Continuous tapes of polypropylene (PP) and high-density polyethylene (HDPE) were produced using a novel multiplication co-extrusion process. The structure of the PP/HDPE tapes consists of co-continuous PP and HDPE domains aligned in the extrusion direction, forming a fiber-like composite structure with individual domain thicknesses of 200-500 nm. This unique structure created a significantly large contact interface between the polymer domains. AFM images suggest strong interfacial interactions between incompatible PP and HDPE domains. Orientation at 130 °C was possible due to the enhanced adhesion arising from epitaxial crystallization and the large interfacial area. The modulus, tensile strength, and orientation factor of the oriented composite tapes increased as the draw ratio increased. The existence of two independent shish kabab-like morphologies in the oriented tapes at different draw ratios was indicated by the appearance of two melting peaks for each material. After one-step orientation at 130 °C to a draw ratio of 25, the moduli of the oriented tapes increased to approximately 10 GPa, and the tensile strength increased to approximately 540 MPa. These oriented tapes are stiffer and stronger than commercial tapes and do not fibrillate during the orientation process indicating some interfacial interaction between the domains.
Keywords: PP/HDPE blend; PP/HDPE interface; mechanical properties; multiplication co-extrusion; post-extrusion orientation.