Yarn Technology

YARN
TECHNOLOGY

(FILAMENT YARN)

NOOR ROSMAWATI MOHD YUSOF
KHAIRUDDIN ISHAK

JABATAN KEJURUTERAAN MEKANIKAL
POLITEKNIK SEBERANG PERAI

YARN
TECHNOLOGY

(FILAMENT YARN)

Noor Rosmawati Yusuf
Khairuddin Ishak
2022

MECHANICAL ENGINEERING DEPARTMENT

©All rights reserved for electronic, mechanical, recording, or otherwise, without prior permission
in writing from Politeknik Seberang Perai.

ii eBook PSP | 2022

All rights reserved

No part of this publication may be translated or reproduced in any retrieval system or transmitted
in any form or by any means, electronic, mechanical, recording, or otherwise, without prior
permission in writing from Politeknik Seberang Perai.

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Perpustakaan Negara Malaysia Cataloguing-in-Publication Data

Noor Rosmawati Yusuf, 1970-
YARN TECHNOLOGY : (FILAMENT YARN) / Noor Rosmawati Yusuf, Khairuddin Ishak.
Mode of access: Internet
eISBN 978-967-2774-25-9
1. Yarn.
2. Spun yarn industry.
3. Government publications--Malaysia.
4. Electronic books.
I. Khairuddin Ishak.
II. Title.
677.02862

eBook PSP | 2022 iii

Acknowledgment

In the name of Allah, the most compassionate and generous. First and foremost, we are grateful
to Almighty ALLAH for providing us with the courage, knowledge, talent, and opportunity to
undertake and successfully finish this mission. We are grateful to Allah SWT for completing the
academic writing for the construction of an eBook to help students learn about this subject. We
would like to express our gratitude to Mr. Ahmad Azlan bin Ahmad, our program coordinator, for
making this possible. His guidance and recommendations guided us through the whole process of
writing this eBook. We'd like to express our deepest appreciation to everyone who helped us finish
this book. Special thanks to Mr. Muhammad Nasir Bin Marzuki, our Head of Department, whose
fresh ideas and assistance enabled us to arrange our activity, notably in developing this eBook.

Ms. Ruhil Naznin, the CTTL coordinator, deserves credit for her involvement, insightful remarks and
recommendations, and advice while preparing this eBook. We would also want to express our
gratitude to the members of the Mechanical Engineering Department, particularly the Textiles
Engineering Unit, who contributed thoughts and ideas either directly or indirectly to the
development of this eBook. Last but not least, many thanks go to the director of Politeknik
Seberang Perai, Sr. Harith Fadzilah Bin Abd Khalid, who worked diligently to guide the team to
success.

Noor Rosmawati Yusuf
Khairuddin Bin Ishak

iv eBook PSP | 2022

Preface

Yarn is manufactured in two ways: spun yarn and filament yarn. The yarn manufacturing industry
has seen filament yarn fill 59% of the market, compared to 41% for spun yarn. Filament yarns
contribute significantly to the expansion of the textile industry due to their physical characteristics,
low cost, and adaptability. Rapidly shifting fashion trends, as well as the availability of numerous
types of yarns depending on colour, twist, fiber content, smoothness, and thickness, are a few
significant reasons driving global textile industry growth. This demonstrates that filament yarn
manufacturing is gaining traction in the global market. Filament yarns have long been used in the
textile industry. The greater usage of filament yarn has improved market revenue growth.

This e-book starts with an introduction to filament yarn, which covers the history of synthetic fibers,
several varieties of filament yarn, and their properties. The second topic is the creation of filament
yarn using three popular technologies: melt-spinning, dry spinning, and wet spinning. The Principle
of main texturing methods will be discussed in the third topic, which will go through texturing
methods such as false twist, stuffer box, air jet, and knit de-knit. This book also introduces students
to filament technical yarn in a nutshell so that they may acquire ideas for alternative uses of
filament yarn. Finally, the fifth topic will attempt to address the distinction between the filament
and spun yarn, yarn count computation, and other filament yarn-related topics in brief.

It is believed that this book will equip students with information as well as a larger perspective on
yarn manufacturing, particularly filament yarn production, which is developing a foothold in the
global market. It is also envisaged that as a consequence of this book, Mechanical Engineering
(Textile) graduates would have a significant understanding of the textile industry.

eBook PSP | 2022 v

Table of Content

01 INTRODUCTION TO FILAMENT YARN 1

1.1 Definition 2
1.2 History of Synthetic Fibers 2
1.3 Type of Filament Yarns 3
1.4 Filament Production 6
1.5 Characteristics of Filaments Yarns 8

02 MANUFACTURING OF FILAMENT YARN 11

2.1 Introduction 12
2.2 Dry Spinning 18
2.3 Wet Spinning 19
2.4 Melt Spinning 21
2.5 Man-Made Staple Fiber Production 31

03 PRINCIPLE OF MAIN TEXTURING METHODS 39

3.1 Introduction 40
3.2 Texturing Filament Yarns 41
3.3 Real Twist Texturing 42
3.4 False Twist Texturing 45
3.5 Textured Yarn Process Techniques and Product 50

Development 52
3.6 Methods of Texturization 54
3.7 False Twist 55
3.8 Suffer Box 56
3.9 Air-jet Process 57
3.10 BCF Process 58
3.11 Knit-de-knit

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04 TECHNICAL FILAMENT YARN 60

4.1 Introduction 61
4.2 Aramid Filament Yarn 61
4.3 Glass Filament Yarn 63
4.4 Carbon Filament Yarn 63
4.5 HDPE Filament Yarns 63

REFERENCES 66

eBook PSP | Yarn Technology (Filament Yarn) 1

01

INTRODUCTION TO
FILAMENT YARN

This topic covers the definition of filament yarn and the history of synthetic fibers. It consists of the
type of filament yarn, filament production, and the characteristics of filament yarn.

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1.1 Definition of filament yarn

A filament yarn is made from one or more continuous strands called filaments where each
component filament runs the whole length of the yarn. Those yarns composed of one
filament are called monofilament yarns, and those containing more filaments are known
as multifilament yarns. For apparel applications, a multifilament yarn may contain as few
as two or three filaments or as many as 50 filaments. In carpeting, for example, a filament
yarn could consist of hundreds of filaments. Most manufactured fibers have been
produced in the form of filament yarn. Silk is the only major natural filament yarn.

1.2 History of Synthetic Fibers

First, let's define synthetic fibers. Synthetic fibers are made of fibers. They do not exist
naturally in nature. Examples of natural fibers would be cotton and hemp. In 1924 rayon
made using the viscose process hit the market, with acetate (also a viscose process fiber)
following closely behind. It became the first commercial synthetic fiber on the market. Ten
years later, in 1938, nylon made its first appearance at the World’s Fair. And with this
introduction, and the ability to make cheap affordable women's stockings with better
performance, there was a shift in consumers’ mindset. Synthetic fibers became popular
with the masses and people could not get enough of them.
Advancements in the textile industry come from advances in fibers. Fiber development
happens to fill a need in the market. There are extensive trend and market analysis studies
before developing a new fiber. 100 years ago when synthetic fibers were first starting to
hit the market they were developed to replace natural fibers. For example, rayon was a
cheaper alternative to silk. Today, the consumer market wants natural fibers, because they
are more sustainable. So, instead of replacing natural fibers, synthetic fibers are currently
trying to solve sustainability and environmental issues that the first generation of fibers
left behind.
Continuous-filament yarns (or filament yarns) are used to produce a wide range of woven
and knitted fabrics for various textiles and clothing. Filament yarns are made from filament
fibers. A quick refresher, filament fibers are generally man-made (except silk), and have a
long fiber length. Because filament fibers are less chaotic than staple fibers, their yarns
need very low amounts of twist to hold them together.

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1.3 Type of filament yarns

Filament yarn is made up of very long, continuous filaments that are either twisted together
or simply gathered together. Filament yarn is classified into two types: monofilament yarn
and multifilament yarn. Monofilament yarn is made up of a single filament strand, whereas
multifilament yarn is made up of two or more filament strands that have been plied or
twisted together to generate one yarn. Filament yarn can also be natural, synthetic, or non-
synthetic. Filament yarns provide high consistency as well as high strength. They are silky,
glossy, and refreshing. They don't pill or lint easily.

Filament yarn is yarn consisting of fibers with each end being endless. The continuous and
endless fiber is called a filament. In spun yarn, though the whole yarn is continuous, each
staple fiber is discontinuous. Figure 1.1 already showed the picture of filament yarn.
Filament yarn is often, though not always, twisted before use. The twist level of filament
yarn is usually expressed as Twist Per Metre (TPM) or Twist per Inch (TPI). The twist factor
also called the twist multiplier, is similar to that used for spun yarn.

Filament yarns are categorized into two varieties based on the form of the filaments in the
yarn: untextured (flat) and textured (bulk). A flat yarn's filaments are straight and clean,
parallel to the yarn axis. As a result, flat filament yarns are often tightly compacted and
have smooth surfaces.

