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Li, Liangbin; Pong, Li; Huang, Rui; Wang, Fan; Yunwei, Lü; Hai, Huang

doi:10.1023/a:1006642700833

Cited by 11 publications

(2 citation statements)

References 6 publications

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“…Let us now discuss the effect of high molding pressure on the formation of thick crystalline lamellae, which is frequently addressed as “formation of extended chain lamellae”. ,− Table shows the volume fraction V p,c of uncorrelated, thick lamellar particles with respect to the total volume occupied by the crystalline phase at 30 °C as computed from eq 3. The high molecular weight grades M5 and M6 exhibit the frequently reported increase of the fraction of thick, uncorrelated lamellae as a function of increasing pressure.…”

Section: Usaxs Results and Discussionmentioning

confidence: 99%

Nanostructure Evolution of Isotropic High-Pressure Injection-Molded UHMWPE during Heating

et al. 2002

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Ultrahigh molecular weight polyethylene (UHMWPE) is injection molded under high pressure and studied by ultra-small-angle X-ray scattering (USAXS) during melting in a time-resolved synchrotron radiation experiment. Results concerning melting and recrystallization of crystalline lamellae are compared to data obtained by differential scanning calorimetry (DSC). USAXS analysis reveals a coupled process of melting and crystallization which is not accompanied by external heat flow. Nine isotropic samples differing in molecular weight and molding pressure are heated at a rate of 5 °C/min. 2D USAXS images integrate over temperature intervals between 3 and 7 °C. The materials are considered two-phase semicrystalline polymers. Scattering curves obtained by azimuthal averaging are transformed to interface distribution functions (IDF) which are perfectly fitted by a nanostructural model comprising an ensemble of thick, uncorrelated layers (50 nm thickness) and stacks of short-range correlated crystalline lamellae (20 nm). Crystalline layers are identified from their narrower layer thickness distribution and their melting behavior. After the scattering effect of amorphous layers is eliminated, a composite crystallite thickness distribution is obtained. Its variation is studied as a function of temperature, molecular mass and molding pressure. In DSC thermograms samples prepared at high pressure exhibit a single strong melting peak, whereas the other samples show an additional melting peak at lower temperature. This might lead to the conclusion that the high-pressure samples predominantly contain extended chain crystals. USAXS shows that high-pressure materials contain considerable amounts of imperfect thin crystal lamellae that melt at lower temperature, while thick lamellae are formed. With low-pressure samples, this coupled process of nanostructure transformation during annealing is found to be negligible.

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Section: Usaxs Results and Discussionmentioning

confidence: 99%

Nanostructure Evolution of Isotropic High-Pressure Injection-Molded UHMWPE during Heating

et al. 2002

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“…Although some investigations of the high-pressure crystallization behaviour of PET have been reported, the results have discrepancies [9][10][11]. Recently we have reported that extended-chain crystals of PET with thickness up to 17 µm could be obtained through a high-pressure crystallization process [12][13][14][15][16] could suggest that high pressure may promote the crystallization rate. However, no direct experimental evidence has confirmed this view or concerned the effect of pressure on the process of thickening of PET crystals.…”

Section: Introductionmentioning

confidence: 99%

Effect of pressure on the crystallization behaviour of polyethylene terephthalate

Hong

Huang

2002

J. Phys.: Condens. Matter

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Crystallized polyethylene terephthalate (PET) samples were obtained at high pressures of 200-400 MPa at a temperature of 603 K, and another group of the samples were made at pressures of 250-350 MPa and different temperatures with a fixed supercooling. The samples were investigated by means of differential scanning calorimetry and scanning electron microscopy. Characterization results suggested that high pressure could increase the crystallization rate and promote the thickening process of PET lamellar crystals.

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