effect of punch density, depth of needle penetration and...

Indian Journal of Fibre & Textile Research

Vol. 33, December 2008, pp. 411-418

Effect of punch density, depth of needle penetration and mass per unit area on

compressional behaviour of jute needle-punched nonwoven fabrics using central

composite rotatable experimental design

Surajit Senguptaa

National Institute of Research on Jute and Allied Fibre Technology, 12 Regent Park, Kolkata 700 040, India

Prabir Ray

Institute of Jute Technology, 35 Ballygunge Circular Road, Kolkata 700 019, India

and

Prabal Kumar Majumdar

Government College of Engineering and Textile Technology, Serampore, Hooghly 712 201, India

Received 4 October 2007; revised received and accepted 5 February 2008

The compressional behaviour of jute needle-punched nonwoven fabric has been studied. Statistical models using

central composite rotatable experimental design are developed on compression parameter, recovery parameter, energy loss

and thickness loss, depending on the three important parameters of needled fabric, i.e. needling density, depth of needle

penetration and mass per unit area. From this model and its contour diagrams, the effects of different parameters can be

understood and prediction of compressional behaviour can be made knowing the values of independent parameters. The

correlation coefficients between observed and predicted values are found to be significant in all the cases. It is found that the

15-16 mm depth of needle penetration, 170-180 punches/cm2 needling density and 800-900 g/m2 mass per unit area is a very

critical combination which might be considered for minimum compressibility because the deviation from any of the variable

may be responsible for the increase in compressional behaviour.

Keywords: Central composite rotatable experimental design, Compressional parameter, Energy loss, Jute, Needle-punched

nonwoven, Recovery parameter, Thickness loss

IPC Code: Int. Cl.8 D04H

1 Introduction

Needle-punched nonwoven fabric is a sheet of

fibres made by mechanical entanglement, penetrating

barbed needles into a fibrous mat.1 Such fabric is

extensively used in technical applications. In such

applications, fabric is subjected to normal

compressive loads, and the physical, tensile and

hydraulic properties change with these loads,

depending on the compressional behaviour of the

fabric. The nonwoven geotextile, when used

underground, is subjected to compressional loads,

both static and dynamic. A number of papers have

been published on tensile2,3

, hydralic4,5

and

compressional behaviour6-8

of nonwoven geotextiles.

Some work has been reported on the compressional

behaviour of loose fibre masses.9,10

Jute dominated the world market as packaging material, carpet backing and industrial textiles till the synthetic material came into competition. In search of

diversified uses of this fibre, successful attempts have been made to use this natural and ecofriendly technical fibre in the field of geotextile, floor covering and filtration.

11,12 Punch density, depth of needle

penetration and mass per unit area of jute needle-punched nonwoven are the parameters, which have

significant effect on compression.13

The effect of these parameters on the properties of nonwoven has been reported in number of papers.

14-16 But the

detailed work has not been reported so far regarding the effect of these parameters on compressional behaviour of jute needle-punched nonwoven. In this

study, an attempt has been made to understand the effect of punch density, depth of needle penetration and mass per unit area on compression, recovery, energy loss and thickness loss of jute needle-punched nonwoven geotextiles.

_____________ a To whom all the correspondence should be addressed.

E-mail: [email protected]

INDIAN J. FIBRE TEXT. RES., DECEMBER 2008

412

2 Materials and Methods 2.1 Materials

Tossa jute of grade TD3 (ref. 17) was used to

prepare needle-punched nonwoven fabric, having the

fibre properties: linear density, 2.08 tex; tenacity,

32.30 cN/tex; and extension-at-break, 1.60%.

2.2 Methods

The significant independent variables of jute

needle-punched nonwoven with respect to different

properties, namely needling density, depth of needle

penetration and mass per unit area, were identified.18

The useful limits of the three variables stated above

were selected based on the information available in

literatures14-16

and also by conducting a number of

preliminary experiments. The limits, and actual &

coded values of different factors are given in Table 1.

2.2.1 Developing the Design Matrix

To determine the effects of factors (variables) on

the response parameter, it was decided to use the

statistical technique called central composite surface

design to develop the design matrix. The matrix so

developed was a 20 point central composite design

which consists of a full factorial design 23 (8) plus 6

centre points and 6 star points.19

The 20 experimental

runs thus allowed the estimation of the linear,

quadratic and two-way interactive effects of the

various factors on properties. The design matrix so

developed with coded values of the factors is given in

Table 2.

