Ultra-high molecular weight polyethylene – Evidence for a three-phase morphology (original) (raw)
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On the morphology of some irradiated ultra high molecular weight polyethylenes
Polymer Degradation and Stability, 2009
The morphology of various grades of ultra high molecular weight polyethylene (UHMWPE), prepared for use in orthopaedic implants, has been examined using differential scanning calorimetry (DSC), wide and small angle X-ray diffraction (WAX and SAX) and Raman spectroscopy. Preparation included gamma irradiation at various dose rates and mechanical annealing, and post-irradiation changes were of particular interest. The experimental results are interpreted in terms of previous proposals that UHMWPE is best considered as a three phase material, fully amorphous, all-trans amorphous and fully crystalline. The all-trans amorphous material is thought to be interfacial. The phase analysis shows that the age related increase in crystallinity occurs through conversion of all-trans material to fully crystalline, and there is little change in the total amorphous content of the polymers. SAX patterns show a change in the sharpness of the main diffraction peak and the emergence of a second diffraction peak at a higher q value, and this is considered to arise from crystallisation of all-trans amorphous material. Increasing the irradiation dose rate has a similar effect on the crystallography as does ageing the material. Mechanically annealed polymer also shows a similar trend towards a bimodal crystal population, accompanied by a reduction in interfacial material.
The application of Raman spectroscopy to three-phase characterization of polyethylene crystallinity
Polym Test, 2007
The crystallinity of polyethylenes of various densities was studied by applying the Raman spectroscopy technique. Raman spectra were decomposed into the following three components: the orthorhombic crystalline phase, the melt-like amorphous phase and the interfacial phase, which is located between the crystalline and amorphous phases, with possibly highly oriented or ordered chain segments but not in orthorhombic packing. It was found that the amorphous fraction obtained by the Raman method has a small deviation, and it is more reliable to define the crystallinity of polyethylene samples as (1 À amorphous fraction) Â 100% rather than by using the orthorhombic crystalline fraction itself. The calculated results show good linear correlation with the crystallinities derived from other methods -by density, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) measurements. r
Ultrahigh-molecular-weight polyethylene: Raman spectroscopic study of melt anisotropy
Journal of Polymer Science Part B: Polymer Physics, 1986
The Raman spectrum of ultrahigh-molecular-weight polyethylene (UHMWPE) has been obtained in the temperature interval 135-208'C, a region where optical anisotropy was observed to exist. On the basis of our spectroscopic evidence, we believe that ordered regions persist in the melt above the calorimetrically determined melting point, and that part of the polyethylene chain is in an enviroment which is similar to that of the orthorhombic crystal.
Polymer, 2005
Ultra high molecular weight polyethylene has been irradiated in air and aged for 168 months. On melting and recrystallisation in the differential scanning calorimeter a secondary crystallisation event is observed around 80 8C. This event has been studied using isothermal crystallisation and the results analysed using the Avrami equation and the Lauritzen-Hoffman approach. This suggests that during this event growth occurs through regime II kinetics whereby large numbers of surface nuclei form on the substrate, with multiple nucleations acts commencing before the previous ones have finished. It is postulated that this secondary crystallisation event involves the development of a diffuse semi-ordered interface between the well-developed lamellae and the amorphous phase.
Raman spectroscopic study of the high-pressure phase of polyethylene
Macromolecules, 1981
- Cotton, J. P.; Farnoux, B.; Jannink, G.; Strazielle, C. J. Polym. Sci., Polym. Symp. 1973, No. 42, 981. (5) Cotton, J. P.; Farnoux, B.; Jannink, G. J. Chem. Phys. 1972, 57, 290. Daoud, M.; Cotton, J. P.; Farnoux, B.; Jannink, G.; Sarma, G.; Benoit, H.; Duplessix, R.; Picot, C.; de Gennes, P. G. Macromolecules 1975, 8, 804. (6) Berrv. G. C.: Nakavasu. H.: Fox. T. G. J. Polvm. Sci.. Polvm. . , , , I " Phyi.'Ed. 1979,l f, 1825. (7) Nvstrom, B.; Porsch, B.; Sundelof, L.-0. Eur. Polym. J. 1977, 13, 683. 'Nystrom, B.; Roots, J.; Bergman, R. Po-lymer 1979, 20, 157. Roots, J.; Nystrom, B.; Sundelof, L.-0.; Porsch, B. ABSTRACT: The Raman spectra of polyethylene at 5.1 kbar were obtained as a function of increasing temperature in the orthorhombic, intermediate, and melt phases. It was found that a plot of r = Z(1130)/Z(1090), an order parameter related to the relative concentration of trans bonds, vs. temperature, T, was sigmoidal. The steepest change of r with T occurred in the intermediate phase. Comparison of r values in the intermediate phase with an approximate calibration curve and with values obtained from lipid membrane phase transition data indicates that the intermediate phase has significant but variable trans bond population, ranging from 6 2 to 68%. Analysis of the high-frequency C-H stretching region, which is indicative of changes in lateral
The Transition Phase in Polyethylenes : WAXS and Raman Investigations
Fibres & Textiles in Eastern Europe, 2008
The existence of the third, transition component, apart from the crystalline and amorphous phases, in polyethylenes has already been proved in several papers. In this work, the WAXS patterns of polyethylenes with various branch contents were analysed, aiming at the best method of accounting for the third phase in the procedure of decomposition of the patterns into crystalline peaks and amorphous scattering. It appeared that the best result was obtained when we assumed that the intermediate phase is represented by two peaks located close to the crystalline reflections (110) and (200), on the left sides of these reflections. The calculations performed have shown that both the density and the mass fraction of this intermediate third phase decrease continuously with increasing 1-octene content. A comparison of the mass fractions of the three phases has shown that the total mass fractions of the crystalline and transition phases determined with the WAXS and Raman methods coincide very we...
