1. Introduction

Nonwovens are expanding the importance intechnical textiles ; in particular, the automotive industryis the largest sector of technical nonwovens, which arewidely used in many forms for interiors and structuralcomponents for the noise, vibration and harshness (NVH)performance and weight reduction [1]. In the last decades,the automotive industry has achieved significant progressin reducing vehicle weight through the development ofnew vehicle structural design and the utilization of light-weight materials for fuel economy and emission gasreduction. In addition, great efforts have been made onthe NVH management to improve vehicle interiorquietness and comfort. The car interior plays asignificantly important role in aesthetics, sound andvibration insulations, which can be economically andfunctionally improved by the use of textile materials [2].In fact, nonwovens are widely used in the automotiveindustry due to their excellent characteristics such as lightweight, sound and vibration insulation, flexibility,versatility and easy tailored properties, moldability,recyclability, low material and processing costs [3].About forty automotive parts or components are made ofnonwovens in various forms, such as oil and air filters,headliner, insulator dash/hood, floor mat/carpet, door/side

trim, rear package tray, etc [4].Polyurethane (PU) foams are still the preferred

material for automotive seat cushion construction [5].However, some deficiencies of PU foams have beenrecognized in difficult recycling and toxic gas releaseduring their manufacturing processes. The recognition ofsuch concerns has led to new concept, namely, “textilefoams” to replace the PU foams with textile nonwovenstructures. The advantages of textile foams includereduced fogging and unwanted odors, environmental-friendly laminating process, surface material uniformity,possibility of using reclaimed fibers, and recycling intoreclaimed or recycled fibers [3].In the last decade, the elastomeric polyester fibers,

namely ELKⓇ fibers, have been successfully introducedby Teijin, Japan to replace PU foams in upholsterystructures for public transport vehicles like trains,subways and more recently for airplane seats [6].However, to the authors’ knowledge, the nonwovens,comprising of the elastomeric fibers, are limited to theopen literature, especially with respect to seat cushioningperformances. In this study, our efforts are made tounderstand the textile nonwoven foams, produced by thecarding web formation process using hollow polyesterfibers and elastomeric binder fibers to fully realize thegreater potential for cushion materials to replace PUfoams. The hollow fibers have a continuous hole runningdown the middle, which can provide greater bulkiness,

Preparation of Textile Nonwoven Foams Using Elastomeric Binder Fibersfor Automotive Cushioning Materials

Ki-Young Kim＊1, #, Sung Jun Doh＊1, Jung Nam Im＊1, Won Young Jeong＊1,Hyo Jin An＊1, and Dae Young Lim＊1

＊1 Department of Textile Convergence of Biotechnology & Nanotechnology, Korea Institute of IndustrialTechnology, Ansan, South Korea

# corresponding author

Abstract : The physical and mechanical properties of textile nonwovens have been exploited for the replacement ofpolyurethane (PU) foams in car interiors, in particular, cushioning materials for car seats. Polyethylene terephthalate(PET) hollow fibers and elastomeric bicomponent binder fibers were used to manufacture automotive nonwovens bycarding processes, and post bonding processes such as needle punching, thermal bonding or through-air bonding. Thephysical and mechanical properties of nonwovens were thoroughly investigated with respect to the effects of bondingprocesses. The tensile strength and elongation for the nonwovens were significantly improved by the combined needlepunching and through-air bonding processes. In comparison with the PU foam, the nonwovens showed a greaterhardness, and their higher support factors ranging from 7.7 to 11.0 indicated the improved seating performances withbetter air permeability. (Received June 13, 2012 ; Accepted Oct. 1, 2012)

Transaction

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(a) (b)

compression resilience and lightness with nonwovenfabrics to substitute PU foams in the automotive industry[7,8]. Effects of bonding processes such as needlepunching (NP), thermal bonding (TB) and/or through-airbonding (TA) are explored in terms of the physical andmechanical properties of nonwovens by the establishmentof the relationship between the bonding processes andnonwoven characteristics such as tension, hardness,compression and ball rebound resilience.

2. Experimental

2.1 MaterialsThe commercial grade PET hollow fibers were used

in this study for main matrix fibers, and the fibers weresupplied by Woongjin Chemical, South Korea with 7denier, 64 mm length, 4.1 g/den tenacity, and 29.7 %hollowness. The ELKⓇ fibers (Teijin, Japan) were usedfor binder fibers, having a heat fusible polymer at a lower-melting temperature. The fibers are eccentric sheath/coretype fibers of low-melting elastomeric copolyester andpolyester with 5 denier and 64 mm length. Thecharacteristics and properties of the fibers used are listedin Table 1, and the cross sections of the fibers are shownin Fig. 1.For comparison, flexible molded polyurethane (PU)

