Study On Toughening Modification And Properties Of Biodegradable Poly(Lactic Acid)

Polylactic acid（PLA）is a biomass and biodegradable synthetic polyester material.Among the biodegradable polymer materials,polylactic acid has the performance advantages comparable to certain engineering plastics（polyethylene and polypropylene）,such as high strength,heat resistance and excellent processing properties（for example,it can be formed by extrusion and injection molding）.So,polylactic acid has been widely researched and applied.However,the disadvantage of poor toughness of polylactic acid makes it impossible to meet the demand for areas with high toughness requirements（such as 3D printing materials and blow molding materials）.At present,the toughening modification method of polylactic acid is divided into physical method and chemical method,However,the chemical method has the problems of high cost,complicated operation and difficulty in realizing large-scale industrial production,the physical method is relatively simple and relatively low in cost.In this paper,the toughening modification effect and toughening modification mechanism of poly（lactic acid）by flexible biodegradable bio-polyesters and nanoparticles were studied.1.The experimental results of compound toughening by poly（butylene succinate）（PBS）and nano-silica（SiO₂）:nano-SiO₂ modified with oleic acid（O-SiO₂）was successfully prepared,PLA/PBS/SiO₂ and PLA/PBS/O-SiO₂ nanocomposites were prepared.The addition of SiO₂/O-SiO₂ increased the thermal stability of PLA.In addition,when the content of SiO₂/O-SiO₂ was 3 wt%,PLA/PBS/O-SiO₂nanocomposites is 35%higher than PLA/PBS/SiO₂ nanocomposites;The flexural strength and the flexural modulus of PLA/PBS/O-SiO₂ nanocomposites was 24%and22%higher than that of PLA/PBS/SiO₂ nanocomposites.The SEM images show that impact fracture surface of PLA/PBS/SiO₂ and PLA/PBS/O-SiO₂ nanocomposites was rougher than pure PLA,especially PLA/PBS/O-SiO₂ nanocomposites.In summary,nanocomposite modification improved the toughness of PLA.O-SiO₂ has enhanced adhesion to the matrix,therefore,O-SiO₂ has better reinforcement and toughening effect than SiO₂.2.Experimental results of blending toughening PLA with PBAT:The addition of PBAT has little effect on the thermal stability of PLA.When the content of PBAT was5 wt%,the impact strength and fracture toughness of the PLA/PBAT blend were increased by 35%and 13%.At the same time,the flexural strength and the flexural modulus of the PLA/PBAT blend were reduced by 8%and 14%.In general,when the content of PBAT was 5 wt%,PBAT has the best toughening effect on PLA.The SEM images show that the impact fracture surface of the PLA/PBAT blend is rough and fibrillated.3.The experimental results of compound toughening by PBAT and nano-alumina（Al₂O₃）:The addition of nano-Al₂O₃ reduced the thermal stability of PLA/PBAT blends by a small margin.When the content of nano-Al₂O₃ was 1.0 wt%,compared with PLA/PBAT blends,the impact strength and the fracture toughness of PLA/PBAT/Al₂O₃ nanocomposites increased by 35%and 8%,the flexural strength and the flexural modulus of PLA/PBAT/Al₂O₃ nanocomposites was improved to a varying extent.SEM images show that PLA/PBAT/Al₂O₃ nanocomposites have a rougher surface than PLA/PBAT blends.Summary:PBAT and nano-Al₂O₃ have compoumd toughening effects on PLA.