mechanical properties of recycled cfrp by injection ... - Takahashi

16 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALSMECHANICAL PROPERTIES OF RECYCLED CFRPBY INJECTION MOLDING METHODJun Takahashi *, Nobukuni Matsutsuka *, Tetsuya Okazumi *, Kiyoshi Uzawa *,Isamu Ohsawa *, Koji Yamaguchi ** and Akihiko Kitano *** Department of Environmental and Ocean Engineering, The University of Tokyo, Japan,** Toray Industries, Inc., JapanKeywords: CFRP, Recycle, Injection Molding, Crush, ABS, PPAbstractEnergy consumption of the running stage ofautomobiles can be drastically reduced bylightening their weight by CFRP (carbon fiberreinforced plastics). However, energy consumptionof the CFRP manufacturing is so big to cancel theenergy saving of the running stage. To reduceenergy consumption and cost of CFRPmanufacturing, reuse of carbon fiber is the mosteffective. Then, the objective of this study is todevelop CFRTP (carbon fiber reinforcedthermoplastics) by using waste CFRP, and the targetof the mechanical properties of the recycled CFRPis more than those of secondary structural parts ofcurrent automobile.1 IntroductionFor more than a century, population, foodproduction, industrial production, consumption ofresources and pollution are all growing. Amongthem, we have been studying the increase of energyconsumption by car-orientated society [1-4]. Figure1 shows sectional energy consumption in the world.Comparing sectional energy consumption, that oftransport sector has too much depended on oil for along time, and been increasing firmly. Consideringthe motorization of non-OECD countries, inespecially BRICs, it is easy to predict that energyconsumption of transport sector will more and moregrow from now on. For example, as shown in figure2, energy consumption in transport sector of Chinawill become equal level to the current world energyconsumption in transport sector in the future withoutany drastic measurement [3, 4]. So, we need todevelop effective measurements as soon as possible.Although fuel cell technology is now underdevelopment, it takes much time to be practicalapplication.From such a background, we have focused onlightening the weight of automobile by using CFRP(carbon fiber reinforced plastics). CFRP is used forthe aircraft or space field since their high specificstrength, specific rigidity and lightweight. Howevercurrent CFRP is not suitable to mass productionbecause of its high cost and recyclability [5]. In thispaper we investigated recyclability of CFRP formass production.2 Recycle Method in This StudyAs a method of CFRP recycling, heat recoveryand material recycling have been investigated, andmaterial recycling is better from a viewpoint of LCA(life cycle assessment) since carbon fiber should bereused as not just carbon but carbon fiber. Figure 3shows the energy intensity of parts manufacturing byusing steel, CFRTS (carbon fiber reinforcedthermosetting resin) and CFRTP (carbon fiberreinforced thermoplastics) [6, 7]. As a result,recycling of CFRP contributes to reduce not onlywaste but life cycle energy consumption as shown infigure 4. Furthermore, considering that the cost ofrecycled CFRP must be very cheap as shown infigure 3, establishment of the recycling technologyof CFRP will drastically contribute to lower-pricingof CFRP products. Hence, the recycling technologyof CFRP is indispensable in the mass-productionapplication, in especially passenger automobile, tocontribute global energy saving.As a method of taking out carbon fiber fromwaste CFRP, evaporation [8] and a chemicaldepolymerization of thermosetting resin [9] arereported as shown in figure 5. According to thesemethods, there is a possibility that a high1