foams were taken from a front driver seat in a HyundaiGrandeur TG model. The PU foam was found to have anopen-cell microstructure and density of 37.8 kg/m3. Themicrostructure is shown in Fig. 2 , exhibiting the averagecell diameter of 141 µm, strut thickness of 40 µm, and650 pores/mm2.2.2 Nonwoven manufactureNonwovens were manufactured using a pilot scale

nonwoven carding machine at the Korea Institute ofIndustrial Technology. The hollow and binder fibers weremixed at a weight ratio of 8 : 2, opened and carded for theweb formation. The carded web was laid by a cross lapper

to produce the nonwoven webs with 300 g/m2 and 10 mmthickness. The resultant webs were post-processed andbonded by only a thermal bonding (TB) process, needlepunching and thermal bonding (NP+TB) or needlepunching and through-air bonding (NP+TA) combinedprocesses. The webs were needle punched at a punchingrate of 170 strokes/min and/or thermal bonded by adouble belt press at 170°C at a feeding speed of 2 m/min.Alternatively, the needle-punched webs were bonded byhot air blowing in a through-air bonding chamber at180 °C at a conveying speed of 4 m/min for 90 seconds.Fig. 3 shows the manufacturing processes and sampleidentification in terms of bonding processes.2.3 Test methodSingle fiber testing was performed through Favimat-

Robot (Textechno, Germany) to analyze the tensileproperties and linear density (fineness) of the fibers. Thelinear density was measured by the vibroscopic method,and tensile tests were carried out using a gauge length of20 mm at a crosshead speed of 10 mm/min with apretension of 0.5 cN/dtex.The thickness of nonwovens was measured at a

compressive load of 0.5 gf/cm2 using KES-FB3 (KatoTech, Japan). The density was calculated based on thegeometry of nonwovens and the area density. Airpermeability was evaluated by TEXTEST FX 3300 at adifferential pressure of 125 MPa. Air permeability can beexpressed as the rate of air flow through a fixed fabricarea per second.For tensile tests, the nonwovens were cut into the

standard tensile specimens with the dimension of 5 cm ×25 cm (width × length) in accordance to KS M ISO 9073-

Fig. 1 Cross-sections of fibers : (a) hollow PET fibersand (b) elastomeric sheath/core binder fibers.

Fig. 2 Microstructures of PU foams.

Table 1 Physical and mechanical properties of PEThollow and binder fibers.

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3. The test gauge length is 150 mm, and the tensile testswere performed with an Instron 3340 at a cross headspeed of 100 mm/min. For each specimen type, at leastfive specimens were tested in the machine direction (MD)and the cross direction (CD).Hardness measurement for nonwovens was carried

out in accordance with KS M ISO 6672 with a universaltesting machine (Tinus Olsen, England). The nonwovenswere cut into the size of 5 cm × 5 cm (width × length).The 5 layers of nonwovens were laid up and compressedat a constant speed 10 mm/min using a circular pressurefoot with 100 mm diameter. The hardness was determinedas a measured load when the thickness was deformed to30% of their original thickness. The hysteresis wascalculated by Equation 1 from the load-displacementcurves during the hardness test.

(1)

where Aloading is the area under the load-displacement curveon loading, and Aunloading is the area under the load-displacement curve on unloading.Compressive properties of nonwovens are evaluated

by KES-FB3. The nonwoven was compressed by a 2 cm2

pressure foot at a compressive deformation rate of20 µm/sec. Three parameters of linearity (LC),

compressive energy (WC), and resilience (RC) werecalculated by Equation 2-4 [9].

(2)

(3)

(4)

where A is the compressive area (2 cm2), Fm is themaximum compressive load, F denotes the force duringloading and F’ denotes the force during unloading. Em isthe extension at Fm and Er is the extension after the load isreturned to zero.Permanent shrinkage (PS) or compression sets for

nonwovens was the degree of permanent deformation inaccordance with KS M ISO 6672. The nonwovens werecut to the size of 5 cm × 5 cm (width × length) and the 5layers were stacked to satisfy the minimum thicknessrequirement of 5 cm. The original thickness (T ) of thestacked sample was measured first. The nonwoven waspressed to 50 % of the original thickness using a thickaluminum plate fixture, and then placed in a convectionoven at 70 °C for 22 hours. The aged samples wereremoved from the oven and placed for 30 minutes at astandard condition of 20 °C and 56 % RH with theremoval of the fixture. The final thickness (T1) wasmeasured, and the permanent shrinkage was calculated bythe following equation.

(5)

Ball rebound tests were carried out in accordancewith KS M ISO 8307. A 16.8 g steel ball with 16 mmdiameter was dropped from a height of 516 mm onto the5 layered nonwovens. The rebound height was measuredand corresponded to ball rebound resilience as apercentage of the original height.

