Yang Rui, Dong Xianyin, Chen Gang, Lin Feng, Huang Zhenhua, Manzo Maurizio, Mao Haiyan
Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037, China.
Dehua Tubaobao New Decoration Material Co., Ltd., Huzhou 313200, China.
Polymers (Basel). 2020 Dec 22;13(1):6. doi: 10.3390/polym13010006.
Crystallinity is an essential indicator for evaluating the quality of fiber materials. Terahertz spectroscopy technology has excellent penetrability, no harmful substances, and commendable detection capability of absorption characteristics. The terahertz spectroscopy technology has great application potential in the field of fiber material research, especially for the characterization of the crystallinity of cellulose. In this work, the absorption peak of wood cellulose, microcrystalline cellulose, wood nano cellulose, and cotton nano cellulose were probed in the terahertz band to calculate the crystallinity, and the result compared with XRD and FT-IR analysis. The vibration model of cellulose molecular motion was obtained by density functional theory. The results showed that the average length of wood cellulose (WC) single fiber was 300 μm. The microcrystalline cellulose (MCC) was bar-like, and the average length was 20 μm. The cotton cellulose nanofiber (C-CNF) was a single fibrous substance with a length of 50 μm, while the wood cellulose nanofiber (W-CNF) was with a length of 250 μm. The crystallinity of cellulose samples in THz was calculated as follows: 73% for WC, 78% for MCC, 85% for W-CNF, and 90% for C-CNF. The crystallinity values were obtained by the three methods which were different to some extent. The absorption peak of the terahertz spectra was most obvious when the samples thickness was 1 mm and mixed mass ratio of the polyethylene and cellulose was 1:1. The degree of crystallinity was proportional to the terahertz absorption coefficients of cellulose, the five-movement models of cellulose molecules corresponded to the five absorption peak positions of cellulose.
结晶度是评估纤维材料质量的重要指标。太赫兹光谱技术具有出色的穿透性、无有害物质以及对吸收特性值得称赞的检测能力。太赫兹光谱技术在纤维材料研究领域具有巨大的应用潜力，尤其适用于纤维素结晶度的表征。在这项工作中，对木材纤维素、微晶纤维素、木材纳米纤维素和棉纳米纤维素在太赫兹波段的吸收峰进行了探测以计算结晶度，并将结果与XRD和FT-IR分析进行比较。通过密度泛函理论获得了纤维素分子运动的振动模型。结果表明，木材纤维素（WC）单纤维的平均长度为300μm。微晶纤维素（MCC）呈棒状，平均长度为20μm。棉纤维素纳米纤维（C-CNF）是一种长度为50μm的单一纤维状物质，而木材纤维素纳米纤维（W-CNF）的长度为250μm。纤维素样品在太赫兹波段的结晶度计算如下：WC为73%，MCC为78%，W-CNF为85%，C-CNF为90%。通过三种方法获得的结晶度值在一定程度上有所不同。当样品厚度为1mm且聚乙烯与纤维素的混合质量比为1:1时，太赫兹光谱的吸收峰最为明显。结晶度与纤维素的太赫兹吸收系数成正比，纤维素分子的五种运动模型对应于纤维素的五个吸收峰位置。
