MODULE 1: OVERVIEW OF NONWOVENS

1.1 Nonwovens: What are they?

Introduction to nonwovens Nonwovens are known as engineered fabrics. They are created with a view to targeted

structure and properties by applying a set of scientific principles for a variety of

applications.

Nonwovens are manufactured by high-speed

and low-cost processes. As compared to the

traditional woven and knitting technology, a

larger volume of materials can be produced at a

lower cost by using nonwoven technology.

The manufacturing principles of nonwovens are

manifested in a unique way based on the

technologies of creation of textiles, papers, and

plastics (Figure 1.1), as a result, the structure and properties of nonwovens resemble, to a

great extent, to those of three materials.

1

Figure 1.1

Nonwovens are already found in many applications, but most are hidden and you do not

see them. Figure 1.2 displays a few products prepared by using nonwovens. The readers are

suggested to identify these products and their applications. The most common products made

with nonwovens listed by INDA include:

Disposable nappies

Sanitary napkins and tampons

Sterile wraps, caps, gowns, masks, and curtains used in the medical field

Household and personal wipes

Laundry aids (fabric dryer-sheets)

Apparel interlinings

Carpeting and upholstery fabrics, padding and backing

Wall coverings

Agricultural coverings and seed strips

Automotive headliners and upholstery

Filters

Envelops

Tags

Labels

Insulation

2

Figure 1.2

House wraps

Roofing products

Civil engineering fabrics/geotextiles

Definitions of nonwovensNonwovens are defined in many ways by different standards and different associations.

They are stated below.

As per ISO 9092, nonwoven is defined as “manufactured sheet, web or batt of

directionally or randomly oriented fibers, bonded by friction, and/or cohesion and/or adhesion,

excluding paper and products which are woven, knitted, tufted, stitch-bonded incorporating

binding yarns or filaments or felted by wet-milling, whether or not additionally needled. The

fibers may be of natural or man-made origin. They may be staple or continuous filaments or be

formed in situ.

Note: To distinguish wet-laid nonwovens from wet-laid papers, a material shall be regarded as a

nonwoven if

a) more than 50 % by mass of its fibrous content is made up of fibers (excluding chemically

digested vegetable fibers) with a length to diameter ratio greater than 300; or, if the conditions in

a) do not apply, then

b) If the following conditions are fulfilled:

more than 30 % by mass of its fibrous content is made up of fibers (excluding chemically

digested vegetable fibers) with a length to diameter ratio greater than 300 and its density is less

than 0.40 g/cm3.”

The aforesaid definition of nonwoven, given by ISO 9092, has been adapted by CEN (EN

29092), and consequently by DIN, AFNOR, and all standardization offices in the EU.

But, ASTM prefers to define nonwoven as “a textile structure produced by bonding or

interlocking of fibers, or both, accomplished by mechanical, chemical, thermal, or solvent

means, and combinations thereof.

Note: the term does not include paper, or fabrics which are woven, knitted, tufted, or those made

by wool or other felting processes.”

This definition is available in many ASTM standards including D 123, D 1117, D 2646,

D 3786, D 3787, D 5684, D 5732, D 5733, D 5734, D 5735, and D 5736.

3

Today, there are two leading associations of nonwovens in the world, namely EDANA

(The European Disposables and Nonwovens Association) and INDA (The North America’s

Association of the Nonwoven Fabrics Industry). They have been the voice of the nonwoven

industries in Europe and North America, respectively. Nonwovens are defined by them as well.

Though EDANA has adopted the ISO 9092 or CEN 29092 definition of nonwoven. but, INDA

prefers to define nonwovens in another way. According to INDA, “Nonwoven fabrics are

broadly defined as sheet or web structures bonded together by entangling fiber or filaments (and

by perforating films) mechanically, thermally or chemically. They are flat, porous sheets that are

made directly from separate fibers or from molten plastic or plastic film. They are not made by

weaving or knitting and do not require converting the fibers to yarn.”

It is quite interesting to note that these definitions include raw materials, structures, and

manufacturing processes employed to prepare nonwovens. However, there is no unique

definition of nonwovens found to exist in the world.

