Objective This study aims to investigate the chemical composition, cell wall ultrastructureand supramolecular structure of cellulose in balsa wood fibers, as well as reveal their influence on mechanical properties of balsa wood and demonstrate the relationship between ultrastructure and mechanical properties, to provide a theoretical basis for the high value applications of balsa wood.
Method Balsa wood and poplar wood were comparatively studied. Their chemical composition was analyzed by acid hydrolysis, and the cell wall structure was observed by transmission electron microscopy. Meanwhile, confocal Raman microscope was used to characterize the cell wall topochemistry and the supramolecular structure of cellulose.
Result The acetyl contents in balsa wood and poplar wood were 9.52% and 5.61%, respectively. The thickness of S3 layer of balsa wood fiber cell wall accounted for 5.49% of the total thickness of cell wall, which was higher than that of poplar wood (3.86%). The maximum microfibril angle in S2 layer of balsa wood fiber was 30°, smaller than that of poplar wood (40°). The orientation of cellulose microfibers in the cell lamella and S2 layer of balsa wood was more regular than that in the corresponding layers of poplar wood.
Conclusion The degree of xylan acetylation, cell wall ultrastructure and cellulose supramolecular structure of balsa wood were significantly different from that of poplar wood: the balsa wood exhibited the higher degree of xylan acetylation, the higher proportion of S3 layer in cell wall, the smaller microfibrils angle in S2 layer, and more orderly orientation of cellulose microfibrils in both cell lamella and S2 layer. This study not only explains the main reasons for the excellent mechanical properties of balsa wood with low density, but also provides significant theoretical reference for the cell wall topochemistry, the relationship between ultrastructure and mechanical properties and high value utilization of balsa wood.
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