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在20℃下分别用质量分数为1.5%、3.0%、5.0%、7.5%和8.5%的NaOH溶液抽提脱蜡及部分脱木素后的速生杨木16 h,分别可得到65.6%、71.6%、73.8%、85.6%和89.3%的原半纤维素。木聚糖是速生杨细胞壁中最主要的半纤维素。用FT-IR,13CNMR,GPC来进一步确定分离得到的5种半纤维素样品的特性,结果表明:半纤维素包含了1条由D-吡喃木糖基通过β-1,4键连接起来的主链。分别用丙酰氯、己酰氯、十二酰氯和十六酰氯将在20℃、8.5%NaOH溶液抽提16 h得到的半纤维素酯化,反应在均相的N,N-二甲基酰胺(DMF)/LiCl体系中进行,用4-二甲氨基吡啶作催化剂,用三乙胺作中和剂。初步考查了酰氯/无水木糖单元的摩尔比、三乙胺浓度、反应时间和温度对半纤维素衍生物得率和取代度的影响。在给定反应条件下,取代度在0.44和1.44之间。在最佳反应条件下,摩尔比为3∶1、反应温度为75℃和反应时间为40 min时,半纤维素中70%的羟基被十六酰化。从相对分子质量测定的结果可以看出(相对分子质量为48 000～127 200 g/mol):在60～75℃、25～40 min的快速反应中,大相对分子质量的半纤维素只发生了很小程度的降解。
The dewaxed and partly delignified poplar wood was extracted by NaOH solution of 1.5%, 3.0%, 5.0%, 7.5% and 8.5% respectively at 20 ℃ for 16 h, yielding 65.6%, 71.6 %, 73.8%, 85.6% and 89.3% of the original hemicellulose. Xylan is the most important hemicellulose in poplar poplar cell wall. The properties of the isolated 5 hemicellulose samples were further confirmed by FT-IR, 13CNMR and GPC. The results showed that the hemicellulose contained 1 piece of D-xylopyranosyl linked via β-1,4 linkages The main chain. The hemicellulose obtained by extraction with 8.5% NaOH solution for 16 h at 20 ° C was esterified with propionyl chloride, caproyl chloride, lauroyl chloride and palmitoyl chloride respectively and reacted in a homogeneous N, N-dimethylformamide DMF) / LiCl system using 4-dimethylaminopyridine as a catalyst and triethylamine as a neutralizing agent. The effects of molar ratio of acyl chloride to anhydrous xylose units, triethylamine concentration, reaction time and temperature on the yield and degree of substitution of hemicellulose derivatives were investigated. The degree of substitution is between 0.44 and 1.44 for a given reaction condition. Under the best reaction conditions, the molar ratio of 3: 1, the reaction temperature of 75 ℃ and the reaction time of 40 min, hemicellulose, 70% of the hydroxyl hexadecanoyl. As can be seen from the results of the determination of the relative molecular mass (relative molecular mass of 48 000 ~ 127 200 g / mol): in the rapid reaction of 60 ~ 75 ℃, 25 ~ 40 min, only a relatively high molecular weight hemicellulose occurred A very small degree of degradation.