Origin of the long period and crystallinity in quenched semicrystalline polymers. 1

Robelin-Souffaché, E.; Rault, J.

doi:10.1021/ma00199a015

Cited by 74 publications

(62 citation statements)

References 22 publications

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“…the distance of the crystal lamellae, varies. The data confirm a suggestion by Rault [45] that L is proportional to the chain diameter in the melt, L R ∼ √ M . The invariant crystallinity for changing length scales of the structure means that the amorphous regions always end up at the same entanglement density, which intuitively makes sense.…”

Section: Two Main Open Issues: Crystallinities and Crystallite Textursupporting

confidence: 90%

From the melt via mesomorphic and granular crystalline layers to lamellar crystallites: A major route followed in polymer crystallization?

Strobl

2000

The European Physical Journal E

481

186

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Based on broad and detailed evidence from a large variety of experiments on several polymer systems carried out by other authors and ourselves, a novel concept for understanding the crystallization of polymers from the melt is developed. The experiments generally indicate that the formation and growth of the lamellar crystallites is a multi-step process passing over intermediate states. We suggest a specific route which is compatible with the observations. It is proposed that the initial step is always the creation of a mesomorphic layer which spontaneously thickens, up to a critical value, where it solidifies through a cooperative structural transition. The transition produces a granular crystalline layer, which transforms in the last step into homogeneous lamellar crystallites. The model leads to predictions about the temperature dependencies of the crystal thickness and the growth rate which are at variance with conventional views but in agreement with findings in recent experiments.

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Section: Two Main Open Issues: Crystallinities and Crystallite Textursupporting

confidence: 90%

From the melt via mesomorphic and granular crystalline layers to lamellar crystallites: A major route followed in polymer crystallization?

Strobl

2000

The European Physical Journal E

481

186

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“…If tt is greater than the mean growth time t c , the crystallization is limited by the distortion of the amorphous phase. Using the model proposed by Rault et al 2,23 we are suggesting that the crystallization of the LDPE in the 50/50 HDPE/LDPE blends studied in our work is strongly inhibited by the previous crystallization of the HDPE. This crystallization limits the distortion of the amorphous phase leaving the LDPE component to maintain the entanglements.…”

Section: Characterization Of Samplessupporting

confidence: 59%

Photoluminescence study of β relaxation of polyethylene blends

Martins-Franchetti

Atvars

1993

J of Applied Polymer Sci

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SYNOPSISSecondary p relaxation of polyethylene blends ( 5 0 / 5 0 HDPE/LDPE) were studied by photoluminescence of anthracene molecules dissolved in the polymer bulk. The temperature of the p relaxation has been determined as To = -40°C by the dependence of the ratio of vibronic components of the fluorescence band on the temperature. The molecular mechanism of this relaxation has been discussed considering the possibility of the energy migration involving anthracene molecules in the singlet electronic excited and ground states. IN TRO DU CTI 0 NThe studies of high density polyethylene/low density polyethylene ( HDPE/LDPE) blends are relevant from both the fundamental and technological point of view because the applications of these materials are strongly dependent on their morphology. The morphology is dependent on the chemical structure of the polyethylene, on the crystallization processes, and in the case of blends, on the composition and types of the polymers. In general this research field is related to the studies of morphology that try to establish the conditions of preparation of the blends involving co-crystallization or segregation between the phases. Rault et a1.l.' studied 50/50 HDPE/LDPE blends by small-angle X-ray scattering (SAXS) and described the scattering in terms of a paracrystalline model having a bimodal distribution of the crystalline phases. They concluded that the phase segregation, the morphology, and the crystalline index of each phase are controlled by the weight-average dimension of the coils in the melted state before the crystallization and that the entangled amorphous chains take an important role on the interlamellae crystallization. The entanglements in the melted * To whom correspondence should be addressed. Other studies of crystallization of 50/50 HDPE/ LDPE blends by SAXS suggested that the HDPE component in the blend dominates the process during the early stage and the kinetic process is hardly affected by the LDPE component. The LDPE would separate out to form an amorphous gap between the lamella stacking formed mainly by the HDPE component. These components are crystallized separately on an interlamellar scale and no co-crystallization was obtained. Segregation of the homopolymers is obtained in the case of 50/50 blend upon slow cooling, isothermal crystallization at two successive temperatures ( 110 and 100°C), and in rapidly cooled ( llO°C/min) preparation form^.^^^ From quite general phase diagrams Keller et a1.5y6 established some polymer properties of the polyethylene that could produce greater phase separation: higher branch content in polyethylene chains, higher molecular weight of linear polyethylene, and broader molecular mass grades of branched or linear polyethylenes.Although there are many studies about the morphology of the polyethylene blends, there are only a few works about relaxation processes in these blends. Even for polyethylene the assignments for the a, p, and y relaxations and the glass-transition temperature are c o n t r~v e r s i a l .~-~~ In this ...

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“…Considering for the PE lamellae, an average length from 0.5 to 1 mm as proposed by Michler and Godehardt [33], an average thickness of 20 nm [32] and a reasonably estimated width about 10 times the thickness, the calculated modulus overestimates largely the material modulus. As it has been discussed in Section 2, lamella shape ratios have not been defined precisely by experiments.…”

Section: Resultsmentioning

confidence: 83%

“…The lamella thickness can be measured by small angle Xray scattering (SAXS). The comparison of the crystalline layer thicknesses of several polymers [32] has shown that PE lamellae are thicker than PP ones. In this work, the PP lamellae thickness is about 10 nm while the lamella thickness for HDPE is closer to 20 nm.…”

Section: Morphologymentioning

confidence: 99%