Figure 1.1 Continuous filament yarns

Bulked yarns have a higher volume than flat yarns of the same linear density because the
filaments are crimped or entangled with one another. Texturing is the primary process for
creating bulked filament yarns. Textured yarn is created by including long-lasting crimps,
coils, and loops along the length of the filaments. Because textured yarns have more

4 eBook PSP | Yarn Technology (Filament Yarn)

volume than flat yarns, the air and vapor permeability of textiles manufactured from them
is higher. Flat yarns, on the other hand, may be a better choice for applications requiring
limited air permeability, such as airbag materials.

Continuous filament yarns are unbroken lengths of filaments that comprise natural silk
and filaments extruded from synthetic polymers (e.g., polyester, nylon, polypropylene,
acrylics) and modified natural polymers (e.g., viscose rayon). These filaments are twisted
or knotted to form a continuous filament yarn. Textile fabrics encompass a wide range of
consumer and commercial items created from natural and synthetic fibers. To make fabric
for a certain end purpose, the fiber type must first be selected and then spun into a yarn
structure with the required qualities so that the following woven or knitted structure
provides the desired fabric aesthetics and/or technical performance.

A Simple Analysis of Yarn Structure

Figure 1.2 Scanning electron micrograph of continuous filament and ring-spun yarn structure:
polyester continuous filament yarn (above) and ring-spun yarn (below)

Figure 1.2 depicts greatly enlarged photographic pictures of twisted filament yarn and
staple-spun yarn structures (ring-spun yarn). The following three traits stand out:
1. A linear fiber assembly. The assembly can be any thickness.
2. The twist holds the strands together. However, alternative methods of achieving

cohesiveness may be employed.
3. Fibers have the propensity to lay parallel along the twisting spiral.

Note*
Continuous filaments can be cut into distinct lengths equivalent to natural plant and animal fiber lengths. Both
synthetic and natural fibers may be joined and twisted to make staple-spun yarns. This kind of yarn can be further
classified into plain and decorative yarns

eBook PSP | Yarn Technology (Filament Yarn) 5

Silk Fibers
Several insects make silk strands as continuous protein filaments. Cultured silk, on the
other hand, is created by farmed larvae of a caterpillar called the silkworm, which utilizes
silk to construct its cocoon. This silkworm is Bombyx mori, sometimes known as mulberry
silkworm since the caterpillar feeds on mulberry leaves. Silk culture developed in China
and, according to Chinese mythology, may be traced back to 2640 B.C. The business
gradually moved to Japan, Turkey, Spain, Italy, France, and the United States. There are
also wild silkworms, such as the Eri, Muga, and Tussah (Tussa or Tussur), which are mostly
found in India and China and feed on castor oil plants or, in the case of the Tussah, oak
trees that are pruned to a height of 1.5 to 2 m.

The caterpillar creates silk by wrapping and gumming the silk thread around its body, layer
upon layer. The cocoon thread is degummed and unwound to obtain raw silk with a
fineness of 1.9 to 4.4 dtex, a process known as reeling, and the resulting filament threads
are then twisted together (folded or doubled) to get the desired count of continuous
filament yarn, a process known as silk throwing and the manufacturer a throwster. Thrown
silk is therefore a plied yarn made with continuous strand silk. In spun yarns, distinct-length
silk fiber is important, and waste silk is the primary source material.

Waste Silk
There are two major sources of waste silk: gum waste (which occurs during the reeling
step) and throwster's waste (resulting from the production of thrown silk and the
subsequent processes of cloth production).

According to its length, waste silk may be divided into four qualities:
• First quality: 165 mm average length; spread 73 to 250 mm • Second quality:
114 mm average length; spread 60 to 152 mm
• Third grade: average length 89; range 50-152
• Fourth quality: waste from the manufacturing operations needed to transform
the aforementioned qualities into spun yarns.

The first three characteristics' fiber is gilled into a sliver before being spun into yarn. Silk
noils, the lowest-quality waste, include a high concentration of exceedingly short fibers and
can be used as a mixed component in the production of woolen yarns.

6 eBook PSP | Yarn Technology (Filament Yarn)

1.4 Filament Production

Before the seventeenth century, fiber production was primarily an agricultural enterprise;
hence, except for silk, the available fibers were of very short length (we call these staple
fibers). The yarn manufacturing processes of antiquity were mostly based on stapled yarn
systems. In recent years, the range of raw materials has expanded, and synthetic fibers
are now available. These so-called man-made fibers come in staples and "continuous"
strands. As a result, previously unavailable yarn-making technologies are now available.
As economic pressures other than machine productivity take precedence, this range
expands, albeit at a slower rate.

Figure 1.3 Filament Yarn

Extruded filament yarn manufacture is a short, mechanical process involving only one or
two steps. Yarn is extruded and drawn to approximately the right ‘size’; it then is often
textured to give the final product. A practical system may have a complex liquid polymer
feed and two or more draw zones in a single spline. There are a variety of alternative
systems within this broad category of filament production. Although the production of
filament yarns appears deceptively simple, there are complexities. The processing
conditions have to be very carefully monitored and controlled because heat, humidity, and
mechanical stress affect the polymer in a way that affects the dyeability of the final
product. Thus, those in charge must understand the problems which can arise due to the
chemistry and molecular structure of the polymers from which the fibers are made. This is
in contrast to the mechanical complexities of staple processing.

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Staple yarn manufacture is much more complex from a mechanical standpoint; it involves
many stages of processing before the products are ready for shipping. There are a variety
of staple spinning systems available, but broadly they can be categorized as short- and
long-staple systems. Short-staple spinning is the logical development of the cotton
spinning of history, but the range of fibers has increased dramatically in this century. Long-
staple spinning has a heritage of spinning wool and bast fibers; but in recent times, the
range of long-staple fibers has also increased markedly.

System for Yarn Count
A yarn count is a number giving a measure of the yarn’s linear density. The linear density
is defined as the mass per unit length. In Systèm International (SI) units, the mass is in
grams, and the unit length is in meters. In textiles, a longer length is used for greater
meaningful measurements, since this would average the small, random, mass variations
along the length that are characteristic of spun yarns. There are two systems by which the
count is expressed, as described below.

• Direct system. This expresses the count as the mass of a standard length. The mass
is measured in grams, and the specific length is either 1 km or 9 km.
• Indirect system. This gives the length that weighs a standard mass. The standard
mass is either 1 kg or 1 lb, and the associated length is in meters or yards.

Usually, thousands of meters of yarn are required to weigh 1 kg and, similarly, thousands
of yards to weigh 1 lb. This makes measurements and calculations cumbersome. To
circumvent any such awkwardness, a standard length is used. The standard length can be
1 km, 840 yds, 560 yds, or 250 yds.

The standard lengths in yards are commonly called hanks, or in some cases skeins. Thus,
we can now say that the indirect system gives the number of kilometers that weigh a
kilogram (metric units) or the number of hanks that weigh one pound (English Imperial
units).

8 eBook PSP | Yarn Technology (Filament Yarn)

Figure 1.4 Count range of product areas for continuous filament yarn

1.5 Characteristics of Filament Yarn

The Easiest Way To Differentiate Spun From Filament Yarns
The simplest method is to untwist them! If small fibers emerge, it is spun yarn. It's a
filament if no fibers fall out. Sometimes you can't untwist a yarn because it's in a garment.
So, how can you tell if the fabric has filament or staple yarns? Well, there are three
categories we can look at to give us clues about how the yarn was made. They are
uniformity, smoothness and luster, and strength.
Uniformity
in general filament, textile yarns have a more uniform diameter. This makes sense
because the fibers run the full length of the yarn. So if a yarn has 20 filaments at one point
it should have 20 filaments at every other point. Staple yarns are much more unpredictable
and because of this have slight variations in diameter.

eBook PSP | Yarn Technology (Filament Yarn) 9

Smoothness and Luster
The smoother and rounder a textile yarn, the more luster or shine it will have. Staple-length
yarns tend to have less smoothness and luster than filament yarns. This is because tiny
bits of fibers stick out of staple-length yarns creating a fuzz that is bad for shine.
But what is bad for shine, is a benefit while sewing garments. Sometimes filament yarns
are too smooth and too shiny, and this can create seam slippage. Have you ever had a
dress or top made in satin that starts to develop holes in the seams around the sewing
threads? This is because the filament yarns in the fabric are sliding around and are not
stable.

Strength
Filament yarns are stronger and take more force to break. Staple-length yarns tend to fray
and slip apart.

Filament Yarn Varieties
Monofilament against Multifilament
Monofilament yarns are yarns that have only one filament fiber. Multifilament yarns are
yarns that have multiple filament fibers twisted together. Given the same fiber diameter,
multifilament yarns will have more movement and flexibility than mono. Generally
speaking, the more filaments in a textile yarn the more flexible and less rigid the yarn will
be.
How is this relevant to sustainable fashion? Well, lots of ways. For example, alternative
cruelty-free rayon silks are an example of fabrics with multifilament yarns. I see a lot of
first-time designers focusing on weave density and fabric weight when choosing alternative
silk. The real pros know to ask questions about the yarns. The more fibers, generally the
higher the quality of the fabric.

