength variability in a blend cannot impact bundle strength. If all other factors remain

constant, bundle strength should not be affected by blending cottons having different


18

strengths unless the mean single fiber strength is changed due to blending (Fryer et al.,

1996).

Fiori et al. (1956) have demonstrated that small differences in yarn breaking elongation

correlate with relatively large changes in yarn strength. Since the direct relationship

between yarn elongation and fiber elongation is obvious, this suggests the importance of

fiber elongation as a secondary contributor to yarn strength.

Koo and Suh (1999) have investigated on maximizing the yarn and fabric strength with

the use of variance of HVI elongation. They have highlighted the necessity of controlling

the variance of breaking elongation of constituent fibers of a yarn in order to maximize

the yarn and fabric strengths. Correspondingly, when two cottons differing in fiber

elongation are blended, yarn strengths of the blends appear to be lower than that of the

original samples (Louis et al., 1961a). Blending cotton fibers with different properties is a

requirement in textile industry. As cotton fibers differ considerably in breaking

elongation these observations are noteworthy to obtain good blends without any

deterioration in fiber quality.

Louis et al. (1961b) have concluded that, in general, cotton fiber with high elongation

produces fabric which is superior to fabric made with low elongation cotton fiber, in

qualities such as elongation, breaking and tearing strengths, and flex resistance.

Since cotton is a natural product with very high variability, its tensile properties differ

considerably from sample to sample and fiber to fiber. Thus, it would be wiser to look at

the distributions of the cotton fiber tensile properties rather than their average values.


19

Compared to the distributions of other single fiber tensile properties, fewer studies have

been conducted on the distribution of single fiber breaking elongation (Hu & Hsieh,

1997). Frydrych (1995), and Nachane and Iyer (1980) have emphasized the skewed

nature of the distributions of cotton fiber breaking elongation. Hu & Hsieh (1997) have

further investigated the breaking elongation distributions of cotton fibers, and have

concluded that the distributions are positively skewed. This denotes the presence of a

larger amount of cotton fibers with lower elongations than the mean value and a small

amount of cotton fibers with higher elongations than the mean value. The fibers which

possess the lowest elongation are the ones that are broken first during stretching. And the

broken fibers no longer contribute to the bundle strength. Hence, it critically impacts the

strength of the fiber bundle (Hu & Hsieh, 1997). With a detailed statistical analysis the

authors have determined that ‘Gamma’ function is the appropriate curve fitting function

for the positively skewed elongation distributions.

In contrast to the positive contribution of fiber bundle elongation value to yarn strength

mentioned by Backe (1996), May and Taylor (1998) have reported that selecting for high

fiber bundle elongation among other fiber properties, has provided the least improvement

in yarn tenacity. The study (May & Taylor, 1998) reveals a low genetic correlation

between bundle elongation and yarn tenacity along with a negative correlation (r = -0.35)

between fiber bundle tenacity and bundle elongation determined by the Stelometer.

Scholl and Miller (1976) have also observed a negative genotypic correlation (r = -0.16)

between Stelometer fiber bundle strength and fiber bundle elongation.


20

In a study evaluating genetic association of fiber characteristics with yarn tenacity of

open-end and ring spun yarns, Meredith et al. (1991) reported moderate negative

correlations (r = -0.33 to -0.54) between fiber bundle elongation determined by

Stelometer and yarn tenacity of both open-end and ring spun yarns. These relationships

observed in the study were considered to be mainly due to genetic factors since non-

genetic influences were small. A low negative correlation (r = -0.2) between Stelometer

fiber bundle elongation and yarn strength has also been reported by Green and Culp

(1990).

The correlation between bundle tenacity and elongation could be described by attributing

it to their associations with fiber crystallinity. Several studies have attempted to link

crystallinity with the tensile properties of cotton fibers. Hindeleh (1980) has conducted a

study on the relationships between crystallinity and the physical properties of mature

cotton fiber. Eight varieties of native Egyptian cotton, which had been selected based on

variations in their staple lengths, fineness, tenacity and elongation-at-break, were

employed in the study. The results indicate higher bundle tenacity and lower bundle

elongation values for the long-staple cottons, and lower bundle tenacity and higher

bundle elongation values for the short staple cottons. The cotton types which possess

higher degree of crystallinity depicted higher bundle breaking tenacity and lower bundle

breaking elongation, and vice versa. Figure 1.2 illustrates the contrasting relationships

between crystallinity and the two tensile properties of the native Egyptian cotton types

used in the study.


21

Figure 1.2 Relationships between crystallinity and tensile properties of native Egyptian

cotton (Hindeleh, 1980)

From the above results obtained on a limited set of samples, it appears that the two

properties tenacity and elongation of cotton fibers are inversely proportional to each

other. Yet, it is important to note that in the above study the particular relationship was

observed on fiber bundles and not on single fibers.

In a recent study (Liu et al., 2014) done using 70 lint cottons consisting of Pima fibers

grown in the United States and Upland fibers grown both in and outside of the United

States, the relationship of fiber crystallinity to fiber tenacity and elongation was assessed.

Bundle tenacity of the Pima varieties exhibited an increasing trend with crystallinity

whereas the bundle tenacities of Upland fibers were nearly independent of crystallinity.

There was a decrease in bundle elongation with increasing crystallinity for Upland fibers.

A particular trend could not be detected between crystallinity and bundle elongation of


22

the Pima fibers, which the authors have attributed to the limited number of Pima samples

used in the study. For the Upland fibers Stelometer tenacity and elongation revealed an

insignificant correlation whereas a positive relationship between the two properties was

observed for the Pima varieties. Yet, the authors further state that the precise correlations

between fiber tenacity, elongation and crystallinity are inconclusive based on the limited

fiber samples employed in the study. A possible explanation given for this scenario is that

besides crystallinity, fiber tenacity and elongation could also be affected by crystallite

size, fibril orientation and residual stress (Hsieh et al., 1997).

Nevertheless, it is difficult to compare the relationships observed between strength and

crystallinity in different studies as the extent of crystallinity of mature cottons could

range from 50% to nearly 100% depending upon the measurement techniques (Hsieh,

1999).

Contrary to the widely accepted negative relationship between bundle elongation and

tenacity, Waters et al. (1966) have reported the absence of any relationship between fiber

bundle elongation and strength measured by the Stelometer. However, since the findings

were based on the medium staple cottons used in the study, it may not be applicable to

either shorter or longer cottons.

In a recent genetic study (Ng et al., 2014) with an emphasis on fiber elongation in Upland

cotton, relationships between fiber bundle strength and elongation determined by both

Stelometer and HVI were taken into account. A significant negative correlation (r= -0.20)

was observed between bundle strength and bundle elongation measured by the Stelometer


23

while HVI bundle strength was not correlated with HVI bundle elongation. Stelometer

elongation also showed no correlation with HVI bundle strength.

Another research study (Benzina et al., 2007) has emphasized that the fiber bundle

elongation plays an important role in the work of rupture of fiber bundles. Work of

rupture correlates with the product of tenacity and elongation, and is a very important

factor which determines the processing performance of cotton fibers. The authors have

also demonstrated the negative correlation between fiber bundle elongation and fiber

bundle tenacity. According to the authors, the existence of a weak negative correlation

between fiber tenacity and fiber elongation among samples does not imply that the

simultaneous improvement of the two properties is impossible. In fact, increasing the

tenacity when the elongation is decreased could result in a reduced work of rupture while

the mere improvement of elongation with tenacity remaining the same could create a

higher work of rupture. Ng et al. (2014) have also conveyed that some of the genotypes

used in their study have suggested that breeding for simultaneous improvement of fiber

elongation and strength is possible.

Irrespective of the lack of interest in cotton fiber elongation in breeding programs, it is a

property which possesses high heritability. Heritability is the ratio between genetic and

phenotypic variations. High heritability value for a particular trait suggests the possibility

of improvement of that trait in breeding programs. May & Taylor (1998) have reported

on the high heritability of elongation.


24

CHAPTER II

EVALUATING THE RELATIONSHIPS BETWEEN TENSILE PROPERTIES OF

SINGLE FIBERS AND FIBER BUNDLES OF COTTON

2.1 Introduction

Tensile properties of cotton fibers are of utmost importance in the textile industry as they

are known to greatly affect the processing performance and the quality of the textile

product. Therefore, tensile property measurements are of equal importance to both the

cotton industry and the breeding programs. Tensile tests of cotton fibers can be

performed on single fibers or fiber bundles. It is necessary to gain a better understanding

of the relationships between these two types of tensile testing.

Several studies have examined the relationships between individual fiber and fiber bundle

tensile properties of cotton. Orr et al. (1955) have conducted such a study employing

seven commercial cotton samples belonging to different varieties. The samples possessed

diverse physical properties. They have reported that, bundle strength and elongation

measured with the Stelometer, correlated well with individual fiber strength and

elongation respectively. Rebenfeld (1958) has observed good correlations of single fiber

breaking tenacity and elongation with the corresponding values measured on Pressley

bundles at 5mm gauge length. The study has been conducted using six cotton samples

which represented a wide range in physical properties.

Despite the good correlations between the tensile properties of individual fibers and fiber

bundles, the two types of testing methods are also known to provide noticeably different

results. Especially, fiber bundle strength and individual fiber strength measurements


25

differ substantially from each other. It has been reported that the individual fiber strength

is not completely transmitted to fiber bundle strength and the extent of strength

transmission varies with the cotton (Rebenfeld, 1958). Coleman (1958) has brought up

the idea that bundle tensile strength of a cotton is always less than the average tensile

strength of its individual constituents. Over the years researchers have come up with few

explanations for the differences between the tensile property measurements obtained on

single fibers and fiber bundles.

Variations in fiber breaking elongation, breaking strength and fiber crimp might cause the

differences between the results of single fiber and fiber bundle tensile tests (Cui et al.,

2003). According to Fryer et al. (1996), in order to obtain the maximum bundle strength

from a particular set of fibers, all the fibers in the fiber bundle need to break at the same

elongation. Increased bundle strengths can be acquired by decreasing the standard

deviation of single fiber elongation. As stated by Nachane and Iyer (1980), poor bundle

strength can originate from the unequal extensibility of individual fibers in the bundle.

Not only the tensile property measurements themselves, but also the relationships

between the tensile properties of individual cotton fibers seem to differ from the

relationships between fiber bundle tensile properties. Several studies have reported on the

negative correlation between fiber bundle tenacity and bundle elongation of cotton

(Scholl & Miller (1976); May & Taylor (1998); Ng et al. (2014)). In contrast, positive

correlations between strength and elongation have been observed for individual fibers.


26

Most studies on cotton fiber strength were reported based on fiber bundle measurements.

