Compatibility of polyvinylidene chloride with mechanical recycling of polyolefins

Abstract

The exceptional low permeability to oxygen and water of PVDC and the retention of barrier properties to oxygen even in humid conditions explain its success for packaging in food industry as barrier layer in Polyolefins (PO) multilayer films, whose contribution to the reduction of food waste is largely recognized. Several chemical recycling technologies have emerged in the recent years that, together with methodologies based on separation of layers by the use of solvents, will strongly increase in a near future the extent of recycling of multilayer films, including the PVDC-containing ones. At the same time, it is generally accepted that for several years these technologies will be complemented by the now dominating mechanical recycling. A lack of detailed study in the literature and a general confusion between very different PVDC grades, with and without internal stabilization, led to the idea that the dehydrochlorination of PVDC would cause a low quality of the recyclate obtained by mechanical recycling of PO in presence of PVDC and a corrosion risk for the equipment. In this study, the effect of a stabilized PVDC grade developed for coextrusion, at concentration typical of real life PO mix for mechanical recycling and in suitable condition, has been investigated in a pilot scale extruder and corrosion tests were performed. In conclusion, quantities of PVDC to be found in PO streams for mechanical recycling are compatible with a PO recyclate of excellent characteristics, even at extrusion temperatures as high as 220°C, with no damage to the PO structure, with only minimum discoloration, that can be mitigated by relatively low quantities of additives of general use in PO extrusion, and with no risk of corrosion of the equipment.