AbstractWith increasing demand for automobiles in the global mar-

ket, and a simultaneous pressure to address the issue of sus-tainability, there is continuing need for the incorporation ofnatural fiber based materials into automotives. The focus ofrecent research has been to produce compostable cotton fiber-based composites that can be safely disposed off after theirintended use without polluting the atmosphere, in an envi-ronmentally safe manner. It is evident from studies beingdone jointly at the University of Tennessee, University ofBremen, Germany and USDA, New Orleans, that by suitablycombining cotton and other natural cellulosic fibers, with anappropriate biodegradable binder fiber in the right combina-tion a moldable nonwoven fabric can be produced. Resultsfrom these studies addressing the structure and properties ofthe composites, with respect to their suitability for automotiveapplications are discussed.

KeywordsNonwovens, Composites, Automotive, Biodegradable,

Bonding, Cotton, Compostable, Natural Cellulosic Fibers,Flax, Kenaf.

IntroductionThe history and growth of transportation system shows an

enlightening picture of how scientific, technological, social,and economic factors interplay to change the environment inthis world [1, 2]. Automotive growth is strongly related to theeconomic growth that took place in the early part of 20th cen-

tury. Automotives play an important role in the transportationof people both individual and in groups, as well as goods.Large-scale manufacture of these automobiles, operation ofthe transportation (road) network system, and constructionof the required infrastructure has dominant impacts on eco-nomic growth of the country. There exists a substantial needfor fabricated materials in this entire sector. According to anestimate, there are more than 500 million passenger vehiclesin use in this world and about 50 million new cars are pro-duced every year. At an average of 1500 kg of materials for anautomobile, the consumption of materials is in the tune of 70million tons per year. It means, this quantity has to be pro-duced, used and ultimately recycled or disposed at the end ofuseful life. Continuous efforts are on developing newer oralternative materials to achieve cost effectiveness, fuel effi-ciency, reduced emissions, increased safety, and always with atarget on future ability to recycle or biodegrade.

However, today’s rising cost of fuel is a major factor in themove to utilize composites for all transport vehicles, andthereby to achieve a lightweight construction with an ultimategoal of reduction in fuel consumption and emissions.According to an estimate, about 25% reduction in the weightof the vehicle is equivalent to a savings of 250 million barrelsof crude oil and reduction in CO2 emissions to the tune of 220billion pounds per annum [1]. Automobiles today, have betterfuel economy and safety features than they had 25 years ago.It is estimated that, out of 10 gallons of fuel pumped to the caronly 1.7 gallons goes in motion [3]. One way of improvementwould be to make the vehicles lighter by using compositebased structures. Composites made of two or more materialsare superior to their starting materials. Fiber reinforced poly-mer (FRP) composite materials provide a new range of per-formance materials for an automotive industry. Generally,composites are strong, light, and resistant to corrosion andwear. They have been used in space and military vehicles;

Cotton Fiber NonwovensFor Automotive CompositesBy M. G. Kamath, G. S. Bhat*, D. V. Parikh!, and D. Mueller+, Department of Materials Science andEngineering, The University of Tennessee, Knoxville TN 37996

ORIGINAL PAPER/PEER-REVIEWED

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* To whom all correspondence should be addressed to.! USDA, New Orleans, LA+ Universitat Bremen, Germany

performed well, thus could play bigger role in automotivesthan they do today. This is possible only if they are proveneconomical, and performance is better than the conventionalones. Composites with oriented long fiber reinforcements andfiber volume content (more than 50%) can fulfill these goals.Compared with glass fibers, thermoplastic fiber compositesgenerate higher fiber volumes with a fast, clean processingbehavior. To reduce cost, a suitable blend of natural fibers andsynthetic materials seems to be attractive.

It is a fact that automotive textiles are the growing marketsin terms of quantity, quality and product variety. An averageautomobile utilizes fibers, fabrics, woven or non-woven, tothe tune of 20 square meters [4]. This is in the increasing trenddue to the advantages of lightweight, high strength and low-ering cost of textile products. As many as 40 automotive com-ponents such as trunk and hood liners, floor mats, carpets andpadding, speakers, package trays, door panels, and oil and airfilters contain fiber products [4]. Furthermore, these fiber-based materials can contribute greatly to the automotive man-ufacturers final goal constituting weight reduction of 30% andcost reduction of 20% [5].

