Phase Behavior and Its Effects on Crystallization in a Poly(trimethylene terephthalate)/Phenoxy Resin Blend
Phase behavior and its effects on crystallization in an extruded poly(trimethylene terephthalate) (PTT)/phenoxy resin blend were studied with time-resolved light scattering (TRLS), optical microscopy (OM), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS). During annealing in the molten state, a two-phase structure with unique periodicity and phase connectivity was developed by liquid–liquid phase separation. After the formation of the phase-separated structure, the blend was homogenized by the interchange reactions between the two polymers. The crystallization behavior of PTT predominantly depended on the phase morphology developed during annealing. The pre-existing phase structures disturbed the lamellar orientation, resulting in a poorly ordered spherulitic superstructure.
Morphology development and crystallization behavior of a poly(ethylene terephthalate)/polycarbonate blend
The morphology development and crystallization behavior of an extruded poly(ethylene terephthalate)/polycarbonate blend were studied with optical microscopy, light scattering, and differential scanning calorimetry (DSC). During annealing at 280°C, liquid-liquid phase separation via spinodal decomposition proceeded in a melt-extruded specimen. After the formation of the domain structure, the blend slowly underwent phase homogenization by transesterification between the two polymers. The specimen, annealed for various times (t s 's) at 280°C, was subjected to a temperature drop to 180°C for the isothermal crystallization, and then the effects of liquid-phase changes on crystallization were investigated. The crystal growth rate decreased with t s . The slow crystallization with a large t s value was associated with the composition change of the separated phases and the change of the sequence distribution in the polymer chains during annealing. The influence of t s on the endothermic behavior of the samples was examined. As t s increased, the recrystallization rate was retarded during the DSC scan, displaying multiendothermic behavior. The DSC data also suggested that the increased level of transesterification would give rise to a higher number of species being rejected from the primary crystals, leading to enhanced secondary crystallization.
Miscibility and Crystallization Behavior of Poly(ethylene terephthalate)/Poly(ether imide) Blends
The miscibility and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blends have been investigated by DSC and optical microscopy. PET/PEI blends were prepared by solution precipitation from two solvents: a phenol/ tetrachloroethane mixed solvent and dichloroacetic acid. It was found that the compatibility of the as-prepared blends depended on the solvent used. Dichloroacetic acid appeared to provide better segmental mixing for PET and PEI than the mixed solvent of phenol and tetrachloroethane. The compatibility of the blends as prepared from both solvents could be enhanced by melt annealing. The composition dependence of T g of PET/PEI blends exhibited a cusp at the composition of ω PEI > 0.60 and was analyzed using the classical Gordon-Taylor's equation and the free volume theory of Braun-Kovacs. The PET crystallinity measured from the enthalpy of melting displayed a monotonic drop with increasing PEI content in the composition range of ω PEI > 0.4, while it stayed approximately constant for ω PEI < 0.4. The effect of blending with PEI on the multiple melting behavior of PET was also investigated. The highest melting endotherm was found to diminish with increasing PEI content in the blends, showing that the recrystallization of PET after the initial melting was hindered by the presence of PEI. After the crystallization of PET, a strong segregation of PEI was observed. Such segregation of PEI was accompanied with a significant increase in spherulitic nucleation density. The monitoring of the T g shift during crystallization and the morphological observation by optical microscopy suggested that the crystallization was coupled with a liquid-liquid phase separation, where the miscible melt demixed into the PET-enriched phase and the PEI-rich phase. The morphology created by the liquid-liquid phase separation and the nucleation at the domain interfaces may account for the drastic increase in nucleation density