【作者】 郑霞；

【导师】 徐剑莹；

【作者基本信息】 中南林业科技大学 ， 木材科学与技术， 2012， 博士

【摘要】 我国竹材及农作物秸秆等非木材植物资源丰富,充分利用这些资源可以提高非木材植物资源的附加值,提高农业资源的利用效率,有利于增加农民收入,有利于发展农村循环经济以及实现社会经济可持续发展。同时,还可以解决长期以来农作物秸秆焚烧所带来的环境污染问题,有利于改善人类生存环境。竹材及农作物秸秆的主要成分为木质素、纤维素和半纤维素以及一些灰份杂质,其主要化学组份及结构与木材组份类似,可用于无胶人造板生产。喷蒸热压是一种高效人造板热压工艺,喷蒸热压过程中板坯承受水热协同作用,可以大大缩短人造板热压周期,提高无胶人造板力学强度,显著改善无胶人造板尺寸稳定性。本文分析了苎麻秆、烟秆及竹材制备无胶碎料板的可行性,并通过喷蒸热压工艺分别制备苎麻秆无胶碎料板、烟秆无胶碎料板及竹材加工剩余物无胶碎料板,研究了无胶碎料板密度、喷蒸蒸汽压力及喷蒸时间对无胶碎料板静曲强度、弹性模量、内结合强度以及吸水厚度膨胀率等物理力学性能的影响。研究表明：(1)密度对三种无胶碎料板的静曲强度、弹性模量、内结合强度和吸水厚度膨胀率影响显著,随着三种无胶碎料板密度的增大,其静曲强度、弹性模量、内结合强度都明显增加,吸水厚度膨胀率均先增大后减小。(2)蒸汽压力为1.0MPa时,喷蒸时间对无胶板静曲强度和内结合强度影响显著,随着喷蒸时间的增加无胶板静曲强度和内结合强度值均先增大后减小；蒸汽压力为0.6MPa时,喷蒸时间对无胶板静曲强度和内结合强度影响不明显；蒸汽压力为1.0MPa和0.6MPa时,喷蒸时间对无胶板弹性模量影响显著,随着喷蒸时间的增加三种无胶板弹性模量值均增大：蒸汽压力为1.0MPa、喷蒸时间为7min和l0min时三种无胶板静曲强度、弹性模量、内结合强度值均相对较高；蒸汽压力为1.0MPa和0.6MPa时,喷蒸时间对三种无胶板吸水厚度膨胀率影响较显著,随着喷蒸时间的增加,三种无胶碎料板吸水厚度膨胀率降低；利用喷蒸热压工艺制备的三种无胶碎料板吸水厚度膨胀率值均高于GB/T4897.2-2003标准和日本JIS A5908标准。(3)在同一密度(0.8g/cm3)条件下,喷蒸热压工艺制备的三种无胶碎料板的静曲强度、弹性模量和内结合强度明显高于普通热压工艺制备的无胶碎料板,吸水厚度膨胀率明显低于普通热压工艺制备的无胶碎料板。(4)三种无胶碎料板喷蒸热压优化工艺：密度为0.8g/cm3,蒸汽压力1.0MPa,喷蒸时间为7min。分别采用化学成分分析、高效液相色谱(HPLC)分析、比表面积分析、红外光谱(FTIR)分析、X射线光电子能谱(XPS)、固体核磁共振分析(CP/MAS13C-NMR)、X射线衍射(XRD)分析及热重分析(TG)等手段,分析了普通热压和喷蒸热压前后的三种无胶碎料板化学成分、界面官能团以及纤维素结晶度等的变化,揭示了三种无胶碎料板的无胶胶合机理。研究表明,喷蒸热压过程中水热协同作用使板坯内部发生了更剧烈的化学变化,板坯内部产生了更多的自胶合物质：化学成分分析表明,喷蒸热压后竹材、苎麻秆和烟秆碎料的热水抽提物、苯醇抽提物和木素含量显著增加,半纤维素、综纤维素及a-纤维素含量均明显降低。喷蒸热压过程中碎料的半纤维素和少量低聚合度的纤维素降解为单糖和低聚糖,同时半纤维素和少量低聚合度的纤维素降解产物均能发生脱水反应,生成糠醛、糠醇等有机化合物,木质素及其降解产物(含多酚类物质)可与上述糠醛类化合物发生反应形成类似于酚醛树脂胶的“木质素胶”。高效液相色谱分析结果表明,半纤维素在水热共同作用下可以发生水解,生成低聚多糖和单糖,部分低聚多糖和单糖脱下的羧基可以形成甲酸和乙酸等有机酸,水解产物中的单糖部分脱水后还可以转化成糠醛。生成的有机酸可以进一步促进半纤维素水解,实现半纤维素自生酸催化水解反应。喷蒸热压过程中水、热协同作用更剧烈,半纤维素发生了更大程度的降解,产生了更多的游离糖、有机酸和糠醛等水解产物。快速比表面积及孔隙分析结果表明,竹材、苎麻秆和烟秆的喷蒸热压板碎料热水抽提物残渣形成更多微小孔隙,微小孔隙相互连通成较大的孔隙,形成了更多的中孔和大孔孔隙,比表面积变得最大,说明喷蒸热压过程半纤维素降解程度更大,产生了更多的可溶于热水的低分子化合物。傅里叶红外光谱分析结果表明,喷蒸热压工艺使竹材、苎麻秆和烟秆碎料中的活性—OH数量明显增加,氢键缔合-OH的数目增加；喷蒸热压过程中的水热协同作用使半纤维素发生更大程度的水解,一方面,降解产物产生聚合反应生成了糠醛均聚物——缩聚呋喃树脂,另一方面,降解产物中的糠醛类化合物与具有酚羟基结构的木素发生缩聚反应,形成具有胶粘作用的类似于酚醛树脂的缩合物。X射线光电子能谱分析结果表明,喷蒸热压过程中的水热协同作用使部分半纤维素及少量纤维素更易发生降解反应,生成单糖和低聚糖等降解产物,降解产物可能进一步脱水生成糠醛类化合物,糠醛类化合物又和木质素反应生成类似于胶粘剂的树脂聚合物；与热压前原料相比,喷蒸热压板的碎料中含有羟基(—OH)的纤维素和半纤维素含量显著减小,含有羰基(C=O)的半纤维素以及木质素成分含量变化较小,含有酯基或羧基(—O—C=O)的半纤维素以及抽提物成分显著增加。固体核磁共振分析结果表明,竹材、苎麻秆和烟秆3种材料的热压前碎料、普通热压板碎料及喷蒸热压板碎料的纤维素C1以及木素的C3、C4、C5峰高相差不大,说明热压过程对样品的纤维素和木素影响较小；喷蒸热压过程中半纤维素降解速度加剧,使得半纤维素的相对量减少。与热压前碎料相比,喷蒸热压板碎料谱图中21、172附近的半纤维素中乙酰基C—C及72附近的半纤维素的C2、C3、C5特征峰峰高明显减弱,峰顶渐趋平缓。X射线衍射分析结果表明,喷蒸热压过程中水、热共同作用比普通热压作用更剧烈,水、热协同作用更突出,半纤维素水解程度更大,导致非结晶区得到抽提、结晶区表面微纤丝及非结晶区微纤丝的羟基裸露,其间形成氢键而使非结晶区重结晶,纤维的相对结晶度增加。热重分析结果表明,竹材、苎麻秆和烟秆的3个样品的第一失重阶段和第三失重阶段的失重曲线变化趋势均基本相似,但第二失重阶段的失重曲线明显不同。与热压前碎料相比,喷蒸热压样品进入第二阶段的热解温度明显相对前移,TG曲线斜率更大,说明喷蒸热压过程中剧烈的水热协同作用使样品中更多的半纤维素和纤维素产生降解,生成了更多的易于热解的低分子量的糖类等低分子量碳水化合物；喷蒸热压样品的第二阶段失重率均最小,说明喷蒸热压过程中半纤维素热解产生的糠醛等与木素发生反应,生成了更多的热解温度更高的胶粘成分。非木材植物无胶碎料板喷蒸热压成型机理可能是：(1)水、热协同作用使纤维素分子的活性羟基数量增加,活性羟基中的氢原子除以主价键与氧原子联结外,还与相邻纤维素分子羟基中负电性较强的氢原子以负价键联结成氢键O.H…H。(2)半纤维降解产物——糠醛的树脂化,即半纤维素的木聚糖水解生成糠醛,糠醛可以发生自动氧化和催化氧化反应生成糠酸。在糠酸的催化作用下糠醛可以生成糠醇,糠醇在甲酸、乙酸等有机酸催化作用下可以进行缩聚反应生成有助于碎料板自胶合的成分缩聚呋喃树脂。(3)木聚糖水解生成糠醛类化合物以及纤维水解生产的5-羟甲基-2-糠醛在高温及催化作用下与具有酚羟基结构的木素发生缩聚反应,形成具有类似于酚醛树脂的缩合物。(4)喷蒸热压过程中水、热作用剧烈,板坯内部温度分布更均匀,碎料中的木质素被流展并部分均匀分布在碎料颗粒间,起到了胶粘剂的作用。另外,木质素受水、热作用部分发生降解,生成木质素碎片。这些碎片存在因活化而与木质素发生缩合反应的可能。喷蒸热压过程半纤维素等容易降解的碳水化合物降解后,而使被活化降解的木质素暴露在外面,有利于木质素进行缩合反应而产生交联,在碎料间起到胶粘作用。更多还原

