chapter 2 literature review -...

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CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

Recent years have been marked by a rapid development of unconventional

technologies in textile production. This Chapter is concerned with the literature

review on conventional spinning, compact spinning, doubled yarn, hybrid yarn

and weft knitted fabrics. A considerable amount of work has been carried out on

yarn characteristics of conventional, compact and hybrid spinning, bio finishing of

fabrics, physical and dimensional properties of fabrics, spirality and wicking. This

literature survey is based upon the intensive search of the journals published in

textile technology. Articles from other sources are also included, and the subject is

reviewed under different captions.

The concern of the previous workers with the above aspects, namely,

compact spinning, spirality, wicking of knitted fabrics is reflected in the following

literature review.

2.2 DEVELOPMENTS IN SPINNING

The art of spinning originated in prehistoric times. The technique of cotton

spinning crystallized at the beginning of the industrial revolution says Rohlena

(1974). Revolutionary changes in spinning technology took place during the 1950s

and 1960s, following the post war boom, views Lord (2004). During the 1970s,

there appeared to be a myriad of spinning systems, such as twistless spinning, self-

twist spinning, fascinated yarns, composite yarns, wrap-spun yarns, pot spinning,

continuously felted yarns and the many possible variants in open-end spinning

such as rotor, electrostatic, friction spinning, and vortex spinning (the original

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“Polish” system). At the same time, there were continued developments in ring

spinning, with ventures into rotating ring and traveler systems, individual spindle

drives, high draft systems, modified travelers, double roving spinning, and hybrid

systems. A look at today’s industry reveals that while some systems have

established a successful but small niche- wrap spinning for fancy yarns and

friction spinning for specialty industrial markets -very few systems have survived.

2.3 RING SPINNING

Until the early 60s, the main type of spinning machines were ring spinning

frames, which were used in all types of spinning systems. In the 70s, open end

spinning was developed, mainly rotor spinning, with reference to cotton and

cotton like yarns. However, ring spinning frames are still competitive in relation to

rotor spinning machines, and in some systems they are impossible to replace says

Lewandowski et al (2010).Today, infact ring spinning is by far the most

widespread spinning process, setting clear standards in terms of yarn quality, field

of application and flexibility. Ring spinning has become a truly high-tech process

reveals Stalder (2003).

According to Yafa (2006), yarn that is produced by using a ‘ring’ is ring

spinning. The ring, which spins and winds yarn in one continuous motion onto

bobbins, produces yarn that has a characteristic natural unevenness. Wulfhurst et

al., (2006) reveals that the first ring spinning frame was built in 1828 in the U.S.

Ring spinning consists of three subsequent processing steps, slubbing, ring

spinning and winding.

Ring spinning is used for coarser number and has greater production and

requires less labour than mule spinning. The function of ring spinning is to draw

out the rove and spin it into yarn on a continuous system, opines Dooley

(2008).The method used to produce ring- spun yarns is “a series of operations in




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which a mass of entangled fibers are transformed into a rope-like structure in

which the fibers are more aligned than in the entangled mass. During the last 50

years, ring spinning has a high degree of efficiency. High draft systems have been

developed and it has become possible to attain given standards of yarn regularity

at very much higher levels of draft, says Lord (2004).

Grosberg and Iype (1999) mention that only ring spinning will be

considered as the most widely used method of spinning. Because of ring

spinning’s versatility in terms of fiber types that can be handled, the range of

counts that can be spun and the quality of the yarns produced, it is the standard

against which other systems of spinning are judged. A ring-spinning machine is an

uncomplicated, flexible, low cost device that is well established in the nineteenth

century.

2.3.1 Theory of Ring spinning

The principal of ring spinning is depicted in Figure 2.1. A bundle of

parallel fibers, the roving is fed to the drafting zone, the difference in surface

velocity of the front (faster) and back (slower) drafting roller will attenuate the

roving to a thinner strand of parallel fibers under the control of the double aprons.

The thin strand of parallel fibers emerging from the front roller is then

simultaneously twisted and wound onto a yarn package mounted on a driven

spindle. The twisted thin strand of fibers now called a yarn is threaded through a

traveller and a yarn guide and balloons out between these two elements during

normal spinning. Owing to the careful control during the spinning process, ring

spun yarns have a very high quality and these qualities of ring spun yarns have

been used as a benchmark against which the quality of yarns produced on other

spinning systems is judged. Ring spinning has been an integral part of various yarn

manufacturing systems. It is obvious that ring spinning system holds a dominant




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position in spinning in view of its low cost in comparison with other systems. A

flow chart of yarn production routes is shown in figure 2.2.

FIGURE 2.1 -PRINCIPLE OF RING SPINNING




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FIGURE 2.2 - Flow charts of the cotton system of modern yarn production

routes

Carded yarns

Combed yarns

2.3.2 Ring Spun yarns

Trajkovic et al., (2008) say, quality of the ring- spun yarns is greatly

influenced by the construction of the drafting system and the geometry of the

Blow Room Cards Draw frame 2 passages

Roving Frame Rotor

spinning Ring spinning

Carding

Draw frame

Lap former

Sliver lap

Ribbon lap

Combing Roving

Drawing

Blow room

Ring Spinning

Combing Combing




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spinning triangle formed in the area of spinning. The optimization of the structure

of the drafting system, the spindle, the ring and the traveller, as well as the

automatisation and synchronization of the operation of ring spinning frame

brought about a significant increase of production, better yarn quality and greater

flexibility.

Akaydin (2009) views, combed ring yarns have always been considered as

a quality reference among all the yarns produced by other new spinning systems in

textile industry. Combed cotton is a fiber that is smooth, lustrous and strong

because the fibers are long and straightened so that they lie parallel to each other.

2.3.3. Advantages of Ring spun yarns

Ring- spun yarns have a regular twist structure and because of the good

fiber control during roller drafting, the fibers in the yarn are well straightened and

aligned. Ring spun yarns have excellent tensile properties, which are often

important for technical applications, say Horrocks and Anand (2000). The ring

spinning will continue to be the most widely used form of spinning machine in the

near future, because it exhibits significant advantages in comparison with the new

spinning processes.

It is universally applicable, i.e., any material can be spun to any required

count.

It delivers a material with optimum characteristics, especially with

regard to structure and strength.

It is simple and easy to operate i.e., the know- how is well established

and accessible for everyone. www.textiletechnology.co.cc.


http://www.textiletechnology.co.cc.



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2.3.4 Limitations of Ring spinning

The limitations of the ring spinning technology are well known. One of the

major limitations is the metal – to- metal rubbing contact between the ring and the

traveler, which restricts the spindle speed, opines Dash et al. (2002)

They are expensive and more hairy. The ring spun yarns contain many

uncontrolled fiber ends which are not bound to the yarn body thus the yarn is very

hairy. The yarn hairiness not only affects the quality of yarn and fabric but also

causes many processing problems. Also from an ecological stand point this

amounts to deficient utilization of the raw material (Lucca 1999)

Another limitation of the ring spinning technology is the spinning triangle.

It is not only the yarn formation zone but also the origin of hairiness in ring spun

yarns .In conventional ring spinning, as the strand of fibers emerges from the front

roller nip, each rotation of the traveller inserts one turn of twist to the strand of

fibers by twisting propagation. However, the ribbons form of fibers at the front

roller nip line limits this twist propagation. Hence, the front roller nip is not the

actual yarn formation point. The formation of different types of hairs in the

spinning triangle has been studied in detail by many research workers

(Barella1957, Hearle et al. 1969, Pierce 1947, Wang et al. 1999).