Therefore, the relationships between single fiber tensile properties have not been well

documented. Thus, our study focuses on examining the relationships between the tensile

properties of both the individual fibers and the fiber bundles. Tensile property

measurements obtained from Stelometer, High Volume Instrument (HVI) and FAVIMAT

will be taken into account.

Figure 2.1 Stelometer

The Stelometer instrument (Figure 2.1), which measures fiber bundle force and

elongation properties, is a conventional reference method for measurement of fiber

strength. The instrument operates according to the principle of constant rate of


27

elongation. Prior to obtaining measurements each time, the instrument needs to be

calibrated first using a metal plate, and then using the standard calibration cottons. After

acquiring data, the data needs to be adjusted based on the standards. In addition to that, a

well-trained operator is also required to perform fiber testing with the Stelometer. The

Stelometer consists of the following main components (Figure 2.2).

Figure 2.2 Components of the Stelometer

1) Fiber clamp

2) Clamp carrier

3) Force scale


28

4) Force indicator

5) Elongation scale

6) Elongation indicator

7) Pendulum

8) Trigger

9) Fiber clamp apparatus

The Stelometer operation procedure could be described as follows. A well combed fiber

sample, attached to a small clamp, is placed in a fiber clamp with the help of a fiber

clamp apparatus. The fiber clamp is then inserted at the top of the pendulum. When the

trigger at the bottom right hand side is released, a load is applied on the fiber bundle and

the pendulum starts moving. As it moves stretching the fibers, the fiber clamp comes

apart. The pendulum will continue moving to the right hand side until the occurrence of

fiber breakage. When the pendulum stops, the values indicated by the force and

elongation scales are recorded. Afterwards, fiber clamp is taken out from the instrument

and the excess fibers are removed with a knife from both ends of the clamp. The broken

fiber sample is then weighed using a precision balance. The breaking force and weight

are used in the following equation to determine the tenacity (ASTM D1445).

T = f / m × 15.00*

f = breaking force in Kgf (Kp)

m = mass of the tested fiber bundle in milligrams

T = tenacity in gf/tex

*15.00 stands for the length of the specimen in millimeters


29

HVI (Figure 2.3) provides fiber property measurements such as micronaire, upper half

mean length, length uniformity, strength, elongation, reflectance and yellowness, using

fiber bundles. Bundle tensile tests in HVI are performed on the same specimen that is

used for the length measurement. The specimen is subjected to the tensile test at 3.2 mm

gauge length according to the principle of constant rate of elongation.

HVI allows performing more rapid bundle tensile tests than the Stelometer. The

requirement for measuring the mass of the tested specimen associated with the Stelometer

has been eliminated in HVI. The operator effect related to the Stelometer has also been

greatly reduced in HVI. Yet, owing to the lack of calibration standards it is not capable of

providing consistently accurate data for elongation, whereas, the Stelometer can be

calibrated for elongation.

Figure 2.3 High Volume Instrument (HVI)


30

FAVIMAT (Figure 2.4) provides three main individual fiber tensile property

measurements; elongation-at-break, force-to-break and work-to-break. In addition, other

physical parameters such as tenacity, linear density and crimp could also be measured.

The minimum gauge length to obtain a linear density measurement with FAVIMAT is

the 10 mm gauge length. FAVIMAT has been originally designed for man-made fibers

which possess very little within sample variability. As cotton fibers have a higher within

sample variability, a large number of fibers need to be tested with the FAVIMAT.

Figure 2.4 FAVIMAT


31

2.2 Objectives

To compare the relationships between single fiber and bundle tensile properties of

cotton

To study the relationships between tensile property measurements obtained from

different instruments

2.3 Materials and Methods

From one hundred and four reference cotton samples (Hequet et al., 2006), thirty samples

were selected based on the available FAVIMAT and HVI data, ensuring the presence of a

wide range of strength and elongation values. The samples possessed average FAVIMAT

force-to-break values ranging from 4.24cN to 6.25cN; average FAVIMAT elongation

values ranging from 6.01% to 12.67%; average HVI strength values ranging from

24.33gf/tex to 41.3gf/tex; and average HVI elongation values ranging from 3.59% to

8.28% (Table 2.1).


32

Table 2.1 Descriptive statistics of the FAVIMAT and HVI tensile measurements of the

30 samples selected for the experiment

Tensile Measurement Average Minimum Maximum Range

HVI strength

(gf/tex)

29.95 24.33 41.30 16.97

HVI elongation (%)

5.34 3.59 8.28 4.69

FAVIMAT force-to-

break (cN)

4.95 4.24 6.25 2.01

FAVIMAT elongation-

at-break (%)

8.79 6.01 12.67 6.66

Prior to fiber testing, all the samples were conditioned at the environmental conditions of

70±1◦F and 65±2% relative humidity for at least 48 hours. Spinlab Stelometer 654 was

used in the experiment to obtain bundle tensile property measurements. The three cotton

standards C-39, M-1 and L-2 were used to calibrate the Stelometer. The average tensile

properties of the standards are given in Table 2.2. Selected samples were tested with the

Stelometer at 3.17 mm gauge length to obtain measurements of breaking force and

elongation of fiber bundles. Six replications were performed per sample. A precision

balance (±0.0001 g) was used to weigh the tested specimens. Tenacity of each sample

was calculated as the ratio of breaking load to mass of the tested fiber bundle multiplied

by the sample length (ASTM D1445). Then, the data obtained were corrected using the

three calibration cottons.


33

Table 2.2 Average tensile property measurements of the three calibration cottons used in

the Stelometer

Calibration Cotton Tenacity (gf/tex) Elongation (%)

C-39 25.1 7.1

M-1 30.8 6.4

L-2 18.0 5.6

The available FAVIMAT data of the 30 samples has been obtained at 10mm gauge length

with a test speed of 20mm/min and a pre-tension of 0.2cN/tex. Three replications of 150

individual fibers have been tested per sample. The HVI data consisted of 10 length and

strength readings, 4 micronaire readings, and 4 color and trash readings per sample. The

relationships between tenacity and elongation measurements obtained from each

instrument were analyzed and the results were compared between the three instruments.

2.4 Results and Discussion

Obtaining accurate and precise measurements for cotton fiber tensile properties is

essential for the cotton industry. Thus, it is important to evaluate the two main types of

tensile tests, namely individual fiber and fiber bundle tensile tests. For that reason, a

comprehensive evaluation of the measurements obtained from the two types of methods

is required. In the present study, results obtained from two different bundle tensile tests

(Stelometer and HVI) and one individual fiber tensile test (FAVIMAT), are taken into

account.


34

Descriptive statistics of the Stelometer tensile measurements of the tested samples are

presented in Table 2.3. Both Stelometer tenacity and elongation measurements are spread

over a wide range. FAVIMAT elongation-at-break measurements (Table 2.1) of the

samples, were also spread in a range (6.66%) similar to the Stelometer elongation. Since

we are also interested in assessing the correlations between the tensile properties,

presence of a wide range in the parameters will be important to obtain good correlations

between them.

Table 2.3 Descriptive statistics of the Stelometer tensile measurements of the 30 samples

Tensile Measurement Average Minimum Maximum Range

Stelometer tenacity

(gf/tex)

14.26

12.69 18.89 6.20

Stelometer elongation

(%)

10.57 7.54 14.47 6.93

The relationships between strength and elongation measurements are assessed separately

for each instrument.


35

Figure 2.5 Relationship between tenacity and elongation determined by Stelometer

As demonstrated in Figure 2.5 Stelometer tenacity and elongation measurements display

a very small negative correlation which is not significant. This indicates that bundles with

higher tenacities tend to have lower elongations and those with lower tenacities tend to

have higher elongations. The negative correlation between Stelometer tenacity and

elongation has been previously reported (May & Taylor (1998); Scholl & Miller (1976)).

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

19.0

20.0

6.0 8.0 10.0 12.0 14.0 16.0

Stelometer

Tenacity

(gf/tex)

Stelometer Elongation (%)

Stelometer Tenacity vs. Stelometer Elongation

R² = 0.0748


36

Figure 2.6 Relationship between strength and elongation determined by HVI

Similar to the relationship observed with the Stelometer, HVI strength and elongation are

also negatively correlated (Figure 2.6). This implies that weaker bundles possess higher

elongation whereas stronger bundles possess lower elongation. Nevertheless, the small

negative correlation between HVI strength and elongation is also non-significant which

might be due to the limited number of samples employed in the study.

In general, the negative correlation between tenacity and elongation of cotton fiber

bundles is a widely accepted concept. Fiber strength is evidently considered as a vital

tensile property at all stages of fiber processing. Weaker fibers have a higher propensity

to break. Thus, it could give rise to increased short fiber contents which in turn might

lead to more yarn defects. Fiber strength is also a main criterion in cotton bale selection

and laydown formation. Thus, improving fiber strength is a major concern of the cotton

15.0

20.0

25.0

30.0

35.0

40.0

45.0

2.0 4.0 6.0 8.0 10.0

HVI Strength

(gf/tex)

HVI Elongation (%)

HVI Strength vs. HVI Elongation

R² = 0.1263


37

breeding programs. Because of the negative relationship between tenacity and elongation,

elongation is usually disregarded as it is envisioned that improving fiber elongation

would result in decreased fiber strength. Therefore, cotton breeders hesitate to work on

improving cotton fiber elongation. Yet, elongation is also a crucial tensile property which

plays a significant role in fiber processing and impacts the quality of the textile product.

Figure 2.7 Relationship between force-to-break and elongation-at-break determined by

FAVIMAT

Significant correlations at α =0.05 significance level are denoted by **.

A significant positive correlation exists between the individual fiber force-to-break and

elongation-at-break measured by FAVIMAT (Figure 2.7). According to that stronger

fibers tend to possess higher elongation whereas weaker fibers tend to possess lower

4.0

4.5

5.0

5.5

6.0

6.5

4.0 6.0 8.0 10.0 12.0 14.0

FAVIMAT

Force-to-

Break (cN)

FAVIMAT Elongation-at-break (%)

FAVIMAT Force-to-break vs. FAVIMAT Elongation-

at-break

R² = 0.1344**


38

elongation. This implies the possibility of the fibers to simultaneously possess both

higher strengths and higher elongations. It also suggests that the improvement of fiber

elongation might not always result in inferior fiber strengths. Therefore, comparison of

the results obtained from the three instruments reveals that the relationship between

individual fiber strength and elongation is contradictory to the relationship which exists

between bundle strength and elongation.

The above results indicate that stronger fibers tend to possess higher elongation. In

general, the stronger fibers are more mature than the weaker fibers. Therefore, the

positive correlation between strength and elongation suggests that mature fibers tend to

have higher elongation. This is contrary to the present claim that mature fibers have

lower elongation.

