The effects of processing parameters on the strength of the fusion bonding interface have been investigated. The interface was generated when an isotactic polypropylene homopolymer was injection molded on a solid self-reinforced polypropylene substrate. The interface strength was measured in shear configuration, and the melting behavior of substrate was studied using differential scanning calorimetry. The results show that strong bonding interface can be achieved when the correct processing parameters are chosen. The interfacial strength is largely improved if the interface temperature is higher than the melting temperature of the substrate layer, and in these specimens failure does not take place at the interface. Furthermore, for a fixed interface temperature, interface strength increases with thermal gradient. Finally, in the analyzed holding pressure range, pressure apparently has no effect on strength. (c) 2006 Wiley Periodicals, Inc.