Compatibilisation of polysulphones/polyester blends
Ternary blends comprising Polysulphones [Polyethersulphone (PES) and Polysulphone (PSO)], the Polyhydroxyether of bisphenol-A (Phenoxy), and Polyesters [Poly( ethylene terephthlate) (PET) and Poly(butylene terephthlate) (PBT)] have been studied particularly with the aim in mind of elucidating the factors determining their miscibility and morphology. Binary and ternary combinations, including equivalent systems based on a butylene terephthlate-tetramethylene oxide block copolymer (PBT-TMO), were prepared from solution and by mixing in the melt state using both an internal mixer and a twin screw extruder. Scanning electron microscopy was employed to examme the morphology of these blends. A co-continuous, (interpenetrating), dual-phase morphology was displayed by both the PSO/PBT and PSO/PBT-TMO (70/30) combinations. The compatibility was further increased by the addition of Phenoxy, which was evidenced by the formation of a very fine dispersion of the two phases for both PSO/Phenoxy/PBT and PSO/Phenoxy/PBT-TMO blends, in the weight ratio of (60/15/25). A lower level of compatibility was displayed by the equivalent blends based on PES and PET, as a matrix/dispersed particle type of morpholgy was usually observed. Differential thermal analysis and dynamic mechanical analysis measurements were also employed to ascertain the level of miscibility in these systems. A single composition dependent glass transition temperature was displayed by the binary PBT/Phenoxy and PBT-TMO/Phenoxy melt blends, and the binary PES/Phenoxy and _PSO/Phenoxy solution blends. The remaining blends displayed two separate glass transition temperatures that were often broader and closer together than those of the homopolymers. This effect was more significant for blends containing the Phenoxy compatibiliser, confirming that these systems are semi-miscible. Solvent resistance measurements were made on 500μm thick extruded sheets by measuring the time to failure at stress levels corresponding to 30% and 50% of the tensile strength. The blends displaying a matrix/dispersed particle type of morphology revealed poor solvent resistance and mechanical properties. The blends displaying a cocontinuous interpenetrating dual-phase morphology on the other hand displayed a much higher solvent resistance and enhanced mechanical properties.