2.3.5. Spinning Triangle

The zone between the line of contact of the pair of delivery rollers and the

twisted end of the yarn is called the spinning triangle says Celik et al. (2004) In

conventional spinning, it is formed immediately after the drafting mechanism in

the ring frame (Figures 2.3 and 2.4). The spinning triangle is a weak zone due to

less twist in that region. Under normal working conditions, most of the breaks

occur in the near-vicinity of the spinning triangle. The strength of the fibrous mass




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in the spinning triangle determines the attainable spindle speed. Hence if the

spinning triangle is avoided, or its length reduced, the achievable spindle speed

could be increased, reveals, Sitra (2001)

FIGURE 2.3 - Formation of the Spinning Triangle

Short (a) and long (b) spinning triangle, (c) side view

FIGURE 2.4 – Spinning triangle - influence of the twist

2.4 INTRODUCTION TO COMPACT SPINNING

Ismail and Nagarajan (2011) report that compact is a proven technology,

introduced twenty years ago and it was commercialized twelve years later. But

only in past five years awareness has increased among cloth manufacturers and




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cloth consumers. The spinning process with the minimized spinning triangle is

called compact (condensed, compressed) spinning which is depicted in Figure2.5.

Compact spinning system works between drawing and yarn formation steps

and serves as an interlocutory region. In this interlocutory region, fiber form which

is ready to be drawn is densened by air pressure, mechanical means or magnetic

effect, opines Akaydin (2009).

Factors, which were introduced, led to the rise of new techniques in

spinning, in particular, the ring compact technique. One of the factors essentially

connected with the quality of the yarn, as well as the efficiency of the spinning

process, is the spinnability of fibers, and many working parameters of the spinning

machines are applied in the individual technological operations. However, there is

also a group of technological parameters which are characteristic to the individual

technological operations of the spinning process, Lewandowski et al (2010).

During the last two decades, components of ring spinning machines have

been greatly improved, with changes in drafting system, drive systems and

robotics enabling large gains in productivity, flexibility and quality. Most of the

technical advances in ring spinning were aimed at improving the performances of

the existing technology. In recent years, however a bonafide innovation has

occurred to minimize the width and height of the spinning triangle associated with

ring spinning, says Ahmad (2009). The purpose is to condense a fiber strand after

the drafting system immediately before twist is imparted so that the spinning

triangle is practically eliminated, reveals Niijjaawan (2009).

Compact spinning developed initially for spinning cotton yarn which

belongs to short staple sub groups, remarks Ozdil et al. (2005). These days the

improvements made it possible to use for small, medium and long- staple fiber

spinning express Loganathan et al., (2009).




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Compact spinning process is certainly a good substitute for traditional yarn

spinning, since it reduces the hairiness of single yarns. This can minimize the

twisting angle and improve yarn quality, opine Tyagi and Kumar (2009). The

hairiness of the yarn is also reduced and the tenacity is higher when compared to

ring- spun yarns. The yarn evenness is also improved, says Wulfhurstet el., (2006).

2.4.1 History of Compact Spinning

Compact yarn involves textile technology in which Europe has taken the

lead from discovering the principle to developing equipment and

commercialization. At the European textile machinery exhibition, ITMA 95, a

German company CSM announced its "principles of compacting in spinning"

which consisted of the results of research by the Austrian DrFehrer. The First

compact spinning machine was put into trial production in 1995 in some spinning

mills in Switzerland views Cheng et al. (2003).Four years later three companies,

Rieter, of Switzerland, Sussen and Zinser, of Germany announced pneumatic

condensing systems at the International Textile Machine Fair ITMA 99. This

equipment display attracted attention from visitors. They began commercial

production of compact spinning equipment by getting users from various

countries.Rieter has users mainly in Europe, while Sussen mainly in India and

Pakistan. In 2001, Toyota Industries Corporation displayed a similar model as a

prototype at the 7th Otemas, a Japanese textile machinery exhibition held in Osaka

in 2001. Subsequently, the Italian company Kognetex announced compact

spinning equipment for worsted yarn.

(http://findarticles.com/p/articles/mi_qa5508/is_200202/ai_n21308892/)

Though these systems are somewhat different in each case, the principle of

compact spinning systems is to increase the yarn quality by means of narrowing

and decreasing the width of the band of fibers which come out from the drawing


http://findarticles.com/p/articles/mi_qa5508/is_200202/ai_n21308892/)



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apparatus before it is twisted into yarn, and by the elimination of the twisting

triangle report Jackowski et al. (2004).

2.4.2 Concept of Compact spinning

Compact spinning is designed to reduce hairiness in yarn. In traditional

spinning fibers, the selvedge of strand emerging from front roller nip does not get

fully integrated into yarn because of restriction to twist flow by the spinning

triangle. These fibers, therefore, show up partly as protruding hairs or wild fibers.

To overcome this effect, the spinning triangle is nearly eliminated in compact

spinning by incorporating a condensing zone after main drafting zone. The

condensing zone has a revolving perforated apron with suction underneath. The

fibers are collected on the perforated track and thus get condensed. The width of

the strand under front roller nip is substantially reduced and this enables twist to

flow right up to nip. Eliminating the spinning triangle at the delivery section of the

front roller produces quality yarn with low hairiness and high evenness.

(Figure 2.5)

FIGURE 2.5- Concept of Compact spinning




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2.4.3 Types of Compact spinning system

Since the introduction of the compact spinning process, the market leaders

and pioneers were Rieter and Suessen. Today, there are a number of designs

offered by different machine manufacturers, but they all use the same principle,

namely condensing the fibrous strand at the end of the draft region pneumatically.

According to Zou et al. (2010) the available compact spinning systems today are

1.Perforated drum pattern (Rieter’sComforSpin K44 (Com4), K45)

2. Lattice apron pattern (Suessen’s Elite, Ningbo Dechang’sJee and ShlanLee)

3.Perforated apron pattern (Zinser’s Air-Com-Tex 700)

4. Pneumatic groove pattern (DongHua University’s compact spinning) and

5. Ceramic thickening funnel pattern (Rotorcraft’s RoCoS).

2.4.4 Advantages of Compact yarns

Compact Spinning is basically designed to control those protruding fibers

(uncontrolled fibers) which have become the part of the yarn but have no role in

the yarn formation and ultimately no contribution to yarn strength, but rather than

adverse effect on subsequent processes. After passing through the normal drafting

system, the fibers are entered in to the condensing zone, which is equipped by the

suction system. In this zone, maximum free and protruding fibers becomes parallel

and condensed. Immediately after this condensing zone, this fibrous bundle is

twisted in normal & conventional style. The yarn achieved in this way has better

& uniform yarn formation, and better strength and elongation.

Advantages of compact yarn as compared with conventional ring yarn

Increased yarn strength & elongation.




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Due to better-control & uniform fibers in yarn, the strength & elongation of

yarn is increased by 20% then that of conventional ring spinning even on

low twist

Reduction in yarn hairiness:

As the yarn enters in to front roller nip after the condensing zone for twist

insertion, due to the better spinning triangle, the ends down rate is reduced

significantly which ultimately reduces fluff in spinning department & vice

versa, as depicted in figures (2.6 &2.7)

FIGURE 2.6-Comparison of compact and conventional yarn

FIGURE 2.7- External comparison of yarn package

As maximum number of fibers become parallel & uniform after passing

through condensing zone the hairiness value is reduced about 20 ~ 25 %

than that of normal spinning.




