The CO2 permeability of uniaxially drawn high-density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free...
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The CO2 permeability of uniaxially drawn high-density polyethylene (HDPE) was investigated and drastic changes were observed as a function of draw ratio. An estimation of variations in both density and fractional free volume of the amorphous component in the drawn polymers was made on the basis of experimental data. The dramatic variations in permeability resulting from drawing were shown to be the consequence of changes of fractional free volume in the amorphous phase of the drawn polymer. Good correlation exists between measured solubility and diffusion coefficients of drawn samples and the estimated fractional free volume;this correlation agrees with the existing free volume theory for diffusion in polymers.
We propose a new technique, which is a combination of the test and real particle methods proposed originally by Widom, for the calculation of the chemical potentials of molecular systems from computer simulation. The ...
We propose a new technique, which is a combination of the test and real particle methods proposed originally by Widom, for the calculation of the chemical potentials of molecular systems from computer simulation. The technique involves the creation of a hole in the fluid by removing a particle from the simulated system, and subsequently reinserting it as a test bead. The equations for the calculation of chemical potentials are derived, and it is shown that the results obtained by this method for Lennard-Jones fluids are accurate over larger ranges in temperature and density than other traditional methods. In spite of these advantages for simple systems, the proposed technique is expected to be of greatest value when dealing with complex systems containing ionic or polymeric molecules.
The synthesis of high‐molecular‐weight polyethers and copolyethers based on 4‐hydroxyacetophenone azine and α,ω‐dibromoalkanes was carried out in N ‐methyl‐2‐pyrrolidone via Williamson etherification using th...
The synthesis of high‐molecular‐weight polyethers and copolyethers based on 4‐hydroxyacetophenone azine and α,ω‐dibromoalkanes was carried out in N ‐methyl‐2‐pyrrolidone via Williamson etherification using the caesium salt of the diol. Polyethers were composed of a homologous series of flexible methylene spacers with m = 5−12, while the copolyethers contained a 1:1 mole ratio of two different spacers with m = 5/7, 6/8, 7/9, 8/10, 9/11 and 10/12. polymers with relatively short spacers ( m = 5−8 methylene groups) exhibit enantiotropic mesomorphism, whereas those having m = 8−11 are tentatively identified to be monotropic. The polyether with m = 12 is crystalline. Copolyethers are enantiotropic and their mesophase ranges are considerably wider than those of the homopolyethers. The mesophases were identified to be nematic by polarised light microscopy. The transition temperatures of both the homopolymers and copolymers show classical even‐odd variations as a function of the spacer length.
An analysis of the influence of crystalline microstructure on fatigue crack propagation in polyoxymethylene is presented. A series of test specimens containing a variety of diverse microstructures was prepared through...
An analysis of the influence of crystalline microstructure on fatigue crack propagation in polyoxymethylene is presented. A series of test specimens containing a variety of diverse microstructures was prepared through controlled thermal treatments of plaques from four different lots of polyoxymethylene. Extensive characterization of the crystalline microstructure was carried out in order to permit a direct comparison between the fatigue behaviour and crystalline microstructure. The degree of crystallinity and tie molecule density were both found to have a significant affect on fatigue crack propagation rate while average spherulite size did not appear to influence fatigue behaviour. Additionally, the fatigue fracture surfaces of many of the test specimens were examined. Three distinct surface topographies were observed and found to correlate with different stages of crack growth. In the region near the end of fatigue crack propagation, closely spaced surface markings that resemble fatigue striations were observed.
An examination is made of several melt miscible polymer blends with the aid of dielectric spectroscopy and differential scanning calorimetry (DSC). These included PEO/PMMA, poly(caprolactone) (PCL)/poly(vinyl chloride...
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An examination is made of several melt miscible polymer blends with the aid of dielectric spectroscopy and differential scanning calorimetry (DSC). These included PEO/PMMA, poly(caprolactone) (PCL)/poly(vinyl chloride) (PVC), and poly(butylene terephthalate (PBT)/polyarylate (PAr). It is the goal of this research to understand if the characteristics of the interphase in all cases examined were similar tho those found fpr the PVDF/PMMA system. It is found that that the unusual spectra obtained for the PCl/PVC blend do not constitute an isolated example and suggest strongly that the fundamental physics underlaying the crystal-amorphous interphase in miscible blends is more complicated that thought before.
The solubility behavior of poly(enaminonitrile) (PEAN) solutions and blends has been investigated by using light scattering. PEANs are soluble in a series of polyether solvents (glymes), and those solutions show cloud...
The solubility behavior of poly(enaminonitrile) (PEAN) solutions and blends has been investigated by using light scattering. PEANs are soluble in a series of polyether solvents (glymes), and those solutions show cloud points as the temperature is raised. The same behavior was observed from miscible blends of PEAN with poly(ethylene oxide). Cloud points were determined by laser light scattering measurements.
The equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Tes...
The equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Test results from controlled stress and controlled strain rate measurement were consistent and yielded well-defined steady-state viscosities. Measurements appeared to be unaffected by sample geometry, although proper lubrication is important in achieving steady state. The measured biaxial viscosity appeared to be strain rate thinning above a biaxial strain rate of almost-equal-to 0.01 s-1 at 160-degrees-C. As anticipated in the Newtonian region, biaxial elongational viscosity was approximately six times the shear viscosity. Thinning indices of both shear and biaxial elongational viscosities were 0.75. Data obtained at various temperatures were shifted following the time-temperature superposition principle. The resulting master curve could be fitted by a Carreau model with n almost-equal-to 0.3 and a time constant of 110 s.
In this paper theories of swelling that have been applied to coal are modified to account for hydrogen bonding. The results of various swelling measurements are analyzed and suggest some important conclusions. First, ...
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This is the first of three papers that deal with coal solubility and swelling. An association model has been applied to coal, and this predicts that the mixing of coal with certain solvents will be determined by a bal...
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In this paper we propose a model for coal swelling based on a process called disinterspersion. This allows a calculation of the “molecular weight” or number of aromatic “clusters” between cross-link points under t...
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