Indian Journal of Fibre & Textile Research Vol. 28, September 2003, pp. 343-347

Alkali deweighting of acid-modified multicomponent copolyester fibre

Ruxin Yang"

College of Material Engineering, Soochow University , Suzhou 2 1502 1, P. R. China

Received 27 ALlgLlst 2001; revised received and accepted 8 JLlly 2002

The treatment conditions for alkali deweighting of acid-modified multicomponent copolyester fibres have been opt imized. The sati sfactory silk- like effect is observed under the specific treatment conditions [7.5g/L NaOH , 85°C temperature, 40 min treatment time, I :40 materia l-to-liquor ratio, and 1.0g/L promoter]. After alka li deweighting, the special micro-pit structure occurs on the surface of ac id-modified fibres which enhances the fibre permeability , adhesion regain, capability of colouring and feel. The X-ray diffraction patterns show that the degree of crystallization of fibre decreases after alkali peeling.

Keywords: Multicomponent copolyester fibre, Alkali peeling, Alkali deweighting. Copolyeste r fibre

1 Introduction

The alkali peeling of polyester fabrics is a very complex chemical processing procedure. In this procedure, mainly the heterogeneous hydrolysis reaction occurs between the polyester macromolecule and the sodium hydroxide . The ' ester bond of the polyester macromolecule in the fibre breaks by the hydrolysis from the surface to inside and thus produces the low polymers , namely terephthalic acid and ethy lene glyco l that have different molecular weights . However, there are other components, namely SIPM (3,5-sodium dimethyl isophthalate sulphonate) with -S03Na base, PEG with soft short hydrocarbon chains and inactive inorganic salt fi ll er, in the acid-modified multicomponent copolyester fibre (modified polyester fibre) which change the fibre's physical structure and chemical feature, and create micro-pit structure in the fibres. For example, the specific gravity and crystal lin ity of the acid-modified fibres are lower than that of the common polyester fibres, and therefore the fibre needs modification by the alkali I. The modified fibres are very apt to be damaged if they are not treated properly during the si lk-like processing or the alkali peeling. The present work was, therefore, aimed at optimizing the technology parameters for alka li peeling processing.

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2 Materials and Methods 2.1 Materia ls

The fabrics having warp threads of 75dtex/24f acid-modified polyester filaments and weft threads of 1 L I dtex/36f common polyester fi laments were desized, crumpled for 60min at 120-125 °C using 36° Be' NaOH (l.Og/L ), dispersing agent (2g/L) and sodium hydrosulphite (0 .2g/L) , and then preset at 180°C. By separating the warp and weft threads, the acid-modified polyester and common polyester samples were obtained for the study.

2.2 Methods 2.2.1 Alkali Peeling

The parameters of alkali peeling, such as alkali concentration, temperature, treatment time, and type and quantity of promoter(l631), were optimjzed. The test ing was carried out using orthogonal test ~(34) and 1: 40 material-to-liquor ratio. As per the earl ier studies2

.3, the selected parameters and the levels of

orthogonal test are shown in Table 1.

2.2.2 Measurement of Weight Loss

The fabric samples were kept in a drying container with silica gel for 24h before and after processing and

Table I- Parameters and levels of orthogonal test in the alka li peeling for the polyester fibre

Level

2

3

NaOH conc. gIL

5

7 .5

10

Temperature Treatment time °C min

75 20

85 40

95 60

344 INDIAN J. FIBRE TEXT. RES. , SEPTEMBER 2003

then weighted. Assuming the weights of the samples before and after the processing as Wo and WI, the weight loss percentage (R) due to alkali peeling was calculated using the following formula4

:

2.2.3 Measurement of Strength loss According to the standard method as per the

GB3923-83, the absolute strengths (Poland P02 ) of the fabrics before and after alkali peeling respectively were measured. The loss percentage of strength (S) was calcu lated using the following formula:

2.2.4 Observation of Micro-structure of Fibre The samples were kept on the frame, purified for

5mjn in the vacuum (0.1-0.21), and then sputtered for 1.5-2.0min by Argon ion in the electric field with 1.3kY voltage, 20mA current and 0.071 vacuum to produce a thin film of gold (Au). The scanning electron micrographs were obtained using the mkroscope (Hitachi X-650) . The X-ray diffraction patterns of the samples were produced using the X­ray instrument (Flatplate).