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Increase in productivity

Less twist and high spindle speed.

Less ends down rote due to better spinning triangle.

Advantages in subsequent processes

Reduction in sizing cost

Improved dyeing

Increased efficiency of loom & knitting machines

Ultimate solution for spirality

Improved Wear ability

Reduction in Singeing Cost

Exquisite fabric Feel

(http://www.fazaltextile.com)

General advantages of compact yarn in knitting-Physical properties

Clearer loop structure with less loop cross-infringing fibers

Higher brilliancy and softer handle

Fewer end-breaks

Low emission of fly and dust

Usage of un-waxed yarn is feasible

Reduction in abrasion by 30%

Reduces the wear and tear of needles and other related components,

thus avoiding holes or stripes in the fabric

Fabric appearance is enhanced due to the uniformity and low yarn

hairiness

Structural advantages of compact yarn in knitting contributing to its

cost effectiveness

Significantly lower fabric shrinkage by around 35-40% after fabric

processing, resulting in net saving of 2% in fabric weight loss


http://www.fazaltextile.com)



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Dimensional stability is retained after many washes owing to the

better pilling resistance

Fabric gloss after yarn mercerization is retained even after several

washes

(http://www.suessen.com)

2.4.5 Summary of Previous research work On Compact Spinning

Compact spinning has been investigated by many researchers. Most of

them have focused on two types of research; One on the types of system and its

advantages and the other research on yarn structure of compact yarn. The subject

matter has been discussed in many seminars and conferences. Recently some

papers have been published which compare the properties of compact yarns

produced from various systems.

However, it is noticed that many interesting papers have been published on

compact yarns which have improved our understanding about their structure and

properties. Thus research carried out on compact spinning at Turkey has

demonstrated many facets of compact yarns.

A great deal of work has also been carried out by research workers in India,

USA, Honkong, Poland, Germany, Switzerland, Czechoslovakia, Slovenia

&Pakistan on compact spinning. Table 2.1 shows the research work which has

been carried out on compact spinning.


http://www.suessen.com)



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TABLE 2.1

RESEARCH WORK DONE ON COMPACT SPINNING

Sl.No

Research Worker(S) Year

Experimental

Materials Yarn Produced

System used

Highlights of research

1 Stalder 2000 Cotton 40Ne,50Ne, 60Ne &80Ne Ring and compact yarns

Rieter’sCom4 used Strength is more for compact,CV% of strength is less yarn hariness is low for compact yarns

2 Kadoglu 2001 Cotton 40Nmcarded& 60Nmcombed56Nmcombed cotton

Ring and compact Zinser-Air-Com-Tex-700.Yarns were made with four levels of twist factor for carded and five levels for combed

Compact yarns are characterized by higher tenacity, lower hairiness

3 Dash, Ishtiaque and Alagirusamy

2002 Cotton 24 Ne Combed Winding speeds were varied and yarn characteristics studied

Compact yarns exhibits higher packing ,even after winding yarn hariness is less for compact yarns but increases with winding fabrics made with compact yarn show higher K/S values

4 Krifa,Hequet and Ethridge

2002 Cotton 100%cotton(short staple) 26Ne

Suessen(Elite) Compact spinning resulted in a highly significant improve-ment in both strength and elongation.Yarn hariness is less for compact yarns




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Sl.No


Experimental


System used


5 Artzt 2002 Pima cotton

Nm 70 Carded Combed carding parameters varied. combed waste were 10%,15% and 20%

Unspecified compact spinning

Compact spinning uses twist most effectively than conventional ring spinning.carded material reach maximum strength earlier than the same material with 13% comber waste

6 Nikolic, Stjepanovic, Lesjak& Stritof

2003 Cotton, Polyester, Viscose

100% Combed, 50P/C, 87/13C/V

Conventional,Compact-Suessen and Zinser

For Cotton and cotton Viscose blended yarns compact spinning is eminently suitable for polyester cotton blend.

7 Basal 2003 Cotton P/C 28Ne Suessen 100% ring compact yarn is superior at low twist factor,rate of migration is higher for compact yarns

8 Cheng and Yu 2003 Long Staple Supina cotton

38,50,60 and 80Ne combed

Rieter Com4,Both conventional and compact yarns were Produced

Performance is found to be poor with respect to coarser counts. For finer counts such as 60s and 80s ,compact spinning gives better results




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Sl.No


Experimental


System used


9 Behera,Hari and Ghosh

2003 Cotton Tensile properties were determined for single, two ply and sized yarns. Weavability was determined. 34 Nm ring and compact yarns with three levels of twist were used. yarns were sized with starch at 2%,6%,10% and 14% concentrations

Not specified Packing, fraction of compact yarn is higher than that of ring spun yarn. The weavability of compact yarn is much better than the ring yarn irrespective of twist.The compact requires less size and weavability increases with increase in size-add-on. For compact yarns at lower size add-on improvement in weavability is noticed. Weavability of single compact yarn is comparable to the 2-ply ring yarn irrespective of size add on

10 Mahmood,Jamil, Iftikhar&Saleem

2004 Cotton 20Ne Rieter,Three levels of air guide element ,three levels of TM,three levels of Top roller

Modified top roll pressure,perforated air drum and maximum twist gave best yarn results

11 Celik&Kadoglu 2004 Wool, Polyester, PAN

100%wool,45%wool and 55%pet varying weaving twist factor50%PAN,%PANvarying Knitting twist factor 19 and 25 tex

4 levels of twist Suessen Elite system used

For yarns of 100% wool, compact yarns show lower values of yarn hairiness. Same results for 50% wool and 50% PAN. Yarn hairiness is less for all compact yarns




25

Sl.No


Experimental


System used


12 Ozdil,Ozdogan, Demirel&Oktem

2005 Cotton Properties of interlock fabrics Knitted from 50Ne ring and compact yarns were studied. Dye uptake was studied. Fabrics were bio polished and dyed

Rieter com 4 system were used Bursting strength, Pilling enzymatic finishes and dyeing behavior were studied

Compact yarn knitted fabric is more brilliant and glossier. Fabrics knitted from compact yarns displayed better Bursting strength and pilling abrasion resistance was not different between the samples

13 Goktepe, Yilmaz and OzerGoktepe

2006 100%Cotton combed yarns

20Ne 30Ne Ne 41

System A-Perforated apron System B-Perforated Drum System C-Perforated apron situated at bottom part of the drafting system

System B(K44) gave better performance for finer yarns whilst System A(Air com tex 700) was found to be better for medium to coarse counts

14 Basal &Oxenham

2006 50/50 P/C & 100% Cotton

28Ne Suessen elite. Yarns were produced with five levels of twist were compared

The high tenacity values of compact yarns can be attributed to the higher rate and amplitude offiber migration in compact yarns compared to those in ring yarns. Another important finding was the superiority of compact yarns in terms of tensile properties is less noticeable at highertwist levels and in 50/50 polyester/cotton blend.




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Sl.No


Experimental


System used


15 Kane,Patil&Sudhakar

2007 Cotton 30Ne ring and compact yarn were used to produce knitted fabrics

Effect of Single jersey, single Pique, double pique and honey comb structures varying 3 SCSL(Structural cell Stitch length)on ring and compact yarn properties were studied

Compact yarn fabrics showed better performance in all the structures and their respectiveSCSL. Double pique fabric showed better performance for the summer outer wear and single jersey fabric showed better performance for summer inner wear

16 KretzschmarOzguney,Ozcelik&Ozerdem

2007 Cotton 30Ne and 40Ne varying 2 different twist factors

Knitted fabrics (Single jersey, Rib and Interlock) made from compact (Rieter K44) and conventional ring-spun yarns (Rieter G33). Physical properties were investigated before and after the dyeing process

The hairiness of compact yarns was less and the strength and elongation percentages were higher,the fabrics produced with compact yarns showedless tendency to pilling and had a higher bursting strength.

