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Investigation of Tensile Properties of Nonwoven Fabrics Produced from Recycled Staple Polyester and Core/Sheath Low Melting Staple Polyester Fibres by Using Carding, Needle Punching, Calendaring and Pressing Machines

Abstract

In this study, tensile properties of nonwoven fabrics produced from recycled staple polyester fibres and core/sheath low melting staple polyester fibres at 1%, 5%, 10%, 20% and 50% blending ratios by using carding, needle punching, calendaring and pressing machines were investigated. The recycled staple polyester fibres and core/sheath low melting staple polyester fibres were used as raw materials. The core/sheath low melting staple polyester fibres were blended with recycled staple polyester fibres at ratios 1%, 5%, 10%, 20% and 50%.

This mixing and web forming operations were carried out at laboratory type carding machine. These webs were bonded mechanically at needle punching machine. These needle punched fabrics were calendared and pressed at 120°C.

The weight per unit area, thickness and tensile properties of the needle punched, thermal bonded and pressed nonwoven fabrics were tested according to ISO and ASTM standards.

The results exhibit that the nonwoven fabric tenacity (cN/tex), tensile strength (MPa), specific strength (MPa/g/cm3) and other specific strength (N.m2/g) increase with the increase of core/sheath low melting polyester staple fibres ratio. It was found that nonwoven fabric thickness and elongation values decrease with increase of core/sheath low melting staple polyester fibres ratio.

Key Words: nonwoven fabric, needle punching, recycled polyester fibre, low melting fibre, calendaring technology, thermal bonding.

I. Introductıon

Nonwoven fibrous webs are mainly bonded by means of mechanical, thermally and chemical techniques depending upon the end product properties and cost. In mechanical bonding process, fibrous sheet or web is bonded together through the application of liquid or air jets, punching felting needles and by stitching with yarn. In chemical bonding, different types of chemicals or binders such as latex, synthetic rubber, acrylics, vinyl esters, styrene and different natural resins are sprayed to the nonwoven web. Other chemical bonding methods applied to nonwoven fabrics are coating, saturation, foam application and print bonding. Thermal bonding requires thermoplastic component to be present in the form of fibre, powder or as a sheath as part of a bi-component fibre. The heat is applied until the thermoplastic component becomes melts in an oven or with calendar cylinders. The thermal bonding process is more economic and environmental friendly. [1]

The rising cost of energy and greater awareness of the environmental impact of latex bonding led to a change in direction. As a result of this, the usage of thermal bonding instead of chemical bonding has increased. The high production rates possible with thermal bonding and the significant energy savings as compared to chemical bonding, due to the absence of significant water evaporation during bonding, makes the process economically attractive. In this method, bi-component and low melt fibres as a raw material are mostly used. [2]

In thermal bonding method, core/sheath bi-component and low melt core/sheath staple fibres are used for bonding fibrous web or for increasing breaking strength of nonwoven fabrics. Such fibres have a core/sheath structure with outer layer having a lower melting temperature that that of the core part. These kinds of fibres are blended and mixed with other staple at specific blending ratios. Bi-component and low melt core/sheath staple fibres have specific core/sheath ratio. In this study, low melt polyester staple fibres with 50/50% core/sheath by weight were used.

Bi-component fibres have been commercially available for years; one of the earliest was a side-by-side fibre called Cantrece developed by DuPont in the mid-1960s followed by Monsanto’s Monvel, which was a self-crimping bi-component fibre used by the hosiery industry during the 1970s. [2]

In Hayes (1992) patent, a melt-bondable bi-component fibre is described which is to be used in nonwoven. First component is a polymer with the capability to form a fibre while the second is a polymer with melting point at least 30°C below that of the first component and with the ability to adhere to the first polymer. Further Hayes recommends polyester as the polymer in the second component as polyester gives better adhesion than other polymeric materials. [3], [4]

Bi-component and core/sheath low melt fibres are made from two components distributed over the entire length of the fibre. They may either belong to the same type of polymer or be totally different polymer types. PET/low melt PET is the low melt polyester fibre consisting of same type of polymer. Polyethylene/polypropylene (PE/PP) is the bi-component fibre consisting of different polymer types. By co-extruding two polymers into one single fibre, the different properties of both polymers are combined. Bi-component fibres are classified according to the distribution of each component within cross-sectional area. Typical cross-section configurations include side-by-side, eccentric, core-sheath, islands-in-the-sea and segmented-pie. [5]

Core/sheath bi-component fibre and core/sheath low melt fibre are the most widely used and the most well-known binder fibre. The sheath part of bi-component fibre or low melt fibre is made from polymers with a low melting. The core part of bi-component fibre or low melt fibre is made from polymers with high melting point. When the fibre is heated, the sheath part of the fibre melts.