Pure and Applied Chemistry
Test methods including OM, SEM, TEM, DSC, SAXS, WAXS, and IR were used to characterise supra-molecular structure in three batches of polyethylene (PE), which had weight-average relative molar masses M ¯ w overlineMtextw{\overline{M}}_{\text{w}}overlineMtextw of approximately 0.6 × 106, 5 × 106, and 9 × 106. They were applied to compression mouldings made by the polymer manufacturer. Electron microscopy showed that powders formed in the polymerization reactor consisted of irregularly shaped grains between 50 and 250 μm in diameter. Higher magnification revealed that each grain was an aggregate, composed of particles between 0.4 and 0.8 μm in diameter, which were connected by long, thin fibrils. In compression mouldings, lamellar thicknesses ranged from 7 to 23 nm. Crystallinity varied between 70 and 75 % in reactor powder, but was lower in compression mouldings. Melting peak temperatures ranged from 138 to 145 °C, depending on processing history. DMTA showed that the glass transition temperature θ g was −12...
On the analysis of the Raman internal modes of crystalline polyethylene
Polymer Testing, 1992
The Raman internal modes of a set of polyethylenes have been analyzed in order to quantitatively evaluate their phase structures. Samples were prepared that covered as wide a range in crystallinity level as possible. Four different methods were used to analyze the spectra. One involved the manual decomposition of the spectra, another a computer programmed decomposition. Two methods were used to approximate the Raman band shapes. In one, a combination of 60% Gaussian and 40% Lorenztian functions were used. In the other, an arbitrary combination of these two functions was chosen so as to give the best fit. It was found that all four methods gave essentially the same results. Thus, the criticism of the manual method was unwarranted. We have also confirmed previous results that the density determined level of crystallinity is equal to the sum of the core crystallinity and interracial levels.
High-pressure Raman studies of ultra-high-molecular-weight polyethylene
Polymer, 1990
This paper reports the Raman spectra of ultra-high-molecular-weight polyethylene (UHMWPE) at room temperature and under high pressure employing a Mao-Bell type of miniature diamond-sapphire anvil cell. Davydov splitting near 1065 cm-1 and resonance interactions in the bending (1440-1470cm-1) and C-H stretching (2840-2950cm -1) regions of the Raman spectra of UHMWPE at high pressure are described. The dependences of mode GriJneisen parameters (ri) on vibrational frequency (vi) were determined at several pressures from the Raman spectra and compression experiments of UHMWPE. (
Journal of Materials Science: Materials …, 1998
The effects of four sterilization treatments (gamma radiation in nitrogen, electron-beam radiation, ethylene oxide gas, and no sterilization) on the structure and morphology of ultrahigh molecular weight polyethylene (UHMWPE) were monitored as a function of ageing time in air for a period of 1.5 y. Characterization techniques employed include differential scanning calorimetry, density gradient column, transmission electron microscopy, and small-angle X-ray scattering. Ethylene oxide gas does not affect the structure of the polymer. Both forms of radiation lead to measurable alterations of the material's structure, including an increase in crystallinity, an increase in density, and the enhancement of lamellae crystalline stacking. Most changes in structure occur in the first few months with little differences observed upon subsequent ageing in air. The sharpness of the crystalline-amorphous boundaries decreases with time for irradiated UHMWPE and is believed to be linked to the oxidation of the polymer.