Evaluation of Mechanical Properties and Flame Resistance of Biobased Polymer Compounds.
Biobased polymers have been introduced for some applications ofelectrical, electric, and office appliances to reduce both petroleumresource exhaustion and C[O.sub. emissions. (1) Although polylacticacid (PLA), as one typical biobased polymer, is commercially availableat present, it is necessary to improve its thermal resistance and impactstrength, as its fracture mode is brittle, and the crystallization speedof PLA is very low. (2) A PLA and PC alloy is now commercialized with aPLA content of 30 wt% or less for parts in electrical, electric, andoffice appliances, as a substitute of existing PC and acrylonitrilebutadiene styrene (ABS) alloy petroleum-based polymers in Japan. It is also important for electrical, electric, and officeappliances to maintain fire resistance. As fire resistance is requiredfor plastic materials and parts in electrical household appliances andgas appliances, advanced flame retardants, free of halogenatedretardants, have been developed. (3,4) Test Materials and Methods Materials A compound of PLA and polyamide-11 (PA11) was firstly considered toincrease the botanical percentage of organic elements in the biobasedpolymer alloy. The standard injection grade Terramac TE-2000 PLA(produced by UNITIKA Ltd.) and the injection grade Rilsan[R] BMN PA11(produced by Arkema Co.) were used in this study. The non-halogenphosphoric acid polyester grade PX200 (produced by Daihachi ChemicalIndustry Co.) and ammonium polyphoshate grade AP422 (produced byClariant K.K. (Japan)) were used as the flame retardants. PLA, PA11, acompatibilizer, and a flame retardant were mixed at various compoundingratios and extruded to form pellets. The test specimens were produced bythe injection molding. A reactive compatibilizer was selected to have an affinity to bothPLA and PA11. According to the contents of the compatibilizer, thelarger in quantity the compatibilizer was, up to 25 phr [parts perhundred resin], the greater the mechanical properties were in thepreliminary test. The 25 phr compatibilizer was selected in this study.As a reference, the PLA and PC alloy grade Ecodear[R] V554X51,commercialized with PLA content of 30 wt% or less (produced by TorayIndustries Inc.), was also selected. Compound ratios of the biobasedpolymer, compatibilizer, and flame retardant are shown in Table 1. Test methods The tensile tests specified in JIS K7161 were conducted by theInstron type 55R4206 universal testing machine at the tensile speed of20 mm/min and at 23[degrees]C. The tensile elastic modulus andelongation at breakage were calculated from the stress-strain curves.The Izod impact tests specified in JIS K7110 were conducted by theinstrumented Toyo Seiki Seisaku-sho DB-IB machine at 23[degrees]C. Thespecimen length was 80 mm, the width was 3 mm, and the thickness was 10mm. A 2-mm-deep V-notch was made to the specimen. The thermal analysisspecified in JlS K7121 was conducted with the PerkinEImer Pyris1 DSCdifferential scanning calorimeter (DSC). The melting temperature, degreeof crystallinity, and heat quantity per unit weight of the compoundswere measured. The flammability test was also conducted with the Toyo SeikiSeisaku-sho MCM-2 multi-cone calorimeter to obtain the relation betweenthe heat release rate or the integrated heat release value andcombustion time. (5) The flame-retarding effect level of the compoundswas evaluated according to the UL-94 method. Test Results and Discussion Mechanical properties After injection molding, the specimens were exposed to hot air toaccelerate crystallization at 90[degrees]C, for 3 hours, as the thermaltreatment. Figure 1 shows a comparison of the tensile modulus, the tensilestrength, and the elongation at breakage among various compounds ofbiobased polymer, compatibilizer, and flame retardant. Figure 2 shows acomparison of the Izod impact strength among various compounds ofbiobased polymer, compatibilizer, and flame retardant. Compared with the PLA/PA11 with a compatibilizer and the PLA/PA11without a compatibilizer, the mechanical properties such as theelongation at breakage after the tensile test and the Izod impactstrength were significantly improved by using a compatibilizer, althoughthe tensile modulus and the tensile strength slightly decreased. (6,7)It was also found that the Izod impact strength of the PLA/PA11 with acompatibilizer after the thermal treatment greatly increased, althoughthe elongation at breakage of the PLA/PA11 with a compatibilizer beforethe thermal treatment was high. The larger the content of flame retardant PX200 was, the smallerthe mechanical properties such as the tensile modulus, the tensilestrength, the elongation at breakage, and the Izod impact strength were,gradually. The reason is that the dispersion of flame retardant into thePLA/PA11/compatibilizer was not sufficient. Compared with the Toray Industries PLA and PC alloy grade EcodearV554X51 (mixed flame retardant with PLA content of 30 wt% or less),which is partly commercialized for a casing material and exterior partsof electrical, electric, and office appliances, the mechanicalproperties of the PLA/PA11/compatibilizer containing flame retardant wasquite equivalent to those of Ecodear V554X51, although the tensilemodulus and the tensile strength of the