Preparation And Properties Of Maleic Anhydride Grafted Poly(lactic Acid)Compatibilized Wood Flour/PLA Composites

The natural fiber/poly(lactic acid)composite,an environmentally friendly material,has drawn increasing interest in recent years,owing to both advantages of natural fibers and poly(lactic acid).However,the incompatibility between PLA and wood fiber(hydrophobicity versus hydrophilicity)leads to poor wettability and interfacial adhesion between the two materials.Therefore,interfacial modification between wood flour and PLA matrix is the key to improving the mechanical properties of wood flour/PLA composites.The usual solution is to add maleic anhydride grafted copolymers.In this paper,we discussed the influences of the composition,loading rate and type of maleic anhydride grafted poly(lactic acid)(PLA-g-MAH)on improving the properties of wood flour/PLA composite on the basis of synthesizing the PLA-g-MAH by free-radical melt grafting,aimed to provide the evidence for the design and synthesis of suitable compatibilizer for the natural fiber/PLA composites.Graft copolymers of PLA-g-MAH,PLA-g-GMA and PLA-co-MAH/GMA were prepared by means of free-radical melt grafting.The structure of the graft copolymers were characterized by FT-IR.Wood flour/PLA composites were prepared by injection molding with three kinds of graft copolymers as compatibilizers,and the fractured morphology of composites were investigated.Results showed that the interfacial compatibility of wood flour/PLA composites were improved after adding different graft copolymers,and the best performance was obtained by adding PLA-co-MAH/GMA.Compared to the composite without compatibilizer,the tensile strength and impact strength of wood flour/PLA composites were increased by 9.54%and 7.23%respectively,and the equilibrium torque,shear heat,storage modulus and complex viscosity were all increased after adding PLA-co-MAH/GMA.Styrene-assisted free-radical melt grafting of MAH onto PLA(PLA-g-St/MAH)with different grafting degrees were achieved with dicumyl peroxide(DCP)as the initiator and styrene(St)as the monomer.The structure of graft copolymers were characterized by FT-IR.By comparison the relationship between grafting degrees with mechanical properties of wood flour/PLA composites,we found that the best mechanical properties of the composite were achieved with the grafting degree of 0.56%of compatibilizer,which was synthesized with the formulation of St:MAH = 2:1,4.5 wt%of MAH concentration and the grafting temperature at 180 ℃.And the equilibrium torque increased,the melt flow rate decreased and the thermal stability was improved when compared the PLA-g-St/MAH with this grafting degree with the pure PLA.The study on the rheological,mechanical properties and the interfacial adhesion of wood flour/PLA composites with different loading rate of PLA-g-St/MAH as the compatibilizer showed that the storage modulus,complex viscosity,balance torque and shear heat of the composite were significantly increased after adding the PLA-g-St/MAH and the interfacial adhesion was improved.With the increase loading rate of PLA-g-St/MAH,the tensile strength,flexural strength,impact strength and elongation at break of wood flour/PLA composites increased first and then decreased,and the best comprehensive properties of wood flour/PLA composites were obtained when the loading rate of PLA-g-St/MAH was 3 wt%.When comparing the influences of four kinds of compatibilizers(maleic anhydride grafted polypropylene(MAPP),MAH,PLA-g-MAH and PLA-g-St/MAH)on the mechanical,rheological,thermal stability,crystallization and interfacial properties of wood flour/PLA composites,the results indicated that four kinds of compatibilizers had different effects on the interfacial adhesion of the composites,and the PLA-g-St/MAH showed the optimal effect.The equilibrium torque,shear heat,storage modulus,complex viscosity,thermal stability and crystallization were all increased after adding PLA-g-St/MAH.