Aqueous Calcium Thiocyanate Solution as a Cellulose Solvent. Structure and Interactions with Cellulose
Aqueous Calcium Thiocyanate Solution as a Cellulose Solvent. Structure and Interactions with Cellulose
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DOI：
10.1295/polymj.30.43
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发表时间：
1998-01
期刊：
影响因子：
2.8
通讯作者：
M. Hattori;Takehiro Koga;Y. Shimaya;M. Saito
中科院分区：
文献类型：
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作者：
M. Hattori;Takehiro Koga;Y. Shimaya;M. Saito
研究了纤维素在硫氰酸钙水溶液中的溶解情况，重点是溶剂结构和与纤维素的相互作用。浓度（CCaT）大于48.5 wt%的硫氰酸钙（Ca(SCN)2）水溶液可以溶解任何纤维素。溶剂化测量表明，在CCaT≥48.5wt%中，溶剂体系由Ca(NCS)2·xH2O(x≤4)+yH2O(y≤6)配制，其主要表现出具有高比粘度的非解离硫氰酸盐，这通过溶剂的电导率、比粘度和IR或13C NMR测量作为函数来证明。 硫氰酸钙的浓度。就此而言，通过能量计算得出最稳定的四水硫氰酸钙为反式构型Ca(–N=C=S)·4H2O。 DSC和IR分析表明，纤维素的溶解是通过Ca(NCS)2·xH2O(x≤4)首先攻击纤维素中的环氧而发生的。 Ca(NCS)2·xH2O(x≤4)变成4-水合物结构(Ca的六配位络合物)，纤维素通过吡喃葡萄糖单元中的两个氧原子(O(5)和O(6))配位形成5元环，然后纤维素在加热下溶解。在此过程中，如果水合数大于2，可能会发生一些配体交换。与其他溶剂（例如与O（2）和O（3）羟基配位的氢氧化铜铵相比，纤维素的这种配位非常具有特征。
Dissolution of cellulose into aqueous (aq) calcium thiocyanate solution was investigated with emphasis on solvent structure and interactions with cellulose. The aq calcium thiocyanate (Ca(SCN)2) solution with concentration (CCaT) more than 48.5 wt% could dissolve any celluloses. Solvation measurement revealed that in CCaT≧48.5 wt%, the solvent system is formulated by Ca(NCS)2·xH2O (x≦4)+yH2O (y≦6), which exhibits mainly non-dissociated thiocyanate with high specific viscosity, as proved by electric conductivity, specific viscosity and IR or 13C NMR measurements on solvent as a function of concentration of calcium thiocyanate. In this regard, the most stable 4 hydrate calcium thiocyanate is concluded from energy calculation as trans-trans configuration of Ca(–N=C=S)·4H2O. DSC and IR analyses suggested that dissolution of cellulose takes place by first attack of Ca(NCS)2·xH2O (x≦4) towards ring oxygen in cellulose. Ca(NCS)2·xH2O (x≦4) becomes 4-hydrates-like structure (sixcoordinate complex of Ca) and cellulose forms a 5-membered ring by coordinating two oxygen atoms (O(5) and O(6)) in the glucopyranose unit, and then cellulose dissolves on heating. In this process, some ligand exchange might occur if the hydration number is more than 2. This coordination of cellulose is quite characteristic, compared with other solvents, such as cuprammonium hydroxide, which coordinate with O(2) and O(3) hydroxyl groups.