3 Results and Discussion 3.1 Orthogonal Test and its Analysis

The weight loss percentage due to alkal i peeling of modified and common polyester fibres and the analysis of absolute differences of weight loss percentage are given in the Tables 2 and 3 respectively. To get the ideal deweighting and suitable strength loss, the weight loss percentage due to alkali peeling must be controlled below 25%. In practice, it is always controlled at about 15%.

Table 3 shows that the ideal weight loss percentage due to alkali peeling of acid-modified polyester fibres is 15.40-18.37%, and the combination of parameters is 7.5g/L NaOH, 85°C temperature and 40rrun

treatment time. The parameter's effect on the weight loss percentage due to alkali peeling shows the relationship: temperature>treatment time>NaOH concentration. Another parameter is the error (e). If the value of e is smaller, the orthogonal test is practicable. The weight loss percentage due to alkali peeling of common polyester is lower than that of the modified polyester. So, the technology of alkali peeling process for common polyester fibres must be much harsh.

Duri ng the alkali treatment on the modified polyester, the OW ion promotes the hydrolysis of eSlter base (Scheme I) . The Ar represents the --C6fL­or =C6I-hS03Na and R represents the -CH2CHr base. The OH- ions first attack the positive carbon ions of carbonyl and with nucleophilic addition produces compounds (1) and (2). Then, the W protons are removed due to the effect of OW ions and the carboxy lic acid negative ions (3) and alcohol negative iOllls (4) are produced by bond breaking when the electric charges are transferred. The alcohol negative iOllls (4) then combine with H20 to produce the compound (5). As the side radical -S03Na which is found in third monomer (SIPM) in the modified

Table 2-Weight loss due to alka li peeling in the orthogonal test

Test Weight loss, %

No. Modified Common polyester polyester

I 4.83 0.49

2 14.06 6.70

3 25.30 13.50

4 8.65 4.56

5 20.39 10.16

6 17.77 6.04

7 13.79 7.68

8 12.06 9.58

9 32.72 6.86

Table 3-Analysis of absol ute differences of the weight loss percentage

Level Modified polyester Common polyester

NaOH Temp. Treatment Error NaOH Temp. Treatment Error conc. time (e) conc. time (e)

14.40 8.76 11.22 19.31 6.90 4.25 5.37 5.84

2 15 .60 15.40 18.37 15.2 1 6.92 8.81 6.04 6.81

3 19.19 24.93 19.49 15.34 8.04 8.80 10.45 6.21

Absolute 4.79 16.17 8.27 4.10 1.14 4.56 5.08 0.97

difference (R)

YANG: ALKALI DEWEIGHTING OF ACID-M ODI FIED COPOLY ESTER FIBR E 345

o II

0 -

I

0 -

-Ar-C-OR -Ar-C-OR I

-Ar-C-OR

I I OH 0-

0 (I) (2)

II ... .. -Ar-C + R-O-

H20 (-OH-) ... .. o II

-Ar-C + HOR

I I 0 - 0 -(3) (4) (5)

Scheme I- Alkali hydrolysis of polyes ter es ter linkage

30

25 ,.-..

~ o ';;; 20 en £ 15 -.s=-Ol -a:; 10

~ 5

Temperature (0C) 75 80 85 90 95

1-Temperature 2-Treatment time

o ~~ __ ~ ____ L-__ L-~

10 20 30 40 50

Treatment time (min) Fig. I- Effect of temperature and treatment time on weight loss

polyester increases the charges on the positive carbon ions, it makes it easy to be attacked by OH- ions and hence the alkali hydrolysis occurs.

3.2 Effect of Temperature and Treatment Time on Weight Loss The orthogonal test. on the modified polyester

shows that the change in temperature and treatment time affects the weight loss due to alkali peeling (Fig. 1). The increase in temperature and treatment time increases the weight loss due to alkali peeling. But the rate of increase is different. The weight loss due to alkali peeling increases sharply when the treatment time increases from 10min to 30min. After that, it increases slowly and reaches to 15 .64% after 40min, which is an ideal value. If the temperature goes high, the weight loss due to alkali peeling increases quickly . At 85°C, 15.85% weight loss is observed wh ich is close to the ideal value. After that, it increases more quickly.

