I ndian Journal of Fibre & Texti le Research Vol. 3 1 , June 2006, pp. 3 1 3-3 1 9

Effect of substituting modified polyester for cotton in ring-spun polyester/cotton blended yarn fabrics

Sudipta S Mahish", S K Punj & Bhawna Banwari

The Technological illstitute of Textile & Sciences, Bhiwani , 1 27 02 1 , I ndia

Received / / Ouober 2004; revised received 2 7 }a/luwy 2005; accepted 25 May 2005

The effect of using a tetra channel cross-section polyester fibre with and without microsl its on its surface in place of cotton in a polyester/colton (P/C) blended yarn fabric has been studied. The results have been compared wi th PIC blended yarn fabrics. It is observed that the modified cross-section polyester generally shows better performance with respect to drapabi l i ty, crease recovery, bending rigidity, air permeabi l ity, thermal i nsulation and wicking behaviour as compared to PIC blended fabrics i n temperate weather.

Keywords: Coolplus, Drape, Polyester/colton blend, Thermal insulation, Wieking IPC Code: Int. Cl 8 00 1 0 1 1 100, GO I N33/36

1 Introduction Polyester possesses several desirable properties

such as high strength, attractive handle, dimensional stabi lity, easy-care properties, wash and wear, wrinkle-free characteristics and suitabi l i ty for blending with other types of fibres. However, i t has certain undesirable qual i ties such as Jack of hydrophil ic i ty, generation and accumulation of static charges, and oleophi l ic i ty . Polyester fabrics are, therefore, not as comfortable as natural fibre fabrics. Therefore, regular c ircular cross-section polyester fibres became less popu lar in the 1 980s, when the fashion trend was shifted from femin ine to sporty and casual, and natural fibres became more favoured.

From this point of view, various attempts have been made to i mpart comfort-related properties to synthetic fibres. Out of these different efforts of i mprovement, the modification of fibre cross-section is a major outcome. The characteristics of these new fibre fabrics are found to be very distinct from those of conventional circular cross-section fibre fabrics. Coolplus ™ is one such type of new functional polyester fibres, having '+' cross-section, developed by a Chinese Company (Chung Shing Texti le Co. Ltd, Taiwan). It is made from regular polyester along with special polymer (around 20%) to create four channels on fibre surface for good water transport; microslits can be created after weight reduction of these fibres by alkali treatment.

"To whom all the correspondence should be addressed. E-mail: smahish@yahoo.com

It appli es capil lary action result ing from the four microsl i ts on the fibre surface to rapidly absorb the sweat from the skin surface and diffuse i t to larger area through several actions, such as wicking, diffusing and transporting to make the fabric dry faster. According to its manufacturer, the moisture diffusivity of Coolplus ™ is h igher than that of cotton by 1 2-74% and dry ing rate by 1 1 -47%. The capi l lary action endows the fabric with good characteristics of easy wash, shrink proof, wrinkle res istance, etc.

2 Materials and Methods Specifi cati ons of the fibres used for the sample

preparation are given i n Table I .

2.1 Preparation of Yarn Samples

Fibres were blended through manual blending i n the required quantity and then processed once through MMC card and twice through a Laxmi Rieter drawframe to produce a set of drawn sl ivers of the same l inear densi ty . The set of drawn slivers was passed through s implex to produce roving which was than ring spun into yarn of 40s count. The l ist of yarn

Table I -Raw materials used for sample preparation

Fibre Fibre length Fibre Fibre tenacity mm fineness gpd

Cool plus polyester 38 1 .4 den 4.0 Regular polyester 38 1 .4 den 5.0 Cotton 27.4 4.3/lg/in 3 .5

3 1 4 INDIAN 1 . FIBRE TEXT. RES . , JUNE 2006

samples produced and the corresponding variables are given i n Table 2.

2.2 Preparation of Fabric Samples

Fabric samples were prepared on a loom using the constructional parameters: weave, plain; endslinch, 60; pickslinch, 54; and end use, shirting.