2.2.2 Fabric Preparation

Jute reed was subjected to softening treatment with

4% jute batching oil-in-water emulsion and then

processed in a breaker card. To make jute needle-

punched nonwoven, the breaker card sliver was fed to

Dilo nonwoven plant comprising a roller and clearer

card, a camel back cross-lapper and needle loom

(Model number OD II/6). Twenty samples as per the

design matrix (Table 2) were prepared using five

levels of punch density, depth of needle penetration

and mass per unit area.

2.2.3 Measurement of Compressional Behaviour

The compression and recovery between 0 kPa and

200 kPa were measured on Instron tensile tester

(Model No. 5567). The gauge length between

stationary anvil and pressure foot was set at 0 mm.

The needle-punched nonwoven sample was placed

between 150 mm diameter stationary anvil and

150 mm diameter pressure foot, which are well

separated in the start of experiment. Then the pressure

foot started moving downward at a speed of 2 mm per

min. After reaching the maximum compressional load

of 3532 N (exerts pressure of about 200 kPa), the

pressure foot automatically started moving up with

the same speed (2 mm/min), decreasing the load

accordingly. A diagram, plotting the compressional

load against thickness (Fig. 1), was available along

with a report of compressional deformation at a

required compressional load. Average of ten such

diagrams was considered here.

The initial thickness, compressed thickness and

recovered/final thickness were available from this

graph. Compressional parameter (α) and recovery

parameter (β) were calculated from the best fit

equations as suggested by Sengupta et al. 6,7, 13

For

jute needle-punched fabrics, the following equations

Table 1―Actual and coded values of different factors

Factor Code

-1.682 -1 0 +1 +1.682

Punch density (X1)

punches/cm2 70 106.5 160 213.5 250

Depth of needle

penetration (X2), mm

18 16.4 14 11.6 10

Mass per unit area

(X3), g/cm2 300 442 650 858 1000

Table 2―Constructional details of experimental fabrics

Sample

No.

Experimental

run order

Needling

density

punches/cm2

Depth of

needle

penetration

mm

Mass per

unit area

g/m2

1 4 1 1 1

2 11 -1 1 1

3 9 1 -1 1

4 15 -1 -1 1

5 2 1 1 -1

6 10 –1 1 -1

7 3 1 -1 -1

8 7 -1 -1 -1

9 17 1.682 0 0

10 1 -1.682 0 0

11 16 0 1.682 0

12 19 0 -1.682 0

13 13 0 0 1.682

14 20 0 0 -1.682

15 5 0 0 0

16 18 0 0 0

17 6 0 0 0

18 14 0 0 0

19 12 0 0 0

20 8 0 0 0

SENGUPTA et al. : COMPRESSIONAL BEHAVIOUR OF JUTE NEEDLE-PUNCHED NONWOVEN FABRICS

413

are found to be best fit in describing the compression

and recovery behaviour:

Compression: T/T0 = 1 – α / log e (P/P0)

Recovery: T /Tf = (P/Pf)-β

where T0 and Tf are the initial and the final thicknesses

at initial and final pressures P0 and Pf respectively;

and T, the thickness at any pressure P. In the above

equations, α and β are the dimensionless constants

indicating the compression and recovery parameters

of the fabric respectively.

The per cent energy loss (EL) during compression

and recovery can be calculated as follows:

EL (%) = [(E1 – E2)/ E1 ] × 100

where E1 is the potential energy stored during

compression; and E2, the energy recovered during

recovery. These energies were measured as the area

under the compression or recovery curves from

Instron tester.

The per cent loss in thickness (TL) during

compression and recovery is obtained by the

following relationship:

TL (%) = [(T0 –TF)/T0] × 100

where TF is the thickness after recovery or final

thickness. All these data are shown in Table 3.

2.2.4 Development of Statistical Model Proposed Polynomial

To correlate the effects of factors and the response,

the following second order standard polynomial was

considered20

:

y = b0 + b1 x1 + b2 x2 + b3 x3 + b11 x12 + b22 x2

2

+ b33 x32 + b12 x1 x2 + b13 x1 x3 + b23 x2 x3 … (1)

where y represents the response and b0, b1, b2,

………,b23 are the coefficients of the model.

