Relative susceptibility of the Iα and Iβ phases of cellulose towards acetylation

Abstract

The relative reactivity of the I _α and I _β phases of Valonia cellulose toward partial homogeneous acetylation was investigated by FT-IR and CP/MAS ¹³C-NMR spectroscopy. At the beginning of the acetylation and when only partial reaction was achieved, it was found that the reactivity of the I _α phase was substantially higher than that of the corresponding I _β component. At a later stage of acetylation, the difference in reactivity between the two phases was less pronounced. In correlation with previous ultrastructural observations (Sassi and Chanzy, 1995), it can be concluded that at equivalent accessibility, the I _α phase of cellulose is indeed more reactive toward acetylation than the I _β phase. The homogeneous acetylation of cellulose is essentially a surface reaction that affects only the accessible parts located at the surface of the microfibrils. The decrease in the rate of I _α phase disappearance with acetylation time confirms therefore that the microstructure of Valonia is made of domains that are distributed throughout the thickness of its microfibrils.