It is a well-known fact that cotton is a highly variable product. As a whole, cotton plants

grown in the same field differ from each other. Within a plant, variability occurs among

different branches and among different positions of the same branch, within the cotton

boll, and even within the seed as each of them is exposed to different growth conditions.

Hence, cotton fibers are not homogeneous and their physical properties vary from fiber to

fiber. Therefore, cotton fibers possess higher within sample variability.

In a fiber bundle, there is a population of cotton fibers which differ from each other. Even

though the fibers belong to the same sample, like all other physical properties, the tensile

properties could also vary among the fibers. Therefore, fibers within a bundle could differ

in their elongations. Accordingly, the elongation distribution of the fibers in a particular


39

bundle can be spread over a wide range. When a force is applied on the fiber bundle the

lower elongation fibers of the bundle break first. Then the entire load is applied on the

remaining fibers in the bundle. Even when the average elongation of a sample is high, in

the elongation distribution there are fibers which have less elongation. These fibers with

less elongation seem to dominate the distribution and influence the strength of fiber

bundles.

Since fiber elongation also has an impact on fiber bundle strength, the strength of a fiber

bundle cannot be equal to the average strength of the constituent fibers. Thus, it is

possible for the bundle strength of cotton to be lower than the corresponding individual

fiber strengths.

As previously mentioned, it has been reported that the fiber bundle strength increases

with the decreasing standard deviation of single fiber elongation (Fryer et al., 1996).

Hence, in order to understand the negative relationship between bundle strength and

elongation, it is necessary to find out the association between individual fiber elongation

and its standard deviation. For this purpose, FAVIMAT data of the thirty samples are

evaluated to assess the correlation between the above two parameters (Figure 2.8). It is

also important to note that elongation varies within a wide range in the selected samples.


40

Figure 2.8 Relationship between FAVIMAT elongation and the standard deviation of

FAVIMAT elongation


Figure 2.8 represents a significant positive correlation between individual fiber

elongation and standard deviation of individual fiber elongation. Thus, the standard

deviation of individual fiber elongation increases with increasing individual fiber

elongation. Since fiber bundle strength is inversely proportional to standard deviation of

single fiber elongation, it can explain the negative correlation between bundle strength

and elongation. Therefore, the negative relationship between cotton fiber tenacity and

elongation implied by fiber bundles should be considered with more caution. It should

not be inferred that the simultaneous improvement of the two tensile properties is

impossible.

1.0

1.5

2.0

2.5

3.0

3.5

4.0

5.0 7.0 9.0 11.0 13.0 15.0

Within Sample

Standard

Deviation of

FAVIMAT

Elongation

FAVIMAT Elongation(%)

Standard Deviation of FAVIMAT Elongation vs.

FAVIMAT Elongation

R² = 0.577**


41

Nevertheless, in addition to elongation, other factors can also impact the fiber bundle

strength. In a fiber bundle, the twists and interactions between the constituent fibers also

contribute to the bundle strength. When more fibers are included in a given diameter,

there is more contact between the fibers. Higher contact results in higher friction which

will lead to increased strengths. Due to the occurrence of friction in fiber bundles,

correlation between single fiber strength and bundle strength cannot be one.

In the second stage of the analysis, corresponding tensile properties obtained from the

three instruments are compared.

Figure 2.9 Relationship between Stelometer elongation and FAVIMAT elongation


4.0

6.0

8.0

10.0

12.0

14.0

16.0

4.0 6.0 8.0 10.0 12.0 14.0

Stelometer

Elongation (%)

FAVIMAT Elongation (%)

Stelometer Elongation vs. FAVIMAT Elongation

R² = 0.7164**


42

Figure 2.10 Relationship between HVI elongation and FAVIMAT elongation


For the thirty samples used in the study, bundle elongation measurements obtained from

Stelometer and HVI show significant positive correlations with the individual fiber

elongation measured by FAVIMAT (Figures 2.9 and 2.10).

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

4.0 6.0 8.0 10.0 12.0 14.0

HVI

Elongation (%)

FAVIMAT Elongation (%)

HVI Elongation vs. FAVIMAT Elongation

R² = 0.668**


43

Figure 2.11 Relationship between Stelometer elongation and HVI elongation


A significant positive correlation also exists between the Stelometer and HVI bundle

elongation measurements (Figure 2.11).

4.0

6.0

8.0

10.0

12.0

14.0

16.0

2.0 4.0 6.0 8.0 10.0

Stelometer

Elongation (%)

HVI Elongation (%)

Stelometer Elongation vs. HVI Elongation

R² = 0.8049**


44

Figure 2.12 Relationship between Stelometer tenacity and FAVIMAT force-to-break


Bundle tenacity measured with the Stelometer positively correlates with the FAVIMAT

force-to-break (Figure 2.12). The correlation between the two measurements is also

significant. However, unlike Stelometer tenacity, FAVIMAT force-to-break measurement

is not normalized by weight. Force-to-break depends on the amount of the material

whereas tenacity gives a measurement which is independent of the amount.

8.0

10.0

12.0

14.0

16.0

18.0

20.0

4.0 4.5 5.0 5.5 6.0 6.5

Stelometer

Tenacity

(gf/tex)

FAVIMAT Force-to-break (cN)

Stelometer Tenacity vs. FAVIMAT Force-to-break

R² = 0.4658**


45

Figure 2.13 Relationship between HVI strength and FAVIMAT force-to-break


HVI bundle strength shows a significant positive correlation with FAVIMAT force-to-

break (Figure 2.13).

20.0

25.0

30.0

35.0

40.0

45.0

4.0 4.5 5.0 5.5 6.0 6.5

HVI

Strength

(gf/tex)

FAVIMAT Force-to-break (cN)

HVI Strength vs. FAVIMAT Force-to-break

R² = 0.6434**


46

Figure 2.14 Relationship between Stelometer tenacity and HVI strength


Bundle tenacity values obtained from the Stelometer, shows a significant positive

correlation with the HVI bundle strength values (Figure 2.14).

2.5 Conclusion

Thirty cotton samples representing a wide a range of strength and elongation were used to

examine the relationships between individual fiber and fiber bundle tensile properties.

Bundle tensile properties measured with the Stelometer and HVI, and single fiber tensile

properties measured with the FAVIMAT were taken into consideration. With both bundle

testing instruments negative correlations between bundle strength and elongation were

observed. This indicates higher elongation in weaker bundles and lower elongation in

10.0

12.0

14.0

16.0

18.0

20.0

20.0 25.0 30.0 35.0 40.0 45.0

Stelometer

Tenacity

(gf/tex)

HVI Strength (gf/tex)

Stelometer Tenacity vs. HVI Strength

R² = 0.6932**


47

stronger bundles. The negative correlation between bundle tenacity and elongation has

been a main reason for the lack of interest in elongation in both the cotton industry and

the breeding programs. In contrast to bundle tensile properties, individual fiber strength

and elongation measured with the FAVIMAT were positively correlated. The positive

correlation indicates that stronger fibers tend to have higher elongation. Since stronger

fibers are generally more mature, it can be interpreted that mature fibers tend to have

higher elongation. The suggested positive relationship between elongation and maturity

contradicts with the current conception that mature fibers have less elongation.

The negative relationship observed with fiber bundles can be attributed to the variation in

single fiber elongation of the assembly of fibers in the bundle. Constituent fibers of a

fiber bundle can vary widely in their elongations. Upon exertion of a force on a fiber

bundle, it is the fibers with less elongation that break first. As the entire load is then

applied on the remaining fibers in the bundle, the lower elongation fibers appear to

dominate the elongation distribution. Thus, in order to achieve the maximum bundle

strength, all the fibers in the bundle need to break at the same elongation.

Fiber bundle strength tends to decrease with increasing standard deviation of individual

fiber elongation. FAVIMAT data of the thirty cotton samples suggests that the standard

deviation of individual fiber elongation positively correlates with the individual fiber

elongation. Since higher elongation results in higher standard deviation, it will adversely

impact the bundle strength. Therefore, a negative relationship could be detected between

cotton fiber bundle tenacity and elongation. Thus, to prevent misconceptions on fiber


48

tenacity and elongation, it is essential to correctly understand the negative relationship

between bundle tenacity and elongation.

Bundle tensile property measurements obtained from the Stelometer exhibited good

correlations with those measurements obtained from the HVI. Furthermore, the bundle

strength and elongation measured with the Stelometer and HVI correlated well with the

corresponding values measured on single fibers.


49

CHAPTER III

EVALUATING THE IMPACT OF FIBER PROCESSING ON TENSILE PROPERTIES

OF COTTON FIBERS

3.1 Introduction

Cotton fibers undergo a number of mechanical and chemical procedures during the textile

manufacturing processes. Mechanical processing steps such as ginning, carding, spinning

and weaving affect the cotton fibers. The stresses exerted on fibers during these processes

alter the fiber properties.

As stated by Cantu et al. (2007) most of the neps, trashes and unwanted material are

removed during textile processing. However, processing also adds neps and causes fiber

breakage. More efficient removal of small particles and the increasing processing speeds

are the major advancements in lint cleaning research. Both of these increase fiber damage

and fiber loss (Shofner & Williams, 1986). The required cleaning level depends on the

amount of foreign matter present in the cotton. Since picker and stripper harvesting result

in different amounts of trash in cotton, different machinery sequences are used for

cleaning cotton harvested using these two methods.

The present trend towards improved production speeds has made mechanical processing

more aggressive. The existing fiber testing methods allow the constant evaluation of fiber

properties which facilitates a certain level of fiber quality to be maintained. To determine

the effect of machinery on fiber quality, it is necessary to monitor fiber properties after

each processing step. Bale opening, cleaning, carding, drawing, combing, roving,

spinning, weaving and knitting are the main steps of the textile manufacturing process.


50

Fiber length and length distribution, fiber fineness, and strength are considered as the

most important fiber quality parameters for textile processing. The ranked importance of

these fiber properties differs with the nature of yarn spinning method (Hsieh, 1999).

Length is considered as the most important fiber property in ring spinning whereas fiber

strength comes first in open end rotor spinning. Many studies have focused on relating

cotton fiber length distribution to mechanical processing. Krifa (2006) has highlighted a

relationship between modality of the length distribution and the mechanical damage the

fiber has undergone. He has concluded that cottons with a lower tendency to break

initially possess bimodal length distributions which gradually develop toward unimodal

length distributions after the fiber has been subjected to mechanical stresses. Hosseinali

(2012) has reported that, within-sample, short cotton fibers are on average weaker, less

mature and finer, and throughout mechanical processing the least mature longer cotton

fibers may be broken into shorter fibers.

