Tensile Behavior of the Flax/Polyester Composites after Water Treatment

496Joumal of Donghua Uhiversity (Eng. Ed.) Vol.27, No.4 (2010)Tensile Behavior of the Flax/ Polyester Composites after Water TreatmentWANG Qiu-hong(王秋红)，HUANG Gu(黄故)'"School of Tertiles . Tianjin Polytchnic University, Tianjin 300160 , ChinaSchool of Textile and Light Industry, Dalian Polytechnic Univerity, Dalian 116034, Chinafiber reinforces polymericcomposites inmany fieldsunsaturated polyester as the matrix, composites of two,ranging from construction industry to automotive industry,three, and four layers were fabricated respectively by theduc to its rclative cheapness, ability to recycle, and for thevacum assisted resin infusion (VARI) technique. Tensilefact that it can compete well in terms of strength perstrength of the composites after being saturated in the waterweight of materil0r12].for different durations was tested. The tensile strength ofOne of the restrictions of natural fiber reinforcedthe two-layer composites was decreased after being soaked incomposites is the high moisture absorption of naturalthe water for two, three, and six month, respectively. Fofibers leading to swelling and local or seasonal variationsthe three and four layers specimens, the tensile strength wasin quality that prevents wider use of the composites. Thedecreased initially with water treatment. After reaching thepossibility for the outdoor applications makes it necessaryminimum, the tensile strength was increased. Scanningto analyze their mechanical behaviour under the influenceelectron microscopy ( SEM) confirmed that it might beof weathering, which is not well studied. Rodriguez etcontributed to the thickness of the two-layer composites.al. have reported that glass fiber composite absorbed tenThe thinner specimen is easier to be damaged by thetimes less than the jute, sisal, and flax composites13] .penetrated moisture owing to the delamination between theMoisture absorption studies of sisal fiber reinforcedfiber and the matrix after water immersion. For the threepolypropylene composites has been reported by Chow etand four layers specimens， their contradictory tensilea[L4J. It has been concluded that the tensile strengthstrength suggests that the thicker specimen can delay thedecreased continuously by immersing hot water. Rouisonmoisture permeation and is of better water durability.et al. studied water absorption of hemp fiber/unsaturatedKey words: flax/ polyester compasites; water reaiment;polyester composites and found composite samplestensile strengihimmersed in water reached saturation levels after aboutCc oumber: TQ327.1Document code: Aeight months and showed no signs of cracking due toArticle ID: 1672 - 5220(2010)04 - 0496 - 05seling[ls.,Flax is one of the major natural materials with greatpotential of application in the composite ficld. Flax isIntroductionusually cultivated in the north latitude of the globe. InChina it is usually planted in the northern provinces, likeEnvironmental protection has become one of the majorHeilongjiang. In addition of cellulose, flax also containsconcerns in the world. The disposal of the abandonedgrcater amount of semi-cellulosc, lignin, and pectin. Thefiber is rigid and strong. Because of its competitive strengthenvironmental pollution when high performance fibers areand environmentally friendly character, flax has enjoyedinvolved. Eco materials based on renewable resourceswidespread popularity in composite production, cspeciallyhave attracted growing attention. Around the world, apartin auto industry[15-18].from agricultural uses, different parts of the plants andCompared with high performance fibers, such asfruits of many crops have been found to be viable sourccsglass, carbon, and Kevlar, the flax fiber has much higherof raw materials for industrial needs't]. Natural fibers, as amoisture absorption ability. Questions have been raisedrelatively new group of environmental friendly materialsregarding the property of the flax reinforced materialsand a substitute of glass fiber in the composite components,after long time exposure to high humidity environment.have become more and more interests in the last decadc, byThe effect of moisture on the composites is an importantunifying economy and ecology