2.3 Fabric After Treatment

For the study, the half of the fabric was kept untreated and remaining was treated with alkali to create microslits on the surface of Cool pi us ™ fibre to enhance comfort properties under the conditions : alkali concentration, 6 gllitre; temperature, 1 I ODC; and t ime, 30 min .

2.4 Test Procedure

The fabric samples were exposed to a standard atmosphere of 65% ± 2% RH and 20DC ± 2DC temperature for 24 h before the final measurements.

2.4.1 Drapability

Samples were tested for drapabil i ty on 'BTRA Drape Meter' according to Bri t ish Standard BS 5058-1 973 . The sample of 10 i nch d iameter was mounted on the machine and supported by another supporting disc of 5 i nch. The projection of the disc equal to the sample area was drawn on the plain paper. Then, the weight of the paper of the projected area of specimen disc and the weight of the paper of the projected area of the drape material were measured to obtain drape coefficient using the following relationship:

Drape coefficient (F), % = [( Ws-Ad)/( Wd-Ad)] X 1 00

where Ws i s the weight of paper covered with projection 'of draped specimen i n gram; Wd, the weight of the paper of the area of bigger disc in gram; and Ad, the weight of the paper equal to the area of smaller disc in gram.

2.4.2 Crease Recovery

Crease recovery angle was measured using Shirley Crease Recovery Tester according to Brit ish Standard BS 3086- 1 972. Following parameters were used:

Sample size Load used Creasing time Recovery t ime

2.4.3 Handle Properties

40 x I S mm 2 1b I min 1 min

This test was performed on FAST (Fabric Assurance by S imple Testing) i nstrument. FAST is a

Table 2-Yarn samples and thei r variables

Yarn Fibre Blend ratio Yarn count ref. no.

S , Pol yester/cotton 30/70 2/40s

S2 Polyester/cotton 40/60 2/40s

S3 Polyester/cotton 50/50 2/40s

S4 Polycster/cotton 60/40 2/40s

S, Polyester/cotton 70/30 2/40s

S6 Polyester/Coolplus 30/70 2/40s

S7 Polyester/Cool plus 40/60 2/40s

Sg Polyester/Cool plus 50/50 2/40s

S9 Polyester/Cool plus 60/40 2/40s

S IO Polyester/Coolplus 70/30 2/40s

set of instruments and test methods developed by CSIRO Divis ion of Wool Technology (Australi a) for measuring the properties of fabrics which affect the tailoring performance of the fabrics and the appearance of the garment i n wear. The system consists of three s imple instruments and a test method as given below:

(i) FAST-} Compressioll Meter: I t measures fabric thickness at two predetermined loads of 2 and 1 00 gf/cm 2 .

( i i ) FAST-2 Belldillg Meter: It measures the bending length of the fabric . From th is measurement, the bending rigidity of the fabric may also be calculated. The instrument uses the canti lever bending pri nciple. In FAST-2, the edge of the fabrics i s detected using a photocel l .

( i i i ) FAST-3 Extensioll Meter: It operates on a s imple lever principle by removing weights from the counter balancing beam, the extensibi l i ty of the fabric can be measured at three different loads of 5 , 20 and 1 00 gf/cm respect ively.

( iv) FAST-4 DimellsiollaL StabiLity Test: The final component of FAST is a test method that measures the dimensional stabi l i ty of the fabric. The method involves measurement of the fabric dimensions before and after a wet relaxation process.

Different properties measured by the FAST system are mechanical properti es (FAST- I , 2 and 3) , bending rigidity (FAST-2), shear rigidity (FAST-3) and thickness (FAST- I ) .

2.4.4 Air Permeability

Air permeability tests were conducted on Prolific Air Permeabil ity Tester according to ASTM standard D 737-96. Ten speci mens of 38 .3 cm2 area each were used. The air permeabi l i ty of each specimen can be obtained using the following equation :

MAHISH el al.: POLYESTER/COTTON BLENDED YARN FABRICS 3 1 5

Air permeabi l ity Cm3/m2/min) =kxRotameter reading =0.0 I 667xRotameter reading

where k is the conversion factor.

