Development of WPI and PVA blends aiming their use as flexible plastic packaging for food

Abstract

Given the annual growth in food plastic packaging consumption, it is desirable the existence of raw materials, which are alternative to petroleum, especially those renewable or obtained from industrial byproducts, such as the whey protein isolate (WPI). The present work proposes to evaluate the applicability of WPI and polyvinyl alcohol (PVA) new blends as flexible packaging for food. In order to this, blends of WPI with 10%, 20% and 30% of PVA were developed, aiming to increase the WPI films flexibility. Blends, as well as isolated WPI and PVA films, were characterized regarding the following properties: mechanical (tensile and puncture tests), morphological (Scanning Electron Microscopy – SEM), of interaction (Fourier Transform Infrared – FT-IR), optical (% transmittance), thermal (Thermogravimetric Analysis – TGA and Differential Scanning Calorimetry – DSC), of water vapor permeability, of solubility in water and of interaction with moisture under different water activities and temperatures (water sorption isotherms). The addition of 30% of PVA to WPI matrix produced a blend with lower strength, but with a more ductile behavior, exhibiting a ten times higher elongation when compared to WPI film. The tensile properties obtained for this blend were close to those from low density polyethylene (LDPE). The puncture resistance and the water vapor permeability were not affected by the addition of PVA to the WPI matrix, while solubility in water and optical transmittance were reduced when compared to WPI film. Blends showed glass transition temperature values similar to that from WPI film and a good compatibility between the polymers was indicated by Tg results. The experimental data from water sorption isotherms tests were well adjusted through GAB model and curves showed a more expressive increase of water sorption above water activity (aw) of 0.6. The addition of 30% PVA to WPI made the water sorption process more spontaneous. Through the performed analysis it was possible to conclude that is indicated the addition of 30% of PVA to the WPI matrix in order to obtain a more flexible material without prejudice its water barrier property, as well as, that the application of this blend as flexible packaging is suitable for foods and external environments with aw below 0.90.