镁、铁离子降低羧甲基纤维素保水剂吸水率的机理探讨

Mechanism of decreased water absorbency of crosslinking carboxymethyl cellulose by Mg and Fe cations

采用环氧氯丙烷交联羧甲基纤维素得到交联羧甲基纤维素(CCMC),测试其在含Mg 2+或Fe 3+的盐溶液中的吸水特点,分析其结构变化,对Mg、Fe影响羧甲基纤维素保水剂吸水率的机理进行了研究。CCMC在Mg 2+或Fe 3+的盐溶液中吸水饱和后再放入去离子水中,测试其恢复性能;采用红外光谱和热失重方法分析吸附阳离子的CCMC的结构和交联度变化。结果表明,随着阳离子价态的增大,CCMC的恢复性能减弱。Mg 2+通过单原子螯合方式与CCMC中的羧基结合,而Fe 3+则通过双原子螯合配位;引入Mg 2+后,CCMC热解起始温度降低,质量损失增大,而引入Fe 3+则提高CCMC热解起始温度,降低其质量损失。Mg 2+、Fe 3+降低羧甲基纤维素保水剂的主要机理是通过与羧基结合,降低离子对电离度,同时引入Mg 2+不会改变CCMC的交联度,而引入Fe 3+则大幅提高CCMC的交联度,进而降低吸水能力。

Crosslinking carboxymethyl cellulose(CCMC)was synthesized by carboxymethyl cellulose and epichlorohydrin(ECH).The prepared CCMC was subjected to water absorbency test in Mg 2+or Fe 3+bearing saline.After absorbing each cation,the structure variation was characterized so that the mechanism of decreased water absorbency of CCMC by Mg 2+and Fe 3+was analyzed.The dried CCMC sample was first fully swollen in Mg 2+or Fe 3+bearing saline and was then soaked in deionized water.The recoverability was hence measured.The influence of Mg 2+or Fe 3+on the structure variation and crosslinking degree of CCMC soaked in saline was characterized by FTIR and TG tests.The result showed that the recoverability decreased with the increase in cation valent.Mg 2+combined with carboxyl group of CCMC through monodentate geometry and Fe 3+was through bidentate chelating.The TG results showed that CCMC-Mg had lower initial decomposition temperature and larger mass loss than CCMC while CCMC-Fe had higher initial temperature and smaller mass loss.Mg 2+and Fe 3+decreased water absorbency of CCMC by combining its carboxyl groups and lowered down the dissociation of anion pair.The introduction of Mg 2+had little influence on the crosslinking of CCMC,however,Fe 3+largely increased the crosslinking of CCMC.