AA

TERM PAPER

ON

PPIILLEE SSTTRRUUCCTTUURREE

Submitted to

Prof. V. K. KOTHARI

Submitted by

PULAK DEBNATH 2006TTE3073

DEPARTMENT OF TEXTILE TECHNOLOGY

INDIAN INSTITUTE OF TECHNOLOGY, NEW DELHI-110016

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1. INTRODUCTION

The weave or method of interlacing the warp & weft not only determines the actual structure of the fabric, but also greatly affects its ultimate appearance. Pile fabrics are distinguished by having a large number of threads projecting almost vertically from the body of the cloth. The projecting threads may be cut or uncut thus resulting in tufted or looped pile. The pile is supported by a closely woven ground cloth, the face of which is usually entirely hidden through being covered by the pile. Pile fabrics are produced in great variety, some of simple structure and others involving intricate patterns and complicated interlacing of the various series of yarns. The yarn that forms the pile of a pile fabric is known as the pile warp or the pile filling, as the case may be, the yarn that forms the foundation fabric are known as the ground warp and the ground filling. Weft pile fabrics are composed of one series of warp threads and two series of weft threads, the ground and the pile. In warp pile structure, certain warp ends are used to form loops on the surface of the cloth. Only one series of weft threads is used but the warp consists of two series of threads, the ground and the pile. The pile may appear in different forms in different classes of goods. In some cases, it covers the entire surface of the ground fabric, appearing like a continuous brush of uniform height, as in velvets and plushes; in other cases, it forms cords with a distinct rounded formation, running lengthwise of the goods, as in corduroy fabrics. Sometimes the pile remains in a series of loops of uniform height covering the surface of the ground cloth, as in Brussels carpets, or with the same effect on both the face and back of the fabric, as in Terry towels. In all pile fabrics, the pile yarn is uncut when the cloth is first woven. In the case of weft-pile fabrics, the cutting is the object of a special process performed after the cloth is taken from the loom. In cut warp-pile fabrics, the cutting usually takes place in the loom. The ground weave is closely woven so that the fabric will not fray easily or the pile be loosen from the cloth.

Pile & plush fabric can also be of knitted. Knitted pile fabric may be produced by circular weft knitting machine or flat warp knitting machine. The essential difference between a plush and pile structure is that the pile, normally composed of a different type of yarn, should stand out almost at right angles from the knitted ground surface. Both plush and pile surfaces may consist of either cut or uncut loops of yarn and in the case of high pile, slivers of fibres instead of yarns are used. Another type of pile effect on fabric can be employed by using chenille yarn as weft. Chenille yarns are constructed by twisting core yarns together in chenille yarn

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machines where pile yarns are inserted at right angles and cut to within 1 or 2 mm of the core yarn surface, to create a surface in which the fibers contained in the pile yarns burst and form a soft pile surface to the yarn. Chenille is a difficult and expensive yarn to manufacture. A different form of pile surface is also produced by raising and cropping during fabric finishing operations. This type of pile fabrics are, of course, entirely distinct from those cloths are formed by projecting threads. Another type of fabric, known as fur fabric is also produced by feeding sliver or roving knitting machine to give appearance like pile structure. A pile structure has unique properties like softness, smooth feeling, better absorption ability, compressibility etc. Different types of pile structures are produce according to their application area. Pile fabrics are mostly used for towel, bathrobe, apparel, winter cloth, upholstery, home-furnishing etc. 2. CLASSIFICATION OF PILE FABRICS:1,2

The different varieties of pile fabrics may be classified in several ways, one of which is to make two divisions, one to include those fabrics in which the pile yarn is uncut and remains in the form of loops and other to include those in which the pile is cut. Another classification separates the different varieties of pile fabrics into two divisions, one of which includes those fabrics of a corduroy nature, in which the pile is arranged in cords running lengthwise of the fabric, while the other embraces those in which the pile extends uniformly over the entire face of the cloth. Another system, and the one adopted here, which admits of a definite classification of all pile fabrics, provides for two main classes, namely, warp-pile fabrics, in which the pile is formed of warp yarn, and filling-pile fabrics, in which the pile is formed of weft yarn. So pile fabrics are broadly classified into two categories a) Warp pile b) Weft pile.

2.1 WARP PILE: Warp pile structure in which certain warp ends are used to form loops on the surface of the cloth. Only one series of weft threads is used but the warp consists of two series of threads, the ground and the pile. The former produces with the weft the ground cloth from which the loops formed by the pile ends project. There are two effects obtained with warp pile – one in which the pile yarn is uncut and forms loop on the fabric surface of the fabric and another in which the pile is cut to form a brush-like surface on the fabric. The former is known as Terry pile, while in the latter case Velvet or plush, pile is formed. 2.1.1 Terry pile: The terry piles, also known as Turkish towel are manufactured in special loom. In warp two series of warp namely: ground & pile are used. The loops are remaining uncut. A systematical design plan & diagram is shown in Fig. 1.

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Fig. 1: Design plan for Terry Pile

The loops may be formed on one side only or on both sides of the cloth thus producing single-sided and double-sided structures respectively. Any one pile thread may alternate between the face and the back of the cloth a possibility.

Fig. 2: Different types of terry pile

The schematic diagrams in Figure 2 show at A the single-sided and at B the double-sided continuous terry structures. C conveys the idea of a pile thread alternating between the face and the back. At D the ornamentation is carried further by having two differently coloured sets of threads which mutually alternate between the face and the back thus forming' a figure in one colour on the background of another. All the structures, apart from A, are reversible. 2.1.2 Velvet & Plushes: In case of velvet & plushes fabric, loops are cut during weaving process. Loop length of plushes fabrics is more than velvet. Velvet fabrics are usually made with cotton, linen, or silk ground warp and filling and a silk pile warp. The ground weave is usually either the plain weave or a small rib, basket, or twill weave. The proportion of pile warp and ground warp, as well as the length of the varies with different qualities of fabrics pile.

Fig. 3: Warp pile by wire insertion

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Fig. 3 shows a very common velvet, known as the 2-pick; the warp ends are arranged 1 ground, 1 pile, and 1 ground; the ground weave is the plain weave. Two plushes fabrics can be produced simultaneously in the loom face-to-face, being connected by pile, which passes from one cloth to the other. 2.2 WEFT PILE: Weft pile fabrics are composed of one series of warp threads and two series of weft threads, the ground and the pile. The pile weft is cut in a separate operation after weaving. Surface of weft pile structure consists of short and very dense tufts. A feature of weft pile structures, also termed velveteen, is very high density of shotting which in the finest fabrics may reach 200 picks per cm. Structurally, weft piles may be classified as follows:

1. Plain velveteen 2. Weft plushes 3. Corded velveteen-also known as corduroys and fustians 4. Figured velveteen in which pile figure is produced on bare ground.

