Vibration welding of alpha and beta isotactic polypropylenes: Mechanical properties and structure

Propylene homo- and copolymers (both random and block types) with and without beta nucleation were injection moulded and the related plaques joined by linear vibration welding. The melt flow index (MFI) of the polypropylenes was different. During vibration welding the pressure has been varied (0.5, 2 and 8 MPa). The properties of the welded plaques were determined under both static (tensile) and dynamic conditions (Charpy impact). It was found that the mechanical performance of the welds could strongly be improved when beta nucleated PP plaques were combined with each other. In other combinations the 'weaker' alpha modification controls the mechanical response. The supermolecular structure of the weld was assessed by polarised light microscopy using thin microtomed sections. Formations of the weld morphology along with its effects on the mechanical performance were discussed.