纳米纤维素纤维的表面改性及其对硝化纤维素膜力学性能的影响

采用2，2，6，6-四甲基哌啶氧自由基（TEMPO）氧化-机械法制备纳米纤维素纤维（CNF），通过碱化处理，剥离其带有羧基的表层，以硝酸/二氯甲烷混合物为硝化剂对CNF表面进行硝酸酯化改性，改性产物(NCNF)可稳定悬浮和均匀分散于丙酮中。采用红外光谱、元素分析和透射电子显微镜对NCNF的结构与性能进行分析与表征。将NCNF作为增强相添加到硝化纤维素中，采用溶液浇铸法制备纳米复合膜，并对纳米复合膜的拉伸性能进行测试。测试结果表明：添加质量百分比为3.5%的NCNF可使膜的拉伸强度、杨氏模量、断裂伸长率3个指标均得到显著提高。同时，将以上结果与长径比较低的纳米纤维素晶须（CNW）纳米复合膜的拉伸性能进行了对比分析，分析结果表明CNF比CNW对硝化纤维素膜拉伸性能的改善效果更好。

Surface Modification of Cellulose Nano-fiber and Its Effect on Mechanical Properties of Nitrocellulose Film

Cellulose nano-fibers(CNFs) are prepared by TEMPO-mediated oxidation combined with homogenizing mechanical treatment. The carboxyl groups on the surface of CNFs are removed by an alkalization process. Then CNFs are chemically modified by a mixture of nitric acid and dichloromethane to obtain nitrified CNF(NCNF). NCNFs could readily suspend and well disperse in acetone. The structure and properties of NCNFs are examined using Fourier transform infrared spectroscopy (FTIR)，elemental analysis (EA)，and transmission electron microscopy (TEM). The nano-nitrocellulose composite films with NCNF as reinforcment are prepared by a casting/evaporation technique. The tensile properties of the nanocomposite films are tested. The results show that the tensile strength，Young’s modulus，and elongation at break of the nanocomposite films increase simultaneously in comparison with that of neat NC. The influence of cellulose nanowhiskers(CNWs) and CNFs on the tensile properties of nanocomposite films is studied. As reinforcement, CNFs demonstrate higher efficiency compared to CNWs because of their larger aspect ratio.