Biodegradable, UV absorber and thermal stable bioplastic films from waxy corn starch/polyvinyl alcohol blends

Abstract

AbstractChemically modified waxy corn starch is a promising material for biodegradable bioplastic synthesis. This work is to study the film performance and microbial enzymatic biodegradation of the film made from chemically modified waxy corn starch according to the effect of pre-gelatinization and cardanol oil with various ratios as a mixed plasticizer with sorbitol. The preparation of biodegradable bioplastic films from waxy maize acetylated di-starch adipate (WADA) and waxy maize pregelatinized acetylated di-starch adipate (PWADA) blended with polyvinyl alcohol polymer using sorbitol and cardanol oil mixture as plasticizers were performed. Characterization of biodegradability by enzymes mixture of (alpha-amylase and glucoamylase) and soil burial test. The weight loss reached 96% and the degradation percentage reached 95.5% of PWADA and these results were significantly (p < 0.05) lower than WADA; as proved by high-performance liquid chromatography, increasing osmolality is evidence of the degradation as measured by the osmometer and the physical appearance of the film indicated complete degradation after 21 days. The film morphology, chemical structure, crystallinity, transparency, and thermal stability were studied using a scanning electron microscope, Fourier-transformed infrared, X-ray diffraction, UV–Vis spectrophotometer, and thermal gravimetric analysis. As a result, under the electron microscope, PWADA films had a more homogenous surface. The films’ infra-red spectra showed similar patterns, indicating identical chemical structures. Waxy maize starch has an A-type crystalline structure and after the thermoplasticization, the X-ray diffractogram showed new peaks appeared at 2θ of 13.2°, 19.5°, and 20.8°, which attributed to a V-type crystal pattern. The addition of cardanol oil restricts the transmission of light in the UV region by 250 nm by 69 and 63.4%, respectively, indicating UV absorber films. Furthermore, adding oil to (PWADA) and (WADA) films increased onset deterioration from 272 to 318 °C and from 317 to 320 °C, indicating that their thermal stability is improved. The water uptake rate and water vapor permeability increase after the pre-gelatinization of WADA films without cardanol but slightly decrease after the addition of cardanol oil. Also, pre-gelatinization decreases the elongation by 33.3% while increasing the strength by 10.5% of the films. Hence, waxy-modified maize starch film has the potential to be a biodegradable, thermal stable, and UV absorber film in packaging material.