Indian Journal of Fibre & TextileResearchVol.17,September 1992,pp.124-129

A study on the properties of needle-punched nonwoven fabricsusing a factorial design technique"

V Subramaniam & M MadhusoothananDepartment of TextileTechnology. Anna University, Madras 600 025. India

andCR Debnath

Jute Technological Research Laboratory. 12 Regent Park, Calcutta 700 040, IndiaReceived 31 May 1991; revised received 16June 1992;accepted 19June 1992

The effects of the depth of needle penetration (ONP) and needling density (NO) on the physical pro-perties of needle-punched nonwovens made from acrylic fibres have been studied. It is found that withthe increase in NO and ONP, the tenacity, initial modulus and tensile and compressional resilience in-crease while the breaking elongation decreases. The air permeability first decreases and then increases with in-crease in NO and ONP. The application of the Box and Hunter's central rotatable design in engineering aneedle-punched nonwoven is pointed out.

Keywords: Air permeability, Breaking elongation, Compressional resilience, Fabric tenacity, Factorialdesign, Initial modulus, Needling density, Needle penetration, Nonwoven fabrics

1 IntroductionNeedle punching is one of the main mechanical

methods of manufacturing nonwoven fabrics. Thereexists a considerable knowledge on needled non-wovens, and a number of papers and publicationshave dealt with nonwovens exhaustively. The twomain machine parameters that have been studiedare depth of needle penetration (DNP) and needlingdensity (ND). The general conclusion that can bederived from the published work is that at constantND if the DNP is increased, the tenacity, initialmodulus and abrasion resistance increase, while theelongation shows a decrease. A similar trend is ob-served with the increase in ND at constant DNP. Itcan also be observed from the literature that thetrend observed for one set of conditions may not bethe same for another set of conditions 1 - '".

In the present study, Box and Hunter's central ro-tatable compound design for two variables has beenapplied to investigate the effects of ND and DNP onthe tenacity, breaking elongation, initial modulus,Poisson's ratio, air permeability, and tensile andcompressional resilience of a series of needled fa-brics. Box and Hunter's central rotatable compounddesign has been applied extensively by a number of

'Paper presented at the 31st joint technological conference ofATIRA, BTRA, SITRA & NITRA held at lIT, Delhi. 16-17Feb-ruary 1990.

workers for studying the various processing var-iables in textile processingIO-16•

2 Materials and Methods2.1 Factorial Design

In the Box and Hunter's central rotatable factorialdesign 17 the response Y is given by a second orderpolynomial

, "- --y= bo + I bj Xj + I I bUlXu Xl

J'" 1 14= I J= I

where b.; bj and bUj are regression coefficients asso-ciated with the variable.

In order to find out the regression coefficients, theresponse Y has to be found out using different ex-perimental combinations, where the number of ex-periments must be equal to or greater than the num-ber of coefficients fitted. In this design, the levels ofthe variables are fixed at -1.414, - 1,0, + 1 and+ 1.414 in the coded form. The experimental designfor two variables is given in Table 1, the coded andactual levels of the variables are given in Table 2.

2.2 Fabric Production and TestingThe study was carried out with 3 denier, 64mm

acrylic fibre. The fibres were first opened by handand then blended intimately. Parallel-laid webs wereproduced in a miniature card. The web was pro-

SUBRAMANIAM et aL: NEEDLE-PUNCHED NONWOVEN FABRICS 125

Table I-Experimental design for two variables

Experimental Level of variablecombination

12

34

5678

9lO

11

1213

-1

+1-1

+1- 1.414

+ 1.414

ooooooo

-1-1+1+1

oo

- l.414

+ l.414

ooooo

Table 2-Variables and their required levels

Coded value Actual value

Depth of needlepenetration, mm

Xl

Needling density,punches/ern?

~3l.0

38.858.177.5

85.3

- 1.414

-1

o+1

+ 1.414

9.5lO.914.217.8

19.0

cessed twice to produce a uniform web of 400 g/rn-.Needle-punched fabrics were produced from thesewebs in a lab model fibre locker machine with a15 x 18 x 36 x RlSPx 3+,1/4",9 needle. A series offabrics was produced using various combinationsof DNP and ND in one pass as shown in Table 2. Allother machine parameters were kept constant.

The tenacity, breaking elongation and initial mod-ulus were measured in machine direction using anInstron tensile tester. The sample size and rate ofstraining were chosen according to ASTM standardDl117-80 (Sample size, 7.6 x 2.5 em; cross-headtraverse speed, 300 mmlmin). The tenacity was cal-culated by normalizing the breaking load by fabricweight and width of the specimen as suggested byHearle/.

