Significantly improve film formability of acetylated xylans by structure optimization and solvent screening

Abstract

Acetylated xylans have great potential in fabricating functional film and coating materials, which need a good solubility/dispersibility and film formability in an easily evaporable solvent. However, the changes of film formability with degree of substitution by acetyls (DS_Ac) in different solvent systems for xylans have not been extensively studied, which limit the application of acetylated xylans in film materials. In this study, acetylated xylans with DS_Ac of 0-2 were prepared and the effects of acetyl groups on solubility/dispersibility, crystallinity and film formability of xylans in water and chloroform solvent systems were investigated. Due to the change of polarity, xylans with DS_Ac of 0-0.62 are only soluble in water solvents, while xylans with DS_Ac of 1.13-2 are only soluble in chloroform/ethanol (70/30 v/v) organic solvents. We have found that the film formability of acetylated xylans is highly related to their solubility and crystallization. Film formable xylans all had good solubility in the cast solvents. However, although with good solubility, xylans with DS_Ac of 0-0.3 and DS_Ac of 1.76-2 cannot form intact films, which is due to the forming of xylan hydrate crystals and xylan diacetate crystals. With the increase of DS_Ac, the mechanical property of xylan film increases initially at low DS_Ac and decreases at high DS_Ac. This study provides theoretical basis for applying xylans and their derivatives in advanced functional film and coating materials with great biocompatibility and biodegradability.

Keywords: Acetylation; Film formability; Solubility; Xylan.