Indian Journal of Fibre & Textile ResearchVol. 19, December 1994, pp. 251-255

Influence of cotton content and area density on the properties of cottonthermal-bonded nonwovens"

A N Desai, Kavita R Bhatnagar & N BalasubramanianThe Bombay Textile Research Association, L B S Marg, Ghatkopar (West), Bombay 400 086, India

Received 7 March 1994; revised received 13 June 1994; accepted 19 July 1994

Absorbency increases and strike through time decreases with increase in cotton content in cottonthermal-bonded nonwovens. In general, cotton shows wet back (rewet) properties similar to that ofpolypropylene. Tenacity increases with increase in binder fibre concentration but decreases with increasein area density. Bending length increases with binder fibre content and area density.

Keywords: Absorbency, Cotton, Nonwovens, Tensile strength, Thermal bonding, Wet back (rewet) properties

1 IntroductionOne of the major end use markets where the

nonwovens have established is in the area of healthcare, personal and hygiene goods. These are lightweight materials commonly made by chemical orthermal bonding systems. A sizeable portion ofapparel interlining market is served bythermal-bonded fabrics. The largestthermal-bonded carded staple nonwoven market inthe United States is coverstock for sanitary products 1.

In all such products where absorbency is ofparamount importance, cotton as a raw material canplay a fruitful role. Cotton fibre, because of itssuperior absorption characteristics and soft feel, iseminently suitable for hygienic and health careapplications, such as disposable diapers,coverstocks, wipes and also in interlinings. Theecofriendly character of cotton is of great importancein disposable items and in single use applications.Low micronaire and immature cottons, comber noilsand such fibres which pose problems in spinning canbe profitably employed for nonwovens. However,cotton has only a modest presence as yet in thenonwoven industry which is dominated by thesynthetics. Consumption of bleached cotton innonwovens was only around 60 mlb in 1991 in theUnited States", one of the largest markets fornonwovens.

In the Indian context, use of cotton in nonwovensholds immense scope for product diversification,value addition and increased export. Indepth studies

"Paper presented at the 49th All India Textile Conference held atCoimbatore on 16-17 December 1993.

in this area to arrive at optimum conditions will,therefore, be rewarding.

The nonwoven technology offers alternativesystems such as chemical bonding or thermal bondingfor making cotton light weight nonwovens. Chemicalbonding results in the individual fibres being coatedwith the chemical film, making the resultant fabricstiff and impairing its absorption capacity, thusnullifying the advantages of comfort, absorption andsoftness desired from cotton:'. In contrast, in thethermal bonding process, the binder fibre in cottonnonwovens does not necessarily degrade the desiredproperties. The thermal bonding system is a cleanprocess with no problem of effluents and is aneco-friendly process.

Moreau+ correlated the physical properties ofthermal-bonded cotton/polypropylene nonwovenswith bonding temperature and observed that thebonding temperature has a high influence on breakingstrength whereas the fabric weight has a significantinfluence on fabric stiffness. He concluded that in aconsumer product, where stiffness and breakingstrength are important properties, cotton blendswould be equally effective as 100% polypropylenefabrics. Much of the earlier work on coverstocks isbased on the premise that the best attributes will beprovided by coverstocks with high resistance to wetback and a high strike through rate. Consequently,the hydrophilic synthetic fibres were preferred.Studies by Cottenden et al. S show that the choice offibres has negligible effect on skin comfort. Thestudies were carried out on coverstocks made ofviscose and polyester fibres", As the cotton contentincreases in thermal-bonded nonwovens, discomfort

252 INDIAN J. FffiRE TEXT. RES., DECEMBER 1994

sensation related to surface dampness is reduced. Thisreveals the potential advantages of using cotton innext-to-skin applications". Earlier work at BTRAreveals that absorbency and wicking rate of cottonthermal-bonded nonwovens decrease with theincrease in binder fibre content and bondingpressure",

In the present study, investigations have beencarried out on the cotton thermal-bondednonwovens for their absorption, liquid strike throughtime and wet back characteristics. The influence ofcotton content and area density on these functionalproperties, tensile strength and bending behaviourare also discussed. One of the difficulties in makingthermal-bonded nonwovens is the need to importlow-melt synthetic fibre from abroad. Therefore, theuse of an indigenous polypropylene fibre of normaltype as a binder fibre was attempted. This will help tobring down the raw material cost in thermal-bondednonwovens.