technologicslisl. Naturalissue since such environmental factors are often presented中国煤化工Received date: 2009 -03- 24Foundation items; Project of Tianjin Scicnce and Technology Comitte,MHC N M H Guatinal Comte ofLiaoning Province, China(No. 2006B013)* Correspondence should be addressed to HUANG Gu, E-mail: Huangll@public. tpt. tj. cnJournal of Donghua University (Eng. Ed.) Vol.27, No. 4 (2010) 497in actual service conditionsC1. It is essential that thecomposites retain thcir mechanical properties with lessdcgradation in the moisture environments.It is believed that in the hunid environment, water上8molcculcs will entcr the interface of the composites because of50 mm_the apilarityo.n]. The polymer matrix and the fiber/ matrixss mm. -55 minterface can be degraded by a hydrolysis reaction of unsaturated120 mmgroups within the resin2司]. Debonding may occur at fiber/180 mmmalrix interfacu. A concem with using flax fiber compositesFig.1 Tension specimens formin high hunidity conditions is the limited understanding andsmall database of information of their durabiliy.immersed in a large tub containing distild water. TheThe aim of this study is to find out the tensileroom temperature during the treatment was withinbehaviour of the flax/ unsaturated polyester composites30C. The pancls were taken from the water at planncdafter long term water treatmert and compare the tensiledays, and wiped dry to remove the water on the surface.strength variation of materials with different thickness. InTensile strength was tcsted within 30 min after thethis investigation, two, three, and four layers flax fabricswithdrawal of the samples from the tub.constructed by plain weave were fabricated withAccording to the Chinese Standard GB 1447 - 1983, theunsaturated polyester by using the vaccum associated resintensile strength was tested with the Universal Tensile Testerinfusion ( VARI) technique firstly. Then the laminates(INSTRON 3369, United States) , according to ASTM D3039.composites were put into a water tub. After differentThe distance between the two clampers before the test wassoaking time, the tensile strength of the samples waskept 120 mm, and the testing speed was 2 mm/ min. For eachtested. At last, scanning electron microscopy (SEM) isgroup of composites, the values of the tensile strength were theutilized to investigate the degradation mechanism of the flax/arithmetic mean of at least eight specimens.unsaturated polyester composites after being immcrsed in waterThe broken sections of the flax/ polyester compositefor certain period of time.before and after the water immersion were invcstigated bySEM(Quanta - 2000,Cech).1 Experimental2 Results and DiscussionThe flax yarns used in the experiments were providedby the Jjiamusi Textile Company ( Heilongjiang province,The rsults of the tensile strengh test are shown in Table 1.China). Tbe yarn fineness was 66. 67 tex with the tensileTable 1 The tensile strengths and standard deviationsstrength of 944. 8 cN and elongation at break of 1. 48%.under water immersion with different timesThe fabric was woven on a rapier loom developed by theTianjin Polytechnic University. The fabric was a plainWaterStrength/MPaStandard deviationimmersion TwO Three- Four-Two- Three- Fourweave with the warp count of 100 ends/10cm and wefttime/month layerlayer layer layer layer layer layercount of 100 picks/10cm. The fabric arca weight wa127. 95 g/m2 and thickness 0.587 mm. VARI technique was8.455.212. 5966.6 60.8 64.2 17.11 4.95 3.2used to fabricate the two, three, and four layers laminates50.0 54.4 58.1 2.45 4.11 1.40with the size of 300 mm X 300 mm. Unsaturated polyester48.1 59.0 71.5 2.54 5.52 5. 