Melting and Crystallization Process of Polyethylene under High Pressure

Yasuniwa, Munehisa; Nakafuku, Chitoshi; Takemura, Tetuo

doi:10.1295/polymj.4.526

Cited by 96 publications

(36 citation statements)

References 12 publications

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“…The high pressure DT A curve of pure PE crystallized under high pressure (curve c) is somewhat different in shape from that of the sample crystallized at I atm. The peak and shoulder temperatures in curve c, 239.8°C and 246.1 °c, agree with T,, (ortho-hexa transition temperature) and Tm (melting temperature of the hexagonal phase), as determined by Bassett and Turner 7 and Y asuniwa et al 15 within experimental error. However, the peak temperature in curve b for the FCC sample is 234.2°C, which is about 2°c lower than the transition temperature T,, at 458 MPa determined by these two groups.…”

Section: Effects Of Blending On the High Pressure Phase Of Pesupporting

confidence: 84%

Effects of Blending on the Melting and Crystallization of Polyethylene ahd Polypropylene under High Pressure

Nakafuku

1983

Polym J

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ABSTRACT:The melting and crystallization behavior of polyethylene (PE) and polypropylene (PP) blends under high hydrostatic pressures up to 500 MPa was studied by differential thermal analysis (DTA). These high pressure crystallized blends were also investigated at I atm by DTA, Xray diffraction, and electron microscopy. The melting temperature Tm of PE in the blend under high pressure was determined from the peak temperature of a DTA curve of melting. The Tm versus pressure curve for PE in the blend shifts to the high pressure side with decreasing PE content. In the DT A curve of melting at I atm for a blend crystallized under 450 MPa, an endothermic peak that could not be assigned to the melting of folded PE chain crystals (FCC) appeared on the low temperature side of the melting peak for extended chain crystals (ECC), indicating that small PE crystals different from FCC were formed in the molten PP during crystallization. The X-ray diffraction pattern of this blend showed that no eutectic crystallization occurs even in the isothermal crystallization under high pressure. Electron microscopic observations of the fracture surface of the high pressure crystallized blend showed a clear boundary between the PE and PP domains, suggesting that no interdiffusion of the two polymers occurs.KEY WORDS Blend / Polyethylene / Polypropylene / Melting Crystallization/ High Pressure/ DTA / X-Ray / Electron Microscopy/ Many investigations on polyethylene (PE) and polypropylene (PP) blends have been carried out to improve the low temperature toughness or impact strength of PP. 1 Since it is fundamentally important to obtain information on the compatibility of polymer molecules in blends, many studies on the compatibility of PE and PP have also appeared. Some investigators 2 -4 made microscopic observations on the PE/PP boundary to see whether interdiffusion of the two polymers occurs to give an interphase layer. of a high pressure hexagonal phase was confirmed in the past decade. 7 -9 Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) were used to study thermal behavior of PE/PP blends. Some authors1-5 found in the DTA curve separate endothermic peaks corresponding to the melting of PE and PP.The melting and crystallization of pure polymers under high pressure have been studied by many investigators. 6 In the case of PE, it is widely known that extended chain crystals (ECC) are formed under high pressures above 300 MPa. The existence For PP, melt-crystallization produces the triclinic y form under high pressure, 10 -12 and the monoclinic a: form at 1 atm.The pressure dependence of the cloud point in blend polymer systems has been studied recently,13·14 mainly in regard to the compatibility of amorphous and crystalline polymers or amorphous and amorphous polymers.In this paper, the melting and crystallization of PE and PP in their blends under high pressure are reported. It is shown that the behavior of PE in the blend is different from that in the pure state. High pressure DT A measurements were ...

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Section: Effects Of Blending On the High Pressure Phase Of Pesupporting

confidence: 84%

Effects of Blending on the Melting and Crystallization of Polyethylene ahd Polypropylene under High Pressure

Nakafuku

1983

Polym J

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“…The corresponding DT A peak of normal molecular weight PE is also broad. 8 These results can be explained as follows by the use of entanglement concept. In the powder sample and the normal molecular weight PE, the entanglement density is very high.…”

Section: Resultsmentioning

confidence: 96%

“…Peaks due to the melting (or crystallization) of FCC, extended-chain crystal (ECC) and the high pressure phase in the subsequent DT A curves are denoted by "F", "E", and "H", respectively. Assignments of DT A peaks are based on ref 8 in which melting and crystallization processes of a bulk sample of normal molecular weight PE (Mw; 4.2 x 10 4 ) under high pressure have been studied. Since the high pressure DT A cell used in this work is an inner heating type, applied pressure changes slightly with temperature.…”

Section: Resultsmentioning

confidence: 99%

Melting and Crystallization of Solution Crystallized Ultra-High Molecular Weight Polyethylene under High Pressure

Yasuniwa

Yamaguchi

Nakamura

et al. 1990

Polym J

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“…This led Wunderlich [110] to conjecture that, under high pressures, PE crystals will form a new phase with high mobility along the chain direction. This new phase, later known as the hexagonal phase, was originally observed by Bassett and Turner [111,112] and Yasuniwa [113,114]. It is a columnar phase, which has a two-dimensional long-range order and a one-dimensional short-range order.…”

Section: Hikosaka's Sliding Diffusion Modelmentioning

confidence: 84%

A Review on Polymer Crystallization Theories

2016

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Abstract:It is the aim of this article to review the major theories of polymer crystallization since up to now we still have not completely comprehended the underlying mechanism in a unified framework. A lack of paradigm is an indicator of immaturity of the field itself; thus, the fundamental issue of polymer crystallization remains unsolved. This paper provides an understanding of the basic hypothesis, as well as relevant physical implications and consequences of each theory without too much bias. We try to present the essential aspects of the major theories, and intuitive physical arguments over rigorously mathematical calculations are highlighted. In addition, a detailed comparison of various theories will be made in a logical and self-contained fashion. Our personal view of the existing theories is presented as well, aiming to inspire further open discussions. We expect that new theories based on the framework of kinetics with direct consideration of long-range multi-body correlation will help solve the remaining problems in the field of polymer crystallization.

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Melting and Crystallization Process of Polyethylene under High Pressure

Cited by 96 publications

References 12 publications

Effects of Blending on the Melting and Crystallization of Polyethylene ahd Polypropylene under High Pressure

Effects of Blending on the Melting and Crystallization of Polyethylene ahd Polypropylene under High Pressure

Melting and Crystallization of Solution Crystallized Ultra-High Molecular Weight Polyethylene under High Pressure

A Review on Polymer Crystallization Theories

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