2 Materials and MethodsBengal Desi (bleached) cotton

polypropylene fibre havingspecifications were used:

and indigenousthe following

CottonMean length, mmEffective length, mmShort fibre, %Bundle strength, g/tex(Stelometer 3 mm)

Micronaire

- 15.4-18.0- 8.2-13.6

-7.2

PolypropyleneDenierEffective length, mmSingle fibretenacity, g/tex

Elongation at break, %

- 2.11- 54.0-2.7

- 119

Binder fibre concentration levels of 10,20 and 30%were employed and for each concentration level, threearea density levels were selected, viz. 40, 55 and 70g/m", All the nine samples as planned above wereprepared by blending the two components prior tocarding. The carded batt of required area density waspassed through a calender type of thermal-bondingmachine. The calenders were plain smooth rollers andwere heated by hot oil circulation, maintaining the oiltemperature at 185°C. The actual temperature on therolls was 170°C. Delivery speed of I m/min wasmaintained at a pressure of 42 kP/cm. The materialwas given two passages through the calender bondingmachine.

Standard test methods were followed for testing thearea density, thickness, tensile and bendingbehaviour. Absorbency and strike through time weretested as per EDANA standards. 7-8 sub-sampleswere tested for each property for working out anaverage value. For measuring the strike through time,the nonwoven material was placed over a set of 5standard filter papers which served as the absorbent.Distilled water (5 cc) was made to flow at a standardrate, and pass through the nonwoven material into theunderlying absorbent. The time taken for the passageof water through the nonwoven was taken as the strikethrough time.

Rewet (wet back) property was tested by slightlymodifying the method proposed by Weyerhaeuserand reported by Kevin Hodgson 7• Distilled water (10cc) was used instead of synthetic urine (80 cc)proposed in the method. Distilled water was poured ata prescribed rate onto the test specimen which wassuperimposed on a standard absorbent pad in theliquid strike through tester. The test specimen wasthen allowed to absorb the liquid for 2 min. Twopreweighed filter papers were placed over the point offluid entry and a one psi (7 kg/lOa cm-) weight wasapplied for 2 min. The filter papers were removed andweighed and the net gain in weight was taken as therewet value. Rewet property measures the ability ofthe material to keep the skin of the wearer dry duringuse.

3 Results and Discussion3.1 Thickness

The thickness values of thermal-bonded cottonnonwovens, as seen in Fig. 1, are higher at higher areadensity levels. For the same area density, higherbinder fibre content results in a lower level of thicknessdue to higher number of contact points andcompactness of the material.

3.2 AbsorbencyFig. 2 shows the bar chart for absorbency values of

0.'EUE 0.4u)

:£ 0.'.2 0.1o:c 0.1I- 0__ -'- -'- -'- __ '"

10 10 10Binder fibre concentration ,%

Fig. I-Thickness values of cotton thermal-bonded nonwovens

DESAI et al.: COTION THERMAL-BONDED NONWOVENS 253

1800 ~'. 0.8>? 14000

;>. 1200 rn 0.11

g 1000 , QlCD 800 3 0.4-e800 CD

0 a:C/) 400 0.2.04: 200

0 040' 18 70

Area density. glm'

Fig. 2 -Ahsorbency values of cotton thermal-bondednonwovens

C/) 8a) 7E II

~8g'403~2CD1~ 0 "--_--'- -'---_~~_-'- __ J

U5 18Area density. glm'

Fig. J- Liquid strike through time or cotton thermal-bondednonwovens

40 70

cotton thermal-bonded materials. The absorptionincreases with the increase in cotton content in theblend.