The Poisson's ratio of the fabric samples wasmeasured in the Instron with a 10 x 5 em sampleand extending it to 10% of its gauge length at 1 ern/min extension rate. The width of the sample was

measured using a travelling microscope, from whichthe Poisson's ratio was calculated. The tensile resili-ence was measured in an Instron tester by extending a7.6x 2.5 em sample till a load of 500 glcm widthwas reached, then the cross-head movement was re-versed. From the plot, the tensile energy during ex-tension (WT) and during retraction (WTl )were cal-culated. The tensile resilience (RT) is given by:m -twrvwrj« 100

The compressive resilience was measured in aKawabata KES-FB3 compression tester. Theplunger moving at 1 mml50 s applies a maximumpressure of 50 g/cm". The work done for compres-sion (WC) and the work done for recovery (WC I)were measured by the instrument itself. The com-pressional resilience (RC) was calculated in the fol-lowing manner:RC= (WCl/WC)x 100

The air permeability of the fabrics was measuredin a Metafem air permeability tester at 10 mm waterhead pressure.

Fifteen tests were carried out for each sample. Allthe tests were carried out under the standard atmos-pheric conditions.

3 Results and DiscussionTable 3 gives the test results of all the fabric sam-

ples. With the help of a suitable computer programdeveloped, the regression equations were calculatedfrom the experimental results. The response surfaceequations for all the fabric properties and the coeffi-cient of multiple correlation obtained from the re-sponse surface equations are given in Table 4. Thehigh coefficient of correlation obtained indicatesthat the response surface equations agree well withthe experimental data. The equations were also test-ed for their significance by 'F' test and all the equ-ations are significant at 95% or 90% confidence le-vel. Contour maps were constructed using the re-sponse surface equations.

3.1 TenacityFig. 1 shows HIe effect of ND and DNP on fabric

tenacity. It is observed that with the incr~ase in N~or DNP, the tenacity increases. With the mcrease ill

ND or DNP, more number of fibres will be reorient-ed into the vertical structure'<:" and due to this thefibre entanglement and locking increase. This in-creased fibre locking results in higher fabric tenac-ity. From the figure it is also observed that at higherDNP or ND the increase in tenacity is not appreci-able.

126 INDIAN J. FmRE TEXT. RES., SEPTEMBER 1992

Table 3- Properties of needle-punched nonwoven fabrics

Sample Tenacity Breaking Initial Poisson's Air Tensile CompressionalNo. g/tex elongation modulus ratio permeability resilience resilience

% g/tex m3/m2/s 010 0/0

1 3.372 56.57 1.932 1.832 0.988 17.25 41.26

2 4.523 41.76 4.384 2.473 0.611 23.93 53.38

3 4.091 51.96 3.115 2.272 0.629 23.89 46.654 4.782 34.80 5.986 2.537 0.693 29.33 58.635 3.079 70.74 1.606 1.522 0.769 18.83 41.26

6 4.942 30.20 5.561 2.987 0.606 24.83 57.087 3.719 57.72 2.412 1.845 0.778 20.99 42.558 4.646 41.08 4.553 2.876 0.597 26.51 47.929 4.392 48.04 3.226 2.837 0.690 23.21 45.85

10 4.299 49.35 3.517 2.904 0.644 22.77 46.04II 4.465 47.50 3.885 2.781 0.649 23.34 44.48

12 4.356 45.99 3.367 2.722 0.678 23.01 46.7413 4.472 53.70 3.381 2.831 0.607 22.96 4585

Response

Table 4--Response surface equations for various fabric characteristics

Response surface equation Correlationcoefficient

Tenacity, g/texBreaking elongation, %

Initial modulus, g/texPoisson's ratioAir permeability, mJ/m'/s

Tensile resilience, %

Compressional resilience. %

4.397 + 0.56xl + 0.29x2 - 0.17 xi - 0.08x~ - 0.12x\ x248.92 - 1l.16xl - 4.39x2 - 0.14xi - 0.68x~ - 0.59xlx23.48 + 1.37 XI + 0.72X2 + 0.14x; + 0.08x~ + O.l1x,~2.815 + 0.37xl +0.25x2 - 0.29~ -0.24x~ - 0.09XIX20.654 - 0.068x, -0.067~ + 0.028x; +0.028x~ + 0.llx,x223.06 + 2.58xl + 2.48x2 - 0.412x; + 0.549x~ - 0.31xlx245.8 + 5.8lx, + 2.28x2 + 2.38x; + 0.42x~ - 0.04xl~

0.980.940.990.940.970.980.97

85.3n-~~--.--'-----'----'-'

N

Eu

"-V}w:x:(Jz::>0..

n>-l-V)ZwaC)z..JoWwz

31.0 L----...:~o....._.l..............:"__:u....._~___l~___"_---'

9.5 14.2

DEPTH OF NEEDLE PENETRATION, m mFig. I-Effect ot needling density and depth of needle

penetration on tenacity

It has been reported in the literature 1 - 9 that withthe increase in DNP or ND the tenacity increases,reaches a maximum value and then decreases. Thedecrease is attributed to excessive fibre breakageand reduced contact between the horizontal andvertical structure. In the present study, no such dec-rease is observed with the increase in DNP at anyND or with the increase in ND at any DNP. Thismay be due to the fact that the maximum ND chosenis about 85 punches/em", and at this needling dens-ity the fibre breakage is probably not excessive. Butthe shape of the curves suggests that if DNP or NDis further increased, there will be a drop in tenacity.Among the two parameters considered within theexperimental range, DNP influences the tenacitymore than ND.