1.2 Nonwovens: How do they look like?It is often asked “Nonwovens: How do they look like?” This refers to the structure of

nonwovens. It is necessary to have a sense of structure of nonwovens also to make the study of

nonwoven technology more meaningful. As in case of woven and knit fabrics, the structure of

the fabrics in conjunction with the properties of the constituent fibres and yarns determine the

properties of the fabrics, so is the case in case of nonwovens. While the structure of the woven

fabrics

can be

described

in terms

of the

weave

geometry

and the

density of

warp and

weft,

4

Figure 1.3

similarly the knitted fabrics are described in terms of the intermeshing structure and the density

of courses and wales [1], the structure of nonwovens is described primarily in terms of fibre

packing arrangement and fibre directional arrangement. Sometimes, the geometry of pores in

nonwovens is also studied. Before developing a fundamental understanding of nonwoven

structure, let us first study the characteristics of the constituent materials, that is, fibres – the

building block of fibre-based nonwovens.

Fibre characteristicsFibres are the building block of fibre based nonwovens. One such fibre is displayed in

Figure 1.3. Let us denote fiber mass by m and fibre length by l. The fibre fineness is defined by

mass per unit length of a fibre. Then, the fibre fineness t can be written as . Let fiber

cross-sectional area is s, then fiber volume V can be expressed as . As we known that the

mass per unit volume of a fibre defines the density of the fibre, then , r denotes fiber

density. If fiber perimeter is denoted by p, then fibre surface area A can be expressed as ,

provided the area occupied by the top and bottom surfaces of a fibre, being very very small, can

be neglected.

Let us write the expression of fibre density in another manner. This is shown below.

It can be written as . What it follows is that the larger fibre (higher value of s) may come

out to be finer (smaller value of t) than the smaller fibre (lower value of s). This is because of the

influence of fibre density on fibre fineness, the coarser fibre need not to be heavier always. Let

us illustrate. A 3 denier polyester fibre possesses cross-sectional area of 2.4910-4 mm2, but a 2.5

denier polypropylene fibre possesses cross-sectional area of 3.0510-4 mm2. According to the

definition of fineness, the polyester fibre is coarser than the polypropylene fibre, but according to

the cross-sectional area, the former is smaller than the latter. It indicates that the fibre fineness is

not a purely geometrical characteristic and the traditional definition of fiber fineness does not

truly express the fiber size. The size of fibres can be better characterized by the cross-sectional

area or ratio of the fibres. But, as the measurement of fibre volume is difficult in practice,

the textile technologists prefer to use fibre fineness in order to characterize the size of fibres.

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When the cross-section of the fibres is circular, we can write where

represents fibre diameter. Then the diameter of the fibres can be calculated from the following

expression

.

But, when the cross-section of fibres is not circular, then we assume that the cross-sectional area

s of non-circular fibres is equal to the cross-sectional area of a circle of diameter d., then

is called as equivalent fibre diameter.

It is well-known that the perimeter of a fiber having non-circular cross-section is always

higher than the perimeter of a circle. Then, it is logical to introduce a quantity called fiber shape

factor q such as

.

Clearly, the shape factor of a circular fibre is equal to zero. The fibre perimeter can be written as

, consequently, the fibre surface area can be expressed as .

Often, the surface area of fibres in divided by the mass of the fibres and the resulting ratio

is termed as specific surface area. If the specific surface area of a fibre is denoted by a then it is

possible to write that

.

This terminology is very commonly used in case of nano fibres. But, one can see that the specific

surface area is not a purely geometrical characteristic. In order to obtain a purely geometrical

characteristic, the surface area of fibres is often divided by the volume of the fibres and this ratio

is termed as fibre surface area per unit volume. This is expressed as follows

.

The aforesaid fibre characteristics are often used to study the effect of fibre properties on

physical and transport properties of fibre based nonwovens.

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Let us now solve some numerical problems

Problem 1.1: Calculate the equivalent diameter of a non-circular polyester fiber of 3 denier

fineness and the equivalent diameter of polypropylene fiber of 2 denier fineness. Comment on

the results obtained.

Solution 1.1: We take polyester fiber density as , then the equivalent fiber

diameter d is calculated as follows

Then we take polypropylene fiber density as , then we calculate its equivalent

fiber diameter d as follows

Thus, we see two different fibers having two different fineness show almost the same diameter.

The traditional definition of fiber fineness does not truly reflect the fiber geometry

Problem 1.2: Consider a nonwoven wipe of 100 g weight which is made up of non-cylindrical

cotton fibers of 25.4 mm length, 3 dtex fineness, and shape factor of 0.05. Calculate the total

surface area occupied by the fibers in the wipe.

Solution 1.2: We take cotton fibre density as , then, the cross-sectional area s of a

cotton fiber is calculated as follows

.