Microfilament
Microfilament yarns are even finer than silk, and made of microfibers - we measure them
in micro deniers. And, fabrics made of microfilament yarns are almost indistinguishable
from silk. By blending microfibers with natural fibers we can enhance the quality of yarns
and fabrics. This practice of microfiber blending creates fabrics that feel like natural fibers
but with extra silky drapability.

10 eBook PSP | Yarn Technology (Filament Yarn)

Table 1.1 Characteristics of Spun Yarns and Filament Yarns

Characteristic Spun Yarn Filament Yarn
1. Fibers
2. Length Yarn is made from short-length Yarn made from long-length filament
fibers and the fabrics are like cotton fibers and fabrics are like silk
3. Absorbency and wool
4. Size Short fibers twisted into continuous Long continuous, smooth, closely
5. Twist strands, have protruding ends packed strand.
6. complexity
i. Dull, fuzzy look i. Smooth, lustrous
ii. Lint ii. Do not lint
iii. Subject to pilling iii. Do not pill readily
iv. Soil readily iv. Shed soil
v. Warm (not slippery) v. Cool, slick
vi. Loft and bulk depend vi. Little loaf or bulk
vii. Snagging depends on
on size and twist
vii. Do not snag readily fabric construction
viii. Stretch depends on the viii. Stretch depends on the

amount of twist amount of twist
Are absorbent Absorbency depends on fiber content
Size often expressed in yarn Size in denier
number
Various amounts of twists used Usually very low or very high twist
The most complex manufacturing Least complicated manufacturing
process process.

Conclusion
Spun yarn is made from fibers with short discrete lengths and involves materials like cotton
and wool while filament yarn is made from long, continuous filaments and involves
materials like silk. Moreover, spun yarns are softer and less lustrous and tend to pill more
than filament yarns. Thus, this is the main difference between spun yarn and filament yarn

Note

Sustainable Design Tips
Designing a jacket or dress that you want to last forever? Filament yarns are perfect for
linings in coats and jackets, or dress slips. Why? Because they are inherently slippery. A
filament lining makes it easier to slip in and out of clothing, and garments tend to show
less wear and tear and get fewer snags. Don't skip the step of lining your garment to save
costs. In the long run, it will help create a garment that is less likely to end up in a landfill.

eBook PSP | Yarn Technology (Filament Yarn) 11

02

MANUFACTURING OF
FILAMENT YARN

This topic covers the classification of fibers, polymeric materials, and man-made fibers. It consists
of dry spinning, wet spinning, melt spinning, and man-made staple fiber production.

12 eBook PSP | Yarn Technology (Filament Yarn)

2.1 Introduction

Most manufactured fibers are extruded using either melt spinning, dry spinning, or wet
spinning, although reaction spinning, gel spinning, and dispersion spinning are used in
particular situations. After extrusion, the molecular chains in the filaments are unoriented
and therefore provide no practical strength. The next step is to draw the extruded filaments
to orient the molecular chains. This is conventionally carried out by using two pairs of
rollers, the second of which forwards the filaments at approximately four times the speed
of the first. The drawn filaments are then wound with or without twist onto a package. The
tow of filaments at this stage becomes the flat filament yarn.

Textile fabrics are often soft and malleable, with the capacity to be molded or draped over
non-flat surfaces. The 'hand' of a fabric (which specifies its tactile properties) is critical in
assessing its suitability for a variety of applications. To acquire the appropriate properties
required of clothes, for example, the fabric must be constructed from fine yarns and have
some degree of flexibility for them to move inside the fabric structure. The stiffness of the
hairs or fiber loops emerging from the fabric's surface influences the feeling produced
when human skin comes into touch with it. The finer these exceptional hairs or fibers are,
the softer the cloth feels to the touch. Many textiles are manufactured from fine filaments
or fibers for the same purpose.

Fibers and Filaments
Let us define a filament as a continuous fine strand of such length that it may be deemed
endlessly long. Cotton and wool are examples of staple fibers with relatively short fiber
lengths. To distinguish filaments from fibers, we shall use the terms 'continuous filaments'
and staple fibers.' Silk is an exception to the rule that most natural fibers are stapled fibers.
(Sometimes, silk is cut to form staple fibers.) Man-made fibers can be stapled or
continuously filamented. Because of the incredibly small fibers used in textile materials,
unique units must be utilized to convey the concept of fineness or 'diameter.'
Unfortunately, several industries have developed their ways throughout time.

Another desirable feature of most textile fabrics is a pleasing look. This typically means
that the fabric must be uniform in appearance, with no blotchiness, cloudiness, barré, or
streakiness. This suggests that the yarns should be consistent in fineness, hairiness, and
colour over their whole length. Faults such as thick and thin areas in the yarn and neps

eBook PSP | Yarn Technology (Filament Yarn) 13

should be avoided when working with such materials since they hurt the look of the
garment. (Neps are small fiber balls that impair the look of fabrics.) Furthermore, light
reflects differently from different surfaces, and a change in the structure of yarn (or fabric)
might result in an unfavourable alteration in the look of the fabric. Variations in yarn twist,
hairiness, or fiber fineness, for example, might result in such unpleasant modifications.

Quality must be carefully maintained in various areas; for these and other reasons, quality
control is an essential issue. In the marketplace, appearance is essential. Many yarns go
to considerable lengths to achieve yarn homogeneity in all areas. However, there is a
subset of fabrics that employ colour patterns, random disturbances (such as nubs), and
thick and thin patches in the yarns to create fascinating textures; these yarns are known
as 'fancy yarns' or 'effect yarns.' Nubs are thick areas of yarn that are randomly induced
into the yarn to provide visual effects in the cloth.

Each type of yarn has its own set of physical and mechanical qualities that determine its
performance. To choose the appropriate yarn for a specific application, one must first
understand the properties of the materials. Because there is a relationship between
technology and the features of the yarn produced, it is essential to examine all elements
of these issues.

Classification of Fibers
The primary distinction is between natural and synthetic fibers. Natural fibers are
categorized into three types: vegetable, mineral, and animal fibers. Cotton fibers are the
most significant in this category and will be taken into account. Bast fibers are another
name for stem fibers. Asbestos and glass are the only mineral fibers. Asbestos has recently
been linked to asbestosis and has been prohibited in several areas of the world. Glass is
widely used in industrial insulation, nonwovens, and, more recently, optical fibers for
communication. The glass is melted and extruded, and the manufacturing procedures are
quite similar to those used for man-made fibers. Wool is the most significant animal fiber,
and enormous amounts of it have been used to make carpets and clothing. They are
natural and vary, just like vegetable ones.

14 eBook PSP | Yarn Technology (Filament Yarn)

Figure 2.1 Classification of Fibers
Polymeric materials
Fibers are formed of polymers, some of which are natural and some of which are synthetic.
Between these two classes are regenerated fibers, which are manufactured from
regenerated cellulose from trees, discarded cotton fibers, or other natural sources of
cellulose, and modified natural fibers, which are made by reacting natural polymers with
chemicals to change their characteristics. It is incorrect to consider only synthetic fibers to
be polymers. Natural polymers are grown in the agricultural sector, whereas synthetic
fibers are manufactured in the industrial sector. The synthetic polymer is initially
manufactured in chip or similar form, or it is given straight to extruders in liquid form. If it
is manufactured in the shape of a chip, it is afterward melted or otherwise liquefied and
extruded.
Long-chain molecules make up a textile polymer. A long-chain molecule may be thought of
as a long string of atoms; these 'molecular strings' are flexible (if not cross-linked) and
provide many of the desired properties of fibers. It's no coincidence that the behaviour of
a long flexible fiber is similar to that of a long flexible molecule. However, the similarity
should not be taken too far since the molecular chains that make up the fibers can form
strong connections that are not replicated by the fibers in a yarn.

eBook PSP | Yarn Technology (Filament Yarn) 15

The polymer must be able to endure the end-user circumstances. It would be pointless, for
example, to create a cloth that would melt or soften in hot water. It must also be robust
enough to serve its objective. Other qualities must be considered in the same way. Many
polymers can be set by heating them over their glass transition temperature (Tg),
deforming them, and then cooling them. The temperature at which the polymer softens is
denoted by Tg. Although some fibers (such as cotton) cannot be permanently heat set,
easy care characteristics can be induced into fabrics through a chemical process known
as cross-linking.