The eccentric configuration is used for providing self-crimping properties. The core part of eccentric core/sheath bi-component fibres is out of centre. When then fibre is heated, the fibre curl due to the different shrinking ratios of both polymers. Thus, it is possible to give volume to fibre.

In the side-by-side bi-component fibre, both polymers occupy an equal part of the fibre surface. The fibre may develop more crimp than the eccentric core/sheath configuration.

Segmented pie bi-component fibres are known splittable fibre. Splittables are fibres in which the two polymers share only one common interface and both polymer phases are also exposed.

Island/sea bi-component fibre consists of sea part and islands part. When the sea part of the fibre is dissolved, fabric is produced on the basis of very fine microfibers. These fibres (typically 37 islands) are used in the production of suede fabrics. The process is not often environmentally friendly because of the solvents employed in the removal of the sea part. Evolon® is the commercially spunbonded fabric made from island-in-the-sea polyester/nylon fibres with 16 segmented pie. The polyester and nylon fibres are split and bonded mechanically water-jet (hydroentanglement) technology with high pressure [7], [5]

In this study, the tensile properties of the nonwoven fabrics produced from recycled staple PET polyester fibres and core/sheath (50/50) low melt staple polyester fibres at specific blending ratios by using the carding, needle punching, calendaring and pressing machines were studied. In this regard, the effect of core/sheath low melt staple polyester fibre ratios on nonwoven fabric tenacity was investigated.

Iı. Experimental Study

II.1. Material and Method

In this study, 3 denier 51 mm recycled staple polyester fibres with white colour were used as carrier fibre. 4 denier 51mm core/sheath staple polyester low melting fibres with black colour supplied from Toray Company were used as binder fibre. These fibres are mainly used in the production of needle punched fabric and acquisition distribution layer/fabric (ADL). Table1 and Table2 present main properties of used recycled staple polyester fibre and core/sheath low melting staple polyester fibre.

Low melting polyester staple fibre is used as binder (a bonding agent) to combine staple fibres using heat in the manufacturing process of nonwoven fabric, and it is mainly used in nonwoven fabric used for acoustic insulation material for automotive, acquisition distribution layer (ADL) and cushions for mattress and other furniture. Manufacturers have been switching from the conventional chemical adhesive method using chemical agents, for manufacturing nonwoven fabric, to a thermo-bonding method given the rising awareness for environment-friendliness. Low melting polyester staple fibre is the eco-friendly material used in thermo-bonding and its global market is expanding at a rate of 8% a year. For this reason, the competition in the industry has been intensifying, as manufacturers with top market shares in the LM polyester staple fibre market invests in manufacturing facilities and other companies are newly entering into the market. [8]

The typical cross-section of core/sheath low melt staple polyester fibre is shown in Figure3.  The low melt staple polyester fibre was of core/sheath (50/50) type with a round cross section; core of conventional polyester and a sheath of co-polyester with a melting point of 110°C.

Core/sheath bi-component and low melt polyester staple fibres are utilized for sound absorption in vehicles. There is a rise in automobile applications in emerging economies, as market expands on expansion of requirements for lighter vehicles and for sound absorption. These fibres are used for mattresses, bed padding, sofa cushion materials and in quilt. The fibres are preferred high precision filter for purification. In construction applications, the fibres are used for sound, shock absorption, insulation and for preventing cracks. Other applications of these fibres are cloth interlining, inner soles and agricultural materials.

II.2. Production Method

In the experimental study, the nonwoven fabrics were manufactured at four steps. In the first step, the webs were produced from recycled staple polyester and low melting staple polyester fibres prepared at different blending ratios at carding machine. In the second stage, these webs were mechanically bonded at needle punching machine. In the third stage, needle punched nonwoven fabrics were thermally bonded at calendaring machine. In the fourth stage, thermally and mechanically bonded nonwoven fabrics were pressed. The tensile properties of nonwoven fabrics depend on needle punching machine parameters such as depth of needle penetration, needle type and needling density per cm2.

