Weldline is one of the most common but undesirable defect occurring in injection molded parts, which affects the surface appearance and mechanical properties. In the case of polymer blends, the properties of the weldline are strongly influenced by the morphology and dispersion of the different constituents at the weldline. Here, the effect of polycarbonate oligomer (PC-O) addition on the flow and mechanical properties of polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blend was investigated. The viscosity of the blend decreased significantly by adding only 1 phr of the oligomer, which resulted in the deeper penetration of one flow front into the other at the weldline interface. Moreover, the thickness of the weldline region, which consists of finely dispersed minor phases surrounding the interface, decreased with an increase of PC-O content. This suggests that the homogeneity of the overall dispersion was greatly enhanced with the presence of PC-O. The addition of the oligomer had little effect on the tensile strength of the weldline specimen although the apparent modulus has increased. Considering the fact that the elongation at break deteriorated with increasing PC-O content, the PC-O is thought to be effective in enhancing the rigidity of the PC/ABS blend at the expense of its toughness and deformability..

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