This method binds together groupings of molecular chains, reducing their capacity to move
about one another. The connecting minimizes the energy loss of deformation and
increases the likelihood that the retained energy will be available to restore the fabric to
its original shape; it also stiffens the fiber structure. Many cross-linked fabrics, particularly
those used in garments, are easy to care for. Some fabrics have creases or shapes built
into them, so they keep the appropriate shape or crease even after laundry or cleaning.
Texturing is a technique used to create one type of yarn by shaping the filaments
themselves. When heat or mechanical stress produces a change in the molecular
structure, the way dye is taken up at different points throughout the length of the yarn
might change. It can make fabric appear streaky.

The long-chain synthetic molecules of polyesters are esters of aromatic dicarboxylic acids
and glycols. One of the most prevalent polyesters is polyethylene glycol terephthalate
(PET), which is frequently utilized in staple form. For clothing, it is frequently combined with
cotton. The mixes provide some of the advantages of each component. Cotton's moisture
absorption and feel are thought to offer comfort to cotton-based clothing. Polyester offers
durability and recovery capabilities that contribute to the ease of maintenance of any fabric
created from it.

16 eBook PSP | Yarn Technology (Filament Yarn)

Polyamides are synthetic polymers with long chains derived from diamines and
dicarboxylic acids. The most common is known as nylons, and the various chemical kinds
are denoted by adding numbers that represent the monomers from which they are
generated, such as nylon 6, nylon 6.6, and nylon 11. They are frequently utilized in carpets
in both staple and filament forms. Acrylic fibers, often known as 'modacrylics,' are a kind
of synthetic polymer. Textured acrylic fibers have grown popular for items such as
sweaters, displacing wool in some markets.

Figure 2.2 Man-made fiber – Partial Classification

Polyolefines like polyethylene and polypropylene are created by polymerizing olefins like
ethylene (ethene) and propylene (propene). Polyolefines have become widely used for
wrappings, displacing jute in a substantial portion of that market. Wrapping textiles are not
always formed of traditional yarns; they can be non-wovens or constructed of tapes rather
than more or less cylindrical threads.

Stapel Versus Filament
Most natural fibers are available in discrete lengths; however, synthetic fibers are
manufactured as exceptionally long filaments that may be treated as continuous filament
yarn or transformed into staple fiber. Natural fibers are agricultural products whose
qualities can alter as a result of changes in growth circumstances. Man-made fibers are
normally more precisely regulated, although variances may exist; many of the elements
that do differ have fairly modest impacts.

eBook PSP | Yarn Technology (Filament Yarn) 17

The non-technical end consumer has an extraordinarily strong preference for natural fibers
and mixtures of natural and man-made staple fibers. Hand and aesthetic characteristics
in consumer items are particularly significant in this industry, and some of the expectations
of greater quality from synthetic fibers resulting from closer control have not been
achieved. Users of technical items such as ropes, belting, and other industrial materials
are typically more concerned with strength than with aesthetics, and technical concerns
take precedence. The idea is that there are market segments with vastly different needs.

The manufacturing processes for the two types of fiber, natural and synthetic, are vastly
different and must be described individually. The stark difference in the tactics used in the
two situations will be highlighted. However, it should be noted that a spinner frequently
has to work with both man-made and natural fibers, and there is a need to understand the
sources and peculiarities of each.

Man-made fibers (polymer extrusion and yarn production)
Outline of the process to produce man-made fibers
By liquefying the polymer and driving it through a 'spinneret' to generate a multitude of fine
streams, it is feasible to mimic the silkworm. The liquid streams are then solidified to form
filaments. These filaments are typically 'drawn' at a later stage to better orient the
molecular structure to provide the necessary physical qualities. The technique used to
liquefy the polymer is determined by the kind of polymer. A solvent is utilized in certain
circumstances, while the polymer is melted in others. Polymer solutions are solidified by
evaporating the solvent (dry spinning) or coagulating them in a liquid bath (wet spinning).

Cooling polymer melts below their melting temperatures solidifying them (melt spinning).
Some fibers cannot be melt spun because they break down before melting or because the
melting temperature is outside of an acceptable range. The high temperatures necessary
for melt spinning, for example, might induce discoloration in some acrylic polymers. As a
result, either a wet spinning process or a melt spinning operation with an inert gas blanket
is utilized to prevent oxidation (oxidation causes the yellowing, as well as some other
undesirable changes to the polymer).

18 eBook PSP | Yarn Technology (Filament Yarn)

2.2 Dry spinning

Dry spinning is used to make cellulose acetate fibers from an acetone solution; additional
organic solvent solutions can be used to make vinyl fibers and polyacrylonitrile fibers. The
first step is to prepare the polymer solution, which is then filtered and pushed through the
spinneret, as shown in Figure 2.3. Solvent power, boiling point, the heat of evaporation,
stability, toxicity, hygroscopicity, ease of recovery, and cost are all factors to consider when
selecting a solvent. Low boiling point solvents with high evaporation temps may promote
polymer condensation on the filament's surface, resulting in an unattractive surface.

Dry spinning requires a limited amount of time and energy to remove the solvent from the
filaments. The solvent removal method diminishes productivity and raises expenses. This
is because mass and heat transmission is not immediate. To remove solvents, the spinning
equipment must have a lengthy 'chimney.' Almost all of the volatile solvents used for the
procedure are hazardous and/or flammable. The vapours cannot be discharged into the
atmosphere and must be retrieved. Furthermore, solvents are costly, and recovering them
is both economically and environmentally necessary. Increases in delivery speed may need
disproportional capital expenditures; there is also an upper limit to manufacturing speed.

Normal spinning speeds are in the 800-1000 m/min range. The length of undrawn and
unsupported filament that may be handled is limited. Several variables influence flow
through the spinneret. These include the liquid's pressure and viscosity. A normal solution
has viscosities in the 500-1000 poise range; this viscosity is mostly governed by the
solvent content and the temperature of the combination. The yarn take-up speed is
affected by a variety of variables, including shrinking caused by solidification.

The cross-sectional shapes of the filaments are affected by the polymer and solvent used.
Fibers are seldom circular in cross-section, and differences in cross-sectional forms can
influence the luster and other physical qualities of the fiber. When the material is chopped
into staple fiber, the cross-sectional form might alter fiber cohesion, which affects the
processability and qualities of the finished staple yarn.

eBook PSP | Yarn Technology (Filament Yarn) 19

Figure 2.3 Dry Spinning

2.3 Wet spinning

Wet spinning is a type of chemical precipitation. Coagulation of the filaments includes two-
way mass transfer, with the coagulating agent (e.g., acid) diffusing inside and the
coagulating products (e.g., salts) diffusing outwards. To develop a solution, it is
occasionally essential to employ an intermediary step. In the case of viscose rayon, for
example, a soluble derivative (cellulose xanthate) is created and dissolved in dilute dolium
hydroxide to form a liquid appropriate for extrusion.
The solvent is leached out by the liquid in the bath, which must be miscible with the solvent
but not a polymer solvent. Thus, in a generalized flowchart of such a process, the extrudate
would need to be specified as filtered 'polymer derivative' or 'polymer solution' depending
on whether an intermediary step is required, but in the example described above, the
extrudate is a polymer derivative (Figure 2.4).

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Figure 2.4 Wet Spinning
Several parallel events occur during coagulation, in various ways for distinct
polymer/solvent combinations. Their coagulation is gradual, and up to three drawings are
feasible. The cross-section becomes more inhomogeneous as the coagulation rate
increases. The temperature and solvent distributions inside the fiber are affected by heat
and mass exchanges between the extrudate and the liquid of the coagulation bath. Any
misdistributions make it difficult to achieve consistent characteristics across the strand's
cross-section.
The exterior surface of the filaments hardens, which inhibits essential mass transfer.
Furthermore, the migration of the solvent through this hardened' skin' lowers the volume
of the contained substance, causing the skin to wrinkle. As a result, wet-spun filaments
typically have a convoluted cross-section. Wet spinning is frequently used to make viscose
rayon and polyacrylonitrile (PAN) fibers. The polymer derivative must generally be ripened
since it changes viscosity and character as it matures. To accommodate the aging process,
a storage system is frequently required between the manufacture of the polymer derivative
and the final extrusion.

eBook PSP | Yarn Technology (Filament Yarn) 21

A critical variable is the viscosity of the polymer solution. In general, the higher the polymer
content (preferred for economic reasons), the higher the viscosity. Because the favourable
cohesive benefits of high viscosity exceed the bad effects of inevitable surface tension,
which tends to cause the liquid to degenerate into droplets, high-viscosity solutions spin
effectively. However, a high-viscosity liquid is difficult to filter and pump, therefore a
compromise is required. During filtration, the solution is frequently heated to decrease
viscosity. Cellulose fibers may be spun at temperatures as low as 50°C, but
polyacrylonitrile fibers are typically spun at temperatures ranging from 170°C to 180°C.
Several hundred meters per minute is a common rotation speed.

