Melting Behavior of Poly(ethylene terephthalate) Crystallized and Annealed under Elevated Pressure

Hiramatsu, Nobuyasu; Hirakawa, Susumu

doi:10.1295/polymj.12.105

Cited by 34 publications

(30 citation statements)

References 17 publications

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“…12 The heating and cooling rates were precisely controlled by a pro- The powder sample was prepared in the form of a rod (ca. 1.2mm in diameter and 10 mm in length) by compressing the original powder sample in a piston cylinder type cell at room temperature.…”

Section: Experiments Almentioning

confidence: 99%

Molecular Weight Effect on the High Pressure Crystallization of Polyethylene

Yasuniwa

Tsubakihara

Nakafuku

1988

Polym J

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ABSTRACT:The molecular weight effect on the morphology of high molecular weight polyethylenes (HMW-PE, 2.2 x 10 5 and 6.9 x 10 5 ) crystallized at 590 MPa was studied by scanning electron microscopy. The external shape of the band of the HMW-PE is as that of the medium molecular weight PE (MMW-PE); however with increasing molecular weight the band comes to be comprized of long fibrils. It is suggested that the band of HMW-PE is formed by the parallel arrangement of fibrils. Thermal analysis on the pressure-crystallized PEs in a molecular weight range from 4 x 10 3 to 2.5 x 10 6 was also performed, and the molecular weight dependence of the melting temperature and heat of fusion was obtained. The heat of fusion of the pressure-crystallized sample decreases linearly with logarithm of molecular weight. The melting temperature increases linearly with logarithm of molecular weight in a molecular weight region lower than about 10 5 • Above 10 5 , the melting temperature for the pressure-crystallized powder sample is higher than about 146°C and increases slightly with molecular weight. This considerable increase of the melting temperature is caused by the superheating effect.KEY WORDS Polyethylene / Molecular Weight / High Pressure Crystallization / Melting / Morphology / Fibril / SEM / DSC / High pressure crystallization of polyethylene (PE) has been studied in the past two decades. The growth of the so-called "extendedchain crystal" (ECC) and the formation of the band for a pressure-crystallized medium molecular weight PE (MMW-PE) have been reported. 1 -5 It seems to be commonly accepted that the band is formed by the growth of ECC. The detailed formation mechanism of the band for MMW-PE has been suggested by Asai et al. 6 • 7 crystallized as-polymerized (powder) and bulk samples, respectively. Further, it has been suggested that the band of UHMW-PE is composed of fibrils with parallel arrangement, and that the basic structure of the band is formed in the molten state.In contrast, a strikingly different morphology has been reported recently by Yasuniwa and Nakafuku 8 for a pressurecrystallized ultra-high molecular weight PE (UHMW-PE). Fibrous bands of long fibrils and bands of thick fibrils closely spaced were observed by electron microscopy for pressureThese studies indicate that a drastic change of the morphology of the band occurs in the intermediate region between UHMW and MMW, i.e., high molecular weight (HMW) region, and that the formation mechanism of the band changes in the HMW region. The morphology and the band formation mechanism for the pressure-crystallized PE in the HMW region are the points of emphasis in the present investigation.It is reasonable to consider that the lamellar thickness and crystallinity, which can be esti-1075

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Section: Experiments Almentioning

confidence: 99%

Molecular Weight Effect on the High Pressure Crystallization of Polyethylene

Yasuniwa

Tsubakihara

Nakafuku

1988

Polym J

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“…16 Since this apparatus had a heater set inside the high pressure vessel, the sample could be heated up to 400°C and rapidly cooled (about 100°C min -I). The temperature was precisely controlled within ± 0.5°C.…”

Section: ( 2) Experimental Apparatus and Proceduresmentioning

confidence: 99%

Melting and Transformation Behavior of γ Form Nylon 6 under High Pressure

Hiramatsu

Hirakawa

1982

Polym J

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ABSTRACT:Thermal behavior under high pressure of the y form nylon 6 obtained by iodine treatment was investigated by means of a high pressure differential thermal analysis. The crystalline structures which resulted in the endo-and exo-thermic peaks in the thermogram were examined with the wide angle X-ray diffraction measurement. Under relatively low pressure kg em-2 ), two endothermic peaks were found. With increasing pressure, the lower temperature side endotherm due to the melting of the y form crystal became small, while the higher one due to the melting of the converted rx form crystal became large. Under high pressure (above 2000 kg em -z) an endotherm due to the melting of the converted rx form crystal and an exotherm were observed. This exotherm is attributed to they to rx form transformation. In this case, the transformation occurred without melting the y form crystal, in contrast to the situation at atmospheric pressure. The pressure dependences of the melting peak temperatures of the rx form and they form were almost the same and equal to !Soc per 1000 kg em-2 •

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“…8 -10 The melting point, which is used as criterion for some polymers' extended-chain crystals, was also applied on PET by some researchers. 11 The PET samples with very high melting point [12][13][14] [up to 575 K, which was higher than the equilibrium melting point (553 K) of PET suggested by Wunderlich 15 ] were also obtained. But the higher melting point could not be the direct evidence of the formation of PET extended-chain crystals.…”

Section: Introductionmentioning

confidence: 86%