PLA/PA11/compatibilizercontaining flame retardant were slightly low. Morphology observation Figure 3 shows photographs indicating the dispersion of PA11 andPX200 flame retardant in the PLA region with a scanning electronmicroscope (SEM). In the case without a compatibilizer, there were manyrelatively large-size PA11 grains in the PLA region. PLA and PA11 weremiscible in the case of PLA/PA11/compatibilizer: 100/50/25, as therewere meanwhile small particles of PA11 dispersed in the PLA region. ThePLA and PA11 compound of biobased polymer will be useful as substitutionfor ABS/PC or PLA/PC. Fire resistance is required for casing materialsand exterior parts of electrical, electric, and office appliances. In the case of the PLA/PA11/compatibilizer containing the flameretardant PX200, there were agglomerated particles of PX200 in the PLAand PA11 region as the content of PX200 increased. It was found thatthere were not uniformly dispersed particles of AP422 in the PLA andPA11 regions. Thermal analysis Thermal analysis was conducted with a DSC. The scanning wasperformed for a temperature range of 50 through 200[degrees]C under anitrogen atmosphere. The heating and cooling rates were set at 50 and25[degrees]C/min. Figure 4 shows the heat quantity per unit weight ofPLA/PA11 without a compatibilizer (sample (2) from Table 1), PLA/PA11with a compatibilizer, and PLA/PA11/compatibilizer containing the flameretardant PX200 (6). Figure 5 shows the melting peak temperature ofPLA/PA11 without a compatibilizer (2), PLA/PA11 with a compatibilizer(3), and PUVPA11/compatibilizer containing the flame retardant PX200(6). It was found that the total heat quantity per unit weight ofPLA/PA11 with a compatibilizer decreased resulting in the reaction ofPLA/PA11 and a compatibilizer. However, the effect of the reaction wasreduced in the case of the PLA/PA11/compatibilizer containing flameretardant. Although the melting peak temperature increased more or lessfor PLA/PA11 with a compatibilizer compared with PLA/PA11 without acompatibilizer, the melting peak temperature deceased forPLA/PA11/compatibilizer containing flame retardant. Flammability test results Figure 6 shows the relation between the heat release rate or theintegrated heat release value and the combustion time with respect tovarious compounds. The thickness of the sample was 2 mm, the same as forthe UL-94 specified by JIS Z2391. The curves between the heat releaserate or the integrated heat release value and the combustion time forPLA:100 and PLA/PA11/compatibilizer:100/50/25 were quite different. The curves between the heat release rate or the integrated heatrelease value and the combustion time forPLA/PA11/compatibilizer:100/50/25,PLAIPA11/compatibilizer/PX200:100/50/25/50, andPLA/PA11/compatibilizer/PX200: 100/50/25/100 were similar even if theflame retardant of PX200 was blended to PLA/PA11/compatibilizer. Although the PLA and PC alloy grade Ecodear V554X51 is defined ashaving the V-0 level standardized by the UL-94 method, thePLA/PA11/compatibilizer containing 100 phr of PX200 will be defined asstill having the V-2 level due to incomplete dispersed and agglomeratedparticles of PX200 in the PLA and PA11 region. On the other hand, PLA/PA11/compatibilizer containing 50 phr ormore of AP422 had a good fire resistance satisfied to the V-0 level dueto complete dispersion of AP422 in the PLA and PA11 region. Themechanical properties of compounded materials of PLA and PC, such asEcodear V554X51, are indicated to improve the impact resistance and thethermal resistance of PLA. The PLA/PA11/compatibilizer containing 50 phrof AP422 will be a substitution of Ecodear V554X51, having heatresistance and impact resistance. Conclusions The mechanical properties and the flame resistance of biobasedpolymer compounds of PLA/PA11/compatibilizer containing flame retardantwere evaluated. Flammability tests with the multi-cone calorimeter wereuseful to obtain the relation between the heat release rate or theintegrated heat release value and the combustion time. ThePLA/PA11/compatibilizer containing the flame retardant AP422 will beapplicable for the substitution of compounded materials of PLA and PC,such as Ecodear V554X51. The compatibilizer and fire-resistancetechnology was also applied for high-performance polymer alloys. (8,9) References (1.) T. Yanagisawa et al.: Kobunshi Ronbunshu, Vol. 66, No.2, 49(2009). (2.) M. Iji et al.: NIPPON GOMU KYOKAISHI, Vol.85, 5, 181 (2008). (3.) (4.) F.T. Hung et al.: SPE ANTEC Technical Papers, 57, 291 (2011). (5.) M. Okoshi: Asian Workshop on Polymer Processing, 2012, 146(2012). (6.) M. Kato, S. Kawasaki, H. Nishimura et al.: Seikei-Kakou, Vol.13, 10, 678 (2001). (7.) H. Nishimura, M. Kato, S. Kawasaki et al.: Japan Society ofEnergy and Resources, Vol. 25, No.5, 298 (2004). (8.) N. Imamura et al.: SPE ANTEC Technical Papers,"Evaluation of Mechanical Properties of Used Materials for PlasticsRecycle," 11-2010-0539 (2011). (9.) N. Imamura et al.: SPE ANTEC Technical Papers, "RecycleTechnology of Used Plastic Materials," 12596-150-File00573 (2012). By Nobuyuki Imamura , Hiroki Sakamoto , Yuji Higuchi ,Shinichi Kawasaki , Masayuki Okoshi , Hiroyuki Yamamoto ,Hiroyuki Nishimura , and Takahiro Nishino Osaka Resin Industry Co. Energy Technology Laboratories, Osaka Gas Co. Kyoto Institute of Technology Osaka Gas Chemicals Co.