Polypropylene (PP) and Polyethylene (PE) will not weld. If you try to weld the two materials, the grade of plastic with a lower melting temperature and higher viscosity will melt and flow across the surface of the other material. For most grades of these materials, the PE will have a lower melting temperature and higher viscosity. read more
The accompanying graph shows results of peel-force experiments on laminates of different PE and isotactic PP (iPP) resins. Each data point represents the average of at least four peel tests with an Instron tensile tester. Sheets 1 mm thick were pressed together at 375 F and 160 psi for 10 min and then cooled. read more
In order for two materials to weld, there are three main requirements: The materials must be chemically compatible (i.e. the polymer chains must be able to form secondary bonds). Some plastics are compatible this way, however it is mostly different types of amorphous plastics that are compatible with each other. read more