木纤维表面醛基化改性及自胶合性能评价

Modification of Wood Fiber Surface by Aldehyde Groups and Property Evaluation of Self-Bonding Fiberboards

【目的】以杨木纤维为材料,通过氧化改性增强纤维表面反应活性位点,建立纤维表面羟基、醛基多位点网络结构,制备高强度、低吸水厚度膨胀率无胶纤维板,实现全生物质低碳、可循环生产利用。【方法】采用高碘酸钠氧化改性木纤维表面基团,建立高反应活性醛基网络位点,通过醛基含量测定、扫描电镜(SEM)、傅里叶红外光谱(FTIR)、X射线衍射仪(XRD)、X射线光电子能谱(XPS)、热重分析仪(TG)、差示扫描量热仪(DSC)分析反应前后及不同醛基含量木纤维的微观结构和化学成分变化规律;利用化学键交联在低温热压条件下制备自胶合纤维板,探究醛基化木纤维制备无胶纤维板的力学性能和吸水厚度膨胀率。【结果】通过反应时间、温度、氧化剂浓度等条件控制,可实现木纤维醛基化定量改性;与原纤维对比,醛基化纤维表面粗糙度增大、纤维尺寸变短、纤维素聚合度下降,纤维素-半纤维素-木质素包覆结构疏松,木纤维表面产生大量孔隙;纤维素结晶区随反应强度增加逐渐被破坏,醛基化木纤维的热稳定性随醛基含量升高逐渐降低,有利于无胶纤维板的低温热压成型。醛基化木纤维在热压过程中通过化学键交联可实现自胶合,热压温度和醛基化木纤维醛基含量对无胶纤维板的性能具有显著影响,通过优化原料和工艺条件制备的无胶纤维板具有优异的力学性能和耐水性。【结论】通过控制反应条件可得到不同醛基含量的醛基化木纤维,实现对木纤维表面醛基的可控改性;自胶合过程中温度过低(50℃)易导致醛基化木纤维耐水性差,温度过高(125℃)易造成醛基化木纤维降解,引起鼓泡、膨胀、碳化,降低纤维板力学性能。当高碘酸钠浓度0.07 mol·L^(−1)、反应温度30℃和反应时间6 h时,木纤维醛基含量为1.86 mmol·g^(−1);在热压温度100℃、压力20 MPa和热压5 min时,制备的自胶合醛基化木纤维板力学性能和耐水性达到最佳:抗弯强度78.36 MPa,弹性模量10.88 GPa,内结合强度3.04 MPa,24 h吸水厚度膨胀率仅8.01%。

【Objective】Taking poplar wood fiber as material,enhance the reactive sites on the fiber surface by oxidative modification,establish the multi-site network structure of hydroxyl and aldehyde groups on the fiber surface,and prepare highstrength,low-absorbent thickness expansion rate of self-bonding fiberboard,so as to achieve the whole biomass low-carbon and recyclable production and utilization.【Method】The surface groups of wood fiber were oxidatively modified by sodium periodate to establish highly reactive aldehyde group network sites,and the aldehyde group content was determined by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),thermogravimetric analyze(TG),and differential scanning calorimetry(DSC),which analyzed the microstructure and chemical structure of wood fiber before and after the reaction,as well as the content of different aldehyde groups.Using chemical bond cross-linking in low temperature hot pressing conditions to prepare self-glued fiberboard,to explore the mechanical properties of dialdehyde wood fibers to prepare self-bonding fiberboards and absorbent thickness expansion rate.【Result】The quantitative modification of dialdehyde wood fibers can be realized by controlling the conditions of reaction time,temperature,and concentration of oxidizing agent;comparing with the original fibers,the surface roughness of dialdehyde wood fibers increased,the fiber size became shorter,and the degree of cellulose polymerization decreased,the cellulose-hemicelluloselignin encapsulation structure was loosened,and a large number of pores were produced on the surface of wood fibers.The cellulose crystallization zone was gradually destroyed with the increase of reaction strength,and the thermal stability of dialdehyde wood fibers increased with the increase of reaction strength.The thermal stability of dialdehyde wood fibers gradually decreases with the increase of aldehyde content,which is conducive to the low-temperature hot compression molding of glueless fiberboard.Dialdehyde wood fibers can realize self-gluing through chemical bond cross-linking in the hot pressing process,the hot pressing temperature and aldehyde content of aldehyde-based wood fibers have a significant effect on the performance of the glueless fiberboards,and the self-bonding fiberboards prepared through the optimization of raw materials and process conditions have excellent mechanical properties and water resistance.【Conclusion】Different aldehyde content of dialdehyde wood fibers can be obtained by controlling the reaction conditions,and the controlled modification of aldehyde groups on the surface of wood fibers can be realized;too low a temperature(50℃)in the self-gluing process is likely to lead to poor water resistance of dialdehyde wood fibers,and too high a temperature(125℃)is likely to cause the degradation of dialdehyde wood fibers,which will lead to blistering,swelling,carbonization,and decrease the mechanical properties of the fiberboards.When the concentration of sodium periodate was 0.07 mol·L^(−1),the reaction temperature was 30℃,and the reaction time was 6 h,the aldehyde content of the wood fiber was 1.86 mmol·g^(−1);at a hot pressing temperature of 100℃,a pressure of 20 MPa,and a hot pressing time of 5 min,the mechanical properties of the self-glued dialdehyde wood fiber boards and the water resistance of the fiber boards reached the optimum:the bending strength of 78.36 MPa,the modulus of elasticity of 10.88 GPa,the internal bonding strength of 3.88 GPa,and the water resistance of the fiber boards.The mechanical properties and water resistance of the prepared self-glued dialdehyde wood fiber boards were optimal:flexural strength of 78.36 MPa,modulus of elasticity of 10.88 GPa,internal bonding strength of 3.04 MPa,and the expansion rate of the water-absorbing thickness of 24 h was only 8.01%.