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Effect of Fibre & Nonwoven Fabric Properties on Acoustic Applications

Written by: M Parthiban, V Thirumurugan, M Ramesh Kumar

Abstract: In the present world, noise is a vital area of research. As noise causes a lot of problems in day-to-day life, it is important to control unwanted noise. A lot of products were invented for reducing noise. These materials are used in a wide variety of applications. The influence of pore size, fibre type, source, intensity, distance of the fabric from sound source, number of layers on sound reduction of various needle-punched nonwoven fabrics has been studied in an indigenous instrument. The sound reduction property of nonwovens is higher than woven fabrics. The sound reduction properties of nonwoven needle-punched fabric produced from recycled polyethylene terephthalate (R-PET), jute, viscose, polyester, polypropylene, and flax fibres have been studied.

Introduction

The following have been established by researchers and reported earlier in peer-reviewed journals:

  • The acoustic application of hollow polyester, PET and polypropylene fibres are based on needle-punched nonwoven. In that, 50 per cent polypropylene based nonwoven sample react in a better way and as the polypropylene percentage increases, the acoustic property of the material also increases.1
  • Jute fibres are comparatively coarse in nature and have wide variation in fineness, apart from its mesh-like structure. The high moisture property of jute fibre is suitable to various applications. Thus jute fibre is ideal for the production of needle-punched nonwoven. Jute fibre is also one of the cheapest material available.4
  • R-PET and cotton fibre blended needle-punched nonwoven gives better result and the ratio of R-PET and cotton is 30:70. So the usage of R-PET in the technical textiles leads to a more eco-friendly process.5
  • Recycled cotton and polyester fibres are used to produce air filtration applications. Even though the recycled fibres have poor strength, it does not affect the properties of filtration.6
  • Jute and polypropylene based needle-punched nonwoven fabric exhibits better sound absorption property than 100 per cent jute, 100 per cent polypropylene and its blend. Distance from the sound source to material also affects the effectiveness of needle-punched nonwoven fabric.7

Materials and Methods

Materials: Nonwoven fabrics are ideal material for use as an acoustical insulation product as they have high total surface. The surface area of the fabric is directly related to the denier and cross sectional shape of the fibres in the fabric.4 The nonwoven material (200 GSM) is produced from 65mm of 3 denier fibre by needle punching technique using cross laid web.

S1) 100% jute

S2)100% flax

S3)100% viscose

S4)100% polyester

S5)100% R- PET

S6)100% polypropylene

Manufacturing of needle punched nonwoven fabrics: Dilo nonwoven plant comprises a fibre opener (RE 5) that opens the fibres into small tufts and feeds them to a card feeder (CFL 7). It further opens the fibre and the batt formed is fed into a carding machine (CAL 7). The carding machine produces a thin sheet of carded web and passes it to the lab layer (F7/6) in which the web is cross-laid and formed as batt and sent to needle-punching nonwoven machine. The material is then passed to a needle loom (DI loom OUG -II 6), where the batt is needle-punched and the nonwoven fabric is formed by needle-punching technology.

To prepare the blended fabric, the jute, flax and recycled PET fibres were opened and proportionately stack-mixed. This blend was processed in the Dilo needle-punching loom to produce nonwoven fabrics with areal density of 200 and needle density of 200 punches/cm2 for this study.

fig 1

                                                                                         

Table 1Evaluation of sound insulation property of nonwoven fabrics: A testing apparatus was developed for measuring sound permeability of a nonwoven needle punched fabric (Figure 2). It consists of a thick acrylic transparent plastic material with a top lid. Inside this transparent box, a fixed sound source enters the testing apparatus. A decibel meter is used to measure the source of sound. The other end of this box has another decibel meter to measure the sound intensity of received output sound. In between these two ends of the box, two slot arrangements are used to fix the nonwoven fabric sample vertically. The rise and fall of sound is controlled by the control panel.

fig 2Sound reduction measurement: A particular decibel sound is created by the control panel at one side of the box. The input decibel and the output decibel are measured by suitable circuits in decibel with or without fixing the sample in the sample slot. The same procedure is repeated in the second slot of the box as well. Slot I is at a distance of 8 cm from the sound source and slot II is at 16 cm distance from the sound source. The sound insulation property of a fabric is calculated by measuring and comparing the reading from the decibel meter by using the following method (dbf is the sound reduction for fabric):dBf = (Decibel reduction received value without sample) - (Decibel reduction received value with sample) 

Results and Discussion

Fabric thickness testing: The thickness reading of experimental nonwoven sample fabrics ranged from 3 to 4 mm, which is shown in Table 2. The fabric thickness was measured using a thickness gauge as per the procedures of ASTM D1772. The weight per unit length and thickness of nonwoven material influence the sound absorption property. When the weight per unit length is less, the sound insulation value is less by the material. And when the weight per unit length is high, the sound insulation value is also high. For high weight, the space between the fibres in the nonwoven structure is minimum. The thickness of 100 per cent flax fabric shows highest value of sound absorption and 100 per cent polypropylene fabric shows lowest value. The needle punched flax sample has bulkiness because of its fibre nature. So it shows more thick structure than the other nonwoven samples.