All the above groups may be further subdivided into plain back or twill back structures depending on the type of weave in which the ground picks interlace with the warp. 2.2.1 Plain velveteen In this type of fabric, the pile is uniformly distributed over the entire surface of the cloth. The projecting fibres are of equal length. During designing of fabrics the chief points to note are: (1) The weaves that are used for the ground and pile respectively; and (2) the ratio of pile picks to ground picks. These factors, together with-the ends and picks per cm of the cloth, influence the length, density, and fastness of the pile.

P P P G P P P G

1 2 3 4 5 6 7 8 9 10 11 12

Fig. 4: Weft piles weave & cutting plan

In fig. 4, the pile weave is based on the 1-and-2 twill which yields a weft float of five, and there is three pile picks to each ground pick. The cross-sectional view before

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cutting process is also shown at I. Arrows indicates below the designs to show where cutting races occur. The weft threads projected vertically from ground in form of tufts of fibre, represented at J. The ground weaves mostly used are plain, 2-and-1 twill and 2-and-2 twill, the last weave being employed for very heavy structures. The interlacing of the pile is based on the plain weave, simple twill, sateen, or a sateen derivative. 2.2.2 Fast pile structure: A very important feature of these fabrics is the proper securing of the pile to the ground cloth so that there will be no tendency of the tufts fraying out. As shown in fig. 4, the tufts are bound in by one end only at a place, and the fastness of the pile is chiefly dependent upon the pressure of the picks upon one another. To make a very long pile, the necessary firmness can be secured by interweaving the pile picks more frequently and thus making a `fast' pile. In Fig. 5 design plan & cross-sectional view of fast pile is shown.

Fig. 5: Fast pile structure

2.2.3 Weft Plushes These constructions are similar to the ordinary velveteen but are made with longer pile floats and in heavier weights. Due to the use of the cloth and the length of pile, the pile weft is invariably anchored to the ground cloth on the fast pile principle. Mainly plain design is used for ground; and for pile, interlacing 5-end or 8end sateen are used. The pile consists usually of woolen, mohair, or acrylic yarns although other materials can be used. 2.2.4 Corded velveteen These types of structures are characterized by brush-like cords of pile running in the direction of the length of fabric. These types of fabrics are also known as Corduroy. The pile picks are bound in, at intervals, in a straight line. The cuts are made right up the centre of the space between the pile binding points, with the result that the tufts of fibres project from the foundation in the form of cords or ribs running lengthwise of the fabric. Corduroy is made mostly from cotton. The ground weave for this type of fabrics should be of simple structure such as plain, basket or twill etc.

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A B C

Fig. 6: Corduroy fabric

Fig. 6A shows the appearance of corduroy before and after cutting. In the simplest cord design, the pile picks are bound in plain order on two consecutive ends. Fig. 6B shows the design plan of corduroy with a plain back. The design extends over the width of two cords and each pile pick forms alternately a long and a short float. The difference in the lengths causes the ribs to have a rounded formation; this is shown in Fig. 6C. The arrows indicate the position of the cutting races. 3. PRINCIPLE OF PILE FABRIC PRODUCTION There are various techniques used for production of pile structure. In every pile fabric structure consists of two different structures of ground & pile. Extra yarn has to be fed for pile formation along with ground yarn. Therefore, the manufacturing process of pile structure is different from production of conventional fabric and is quite complicated. Different mechanisms used for pile fabric production, are discussed below. 3.1 WARP PILE PRODUCTION For warp pile fabric, two warps are therefore necessary-one for the ground cloth and another for the pile. Warp piles can be formed different methods as follows1:

1. Using wires, here both loop & cut pile can be produced. 2. By terry motion. Loop piles are formed in loom by special mechanism. 3. Double-plush method. Two cloths are woven simultaneously and produces cut

warp pile. 3.1.1 By using wires In this method, only one kind of weft is required but at least two series of warp threads, separately beamed and tensioned, are essential, viz. ground ends and pile ends. In the production of warp-pile fabrics, the pile is produced by raising the pile warp over a wire and then depressing it to interlace with the ground again. When the pile shed is formed in the loom, the wire is inserted; and as the shed closes on the wire and the lay beats up, the wire is forced up on the surface of the cloth, thus forming the loops. The pile may be looped, if plain wires are used, or cut, if the wire has a cutting blade at its tip end. The plain wire leaving in the cloth upon withdrawal the loops, whilst the cutting wire severs the loops formed upon its shank as it is withdrawn thus leaving the

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cut tufts in the cloth. This is shown schematically at E in Fig. 7. The upper part of E and the cross-sectional shed diagram at F in Fig. 7 also shows the normal shedding arrangements used in the manufacture of these fabrics.

Fig. 7: Principle of warp pile production by wire aids

The wires are not withdrawn immediately after being inserted in the pile shed, but are allowed to remain in the cloth until they are a short distance from the fell of the cloth. Since if the wire were withdrawn immediately, the tension of the warp would pull the pile ends from the cloth if the pile was cut, or pull down the loops if it was not cut. Dobby or jacquard shedding system with special lifting arrangements mostly used to form high shed for wire insertion. The thickness of the wire regulates the size of the loops made by the pile warp, and consequently the length of the pile. Most of the cutting wires are made to operate with a disposable razor-type cutting edge, which fits into a slot at the tip. Weaves & yarns used: The ratio of ground to pile ends and picks to wires may be varied to a considerable extent. Normally, the ground weaves are very simple repeating on two, three or four picks e.g. plain, 2/2 rib, hopsack etc. the wire to weft ratios are most commonly one wire to two, three or four picks. Mostly ground to pile ration 2:1 is used. Cotton, viscose, worsted, wool, silk, polyamide, acrylic, polypropylene yarns are mostly used according to their end-uses e.g. Dress Velvets, Carpets. Thread density, yarn count and height of pile can be varied. The following typical qualities are given for a variety of purposes: a) Dress velvets: Warp density- 10 to 16 pile ends/cm, no. of ground ends depends on pile to ground ratio; ground warp- 20/2 to 32/2 tex cotton and pile warp- 10-20 tex single or two fold such as mercerized cotton, filament rayon, synthetic yarns and spun silk; weft density- 6 to 12 wires/cm, the no. of picks/cm depending on the ratio of picks to wires; weft- 20/2 to 32/2 tex cotton; pile height- 1.5-3 mm. b) Upholstery plushes: warp density- 10 to 12 pile ends/cm; ground warp- 60/2 tex cotton or staple viscose rayon; pile warp- 50/2 tex to 72/2 tex worsted or equivalent counts in polyamide, acrylic or polypropylene yarns; weft setting- 8 to 12 wires/cm, weft counts 60 tex two-fold or single cotton or staple viscose; pile height 2-5 mm

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3.1.2 Terry pile production: Terry towels are produced in the loom by means of two warps-a ground and a pile warp-as is the case with all warp-pile fabrics, but the method of producing the pile is different. The ground warp is arranged with a heavy tension, while the beam of the pile warp is only under slight tension, which is placed above the loom. Passage of warp yarn and tension controlling system is shown in fig. 8.

