Crystallization Kinetics Of Blends Research Articles

Kinetics pathway in the phase separation and crystallization of iPP/OBC blends

Mesophase separation between the incompatible blocks in multiblock copolymers OBC (Olefin Block Copolymers), coupled with the macrophase separation in its blends with iPP (isotactic polypropylene), makes iPP/OBC a unique blend system to understand the interaction between multiple phase separations and the subsequent or simultaneous crystallization in multi-scales. The role played by OBC content as well as its molecular structure on phase morphology and crystallization kinetics in blends of iPP/OBC has been investigated systematically to demonstrate synergistic coupling between thermodynamics and kinetics. The total isothermal crystallization rate, nucleation density (the nuclei number per unit volume) and linear growth rate of iPP are found to be composition and component dependent, which can be attributed to the interplay among the enhanced mobility due to the presence of a more mobile component (lower glass transition temperature and lower melting temperature) serving as an “accelerant”, the associated composition dependent inter-diffusion coefficient, and the obstruction effect caused by the OBC aggregates with increasing the diluent concentration. Furthermore, the distinct phase separation morphology determined by the compatibility between iPP and various OBC influenced the growth rate of iPP spherulite as well.

Nanoscale-confined crystallization in epoxy resin and polyethylene-block-poly(ethylene oxide) diblock copolymer blends

In this paper, the nanoscale-confined crystallization behavior and crystallization kinetics in blends of double-crystalline polyethylene-block-poly(ethylene oxide) (PE-b-PEO) diblock copolymer with diglycidyl ether of bisphenol A epoxy resin were investigated. The results showed that there appeared three crystallization regimes related to the crystallization of the PE block within three different microenvironments in the epoxy resin/PE-b-PEO blends. The Avrami index n is around 1.8–2.4, suggesting PE block of the copolymer in the blends exhibited nanoscale-confined crystallization behavior by homogeneous nucleation. The PE block nanoscale-confined crystallization is ascribed to the formation of the strong intermolecular hydrogen bonding interaction between hydroxyl groups of amine-cured epoxy and ether oxygen atoms of PEO, as seen from Fourier transform infrared spectroscopy spectra.

Thermal analysis of isothermal crystallization kinetics in blends of cocoa butter with milk fat or milk fat fractions

AbstractThe kinetics of isothermal crystallization of binary mixtures of cocoa butter with milk fat and milk fat fractions were evaluated by applying the Avrami equation. Application of the Avrami equation to isothermal crystallization of the fats and the binary fat blends revealed different nucleation and growth mechanisms for the fats, based on the Avrami exponent. The suggested mechanism for cocoa butter crystallization was heterogeneous nucleation and spherulitic growth from sporadic nuclei. For milk fat, the mechanism was instantaneous heterogeneous nucleation followed by spherulitic growth. For milk fat fractions, the mechanism was high nucleation rate at the beginning of crystallization, which decreased with time, and plate‐like growth. Addition of milk fat fractions did not cause a significant change in the suggested nucleation and growth mechanism of cocoa butter.

Poly(p-phenylene sulfide)/liquid crystalline polymer blends. II. Crystallization kinetics

The crystallization kinetics of blends made of poly(p-phenylene sulfide) (PPS), with a liquid crystalline polymer (LCP) was studied. The blends were found to be immiscible by dynamic mechanical thermal analysis (DMTA). Results of non-isothermal and isothermal crystallization experiments made by differential scanning calorimetry (DSC) showed that both components had their crystallization temperatures increased ; also the LCP melting temperature was found to increase in the blends. It was concluded that the addition of LCP to the PPS increased the PPS overall crystallization rate due to heterogeneous nucleation. The fold interfacial free energy, σ e , of the PPS in the blends was observed not to vary with composition.

Crystallization kinetics in blends of isotactic and atactic poly(β-hydroxybutyrate)

Isothermal crystallization kinetics in the miscible blend system isotactic/atactic poly(β-hydroxybutyrate) (PHB) are examined by optical microscopy. The presence of the atactic component results in a reduction in spherulitic growth rate of the isotactic polymer. Analysis of the growth rates using the Lauritzen-Hoffman model shows that a regime II→III transition is present for all blend compositions investigated (0–50 wt% atactic), and that this transition occurs at a constant temperature of 140°C. The ratio of the nucleation constants for the two regimes, K III g K II g , is found to deviate from the theoretical value of 2.0 in the blend system. It is shown that a modified version of the Lauritzen-Hoffman equation incorporating entropic effects is unable to account for these deviations. The work of chain-folding, q, is calculated to be 5.1 kcal mol −1 for isotactic PHB. The implications of using assumed values of the transport parameters in the kinetic analysis are discussed.

Miscibility and crystallization kinetics in blends of poly(ethylene terephtalate) and thermotropic liquid crystal polyesters

AbstractBinary blends of poly(ethylene terephtalate) (PET) and thermotropic liquid crystal polyester (TLCP) have been prepared by both solution and melt blending methods. The TLCPs utilized were Vectra (Hoechst Celanese), TR‐4, a TLCP synthesized in our laboratory, and a block copolymer consisting of three TR‐4 units followed by three PET units. The phase behavior of the blends was studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and optical microscopy. The results show that none of the blends is miscible, but significant interactions exist between the PET phase and the TLCP phase in the case of TR‐4 and TR‐4 block copolymer blends. These interactions lead to a different nucleation mechanism in these blends compared to that in PET/Vectra.