Over the years, most research in the field of cotton has been oriented towards evaluating

the impact of fiber tensile properties on processing efficiency and end-product quality in

the textile industry. Yet, the impact of processing on tensile properties of cotton fibers

has not been studied well. Especially single fiber tensile properties have been rarely

studied since it is extensively time consuming. Most approaches were confined to

monitoring the changes in bundle tensile properties. Thus, our study mainly focuses on

the impact of mechanical processing on single fiber tensile properties.

In order to examine the impact of processing on cotton fiber properties Advanced Fiber

Information System (AFIS) was used as the fiber processing instrument at the initial


51

phase of this experiment. AFIS (Figure 3.1) provides several different fiber property

measurements as well as distributions. The main measurements include mean length by

number and by weight, upper quartile length, short fiber content by number and by

weight, length CV(%) by number and by weight, maturity, fineness, neps and trash.

Length (by number and by weight), fineness, maturity, neps and trash size are the

distributions that can be obtained from AFIS.

Figure 3.1 Advanced Fiber Information System (AFIS)

For the AFIS measurements, fibers need to be individualized first. During fiber

individualization, AFIS exerts an opening action on the fibers. Therefore, with AFIS,

fiber breakage can occur during the testing procedure itself (Krifa, 2006).


52

Figure 3.2 AFIS fiber individualizer

For the second phase of the experiment, in addition to AFIS, Microdust and Trash

Monitor (MTM) was also employed as a fiber processing instrument. MTM (Figure 3.3)

is an instrument which is capable of measuring foreign matter in bale or processed fiber.

MTM aero-mechanically separates trash from the lint and provides accurate, standard

measurements for microdust, dust and trash (Shofner et al., 1983).

MTM is more aggressive than AFIS which is the other processing equipment used in this

experiment. This facilitates a comparison of the impacts caused by light processing

(AFIS) and aggressive processing (MTM). This will also be helpful to identify the tensile

properties which play a significant role in fiber breakage.


53

Figure 3.3 Microdust and Trash Monitor (MTM)

3.2 Objectives

To investigate the impact of fiber processing on cotton fiber tensile properties

To study the relationships between cotton fiber properties and fiber breakage


Five commercial cotton samples, namely 8, 25, 3552, 3643 and 3653, were selected for

this experiment. These samples possessed a wide range of strength, maturity and length

while the elongation values varied within a small range. At stage I, average fiber

properties of the samples varied as follows. Average force-to-break measured with

FAVIMAT ranged from 3.92 cN to 5.26 cN; AFIS maturity ratio ranged from 0.78 to

0.91; AFIS length by number ranged from 0.68 inch to 0.85 inch and FAVIMAT

elongation-at-break ranged from 10.19% to 13.59% (Tables 3.1 and 3.2). Among the

selected samples ‘25’ had the highest force-to-break while ‘3552’ had the lowest. ‘3552’


54

was also the least mature cotton whereas ‘3643’ was the most mature. Sample ‘8’

possessed the shortest lengths while ‘3653’ was the longest cotton.

Table 3.1 Mean tensile property measurements of the selected samples for stage I

(measured by FAVIMAT)

Sample ID Elongation-at-

break (%)

Force-to-break

(cN)

Work-to-break

(cNcm)

8 10.32 4.42 0.070

25 13.38 5.26 0.104

3552 13.59 3.92 0.086

3643 10.19 4.75 0.071

3653 10.59 4.65 0.072

Table 3.2 Mean AFIS fiber properties of the selected samples for stage I

Sample ID Length by

Number (inch)

Maturity

Ratio

SFC by

Number (%)

8 0.68 0.86 33.0

25 0.83 0.88 18.1

3552 0.73 0.78 31.8

3643 0.79 0.91 26.8

3653 0.85 0.88 20.9

SFC - Short Fiber Content


55

Prior to the experiment the samples were preconditioned at 70±1◦F and 65±2% relative

humidity for 48 hours. From each sample, 5g of cotton was sub-sampled and blended

using a specially designed table top blender which does not cause any fiber breakage. The

blended fiber samples were passed once through USTER AFIS PRO and were considered

as the first stage of the experiment. An additional set of blended cotton samples was

passed through the AFIS twice. The resultant samples were considered as the second

stage of the experiment. As the third stage of the experiment another set of blended

cotton samples were passed thrice through the AFIS (Figure 3.4).

Tensile properties of all the cotton samples belonging to the three stages were tested with

the FAVIMAT. Per sample, 3 replicates of 150 individual fibers were tested with the

FAVIMAT using a 3mm gauge length, with a test speed of 20mm/min and a pre-tension

of 0.2cN/dtex. Single fiber tensile testing was carried out at the smallest gauge length so

that short fibers could also be measured.

The AFIS measurements consisted of 20 replicates (slivers) of 10,000 fibers. Fiber

processing and testing were carried out in a conditioned environment at 70±1◦F and

65±2% relative humidity.


56

Figure 3.4 Procedure for evaluating the impact of less aggressive (AFIS) processing

The second phase of the experiment was mainly focused on investigating the impact of

fiber processing by a very aggressive instrument such as the MTM. The experiment was

conducted using the same 5 samples which were used to study the impact of light

processing by AFIS. Sub samples of 30g cotton were obtained from each sample and

were blended using the table top blender. From the blended cotton, 20g was used for

processing in MTM while the remaining cotton was kept aside for initial AFIS

measurements. The 5 cotton samples were subjected to two consecutive runs through the

MTM (Figure 3.5). Fiber property measurements of the resultant fibers were obtained

from FAVIMAT and AFIS. FAVIMAT measurements consisted of three replicates of

150 fibers tested at 3mm gauge length. AFIS measurements of both blended and MTM

processed samples consisted of five replicates of 3,000 fibers.


57

Figure 3.5 Procedure for evaluating the impact of very aggressive (MTM) processing


Comparison of the length distributions prior to and after processing provides an insight

into the extent of fiber breakage caused by the equipment. As visible from the length

distribution in Figure 3.6, when processed with AFIS, at the later stages higher amounts

of short fibers are present in the cotton samples than at the earlier stage. Short fiber

content of cotton is a major concern in the textile industry as the presence of excessive

amounts of short fibers can give rise to low production efficiencies and poor quality of

the textile product.

When cotton is passed through the AFIS, the forces exerted on the fibers eventually result

in fiber breakage. Especially, the opening roller contains metal teeth that can damage the

fibers during fiber individualization. Therefore, the subsequent increase in short fiber

content due to AFIS processing demonstrates that AFIS effectively causes fiber breakage.


58

Figure 3.6 AFIS length distribution of sample 3643 in the 3 stages

The difference between the length distributions of the stages 1 and 2 is greater than the

difference between the stages 2 and 3. Most of the fibers with higher propensity to break

are broken at stage 2. Therefore, less of the fibers that have higher propensity to break are

left in the remaining population. Thus, comparatively less fiber breakage occurs at stage

3, which is the reason for the less difference between those two stages.

One of the main considerations of the present study is to evaluate the impact of fiber

processing on cotton fiber tensile properties. Thus, alterations in the three main tensile

properties elongation-at-break, force-to-break and work-to-break are assessed at each

processing stage. To determine the presence or absence of a significant difference

between the stages, for each tensile property, Analysis of variance (ANOVA) is

conducted using version 10 of the JMP Pro software.

0

1

2

3

4

5

6

7

8

9

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5

Fre

qu

ency

Length by number (inch)

3643

3643 - Stage 1

3643 - Stage 2

3643 - Stage 3


59

Figure 3.7 Mean elongation-at-break values of the 5 samples across the 3 stages

As demonstrated in Figure 3.7, elongation-at-break is not significantly different across

the three processing stages. Due to the extremely narrow range of elongation of the 5

samples, and the less aggressive nature of processing, it is not possible to see a significant

impact on elongation-at-break.

8

9

10

11

12

13

14

15

8 25 3552 3643 3653

Elo

ng

ati

on

-at-

bre

ak

(%

)

Sample ID

Stage 1

Stage 2

Stage 3

---NS-- ---NS-- ---NS-- ---NS-- ---NS--


60

Figure 3.8 Mean force-to-break values of the 5 samples across the 3 stages

*Levels not connected by the same letter are significantly different at α =0.05

significance level.

A significant difference in force-to-break between the stages can be observed for three

samples (Figure 3.8). For 8, 3643 and 3653, force-to-break values of the second and third

stages are significantly higher than that of the first stage. The significant increase in

force-to-break at the later stages indicates that the proportion of strong fibers is also

higher at those stages. This can be attributed to the lower propensity to break of the high

force-to-break fibers. Accordingly fibers with high force-to-break have survived better

during processing resulting in higher proportions in the subsequent processed samples.

Since most of the fibers with higher propensity to break might have been broken at stage

2, less of those fibers are present in the subsequent population. Therefore, the difference

3

3.5

4

4.5

5

5.5

6

8 25 3552 3643 3653

Fo

rce-

to-b

rea

k (

cN)

Sample ID

Stage 1

Stage 2

Stage 3

--NS-- --NS-- b a a b a a

a

b a a


61

in force-to-break between the second and third stages is not significant for the above 3

samples. However, as a whole force-to-break is not significantly different between the

stages. The higher maturity of the above three samples might have caused the significant

difference in force-to-break that can be observed with those samples.

Figure 3.9 Mean work-to-break values of the 5 samples across the 3 stages


significance level.

Except for sample 8, work-to-break of the other samples does not significantly differ

between the three stages (Figure 3.9). The significant difference observed in sample 8

might be due to its low work-to-break. Sample 8 had the lowest work-to-break at the first

stage. Thus, compared to the other samples a slighter magnitude of change in work-to-

break between the stages could turn out to be significant. Force-to-break of sample 8 also

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0.11

8 25 3552 3643 3653

Work

-to-b

reak

(cN

cm)

Sample ID

Stage 1

Stage 2

Stage 3

---NS--- ---NS--- ---NS--- ---NS---

b a ab


62

significantly differs across the stages. As work-to-break is a combination of force-to-

break and elongation-at-break, the significant difference in force-to-break of sample 8

might have also caused the significant difference in work-to-break of that sample. Even

though work-to-break of sample 8 significantly differs between the first two stages, the

third stage does not significantly differ from any of the other two stages.

Considering all the samples in general, work-to-break does not significantly differ

between the 3 stages. Since both elongation and force do not display significant

differences between the processing stages work-to-break also has to be non-significant.

Overall, none of the tensile properties are significantly different between the fiber

samples belonging to the 3 different stages. All the samples have behaved the same when

processed with AFIS. Processing did not have any significant impact on cotton fiber

tensile properties when these selected samples were processed with less aggressive

equipment like AFIS. Therefore, AFIS is not aggressive enough to reveal the impact of

processing. Hence, it can be stated that light processing does not cause enough fiber

breakage to see a significant impact of processing. As mentioned earlier elongation-at-

break of the 5 samples varies within a small range. Thus, it also appears that light

processing does not have any impact on cotton fiber tensile properties when the samples

possess a narrow range of elongation.

