Mapping of microfibril angles and chemical compositions in a tree.

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Wood cell walls are a composite material consisting of cellulose, hemicellulose, lignin and other minor components, such as pectin and extractives. Two main factors, cellulose microfibril angle (MFA) in S2 layer (thickest layer) and chemical composition, govern functional properties of the cell wall such as Young's modulus and growth-stress. In this study, change of MFA and chemical composition were investigated by small angle X-ray scattering (SAXS) and FT-IR. In summary, cellulose content decreases continuously from the trunk to the tip and upper. parts had generally more cellulose than, lower parts. Variation of MFA and small changes of chemical composition in cell wall were observed. In both softwood and hardwood, these changes seemed to be well regulated to manifest the mechanical function in order to keeping the branch in its ideal orientation. We examined the correlations between MFAs, chemical components and measured peak height at three wavenumbers. The peak at 1034cm-1 (cellulose) was used for both softwood and hardwood. Moreover, the peak at 1219cm-1 (lignin) was used for softwood. The peak at 1239 cm-1 (xylan), which appeared characteristically in hardwood, was used for hardwood. In softwood, the correlation of MFAs with lignin content was positive relationship. On the other hand, there was a negative correlation between MFAs and cellulose content. In. hardwood, although apparent correlation between MFAs and cellulose was not shown, the positive correlation between MFAs and xylan content could be seen. The SR-X-ray experiments were performed at BL40B2, Spring-8, Harima, Japan, Project number, 2002A0250 and 2002B0440.