The dielectric properties of polyamide-4,6 were examined as functions of frequency, temperature a... more The dielectric properties of polyamide-4,6 were examined as functions of frequency, temperature and moisture content. The dielectric spectra were compared with the results of dynamic mechanical measurements in torsion at 0.2153 Hz, as a function of temperature, and with the dynamic dielectric properties of commercial polyamide-6,6. Three relaxation processes are observed in polyamide-4,6, which are related to either local or collective molecular mechanisms of motion, similar to the relaxation processes observed in other polyamides. At temperatures above the glass transition temperature, ionic conductivity is observed, which, due to the semicrystalline structure of the material, gives rise to a strong Maxwell-Wagner-Sillars (MWS) polarization. With increasing temperature, the conductivity increases sharply, eventually causing electrode polarization, and thus obscuring the dielectric effects in the material. All loss processes shift to lower temperatures with increasing water content. The activation energies of the secondary relaxations decrease with increasing water uptake, while the fl and ct relaxations are enhanced in magnitude.
Journal of Polymer Science Part B: Polymer Physics, 1994
The structural aspects of rigid suspension poly (vinyl chloride), PVC, have been investigated on ... more The structural aspects of rigid suspension poly (vinyl chloride), PVC, have been investigated on the basis of two independent series of suspension PVC samples, polymerized at temperatures between 26 and 84°C. The reproducibility of the suspension polymerization process and the importance of the polymerization temperature with respect to the macro-and microstructure is demonstrated. Quantitative examination of the grain structure by small angle neutron scattering, Brunauer-Emmett-Teller absorption technique, and mercury porosimetry clarifies the gradual increase of the specific surface on lowering the polymerization temperature. A detailed WAXS study shows an increasing degree of crystallinity on lowering the polymerization temperature, which can be associated with the corresponding increase of the syndiotacticity. Furthermore, the presence of a polymerization history in the PVC powders with respect to the crystallinity is evidenced. This effect seems to be related to chain mobility restrictions during the polymerization process and is determined by the difference between the polymerization temperature and the glass-transition temperature ( T,) of rigid PVC. This so-called Tg effect is indicative of the fact that no appreciable swelling of PVC by its monomer occurs. 0 1994 John Wiley & Sons, Inc. Keywords: poly(viny1 chloride) polymerisation conversion tacticity molar mass polymerization temperature microstructure macrostructure wide angle x-ray scattering small-angle neutron scattering Brunauer-Emmett-Teller absorption technique
Fracture properties of model elastomeric networks of polyurethane have been investigated with a d... more Fracture properties of model elastomeric networks of polyurethane have been investigated with a double-edge notch geometry. The networks were synthesized from monodisperse end-functionalized polypropylene glycol precursors and a trifunctional isocyanate. All reagents were carefully purified and nearly defect-free ideal networks were prepared at a stoichiometry very close to the theoretical one. Three networks were prepared: an unentangled network of short chains (M n ¼ 4 kg mol À1 ), an entangled network of longer chains (M n ¼ 8 kg mol À1 ) and a bimodal network with 8 kg mol À1 and 1 kg mol À1 chains. The presence of entanglements was found to increase significantly the toughness of the rubber, in particular at room temperature, relative to the bimodal networks and to the short chains network.
Model calculations were performed in order to investigate the sensitivity of various rheological ... more Model calculations were performed in order to investigate the sensitivity of various rheological polydispersity parameters for variations in the moments of the molar mass distribution (MMD) of linear polymers. Molar mass distributions were generated with the Gaussian and the Generalised exponential distribution functions, using a fixed weight average molar mass M w and variable M w /M n and M z /M n . Assuming linear entangled polymeric chains, the linear viscoelastic properties were predicted by calculating the stress relaxation modulus of the consecutive monodisperse fractions with the BSW relaxation time spectrum and blending these curves with the double reptation blending rule. BSW relaxation parameters appropriate for polypropylene were used.
