Development of an acetylation reaction of switchgrass hemicellulose in ionic liquid without catalyst

Abstract

Hemicellulose material is an abundant and relatively under-utilized hetero-polysaccharides material present in lignocellulosic materials. In this research, an alkaline treatment was applied to switchgrass in order to extract hemicelluloses to subsequently produce an acetylated product. An extraction at 75°C recovered 27% of the biomass as a predominantly hemicellulose material with a number average degree of polymerization of ∼500 determined by gel permeation chromatography. These hemicelluloses were acetylated with acetic anhydride in 1-allyl-3-methylimidazolium chloride ([Amim]+Cl−) ionic liquid in a complete homogeneous procedure without catalyst for the first time. It was determined that the yield and degree of substitution increased with reaction temperature from 30 to 80°C and reaction time from 1 to 20h. The product was characterized by FTIR spectroscopy, NMR, gel permeation chromatography for molecular weight and water contact angle analysis. FTIR spectroscopic analysis showed that the characteristic absorption intensities of acetylated hemicellulose increased and the hydroxyl group decreased with the increase in the degree of substitution. Increased degree of substitution increased the water contact angle and thermal stability in nitrogen. It was possible to cast films of the acetylated hemicellulose although the films were brittle. The results obtained indicate a promising combination between the effective extraction of hemicellulose from grasses and an environmentally friendly process using acetic anhydride in an ionic liquid without a catalyst to generate hemicellulose acetate with high degree of polymerization for use in various industrial applications.