Evidence for isothermal lamellar thickening at and behind the growth front as polyethylene crystallizes from the melt

Maaty, M.I Abo el; Bassett, D. C.

doi:10.1016/j.polymer.2005.05.153

Cited by 24 publications

(18 citation statements)

References 13 publications

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“…There is increasing evidence that in the melt crystallization of polymers, the two processes occur together and the secondary process accounts for the thickening of the lamellae, since it is possible to observe directly the develop of overgrowths on the top surface of lamellae . Bassett et al from electron microscopy has observed that isothermal thickening of the lamellae develops at and behind the growth of polyethylene crystals from the melt and that the lamellar thickness tapers from the center of the spherulite to the outside circumference. They concluded that the thickening occurred alongside the growth of the lamellae and was the mechanism of secondary crystallization.…”

Section: Resultsmentioning

confidence: 99%

Secondary crystallization kinetics

Hay

2018

Polymer Crystallization

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The overlap between primary and secondary crystallization is the cause of the repeated observations of fractional constant n values, of no theoretical significance, in the analysis of polymer crystallization by the Avrami equation. The time dependence of the growth nuclei in primary and secondary crystallization are explained in terms of reptation and nucleation theory. A composite equation involving both primary and secondary crystallization has been derived to account for the development of the total fractional crystallinity, Xt, with time, Xt = Xp,∞ (1–exp (–Zptn).(1 + ks t1/2) and procedures derived for determining the rate constants, Zp and ks, and the limiting fractional crystallinity of the primary process, Xp,∞, such that they are not treated as adjustable parameters. The fit of the equation to experimental crystallinity/time data was within experimental error. This interpretation accounted for n values in excess of those expected for the crystallization mechanisms adopted in deriving the Avrami equation but values >3.5 and <4.0 are attributed to the presence of induction times due to homogeneous primary nucleation of the lamellae. Evidence is presented for the presence of two simultaneous processes, primary and secondary, in the crystallization of polymers, which occur with different mechanisms and are readily distinguished by their dependence on time: an exponential increase and an increase with the square root of time. Differences arise from the critical growth nuclei, whose growth is limited by chain entanglements in the case of primary and local reptation in the case of secondary.

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Section: Resultsmentioning

confidence: 99%

Secondary crystallization kinetics

Hay

2018

Polymer Crystallization

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“…If as has been suggested lamellae thickening occurs at edge and step dislocations [22], the reduced surface energy contribution to the energy of formation of the nucleus will decrease the critical thickness of the tertiary nuclei to…”

Section: Discussionmentioning

confidence: 96%

“…This does not have the characteristics of a nucleation controlled process but increases in rate with increasing temperature. Since it has been observed [22] that the thickness of lamellae at a fixed radius within a spherulite is constant and decreases as the radius increases secondary crystallization must develop as soon as the lamella develops from the melt and continue to develop with the square root of the lapsed time. This is also consistent with melting being observed to start from the boundary of the spherulites where the thinnest lamellae are present.…”

Section: Discussionmentioning

confidence: 99%

The kinetics of crystallization of poly(ε-caprolactone) measured by FTIR spectroscopy

Phillipson

Jenkins

Hay

2015

J Therm Anal Calorim

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The kinetics of crystallization of poly(ecaprolactone), PCL, have been measured by FTIR spectroscopy using the absorbance of the crystalline and amorphous phase carbonyl bands at 1725 and 1735 cm -1 , respectively, to determine the fractional crystallinity as a function of time and over the temperature range 43-47°C. A comparison was also made with DSC which was found to have limited sensitivity such that it could only measure the primary stage of the crystallization and not the secondary. Both primary and secondary crystallization could be measured by FTIR spectroscopy with sufficient accuracy to measure the kinetics of each and limited only by the length of time over which the measurements were made.

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“…One is that the thickness of the growth edge increases linearly with the logarithm of elapsed time, the other that there is thickening behind the growth front. The latter is restricted by adjacent lamellae in row structures leaving the first-formed lamellae lower melting than those formed later [39] in marked contrast to polyethylene spherulites, whose melting point is highest at the centre [40].…”

Section: Isothermal Lamellar Thickeningmentioning

confidence: 99%

Linear nucleation of polymers

Bassett

2006

Polymer

Self Cite

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The use of high-melting fibres as linear nuclei for quiescent polymeric melts is instrumental in providing the superior mechanical properties of polymeric self-composites. It also has inherent advantages in the elucidation of fundamental aspects of polymeric crystallization and selforganization, not least in allowing systematic microscopic studies of polymeric crystallization from nucleation through to the growth interface. This has demonstrated explicitly that lamellae develop in two distinct ways, for slower and faster growth, depending on whether fold packing has or has not time to order before the next molecular layer is added with only the former leading to banded growth in linear polyethylene. Other gains in understanding concern cellulation and morphological instability, internuclear interference, isothermal lamellar thickening and banded growth being a consequence of the partial relief of initial surface stress. q

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Evidence for isothermal lamellar thickening at and behind the growth front as polyethylene crystallizes from the melt

Cited by 24 publications

References 13 publications

Secondary crystallization kinetics

Secondary crystallization kinetics

The kinetics of crystallization of poly(ε-caprolactone) measured by FTIR spectroscopy

Linear nucleation of polymers

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