3. Results and discussion

3.1 Nonwoven morphology and propertiesFig. 4 shows the SEM micrographs to illustrate the

surface morphology of the nonwovens with bondingstructures between the hollow fibers and binder fibers.The larger diameter hollow fibers are randomlydistributed, and the smaller diameter low-melting binderfibers fuse and flow over the hollow matrix fibers, leadingto fiber conjunction and bonding at their crossover areas.However, the SEM micrographs do not reveal distinct

Fig. 3 Schematic of manufacturing processes fornonwovens.

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(b)

(c)

(a)

bonding structures between the different bondingprocesses.The area density, thickness and air permeability of

nonwovens are summarized in Table 2. The area densityand thickness show around 5 % to 20 % variations fromthe processing set values of 300 g/m2 and 10 mm,

respectively, due to unknown parameters such as fiberproperties and manufacturing conditions. The thickness ofNP+TB nonwovens is slightly lower than that of TB andNP+TA nonwovens because the combined needlepunching and thermal bonding processes result in fiberentanglements and compression through the thicknessdirection of the webs, respectively, leading to the denserfabric structures. On the other hand, the NP+TAnonwovens show the highest bulkiness due to the abilityof through-air thermal bonding without the physical webcontact and compression.The relationship between the density and air

permeability in Table 2 demonstrates that the NP+TAnonwovens have the slightly higher air permeability thanthe other nonwovens due to their bulky structures. It isusually observed that air permeability increasesnonlinearly as thickness and area density decrease, andthe area density has a more significant influence on airpermeability than either thickness or fiber size [10].Compared to the PU foam, the higher permeability andlightness for the nonwovens demonstrates seating comfortwith fresh sensation and lightness for seat cushioningpads.Effects of bonding processes on the tensile

properties of bonded nonwovens are clearly demonstratedby the load-displacement curves of nonwovens in Fig. 5,although all the nonwovens have a comparable thicknessand area density. For the machine direction (MD), thenonwoven strength is significantly affected by thebonding processes. The NP+TA nonwoven, bonded bythe combination of the needle punching and through-airbonding, shows the remarkably higher tensile peak loadthan the nonwovens bonded by the other bondingprocesses. The only thermal bonded nonwoven (TB) hasthe similar strength to the NP+TB nonwoven but thelower elongation in comparison with the NP+TB and NP+TA nonwovens. The needle punched and through-airbonded nonwoven has the better performance than theother bonded nonwovens in terms of strength andelongation. The higher strength and elongation can beattributed to the fiber entanglements through the needlepunching process, and better consolidated structures dueto more thermally bonded inter-fiber conjunctions via thethrough-air bonding process. The tensile peak load in thecross direction (CD) exhibits the lower value for all testedsamples than in the MD direction. The significant dropsof the peak load in the CD direction are in goodagreement with those reported in the literature [11] due tomore aligned fibers in the MD direction by the maincylinders and the workers in carding processes.

Fig. 4 SEM micrographs of nonwovens : (a) TB,(b) NP+TB and (c) NP+TA.

Table 2 Physical properties of PU foams and nonwovens.

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(b)

(a)

Hardness is the resistance of materials todeformation under an applied force, which is one ofimportant test parameters to determine seating comfort ordiscomfort. The load-compressive ratio curves for the PUfoam and nonwovens in the hardness tests are shown inFig. 6. The typical curve of PU foams exhibits threedistinct regions : linear elastic region, plateau region anddensification (hardening) region [12]. The PU foam hasthe higher load than the nonwovens in the elastic region.However, the load reaches the plateau value while theload for the nonwovens sharply increases. Finally, thehardness of the PU foam, measured by the indentation

force deflection (IFD) at a compressive ratio of 70 %, islower than that of all the nonwovens (Table 3). The NP+TA nonwoven shows the highest softness with the lowestmaximum load among the other nonwovens due to itsbulkiness, and the nonwoven is similar to the PU foam. Itis worthy to note that the additional needle punchingprocesses increases hardness for nonwovens due to denserfabric structures, and the incorporation of through-airbonding process into nonwovens increases the softnessand bulkiness by maintaining the web thickness.A support factor or sag, defined by the ratio between