Evaluation of Coefficients of Model

The coefficients of main and interaction effects

were determined by using the standard method.21

Table 3―Various parameters expressing the compressional behaviour

Sample

number

Initial

thickness

mm

Compressed

thickness

mm

Final thickness

mm

Compressional

parameter

(α)

Recovery

parameter

(β)

Energy

loss

%

Thickness

loss

%

1 7.550 1.372 4.291 0.107655 0.150015 67.72 43.17

2 8.815 2.371 5.829 0.096176 0.118345 70.88 33.87

3 5.152 1.465 3.152 0.094153 0.100801 74.77 38.82

4 5.795 2.088 3.827 0.084160 0.079711 74.12 33.96

5 5.315 0.424 2.957 0.121068 0.255522 68.61 44.36

6 7.195 1.623 4.380 0.101886 0.130612 71.86 39.12

7 4.967 1.273 3.015 0.097845 0.113437 74.09 39.30

8 5.505 1.590 3.681 0.093564 0.110441 76.68 33.13

9 8.023 1.212 4.704 0.111689 0.178418 73.99 41.37

10 5.690 2.098 3.524 0.083054 0.068230 78.24 38.07

11 7.395 0.926 3.615 0.115089 0.179186 73.86 51.12

12 5.120 1.628 3.263 0.089730 0.091475 73.13 36.27

13 4.525 0.710 2.284 0.110920 0.153721 76.73 49.52

14 6.880 2.880 4.687 0.076490 0.064072 76.48 31.87

15 5.821 1.869 2.573 0.089320 0.042057 76.18 55.80

16 4.737 1.992 3.521 0.076238 0.074939 77.55 25.67

17 5.392 1.899 2.649 0.085228 0.043791 78.47 50.87

18 5.562 1.491 3.406 0.096295 0.108683 75.86 38.76

19 4.468 1.998 3.047 0.072731 0.055521 76.63 31.80

20 5.439 1.229 3.844 0.101835 0.150023 78.21 29.32

Fig. 1―A typical experimental pressure-thickness curve of a jute

needle-punched nonwoven fabric


414

Table 4 shows the regression coefficients of the

proposed model for different parameters.

Correlation between Observed and Calculated Values

The correlation coefficients between the observed

values and the predicted values by proposed model

are shown in Table 5. It shows a very good

correlation.

Checking the Adequacy of Models

The analysis of variance (ANOVA) technique was

used to check the adequacy of the developed models.

The ANOVA results of proposed model are given in

Table 6. Accordingly F-ratios of the developed

models were calculated for 95% level of confidence

and were compared with the corresponding tabulated

values. If the calculated values of F-ratio did not

exceed the corresponding tabulated value then the

models were considered adequate. The tabulated

value of F-ratio at 95% confidence level is 5.05. For

this purpose the F-ratio is defined as follows:

F-ratio = Lack of fit (mean square) / Error (mean square)

3 Results and Discussion Table 3 shows the values of dependable

parameters, i.e. compressional parameter (α),

recovery parameter (β), energy loss (EL) and thickness

loss (TL), obtained from the compression testing. To

establish the relationships between the independent

and the dependent variables, regression analysis was

done. The regression coefficients (Table 4) were used

in the quadratic Eq. (1) for the determination of

predicted response values. The correlation

coefficients between the observed values and the

predicted values by proposed model illustrate a very

good correlation (Table 5). The values of the

calculated correlation coefficient are much higher in

all the cases than the standard value of correlation

coefficient (i.e. 0.444) at 5% level and 18 degree of

freedom.22

It indicates that the observed values of

needle-punched nonwoven has a real degree of

association with the predicted values of the fabric.

The significance of the effect of the variables was

tested by F-ratios (Table 6). These quadratic

equations were also used to arrive at possible

combinations for each assessment and the respective

response using these values. The contour diagrams

were plotted to study the effect of variables on the

responses (Figs 2 – 5).

The regression coefficients have a value either

positive or negative and accordingly have an effect on

the experimental results. For a variable to have a

significant effect, its coefficient must be greater than

twice the standard error. However, the non-significant

coefficients should not be eliminated altogether.

