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The effect of multi-walled carbon nanotubes on the crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has been investigated. The results have shown that carbon nanotubes (CNTs) act as an effective heterogeneous nucleation agent, inducing an increase in crystallinity and crystallite sizes. Comparing with the double melting peaks in pure PHBV, there is only one peak in the melting curves of nanocomposites. The isothermal crystallization kinetics of PHBV and its nanocomposite containing 0.5% CNTs were examined based on Avrami equation, indicating that the crystallization half-time decreases while the overall crystallization rate k increases dramatically with CNTs addition. The spherulitic nucleation and growth kinetics were also discussed grounded on Lauritzen-Hoffman equation. It is found that there is a spherulitic growth rates ( G) maximum within selected temperature range in our study. Also, the temperatures corresponding to G maximum shift to a high level with addition of CNTs. The parameters of the equilibrium melting temperature $$ T_m^0 $$, the nucleation parameter K, the lateral surface free energy σ, the fold surface free energy σ, and the work of chain folding q of PHBV and its composite containing 0.5% CNTs were all calculated. The reductions of K, σ and q values of nanocomposite are in agreement with the fact that the crystallization rate of PHBV increases greatly by addition of CNTs. [ABSTRACT FROM AUTHOR]

Abstract  Different sample thicknesses were adopted to investigate the effect of temperature gradient on the development of β phase polypropylene (PP) in the compression-molded dynamically vulcanized thermoplastic elastomers (TPVs) based on PP/ethylene-propylene-diene rubber blend. Differential scanning calorimetry and wide-angle X-ray diffraction were employed to study the melting behavior and crystalline structures. The results indicated that the content of β phase increased with the sample thickness of TPV increasing, while the total crystallinity of PP almost kept constant. The simulation of the temperature field showed that there was a temperature gradient along the direction of sample thickness, and the strength of the temperature gradient increased with the thickness of TPV increasing. The reason for the change of β phase content was found to lie in the reduction of the entropy in the temperature gradient field, which was a result from the decrease of the molecular chain conformation. [ABSTRACT FROM AUTHOR]