ABSTRACT Gloss is a critical property for many powder coating applications and is related to the ... more ABSTRACT Gloss is a critical property for many powder coating applications and is related to the amount of light reflected by the coating layer on a substrate. Gloss of powder coatings can, depending on the composition, vary from excellent to matt. It is well known in the powder coatings industry that increasing loadings of pigment, especially TiO2, causes a detrimental loss of gloss. In order to understand the cause of this phenomenon two questions have to be addressed: firstly, what is the relation between the optical properties and the surface topography of the powder coating and, secondly, how do the powder coating composition and curing conditions affect the surface topography? In order to answer the first question, the typical features of the surface of a cured powder coating have been studied in detail. Using a white light interferometer, it has been shown that the surface topography consists of both short wave and long wave patterns. Each of these patterns could be described by using two statistical parameters only, the root mean square height of the roughness and its correlation length. The effect of both the short and long wave roughness on the gloss has been simulated with a single wave pattern model, based on an approximation of the Kirchoff scattering theory [9]. These simulations illustrated that neither the short nor the long wave roughness on itself determines the optical properties. In order to quantify the combined effect of the long and short wave surface features a two-scale modelling approach was followed. The predictions of this model were in good agreement with experimental gloss data of coatings containing different amounts and types of pigments.
Model composites of spherical glass particles dispersed in a matrix of high-density polyethylene ... more Model composites of spherical glass particles dispersed in a matrix of high-density polyethylene (HDPE) were prepared. Samples of the composite material were, after careful drying, exposed to several relative humidities at room temperature. The dielectric properties and the mass gain of the composite samples were monitored during the water absorption from the environment. The dielectric measurements covered the frequency range from 0.1 Hz to 50 kHz. A theoretical model for the dielectric properties of composites with an interlayer describes the detected dielectric loss processes due to the electrically conducting layer of adsorbed water at the filler-matrix interface. A quantitative relationship between the amount of absorbed water and the frequency of maximum dielectric loss can be established by taking into account the thickness dependence of the conductivity of the interfacial water layer.
One option to understand and possibly improve the properties of thermosets is to investigate well... more One option to understand and possibly improve the properties of thermosets is to investigate well-defined polymer networks. Various novel, α,ω-ethylmaleate functionalized poly(propylene glycol)s were endlinked with a trifunctional thiol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol tris(3-mercaptopropionate) (EHPT). Model reactions of EHPT and diethyl maleate indicated that a substitution effect in the thiol is absent. Characterization of the model networks revealed that the molecular weight between
The rheological and mechanical properties of a series of linear and randomly branched polyamide 6... more The rheological and mechanical properties of a series of linear and randomly branched polyamide 6 samples, with varying molar mass and varying degree of moderate branching, have been investigated.
The dielectric properties of polyamide-4,6 were examined as functions of frequency, temperature a... more The dielectric properties of polyamide-4,6 were examined as functions of frequency, temperature and moisture content. The dielectric spectra were compared with the results of dynamic mechanical measurements in torsion at 0.2153 Hz, as a function of temperature, and with the dynamic dielectric properties of commercial polyamide-6,6. Three relaxation processes are observed in polyamide-4,6, which are related to either local or collective molecular mechanisms of motion, similar to the relaxation processes observed in other polyamides. At temperatures above the glass transition temperature, ionic conductivity is observed, which, due to the semicrystalline structure of the material, gives rise to a strong Maxwell-Wagner-Sillars (MWS) polarization. With increasing temperature, the conductivity increases sharply, eventually causing electrode polarization, and thus obscuring the dielectric effects in the material. All loss processes shift to lower temperatures with increasing water content. The activation energies of the secondary relaxations decrease with increasing water uptake, while the fl and ct relaxations are enhanced in magnitude.
Journal of Polymer Science Part B: Polymer Physics, 1994
The structural aspects of rigid suspension poly (vinyl chloride), PVC, have been investigated on ... more The structural aspects of rigid suspension poly (vinyl chloride), PVC, have been investigated on the basis of two independent series of suspension PVC samples, polymerized at temperatures between 26 and 84°C. The reproducibility of the suspension polymerization process and the importance of the polymerization temperature with respect to the macro-and microstructure is demonstrated. Quantitative examination of the grain structure by small angle neutron scattering, Brunauer-Emmett-Teller absorption technique, and mercury porosimetry clarifies the gradual increase of the specific surface on lowering the polymerization temperature. A detailed WAXS study shows an increasing degree of crystallinity on lowering the polymerization temperature, which can be associated with the corresponding increase of the syndiotacticity. Furthermore, the presence of a polymerization history in the PVC powders with respect to the crystallinity is evidenced. This effect seems to be related to chain mobility restrictions during the polymerization process and is determined by the difference between the polymerization temperature and the glass-transition temperature ( T,) of rigid PVC. This so-called Tg effect is indicative of the fact that no appreciable swelling of PVC by its monomer occurs. 0 1994 John Wiley & Sons, Inc. Keywords: poly(viny1 chloride) polymerisation conversion tacticity molar mass polymerization temperature microstructure macrostructure wide angle x-ray scattering small-angle neutron scattering Brunauer-Emmett-Teller absorption technique
Fracture properties of model elastomeric networks of polyurethane have been investigated with a d... more Fracture properties of model elastomeric networks of polyurethane have been investigated with a double-edge notch geometry. The networks were synthesized from monodisperse end-functionalized polypropylene glycol precursors and a trifunctional isocyanate. All reagents were carefully purified and nearly defect-free ideal networks were prepared at a stoichiometry very close to the theoretical one. Three networks were prepared: an unentangled network of short chains (M n ¼ 4 kg mol À1 ), an entangled network of longer chains (M n ¼ 8 kg mol À1 ) and a bimodal network with 8 kg mol À1 and 1 kg mol À1 chains. The presence of entanglements was found to increase significantly the toughness of the rubber, in particular at room temperature, relative to the bimodal networks and to the short chains network.
