Improvement of dimensional stability of poplar scrimber by pre-compression treatment gluing technology
As one of the fastest-growing wood resources,poplar wood is widely used in many fields.However,the uti-lization of the polar wood is limited due to its poor mechanical properties,high hygroscopicity and low dimensional stability.A novel technique for the manufacturing of wood scrimber was proposed by the Research Institute of Wood Industry,Chinese Academy of Forestry.The wood scrimber produced by this novel method had enhanced mechanical properties and an improved dimensional stability compared with solid wood and other wood-based composites.There-fore,it was a promising alternative to high-quality hard wood.However,the dimensional stability of the wood scrim-ber manufactured by this novel approach was still not good enough for outdoor products.The liquid penetration of pre-compressed technology was developed in the manufacture method of wood scrimber to improve the dimensional stabili-ty for outdoor applications.In the glue impregnation process,the oriented wood fiber mats(OWFMs)were immersed in the phenol formaldehyde(PF)resin with pre-compressed treatment by repeating several times and then were made for wood scrimber(WSP)by hot-pressing.The scanning electron microscope(SEM),mercury intrusion porosimetry(MIP),laser scanning confocal microscope(LSCM)and ultra-depth three-dimensional microscope(UTDM)were used to examine the changes of OWFMs and wood scrimber in the microstructure and resin distribution,as well as the physical and mechanical properties.The relationship between the internal structure,the distribution of PF resin,and the physical and mechanical properties of the wood scrimber were established.The results showed that the OWFMs with the pre-compressed treatment had higher specific surface area and the PF resin penetrated more deeply and distri-buted more uniformly in OWFMs and WSP.Meanwhile,the densification of the WSP increased compared with that of control samples at the same density.As a result,the thickness swelling rate(TSR)and the width swelling rate(WSR)of the WSP decreased significantly compared with that of control samples.There were 43.34%and 12.82%reduction of TSR and WSR in the 63 ℃/24 h test,and 50.94%and 51.48%reduction in the 28-h cycle test.Mean-while,the modulus of rupture(MOR),the modulus of elasticity(MOE)and the short-beam strength(SS)of the WSP samples increased by 1.63%,12.15%and 21.34%,respectively.The results of this study will provide a techni-cal basis to improve the wood scrimber quality.