壳聚糖及其金属配位聚合物在木材工业中的应用现状与展望

壳聚糖(chitosan)是从虾、蟹等甲壳动物中提取的一种天然碱性高分子多糖,壳聚糖易与过渡金属及稀土金属配位形成壳聚糖金属配位聚合物[chitosan metal complexes(CMC)],壳聚糖及壳聚糖金属配位聚合物是目前研究广泛的一类新型高分子生物材料,近年来的研究表明壳聚糖及壳聚糖金属配位聚合物在木材工业中有着广泛的应用前景,例如作为环保型木材防腐剂,促进木材防腐工业的持续发展。笔者介绍了其基本应用,重点报道其在木材染色、木材保护及用于木质材料胶合方面的应用及研究进展。     

Development of new natural polymer-based wood adhesives I: dry bond strength and water resistance of konjac glucomannan,chitosan, and their composites

 Bonding properties of konjac glucomannan (KGM), chitosan, and their composites were investigated. After preparing three-ply plywood glued with these materials, the dry bond strength and the bond strength after water immersion treatment were measured. The bond strength of urea-formaldehyde resin adhesive, casein, and soybean glues was also studied for comparison. KGM developed relatively good dry bond strength in extremely small solid amounts, irrespective of alkaline treatment. However, the water resistance was extremely low for all of the conditions. Chitosan also developed good dry bond strength in small solid amounts and was better than conventional adhesives. Chitosan also exhibited excellent water resistance compared to casein and soybean glues. When KGM and chitosan were combined, the adhesiveness under the dry condition was enhanced, and the bonding properties were superior to those of casein and soybean glues. Therefore, it is expected that chitosan and chitosan–KGM composite can be used as environmentally friendly wood adhesives. Received: March 18, 2002 / Accepted: July 5, 2002 RID="*" ID="*" Part of this paper was presented at the 51th Annual Meeting of the Japan Wood Research Society, Tokyo, April 2001     

Effect of postcure conditions on the dynamic mechanical behavior of water-based polymer-isocyanate adhesive for wood

To study the effect of postcure conditions on the viscoelastic behavior of water-based polymer isocyanate adhesives for wood (API adhesive), dynamic mechanical analysis (DMA) was performed for a simplified model of API adhesives under various postcure conditions. These conditions were achieved by storing the samples at room temperature or by heating them in an oven. Fourier transform infrared (FT-IR) spectroscopy was performed to test for residual isocyanate groups (NCO) and isocyanate derivatives to elucidate the reaction mechanism under the postcure conditions. DMA revealed that the postcure conditions led to wide variations in the viscoelastic behaviors of API films. FT-IR analysis confirmed the decrease of residual isocyanate during postcure treatments. However, the complete consumption of isocyanate could not be achieved under the postcure conditions. A good correlation was found between the DMA result and the chemical changes in the API samples heated above 140°C. However, no correlation was observed in the case of the samples heated at temperatures less than 140°C. This implies that postcure conditions led to a difference in the reaction chemistry of API. Part of this article was presented at the 55th Annual Meeting of the Japan Wood Research Society, Kyoto, March 2005     

Durability of isocyanate resin adhesives for wood V: changes of color and chemical structure in photodegradation

The effect of ultraviolet (UV) light irradiation on the color and chemical structure of water-cured polymeric diphenylmethane diisocyanate (PMDI) was investigated using a UV long-life fade meter. Control treatment was performed without UV light irradiation using a thermohygrostat for comparison. Two kinds of resin were used in this study: that to which only water had been added, and resin to which a small amount of polyol and water had been added. In addition, lauan (Shorea spp.) wood was used as a reference. The photodegradation of the resins over a period of up to 300 h was observed using a colorimeter and Fourier transform infrared (FT-IR) spectroscopy. When the resins were treated with UV light, the color difference (ΔE ^* ab) of the resins increased signifi cantly in a short time, and then reached a near-constant value. For lightness, L ^* decreased rapidly for a few hours and then decreased gradually. The color darkened compared with that of the wood used. When treatment was performed without UV light irradiation, ΔE ^* ab and ΔL ^* of the resins showed negligible change. Based on the results of FT-IR analysis, severe degradation such as cleavage of the main chemical bond was hardly observed under UV light irradiation irrespective of the type of resin. Part of this report was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, Japan, and at the 6th International Wood Science Symposium, Bali, Indonesia     

木质废料/无机胶黏剂刨花板的制备及其阻燃性能研究

以废旧建筑模板和家具为原料,使用环保型无机胶黏剂制备刨花板。利用扫描电子显微镜(SEM)观察刨花板的微观形貌,同时利用量热仪、氧指数测定仪、同步热分析仪等评价板材的阻燃性及热稳定性。结果表明:当板材密度为0.95g/cm^3时,除24h吸水厚度膨胀率外,其余物理力学性能均符合国标中的P3型刨花板要求;SEM观察到无机胶黏剂包覆刨花,填充板材孔隙,使板材物理力学强度大幅提高;选择氯化镁为固化剂,当表层/芯层刨花的固化剂用量为4.5%/5.0%时,压制的密度为0.95g/cm^3的刨花板,其氧指数为31%,具有较好阻燃性能。     

