H. Van Oene

The Rheology of Wetting By Polymer Melts

Abstract Theoretically, the rate of capillary penetration of a polymer melt into a slit, a model for a surface irregularity, has been shown to depend on γcosθ/η) where γ refers to the surface tension of the liquid, η its viscosity and θ a time-dependent contact angle. Analytical expressions relating the depth of penetration with time have been experimentally verified by observations of the penetration of molten polyethylene and poly-(ethylene-vinyl acetate) into aluminum channels. Values of η, calculated from the observed data, agree closely with independent determinations of this material parameter. A theoretical treatment has also been developed which describes the velocity of spreading of a liquid drop over a flat surface. Flow equations for the flow of free films were adapted for this purpose. The spreading velocity is predicted to depend on the product of three factors (1) a scaling factor, (γ/η1Ro), where Ro is the initial radius of curvature, (2) cosθ∞. (l-cosθ/cosθ∞) where θ∞ refers to the equilib...

Shear properties and a stress analysis obtained from vinyl-ester losipescu specimens

The use of losipescu specimens for the determination of the shear properties of a vinyl-ester resin was investigated. The antisymmetric four-point bend and the Adams and Walrath fixtures were studied for their suitability in loading these specimens. Photoelastic and strain-gage data in addition to published finite-element results show that the latter fixture distorts the stress field in the gage section. The antisymmetric four-point bend fixture is found to give the purest shear-stress field in the gage section and to yield the most reliable shear-modulus values. A refined photoelastic analysis shows that the shear-stress distribution between the notch roots is essentially uniform with a relative maximum or minimum at the centroid depending on the depths of the notches. Also, stress risers of up to 30 percent are observed near the notch roots. Except at the roots, finite-element predictions are presented which are in excellent agreement with photoelastic data. The failure mode of this vinyl-ester resin is tensile and the corresponding tensile stress calculated from the average shear stress in the gage section of the losipescu specimen is in excellent agreement with failure data acquired in tension.

Rheology of Polymer Blends and Dispersions

Publisher Summary This chapter provides an overview of the rheology of polymer blends and polymer dispersions. It discusses the macro rheological behavior, expressed in terms of a shear-dependent viscosity and shear-dependent normal stress functions, and the micro rheological processes. It also provides a detailed account of the rheological behavior of suspensions of rigid axisymmetric particles in viscoelastic fluids, filled polymers, polymer blends, and suspensions of deformable droplets. The rheology of dispersions is studied at two levels: (1) the macro rheological level that involves measurement of the rheological properties of the dispersion such as the viscosity and normal stresses; and (2) the micro rheological level that concentrates on the detailed motions of the individual particles. Morphology, orientation, and distribution of the dispersed phase are essentially established by processes that take place at the micro rheological level and reflect the hydrodynamic forces acting on a fluid element. Studying the rheological behavior of polymer blends, two distinct modes of dispersion are observed: (1) stratification dispersion and (2) droplet-fiber-type dispersion. These modes of dispersion are independent of the magnitude of the shear stress and temperature. Low-shear mixing, such as that occurring in a static mixer, has been proved more successful in obtaining dispersions with a fine texture.

Nitroxide kinetics during photodegradation of acrylic/melamine coatings

Photooxidation of bis (2,2,6,6-tetramethylpiperidinyl-4) sebacate to nitroxide has been followed by electron paramagnetic resonance in acrylic melamine coatings under a number of ultraviolet light exposure conditions. The strong relationships observed between nitroxide kinetic behaviour, coating composition and exposure condition suggest that nitroxide kinetics analysis could be useful in probing coating photodegradation. This approach, together with infrared spectroscopic measurements of chemical changes on degradation, has suggested a novel mechanism, viz. photo-assisted hydrolysis, to explain the observation that photodegradation in acrylic melamine coatings proceeds more rapidly under more humid conditions. Photo-assisted hydrolysis of melamine ether crosslinks yields formaldehyde which can promote free radical oxidation leading to a more rapid photodegradation of these coatings under humid conditions than under dry conditions.

