C-13-NMR analysis of acetyl groups in acetylated wood .1. Acetyl groups in cellulose and hemicellulose

The acetyl groups in cellulose and hemicellulose within acetylated wood was analyzed by C-13-NMR (carbon 13 nuclear magnetic resonance) spectroscopy. Before the analysis, the acetylated wood was delignified lightly with a sodium chlorite procedure (Wise method) to dissolve in a MMNO/DMSO-d(6) mixture. The degree of delignification ranged from 40 to 70%, depending on the WPG (weight percent gain). It was indicated that the delignification caused no changes in the acetyl distributions in the xylan and cellulose. The X-ray diffraction analysis of the acetylated wood indicated that the crystalline region of the cellulose started to be reacted above the WPG of about 20%. The xylan in the wood was reactive during the acetylation, producing the mono- and the disubstitutions of hydroxyl groups at small WPGs. The increase in WPG increased the di-substitution in the xylan. All the hydroxyl groups in xylan were not substituted for at the WPG of about 20%. The cellulose in the wood was less reactive than the xylan, although the mono-, the di-, and the tri-substitutions were produced at small WPGs. The increasing WPG increased the di- and the tri-substitutions in the cellulose. The free hydroxyl groups in the non-crystalline region of the cellulose remained at the WPG of about 20%, at which point the crystalline region of the cellulose started to be reacted. The greater increase in WPG increased the di- and the tri-substitutions in cellulose.