Spectroscopic Interrogation of the Acetylation Selectivity of Hardwood Biopolymers

Acetylation of wood is an age-old chemical platform known to improve its chemical and physical properties in direct correlation with the degree of acetylation. However, as of yet, no systematic study has been undertaken to probe the selectivity of acetylation of wood. A fundamental understanding of the molecular basis for acetylation of the constituent biopolymers, viz., holocellulose, and lignin for tropical hardwood, an emerging building material, is therefore undertaken. Wood samples are treated with acetic anhydride at 120 degrees C over a wide range of time periods. The degrees of acetylation and acetyl content of the tropical hardwood are measured to reveal that the acetyl content in which the hydroxyl groups of wood correspond to an increment in weight percent gain as confirmed by FT-IR for individual wood biopolymers and whole wood. However, surprisingly, P-31-NMR establishes the order of reactivity for the hydroxyl groups as lignin > hemicelluloses > whole wood in direct opposition to their proportions in wood, but in correlation to their direct accessibilities and reactivities.