Then we obtain the volume V of a cotton fiber as follows

.

Now the mass m of a cotton fiber is obtained as follows

.

The equivalent diameter d of cotton fiber is calculated as follows

7

.

Then the surface area of a cotton fiber is calculated as follows

.

Now the number n of cotton fibers present in the wipe having mass M of 100 g is calculated as

follows

.

Then the total surface area Y occupied by all cotton fibers present in this wipe is

.

Fibre packing arrangement

8

The fiber packing arrangement is usually characterized by fiber packing density. Note

that fiber packing density is known as fiber volume fraction or solid volume fraction. Figure 1.4

displays the image of a nonwoven fabric. Let the volume of this fabric is and the volume of

all fibers in the fabric is V. As the fibre packing density is defined by the ratio of the volume

occupied

by the

fibres to

the

volume

of the

fabric, we

can write

, where µ

denotes

fiber

packing

density.

Evidently, the value of fibre packing density lies from zero to one. Sometimes fiber packing

density is interpreted in terms of density. Let the mass of a nonwoven fabric be M, then the

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Figure 1.4

Figure 1.5

density of the fabric is . Similarly, the density of fiber is . As we know

, then . Also, fiber packing density is interpreted in terms of sectional area.

Figure 1.5 shows a thin section of a nonwoven fabric and a thin section of a fibre. The total

volume of this infinitesimally thin section of a nonwoven fabric is , where

is the sectional area of the thin section of the fabric. The volume of all fibers in the thin

section of the fabric is , where is the sectional area of the

fibres in the thin section of the fabric. Then the fibre packing density can be expressed as follows

.

Let us now solve some numerical problems.

Problem 1.3: Consider a laminated nonwoven material which is made up of polypropylene fiber

and has the following dimensions: 10 cm length, 10 cm width, and 0.7 mm thickness. Its weight

is 2.82 g. Calculate fiber packing density in this material.

Solution 1.3: The weight (M) of the nonwoven material is 2.82 10-3 Kg and its volume (VF) is

710-6 m3. So, its (mass) density (r*) is calculated as follows:

Let us consider the polypropylene fiber density (r) be 910 Kg×m-3. Therefore, fiber packing

density (m) is calculated as follows

.

Problem 1.4: Take a needlebonded fiber web, made up of polyester fiber, has 2 mm thickness

and 100 g×m-2 basis weight. Calculate fiber packing density in this material.

Solution 1.4: The basis weight (W) of the needlebonded fiber web is 10010-3 Kg×m-2 and its

thickness is (T) is 210-3 m. So, its (mass) density (r*) is calculated as follows

.

Let us consider the polyester fiber density (r) be 1380 Kg×m-3. Therefore, fiber packing density

(m) is calculated as follows

10

.

Often the packing arrangement of real nonwoven structure is compared with the idealized

fibrous

structures. In an idealized fibrous structure, the circular fibers are parallelly and uniformly

distributed along the axis of the structure [2]. In such a structure, the fibers are arranged in a

configuration around a single core fiber as shown in Figure 1.6(a). The repeat of the unit

structure gives an equilateral triangle as shown in Figure 1.6(b). The packing density of such a

structure can be determined as follows

11

Figure 1.6

Let us further consider four variants of this idealized structure. In the first variant, the fibre are

touching each other, that is, h=0. Then the packing density can be obtained as m=0.91. Let us call

this structure as the tightest structure. It shows the highest resistance to mechanical deformation,

but it offers least softness. In the second variant, , then the packing density takes on

. Let us call this structure as tight structure. It shows the high resistance to

mechanical deformation, but it offers low softness. In the third variant, , then the

packing density takes on . Let us call this structure as intermediate structure. It

shows the moderate resistance to mechanical deformation, and at the same time it offers

moderate softness. In the forth variant, , then the packing density takes on . Let us

call this structure as loose structure. It shows the least resistance to mechanical deformation, but

it offers highest softness. Figure 1.7 gives a better visualization of these idealized structures.

Fibre directional arrangement

12

Figure 1.7

The arrangement of fibers in nonwovens is described not only by the fiber packing

arrangement, but also by the fiber directional arrangement (fiber orientation). Let us now discuss

about fibre orientation [2]. We consider one such fiber, shown by thin green line in Figure 1.8.

