Morphological changes induced in wood samples by aqueous NaOH treatment and their effects on the conversion of cellulose I to cellulose II

The contraction along the longitudinal direction of Yezo spruce has been examined. The lignin and hemicelluloses (matrix) were removed from the samples with acetic acid and H2O2 for different treatment times, and by this way the matrix content of the samples was diminished step by step. Then the chemically pretreated samples were submitted to aqueous NaOH treatments with varied concentrations. Mechanically isolated tracheids with the same matrix content as wood samples were also NaOH treated. The aim was to detect the longitudinal contraction behaviors of these samples as a function of the degree of matrix removal and the severity of NaOH treatment. The contraction behaviors of the samples were clearly depended on the NaOH concentration as well as on content and composition of the matrix. The differences in contraction behavior are due to the restrictive forces caused by matrices between cellulose microfibrils (CMFs) or between tracheids that prevent the contraction of CMFs also in the longitudinal direction. This is the reason why it is difficult to convert cellulose I to cellulose II in wood cells.