2.4.5 Thermal Insulation

Thermal conductivity of the fabric i s its insulation power, i .e. amount of heat loss it can resist. Clo is a unit of insulation and i s the amount of i nsulation necessary to maintain comfort and a mean skin temperature of 92°F in a room at 70°F with air metabol ism of 50 calories/ m2 h.

Thermal insulation value was measured on Sasmira Thermal Conductiv i ty Tester, which conform to the standards of Niven' s hot plate. The test results for the thermal insulation values are subject to an overall error of ±3% to ±3 .5%, depending on the accuracy of determination of temperature and variation in thermal conductivity of standard with mean temperature of the disc. As a consequence the r·�peatabil i ty of the clo values has been found to be approximately 85%. The tolerance values of the clo are 0.4 and 1 0 with materials of thickness not exceeding 50 mm.

2.4.6 Wickil/g Behaviour

Wicking behaviour was studied according to AATCC 79 (Strip Test) using the specimen size of 9x l inch and treatment t ime of 30 min .

3 Results and Discussion

3.1 Fabric Thickness

Fig. 1 shows that as the polyester content i ncreases in PIC (polyester/cotton) blended fabrics, there i s decrease in thickness, which i s possibly due to more fi neness of regular polyester fibre. Secondly, the less hairiness of polyester-rich yarns also contributes to lower thickness. In P/CP (polyester/coolplus) blend, as the polyester content increases there is decrease in thickness. This may be due to more bulky nature of Coolplus ™ fibre as compared to regular polyester due to i ts tetra channel cross-section.

If PIC and P/CP blends are compared, the thickness of Cool plus blended fabrics is found to be less. This may be due to less hairiness of Cool plus blended yarns as compared to cotton b lended yarns. Thi s may be attributed to the fibre length variation and shorter staple length in cotton as compared to Cool plus fibres.

3.2 Drapability

Table 3 shows that the drape coefficient decreases with the increase in polyester content, which is due to

0.55 (a)

0.50

P/CP 0.45

E � 0.40 '" ] 0.55 r----------------.S! --________ 'P·I\IC (b) -5 ----. u � 0 .5 0 �

0 .40 �, ----,r----------�----.J 2 0 3 0 40 s o 60 70 80

Polyester content, %

Fig. I-Effect of blend ratio and tibre type on thickness of (a) untreated and (b) alkali-treated fabrics

Table 3-Effect of blend composition and fibre type on drape coefficient

Fibre type B lend ratio DraQe coefficient Treated Untreated

Polyester/cotton 30170 0.465 0.470

Pol yester/cotton 40/60 0.454 0.460

Polyester/cotton 50/50 0.452 0.458

Polyester/cotton 60/40 0.436 0.437

Polyester/cotton 70/30 0.4 1 8 0.422

Polyester/Coolplus 30170 0.420 0.43 1

Polyester/Coolplus 40/60 0.4 1 3 0.425

Polyester/Cool plus 50/50 0.407 0.408

Polyester/Coolplus 60/40 0.38 1 0.39 1

Polyester/Cool plus 70/30 0.372 0.38 1

the fact that the bending length i s found to decrease with the increase in polyester content. Lower bending length i s i ndicative of lower fabric stiffness, and as the proportion of polyester i n the blend i ncreases, the fabric requires less energy to bend and is flexible. Therefore, the decrease in drape coefficient with the i ncrease in polyester content i s a d irect reflection of decreased bending stiffness for fabrics that have high polyester content. I

Since drape coefficient i s i nversely proportional to drapabi l i ty , the drapabil i ty i ncreases wi th an increase in polyester content.

If PIC and P/CP blended yarn fabrics are compared, it is observed that the blends having Cool plus fibre have less drape coeffic ient, i .e . better drapabi l ity. as

3 1 6 I N D I A N J. FI 1 3RE TEXT. RES .. J U N E 2006

compared to blends hav ing cotton fibre. This i s due to lesser flexural rigidi ty of Cool plus blended yarns and less bending length of Cool plus fibre fabrics .

