The effect of different impact modifiers in halogen-free flame retarded polycarbonate blends - I. Pyrolysis

In this first of two papers, the thermal decomposition of bisphenol A bis(diphenyl phosphate)-flame retarded polycarbonate (PC) blends with different impact modifiers was studied. The impact modifiers were an acrylonitrile-butadiene-styrene (ABS), a poly(n-butyl acrylate) (PBA) rubber with a poly(methyl methacrylate) (PMMA) shell and two silicone-acrylate rubbers consisting of PBA with different amounts of polydimethylsiloxane (PDMS) and different shells (PMMA and styrene-acrylonitrile, SAN). The focus of this work was to study the impact of the acrylate and silicon-acrylate rubbers with respect to pyrolysis and flame retardancy in comparison to common ABS. Thermogravimetry (TG) was performed to investigate the pyrolysis behaviour and reaction kinetics. TG in combination with FTIR identified the pyrolysis gases. Solid residues were investigated by FTIR-ATR. PC/ABS shows two-step decomposition, with PC decomposing independently from ABS at higher temperatures. Pure acrylate rubber destabilises PC due to interactions between the rubber and PC, which leads to earlier decomposition of PC. Using silicone-acrylate rubbers led to similar results as PC/ABS with respect to pyrolysis, reaction kinetics and analysis of the solid residue; hence the exchange of ABS for the silicone-acrylate rubbers is possible.