Study On Preparation And Properties Of Fully Biodegradable PLLA Composites

Environmental pollution is always the big problems of the society.It also encourages people to pay attention to fully biodegrade materials greatly.Polylactic acid with excellent performance(high strength and high modulus,biocompatibility,high transparency,and processability)becomes one of the most potential biodegrade materials.However,the polylactic acid material also has obvious disadvantages,such as brittleness,poor heat resistance,slow crystallization rate,etc.Thus,in order to improve the performance of PLLA and maintain its biodegradability,poly(lactic acid)(PLLA)was enhanced and toughened by boehmite nanorods(BNRs)and the ductile biodegradable polymer poly(1,4-butylene succinate)(PBSU)in this work.The main research contents and conclusions are as follows:(1)Study on the structure and properties of boehmite nanorods(BNRs)/PLLA composites: pristine boehmite nanorods(p-BNRs)were synthesized by hydrothermal reaction and modified boehmite nanorods(m-BNRs)were successfully synthesized by grafting silane coupling agent KH560 on the surface of p-BNRs.After that,the boehmite nanorods(BNRs)/PLLA composites were successfully prepared through melting blend and the modification properties of PLLA through two kinds of bomolite nanorods were compared.It was found that both two kinds of boehmite nanorods all could be uniformly dispersed in the matrix of polylactic acid.The addition of p-BNRs degraded the properties of the composites.However,m-BNRs modified with a large number of epoxy groups could react with the polymer matrix so that it can enhance the interfacial adhesion between m-BNRs and polylactic acid matrix to improve the tensile strength and elongation at break of the nanocomposites.In addition,both two composites could maintain high transmittance and low haze under the condition of low additive content.(2)Study on the structure and properties of pristine boehmite nanorods(p-BNRs)/PLLA/PBSU(70/30)ternary blend system: In order to strengthen and toughen PLLA,p-BNRs /PLLA/PBSU ternary composites were prepared.Interestingly,it was found that p-BNRs were located at the interface of PLLA and PBSU,which made the dispersed phase size significantly reduce.However,the p-BNRs at the interface could improve the tensile strength of the blend and damage the elongation at break and impact strength significantly.This is because p-BNRs can be located at the interface of PLLA and PBSU thermally.The p-BNRs have weak interactions and no covalent bonding with PBSU and PLLA so that p-BNRs cannot improve the mechanical properties of the blend significantly.(3)Study on the structure and properties of modified boehmite nanorods(m-BNRs)/PLLA/PBSU 70/30)ternary blend system and the effects of modified boehmite nanorods on the structure and properties of blends were investigated: In the m-BNRs/PLLA/PBSU blend nanocomposites,it was found that m-BNRs were located at the interface of PLLA and PBSU,which made the dispersed phase size significantly reduce.Unlike the p-BNRs system,at a certain amount of addition the m-BNRs can not only improve the tensile strength of the blend,but also improve its impact strength.This is because m-BNRs modified with a large number of epoxy groups can react with the polymer matrix during the melting blending process to form a good double-grafted structure,and then the double-grafted m-BNRs can located at the interface of PLLA and PBSU to improve the mechanical properties of the blends by chain entanglement between those grafted chains and the polymer matrix.M-BNRs were used to efficiently increase the compatibility of PLLA/PBSU and a fully biodegradable polymer blend nanocomposite with significantly improved strength and toughness was prepared.(4)The "splicing" method was used to construct the co-continuous structure of immiscible PLLA/PBSU blend system: The reaction between the epoxy groups on the surface of boehmite nanorods(m-BNRs)and the two components of the blend was reasonably adjusted and controlled by the splicing method.M-BNRs can be located in two phases or interface.So the m-BNRs formed a good double grafted structure in the melting blend process so that the PLLA/PBSU(50/50)co-continuous composite materials compatibilized by m-BNRs were obtained.The m-BNRs not only improved the tensile strength of the blends,but also improved their elongation at break and impact strength.Therefore,the rigid-toughness balance of the blend nanocomposites was also achieved.