Surajit Sengupta a. National Institute of Research on Jute and Allied Fibre Technology, 12 Regent Park, Kolkata , India.

Transcription

1 Indian Journal of Fibre & Textile Research Vol. 33, December 2008, pp 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 Sengupta a National Institute of Research on Jute and Allied Fibre Technology, 12 Regent Park, Kolkata , India Prabir Ray Institute of Jute Technology, 35 Ballygunge Circular Road, Kolkata , India and Prabal Kumar Majumdar Government College of Engineering and Textile Technology, Serampore, Hooghly , 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 mm depth of needle penetration, punches/cm 2 needling density and g/m 2 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 tensile 2,3, hydralic 4,5 and compressional behaviour 6-8 of nonwoven geotextiles. Some work has been reported on the compressional behaviour of loose fibre masses. 9,10 a To whom all the correspondence should be addressed. ssg_42@rediffmail.com 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 needlepunched 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 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.

2 412 INDIAN J. FIBRE TEXT. RES., DECEMBER Materials and Methods 2.1 Materials Tossa jute of grade TD 3 (ref. 17) was used to prepare needle-punched nonwoven fabric, having the fibre properties: linear density, 2.08 tex; tenacity, 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 literatures and also by conducting a number of preliminary experiments. The limits, and actual & coded values of different factors are given in Table 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 2 3 (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 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 needlepunched 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 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 Factor Table 1 Actual and coded values of different factors Code Punch density (X 1 ) punches/cm 2 Depth of needle penetration (X 2 ), mm Mass per unit area (X 3 ), g/cm Sample No. Table 2 Constructional details of experimental fabrics Experimental run order Needling density punches/cm 2 Depth of needle penetration mm Mass per unit area g/m 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

3 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/T 0 = 1 α / log e (P/P 0 ) Recovery: T /T f = (P/P f ) -β where T 0 and T f are the initial and the final thicknesses at initial and final pressures P 0 and P f 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 (E L ) during compression and recovery can be calculated as follows: E L (%) = [(E 1 E 2 )/ E 1 ] 100 Fig. 1 A typical experimental pressure-thickness curve of a jute needle-punched nonwoven fabric where E 1 is the potential energy stored during compression; and E 2, 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 (T L ) during compression and recovery is obtained by the following relationship: T L (%) = [(T 0 T F )/T 0 ] 100 where T F is the thickness after recovery or final thickness. All these data are shown in Table Development of Statistical Model Proposed Polynomial To correlate the effects of factors and the response, the following second order standard polynomial was considered 20 : y = b 0 + b 1 x 1 + b 2 x 2 + b 3 x 3 + b 11 x b 22 x b 33 x b 12 x 1 x 2 + b 13 x 1 x 3 + b 23 x 2 x 3 (1) where y represents the response and b 0, b 1, b 2,,b 23 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 %

4 414 INDIAN J. FIBRE TEXT. RES., DECEMBER 2008 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 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 (E L ) and thickness loss (T L ), 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 Table 4 Regression coefficients of model Coefficient α β E L T L b b b b b b b b b b α Compressional parameter, β Recovery parameter, E L Energy loss, and T L Thickness loss. 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 ) 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 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 freedom 22 Remark Compressional parameter (α) Significant Recovery parameter (β) Significant Energy loss (E L ) Significant Thickness loss (T L ) Significant Parameters 1 st order term Table 6 ANOVA of the proposed model 2 nd order term Lack of fit Error F-ratio d.f α SS MS β E L T L SS MS SS MS SS MS d.f. Degree of freedom; SS Sum square, and MS Mean square.

5 SENGUPTA et al. : COMPRESSIONAL BEHAVIOUR OF JUTE NEEDLE-PUNCHED NONWOVEN FABRICS 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. Fig 2 Contours of compressional parameter (a) with mass per unit area 500 g/m 2, (b) with needle penetration 15 mm, and (c) with needling density 198 punches/cm 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/m 2. 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/cm 2. 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, mm; needling density, punches/cm 2 and mass per unit area, g/m 2. 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/m 2, 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/cm 2. It is observed from the figures that

6 416 INDIAN J. FIBRE TEXT. RES., DECEMBER 2008 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/cm2) 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, mm; needling density, 170 punches/cm2; and mass per unit area, 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

7 SENGUPTA et al. : COMPRESSIONAL BEHAVIOUR OF JUTE NEEDLE-PUNCHED NONWOVEN FABRICS 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/m 2 ), the increase in needling density above 210 punches/cm 2 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 needlepunched 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. Fig. 5 Contours of thickness loss (a) with mass per unit area 500 g/m 2, (b) with needle penetration 15 mm, and (c) with needling density 198 punches/cm 2 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.

8 418 INDIAN J. FIBRE TEXT. RES., DECEMBER It is found that mm depth of needle penetration, punches/cm 2 needling density and g/m 2 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/cm 2 ), the increase in mass per unit area above 750 g/m 2 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/m 2 ), the increase in needling density above 210 punches/cm 2 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. References 1 Purdy A T, Needle-punching (The Textile Institute, Manchester), 1980, Raumann G, Some tensile test methods for geotextiles, paper presented at the 8th Technological Symposium on Nonwoven Fabrics for the Future, Kissimmee, Florida, USA, March McGown A, Andrawes K Z & Kabir M H, Load-extension testing of geotextiles confined in-soil, paper presented at the 2nd International Conference on Geotextiles, IFAI, Las Vegas, Nevada, USA, 1-6 August Raumann G, In plane permeability of compressed geotextiles, paper presented at the 2nd International Conference on Geotextiles, IFAI, Las Vegas, Nevada, USA, 1-6 August McGown A, Kabir M H & Murray R T, Compressibility and hydraulic conductivity of geotextiles, paper presented at the 2nd International Conference on Geotextiles, IFAI, Las Vegas, Nevada, USA, 1-6 August Kothari V K & Das A, J Text Inst, 84 (1) (1993) Kothari V K & Das A, Geotext Geomembr, 11 (1992) Kothari V K & Das A, Geotext Geomembr, 12 (1993) Van Wyk C M, J Text Inst, 37 (1946) T Dunlop J I, J Text Inst, 74 (1983) Ganguly P K & Samajpati S, A versatile and cost effective route of jute diversification, paper presented at the seminar on Technology Today-Transfer Tomorrow, Calcutta, 2 February Pandey S N, Samajpati S & Ganguly P K, Potential for use of natural fibres in civil engineering and geotextile, Proceedings, National Conference on Jute and Allied Fibres (JTRL, Calcutta), Sengupta S, Majumdar P K & Ray P, Manmade Textiles in India, 48 (10) (2005) Ganguly P K, Sengupta S & Samajpati S, Indian J Fibre Text Res, 22 (3) (1997) Ganguly P K, Sengupta S & Samajpati S, Indian J Fibre Text Res, 24 (1) (1999) Sengupta S, Samajpati S & Ganguly P K, Indian J Fibre Text Res, 24 (2) (1999) Indian Standards Specifications IS: 271 (Bureau of Indian Standards, New Delhi), Sengupta S, Ray P & Majumdar P K, Asian Text J, 14 (6) (2005) Lunenschloss J & Albrecht W, Nonwoven Bonded Fabics (Ellis Horwood Ltd., England), Devies O L, The Design and Analysis of Industrial Experiments (Longman Group Ltd., New York) 1978, 508 & Cochran W G & Cox G M, Experimental Design (Asia Publishing House, Bombay, India), 1963, Chambers E G, Statistical Calculation for Beginners (The University Press, Cambridge), 1958, 61.