Table 2fig 3

Air permeability: Air permeability test was carried out as per the standard (ASTM-D 4491-92).  From the table, the thickness of the nonwoven fabric and air permeability are interrelated. If the thickness changes, the air permeability of nonwoven fabric also changes. It has been seen that when the increase in thickness increases the number of fibers per unit cross section of the nonwoven fabric, the free spaces in nonwoven fabric will be reduced which further reduces the free movement of air through the fabric. Besides this the effect of needle punching nonwoven technique aid in the result due to the entanglement of fibres which reduces the pore spaces and free area between fibres which in turn decreases fabric air permeability. Thus pore spaces in the fabrics will be decreased due to fabric bulkiness and so the ability of air to pass through the fabric will be also reduced.

Table 3

fig 4

Table 3 shows air permeability of needle punched nonwoven samples. The air permeability is closely related to the arrangement of the fibres and percentage of open area present in the sample. The thickness is also one of the main factors for determining air permeability of the fabric. The natural fibre based needle punching nonwoven samples exhibit less air through their structure, this is due to the arrangement of fibre in the structure of nonwoven samples. The R-PET fibre and its blend have more permeability which release more air than the natural fibre samples.

Effect of pore size: The effect of noise in the residential area and workplace environments are controlled by textile materials especially with the help of nonwoven materials. Generally nonwoven material is used for sound insulation due to its high weight per unit length of material. The fine fibres used for the production of nonwoven material exhibit high insulation value than the coarse fibres. And also the surface finishes affect the sound absorption characteristic of needle punched nonwoven fabrics. For higher pores in the nonwoven sample, the sound absorption coefficient through the sample is more, and air and sound flow is recorded as a function of acoustic properties. Porosity and air permeability have a positive correlation. A more porosity structure leads to an increase in air permeability. The fabrics produced from finer fibers which are arranged tightly absorb sound wave more effectively and samples with no surface treatment gives the highest sound absorption. The sample has more areal density cause sound reduction coefficient of the fabrics to be more value and chemical finishing seriously affect the sound absorption characteristics of the sample.

Table 5 & Fig 5 

From Table 4, in the pore size testing, the 100 per cent jute fibre mean flow diameter is very less compared to all other samples. This is because of the jute fibres arrangement in the needle punched nonwoven technique. The up and down movement of the barbed needle makes the highest degree of entanglement of jute fibres. So the binding force is more and the gap between the fibres is very less. The jute blended nonwoven sample has less mean flow diameter. Flax nonwoven showed moderate value. Natural fibres based nonwoven samples with rough surface area exhibited highest degree of entanglement of fibres. This value highly affects the sound reduction property of nonwoven sample. The R-PET fibre shows very good mean flow pore diameter value.

Sound reduction testSound reduction test: The figure shows the sound reduction of 200g/m² needle punched nonwoven fabrics made up of different raw materials i.e. pure jute, pure flax, fully recycled polyester and their blends. The evaluation has been done by keeping the fabric at slot I (8 cm), slot II (16 cm) and the receiver meter at 24 cm in the same side from the sound source.

fig 6 & 7

Figure 6 shows the decibel value of different sample at slot 1 while measuring sound reduction. The source decibel value and the receipt decibel have been measured by suitable source and receiver circuits without or with sample. The input decibel value of 120 is fixed as standard. The output decibel value is based upon the sound reduction value of the sample, which is fixed in the slot I. It is seen that the 100 per cent viscose sample is effective for sound reduction due to the irregular arrangement of fibres in the nonwoven sample by barbed needle loom. And also it is seen that the pure polyester sample gives nearest value of sound reduction to viscose. As per this test, when the distance between the sound source and material is less, the viscose fibre nonwoven material is suitable for sound reduction in end user applications.

Figure 7 shows the decibel value of different sample at slot II in the sound reduction measurement. The source decibel value and the receipt decibel have been measured by suitable source and receiver circuits without or with sample. The input decibel value of 120 is fixed as standard. The output decibel value is based on the sound reduction value of the sample, which is fixed in slot I. It is seen that the 100 per cent viscose sample is effective for sound reduction due to the irregular arrangement of fibres in the nonwoven sample by barbed needle loom. It is also seen that the 100 per cent polyester sample gives nearest value of sound reduction to viscose. As per this test, when the distance between the sound source and material is more, the viscose fibre nonwoven material is suitable for sound reduction.

fig 8

Figure 8, shows the decibel value of different samples at slot 1 & 2 in the sound reduction measurement. The source decibel and receipt decibel have been measured by suitable source and receiver circuits without or with sample. It is seen that the viscose sample is effective for sound reduction when comparing to other samples. The polyester fibre also has sound reduction value next to viscose. For sound reduction, as per this test, irrespective of whether the distance between the sound source and material is less or more, the viscose fibre nonwoven material is suitable for various textile-related acoustic applications.

Conclusions

Considering environmental issues, the potential market growth for environment-friendly nonwoven materials as interior and automotive applications, particularly car interiors is high. Nonwoven materials were produced from fibres like pure forms of jute, flax, viscose, polypropylene, polyester, R-PET, etc, by needle-punching technology with the GSM of 200. The nonwovens were tested for thickness, air permeability, porosity and sound reduction test. It was observed that viscose fibres have very good sound reduction value. Even though they have moderate value in thickness, air permeability and porosity, the sound reduction property of viscose nonwoven sample is very good. Hence it is concluded that nonwoven produced from viscose maybe suitable for automobile interiors and other applications like floor mats and acoustic wall coverings for auditoriums, theatres and generator rooms.

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