18 Ozguney , KretzschmarOzcelik&Ozerdem

2008 cotton 30Ne and 40Ne varying 2 different twist factors

Knitted fabrics (Single jersey Rib and Interlock) made from compact (Rieter K44) and conventional ring-spun yarns (Rieter G33). Physical properties were investigated before and after the printing process

In general, it was observed that compact yarns weremore advantageous with regard to ring yarns for both theyarn counts and twist coefficients, therefore, it can be concludedthat the compact spinning technique brings advantagesregarding quality and production




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Sl.No


Experimental


System used


19 Akaydin 2009 Cotton 30Ne and 40 Ne Single jersey, Rib and Interlock fabrics were produced

Rieter K44 Rieter G 33

It is observed that the differences between the structures of ring and compact yarn play a significant role on the fabric properties. The fabric produced from compact yarns are found to have better abrasion resistance,higher burst strength, less pilling tendency, better dye absorption and dyeability in more vivid colors

20 Yilmaz&Usal 2010 Cotton 30Ne were produced on three different yarn spinning system with the same material

Rocos compact Conventional ring Compact jet

It was determined that the compact-jet yarn properties air jet nozzles are different from that of the conventional ring and compact yarns. The compact-jet spinning system is mainly effective on yarn hairiness and compact-jet yarn is superior compared with Other yarns.




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Sl.No


Experimental


System used


21 Lewandowski,Drobina,Jozkowicz

2010 Combed cotton

20 tex Classic ring frame-G33 Compact Ring frame-K44

The physical properties of both yarns were analyzed by means of statistical models based on multiple regression and it was confirmed that the percentage of noils and the metric co-efficient of the twist were important factor in quality of yarn and efficiency of production

.




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2.5 INTRODUCTION TO WEIBULL DISTRIBUTION

Waloddi Weibull invented the Weibull distribution in 1937 and delivered

his hallmark American paper on this subject in 1951. He claimed that his

distribution applied to a wide range of problems. He illustrated this point with

seven examples ranging from the strength of steel to the height of adult males in

the British Isles. He claimed that the function "…may sometimes render good

service." He did not claim that it always worked. Time has shown that Waloddi

Weibull was correct in both of these statements.

Weibull distribution is one of the most widely used lifetime distributions in

reliability and survival analysis. This parametric model is commonly used to

estimate important life characteristics of a product such as reliability or probability

of failure at a specific time, the average life of the product, and to determine

warranty time. It is a versatile simple distribution that specializes to other types of

distributions, based on the value of the shape parameter. These features of the

Weibull distribution have made it a useful distributional model in reliability and

survival analysis. The weibull modulus is not a material constant, but gives a good

indication of how homogenous it is

2.5.1. Advantages of Weibull Analysis

The primary advantage of Weibull analysis is the ability to provide

reasonably accurate failure analysis and failure forecasts with extremely small

samples. Solutions are possible at the earliest indications of a problem without

having to "crash a few more." Small samples also allow cost effective component

testing. For example, "sudden death" Weibull tests are completed when the first

failure occurs in each group of components, (say, groups of four bearings). If all

the bearings are tested to failure, the cost and time required is much greater.




30

Another advantage of Weibull analysis is that it provides a simple and

useful graphical plot. The data plot is extremely important to the engineer and to

the manager. The Weibull data plot is particularly informative as Weibull pointed

out in his 1951 paper. Figure 2.8 is a typical Weibull plot. The horizontal scale is a

measure of life or aging. Start/stop cycles, mileage, operating time, landings or

mission cycles are examples of aging parameters. The vertical scale is the

cumulative percentage failed. The two defining parameters of the Weibull line are

the slope, beta, and the characteristic life, et. The slope of the line, β, is

particularly significant and may provide a clue to the physics of the failure. The

characteristic life, η , is the typical time to failure in Weibull analysis. It is related

to the mean time to failure.

FIGURE 2.8- Weibull plot

2.5.2.Scope of Weibull Analysis

Weibull analysis includes:

Plotting the data and interpreting the plot

Failure forecasting and prediction




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Evaluating corrective action plans

Engineering change substantiation

Maintenance planning and cost effective replacement strategies

Spare parts forecasting

Warranty analysis and support cost predictions

Calibration of complex design systems, i.e., CAD\CAM, finite element

analysis, etc.

Recommendations to management in response to service problems

(http://quanterion.com/Publications/WeibullHandbook/ChapterOne.pdf)

2.5.3 Weibull theory

Using the classical weakest-link scaling of Peirce, Realff et al (1991) have

predicted the probability distribution (x)Fl for the strength of a yam at any gauge

length l from knowledge of the strength distribution (x)F0l , at a given length 0l by

,(x)]F[11(x)F mll 0

(1)

where m = 0ll

. Moreover if )x(0lF follows a two-parameter Weibull

distribution ,

0l x

xexp1(x)F0

, (2)

where x0 and r are positive constants called the scale parameter and the

shape parameter (or modulus), respectively, then


http://quanterion.com/Publications/WeibullHandbook/ChapterOne.pdf)



32

ll x

xexp1(x)F , (3)

where x1 = x0m-1/r. For data following a Weibull distribution with scale parameter

x0 and shape parameter r, the mean and variance are given by

1/r)Γ(1xμ 0

220

2 1/r)Γ(12/r)Γ(1xσ , (4)

where )( is the classical “gamma function.” Notice that the coefficient of

variation / is a function of r alone. Realff et al. have used the Weibull

distribution and the weakest-link scaling theorem to examine data obtained on

yarn strength distributions, thereby including effects of changes in both the mean

and the variation in strength with gauge length.

2.5.4. Review of Related Research

Hussainet at (1990) studied the effect of tensile specimen gauge length on

cotton yam strength. They found that yarn tenacity was a modified power-law

function of gauge length manifesting lower mean strength values at longer gauge

lengths. They also found that significant differences in this gauge length effect

occurred between pairs of ring versus rotor spun yarns of comparable structures

(29.5 tex and 4.0 twist multiple) and of three different cotton varieties. The gauge

length effect, which they expressed as a ratio between the tenacity of a given

gauge and that of a 1 cm length, showed no significant difference between ring

versus rotor spun yams at relatively short lengths. But the differences were

statistically significant at long (70 cm) lengths. Hussain et al. measured the effect




33

of gauge length on strength variability, but they did not explore its implications

further, nor did they compare their yam results with corresponding fabric

response.

An earlier experimental investigation by Lord and Radhakrishnaiah (1988)

examined the tensile strength of fabrics constructed of rotor, friction, and ring

spun weft yarns, each combined with several different warp yarns in both plain

and 3/ 1 twill constructions. Testing the yarn at 500 mm gauge lengths, they

reported yarn tenacities of 8.4, 10.1, and 14.7 cN/tex for the friction, rotor, and

ring spun yarns, respectively. For yarns tested in fabrics, the strength ratios for the

different spinning systems were, in most cases, markedly different from those

between the yams when tested alone. For fabrics tested in the weft direction, the

strength ratios of friction spun weft fabrics to ring spun weft fabrics were reported

as 0.68 and 0.74 for two plain weave constructions versus a strength ratio of 0.58

for the corresponding yarn tests. Further, when warp wise strength tests were

conducted on cloths with identical warp yams, but with different spinning system

weft yarns, the data showed higher warp strengths in the presence of friction spun

weft than for cases of ring spun weft (1.04 and 1.12 for the warp strength ratios of

friction to ring spun weft fabrics).

