Mo-Fung Cheung

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).

Conductive modification of injection molded thermoplastics: electrical properties and electrostatic paintability

Conductively modified thermoplastic substrates have been developed using low levels of conductive carbon fillers, <6 weight percent, without sacrificing the favorable mechanical and rheological properties exhibited by these materials for the automotive market. The bulk electrical properties of these materials exhibit traditional percolation behavior when the samples are compression molded. Conductively modified injection molded materials exhibit a high surface resistivity, typically greater than 10/sup 16/ ohm cm, which is compensated by a relatively low resistivity interior, less than 10/sup 8/ ohm cm. The threshold for electrostatic paintability has been identified based on core resistivity measurements and electrostatic dissipation results. This core resistivity must be less that 10/sup 9/ ohm cm for charge dissipation to occur and for any significant increase in paint film builds to be observed. The surface to core resistivity transformation is intimately related to the material cooling rate and thus the distance of the sampled area to the injection molding tool surface. Using these conductively modified materials, high solids paint coating film, builds and transfer efficiency have been increased in excess of 100 percent relative to unmodified samples. The use of conductively modified thermoplastic substrates in the electrostatic painting process can eliminate the need for conducting primers when adhesion between the base coat and substrate surface is maintained.

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.

Hydrolytic Stability of Polyphenylene Sulfide/Polyarylate Blends

Abstract In the immiscible blends of poly(phenylene sulfide) (PPS) and polyarylate (PAR), absorbed moisture partitioned into each phase according to the equilibrium value of the homopolymers. The water diffusivity was observed to decrease with increasing PPS concentration and at >45%, when PPS became the major component in the skin region, the diffusivity was equal to that of neat PPS. The molecular weight of the PAR fraction was found to degrade linearly with time due to hydrolysis.