A series of polycarbonate-poly(butylene terephthalate) blends has been formed via melt blending in a torque rheometer. Initially polycarbonate and poly(butylene terephthalate) were blended alone to determine the extent to which the two homopolymers were able to cross-react (transesterify), and hence, how the morphology of the blends developed as a result of transesterification. Subsequently the degree of transesterification between the two homopolymers was controlled by the incorporation of an alkyl titanium catalyst, and the effect on morphological development determined. Resultant uncatalysed and catalysed materials were characterised by DSC, DMA, FTIR, microscopy, solubility studies and X-ray scattering. No evidence for direct inter-chain transesterification was seen for the uncatalysed blends. No new thermal transitions or absorptions were noted from DSC, DMA or FTIR, nor was there any evidence for phase refinement from microscopy, or variation in solubility behaviour. However, there was evidence for some degree of phase mixing from DMA damping behaviour, indicated by convolution of the PC and PBT transition peaks. Due to the lack of transesterification relatively coarse morphologies, indicative of an immiscible two phase blend, were apparent from microscopical analysis. Thermal behaviour of the uncatalysed blends showed evidence of thermal degradation above 270°C, promoting transesterification via acidolysis. As the degree of transesterification was increased (catalysed materials) the composition of the blends became increasingly complex, comprising mixtures of the homopolymers and various AB-type block copolymers of polycarbonate and poly(butylene terephthalate), with concomitant changes in their thermal behaviour. DSC and FTIR proved useful in analysing blends containing greater than 150 ppm of added catalyst, whilst DMA highlighted the subtle differences in the blends with less than 200 ppm additional titanium transesterification catalyst. Microscopical analysis provided visual evidence for the transformation in the materials morphology through progressive transesterification: the relatively coarse structure characteristic of two phase blends developing into a more refined sub-micron iv structure exhibited by blends containing a significant volume of interphase material. This morphological change was due to the formation of increasing concentrations of random block copolymers. At increasing degrees of transesterification this change in morphology was accompanied by variations in the solubility of the blends. With increasing amounts of additional catalyst up to 150 ppm, the blends became increasingly resistant to solvent (dichloromethane). Whereas above this level the blends became increasingly soluble, as copolymers of a more random nature (with increased solubility) were formed. X-ray scattering showed the pure PBT to exhibit highly reproducible crystallisation behaviour. In contrast a 50/50 blend showed a progressive reduction in the degree of crystallinity, melting and crystallisation temperatures with increasing transesterification.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:337270 |
| Date | January 1997 |
| Creators | Tattum, Steven Burgess |
| Publisher | Manchester Metropolitan University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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