Addition of corn stover arabinoxylan into hardwood during pulping for improved physical properties, TAPPI JOURNAL September 2017
ABSTRACT: Agricultural residues, such as corn stover, are being considered for biofuels and bioproducts. Theyrepresent inexpensive, pentosan-rich feedstock that are available in abundance. These materials are typically pre-treated to make them more amenable to biological processes such as fermentation. One such treatment involves extraction using alkali to remove the hemicellulose, leaving the cellulose more accessible for chemical or enzymatic hydrolysis. Extracted xylan hemicellulose may be considered for use in pulp and paper, or for providing a potential value stream from cellulosic ethanol biorefineries. To be useful, the extracted xylan should be concentrated and adsorbed into the pulp using existing equipment or a minimal number of new unit operations. In this work, we explored the concept of size-exclusion membrane-filtration to concentrate xylan that was extracted from corn stover in mild alkaline conditions. We examined hollow-fiber and tangential-flow filtration types and achieved a nearly two-fold increase in the xylan concentration using the former with a 50 kDa molecular weight cut-off (MWCO) membrane. Cassette-type tangential-flow filtration resulted in slightly greater xylan concentration with the use of a 10 kDa MWCO membrane. Hemicellulose extracts were then used as an additive during kraft pulping of hybrid poplar to show that the xylan could be adsorbed onto pulp fibers and retained even after washing. Pulp tensile strength improved after xylan addition following refining. An average of 33% of the xylan added in this method was retained, with xylan loading between 5 wt% and 20 wt%, compared with the control pulp sample that did not have added xylan. These results suggest potential for further exploration of biorefinery extracts use as additive feedstock for pulping. The study, being an evaluation of the proof-of-concept, aims to push research and optimization in this area that will lend well to scale-up and commercialization.
Application: This work benefits mills in demonstrating that adjunct hemicelluloses may be incorporated into their pulp products, and if obtained from a low-cost source, could provide an increase in sellable pulp mass. This work also underlines the importance of hemicellulose content on pulp properties.
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