Mechanical, microscopical and fire retardant studies of ABS polymers

Antimony trioxide (Sb2O3) is a common additive in ABS flame retardant formulations and the effects of adding it, with four commercial brominated materials, to ABS are reported here. The results focus upon mechanical, rheological, microscopical and flame retardant properties, and the effects of four Sb2O3 materials with average particle sizes ranging from 0.5 to 11.8 mu m. Compounds were produced using a twin-screw co-rotating machine and subsequently injection moulded into flexural and impact specimens, the latter being tested with instrumented falling weight equipment. The effects on rheological properties were studied using a capillary rheometer. Dynamic mechanical thermal analysis (DMTA) and LOI flame testing were also carried our. The brominated materials had more influence than Sb2O3 on the ABS rheology, although a trend of increased melt viscosity with increasing Sb2O3 particle site and loading was noted. The brominated materials generally increased the flexural modulus and reduced the deflection at peak force values, whereas the modulus and strength were relatively unaltered with Sb2O3 at the loadings studied. The impact strength of the ABS was detrimentally affected by both additives as loading level and average particle size increased. The presence of 5 wt% sub-micron Sb2O3 caused a 20% reduction in impact strength whilst the reduction due to the brominated materials depended upon the specific halogenated compound used. Scanning Electron Microscopy (SEM) showed good dispersion of Sb2O3 regardless of particle size and Transmission Electron Microscopy (TEM) revealed that Sb2O3 resided in the SAN phase of the polymer. The DMTA response of ABS was not altered by Sb2O3 (C) 1999 Elsevier Science Ltd. All rights reserved.