65 % IFD and 25 % IFD, is one of the most importantcharacteristics of foams because it governs comfort anddurability [13]. The definition of support is the ability tohold up the weight of a person. Good supportive foams donot “bottom out” or compress to a point where they nolonger hold up the weight of the person, and also arecapable of distributing the weight of the person. TypicalPU foams have the support factor ranging from 1.8 to 3.0[14]. The higher the number is, the greater the foam’sability is to provide support. The support factor of the PUfoam show in Table 3 has the value of 2.8. The 2.8 orhigher values are regarded as providing good comfort[15]. If the cushioning material has a higher initialcollapse stress, the factor is likely to be low and the seatmay be uncomfortable. The higher support factors for thenonwovens demonstrate greater potential for comfortcushioning materials.The permanent shrinkage (PS) indicates the

irreversible deflection after exposure to 70 °C for 22hours. Table 4 shows that the foam has the lowerpermanent shrinkage compared to all the nonwovens. Thehigher permanent shrinkage for the nonwovens impliesthe inferior thickness recovery after compressivedeflection, which may be problematic in durability forcushioning materials such as the service-in thicknessreduction and hardness change. With regarding to theeffects of bonding processes on the nonwovens, NP+TAshows the higher permanent shrinkage than the othernonwovens. It is believed that although fiberentanglement and secure fiber bonding can be induced vianeedle punching and through-air bonding, the bulkinessand softness will deteriorate the thickness recovery andthe resistance to compressive forces.The compression behavior for the PU foam and the

nonwovens is depicted in Fig. 7. Three parameters oflinearity (LC), energy (WC), and resilience (RC) ofcompression are tabulated in Table 4. The LC indicatesthe linear response in the load-displacement curve incompression. The nonwovens show the lower LC and

Fig. 5 Tensile load-displacement curves of nonwovens:(a) machine direction and (b) cross direction.

Table 3 Mechanical properties of PU foams andnonwovens.

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(b)

(c)

(d)

(a)

WC than those of the PU foam, indicating that thenonwovens are more compressible and flexible. Thecompression resilience is the ability to return to theoriginal thickness after compression. The nonwovens,

except NP+TA, are more resilient than the PU foam. Theresilient nonwovens will present better performances withseating comfort and softness for seating pads. The onlythermal bonded nonwoven (TB) shows the larger RC thanNP+TB and NP+TA, that is contrary to the previousreport [16]. The needle punching bonding process fornonwovens results in better consolidation and more fiberentanglement, reducing the fiber-to-fiber slippage duringcompression and improving the compression resilience.Although the contrary results cannot be clearly verified inthis study, the possible explanation may be associatedwith the collapsing of through-thickness oriented fibers

Fig. 7 Typical compressive load-extension curves ofPU foam and nonwovens by KES-FB3.

Table 4 Compressive properties by KES-FB3 andpermanent shrinkage (PS) of PU foams andnonwovens.

Fig. 6 Typical load-compressive ratio curves of PUfoam and nonwovens during hardness tests ;(a) PU foam, (b) TB, (c) NP+TB and (d) NP+TA.

Fig. 8 Ball bound height and resilience of PU foamand nonwovens.

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through the needle punching process and then the loss inthe recovery to the original thickness after compression.The test results for ball rebound tests are shown in

Fig. 8. The rebound height and resilience for TB and NP+TB nonwovens show the slightly higher values than thePU foam. The rebound resilience shows the similar trendto the compression resilience measured by KES-FB3. Thepotential energy of a ball is transferred into thecushioning materials upon impact. The energy is absorbedpartially by the materials and the remaining energy istransferred back to the ball rebound. The low reboundheight indicates high energy absorption materials, andthus the ball rebound height shows a good correlationwith compression resilience. The previous study showsthat the ball rebound resilience was found to increase withdecreasing hysteresis loss. However, the relationship wasnot sufficiently quantitative since the ball rebound energywas less than that predicted from the stored energy [17].The lowest ball rebound resilient NP+TA nonwoven canbe explained by the bulky fibrous structure, beingresponsible to facilitate the energy loss mechanisms suchas reorientation and friction between fibers.

4. Conclusions

The seating comfort performance of elastic textilenonwoven foams were evaluated through the assessmentof tensile properties, hardness, compression propertiesand ball rebound resilience with regard to effects ofbonding processes. The study demonstrated the greaterpotential of the nonwovens for cushion materials, whichexhibited the excellent properties and were comparable tothe PU foam.The experimental results showed that the bonding

processes significantly affected the mechanical propertiesfor the nonwovens, implying the greater design flexibilityto satisfy the variety of performance requirements for theautomotive industry. The higher tensile strength andelongation were attributed to the fiber entanglements andbetter consolidated structures through the combinedneedle punching and through-air bonding processes.However, the bulky structure was found to decrease thecompressive and ball rebound resilience. The hardness,support factor, compressive and ball rebound resiliencewere found to be the important test parameters todetermine seating comfort although the correlationbetween the cushioning characteristics and seat comfortwas difficult to determine qualitatively because seatcomfort was extensively dependent on occupant

preferences. Compared with the PU foam, the nonwovenshowed firmness but higher support factor, leading tohigh level of performances, e.g. good seating comfort.The results of compressive and ball rebound resilienceindicated that the nonwovens were more resilient andcomfortable than the PU foam with the better airpermeability.

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