Increased social awareness of environmental problemsposed by the non-degradable, non-recyclable contents of thesalvaged automobiles is forcing automotive manufacturers toenhance the biodegradable content which is in favor ofswitching to natural fibers. If biodegradable fibers are chosento substitute many of the existing composites, the finishedproducts do not pose disposing difficulty [6]. To accelerate thisprocess of switching to recyclable and biodegradable con-stituents, the legislations in US and Europe have issued a spe-cific directive [7] on the end-of-life vehicles that promotes theuse of environmentally safe products and reduces the landfillspace requirements. The directive, which came into effect atthe turn of this century, predetermines the deposition fractionof a vehicle to 15% for the year 2005, then gradually reducedto 5% for the year 2015.

Nonwoven webs are one of the products popularly used inmaking composites for many applications since they possess agood blend of strength, lightweight, and flexibility comparedto conventional materials [8]. These nonwovens have animportant inherent quality that provides excellent z-direction-al properties that minimizes delamination problem.Formation of composites by using flax fibers and biodegrad-able melt blown (PVA, PLA and PEA) polymers as main com-ponents have been studied by Muller and Krobjilowski [9-12].These natural fiber based composites made of biodegradablemelt blown fabrics as binder, possess many of the requiredproperties that are comparable to the traditional polypropy-lene based composites. Further, flax fiber based compositesare generally stronger, but somewhat brittle, due to the inher-ent nature of the fiber. Use of natural fibers to improve impactstrength of fiber-reinforced composites has been studied [13].Incorporation of cotton is likely to increase the impact resis-tance of these structures that will make such composites suit-able for many more applications. Among all natural cellulosicfibers, cotton is well known for its excellent absorbency, com-fort properties, and natural feel. In addition, biodegradable

nature of cotton is an important quality that makes it an attrac-tive and strong candidate in a situation, where waste disposalis becoming a major concern.

In order to produce nonwovens from natural fibers it can beblended with a synthetic binder fiber or a polymeric chemicalbinder. At present, the most common synthetic binder fibersare polyolefins or polyolefin-based bicomponant fibers thatare not biodegradable. Many of the biodegradable syntheticfiber forming polymers are still at the developmental stageand very few have reached commercial production stage.Cellulose acetate (CA) is a modified cellulosic fiber, wellknown for its properties such as biodegradability, wettability,and liquid transport. Moreover, it is made from cheaperrenewable sources such as wood pulp or cotton linters.Thermoplastic nature of CA makes it a suitable binder fiberthat can undergo thermal calendaring while producing non-wovens out of blends containing cotton and CA. These blendscan produce good quality nonwovens and they are com-postable at the end of their useful life [9-14]. It is also observedthat the plasticized CA fibers have good thermal bonding abil-ity and could achieve acceptable tensile properties.

Other promising candidates for thermoplastic andbiodegradable binder fibers are the recently developed mate-rials in the markets such as PTAT or EastarBio from EastmanChemical Company [15], BioPET or Biomax from Dupont [16],Ecoflex from BASF, Polylactic acid (PLA) from Dow-Cargill[17], and PHBV from Metabolix. Most of these contain chem-icals that are tasty to the degrading organisms so that theproduct undergoes degradation in the composting atmos-phere and the products are safe. PTAT, a biodegradable ther-moplastic is a copolyester with a melting point 120OC. Initialexperimental studies in the laboratory showed promisingresults of using this biodegradable copolyester as a binderfiber [18]. Polylactic acid (PLA), a biodegradable fiber that isproduced from the cornstarch, has a melting temperature of170OC, and tensile properties comparable to that of PET fibers[19]. BioPET a hydro/biodegradable polyester, presently usedin packaging such as sandwich wraps, has a melting point of200OC and could be tried for bonding with cotton. Bayer hasdiscontinued its product BAK, a polyester amide biodegrad-able plastic that it claimed as 100% biodegradable and recy-clable, and had desirable properties such as high tensilestrength.

