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

The relative reactivity of the I-alpha and I-beta phases of Valonia cellulose toward partial homogeneous acetylation was investigated by FT-IR and CP/MAS C-13-NMR spectroscopy. At the beginning of the acetylation and when only partial reaction was achieved, it was found that the reactivity of the I-alpha phase was substantially higher than that of the corresponding I-beta 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-alpha phase of cellulose is indeed more reactive toward acetylation than the I-beta 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-alpha 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.