Zein films with porous polylactic acid coatings via cold plasma pre-treatment

In this study, a two-step strategy is proposed to form a porous polylactic acid (PLA) coating on zein films aimed at improving their function. The effect of cold plasma (CP) pre-treatment on the structure and the properties of the films were evaluated. The CP pre-treatment augmented the compatibility and adhesiveness between the zein and PLA layers. The subsequent breath-figure assembly compacted and ordered the porous morphology structure of the PLA layer. Analysis by attenuated total reflectance Fourier transform infrared spectroscopy confirmed that the CP pre-treatment led to a change in the protein conformation and promoted hydrogen bonding interactions between zein and PLA. Exposure of the zein to the CP for 60 s before PLA coating improved the surface hydrophobicity by 24.11 %, the tensile strength by 50.47 %, the elongation at the break by 29.67 %, and water vapor barrier by 44.34 % compared with the untreated zein film. Moreover, the modified coating films exhibited a high UV barrier and excellent biodegradable performances. The strategy of adding a porous PLA coating on the zein films achieved the properties enhancement of zein and expanded its application scope, especially in the field of biodegradable packaging.