New products are being developed that can be made fromblends of all natural and manmade fibers, including fiber-glass, wood, coconut and even straw [20]. According to OttoAngleitner, a leader in the air lay market these high loft fiberwebs are possible at both high and low basis weights in uni-formly blended composites or as layered webs. Products cango for molded, needled, insulation, automotive, high loft, geo-textiles, apparel, furnishings, mattresses, carpets, carpet fiberpads, fiberglass mats, filtration, and other applications.

The polymer composite system [21] consisting of celluloseacetate butyrate and lyocell, a high modulus, regenerated cel-lulose fiber exhibited both the interfacial adhesion betweenthe fiber and matrix and the consolidation process in the mak-ing of composite materials. Interfacial adhesion was found to

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be substantial due to the relatively less fiber pullout after ten-sile failure in the unmodified fiber composites. These obser-vations indicate that cotton-based nonwovens have a goodpotential in the fabrication of composite materials for auto-motive applications.

ExperimentalExperiments were carried out to produce composites using

natural fibers, with raw cotton as the major component fiberand various binder polymers as matrix. The binder materialsinvestigated include PTAT and PTAT/PP bicomponent fiberssupplied by Eastman Chemical Co., Kingsport, TN, BioPETand PE/PET bicomponent fibers provided by DuPont, BioPEfilm provided by Maverick, PLA provided by Cargill andPlasticized Cellulose Acetate (PCA) from Celanese Acetate. Todetermine the melting temperature of various binder fibers,differential scanning calorimetric (DSC) scans were obtainedusing the Mettler 821 DSC system. A heating rate of 10OC /minwas used under the nitrogen blanket (200ml/min).

For producing composite panels, a [Wabash] hydraulic hotpress with the capability of controlled heating of both upperand lower plates and applying pressure on the composite wasused for all experiments. First set of experiments were con-ducted using available fibers, film and melt blown webs toproduce sandwich type composites, wherein the core consistsof natural fiber (layer B) and surface binder polymers (layerA), or they are placed in alternating layers by hand as shownin Figure 1.

When this sandwich is heated under pressure in the hotpress, binder is expected to melt, flow and provide goodbonding with the natural fibers. For the second set of experi-ments, a uniform blend of natural fibers and binder fibers (byair laying or carding) was used to produce mixed-fiber com-posites (Figure 2), wherein the composition is expected to beuniform throughout the product.

When this mixed fiber web is heated under pressure in thehot press, bonding takes place due to the melting and flow ofbinder fibers around the natural fibers forming a continuousmatrix. The design of experiments consisted of production ofthe composite samples under various process parameters likecuring time, temp, and pressure for various compositions.Bonding conditions were set based on the melting tempera-ture range as determined by the DSC.

In the next set of experiments, mixed fiber webs were used

to produce composites. Fibers were well mixed by hand andor dry laid using air jets, or carded, where possible, beforemaking composites. Initially a few samples of composites

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Table 1 BASIC PROPERTIES OF FIBERS

Figure 1SANDWICH CONSTRUCTION FOR MAKING

COMPOSITES

Figure 2WELL-MIXED FIBERS OR CARDED WEBS

FOR MAKING COMPOSITES

PROPERTIES OF FIBERSNATURAL FIBERS BINDER FIBERSCotton Kenaf Flax PP PTAT PTAT/PP bico

Denier dtex 0.8 to 2.5 2.6 - 4.1 0.8 - 3.4 3.3 4.4 4.4Fiber length mm 12 to 38 12 to 50 12 to 75 35 20 35Tenacity cN/dtex 22 to 34 35 to 77 32 to 78 45 22 42Elongation at failure % 6 - 8 4 - 5 3 - 5 30 35 32

were made to establish the procedure. The various sets ofmixed fibers produced to conduct more studies on compositesare shown in Table 2. A Hollingsworth card was used to make12-inch wide webs from small amount of fiber samples insome cases. These mixed fibers were subjected to thermalbonding in the hot press at a temperature of about 20OC high-er than the melting temperature of the binder, at 1Bar pressurefor 5 minutes. In the third set of experiment, BioPET was usedas the binder fiber. The fourth set of experiment was carriedout with PLA as the binder fiber.