Lord and Radhakrishnaiah (1988) submit that the difference between the

yarn strength ratios and the fabric strength ratios arises from fabric assistance that

is, the effects of friction at crossovers, crimp, and the like. They further argue that

due to the hooking and fold back geometries of the friction spun yarns, the fibers

behave as if they were and “shorter than they really are” The pressure points due

to the interlacing of weft with warp serve to retard fiber slippage, allowing each

fiber to carry higher tensile loads. In support of this concept, they report the yam

strength ratio for friction to ring spun yams to be 0.68 for a gauge length of 6 mm

versus 0.57 at 500 mm.




34

Shahpurwala and Schwartz (1989) attempted to predict the tensile strength

of woven fabrics once they had determined the strength distributions of the

constituent yarns. They began with a simple analysis based on Daniels (1945) in

which the fabric was modeled as a loose bundle of yarns with no yarn interaction.

Under these assumptions, the fabric strength distribution should be asymptotically

Gaussian. They then applied the Daniels model to three different 100% cotton

fabrics, plain, 3/1 twill, and 4/1 satin, in an attempt to predict fabric strength from

a knowledge of yam strength obtained from tests taken at a gauge length of 152.4

(1 1 + c) mm, where c was the value of yam crimp in the test direction. They

found that the simple bundle model, using this gauge length as the “Daniels

bundle” length, under predicts fabric strength by as much, in one case, as a factor

of 0.67.They then determined the sub-bundle tensile gauge length (in a chain-of-

bundles model) needed to predict fabric strength from yarn strength distributions.

They accomplished this by back calculation, using weakest link scaling, on the

basis of known fabric and yam strength distributions. The sub-bundle lengths

ranged from a high of 18.7 mm to a low of 6 mm (all well below the average

cotton staple length). This provided additional evidence that the tensile behavior of

a yam in a fabric differs from that observed in out-of-fabric yam tensile tests

performed at gauge lengths well above the staple length.

The Daniels bundle model has serious deficiencies when applied to fabrics,

in that it does not account for (a) the role of the cross yams in the

“compartmentalization” of a yam break and in the subsequent redistribution of the

load from the failed yam to its surviving neighbors, (b) the effect of yam surface

topography, yam mechanical properties, and woven fabric structure on load

sharing mechanisms, and (c) changes in yam failure mechanisms at short lengths,

especially as the length passes below the average fiber staple length in the

presence of inter yam pressures that may allow the yam to carry greater loads.




35

Pan (1996) demonstrated in his study that the Weibull function is a good

approximation to yarn tensile strength when used to predict fabric strength; and

the yarn failure mechanism in a fabric during fabric extension is likely to be

different from the yarn failure behavior observed on a strength tester using a

correspondingly adjusted gauge length

The influence of different configurations in the sample preparation process

on commercial polyacrylonitrile-based carbon fibers mechanical tests were studied

by Pereira et al. (2010). Mechanical properties, such as tensile strength, Young’s

modulus, elongation and Weibull modulus, were evaluated. The results showed

that all sample preparation steps may have strong influence on the results.

A theoretical model has been developed by Das and Neckar (2005) for

predicting yarn strength at different gauge lengths as a summation of two mutually

independent stationary, ergodic, Markovian and Gaussian stochastic processes and

then experimentally verified with different cotton yarns produced from different

spinning technologies. A new methodology to measure yarn strength at a gauge

length longer than that of the longest fibre in yarn has been devised and special

data evaluation techniques developed. With this, it is possible to obtain a new

characterization of yarn strength as well as to predict actual yarn strength behavior

at different gauge lengths. It is experimentally observed that the strengths of

neighbouring short sections along a yarn are correlated and this correlation is

different in different yarns. Depending on the degree of this correlation, the

empirical equations relating yarn strength and gauge length are found to be

different in different yarns.

Realff et al. (1991) conducted a detailed study to establish the effect of test

gauge length on yarn properties. Yarns produced on each of the three major

spinning systems were tensile tested at varying gauge lengths. Yarn strength data

were fit to two-parameter Weibull distributions and corresponding shape and scale




36

parameters were determined. Realff et al. in their study observed that strength

increased as gauge lengths decreased, a trend indicated by the weakest-link theory.

At very short gauge lengths, however, the data deviated from prediction based on

the weakest-link theory, thus suggesting a change in the yam failure mechanism,

as one would expect when the gauge length approximates the staple length.

Ghosh (2005) the phenomenon of spun yarn failure is strongly dependent

on the yarn structure namely, the configuration, alignment and packing of the

constituent fibers in the yarn cross-section. The structure of yarn is solely

determined by the methods of consolidating the fibers into yarns. In the present

study, ring, rotor, air-jet and open-end friction spun yarns were produced from

identical fibers and their structural parameters; namely, mean fiber extent,

spinning-in-coefficient, helix angle of the fibers, percentage of different hooks and

their extents, number of fibers in yarn cross-section and yarn diameter were

measured. These yarns were subjected to uniaxial loading on the tensile testers

with a large range of gauge lengths (0 to 500 mm) and strain rates (5 to 400

m/min). The results showed that the strength of yarns largely depends on the

structure of the yarns, gauge lengths and strain rates. A combined effect of fiber

extent in the yarn and gauge length influences the yarn strength. At high strain

rates the yarn failure is dominated by the breakage of fibers rather than the

slippage of fibers. Furthermore, the analysis of the region of yarn failure provides

more direct evidences of the influence of yarn structure and testing parameters on

the strength of different spun yarns. The determination of the tensile strength of high strength carbon fibers and

their gauge length dependence were analyzed by means of the Weibull model. The

influences of the estimator chosen and of the sample size on the calculated value

of the tensile strength of the fiber were first determined. Secondly, the accuracy of

the three- and the two-parameter Weibull distributions is examined. Finally, it is

shown that the most appropriate extrapolation at short length is performed by




37

means of a linear logarithmic dependence on gauge length of the tensile strength.

This method seems to be valid for untreated as well as for surface-treated high

strength carbon fibers, Asloun et al. (1989)

Rengasamy et al. (2005) have predicted the spun yarn strength at different

gauge lengths using Weibull distribution. The shape and scale parameters of

Weibull distribution have been determined. It has been observed that the data of

yarn tenacity fit well to two-parameter Weibull distribution. The Weibull shape

parameter diminishes as the gauge length decreases. None of the yarns strictly

follow the classical weakest link theory and there is a considerable change in

failure mechanism for all the yarns as the gauge length is varied.

Raghunathan et al. (2002) have studied the characteristics of ring and rotor

yarns using modified Weibull distribution. The influence of gauge length on the

tensile strength of ring and rotor yarns has been investigated. A modified Weibull

distribution was verified through Kolmogorov-Smirnov goodness test. The

tenacity of all the ring and rotor yarns studied is found to decrease with the

increase in gauge length and fits well with Weibull distribution. The strength

variation is found to be high at lower gauge lengths.

2.6 OBJECTIVES OF DOUBLED YARN

The folded yarn is produced by folding two or more single yarns together.

