The Effect of pH on the Morphological, Thermal, and Mechanical Properties of Cross-Linked Starch Edible Films.

Abstract

This study evaluated the chemical and physical properties of edible films formed by cross-linked tapioca starch that was plasticized by glycerol. To optimize the formula of the film formation solution and enhance the mechanical and thermal properties of the material, the pH values of the solutions were adjusted to 3, 5, 7, 9, 11, respectively. The specific film properties that were evaluated included the degree of cross-linking, crystallinity, morphology, thermal stability and mechanical functionalities. These properties were analyzed using Attenuated Total Reflection Fourier Transformation Infrared Spectroscopy (ATR-FTIR), x-ray diffraction (XRD), thermal gravimetric analysis (TGA), and tensile profile analysis (TPA). The ATR-FTIR results showed that pH 7 and 9 were optimum for increasing the degree of cross-linking. The XRD results showed that crystallinity increased with increasing pH values up to pH 11. The TGA results showed that pH 9 provided the cross-linked starch film with optimized heat resistance. The TPA results showed that pH 9 provided the cross-linked starch film with the highest tensile strength and elastic modulus, but with the lowest percent elongation. This research showed how the pH of a tapioca starch film forming solution could be adjusted to modify the properties of dried films subsequently produced.