Rebenfeld (1957) stated that the extent of fiber property changes due to processing is not

the same for all the cottons and mostly these changes are functions of the native fiber


63

properties. Correspondingly, according to our results, characteristic fiber properties of

cotton as well as their ranges seem to influence the impacts caused by fiber processing.

In order to understand the relationships between cotton fiber properties and fiber

breakage, length distributions of the 5 cotton samples are compared. Out of the 5

samples, sample 25 possesses the highest force-to-break whereas sample 3552 possesses

the lowest force-to-break. Considering the length distributions of these two samples

(Figures 3.10 and 3.11) through the 3 stages, sample 25 (Figure 3.10) displays less

difference between the stages compared to sample 3552 (Figure 3.11). This can be

attributed to the unequal extents of fiber breakage that has occurred in the two cottons

due to processing. The stronger cotton which can better withstand the processing stresses

demonstrates less fiber breakage compared to the weaker cotton. Thus, in the length

distribution of sample 25 slight differences can be observed between the 3 stages whereas

comparatively larger differences can be observed for sample 3552.


64



0

1

2

3

4

5

6

7

8

9

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25

Fre

qu

ency


25

25 - Stage 1

25 - Stage 2

25 - Stage 3

0

1

2

3

4

5

6

7

8

9

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5

Fre

qu

ency


3552

3552 - Stage 1

3552 - Stage 2

3552 - Stage 3


65

AFIS is considered as an instrument which quite well simulates the behavior of cotton

during further textile manufacturing processes. Cotton which shows high fiber breakage

when passing through the AFIS also has a high tendency for fiber breakage during textile

processing steps such as carding. Hence, the AFIS length distributions indicate that a

strong cotton like 25 will result in less fiber breakage at textile processing than a weak

cotton like 3552.

To study the relationships between fiber length and fiber breakage caused by the AFIS,

length distributions of the longest and the shortest cottons are taken into account. From

the 5 samples, sample 3653 has the highest mean length (0.85 inch) while sample 8 has

the shortest mean length (0.68 inch).


0

1

2

3

4

5

6

7

8

9

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5

Fre

qu

ency


3653

3653 - Stage 1

3653 - Stage 2

3653 - Stage 3


66


Comparison of the length distributions shows that the difference between the stages is

comparatively higher for sample 3653 (Figure 3.12) than for sample 8 (Figure 3.13). In

order for the AFIS individualizer to apply force on fibers, fibers must extend from the

feed roller to the individualizer. Therefore, to be broken by the AFIS, fibers need to be

more than 0.63 inch (16mm) long. When the mean lengths of the two samples are

considered, it is apparent that 3653 possesses a higher amount of fibers that are longer

than 0.63 inch compared to sample 8. Consequently 3653 may have more fiber breakage

with AFIS than sample 8. Since more fibers are broken, difference between the stages is

greater for the longer cotton. Thus, the longer the cotton is, the greater the fiber breakage

that occurs when passing through the AFIS.

0

1

2

3

4

5

6

7

8

9

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5

Fre

qu

ency


8

8 - Stage 1

8 - Stage 2

8 - Stage 3


67

Maturity and fineness are the other main fiber properties measured by AFIS. Both

maturity and fineness of the cotton samples remained the same along processing with

AFIS.

As the second phase of the experiment the impacts caused by light and aggressive

processing are compared. The aggressive processing instrument used in the experiment

was MTM. AFIS which is less aggressive than MTM was considered as the light

processing equipment. In this context, light processing represents the samples that had

been passed once through the AFIS. The samples which were subjected to two runs

through the MTM are represented by aggressive processing.

Figure 3.14 AFIS length distribution of sample 25 at light and aggressive processing

stages

0

1

2

3

4

5

6

7

8

9

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25

Fre

qu

ency


25

25 - Light

processing

25 - Aggressive

processing


68

As visible from the length distribution of sample 25 in Figure 3.14, aggressive processing

results in a higher short fiber content than light processing. This implies the occurrence of

more fiber breakage with MTM than with AFIS. In other words, aggressive processing

tends to cause more fiber breakage than light processing.

To explore the variations between the two extents of processing main tensile properties

are analyzed at each processing step.

Figure 3.15 Mean force-to-break values of the 5 samples at the 2 processing stages

Mean force-to-break (Figure 3.15) is not significantly different between the light and

aggressive processing stages for any of the samples.

At the early stage of this experiment, when light processing was considered, few samples

displayed a significant increase in force-to-break at the later processing stages (Figure

3.0

3.5

4.0

4.5

5.0

5.5

8 25 3552 3643 3653

Forc

e-to

-bre

ak

(cN

)

Sample ID

Light

processing

Aggressive

processing--NS-- --NS-- --NS-- --NS-- --NS--


69

3.8). It indicated that stronger fibers which possessed lower propensity to break have

survived better during light processing. Yet, the absence of a significant increase in force-

to-break with aggressive processing emphasizes that stronger fibers have not exhibited a

better survival when much greater stresses are exerted on the fibers.

Figure 3.16 Mean elongation-at-break values of the 5 samples at the 2 processing stages


significance level.

As illustrated in Figure 3.16 mean elongation-at-break values of the aggressively

processed samples are significantly higher than the samples which were lightly

processed. This is true for all 5 cotton samples used in the study. Unlike in light

processing with the AFIS, processing with the MTM seems to have a major impact on

elongation. When processed with the aggressive instrument (MTM) many of the fibers

8

9

10

11

12

13

14

15

16

8 25 3552 3643 3653

Elo

ngati

on

-at-

bre

ak

(%

)

Sample ID

Light

processing

Aggressive

processing

b a b a b a b a b a


70

that have low elongation have been broken, whereas the fibers with high elongation have

survived better. Thus, compared to light processing a significantly higher amount of high

elongation fibers could be seen after aggressive processing. Therefore, completely

different observations are obtained when the samples are processed with the AFIS and

the MTM. With light processing the fibers that are broken are the weaker fibers whereas

with harsh processing the fibers that are broken are those which possess low elongation.

Improvements in the efficiency and productivity of textile processes are essential for the

development of textile industry. Even though modern automated systems bring about

increased processing speeds, and save cost and man power, the stresses applied on fibers

have also dramatically increased compared to the conventional machinery. These

intensified forces exerted on fibers result in aggravated fiber damage which can adversely

affect the quality of the textile product. For instance, development of high speed carding

machines and faster spinning technologies has increased the degree of fiber damage

which occurs at processing. Open-end rotor spinning, which is now a major spinning

technology, is completely automated. Rotors turn at a speed of 140,000 rpm applying a

huge stress on fibers. Thus, in order to compensate for the increasing mechanical stresses

it is necessary to produce cotton which can endure harsh processing.

According to our results fibers with high elongation show better survival than low

elongation fibers when subjected to harsh processing. In addition, strong fibers have not

displayed better performance when it comes to harsh processing. Therefore, in terms of

aggressive processing elongation seems to be more important than force-to-break.

Accordingly fibers with improved elongation would be a very good alternative to the


71

arising problem of extensive forces related to high processing speeds in the textile

industry.

Figure 3.17 Mean work-to-break values of the 5 samples at the 2 processing stages


significance level.

Mean values of work-to-break significantly differ between the two processing types

(Figure 3.17). Work-to-break is a combined measurement of elongation-at-break and

force-to-break. Thus, the significant impact observed in work-to-break is consistent with

the significant impact which exists in elongation. The significantly higher work-to-break

in aggressive processing represents a higher proportion of high work-to-break fibers in

the aggressively processed samples. Therefore, fibers with high work of rupture have

survived during processing while those with low work of rupture have been broken.

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

8 25 3552 3643 3653

Work

-to-b

rea

k (

cNcm

)

Sample ID

Light

processing

Aggressive

processing

b a b a b a b a b a


72

Maturity and fineness distributions of the raw and MTM processed samples are also

compared. Noticeable differences cannot be detected between the raw and processed

samples with regard to maturity or fineness. Similar to processing with AFIS both

parameters have remained the same when processed with MTM.

3.5 Conclusion

Five cotton samples representing a wide range of strength and maturity and a small range

of elongation were employed in the study. To evaluate the impact of fiber processing on

cotton fiber tensile properties two different levels of processing were used. AFIS was

considered as the light processing instrument while MTM was the aggressive processing

instrument. The selected samples were processed separately with the two instruments and

their impacts on tensile properties were compared.

As the initial phase of the study the samples were blended and then processed with AFIS

in three different processing stages. The samples which were passed though the AFIS

once, twice and thrice were respectively named as first, second and third stages.

According to the results obtained, when fibers are passed through the AFIS some amount

of fiber breakage occurs. Degree of fiber breakage is influenced by the characteristic fiber

properties of the cotton samples such as strength and length. None of the tensile

properties differed significantly between the three processing stages. Hence, it can be

concluded that AFIS is not aggressive enough to reveal the impact of processing. In

addition, when elongation of the samples varies within a small range, light processing

does not seem to have any impact on cotton fiber tensile properties. Although the overall

effect on force-to-break was not significantly different, few samples resulted in a


73

significant increase in force-to-break at the later stages indicating the breakage of weak

fibers and the survival of strong fibers.

Results obtained in the second phase of the study indicate that aggressive processing with

MTM causes more fiber breakage than light processing. Significant differences between

the two types of processing were detected for both elongation-at-break and work-to-

break. Compared to light processing, aggressive processing has resulted in significantly

higher elongation and work-to-break values. Fibers which possessed high elongation

were able to withstand the stresses of harsh processing, whereas those with low

elongation have undergone fiber breakage. Thus, elongation seems to be the dominant

tensile property in aggressive processing.

Hence, different effects were observed with the two levels of fiber processing. Light

processing is not aggressive enough and does not cause enough fiber breakage to reveal a

significant impact of processing. But during harsh processing low elongation fibers tend

to have a higher propensity to break. With the gradually increasing processing speeds of

the textile industry the necessity of improving stress endurance of fibers is highly felt. As

implied by the results of the present study, fibers with high elongation are capable of

surviving aggressive processing better than those with low elongation. Therefore, cotton

fibers with improved elongation would serve this purpose. Thus, it can be interpreted that

fiber elongation might be the most important tensile property in textile processing.


74

CHAPTER IV

EVALUATING THE IMPORTANCE OF COTTON FIBER ELONGATION IN TERMS

OF FIBER PROCESSING

4.1 Introduction

Developing cottons with improved fiber quality is a major concern of the breeding

programs around the world. Priority of these programs is most often given to the

improvement of fiber strength and length while fiber elongation has generally been

neglected in the selection process.

