| Wood Plastic Composites(WPC)have many advantages such as sound insulation,moisture resistance,hydrophobicity,corrosion resistance,insect protection,termite prevention,simple installation,convenient construction,and can be recycled and reused.As an emerging green and recyclable environmentally friendly material,wood-plastic composites have been used in the fields of boardwalk,outdoor floor and park facilities for a long time,which have been in constant contact with the soil.In outdoor soil environment,wood-plastic composites are prone to aging,serious fading of the composite surfaces,and the decline of the main performance indexes,which seriously affect its function and service life.At present,wood-plastic composites using rice husks as filler are widely used.It is of great significance to study the aging problem of wood-plastic composites using rice husks as filler in outdoor soil environment.In this paper,the rice husk was used as the main filler,wood-plastic composites were prepared by extrusion molding using polyvinyl chloride(PVC)as a matrix,a simulated soil accelerated aging test was performed to study soil aging resistance ability of wood-plastic composites.Establishing a link between the simulated soil accelerated aging and the natural soil aging,and mathematical model prediction was used to predict the linear thermal expansion coefficient of rice husk/PVC wood-plastic composites.The aging resistance behavior of different plastic substrates(PVC,PP and HDPE)/rice husk wood-plastic composites was compared.Four kinds of pretreatment methods were used to pretreat the rice husk fibers and improve the interfacial bonding quality of composites,and their aging resistance properties were analyzed.The wear resistance behavior of three kinds of inorganic fibers reinforced wood-plastic composites was studied before and after aging,and the physical and mechanical properties of three types of colorants filled wood-plastic composites were studied before and after aging.The main conclusions were as follows:(1)The simulated soil accelerated aging conditions were determined,the soil temperature was 65?,the soil moisture content was 45%,the soil pH was 2.5,and soil thickness ratio was 3:7.After the simulated soil accelerated aging,the tensile strength and flexural strength of rice husk/PVC wood-plastic composites were decreased by 33.9%and 52.3%,respectively,compared to those composites without aging.After the natural soil aging,the tensile and flexural strength were reduced by 53.5%and 72.2%,respectively.According to the linear fitting,it could be known that the simulated soil accelerated aging for 21 days was equivalent to about 250 days of the natural soil aging.The thermogravimetric properties of rice husk/PVC wood-plastic composites in the two aging modes were analyzed.During the aging process of rice husk/PVC wood-plastic composites,the overall weight loss increased,the heat resistance ability of wood-plastic composites decreased,the natural soil aging had a deeper influence than the simulated soil accelerated soil aging,and the initial decomposition temperature of the rice husk/PVC wood-plastic composites after the natural soil aging decreased to 255.5?.The linear thermal expansion coefficient of rice husk/PVC wood-plastic composites was analyzed at different aging periods.It was found that:the longer aging time,the larger linear thermal expansion coefficient of rice husk/PVC wood-plastic composites.The quality of interfacial bonding of rice husk/PVC wood-plastic composites gradually decreased with the increasing aging time,the fiber-matrix bonding gradually become worse,and cracks and holes happened.(2)The linear thermal expansion coefficient of rice husk/PVC wood-plastic composites in the range of-30?-60? was analyzed,and its linear thermal expansion coefficient was also predicted.Mathematical fitting was performed to get a curve equation.The fitting results showed that the determination coefficient R square reached 0.99778,which could accurately predict the linear thermal expansion coefficient of rice husk/PVC wood-plastic composites.Curve equation was Y=0.17963X-0.00453X2+(2.4621E-4)X3(5.60208E-6)X4+(3.97678E-8)X5+22.56374.(3)Rice husk was pretreated using four methods(benzoylation treatment,alkali treatment,microwave treatment,and hydrothermal treatment),and the treatment effects of the four kinds of pretreatment methods were compared.The results showed that the benzoylation treatment had the best effect,the benzoylated rice husk contained the least hydroxyl groups,the benzoylated rice husk/PVC wood-plastic composites had a relatively flat surface with fewer cracks and pits.After 21 days of the simulated soil accelerated aging,the lowest moisture absorption rates and mass loss rate of the benzoylated rice husk/PVC wood-plastic composites were 1.97%and 1.2%,respectively.The superior physical and mechanical properties indicated that rice husk/PVC wood-plastic composites had a good internal bonding,the fibers were arranged in an orderly manner,and the adhesion to the matrix was tight.Four kinds of pretreatment methods can improve the anti-aging performance of rice husk/PVC wood-plastic composites,and the comparison showed that the order of the four kinds of the pretreatment methods were benzoylation treatment>alkali treatment>hydrothermal treatment>microwave treatment.(4)Compared the wear resistance properties of three inorganic fibers(zirconia fiber,aluminum silicate fiber,and basalt fiber)reinforced rice husk/PVC wood-plastic composites.The results showed that the zirconia fiber reinforced rice husk/PVC wood-plastic composites had relatively excellent wear resistance ability after 21 days of the simulated soil accelerated aging,the specific wear rate and friction coefficient were 10.4×10-5 mm3/(N·m)and 0.5475,respectively.The quality of the worn surface was better,no fiber pullouts and holes,and only a few scratches can be observed.The tensile,flexural,impact strength and hardness of zirconia fiber reinforced rice husk/PVC wood-plastic composites had reached 15.8MPa,23.6MPa,2.49KJ/m2 and 41HRR,respectively.The interfacial bonding quality of the composites was the tightest and the coating was strong.The order of the three inorganic fiber reinforcement effects was zirconia fiber>aluminum silicate fiber>basalt fiber.The mechanical and wear resistance properties of zirconia fiber reinforced rice husk/PVC wood-plastic composites were predicted by gray prediction method and the prediction equation was determined.(5)The aging resistance ability of the three kinds of colorants(iron oxide red,iron oxide yellow and iron oxide blue)added rice husk/PVC wood-plastic composites were compared.The results showed that the total color difference(?E*)of the three kinds of colorants added rice husk/PVC wood-plastic composites increased with the increasing aging time.After 21 days of the simulated soil accelerated aging,the total color difference of the iron oxide red added rice husk l PVC wood-plastic composites was the smallest,followed by iron oxide blue,and iron oxide yellow was the largest.The iron oxide red added rice husk/PVC wood-plastic composites had the smallest water absorption(5.19%)and the largest contact angle(109.3°),and the tensile,flexural,impact strength and hardness were the largest,14.1MPa,22.8MPa,2.07KJ/m2 and 33.9HRR,respectively.The iron oxide red added rice husk/PVC wood-plastic composites had fewer pits on the surface,without obvious holes,which had tightly bonded interface,so it had excellent comprehensive performance.(6)The flexural properties of three plastic substrates(PVC,PP and HDPE)/rice husk wood-plastic composites were analyzed under simulated soil accelerated aging conditions.The results showed that rice husk/PVC wood-plastic composites had better flexural resistance ability,which had a more stable interface.After the simulated soil accelerated aging for 21 days,there were no holes at the interface,and the strength decreased slightly.The flexural strength and modulus of the rice husk/PVC wood-plastic composites were 14.82MPa and 1031.8MPa,respectively.Under different stresses(3.5MPa,7MPa and 10.5MPa),the flexural creep deformation values of rice husk/PVC wood-plastic composites were 0.00307,0.00359 and 0.00383,these deformation values were the smallest compared to other two composites. |
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