【Abstract】 Non-wood plant resources such as bamboo and crop straw have its huge storage in China, the added value of non-wood plant resources and the use efficiency of agricultural resources was improved by making full use of those resources, in this way, the peasants’ income was increased, meanwhile, environmental pollution problem caused by crop straw burning can be solved, human living environment was improved. The main component of bamboo and crop straw were lignin, cellulose, hemicellulose and some ash contents, the chemistry component and structure of those non-wood plant resources is similar to timber, those non-wood plant resource can be used in the production of binderless wood based panel. Steam-injection pressing is a kind of high efficient hot pressing process, in the process of which hot pressing cycle was shortened obviously, the mechanical strength and dimensional stability of binderless wood based panel was improved by the effect of hydrothermal synergistic.This paper analyze the preparation feasibility of binderless particleboard with ramie, tabacco stem and bamboo, the binderless particleboard of ramie, tabacco stem and bamboo were prepared by steam-injection pressing process respectively. The effect on static bending strength, elastic modulus, internal bond strength and thickness swelling of binderless particleboard made by board density, steam pressure and steam injection time were studied. The research has showed that:(1) the effect made by density on the four physical and mechanical properties is obvious, with the density of three different board increased, static bending strength, elastic modulus and internal bond strength were increased obviously, but thickness swelling was firstly increased and then decreased;(2) when the steam pressure is1.0Mpa, the effect on static bending strength and internal bond strength made by steam injection time was obvious, with the steam injection time increased, the static bending strength and internal bond strength was firstly increased and then decreased; when the steam pressure is0.6Mpa, the effect on static bending strength and internal bond strength made by steam injection time was not obvious, when the steam pressure is1.0Mpa or0.6Mpa, the effect on elastic modulus made by steam injection time was obvious, with the steam injection time increased, the elastic modulus of the three different board were increased; when the steam pressure is1.0Mpa and the steam injection time is7min or10min, the elastic modulus, static bending strength and internal bond strength value of the three different board were relatively high; when the steam pressure is1.OMpa or0.6Mpa, the effect on thickness swelling of the three different board made by steam injection time is relatively obvious, with the steam injection time increased, the thickness swelling was decreased; the thickness swelling of the three different binderless particleboard which is prepared by steam injection pressing process meet the standard of GB/T4897.2-2003AND JISA5908;(3) the static bending strength, elastic modulus and internal bond strength of the three different binderless particleboard prepared by steam injection pressing process is obviously higher than that of ordinary hot pressing process. But the thickness swelling is obviously lower than that of ordinary hot pressing under the some condition that the density is0.8g/cm3.The chemical constituents, interface functional groups and cellulose crystallinity variation of the three different binderless particleboard were analyzed by the method of HPLC, FTIR, XPS, CP/MAS13C-NMR, XRD, TG, specific surface area and chemical constituents, non-adhesive bonding mechanisms of the three different binderless