Adhesion control for injection overmolding of elastomeric propylene copolymers on polypropylene. Effects of block and random microstructures

The influence of chemical compositions and microstructures of ethylene–propylene copolymers on its adhesion strength to polypropylene was studied. DSC, WAXS and Raman micro spectroscopy were used to examine details of three ethylene propylene copolymers chemical compositions with amorphous and semicrystalline microstructures. Copolymers microstructures include from random to tapered blocky comonomers distributions. Semicrystalline copolymers strips were injection overmolded on a core polypropylene base, and peeling tests were conducted at room temperature. Adhesion strength depending on copolymers composition and microstructure are discussed on the basis of two mechanisms: fingering along amorphous polypropylene phase and co-crystalization. Injection adhesion after overmolding cannot be easily controlled via interphase melt temperature, as done before for other ethylene copolymers, mainly because of the very favorable Flory interaction parameter values. The used copolymers are classified for use for specific purposes, from easy recycling to high tenacity.