Study On Basic Theory And Key Technology Of Salix Medium Density Fiberboard Reinforced By Poplar Or Willow Wood Fiber

Past two decades, the development and promotion of of Salix medium density fiberboard becomes an effective way to utilize the desert shrubs comprehensively. Due to shorter in Salix fiber length, small in aspect ratio and wall thickness, in addition the existing production conditions difficult to achieve Salix wood peeling, higher in content of Salix fiber bark, so that compared to arbor-based medium density fiberboard, there are several shortages such as the thickness swelling and poor mechanical properties.In response to this situation, during the research, putting better Salix wood fibers and Poplar fiber into Salix wood fibers to the preparation of the medium density fiberboard.The preparation of Salix medium density fiberboard that reinforced by Poplar/Willow and its related theory and key technology was studied in this paper. On the research basis of the characteristics fiber morphology, chemical composition, pH, and the relative degree of crystallinity, surface functional groups of three wood raw materials, the bonding mechanism of wood fiber and urea formaldehyde (UF) resin was analyzed with Electron Spin Resonance (ESR) and Fourier Transform Infrared Spectroscopy (FTIR). The effect of the curing agent and waterproofing agent on the absorption exothermic phenomenon and the thermo-mechanical properties of UF resin curing process was explored by Differential Scan Calorimeter (DSC) and Dynamic Mechanical Analyzer (DMA) technology. Meanwhile, the key preparation technology of Salix medium density fiberboard reinforced by Poplar/Willow wood fiber has been optimized. The results were as follows:(1) The fiber wall thickness, length and length-width ratio of Poplar and Salix matsudana was significantly greater than Salix psammophila wood fiber. The ratio of wall to cavity of the three wood fiber were all smaller than1, so were all good fiber raw material. After refining processing, holocellulose content of wood fiber lower, the content of lignin, ash and extract increased, the pH value and acid-base buffering capacity, the relative crystallinity degree of cellulose increased. Compared with the other two fibers, the content of Salix matsudana fiber becomes higher, the extractives content of Salix psammophila becomes higher, pH value becomes lower and acid-base buffering capacity becomes higher. The change of the relative crystallinity degree of cellulose and lignin content of the three wood fibers wan not obvious. The active groups on wood surface with refining treatment was significantly enhanced, that was conducive to glue.(2) ESR results showed that the concentration of free radicals on the wood surface significantly enhanced by refining processing, the concentration of free radicals of Salix matsudana was highest, and Salix psammophila minimum. According to FTIR spectra,-OH of wood fiber reacted with-CH2OH of UF and formed the ether bond while in the gluing process of wood fiber and UF. The hydrophilic group of wood fibers and UF weakened and water resistance groups enhanced, the probability of formation of the-NH-moiety also reduced by joining the paraffin emulsion, not conducive to the curing of UF resin.Curing agent, promoted the cross-linking reaction of the related groups OH、-NH2、-CH2OHofUF.(3) DSC results showed that the increasing amount of curing agent could promote the curing of UF when the addition amount exceeds3%. When the addition amount is2%-3%, also promoting the degradation of the UF resin. Increasing the amount of paraffin emulsion will increase the peak temperature of UF resin curing peak, which is not conducive to the curing of UF. When curing agent was1%, the resin curing reaction activation energy, reaction order, frequency factor and the rate constants of UF by add ammonium persulfate were higher than ammonium sulfate and ammonium chloride.(4) DMA measurements showed that with the increase in the amount of curing agent, the peak temperature of the storage modulus of the UF resin curing process, the glass transition temperature decreased, and promote the UF resin curing process. The storage modulus of UF resin curing process was highest when the amount of ammonium chloride, ammonium sulfate and ammonium persulfate was1%,2%and3%, respectively.(5) The better preparation technology of Poplar/Willow fiber-reinforced Salix medium density fiberboard was:the hot pressing temperature of180℃, time of0.6min/mm, the pressure of3MPa, UF resin content of12%, the amount of paraffin emulsion of1.5%, the amount of curing agent for ammonium chloride of1%or ammonium sulfate of2%, or ammonium persulfate of0.5%. Salix wood fiber as a fiber material body, with the increasing amount in Salix wood fiber, the Poplar/Willow fiber, the mechanical properties increasing, lower water absorption; curing agent the amount of ammonium persulfate was0.5%, paraffin1.5%, Willow wood fiber by adding10%to50%, comparing Salix/Willow medium density fiberboard with Salix density fiberboard in MOR, MOE and IB increased from1.11to9.18%,2.26to15.31%, Ito19.74%, the TS decreased from1.30to5.89%; Poplar fiber by adding10%to50%, comparing Salix/Poplar medium density fiberboard with Salix medium density fiberboard in MOR, MOE and IB increased from3.93to16.33%,4.61to22.05%,4.61to26.08%, the TS decreased from2.77to8.58%;the performance of Salix/Poplar medium density fiberboard is better than Salix/Willow medium density fiberboard.The results of this study showed that Poplar/Willow wood fiber reinforced Salix medium density fiberboard the better performance than the Salix medium density fiberboard; using DSC, DMA, and other means to study the course and the mechanical properties of UF resin curing, and be able to predict the process parameters on the fiberboard performance impact, which can be selected as fiberboard process parameters effective adjunct.