柠檬酸预处理杉木压缩变形固定及性能

Compression deformation fixation and properties of Chinese fir pretreated with citric acid

【目的】为提高速度材杉木利用价值,探究柠檬酸预处理和热压缩处理对杉木压缩变形的影响,从而改善其密度低、尺寸稳定性差和力学性能不佳等缺点。【方法】采用柠檬酸预处理和热压缩,通过调控柠檬酸质量分数和热压温度制备杉木压缩材,并测定压缩材的吸水回复率和吸湿回复率。采用应力松弛测试和傅里叶红外光谱探究柠檬酸预处理杉木压缩材的变形固定机理,并表征杉木压缩材的物理力学性能。【结果】柠檬酸预处理杉木压缩材吸水回复率随着柠檬酸溶液质量分数的增加先减小后略微增加,随着热压温度的升高而降低,且吸水和吸湿回复率最低分别为10.78%和1.38%。柠檬酸预处理过程杉木细胞壁组分产生微量降解,切断杉木细胞壁组分之间少部分连接而释放压缩过程产生的内应力。此外,柠檬酸可能与杉木中的少部分游离羟基酯化反应形成交联网络。在热压过程中,填充在木材细胞壁间隙中的柠檬酸酯化生成的聚合物在高温下发生软化并流动,促进了木材内应力的释放,最终固定杉木压缩材形变。杉木压缩材的密度随压缩率的增大而增大,并在压缩率为50%时达到最大值0.717 g/cm^(3),相较于未处理材密度提高了94.8%,同时其抗弯强度提高了70.6%,抗弯弹性模量提高了278.2%,硬度整体提高了52.5%。【结论】柠檬酸预处理能够较好地实现杉木压缩材的变形固定,杉木压缩材的物理力学性能得到显著提升,本研究结果可为速生材杉木高值化利用提供理论支撑与技术参考。

[Objective]In order to improve the use value of fast-growing wood Chinese fir,this study investigated the effects of citric acid pretreatment and thermal compression treatment on the compression set of Chinese fir,so as to improve its shortcomings such as low density,poor dimensional stability and poor mechanical properties.[Method]In this study,Chinese fir pretreated with an aqueous solution of citric acid with varying mass fractions was evaluated at different hot-pressing temperature,then the set-recovery for water absorption and the set-recovery for moisture absorption of Chinese fir compressed wood were measured.Stress relaxation and Fourier infrared spectroscopy were used to investigate the deformation and fixation mechanism of Chinese fir compressed wood pretreated with citric acid,and physical and mechanical properties of Chinese fir compressed wood were characterized.[Result]The set-recovery for water absorption of Chinese fir compressed wood decreased with the citric acid mass fractions and then increased slightly,while decreased with the hot-pressing temperature.The lowest set-recovery for water absorption and moisture absorption was 10.78%and 1.38%,respectively.This could be attributed to the fact that some components of wood were degraded by citric acid,inducing partial cleavage of connections among Chinese fir components,therefore the internal stress of Chinese fir compressed wood was released.In addition,citric acid may react with a small amount of hydroxyl of Chinese fir to form a cross-linked network.The polymer formed by the esterification of citric acid filled in the intercellular space of cell wall during the process of compression.At higher temperature,the polymer was soft and flexible,which promoted the release of the internal stress and the fixation of Chinese fir compressed wood.The density of Chinese fir compressed wood increased with the compression ratios,and reached a maximum value of 0.717 g/cm;when the compression ratio was 50%.Compared with the control,its density,bending strength,flexural elastic modulus and the hardness of compressed wood increased by 94.8%,70.6%,278.2%and 52.5%,respectively.[Conclusion]The deformation of Chinese fir compressed wood is fixed effectively by citric acid pretreatment,and the physical and mechanical properties of Chinese fir compressed wood are improved significantly.The results of this study provide theoretical support and technical reference for adding highvalue to application of fast-growing wood.