Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2019
Publication Date: 3/6/2019
Citation: Stoklosa, R.J., Latona, R.J., Yadav, M.P., Bonnaillie, L. 2019. Evaluation of arabinoxylan isolated from sorghum bran, biomass, and bagasse for film formation. Carbohydrate Polymers. 213:382-392. https://doi.org/10.1016/j.carbpol.2019.03.018.
Interpretive Summary: Sorghum is an agricultural feedstock grown in sufficient quantities in the United States that it has the potential be utilized as a bioenergy crop. Not only can sorghum be utilized to make fuel ethanol, but also it can generate value added co-products. Some of these co-products can be utilized to produce renewable plastic materials that can replace petroleum derived plastics. A large component in bran cereal grain and plant cell walls are polysaccharides (mainly cellulose and hemicellulose). In sorghum the primary hemicellulose polysaccharide is arabinoxylan (AX). AX from other cereal grains have previously been identified as a promising material to make plastic films, however, very little research has occurred with sorghum-based AX. In this study three separate AX fractions were isolated from sorghum bran (the outer cereal grain layer), sorghum biomass (the plant stalk portion of high mass yielding sorghum), and sorghum bagasse (the plant material remaining after sweet sorghum juice has been extracted). All three fractions were utilized to prepare films with and without glycerol, a component that can make plastic films more flexible by acting as a ‘plasticizer’. The films from each fraction exhibited high sensitivities to moisture at high relative humidity (RH). Also, the films were porous to water. The best water vapor permeability (WVP) was obtained from sorghum biomass AX while sorghum bagasse AX had the highest WVP. However, sorghum bran AX showed adequate mechanical strength properties similar to AX isolated from other cereal grains. Sorghum biomass and sorghum bagasse AX were unable to be tested for mechanical properties as they produced very brittle films even with glycerol addition. Although future research should focus on water barrier improvements to sorghum AX, the mechanical strength properties indicate that AX from sorghum bran could be utilized as a biodegradable packaging material.
Technical Abstract: Hemicellulose arabinoxylans (AX) are potential high value co-products that can be recovered in a biorefinery for renewable material applications. The agricultural feedstock sorghum has seen increased production in the last decade as a potential bioenergy crop that can be utilized in similar ways to other cereal crops. AX from three sorghum fractions (bran, bagasse, and biomass) were isolated to determine film forming properties. All three AX fractions exhibited moisture sensitivity and high water permeability. AX from sorghum biomass produced the lowest water permeability while sorghum bagasse AX gave the highest. In terms of mechanical properties, sorghum bran AX exhibited a decrease in tensile strength and Young’s modulus with increasing plasticizer content. Dynamic mechanical analysis (DMA) showed a near linear decrease in storage modulus (E’) and loss modulus (E’’) for sorghum bran AX films at both increasing temperature and increasing plasticizer loading. Property transition regions could be identified with DMA testing. With increasing plasticizer content, the rubber-to-plastic temperature onset point occurred at lower temperatures as the content of plasticizer increased. Although sorghum bran AX films will need improvements towards water sensitivity, the films strength performance was similar to AX isolated from other cereal grains.