Porosity, thickness distribution and water vapour sorption of thermoformed foamed PP films with dispersed sodium chloride for humidity regulation

Abstract

Abstract Packaging materials containing certain salts can regulate the humidity of packaged products. This study investigated whether thermoforming of foamed monolayer PP films with dispersed NaCl increases the water vapour sorption capacity and rate. Foamed monolayer PP-films (thickness 630 μm, porosity 0.28) with 6 (g/100 g) dispersed NaCl crystals were thermoformed to cups with depths up to 90 mm. By thermoforming the porosity increased up to 0.63 and the effective water vapour diffusion coefficient elevated by one order of magnitude from 10−11 to 10−10 cm²∙s−1. Therefore, such films absorb and desorb water vapour with a higher rate and they can bind more salt solution which is formed from solid salt crystals by water vapour absorption. Our results are important for packaging producers who thermoform films to cups and trays. This study addresses markets for fresh produce and other products with a high water activity.