微波-尿素协同处理对压缩密实化木材尺寸稳定性及抗弯性能的影响OA

This study investigated the effect of microwave pretreatment time on the dimensional stability and bending properties of compression-densified wood(referred as densified wood).Paulownia tomentosa was pretreatment by microwave,then softened by urea solution(mass fraction of 30%),and followed by hot-pressing to produce densified wood.The results showed that when the hot pressing temperature was 170℃,the weight percent gain and density of densified wood significantly increased(P<0.01)with the extension of microwave pretreatment time.Compared with untreated wood,these two indexes were increased by 7.42%～136.13%and 10.71%～39.29%,respectively,with the density profile becoming relatively uniform.Microwave urea synergistic treatment significantly improved the dimensional stability of densified wood(P<0.01).When the microwave pretreatment time was 10～50 s,the set recovery rate and swelling efficiency were decreased by 44.95%～60.81%and 31.08%～50.00%,respectively,compared with control group(treated only by hot-pressing).Both bending strength and modulus of elasticity of densified wood were initially increased and then decreased with the extension of microwave pretreatment time,reaching their maximum at a microwave pretreatment time of 40 seconds(critical time),which increased by 45.45%and 37.62%,respectively,compared with untreated wood(P<0.05).The combined effect of microwave-urea was demonstrated,i.e.,microwave treatment induced puffing within the wood,allowing the urea solution to fully penetrate the wood cell walls.During hot-pressing,urea softened and crosslinked with the cell walls,effectively reducing the set recovery rate of densified wood and improving its bending performance.The research results could provide a theoretical basis for the preparation and application of high-performance densified wood.