Preparation And Characterization Of Wood Fiber/PLA Composite Modified By Interfacial Compatibilizer

In recent years,one strong trend is to explore and develop bio-based composites in academic and industrial application,aiming at reducing the influence of fossil energy to natural environment.PLA-based composites reinforced with wood fiber,there are advantages,such as good impact resistance,water resistance,not easily corroded and high mechanical strength,Which has been widely used in many fields such as packaging materials and automobile decorative parts.At present,the interfacial compatibility of the composites is improved by directly adding glycerin or a silane coupling agent,etc.,but there is little research on the true coupling between the matrix phase and the packed phase,for instance,using modified PLA to prepare the compatibilizer firstly,then which is used to reinforce PLA-based composites.In this thesis,Maleic anhydride(MAH),silane coupling agent(KH550)and hydroxyethyl methacrylate(HEMA)was used as the grafting monomer,which was prepared by melt grafting reaction in the twin screw extruder with the initiator,polylactic acid grafted with maleic anhydride(MAH-g-PLA),silane coupling agent(KH5 5 0-g-PL A)and hydroxyethyl methacrylate grafted polylactic acid(HEMA-g-PLA)was successfully prepared as the interface compatibilizer.The PLA/Wood fiber composites were prepared by melt blending and injection molding with different proportions of compatibilizer added,within which PLA was for the matrix phase and wood fiber was for the reinforcing phase.The crystallinity,microstructure,thermal stability and dynamic thermomechanical property of the composites were studied by X-ray diffraction(XRD),scanning electron microscope(SEM),thermo gravimetric analyzer(TGA)and dynamic mechanical thermal analysis(DMA).Furthermore,the mechanical properties of the composites were also characterized,aiming to find a link between the interface compatibilizer content and the properties of the graft Wood fiber/PLA composite.The results showed that MAH-g-PLA can improve the mechanical strength of the composites as the interface compatibilizer,and attained the highest at 30%MAH-g-PLA added.The anhydride groups in MAH react with the hydroxyl groups in PLA and wood fibers to provide a good coupling between wood fibers and PLA macromolecules,greatly improving interfacial adhesion.When KH550-g-PLA was used as the interface compatibilizer,the mechanical properties of the composites were also greatly improved.The imino group exists in KH550-g-PLA and the N atom in the imino group with the hydroxyl groups on the surface of the fibers formed intermolecular hydrogen bonds,which greatly enhanced the interfacial adhesion of the composites.When HEMA-g-PLA was used as an interfacial compatibilizer,the two-phase compatibility of the composites was greatly improved by wood fiber and PLA macromolecules coupled to a large extent,which attained the highest at 30wt%HEMA-g-PLA added.In order to verify the synergistic effect between different modifiers,with adding each graft modification,selecteing three variables of MAH-g-PLA,KH550-g-PLA and HEMA-g-PLA as the indicators,and the three addition amounts of the interface agent were investigated as the level,which was set as the orthogonal experimental scheme.The tensile strength,flexural strength,elongation at break and crystallization property of the composites were measured as the best ratio:the addition contents of MAH-g-PLA was(30wt%),the contents of KH550-g-PLA added was(20wt%),and the contents of HEMA-g-PLA added was(20wt%).The interfacial compatibilizer prepared by graft modification of PLA successfully introduced a polar group on the non-polar PLA macromolecular chain,and its molecular chain has a structure similar to that of PLA molecule at one end,which can be well fused with the matrix phase(PLA)in the composites system.The polar group at the other end of the molecular chain can react with a large number of hydroxyl groups on the surface of the wood fiber or form intermolecular hydrogen bonds,thereby improving the interfacial adhesion between the wood fiber and the PLA in the composite system;adding the appropriate amount of graft modification into the wood fiber/PLA composite enables the two phases in the composite to achieve true coupling and the performance of the wood fiber/PLA composite was ultimately improved.