木材抽提物与木材胶合性能浅析

木材抽提物是指木材中除了构成细胞壁的纤维素、半纤维素和木质素以外,由中性有机溶剂或水抽提出来的物质的总称。尽管它们不是木材组织的结构物质,且大多含量不高,但木材抽提物成分和数量的变化,对于木材的材性有着重要的影响。笔者仅就抽提物对木材胶合性能的影响和生产工艺中应采取的措施作一分析。一、抽提物污染了水质材料界面水质材料界面特性性对予木材胶合性能的好坏,影响极大。木质材料界面的污染物,常常妨碍涂胶时咬液向木材表面扩散,导致胶层固化不良,降低胶合强度。抽提物质是引起太质材料界面污染的主要来源。     

浅析影响难胶材胶合的主要因素

文章介绍了难胶合材的主要特征。论述了影响难胶合材胶合的几个主要因素,诸如解剖结构特征、抽提物、PH值、密度和表面机械加工特征。     

人工林混合树种木材胶合的研究

研究杉木、杨树和巨桉等6种人工林木材两两混合胶合的剪切强度、木破率和剪切强度效率(剪切强度与密度的比值)等性能的差异.结果表明:人工林木材混合胶合是可行的,不同组合间胶合性能差异显著;"中与中"密度组合的胶合性能较好,"低与中"密度和"中与高"密度组合的次之,"低与高"密度组合的最差.     

不同水性高分子异氰酸酯胶对人工林木材胶合性能的影响

采用同一类型的高分子化合物、填料和乳胶按不同配比组成2种主剂,然后与贮存期不等的交联剂组成不同的水性高分子异氰酸酯胶黏剂(API),用来黏接杉木、杨木、巨桉、尾巨桉、柠檬桉和窿缘桉等6种人工林木材试样以研究 API主剂特征和交联剂贮存时间对人工林木材胶合性能的影响。试验结果表明:1)API主剂特征显著影响6种人工林木材的胶合性能。2)随着交联剂贮存期的增长,人工林试材的胶合性能有降低趋势,但胶合杉木、杨树、巨桉和尾巨桉4 种人工林木材时仍能达到标准要求。     

柚木苯醇抽提物对西南桦木材MUF胶合效果的影响

经柚木苯醇抽提物液作木材表面处理的西南桦木材试件的MUF胶合效果的试验结果表明:积聚在其木材表面的柚木木材苯醇抽提物(LEBAT)妨碍了MUF对被胶合材表面的润湿性和物理渗透性,从而影响了被胶合材与MUF胶合层胶钉的机械结合效应的形成,降低了被胶合材的胶合效果;但LEBAT并不影响被胶合材与MUF化学结合中的胶合效应。故为获得柚木木材满意的胶合效果,应采取避免柚木木材苯醇抽提物在其木材表面积聚的措施。     

三种松木单板的胶合工艺条件和胶合性能的改善

用ＵＦ、ＭＵＦ胶制作三种松木胶合板，分别就单板厚度、涂胶量及抽提物含量对胶合性能的影响，松木与柳安混合树种组坯、特殊添加剂对改善胶合性能的作用进行了研究。结果表明：除了老挝松边材ＭＵＦ胶合板以外，１．５和２．０ｍｍ厚的单板胶合强度均达到或超过日本ＪＡＳ普通胶合板的要求。合板胶合强度随单板厚度增加而下降，在一定范围内增加涂胶量可以提高合板胶合强度，混合组坯及施加特殊添加剂具有改善松木单板胶合性能的作用。     

展平竹与木材正交胶合材性能研究进展

因我国天然林禁伐,人工速生林木材和竹材成为当前木材加工利用的主要原材料,但人工速生林材质不及天然林材质,且竹材也存在截面尺寸小、用胶量大、原料利用率低等缺点。展平竹与木材正交胶合材（CLBT）由展平竹材和人工林锯材层板正交层叠制成,充分发挥了竹材优异力学性能与木材易加工等优势,既保留竹子和木材的天然纹理与结构特性,又克服了人工速生林材性的不足,实现了人工林资源的高附加值利用,是符合我国装配式建筑发展趋势的竹木质工程材产品。文中阐述了CLBT工艺技术、材料优势、构件性能及其影响因素等研究现状,介绍CLBT在我国多高层板式结构建筑中的应用前景,并提出今后研究方向。     

桉树人工林木材加工过程中几个问题的探讨

就桉树人工林木材在加工过程中出现的:采伐时产生端部开裂、制材加工困难、易产生劈裂、干燥时容易发生皱缩和开裂、机械加工困难、胶合和涂饰困难等5个生产问题进行了理论分析,探讨了出现这些问题的原因,提出解决这些问题的具体措施.     

