【作者】 关鑫；

【导师】 郭明辉；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2012， 博士

【摘要】 随着世界经济的高速增长,生态安全、人类健康和经济社会的和谐发展成为区域乃至国家发展的重要评价标准,人造板作为林业产业的重要组成部分,其发展一直受到游离甲醛的制约,而漆酶作为生物环保型酵素的出现无疑成为解决这一问题的有效途径,且对保障生态安全、发展低碳经济、推进节能减排、构建资源节约型社会具有重要意义。本研究以木纤维为原料,应用漆酶介体体系活化木质素生成天然胶粘物质,采用高温高压热处理法制备中密度纤维板,其主要包括四部分内容：(1)基于酚型(愈创木酚)和非酚型(藜芦醇)木质素模型化合物初步确定漆酶、人工介体(ABTS)和天然介体(香草醛)的配比和反应条件；(2)基于傅里叶变换红外光谱和X射线衍射图谱确定紫外光预处理工艺,基于响应面法优化酶促反应工艺参数和热压工艺参数,基于力学性质和物化性质确定提高尺寸稳定性的处理工艺,由上述三部分内容得到漆酶介体体系活化木纤维制备中密度纤维板的优化工艺；(3)借助傅里叶变换红外光谱、X射线衍射仪、环境扫描电镜、接触角测定仪和X射线光电子能谱探究中密度纤维板的结合机理；(4)基于人工加速老化试验研究漆酶介体体系活化木纤维制备中密度纤维板的碳素储存能力。本研究得到的结论归纳如下：(1)木纤维紫外光预处理的辐照时间为24h,辐照距离为50cm,辐照强度为150W/m2。此时,纤维素部分降解,增加木纤维的漆酶反应活性点,同时少量木质素降解为烷基醛,其可作为漆酶介体催化氧化非酚型木质素；(2)基于木质素模型化合物得到的漆酶介体体系活化木纤维的优化工艺为pH5.0,反应温度50℃,反应时间55min,木纤维体积分数4.0%,ABTS摩尔浓度0.28mmol/L,香草醛摩尔浓度1.66mmol/L,漆酶活性60U/mL；中密度纤维板的热压优化工艺为热压温度165℃,热压压力10MPa,热压时间512s。热压过程分为干燥过程和塑化过程,其中干燥过程设定为3周期循环干燥,每一周期均采用先升压到10MPa保压52s,而后降压至4MPa保压52s；塑化阶段在10MPa保压200s；(3)以未经尺寸稳定性处理的中密度纤维板为参照样,分别从物理力学性能、接触角、官能团、纤维素结晶度和微观形貌几方面对比分析壳聚糖和固体石蜡对尺寸稳定性的影响,研究认为固体石蜡是借助石蜡分子的疏水性质,通过封闭水分子的流通路径来提高中密度纤维板的尺寸稳定性,但时效短,降低力学强度；壳聚糖是以化学键合的方式加强木纤维之间的黏结,减少或阻断水分子流通路径来提高中密度纤维板的尺寸稳定性,时效长,提高力学强度。因此,采用壳聚糖来提高中密度纤维板的尺寸稳定性,合理的添加量为1.2%；(4)基于优化工艺制备的中密度纤维板静曲强度为34.41MPa,弹性模量为2887.9MPa,内结合为0.89MPa,吸收厚度膨胀率为24.80%,根据国标GB/T11718-2009可知,其达到潮湿状态下使用的家具型中密度纤维板(MDF-FN MR)性能要求：(5)通过傅里叶变换红外谱图、纤维素相对结晶度和x射线光电子能谱分析可知,中密度纤维板的无胶胶合主要借助于酯化反应、氢键键合、缩聚反应、耦合反应和schiff碱反应,其中耦合反应和缩聚反应是主反应。这些化学反应促使纤维素内生成新的结晶区,提高中密度纤维板的力学强度。热压时,木质素在中密度纤维板内部流动,使得中密度纤维板表面的羧基含量相对较多,内部的醛基含量相对较多,从而使得纤维板内部和表面的化学键合方式存在一定的差异性；(6)不同人工加速老化时间段的试样碳素储存量>参照样2碳素储存量>参照样1碳素储存量,且均随着人工加速老化时间的延长而减少,其减少速率逐渐降低,但参照样1的碳素储存量流失速率大于试样和参照样2。碳素储存量减少的根本原因在于中密度纤维板内C-O和C-C键的断裂及芳香环的降解,而直接原因是扩散-渗透系数的增大,短期来看,扩散-渗透系数的增大加速中密度纤维板的腐朽,木腐菌(白腐菌和褐腐菌等)破坏板材中的纤维素、半纤维素或木质素的结构,从而降低碳素储存量；长期来看,腐朽程度的增强会显著降低板材的密度,加速提高板材的吸湿性和渗透性,促其产生翘曲变形,减少其受用寿命,从而缩短中密度纤维板的碳素储存时间。更多还原

