Atsuo Konda

MORPHOLOGY OF POLY (BUTYLENE TEREPHTHALATE)/POLY (BISPHENOL A CARBONATE) MELT BLENDS

Morphology and mechanical properties of poly (butylene terephthalate) (PBT)/poly (bisphenol A carbonate) (PC) and PBT/PC/di-n-octadecyl phosphate (DNOP) melt blends have been examined as a function of PC fraction with DSC, X-ray diffraction, FT-IR and SEM. Mechanical properties and dynamic viscoelastic properties of the blend filaments were also studied. The cross section of 90/10/0.5 blend etched by 4 vol% CH2Cl2/CCl4 mixture shows one phase structure, while network structure of PBT rich phase is observed for 70/30/0.5 blends, further the 10/90/0.5 blend is dissolved by the mixture. Two glass transitions are observed in DSC curves for 70/30/0.5 to 30/70/0.5 blends. The lower glass transition occurs at about the constant temperature, while the temperature of higher glass transition increases with the PC fraction. It is considered that the above two transitions are ascribed to PBT rich and PC rich phase, respectively. For 100/0 to 50/50 blends, dynamic storage modulus drops drastically at the glass transition temperature of PBT rich phase, whereas it drops at that of PC rich phase for 30/70 to 0/100 blends. Youngs modulus and yielding stress of PBT/PC blends are higher than those estimated by assuming the additivity. Therefore, must be strong interactions between PBT and PC chains. The amount of transesterification occurring between PBT and PC chains is too little to be observed by FT-IR. Accordingly, the interaction can be caused by rearrangement of chain packing with mutual diffusion of the chains. This indicates partial miscibility between PBT and PC chains in the melt state. The crystallization of PBT chains in the blends is restrained by PC chains. In the PBT rich phase, crystallization rate becomes slower and the cold crystallization becomes unclear with diffusion of PC chains. On the other hand, PBT chains in the PC rich phase crystallize suddenly when the temperature exceeds the glass transition temperature of the phase. The morphology and the higher glass transition become clear by addition of DNOP. It is considered that DNOP accelerates the degradation of PBT chains.