90resin (196s) was selected as the matrix, whose viscosity was0.22 -0.44 Pa●s under 25C, and corresponding hardenermethyl ethyl ketone peroxide(MEKP) as well as promoterFrom Table 1, it can be seen that the tensile behaviorcobalt naphthenate were included in the ingredient. Theof different composites was different. The tensile strengthpercentage was 100 : 1.2 : 1.5 in weight. Forty-eightof the two-layer composites for two, three, and sixhours after the fabrication, laminates were cut along themonths, the three-laycr for one, two and three months,warp direction of the fabric. All the samplcs were preparedand the four-layer for one and two months was decreasedaccording to the Chincse Standard GB 1447 - 1983. Figureafter immersion in the water. The results obtained in this1 ilustrated the tensile secimens form.experiment may be a consequence of the different effectsSamples wcre divided into five groups corresponding towhi中国煤化工h of the composites:different water immersion periods. In the experiment, five(1)_terfacial debonding;time intervals were used, i.e., zero, one, two, three,(3)MHc N M H Gwhen the compsisand six months respectively. The composite pancls werehad been immersed in the water, water molecules firstly498Joumal of Donghua University (Eng. Ed.) Vol.27, No. 4 (2010)entered the free space of voids and cracks in thelayers beforc and after the water immersion, respectively.composites, at the same time, water molecules couldFigure 2 shows that the matrix is closely adhered to therapidly penetrate and diffuse along the interface betweenflax fiber bundle. Delamination between the fiber and thethe fiber and matrix owing to the capillarity. Thematrix can't be detected. During the tensile strength test,interfacial bond strength had been weakened by thno pull out of the fibers from the matrix was found. All ofplasticization effct of the absorbed water. On the otherthese results prove that the interface between the flax fiberhand, water molecules would be attracted by theand the polyester matrix is perfect.hydrophilic groups in the flax fiber and the unsaturatedpolyester. After a longer time of immersion in the water,hydrophilic groups of the polyester and the flax fiber wouldhave chemical reactions with water molecules. The resultsuggested an irreversible process might be the causc of thestrength deterioration of the materials.Compared with the original specimens, the values ofthe tensile strength of the three-layer composites for sixmonths and the four-layer for three and six months increaseafter water treatment. As discussed above, the matrix, thereinforcing material, and theinterface were alsodeteriorated unavoidable. However, the water may act as aFig.2 Broken section of the original sample(two-layer, without water treatment)plasticizer to favour the tensile strength. Compared withthe original air molecules trapped in the voids before waterAfter three month water immersion, Fig. 3 shows thatimmersion, water molecules would be more active inthe surface of some fibers in the two-layer specimen is bareresisting the tensile action. Morcover, the increase of thewith fewer adhered resin particles which are pulled out oftensile strength may contribute to the thickness of the threethe matrix during the tensile strength testing. This mayand four layers specimens. Longer time was needed for theilustrate that debonding has happened between the fiberwater molecule to penetrate into the inside of the thickerand the matrix. During the moisture absorption, waterspecimens, which delayed the decline of the tensilemolecules come into the free space of polymers or micro-strength. In addition, the specimens tested after thevoids formed by cavities and cracks, which induce morewithdrawal from the water were not completely dried, andnew macro-cavities and cracks with time prolonged, andthis promoted to the tensile strength because the wet flaxthus the interface is gradually damaged.was swelling adequately and wet strength of flax was muchlarger than its dry strength. Finally, the complex curingand fabricating processes leading to the consolidation of thecompositcs was incomplete. After a long time of immersionin the water, the unsaturated polyester may have oxidationreactions with the oxygen in the water, which may arousean increase of the cross-linking density of the matrix andfurther enhance the tensile strength of the materials.There was one exception of the data in the table.Compared with the other two-layer specimens, the tensilestrength of the two-layer composites was increased a greatdeal after one-month soaking in the water. The higherFig. 