纤维素是一种可再生天然亲水性高聚物, 其庞大的氢键网格形成多种不同的晶体结构形式。 在其五种结晶变体（纤维素Ⅰ, Ⅱ, Ⅲ, Ⅳ和Ⅹ）中, 纤维素Ⅱ由纤维素Ⅰ（天然纤维素）经再生或丝光化处理获得, 是表面自由能最低、 性能最稳定的纤维素, 这主要归因于纤维素Ⅱ具有与纤维素Ⅰ晶型平行链结构相反的反平行链结构, 且相比于纤维素Ⅰ有附加的分子间氢键。 基于近红外光谱（NIRS）对含氢基团的敏感性及纤维素的结晶结构中有大量氢键, 使通过NIRS定性检测、 定量评价纤维素的结晶结构成为可能。 目前, 用NIRS对纤维素结晶变体氢键结合的研究甚少, 针对竹材纤维素Ⅱ及其衍生材料氢键结合的研究国内外尚未见相关报道。 用竹材制备纤维素Ⅰ, 经丝光化处理得到竹基纤维素Ⅱ, 通过NIRS研究其氢键结合状况, 结果与竹粉及竹基纤维素Ⅰ相比较。 此外, 研究还通过NIRS对竹粉及竹基纤维素的结晶度做了定量评价。 结果表明: (1）在无定形区, 竹基纤维素Ⅰ、 Ⅱ和竹粉相比光谱差异不大, 氢键结合只有量的变化, 而无质的差异; (2）在半结晶区, 与竹粉相比, 竹基纤维素Ⅰ晶型结构保持不变, 而竹基纤维素Ⅱ形成双峰; (3）在纤维素结晶区的近红外谱带范围内, 反映竹基纤维素Ⅰ结晶表面纤维素分子内氢键O2—H2…O6的强氢键结合的羟基伸缩振动的一次倍频吸收峰由6 292 cm-1向高波数转移到6 354 cm-1, 该处与竹基纤维素Ⅱ形成的强氢键结合的分子间氢键O2—H2…O2反平行构造相对应; (4）NIRS预测的结晶度与XRD分析结果有良好相关性。 上述结果表明, 纤维素结晶区内的氢键结合在近红外特征谱带出现转移且在半结晶区形成双峰, 是区别竹基纤维素Ⅱ和Ⅰ的主要特征。 研究也表明NIRS对探讨纤维素多种变体的氢键结合及结晶度预测是可靠的。

Cellulose is a renewable natural hydrophilic polymer, and its huge hydrogen bond grid forms a variety of different crystal structures. There are five crystalline variants of cellulose (cellulose Ⅰ, Ⅱ, Ⅲ, Ⅳ and Ⅹ), of which cellulose Ⅱ is formed from cellulose Ⅰ (natural cellulose) after regeneration or mercerization, is the lowest surface free energy and the most stable performance among the five crystal varieties, mainly due to the antiparallel chain structure of cellulose Ⅱ, which is opposite to the parallel chain structure of cellulose I, and has additional intermolecular hydrogen bonds compared with cellulose I. Therefore, in view of the sensitivity of near-infrared spectroscopy (NIRS) to the hydrogen-containing group, and the crystalline structure of cellulose contains a large number of hydrogen bonds, this makes it possible for NIRS to analyze the degree of hydrogen bond destruction of cellulose by hydrogen containing functional groups, and to detect and quantitatively evaluate the crystalline structure of cellulose qualitatively. So far, there are very few studies on the hydrogen bonding of cellulose crystal variants, and the hydrogen bonding of bamboo cellulose Ⅱ and its derivatives has not been reported at home and abroad. In the study, cellulose Ⅰ was prepared from bamboo, and bamboo-based cellulose Ⅱ was obtained through mercerization, which NIRS investigated hydrogen bonds, the results were compared with bamboo powder and bamboo-based cellulose Ⅰ. Besides, the crystallinity of bamboo powder and bamboo-based cellulose was quantitatively evaluated by NIRS. The results can be drawn as follows: (1) the differences of NIRS among bamboo powder, bamboo-based cellulose Ⅰ and Ⅱ varied little, hydrogen bonding were quantitatively remarkable, but were qualitatively slight in the amorphous region; (2) compared with bamboo powder, the crystal structure of bamboo-based cellulose I remained unchanged, while bamboo-based cellulose Ⅱ occurred two absorbance peaks in the semi-crystalline region; (3) in the crystalline region a strong hydrogen bonding absorbance peak reflected the first overtone of hydroxyl group stretching vibration was observed at the wavenumber of 6 292 cm-1 assigned to the intermolecular bond of O2—H2…O6 of cellulose Ⅰ, which shifted to 6 354 cm-1 for bamboo-based cellulose Ⅱ. We deduced the absorbance peak in cellulose Ⅱ was assigned to the intermolecular bond of O2—H2…O2 due to anti-parallel structure of cellulose confirmation; (4) a good correlation among crystallinity was obtained by NIRS with the results of XRD analysis. The above research shows that the hydrogen bonding in the crystalline region of cellulose shifts in the near-infrared characteristic band and forms double peaks in the semi-crystalline region, which were the main characteristics of bamboo-based cellulose Ⅱ different from bamboo-based cellulose Ⅰ. Simultaneously, it is feasible to use NIRS to study the hydrogen bonding of various celluloses and predict their crystallinity.