Melting Kinetics of Nascent Poly(tetrafluoroethylene) Powder

Christakopoulos, Fotis; Troisi, EM Enrico; Tervoort, Theo A.

doi:10.3390/polym12040791

Cited by 9 publications

(3 citation statements)

References 41 publications

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“…Isoconversional analysis evaluates reactions at the same extent of conversion, α, from data acquired through calorimetric experiments with different temperature programs. This is achieved in a model‐free way, without assuming a reaction model beforehand 24,38–41 . In the case of crystallization of polymers this can be achieved by conducting non‐isothermal, constant cooling rate experiments with a different cooling program (cooling rate, β) between each experiment.…”

Section: Methodsmentioning

confidence: 99%

“…This is achieved in a model-free way, without assuming a reaction model beforehand. 24,[38][39][40][41] In the case of crystallization of polymers this can be achieved by conducting non-isothermal, constant cooling rate experiments with a different cooling program (cooling rate, β) between each experiment. Isoconversional kinetic analysis evaluates a dependence of the apparent activation energy, E α , on conversion or temperature of thermally stimulated processes.…”

Section: Isoconversional Analysismentioning

confidence: 99%

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Gas‐phase polymerization of ultra‐high molecular weight polyethylene with decreased entanglement density

Rosario

Christakopoulos

Tervoort

et al. 2023

Journal of Polymer Science

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It is well known that ultra‐high molecular weight polyethylene (UHMWPE) is a polymer with long chains and very high molecular weight that poses difficulties in terms of processability due to the presence of chain entanglements. In many cases is thus necessary to treat the material in different ways after the polymerization to minimize the amount of entanglements and improve the processability. Based on observations that the use of inert condensing agents (ICA) had a noticeable impact on molecular weight and crystallinity, it was decided to develop a gas‐phase polymerization process with addition of ICA for UHMWPE with a high fraction of disentangled chains. For the optimization of this process, the comparison with slurry is important for the understanding the improvement. Thus, a clear difference between slurry and gas phase is observed in terms of crystallinity and the lamellar thickness of the crystals, molecular weight and entanglements. Characterization techniques are developed to measure the properties of the reactor powder and understand the impact of the alkanes in situ. Using solid‐state drawability, the entanglement degree of the reactor powder is analyzed. From the small‐angle x‐ray scattering and wide‐angle x‐ray scattering techniques, it is possible to find a correlation of entanglements and lamellar thickness. Moreover, crystallization kinetics measurements of the polymer in presence of ICA constitutes a powerful method to explain the phenomena of entanglement and crystal formation.

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Section: Methodsmentioning

confidence: 99%

Section: Isoconversional Analysismentioning

confidence: 99%

Gas‐phase polymerization of ultra‐high molecular weight polyethylene with decreased entanglement density

Rosario

Christakopoulos

Tervoort

et al. 2023

Journal of Polymer Science

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“…Toda et al [20,60] proposed a nucleation model for polymer fusion which fusion starts with melting the cylindrical cores. However, Friedman's isoconversional model is powerful to study the fusion kinetics and evaluate a E under superheating [61] . In those situations, a decrease in s of the fusions upon temperature increase is expected [62] .…”

Section: Activation Energy ( a E ) -First Fusionmentioning

confidence: 99%

Crystallization and fusion kinetics of Poly(butylene terephthalate)/Titanium Dioxide

et al. 2023

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In this paper, the crystallization, fusion, and activation energy (Ea) of PBT/TiO 2 were thoroughly evaluated using DSC. Increasing the rates shifted the peaks of melt crystallization to lower temperatures while the fusions were almost unaffected. TiO 2 hindered the melt crystallization of PBT and lower crystallization rates, i.e., CMAX and K' were acquired, in general, the crystallinity degree (Xc) was 4% higher in PBT/TiO 2 which is in the marginal error. Pseudo-Avrami and Mo models were applied to evaluate the melt crystallization kinetics; both fitted the melt crystallization quite well; deviations were observed at the beginning and the crystallization end most due to the nucleation and spherulites impingement during the secondary crystallization. Ea was evaluated using the Friedman model, considering the values of Ea less energy has to be removed from PBT/TiO 2 when compared to PBT, specifically at 1% of TiO 2 .

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Thickening of Isolated and Multilayered Crystals and Its Implications on Melting Kinetics; The Role of Inter‐ and intra‐crystalline Regions

Rastogi¹,

Romano²

2022

Macromolecular Engineering

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Melting of crystalline region in a semicrystalline polymer is a complex phenomenon, which is strongly influenced by the topological constraints present in the noncrystalline region. In an isolated crystal, detachment of chain stems from its crystalline surface can occur in succession or in cluster. The difference in detachment of the chain stems strongly depends on the topological constraints of the chain segments on the fold surface. Successive detachment of the chain stems, observed on melting of crystals while annealing at the onset of the peak melting temperature, appears to occur when chain folding is facilitated by adjacent reentry. In the annealing process, no crystal thickening in isolated crystals, having molar mass sufficiently high to suppress the effect of chain ends, is observed, as the crystal thickening will require cooperative chain mobility of the chain stems within the crystal linked by the chain segments in the fold. Retrospectively, because of the possibility of successive chain detachment, melting temperature decreases with decreasing heating rate, contradicting the assumption of increase in melting temperature on annealing. In the isolated crystals, having complex reentrant chains on the fold surface, successive detachment of chains from a crystal surface is frustrated, and cluster melting is promoted. Such crystals, though isolated, do not show melting on annealing. However, in contrast to the isolated crystals, in multilayered crystals instead of melting on annealing at the onset melting temperature, crystal thickening will occur that would cause increase in the melting temperature. This thickening process is facilitated, as it requires the localized motion only rather than the cooperative motion of the chain stems within the crystals. Thickening in the isolated crystals, if observed during polymerization or due to the appearance of a transient mobile phase, is referred as the primary thickening, whereas the crystal thickening in the multilayered crystals is called the secondary thickening.

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Melting Kinetics of Nascent Poly(tetrafluoroethylene) Powder

Cited by 9 publications

References 41 publications

Gas‐phase polymerization of ultra‐high molecular weight polyethylene with decreased entanglement density

Gas‐phase polymerization of ultra‐high molecular weight polyethylene with decreased entanglement density

Crystallization and fusion kinetics of Poly(butylene terephthalate)/Titanium Dioxide

Thickening of Isolated and Multilayered Crystals and Its Implications on Melting Kinetics; The Role of Inter‐ and intra‐crystalline Regions

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