Study on bursting behavior of spunbonded nonwoven fabrics: Part II Change in fabric characteristics due to repeated bursting cycle

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1 Indian Journal of.fibre & Textile Research Vol. 36, March 2011, pp Study on bursting behavior of spunbonded nonwoven fabrics: Part II Change in fabric characteristics due to repeated bursting cycle A Das a & R J Raghav Department of Textile Technology, Indian Institute of Technology, New Delhi , India Received 7 January 2010; revised received and accepted 25 March 2010 The change in the properties, such as tensile characteristics, compressional behaviour and air permeability, of a wide range of polypropylene heat-sealed spunbonded nonwoven fabrics has been studied after cyclic bursting pressure. It is observed that the cyclic bursting pressure results in change in tensile, compressional and transmission characteristics of fabrics to a great extent. The air permeability is found to be increased after the application of cyclic pressure, whereas the compressibility and recovery tendency increase marginally after the application of cyclic pressure. The cyclic bursting pressure also have significant impact on the tensile strength of spunbonded nonwoven fabrics. The tensile strength reduces after the application of cyclic pressure. The increase in the pressure level during cyclic loading significantly decreases the tensile strength. Keywords: Air permeability, Bursting strength, Compressibility, Cyclic pressure, Spunbonded nonwoven, Tensile strength 1 Introduction In many applications, the nonwoven fabrics are subjected to repeated cyclic bursting pressures which result in substantial changes in their characteristics. For example, in geotextile or filter applications, the fabrics are subjected to repeated bursting pressure. These repeated bursting pressures are generally not up to the extent of bursting point, i.e. they are generally much below the bursting failure pressure, but they are sufficient for structural deformation of fabrics and thus the properties of fabrics also get affected. Geotextiles, when in use, are subjected to repetitive loading and unloading. It is very important to know the compressional behavior of nonwoven during cyclic loading. The compressional behavior of a nonwoven geotextile is an important mechanical property, as it affects the tensile and hydraulic properties and is necessary to characterize the compressional and recovery behavior of these fabrics when predicting their behavior while in use. There are a large number of applications in which nonwoven fabrics are used for their compressional properties. The typical examples can be found in the field of geotextiles, e.g. for drainage and filtration purpose. a To whom all the correspondence should be addressed. apurba65@gmail.com The transmission and the tensile characteristics of spunbonded nonwoven fabrics also change due to repeated cyclic loading. In Part I of this series 1 the bursting behavior of fabric under different loading conditions has been reported. A number of studies 2-5 have been reported on the compressional properties of loose fibre masses. However, very little work has been reported on the compressional behavior of nonwoven fabrics Several theories and empirical equations have been given by researchers 2-4 for the compressional characteristics of fibre masses. Most of these equations are not applicable to nonwoven fabrics, because the fibres in the nonwoven fabrics have certain degree of order and are bonded together with varying fibre arrangement, depending on the type of nonwoven fabric, method of web preparation and bonding. The compressional and recovery properties of different types of nonwoven fabrics have been studied and characterized by Kothari and Das 6,7 in terms of two independent parameters (α and β), where α is the compressional parameter and β, the recovery parameter. They derived following equations for compression and recovery behaviour of heat-sealed spunbonded nonwoven fabrics. The following equations represent the loading and unloading behaviour of heat-sealed spunbonded nonwoven fabrics:

2 54 INDIAN J. FIBRE TEXT. RES., MARCH 2011 Compression: T/T o = 1-α log e (P/P o ). (1) Recovery : T/T f = 1-β log e (P/P f ). (2) where T o and T f are the initial and final thicknesses at initial (P 0 ) and final (P f ) pressures respectively; and T, the thickness at any pressure (P). In the above equations, α and β are dimensionless constants, and they indicate the nature of compression and recovery behaviour of different types of nonwoven fabrics. A higher value of α means greater compressibility and a greater value of β indicates a greater amount of recovery from compressed final thickness (T f ). When the fabrics are subjected to repeated loadingunloading cycles, it is expected that their mechanical and transmission characteristics will get changed. The present study deals with the changes in fabric characteristics, like tensile characteristics, compressional behaviour and air permeability, after repeated pressure cycles. The basic objective of this work is to study the effect of cyclic bursting pressure on the changes in compressional, tensile and air transmission characteristics of a wide range of spunbonded nonwoven fabrics. The same sets of spunbonded nonwoven fabrics, as used in Part I of this series, have been used in the present study. The cyclic pressures were applied at four different levels of bursting pressure, namely 20, 40, 60 and 80%. Three types of bursting cycles were applied, namely continuous increase and decrease of pressure (termed as continuous), resting for 1 min at maximum pressure during cycle (termed as 1 min) and resting for 5 min at maximum pressure during cycle (termed as 5 min). The changes in the above characteristics before and after the cyclic bursting pressures have been reported. Sample No. Mass per unit area g/m 2 2 Materials and Methods 2.1 Materials The same set of polypropylene spunbonded nonwoven fabrics, as used in Part I 1 of this series, was used in the present study. The mass per unit area of fabrics varies from 54 g/m 2 to 289 g/m 2. A series of polypropylene nonwoven fabric with varying mass per unit area and thickness was used to study the changes in fabric characteristics during bursting cycle. All the fabrics used were spun-laid thermally bonded nonwoven samples. The characteristics of fabrics before the application of cyclic pressure are given in Table Methods Air permeability of the fabric was measured by TEXTEST FX 3300 air permeability tester as per ASTM D737. Essdiel thickness tester was used to study the compressional behavior. Fabric samples were placed on an anvil and pressure foot of 20mm diameter was brought down to apply a pressure of 2 kpa on the fabric for 30s and the thickness was measured as initial thickness (T 0 ). The compressive load was increased in steps and corresponding thicknesses were recorded after waiting for 30s. After reaching a pressure of 200 kpa, the pressure was gradually reduced in steps and the corresponding thicknesses were recorded in the same way during the recovery cycles. Tensile characteristics were measured on Instron tensile tester as per ASTM D Care has been taken so that the previously bursting cycle tested portion remains at center. 3 Results and Discussion All the fabric samples were subjected to cyclic bursting pressures up to 20 cycles at different levels of bursting pressures. The spunbonded nonwoven fabric Table 1 Characteristics of spunbonded nonwovens before cyclic pressure Bursting strength kg/cm 2 Air permeability cm 3 /cm 2 /s Compressional parameter (α) Recovery parameter (β) Tensile load kg S S S S S S S S S S S S S

3 DAS & RAGHAV: BURSTING BEHAVIOR OF SPUNBONDED NONWOVEN FABRICS: PART II 55 samples were subjected to cyclic loadings at 20, 40, 60 and 80% of bursting pressures of the respective fabric sample. During the application of cyclic bursting pressure the fabrics undergo structural changes, thus the characteristics of these fabrics also change. The nature of changes in properties of spunbonded nonwovens, such as air permeability, compressional characteristics and tensile strength, has been discussed in the present section. Two representative spunbonded nonwoven fabrics (S5 and S10) have been chosen for the detailed discussion. The trends for the other fabric samples are found to be almost similar. At 80% of the bursting pressure, for fabric sample S10, the fabric got damaged before the completion of 20 cycles with 1 min and 5 min dwell time. So, there are no data available for these experiments. Fig. 1 Air permeability of S5 sample after different proportions of cyclic bursting pressure 3.1 Air Permeability Table 1 shows the air permeability of all the application of cyclic bursting pressure. It is evident from Table 1 that the fabrics with lower mass per unit area show higher air permeability and the air permeability reduces with the increase in fabric mass per unit area. The lower air permeability in case of heavier fabric is mainly due to more resistance of air flow by the higher number of fibres present in the fabric cross-section and higher fabric density 1. It can be observed from Fig. 1 that the cyclic bursting pressure has significant impact on the air permeability of spunbonded nonwoven fabrics. The air permeability, in general, increases after the application of cyclic pressure. This may be due to the fact that the application of cyclic outward pressure results in distortion of the fabric structure due to extension of component fibres and breakage of interfibre bonds. It is also evident from Fig. 1 that the increase in the pressure level during cyclic loading results in increase in air permeability to a great extent. This is mainly due to the fact that the increase in pressure level increases the extent of structural distortion by opening up of the structural consolidation and more breakage of inter-fibre bonds. The type of pressure cycle, i.e. time of rest at maximum pressure during pressure cycle, shows definite trend but the change is at lesser extent. As the time of rest at maximum pressure during pressure cycle increases the air permeability increases. This may be due to the fact that during the rest at higher pressure the permanent structural deformation takes place due to creep effect. The similar trends have been observed in case of other fabrics also. 3.2 Compressional Behaviour The values of compressional parameters (α) and recovery parameter (β) for all the samples have been calculated by applying the respective equations from the pressure-thickness data during compression and recovery cycle. Higher compression parameter (α) shows the higher compression from certain initial thickness and higher recovery parameter (β) shows higher recovery from certain compressed thickness. Compressional parameters (α) of all the application of cyclic bursting pressure are given in Table 1. It can be observed from Table 1 that, in general, the fabrics with lower mass per unit area show higher compressibility and it reduces with the increase in fabric mass per unit area. The lower compressibility in case of heavier fabric is mainly due to more compact structure of heavier spunbonded nonwovens 1. It is evident from Fig. 2 that the cyclic bursting pressure has some effect on the compressibility of spunbonded nonwoven fabrics. The compressibility increases marginally after the application of cyclic pressure. This may be due to the fact that the application of cyclic outward pressure results in breakage of inter-fibre bonds to some extent. It can also be seen from Fig. 2 that the increase in the pressure level during cyclic loading results in increase in compressibility to some extent. This is mainly due to the fact that the increase in pressure level increases the extent of structural distortion by more number of breakages of inter-fibre bonds. The types of pressure cycle, i.e. time of rest at maximum pressure during pressure cycle, show definite trend but the changes are at lesser extent. As the time of rest at maximum pressure during pressure cycle increases the