Wool type carding machine is the most used machine for web forming from staple natural and synthetic fibres. Carding is defined that a process for making fibrous webs in which the fibres are aligned parallel or to each other or random orientated. The fibrous web is produced at the end of the carding machine. In the study, laboratory type sample carding machine was used for making webs as you can see in following figure. [9], [10]

337A laboratory wool type sample carding machine of Mesdan S.P.A. was used for web forming operations. The machine has 4-5kg/h production capacity and 10-15m/min web delivery speed.

The machine is designed to assess the carding performance and quality of staple fibres as well as to produce webs. In addition to this, this machine is suitable for preparing homogeneous coloured fibre samples.

The equipment is composed by a wide conveyor, a pair of feed rollers, three pairs of workers and strippers, main carding cylinder, doffing roller, fancy roller and clearer together with a web collecting drum.

In the first step, the recycled staple polyester fibres and low melting staple polyester fibres were weighted according to blending ratio.

These fibres were mixture by hand before carding machine.

These fibre mixtures were run through the carding machine two times, first time for opening the fibres and second time for blending. Webs were produced at the end of the carding machine.

Needle punching technology was used to consolidate of fibrous structures (web).

Needle punching is a process of bonding nonwoven fibrous web structures by mechanically interlocking the fibres through the web. Barbed needles mounted on a board, punch fibres into the web and then withdraw leaving the fibres entangled.

By varying the stroke per minute, the advance rate of the web, and the degree of penetration of the needles, a wide range of fabric densities can be achieved. [9], [10]

The bonding of staple fibres in these webs was carried out at needle punching machine by using felting needles. 74.3punch needling density per cm2 and 12.5mm needle penetration depth at pre-needling machine was applied to webs. The pre-needled nonwoven fabrics were bonded in the second and third needling machines at 123punch/cm2 and 125punch/cm2 needling density and 10mm and 8mm needle penetration depth respectively.

Needle punched fabrics were thermally bonded by passing through the smooth calendar cylinders at 120°C. The needle punched and thermally bonded nonwoven fabrics were pressed at machine for better melting of low melting fibre at 120°C for 120second under 120bar pressure.

Thermally bonding is the process of using heat to bond or stabilize a web structure that consists of a thermoplastic fibre. Thermally bonding is known melt bonding or heat bonding. [12] The basic concept of thermally bonding was introduced by Reed in 1942. [2] The process is relatively simple. There are mostly used two kind of thermally bonding methods. One of them is bonding with calendar cylinders. Another method is through-air ovens. Hot calendaring and hot oven are the most frequently used methods for thermally bonding of nonwoven webs and fabrics. [9], [10]

II.3. Testing Methods

The weight, thickness and tensile properties of the produced mechanically needle punched, thermally calendar cylinders bonded and pressed nonwoven fabrics were done according to ISO ad ASTM standards.

II.3.1. Thickness Test

The thickness of fabrics is determined as the distance between the upper and the lower surfaces of the material, measured under a specified pressure. Thicknesses of nonwoven fabrics were measured at R&B Cloth Thickness Tester produced from James H.Heal&Co.Ltd Halifax England. Thickness test was done according to TS EN ISO 9073-2 standard. Thickness of nonwoven fabric was measured under 1g per cm2 and 5g per cm2 pressure respectively at the R&B Cloth Thickness Tester. Obtained results were averaged. It was seen that thickness of nonwoven fabric decreased with increase of low melting fibre ratio. [13], [14]

II.3.2. Tensile Strength Test

Instron 4411 tensile testing machine was used to measure the tensile and breaking strength of nonwoven test samples as specified in ASTM D5035-06 Standard Test Method for Breaking Force and Elongation of Textile Fabrics according to strip method. The nonwoven fabric tenacity (cN/tex) was determined according to following equation. Six samples were taken only machine direction (MD). The samples were cut and prepared at 50x175mm dimensions. Test length (the distance between the fixtures) was adjusted to 75mm. Test speed was 300mm per minute. A mean of six test results has been calculated in only machine direction (MD). All samples were conditioned at 65%±2°% relative humidity and temperature of 20±2°C prior to each test at physical testing laboratory of Marmara University Technology Faculty Textile Engineering Department.

