Study On Preparation And Properties Of PLA-based Biodegradable Materials

Recently,the use of large-scale of traditional petroleum-based plastics has resulted in serious white pollution and"microplastics"problems,which poses a critical threat to the natural environment and human health.Biodegradability,sustainable development and recyclability of bio-based polymer materials can not only decrease pollution problems,but also reduce the dependency of petrochemical resources.Among them,poly(lactic acid)(PLA)has unparalleled advantages of other biomaterials,which can be used in food packaging,medical and agriculture fields.Brittleness,poor heat resistance and crystallization of PLA were limited to its further development.Hence,for the shortcomings above,the main research works were as follows:(1)In the first part,anhydroxylitol tripelargonate(AXP),a novel environmentally sustainable plasticizer for poly(lactic acid)/poly(butylene succinate)(PLA/PBS)blends,was successfully synthesized.The chemical structure of AXP was confirmed by FTIR and1H-NMR.The influence of varying the addition of AXP on mechanical property,thermal property,crystallization,rheological behavior and micromorphology of PLA/PBS blends was investigated in detail.The results showed that the toughness and elongation at break of the blends were improved gradually with the increase of plasticizer addition,which indicated that plasticizer played a good plasticizing role in toughening blends.Furthermore,the introduction of AXP reduced the glass transition temperature(T_g)of the blends and simultaneously enhanced its crystallization and processability.Observing the impact section of blends by SEM,it can be found that plasticizer AXP could change the blend from brittle fracture to ductile fracture.Additionally,the plasticization of AXP rivalled those petro-based plasticizers and the cost was lower than isosorbide-based plasticizer,which could be potential substitute to supplant phthalates and isosorbide-based plasticizer in the future industry.(2)In the second part,a thermoplastic starch(TPS)was synthesized by using plasticizer AXP to modify corn starch,and a series of PLA/TPS blends with different compositions were prepared.The effects of TPS additions on the properties of PLA/TPS blends were studied.The results showed that with the increase of TPS additions,the T_g and crystallization and processing properties of the blends were enhanced.At the same time,the introduction of TPS improved the mechanical properties of the blends.Using SEM to observe the morphological structure of the blend,it can be found that TPS can be well dispersed in the PLA matrix.(3)In the third part,the surface of PLA was modified by GMA,and the grafted branches of PLA-g-GMA were prepared.The TPS content was fixed to 30%and a series of PLA-g-GMA/PBAT/TPS blends with different content were prepared,and the effect of poly(butylene adipate-co-terephthalate)(PBAT)additions on the properties of the blends was studied.The results showed that the crystallinity and T_g of the blends decreased with the increase of the addition of PBAT.The introduction of flexible fatty chain and aromatic ring of PBAT enhanced the toughness and processing property and of the blends.The microstructure analysis showed that the fracture mode of the blends was changed from brittle fracture to ductile fracture,and the compatibility between PBAT and matrix was good.(4)In the fourth part,in order to improve the heat resistance of PLA,PLA and wollastonite fiber(AH0026)were blended by melt blending,and the effect of wollastonite content on the properties of the blend was studied.Studies have shown that the addition of wollastonite was increased the T_g,the processing,mechanical properties and the thermal stability.At the same time,the introduction of wollastonite enhanced the crystallization of the blends and played a role of heterogeneous nucleation in PLA matrix.The SEM analysis showed that the wollastonite was well dispersed in the PLA matrix.