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The effect of moisture content and film composition on biodegradability is the focus of this study. Flexible films were first characterized for the effect on water sorption isotherms of relative humidity, temperature, zein content, and the addition of the plasticizers stearic acid, poly(ethylene glycol), or etoxylated ricine oil. Zein/ethylcellulose (EC) mixture films had a behavior between that for pure zein and EC films, which had the lowest water sorption. For films with plasticizer, the lowest water sorption at 25 degrees C was observed for those with stearic acid. Biodegradability of zein/EC films, evaluated using bacterial cultures selected for their zein proteolytic activity and isolated from a local solid waste landfill and a lagoon, showed no plasticizer effect even though its effect on moisture content was significant. Large differences were observed at different film zein concentration with the highest biodegradability for 100% zein. However, biodegradability did not mimic the water sorption behavior of zein/EC mixture films.

In this study, extruded films of corn starch (CS) plasticized with coconut oil (CO) (as an alternative plasticizer to glycerol) in the presence of Yucca schidigera extract (YSE) as a surfactant were investigated. It was observed that corn starch films (CSF) plasticized with a lower concentration (15 wt%) of CO showed a better equilibrium of mechanical properties, a higher WVP (5.8 ± 0.2 × 10−9 g m−1 s−1 Pa−1) and percentage of elongation (8 ± 0.5), and a lower Young modulus (99 ± 8 MPa) than those with a higher amount of plasticizer. However, films with Yucca schidigera extract (YSE) as a surfactant showed a decrease in WVP (4.9 ± 0.2 × 10−9 g m−1 s−1 Pa−1), a lower Young modulus (61 ± 2 MPa) and an increase in the percentage of elongation (13 ± 0.4). In order to describe the viscoelastic properties before the extrusion processes in materials in water suspensions and after extrusion process in CSF, rheological and DMTA analysis were performed, showing consistent behaviors for both samples.

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All references to the use of polyethylene glycol as plasticizer in the experimental work here reported are in error. Stearic acid, propylene glycol, and etoxylated ricin oil were the only plasticizers evaluated in this work. JF040190N 10.