2.4 Melt spinning

The material delivered to the extruder in melt spinning is occasionally in a solid granular
or 'chip' form, especially for small operations. In this scenario, a pneumatic transport
system transports the chip from the storage silo to the extruder hoppers. The polymer is
carried via an 'auger' or 'screw' from each hopper to the extruder (Figure 2.5). The polymer
is then melted by the hot barrel and the screw's friction. The viscosity of the liquid polymer
in the operating extruder is mostly determined by heat flow. The viscosity of the liquid
polymer influences the pressure created by the screw driving it through the spinneret. A
filter pack creates additional back pressure.

In other circumstances, the polymer can be delivered continuously molten from the
polymerization reactor or an intermediary heated storage tank. By delivering the polymer
through heated pipes, it may be kept liquid and air can be readily excluded, preventing
oxidation and its negative consequences. Several types of pumps, including the extruder
screw, can pump the liquid polymer through the filter pack and spinneret. Back leakage,
polymer overheating, and deterioration due to excessive working are all problems to
consider when selecting a suitable pumping system. It should be emphasized that these
polymerization/spinning systems are quite massive, and the complete polymer synthesis
and extrusion equipment need a significant amount of floor space and headroom. Usually,
a multi-story building is required. The capital cost is very high.

22 eBook PSP | Yarn Technology (Filament Yarn)

Figure 2.5 Simple Fiber Extrusion
The pace at which heat is transferred from the extruder barrel into the polymer is critical
in influencing the viscosity of the molten material approaching the spinneret. This, in turn,
aids in determining flow rates and final yarn qualities. The pace of heat flow away from the
extruded filaments leaving the spinneret contributes to the yarn's morphological structure.
Morphology is concerned with crystallinity and orientation. The shear rate in the extrusion
zone (which is a function of the filament velocity) also influences the morphological
structure at high speeds. The quantity of consecutive drawings of these filaments changes
the yarn's characteristics even further. This sketching might be done near the extrusion
procedure, during texturing, or both.
The mechanical method looks to be straightforward. However, several less evident
difficulties become critical at the high speeds already in use (of the order of 5000 m/min).
Because the mechanical nature of the process limits the drawing speed, the extruder
delivery speed would become essentially locked at a rather low level if the filaments were
fully drawn. When a portion of the drawing step is postponed until the material is in the
texturing machine, the yarn exiting the extrusion frame is only partially orientated. Drawing
in the texturing process completes the orientation, and using this method results in an
economic gain. Draw ratio changes affect the strength of the partially oriented yarn (POY).

eBook PSP | Yarn Technology (Filament Yarn) 23

The strength of the POY generated at low draw ratios is insufficient for high-speed
texturing, hence drawing at the texturing step is desired to boost the filament strength. To
provide the POY enough strength and stability, some drawing is required during the
extrusion step. As a result, when the POY is created for draw-texturing, the texturing speeds
become in effect connected to the extrusion speeds. The process of drawing at texturing
is referred to as draw-texturing. Because it is more cost-effective to conduct as much
drawing as possible at the texturing step, the draw ratio at spinning becomes quite
important.

Extrusion of commercial filaments is a complicated procedure. The filters are larger, and
the molten polymer is dispersed to groups of spin packs that are supplied by a central spin
distributor and pump system. The entire system is meticulously designed to
minimize stagnant flow zones, conserve heat, and maintain melt temperature with heat
transfer fluids that are often two-phase in nature and retain the temperature at the boiling
point of the fluid.

It will be seen that controlling the temperature and viscosity of the melt is critical since the
uniformity of the yarn is dependent on it. For example, for some polyesters, the
temperature must be kept between 300 and 1°C. Because the mechanical functioning of
the melt impacts viscosity, the design of the extrusion and distribution systems is crucial.
Extrusion systems must also be designed such that filters and spinning heads may be
changed with minimum disturbance to production. It must be understood that the halt of
flow causes issues, and allowing the polymer to harden is a calamity!

The extruder
An extruder's screw and barrel serve several purposes. To begin, the screw serves as a
propulsion unit, transporting the feed material to the spinneret. Second, it functions as a
pump, compacting or compressing the feed and then forcing it past the different barriers
ahead (once the polymer has melted). Third, it works the melt and makes it more
homogenous. The barrel functions as part of a heat exchanger to maintain or melt the
temperature of the flowing polymer.

Before it can reach the spinneret, the molten material must be filtered (perhaps with the
use of increased pressure). The first stage of the process is contained within the extruder

24 eBook PSP | Yarn Technology (Filament Yarn)

head and includes the stages of propulsion, compression, heating, working, filtering,
metering, and polymer extrusion via the spinneret. The second stage involves quenching,
drawing, and winding the filaments.

The clearance between the screw and the barrel (Figure 2.6) is significant. If the clearance
is too great, significant pressure loss occurs, and the molten polymer seeps backward
down the screw. The screw may seize if the clearance is too tiny. The bore diameter grows
when the barrel heats owing to metal expansion and decreases as it cools due to
contraction. The barrel might cool down quicker than the screw due to thermal inertia. It
must be ensured that the contracting barrel does not grab the screw and induce a seizure.

Figure 2.6 Polymer flow in the extruder barrel

Of course, the extruder should be empty or the polymer in the barrel should be heated to
liquefy it before starting. If the polymer became crosslinked owing to oxidation and could
no longer be melted, it would have to be chipped away mechanically. To prevent these
issues, it is usual to run extruders constantly 24 hours a day, seven days a week.

The screw turns, and the movement of the helical portion's surface in direction D causes
the polymer to travel in direction C. (Figure 2.6). Polymer flows along the screw groove, and
the mass flow, Q, at any cross-section, such as (X-X), is given by:

Q = ρAV [2.1]
where Q denotes the mass flow
ρ is the density of the polymer (defined as 1/specific volume)
A represents the cross-sectional area
V is the mean velocity component in direction of flow.

eBook PSP | Yarn Technology (Filament Yarn) 25

As the chip is compacted, liquefied, and then pressurized, ρ changes and it is necessary
for AV to change accordingly. As a result, the metal screw's core is tapered, with the thick
end towards the exit. The forced flow pressurizes the fluid polymer so that it may be sent
to the pump/filter system that comes before the spinneret. The spinneret should create
one filament per hole, hence a regular yarn must have a lot of fine holes. The cross-
sectional form of the filament is determined by the shape of the holes; however, the cross-
sectional areas of the filaments differ from those of the spinneret holes for reasons that
will be described later.

Rather than employing direct heating, hot fluids are frequently circulated via channels in
the barrel to create heat. The heat flow into the polymer is proportional to the heat flow
from the heating medium plus local frictional heating. The absorbed energy is taken away
from the system by the polymer as its state changes from solid to liquid and/or
temperature changes. Changes in condition and temperature also have an impact on heat
transfer characteristics. The changes in the polymer have a direct effect on the frictional
heating component and the heat delivered from the heater, creating a very complicated
dynamic scenario. The temperature of the polymer affects the local pressures, specific
volumes, coefficients of friction, and viscosities of the melt. Because the actual extrusion
through the spinnerets is strongly reliant on the viscosity of the melt, the factors must be
carefully controlled.

The intricacy of the operating circumstances, along with the ambiguity in flow induced by
the plurality of parallel flow streams, raises the risk of unequal polymer flow distribution.
This 'channelling' effect can cause more polymer to flow through some spinneret holes
than others. As a result, the linear density of filaments varies. Furthermore, if the polymer
viscosity is improper, the flow pattern might alter continuously throughout the operation.
Working under such defective settings causes quality control issues with 'denier'
differences.

It is critical to preserve the polymer against oxidation at high temperatures. Any oxidation
causes viscosity changes, cross-linking, and degradation in the final product. As a result,
antioxidants are frequently added to the first polymer chip or molten polymer supply. Also,
by drying the polymer right before extrusion, the hydrolytic breakdown is reduced.

26 eBook PSP | Yarn Technology (Filament Yarn)

Filtering and metering
The material that emerges through the screw may not be homogenous. It is critical to
remove any hard materials or excessively viscous concentrations (i.e. gels) from the fluid
polymer stream lest they clog the spinneret's very thin pores. A die is a metal block in which
the holes are bored. Such impediments not only disrupt the individual fluid streams from
the damaged holes, but it is improbable that a filament will be re-established even if the
barrier is removed. Instead, a trickle is more likely (which is unoriented). Such undesired
polymer drips can combine with neighbouring filaments, resulting in a flaw that can
substantially disrupt future processes in the creation of staple or textured yarn.

For these reasons, filtering the molten material before it reaches the spinneret is usual.
Metal webs, cloth, or precisely graded sand are frequently used for this purpose, however,
the body of the filter must be carefully designed in the latter instance to prevent sand
particles from clogging the spinneret holes. The filter causes significant shear stress in the
polymer, which alters its viscosity and complicates matters further. In certain
circumstances, the filter assembly is divided into two pieces, one of which is idle while the
other is in use. When the pressure drop has increased or a certain duration of usage has
ended, the second filter is replaced.

