蔗渣纳米纤维素的制备与表征

摘要

以甘蔗渣为原料,通过无废酸的一步法、两步法和三步法制备了蔗渣纳米纤维素(BNC),并与酸解法进行对比.采用傅里叶红外光谱(FTIR)、扫描电子显微镜(SEM)、X射线衍射(XRD)和热重分析(TGA)等手段表征了纳米纤维素的光谱性质、形貌结构、结晶性能及热稳定性能.结果表明,4种方法处理后纤维形貌尺寸均可达到纳米级别且在一定浓度的水溶液中均可形成类果冻状的胶体,其中酸解法和三步法所制备的纳米纤维素长径比较小,形貌多为短棒状,在水溶液中分散稳定性较好,可稳定悬浮超过30 d;一步法和两步法所制备的纳米纤维素长径比较大,为类纤维状结构,分散稳定性相对较差,但也可稳定悬浮至少5 d;一步法所制备的纳米纤维素晶型为纤维素Ⅰ型和纤维素Ⅱ型的混合物,两步法、三步法和酸解法处理后的纤维晶型没有改变,仍然保持纤维素Ⅰ型.与酸解法相比,无废酸法所制备的纳米纤维素热稳定性更优,无废酸法工艺简单,反应条件温和,而酸解法反应步骤繁复,会产生大量废酸增加后续处理成本.%In comparison with sulfuric acid hydrolysis,three preparation methods without using acid(named as one-step,two-step and three-step methods,respectively) were employed to prepare bagasse nanocellulose(BNC).The spectrum properties,morphological structure,crystallinity and thermal stability of nanocellulose were fully characterized by Fourier transform infrared spectroscopy(FTIR),scanning electron microscope(SEM),X-ray diffraction(XRD) and thermal gravimetric analyzer(TGA).It was found that the size of the as-obtained BNC was at the nanometer level.When dispersed in water with the help of ultrasonication technique,all the BNC suspensions exhibited jelly-like colloid.Furthermore,the results showed that the two BNC samples obtained from three-step method and conventional sulfuric acid hydrolysis were very similar in morphology,both exhibiting rod-like structures with small length to diameter ratio.After ultrasonic processing,the two BNC samples can be evenly dispersed in the aqueous solution to form a stable suspension for more than 30 d.The BNCs,prepared by one-step method and two-step method,exhibited a fibrous structure with large length to diameter ratio and a good quality dispersion in water for 5 d can be achieved.The XRD result revealed that the crystal type of the BNC gained from one-step method contained a part of cellulose Ⅱ crystal and the other three BNCs were only crystal Ⅰ.In conclusion,sulfuric acid hydrolysis would produce a large amount of waste acid.Recycling and disposal of waste acid would increase subsequent processing cost.Compared with the complex sulfuric acid method,the eco-friendly no-acid method could not only enhance the thermal stability of nanocellulose at different levels,but also simplify the production process.