TEMPO催化氧化体系制备表面羧基化竹材纳米纤维素1

摘要

以竹粉为原料，首先利用亚氯酸钠和氢氧化钾处理脱除竹粉中的木质素和半纤维素组分，然后借助2,2,6,6-四甲基哌啶-1-氧自由基（TEMPO）/次氯酸钠/溴化钠催化氧化体系选择性地将竹纤维素C6上的伯醇羟基氧化成醛基或羧基，并在酸性条件下利用亚氯酸钠处理进一步提高伯羟基的羧基化转化率。对产物进行解纤处理后，制得了表面羧基化的竹纳米纤维素（BNFC）。结果表明：产物竹纳米纤维素的主要组分为纤维素，其晶型结构为纤维素Ⅰ型。TEMPO 催化氧化体系处理对竹纤维素内部的结晶结构影响较小，其氧化过程主要发生在纳米纤维素的表面。亚氯酸钠氧化处理同样对竹纤维素内部的结晶结构影响较小，经过亚氯酸钠氧化处理后制得的纳米纤维素的尺寸更加精细，直径分布更加均匀。竹纳米纤维素的热降解温度开始于312℃，较竹粉（245℃）有较大提高。%Using Bamboo as the raw material, lignin and hemicellulose was first respectively removed from Bamboo powders by adding sodium chlorite and potassium hydroxide solution. Then, the C6 hydroxyl groups on surfaces of the cellulose were selectively oxidized to aldehyde groups or carboxyl groups by (2,2,6,6-tetramethylpiperidinyl-1-oxyl) TEMPO/NaClO/NaBr-mediated oxidation. Next, the aldehyde groups were further oxidized by sodium chlorite under acidic conditions. After several days of magnetic stirring, the cellulose pulps were fibrillated into Bamboo nanofibrillated cellulose (BNFC). Results are summarized as follows:TEMPO-mediated oxidation would not destroy the crystal structure inside of the cellulose. The oxidation process took place on surface of the BNFC. Within a certain range, the more NaClO added into the TEMPO-mediated oxidation system, the higher nanofibrillation degree of the final BNFC reached. After further oxidation by NaClO2, the BNFC became more slender. The thermal degradation temperature of the BNFC reached 312℃, much higher than that of Bamboo powders.