3.3 Crease Recovery Table 4 <.hows that with the i ncrease i n polyester

COl i tent i n PIC blend there i s an i ncrease in crease recovery angle. Such t rends have been observed in both the cases when compared wi th in the untreated and al kal i -treated fabrics separately. Thus. it may be said that the trend is i rrespecti ve of the treatment g iven to the fabric. The observed trend i s due to the vary i ng i nherent characteris t ics of these fibres . From the statement gi ven by Hamburger ('{ (I/?, polyester has h igh elastic recovery properties and hence it may be �;; t i d that the i ncrease in fabric crease recovery with the i l lcrease i , ; polyester fibres i n the PIC blend i s only due to the substi tut ion of better elastic recovery fi bres . The crease recovcry of P/CP bknrJed fabric for varIOUS blend composi t ions does not change

Table 4-EllL:et of blend composit ion and fi bre type on crease recovery of fabric

Fi bre Iype Blend Crease recovery angle. deg rat i o Unlreated A l ka l i treated

Warp We ft Warp Weft

Polyester/eotlon 30170 l 09 g I OlJ . 8 1 02.lJ 1 06.8

P()lyesler/cotton 40/60 1 2 1 .9 1 22 . 7 1 08.8 1 07 . 1

l 'olyesler/c(HIOn 50/50 1 23 . 1 1 2lJ.4 1 1 6 . 1 1 1 6.6

I'olye,tt:r/cotlon 60/40 1 25 . 8 1 34.4 1 1 8 .7 1 27 .8

Polyeste r/cott(Hl 70/30 1 2 7.6 1 36.4 1 24.6 1 32.0

Polyestcr/Coolp l lis 30170 1 24.3 1 3 1 .2 1 29.3 1 33,4

Pol yester/Cool pi us 40/60 1 30.8 1 36.6 1 26.5 1 30.5

Polyester/Coolplus 50/50 1 27.4 1 29.7 1 27 . 6 1 3 1 .8

Pol yester/Cool pi us 60/40 1 29.2 1 33,X 1 28.5 1 34.3

Polyester/Coolplus 70/30 1 30.7 1 34.4 1 32.4 1 35 .6

sign i ficantly . This may be due to the s im i lar elastic recovery properties of both the fibres.

Furthermore, fabrics having Coolplus fibre have better crease recovery properties as compared to those having cotton . Thi s may be due to better elastic recovery properties of Cool plus fibre. If crease recovery properties are compared before and after treatment al most s im i lar results are obtai ned . . 1

3.4 Gending Rigidity

Bending r ig id i ty of a fabric i s the mcasure of the couple requ i red to bend the fabric and is closely related to the fabric th ickness and the properties or const i tuent yarns. The tolerance values for bending rigid i ty measured by th is i nstrument l i e i n the range of 5 - 1 4 flN .m . The ma in problems occur i n fabrics that have lower values than 5flN . Il1, g iV Ing low formabi l i ty . But it should be on the lower s ide for good handle property, wrinkle res i stance and crease resistance in apparels . When PIC and P/CP blends are compared, the st iffness values for Cool plus fi bre fabrics are, i n general, lower than those for cotton (Table 5 ) . Bending r igidi ty of a fabric strongly depends on yarn diameter, fibre cross-sectional shape and fibre flexural r igidi ty . Due to thl': i rregular 3-D convoluted structure of cotton fibres, the cotton-rich yarns exhibi t larger diameter, providing h igher bending rigidity to the fabrics . On the contrary, Cool pI us fibres, having a regu lar terta channel cross­sect ional shape, provide less tlexural r igidity to the yarns; more c i rcu larity of the fibre cross-sect ion provides more rigidity to the yarns due to more compactness. Also, the fibre tlexural r igidity supports th is finding, which was found to be in the order of: cotton>polyester>Coolplus (concluded from the fabric bendi ng rigidity data as: cotton fabric,

Table 5-EITect or blend composi t ion and fibre type on bending rigi d i ty and shear r ig id i ty of fabric

Fibre type Blend rati o Bend i ng rigidi t�. pN . m Shear rigid i ty, N/m

U nlreated A l ka l i treated U nlreated A l k a l i treated

Warp Weft Warp Weft

Polyester!cottoll 30170 8.9 5.7 9.3 6. 1 40.3 SO.O Polyester/vllwll 40/60 7 .9 5.6 7.6 5.6 37.0 46.4