3.3 Liquid Strike Through TimeFig. 3 shows the strike through time values. A

higher cotton content generally shows a lower strikethrough time, indicating a faster passage of liquidpossibly because of absorption of water in the cottonmatrix. A trend towards lower strike through timewith higher area density is seen. This could be becauseof the increase in cotton content with increasing areadensity and the consequent absorption of liquidduring its passage. In the case of 100% polypropylenethermal-bonded material also, an increasing trend instrike through time with area density is noticed sincethe liquid has to pass through a thicker material withhigher weight. .

3.4 Rewet (Wet Back) Property

Fig. 4 shows that the rewet property is at a peak withhigh cotton content and higher level of area density,as seen with 70 g/m2 material in 90/10 and 80/20cotton/polypropylene blends. Under theseconditions, the liquid held by the material is likely tobe higher and the same is reflected in the wet backproperties. Similarly, with 100% polypropylene

40 55 70

Area jensity. glm'

Fig. 4-- Rewet values of cotton thermal-bonded nonwovens

Cot"'1PI" : _ 110/10_ 80/20 070/30

Irn 1.4""". 1.2:g, 100

5i 0.'~ 0.'CD0.4

'ii5 0.2c ol(,...--=~------'=------'-"''-----'~

Fig. 5

40 18 70Area density. glm'

Tenacity of cotton thermal-bonded nonwovens

thermal-bonded materials, rewet increases with theincrease in weight of the material as observed fer 40and 70 g/m? polypropylene materials.

It is further seen that the rewet properties are notsignificantly affected by the type of fibre used,indicating that cotton can be successfully used forcoverstock materials. This confirms the conclusionsof earlier workers+" that the choice of fibres hasnegligible effect on skin comfort.

3.5 TenacityThe tenacity increases with increase in binder fibre

content (Fig. 5) due to increased number of bondingpoints and decreases with increase in area density. Thisis because the greater thickness at higher area densitylevels makes it difficult to obtain optimum bondingconditions throughout the fabric. Heavier webs are thusa limitation in calender type of thermal bonding.

3.6 Bending LengthThe cotton nonwovens tend to become stiffer with

increase in binder fibre content and weight of material(Fig. 6). The drop in thickness is accompanied by anincrease in bending length at higher binder fibrecontent.

3.7 Statistical AnalysisThe results of absorbency, strike through time and

rewet properties were subjected to statistical analysis.Analysis of variance was carried out to bring out the

254 INDIAN J. FIBRE TEXT. RES., DECEMBER 1994

55r------------------------------------, 1500

1400

D

EIIOE- 45

~.§ 40

~35 ~ 1200~ t::=-__-----------r- ~CD 31) 1; II 00

m 25L.~====::==========-------------- __~ ~10 20 30 ;: 1000Binder fibre content, % <

Fig. 6-lnftuence of binder fibre content on bending length

Table I-Analysis of variance of absorbency data

Source DF Response variable-Absorbency

Sum-square Mean-square F-Ratio

A (Cotton content) 2 142934.6B (Area density) 2 237747.7AB 4 565833.8Error 36 850362.4Total 44 3083290"Significant (99%); "Significant (95%)

714672.9118873.8142458.523621.2

80.26"5.03h

5.99"

Table 2-Analysis of variance of strike through time data

Source DF Response variable -Strikethrough time

Sum-square Mean-square F-Ratio

A (Cotton content) 2 13.8B (Area density) 2 9.3AB 4 O~Error 34 18.1Total 42 43.1"Significant (99%); hNon-significant

6.94.60.20.5

12.92"8.70"O.40h

Table 3--Analysis of variance of rewet data

Source DF Response variable-Rewet property

Sum-square Mean-square F- Ratio

A (Cotton content) 2 105.6 52.8 10.1"B (Area density) 2 96.3 48.1 9.2"AB 4 89.6 22.4 4.3"Error 33 122.7 5.2Total 41 475.4"Significant (99%)

effect of cotton content and area density on theproperties.