If the linear density of the filaments is to be maintained, both the liquid flow rate and the
yarn or tow take-up rate must be precisely controlled. To precisely regulate the flow rate of
the liquid polymer, a metering device must be used such that variations in viscosity and
viscosity distribution do not influence the mass flow rate. The pressure upstream of the
metering pump must be adjusted so that the metering device does not have an
undesirable effect.

Leaks in the metering pump can also harm the denier of the filaments. Such variances are
difficult to detect during the extrusion step, thus extremely careful inspection and testing
are essential to produce a high-quality product. Any deviations that are allowed to go
undetected are likely to manifest in the final product as flaws in dyeability and bulk,
resulting in consumer complaints. The linear density of the filament is determined by D1
(Figure 2.7) and polymer density (ρ). This is defined by the mass flow (Q) and the take-up
velocity (V). The mass flow is constant across all cross-sections.

eBook PSP | Yarn Technology (Filament Yarn) 27

Figure 2.7 Polymer bulge

It will be observed that the size of the spinneret hole, D1, has no direct effect on the linear
density of the filament. The form and size of the hole, on the other hand, dictate the flow
lines in the polymer as it begins to harden, and the geometry of the hole does alter the
cross-sectional shape of the filament. The ratio D1/D3 is also affected by the form of the
hole, the viscoelastic factors of the polymer, and the rate of take-up. These parameters
can have a significant impact on the morphological nature of the filaments generated if
the polymer hardens soon after exiting the spinneret.

This is because differences in shear stress, temperature, and viscosity near the spinneret
holes impact crystal nucleation. Furthermore, under some conditions, periodic changes in
D2 can occur owing to vibrations inside the polymer stream, and these vibrations can
cause fluctuations in the denier of the fibers. Filtering does not diminish the debris formed
at the output of the extruder die, and such material may cause problems in subsequent
operations. Quality control requires good housekeeping throughout the extrusion step.

Quenching
At an acceptable distance from the spinneret face, the liquid that emerges from the
spinneret must be transformed into a solid filament (i.e. the corresponding temperature
has to fall below Tm). At that point, it is quite difficult to manage and draw the filaments.
Because of the absence of direction, delayed crystallization may make it exceedingly
difficult to manage the filaments after they are formed. As a result, it is common to practice
quenching the newly forming material with a low-speed flow of dry air or inert gas, typically
blasted perpendicular to the polymer stream. It is critical to limit the velocity of the gas
flow to avoid one molten (or semi-molten) filament from blowing into the path of another.

28 eBook PSP | Yarn Technology (Filament Yarn)

When such filaments come into contact, they frequently cohere and form' married fibers,'
which may be very annoying. Materials with a high concentration of married fibers or
polymer drips are ineligible for usage and are discarded. The requirement for identical
cooling rates over the whole filament bundle necessitates equal dispersion of the quench
medium. Uneven cooling rates not only change the shape of filaments across the bundle
but also render certain filaments more prone to breaking than others. This, in turn, impacts
the pace at which unwanted drips form. In any scenario, the negative consequences would
manifest themselves in the final product as variations in dye affinity.

The speed of the filaments has a substantial impact on the quenching rates at extremely
high production rates. Where the polymer is intended to be oriented during extension, the
filaments must be promptly chilled before the effects of stream orientation are dissipated.
The elongational pressures acting on the viscous fluid as it passes through the draw-down
zone, when the semi-molten polymer solidifies, tend to align the molecules. When swiftly
cooled, such orientation can be frozen, resulting in a material that can be handled and, if
research results can be applied to commercial applications, may be acceptable for use in
draw-texturing.

The relative velocity of the quench air influences the Reynolds Number of the air' skin'
around the polymer stream, which influences heat transfer or cooling rate during the
quenching phase. (The Reynolds Number is a dimensionless quantity used in
standardizing the mathematical units; it represents the viscous ratio and inertia forces.)
The cooling rate influences the morphology of the POY. Because of the quantity and size
of spinnerets, as well as the density with which the filaments are packed in the extrusion
zones, tow manufacturing presents the most severe quenching challenge. Furthermore,
because there are so many ends, the odds of a break are substantially higher.

Filament take-off and drawing
Devices that grab without squashing solidified filaments collect and transport them from
the spinning zone. The filaments are frequently wrapped around revolving cylinders or
'godets,' and the capstan friction created provides a sufficient driving force to withdraw,
draw, and carry them to the take-up system. The take-up speed is quite fast, although the
filaments are rarely pulled appreciably at this point. The filaments are at least partly
aligned after the draw step, and the delivery speed is even faster than the take-up pace.

eBook PSP | Yarn Technology (Filament Yarn) 29

However, drawing the freshly extruded filaments at some point is required to orient the
molecular structure and provide the requisite mechanical characteristics.

It should also be noted that it is critical that the drawing be consistent from the filament
to the filament and along the length of each filament. As a result, any mechanical errors
in the draw rollers cause periodic fluctuations in the draw. The uneven build-up of finish
on the rolls is a typical source of this type of mistake. Unfortunately, this generates not
only variances in linear density but also variations in dye affinity, which results in streaking
and barré. Drawing yarn can cause filament-to-filament differences in draw ratio, which
can have comparable negative effects. A neck is generated during normal drawing, and
the location of this neck is normally fixed with a hot pin or plate.

Undrawn polymers alter their properties quite quickly; this is known as ageing. The more
polymers that have been drawn, the slower the ageing process, and fully drawn filaments
have an extremely long shelf life. The ageing of the spun, undrawn yarn in drawing
filaments must be managed because it influences the natural draw ratio, drawing tension,
and physical properties of the material. When working with POY, the extrusion and final
drawing processes occur at different places, and the material is stored in the interim. As a
result, effective inventory management is required to keep the product within acceptable
time limitations between extrusion and final drawing.

An aspirator is required to start a high-speed drawing process. A mechanism like this
suckers yarn from the spinneret as fast as it is generated (it is realized that the source
cannot be shut off in many cases). The ends are then 'painted' around the thread line and
wrapped around the take-up godet or rolls before being cut free from the material within
the aspirator - a simple procedure but require talent to do.

Fiber finish and treatments
Fiber finishes are required to lubricate the fibers or filaments and prevent static
electrification during subsequent operations; these finishes are typically applied by the
fiber manufacturer. Without such 'spin finishes,' the increased drag caused by the high
coefficients of friction may result in end breaks or other processing issues. Static electricity
attracts or repels fibers and causes certain fibers to attach to other surfaces (such as

30 eBook PSP | Yarn Technology (Filament Yarn)

machine parts). In any instance, a large level of static charge complicates processing
significantly.

In some circumstances, fiber finishes can be utilized to promote cohesiveness between
filaments by serving as a type of sizing, similar to that used in weaving. They also protect
machine surfaces from wear and can inhibit fiber fusion at the local level (especially at
points where the fibers or filaments rub guides and other machine parts during high-speed
winding). A basic lubricant, an antistatic agent, an emulsifier or solubilizing agent, and
numerous specific additives are typically included in fiber finishes.

Bactericides, antioxidants, and friction modifiers are among the unique additions. Alkyl
esters of fatty acids, hydrocarbon oils, waxes, vegetable oils, or mixes thereof are often
used as base lubricants. These finishes must be developed with sorption, moisture
absorption, and surface tension characteristics in mind, as well as their influence on the
finish's dielectric and flow properties. Controlling the finish's volatility, smoke potential,
and flash point is also important to minimize issues in the following processing. These
parameters are especially relevant in texturing when fiber surface temperatures can reach
extreme ranges. During processing, finish and fiber particles become separated and
deposited on various machine surfaces.

They can leave deposits on the heaters and other operating parts while texturing. Deposits
in the rotor might be problematic while the rotor rotates. It is critical that the amount of
finish applied to the fiber be tightly regulated, and that the type of the debris be such that
issues in the subsequent procedures are minimized. Furthermore, the finish should not
negatively impact the packaging, including its shelf life. As brighteners or other modifiers,
polymers may contain chemicals such as titanium dioxide (TiO2). Brighteners hide any
yellowness in fabrics manufactured from the fibers and make colours more vibrant,
although the additives can be irritating at times.

eBook PSP | Yarn Technology (Filament Yarn) 31

2.5 Man-Made Staple Fiber Production

Tow
Tow is the first fiber manufactured for the production of man-made staple yarn. The term
'tow' has several meanings, but it refers to a dense bundle of continuous threads in this
context. Tow must be cut, broken, or abraded to be converted into staple fiber. The
abrasion technique is limited to mild tows and a few specific applications; it will not be
addressed further here.

To guarantee product homogeneity, fiber producers cut and combine tow before baling it.
For short-staple spinners, a huge volume of fiber is chopped in this manner. Some long-
staple is handled similarly, although some are delivered to the mill in tow form. In the mill,
this tow is sliced or stretched-broken. Tow intended for stretch-breaking in the mill typically
has a linear density of around 500,000 deniers. (The linear density of tows used by fiber
manufacturers for cutting into staples is many times higher.) Because the demands vary
so significantly, it is difficult to identify common ground in the early stages, as seen in the
table below.

