Effects of chemical modification on the structure and mechanical properties of starch-based biofilms

In this work, chemically modified corn starch and plasticized corn starch biofilms were obtained and characterized in four steps: (1) preparation of corn starch microparticles, (2) preparation of malic acid-modified corn starch microparticles (MA-SM), (3) preparation of corn starch biofilms and MA-SM-plasticized corn starch biofilms, and (4) characterization of the biofilms. The effects of MA-SM concentration (4, 8, and 12% based on the amount of corn starch) on the structural characteristics and mechanical properties of the biofilms were investigated. Changes in the starch granules after chemical modification were studied by X-ray diffraction, FT-IR spectroscopy, and scanning electron microscopy. The presence of ester carbonyl group stretching vibration at 1,720 cm(-1) in FT-IR spectra was evidence of reaction of the starch microparticles with malic acid. The tensile yield strength and Young's modulus of the films increased with increasing MA-SM content. Water uptake decreased from 69.8% for biofilm without MA-SM to 52.7% for biofilm with MA-SM. The improvement of these properties in the plasticized product could be attributed to the good interaction between the MA-SM filler and the corn starch.