Fiber elongation or extensibility is one of the main contributing factors of yarn quality.

Improved fiber elongation results in improved work of rupture of the fiber. Thus, less

fiber breakage occurs at the gin and other processing stages, which leads to a reduced

short fiber content. Subsequently, a better yarn evenness can be achieved.

High Volume Instrument (HVI) is the cotton classification instrument that is considered

as the standard method for the measurement of fiber properties. Nevertheless, the HVI

lacks calibration procedures for elongation measurement that prevents the instrument

from providing a precise measurement for the property, which is one of the reasons for

the lack of interest in elongation in the breeding programs. Even though the Stelometer

can be properly calibrated for elongation, it is not feasible for extensive use since it is

extremely slow. In addition, the weak negative correlation between elongation and

tenacity is preventing the breeders from working on elongation assuming that it would

give rise to lower tenacity. Thus, there is a lack of interest among cotton breeders to

improve fiber elongation. However, the presence of a weak negative correlation should


75

not hinder the improvement of both tenacity and elongation simultaneously. In fact, being

restricted to fiber tenacity in terms of improving the work-to-break is inaccurate (Benzina

et al., 2007). The use of strength alone as the basis for selection or rejection of

experimental cotton varieties might be inadequate (Fiori et al., 1956).

In a previous experiment of the present study, a positive correlation was observed

between individual fiber tenacity and elongation (measured by FAVIMAT) which

reinforced the importance of improving elongation. In addition, the impact of fiber

processing on tensile properties was evaluated in Chapter 3. According to the results

obtained, it appears that fiber elongation is the critical tensile property in aggressive

processing. Therefore, the results of the above two experiments suggested the necessity

of further evaluating the importance of elongation. Hence, the current experiment focuses

on investigating the importance of elongation in fiber processing. This will be helpful to

determine whether selection of cotton cultivars based on their elongations would be

beneficial during processing of cotton fibers in the textile industry. In addition, the

relationships between elongation and other major fiber properties are also assessed in this

chapter.

To fulfill the main intention of determining the importance of elongation, it is necessary

to isolate elongation from other fiber properties. Therefore, cotton samples that are

similar in all other fiber properties except elongation are selected to serve this purpose.

The selected samples also represent a wide range of elongation, which will be more

favorable in assessing the impact of elongation.


76

In order to evaluate the impact of processing, Micro Dust and Trash Analyzer 3 (MDTA

3) is used as the processing equipment in this experiment. MDTA 3 (Figure 4.1) is

basically used to determine the trash content of a sample and to separate the lint, trash,

fiber fragments and dust. It opens up the fiber tufts to single fibers which are then

cleaned, blended and finally formed into a sliver. MDTA 3 also has the potential to cause

fiber breakage and may remove some short fibers as well. It is considered as an

aggressive fiber processing instrument.

Figure 4.1 Micro Dust and Trash Analyzer 3 (MDTA 3)

In this chapter, fiber properties measured using FAVIMAT, Advanced Fiber Information

System (AFIS) and Cottonscope are taken into consideration. Tensile property

measurements of the fibers are acquired from the FAVIMAT. AFIS is used to obtain

length, fineness and maturity distributions. Cottonscope (Figure 4.2) provides accurate


77

measurements of fiber fineness, maturity ratio, ribbon width and micronaire with the use

of fiber snippets. Polarized light microscopy and image analysis are the techniques used

in the Cottonscope.

Figure 4.2 Cottonscope

4.2 Hypotheses

When the impact of fiber processing on tensile properties was assessed (Chapter 3),

elongation appeared to be the most important tensile property in aggressive fiber

processing. In accordance with that, it can be hypothesized that fibers with higher

elongations may perform better when subjected to processing than those with lower

elongations.

The MDTA3, which is the fiber processing equipment used in this experiment is also

aggressive. Thus, we expect to see a difference between the tensile property distributions


78

of the raw and processed stages. As the higher elongation fibers may withstand

processing better and may result in less fiber breakage, it is hypothesized that the

proportion of higher elongation fibers in the processed samples will be higher than that of

the raw samples (Figure 4.3).

Figure 4.3 Hypothesized elongation-at-break distributions of the raw and processed

stages

Since cotton samples with a wide range of elongation are employed in the experiment, it

is assumed that the better performance of higher elongation fibers will be portrayed in the

elongation-at-break distributions of the raw and processed samples belonging to the

different elongation groups. As observed in Chapter 2 (Figure 2.8) of the present study,

standard deviation of individual fiber elongation increases with higher elongations.

Because high elongation cotton has higher variation, it can be hypothesized that higher

the elongation, higher will be the difference between the raw and processed stages.


79

Therefore, for the high elongation cottons, we expect to see a greater difference between

the elongation-at-break distributions of the two stages.

4.3 Objectives

To investigate the importance of cotton fiber elongation in terms of fiber

processing

To assess the relationships between elongation and other important fiber

properties such as strength and length


Thirty two cotton samples were selected for the experiment based on their High Volume

Instrument (HVI) elongation values. The selected samples possess a wide variation in

their elongations ranging from 10.04% to 16.17% (Table 4.1), while all other fiber

properties are nearly the same within each family. These samples resulted from a

breeding program aimed at improving cotton fiber elongation. The statistical design of

the relevant field experiment had been randomized complete block design with four field

replications per breeding line. The thirty two samples belong to two families; ‘1’ and ‘2’.

Each family consists of two groups; the HVI higher elongation group and the lower

elongation group. Each elongation group is comprised of samples which were grown in

two different locations; A and B (Figure 4.4). Altogether there are four different breeding

lines in two locations (A and B), designated respectively with the corresponding family

name, HVI elongation group and the location as follows; 1 Low A, 1 Low B, 1 High A, 1

High B, 2 Low A, 2 Low B, 2 High A and 2 High B.


80

Figure 4.4 The cotton samples selected for the experiment


81

Table 4.1 Mean tensile property measurements of each group for the raw stage

Group Elongation-at-

break (%)

Force-to-break

(cN)

Work-to-break

(cNcm)

1 Low A 12.13 5.31 0.096

1 Low B 10.93 4.90 0.080

1 High A 16.17 5.29 0.130

1 High B 15.44 5.30 0.126

2 Low A 10.14 4.88 0.073

2 Low B 10.04 4.72 0.070

2 High A 14.74 4.95 0.114

2 High B 13.65 5.03 0.107

Prior to the experiment the samples were preconditioned at 70±1◦F and 65±2% relative

humidity for at least 48 hours. For fiber testing two sub samples of 5g lint were obtained

from each original sample. The raw (unprocessed) lint samples were tested with USTER

AFIS PRO, FAVIMAT (Textechno Herbert Stein GmbH. & Co.KG) and Cottonscope.

AFIS data for each sample consisted of five replicates of 3,000 individual fibers.

FAVIMAT measurements included two replicates of one hundred and fifty individual

fibers per sample. Individual fiber tensile testing with the FAVIMAT was carried out at

3mm gauge length, with a test speed of 20mm/min and a pre-tension of 0.2cN/dtex. The

minimum gauge length was used so that the short fibers could be analyzed as well. Six

replications of 50±1 mg were analyzed for each sample using the Cottonscope, primarily

to measure fineness, maturity ratio, micronaire, and ribbon width.


82

As the second phase of the experiment, the thirty two samples were subjected to

processing in the Micro Dust and Trash Analyzer 3 (MDTA 3). This was performed to

investigate the impact of processing and to evaluate the significance of elongation in

terms of processing. For fiber processing two sub samples of 5g lint were drawn from

each initial sample. After being run through the MDTA 3 twice, the processed samples

were tested with the AFIS, FAVIMAT and Cottonscope employing the same testing

procedure as for the first set of samples. All the fiber testing and processing were carried

out in a conditioned environment at 70±1◦F and 65±2% relative humidity.


AFIS length distributions of the raw and processed samples are compared within each

elongation group of each family to examine the impact of processing using the MDTA3.

The processed samples contain a higher short fiber content compared to the

corresponding raw samples (Figure 4.5). This observation holds true for both elongation

groups of both families. The resultant increase in short fiber content after processing with

the MDTA3, implies that the instrument causes fiber breakage.


83

Figure 4.5 AFIS length distributions of lower elongation group of family 1 in raw and

processed stages

The three tensile property measurements obtained from FAVIMAT, namely elongation-

at-break, force-to-break and work-to-break, are taken into account during the analysis of

the FAVIMAT data. Several sources of variability can be found in the experiment;

family, elongation group, location, field replications and test replications. Therefore, to

determine which of these influencing parameters are statistically significant, analysis of

variance (ANOVA) is performed. For each tensile property, ANOVA is conducted using

version 10 of the JMP Pro software to determine the differences between the two

families, two elongation groups and the two locations. The null hypotheses tested in all

the above instances are that the mean values for a particular parameter are equal for the

two families, two elongation groups and the two locations. Significance of the interaction

0

1

2

3

4

5

6

7

8

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25

Fre

qu

ency


Family 1 - Low

1 - Low - Raw

1 - Low - Processed


84

between the two factors, elongation group and location, is also assessed. The differences

between the mean tensile property measurements of the processed and raw stages are

used to perform the ANOVA test at the 0.05 significance level.

Figure 4.6 Mean elongation-at-break values of the 8 groups for the two stages


significance level.

Except for location A of the lower elongation group of family 2, mean elongation-at-

break values show a significant increase in the processed samples for all the other groups

(Figure 4.6). This indicates that fibers with high elongations tend to have a lower

propensity to break. In a population of fibers both higher and lower elongation fibers are

present. When subjected to processing, the higher elongation fibers tend to survive better

6

8

10

12

14

16

18

20

1 Low

A

1 Low

B

1 High

A

1 High

B

2 Low

A

2 Low

B

2 High

A

2 High

B

Elo

ngati

on

-at-

bre

ak

(%

)

Group

Raw

Processed

b a a a b a b a b a b a

Family **

Elongation group **

Location NS

Elongation group*Location **

b a b a


85

than the lower elongation fibers. Since lower elongation fibers have been broken during

processing, a higher amount of higher elongation fibers is present in the subsequent

samples, which results in an increase in elongation.

Significant differences in elongation-at-break values are detected between the two

families and the two HVI elongation groups while there is no significant difference

between the two locations. HVI higher elongation groups of both families possess

significantly higher elongations than the corresponding lower elongation groups. From

the two families, elongation-at-break values of family 1 are significantly higher than that

of family 2. The two locations within each elongation group of each family are very

similar in terms of elongation. As the interaction between elongation group and location

is also significant, mean separation is performed using student’s t-test in JMP Pro 10

(Table 4.2).


