固体核磁共振和原子力显微镜分析不同半纤维素含量植物纤维的微观结构

Analysis of Microstructure of Plant Fibers with Different Hemicellulose Content by Solid State Nuclear Magnetic Resonance and Atomic Force Microscope

采用交叉极化结合魔角旋转技术13C核磁共振法和原子力显微镜研究了半纤维素的脱除对纤维微观结构的影响。分别对NMR光谱C1区(δ102～108)和C4区(δ80～92)进行拟合。结果表明,随着半纤维素的脱除,次晶纤维素的相对含量从20%增加到33%,基原纤尺寸在4.0～4.3nm之间相对稳定,而基原纤聚集尺寸从17.9nm增加至22.2nm,且与半纤维素含量呈良好的线性关系。AMF图像观察到高半纤维素含量的纤维具有疏松的表面结构,而低半纤维素含量的纤维由于基原纤聚集尺寸的增加使得表面结构更加紧密。随着半纤维素含量的降低,向内收紧的拉力使得纤维细胞壁上的孔隙发生关闭,平均孔径减小。但是当半纤维素的脱除累积到一定量时,纤维孔隙结构反而能够得到改善。

Fibers with different hemicellulose contents were produced using various degree removal of hemicellulose to obtain large differences in cellulose and hemicellulose proportions at a similar lignin content. Solid state cross polarisation magic angle spinning carbon-13 nuclear magnetic resonance（ CP/MAS 13C-NMR） and atomic force microscope（ AFM） had been employed to investigate the microstructure of fibers. The results showed that there was an increase in relative content of para-crystalline cellulose with the decreas of hemicellulose content obtained by the spectral fitting for the cellulose C1-region（ δ 102-108） . The elementary fibril size was relatively constant between 4. 0 and 4. 3 nm for the three samples obtained by the spectral fitting for the cellulose C4-region（ δ 80-92） . The difference in elementary fibril size between the samples was not significant. However,the elementary fibril aggregate size increased from 17. 9 to 22. 2 nm with the decreas of hemicellulose content,which was a significant change. The results of AFM analysis showed that the fiber with a high hemicellulose content had a porous surface structure. In fibres with a low hemicellulose content,the elementary fibril aggregates formed a much more compact surface structure. Lower hemicellulose content can promote the partially irreversible microfibril aggregation,which caused tensions in the microfibrils due to the finite dimensions of the cell wall,amounting to stress in the microfibrils. However,the porous structure can be improved as hemicellulose content decreased to a certain extent.