MECHANICAL PROPERTIES OF RECYCLED CFRP BY INJECTION MOLDING METHODmechanical properties by using the injection moldedplates to understand an actual performance ofinjection molded automotive parts. The injectiongate of the metal mold of the panel is designed asone place so that anisotropy similar to actualinjection molded parts might appear to the moldedpanels. Then, in order to examine the directionalproperties, flexural test specimens are cut out fromthese panels in both the direction of injection and thevertical direction.4 Experimental Results of Panel SpecimensThe size of the flexural test specimens werelength 80 mm * width 15 mm * thickness 3 mm, andthree points bending test and Izot impact energyabsorption test were performed. Five times testswere performed for every condition; thermoplasticswithout CF, longitudinal and transversal specimensof CFRTP with Vf = 30 % of fresh CF, longitudinaland transversal specimens of CFRTP with Vf = 7, 15,24 and 30 % of recycled CF.The result of these tests is summarized in figures7 and 8, where “F” means the specimen made byfresh CF, “L” means longitudinal specimen and “T”means transversal specimen, and the number meansvolume fraction of recycled CF respectively. Brittlefracture occurred in compressive side in everyspecimen.In the same manner, we investigated theinfluence of the repetition of recycling. RecycledCF/PP specimens whose fiber volume fraction is15 % were crushed and remolded by injectionmolding method to obtain the second, third andfourth recycled specimens. The results aresummarized in figures 9.5 Discussions5.1 JIS Standard SpecimensIn case of the flexural test shown in figure 6,there is little difference in mechanical propertiesbetween Fresh 30 and Recycle 30, hence thedegradation may be quite little in recycling process.In terms of the flexural strength, the specimens withthe fiber volume fraction of 24 % show higherstrength than those with the fiber volume fraction of30 %. It may be caused by the poor impregnation ofthermoplastics into recycled CF in the cases that thefiber volume fraction is larger than 24 %. Then, theappropriate volume fraction at this recycle methodmay be around 24 % or less.In case of the tensile test, fresh material hadhighest mechanical property. Difference from theflexural test was that the fracture occurred at theweakest point of the specimen in tensile test. Andthe weak point may caused by the poor impregnationof thermoplastics into recycled CF.In case of the Izot impact energy absorption test,even in the CFRTP made by fresh CF, energyabsorption ability fell down drastically due to themixture of CF in thermoplastics.5.2 Specimens Cut Out From The InjectionMolded PanelAs shown in figures 7 (a) and 8 (a), a bigdifference between longitudinal and transversaldirection was shown especially in flexural modulus.The flexural modulus of longitudinal directionbecame large almost in proportion to the fibervolume fraction like JIS standard specimen, howeverthose of transversal direction showed low and almostconstant regardless of fiber volume fraction.Consequently, when the fiber volume fractionbecame larger, anisotropy became stronger.Furthermore, although the influence of fiber volumefraction on the flexural modulus of longitudinaldirection showed almost the same tendency as JISstandard specimens, the values were about 70 % ofJIS standard specimens. This is because theanisotropy of JIS standard specimen was muchstronger.Although the failure strain of transversaldirection was larger than that of longitudinaldirection, there was not so much difference whichwas shown in flexural modulus. When the fibervolume fraction becomes smaller, failure strain ofboth transversal and longitudinal direction becomeslarger, which is the same tendency of JIS standardspecimens. However, it should be noted that eventhe failure strain of the longitudinal direction is morethan twice of the JIS standard specimens.As a result, like JIS standard specimens,recommended fiber volume fraction is about 24 %since a peak value of the strength was shown around24 %. However, since almost the same strengthholds to the fiber volume fraction of 15 %, recycledCFRTP with fiber volume fraction of about 15 % isalso recommended for a purpose of larger failurestrain if the rigidity is not so serious requirement.By the way, the strength of longitudinaldirection shows approximately 20 % smaller thanthat of JIS standard specimens. To a contrary,injection molded CF/PP parts whose fiber volumefraction is between 15 to 24 % are expected the3

Jun Takahashi, N. Matsutsuka, T. Okazumi, K. Uzawa, I. Ohsawa, K. Yamaguchi and A. KitanoFlexural modulus (GPa)2520151050Fresh 30 24 15 7ABS(a) Flexural modulusFlexuralmodulus(GPa)181614121086420FL FT30L30T24L24T15L15T7L 7TABS(a) Flexural modulusFlexural strength (MPa)200180160140120100806040200Fresh 30 24 15 7 ABS(b) Flexural strengthFlexuralstrength(MPa)180160140120100806040200FL FT30L30T24L24T15L15T7L 7T ABS(b) Flexural strengthFlexural strain (%)3.02.52.01.51.00.50.0Fresh 30 24 15 7 ABS(c) Flexural failure strainFlexuralfailurestrain(%)3.02.52.01.51.00.50.0FL FT 30L30T24L24T15L15T 7L 7T ABS(c) Flexural failure strainIZOD Impact energyabsorption (kJ/m 2 )140120100806040200Vf7 Vf15 Vf24 Vf30 Fresh ABS(d) Izod impact energy absorptionFig. 6. Flexural properties of the recycled CF/ABSJIS standard specimens.Izodimpactenergyabsorption(kJ/m 2 )8070605040302010030L 30T 24L 24T 15L 15T 7L(d) Izod impact energy absorption7T ABSFig. 7. Flexural properties of the recycled CF/ABSspecimens cut out from the injection molded plate.4

MECHANICAL PROPERTIES OF RECYCLED CFRP BY INJECTION MOLDING METHODFlexuralmodulus(GPa)18161412108642030L 30T 24L24T15L15T 7L 7T PP(a) Flexural modulusFlexuralmodulus(GPa)876543210F L F T 1 st L 1 st T 2 nd L 2 nd T 3 rd L 3 rd T 4 th L 4 th T(a) Flexural modulusFlexuralstrength(MPa)Flexuralfailurestrain(%)Izodimpactenergyabsorption(kJ/m 2 )12010080604020030L 30T 24L24T15L15T 7L 7T PP(b) Flexural strength7654321030L 30T 24L 24T15L 15T 7L 7T(c) Flexural failure strain35302520151050PP30L 30T 24L 24T 15L 15T 7L 7T PP(d) Izod impact energy absorptionFig. 8. Flexural properties of the recycled CF/PPspecimens cut out from the injection molded plate.Flexuralstrength(MPa)Flexuralfailurestrain(%)10090807060504030201003210Izodimpactenergyabsorption(kJ/m 2 )F L F T 1 st L 1 st T 2 nd L 2 nd T 3 rd L 3 rd T 4 th L 4 th T(b) Flexural strengthF L F T 1 st L 1 st T 2 nd L 2 nd T 3 rd L 3 rd T 4 th L 4 th T302520151050(c) Flexural failure strainF L F T 1 st L 1 st T 2 nd L 2 nd T 3 rd L 3 rd T 4 th L 4 th T(d) Izod impact energy absorptionFig. 9. Influence of the repetition of recycling on theflexural properties of the CF/PP.5