The composition and microstructure of a blend of bisphenol‐A polycarbonate (PC) and poly (butylene terephthalate) (PBT) have been established by a variety of physical methods. The composition was established by solvent extraction and infra‐red spectrophotometry, while the microstructure was determined by these and the additional methods of differential scanning calorimetry and dynamic mechanical thermal analysis. The PBT retained its crystallinity in the commercial blend, (Xenoy CL‐100), but blending reduced the main glass‐rubber transition of the PC from 147°C to approximately 100°C. Conditioning of the blend at high temperatures resulted in progressive transesterification: 3 minutes at 240°C gave a small but significant effect, while 30 minutes at 270°C yielded large changes in the structure. These findings are important in respect of processing the material, and the limitations which might be incurred in plant recycling of scrap.

The mechanical properties (tensile strength, low temperature falling weight impact strength) of XENOY CL‐100 (a blend of polycarbonate and polybutylene terephthalate) have been studied. This blend is comprised of tough components and the property combinations that result may be useful for certain applications. The hydrolysis resistance of the blend in deionised water at 40°C has been studied. After 30 weeks it did not lose its tensile strength, but subsequently it did lose 50% of the low temperature (−70°C) falling weight impact strength. If the −70°C low temperature toughness is an important quality, this should be taken into account. However, the low temperature (−70°C) falling weight impact strength of pure polycarbonate and of pure poly(butylene terephthalate) is very low, whilst XENOY CL‐100 is still tough material, even after 30 weeks immersion at 40°C. Further study of the composition of XENOY CL‐100 showed that this blend is composed of polycarbonate. poly(butylene terephthalate) and crosslinked acrylic rubber; traces of titanium‐catalyst residue for the poly(butylene terephthalate) polymeristaion and black dye have also been found.