19.0

3.2 Breaking ElongationThe effect of ND and DNP on the breaking elon-

gation of the fabric is shown in Fig. 2. It is observedthat with the increase in ND or DNP the fabricbreaking elongation decreases. With the increase inDNP or ND the consolidation of the fabric in-

SUBRAMANIAM et aL: NEEDlE-PUNCHED NONWOVEN FABRICS

85.3 .----r--~-r--____..-~--,--__,

127

N

EN

VE<,v

If) ..••.ILl en:I:U ILlz 53.1 :x::::> U 53.1Q. z>-~ :::>

Q.

~ •...If)

>-~zIf)ILl

0 ZILl

C) 0z C)...J Z0 :::iILl 0ILl ILlZ ILl

z

310 31.09.5 14.2 19.0 9.5 14.2 19.0

DEPTH OF NEEDLE PENETRATION ,mm

Fig. 2-Effect of needling density and depth of needlepenetration on breaking elongation

creases and due to this the fibre mobility decreases.This results in decrease in breaking elongation. An-other possible reason for lower breaking elongationat high ND. and DNP is the reduced average fibrelength. The results obtained agree with the findingsreported in the literature'<".

3.3 Initial ModulusFig. 3 shows the effect of ND and DNP on the in-

itial modulus. It is observed that with the increase inND or DNP the initial modulus of the fabric in-creases. With the increase in ND or DNP the en-tanglement of fibres in the fabric increases and thisreduces the fibre slippage and produces a good self-locking structure. Due to this the initial modulus in-creases. It has been reported in the literarure+" thatat high ND or DNP the initial modulus decreasesdue to the increase in short fibre content. But in thepresent study no such decrease in initial modulus isobserved. This may be due to the fact that the needl-ing conditions are not severe enough to cause exces-sive fibre breakage at this web weight.

3.4 Poisson's RatioFig. 4 shows the effect of ND and DNP on the fa-

bric Poisson's ratio. It is observed that with the in-crease in ND or DNP, the Poisson's ratio first in-creases, reaches a maximum value and then dec-reases. At lower ND or DNP, the fibre entanglementwill not be high and hence the load developed for agiven extension will be less. Due to this, the forces

DEPTH OF NEEDLE PENETRATION ,mm

Fig. 3-Effect of needling density and depth of needlepenetration on initial modulus

N

Ev

<,If)ILl:I:U~ 53.1Q.

">-~If)ZILloC)Z...JoILlWZ

31.0~--....>o....>---"--'>--">"--'>-.JL..::>....--'O:>~ £.J

9.5 142 19.0

Fig. 4-Effect of needling density and depth of needleDEPTH OF NEEDLE PENETRATION, mm

acting in the transverse direction will also be less, re-sulting in lower Poisson's ratio. With the increase inND or DNP, the load developed will increase andthe forces acting in the transverse direction will alsoincrease, resulting in greater contraction in thetransverse direction. At high ND or DNP, the con-solidation of the fabric will be very high and thiswould restrict width-wise contraction. Due to this,the Poisson's ratio WIlldecrease at high ND or D1'.TJ>.

128 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 1992

3.5 Air PermeabilityThe effect of ND and DNP on the air permeabil-

ity offabrics is shown in Fig. 5. It is observed that atlow levels of DNP if ND is increased, the air perm-eability decreases. A similar trend is observed at lowlevels of ND if DNP is increased. At lower DNP ifND is increased or at lower ND if DNP is increased,the consolidation of the web increases which resultsin lower air permeability. This agrees with the find-ings reported by other workers8.9.19.20.

At high levels of ND or DNP if the other variableis increased, the air permeability also increases. Un-der the above conditions, the fibre rupture increasesand channels are created in the fabric which in-crease the interstices in fabric due to which the airpermeability increases. This agrees with the resultsreported by other workers8.9,19,20,

3.6 ResilienceFig. 6 shows the effect of DNP and ND on the

tensile resilience of fabrics. It is observed that withthe increase in DNP or ND the tensile resilience in-creases. With the increase in DNP or ND, the inter-locking of fibres in the fabric increases. Due to thiswhen the tensile load is removed the fabric is able torecover well. The tensile resilience of needled fabricis poor even at high levels of ND or DNP. This is be-cause in a needled fabric when a tensile load is ap-plied the fibres in the structure start to slip immedi-ately. The self-locking nature of the structure comesinto effect only after sufficient fibre slippage whichis not recoverable.

