The thermal behaviour and isothermal crystallisation of cyclic poly(butylene terephthalate)and its blends

Abstract

This thesis concerns the thermal behaviour and isothermal crystallisation kinetics study of cyclic polyesters and its blends, in particular cyclic poly (butylene terephthalate) (c-PBT). The production of c-PBT is interesting; in fact it is different from production of conventional linear PBT since c-PBT is produced by in situ polymerisation of cyclic butylene terephthalate oligomers (CBT) in the presence of suitable initiators or catalysts. These relatively novel materials, i.e. CBT offer many advantages in properties and the most unusual and useful is that they can be processed at low viscosity (water like) and exhibit rapid crystallisation. The thermal behaviour and isothermal crystallisation kinetics of CBT and c-PBT were analysed. The most significant achievement of this project is blending where blends of c-PBT and styrene maleimide (SMI) were prepared by simultaneous in situ polymerisation and melt blending of solid dispersion CBT/SMI powder. This is unique and novel and the results show consistency and signs of miscibility although there are no external forces applied during the melt blending. It was found that the presence of 30 wt % and above of SMI impeded the crystallisation of c-PBT. This suggests that miscibility occurred. The miscibility of these c-PBT/SMI blends was support with the presence of a single composition-dependent glass transition temperature and negative Flory-Huggins interaction parameter. Studies on crystallisation kinetics of c-PBT were also done by Avrami analysis and using the Hoffman-Lauritzen theory. Previously there have been very limited studies of the crystallisation kinetics of PBT produced from its oligomer. Further work on crystallisation of c-PBT/SMI blends was also performed