The fabric density (g/cm3) was calculated by dividing fabric weight per area (g/m2) by fabric thickness (mm) [15] [16]

The nonwoven fabric tenacity (cN/tex) and specific strength was determined according to following equations.

Specific strength (MPa/g/cm3) is generally used for removing effects of the fabric thickness and fabric weight per unit area on tenacity and strength of nonwoven fabrics. Specific strength (MPa) can be calculated by dividing tensile strength (MPa) by fabric density (g/cm3).

Other specific strength (N/m2/g) was found by considering the breaking strength (N) and fabric areal weight (g/m2) of needle punched, thermally calendar cylinders bonded and pressed nonwoven fabrics. Specific strength was calculated by dividing breaking strength (N) by fabric areal weight (g/m2). Thus, it is possible to compare similar nonwoven fabrics with different basis weight. [17]

Results

Table3 presents the mean of measuring areal weight, thickness and breaking strength values. It was clearly seen that thickness of nonwoven fabric decreases with increase of low melting fibre ratio in the mechanically needle punched, thermally calendared and pressed nonwoven fabric.

The results clearly showed that low melt fibre percentage had a significant impact on nonwoven fabric thickness and thickness of nonwoven fabric decreases with increase of core/sheath low melt staple polyester fibre ratio.

The breaking strength test results of needle punched, thermally calendar cylinders bonded and pressed nonwoven fabrics show that increase of core/sheath low melting staple polyester fibre ratios from 1%, %5, 10%, 20% and to 50% increase the fabric tenacity by 4.57cN/tex, 5,25cN/tex, 5.28cN/tex, 5,46cN/tex and 5.58cN/tex respectively.  On the other hand, increase of core/sheath low melting staple polyester fibre ratios from 1%, %5, 10%, 20% and to 50% decrease elongation (%) values by 71,52%, 47,97%, 40,14%, 33,11% and 28,91% respectively.

Figure8 shows effect of core/sheath low melting staple polyester fibre ratio on nonwoven fabric tenacity (cN/tex). The results show that fabric tenacity (cN/tex) increases slowly with increase of core/sheath low melting staple polyester fibre ratio. This can be explained by the fact that the core/sheath low melting staple polyester fibres have high bonding force.

Figure9 indicates effect of core/sheath low melting staple polyester fibre ratio on breaking elongation (%). Elongation results show that breaking elongation (%) decreases considerably with increase of core/sheath low melting polyester staple fibre ratio.

Figure10 shows effect of low melting staple polyester fibre ratio on tensile strength (MPa). Results show that tensile strength (MPa) increases considerably with increase of core/sheath low melting staple polyester fibre ratio.

Figure11 shows effect of low melting polyester staple fibre ratio on specific strength (MPa/g/cm3).  Results show that specific strength (MPa/g/cm3) increases with increase of core/sheath low melting staple polyester fibre ratio.

Figure12 shows effect of core/sheath low melting polyester staple fibres ratio on specific strength (N.m2/g). Results show that specific strength ((N/m2/g) increases with increase of core/sheath low melting staple polyester fibre ratio.

Conclusion

This experimental study clearly shows the effect of core/sheath low melting polyester staple fibre on tensile strength test results of mechanically needle punched, thermally calendar cylinders bonded and pressed nonwoven fabrics. The recycled staple polyester fibres (r-PES) were blended with core/sheath low melting staple polyester fibre (bi-co PES). The core/sheath low melting staple polyester fibres were used at %1, 5%, 10%, 20% and 50% ratios. The nonwoven fabric production was carried out at carding, needle punching, calendaring and press machines. The following results have been obtained.

•Thickness of nonwoven fabric considerably decreases with increase of core/sheath low melting polyester staple fibre ratio.

•Fabric tenacity (cN/tex) increases with increase of core/sheath low melting polyester staple fibre ratio.

•Elongation values (%) decrease considerably with increase of core/sheath low melting polyester staple fibre ratio.

•Tensile strength (MPa), specific strength (MPa/g(cm3) and specific strength (N.m2/g) increase with increase of core/sheath low melting polyester staple fibre ratio.

Acknowledgement

I would like to thank to Hassan Group for support.

References

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