As shown, the curvature of the fibres varies

widely. Simply, it has many directions. Then

how can we describe this fiber in terms of its

direction? To answer this question, let us divide

this fiber into small segments. Thus, we get

fiber segments. Consider a fiber segment of

finite length (thick green line), which can be

assigned by a suitable orientation vector i. This

vector has a direction of joining the end points

(A and B) of the fiber segment and it is unitary. When its direction is given by its

tangent.

It

is

generally

known

that the

orientation of fibres in the thickness direction (z-direction) is not significant and we will discuss

here about the orientation of fibres in two-dimensional plane of nonwovens. Such an orientation

of fibres is known as planar orientation of fibres. We will first consider planar isotropic

orientation of fibres, that is, purely random orientation of fibres in plane. Let us think about fiber

segments. The direction of these fiber segments can be described by their orientation angles

, as shown in Figure 1.9. In this case, all fiber segments are equally distributed

in all directions. Therefore, the probability density function of their orientation is

. Then

13

Figure 1.8

Figure 1.9

(Think that the area under the probability curve is equal to

one.) then, . The behavior of this function is shown in Figure 1.10.

Often, fiber segments, during their processing, take a direction near to a preferential

direction because they are mechanically affected by 1) other fiber segments of the same or other

fiber and 2) technological (machine) elements like pins, cylinders, rollers, etc. This can be

analogously described by a flexible felt equipped with spikes being extended in a particular

direction (preferential direction), as shown in Figure 1.11 [2]. Here,

14

Figure 1.10

. Then,

. Then, . Further, differentiation

of with respect to yields

15

Figure 1.11

Here,

denotes

the

probability density function of orientation before extension. Then, the relative frequency of fiber

segments in an elementary class before extension is . Let us consider that

represents the probability density function of orientation after extension and refers to

the relative frequency of fiber segments in an elementary class after extension. Both of these

relative frequencies must be the same. Therefore, Substituting

and into this, we obtain

. Clearly, the maximum value of is and

the minimum value of is . The value of extension C is known as a

measure of preference, that is, measure of anisotropy. Here, . The behavior of the

probability density function for different values of the anisotropy parameter C is shown in Figure

1.12. The corresponding distribution function is

16

Figure 1.12

Sometimes, the preferential direction of fibre orientation may be something other than the

direction of y-axis. Let us assume that the preferential direction (/) is described by the

preferential angle with y-axis, shown in Figure 1.13. Here, x is the angle of fiber segment from

preferential direction and y is the angle of fiber segment from y-axis. Then

. Since and ,

we obtain .

Let us see if the orientation of fibres in a real nonwoven fabric can be explained in terms

of the aforesaid theory of fibre orientation. A nonwoven fabric was developed by using polyester

fibres of

51 mm

length

and 1.1

dtex

fineness

and

employing opening, carding, cross-lapping, needle-punch technology. This fabric is shown in

Figure 1.14. A sample of this fleece was placed on a mirror, and the light was allowed to pass

through the fleece and reflect off the mirror surface vertically back to the camera. The fibers,

17

Figure 1.14

regardless of their position within the fleece, could merely block the light, appeared dark, and

were in focus. The result was an image with excellent contrast and uniformity. The image was

“thresholded” to separate the fibers from the black and white background to obtain a binary

image. This binary image was then analyzed to determine the orientation of 1500 fixed 24-pixel

fiber segments. Thirty such images were taken randomly from different parts of the fleece, thus

the orientation of 45000 fiber segments was determined. This large set of orientation data was

summarized by frequency distribution in ten classes each of 18 degree width. The resulting

histogram is displayed in Figure 1.15. The continuous line corresponds to the probability density

function of fiber orientation in nonwoven for C=1.1678. This was obtained by using the standard

non-linear regression technique. Evidently, the theoretical result corresponded well to the

experimental one. Note that this nonwoven material shows lowest value of probability density

function of fibre orientation in the machine direction . Why? The answer lies in

understanding of the cross-lay process. The readers are encouraged to first study the cross-lay

process and then provide a meaningful answer to this question.

The images of some major types of nonwovens are shown in Figure 1.16. The manufacturing

processes of these fabrics will be discussed in detail later on.

18

Figure 1.15

19

Figure 1.16

Pore structure in nonwovensA nonwoven fabric generally consists of a large number of fibers and a large (volume)

portion of

this

material

is

occupied

by air. If

we

project

this fabric

onto a two-dimensional plane, we obtain an “elementary plane” of this fabric. This is shown in

Figure 1.17. Evidently, this plane consists of numerous fibers and many air spaces are

surrounded by fibers. We call these air spaces as pores. One such pore is shown in Figure 1.17.

