节子类型和数量对尾巨桉胶合板物理力学性能与界面胶合的影响OA

Eucalyptus urophylla×E.grandis is widely used in wood-based panel manufacturing,papermaking,and other industries due to its rapid growth rate,uniform stand,and strong stress resistance.However,the defect of knots leads to the cracking and deformation of Eucalyptus urophylla×E.grandis during processing,which limits its efficient utilization.Knots are natural defects in wood.Based on the grain pattern and their connection to the surrounding wood,they can be classified as live knots and dead knots.Due to the differences in hardness and fiber direction between knots and the surrounding normal wood,they not only cause great damage to the tool,and affect the wood's appearance,but also compromise their integrity and uniformity,leading to a decline in overall wood quality.To investigate the impact of knots on the physical and mechanical properties of plywood,samples were prepared using clear wood and knot-containing wood from 6-year-old Eucalyptus urophylla×E.grandis.The moisture content,bonding strength,wood failure ratio,modulus of rupture(MOR),and modulus of elasticity(MOE)were measured,and the bonding interfaces were examined by the fluorescence microscope and the scanning electron microscope to analyze the effects of knot types and numbers on the properties of plywood.The results showed that:(1)The difference in average moisture content of each type of plywood and the difference in moisture content between different parts of the plywood were not statistically significant at 0.05 significance level,indicating that the types and numbers of knots had no effects on the moisture content of plywood.(2)The penetration depth of the UF adhesive in the plywood was affected by knots.Compared with the plywood made from clear wood,the depth of average penetration(AP)and the depth of effective penetration(EP)of plywood made from live knots decreased by 16.42%and 14.63%,respectively,and the AP and EP of plywood samples with dead knots decreased by 36.16%and 23.48%,respectively.(3)The mechanical properties of plywood were affected by knots.Compared with the plywood samples made from clear wood,the bonding strength,wood failure ratio,MOR,and MOE of the plywood made from the wood containing knots were significantly decreased,and the influence of dead knots was greater than that of live knots.(4)Under the experimental conditions of this study,when the area proportion of dead knots in veneer reached 9.4%,the bonding strength of plywood was lower than the requirements of Class Ⅲ Eucalyptus plywood in GB/T 9846-2015"Plywood for general use".Therefore,the area proportion of dead knots in veneers should be controlled in the production of plywood.This study revealed that the adverse effects of knot types and numbers on the mechanical properties of Eucalyptus urophylla×E.grandis plywood,indicating that the area proportion of dead knots of veneer should be controlled in plywood production.The findings of this study provide theoretical basis for improving the performance of Eucalyptus urophylla×E.grandis plywood during its service.