Table 2.1 Fiber to sliver conversion

Stretch-breaking tow
Stretch-breaking is a type of drawing in which the draw ratio exceeds the filaments'
breaking elongation, causing them to break as they travel through the draw zone and
produce staple fibers. Stretch-breaking is most commonly used to make long-staple slivers
from which high-bulk staple yarns are formed. Various steps in the process will be detailed
separately, however, all of them are frequently combined into a single machine. The steps
are as follows: (1) heat the unbroken filaments and cool them under strain, (2) break the

32 eBook PSP | Yarn Technology (Filament Yarn)

fibers by adding elongation stress, perhaps with a beating motion, and (3) relax the fibers
by heating to form bulk in the result.

Before stage 3, there may be one or more repetition stages of phase (2) (referred to as re-
breaking) (3). In its most basic version, the machine generates varying fiber lengths, with
the mean length dictated by the ratch setting (the distance between consecutive roll pairs
in a roller drawing system). To break a huge bundle of strong filaments, an extremely robust
set of drawing components with high grasping force is required. As a result, the total fiber
denier must be regulated simply because the weight cannot exceed the rolls' gripping
power. Damage to the rolls must also be prevented. Uneven breaking will occur if load-
sharing between filaments in a disordered bundle is weak.

As a result, it is preferable to have a sheet of parallel fibers penetrate the break zone,
however, this is not feasible. Tows heavier than around 100 000 1.5 dpf filaments could
not be processed on early stretch-breaking machines. Modern machines can process tows
containing up to 500 000 filaments, and the allowable fiber fineness has also grown.
Because the qualities play a big influence in determining allowed loads, the exact definition
of machine capabilities is dependent on the fiber. The loads on the rollers are measured
in tonnes, therefore the machinery must be extremely durable. The machines are mostly
employed as tow-to-top silver producers. A sliver is known as a 'top' in the wool processing
Industry.

Figure 2.8 (a) Stretch-breaking tow

eBook PSP | Yarn Technology (Filament Yarn) 33

Figure 2.8 (b) Stretch-breaking tow

It is common to practice to heat the filaments over Tg (glass transition temperature) while
they are under strain and then allow them to cool before releasing the tension (phase 1).
The process's heat-stretch phase (Figure 2.8 (a)) minimizes breaking elongation in the
stretch-break zones, making this aspect of the operation easier. The stretch-break zones
follow the heat-stretch zones when the cooled, heat-stretched tow is split into staple fibers
(phase 2). When the fibers are warmed above Tg, the locked-in extension is released,
resulting in shrinking (phase 3).

This is an effective method of increasing the material's volume. To adjust the staple length
on older machines, intersecting breaker bars were utilized (Figure 2.8 (b)). This practice is
dwindling, and stretch-break/re-break systems are supplanting it. The re-break stage is
just stretching a previously stretched sliver; the second stage selectively breaks the longer
fibers and decreases the variance in length. The intersecting breaker bars have a high duty
and wear rates are an issue. Modern machines are extremely durable and built to operate
at high rates. The initial cost is considerable, but they can be cost-effective in situations
when 100% man-made fibers are to be processed and the system can be integrated into
the operation without causing an undue disturbance.

Stretch-breaking alters not only the linear density of the bundle by drawing but also the
linear density of each filament. The filaments are stretched to their breaking point,
resulting in fiber elongation. Elongation is followed by a decrease in the fiber's linear
density; the change in dpf can be considerable. Because the fibers are stretched while
heated, flats form on their surfaces, giving the final yarns a crisper hand than would
otherwise be the case.

34 eBook PSP | Yarn Technology (Filament Yarn)

Fiber cohesiveness is poor in freshly split tow, and it must be improved by fiber crimping
to manage the material. The typical crimper is a stuffer box in which the sliver is fed at a
quicker rate than the offtake to a hot stuffer chamber. Under compressive pressure, fibers
collapse and get crimped (16 to 20 crimps/inch is usual). Crimped fibers cohere nicely,
and a sliver produced of them may be handled and carded correctly. Significant volumes
of fly (airborne fiber and debris) can be formed when breaker bars are utilized, and this fly
must be removed from the breaker zone or the product would get polluted, affecting
subsequent knitting processes.

One significant benefit of the stretch-breaking method is the production of high-bulk yarns.
Bulk is produced by differential shrinking of the fibers, which occurs in the heat-stretch
zone. Because not all fibers experience the same stresses or reach the same
temperatures, they do not all shrink equally. The fibers that shrink the most compress the
others along their length, causing the squeezed fibers to buckle and the buckled fibers to
take up more space. A stretch-broken sliver is inherently bulky, but the effect can be
enhanced by combining a non-heat-stretched sliver with a heat-stretched sliver at the draw
frame and then autoclaving (heating with steam under pressure) to achieve the desired
shrinkage.

These bulky stretch-broken yarns are a near match for wool yarns, producing soft 'woolly'
garments. The yarns are also known as high-bulk staple yarns. While an autoclave was
traditionally used to develop the bulk, some newer machines have a continuous heating
system linked to them that serves the same purpose. The working temperature is around
115°C, and steam is frequently utilized as a heating medium. Within limitations,
increasing the heater temperature or draw ratio typically enhances the tenacity of the fiber,
but too high a temperature causes polymer breakdown, which results in a loss of strength.

Too high a draw ratio or too low a heater temperature produces end-breakages (i.e.
stoppages) during processing, resulting in increased flies. Stretch-breaking is technically
viable for both tow-to-yarn and tow-to-top systems (tow-to-sliver), but the high expense of
proper tows makes the system uneconomical for direct spinning. There is also no
possibility of combining the outputs of multiple machines to lessen the danger of barré.
The takeaway here is that manufacturing efficiency cannot always be matched with
product quality.

eBook PSP | Yarn Technology (Filament Yarn) 35

Cutting tow for long staple
A spiral cutter is typically used to cut tow to generate long-staple fibers, which mesh with
a smooth, hardened anvil roller, as seen in Figure 2.9 (a). Before travelling through the
cutter, the tow is spread out into a uniformly thick sheet. The pitch of the cutting edges
and, to a lesser degree, the angle at which the fibers move through the system regulate
the staple length. In addition, unintentional changes in fiber attitude generate a difference
in staple length, as shown in Figure 2.9 (c). It is possible to slightly modify the staple length
by adjusting the angle at which the tow travels through the cutter, as illustrated in Figure
2.9 (d).

Only slight adjustments may be accomplished by adjusting this angle, and any large
alterations necessitate the use of a new cutter. Any damage to a cutting edge is likely to
allow double-length fibers to discharge, causing problems in the subsequent drawing and
drafting operations. As a result, the cutting edges are rectangular rather than razor-like,
and they work by locally crushing the filaments at the point of contact between the cutter
and anvil roller. Handling fine denier fibers is challenging if the cutter is not properly
adjusted and in pristine condition. The cutter's maintenance is an essential aspect of the
operation.

The pressure exerted by the cutter tends to connect fibers along the cuts, which is
undesirable. As a result, the ribbon is flexed to induce shear, which debonds the fibers, as
seen in Figure 2.9. (b). Furthermore, because there is little fiber entanglement, tow exiting
the cutter exhibits well-defined areas of weakness with each cut. If the newly cut tow ribbon
was merely compacted, the resulting sliver would be incredibly weak.

To address this, the sheet is sheared by a process known as 'shuffling,' as seen in Figure
2.9 (e). In the example, an apron is employed as the bottom element to react to the two
upper rolls. The cut end on the top of the sheet is now offset from those below, as seen in
Figure 2.9 (g). The dispersion of chopped ends disperses the weak points. Finally, the cut
fiber sheet is rolled to form a sliver, as illustrated in Figure 2.9 (f). The elements depicted
in these diagrams are frequently components of a single machine, with filament tow as
the input and staple fiber in sliver form as the output.

36 eBook PSP | Yarn Technology (Filament Yarn)

Fiber finish and subsequent dressings are frequently applied in the mill to help with the
tow-cutting process, however, such additives might hurt the performance of the sliver in
the yarn production operation. A dressing that facilitates cutting may lead fibers to cohere
unevenly. This may result in unevenness in the yarns produced. The Pacific Converter
cutting equipment mentioned above is frequently used to generate a sliver or top, however,
the cutters used to produce short-staple fibers are considerably different.

Figure 2.9 Tow-to-top conversion by cutting

eBook PSP | Yarn Technology (Filament Yarn) 37

Cutting tow for short-staple
Long-staple processing is more tolerant of multi-length fibers than short-staple processing.
Short-staple or mid-range systems are less tolerant of fibers greater than the ratch setting
of the drafting system because they span the drafting zones and either break or slip at the
drafting rolls. A ratch setting is a distance between neighboring sets of rolls in a drafting
system. These occurrences disrupt the regular flow of fibers. This is harmful to the
process's efficiency and product quality. One method is to wrap the tow around a cutter of
the sort illustrated in Figure 2.10, first to produce pressure between the filaments and the
cutting edges, and then to apply internal suction.

