Structural changes of cellulose crystallites induced by mercerisation in different solvent systems; determined by powder X-ray diffraction method
Structural changes of cellulose crystallites induced by mercerisation in different solvent systems; determined by powder X-ray diffraction method
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DOI：
10.1007/s10570-004-3132-1
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发表时间：
2005-06-01
期刊：
影响因子：
5.7
通讯作者：
Rissanen, K
中科院分区：
文献类型：
--
作者：
Mansikkamäki, P;Lahtinen, M;Rissanen, K
通过X射线粉末衍射法研究纤维素从纤维素I（C-I）到纤维素II（C-II）的结晶区域的变化，可以评价丝光的完全性。本文报道了在乙醇/水、丙酮、二甲基亚砜和二甲苯四种不同溶液体系中的丝光实验。研究了添加剂、外加压力、处理时间和碱化温度对处理效果的影响。在两相溶剂体系中，纤维素微晶的结构变化主要取决于氢氧化钠在溶剂相中的分布和溶解度。亲水相中的氢氧化钠浓度必须超过7-8 w/w-%，才能发生从C-I到C-II的完全晶体变化。由于高浓度氢氧化钠沉淀，阻碍了在淤浆法中成功使用单相乙醇/水体系。相反，2-丙醇/水/氢氧化钠体系分离成两层;富水下层和富2-丙醇上层，其中氢氧化钠主要保留在富水下层中。这可以防止氢氧化钠沉淀并促进纤维素的碱化。氯化铵和氢氧化铵通过促进晶体变化明显具有积极作用，然而，本研究中使用的尿素浓度明显过小。在有利的两相2-丙醇/水体系中，当处理温度保持在0和10 ℃之间时，碱化时间仅为15分钟。降低外部压力被发现有一个小的，但仍然可以检测到的积极影响纤维素碱化，而超压防止晶体变化。
The completeness of mercerisation can be evaluated by investigating the changes in the crystalline regions of cellulose from cellulose I (C-I) to cellulose II (C-II) by the X-ray powder diffraction method. Mercerisation experiments in four different solution systems: ethanol/water, acetone, DMSO and xylene, are reported. Also the effect of some additives, external pressure, treatment time and alkalisation temperature were studied. In two-phase solvent systems, structural changes of cellulose crystallites depended primarily on the distribution and solubility of sodium hydroxide in the solvent phases. The sodium hydroxide concentration in the hydrophilic phase must exceed 7-8 w/w-% before complete crystal change from C-I to C-II can occur. The precipitation of sodium hydroxide due to high concentration prevents the successful use of one-phase ethanol/water system in slurry process. On the contrary, the 2-propanol/water/sodium hydroxide system separates into two layers; to the water-rich lower layer and the 2-propanol-rich upper layer, where the sodium hydroxide remains mainly in the water-rich lower layer. This prevents the precipitation of sodium hydroxide and promotes the alkalisation of cellulose. Ammonium chloride and ammonium hydroxide clearly had a positive effect by promoting the crystal changes, however, the urea concentration used in this study was obviously too small. In the advantageous two-phase 2-propanol/water systems, the alkalisation time was only 15 min when the treatment temperature was kept between 0 and 10 degrees C. Reduced external pressure was found to have a small but still detectable positive effect on cellulose alkalisation while over-pressure prevented crystal changes.