Thin wall injection-overmoulding of polyamide 6/polypropylene multilayer parts: PA6/PP-g-ma interfacial adhesion investigations

Abstract

This work investigates the interfacial adhesion of PA6/PP-g-MA in a thin-walled multilayer part obtained by injection overmoulding. This process is a good solution to the need of weight reduction for the sustainable and economic growth of food packaging. A rigid plastic food package is a complex multilayer structure obtained from the association of polymers with different properties to achieve good barrier, environment, or thermo-mechanical performance. The present study aims to obtain a complete understanding of the interfacial adhesion of PA6/PP-g-MA interface in a three-layer PA6/sealant/PP assembly through microscopy analysis, mechanical characterization, and inter-diffusion models. Optical microscopy, XPS, and AFM analyses showed the presence of a copolymer interphase. This layer is greatly dependent on the holding pressure applied, which revealed to be the key parameter to obtain the best results in terms of failure strength. A better interface wettability improves the inter-diffusion distance and thus chemical grafting efficiency. Other interface improvements were achieved by the addition of EVA in the PP-g-MA layer. The lowest viscosity of the EVA dispersed phase has led to a fully cohesive failure due to an interface diffusion efficiency. The presence of EVA increased more than 80% of the peeling performance of the assemblies.