In spinning, the purpose of folding is to join together two or several yarns to give

them a twist that improves the strength, the regularity and the yarn aspect Gupta et

al. (1984) opined that plied yarns are widely used in many areas of textile industry

due to their unique physical characteristics over single yarns. Double yarns are

more uniform and have high strength, less hairiness, very smooth surface than the

single yarns. They are used in sewing threads and are excellent choice for mittens,

socks and dress items. Doubling is the process of equalizing and compensating




38

single –strand unevenness, thin and thick places. It is also reported that there is

reduction in yarn hairiness after doubling due to entrapping of the protruding

fibers between constituent yarns

2.6.1. Benefits of Doubled yarn

Folded yarns and plied yarns are used especially where single yarns are

incapable of withstanding the demands made by them in manufacture or end use.

Hence the folded yarn has continued to maintain its status in the production cycle

despite occupying a disproportionate share of production cost says Magel et al.,

(1999). Zaghouani, et al., (2009) states that the ring yarns are known for the

remarkable resistance and for their homogenous structure. The open end yarns

which are less resistant present a good regularity and a less production cost. To

balance the two structures it is interesting to realize a hybrid folded yarn consisted

of one ring yarn and another open-end. This allows, in theory to obtain more

tenacity than open-end folded yarns and have a better regularity than ring folded

yarns

2.6.2. Related studies concerning Doubled yarn

A number of research workers in the past have contributed to the study of

doubled yarn. Coulson and Dakin (1957) did pioneering work on the properties of

doubled yarn. They studied the doubled yarn properties as a function of doubling

twist, ratio of doubled yarn twist to single yarn twist, doubling, tension. Based on

the comprehensive study several findings which were obtained were found to be

very useful to the industry. When they studied these properties conventional ring

spun yarns only were available. In 1985, Hari et al. studied the effect of doubling

on the tenacity of rotor spun yarns. They concluded that twist-over-twist doubling

of low-twist singles rotor-spun yarn gave a significant improvement in the tenacity

of doubled rotor-spun yarn and the differences in the strengths of ring and rotor-




39

spun doubled yarn was considerably reduced. Almost at the same time Gupta et al.

(1984) reported on the effect of doubling of yarn on classimat yarn faults. They

found that the number of faults showed a considerable reduction following

doubling of cotton and polyester/cotton yarns. This finding is collaborated by

Magel et al. (1999) in their study on controlling the properties of folded yarns.

They concluded that yarns spun on long-staple and short staple systems exhibited

similar behavior when converted to two fold yarns with folding twist in the same

direction and counted to the singles twist at different twist levels. It is pointed out

that folded yarns produced with cotton and wool yarns became appreciably more

even as a result of the folding process and had lower hairiness, highest strength

and extension and higher abrasion resistance.

Lin et al. (1998) have made a comparative study of the properties of

doubled yarn produced by the ring twister, the two-for-one twister and the novel

twister designed by them. Their results showed that the rotor twister had a twisting

tension lower or equal to that of ring twister and that the physical properties of the

plied yarns produced on it were better than those of the ring twister and those of

the two-for-one twister under constant twisting conditions.

Onder, et al. (2003) has studied the mechanical properties and air

permeability of light weight wool blend apparel fabrics. The mechanical responses

in uniaxial, tensile and tear tests of gray-state fabrics and low deformation

characteristics were reported by them. The use of sirospun yarn had led to a slight

drop in shear rigidity and higher air permeability of fabrics. Thus the effect of siro

doubled yarn structure on the properties of fabrics has been examined.

Ishtiaque, et al. (2009) has studied the structural and tensile properties, of

ring and compact plied yarns. The structural parameter, namely fiber extent,

spinning- in- coefficient, fiber pair overlap length and packing density show an

increase while migration parameters show a decrease for both ring and compact




40

yarns. The difference in tenacity between ring and compact yarns when doubled

shows a decrease compared to before doubling and elongation of yarn shows a

drop following doubling of yarn. Thus while Gupta et al and Magel et al (1999)

have studied the imperfections in yarns following doubling. Ishtiaque et al. (2009) studied the structural changes. They also report on

the reduction in hairiness of two fold yarns in ring and compact, single and plied

yarns. That reduction in hairiness is quite significant in ring yarns has been

pointed out by them. Recently there has been increased interest in studying the

properties of doubled yarn. Zaghouani, et al. (2009) studied the effect of various spinning and folding

parameters on the yarn quality for ring, Open-end and hybrid folded yarn. The

folding twist factor has been found to be the most influential factor which affects

the strength of doubled yarn. A comparative study of the quality of the hybrid

folded yarns showed that the hybrid folded yarns have a better quality than the

open-end folded ones and very close to ring folded yarns. The experiments were

performed with three levels of linear density, three levels of folding twist factor

and three levels of folding tension. Treloar (1956) dealt with the geometry of

multi-ply yarns which was based on the assumption that the individual filament in

the ply had the form of a double wound helix (ie) of a helix wound about a helical

axis. 2.7 NATURE OF SPIRALITY

Fabric spirality is a major problem, especially in plainknitted fabrics, and

comes mainly from two sources: from the yarn and from the machine. The

spirality problem is that when knitting a rectangular piece of fabric, it leans

towards one side and becomes a parallelogram. The wales are no longer at right

angles with the courses. The spirality is measured with an angle θsp which is the

angle between the direction at right angles with the courses and the distorted wale




41

direction as seen in Figure 2.9. If the spirality angle θsp exceeds 5° it is considered

an important problem described Kurbak et al. (2008). This is a very common in

single jersey knits and it may exist in grey, washed or finished state and has an

obvious influence on both the aesthetic and functional performance of knitwear.

However, it does not appear in interlock and rib knits because the wale on the face

is counter balanced by a wale on the back (www.textiletoday.com).

FIGURE 2.9 –Schematic representation of Spirality problem

(a) Normal fabric b)Spiral Fabric

One of the problems inherent in plain knitted fabrics is course spirality.

Some of the practical problems arising from loop spirality are encountered in

garments produced from knitted materials, such as the displacement or shifting of

seams, mismatched patterns, and sewing difficulties etc. These problems are often

corrected by finishing steps such as setting with resins, heat, and steam, so that the

wale lines are perpendicular to the course lines. However, such setting is often not

stable and after repeated washings, skewing of the wales normally re-occurs.

Spirality has an obvious influence on both the aesthetic and functional

performance of knitwear says chen et al. (2003). Slack fabric presents higher

spirality angle compared to tightly knitted fabrics. At each level of yarn twist


http://www.textiletoday.com).



42

factor, the degree of spirality decreases linearly with fabric tightness factor, report

Das(2008).

2.7.1.Direction of spirality

The direction of spirality is determined by the direction of the twist.Z and S

directions of the twist in the yarn generate spirality in the Z and S direction

respectively.Z-twist yarns make the wales go to the right, givinga Z-skew, and

S-twist yarns make the wales go to the left, giving an S-skew to the fabric.

Furthermore, with multifeed machines, the fabric is created in a helix,which gives

rise to course inclination and consequently wale spirality. The wales will be

inclined to the right,giving a Z-skew in machines that rotate counterclockwiseand

to the left giving an S-skew in machines that rotate clockwise opines Palaniswamy

et al. (2005)

2.7.2. Methods of Determining the Spirality

There are four well known standard test methods, IWS test method no.276,

British standard 2819, ASTM D3882-88, AATCC 179 test method are available

for determining the spirality of knitted fabrics, says Tao et al (1997).

