Valorization of hemicellulose waste streams for moisture barrier coatings and hydrophobic films

Abstract Replacing plastics with renewable and environmentally friendly substitutes is becoming ever more critical as we begin to realize the consequences of their negative impacts on the environment. Plant polysaccharides are the most abundant biopolymers on Earth, and hemicelluloses like xylan that are enriched in many agro-industrial waste streams have vast potential as eco-friendly building blocks for polymer science and engineering. However, xylan is one of the less studied natural polymers for applications that are relevant to the synthetic plastics and polymeric materials markets. Hemicellulose isolated from viscose and Lyocell fiber mills is largely seen as a waste product due to difficulties arising from the potential for structural heterogeneity and its lack of solubility after enrichment. In this work, we developed a strategy to valorize hemicellulose by functionalization with octyl isocyanate to achieve solubility and thermoplastic/hydrophobic properties. Xylan isolated from dissolving pulp waste streams was successfully functionalized with octyl isocyanate in DMSO at an estimated 79% hydroxyl conversion. Reaction parameters, including temperature, time, and stoichiometry were optimized for each reaction. The resultant carbamates of xylan oligo- and monosaccharides have good solubility in chloroform and impressive hydrophobic film forming properties yet retain the composability properties desired for renewable materials that are envisioned to enter the circular bioeconomy. Functionalization of xylan with an aliphatic chain through formation of an aliphatic carbamate is not expected to harbor the same toxicity or carcinogenic characteristics as the reactive isocyanate it is derived from, and thus should not inherently restrict these materials for use in diverse packaging applications. These modified physical properties show that xylan from agro-industrial waste streams has considerable potential to replace petroleum-based feedstocks in the existing packaging industry. In the future, we will continue to further develop strategies for valorization of these materials. Graphical Abstract