The effects of variables or interaction of variables

on compressional parameter (α), recovery parameter

Table 4―Regression coefficients of model

Coefficient α β EL TL

b0 0.086907 0.078936 75.91440 38.81235

b1 -0.001167 -0.001770 0.79709 0.04024

b2 -0.007301 -0.029115 1.41892 -2.94973

b3 -0.007530 -0.024269 0.58064 -4.04492

b11 0.003914 0.017134 -0.53518 -0.34141

b22 0.005696 0.021378 -1.46297 1.06393

b33 0.002618 0.012033 -0.36170 0.00587

b12 -0.000753 -0.009301 0.00177 -0.84963

b13 -0.000249 -0.009393 0.41545 0.34307

b23 0.002048 0.016562 -0.55932 0.43833

α – Compressional parameter, β – Recovery parameter, EL –

Energy loss, and TL –Thickness loss.

Table 5―Correlation coefficients between the observed values

and the predicted values by proposed model

Parameter Calculated

correlation

coefficient

Correlation

coefficient at

5% level and

18 degree of

freedom22

Remark

Compressional parameter (α) 0.86 0.444 Significant

Recovery parameter (β) 0.84 0.444 Significant

Energy loss (EL) 0.77 0.444 Significant

Thickness loss (TL) 0.90 0.444 Significant

Table 6―ANOVA of the proposed model

Parameters 1st order

term

2nd order

term

Lack of fit Error F-ratio

d.f. 3 6 5 5 -

α

SS 0.001521 0.000826 0.000619 0.000634

MS 0.001521 0.000826 0.000124 0.000127 0.976

β

SS 0.019664 0.016497 0.011133 0.009097

MS 0.019664 0.016497 0.002227 0.001819 1.224

EL

SS 40.7768 40.7406 62.7683 27.0074

MS 40.7768 40.7406 12.5537 5.4015 2.324

TL

SS 342.2940 26.2470 83.4060 745.7100

MS 342.2940 26.2470 16.6812 149.1419 0.112

d.f.— Degree of freedom; SS— Sum square, and MS— Mean

square.


415

(β), energy loss (%) and thickness loss (%) can

effectively be interpreted and explained by regression

coefficients and contours. The information available

from contour diagrams regarding the interactions of

parameters on compressional behaviour is very much

useful to design a jute needle-punched nonwoven for

various applications.

3.1 Compressional Parameter

Figure 2a shows the contour diagram of

compressional parameter (α) of jute needle- punched

nonwoven with respect to the workable range of

needling density and depth of needle penetration for

mass per unit area of 500 g/m2. Similarly, Fig. 2b

shows contour diagram of α with respect to mass per

unit area and needling density for depth of needle

penetration of 15 mm. Again, Fig. 2c shows the

contours of α with respect to mass per unit area and

depth of needle penetration for fabric with 198

punches/cm2. From these diagrams, it is observed that

with the increase in depth of needle penetration or

needling density or mass per unit area, α initially

decreases up to a minimum value and then it

increases. Higher the needling density or depth of

needle penetration, higher is the entanglement and

consolidation and hence α is decreased initially. Beyond a certain value, the increase in above

parameters also increases α, which may be due to

fibre breakage in severe action of needles, resulting in

lower consolidation as suggested by Purdy.1 The same

phenomenon has been observed by other workers and

explained in similar way.14,15

Higher mass per unit area offers more number of

fibres to the needle barb to rearrange in vertical

direction, resulting in higher consolidation. Hence,

there is a decrease in α value. After a certain mass per

unit area, needle penetration is much difficult and the

fibre carrying capacity of the needle barb is reached to

maximum and chances of fibre breakage increases,

which causes lower consolidation and that is why

there is an increase in α value.

The center of minimum α is achieved using the

combination of depth of needle penetration, 15-16

mm; needling density, 170-180 punches/cm2 and mass

per unit area, 800-900 g/m2. A deviation in either side

of these combination results in the increase in

compressibility for jute needle-punched cross-laid

nonwoven fabric.

3.2 Recovery Parameter

Contour diagrams of recovery parameter (β) with

respect to the workable range of needling density and

depth of needle penetration for mass per unit area of

500 g/m2, and of mass per unit area and needling

density for depth of needle penetration of 15 mm are

shown in Figs 3a and 3b. Similarly, Fig. 3c

demonstrates the effect of mass per unit area and

depth of needle penetration on β of fabric with 198

punches/cm2. It is observed from the figures that

Fig 2―Contours of compressional parameter (a) with mass per

unit area 500 g/m2, (b) with needle penetration 15 mm, and (c)

with needling density 198 punches/cm2


416

β value decreases with the increase in needling

density, depth of needle penetration and mass per unit

area due to higher entanglement, resulting in more

compact fabric structure. In case of very high (240

punches/cm2) or very low (100 punches/cm

2) needling

density, the increase in needle penetration above

15 mm or mass per unit area above 750 g/m2 shows

increase in β value due to lower consolidation

(Figs 3a and 3b). The minimum point is achieved

using the parameters, depth of needle penetration,

15-16 mm; needling density, 170 punches/cm2; and

mass per unit area, 800-900 g/m2.