Model calculations were performed in order to investigate the sensitivity of various rheological ... more Model calculations were performed in order to investigate the sensitivity of various rheological polydispersity parameters for variations in the moments of the molar mass distribution (MMD) of linear polymers. Molar mass distributions were generated with the Gaussian and the Generalised exponential distribution functions, using a fixed weight average molar mass M w and variable M w /M n and M z /M n . Assuming linear entangled polymeric chains, the linear viscoelastic properties were predicted by calculating the stress relaxation modulus of the consecutive monodisperse fractions with the BSW relaxation time spectrum and blending these curves with the double reptation blending rule. BSW relaxation parameters appropriate for polypropylene were used.
ABSTRACT Gloss is a critical property for many powder coating applications and is related to the ... more ABSTRACT Gloss is a critical property for many powder coating applications and is related to the amount of light reflected by the coating layer on a substrate. Gloss of powder coatings can, depending on the composition, vary from excellent to matt. It is well known in the powder coatings industry that increasing loadings of pigment, especially TiO2, causes a detrimental loss of gloss. In order to understand the cause of this phenomenon two questions have to be addressed: firstly, what is the relation between the optical properties and the surface topography of the powder coating and, secondly, how do the powder coating composition and curing conditions affect the surface topography? In order to answer the first question, the typical features of the surface of a cured powder coating have been studied in detail. Using a white light interferometer, it has been shown that the surface topography consists of both short wave and long wave patterns. Each of these patterns could be described by using two statistical parameters only, the root mean square height of the roughness and its correlation length. The effect of both the short and long wave roughness on the gloss has been simulated with a single wave pattern model, based on an approximation of the Kirchoff scattering theory [9]. These simulations illustrated that neither the short nor the long wave roughness on itself determines the optical properties. In order to quantify the combined effect of the long and short wave surface features a two-scale modelling approach was followed. The predictions of this model were in good agreement with experimental gloss data of coatings containing different amounts and types of pigments.
Model composites of spherical glass particles dispersed in a matrix of high-density polyethylene ... more Model composites of spherical glass particles dispersed in a matrix of high-density polyethylene (HDPE) were prepared. Samples of the composite material were, after careful drying, exposed to several relative humidities at room temperature. The dielectric properties and the mass gain of the composite samples were monitored during the water absorption from the environment. The dielectric measurements covered the frequency range from 0.1 Hz to 50 kHz. A theoretical model for the dielectric properties of composites with an interlayer describes the detected dielectric loss processes due to the electrically conducting layer of adsorbed water at the filler-matrix interface. A quantitative relationship between the amount of absorbed water and the frequency of maximum dielectric loss can be established by taking into account the thickness dependence of the conductivity of the interfacial water layer.
One option to understand and possibly improve the properties of thermosets is to investigate well... more One option to understand and possibly improve the properties of thermosets is to investigate well-defined polymer networks. Various novel, α,ω-ethylmaleate functionalized poly(propylene glycol)s were endlinked with a trifunctional thiol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol tris(3-mercaptopropionate) (EHPT). Model reactions of EHPT and diethyl maleate indicated that a substitution effect in the thiol is absent. Characterization of the model networks revealed that the molecular weight between
The rheological and mechanical properties of a series of linear and randomly branched polyamide 6... more The rheological and mechanical properties of a series of linear and randomly branched polyamide 6 samples, with varying molar mass and varying degree of moderate branching, have been investigated.
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