The Preparation And Properties Of Poly(Lactic Acid) Modified By Hemp Fiber

Poly(lactic acid)is an environment-friendly biopolymer material,and it has become the leader among many biopolymers due to its excellent physical and mechanical properties,renewability,biodegradability and reusability It is one of the most widely researched and applied biopolymers.Natural fiber reinforced polylactic acid composites can improve some disadvantages of PLA,and it is an ideal choice for developing biodegradable materials in different application fields due to its green and complete degradability.The two-phase interface of the composite greatly influences the mechanical and other properties of the material.Adding the interfacial compatibilizer into the composite can effectively increase the interfacial strength and improve the mechanical properties of the composite.Maleic anhydride is widely used because of its unique advantages,usually grafted with polylactic acid to prepare PLA-g-MAH graft copolymer,added in natural fiber /polylactic acid composites as a compatibilizer to improve the properties of the composites However,excessive maleic anhydride can lead to degradation of PLA,decrease the molecular weight of the compatibilizer,and lower grafting rate of maleic anhydride.In this paper,a second graft monomer was introduced in the preparation of compatibilizer in order to increase the grafting rate of maleic anhydride.The second graft monomer containing different number of functional groups was expected to increasing the molecular weight of the graft copolymer.The PLA chain forms a radical under the action of the initiator,and reacts with the double bond of maleic anhydride to form a PLA-g-MAH graft.As the concentration of MAH increases,the grafting rate of the graft increases first and then decrease.When the graft is added to the epoxy group,the epoxy group is opened and reacted with maleic anhydride grafted on the polylactic acid.The epoxy group without graft reaction reacts with the hydroxyl group/terminal carboxyl group of the polylactic acid molecular chain.The compatibilizer effectively enhances the interfacial strength of the composite and improves the mechanical properties.However,the epoxy resin consumes a portion of the grafted anhydride groups,which lowers the graft ratio of the graft,and the epoxy group has no effect on the hydroxyl group on the surface of the hemp fiber and the compatibilization effect on the ester group in the polylactic acid.