Hemicellulose polysaccharide recovery from flax shive using alkaline solutions with sodium ethoxide pretreatment

Abstract

Flax shive is a by-product of decortication of flax straw for fibre recovery, and consists of ligno-cellulosic xylem tissue. It is available in large quantities at low cost, and shows promise as a biorefining feedstock for recovery of multiple products. The objectives of this work were to investigate hemicellulose polysaccharide extractions from flax shive using alkaline reagents at mild conditions, and to determine impacts of pretreatment using sodium ethoxide in anhydrous ethanol. Sodium ethoxide is similar to the catalyst for industrial biodiesel, and had been shown previously to recover phenolic constituents from flax shive. In this work, carbohydrates extracted from flax shive were evaluated quantitatively, in terms of recovered precipitate mass, and qualitatively, in terms of backbone monomer composition. Extracts obtained using 1.0M sodium hydroxide, alone or following pretreatment, showed no difference in mass yield, with mean recovery of 99.4±5.1mg/g on a dry basis. In terms of composition, extracts obtained using 1.0M sodium hydroxide, alone or following pretreatment, showed no detectable mannose and no difference in molar concentration ratio of xylose-to-glucose, with mean ratio of 25.5±3.4. Results inferred that no glucomannan polymer was extracted, and that glucuronoxylan polymer was present at high concentration, greater than 90% of the product stream. Tests using saturated barium hydroxide showed poor mass yield, with possible inhibitory effects in mixed solutions. The use of saturated barium hydroxide or elevated sodium hydroxide resulted in lower glucuronoxylan concentration. Flax shive showed good potential for carbohydrate extraction, and the technical feasibility of recovering multiple products was demonstrated.