Fig. 8: Passage of warp in Terry towel loom5

Terry towel can be woven 2, 3, 4, 5 or more pick terry weaves. The most common type is 3-pick terry toweling. In 3-pick terry, weaving two picks are inserted at a variable distance- the loose pick distance- from the cloth fell as indicated schematically at E in Figure 9. The loose pick distance is varied according to the desired loop height. When the loose pick is beaten-up, the reed pushes the pick group, which included three picks, on the tightly tensioned ground warp, towards the fell, and the loose pile warps woven into the three-pick group are uprighted and form loops. During this action, the three picks are capable of sliding between the ground ends, which are kept very taut, as depicted at F. Tension control is a critical parameter in terry weaving. During fast beat-up pile warp must be slacken.

Fig. 9: Formation of terry pile

The gap is created either by 1) Those in which the reed is drawn back the required distance before reaching the fell on the two picks in question. 2) Those in which the fell of the cloth itself is made to recede away from the on-coming reed during the insertion of the two succeeding picks.

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Weaves and Yarns used: Commonly, for ground structure 1/1 plain weave, 2/1, 2/2 or 3/1 rib weaves are employed. For shedding cam, dobby, jacquard can be used. However, dobby or jacquard normally used to produce figured terry towel. The warp threads can be arranged 1 ground, 1 pile or 2 G, 2 pile or 1 G, 1 face pile, 1 G, 1 back pile or 1 G, 1 face pile, 1 back pile, 1 G etc. for toweling, normally thread density is kept between 15-25 picks/cm and 20-30 ends/cm. In terry towel there are four groups yarn employed i.e. pile warp, ground warp, weft and border weft. For pile warp 100% cotton, combed or carded, bulkier and absorbent yarns are used. When high quality is required, two or more ply yarns are used. Carded yarns of 100% cotton or polyester blend ply yarns are used for ground warp. Carded 100% cotton single yarns are used as weft. For border with fancy weave, decorative, shiny, bulky yarns of rayon, polyester, chenille or mercerized cotton can be used. Other than cotton, nowadays, many fibres are used for towel yarn e.g. bamboo, Modal, lyocel, soybean, micro fibre etc5. 3.1.3 Double-plush method: By the system of weaving warp pile fabric known as double-plush, two plush fabrics are formed in the loom face to face, being connected by the pile, which passes from one cloth to the other. After the filling is inserted, the two cloths are wound on separate cloth rollers, the pile being cut by a knife, thus leaving a pile face on each fabric. Two separate ground fabrics with space between them, each with its own warp and weft, are woven on the unstitched double-cloth principle1,2,4.

Fig. 10: Face-to-Face double pile fabric production Most of the modern machines used for this class of structure instead of shuttles employ double or single rigid rapiers in a twinned (two-tier) arrangement, one set inserting weft at the top, and the other at the bottom cloth level. The distance between the ground fabrics is regulated according to the required length of pile. Plain velvets, plushes, carpets etc may be manufactured by this method. Pile yarns consist of cotton, staple or filament rayon, mohair, worsted and various synthetic materials. The main advantage of this system is large production and no time wastage for cutting operation.

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Apart from these methods, spool and gripper Axminster weaving is used for carpet manufacturing. Tufting method also used where figured pile structure with many colour is to be produced. Figure 11 shows the main elements controlling the tufting action of a cut pile machine4.

Fig. 11: Tufting mechanism showing controlling the tufting actions

The yarn is fed from a suitable 'supply creel'. It enters the ends of the 'guide tubes’, which lead all the individual yarns in the creel to the top of the tufting machine. Then the yarn passes through the 'guide bars', 'feed rollers' 'movable yarn guide' and a further yarn guide which is attached to the 'needle bar'. The needle bar moves up & down during insertion and withdrawal of the needles. Up and down motion is given to needle bar by means of an 'eccentric shaft'. The backing fabric is supplied from cloth roll. On insertion of the needle into the backing fabric a 'looper’ is actuated by the 'looper shaft' and moves forward to pass between the yarn and the needle, forming a loop on the looper as the needle rises. A 'presser bar' prevents the primary backing from rising as the needles withdraw. Thus, pile structure is produced on backing fabric. 3.2 WEFT PILE MANUFACTURING:1,2

In weft pile production, one series of warp for ground and two series of weft yarns for pile and ground are required. All type of filling piles e.g. velveteen, corduroy etc. are produced by same mechanism, only their design plan differs. Very high weft density is employed in weft pile fabric, which may reach 200 picks per cm. In order to reach such weft densities the warp density should be comparatively low and the warp yarn has to be kept very taut. Due to the high warp tension heavy loom with positive shedding mechanisms are used. When the ground filling is inserted in the cloth, the sheds are so formed as to cause it to interlace with the warp in such a manner as to form the ground cloth. When, the pile filling is inserted, all the warp is depressed with the exception of certain ends that are raised so as to allow the pile yarn to be bound to the ground cloth. The pile filling, therefore, floats over the ground cloth in long floats. The pile effect in the velveteen is a result of a cutting operation during clot finishing. Before cutting, the cloth is prepared for the operation by stiffening the surface float in order to define the cutting races more precisely and to ensure crisper cutting. The back

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of the cloth is also treated by an application of an adhesive, usually starch, to ensure that the tufts during cutting are not plucked out from the ground structure. The cutting of filling-pile fabrics is accomplished with a knife, shown in Fig. 12, having a sharp-pointed blade2.

