Study On Particleboard Made From Heat Treated Poplar And Its Characteristics Of Set-recovery In Thickness

This paper used poplar as raw material which was heat-treated at 220?,boric acid as pretreatment reagent to prepared binderless particleboard.At the same time,the laboratory self-made hot pressing device(which can realize continuous temperature,pressure,displacement and other online tests)is used to systematically study the compression and rebound characteristics of the binderless particleboard during the hot pressing process,which provides a theoretical basis for the efficient preparation of the binderless particleboard.The main research contents and conclusions are as follows:1.The preparation process experiment of binderless particleboard showed that the solution pretreatment could significantly improve the dimensional stability and mechanical properties of the particleboard.The optimal process parameters for preparing binderless particleboard were as follows:the concentration of boric acid solution was 8%,the pretreatment time was 0.5 h,the hot pressing temperature was 200?,and the hot pressing time was 20min.The bending strength,elastic modulus,internal bonding strength and water absorption thickness of BA-PB(Particleboard prepared from heat treated poplar particle pretreated with boric acid)prepared by the optimal process were 14.54 MPa,1731.36 MPa,0.32 MPa and 8.25%respectively.2.The analysis of physicochemical properties of particles before and after boric acid pretreatment showed that the particles formed boron ester bond or ring complex,which improved the crystallinity and thermal stability of the particle,and ensured the dimensional stability of the particleboard products.In addition,boric acid pretreatment promotes the decomposition of lignin to form small molecules,which is beneficial to the adhesion of particles during hot pressing.Compared with HT-WP(heat-treated poplar particle),the lignin content of BA-WP(heat-treated poplar particles pretreated with boric acid)decreased from 32.82%to 29.81%,and the cellulose content increased from 35.11%to 40.82%.Compared with HT-WP FTIR spectrum,BA-WP showed characteristic peaks of boric acid,which were hydroxyl stretching vibration absorption peak in boric acid at 3200 cm^-1,bridge stretching vibration peak of B-O-B and B-O-C bond at1430 cm^-1,etc.X-ray diffraction showed that boric acid solution pretreatment improved the crystallinity of particles,and the crystallinity of BA-WP and HT-WP were 51.68,44.15%,respectively.The mass residual rates of HT-WP and BA-WP were 22%,50.6%,respectively,the results showed that the pretreatment of boric acid solution could improve the thermal stability of raw materials.DSC analysis showed that the pretreatment with boric acid solution changed the crystallization and melting behavior of heat treated poplar particle and promoted the fracture,recombination of lignin and hemicellulose.3.The dynamic viscoelastic results of heat-treated poplar showed that the boric acid solution pretreatment could reduce the stiffness of heat-treated poplar,reduce the hot pressing pressure required in the hot-pressing process and the production cost of particleboard.The storage modulus and loss modulus of HT-WB(heat-treated poplar block)were higher than that of BA-WB(heat-treated poplar block pretreated with boric acid).4.The study on the whole process of hot pressing of binderless particleboard showed that the process parameters(hot pressing temperature,hot pressing time,pressure relief mode)can be adjusted to promote the release of internal stress of particleboard in order to reduce the set-recovery in thickness of particleboard and improve the quality of particleboard products.At the same conditions of other hot pressing processes,the hot pressing pressure of particleboard can be reduced when the particles pretreated with boric acid.When the hot pressing temperature was200?,the hot pressing time was 8min,the maximum hot pressing pressure of BA-PB decreases from 20117 N to 13748 N compared with HT-PB.The higher the hot pressing temperature,the faster the internal stress release of particleboard;The internal stress of the particleboard is released step by step when the pressure is relieved by section,while the internal stress of the particleboard is changed continuously when the pressure is relieved by direct pressure.The longer the hot pressing time is,the faster the internal stress in particleboard was released.The more complete the stress release in the particleboard,the lower the thickness swell.