All the composite samples produced in the experimentswere analyzed for physical properties and structure understandard laboratory conditions. The physical propertiesinclude weight and thickness, using TMI thickness tester.Tensile properties were determined using the United TensileTester. Samples cut to 25.4 mm wide, 76.2 mm long wereclamped and stretched to break at a uniform strain rate. Thestructural evaluation consists of tensile characteristics, failuremechanism and morphology. Scanning Electron Micrographsof the samples and the fractured samples provide additional

information to understand the structure and correlate theproperties.

Results and DiscussionResults from the DSC of the binder fibers areshown in Figure 3. PTAT and PE shows abroad melting endotherm around 110 and120OC respectively. PP and BioPET show a rel-atively higher melting temperature around163 and 200OC respectively. The DSC scan ofthe bicomponent fiber shows two meltingpeaks. The two peaks for PTAT/PP fibers aredue to early melting of PTAT sheath at 110OCand the PP core polymer melting at 165OC.

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Figure 3DSC SCANS OF VARIOUS BINDER POLYMERS

[HEATING RATE OF 10OC/MIN]

Table 3TENSILE TEST RESULTS OF HOT PRESS BONDED SAMPLES

Table 2DETAILS OF THE FIBER MIXTURES PRODUCED

** Standardized for 200gsm basis weightNotes: 1. Cotton to cotton bonded by needlepunching2. Hot press operated at ~ 20OC above the melt temp of the binder component, 1Bar, 10min.3. Maverickfilm is a biodegradable (PE film with proprietary additives) from Maverick Enterprises4. * EastarPP: Bi-component fiber with PP core 5. Biomax chips cotton composite was uniform.

Sam. Type Binder Natural Ratio of Thick- Weight Peak Peak Break Break# Comp. Fiber Binder: ness Load** Elong. Load** Elong.

Natural mm gsm N % N %Control Cotton Cotton 1.660 186 30.1 101.5 5.6 120.91 Sandwich Eastarfilm Cotton 50:50 0.450 174 66.6 38.5 18.2 45.82 Sandwich Maverickfilm Cotton 50:50 0.345 176 90.6 18.6 18.1 29.33 Sandwich MeltblownPP Cotton 30:70 0.487 132 93.5 4.8 88.5 5.24 Sandwich Biomaxchips Cotton 50:50 0.546 519 82.9 3.9 53.7 4.15 Fiber Mix Eastar Cotton 30:70 0.520 137 53.0 7.7 26.0 10.26 Fiber Mix Eastar Cotton 50:50 0.667 129 24.0 6.3 10.1 12.17 Fiber Mix EastarPP* Cotton 30:70 0.813 210 49.1 7.5 9.4 19.88 Fiber Mix EastarPP* Cotton 50:50 0.668 261 92.3 14.3 7.3 21.39 Fiber Mix PCA Cotton 30:70 0.473 153 131.8 3.5 91.1 3.7

Sample No. Binder Cotton Kenaf Flax1 50 502 50 25 253 50 25 254 50 505 50 50

The results from tensile testing of the first set of experi-ments with various composite web samples are summarizedin Table-3 and Figure 4. Most of the samples had a comparablebasis weight, and the web thickness was in the range of 400-600 microns, at least about a third of the original web thick-ness. For each sample, five specimens were tested and aver-age value was taken. Further, values were normalized for thebasis weight of the control sample and plotted. As evidentfrom the data, though the sandwich type composites showedgood tensile strength, tensile failure occurs with separation ofits layers (Figure 5) indicating poor bonding across the thick-ness. Although tensile load data shows good results, whenobserved in comparison to fabric weight of the samples,

Eastar PP and PCA show very good strength, and compositesproduced via the formation of fiber mix give better results.For sandwich type construction, higher load is also associatedwith higher elongation, which is the result of different failuremechanism. Especially when films are used in the sandwich,the higher load and elongation are the result of the film ratherthan that of the true composite. That is further evident fromcontinuous film structures in combination with free fiberswithout any matrix around them that can be seen in the SEMphotograph of the composites as shown in Figure 5.

