Study On The Preparation And Properties Of Hemp Stalk Powder/polylactic Acid Wood-plastic Composite Material

There are some issues with wood-plastic composites such as large demand for wood,high energy consumption and high recycling costs,which not only cause the lack of forest resources,but also bring more ecological and environmental problems.In this study,waste hemp hurd flour and degradable poly(lactic acid)were used to replace the wood flour and the polypropylene.The compression molding process,influence of the particle size and content of hemp hurd flour on composites were studied.Then the modification and applicability of the high-filled hurd flour/poly(lactic acid)biocomposites were investigated.Extrusion process with extrusion temperature of 170?180 ? and screw speed of 100r/min was determined at first.Through the range and variance analysis of multi?index orthogonal test,the optimal heating temperature is 160 ?,optimal pressing pressure is 7.5MPa,and optimal holding pressure time is 5 min.Through the analysis of wood-plastic composites properties with different particle size and content,it showed that as the particle size decreases,the density increase and water content of composites decrease gradually,the water absorption rate,tensile strength,tensile modulus and flexural strength increase first and then decrease.With the increase of content,the density,water content and water absorption rate increase gradually.Tensile strength and tensile modulus increase first and then decrease.Flexural strength decreases,and flexural modulus increases gradually.The more content of hurd flour,the worse the toughness of composites.When the particle size is 40 mesh and the content is 30%,mechanical properties of composites are superior.The tensile strength,tensile modulus,flexural strength and flexural modulus are 40.26MPa,2056.37MPa and 73.84MPa,4346.98MPa,respectively.Through regression analysis,the prediction model of mechanical properties of composites based on the particle size and content of hemp hurd flour was established.The model accuracy is 96.20%.High-filled hemp hurd flour composites were modified using coupling agent,toughening agent and antioxidant.The modification effect of silane coupling agent is better than that of titanate coupling agent.The tensile modulus,flexural strength and flexural modulus are increased by 24.1%,61.2%and 17.2%,respectively,compared with untreated composites.The tensile strength,flexural strength and elongation at break of composites with elastomeric SBS increased by 41.5%,25.7%and 18.8%,respectively,compared with the untreated.When the antioxidant content is 0.6wt%?the tensile strength and flexural strength are the largest,respectively 34.63MPa and 67.12MPa,and the thermal stability is significantly improved.The density,water absorption and mechanical properties of high-filled hemp hurd flour/poly(lactic acid)composites meet the perfonnance requirements of wood-plastic composites in the country and industry.