R. P. Burford

A general review of polymeric insulation for use in HVDC cables

The authors present a review article of the properties of XLPE and an examination of the origins of space charge and how it is measured. The space charge in the insulation and the conduction current can affect the electric stress distribution in the insulation. The effect of morphology on the electrical properties of polyethylene is discussed in detail.

Cell attachment to laser-induced AAm-and HEMA-grafted ethylenepropylene rubber as biomaterial: in vivo study

With the purpose of improved tissue compatibility, ethylene-propylene rubber (EPR)-based vulcanizates have been surface grafted with acrylamide (AAm) and 2-hydroxyethyl methacrylate (HEMA) using CO2-pulsed laser as excitation source. Grafted surfaces were characterized by performing scanning electron microscopy combined with energy dispersive X-ray analysis and attenuated total reflectance infrared spectroscopy to study the surface morphology and grafting. Surface hydrophilicity (measured by water drop contact angle) increased for the grafted samples. Fractal type of morphology is formed by the grafted poly(AAm) and poly(HEMA) chains on the surface of EPR, which provides both hydrophilic and hydrophobic sites. In vivo tissue compatibility was assessed by implanting test samples in the deep intramuscular and peritoneal layers of rabbits. After 8 weeks of implantation, comparative results indicate that the adhesion of macrophages to EPR samples modified with AAm and HEMA, with no respiratory burst and cellular damage, is significantly lower than their adhesion on unmodified surfaces which show an activated state of the attached macrophages. Also, no acute or chronic inflammatory reaction was observed at the site of implantation and a thinner fibrous tissue capsule formed around the modified samples, whereas foreign body giant cells adhered to unmodified EPR.

Novel membranes from conducting polymers

Abstract The first part of this paper presents the preparation and morphological studies of high surface area polypyrrole with fibrillar morphology. Mode of fibre growth within host membrane pores has been examined by ultra-microtome techniques. The rate of fibre growth in different solvents has been determined. The second part of this paper describes the formation of conducting composite membranes of polypyrrole with in-house prepared and commercial (“Biotran”) microporous polyamides. The conducting polymer was chemically polymerized using several techniques in association with the membranes in these studies. Surface and cross-sectional membrane morphology was studied by high-resolution field emission scanning electron microscopy, optical microscopy and transmission electron microscopy. Environmental stability of composite membranes has been examined by measuring the conductivity as a function of time.

Stability and mechanical properties of electrochemically prepared conducting polypyrrole films

The stability and mechanical properties of polypyrrolep-toluene sulphonate films prepared under various preparation conditions were studied and are reported here. Relatively high retention of conductivity and flexibility properties in air at room temperature were found for the films. More stable films were produced from propylene carbonate diluent than from acetonitrile and solvent mixtures. Acid treatment caused conductivity to increase and the mechanical properties to decrease slightly. However, both properties decreased dramatically after exposure of the films to sodium hydroxide solution. The effect of solutions containing different vanadium ions was also observed, the films being stable in V3+ and V4+ acid solutions, but unstable in V5+ solutions. The thermal stability of polypyrrole films grown at different temperatures and from different solvents was considerably high and fairly constant. Anisotropy in the mechanical properties was also observed for the two directions (along and across) within the same plane of the film. Incorporation of the plasticizer, di-iso-butyl phthalate (DIBP) into the films improved the mechanical properties. A high extendable acrylic-polypyrrole composite film was also prepared, capable of straining over 100%.

Morphology and properties of acrylate styrene acrylonitrile/polybutylene terephthalate blends

The structure and mechanical properties of acrylate styrene acrylonitrile (ASA) and ASA/polybutylene terephthalate (PBT) blends have been studied. The morphology of ASA is found to conform to a previous model. 40/60 and 60/40 blends of ASA/PBT have a two-phase, dispersed morphology while the 50/50 blend is shown to have a co-continuous structure. As processing temperature is increased, the mechanical properties decrease, due to PBT degradation. The 60/40 ASA/PBT blend has very poor impact resistance because of the continuous, degraded PBT matrix. Better mechanical properties are observed for blends with a continuous ASA matrix, particularly in the 50/50 blend. Fracture surface analysis reveals a unique morphology of mushroom-like PBT fibrils for the low processing temperature samples near the crack tip. This is thought to occur due to the competition of cohesion and adhesion of the PBT with the ASA matrix.

Structure, strength and electrical performance of conducting polypyrroles

Polypyrrole films, typically 0.2 mm thick, were prepared by electrodeposition withp toluene sulphonate as dopant anions. Conductivities of up to 340 S cm−1 were found, comparing favourably with other cited examples. Conductivity along each sample was found to be much greater than across: such asymmetry may be exploitable. Electrodeposition temperatures (0° C) lead to higher conductivities than at 25° C. The structure was amorphous as indicated by X-ray diffraction, and the morphology was found to be nodular by using optical and scanning electron microscopy. Films were found to be quite strong and tough, although some reduction in mechanical performance was found after ageing in air. Fracture surfaces of tensile test pieces suggest a layered structure, with little evidence for viscous deformation being evident.

In-situ mechanical properties of tosylate doped (pts) polypyrrole

The in-situ mechanical properties of electrochemically prepared polypyrrole films have been measured whilst immersed in various electrolyte solutions and under the influence of applied electrical potential. The mechanical properties were observed to be sensitive to the oxidation state of the polymer, with the reduced form of the polymer showing a lower modulus and higher elongation at break. The electrolyte cation affected the potential at which the ductile-brittle transition occurs.

A kinetic study of polypyrrole degradation

Conducting polypyrrole films with p-toluenesulphonate, perchlorate and tetrafluoroborate dopants were aged at elevated temperatures in oxidizing and inert environments. Their decline in electrical conductivity was analysed using a first-order decay model. Films were also examined by X-ray photoelectron spectroscopy, differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. Changes in polymer morphology, degree of oxidation and dopant integrity were determined.

Fabrication and activation studies of conducting plastic composite electrodes for redox cells

Abstract Conducting polyethylene (PE) composite material is fabricated by mixing polyethylene with conducting fillers. Electrical, mechanical, permeation and electrochemical studies show that the PE composite is a good electrode matrix material for the vanadium redox battery. Chemical treatment studies on two kinds of PE composites show that the material with a high graphite-fibre content has good electrochemical activity and stability after treatment. Further cyclic voltammetry and SEM investigations indicate that chemical treatment increases the active surface area of the PE composite.

Electrochemical induced ductile—brittle transition in tosylate-doped (pTS) polypyrrole

Abstract A transition from a ductile to brittle behaviour has been observed in tosylate-doped polypyrrole resulting from reduction and oxidation of the polymer. The electrochemical potential at which the transition occurred was found to depend upon the electrolyte used, with sodium nitrate and sodium chloride undergoing reduction at higher potentials than occurred with magnesium nitrate and magnesium chloride. The ductile—brittle transition observed was found to be due to the formation of ionic crosslinking during oxidation, and their removal during reduction. The plasticization expected from the concomitant incorporation and expulsion of ionic species (with considerable water of hydration) was found to have a smaller effect.