particleboard were revealed. The study has showed that there are intense chemical changes in the inner slab by the synergistic effect of hydrothermal in the process of steam injection pressing, the self-adhesive materials were produced in the inner slab:the chemical constituent analysis has showed that the hot water, alcohol benzene extract and lignin content of bamboo, ramie, tabacco stem was obviously increased, the content of hemicellulose, holocellulose and a-cellulose were obviously decreased after steam injection pressing, hemicellulose and some cellulose with low polymerization degree were degraded into monosaccharide and oligosaccharide, meanwhile, the dehydration reaction of degradation products from hemicellulose and a few low polymerization degree cellulose produced furfural and furfuryl alcohol which can react with lignin and its degradation products and produce " lignin-adhesive" which is similar to phenol formaldehyde resin adhesive (PF); the analysis results of HPLC has showed that the hydrolysis of hemicellulose under the synergistic effect of hydrothermal produced oligosaccharides and monosaccharide. The carboxyl from the decarboxylation reaction of oligosaccharides and monosaccharide produced organic acids such as formic acid and acetic acid, the dehydration of partial monosaccharide was converted to furfural. Those organic acids promoted the hydrolysis of hemicellulose and made the hemicellulose hydrolyzed by its own acids. In the process of steam injection pressing, the hydrolysis effect of was more intense, hemicellulose was degraded in a more great extent, which produced more free sugars, organic acids and furfural. The analysis results of specific surface and pore have showed that the hot water extract’ residue from the three different materials after steam injection pressing formed more micro pore, which formed more mesopore and macropore by linking together and made the specific surface greatest, the degradation of hemicellulose in the process of steam injection pressing produced more low molecular weight compounds which is soluble in hot water. The analysis results of FTIR have showed that the amount of active hydroxyl in the three different particles was increased obviously by steam injection pressing; the synergistic effect of hydrothermal made hemicellulose hydrolyzed in a more great extent, the polymerization of degradation products produced furfural homopolymer. The analysis results of XPS have showed that the synergistic effect of hydrothermal made partial hemicellulose and a few cellulose degraded more easily, the degradation produced monosaccharide and oligosaccharide, those degradation products was dehydrated and produced furfural compounds, those furfural compounds reacted with lignin and produced a resin polymer which is similar to adhesive; compared to the materials before hot pressing, the content of hemicellulose and cellulose which have hydroxyl in its surface was decreased obviously, the content of hemicellulose and lignin which have carboxyl was hardly changed, the content of hemicellulose and extract which have ester group and carboxyl was increased obviously. The analysis results of CP/MAS13C-NMR have showed that the C1peak of cellulose and the C3, C4, C5peak of lignin from the raw materials, ordinary hot pressing materials and steam injection pressing materials was nearly the same, which showed that hot pressing has a little effect on cellulose and lignin; the degradation speed of