碱预处理对棉纤维选择性氧化的影响

Effect of alkali pretreatment on selective oxidation of cotton fibers

采用氢氧化钠对棉纤维进行预处理,再进行选择性氧化,可以有效提高氧化棉纤维的醛基生成量。对比研究经高碘酸盐选择性氧化后碱预处理棉纤维与普通棉纤维的结构与性能。结果表明:经碱预处理后棉纤维化学组成无变化,但当碱液质量分数增加到25%,其晶形结构从纤维素Ⅰ逐渐转化为纤维素Ⅱ,且结晶度不断下降,使棉纤维对高碘酸盐的可及度和反应性大大提高。通过红外光谱分析可知,经碱预处理的氧化棉纤维醛基吸收峰强度大于未预处理的氧化棉纤维。在8和32 g/L高碘酸钠氧化条件下,氧化棉纤维醛基含量随碱液质量分数增加均不断提高,而其结晶度不断下降,但当碱液浓度和氧化剂质量分数较高时,氧化过程中棉纤维的醛基增加量和降解程度都趋于平缓。

In order to improve the aldehyde production quantity of oxidized cotton fibers, the pretreatment of cotton fibers with sodium hydroxide was performed before selective oxidation in this paper. The structure and properties of selective oxidized cotton fibers before and after alkali pretreatment are compared. The results show that after alkali pretreatment, the chemical structure of the cotton fibers has little change. While the cellulose crystal has been transformed from cellulose Ⅰ to Ⅱ structure and the crystallinity has been decreased constantly with increasing alkali concentration to 25 %, which has greatly improved the accessibility and the reactivity of the cotton fibers. FT-IR study shows that the intensity of the aldehyde absorption peak for the oxidized cotton fibers after alkali pretreatment exhibits stronger than that before pretreatment. Under 8 g/L and 32 g/L NaIO4 conditions, increasing alkali concentration enhances the aldehyde group content of the oxidized cotton fibers and decreases gradually the crystallinity of the samples. However, at higher concentration of alkali and oxidant, the increment of the aldehyde content and the degradation degree of cotton fibers slows down during the oxidation process.