WELD LINES IN INJECTION-MOLDED IMMISCIBLE BLENDS - MODEL PREDICTIONS AND EXPERIMENTAL RESULTS

In this work, a theoretical approach based on diffusion and the Flory- Huggins theory of the free energy of mixing is considered to predict t he weld-line strength in injection-moulded polycarbonate (PC) and its blend with high-density polyethylene (PE) as a function of melt temper ature and contact time. A comparison between the model predictions and experimental results was also performed for pure PC as well as for it s blend. Different melt temperatures ranging from 220 to 300 degrees C and a constant total cooling time of 15s were used. Two types of spec imen were produced, one with a dual-gate mould cavity and another with a single gate. In the case of PC, the model predicts satisfactorily t he weld-line strength as a function of injection temperature. High-den sity PE was also moulded in the same conditions but in a lower tempera ture range (145 to 220 degrees C). The results showed that the tensile strength of PE remains unchanged in the presence of weld lines. For t he PC/PE blend, the results showed a good agreement between the model predictions and the experimental results. It was also possible to pred ict the weld-line strength of the blend as a function of its compositi on and temperature.