3 Broken section of the two-layer composite(three-month water treatment)standard deviation showed an unsteady trend which mightbe caused by the testing error.The results indicate that the materials haveThe panel thickness may influence the tensile strengthexperienced some forms of physical damage and/ortesting resuting in water durability studies if the durationchemical degradation. The weakness of bonding betweenof the treating time is relatively short.fiber and matrix and softening of matrix material result inthe composite strength reduction.3 Failure Mode中国煤化工n of the four-layerspecimFnt. After six-monthFigures 2 and 3 show the SEM images takcn from thewaterYHCNMHGsilheidbythebrokcn sections of the flax/ polyester composites with twopolyester resin closely without obvious debonding. TheJoural of Donghua Uhiversity (Eng. Ed.) Vol.27, No.4 (2010) 499thicker specimen can dclay the moisture permeation, in thiscapillarity effect would encourage the water penetration.ase the degradation effect of the materials may beWith time prolonged, it was understood that chemicaloverweighed by the enhancement effect of the wet flax fiber.reactions would happen between the water molecules andthe flax fiber as well as the matrix. This would damage thetensile property of the material. On the other hand, thewater molecules were considered to be responsible for theincrease of the tensile strength with longer time of watertreatment. The material was even more than the originalpenal because of the illd voids and cracks by the watermolecules, and the fiber and matrix would be bonded withthe hydroxyl group of the water. This would resist thedamage during the tensile testing. At the same time, thewater might work as a plasticizer for flax fiber to resist thetensile action resulting in an increased tensile strength. SoFig.4 Broken section of the four-ayer specimeathe moisture durability of the composites may be improved(six-month water treatmeat)by the aplication of the flax fiber.Therefore, moisture absorption should be taken into4 Conclusionsconsideration when flax fiber is employed as thereinforcement in the composites because of its hydrophilicIn this research, flax plain fabrics were used asnature in order to obtain reliable composite materials.reinforcement and unsaturated polyester as matrix. Thecomposites of two, three, and four layers were fabricatedReferencesrespectively by the VARI technique. The experiment wasilustrated that water molecules played a significant role of[1 ] Schinner G, Brandt J, Richter H. Recycling Carbon Fiber.Reinforced Thermnoplastic Composites [J]. Joumnal ofinfluencing the tensile behavior of the composites.Most of the three and four layers composites have a .Thermoplastic Composite Materials, 1996, 9(3); 239 - 245.relatively better water durability. Although the tensile[2] LiuZQ, Cunba A M, YiX s, et al. Green CompositesBased on Cellulose and Starch: Proessing, Structure andstrength for two-month immersion was decrcased by 12. 9%Properties [C]. The 13th International Conference onand 13.7%，it was increased by 27.4% and 6. 2% later.Composite Materials, Beijing, China, 2001. (in Chinese)The tensile strength of the four-layer materials for six-[ 3] Brouwer W D. Natural Fiber Composites Saving Weightmonth water treatment was lower than that for three-and Cost with Renewable Materials [C]. The 13thmonth. The reason might be that the water immersionInternational Conference on Composite Materials, Bejing,aging affected the microstructure of integrity of theChina, 2001.laminated plates causing numcrous defects. In this way it[4] Khan M A, Hassan M M，Drzal L T. Effee of 2-was still higher than that of the original specimens.Hydroxyethyl Methacrylate (HEMA) on the Mechanicaland Thermal Propertics of Jute .Polycarbonate CompositeFor the composite aimed as reinforcement material, it[J] Composies Part A: Applied Science andwas not beneficial if the material was too thin. It could beMarnufacturing, 2005, 36(1); 71- 81.ilustrated by the reduced tensile strength of the two-layer[5] Oksman K, Skrifvars M, Selin J F. Natural Fibers ascomposites resulted from the deteriorated fiber, matrix,Reinforcement in Polylactic Acid (PLA) Composites[J].and interface. The maximum decrease rate of the tensileComporites Science and Technology, 2003, 63(9); 1317 -strength was 21. 5%. For the thinner laminates employed1324.in the research, the penctration of the moisture into the[6] Bledzki A K，Zhang W Y, Chate A. Natural-Fiber-materials was thoroughly in shorter time. In theReinforced Polyurethane Microfoams [J]. Comporitescircumstances the chemical reaction of the water moleculesSeience and Technology, 2001, 61(16): 2405 - 2411.with the fiber and the matrix would be faster and earlier.