木材胶合界面性能表征技术研究进展

木材胶合界面是指同时包含木材细胞壁和胶粘剂的区域。在木质胶合产品的加工工艺选择与使用性能评价中,胶合界面发挥着重要作用,其中胶粘剂渗透性能和界面力学性能是重要的评判标准。目前,用于表征胶合界面性能的技术包括光学显微技术、电子显微技术、X射线成像技术、微观力学测试技术等。文中通过对比各表征技术,提出进一步研究界面结合强度的表征、微观力学模型的建立、界面力学特性与木质胶合产品宏观性能的关系等将是未来的探索方向。     

正交胶合木胶合性能研究现状及展望

胶合性能是胶合木制品的重要性能之一。在正交胶合木（CLT）中木材特征、胶黏剂性能以及木材与胶黏剂之间界面性能共同决定了正交胶合木的胶合性能。木材作为一种天然各向异性材料，其纹理方向不同，造成组坯方式对于胶合性能影响巨大。在胶合性能测试中，取样尺寸、取样形状对于胶合性能的测试结果都有一定的影响。胶合界面性能表征方面的研究正逐渐兴起，但是针对CLT胶合界面性能表征的相关研究报道并不多。有关CLT胶合的研究多集中在胶黏剂和胶合工艺方面，而针对不同锯材单元的特性对胶合性能尤其是耐久性影响的研究尚少有报道。文中基于现有研究对CLT胶合界面性能影响因素进行总结，梳理对比CLT胶合性能测试方法以及胶合界面性能表征技术，并对今后研究方向提出意见和建议。     

Distribution,properties and formation of some wood extractives

Summary In the future, wood will be used largely for the manufacture of fibre products and particle board. The quality of wood used to meet increasing world demand will vary considerably. One feature of quality that can affect utilisation is the amount and type of wood extractives present. The distribution and variation in composition of extractives in the tree, as well as their effect on pulp manufacture, durability and surface films, are summarized. Methods to reduce the effects of some extractives in existing trees are described. Extractives can be reduced in plantation material by minimizing heartwood formation and by using silvicultural methods which result in small amounts of extractives being formed in this tissue. Current knowledge on heartwood formation is summarized.Paper presented to the 3rd Plenary Meeting of the International Academy of Wood Science held at the N. C. State University, Raleigh, March 11, 1971.     

Studies on wood gluing

Summary The purpose of this paper was to clarify the gluability and adhesion mechanism of polypropylene as a hot melt wood adhesive for plywood bonding. The gluability of plywood glued with nonpolar and modified polypropylene satisfied approximately the specification of the Japan Agricultural Standard, Designation Types 1 and 2. The moisture content (8 to 25 %) of the core veneer had no recognizable effect on gluability. The durability of polypropylene and that of modified polypropylene were the same as that of melamine-formaldehyde resin. Molten polypropylene made good contact with veneer surface, and penetrated into the lumina of wood cells and other spaces. In the separated glue lines, casts of glue which had penetrated into the vessels had many mushroom-like projections which had filled the bordered pit cavities. It was indicated that the anchoring effect of polypropylene which had penetrated into various wood elements and spaces in the veneer contributed dominantly to the gluability.Part of the paper was presented at the IUFRO-Working Party of Wood Gluing, October 2–9, 1977, Merida, Venezuela.     

Radial patterns of carbon isotopes in the xylem extractives and cellulose of Douglas-fir

Heartwood extractives (nonstructural wood components) are believed to be formed from a combination of compounds present in the adjacent sapwood and materials imported from the phloem. The roles of local compounds and imported material in heartwood formation could have important implications for the wood quality of species having naturally durable wood. Stable isotope composition (delta(13)C) was analyzed to assess radial variation in sapwood extractives, and to estimate the relative importance of adjacent sapwood extractives and imported photosynthate in the formation of heartwood extractives. Cellulose and extractives from the outer 39 annual rings of six Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees were isolated and their delta(13)C composition determined. Although the extractives and the cellulose showed different absolute delta(13)C values, the patterns of change over time (as represented by the annual rings) were similar in most cases. Within an annual ring, carbon isotope ratios of extractives were correlated with the cellulose isotope ratio (R2 = 0.33 in sapwood, R2 = 0.34 in heartwood for aqueous acetone-soluble extractives; R2 = 0.41 in sapwood for hot-water-soluble extractives). These data suggest that some sapwood extractives are formed when the wood ring forms, and remain in place until they are converted to heartwood extractives many years later. Sapwood extractives appear to be important sources of materials for the biosynthesis of heartwood extractives in Douglas-fir.     