An elasticity analysis for the generally and specially orthotropic beams subjected to concentrated loads

Abstract A classical elasticity solution for the stress and displacement fields in loaded orthotropic beams is presented. The corresponding stress equations, derived from a stress function which satisfies the orthotropic analogue of the biharmonic equation, are written as Fourier series. From these expressions, the stress distributions in a series of centrally loaded generally and specially orthotropic beams are calculated. A detailed discussion of these stress distributions at selected beam sections and their symmetry about the loading axis is also presented. The stress fields are found to be unique relative to what is calculable from beam theory; for example, the stress distribution about the loading axis of a generally orthotropic beam is not symmetric. Finally, regions where beam theory coincides with the classical theory are identified.

Polysulphone and poly(phenylene sulphide) blends: 1. Thermal characterization and phase morphology

Abstract The phase behaviour and morphology of injection moulded specimens of polysulphone (PSF) and poly(phenylene sulphide) (PPS) blends were studied by differential scanning calorimetry (d.s.c.), dynamical mechanical thermal analysis (d.m.t.a.) and transmission electron microscopy (TEM). The blends are phase separated regardless of the blend composition as revealed by d.s.c., d.m.t.a. and TEM. Upon annealing at 160°C for 2 h, d.m.t.a. results indicate that the PPS phase remains in the amorphous state at compositions

Polysulphone and poly(phenylene sulphide) blends: 2. Mechanical behaviour

Abstract This paper reports the mechanical behaviour of injection moulded blends of polysulphone (PSF) and poly(phenylene sulphide) (PPS). The blends prepared by melt-extrusion and subsequent injection moulding are phase separated. Depending on moulding conditions, thermal history, and composition, tensile behaviour ranged from brittle to ductile, with or without cold drawing. Cold drawing was observed in compositions as-moulded with up to 50% by weight PPS. Upon annealing for 2h at 160°C, ductile failure was maintained for blends containing up to 35% by weight PPS. All other compositions failed in brittle fashion. Flexural strength and modulus, before and after annealing, exhibited negative deviation from the rule of mixtures. All the blends were found to be notch sensitive.

Polysulfone and poly(phenylene sulfide) blends: 3. Rubber toughening

Abstract Melt-blended polysulfone (PSF) and poly(phenylene sulfide) (PPS) are notch sensitive. A significant improvement in the notched Izod impact toughness occurs when at least 10 wt% of a shell-core rubber modifier is incorporated into the blend. At rubber modifier levels above 15 wt%, the notched Izod impact strength was essentially retained upon annealing at 160°C for 2 h, while below 15 wt% of rubber modifier, the notched Izod impact strength decreases after annealing under the same conditions. Izod impact fracture surface morphology was studied using scanning electron microscopy (SEM). Fracture surfaces without a rubber modifier exhibit cavitation around the dispersed phase, i.e. PPS. On the other hand, fracture surface morphology of the rubber toughened blends with the same PSF/PPS composition show no cavitation surrounding the dispersed phase. Blend morphology was also studied using transmission electron microscopy (TEM).

Transmission photoelasticity of centrally loaded generally and specially orthotropic beams

Transmission photoelastic patterns for generally and specially orthotropic beams and an isotropic beam are presented. Theoretical isochromatic and isoclinic results for these beams, calculated from classical elasticity stress equations and stress-optic laws, are also presented and compared with experiment. The agreement between the theory and experiment is excellent. For the orthotropic beams, a stressoptic law which accounts for the effects of residual birefringence was used. The residual birefringence observed for the composite used in this study is greater than one fringe order and results from a matrix residual tension which is about one fourth of the resins ultimate tensile strength. Finally, the influence of such a large residual birefringence on beam and calibration photoelastic data is discussed in detail.

The Impact Behavior of Glass and Carbon Fiber Composites

Abstract Impact behavior of glass and carbon fiber composites has been studied in some detail both with respect to methodology of testing and to interpretation of the influence of fiber orientation and viscoelastic resin properties on the measured fracture energies [14]. Most authors use some variation of the Charpy drop- weight test in which the impacted beam specimen is placed between two anvils. It is known that when the ratio of the span between the anvils to specimen thickness is small, e.g., less than 10, shear effects are very important. Most authors, therefore, test specimens at a larger span-to-thickness ratio, usually 16 and above. At these ratios the failure induced will be essentially a tensile fail- ure, dominated by fiber orientation and volume.