Mainly two methods for determining the spirality of knitted fabric are

available in literature. The Manual Method and the theoretical method; The

manual method consists of measuring manually the spirality angle on a real fabric

by using a protractor. This method presents some difficulties such as Wales and

courses deformation during measurement and depends on human precision. The

theoretical method permits to calculate fabric spirality from fabric and machine

parameters; number of feeders on the knitting machine, loop’s length and number

of courses and number of wales per fabric unit length. The large number of

measured parameters increases the number of error sources and affects the

reproducibility of this method, says Abdessalem et al. (2008).




43

2.7.3. Synopsis of previous research work investigated on spirality of weft

knitted fabrics

De Araujo et al.(1989) have investigated spirality in both dry and fully

relaxed jersey fabrics producedfrom a series of relaxed spun yams and reported

that spirality depends on feed density, machine cut, and loop shape, but the

magnitude of spirality can be offset by the selection of yarn twist direction. In

addition, they have shown that a reduction in yarn "torque" can only partially

reduce fabric spirality, but the use of plied yarns and plaiting techniques may

completely eliminate it. In three-end fleece fabrics, spirality can be substantially

reduced by balancing the twist direction in the face and binder yarns. We have

also developed a theory to explain the mechanism of loop inclination and loop

rotation in single knit fabrics.

Celik et al. (2005) studied to develop an algorithm to determine the angle

of spirality using image analysis. The proposed algorithm has yielded fast and

accurate results.It is established that the algorithm is quite satisfactory in

determining the angle of spirality in knitted fabrics. Therefore this algorithm,

which is simple, fast and objective, can be very useful in determining the spirality

angle during both laboratory work and manufacturing.

Murrells et al. (2009) proposed an artificial neural network model for the

prediction of the degree of spirality of single jersey fabrics made from 100 %

cotton conventional and modified ring spun yarns. The factors investigated were

the yarn residual torque as the measured twist liveliness, yarn type, yarn linear

density, fabric tightness factor, the number of feeders, rotational direction and

gauge of the knitting machine and dyeing method. The artificial neural network

model was compared with a multiple regression model,demonstrating that the

neural network model produced superior results to predict the degree of fabric

spirality after three washing and drying cycles.




44

A new intelligent method was used by Semnani et al.(2009) to evaluate the

deformation of stitches in various weft-knitted fabrics based on an ideal shape of

stitches and angle of direction of stitches in a knitting machine. To measure

deviation of stitch direction against internal stresses, an image analysis technique

was applied to images taken from different fabrics with constant front light. In this

method, evaluation of fabric regularity with emphasis on the deformation of

stitches was studied based on analyzing the images of the fabric using Radon

transformation analysis. The index of fabric regularity was obtained from the

deviation of stitches from the original direction of ideal regular fabric. Also, the

grading of weft knitted fabric was expanded with a new aspect of regularity grades

as a novel grading development.The computer vision method was applied to

models of ideal fabric with different stitch sizes. Different weft-knitted fabrics of

various structures and yarns were evaluated by the computer vision method. The

results showed that this method is capable of grading various weft-knitted fabrics

with different fabric structures, densities and yarn types. Therefore, it is possible

to use this method for every type of weft-knitted fabric. The results indicated that

tuck and miss stitches caused more regularity in fabric, where as the type of yarn

has a major effect on fabric regularity.

The nature, origin and characteristics of the spirality have been examined

in detail by Primentas (2003) and reports that the distinction between the spirality

effect and other fabrics distortions contribute towards the verification,by

experiment, that the prime reason for spirality is the yarn twist livliness.Tao et al

(1997) presents an experimental investigation of the effects of yarn and fabric

constructional variables on the spirality of laboratory produced cotton single jersey

fabrics.




45

2.8 COMFORT PROPERTIES

Comfort properties of textiles are extremely important than the aesthetic

properties when the garments are next to skin. Among all the comfort properties,

good absorption and easy drying is one of the major requirements. Garment next

to the skin should absorb the sweat quickly and transport it to the outer surface of

the garment. From the outer surface, sweat should be evaporated quickly to keep

the body dry or cool. All these desired phenomena come under one technical term

called “Moisture management”, explains Ghosh (2004). Jinliantlu (2008) says,

moisture has a big impact on thermal comfort, but also on sensory comfort. This

sensory comfort may change with different activity rates and environmental

conditions, along with different garment designs. Capillary action or capillarity

can be defined as the macroscopic motion or flow of a liquid under the influence

of its own surface, opine Sharabaty et al. (2008).

According to Singh and Chatterjee (2010), physiological comfort is very

basic and necessary property of the fabric and the fabric structure plays an

important role in comfort of any garment. The comfort has been an inherent

feature of the knitted textiles as it is mostly used for inner garment and the wears

of delicate use such as ladies and infant dress materials. (www.nopr.niscair.res.in)

Thermal comfort relates to sensations of hot, cold, dry or dampness in clothes and

is usually associated with environmental factors such as heat, moisture and air

velocity, say Parthiban and Maruthamani (2006).

2.8.1 Definition of wickability

Mahadevan (2004) defines, the ability of a fabric to take in moisture.

Absorbency is a very important property which affects many other characteristics

such as skin comfort, static build- up, shrinkage, stain removal, water repellency

and wrinkle recovery. The ability of a fibre or a fabric to disperse moisture and


http://www.nopr.niscair.res.in)



46

allow it to pass through to the surface of the fabric, so that evaporation can take

place, opines Brown (2004). Wickability is the ability to sustain capillary flow

whereas wettability describes the initial behavior of a fabric, yarn or fibre when

brought into contact with water, state Sharabaty et al., (2008).

Wickability is the time taken by a strip of fabric sample to absorb water for

a distance of 1 cm. This strip is suspended vertically with its lower edge in a

reservoir of distilled water. The spaces between fibres act as capillaries. The

capillary network within a fibre will vary in different direction within the fabric.

Wettability is the ability of the fabric to become wet. It is calculated by the weight

of water absorbed by a fabric sample in a given direction when impressed in

water, express Thayumanavan et al., (2006). According to Pandey et al., (2010),

wicking ability was determined by the method suggested by Booth. Following

formula was used in this test.

Wicking percent = 100sampleofweightDry

sample ofweight Dry-sample of weight Wet

2.8.2 Wetting And Wicking

Wetting and wicking are important phenomena in the processing and

applications of fibrous materials. Various aspects of liquid- fibre interactions such

as wetting, transport and retention have received much attention both in terms of

fundamental research and for product and process development. Wetting of a

fibrous assembly affects many manufacturing processes, as well as the end-use

performance of materials. Wetting is a complex process complicated further by

structure of the fibrous assembly e.g. yarns, woven/ nonwoven/ knitted fabrics and

pre- forms for composites. The transport of a liquid into a fibrous assembly, such

as a yarn or fabric, may be caused by external forces or by capillary forces.

Wicking can only occur when a liquid wets fibres assembled with capillary spaces




47

between them. The resulting capillary forces drive the liquid into the capillary

spaces, explain Patnaik et al. (2006).

According to Pan and Zhong (2006), the term ‘wetting’ is usually used to

describe the displacement of a solid- air interface with a solid- liquid interface.

When a small liquid droplet is put in contact with a flat solid surface, two distinct

equilibrium regimes may be found; partial wetting with a finite contact angle !, or

complete wetting with a zero contact angle. Wicking is the spontaneous flow of a

liquid in a porous substrate, driven by capillary forces. As capillary forces are

caused by wetting, wicking is a result of spontaneous wetting in a capillary

system. Both wicking and wetting behaviours are determined by surface tensions

(of solid and liquid) and liquid/ solid interfacial tensions. The result of wicking

depends on a series of factors, for example those which influence interfacial

tensions (temperature, pressure, impurities, polarity…), the other properties of

liquid (viscosity, liquid evaporation…) and fibre properties (surface articulation,

fibre fineness…), reveal Wiener and Dejlova (2003).

