Wang Haiying, Li Suiyi, Wu Tiantian, Wang Xiaoxuan, Cheng Xudong, Li Dagang
College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037, China.
Polymers (Basel). 2019 Jan 17;11(1):153. doi: 10.3390/polym11010153.
Polymorphic changes in cellulose nanofibers (CNFs) are closely related to their properties and applications, and it is of interest to investigate how polymorphic changes influence their properties. A comparative study on the properties of CNFs with cellulose I, I/II, and II polymorphs from wood was conducted herein. CNFs were obtained by chemical extraction combined with a simple and efficient mechanical treatment (one pass through a grinder). This process resulted in a relatively high yield of 80⁻85% after a simple grinding treatment. The polymorphic changes in the CNFs and the chemical composition, morphology, tensile performances, and thermal properties were systematically characterized and compared. The X-ray diffraction and FTIR analyses verified the existence of three types of purified pulps and CNFs with cellulose I, cellulose I/II, and cellulose II polymorphs (CNF-I, CNF-I/II, CNF-II). Morphological observations presented that these three types of CNFs all exhibited high aspect ratios and entangled structures. Tensile testing showed that the CNF films all exhibited high tensile strengths, and the fracture strains of the CNF-I/II (11.8%) and CNF-II (13.0%) films were noticeably increased compared to those of the CNF-I film (6.0%). If CNF-II is used as reinforcing material, its larger fracture strain can improve the mechanical performance of the CNF composites, such as fracture toughness and impact strength. In addition, CNF-I, CNF-I/II, and CNF-II films showed very low thermal expansion in the range 20⁻150 °C, with the coefficient of thermal expansion values of 9.4, 17.1, and 17.3 ppm/K, respectively. Thermogravimetric analysis (TGA) revealed that the degradation temperature of CNF-I and CNF-II was greater than that of CNF-I/II, which was likely due to increased α-cellulose content. This comparative study of the characterization of CNF-I, CNF-I/II, and CNF-II provides a theoretical basis for the application of CNFs with different polymorphs and could broaden the applications of CNFs.
纤维素纳米纤维（CNFs）的多晶型变化与其性能和应用密切相关，研究多晶型变化如何影响其性能具有重要意义。本文对来自木材的纤维素I、I/II和II多晶型的CNFs的性能进行了比较研究。通过化学提取结合简单高效的机械处理（通过研磨机一次）获得了CNFs。经过简单的研磨处理后，该工艺的产率相对较高，为80⁻85%。对CNFs的多晶型变化以及化学成分、形态、拉伸性能和热性能进行了系统的表征和比较。X射线衍射和傅里叶变换红外光谱分析证实了存在三种类型的纯化纸浆和具有纤维素I、纤维素I/II和纤维素II多晶型的CNFs（CNF-I、CNF-I/II、CNF-II）。形态学观察表明，这三种类型的CNFs均表现出高长径比和缠结结构。拉伸测试表明，CNF薄膜均表现出较高的拉伸强度，与CNF-I薄膜（6.0%）相比，CNF-I/II（11.8%）和CNF-II（13.0%）薄膜的断裂应变显著增加。如果将CNF-II用作增强材料，其较大的断裂应变可以提高CNF复合材料的机械性能，如断裂韧性和冲击强度。此外，CNF-I、CNF-I/II和CNF-II薄膜在20⁻150°C范围内表现出非常低的热膨胀，热膨胀系数值分别为9.4、17.1和17.3 ppm/K。热重分析（TGA）表明，CNF-I和CNF-II的降解温度高于CNF-I/II，这可能是由于α-纤维素含量增加所致。对CNF-I、CNF-I/II和CNF-II的表征进行的比较研究为不同多晶型CNFs的应用提供了理论基础，并可拓宽CNFs的应用范围。
