Recrystallization phenomena in high molecular weight compounds and their role in the dynamics of melting

Yagfarov, M.Sh.

doi:10.1016/0032-3950(82)90244-1

Cited by 8 publications

(3 citation statements)

References 8 publications

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“…The absence of the double peaks for 1.0 mm could be because the stress history is affected by crimping that may have distorted the lamellae shapes and/or the restraint that crimping/encapsulation provides to the expansion of the melted specimen during testing thereby compressing the polymer and forcing recrystallisation and perfection of the lamellae during DSC scan. The latter has been postulated by many investigators (e.g., Nealy et al 1970;Holdsworth and Jones 1971;Sweet and Bell 1972;Todoki and Kawaguchi 1977;Yagfarov 1982;Imai et al 1994;Qiu et al 1998). It can also be postulated that the effect of stress and thermal history did not affect the population of the lamellae sufficiently to cause the formation of the double peak and because the GMBs were made from the same resin they had identical DSC scans.…”

Section: Enthalpies Of Melting and Crystallisationmentioning

confidence: 90%

Effects of blown film process on initial properties of HPDE geomembranes of different thicknesses

Ewais¹,

Rowe²

2014

Geosynthetics International

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The differences in the properties of five high density polyethylene geomembranes (GMBs) of different thicknesses made by the same manufacturer from same GMB resin are investigated. The 1.0, 1.5, 2.0 and 2.4 mm thick GMBs investigated were manufactured during the same production run by changing the pulling speed of the GMB out of the extrusion die, such that, the pulling speed decreased with increasing thickness. There were no differences in the initial HP-OIT or Std-OIT values of the different GMBs. However, there were differences in the key mechanical and physical properties of the GMBs that cannot be simply explained by the increase in the amount of material due to increasing GMB thickness. These differences are explained by differences in the morphological structure of the GMBs arising from the different thermal and stress histories experienced during the manufacturing process. The effects of the differences in the morphological structure are discussed in terms of: the decrease in the relative differences between the stress-elongation curves in the machine and cross-machine directions as thickness increases; changes in the enthalpies of melting and crystallisation by differential scanning calorimetry with changing thickness; and the different stress crack resistance (SCR) for the GMBs. For example, thinner GMBs had a greater difference between the SCR in the machine and cross-machine direction. Increasing the GMB thickness from 1.5 to 2.4 mm resulted in increasing the SCR from , 800 to , 1100 h in the cross-machine direction and decreasing its SCR from , 4100 to , 2000 h in the machine direction. Thus, GMBs of different thickness manufactured from the same resin can be expected to have differences in their physical and mechanical properties that are dependent on the additional material but also the difference in the tension and cooling rate experienced during the manufacturing process.

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Section: Enthalpies Of Melting and Crystallisationmentioning

confidence: 90%

Effects of blown film process on initial properties of HPDE geomembranes of different thicknesses

Ewais¹,

Rowe²

2014

Geosynthetics International

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“…The solid-state properties of a semicrystalline polymer are complex functions of its thermal history. The complexity of this dependence partially results from the out-of-equilibrium, or metastable character, of semicrystalline structures . This metastability can be revealed in very simple experiments with heating−cooling cycles, performed below the main melting region of the polymer.…”

Section: Introductionmentioning

confidence: 99%

“…The complexity of this dependence partially results from the out-of-equilibrium, or metastable character, of semicrystalline structures. 1 This metastability can be revealed in very simple experiments with heating-cooling cycles, performed below the main melting region of the polymer. The changes in some structural parameters induced by this thermal cycling can be classified with respect to their reversibility.…”

Section: Introductionmentioning

confidence: 99%

Isothermal Growth and Reorganization upon Heating of a Single Poly(aryl−ether−ether−ketone) (PEEK) Spherulite, As Imaged by Atomic Force Microscopy

Ivanov

Jonas

1998

Macromolecules

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We have studied by atomic force microscopy (AFM, topographical imaging) the evolution of a single PEEK spherulite in a thin film during isothermal cold-crystallization and upon subsequent reheating to increasingly higher temperatures. To open the spherulitic microstructure, we added 30% w/w of an amorphous diluent (poly(ether−imide), PEI) serving as a marker. Small-angle X-ray scattering and dynamic mechanical analysis were used to check on bulk samples that similar structural evolutions are obtained when reheating cold-crystallized PEEK and a 70/30 PEEK/PEI blend. We then monitored at T c = 180 °C the isothermal growth of a single PEEK spherulite in a thin film of the PEEK/PEI blend and followed the growth and branching of individual PEEK fibrils, separated by channels of rejected PEI. Further, we examined the changes in semicrystalline morphology induced by subsequent reheating. The spatial locations of the fibrils (i.e., lamellar stacks) of this very spherulite were not modified up to an annealing temperature of about 300 °C. However, the surface of the fibrils became covered with numerous small protuberances (diameter: 50−200 nm) growing in size and in number as annealing temperature increased. We consider these images to be the first direct-space proof for the existence of a large-scale melting−recrystallization process occurring when reheating cold-crystallized PEEK.

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The origin of multiple melting endotherms in the thermal analysis of polymers

Nichols

Robertson

1992

J Polym Sci B Polym Phys

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Recrystallization phenomena in high molecular weight compounds and their role in the dynamics of melting

Cited by 8 publications

References 8 publications

Effects of blown film process on initial properties of HPDE geomembranes of different thicknesses

Effects of blown film process on initial properties of HPDE geomembranes of different thicknesses

Isothermal Growth and Reorganization upon Heating of a Single Poly(aryl−ether−ether−ketone) (PEEK) Spherulite, As Imaged by Atomic Force Microscopy

The origin of multiple melting endotherms in the thermal analysis of polymers

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