Effects of ultrasonic and ozone modification on the morphology, mechanical, thermal and barrier properties of corn starch films

Biodegradable starch material is considered one of the best alternatives to traditional petroleum-based synthetic plastics. The effects of ultrasound (40 kHz) and ozone (20 g/h) modifications on corn starch were investigated using ultraviolet absorption, titration, Fourier transform, differential scanning calorimetry, and X-ray diffraction. As well as the effects of the dual modification on biodegradable films' morphology, thickness, water content, water solubility, moisture absorption, water vapor permeation, opacity, water contact angle, and mechanical and thermal properties were evaluated. For dual modification, the ultrasonic modification was carried out first, followed by oxidation under the same conditions as an individual modification. After ultrasonic and ozone modification, the crystallinity of starch decreased, and the solubility increased to some extent. Starch's swelling power and solubility increased by 4.90% and 159%, respectively, after 10 min of ozone treatment. The tensile strength of the films modified by ozone for 10 min increased by 276%, the elongation at break increased by 72.5%, the water contact angle of the films modified by ozone increased by 154%, and the water vapor permeability decreased by 34.7%. Compared with the natural and single-modified starch films, the dual-modified ones had lower water vapor transmittance, moisture absorption rate, and higher transparency. The water vapor permeability decreased by 32.2%, and the transparency increased by 73.7%. The modification in this study had little effect on the solubility of the films.