The increase in weight loss due to alkali peeling at di fferent temperature and treatment time is shown in Table 4. It is observed that the effect of increase in temperature to promote the weight loss due to alkali peeling is more than that of the increase in treatment

Table 4-Increase in weight loss due to alkali peeling under different temperature and treatment time

Temp. oC % Increase in Treatment % Increase in weight loss time, min weight loss

75-80 3.15 10-20 4.26

80-85 3.70 20-30 2.95

85-90 4.95 30-40 2.45

90-95 7.85 40-50 2.02

time. The increase in treatment time can have the well-distributed effect because it affects the weight loss more mildly than the ri sing temperature does.

The alkali hydrolysis procedure in case of polyester is a dual diffusion reaction procedure4

. The reactants in solution diffuse to the non-crystalline region and border of crystalline region of the surface fibres while the products of hydrol ys is di ffuse from the fi bre surface to the solution . When the temperature rises, the speed of di ffusion is enhanced. Thi s makes the constant of reaction ve locity to increase in exponenti al function, macromolecule's chain segment move much acutely, the fi bre density degrades, and the contact and reaction between the carbonyl carbon and the OH- ions become more frequent, which is good fo r the fibre alkali hydro lysis.

3.3 Relationship between Weight Loss and Strength Loss As it is inconvenient to measure the fibre strength ,

the warp strength of sample was used to represent the strength of the modifi ed polyester. The relationshi ps between weight loss percentage, the warp strength and strength loss percentage due to alkali peeling at di ffe rent temperature and treatment time are shown in Figs 2 and 3 respecti vely. The effects of temperature and treatment time on the warp strength are shown in FigA .The relationship between the relati ve strength of the modified and common polyesters and the wei ght loss due to alkali peeling is shown in Fig. 5.

346 INDIAN J. FIBRE T EXT. RES .. SEPTEMBER 2003

Temperature (oC) 70 75 80 85 <;In 9S

700 50

650 40 ~ Z .......

--:; 600 en

0, 30 .Q

~ 550 ~

L- 20 0, U5 c::

Q)

500 L-

ID U5

450 0

0 4 8 12 16 20

Weight loss (%)

Fig.2-Relationships betwee n we ight loss. warp strength and strength loss at different temperatures [I--strength-weight loss. 2--strength loss- weight loss, and 3- strength -temperature]

600

----~ 550 ~ 0, 500 c:: Q)

!:: 450 (J)

400

Treatment time (min) 20 25 30 35 40 45

o 4 8 1215 20

Weight loss (%)

40 l:l .2

Fig.3--Relat ionships between weight loss, warp strength and strength-loss at d ifferent treatment time [I--strength wei ght loss, 2--strength loss- weight loss, and }-strength - treatJTIent time]

Figs 2 and 3 show that the temperature and treatment time have the positive effect on the weight loss due to alkali peeli ng. The strength of the modified polyester decreases as the weight loss percentage increases. Hence, both the strength loss percentage and weight loss percentage due to alkali peeling increase. When the temperature is 95°C, the weight loss percentage due to alkali pee ling is 16.91 % which is an ideal value. Fig. 4 shows that the temperature for alkali peeling should be retained at 95°C. It is a bit higher than the optimized temperature 85°C for the modified polyester. When the treatment time is 35 min, the weight loss due to alkali peeling is J 6.05% and the effect is good.

As the strength decreases with the increase in weight loss percentage due to alkali peeling, the fibre diameter becomes small and the strength loss percentage increases; the rate of increment is however more than that of the weight loss percentage. When the weight loss percentage; due to alkali peeling is

Temperature (oC) 70 75 80 85 90 95 100

650

600 ~.~ ----~550 ~ - /} "El g>500 ----Q)

'::'450 (J) ----A-- Treatment time

400 -e- Temperature

350 20 25 30 35 40 45

Treatment timE: (min)

Fig. 4-Effect of temperat'_lre a nd treatment time on strength

o

10 12 14 16 18 20

Weight loss (%) 22

'Fig.5--Relationships between re lati ve strength and weight 10ss fo r (-0-) modified, and (- 6 -) eOllllllon pol yes ter fibres

between 15% and 20%, the fibre has a good silk-like fee l. At 20% weight loss, the strength loss is more than 40%. Thus, the strength loss percentage should be maintained between 20% and 40%.

