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

Yasuniwa, Munehisa; Yamaguchi, Masashi; Nakamura, Atsushi; Tsubakihara, Shinsuke

doi:10.1295/polymj.22.411

Cited by 12 publications

(5 citation statements)

References 10 publications

(7 reference statements)

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“…The crystallization temperature is dependent upon the external condition and increases gradually as the hydrostatic pressure is increased, for example. As the temperature is decreased from the melt under such high pressure condition, the PE crystallizes firstly to the hexagonal phase and then to the normal orthorhombic phase. − This hexagonal phase plays an important role as an intermediate phase in the crystallization process from the melt to the extended chain crystal . The structure of the hexagonal phase was investigated by X-ray diffraction ,, and Raman spectral measurements .…”

Section: Introductionmentioning

confidence: 99%

Structural Investigation of Orthorhombic-to-Hexagonal Phase Transition in Polyethylene Crystal: The Experimental Confirmation of the Conformationally Disordered Structure by X-ray Diffraction and Infrared/Raman Spectroscopic Measurements

1996

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Structural changes in the orthorhombic-to-hexagonal phase transition of polyethylene crystal has been investigated by measuring the differential scanning calorimetry, X-ray diffraction, and infrared and Raman spectra for the geometrically-constrained ultradrawn samples in the course of heating up to the melting temperature. The infrared and Raman spectral patterns characteristic of the hexagonal phase have been confirmed. In particular, the bands characteristic of the disordered short trans segments (shorter than five CH2 units) and the bands of the kink or double gauche linkages have been detected definitely. The degree of orientation of the averaged chain axis, as detected from the temperature dependence of the X-ray fiber diagram, was reserved well enough even in the hexagonal phase, while the orientational degree of the methylene units, as detected from the polarized infrared spectral measurement, was found to be lowered appreciably. This finding, combined with the observation of the trans and gauche bands, has confirmed experimentally and definitely the existence of the conformationally disordered chains in the hexagonal phase.

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Section: Introductionmentioning

confidence: 99%

Structural Investigation of Orthorhombic-to-Hexagonal Phase Transition in Polyethylene Crystal: The Experimental Confirmation of the Conformationally Disordered Structure by X-ray Diffraction and Infrared/Raman Spectroscopic Measurements

1996

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“…Interestingly, the metastable hexagonal form is also reported to appear at normal conditions in a constrained PE gel–film during melting . It is also hypothesized that upon cooling from melt, PE crystallizes into a hexagonal lattice first and then changes into the orthorhombic form. − There could be other changes in crystal structure possible prior to actual melting, causing distortion of the lattice, such as appearance of rotator phases, , as indicated by previous studies . These molecular changes are observable with Raman spectroscopy.…”

mentioning

confidence: 73%

Estimating Percent Crystallinity of Polyethylene as a Function of Temperature by Raman Spectroscopy Multivariate Curve Resolution by Alternating Least Squares

Samuel¹,

Lai²,

Lan³

et al. 2017

Anal. Chem.

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We have recently demonstrated a methodology to estimate the percent crystallinity (PC) of polymers directly with Raman spectroscopy and multivariate curve resolution (MCR) by alternating least-squares (ALS). In the MCR-ALS methodology, the Raman spectrum of a semicrystalline polymer is separated into two constituent components (crystalline and molten/amorphous) and their corresponding concentrations. The methodology necessitates that the Raman spectrum at any temperature be a linear combination of two MCR spectral components (one molten and one crystalline). This is true in the case of simple systems such as crystalline pendant alkyl domains in polymers (Samuel et al. Anal. Chem. 2016, 88, 4644). However, in the case of main chain polymer crystals (e.g., polyethylene), the situation can be complicated owing to several molecular changes in the lattice in addition to conformational reorganizations during melting. Under this circumstance, a simple two-state model may not be adequate and we describe the modifications required to treat such systems, keeping the basic principles of the proposed methodology unchanged. A comparative study with wide-angle X-ray scattering (WAXS) and Raman spectroscopy is also performed to substantiate our findings. In addition to estimating percent crystallinity (PC), our methodology is capable of revealing additional information, such as interchain interactions in crystal lattice, that in principle will help distinguishing polymorphic transformations, subtle changes in lamellar lattice dimensions, and other phase changes in polymers.

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

Cited by 12 publications

References 10 publications

Structural Investigation of Orthorhombic-to-Hexagonal Phase Transition in Polyethylene Crystal: The Experimental Confirmation of the Conformationally Disordered Structure by X-ray Diffraction and Infrared/Raman Spectroscopic Measurements

Structural Investigation of Orthorhombic-to-Hexagonal Phase Transition in Polyethylene Crystal: The Experimental Confirmation of the Conformationally Disordered Structure by X-ray Diffraction and Infrared/Raman Spectroscopic Measurements

Estimating Percent Crystallinity of Polyethylene as a Function of Temperature by Raman Spectroscopy Multivariate Curve Resolution by Alternating Least Squares

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

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