Polyesler!cottoll 50/50 7.0 5.5 7 .4 5.4 30.0 48.3

Polyester/cotton 60/40 6.9 5.4 7 . 6 5 . 6 37.8 47.2

Polyester/eolton 70/30 6.0 5 .4 7 . 1 5 .3 42.4 46.4

Polyester/Coolplus 30170 6.5 4 . 7 6.5 4.7 3 1 .0 33.7

Polyester/Coolplus 40/60 6.8 4.8 7 . 1 4.5 3 1 .5 36.9

Polyester/Coolplus 50/50 6.7 4.8 8.0 4.6 30.5 33.0

Polyester/Coolplus 60/40 6.6 4.6 7.5 4.6 34.0 36.7

Polyester/Coolplus 70/30 5 . 8 4.9 7 .0 4.7 38.6 34.0

M A H I S H 1'/ al. : POL YESTER/COTTON B LENDED YARN FAB RICS 3 1 7

9 .8/7 .8� N.m; polyester fabric, 7 .017 .8�N.m; and Coolplus fabric, 5 .4/4.7� N.m) . The cotton-rich fabrics additi onally, being more thick than the Coolplus-rich fabrics, provides more rigidity.

3.5 Shear Rigidity

Fabric shear rigidity along wi th i ts bending r igidity largely determines the abi l i ty of a fabric to drape. The tolerance values of shear r igidi ty measured by this method l ie i n the range of 30-80N/m. Below 30N/m, the fabric deforms so eas i ly that it may give problems in handl ing, lay ing-up and sewing. I f it is h igher than 80N/m, the fabric wi l l be d ifficult to overfeed, mould and create fu l l ness over the sleeve head. But the shear rigidity of a fabric should be on the lower side for beller formabi l i ty property . A l though no clear trend i s available regarding relationship of sheari ng deformation and blend proportion of the selected samples as shown in Table 5, a c lose observation may enl ighten us about the fact l)'at the Cool plus fibre fabrics (both before and after alkal i treatment) show less shear rigidi ty than cotton fibre fabrics. Thi s i s possibly due t o more pl iable and flexible nature of Coolplus fibres (due to regu lar non-c i rcu lar cross­section) ,!S compared to cotton fibres. This is i n agreement w i t h the findi ngs of Tarafder e f al.4 that more pl iable and flex ible fibres show less shear rigidity .

3.6 A i r Permeabil ity

Fig. 2 shows an increase i n a l l' permeabi l i ty of fabric with an i ncrease in polyester content in both PIC and P/CP blends. This is possibly due to the decrease in thickness of fabric wi th the i ncrease i n polyester percentage. I t has been observed that Cool plus fibre fabrics have more air permeab i l i ty than cotton fibre fabrics . Fabric porosity, which is defi ned as pore al'ea per uni t fabric area, and thickness are correlated to the diameter and length of yarn in a un i t area of the fabric . The yarn diameter, in turn, i s determined by the yarn l inear dens i ty and t he packing factor of fibres. Because of the i rregular three­dimensional crimps, cotton fibres produce a less dense and consequently larger d iameter yarns as the amount of cotton fibre i ncreases i n the yarn for the same yarn l i near densi ty . Thi s accounts for lesser in ter-yarn space and consequent ly less porosi ty in the cotton-rich fabrics. But the Coolplus fibres, hav ing regular terta channel cross-sectional shape, fac i l i tate smooth flow of air through the channels This may also be attributed to the l ess thickness of Cool plus fibre fabrics, thereby offeri ng less res is tance to

1 80 r-' 1 60 (a) __ P/C-

P----

---------�

1 40 120 1 00 I c

j E J �E � 80

:.c 1 80 I-�-'-� , -------------� 160 J' P/� "<

::: j 80 1

(b)

PIC / -----_, --.�

20 30 40 50 60 70 80 Polyester content, %

Fig. 2-Ellcct of fibre type and blend ratio on a ir permeabi l ity or (a) untreated and (b) alkal i -treated fabrics

passage of air, which is due to the decrease in yarn diameter because of the lower density of Cool pI us fibre.