853,..--------------,

06

'"Ev

<,

IIIW:ruz

53.1~Cl.

>-~~IIIZW0

'-~z--'0wwz

31.09.5

065

14.2 19.0

DEPTH OF NEEDLE PENETRATION, m m

Fig. 5-Effect of needling density and depth of needlepenetration on air permeability

The effect of ND and DNP on the compressionalresilience is shown in Fig. 7. It is observed that withthe increase in ND or DNP the compressional resili-ence increases. The poor recovery at low levels ofND or DNP is again due to the poor consolidation

N

Eu<,

2928

II)w:ruz~o,.;-t:II)zwoCIz::;owwZ

31.0L......---'-----L.~ ~-L.l.._....l._._ _l__..l.J

9.5 14.2 19.0

DEPTH OF NEEDLE PENETRATION, m mFig. 6-Effect of needling density and depth of needle

penetration on tensile resilience

85.3,....----------..,---.--..----r--r-,...--,---,

('oJ

Eu"-II)w::to~ 53.1Cl.~>-~II)zwoCIZ..J

oWwz

31.0 ~_~ __ __L_ .•...•...---''---'---'---.L-..J~

9.5 14.2 19.0

DEPTH OF NEEDLE PENETRATION, mmFig. 7-Effect of needling density and depth of needle

penetration on compressional resilience

SUBRAMANIAM et al.: NEEDLE-PUNCHED NONWOVEN FABRICS 129

of the fabric, whereas the higher recovery at higherlevels of ND or DNP is due to the restriction in thefibre movement in a tightly packed structure.

4 ConclusionsWith the increase in ND and DNP, the tenacity,

initial modulus and tensile and compressional resili-ence increase while the breaking elongation dec-reases. This is due to better interlocking of fibres inthe fabric. The air permeability first decreases andthen increases with the increase in DNP or ND. Thedecrease is due to hetter consolidation and increaseis due to channels created in the fabric. The Pois-son's ratio first increases and then decreases. Thistrend is also due to better consolidation in the fa-brics. These results suggest that it is possible to engi-neer a needle-punched nonwoven fabric with therequisite properties for a particular applicationusing a factorial design technique.

References1 Purdv A T, Needle punching (The Textile Institute, Man-

chester), 1980.2 Hearle J W S & Sultan MAl, J Text Inst, 59 (1968) 103.3 HearleJ W S & Purdy AT, FibreSci Techno!, 5 (1972) 113.4 Purdy A T, Non-wovens 71, edited by P Lennox-Kerr (The

Textile Trade Press, Manchester), 1971.

5 Smith P A, Non-wovens 71, edited by P Lennox-Kerr (TheTextile Trade Press, Manchester), 1971.

6 Hearle J W S & Purdy AT, J Text Inst, 65 (1974) 6.7 Sengupta A K, Sinha A K & Debnath C R, Indian J Text Res,

10 (1985) 91.8 Rakshit A K, Desai AN & Balasubramanian N, Engineering

needle- punched nonwovens to meet functional properties, pa-per presented at the 30th joint technological conference ofAT1RA, BTRA, SITRA & NITRA, held at AT1RA, Ahmed-abad,1986.

9 Rakshit A K, Desai AN & Balasubramanian N, Indian J Fi-bre Text Res, 15 (1990) 41.

10 Madhusoothanan M, A study of the properties of needle-punched nonwovens using a factorial design technique, Ph.D.thesis, Anna University, Madras, 1990.

11 Barella A, Vigo J P, Tura J M & Esperson H 0, J Text Inst,67 (1976) 253.

12 Barella A, Vigo J P, Tura J M & Esperson H 0, J Text Inst,67 (1976) 325.

13 Barella A & Vigo J P, J Text Inst; 68 (1977) 143.14 Salhotra K R & Balasubramaniam P, s, Text Inst, 77 (1986)

128.15 Salhotra K R & Balasubramaniam P, Indian J Text Res, 10

(1985) 100.16 Subramaniam V, Srinivasamurthy V R & Peer Mohamed A,

Text Res J, 59 (1989) 762.17 Box G E & Hunter J S, Ann Math Stat, 28 (1957) 195.18 Hearle J W S & Purdy A T, Fibre Sci Technol; 4 (1971) 81.19 Sengupta A K, Sinha A K & Debnath C R, Indian J Text Res,

10 (1985) 147.20 Igwe G J I & Smith P A, Melliand Textilber, 67 (1986) E287.