Dissolution studies of α-chitin fibers in freezing NaOH(aq)

Abstract

Our gradual understanding of the capabilities of organic solvent systems has allowed us to realize a rich diversity of valuable polysaccharide applications; however, their industrial scale implementation remains a challenge for the sustainable societies of the next generations. While exploring a systems thinking approach, researchers studying aqueous alkali solutions have shown that the overlooked region of subzero temperatures offers a dynamic driving force for efficient solubilization of natural carbohydrate polymers. Herein, α-chitin fibers of decreasing crystallinities/molecular weights (MW) dissolve rapidly by stirring in cold 19 wt% NaOH(aq) and freezing at − 28 °C. Kinematic viscosity measurements confirm the polymers’ stretched exponential solution dynamics for solubilities > 97% (up to ~ 130 g/L). A preliminary mechanistic hypothesis involves higher diffusion rates of the solvent’s hydrated counter ions for decreasing temperatures. The method was used with subsequent casting to fabricate 5 wt% films from high crystallinity/MW fibers. This proof of concept allows for homogeneous chitin deacetylation as well as for additive-free technology drivers towards sustainable commercial exploitation of abundant natural polysaccharide streams.