The High Performance Studies On Biobased And Biodegradable Polylactide Materials

Being one of the most promising biopolymers,polylactide(PLA)has been attracting much attention due to its excellent performances in renewability,ideal carbon cycle excluding petroleum resources,biocompatibility and biodegradability.However,commercial PLA products shows some inherent drawbacks including low crystallization rate,low toughness and low flame retardance,which restrict particular applications of PLA materials in long-term commercial uses,such as automotive and electronics.In this thesis,a series of studies is presented aiming to overcome these drawbacks of PLA and extend its application.Furthermore,phase morphologies and interface interactions are detailedly characterized in an attempt to analyze the possible toughnening mechanism.The specific content includes the following aspects:1.Through thermal annealing at above the glass transition temperature,a supertoughened binary blend.The binary blend was composed of biocompatible and biodegradable polylactide(PLA)and ethylene-acrylic ester-glycidyl methacrylate terpolymer(EGMA)elastomer at the composition of PLA/EGMA 80/20.Moreover,this super-toughened binary blend also displayed a much high heat deflection temperature for application.Thermal annealing induced crystallization of PLA matrix in the blend and a linear correlation between the notched Izod impact strength and crystallinity were revealed.The possible toughening mechanism for the PLA/EGMA 80/20 blend with thermal annealing was analyzed from the viewpoint of negative pressure effects.2.A supertoughened ternary polylactide(PLA)blend with high heat deflection temperature was reported in this study.The ternary blend was composed of two major biocompatible and biodegradable polymers,namely,PLA and polyamide-11(PA11),and one minor reactive elastomer ethylene-acrylic ester-glycidyl methacrylate terpolymer(EGMA)as a toughener.Shear processing with a very high rotation speed was utilized to prepare the blend by melt blending,which exhibited a significant effect on toughness.At the high screw rotation speed of 1000 rpm of the twin-screw extruder,the PLA/PA11/EGMA 40/40/20 ternary blend displayed simultaneous increases in tensile toughness and notched Izod impact strength.Differential scanning calorimeter was utilized to examine the changes of glass transition temperature with increasing screw rotation speed for the blends,and transmission electron microscope was used to observe the phase domain distributions for PLA,PA11 and EGMA components in the ternary blend,aiming to reveal the underlying toughening mechanism.Moreover,a much higher heat deflection temperature was obtained for this supertoughened ternary blend as compared with neat PLA and PLA/EGMA blend without PA11.3.Biocompatible and biodegradable polylactide(PLA)composites with supertough mechanical property and sufficient flame retardancy were fabricated by employing a facile approach involving reactive blending of PLA and ethylene-acrylic ester-glycidyl methacrylate terpolymer(EGMA)with addition of aluminum hypophosphite(AHP)as an effective flame retardant.Thermogravimetric analysis and microscale combustion calorimetry were further applied to reveal the thermal decomposition and combustion behaviors,respectively.The phase separation morphology,dispersion of AHP particles in PLA/EGMA 80/20 matrix,and fracture surfaces and char residues after flame burning were examined by phase contrast optical microscopy and scanning electron microscopy,respectively,which helped comprehend the results obtained from the mechanical property and flame retardancy tests.4.In order to futher increase the toughness of PLA/EGMA 80/20 reactive blend,PA11 as rigid particle toughening modifiers was incoported into the binary blend.Significant improvements in impact strength were observed after PA11 incorporation.EGMA and PA11 shows synergistic effects in toughening PLA.