Fig. 12: Cutting blade

In operation, the point of the sheath ‘b’ is inserted in the race of floats formed on the surface of the cloth, and as the knife is pushed forwards the yarn is raised by the sheath until it comes in contact with the sharp cutting edge of the knife ‘a’ and is severed. After the pile is cut, corduroy fabrics are brushed and singed in order to obtain a smooth, rounded cord. Weaves & Yarns used: During designs for pile fabrics the main points to note are: (1) The weaves that are used for the ground and pile respectively; and (2) the ratio of pile picks to ground picks. These factors, together with-the ends and picks per cm of the cloth, influence the length, density, and fastness of the pile. The ground weaves mostly used are plain, 2/1 twill and 2/2 twill, basket etc. The interlacing of the pile is almost invariably based on the plain weave, simple twill, sateen, or a sateen derivative. Pile pick to ground pick ratio varies according to weave, it may be 2:1, 3:1, 4:1, 5:1 etc. For these types of structures, mostly cotton, filament, rayon, mohair, worsted, acrylic etc. yarns are used in pile. Some typical constructions are as follows: Velveteen: Warp- 20/2 tex, 28 Ends/cm; Weft: 15 tex, 120 Picks/cm 420 tufts/cm2. Warp- 17/2 tex, 28 Ends/cm; Weft: 10 tex, 176 Picks/cm 496 tufts/cm2. Corduroy: Warp- 20/2 tex, 28 ends/cm; Weft: 12 tex, 140 picks/cm, 294 tufts/cm2. Warp- 74/2 tex, 13 Ends/cm; Weft: 32 tex, 176 Picks/cm 496 tufts/cm2. 3.3 KNITTED PILE MANUFACTURING:3

The production of knitted pile fabrics tends to be a very specialized technique for both knitting and finishing. One or more of the following techniques is normally involved in the production of the two types of fabric: special points or other elements in the knitting machine, excess feeding of the pile yarn and raising or brushing of the pile surface during finishing. Although a certain amount of double-faced pile fabric is produced, the majority of plush and pile fabric has its surface effect on the technical back of single-faced constructions with the sinker loops or under-laps being used to produce the effect. A variation of this technique is to use a double needle bar machine, pressing off on the second set of needles to produce the pile surface. Yet another method is to employ a double needle bar Raschel machine to produce pile structure.

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3.3.1 Weft Knitting m/c for Pile fabric production: The bearded needle Sinkerwheel has long been renowned for this type of fabric construction. Also Sinker Top Latch Needle Machines are used for the same. The loop forming mechanism is shown in fig. 13.

Fig. 13: Pile formation on Sinker Top Latch Needle Machine

The ground yarn is fed into the sinker throat and the sinker is then advanced so that the plush yarn fed at a higher level is drawn over the sinker nib. Horizontal pattern wheels may select onto the backs of sinkers and thus produce designs in plain and plush stitches. A range of pile heights from 2 to 4 mm is possible using different sinker heights. 3.3.2 Sliver or High-Pile Knitting To produce high pile knitted fabric single jersey circular machine with sliver feed mechanism is used31. The stock- or dope-dyed slivers are drawn from cans and then prepared mini three-roller drafting card units followed by two wire-covered rollers, which is shown in Fig. 14.

Fig. 14: Sliver Knitting

At each sliver feed, the needles are lifted to an extra high level where they rise through the wires of the doffer roller to collect tuft of staple fibres. Air jet nozzles over the knitting points ensure that the tufts are retained in the needle hooks and that the free fibre ends are orientated through to the inside of the fabric tube (the technical back) which is the pile side. At a time, 12-16 slivers can be feed. Fibre staple length can range from 20-120 mm, sliver weights from 8-25 gm/mtr, fabric weight varies from 300-2000 g/m2.

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3.3.3 Warp knitting m/c for pile structure production: There are two main groups of pile fabrics produced on double-bed Raschels, cut pile and point pile. Cut pile is achieved by knitting a separate base fabric on each needle bed but joining the two together by the lapping movement of the pile which. Point or looped pile is produced by replacing the front bar needles by a point or pin bar around which the pile yarns are overlapped. Fig. 15 shows a more popular construction using five guide bars, by lapping the pile yarn into two wales.

Fig. 15: Double bed Raschels

Here two separate ground constructions each with its own yarns, one on each needle bar and to supply the pile yarn across between the two needle bars. The pile is later cut to separate the two needle bar ground fabrics and thus produce two separate single-sided cut pile fabrics. 4. PARAMETERS OF PILE FABRIC:

Apart from parameters of conventional fabric e.g. EPI, PPI, there are some parameters which considers for pile fabric1. They are discussed below: 1. Pile height: Pile height is the measure of the length of a pile from the top surface of the backing to the top of the pile. The length of the backing is not included in this measurement. It is cleared that pile height depends on length of pile. In case of weft pile fabric, the pile height varies according to the ends/cm of the cloth and the number of ends over which the pile weft floats. An increased height of pile is obtained either by reducing the ends/cm or by increasing the number of ends over which the pile weft passes or vice versa. The height of terry pile depends on the creation of a gap between the fell of the cloth and two succeeding picks of weft.1 With today’s machine, maximum 24 mm loose pick distance can be achieved, which gives 12 mm pile height. Durability, softness, compression, absorbency etc. depends on pile height. 2. Pile density: Pile density is expressed as tufts per square meter. The density of the pile depends on

1. Thickness of the weft. 2. Length of the pile. 3. Design and construction of the fabric.

An increase in the thickness of the weft tends to make the pile coarser, but other things being equal the density is increased. A long pile causes the surface of the

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cloth to be better covered. Pile density can be calculated by the following formula: Tufts/cm2 = (Ends per cm X pile picks per cm)/Ends in repeat of pile weave. The density of the pile can be changed by various way, for example:

1. By varying the number of picks/cm, or the thickness of the weft in the same design and sett.

2. Alternatively the design may be changed in order to obtain a proportion of pile to ground picks.

Table 1 shows the result which will occur under the different conditions of a given design1.

Table:1

Conditions

Ratio of pile picks to ground picks

Groundpicks/cm

Pile picks/

cm

Total picks/

cm

Tufts/ cm2 Remarks

Original structure 4 to 1 32 128 160 448 Original structure

5 to 1 27 135 162 473 Density of pile increased. Ground texture less firm.

To retain same total picks as original structure

3 to 1 40 120 160 420 Density of pile reduced. Ground texture firmer

5 to 1 26 130 156 455 Total picks reduced. Ground texture less firm.

To retain same density of pile as original structure

3 to 1 43 129 172 452 Total picks increased. Ground texture firmer.

5 to 1 32 160 192 560 Density of pile increased. Total picks increased

To retain same ground texture as original structure

3 to 1 32 96 128 336 Density of pile reduced. Total picks reduced.

3. Pile ratio: This term is applicable for warp pile structure. Pile ratio is described as the length of pile warp per unit length of fabric in warp direction. This ratio has direct effect on the fabric weight and thickness. As the ratio increases, the weight and thickness of the fabric increases.

4. Gram square meter: As pile height and density varies for different pile structure, so weight of pile fabric is a crucial parameter. Weight of pile fabric depends on count of yarn, EPI, PPI, pile ratio, pile height etc.

