Alkaline extraction and carboxymethylation of xylans from corn fiber

Abstract

In the corn crop industry, of all the biomass produced, about 80% are residues. The so-called corn fibers, one of the most important residues of the corn processing industry, represent about 9% of the corn kernel weight, being a low value material that could, potentially, be used for making higher added value products. This work aimed to extract the hemicelluloses present in the corn fiber via alkaline extraction, with their subsequent functionalization for production of carboxymethyl xylans in mild conditions. The corn fibers were characterized for their contents of carbohydrates, lignin, extractives, total uronic acids, acetyl groups, and ash. Their arabinoxylans were extracted by 2–18% (w/v) sodium hydroxide at room temperature, for 5 h at 10% consistency, precipitated with ethanol, washed and then vacuum dried. The resulting extract was characterized by FT-IR, viscosity, arabinoxylan content and purity. It was demonstrated that CCE treatment provides a high purity and little degraded xylan, but the extraction yields are relatively low, in the range of 4.0–23.9% wt/wt depending upon extraction conditions. The use of corn fiber arabinoxylans to obtain hemicellulosic derivatives through chemical modification reactions was also evaluated. The arabinoxylans were derivatized by carboxymethylation with sodium monochloroacetate in a 2-propanol alkaline medium using different proportions of alcohol and alkali. The product carboxymethyl xylan was characterized by degree of substitution, FT-IR, DSC, and yield, and showed high degree of substitution, yield and enthalpy of fusion. This work proved the feasibility of producing hemicellulosic derivatives from corn fibers, which excludes the use of extreme conditions of solvents and temperature.