麦草碱木素分级和结构特性的研究

用酸沉淀法对山东兖州市造纸厂麦草碱木素按分子量进行沉淀分级．共分为3个级分。探讨了影响分级效果的因素，确定了分级的优化条件。各级分经纯化后分析其结构特性。发现，随着体系PH值的降低，沉淀出的各级分的分子量逐渐降低。碱木素中碳水化合物含量降低，且主要分布于小分子级分中．分级后，碱木素分子量的分布有不同程度的变窄，但各级分的分子量均有相当程度的重叠．硝基苯氧化结果表明，在高分子量级分中，木素的缩会程度较为严重。该方法用于碱木素的简易分级是可行的．

Fractionation and characterization of wheat straw soda lignin

Wheat Straw soda lignin produced by Yanzhou Paper Mill was ftactionated byacid precipitation. Three fractions named as Fraction A, B and C were collected at pH6. 0, pH 5. 1 and pH < 5. 1 respectively. Optimum condition for fractionation istemperature 60℃, acid concentration 5%~10% and the rate of acid addition 0. 05~0. 1mL/s. The yield of fractiohation product was 78. 8%. The percentage of Fraction A,B and C was 31. 7%, 29. 2% and 39. 1 % respectively. The content of carbonhydrates andash were found to be lower than that of unfractionated lignin. GPC diagrams indicatedthat acid precipitation could separate soda lignin into several fractions. according tomolecular weight. Relatively small dispersing coefficients indicated that the fractions hadrelatively narrow molecular weight distributions when compared with unfractionatedlignin. The dispersing coeffcient d, defined as Mw/Mn, was measureed to be 3. 63, 3. 05and 2. 73 respectively. It was smaller than that of unfractionated lignin. The content offunctional groups and the elemental composition of the fractions were compared.Alkaline nitrobenzene oxidation indicated the uncondensed structural units are mainlycomposed of syringyl and guaiacyl propane units and the fractions with higher molecularweight were highly condensed.