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5. PILE STRUCTURE: 5.1 Structural behavior of pile loop: In fig. 16, two types of loops are shown. (I) is an upright loop and (II) is a spiral loop5.

Fig. 16: Types of loop and loop structure

Pile warps may be single yarns and two-ply yarns. As single yarns have ‘Z’ twist, their piles are twisted in the right direction. On the other, as two-ply yarns have ‘S’ twist, their piles are twisted in the left. Nishimastu & Sawaki6 carried out a study on terry pile fabric. It had been observed that piles incline to the cloth fell if single yarn used for pile warp as shown in fig. 11(a&b). In case of two ply pile warp, piles incline to the opposite side of the fell as shown in fig. 11(c&d). 5.2 Pile Inclination: The pile is held by the yarn-to-yarn friction caused among pile warps, ground warps, and wefts. A model of inclined pile is shown in fig. 17. It is assumed that point A is on the perpendicular line to the warp axis, and touches the first weft yarn. Numbers 1, 2 and 3 show the first, the second and the third weft yarns.

Fig.17: Side view of pile model From the model, inclination angle of pile can be determined by the following formula6: θ = cos-1(W/lh') where, W = w+3d+(5/2)dp = 1/m+1/2dp= 1/0.33 ES+1/2dp lh' = lh + 1/2dp,and lh = (Rp/m-(d+dp)Π/2) k/F(k, Π/2)

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Rp : Pile ratio, d: Weft yarn diameter (cm), dp : Pile warp diameter (cm), l: Unit per length (= 1 cm), ES : Weft density (ends/cm) , m : Numbers of piles per 1 cm warp distance (numbers/cm), lp: Pile length (cm), w : Distance from the first weft to the third weft (cm), 6. PROPERTIES OF PILE STUCTURE

Pile fabrics have some unique properties like absorbency, compression, soft feeling etc. Some properties of pile fabric are discussed below. 6.1 ABSORBENCY OF PILE FABRIC: Absorbency refers to a fabric’s ability to remove liquid water from the skin. Absorbency is the most important property of terry pile fabric. High absorbency can be achieved in towel by increasing surface area with pile yarns and using cotton yarns with lower twists than the ground yarns. Plied pile yarns have more absorbency than single pile yarn. Micro-fibre towels can absorb 5-7 times water of their weight5. Although yarn material is the main parameter in determining water absorption properties of terry fabrics, terry fabric construction also has some effect on it. Karahan and Eren7 investigated effect of fabric parameters on water absorption of terry fabric. It has been observed that the type of yarn used in the production of terry fabrics had the most significant effect on their water absorption properties. Two-ply ring- spun yarn showed a higher water absorption value than two-ply open-end yarn and single-ply ring-spun yarn. This is because two-ply ring-spun yarns have more space for water penetration than single ring-spun yarns and two ply OE- yarns are more twisted. The warp density, weft density and pile length of terry fabrics also had some effect on the water absorption properties. An increase in weft and/or warp density reduced the percentage of water absorption due to dense structure, and an increase in pile length increased that percentage. The effect of pile length on static water absorption was found to be more pronounced compared to warp and weft density. However, there is certain limit for the pile height value beyond which the absorbency tends to decrease which is shown in fig. 18.

Fig. 18: The variations of sinking time with pile height; ♦-500-550 g/m2, ■-412-435 g/m2.

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This limit depends on the yarn number, twist, type of raw material and density, and varies from towel to towel8. As can be seen from region I, increasing pile height up to a certain value (7.4), increases the surface being contacted with water and hence decreases the sinking time for both aerial density intervals. After this certain value, sinking time starts to increase slightly (region II), meaning that at these relatively higher pile height values, the loops tend to be bent with their aerial density and consequently cover the surface of the fabric, which in turn restricts the water absorption Zervent & Koç8 have observed that the hydrophility degree and dimensional variation depends on pile height, aerial density, softeners and the coloration process. The highest hydrophility degree or the lowest sinking time was ensured with silicone softener. Absorbency of cut pile in less than that of the uncut pile towels; this is attributed to the twist loss of the pile warp being opened after cutting process, and hence causing a decrease in water absorption5,8. Kim Hun & Kim Joo9 investigated the water absorption properties of a split-type nylon/polyester (N/P) microfiber pile knit fabric. Maximum water absorption (%) is 28.1% of weight loss was observed. High density microfiber loops lead to fast absorption of fluid. The increased number of pores as a result of the formation of highly dense microfiber loops has the ability to retain much fluid, which is related to changes in maximum water absorption. 6.2 FRICTIONAL CHARACTERISTICS OF PILE FABRIC: Many studies have been reported, dealing with the frictional mechanisms pile fabrics fabrics6,10,11,12,13. The friction coefficient of the fabric determine the fabric’s smoothness or roughness. The frictional force between terry pile yarns and a frictional slider is given by equation (1) that the frictional force is divided into two components:10 F= FA + FB ……..(1) where FA is a component of frictional force between pile yarns and a frictional slider, FB a component due to the loss energy caused by the interfiber friction during compressive deformation when pile fabrics are subjected to rubbing. It has been observed that the backing layer which forms the middle layer of the pile fabric doesn't influence on the frictional force, if the yarn count of pile warps, the pile ratio and numbers of the pile unit per area were identical6. The contact area with the frictional slider as well as frictional force increases as the pile ratio increases10. Frictional properties of pile fabrics were studied by changing sliding speed, relative humidity, twist number and frictional direction11. Frictional force decreases with increasing the sliding speed at low speed (0.5-5mm/s). But at high speed the frictional force increases gradually. The frictional force increases with increasing relative humidity. With increasing twist of apile yarns, the real area contact area between pile warps and frictional slider becomes smaller, and the frictional force decreases. The frictional coefficient obtained by sliding against inclined piles in higher that that obtained by sliding along inclined piles. It have been seen that the friction coefficients determined in the warp and weft directions significantly decrease after washing of the fabric. The addition of flax or hemp in the pile caused these fabrics to have a higher friction coefficient than pure cotton fabrics13.