On comparing the effect of treatment, it i s observed that there is an i ncrease i n air permeabi l i ty in P/CP blend after treatment, which is due to the removal of part of surface from the fibres and assoc iated weight loss; hence more air can pass through the fabric very easi ly and also the microsl i ts created on the fibre surface of Cool plus fibre fac i l i tate passage of air. Dave et al.3 reported that the decrease i n diameter of fi laments or fibres i n the process of alkal ine hydrolysis i ncreases the inter-fibre and inter-yarn spaces in polyester fabric . This resul ts in a gradual i ncrease i n porosity and consequently an i ncrease i n a i r permeab i l i ty o f the fabrics. B u t i f the comparison of PIC blend is studied before and after treatment. it i s evident that the a i r permeab i l i ty reduces after treatment , which may be due to the blocking of the pores as a result of swel l ing and shrinkage of cotton fibres.

3.7 Thermal Insulation

From Fig. 3 it is evident that as the polyester percentage i ncreases in PIC and P/CP blends, thermal i nsulat ion values decrease i n untreated fabrics. Thi s is i n accordance w i th the statement given by U kponmwan5 and B acker6 that 'the thicker a fabric for a given construction , the greater i s i ts heat i nsulat ion value' . S ince the thickness of fabric i s

3 1 8 INDIAN 1. FIBRE TEXT. RES., JUNE 2006

0.6

0.55

0.5

0.45 ., :J 0.4 OJ t > 0 0.6 U

I 0.55 I 0.5

0.45

0.4 20

=.� PICP I .�----- - J ··-�----T

. ---�

30 . . �---"-T�

40 50 60 Polyester content, %

PIC I

P/CP

70 80

Fig. 3-Effect of fibre type and blend ratio on thermal insulation of (a) untreated and (b) alkal i-treated fabrics

found to decrease with an increase i n polyester content, i ts thermal insulation value reduces. Also, i t i s observed from the results obtained for air permeabil i ty (Fig. 2) and hairiness (Table 6) that there is an i ncrease in air permeabil i ty and decrease in hairiness with the i ncrease i n polyester content. Both these factors also contribute for reduction of thermal insulation value with correspondi ng increase i n polyester content.

If PICP blends are observed before and after treatment, i t is found that with i ncreasing Coolplus content the thermal insulation value increases in both the cases. Thi s is mainly attributed to more air entrapment by the modified cross-section of the Cool plus fibres (as compared to the circular cross­section regular polyester). Also, both the component being polyester the trends are similar after alkal i ne hydrolysis. But reverse trends are also observed i n case of treated PIC blended fabrics; alkali treatment causes two opposing effects on the two components of the blend. The cotton component swells making the fabric more cOlupact, whereas the polyester component looses weight due to surface hydrolysis, i ncreasing effective gaps between yarns and cross-

. over points resulting i n more air entrapment inside the fabrics. Therefore, as the cotton component i ncreases in the blend the swelling factor predominates and vice-versa. Hence, with i ncreasing cotton component the thermal i nsulation reduces after alkal i treatment. Also, as discussed earlier the cotton-rich yarns are

Table 6-Effect of blend composition and fibre type on tenacity, U% and hairiness of yarns

Fibre type B lend Tenacity U% Hairi ness ratio g/tex (>3mm)

Polyester/cotton 30170 1 8.64 1 0.96 37 Polyester/cotton 40/60 20.96 1 1 .37 33 Polyester!cotton 50/50 22.8 1 1 .79 27 Polyester/conon 60/40 25.09 1 1 .06 1 6 Polyester/cotton 70/30 25. 1 4 10.2 1 1 2 Polyester/Coolplus 30170 23.5 1 0.56 25 Pol yester/Cool plus 40/60 25.57 · 1 0.63 I I Polyester/Coolplus 50/50 28.66 1 1 . 1 8 8 Polyester/Cool plus 60/40 29.09 1 1 .0 1 6 Polyester/Cool plus 70/30 30.9 1 1 0.32 6