We will now study the structure of these pores present in such an elementary plane of a

nonwoven fabric.

Let the fibers be distributed randomly in an elementary plane of unit area and the

probability P(n) that any given point is covered by n fibers present per unit area of the plane is

given by Poisson distribution of the following form

,

where c is the total projected area of fibers per unit area of the plane. (c is termed as coverage.)

Evidently, , where l is fiber length, and d is fiber width (diameter). According to the

geometrical definition of probability, P(n) is the area covered by n fibers per unit area of the

plane, that is, P(n) is the fraction of unit area covered by n fibers. If so then P(0) is the fraction of

unit area not covered by fibers, then P(0) represents the open area fraction of the plane. Then,

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Figure 1.17

Figure 1.18

. Clearly, 1-x is the fraction of the unit area covered by fibers. Similarly, P(1) is

the fraction of area covered by one fiber, P(2) is the fraction of area covered by two fibers, and

so on. Let us assume that a point covered by n fibers is covered by n-1 crossings. This is

illustrated in Figure 1.18.

Therefore, the total area Ac occupied by all fiber crossings per unit area of the plane is

.

Thus, the total area of fiber crossings Ac is the difference between the total coverage c and the

fraction of the unit area covered by fibers (1-x). The area ac occupied by one fiber crossing

(Figure 1.19) is given by . Then the number nc of fiber crossings per unit

area of the plane is

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Fiber crossings form the vertices of polygons in the plane. Each polygon simulates a

pore. According to Kallmes and Corte [4], the expression for number of such pores np is

. The mean cross-sectional area ap of pore is given by

. Generally, , then,

.

Thus, the mean pore cross-sectional area ap is inversely proportional to the square of the total

length (nl) of fiber deposited. We consider the mean cross-sectional area ap of pore is equal to

the area of a circle of diameter . Then we write

We call as equivalent pore diameter or simply, pore diameter. Here the pore diameter (dp) is

inversely proportional to the total length (nl) of fiber deposited. Note that we assumed all fibers

were randomly deposited in an elementary plane, therefore, all these relations are valid for such

plane only.

So far we have studied about the pore structure in an elementary plane. We imagine that

many such identical elementary planes are stacked one on the other in order to make the ultimate

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Figure 1.19

nonwoven fabric. Let us now assume that (1) The thickness T of such a plane is equal to the

thickness of two fibers, that is, T=2d (Figure 1.20) and (2) The center of fibers lie on or within

this plane, that means, in principle, as many as three fibers can intersect within this plane. Hence,

this model holds whenever P(4) <<1. Apparently, the pore structure of an elementary plane is

decided by the pore structure of other elementary planes. Then, how many elementary planes

must be considered to determine the effective pore structure of a given plane? This depends upon

how densely the elementary planes are packed together. This is, of course, decided by the fiber

material used and the process technology employed for making the nonwovens. Whatsoever, at

least minimum of two elementary planes always interact to determine the effective pore structure

of a given plane. Let be the number of elementary planes that must be taken into account

together to describe the pore structure in nonwoven and we assume Then,

Here V is total volume of all fibers, VF is total volume of fabric, m is packing density, y is

porosity.

23

Figure 1.20

Let us see if the pore structure of a real nonwoven fabric can be explained in terms of the

aforesaid theory of pore structure. A series of spunbond nonwovens was prepared with varying

basis weight (weight per unit area), thickness, and porosity. The fibre diameter was measured as

3.82 micron. The pore diameter was measured by using the standard image analysis technique.

Table 1.1 shows the results of experiments. The pore diameter was also calculated from the

above theory. The theoretical results are also shown in Table 1.1. Evidently, the theoretical

results correspond very well with the experimental results.

1.3 Nonwovens: How are they created?

Basic nonwoven processesLet us take that the nonwoven manufacturing technology that produces fibre-based

nonwovens generally consists of four basic nonwoven processes namely, fibre preparation

process, web formation process, web bonding process and finishing process. A brief summary of

the nonwoven processes is illustrated in Figure 1.21.