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Hirai Ikuko and Gunji Toshihiro12 examined on coefficient of friction of carpet pile made of nylon. They observed slipperiness of carpets is more influenced by a pile form than by a pile material. In tufted carpets, ribs occur due to tufting a pile yarn in the machine tufting direction. A coefficient of friction in the cross-wise direction is greater than that in the machine tufting direction, because of the ribs. The coefficient of friction of loop-pile carpets with rather clear ribs is greater than that of cut-pile carpets. The coefficient of friction of wetted carpet is more than dried carpet due to an increased contact area caused by falling of wetted soft pile fibers. 6.3 COMPRESSION:

Compressibility is one of the critical parameter of pile structure as it determines the hand value of fabric. Many research works have been done on compression property of pile structure. In one experiment6,14 on terry towel a sample (40 x 40 mm2) were compressed under 10 gf/cm2 pressure, and recovered gradually till 0 gf/cm2 while the Pressure-Thickness curves were measured. The area of the compressive plate was 40 x 40 mm2, the compressive speed being 5 mm/min at 20°C and 65 %RH. Compressive properties i.e. compressive ratio (Ra), compressive energy (Ec), recovery energy (Ec’), compressive resilience (Re), compressive modulus (Dr) and compressive recovery ratio (Kr) from the measured Pressure-Thickness curves. It was found that compressive properties (energy, compressive, resilience, compressive modulus and compressive recovery ratio) were not influenced by the fabric density of the backing layer, if the yarn count of pile warps, the pile ratio and numbers of piles per unit area were identical. Compression property is very crucial for carpet. One of the most important quality factors in carpets is thickness loss due to deformation in compression by static and dy-namic loads. By this loss, not only does the carpet appearance on the face lose its original form, but the carpet’s resilience capability is also lost16. Kimura & Kawabata15 developed a compressive deformation theory of carpet. According to the theory, the compression process can be divided into the following three stages of deformation: 1. Bending deformation region: A region in which only the bending deformation is effective (until neighboring piles come in contact). 2. Mixed region of bending and compressive deformations: A region in which both the bending and the compressive deformations are effective, i.e., the concurrence of the bending deformation of piles which do not come in contact with neighboring piles and the compressive deformation of piles which come in contact. 3. Compressive deformation region: A region in which only the compressive deformation is effective (after all the piles are completely fallen down). Compressibility of carpet depends on diameter of yarn used for pile. By compressive deformation model of cut pile carpets, the compressive deformation curve of the cut pile carpets can be calculated from the mechanical properties of pile yarns, i.e., compressive properties and bending rigidity. Fig. 19 shows schematic diagrams of deformed modes for cut and looped pile yarns under initial compression18. Complex dynamic modulus of carpets mainly related to three factors, i.e. deformed mode of pile yarn, volume fraction of fiber phase and pile yarn material.

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Fig. 19: Schematic diagrams of compressive deformed modes for cut pile and looped pile. It has been observed that compressibility and compressive elasticity modulus of cut-pile carpets are greater than those of loop-pile carpets. This fact suggests that piles of cut-pile carpet tend to fall down easily by vertical load and to recover easily, because a cut-pile carpet is soft12. The characteristic parameters i.e. compression sensitivity S(%), permanent deformation DP(%), elasticity E(%) and resilience R(%) determine the carpet’s behaviours16. A study was done to on the performance of carpets against static loading of wilton-type carpets produced with wool, acrylic and PP pile materials. The results obtained are shown in fig. 20.

Parameters Acrylic Wool PP S% 35.55 18.79 30.88DP% 22.99 3.34 7.58E% 35.33 82.25 75.46

Fig. 20: Characteristic parameters of the carpet samples. From the aspect of the permanent deformation (Dp) and the elasticity (E), after recovery for 24 hour, it was found that the wool carpet is best and the acrylic carpet is worst. From the point of view of the end use, the carpet with wool and PP piles may be preferred where heavier, massive and stationary goods are used, due to the better resilience capability against static loading.

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Patyk & Korliński17 investigated pile properties of fur knittings during the process of compression. Fur knitted fabric can be presented by a three-layer geometrical model as shown in Figure 21.

Fig. 21: The layer model of fur products with the graph of compression the fur product. Layer 1: This layer is spread from thickness g’ to thickness g0 (where g’ is the greatest height of single fibres(hairs), and the free thickness g0 is determined by the experimental fur height at the pressure value =0); Layer 2: This is the real layer of the fibrous pile spread from thickness g0 to thickness gd (where gd is the thickness of the dermis). Layer 3: This layer of thickness gd consists of the dermis or of the knitting which joins the fibres. It was obseved that the apparent density has fundamental importance for the resistance of heat- and air-flow. Higher elasticity E and lower permanent deformation Dp observed for the lowest densities in the groups of both knitted and natural furs. Apart from the features mentioned above, it should be noted that the values of E and Dp are similar for natural and knitted furs, despite the aerial masses of knitted furs being 2-3 times lower than of the natural furs. 6.4 DIMENSIONAL STABILITY

The towels (woven or knitted fabrics) have almost similar physical properties apart from border, short pile distance, & strength. In addition to this, they should also for end use have such properties as hydrophility, softness and dimensional variation8,19,20. Dimensional stability tests carried out according to the AATCC 135/150 method. The terry fabric sample dimensions were measured before washing, and then after three successive washings. The lengthwise and widthwise dimension changes were calculated as percentages20. In general, the dimensional variation or size change of towel sample may be in the form of shrinkage or extension, according to ASTM D5433-00, the acceptable limits of weft and warp side for towels are 5% and 10% respectively It was observed the contractions after washing changed between 5.0% and 11.0% depending on the terry fabric construction. The pile length did not have any effect on contractions either during weaving or after washing. In addition to this the dimensional

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change in warp side was measured to be higher than the variation in the weft side and increasing the arial density decreases the dimensional variation of towels8,20. In carpet, a secondary backing layer is laminated to add dimensional stability to the finished carpet. Jute backing has a good dimensional stability. Other materials like polypropylene, polyester non-woven can be used as backing material4. Anand and Lawton21,22 studied pile-loop knit fabric and presented several empirical models to predict dimensional properties. They reported that the dimensional parameters of pile knit fabrics are largely controlled by the stitch length in the ground structure and state of relaxation. After static soak plus tumble-drying treatment, single-jersey pile knit fabrics constructed from flat continuous-filament polyamide-fibre ground and 100% cotton pile yarns, experience a substantial area consolidation. The type of pile yarn influences the dry-relaxed dimension but has a little effect on the dimensions of the fully-relaxed fabrics. It has also been seen that ground loops are much tighter than the pile loops. By another experimental work23, it has been observed that presence of lyocell in cotton pile yarn increases lengthwise shrinkage & widthwise extension of pile loop knit fabric. This is due to the higher swelling properties of lyocell. Cut-pile fabric shows more dimensional changes than pile-loop fabric because of free movement of cut piles. 6.5 BENDING RIGIDITY, SOFTNESS AND LUSTER:

Softness is another property required for terry pile fabric whereas luster is concerned with cut pile fabrics. The degree of softness should be as high as possible, because of contact with skin during daily use. TS 1409(‘Stiffness Determination of Woven Textiles’) has been taken as a primary test method to determine the softness degree of samples. According to this procedure, the greater the bending resistance, the lower softness degree of the towel concerned was assigned19. Type of softener, coloration method, construction of weaving etc. significantly affects the bending resistance. This effect was very pronounced for the velvet towels, softness degree of which was found to be better than that of the un-cut pile towels. The results obtained showed that the bending resistance increases as well as softness of towels decreased with the increase in aerial density and pile height. Since the pile height of velvet towels are shorter than that of the un-cut pile towel, fabric thickness in this case becomes less than that of the others; this is expected to be responsible for the lower resistance to bending than that of the un-cut pile towels. High luster continues to be one of the most important requirements of a successful cut-pile fabric. One of the most satisfactory ways to characterize the luster of pile fabrics is by goniophotometry24. The higher level and narrowness of reflectance peak related to uniformity of pile lay, straightness of fibres and basic properties of fibre. It has been observed that high-peak directional reflectance (high luster) when pile is brushed down and low directional reflectance when pile is brushed down.

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6.6 NOISE ABSORPTION & FILTRATION:

Textile materials absorb the sound energy, then convert or attenuate it into some other form of energy, usually heat. The use of carpets can control noise in a number of ways:

• Sound absorption. • Sound deadening. • Minimizing the transmission of noise through floors into other rooms.

The absorption ability is expressed by noise absorption coefficient (NAC) or noise reduction coefficient (NRC). NAC is the amount of energy absorbed on striking the surface. The noise reducing power depends on many factors e.g. carpet construction, pile height, pile density etc. As the weight and thickness of a carpet increases, its noise reducing power also increases. Cut pile carpets are generally more effective at absorbing airborne sound than loop pile carpets; because their surface is more open. The use of underlay/backing will increase the absorption coefficient. Sound absorption is reduced if the carpet backing is too impermeable, as it will reflect sound back into the room. The more permeable the carpet backing, the more sound energy can penetrate into the underlay and the higher the resulting NRC. The fiber content of the non-woven backing has little effect on the NAC. A cotton backing is slightly better than an acrylic backing, especially for one layer in the range 500-1000 Hz25,26.

Fig.: Noise reduction effects of carpets & underlay

The average value (NRC) does show an increasing trend with increasing pile height. For a given yarn count and pile height, increasing pile density results in an increase in NAC regardless of fiber type and construction. Because of the energy dissipated due to the friction between the vibrating air molecules and the pile of the carpet increases with an increasing area of contact between the piles and the air phases27. Nishimura, Goto and Kobayashi28 investigated the effect of pile fabric’s parameters on reducing aerodynamic noise. They observed that the noise reducing mechanism of pile fabrics is supposed that it makes the shear layer gentle and the maximum turbulent region far away and that the flow resistance attenuates vortex motion gently and reduces acceleration of vortices. The flow resistance of pile-fabrics is an important parameter to reduce aerodynamic noise. Fiber length and filling rate of piles are also important parameters. At least 3mm in protruding length of fiber is enough to reduce aerodynamic noise. Fiber diameter and stiffness is not so important. Filtration is another important property mainly applicable for knitted pile fabrics. Unlike conventional woven and needled textiles, seamless circular knit fabric consisting "loop

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pile" surface can be used as filter. The thickness and fiber density of a circular knit fabric provides a high permeability, reducing pressure drop conditions, with excellent filtration efficiencies of 99.5 to 99.99%. The physical movement of the "loop pile" surface on the cleaning cycle easily removes heavy dust formations while preventing blinding or lugging of the fabric29,30. 7. APPLICATIONS Variety wise uses of pile fabrics are given below:

Woven Pile Fabrics:

• Velveteen: Dress material, home furnishing.

• Weft plushes: Upholstery cloths.

• Corduroy: Dress materials, upholstery etc.

• Terry towel: Bath towel, bath robe, hand towel, kitchen towel, face towel. Mixed

color terry fabrics are used for fancy toweling, beach wear, mats etc.

• Warp pile: Loop pile fabrics are used for upholstery. Cut pile fabrics for apparel

wear, curtaining and upholstery. Carpet are for floor covering, furnishing, wall

hanging.

Knitted Pile Fabric:

• Plushes structure: Knitted pile fabric used for terry towel, sportswear, socks,

• Sliver knit: fun fur, linings, gloves, cushions, industrial polishers, and paint roller.

• Velvet knit: apparel and furnishing

• Cut pile knit: fur & skin fabrics, upholstery, coat lining, floor covering and

carpeting.

Apart from these pile fabric are also used for artificial turf, filtration, thermal insulation,

noise reduction in aerodynamic etc.

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8. SUMMARY: Pile fabrics are having a large number of threads projecting almost vertically from the

ground of the cloth. Pile fabrics are produced in great variety, some of simple

structure and others involving intricate patterns and complicated interlacing of the

various series of yarns. Pile fabrics are divided mainly in two groups: warp pile and

weft pile. To produce pile structure, always two series of warp with one series of weft

or two series of weft with one series of warp are required. Pile may be cut or in loop

form. Other methods can be used to produce pile effect on fabric surface e.g. sliver

knitting, using chenille yarn in weft, tufting etc. Nowadays terry towels are mostly

produced in air jet or rapier loom with special mechanism. Carpet pile structures can be

manufactured by face-to-face method, tufting method, axminster weaving. Knitted pile

fabrics are produced on sinker wheel m/c, sinker top latch needle m/c, double bed

Raschels m/c, sliver knit m/c. Mostly cotton, polyester, nylon, wool, acrylic, mohair,

polypropylene yarns are used according to end uses for pile fabric. Pile fabric has some

important properties like compressibility, absorbency, noise absorption, filtration etc. pile

height, pile density, type of pile (i.e. cut or loop), GSM etc. influences properties of

fabric. Absorbency increases with increase in pile height whereas it decreases with

increase in thread density. Cut pile single yarn shows less absorbency than loop pile plied

yarn. Ground structure does not influence frictional properties of pile fabrics.

Compressibility of carpet depends on diameter of yarn used for pile. Compressibility and

compressive elasticity modulus of cut-pile carpets are greater than those of loop-pile

carpets. The bending resistance increases as well as softness of towels decreased with the

increase in aerial density and pile height. The noise reducing power increases with

increase in weight and thickness of a carpet. Cut pile carpets are generally more effective

at absorbing airborne sound than loop pile carpets. in case of knitted pile fabric, type,

linear density, and stitch length of the yarn used in pile structure would influence some

fabric characteristics such as fabric tightness, area density, air-permeability etc. Non-

woven pile structure can be manufactured by adhesion fixing of pile yarn with backing

material. Pile fabrics are widely used for bath towel, upholstery, home furnishing, dress

material, floor covering, artificial turf, filtration etc.