hemicellulose was accelerated in the process of steam injection pressing, which made the relative content of hemicelloluse was decreased. Compared to the materials before hot pressing, in the spectra of materials after steam injection pressing, the characteristic peak height of acetyl from hemocellulose near21,72and C2, C3, C5from hemicellulose near72were decreased obviously, the peak tend to gentle. The analysis results of XRD have showed that the synergistic effect of hydrothermal in the process of steam injection pressing was more intense than that of ordinary hot pressing, the hemicellulose was hydrolyzed in a more great extent than that of ordinary hot pressing, which made the non-crystalline region extracted and made the microfibril’hydroxy of crystalline region surface and non-crystalline region exposed, those exposed hydroxy formed hydrogen bond which made non-crystalline region recrystallized, the relative crystallinity of fibers was increased. The analysis results of TG have showed that the TG curve changing trend of the first weight loss stage for the three different materials and that of the third weight loss stage was nearly the same, but the second weight loss stage of TG curve was obviously different. Compared to the materials before hot pressing, the pyrolysis temperature of the second weight loss stage in the process of steam injection pressing moved forward relatively, the slope of TG curve was bigger, which showed that the synergistic effect of hydrothermal in the process of steam injection pressing made more hemicellulose and cellulose degraded and produced some low molecular weight carbohydrate such as low molecular weight sugar which is easy to pyrolysis; the weight loss rate of samples in the third stage was minimum, which explained that in the process of steam injection pressing the furfural from hemicellulose’pyrolysis reacted with lignin and produced some components for adhesion which have higher pyrolysis temperature.The possible mechanism for steam injection molding of non-wood plants binderless particleboard was that:(1) the synergistic effect of hydrothermal made the amount of hydroxyl increased, the hydrogen atom from active hydroxyl combined oxygen atom with its main valence chemical bond and combined the hydrogen atom from near cellulose molecule’hydroxyl which have strong electronegativity with negative-valence chemical bond by forming hydrogen bond (O-H…H).(2)the resinification of furfural which is the degradation product of hemicellulose, furfural can produce furfuryl alcohol with the catalysis of furoic acid, the polycondensation of furfuryl alcohol, with the catalysis of organic acids such as formic acid and acetic acid, can produce condensation furan resins which is helpful to self-adhesion for particle board;(3) under the condition of high temperature and catalysis, the polycondensation between furfural compounds from the hydrolysis of xylan,5-hydroxymethyl-2-furfural from the hydrolysis of fibers and lignin which has phenolic hydroxyl produced a kind of condensation polymer which is similar to phenolic resin;(4) the degradation of partial lignin can produce lignin debris under the effect of hydrothermal. There is chance for the polycondensation between those activated debris and lignin. The degradation of carbohydrate such as hemicellulose made the degraded and activated lignin exposed, which is helpful to the polycondensation of lignin and have the effect of adhesion among those debris.更多还原