魔芋粉-壳聚糖-聚乙烯醇共混胶黏剂的性能及其胶合机理

为了提高魔芋粉的利用价值,开发环境友好型木材胶黏剂,以魔芋葡甘聚糖、壳聚糖为胶黏剂主料,添加聚乙烯醇制备三元共混胶黏剂。通过差示扫描量热法（DSC）,分析共混胶的热特性,确定了热压温度参数;采用正交试验法,探讨热压工艺参数对胶合板强度的影响,并进一步对比了二元共混胶和三元共混胶的强度;通过红外光谱（FTIR）和扫描电子显微镜（SEM）进行了微观结构分析。结果表明：在热压温度130℃,热压时间15 min,压力4 MPa,胶存放时间24 h的条件下,用该胶黏剂压制的胶合板,干湿状胶合强度最大;FTIR分析发现3种高分子之间存在着氢键等强烈的相互作用;SEM分析表明三元共混胶黏剂中存在网状结构,使胶合强度得到提高。研究结果为加速环保木材胶黏剂研发进程和完善加工工艺条件提供了科学依据。     

魔芋粉-壳聚糖-聚乙烯醇共混胶黏剂的流变模型

为了拓宽魔芋粉的应用领域,开发环境友好型木材胶黏剂,并更准确地把握该胶在胶合板生产中的工艺参数,该文在前期葡甘聚糖-壳聚糖-聚乙烯醇共混胶黏剂的胶合机理、微观结构表征和流变特性的研究基础上,通过TA流变仪的扫描测试进一步研究了该共混胶黏剂的流变模型。首先对胶黏剂分别进行动态温度扫描和等温时间扫描曲线分析,接着进行稳态和动态流变曲线分析建立了复数黏度与剪切黏度的对应关系,然后根据Dual-Arrhenius方程建立了复合胶黏剂的化学流变模型,最后对胶黏剂的黏度和工艺条件进行了预测。结果表明:通过动态温度扫描曲线分析,温度较低时,复数黏度缓慢下降;从玻璃化温度到凝胶化温度,复数黏度迅速下降;从凝胶化温度到160℃左右,复数黏度出现平台区;160℃以上复数黏度急剧增大;通过等温时间扫描曲线分析得到随着温度的升高,反应速率加快,温度越高固化增黏时间越短;通过对比稳态和动态流变曲线,验证了Cox-Merz定律对于该胶的有效性;100~160℃时胶黏剂体系的相对黏度特性符合Dual-Arrhenius黏度方程;该模型与测试结果吻合性较好,利用该模型可以预测胶合板热压工艺所需要的工艺参数,并能动态模拟整个热压工艺过程中的黏度变化;综合得出在160℃附近黏度急剧上升,黏度随时间延长增加,理想的加压时机是温度升至130℃后保温15~20 min。该研究成果为胶黏剂固化工艺条件的确定提供了理论依据。     

大豆基木材胶粘剂耐水性的研究

简要回顾了大豆基木材胶粘剂的发展状况,指出耐水性差和抗生物降解能力弱是限制豆胶继续发展的两大瓶颈问题。探索大豆基木材胶粘剂耐水性的形成机理,详细介绍了强化耐水性的几种可能方法。提出在不使蛋白过度水解的条件下,将大豆球蛋白中具有化学反应活性的官能团最充分地暴露出来,仿效大自然中耐水性蛋白结构形成的化学机理,提出了仿生强化改性法,为提高大豆胶耐水性和胶合强度提供了科学依据。     

用水性高分子异氰酸酯生产无醛胶合板生产工艺的研究

用低成本高分子异氰酸酯胶粘剂生产无醛胶合板，其生产工艺与常规脲醛树脂生产胶合板生产工艺相同，成本只有其它非甲醛系胶粘剂的50％，并彻底解决了游离甲醛释放问题。     

Durability of isocyanate resin adhesives for wood IV: degradation under constant steam heating

The durability of isocyanate resins consisting of emulsion-type polymeric diphenylmethane diisocyanate (EMDI) was investigated under constant steam heating. Two kinds of resin, water only-added resin and polyol/water-added resin, were used in this study. The degradation of the resins under steam heating was observed using Fourier transform infrared spectroscopy (FT-IR), weight changes, and thermogravimetric analysis (TGA). FT-IR analysis showed that the degradation reaction of the resins scarcely proceeded for a few hours and then increased significantly. The weights of the resins decreased linearly during steam heating. The thermal stability of steam-treated resins was made clear by TGA. The bond strength reductions of the specimens bonded with the resins were also observed. The best fitting regression function for the behavior of bond strength reduction was determined statistically. The apparent activation energy of each resin was calculated from the regression function, for the half-life period. Considering the calculated values, the adhesion durability of using polyol-added resin was superior to that of using water only-added resin. It was clarified that the durability of the isocyanate resins under steam heating was markedly inferior to that under dry heating.Part of this paper was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, 2000