The influence of calcium chloride concentration on the mechanical and barrier properties of high amylose corn starch film

Abstract

In this study, high amylose corn starch (HACS) films were prepared using CaCl2 as cosolvent. The interaction between CaCl2 and HACS during the preparation was investigated. Differences in physicochemical properties between HACS films with and without CaCl2 were characterized using wide-angle X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), water vapor permeability (WVP), thermogravimetric analysis (TG) and atomic force microscopy (AFM). The tensile strength and elongation at break increased to 27.01 ± 1.13 MPa and 17.4 ± 1.9%, respectively, CaCl2 had plasticizing effect and provided mechanical reinforcement to the formed HACS films. The reinforcement was mainly due to (ⅰ) CaCl2 increased the content of free amylose chains in the aqueous phase, and (ⅱ) chelation between Ca2+ and starch chains enhanced the entanglement between HACS chains. The results of XRD and FTIR indicated the crystalline region and shot-range orderliness of films decreased, CaCl2 significantly increased the dispersion of starch chains and made the HACS films more homogeneous. CaCl2 improved the barrier properties and surface morphology. The surface roughness of the HACS films decreased fromRa = 189 nm, Rq = 242 nm toRa = 103 nm, Rq = 152 nm as the concentration of CaCl2 increased. However, high concentration of CaCl2 destroyed the inner and surface structure of the film to some extent.