There are few over-length fibers in the output, and the method is best suited for
manufacturing short or mid-range staple fiber. The fibers are baled before being sent to
the mill. Carding requires that the fibers be crimped such that there is some degree of
mutual cohesion, as previously mentioned. Tow size and quality are critical; the greater the
tow, the more difficult it is to maintain consistent tension during processing. A lack of
homogeneity in thickness across the tow sheet might pose issues, as can the tendency for
the sheet to fold at the edges. Tow knotting is an operational issue as well since the knots
must be removed before cutting. The knot removal operation can leave gaps in the ensuing
webs which result in excessive waste

Figure 2.10 Tow cutter for short-staple

Fiber crimping and finish
Crimping the fibers is typical. Overfeeding a ribbon of fibers into a stuffer box or running it
through the mesh of fine-toothed gears, as shown in Figure 2.11, might distort it under
heat. The tow can also be stretched hot and then cooled to lock in the extension as

38 eBook PSP | Yarn Technology (Filament Yarn)

previously mentioned. To avoid damage during the opening and carding procedures, the
fibers must be thoroughly lubricated. Furthermore, the finish provided to the fiber must
reduce any potential for the fibers to charge electrically owing to friction during processing.
Electrostatic charges interfere with proper processing, thus applying a good finish in
adequate proportions is critical.

Figure 2.11 Fiber Crimping
General remarks
Tow-to-sliver conversion is a simple mechanical operation that may be summarised in a
few words. However, good quality control includes not only mechanical procedures but also
the chemical and morphological properties of the polymer and fiber finish. The fact that
the explanation is brief does not imply that any of the processes is insignificant.

eBook PSP | Yarn Technology (Filament Yarn) 39

03

PRINCIPLE OF MAIN
TEXTURING METHODS

This topic covers textured yarn production. It consists of texturing filament yarns that are real twist
and false twist texturing. It also covers textured yarn process techniques and product
developments, and methods of texturization from the false twist, stuffer box, air jet process, BCF
process, and knit-de-knit.

40 eBook PSP | Yarn Technology (Filament Yarn)

3.1 Introduction

There are many methods for yarn texturing, including false-twist, air-texturing, knit-de-knit,
stuffer box, and gear crimp. Among these, the false twist is the most popular method.

For many applications, flat filament yarns are textured to gain increased bulkiness,
porosity, softness, and elasticity in some situations. Thermoplastic filament yarns are used
in most texturing processes. The inter-fiber bonds break and reform during the texturing
process. A filament yarn is generally textured through three steps.

1. The first step is to distort the filament in the yarn so that the inter-fiber bond is
broken. Twisting or other means are used to distort the filaments within a yarn.

2. The second step is to heat the yarn, which breaks bonds between polymers,
allowing the filaments to stay crimped.

3. The last step is to cool the yarn in the distorted state to enable new bonds to form
between the polymers.

When the yarn is untwisted or otherwise released from its distorted state, the filaments
remain in a coiled or crimped condition.

Textured Yarn Production
In yarn production, the polymer is supplied either directly from the chemical reactor or as
a polymer chip. The polymer is fed to an extruder in which a rotating screw or auger
transports the input material through the extruder barrel and pressurizes it; as the polymer
passes through the barrel it is melted or maintained in the molten condition. The extruder
changes the form of the molten polymer, from a relatively slowly moving mass to the high-
speed thin jets of polymer which form the yarn. It is metered and filtered before passing
through the spinneret, which contains one tiny hole for each filament. The emerging
filaments cool rapidly and solidify; they are also ‘drawn’ by taking them up at a faster rate
than that of the supply. Drawing is a very important part of the process because it stabilizes
the molecular structure and strengthens the yarn by improving the molecular orientation.

The main idea in most texturing systems is to heat set the filaments into some sort of
crimped or convoluted form, such that each filament is held as separate from its
neighbours as possible. In this way, the yarn contains the many air pockets needed to
produce insulation properties, permeability, and softness. Furthermore, the yarn now
occupies a greater volume, which is also very important since the purpose of most textile

eBook PSP | Yarn Technology (Filament Yarn) 41

materials is to cover some underlying strata; the greater the bulk, the better the cover.
Also, the yarn becomes more extensible and this, too, is an added attraction. It is possible
to get various combinations of stretch and bulk. For filaments (such as rayon) that cannot
be heat set, it is possible to tangle the fibers to lock them mechanically.

An example of this is air-jet texturing. Sometimes it is desirable to combine air jet with
false-twist texturing. Air-jet texturing gives a product that is nearer to a staple yarn than a
false-twist textured yarn. It has much of the hand and appearance of the staple product.
False-twist machines with built-in air jets are now becoming common.

3.2 Texturing filament yarns

Purposes of texturing
The prime purpose of texturing filament yarn is to create a bulky structure that is desirable
for the following reasons:

1 The voids in the structure cause the material to have good insulation properties.
2 The voids in the structure change the density of the material (which makes
possible a lightweight yarn with good covering properties).
3 The disorganized (or less organized) surface of the yarn gives dispersed light
reflections, which, in turn, give a desirable matte appearance.
4 The sponge-like structure feels softer than a lean twisted ‘flat’ yarn.
5 The crimped or coiled filament structure gives a lower effective modulus of
elasticity to the structure when compared with that of a flat yarn.

From this, it will be realized that to make yarns to these specifications, it is necessary to
deform the individual filaments and set, or otherwise hold, them in the desired deformed
condition. When deformed in this way, the filaments in the whole bundle are unable to lie
side by side in close contact and the required voids are produced.

Furthermore, the non-straight, separated filaments are much more easily deformed than
those in a flat yarn, and one obtains a softer hand and greater ‘stretch’. There are two
general classes of textured yarns that relate respectively to thermoplastic yarns only and
to those which can be more widely used.

42 eBook PSP | Yarn Technology (Filament Yarn)

In general, the first classification involves the stages of deforming, heating, cooling, and
relaxing the filaments. The process is known as heat setting even though it is the cooling
that does the setting. In the second case, the texturing of non-thermoplastic materials,
filaments are deformed and are held in their deformed state by frictional contact with the
neighbouring filaments.

The physical basis of texturing
Before considering the methods of false twisting, let us review the mechanics involved. It
will be recalled that the process phases in false twist texturing consist of:
1. Deforming the filaments.
2. Applying heat to raise the filament temperature above the glass transition

temperature, Tg.
3. Cooling the filaments to below Tg.
4. Rearranging the filaments under suitable tension.
5. Winding the textured yarn.

Theoretically, phases (1) and (2) can be interchanged or be coincident, provided the
deformation persists until the filaments are cooled below Tg and the polymer becomes set.
However, time is a factor in determining the degree of set achieved, and, in high-speed
machinery, it is usual to apply heat as soon as possible in the process. If temperatures of
some polymers are raised too high, they tend to be yellow and this gives trouble with the
end products, particularly those of light colour shades. The deformation can be of any kind,
but in false or real twisting, the primary modes of deformation are torsion and bending.
Since the real twist process is simple, it will be used for explanation although it is no longer
commercially important

3.3 Real twist texturing

Explanations are a little easier if we consider the early types of discontinuous processes.
Various forms of twister were used to induce the initial deformation. A batch of packages
of yarn was then taken from the twister and placed in an autoclave.1 The temperature of
the yarn was raised above Tg (but below Tm), and then allowed to cool. The product taken
from the autoclave was non-twist lively or ‘dead’ (see Figure 3.1), but the fiber
deformations were set into their newly twisted shapes. To develop the bulk, it was

eBook PSP | Yarn Technology (Filament Yarn) 43

necessary to untwist the yarns until the filaments were approximately parallel and
separated, and then relax them. It will be noted that filament separation in phase (4) was
necessary for the bulk to form without undue interference between neighbouring
filaments.

Figure 3.1 Theoretical yarn structure

In untwisting yarn from the set condition, a torque is applied to each filament. The sum of
the individual torques is the total applied to the yarn. The torque places it in a state of
stress, which is retained until the fibers are relaxed. Untwisting and relaxing the yarn allows
the newly imposed stresses to be relieved by changes in the shape of the filaments as they
move within the structure during the process of relaxation. This form of texturing is shown
diagrammatically in Figure 3.2. When relaxed, each filament seeks a minimum energy
state, two of which are depicted in Figure 3.1. If the structure is open enough, most of the
filaments will achieve one of the minimum energy shapes, but a tight structure prevents
full relaxation. In the latter case, not all the potential bulk is developed. A normal yarn
structure will consist of shapes similar to those shown, or combinations of them if the yarn
is untwisted and the filaments are separated before release. Some methods of texturing
produce alternating directions of coiling. The result is that the yarn produced has little or
no twist liveliness because torques from the opposing filament coils cancel. This form of
texturing is shown diagrammatically in Figure 3.2.