In most of the sandwich type structures, there was no inti-mate mixing between cotton and binders and it was not pos-sible to obtain good consolidation of the webs. In addition,when pellets, film or melt blown webs were used, there wasnot sufficient flow to uniformly spread the matrix resin allaround the webs. That is why the strength of the webs was notas high as expected. Fiber mix of PTAT-cotton was very poorthat leads to poor tensile strength of the same. PCA-Cotton

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Figure 4TENSILE PROPERTIES OF VARIOUS

COMPOSITE WEBSS – SANDWICH TYPE, F – FIBER MIX TYPE.

Figure 5SEM PICTURE SHOWING SANDWICH COM-POSITE FAILURE WITH SEPARATION OF ITS

LAYERS

Figure 6SEM PICTURE SHOWING FIBER MIX COM-

POSITE WITH GOOD BONDING

Figure 6SEM PICTURE SHOWING FIBER BREAKAGE

DURING PULL-OUT DURING TENSILE FRAC-TURE [FIBER MIX COMPOSITE]

fiber mix composite (Figure 6) showed very encouragingresults attributable to good bonding between cotton and thebinder.

The results from tensile testing of the set of experimentswith a more intimate mixing of fibers in the composite websamples are summarized in Figure 8. BioPET binder fiber wasused in all these samples. There is a substantial increase intensile strength when flax or kenaf is present along with cot-ton. The SEM photographs (Figures 9a and 9b) show the strongbonding of the binder fibers with the natural fibers in thecomposites. The melting and flow of the binder fiber over thecellulosic fibers takes place and appears to form good bond bythe binder fiber. This is a promising situation indicating goodbonding with cellulose from the binder fibers made fromBioPET. Interfacial adhesion was found to be substantial dueto relatively less fiber pull-out after tensile failure [Figure 9b]in the unmodified fiber composites These are the samplesfrom one-shot attempts at one set of conditions to provide anindication of performance. However, it is clear that theapproach in this process is to understand the behavior of non-wovens made of blend of fibers and it is the most promisingstep in order to develop biodegradable composites.

The tensile results for samples with PLA binder are sum-marized in Figure 10. The results show the trend similar to theone seen in the samples with BioPET. It can be seen thatblending of kenaf or flax increases the tensile strength andmodulus of the cotton composite with the PLA binder.Overall, the tensile properties of the composites with PLAmatrix are slightly better than that of those produced fromfibermix with BioPET binder fibers.

ConclusionsThe initial studies have shown that these natural fibers such

as cotton, kenaf, and flax have the ability to form a good bondbetween thermoplastic binder polymers such as polyolefins,

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Figure 8TENSILE PROPERTIES OF COMPOSITE WEBS

WITH BIOPET AS THE BINDER

Figure 9aBIOPET- COTTON- KENAF (50:25:25)

Figure 9bFRACTURED SAMPLE AFTER TENSILE TEST

Figure 10TENSILE STRESS-STRAIN PROPERTIES OFCOMPOSITE WEBS WITH PLA AS BINDER

PTAT, BioPET, PCA and PLA. Bonding between cotton or nat-ural fibers and the binder polymer is very good when com-posites are made from mixed fiber or carded webs. Intimateblending of the binder fiber with cellulosic fibers is the key tothe manufacture of composites with good properties. Further,it is demonstrated that blending of kenaf or flax enhances ten-sile strength and modulus of the cotton composite. Also forkenaf and flax fibers, adding cotton helps in increasing thetensile elongation of the composites. In addition, it can be con-cluded that in order to produce biodegradable composites outof natural fibers, both PLA and BioPET are suitable candidatesthat act as good binders. Techniques such as Air-laying orCarding produce more uniform webs that improve the tensileproperties of the composites. As a result, by suitably combin-ing cotton, kenaf, and flax with an appropriate biodegradablebinder fiber in the right combination a moldable fabric that issuitable for automotive applications can be produced.