【Abstract】 With the rapid growth of world economy, ecological security, human health and harmonious development became an important evaluation criterion of the international community. Wood based panel as the important ingredient in forestry industry, the free formaldehyde restricted its development all the time. However, laccase was proved to be an effective method to resolve this problem. Meanwhile, laccase had special significance in the insurance of ecological environment security, the development of low carbon economy, the advancement of energy conservation and the construction of a resource-efficient society.According to the activation of laccase mediator system, wood fibers were made binderless medium density fiberboard by hot-press. This research focused on four aspects, which were:(1) based on the models of phenol compound (guaiacol) and non-phenol compound (veratryl alcohol), the proportion and reaction conditions of laccase, artificial mediator (ABTS) and natural mediator (vanillin) were determined primarily;(2) UV pretreatment process was determined in view of FTIR and XRD. The technological parameters of enzymatic reaction and hot-press were optimized based on response surface methods. Dimensional stability process was determined by mechanical analysis, physical and chemical analysis. Then optimized technology of medium density fiberboard based on laccase mediator system activation on wood fiber was achieved by above three sections;(3) the binding mechanism of binderless medium density fiberboard was explored by FTIR, XRD, SEM, XPS and contact angle measuring instrument;(4) carbon storage of medium density fiberboard based on laccase mediator system activation on wood fiber was researched by artificial weathering test.The conclusions of this research were summarized as follows:(1) The process parameters of UV pretreatment were as follows:the UV irradiation time was24h, the UV irradiation distance was50cm and the UV irradiation intensity was150W/m2At the moment, cellulose was degraded which increased the reaction activity sites of laccase. Meanwhile, a little lignin was degraded into alkyl aldehyde which be used for mediator to catalyze non-phenol lignin;(2) Based on the model compounds of lignin, the optimized technologies of laccase mediator system activation on wood fibers were as follows:pH value was5.0, the reaction temperature was50℃, the reaction time was55min, the volume fraction of wood fibers was4.0%, the molarity of ABTS was0.28mmol/L, the molarity of vanillin was1.66mmol/L and the laccase activity was60U/mL. The hot-press optimized technologies of medium density fiberboard were as follows:the hot-press temperature was165℃, the hot-press pressure was10MPa and the hot-press time was512s. The hot-press process consisted of dry process and plastics process. Dry process was three cycles, and each cycle was52s at10MPa firstly, and then52s at4MPa. Plastics process was200s at10MPa.(3) Binderless medium density fiberboard without dimension stability treatment was as control sample. The effects of chitosan and solid paraffin on dimension stability were comparative analysis based on physical properties, mechanical properties, contact angle, functional groups, cellulose crystallinity and morphology. The results showed that solid paraffin closed water-flow path with hydrophobic property which could improve the dimension stability of medium density fiberboard, but the mechanical strength was reduced and the effective time was relatively short. Chitosan decreased or blocked the water-flow path by chemical bonding to improve the dimension stability, while the effective time was relatively long and enhanced the mechanical strength. Therefore, chitosan was chosen to improve the dimension stability, and the suitable mass fraction was1.2%;(4) Based on the optimized technologies, the MOR of medium density fiberboard was34.41MPa, the MOE was2887.9MPa, the IB was0.89MPa and the TS was24.80%. On the basis of Chinese National Standard GB/T11718-2009, the binderless medium density fiberboard reached the performance requirement of MDF-FN MR.(5) By the analysis of FTIR, XRD and XPS, the reactions of binderless medium density fiberboard consisted of esterification, hydrogen bonding, polycondensation, coupling reaction and Schiff base reaction. Polycondensation and coupling reaction were main reactions. These reactions helped to bring about new crystalline regions which enhanced the mechanical strength. During the hot-press, lignin flowed in the interior of medium density fiberboard, and then the carboxyl group increased on the surface of medium density fiberboard, while the aldehyde group increased in the interior of medium density fiberboard. Therefore, the bonding types were different between the surface and the interior of binderless medium density fiberboard;(6) Under the different artificial weathering time, the carbon storage of test sample was most, and then was control2and control1. The carbon storage decreased with the increasing time, but the rate reduced gradually. The loss rate of controll was greater than test sample and control2. The primary cause of decreasing carbon storage was the breakage of C-O/C-C and the degradation of aromatic ring in medium density fiberboard. The efficient cause was the increasing of diffusion-permeability coefficient. In the short time, the increasing of diffusion-permeability coefficient accelerated the medium density fiberboard to decay. The wood rotting fungi (white-rot fungi and brown-rot fungi) damaged the structures of cellulose, hemicelluloses and lignin which decreased the carbon storage. In the long time, the increasing degree of wood rotting reduced the density of fiberboard observably, and enhanced the hygroscopicity and permeability. Therefore, the medium density fiberboard would create destabilizing buckling deformation which reduced the service life. Consequently, the carbon storage time of medium density fiberboard was reduced.更多还原