The influence of heartwood on the pulping properties of Acacia melanoxylon wood

The pulping wood quality of Acacia melanoxylon was evaluated in relation to the presence of heartwood. The sapwood and heartwood from 20 trees from four sites in Portugal were evaluated separately at 5% stem height level in terms of chemical composition and kraft pulping aptitude. Heartwood had more extractives than sapwood ranging from 7.4% to 9.5% and from 4.0% to 4.2%, respectively, and with a heartwood-to-sapwood ratio for extractives ranging from 1.9 to 2.3. The major component of heartwood extractives was made up of ethanol-soluble compounds (70% of total extractives). Lignin content was similar in sapwood and heartwood (21.5% and 20.7%, respectively) as well as the sugar composition. Site did not influence the chemical composition. Pulping heartwood differed from sapwood in chemical and optical terms: lower values of pulp yield (53% vs 56% respectively), higher kappa number (11 vs. 7), and lower brightness (28% vs 49%). Acacia melanoxylon wood showed an overall good pulping aptitude, but the presence of heartwood should be taken into account because it decreases the raw-material quality for pulping. Heartwood content should therefore be considered as a quality variable when using A. melanoxylon wood in pulp industries     

Dendrochronological investigation of wood extractives

X-ray microdensitometry was applied to a set of Scots pinewood (i.e. low extractive content). Earlywood and latewood properties were determined as minimum and maximum densities of each tree ring and the potential influence of acetone-soluble extractives (i.e. non-structural and secondary constituents of wood) was estimated using tree-ring statistics. The occurrence of extractives in different portions of wood was determined using dendrochronological methods, by comparing the densities of unextracted and extracted wood. It was not only found that unextracted samples exhibited inflated earlywood and latewood density values, but the growth trends were also altered. Extractives flattened the inter-annual growth variability, both in earlywood and latewood, and influenced the estimation of intra-annual radial growth variations. Characterizing the varying amount of extractives is of inter-disciplinary importance. The results in this study describe their occurrence and show that the radial variations in extractives could be highly detailed by simply using densitometry-based dendrochronology.     

木材水抽提物对石膏及石膏刨花板的凝固及其性能的影响

本文研究了在商用缓凝剂(Retardan P)的存在下木材水抽提物对石膏浆料和石膏刨花板凝固时间及其强度的综合影响。结果表明:1.木材水抽提物能使石膏浆料和石膏刨花板产生缓凝,并导致强度下降,其影响程度与树种和石膏质量均有关系。2.木材水抽提物能加强Retarda P的缓凝作用,并且用两者交互作用下石膏浆料的凝固时间,可以指示石膏刨花板的凝固时间。3.石膏刨花板的静曲强度受刨花树种的影响,但缓凝剂的添加量却无显著作用。     

人工林米老排木材化学成分及其在树干高度上的变异

采用我国木材化学成分分析国家标准,对人工林米老排木材化学成分进行了测定和研究分析.结果表明:人工林米老排木材冷水抽提物含量和热水抽提物含量分别为2.67%和3.12%,1%NaOH抽提物含量为17.08%,纤维素含量为47.49%,综纤维素含量为80.42%,木素含量为28.80%,pH值为5.44;木材冷水抽提物和综纤维素含量在树干的不同高度上略有差异,但方差分析检验,差异不显著,热水抽提物、1%NaOH抽提物、纤维素和木素含量在树干的不同高度上差异显著,达到1%显著性水平;由树基往上,热水抽提物含量略呈两端高、中间低的趋势,冷水抽提物、1%NaOH抽提物和木素的含量逐渐降低,综纤维素含量和木材pH值逐渐升高;纤维素含量在树干上的分布规律为中间高、两端低,而且从树干中部往上的降低幅度较大.     

长白鱼鳞云杉和臭冷杉的木材及其抽出物化学组成的研究

研究长白鱼鳞云杉、臭冷杉的木材及其抽出物化学组成，并分析生材与气干材、心材与边材中各种化学组成变化的规律。同时检测出抽出物中弱酸性物质、中性物质和强酸性物质的含量及弱酸性物质中树脂酸和脂肪酸的组成含量。     

木材的机械加工性能研究现状与进展

本文概述了木材机械加工性能研究的现状，介绍了木材加工性能测试和评价的标准。分析了进行木材机械加工性能研究的重要性和迫切性，并对木材机械加工性能的研究方向和发展趋势提出了建议。