| Being a major cause of global environmental pollution,discarding used rubber inevitably wastes valuable rubber materials.Natural degradation of rubber is a slow process,as cross-links between rubber polymer chains,and the many additives and stabilizers within its structure,which make it extremely resistant to biodegradation.Since rubber consumption in China ranks the highest in the world,a huge amount of waste rubber has been created each year,causing serious environmental problems.Meanwhile,because of the shortage of forest resources,plantation forest has played an important role in solving the forest shortage problem.The comprehensive utilization of waste rubber and wood to make wood and rubber functional composite material is an effective waste management strategy for reducing the "black pollution".The wood rubber composites(WRCs)prepared using rubber and wood fiber mixing,tabletting and curing molding processes,in which different wood rubber materials including fibrous or powder wood fiber,reclaimed rubber or waste rubber powder and rubber compound,were tested based on the recycling of waste materials and the purpose of environmental protection.Technology of the preparation of wood rubber composites without adhesive was explored.The effect of the physical and chemical modification methods on the uniform dispersion and interface bonding of waste rubber powder or wood flour in the rubber matrix was investigated.The main results obtained are as follows:1)Design and simulation test of adjustable speed rotor of wood fiber rubber mixerTo avoid poor wood fiber distribution during the mixing process,using the fundamental design theory of mixing key components-rotor,the influence of the section geometry,geometry structure and rotational speed on the mixing process was analyzed.The 3D solid model of the rotor was developed using the Pro/E software with the method of scanning and shaping.Using the finite element analysis software of ANSYS,the strength and deformation of the rotor were examined by the analysis of stress and deformation values.A special rotor that was suitable for wood fiber/rubber composites was designed and fabricated.During the mixing process,the mixture of wood fiber/rubber along the axial direction and circumferential direction was reinforced to improve the uniform dispersion of wood fiber in the rubber matrix.2)Fabrication of wood fiber rubber compound compositesWRCs were prepared using mixing,tabletting and curing molding processes with a wood fiber content of 0-50%at a rotor rotational speed of 15-45rpm and a filling coefficient of 0.55-0.75.According to experimental data,four regression equations were developed,in which the influence factors were the amount of wood fibers,the main rotor speed and the mixing chamber filling coefficient,while the performance indicators were the tensile strength,elongation at break,hardness and resilience.Based on the different applications of the composites,the nonlinear programming model was established,and the optimal preparation technology of WRCs was obtained.When the maximum hardness of WRCs is needed,the 32%wood fiber,0.63 filling coefficient and 30rpm main rotor speed can be used to obtain the maximum hardness value of WRCs of 87.78 Shore A,while the tensile strength,elongation at break and resilience are 6.08 MPa,239.29%,and 38.02%,respectively.The scanning electron microscope image showed that the wood fiber was well embedded in the rubber matrix,which meets the requirements of China chemical industry standard(HG/T 3747.1-2011)for rubber and plastic flooring materials.3)Addition of reclaimed rubber into the preparation of wood rubber compositesWRCs containing reclaimed rubber were made using mixing,tabletting and curing molding processes with a reclaimed rubber content of 0-50%,mixing time of 6-14 minutes and vulcanization temperature of 150-170?.According to experimental data,four regression equations were also developed,in which the influence factors were the amount of reclaimed rubber,the mixing time and curing temperature,the performance indicators were tensile strength,elongation at break,hardness and resilience.Based on the different needs of composites,a nonlinear programming model was established,and the optimal performance of WRCs containing the reclaimed rubber was obtained.As seen from the brittle fracture surface SEM images of the specimen in parallel to the thickness direction,the wood fibers can well wet the reclaimed rubber/rubber compound matrix and can be uniformly embedded into the rubber compound/reclaimed rubber matrix when the reclaimed rubber contents were less than 20%.The average tensile strength of WRCs was increased by 33.9%(p<0.05),the swelling ratio of toluene in 72 hours and the water absorption in 24 hours were decreased by 13%and 42%(p<0.05)respectively.The 72 hours accelerated aging test of wood rubber composites showed that the wood/rubber composites containing reclaimed rubber had good ageing resistance.4)The incorporation of waste rubber powder into the preparation of wood rubber compositesWRCs containing waste rubber powder was made using mixing,tabletting and curing molding processes with a waste rubber powder content of 0-25%,waste rubber powder particle size of 20-70 mesh and microwave power of 100-800W.The effect of waste rubber powder particle size and microwave modification conditions on the physical and mechanical properties of the wood rubber composites were investigated and the optimal modification conditions and preparation process were proposed.5)The effect of modification of wood flour on the properties of wood rubber compositesThe cell walls of the wood flour were modified using glutaraldehyde(GA)and 3-aminopropyltriethoxysilane(KH550)to increase wood fiber surface areas and improve the rubber matrix interfacial bonding property with the wood flour content of 30%.The mechanical properties test results showed that the elongation at break of the wood rubber composites increased significantly after the GA modification.When the concentration of 5%GA was used,the elongation at break increased by 26%(p<0.05)and the tensile strength increased by 11%(p<0.05)compared with the control samples.The rheological properties and the results of SEM showed that the interface of the modified wood/rubber composite sample was improved with different degree of concentration,when the concentration of GA was 5%and the concentration of KH550 was 15%,the interface of the modified composite was the better.6)The numerical simulation of wood rubber compound blends mixingThrough the analysis of the rheological properties of wood rubber compound blends,it was found that the rheological behavior of wood rubber compound blends was in accordance with the shear thinning of the pseudo plastic fluid.Thus,the Bird-carreau model was employed as a WRCs descriptive equation for simulating the process of the wood fiber mixing and dispersion in the rubber compound.The real-time numerical simulation analysis was carried out on the wood rubber compound blending process with the software of POLYFLOW.Based on the numerical simulation and experiments,the velocity distribution,shear rate distribution and the concentration distribution of wood fiber in the wood fiber rubber compound mixing flow field were obtained.The comparisons of simulation and experimental results indicated that errors of the simulation model were within ±5%.The developed model can be used as a guide-line for the manufacturing of WRCs.Innovative Points:1)Without adhesive,wood rubber composites were fabricated using the rubber mixing technology.2)Using nonlinear programming,the prediction model of physical and mechanical properties of was established.3)The real-time numerical simulation and process parameters matching were developed for the wood fiber rubber compound blending process with the software of POLYFLOW. |
PDF Full Text Request