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Crystallization kinetics of metallocene type polypropylenes

Influence of molecular weight and comparison with Ziegler-Natta type systems

Journal of Thermal Analysis and Calorimetry
Authors: M. J. Galante, L. Mandelkern, R. G. Alamo, A. Lehtinen, and R. Paukker

The crystallization kinetics from the melt of metallocene type isotactic poly(propylenes) having the same chain defect concentration and molecular weights ranging from 68480 to 288430 have been studied by differential scanning calorimetry. The crystallization rates and the variation of the rates with crystallization temperature follow a pattern that is basically independent of molecular weight. This result contrasts with the molecular weight dependence on the crystallization rate observed in linear polyethylene, random ethylene copolymers as well as other semicrystalline systems.

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Abstract  

Crystallization kinetics and thermodynamic properties of nucleated isotactic polypropylene (PP) are analyzed using Hoffman—Lauritzen crystallization theory to determine the mechanistic effects of the nucleators. Calorimetric data provides quantitative comparisons between nucleating efficiences of the (Millad) and (NJSTAR) nucleator in Metallocene (M) and Ziegler—Natta (ZN) PP. The two types of PP without nucleators showed similar crystallization behavior though the T°m for ZN-iPP was about 10°C higher than M-iPP. Both nucleators show significant improvement in crystallization rate in both types of PP. In addition, Millad outperforms NJSTAR. The magnitude of the kinetic response is,however, different and both the nucleators appear to function better in ZN than in Metallocene PP. nucleated PP shows predominantly the form. The amount of the form is thermal history dependent and changes with supercooling ( T=T°mT c). Similar equilibrium melting temperature (T°m) in the nucleated and control PPs indicates the lack of any thermodynamic effect of the nucleator. All nucleated PPs show a much lower secondary nucleation rate constant, K g.

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Abstract  

The crystallization kinetics of branched and partially crosslinked poly(ethylene terephthalate) (PET), prepared using trimethyl trimellitate as branching agent was studied using DSC and WAXD. Crystallization rates were retarded with increasing branching agent content. Avrami equation was used in the isothermal crystallization, while for the non-isothermal process the Ozawa model was applied. Isothermal crystallization half-times increased with branching agent content and crystallization peak temperatures during cooling, decreased. WAXD showed big broadening and reduced degree of crystallinity compared to the neat polyester. Though, the crystal lattice parameters did not seem to alter, crystal size reduction was evidenced.

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The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se7Te3) have been studied by DTA measurements at different heating rates (α=5 deg·min−1, 10 deg·min−1, 15 deg·min−1 and 20 deg·min−1). From the heating rate dependence of the values ofT g,T c andT p, the glass transition activation energy (E t) and the crystallization activation energy (E c) have been obtained for different compositions of (Se7Te3)100−xInx (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence ofT g and crystallization kinetics are discussed in terms of the modification of the structure of the Se−Te system.

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Abstract  

The injection moulding of semi-crystalline thermoplastic polymers requires an exact knowledge of the thermodynamic data and of the crystallization kinetics. The behaviour of the polymer melt during rapid cooling in the mould determines, to a great extent, the quality and usability of a final product. Technical raw materials are often equipped with nucleating agents in order to obtain crystallization within the desired temperature range and at the required rate. The use of recycled material (regranulate) shows an analogous effect such as the addition of nucleating agents, i.e. crystallization begins at a higher temperature and a higher crystallization rate is detected compared to materials without added regranulate. Heat flux DSC was used to study the crystallization of polyamides, polyolefins and polyoxymethylene during cooling at various cooling rates. Although the temperature gradients and pressures which occur in the proceesing machine cannot be realised in DSC tests, the DSC results reproduce the direction of influence of the regranulate additive very clearly.

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Abstract  

The melting behavior and the crystallization kinetics of poly(butylene terephthalate/thiodiethylene terephthalate) copolymers were investigated by DSC technique. The multiple endotherms were influenced both by T c and composition. By applying the Hoffman—Weeks' method, T m 0 the of the copolymers was derived. The isothermal crystallization kinetics was analyzed according to the Avrami's treatment. Values of the exponent n close to 3 were obtained, independently of T c and composition. The introduction of thiodiethylene terephthalate units decreased the PBT crystallization rate. H m was correlated to c p for samples with different degree of crystallinity and the results were interpreted on the basis of the existence of an interphase.

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phase, the so called “rigid-amorphous phase” (RAP) or “inter-phase” between crystalline and amorphous layers has to be taken into consideration in these structures. In this view, herein the melting behavior and the isothermal crystallization kinetics of

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γ forms and dimensional distribution of spherulites of PP in composites. The investigation of crystallization kinetics on filler nucleating function, therefore, will give direct evidence of alteration of crystalline phase of PP in composites. The

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requirement of high cooling rates is fulfilled by this type of glass preparation. The crucial factor of preparation of these progressive materials in glassy form is the crystallization kinetics [ 3 – 8 ]. The crystallization kinetics of two binary

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