Table 7-Effect of blend composition and fibre type on wicking height of fabric

Fibre type B lend Wicking height, cm ratio Untreated Alkali treated

Warp Weft Warp Weft

Polyester/conon 30170 2.9 2.6 1 1 .7 1 0.7 Polyester/conon 40/60 4.0 4.0 t 1 .8 t 1 .0 Polyester/cotton 50/50 5.6 5.4 1 1 .9 1 1 .4 Polyester/cotton 60/40 5 .8 5 .5 1 2 .8 1 2.3 Pol yester!cotton 70/30 7.2 6.8 1 2.4 1 2 .5 Polyester/Cool plus 30170 6.5 6. 1 7.4 7.5 Polyester/Cool plus 40/60 9.0 7.0 9.7 9.6 Polyester/Coolplus 50/50 6.9 6.4 7.8 7.0 Polyester/Cootplus 60/40 6.6 6.3 7.7 7. 1 Polyester/Cool plus 70/30 6.2 6.2 7.6 7.6

more voluminous. Although the fabric porosity is less, the yarns themselves entrap lot of air, providing high thermal insulation to the fabric .

On comparison of PIC and PICP blends, i t i s observed that thermal insulation values are lower for Cool plus blended fabrics as compared to those for cotton blended fabrics. As d iscussed earlier, cotton fibres produce a less dense and thus a larger diameter yarn which produces a thicker (also due to more hairiness of cotton-rich yarns) and less porous fabric . Consequently, for the same fabric volume the occupied fibre volume wi l l be lesser for cotton fibre fabrics, facil i tating more air entrapment which results in more thermal i nsulation.

3.8 Wicking Behaviour

Table 7 shows that as the polyester content i ncreases in PIC blend there is an i ncrease in wicking height in both warp and weft directions which is due to better capi llary action in polyester fibre because of its smooth surface and greater surface tension. But i n

MAHISH et al. : POLYESTER/COTTON BLENDED YARN FABRICS 3 1 9

case of P/CP blend as polyester content i ncreases, the wicking height i ncreases upto 40% and then decreases with the further i ncrease i n polyester content. Wicking action of P/CP blend is effected by two factors, tetra channel cross-section of Cool plus fibre and greater surface tension of regular polyester fibre due to circulari ty. Wicking action of Coolplus yarns i s due to four channels present on thei r surface and that of regular circular polyester i s due to i ts greater surface tension. When Coolplus content increases from 30% to 60% i n P/CP blend, wicking height i ncreases because upto 60% terta channel effect i s predominant, but after that the reduced amount of regular polyester fibre reduces the wicking height of the yarn drastically due to effectively lower surface tension contribution.

4 Conclusions

4.1 Aesthetic properties l ike drapabi l i ty and crease recovery are found to be better for fabrics having Coolplus fibre when compared with cotton b lended fabrics.

4.2 Handle properties are better for Cool plus fibre fabrics, l ike bending rigidity ; shear rigidi ty i s lesser as compared to cotton-rich fabrics.

4.3 Coolplus fibre fabrics are more comfortable which is quite c lear from the results of air permeabil i ty and thermal i nsulat ion. Air permeabi l i ty i s higher and thermal i nsulation i s lower for Coolplus blended fabrics before alkal ine hydrolysis. This i ndicates that the Cool plus fibre fabrics can do well i n temperate environment. But after alkali treatment the

thermal insulation value of h ighly Coolplus-rich fabric exceeds that of cotton-rich fabrics .

4.4 I f another comfort-related property (wicking) is compared, i t i s found that P/CP blended fabrics show better wicking action i n untreated state. B ut when PIC and P/CP blends are alkali treated, trends are reversed and PIC blends show better w icking action. Thus, i t cannot be concluded that cotton blended fabrics provide more comfort when they are alkali treated, because according to Sule et aC there should be balance between wicking action and drying rate, otherwise perspiration of body i s transferred back accumulating around the skin which wil l create discomfort. Also, according to manufacturer' s claim, Coolplus has h igher moisture diffusivi ty and also synthetic fibres show better drying properti es as compared to cotton fibres.s Hence, in that case too, Cool plus blended fabrics are more comfortable.

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