Control of mechanical and hydrophobic properties of silylated chitosan-starch films by cross-linking using carboxylic acids

Abstract

We prepared polysaccharide films from silylated chitosan cross-linked with starch using six kinds of carboxylic acids (oxalic, maleic, citric, succinic, azelaic and sebacic acids) to explore the effects of molecular structures of cross-linkers on the mechanical, hydrophobic and water vapor permeability properties of these hydrophobicity-enhanced films. The films were analyzed by FT-IR, SEM, mechanical tests (stress versus strain, tensile strength and elongation at break curves) as well as the measurements of water contact angle, water solubility and water vapor permeability rate. We observed that the cross-linkers with a long chain provide a large mechanical strength; the tensile strength increases from 6 to 27 MPa with the chain length of dicarboxylates. The hydrophobicity, evaluated by the contact angle (ranging 80° ∼ 120°), increased with the chain length of the cross-linkers and was correlated well with the decreases of the solubility (94 ∼ 17%) and vapor permeability rate of water (14.5 ∼ 1.5 × 10−12 g s−1 m−1 Pa−1). We demonstrate that these mechanical, hydrophobic and water permeability properties are varied considerably only by the choice of the cross-linking acid also in the hydrophobicity-enhanced film by pre-silylation, which may widen the range of potential applications of polysaccharide film such as food packaging.