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Table 1.1

Fabric code Measured value (Experiment) Calculated

values of

average pore

diameter

(micron)

Basis weight

(g.m-2)

Thickness

(mm)

Porosity (-) Average pore

diameter

(micron)

A 34.20 0.3140 0.90 15.70 14.99

B 50.0 0.3430 0.87 11.70 11.53

C 65.0 0.3360 0.83 10.00 8.82

D 96.0 0.4690 0.82 8.80 8.33

E 111.0 0.5060 0.81 8.40 7.89

Figure 1.21

The fibre preparation process prepares fibres for web formation process. It includes fibre

opening and mixing and fibre feeding to carding machine or air-lay machine. The web formation

process, as the name implies, indicates those processes that disperses the fibres or filaments to

form a sheet or web and also stacks the webs to form multi-layered webs, sometimes called as

batts. The web bonding processes imparts integrity to the web and the resulting material is often

called as fabrics. Often, the fabrics undergo mechanical or chemical finishing or both in order to

achieve enhanced properties and appearance.

As expected, these processes along with the choice of fibres determine the structures and

properties of the nonwoven fabrics. It is often said that the nonwoven fabrics are engineered in a

unique way by the nonwoven technology employed and the fibre materials used so as to offer a

set of targeted properties. Here, the word technology implies a system of sequence of basic

processes. As a nonwoven technologist, it is imperative to learn how these basic processes can be

arranged to engineer a wide spectrum of nonwoven fabrics for a wide variety of applications.

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Process augmentations

Often the technology of nonwovens is implied by the name of the nonwoven materials

which are prepared by utilizing a particular sequence of basic nonwoven processes [1]. For

example, carded nonwovens refer to a technology in which the staple fibres undergo a sequence

of opening and mixing process, followed by web formation by carding processes, and then

followed by adhesive bonding or thermal bonding. Similarly, perpendicular-laid nonwovens refer

to a technology in which the staple fibres undergo a sequence of opening and mixing process,

followed by web formation by carding processes, and then web stacking by perpendicular-lay

process and finally followed by through-air thermal bonding process. In a similar manner, air-

laid nonwovens refer to a technology in which the staple fibres undergo a sequence of opening

and mixing process, followed by web formation by air-lay processes, and then followed by

thermal bonding or adhesive bonding. In the same vein, wet-laid nonwovens refer to a

technology in which the staple fibres undergo a sequence of opening and mixing process,

followed by web formation by wet-lay processes, and then followed by adhesive bonding or

thermal bonding. In these cases, the web formation processes tend to give the name to the

technology.

In contrast, the needle-punch technology often refers to systems in which the staple

fibres, taken from bales, are opened, carded by using roller top card or flat top card, cross-lapped

to achieve the desired basis weight of the final web (batt), passed through a needle loom for

bonding and then given a finishing treatment. Similarly, hydroentanglement technology refers to

a system in which the staple fibres are opened and formed into a web by using air-lay

technology, and finally bonded by hydroentanglement machine. To enhance the properties of

fabrics for specific end-uses, an additional step of resin bonding, drying, and curing may follow;

one may think of this as a finishing process. Note that the hydroentanglement technology is also

called as spunlace technology. In these cases, the web bonding processes tend to give the name

to the technology.

The next set of technologies was developed as a combination of at least polymer

preparation process, web formation process, and web bonding process. We refer to spunbond

technology and meltblown technology. In these technologies, the characteristics of the polymers

used and the principles of the processes followed are highly different; as a result, the structures

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and the properties of the resulting nonwovens are very much different, which demands for

different applications of these nonwovens.

In this course, we will first focus on the nonwoven technologies that are relevant to staple

fibre nonwovens. Then we will focus on polymer-extrusion based nonwoven technologies

namely, spunbond technology and meltblown technology.

Note that in recent years many attempts are made to develop new nonwoven technologies

by combing these processes in a unique way, for example, Evolon technology, Coform

technology, SMS technology, etc. These technologies are often described as composite

nonwoven technologies, which are, however, beyond the scope of this course.

References[1] Batra, S., Pourdeyhimi, B., Shiffler, D., TT 305 Fibre Web and Nonwoven Production,

Desk Copy, North Carolina State University, USA, 2004.

[2] Neckar, B. and Das, D., Theory of structure and mechanics of fibrous assemblies,

Woodhead Publishing India Ltd., New Delhi, 2011.

[3] Simmonds, G. E., Bomberger, J. D., Bryner, M. A., Designing nonwovens to meet pore

size specifications, Journal of Engineered Fibres and Fabrics 2 (1), 1-15, 2007.

[4] Kallmes, O. and Corte, H., TAPPI 43 (9), 737-752, 1960.

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