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9. REFERENCES:

1. Grosicki, Z. J., Watson’s Advance Textile Design: Compound Woven Structures

2. Staff, I. C. S., Advance Textile Designing

3. Spencer, D. J., Knitting Technology

4. Crawshaw, G. H., The Manufacture of Wool Carpets, Manual of Textile Technology, The Textile Institute

5. Powell, N.B and Yilmaz, N.D., ‘The Technology of Terry towel production’ Journal of Textile and Apparel, Management and Technology, summer 2005, Vol-1, Issue-4.

6. Nishimatsu and Sawaki, “Study on Pile Fabrics Part 2: Structures of Pile Fabrics” J. Text. Mach. Soc., Japan, vol-30, n-1, p-13-17 (1982).

7. Karahan, M. and Eren R., ‘Experimental Investigation of the Effect of Fabric Parameters on Static Water Absorption in Terry Fabrics’ Fibres & Textiles in Eastern Europe April / June, Vol. 14, No. 2 (56), p: 59-63, 2006.

8. Koç E., Zervent B., ‘An Experimental Approach on the Performance of Towels Part II. Degree of Hydrophility and Dimensional Variation’, Fibres & Textiles in Eastern Europe, April-June, vol. 14, No. 2(56), p: 64-70, 2006

9. Kim, S. J., Kim, S. H., ‘Water absorption and mechanical properties of pile-knit fabrics based on conjugate N/P microfibers’ Textile Research Journal, June 2003, vol-73, pp. 489 - 495

10. Nishimatsu and Sawaki; ‘Study on Pile Fabrics Part 3: Frictional Properties of Pile Fabrics’ J. Text. Mach. Soc., Japan, vol-30, n-3, p67-71(1984).

11. Nishimatsu and Sawaki; ‘Study on Pile Fabrics Part 4: Investigation of Factors Affecting Frictional Properties of Pile Fabrics’ J. Text. Mach. Soc., Japan, vol-30, n-4, p100-106(1984).

12. Ikuko, H. and Toshihiro G., ‘Slipperiness and Coefficient of friction on the Carpets’, Journal of Textile Engineering, vol-47, n-2, p53-58(2001).

13. Frontczak-Wasiak I., Snycerski M., ‘Use Properties of Terry Woven Fabrics’ Fibres & Textiles in Eastern Europe, January/March, Vol. 12, No.1 (45), 2004.

14. Nishimatsu and Sawaki; ‘Study on Pile Fabrics Part 1: Hand of Pile Fabrics’ Journal of Text. Mach. Soc., Japan, vol-30, n-3, p67-71(1984).

15. Kimura and Kawabata, ‘Improvement of Compressive Deformation Theory of Carpets and Its Application to Carpet Woven with Compressible Yarns’, Journal of Text. Mach. Soc., Japan, vol-18, n-5/6, p141-148(1972).

16. Erdem Koc, E., Celik, N., and Teki, M., ‘An Experimental Study on Thickness Loss of Wilton-Type Carpets Produced with Different Pile Materials after Prolonged Heavy Static Loading. Part-I: Characteristic Parameters and Carpet Behavior’ Fibres & Textiles in Eastern, Oct/Dec, Vol. 13, No. (52), p: 56-62, 2005

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17. Patyk, B. and Korliński, W., ‘Preliminary Analysis of the Pile Properties of Fur Knitting’s During the Process of Compression’, Fibres & Textiles in Eastern, Oct/Dec, p: 49-51, 2002

18. Horino, T. and Shimonishi, S., ‘Viscoelastic Behavior of Carpets Part 2: Experimental Analysis of Factors Influencing the Viscoelastic Behavior’ Journal of Text. Mach. Soc., Japan, vol-18, p21-29(1972).

19. Koç E., Zervent B., ‘An Experimental Approach on the Performance of Towels Part I. Bending Resistance or Softness Analysis’ , Fibres & Textiles in Eastern Europe, Jan-March, vol. 14, No. 1, p: 39-46, 2006

20. Karahan, M., Eren, R. and Alpay, H. R., ‘An Investigation into the Parameters of Terry Fabrics Regarding the Production’, Fibres & Textiles in Eastern Europe, April/June, vol. 13, No. 2(50), p: 20-25, 2005

21. Anand, S.C., and Lawton, P.J., ‘The Dimensional Properties of Single-jersey Loop-Pile Fabrics, Part I: Studies of Fabrics with Flat Continuous-filament Yarns Used in the Ground Structure’, Journal of Textile Institute, No.-5, p.326-348, 1987

22. Anand, S.C., and Lawton, P.J., ‘The Dimensional Properties of Single-jersey Loop-Pile Fabrics, Part II: Studies of Fabrics with Textured Continuous-filament Yarns Used in the Ground Structure’, Journal of Textile Institute, No.-5, p.349-356, 1987

23. Uçar, N. and Karakas, H.C., ‘Effect of Lyocell Blend Yarn and Pile Type on the Properties of Pile Loop Knit Fabrics’ Textile Research Journal, vol. 75(4) pp. 352 - 356. 2005

24. Johnson, L.D., ‘The Relationship of Directional Reflectance Properties to Acrylic Pile Fabric and Fiber Characteristics’ Textile Research Journal, n-7, vol. 40: pp. 650 – 655, 1970

25. ‘Electrostatic and noise absorption properties’, Commonwealth Scientific and Industrial Research Organization (CSIRO) Publication, Oct 2006

26. Shoshani, Y.Z., Effect of Non-woven Backings on the Noise Absorption Capacity of Tufted Carpets’, Textile Research Jounal, N-8, vol. 60, pp. 452 – 456, 1990

27. Y.Z. Shoshani, Y.Z. and M.A. Wilding, M.A, ‘Effect of Pile Parameters on the Noise Absorption Capacity of Tufted Carpets’ Textile Research Journal, n-12 vol. 61: pp. 736 – 742, 1991

28. Nishimura , M., Goto, T. and Kobayashi, K., ‘Effect of Several Kinds of Pile-Fabrics on Reducing Aerodynamic Noise’, 11th AIAA/CEAS Aero-acoustics Conference, May 2005, California

29. Anand, S.C., and Lawton, P.J., ‘The Development of Knitted Structure for Filtration’, Journal of Textile Institute, p.326-348, 1987

30. www.apelfilters.com/air%20filter%20data/Beane%20Style%20Air%20Filters.html

31. Sliver Knitting Report- Part II, Knitting International, November, 2004