4 56 INDIAN J. FIBRE TEXT. RES., MARCH 2011 Fig. 2 Compressional parameters of S5 sample after different proportions of cyclic bursting pressure compressibility increases. This may be due to the fact that during the rest at higher pressure the chances of bond breakages are higher. As far as the recovery parameter (β) is concerned (Table 1 and Fig. 3) it follows almost the similar trend as that of the compressional parameter. The recovery, in general, depends on the type of fabric structure, nature of structural deformations during compression and fibre characteristics 6, 7. So, the phenomenon of recovery is not that straight forward. Similar trends have been observed in case of other fabrics also. 3.3 Tensile Strength Table 1 shows the tensile strength of all the application of cyclic bursting pressure. It is evident from Table 1 that the fabrics with lower mass per unit area show lower tensile strength and the tensile strength, in general, increases with the increase in fabric mass per unit area. The higher tensile strength in case of heavier fabric is mainly due to higher number of fibres present in the fabric cross-section which exerts higher resistance during tensile loading. In addition to the number of fibres present in the fabric cross-section the tensile strength of spunbonded nonwovens also depends on the fibre orientation. It is clear from Fig. 4 that the cyclic bursting pressure has significant impact on the tensile strength of spunbonded nonwoven fabrics. The tensile strength reduces after the application of cyclic pressure. This is due to the fact that the application of cyclic outward pressure results in distortion of the fabric structure due to breakage of inter-fibre bonds and may be by breakage of some of the component fibres. It is also evident from Fig. 4 that the increase in the pressure level during cyclic loading results in significant decrease in tensile strength. This is mainly due to the Fig. 3 Recovery parameters of S5 sample after different proportions of cyclic bursting pressure Fig. 4 Tensile strength of S5 sample after different proportions of cyclic bursting pressure fact that the increase in pressure level increases the extent of structural distortion by opening up of the structural consolidation and more breakage of inter-fibre bonds and component fibres. The types of pressure cycle, i.e. time of rest at maximum pressure during pressure cycle, do not show any particular trend. The time of rest at maximum pressure during pressure cycle results in the permanent structural deformation due to creep effect and more number of inter-fibre bond breakages. At the same time fibres become more independent, which allows them to get aligned towards the load direction during tensile breakage and results in increase in tensile strength. The similar trends have been observed in case of other fabrics also.

5 DAS & RAGHAV: BURSTING BEHAVIOR OF SPUNBONDED NONWOVEN FABRICS: PART II 57 4 Conclusion 4.1 The air permeability decreases with the increase in fabric mass per unit area. However, in general, it increases after the application of cyclic pressure. The increase in the pressure level during cyclic loading results in increase in air permeability to a great extent. With the increase in time of rest at maximum pressure during pressure cycle the air permeability increases. 4.2 The compressibility of spunbonded nonwovens decreases with the increase in fabric mass per unit area. However, it increases marginally after the application of cyclic pressure. The increase in the pressure level during cyclic loading results in increase in compressibility to some extent. With the increase in time of rest at maximum pressure during pressure cycle the compressibility increases. 4.3 The recovery parameter follows almost the similar trend as that of the compressional parameter. The fabrics with lower mass per unit area show lower tensile strength and the tensile strength, in general, increases with the increase in fabric mass per unit area. However it decreases after the application of cyclic pressure. References 1 Das A & Raghav R J, Indian J Fibre Text Res, 34 (2009) Dunlop J I, J Text Inst, 74 (1983) Van Wyk C M, J Text Inst, 37 (1946) T Young M D & Dircks A D, Text Res J, 55 (1985) Sebestyen E & Hickie T S, J Text Inst, 62 (1971) Kothari V K & Das A, Geotext Geomemb, 11 (1992) Kothari V K & Das A, J Text Inst, 84 (1993) Kothari V K & Das A, Indian J Fibre Text Res, 19 (1994) Kothari V K & Das A, Geotext Geomemb, 13 (1994) Das A, Alagirusamy R & Banerjee B, J Text Inst, 100 (2009) 10.

Study of cyclic bursting loading on needle-punched nonwovens: Part II Change in air permeability and compression behavior

Indian Journal of Fibre & Textile Research Vol. 43, June 2018, pp. 203-208 Study of cyclic bursting loading on needle-punched nonwovens: Part II Change in air permeability and compression behavior Bipin