| Polylactic acid(PLA) can be completely biodegraded without damage to the environment,and has good mechanical properties and processing properties,but the price is high.While the starch(ST)which is an abundant and lower cost biomaterial has poor thermoplastic processing.Since the interface compatibility of polylactic acid and starch is very poor,and the performances product of PLLA and starch blends are not achieved the national standards.Therefore,this paper mainly uses a torque rheometer to physically modify the polylactic acid / starch composite material(nanocomposite,flexible polymer material blending)and chemical modification(crosslinking,grafting)to enhance its interfacial compatibility,mechanical properties,thermal resistance stability,melt strength etc.The content of this thesis can be divided into the following three parts.Part one: Effects of nano-materials and flexible polymer materials on the mechanical properties of polylactic acid/starch composites.Experimental results showed that the modification effect of nanomaterials is better than that of flexible polymers,and the nano-silica has best modification effect for improving the interfacial compatibility and thermal resistance stability among the calcium carbonate,hydrotalcite,and silica.In addition,nano-silica can act as a heterogeneous nucleating agent for enhancing the crystallization rate of the composites.The elongation at break of PLA/starch composites was increased to 97.0% which was 2.5 times higher than that without adding nanomaterials(39.5%)when adding 5 phr of nano-silica.Part two: Effect of nano-silica content on the properties of polylactic acid/starch composites.The results showed that the mechanical properties of the PLA/starch composites were showed best properties when adding 10 phr of nano-silica.At this condition,the tensile strength of the composite is increased from 18.26 MPa to 23.08 MPa,and the elongation at break was increased from 39.5% to 165.28%.Part three: Effects of crosslinking and grafting on the properties of polylactic acid/starch composites.The results showed that the interfacial compatibility,melt strength and mechanical properties of polylactic acid/starch composites were significantly improved after cross-linking.When added the 0.1 phr of TBEC and 0.3 phr of TAIC,the tensile strength of the composite was increased from 23.08 MPa to 26.4 MPa,and the elongation at break was increased from 165.3% to 248.8%.In addition,the effect of crosslinking on tensile strength of composite was better than that of grafting,whereas effect of grafting on break at elongation of composite was better than that of crosslinking. |
