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

ABSTRACT

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 ~(13)C-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.