3.7.1 AbsorbencyThe results of analysis of variance of absorbency

data (Table I) indicate that the cotton content has a

1300

o

D

900 r = -0·87

800-- ElCp~ct~d Valu~s

o Actual Valu~s

700 o600.~ __ ~ __ -L__~ ~ __-L__~ __~

0·\1 0·12 0·13 0·14 0·15 0·16 0·17 0·19D~nsity,9/cc

Fig. 7-Correlation between absorbency and density of cottonthermal-bonded nonwovens

predominent influence on the absorbency property.Area density and its interaction with cotton contentalso have a statistically significant influence on theabsorption characteristics of thermal-bondedcotton nonwoven. Density (g/cc) takes intoconsideration the area density (g/rn") and thicknessof the fabric. Density of fabric is found to show a goodnegative correlation ( - 0.87) with absorbency (Fig.7), indicating a drop in absorbency with increase indensity.

3.7.2 Strike Through TimeThe results of analysis of variance of strike through

time data (Table 2) indicate that both cotton contentand area density significantly influence the strikethrough time, but their interaction is not significant.This shows that the two factors independentlyinfluence the rate of passage of liquid through thematerial. This is because of the hydrophilic nature ofcotton.

3.7.3 Rewet PropertyThe results of analysis of variance of rewet data

(Table 3) show that the wet back property issignificantly affected by the cotton content andweight of the material and that their interaction is alsosignificant.

5 Conclusions5.1 The thickness of cotton thermal-bondednonwovens decreases while stiffness increases withincrease in binder fibre concentration.

5.2 Absorbency increases and strike through timedecreases with increase in cotton content in the

DESAI et al.: COTION THERMAL-BONDED NONWOVENS 255

thermal-bonded nonwovens. Absorbency increaseswith decrease in the density of fabric.5.3 Higher cotton content and higher area densityresult in higher wet back property. However, ingeneral, cotton shows similar wet back properties aspolypropylene and hence can be used for coverstockmaterials.5.4 Tenacity increases with increase in binder fibreconcentration but decreases with increase in areadensity.5.5 Bending length increases with increase in binderfibre content and area density of cottonthermal-bonded nonwovens. However, the binderfibre content has a greater influence than area densityon bending length.

AcknowledgementThe authors are grateful to Dr S.M. Betrabet,

Director, BTRA, for his .keen interest during thisstudy.

ReferencesI Subhash K B & Dharmadhikary R. Globalisation of the

nonwoven industry-Implications for the developingcountries, Proceedings, International Conference on Nonwovens(The Textile Institute, North India Section, New Delhi) 1992,I.

2 McGann G L, The marketing of cotton in nonwovens,Proceedings, Beltwide Cotton Conference, (\993) 14\0.

3 Thomas F G, Nayak R K & Mansour Mohamed, A novelthermal bonding process for cellulosic nonwovens,Proceedings, INDA-Technical Symposium (Association ofNonwoven Fabric Industry, USA), 1992, 249.

4 Moreau J P, INDA J Nonwovens Res, 2 (2) (1990) 14.5 Cottenden AM, Buchers D, Malove-Lee J G, Fader M J, Barnes

K E & Garside J, Nonwoven requirements for incontinenceproducts, Book of Papers, Nonwovens Conference (UMIST),1988, 101.

6 Desai A N, Jade B D & Balasubramanian N, Some studies ontensile and absorbency characteristics of cotton nonwovens,Resume of Papers, 34th Joint Technological Conference ofATlRA, BTRA, SITRA and NITRA, (ATIRA, Ahmedabad)1993,183.

7 Kevin Hodgson, Factors affecting rewet performance ofabsorbent cores, Nonwoven Ind, 23(4) {1992) 34.

Erratum

5 Conclusions should be read as 4 Conclusions and5.1-5.5 as 4.1 - 4.5