Memory effect in liquid polyolefine

Rault, J.; Robelin, E.

doi:10.1007/bf01064367

Cited by 20 publications

(15 citation statements)

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“…In connection with this, we refer to the work of Rault and Robelin [21], who showed that the long period in polyethylene is uniquely determined by the temperature of the melt before crystallization, for high enough cooling rates. In that case, the occurrence of conformational changes which lead to coil expansion during cooling is limited.…”

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confidence: 99%

The plastic deformation of ultra-high molecular weight polyethylene

1985

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Gel-spun filaments of different initial morphologies have been subjected to controlled drawing at elevated temperatures. The drawn samples have been examined by highresolution scanning electron microscopy. The deformation mechanism at temperatures up to 120 ~ C is very similar to crazing, especially in the case of unoriented gel-spun filaments. Filaments exhibiting a shish-kebab morphology offer the opportunity of examining the deformation of elementary fibrils in a quantitative way. The transformation of individual lamellae into fibrils is the initial deformation mode, which is followed by slip of fibrils at a later stage. This is concluded from a comparison of experimental data and model calculations of the maximum draw ratio. Drawing at 144 ~ C results in the formation of globular aggregates of lamellae, with a characteristic long period of 40 nm. This long period persists until all the globules have been converted, by micronecking, into aggregate fibrils of extended-chain character. On a molecular scale, the various processes can be described as the temperature-dependent flow behaviour of an entanglement network.

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confidence: 99%

The plastic deformation of ultra-high molecular weight polyethylene

1985

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“…Introduction. -We have reported recently [ 1,2,3] the correlations existing between the solid state and the melt of polyolefines. In quenched polyethylene fractions of molecular weight M M*, the long period L varies as the end-to-end distance ro of the coils in the liquid state, and is of the same order of magnitude.…”

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“…This fact is to be related to the independence of the growth rate with the molecular weight for high molecular weight materials [7] and to the independence of the density and surface energy with MN for materials having a number molecular weight higher than a critical value of the order of M * [8]. For (2) and Slutsker (1,3) analysis as a function of the square root of the molecular weight. effect shows that the polydispersity decreases somewhat the regularity of the lamella structure.…”

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Crystallization of quenched polyethylene. Part III : Mixtures of fractions

Rault

Robelin²

1982

J. Phys. France

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Abstract. 2014 The crystallization of mixtures of P.E. fractions quenched from the melt has been studied by SAXS, WAXS and DTA. The laws of variation of the long period with the weight and number average molecular weights are given. It is shown that the long period, L, of the semi-crystalline state is given by the weight average of the end-to-end distance rw of the coils in the liquid state before quenching. For mixtures containing high molecular weight M > M* = 105, the long chains behave like a series of segments of chains of molecular weight M* which crystallize independently. The crystallinity measured by WAXS and DTA varies with the molecular weight and its distribution as the linear crystallinity lc/L ~ lc/rw where lc is the crystalline lamella thickness and is independent of the molecular weight. The correlations emphasized in this paper between the solid and melt states of P.E. support the contention that the structure of lamellar semi-crystalline P.E. is not controlled by the phenomenon of secondary nucleation, but by the dimensions and the rigidity of the coils just before crystallization. The results reported in this paper show that the process of crystallization of short and long chains are different ; that would explain the differences observed in studies of the kinetics of crystallization, and in the morphology of the semicrystalline state when the molecular weight is increased.

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“…It appears from this work that the measurements by SAXS technique of the variation of the long period with the temperature and time of annealing of the melt is a valuable method in order to characterize the nature of the polymer chains [22].…”

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“…is measured. The relationship between this relaxation time and the molecular weight is given in reference [22]. 7.…”

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Crystallization of polymers. Part I : Polydispersed polymers quenched from the liquid state

et al. 1980

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Résumé. 2014 Nous avons mesuré les longues périodes de plusieurs polymères trempés à partir de l'état fondu. Nous donnons la relation entre la longue période mesurée dans la phase semi-cristalline et la rigidité de la chaîne dans l'état liquide juste avant la cristallisation. On montre que la mesure des longues périodes d'échantillons préala-blement recuits à l'état fondu, à différentes températures, et pendant des temps différents, nous permet de remonter à un temps de relaxation des pelottes dans le fondu.Abstract. 2014 The long spacing L of several crystalline polydispersed polymers quenched from the liquid state at various temperatures has been measured. We correlate the variations of the long period L with the variations of the dimension r0 > of the ideal coils in the melt just before the crystallization. The relationship between L and the rigidity C of the liquid chain is given. The annealing of the melt at different temperatures and for different times, and the subsequent crystallization allow us to measure the relaxation time of the coils in the liquid state.

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Memory effect in liquid polyolefine

Cited by 20 publications

References 1 publication

The plastic deformation of ultra-high molecular weight polyethylene

The plastic deformation of ultra-high molecular weight polyethylene

Crystallization of quenched polyethylene. Part III : Mixtures of fractions

Crystallization of polymers. Part I : Polydispersed polymers quenched from the liquid state

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