86

Table 4.2 Student’s t-test ranking of difference between raw and processed cotton in

mean elongation-at-break of the 32 samples

Elongation group **

Location NS

Elongation group x Location **

Level

Difference between raw and processed

cotton in mean elongation-at-break

Ranking

High, A

2.64 A

High, B

2.00 A B

Low, B

1.34 B C

Low, A

0.84 C

*Significant differences between the levels (α =0.05) are denoted by different letters.

Due to the significant interaction between elongation group and location, differences in

mean elongation-at-break between the raw and processed stages, are greater for the

higher elongation groups than for the lower elongation groups. Table 4.2 provides

supporting evidence for the hypothesis that the high elongation cotton shows higher

difference between the raw and processed stages.

The difference between the mean elongation-at-break values of the raw and processed

stages is analyzed family-wise using the student’s t-test (Table 4.3).


87

Table 4.3 Mean separation of difference between raw and processed cotton in mean

elongation-at-break of the two families

Level


cotton in mean elongation-at-break

Ranking

Family 1 1.97 A

Family 2 1.43 B

Among the two families, difference between the raw and processed stages is more

prominent in family 1 than in family 2 (Table 4.3). At the raw stage, family 1 shows more

variation in elongation, ranging from 10.93% to 16.17%, than family 2, in which

elongation varies from 10.04% to 14.74% (Table 4.1). Thus, the family which possesses a

wider variation in elongation shows a greater difference between the elongation

measurements of the raw and processed stages.


88

Figure 4.7 Mean force-to-break values of the 8 groups for the two stages

Mean force-to-break values of the processed stage are not significantly different from

those of the raw stage, for any of the groups (Figure 4.7). As it is not possible to detect a

significant increase in the amount of stronger fibers after processing, it can be interpreted

that the fibers with higher force-to-break might not have displayed better survival when

subjected to processing with the MDTA3. No significant effect of the three factors

family, elongation group and location could be identified with regard to the force-to-

break values. Nevertheless, the interaction between the two factors elongation group and

location demonstrates a significant impact on force-to-break. The significant interaction

between elongation group and location is analyzed using student’s t-test (Table 4.4).

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

5.6

1 Low

A

1 Low

B

1 High

A

1 High

B

2 Low

A

2 Low

B

2 High

A

2 High

B

Fo

rce-

to-b

rea

k (

cN)

Group

Raw

Processed

-NS-

Family NS

Elongation group NS

Location NS


-NS- -NS- -NS- -NS- -NS- -NS- -NS-


89


mean force-to-break of the 32 samples

Elongation group NS

Location NS


Level


cotton in mean force-to-break

Ranking

High, A

0.2214 A

Low, B

0.0300 A B

High, B

-0.0114 A B

Low, A

-0.1194 B


As visible from Table 4.4, two of the levels display a slight increase in force-to-break due

to processing, while the other two levels display a very slight decrease in force-to-break.


90

Figure 4.8 Mean work-to-break values of the 8 groups for the two stages


significance level.

Work-to-break is a combination of elongation-at-break and force-to-break. Thus,

consistent with elongation-at-break, mean work-to-break values also demonstrate a

significant increase in the processed samples (Figure 4.8). This holds true for all the

groups except for location A of the lower elongation group of family 1. The consequent

significant increase in work-to-break indicates the lower propensity to break of the fibers

which possess higher work-to-break. Therefore, the fibers with higher work-to-break

seem to have survived better during processing. As a result, a high amount of fibers

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

1 Low

A

1 Low

B

1 High

A

1 High

B

2 Low

A

2 Low

B

2 High

A

2 High

B

Wo

rk-t

o-b

rea

k (

cNcm

)

Group

Raw

Processed

b a b a b a b a b a b a b a

Family NS

Elongation group **

Location NS


a a


91

having higher work-to-break is left in the subsequent population, giving rise to an

increase in work-to-break.

Similar to elongation-at-break, work-to-break also significantly differs between the HVI

elongation groups. Higher elongation groups of both families possess significantly higher

work-to-break values than the corresponding lower elongation groups. But, unlike

elongation-at-break, work-to-break does not significantly differ between the two families.

Similar to both elongation-at-break and force-to-break, location does not have a

significant impact on work-to-break, whereas the interaction between elongation group

and location is significant. Thus, mean separation is performed using student’s t-test

(Table 4.5).


mean work-to-break of the 32 samples

Elongation group **

Location NS


Level


cotton in mean work-to-break

Ranking

High, A 0.0248 A

High, B 0.0166 A B

Low, B 0.0132 B C

Low, A 0.0056 C



92

Owing to the significant interaction between elongation group and location, differences in

mean work-to-break between the raw and processed stages, are greater for the higher

elongation groups than for the lower elongation groups (Table 4.5).

Considering the observations of the tensile properties, it appears that processing did not

have a significant impact on force-to-break. Hence, it can be stated that the impact of

elongation has been isolated in the selected 32 samples. Thus, the selected materials are

suitable and adequate to test our objective of evaluating the importance of elongation in

fiber processing.

Due to the high variability of cotton fibers, their mean tensile properties do not represent

the characteristics of the entire distribution. Therefore, it is essential to examine the

tensile property distributions of the raw and processed stages.

As mentioned previously, field replications are a source of variability among the selected

32 samples. Thus, the tensile property distributions of each group are inspected to study

the variability among the four field replications within a group. Figure 4.9 illustrates the

elongation-at-break distributions of the four field replications which belong to location A

of higher elongation group of family 1 at the raw stage.


93

Figure 4.9 Elongation-at-break distributions of the 4 field replications of location A of

higher elongation group of family 1 at the raw stage

As visible from Figure 4.9, the field replications within a group are nearly the same.

Hence, the difference between the field replications will not be considered during further

analysis of the distributions. According to the ANOVA results, location effect was not

significant for any of the tensile properties. Therefore, to facilitate clear interpretation of

the distributions, difference between the two locations will also be disregarded

henceforth. Consequently the distributions of the HVI higher and lower elongation

groups of both families at the raw and processed stages will be taken into account.

0.00

0.05

0.10

0.15

0.20

5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5

Relative

Frequency

Elongation-at-break (%)

Family 1 - High - A - Raw

1 - High - A - 1

1 - High - A - 2

1 - High - A - 3

1 - High - A - 4


94

Figure 4.10 Elongation-at-break distributions of the two elongation groups of family 1

for both raw and processed stages

The above elongation-at-break distribution elucidates a clear clustering based on the HVI

elongation group which is analogous to the significant impact of elongation group that

was detected with the statistical analysis. Figure 4.10 also demonstrate a shift in the

distributions of the processed samples. The distributions of the processed samples are

shifted towards the higher elongations, compared to the distributions of the corresponding

raw samples. Since lower elongation fibers tend to be broken during processing, a high

amount of higher elongation fibers is left in the successive population. The resultant

increase in elongation is displayed by the shift in the distributions. These distributions

comply well with the hypothesized elongation-at-break distributions.

0.00

0.05

0.10

0.15

0.20

0.25

5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5 35 37.5

Relative

Frequency


Family 1

1 - High - Processed

1 - High - Raw

1 - Low - Processed

1 - Low - Raw


95

In addition, the shift in the distributions of the processed samples is prominently visible

in the higher elongation groups (Figure 4.10). As visible from the elongation-at-break

distributions, in the higher elongation groups elongation varies over a wider range,

whereas it varies over a narrower range in the lower elongation groups. Therefore, high

elongation cotton has a wider distribution. The difference between the raw and processed

stages is high for the higher elongation groups. Accordingly, a bigger shift in the

distributions can be observed for the higher elongation groups. This supports the

hypothesis that the difference between the stages increases with increasing elongation.

The elongation-at-break distributions of family 2 (Figure 4.11) also illustrate the same

trends which are observed with family 1. Comparison of the distributions of the two

families reveals that family 1 (Figure 4.10) shows higher differences between the raw and

processed stages than family 2 (Figure 4.11).


96

Figure 4.11 Elongation-at-break distributions of the two elongation groups of family 2

for both raw and processed stages

In order to be tested with the FAVIMAT, fibers need to be clamped on both ends. Thus,

from a fiber sample only the fibers which are long enough to be caught on both ends

could be tested with the FAVIMAT. For instance, approximately the fibers need to be at

least 11mm long to be tested with FAVIMAT employing the 3mm gauge length. Fiber

processing always results in some amount of fiber breakage. As a consequence, short

fibers are generated during fiber processing. These short fibers cannot be tested with

FAVIMAT. Thus, among the fibers with a higher tendency to break, breakage of short

fibers would be less visible in the distributions while breakage of longer fibers would be

more visible.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5 35

Relative

Frequency


Family 2


2 - High - Raw

2 - Low - Processed

2 - Low - Raw


97

The force-to-break distributions of the two families are illustrated below (Figures 4.12

and 4.13).

Figure 4.12 Force-to-break distributions of the two elongation groups of family 1 for

both raw and processed stages

0.00

0.05

0.10

0.15

0.20

1 2 3 4 5 6 7 8 9 10 11 12 13

Relative

Frequency

Force-to-break (cN)

Family 1


1 - High - Raw

1 - Low - Processed

1 - Low - Raw


98

Figure 4.13 Force-to-break distributions of the two elongation groups of family 2 for


As visible from Figures 4.12 and 4.13, the force-to-break distributions are not noticeably

different between the two elongation groups as well as the raw and processed stages. The

32 samples have been selected for the experiment ensuring that all the fiber properties

except elongation are nearly constant within each family. Since the above distributions

indicate that the two elongation groups within a family do not differ in terms of force-to-

break, it provides evidence that the sample selection was ideal. In addition, the

distributions clearly depict the absence of a processing impact on force-to-break. This

implies that the fibers with higher force-to-break have not displayed a considerably better

survival when subjected to processing in MDTA3.

0.00

0.05

0.10

0.15

0.20

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Relative

Frequency

Force-to-break (cN)

Family 2


2 - High - Raw

2 - Low - Processed

2 - Low - Raw


99

Figure 4.14 Work-to-break distributions of the two elongation groups of family 1 for


0.00

0.05

0.10

0.15

0.20

0.02 0.06 0.1 0.14 0.18 0.22 0.26 0.3 0.34 0.38

Relative

Frequency

Work-to-break (cNcm)

Family 1


1 - High - Raw

1 - Low - Processed

1 - Low - Raw


100

Figure 4.15 Work-to-break distributions of the two elongation groups of family 2 for


As work-to-break is a combination of force-to-break and elongation-at-break, the trends

and relationships revealed by the work-to-break distributions (Figures 4.14 and 4.15) are

consistent with the elongation-at-break distributions. The distributions of the processed

samples are shifted towards the higher work-to-break values. This indicates that the fibers

with higher work-to-break have survived better during processing than those with lower

work-to-break. Thus, a high amount of fibers which possess higher work-to-break, is left

in the subsequent population which causes the shift in the distributions towards the higher

work-to-break.

