高温热处理对杨木PF浸渍材尺寸稳定性的影响

为研究高温热处理对杨木PF浸渍材尺寸稳定性的影响,对速生杨木素材和PF浸渍材进行高温热处理,系统研究杨木素材、PF浸渍材、热处理材和PF浸渍-热处理材的吸水性、线性(径向和弦向)和体积吸水膨胀率、吸湿含水率、表面润湿性。结果表明:高温热处理可显著降低材料的吸水性、吸水膨胀率、吸湿含水率、表面润湿性,提高尺寸稳定性。相比于素材,浸水8 d后,PF浸渍材吸水量降低了17.37%,热处理材最高降低了63.8%,PF浸渍-热处理材最高降低了74.7%;PF浸渍材径向、弦向及体积吸水膨胀率分别降低14.71%、36.93%、30.19%,热处理材最高分别降低了64.99%、74.94%、72.33%,PF浸渍-热处理材最高分别降低94.4%、90.61%、91.37%;PF浸渍材吸湿含水率降低了11.14%,热处理材最高降低了55.57%,PF浸渍-热处理材最高降低了60.62%。与素材相比,PF浸渍材的表面接触角相差不大,热处理材最高提高了143.7%,PF浸渍-热处理材最高提高了139.4%,后2种木材的表面润湿性明显降低。相同热处理条件下,PF浸渍-热处理材尺寸稳定性更优异。红外光谱图中,PF浸渍材羟基、羰基和羧基吸收峰减弱、苯环碳骨架振动加强,热处理后羟基和乙酰基吸收峰减弱,表明PF浸渍处理和热处理对木材亲水性基团的减少和尺寸稳定性提高均有贡献,作为一种联合改性技术对于速生材尺寸稳定性的提高和开发利用具有实际意义。 

Effect of heat treatment on dimensional stability of phenolic resin impregnated poplar wood

The poplar wood and phenol formaldehyde ( PF) impregnated wood were subjected to heat treatment at 160, 180, 200 and 220 ℃ for 1 to 4 hrs. Hydroscopicity, hygroscopicity, linear ( radial and tangential) and volume swelling, and surface wettability of the control and PF impregnated wood after heat treatment were measured. The results showed that the dimensional stability can be improved considerably after heat treatment. The water absorption of PF impregnated wood was reduced by 17. 37%compared with that of control group after soaking in water for eight days, and the maximum decline could reach up to 63. 8% and 74. 7% for heat-treated wood and PF impregnated heat-treated wood, respectively. The swelling ratio of PF impregnated wood was reduced by 14. 71%, 36. 93%, and 30. 19% for radial, tangential, and volume, respectively, as compared to that of untreated wood, whereas the maximum reduction could reach up to 64. 99%, 74. 94%, and 72. 33% for heat-treated wood and 94. 4%, 90. 61%, and 91. 37% for PF impregnated heat-treated wood. The adsorption moisture content decreased by 11. 14% for PF impregnated wood compared with that of control group, while 55. 57% and 60. 62% reduction was observed for heat-treated wood and PF impregnated heat-treated wood, respectively. The contact angle of PF impregnated was close to that of control group, while the maximum increase could reach up to 143. 7% and 139. 4% for heat-treated wood and PF impregnated heat-treated wood, respectively, indicating that the surface wettability of heat-treated wood and PF impregnated heat-treated wood were decreased significantly. After heat treatment, significant changes can be found in infrared spectrogram. The improved dimensional stability of PF impregnated heat-treated wood was attributed to the reduction of hydroxyl, carboxyl and carbonyl which was mainly caused by the degradation of hemicellulose and the formation of chemical bonds between PF resin components and the cell wall polymers. PF resin impregnation combined with heat treatment was one of effective methods to improve the dimensional stability of poplar wood.