| Wood-plastic composites(WPC),as a new type of green environmental material,have a high level of performance.However,there are some difficulties in the process of preparing WPC.The preparation of high-quality wood fibers and the interfacial compatibility between bio-fibers and the plastic matrix,in addition to the dispersion of fibers in thermoplastics are key obstacles to overcome in enhancing the physical and chemical properties of WPC.The paper focuses on the research of the orientable preparation of wood fiber,and mainly discusses the effect of the wood fiber geometry,initial moisture content of raw materials and species on the the mechanical properties of WPC,the aim is to find out the correlation between the fiber geometry,initial moisture content of raw materials and species when the mechanical properties of WPC was the best,in order to build advanced technology systems of wood fiber orientable preparation.On this basis,the paper focuses on the high temperature and pressurized steam treatment or composite modifications using environmentally friendly organic silanes with special chemical structures.Through improving the dispersion and mobility of fibers in the plastic fusant,and enhancing the compatibility and adhesion strength between fibers and plastics,the project studies the patterns in effects that composite modifications have on the interfacial compatibility of composite materials and rheological properties of fusants,aiming to investigate the mechanisms in the modifications.In developing and perfecting the bio-fiber modification system,the project intends to provide the theoretical foundation and technical supports for the massive and effective use of bio-resources and the optimization of WPC products.The details are as follows:(1)According to the processing theory of the wood fiber Crushing equipment and performance of the raw biomass materials,eventual adoption of the principle of grinding roll-milling equipment,by improving its reasonable design and manufacture wood fiber Crushing equipment.The geometry,size and quality of wood fiber which the equipment processed had been met the ideal requirements of wood fibers.The study measured the wood fibers for different materials.The results showed that:the length to diameter ratio of wood fiber within 40-80 mesh was 5.3,and its proportion was 74.02%,built advanced technology systems of wood fiber orientable preparation and could satisfy the requirements of the high quality WPC.(2)The mechanical properties of wood fiber in different diameters and different materials were investigated.The results showed that the mechanical properties were enhanced with the increase of fiber diameter and then decreased as the fiber diameter further increased.When the wood fiber diameter was 0.21 mm?d?0.29mm(60-80mesh)and the aspect ratio of WPC was 5 to 8 which could be given better mechanical properties of WPC.Compared to the the fiber diameter was 0.21 mm,the impact strength,tensile strength,and bending properties of WPC increased by 14.65%?10.12%,and 6.13%.The mechanical strength were enhanced with the increase of moisture content and then decreased as the moisture content further increased.When the moisture content of the materials was 30%,the impact strength,tensile strength and flexural strength of WPC reached their maximum values;Furthermore,when wood fiber was prepared by the raw material pine board,the impact strength,tensile strength and bending strength of WPC were slightly lower than the initial pine wood chips;either tensile strength,flexural strength or impact strength,the composites which were made of pine fibers are higher than which were made of poplar fibers.(3)By studying the impacts of the orthogonal experiment analysis of a high temperature and pressurized steam treatment to the mechanical properties of wood-plastic composites.The main findings indicated that the mechanical properties of the wood fiber/HDPE composites were enhanced due to the fact that through high temperature and pressurized steam treatment,the surface roughness of the wood fibers increased.A temperature of 170 ?,a steam pressure of 0.8 MPa,and a processing time of 20 min were determined as the optimum parameters for fiber modification.Compared to the composites prepared from untreated fibers,the tensile,flexural,and impact strength of the composites prepared from modified fibers increased by 18.5%,13.66%,and 16.17%,and the water absorption and thickness swelling rate of WPC extremely decreased by 42.11%and 55.89%,respectively.When exposed to a high temperature and pressurized steam treatment,the number of hydroxyl groups and the surface polarity of the wood fibers decreased.With increasing steam temperature,pressure,and processing time,the hollocellulose content and the pH of wood fibers gradually decreased however,the crystallinity of wood fibers increased.In addition,the thermal stability,storage modulus and the mechanical properties of WPC significantly improved.(4)By studying the effect of using different organic silanes with five special chemical structures on the mechanical properties of wood-plastic composites.The results show that the mechanical properties of WPC were enhanced with the increasing of the silane content.When the silane content was 5%,the prepared composites showed the best mechanical properties.Compared to the composites prepared from untreated fibers,the tensile,flexural,and impact strength of the composites prepared from modified fibers increased by 22.6%,18.82%,and 20.5%,and the water absorption and thickness swelling rate of WPC extremely decreased by 51.75%and 59.26%,respectively.The water absorption and thickness swelling rate of WPC modified using different chemical structures of silane coupling agent dramatic decreased.and the water absorption and thickness swelling rate,the mechanical properties of WPC modified by A-171 were the most obvious effect,and superior to the high temperature and pressurized steam treatment.(5)By studying the effect of high temperature and pressurized steaming/silane coupling co?modification on the mechanical properties of wood-plastic composites.The results show that the co-modification could decrease the amount of hydroxyl groups on the surface of the fibers and surface polarity of the fibers,which can achieve a better modification effect than the modification effect by silane coupling agent alone.Moreover,the addition of a small amount of silane to the wood fibers exposed to steam at 170? and 0.8 MPa provided even better results;when 2%silane was added,the composites showed the best mechanical properties.Compared to the composites prepared from untreated fibers,the tensile,flexural,and impact strength of the composites prepared from modified fibers increased by 32.07%,29.88%,and 31.65%,and the water absorption and thickness swelling rate of WPC extremely decreased by 59.12%and 68.91%,respectively.The project provided the theoretical foundation and technical supports for the massive and effective use of bio-resources and the optimization of WPC products. |
PDF Full Text Request