棒状纳米微晶纤维素的热降解行为

文中对水解制备得到的纳米微晶纤维素采用了两种不同的处理方法以提高其热稳定性:于60℃下反复加热洗涤以减少其硫酸氢根含量或加入NaOH中和表面的硫酸氢根.研究表明:这两种方法都可以有效提高纳米微晶纤维素的热稳定性.与普通纤维素在热降解过程中只形成一个主要裂解区间不同,所有纳米微晶纤维素样品不仅存在主要裂解区间,而且在高温区域( >400℃)还存在一个明显的第二裂解区间.同时所有纳米微晶纤维素样品最终生成的焦炭产量很相近(3.5% ～5.0%).这说明当纤维素颗粒的粒径小至纳米尺寸时,外部催化剂的存在只是改变了其热降解的途径,但其整体热降解行为和最终的焦炭产量受其纳米颗粒特性所主导.文中还利用分峰拟合的方法表明在纳米微晶纤维素的主要裂解区间存在两个平行的竞争反应.

Thermal Degradation Behaviors of Cellulose Whiskers

In order to improve the thermal stability of the cellulose whiskers obtained by the hydrolysis with sulfuric acid, two methods were adopted to treat the cellulose whiskers. One is the repeated desulfation with heating at 60℃ to reduce the hydrosulfate content, and the other is the neutralization with NaOH solution to neutralize the hydrosulfate on the surface. The results indicate that both the two methods can effectively improve the thermal stability of cellulose whiskers. As compared with microcrystalline cellulose, cellulose whiskers have a second pyrolysis stage at high temperature ( more than 400℃ ) except the primary pyrolysis stage, and the final char yields are very similar in amount (3.5% ～ 5.0% ). All these above-mentioned findings show that, for cellulose whiskers, the presence of external catalyst can only change the thermal decomposition pathway, and that the thermal pyrolysis and the final char yield are determined by the characteristics of the nano-sized particles. Moreover, the profile analysis of thermo gravimetric derivative curves shows that there are two remarkably competitive reactions in the primary pyrolysis stage of cellulose whiskers.