Within a family, the work-to-break distributions of the two elongation groups could be

clearly distinguished from each other. The higher elongation groups possess a wider

0.00

0.05

0.10

0.15

0.20

0.25

0.02 0.06 0.1 0.14 0.18 0.22 0.26 0.3 0.34 0.38

Relative

Frequency

Work-to-break (cNcm)

Family 2


2 - High - Raw

2 - Low - Processed

2 - Low - Raw


101

variation in work-to-break than the lower elongation groups. The difference between the

raw and processed stages is also high for the higher elongation groups.

The statistical analyses of the FAVIMAT data and the tensile property distributions

confirm all the hypotheses formulated prior to the experiment. Therefore, the FAVIMAT

results clearly demonstrate the better performance of higher elongation fibers in terms of

fiber processing. Furthermore, AFIS length distributions of the raw and processed stages

(Figures 4.16 and 4.17) also provide supporting evidence to the better performance of

higher elongation fibers.

Figure 4.16 AFIS length distributions of the two elongation groups of family 1 at the raw

stage

0

1

2

3

4

5

6

7

8

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2

Fre

qu

ency


Family 1 - Raw

1 - High - Raw

1 - Low - Raw


102

At the raw stage, short fiber content of the samples belonging to the higher elongation

group of family 1, appears to be lower than the corresponding lower elongation group

(Figure 4.16). Even though the above samples belong to the raw stage, as the AFIS fiber

testing procedure causes some fiber breakage, the length distributions display the

breakage of fibers. Therefore, the lower short fiber content in the higher elongation group

suggests less fiber breakage in that group.

Figure 4.17 AFIS length distributions of the two elongation groups of family 1 at the

processed stage

Figure 4.17 illustrates the AFIS length distributions of the same elongation groups at their

processed stage. It also indicates less short fiber content in the higher elongation group,

which implies less fiber breakage in the higher elongation group. Thus, the better

0

1

2

3

4

5

6

7

8

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2

Fre

qu

ency


Family 1 - Processed


1 - Low - Processed


103

performance of higher elongation fibers is portrayed not only in the tensile property

distributions, but also in the length distributions.

If elongation was considered in the cotton breeding programs, it could result in better

fiber length distributions. Better fiber length distributions lead to better yarn evenness

which ultimately results in better fabric quality. Thus, having improved elongations tends

to positively influence the overall fiber quality.

Fineness and maturity distributions provided by the AFIS are also evaluated in the

experiment. The fineness distributions indicate a slight shift towards the higher end in the

processed samples. In other words, the processed samples possess a higher amount of

fibers with higher fineness compared to the corresponding raw samples. The removal of

very fine fibers during processing might have resulted in the above observation. For all

the elongation groups, the maturity distributions remain nearly the same prior and after

processing.

With regard to Cottonscope data, according to the ANOVA results, maturity ratio,

fineness, micronaire and ribbon width do not significantly differ between the raw and

processed stages. In addition, family, elongation group, location and the interaction

between elongation group and location do not have a significant impact for any of the

above parameters measured with the Cottonscope.

A positive correlation between elongation and tenacity of individual fibers was observed

in Chapter 2 (Figure 2.7) of the present study. The above relationship is also assessed for


104

the thirty two samples using their force-elongation scatter plots. The scatter plots of three

selected groups are illustrated below.

Figure 4.18 Individual fiber force-elongation scatter plot of location A of higher

elongation group of family 1

0

2

4

6

8

10

12

14

0 10 20 30 40

Forc

e-to

-bre

ak

(cN

)


Family 1 High - A

1 High A - Raw

1 High A - Processed


105

Figure 4.19 Individual fiber force-elongation scatter plot of location A of lower


Figure 4.20 Individual fiber force-elongation scatter plot of location A of higher


0

2

4

6

8

10

12

14

0 10 20 30 40

Fo

rce-

to-b

rea

k (

cN)


Family 1 Low - A

1 Low A - Raw

1 Low A - Processed

0

2

4

6

8

10

12

14

0 10 20 30 40

Fo

rce-

to-b

reak

(cN

)


Family 2 High - A

2 High A - Raw

2 High A - Processed


106

The force-elongation scatter plots of the 32 samples demonstrate a positive correlation

between the two tensile properties at both raw and processed stages (Figures 4.18, 4.19

and 4.20). Similar to the elongation-at-break distributions, the force elongation scatter

plots also reveal that the difference between the raw and processed stages is more

noticeable in the higher elongation groups (Figure 4.18) than in the lower elongation

groups (Figure 4.19). When the two families are considered, family 1 (Figure 4.18),

which has higher elongations compared to family 2, shows more pronounced differences

between the raw and processed stages than family 2 (Figure 4.20). Moreover, the higher

variation in the HVI higher elongation group shown by the distributions is also detectable

in the scatter plots (Figure 4.18).

As seen by the scatter plots, among the data points of the processed samples (red dots),

there are some fibers which have higher elongation-at-break and lower force-to-break

values. Since those fibers have been able to endure processing, it indicates that the higher

elongation fibers tend to resist better to breakage even when they are not strong. This also

emphasizes the importance of elongation.

4.6 Conclusion

The importance of elongation suggested by the previous experiments was further

evaluated in the current experiment. The thirty two cotton samples selected had diverse

elongations. Yet, all the other fiber properties of the samples were constant within a

family. Each family consisted of two different elongation groups, namely the HVI higher

elongation group and the HVI lower elongation group. The above sample selection

procedure was intended to isolate the impact of elongation from the other fiber properties.


107

Since the objective was to evaluate the importance of elongation in terms of fiber

processing, MDTA3 was used as the processing instrument. FAVIMAT, AFIS and

Cottonscope data of the raw and processed stages were taken into consideration during

the analysis. The statistical analysis of the FAVIMAT data revealed a significant impact

of processing on the elongation-at-break and work-to-break measurements while force-

to-break was not impacted. According to the results, the higher elongation fibers tend to

have lower propensity to break. Thus, they tend to survive better during processing

resulting in a significant increase in elongation-at-break in the processed samples. A

similar increase in work-to-break was observed for the processed samples, as it is a

combination of elongation-at-break and force-to-break. The higher elongation groups

demonstrated a greater difference between the raw and processed stages than the lower

elongation groups. Thus, the impact of processing was more prominently expressed in the

higher elongation groups. The higher elongation groups also displayed wider

distributions than the lower elongation groups.

The AFIS length distributions also revealed less fiber breakage in the higher elongation

groups. This suggests that breeding for improved elongations would give rise to better

length distributions. Since higher elongation fibers tend to have lower propensity to

break, these fibers would perform better in spinning and other textile processing steps.

For instance, as the higher elongation fibers result in less fiber breakage during spinning,

it would give rise to fewer yarn defects. Thus, higher elongations would eventually

improve the quality of the textile product. With the gradually increasing textile

processing speeds, the importance of elongation will be more significant.


108

Therefore, it appears that fiber elongation is a vital tensile property in terms of fiber

processing. Moreover, the results suggest that the weaker fibers which possess higher

elongations also tend to perform better in processing. Thus, in terms of processing, fiber

elongation seems to be even more important than fiber strength.

The FAVIMAT results of the 32 samples also indicated a positive correlation between

individual fiber elongation and tenacity. This emphasizes the possibility of the

simultaneous improvement of both tensile properties. Thus, the mere presence of a

negative correlation between bundle elongation and tenacity should not hinder the

improvement of elongation. As a whole, the results convey that cotton fiber elongation

should no longer be neglected in the breeding programs.


109

CHAPTER V

SUMMARY AND CONCLUSION

In order to meet the rapidly increasing demands of the textile industry, the improvement

of production rates is essential. The necessity of increased productivity has resulted in the

associated development of novel, high speed manufacturing technologies. These rapid

processing speeds greatly intensify the stresses applied on fibers, compromising the fiber

quality, which will consequently deteriorate the yarn and fabric quality. Thus, the

increasing trend of vigorous fiber processing, places an emphasis on breeding for fibers

that can endure harsh processing. In order to produce cotton which can better withstand

the processing stresses, it is necessary to identify the tensile properties which play a

significant role in cotton fiber processing.

Currently strength is considered as the predominant tensile property in terms of fiber

processing. Even though the importance of cotton fiber elongation has also been reported

over the years, breeding for improved elongations has generally been neglected. The

negative correlation between bundle tenacity and elongation has been a main reason for

the lack of interest in elongation, as it is assumed that breeding for improved elongations

might bring reduced strengths. Thus, to investigate this concept, the relationship between

tenacity and elongation of single fibers and fiber bundles was evaluated in the present

study. A positive correlation was observed between individual fiber strength and

elongation, while the two tensile properties were negatively correlated when measured on

fiber bundles. The positive correlation suggests that the stronger fibers tend to have

higher elongation. This implies the possibility of having both improved strengths and


110

elongations simultaneously. Since stronger fibers are usually more mature, the results

also suggest that mature fibers tend to have higher elongation, which is contrary to the

present concept that mature fibers possess lower elongation.

The results also indicated a positive correlation between individual fiber elongation and

its standard deviation. As the standard deviation of individual fiber elongation increases

with elongation, this might be the reason behind the negative correlation between bundle

elongation and tenacity. Thus, the negative correlation observed with fiber bundles can be

attributed to the variation in individual fiber elongation of the constituent fibers.

Therefore, it is inaccurate to conclude that higher elongations will always result in lower

strengths.

To investigate the impact of processing on tensile properties, two different levels of

processing were studied; light processing and aggressive processing. Light processing

does not break enough fibers to see a significant impact of processing. But with harsh

processing higher elongation fibers tend to have a lower propensity to break. Therefore,

to ensure better survival of fibers during processing, emphasis should be placed on

improving both strength and elongation. Especially with the rapidly increasing processing

speeds, fiber elongation will increase in importance in the near future.

The better performance of higher elongation fibers suggested at the earlier stages of the

study was mechanically assessed, employing cotton samples which had a wide variation

in elongation while all other fiber properties were constant within a family. The results

clearly demonstrated that the higher elongation fibers can better withstand the processing


111

stresses. The superior performance of higher elongation fibers was detected with the

tensile property measurements as well as with the length distributions. Therefore, if more

consideration is given to elongation in the breeding programs, it will give rise to less fiber

breakage and better length distributions. As a result, a better yarn evenness will be

achieved which will ultimately lead to a better fabric quality. Enhanced fabric quality will

bring about better revenue. Thus, for the advancement of the cotton industry, fiber

elongation should certainly be included in the breeding programs.


112

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