SUMMARYThe flammability of eight halogen-free styrene resins and one halogen-containing styrene resin was characterized by UL 94 VB, LOI and cone calorimeter tests. Their burning behaviour was also measured when exposed to three external ignition sources (methenamine tablet, candle, paper ball). Five resins were used for 19 00 monitor housings and the others for 25 00 TV. The LOI values of UL 94 V-2, V-1 and V-0 rated resins were higher than that of HB. The heat release rate decreased as the UL 94 ratings increased from HB to V-0. When these resins were exposed to three external ignition sources, UL 94 V-1 and V-0 rated resins showed a self-extinguishing property after removal of the fire and did not cause fire growth in either 19 00 monitor or the 25 00 TV housings in all cases. However, UL 94 V-2 and HB rated resins were easily ignited and spread fire by dripping burning trickles. The burning rate of V-2 resin was slower than that of HB.

In order to understand the relationship between processing conditions and the properties of weld‐lines on a molecular level, it is necessary to evaluate the true strength of the weld‐line that is not affected by the V‐shape notch on the surface of the weld‐line zone. In this experiment, the weld‐line strength of several brittle, ductile, or phase‐separated polymers was evaluated using the compact tension test by measuring the critical stress intensity factor, KIC, or the critical J‐value, JIC, and the results were compared with those obtained by tensile testing. For brittle polymers such as poly(methyl methacrylate) (PMMA) or styrene acrylonitrile copolymer (SAN), the value of the weld‐line factor, i.e., the strength ratio between the welded and the non‐welded specimen, is higher than that measured by tensile testing, because of the notch sensitivity of brittle thermoplastics and the notch dependence of tensile strength. On the other hand, in the case of ductile polymers such as polycarbonate (PC), the weld‐line factor is similar for both the tensile and compact tension tests. However, the dependency of the weld‐line factor on melt temperature is more obvious in the compact tension test. From these results, it seems that the compact tension test is more appropriate for measuring the interfacial adhesion strength across the weld‐line, which excludes the notch effect.

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