Research On Properties And Nano Silicon Carbide Modification Of Wheat Straw/HDPE Composites

Wheat straw is a very rich biomass resource in my country,and its use in the preparation of plant fiber composites is an environmentally friendly and economical high-value utilization method.The research and modified enhancement of various properties of wheat straw composites will help expand the scope of its application,and have long-term practical significance in plant fiber recycling and resource utilization,green environmental protection and new material development.In this paper,wheat straw fiber(WSF)and high-density polyethylene(HDPE)were used as raw materials to prepare WSF/HDPE composites through melt blending and vertical injection processes.The fiber morphology,chemical structure,crystallization properties and thermal stability and other properties of WSF with different meshes were systematically analyzed,and the influence of different fiber contents and meshes,and nano silicon carbide(SiC)modification on the mechanical,thermal stability,crystallization and melting,water absorption,interface and other properties of WSF/HDPE composites were systematically investigated.The research conclusions are as follows:(1)The larger the mesh,the smaller the aspect ratio of WSF,and the thinner and shorter the shape.As the mesh increases,the polarity and water absorption of WSF increased.After the mesh increased,the crystallinity and crystal size of WSF were reduced,and the crystalline transformation of cellulose from type Ⅰ to type Ⅱ will occur.The increase of the mesh led to the decrease of the activation energy of WSF,the decrease of thermal stability,and the easy formation of carbon residues.(2)With the increase of fiber content,the tensile strength,flexural strength and flexural modulus of WSF/HDPE composites respectively showed a decreasing,first increasing and then decreasing,increasing trend.The influence of fiber mesh on the tensile and flexural strength of WSF/HDPE composites was related to the level of fiber content,while the flexural modulus was higher when the fiber mesh was smaller.When the fiber content and mesh are 30%and 60 mesh,respectively,the comprehensive mechanical properties of WSF/HDPE composites are the best,and its tensile strength,flexural strength and flexural modulus are 18.1 MPa,29.5 MPa,and 2137.9 MPa,respectively.The higher the fiber content,the weaker the thermal stability of WSF/HDPE composites,but the larger the fiber mesh,the stronger the thermal stability.The crystallinity of WSF/HDPE composites increased first and then decreased with the increase of fiber content and mesh.The increase of fiber content will increase the water absorption,thickness expansion rate and water molecule diffusion coefficient of WSF/HDPE composites,while the increase of fiber mesh will reduce the water absorption of composites.The higher the fiber content of WSF/HDPE composites,the worse the interface properties,but the interface properties will improve with the increase of fiber mesh.(3)After the modification of nano-SiC,the surface roughness of WSF increased and the polarity weakened,while the crystal type unchanged,but too much nano-SiC will aggravate the agglomeration phenomenon and enhance the polarity.The mechanical properties of WSF/HDPE composites were enhanced by nano-SiC modification,and as the content of nano-SiC increases,the tensile strength,flexural strength and flexural modulus all increased first and then decreased.When the content of nano-SiC is 0.4%,the WSF/HDPE composites has the best mechanical properties,and the tensile strength,flexural strength and flexural modulus were increased by 15.5%,11.5%,and 12.4%,respectively.Nano-SiC modification reduced the thermal stability of WSF/HDPE composites,but improved crystallinity of composites.The water absorption of WSF/HDPE composites was reduced by nano-SiC modification,and the water absorption rate,thickness expansion rate and water molecule diffusion coefficient were all reduced,but too much nano-SiC will increase the water absorption.Nano-SiC modification reduced the cracks and pores on the surface and the tensile fracture surface of the WSF/HDPE composites,and improved the interface properties of composites,while too much nano-SiC will reduce the interface properties.