Fig. 5 shows that when the weight loss percentage due to alkali peeling increases, the relative strength of the common polyester almost does not change. As the modified polyester has low leve l of densi ty , its critical dissolving time (COT) is 13.4s, which is remarkably lower than that of the common polyester (43.5 s) I. SO, its re lative strength falls obviously . This shows that the technology conditions of the alkali peeling process for modified polyester fibres must be mild.

3.4 Microscopic and X-ray DilTraction Patterns

The inactive inorganic salts partic les present in the modified polyester fibres are pee led off during the hydrolysis and corrosion of polyester macromolecules on the fibre surface occurs. This leaves pits on the fibre surface. From the scanning elec tron photo-

YANG: ALKALI DEW EIGHTING OF AC ID-MODIFI ED COPOLYEST ER FIBR E 347

(al (hi

Fig. 6- X-ray diffraction patlerns of modifi ed polyester fib res: (a) before alkali peeling, and (b) after alka li peeling

micrographs of the modifi ed polyester fibres before and after alkali peeling under the optimi zed

conditions [NaOH 7.Sg/L, temperature 85°C, treat­ment time 40 mjn , promoter (163 1) 1.0g/L, materi al­to-liquor ratio 1 :40] and that of the common polyester fibres after alkali peeling, it is obvious that there are pits with 1.0 Ilm diameter on the surface of modified polyester fibres processed by alkali peeling. They are bigger than the inorganic salts particles (diameter 0.3-0.6 Ilm) added during the copo lymerizations. This is caused by the peeling off of the inorganic salts particles added in the copolymerization after they are corroded by NaOH. On the other hand, the surface of the common polyester fibres appears smooth after the alkali peeling. The micro-pit structure on the fibre surface after alkali peeling is one of the characteri sti c features of the acid-modified multicomponent copolyester fibres which enhances the fibre permeability, adhesion regain , colouring capability and fee l.

Fig. 6 shows the X-ray di ffraction patterns of the modi fied polyester fibres . The diffraction patterns that reflect the status of crystallizati on on the equator are changed from the dotted shape to the short curve

shape. This is because the degree of crystalli zati on decreases after alkali peeling.

4 Conclusions 4.1 The treatment conditions for alkali peeling of the acid-modified multicomponent copolyester fibres must be milder than that of the common polyester fibres. If the weight loss percentage due to alkali peel­ing is about 15%, the treatment conditi ons to obtain

satisfied silk-like effect are 7.Sg/L NaOH , 85°C tem­perature, 40 min treatment time, 1:40 materi al-to­liquor ratio, and 19/L promoter. 4.2 Among all the parameters studied fo r the a lka li peeling, the temperature has the most notab le effect fo llowed by treatment time and NaOH concentrat ion. 4.3 Alkali peeling process leaves micro-pit on the fibre surface. Thi s is caused by the peeling off of the inorganic salts particles added in the copolymeri zat in after they are corroded by NaOH . The fibre crysta lli ­zati on degree shows a decreasing trend.

Acknowledgement The authors are thankful to the China Petroleum

and Chemi ca l Industry Corporation (contract No.292003) fo r the support.

References I Ruxin Yang & Mengzhuo Dai, J Textlnst, 89 Part 1(2) ( 1998)

173. 2 Shanchang Zhu , Dyeing Finishillg , 23 ( 1997) 15. 3 li anping Zhao Xinkui li ang & Li ubao Fan , Dyeing Fillishing,

22 ( 1996) 25. 4 ling G uo, Synthetic Fibers, 20 ( 199 1) I.

5 Suzhou Institu te of S il k Text ile Techno logy. The identifi ca tion material for the techno logy developme nt project ( Co ntract No. 292003) of China Petroleum and Che mica l Industry Cor­pOl'a li on, 1995.