不同针叶木化学浆在碱尿素水溶液体系中溶解行为的研究

以用于生产黏胶纤维的漂白针叶木硫酸盐浆(BSK)和硫酸盐法针叶木溶解浆为原料,通过测定纸浆纤维-纤维素-溶剂(7%NaOH/12%尿素水溶液)溶解体系的透光率及溶解生成的纤维素溶液的黏度、观察纸浆纤维冷冻过程的微观形态、分析溶解前后纸浆纤维长度和宽度的变化、检测未溶部分的X射线衍射谱图,研究对比了这两种浆在7%NaOH/12%尿素水溶液体系中溶解行为的差异。结果表明,相同浆浓下,聚合度高的漂白针叶木硫酸盐浆在7%NaOH/12%尿素水溶液中溶解后体系的透明度比聚合度低的针叶木溶解浆体系的高,前者溶解生成的纤维素溶液的黏度大于后者溶解生成的纤维素溶液的黏度,即纤维素含量高、聚合度低的溶解浆反而较难溶解在7%NaOH/12%尿素水溶液中。针叶木硫酸盐浆溶解后纤维变短且变粗,而针叶木溶解浆因大部分短小纤维被溶解导致溶解后纤维的平均长度变长,且宽度变化较小。针叶木硫酸盐浆保留了完整的纹孔结构,溶剂渗透性较好,其溶解效果优于在制浆过程中细胞壁经受严重破坏的针叶木溶解浆的溶解效果。

Study on Dissolution Behavior of Cellulose Fibers from Different Softwood Chemical Pulps inNaOH/Urea Aqueous Solution

Bleached softwood kraft pulp and softwood dissolving pulp were selected to study in this work, and the difference in dissolution behavior of these two pulps in 7% NaOH/12% urea aqueous solution was investigated by determining transmittance of pulp fiber-cellulose-solvent dissolving system, viscosity of dissolved cellulose solution, observing on the dissolution behavior of pulp fiber by freezing microscope, comparing the changes of fiber length and width before and after dissolution and testing the X-ray diffraction of undisssolved fraction. The results showed that, under the same pulp concentration, the transparency of mixture from dissolution of bleached softwood kraft pulp with higher polymerization degree in 7% NaOH/12% urea aqueous solution was higher than that of the bleached softwood dissolving pulp with lower polymerization degree in 7% NaOH/12% urea aqueous solution. Moreover, the viscosity of the cellulose solution of the former was higher than that of the latter, namely, dissolving pulp with lower polymerization degree and higher cellulose content was more difficult to dissolve in 7% NaOH/12% urea aqueous solution. The fibers of softwood kraft pulp became shorter and thicker after being dissolved, while the fibers of softwood dissolving pulp became longer in length and almost no change in width after being dissolved because of dissolution of most short fibers. The dissolving efficiency of softwood kraft pulp with intact fiber pit structure was better than that of softwood dissolving pulp with cell wall damaged in pulping process because of its better solvent permeability. Contrast to the dissolution of pure cellulose in NaOH/urea aqueous solution, the crystallinity and quality of pulp fiber, the morphology of fiber cells, hemicellulose components and molecular weight distribution of cellulose in pulp fiber all could affect its dissolution behavior in NaOH/ urea aqueous solution.