[7] Thwea M M, Liao K. Durability of Bamboo-Glass FiberReinforced Polymer Matrix Hybrid Composites [J]. .The interface was easy to be delaminated and graduallyComposies Science and Technology, 2003, 63(3/4): 375 -damaged.387 .For the material with suitable thickness, the serrate[8]中国煤化工Fonseca vM, etal.change of the tensile behavior revealed that there wereof Polyester/Hybridconflict effects in the material. When the composites wereHC N M H G]. Polmer Tesring, ,immersed in the water, the voids and cracks in the material2004, 23(2): 131- 135.would be gradually flled with water molecules, and the[9] Bulions T A，Hoffman D, illspie R A，et al.500Jourmal of Donghua University (Eng. Ed.) Vol. 27, No.4 (2010)Contributions of Feather Fibers and Various CelluloseManufacturing, 2004. 35(6): 703 -710.Fibers to the Mechanical Propertics of Polypropylene[19] Kawaguchi T, Pearson R A. The Moisture Effect on theMatrix Composites[J]. Comporites Science and Technology,Fatigue Crack Growth of Glass Particle and Fiber2006. 66(1); 102- 114.Reinforced Epoxies with Strong and Weak Bonding[10] leBras M，Duquesne s, Fois M，et al. IntumesentConditions; Part 2. A Microscopic Study on TougheningPolypropylene/Flax Blends: a Preliminary Study [J].Mechanism[J]. Composites Science and Technology, 2004,Polymer Degradation and Slabilty, 2005, 88(1): 80 - 84.64(13/14): 1991 - 2007.[11] Baysal E，Yalinkilic M K，Altinok M，et al. Some[20] ZhangJ H, Zhan M s. Visual Experiments for WaterPhysical, Biological, Mechancal, and Fire Propertics ofAbsorbing Process of Fiber-Reinforced Composites [J].Wood Polymer Composite ( WPC) Pretreated with BoricJournal of Compasite Materials, 2004, 38(9); 779 - 790.Acid and Borax Mixture[J]. Constrction and Building[21] Godin N, Huguet s, Gaertner R. Infuence of HydrolyticMarerials, 2007, 21(9); 1879- 1885.Ageing on the Acoustic Emission Signaturces of Damage[12] John M J, Thomas s. Biofibers and Biocomposites [J].Mechanisms Occurring during Tensile Tests on a PolyesterCarbohydrate Polymers, 2008, 71(3): 343 - 364.Compositc: Application of a Kohonen's Map [J].[13] Rodrigucz E, Petrucci R, Puglia D, et al. CharacterizationComporite Structures, 2006, 72(1); 79- 85. ,of Composites Based on Natural and Gilass Fibers Obtained[22] Kotoos A, Mouritz A P. Seawater Durbility of Glassby Vacum Infusion[J]. Journal of Composite Materials,and Carbon-Polymer Compositcs[J]. Comporites Science2005, 39(3); 265- 282.and Technology, 2004, 64(10/11); 1503 - 1511.[14] ChowCPL. XingXS, LiR K Y. Moisture Absorption[23] SuriC, Hamada H，Koyama K. Blister Appearance inStudies of Sisal Fiber Rcinforced Polypropylene CompositesThermoplastic Composites [J ]. Advanced Composite[J]. Composites Science and Technology, 2007, 67 (2);Materials, 2001, 10(1); 63- 75.306-313.[24] HodzicA, KimJ K, LowcAE, et al. The Effts of[15] Rouison D, Couturier M, Sain M, et al. Water AbsorptionWater Aging on the Interphase Region and Interlaminarof Hemp Fiber/Unsaturated Polyester Composites [J].Fracture Toughness in Polymer-Glass Conuposites [J].Polymer Composites, 2005, 26(4): 509 - 525.Composites Science and Technology, 2004, 64 (13/14);[16] Bodros E, Pllin 1, Montrelay N, et al. Could Biopolymers2185 - 2195.Reinforced by Randomly Scattered Flax Fiber be Used in[25] Alvarez V A, Vazqucz A. Effect of Water Sorption on theStructural Applications? [J]. Compoites Science andFlexural Propertics of Fully Biodegradable Composites[J].Technology, 2007, 67(3/4); 462 - 470.Journal of Composite Materials, 2004, 38(13); 1165 -[17] Huang X s, Netravali A. Characterization of Flax Fiber1181.Reinforced Soy Protein Resin Based Green Composites[26] Imilifska K，Cuillaumat L. The Effee of WaterModified with Nano-Clay Particles[J]. Composites ScienceImmersion Ageing on Low-Velocity Impact Behaviour ofand Technology, 2007, 67(10); 2005- 2014.Woven Aramid-Glass Fiber/Epoxy Composites [ J ].[18] Baiardo M，Zini E, Scandola M. Flax Fiber PolyesterComposies Science and Technology, 2004， 64 (13/14);Composites[J]. Composites Part A: Applied Science and2271 - 2278.中国煤化工MYHCNMHG