Analysis of the effects of restriction of longitudinal contraction on the conversion from cellulose I to cellulose II using CP/MAS 13C NMR: mercerization of ramie fibers under noncooling and cooling conditions

Ramie fiber samples were treated with aqueous NaOH at room temperature and −5 °C with and without contraction restriction along the length. The effects of contraction restriction at both temperatures on conversion from cellulose I to cellulose II were quantitatively estimated based on the intensity change in the deconvoluted resonances of C1, C4, and C6 spectra obtained using CP/MAS 13C NMR. Contraction restriction along the length makes the changes in the C1-up, C4-down and C6-down resonances that remain constant in the initial stage during NaOH treatment regardless of the temperature: their resonances are related to the remaining ratio of cellulose I, the cellulose crystallinity and degree of conversion from cellulose I to cellulose II, respectively. Furthermore, their change in spectral intensity without restriction corresponds to the change in longitudinal dimension. These experimental results demonstrate that the longitudinal contraction is indispensable to the conversion from cellulose I to cellulose II.