AcknowledgmentsThis research was supported by funding from Cotton

Incorporated. Authors would like to acknowledge the sup-port received from Dupont Company, Eastman ChemicalsCompany, Foss Manufacturing, Maverick Enterprises, Vifanand Celanese Acetate by providing binder fibers/film/poly-mers.

References1. R. Lan Mair, Tomorrow’s Plastic Cars, ATSE Focus #113

Jul-Aug 2000. 2. K. Hess, “The growth of Automotive Transportation,”

June 9, 1996.3. Current, Michigan State University Newsletter, Vol 93,

Summer 1999.4. W. Kinkel, Naturfasern im Automobil – Einsatzgebiete,

Prozeßtechniken und Marktvolumina, Presentation,Symposium „Marktinnovation Hanf - Verbundwerkstoffe mitHanffasern, Märkte und Ökonomie”, Wolfsburg/Germany,May 26th, 1999.

5. W. Fung and M. Hardcastle, “Textiles in automotive engi-neering”, Woodhead Publishing Ltd, Cambridge, England.

6. D. H. Mueller, A. Krobjilowski, H. Schachtschneider, J.Muessig, G. Cescutti, Acoustical properties of reinforced com-posite materials and layered structures basing on naturalfibers, Proceedings of the INTC-International NonwovensTechnical Conference, Atlanta, GA/USA, 24-26. September2002.

7. N. N., Directive 2000/53/EC of the European Parliamentand the Council of end-of-life vehicles, Office Journal of theEuropean Communities, October 21st, 2000, ABl. EG Nr. L 269S. 34L 269/34.

8. G. S. Bhat, “Nonwovens as Three-Dimensional Textilesfor Composites,” Materials and Manufacturing Processes, Vol.10,No.4, 667-688-1995.

9. D. H. Mueller and A. Krobjilowski, “Meltblowing ofBiodegradable Polymers and New Applications forMeltblown Fabrics,” Proceedings of the Ninth TANDECAnnual Conference, Knoxville, TN -1999).

10. D. H. Mueller and A. Krobjilowski, Meltblown Fabricsfrom Biodegradable Polymers, Proceedings of the INTC-International Nonwovens Technical Conference, Dallas,Texas/USA, September 26-28, 2000.

11. D. H. Mueller, A. Krobjilowski, Meltblown Fabrics fromBiodgradable Polymers, International Nonwovens Journal,Volume 10, No. 1, Spring 2001, pages 11-18.

12. D. H. Mueller, A. Krobjilowski, Meltblown Fabrics fromBiodegradable Polymers, Proceedings of the INTC-International Nonwovens Technical Conference, Baltimore,Maryland/USA, September 5-7, 2001.

13. D. H. Mueller, Improving the Impact Strength of NaturalFiber Reinforce Composites by Specifically Designed Materialand Process Parameters, International Nonwovens Journal,Volume 13, No. 4, Winter 2004, pages 31-38.

14. H. Suh, K. E. Duckett and G. S. Bhat, “Biodegradableand Tensile Properties of Cotton/Cellulose AcetateNonwovens,” Textile Research Journal, 66 (4) 230-237 (1996).

15. W.A.Haile, “New Biodegradable Polyesters,” EDANA’SNonwoven Symposium 2001.

16. Trade catalog, www.dupont.com/packaging/prod-ucts/biomax.html.

17. “Ecological Fiber Made from Corn,”http://www.kanebotx.com/english/new/corn-f.htm.

18. G. S. Bhat, H. Rong, K. E. Duckett, and Mac McLean,“Biodegradable Nonwovens from Cotton-BasedCompositions,” Proceedings of the 2000 Beltwide Conference–2000.

19. J. Dugan, “Novel Properties of PLA,” Fiber InnovationTechnology, Inc.

20. Air Lay systems, www.textilenews.com, Nov 12, 2001.21. Seavy, “Lyocell FRP Composites,” M.S.Thesis, 1999,

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