Effect of molecular weight on the rate of crystallization of polyethylene fractions at high undercooling

Barrales‐Rienda, J. M.; Fatou, J. M. G.

doi:10.1016/0032-3861(72)90062-6

Cited by 24 publications

(14 citation statements)

References 15 publications

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“…Spherulite growth rate measurement and its variation with molecular weight follow the pattern of growth rate against log molecular weight and the half‐life of crystallization plots, as discussed in the previous section. This observation is similar to those already reported for other polymeric systems by Barrels et al12–16 and thus is not discussed further herein.…”

Section: Resultssupporting

confidence: 92%

“…This represents a primary process of spherulitic growth for which n = 3 and a secondary process of annealing or interlamella growth occurs with n values between 1.0 and 1.8 11, 12. An Avrami value of 1.8 is characteristic of a crystallization process with one‐dimensional growth, linear growth, and heterogeneous nucleation 13, 14. This suggests that molecular weight fractionation or rejection in broad distribution samples and impurity segregation in low stereoregular samples could result in low n values.…”

Section: Resultsmentioning

confidence: 99%

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Crystallization regimes and reptation in polypropylene molecular weight fractions

Ibhadon

1999

J. Appl. Polym. Sci.

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Crystal growth rate data based on the kinetic nucleation theory of chain folding and the effect of reptation, have been used to predict the rate of crystal growth at moderate to high supercoolings in iPP molecular weight fractions. Growth rate data obtained for the fractions seem to be in agreement with the theoretical predictions of the regime theory. However, an extension of the gambler ruin treatment to the iPP data has not been successful with regard to the dominant morphology in regime II. The variable cluster model suggested as the morphology for polyethylene in regime II does not appear to be evident from this study. The effect of polydispersity, molecular weight, and tacticity on the crystallization behavior of iPP fractions have also been studied and correlated with the structure of polymer samples investigated.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Crystallization regimes and reptation in polypropylene molecular weight fractions

Ibhadon

1999

J. Appl. Polym. Sci.

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“…It is worthy to noticing that when the branches content is higher than 12%, L and Lc remains essentially unchanged. For copolymers with low comonomer contents, the backbone chain length between branches is an important parameter which has a great influence on crystallization [34][35][36]. In the case of the copolymers with large amount of octene branches, the influence of chain length on crystallization is likely to be weak because the increased friction which reduced mobility and the flexibility of sequences for crystallization has reached a maximum to a certain degree.…”

Section: Resultsmentioning

confidence: 98%

Shear effects on crystallization behavior of poly(ethylene-co-octene) copolymers

Wen

et al. 2011

J Polym Res

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Crystallization behavior of sheared polymer melts of a series of poly(ethylene-co-octene)s with different octene content was investigated by different scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and synchrotron small-angle X-ray scattering (SR-SAXS) techniques. The DSC results indicated that the hexyl branches content had dramatic effects on the thermal properties and crystallinity of polyethylene. It was also found that shear had no obvious effects on the size of either crystallite or lamellae. However, both crystallite and lamellae were oriented by shearing, especially for the lamellae. All obtained results indicate that the initial states of the polymer melt play an important role in affecting the crystallization behaviors. The difference of the shear-induced crystalline structure evolution and the orientation between crystallite and lamellae support the preordered mesomorphic phase of flexible polymer crystallization process proposed by Strobl.

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“…In reality, the relationship between the surface free energy (σ e , proportional to ΔG*) of crystals and the molecular weight has been well established. 33 In most cases, the σ e is reported to increase with the increase in molecular weight of polymers. 38 A transition of chain morphology in crystallites from extended state to folded state can be observed with the increase in the molecular weight.…”

Section: Introductionmentioning

confidence: 99%

“…31 The nature of the nucleation efficiency is related to the free energy for a stable nucleus formation (ΔG*) and the energy of transport term (E D ) in the solid−liquid interface. 33 Therefore, the influence of molecular weight on the crystallization rate can be actually interpreted as the effect of molecular weight on ΔG* and E D . In reality, the relationship between the surface free energy (σ e , proportional to ΔG*) of crystals and the molecular weight has been well established.…”

Section: Introductionmentioning

confidence: 99%

Ratio between Random Coil Size and Crystalline Spacing Determines Mesophase Formation in Quenched Isotactic Polypropylene

Lu,

Lyu,

Men

2023

Macromolecules

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The relationship between the molecular weight of isotactic polypropylene (iPP) and mesophase formation during quenching was successfully established. Surprisingly, a unique number-average molecular weight (M n ) dependent mesophase formation was identified that iPP with a lower or higher M n preferred to form a pure mesophase but the ones with moderate M n failed in inducing a high fraction mesophase when the same quenching processes were applied. It was interpreted by the effect of coupling between the sizes of random coils and the crystalline spacing on the crystallization rate, which further affected the formation of mesophase. The M n represents the largest population of units possessing the same molecular weight in the system. Therefore, the crystallization rate was mainly controlled by the molecular chains with similar length of the largest fraction. A comparison between the radius of gyration of random coils in the melt and the final spacing of crystals induced during quenching suggests that the molecular chains in iPP with a lower M n needed to be disentangled before crystallization and the ones in iPP with a higher M n must be folded forth and back in crystallites during growth stage. Both cases led to a slow crystallization rate, benefiting the mesophase formation during quenching.

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Effect of molecular weight on the rate of crystallization of polyethylene fractions at high undercooling

Cited by 24 publications

References 15 publications

Crystallization regimes and reptation in polypropylene molecular weight fractions

Crystallization regimes and reptation in polypropylene molecular weight fractions

Shear effects on crystallization behavior of poly(ethylene-co-octene) copolymers

Ratio between Random Coil Size and Crystalline Spacing Determines Mesophase Formation in Quenched Isotactic Polypropylene

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