羧基化纤维素纳米晶制备工艺优化及其性能表征

Optimization of Preparation Process and Characterization of Carboxylated Cellulose Nanocrystals

该研究以微晶纤维素(microcrystalline cellulose,MCC)为原料,采用超声辅助柠檬酸酸解法制备含有羧基的纤维素纳米晶(cellulose nanocrystals,CNCs),并利用单因素试验和响应面试验优化其制备工艺。对制备得到的CNCs进行性能表征。结果表明,响应面优化得到最佳酸解条件为液料比51∶1(mL/g),反应时间3.75 h,反应温度80℃,在此条件下CNCs的羧基含量预测值为1.19 mmol/g。最佳酸解条件经过3次验证试验,所得CNCs的羧基含量实测平均值为1.18 mmol/g,实测值与预测值接近。结果分析表明该条件下制备的CNCs在1735 cm^(-1)处出现C=O基团,表明柠檬酸成功接枝在MCC表面;CNCs属于纤维素I型,其结晶度(74.06%)远高于MCC(69.07%);CNCs呈短棒状,直径约为10 nm~30 nm,长度约为80 nm~200 nm,平均粒度和Zeta电位分别为358 nm和-39.8 mV;柠檬酸上的羧基与MCC的C6原子上的羟基发生了酯化反应。该研究结果可为羧基化CNCs的制备提供一种简便的途径。

In this study,cellulose nanocrystals(CNCs)containing carboxyl groups were prepared by ultrasonicassisted citric acid hydrolysis using microcrystalline cellulose(MCC)as raw material,and the preparation process was optimized by single factor test and response surface test.The performance of the prepared CNCs was characterized.The results showed that the optimal acid hydrolysis conditions obtained by response surface optimization were 51∶1(mL/g)of liquid-solid ratio,80℃of reaction temperature,and 3.75 h of reaction time,under these conditions,the predicted carboxyl content of CNCs was 1.19 mmol/g.After three times of verification experiments on the optimum acid hydrolysis conditions,the measured average carboxyl content of CNCs was 1.18 mmol/g,and the measured value was close to the predicted value.The results showed that the C=O group appeared at 1735 cm^(-1) of CNCs prepared under this condition,indicating that citric acid was successfully grafted onto the surface of MCC;CNCs belonged to cellulose type I,and its crystallinity(74.06%)was much higher than that of MCC(69.07%);the CNCs were short rod-shaped with a diameter of about 10 nm-30 nm and a length of about 80 nm-200 nm.The average particle size and Zeta potential were 358 nm and-39.8 mV,respectively.The carboxyl group on citric acid reacted with the hydroxyl group on the C6 atom of MCC.The results of this study can provide a simple way to prepare carboxylated CNCs.