Polyolefin monolayer films with tuneable permeability for food packaging applications

The present work is aimed at tuning barrier properties, that is here attained by melt blending proper polyolefin materials with different densities, that, in turn, influence the gas transport behaviour. In particular, it has been shown that the use of cyclic monomers infers higher barrier, high rigidity and strength to the final materials, while the use of branched monomers increases polymer free volume with consequent higher permeability. Thus, flexible monolayer films with tuneable permeability were achieved by melt blending selected commercial polyolefins, commonly used as food contact materials. Indeed, melt blending is a less complicated and less costly technology with respect to lamination and coating, to improve barrier properties, or microperforation, to enhance gas permeability. A significant decrease of O2 and CO2 permeability was observed for films obtained from blends of a LDPE matrix and an ethylene/norbornene copolymer (COC) with COC content from 5 to 20 wt %. On the other hand, films prepared from blends of a commercial PP and increasing amounts (5÷20 wt %) of poly(4-methyl-1-pentene), PMP, showed improved diffusional properties, e.g. suitable for fresh vegetables.