A PRELIMINARY INVESTIGATION OF FLASH FORMATION DURING INJECTION-MOLDING OF POLYPHENYLENE SULFIDE AND LIQUID-CRYSTALLINE POLYMER BLENDS

Flashing in pure polyphenylene sulfide (PPS) and a blend containing PP S and liquid crystalline polymer (LCP) during injection molding was in vestigated by differential scanning calorimetry and scanning electron microscopy. The shape of the flash was observed by use of a projector. Flashing was detected in pure PPS and 90/10 PPS/LCP blend but was not found in other compositions, including pure LCP. The DSC thermograms of the flash revealed both exothermic and endothermic peaks at around 120 degrees and 285 degrees C. The first peak, known as crystallizatio n temperature on heating, occurred as a result of early crystallizatio n of PPS. The observed double peaks indicated that the degree of cryst allinity was lower in the flash than in the molded part. The morpholog ical studies revealed the presence of LCP fibrils in the skin region a nd droplets in the core region of 90/10 PPS blend. The absence of flas h was attributed to the diameters of the fibrils and droplets, which w ere found to increase with increasing LCP component.