Fig. 3―Contours of recovery parameter (a) with mass per unit

area 500 g/m2, (b) with needle penetration 15 mm, and (c) with

needling density 198 punches/cm2

Fig. 4―Contours of energy loss (a) with mass per unit area 500

g/m2, (b) with needle penetration 15 mm, and (c) with needling

density 198 punches/cm2


417

3.3 Energy Loss

Energy loss is basically the difference between the

energy stored during compression and energy gained

during recovery. Contour diagrams of energy loss due

to one complete compression-recovery cycle have

been shown in Figs 4a – 4c in different combinations

of needling density, depth of needle penetration and

mass per unit area. This effect basically depends on

the complicated and combined interaction of energy

gain by compression and energy loss by recovery. As

needling density is increased within the workable

range, energy loss always decreases. With the

increase in needle penetration, mass per unit area or

depth of needle penetration, the energy loss increases

due to more compact structure of fabric, which

requires higher energy to compress. In low mass per

unit area (around 400 g/m2), the increase in needling

density above 210 punches/cm2 or depth of needle

penetration above 15 mm shows decrease in energy

loss value (Figs 4b and 4c) due to lower consolidation

in structure.

3.4 Thickness Loss

Effect of needling density, depth of needle

penetration and mass per unit area on thickness loss

due to one compression-recovery cycle of jute needle-

punched nonwoven fabric is shown in Figs 5a – 5c.

With the increase in any of these parameters, the

thickness loss always decreases. Thickness loss

denotes the difference between initial thickness and

final thickness after recovery. As any of these

parameters increases, the structure of fabric becomes

more compact. This resists compression and

facilitates recovery, resulting in lower thickness loss.

Figure 5a shows that the increase in needling density

for any depth of needle penetration has hardly any

effect on thickness loss.

4 Conclusions

4.1 Statistical models are developed relating the

compressional behaviour (compressional parameter or

recovery parameter or energy loss or thickness loss)

and three effective independent parameters, i.e.

needling density, depth of needle penetration and

mass per unit area of jute cross-laid needle-punched

nonwoven. From this model, one can understand the

effects of different parameters on compressional

behaviour and can also predict the compressional

behaviour approximately knowing the values of

factors or parameters.

4.2 The information available from contour

diagrams regarding the interactions of parameters on

compressional behaviour is very much useful to

design a jute needle-punched nonwoven for various

applications.

Fig. 5―Contours of thickness loss (a) with mass per unit area 500

g/m2, (b) with needle penetration 15 mm, and (c) with needling

density 198 punches/cm2


418

4.3 It is found that 15-16 mm depth of needle

penetration, 170-180 punches/cm2 needling density

and 800-900 g/m2 mass per unit area is a very critical

combination which might be considered for minimum

compressibility because deviation from any of the

variables may be responsible for the increase in

compressional behaviour.

4.4 In general, with the increase in needling density

or depth of needle penetration or mass per unit area,

compressional parameter decreases, recovery

parameter decreases, energy loss increases and

thickness loss decreases.

4.5 In case of high needling density (around 230

punches/cm2), the increase in mass per unit area

above 750 g/m2 or needle penetration above 15 mm

shows increase in both compressional and recovery

parameters.

4.6 In low mass per unit area (around 400 g/m2),

the increase in needling density above 210

punches/cm2 or depth of needle penetration above 15

mm shows decrease in energy loss value.

4.7 Increase in needling density for any depth of

needle penetration has hardly any effect on thickness

loss.

Industrial Importance: This study will be helpful in

designing the jute needle-punched nonwoven fabric

for better performance with respect to compressional

behaviour which is an important property for some

industrial uses.

Acknowledgement One of the authors (SS) expresses his sincere

gratitude to Dr S K Bhattacharyya, Director, National

Institute of Research on Jute and Allied Fibre

Technology, Kolkata, for providing study leave to

carry out this work.

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