Non‐isothermal crystallization kinetics of PET

Piccarolo, S.; Brucato, V.; Kiflie, Zebene

doi:10.1002/pen.11254

Cited by 35 publications

(58 citation statements)

References 26 publications

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“…Such cooling rates are orders of magnitude lower than those experienced by the material during polymer processing. In recent years, our group undertook quantitative studies of crystallization under high cooling rates (continuous cooling transformation, CCT 14 ) with reference to different materials, such as poly(ethylene terephthalate) (PET) 15 and polyamide6 (PA6). 16,17 Furthermore, the crystalline structure of iPP quenched from the melt is affected not only by cooling rate, or generally by processing conditions, but also by molecular parameters like molecular mass (M w ) and molecular mass distribution (MWD).…”

Section: Introductionmentioning

confidence: 99%

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

Carrubba

Piccarolo

Brucato

2007

J of Applied Polymer Sci

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An analysis of the crystallization kinetics of different grades of isotactic polypropylene (iPP) is here presented. To describe the crystallization kinetics as a function of molecular and operating parameters, the methodological path followed was the preparation of quenched samples of known cooling histories, calorimetric crystallization isotherms tests, differential scanning calorimetry cooling ramps, wide angle X-ray diffraction (WAXD) measurements, and density determination. The WAXD analysis performed on the quenched iPP samples confirmed that during the fast cooling at least a crystalline structure and a mesomorphic one form. The diffractograms were analyzed by a deconvolution procedure, to identify the relationship between the cooling history and the distribution of the crystalline phases. The whole body of results (including calorimetric ones) provides a wide basis for the identification of a crystallization model suitable to describe solidification in polymer-processing operations, based on the KolmogoroffAvrami-Evans nonisothermal approach. The kinetic parameters, determined for all the materials, are discussed, highlighting the effect of molecular parameters on the crystallization kinetics: molecular mass and distribution, tacticity, nucleating agents, and ethylene units content.

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Section: Introductionmentioning

confidence: 99%

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

Carrubba

Piccarolo

Brucato

2007

J of Applied Polymer Sci

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“…In contrast to the peculiar cooling rate dependence of the density, MH monotonously decreases as a function of the cooling rate, as is common for all the polymers investigated so far 44,45 [cf. Fig.…”

Section: Resultsmentioning

confidence: 98%

“…[44][45][46][47] By plotting MH as a function of the density, one gets the data reported in Figure 6(c). There are two branches clearly visible, which are related to the relative amounts of the phases formed: in the upper part, MH increases with the density because of the increase in the dense b-phase content, whereas in the lower part, MH decreases with increasing density, and this observation should be related to the parallel decrease in the amount of the low-density a phase (in the absence of the b phase).…”

Section: Resultsmentioning

confidence: 99%

“…It is worth noticing, however, that the overall span of MH from the maximum, occurring at low cooling rates, to the minimum, observed at high cooling rates, is quite small (30 MPa) with respect to the typical MH drop for other semicrystalline polymers spanning even smaller crystalline contents in the same cooling rate range. [44][45][46][47] Three regions can be distinguished in Figure 6(a): for cooling rates below 1 8C/s, there is a significant drop in MH with a remarkable dependence of the mechanical response on the cooling rate; in an intermediate zone (from ca. 1 to ca.…”

Section: Resultsmentioning

confidence: 99%

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Solidification of syndiotactic polystyrene by a continuous cooling transformation approach

Carrubba

Piccarolo

Brucato

2007

J Polym Sci B Polym Phys

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Syndiotactic polystyrene (sPS) was solidified from the melt under drastic conditions according to a continuous cooling transformation methodology developed by the authors, which covered a cooling rate range spanning from approximately 0.03 to 3000 8C/s. The samples produced, structurally homogeneous across both their thickness and surface, were analyzed by macroscopic methods, such as density, wide-angle X-ray diffraction (WAXD), and microhardness (MH) measurements. The density was strictly related to the phase content, as confirmed by WAXD deconvolution. The peculiar behavior encountered (the density first decreasing and then increasing with the cooling rate) was attributed to the singularity of the phases formed in sPS; that is, one of the crystalline phases (a) was less dense than the amorphous phase, and the latter, in turn, was less dense than the other crystalline phase (b). With an increasing cooling rate, the thermodynamically stable phase (b) disappeared first, and it was followed by the a phase. On the other hand, the MH values remarkably depended on the amount of the b phase, the a-phase content influencing the mechanical properties only to a minor extent. The behavior of the crystallization kinetics was described through a modified multiphase Kolmogoroff-Avrami-Evans model for nonisothermal crystallization.

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“…18 The formation of metastable phases normally takes place in a cooling rate range not achievable using the conventional techniques mentioned above; nevertheless, it is worth recalling that the behavior of a given semicrystalline polymer is greatly influenced by the relative amount of the constitutive phases. From this general background, the lack of literature data in this particular field of investigation should not be surprising, due to the complexity of the subject involved.…”

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The continuous cooling transformation (CCT) as a flexible tool to investigate polymer crystallization under processing conditions

et al. 2009

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An experimental route for investigating polymer crystallization over a wide range of cooling rates (from 0.01 to 1000◦C/s) and pressures (from 0.1 to 40 MPa) is illustrated, using a method that recalls the approach adopted in metallurgy for studying structure development in metals. Two types of experimental setup were used, namely an apparatus for fast cooling of thin films (100–200 μm thick) at various cooling rates under atmospheric pressure and a device (based on a on-purpose modified injection molding machine) for quenching massive samples (about 1–2 cm3) under hydrostatic pressure fields. In both cases, ex situ characterization experiments were carried out to probe the resulting structure, using techniques such as density measurements and wide-angle x-ray diffraction (WAXD) patterns. The cooling mechanism and temperature distribution across the sample thickness were analyzed. Results show that the final structure is determined only by the imposed thermal history and pressure. Experimental results for isotactic polypropylene (iPP), poly(ethylene terephthalate) (PET), polyamide 6 (PA6), and syndiotactic polystyrene (sPS) are reported, showing the reliability of this experimental approach to assess not only quantitative information but also a qualitative description of the crystallization behavior of different classes of semicrystalline polymers. The present study gives an opportunity to evaluate how the combined effect of the cooling rate and pressure influences the crystallization kinetics for various classes of polymer of commercial interest. An increase in the cooling rate translates into a decrease in crystallinity and density, which both experience a sudden drop around the specific “crystallizability” (or “critical cooling rate”) of the material examined. The exception is sPS where competition among the various crystalline modifications determines a minimum in the plot of density vs. cooling rate. As for the effect of pressure, iPP exhibits a “negative dependence” of crystallization kinetics upon pressure, with a decrease of density and degree of crystallinity with increasing pressure, owing to kinetic constraints. PA6 and PET, on the other hand, due to thermodynamic factors resulting in an increase in Tm with pressure, exhibits a “positive dependence” of crystallization kinetics upon pressure. Finally, recent original results concerning sPS have shown that the minimum in the density vs. cooling rate curve shifts toward larger cooling rates upon increasing pressure

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Non‐isothermal crystallization kinetics of PET

Cited by 35 publications

References 26 publications

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

Crystallization kinetics of iPP: Influence of operating conditions and molecular parameters

Solidification of syndiotactic polystyrene by a continuous cooling transformation approach

The continuous cooling transformation (CCT) as a flexible tool to investigate polymer crystallization under processing conditions

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