Wetting, wicking and moisture vapour transmission properties are critical

aspects for assessing the comfort performance of textile products. There are

certain difference between wetting and wicking. Wickability can be defined as the

ability to sustain capillary flow and wettability can be defined as interaction

between liquid and the substrate before wicking takes place. So one can say that

wetting is a prerequisite of wicking, say Ramachandran et al., (2009). The surface

wetting characteristics of textiles affect their processability in finished products

and their performance when the fibres contact fluids. Wettability can be valuable

for characterizing fibre surfaces, liquid transport and interaction of fibres with

liquids, surfactants and adhesion with polymers, opine Mazloompour et al.,

(2007). Raul (2005) says, the ability of fabric to absorb water, especially by

wicking or capillary action may be observed by timing the rate at which water




48

climates up a narrow strip of fabric suspended vertically with its lower end

dipping into the water.

Wetting is the displacement of a fibre- air interface with a fibre- liquid

interface. Wicking is the spontaneous flow of a liquid in a porous substrate, driven

by capillary forces. Because capillary forces are caused by wetting, wicking is a

result of spontaneous wetting in a capillary system. Wicking processes can be

divided into two groups; wicking from an infinite liquid reservoir (immersion,

transplanar wicking and longitudinal wicking), wicking from a finite liquid

reservoir (a single drop wicking into a fabric).According to Samajpati and

Sengupta (2006), the phenomenon of wetting or non- wetting of a solid by a liquid

is better understood by studying the contact angle. It describes the shape of a

liquid drop resting on a solid surface by drawing a tangent line from the drop

shape to the touch of the solid surface.

For wicking to take place the fibre has first to be wet by the liquid. In fact it

is the balance of forces involved in wetting the fibre surface that drives the

wicking process. When a fibre is wetted by a liquid the existing fibre- air interface

is displaced by a new fibre- liquid interface. The forces involved in the

equilibrium that exists when a liquid is in contact with a solid and a vapour at the

same time are given by the following equation;

A SV - A SL = A LV cos !

where A represents the interfacial tensions that exist between the various

combinations of solid, liquid and vapour; the subscripts S, L and V standing for

solid, liquid and vapour,! = equilibrium contact angle, A LV = the surface tension

of the liquid. The contact angle is defined as the angle between the solid surface

and the tangent to the water surface as it approaches the solid; the angle is shown

as !, reveals Saville (2000).




49

2.8.3 Types of Wicking

Wicking is defined as the spontaneous movement of fluid through a

material driven by capillary forces. Wicking is an important property of fabrics

used in apparel for the following market segments; athletics, industrial uniforms

and protective services, say Leisen et al. (2008). Raul (2005) defines, the ability of

fabric to absorb water, especially by wicking or capillary action may be observed

by timing the rate at which water climates up a narrow strip of fabric suspended

vertically with its lower end dipping into the water.

At such times, the surface energy on inside face of the fabric plays an

influential role in wicking. Moisture is absorbed into a fabric in three directions

i.e., spreading outward on the inner surface of the fabric; transferring through the

fabric from the inside to the outer surface and spreading outward on the outer

surface and finally evaporating. Various testing methods such as water absorbency

and wicking property are used to measure the liquid transfer in clothing materials,

say Singh and Gupta (2010). Wiener and Dejlova (2003) point out, if the liquid

rises (by absorption) in fabric, it can be used as a liquid perspiration outlet from

the skin, for the production of hand towels and dish cloths, textiles for cleaning

works and many other such applications.

There are two types of wicking;

1) Longitudinal wicking

2) Transverse wicking

Longitudinal Wicking: If the material is vertical, the height to which the

liquid wicks is limited by gravitational forces and ceases when capillary forces are

balanced by the weight of the liquid.




50

Transverse Wicking: Transverse wicking is the transmission of water

through the thickness of the fabric i.e., perpendicular to the plane of the fabric.

Transverse wicking is more difficult to measure because the distances involved are

very small and hence the time taken to transverse the thickness of the fabric is

short. (www.fibre2fashion.com).

2.8.4. Longitudinal Wicking

Patnaik et al., (2006) say,it is a common practice to use in- plane wicking

measurements to evaluate the absorbing power or liquid transport capabilities of

fibrous sheet materials. Most versions of the test methods used for this purpose

start out by dipping one end of a sheet into a liquid and monitoring its subsequent

upward movement into the sheet, either by following the position of the liquid

front or by gravimetric or volumetric changes. During vertical upward wicking,

the flow of liquid is unsteady due to gravity effects. At the onset of absorption in a

vertical capillary system, the absorbed liquid is relatively close to the liquid source

and the effect of gravity can be neglected in this situation. However, at a longer

period of time (or upward wicking distance), gravity plays an increasingly

important role.

2.8.5 Related Studies

Ucar et al., (2007) carried out a study on physical and comfort properties of

the hoisery knit product containing intermingled nylon elastomeric yarn and it was

found that wickability in course direction is less than that of wale direction. Patil et al., (2009) in their study wickability behaviour of single-knit

structures found out that wickability increased with structural-cell stitch length and

among the different structures of fabrics, single jersey with higher structural-cell

stitch length showed better performance of wickability and absorption of water.


http://www.fibre2fashion.com).



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Among the directions, wale-wise specimen showed better wicking behaviour. The

distilled water showed good wicking behaviour as compared with other liquids. A comparative study on wicking behaviour of regular ring, jet ring -spun

and other types of compact yarns was carried out by Subramanian et al., (2007)

and from the study it was noted that wickability can be taken as a measure of

compactness; the lower the wickability the better is the compactness and

viceversa.

Comfort characteristics of fabrics made of compact yarns was studied by

Das et al., (2007) and it was found that fabrics developed from the EliTe®

compact yarns have shown slightly higher values of MVTR (moisture vapor

transmission rate) as compared to the fabrics made from the normal yarns. The

wicking characteristic of fabrics developed from EliTe® compact yarns was

slightly higher than the fabrics developed from normal yarns.

Manonmani et al., (2010) in their study suitability of compact yarn for

manufacturing of eco-friendly processed weft knitted fabrics noticed that the

compact spun yarn knitted fabrics have higher wicking height compared to the

ring spun yarn fabrics because of uniform packing of fibres and lower yarn twist in

compact yarn structure and uniform yarn surface which imparts the surface tension

to rise the wicking. The wicking characteristics of single jersey fabrics were found

to be good when compared to rib and interlock fabrics due to higher fabric density

and resistance to water rise. It was found that single jersey fabrics made of higher

stitch length showed higher wicking height because of the increased surface

tension.

Liquid transporting and drying rate are two vital factors affecting the

physiological comfort of sport garments. In a study conducted by Fangueiro et al.

(2010), plated knitted fabrics were produced with functional fiber yarns in the




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back of the knit (close to the body), combined with polypropylene or polyester in

the face (outer surface) and were tested in terms of their wicking behavior and

drying rate capacity. Functional knitted fabrics were evaluated by vertical and

horizontal wicking tests. The drying capability was assessed by drying rate tests

under two different conditions, namely,at 20±2°C and 65±3% relative humidity

and, in an oven, at 33±2°C, in order to simulate the human body temperature. The

influence of the functional fiber used and that of the ground material, polyester or

polypropylene, was analyzed and discussed.




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