C. A. Bernardo

Mechanical, surface and interfacial characterisation of pitch and PAN-based carbon fibres

Abstract The mechanical and surface characteristics of pitch and PAN-based carbon fibres were studied by tensile testing, XPS, SEM analysis and wetting measurements. The pitch-based fibres had two different geometries, with circular and ellipsoidal (ribbon-shaped) cross sections. Plasma oxidation was used to treat the surface of the fibres. The interfacial characteristics of untreated and treated fibres were measured by fragmentation tests of single filament composites. The effect of the surface treatment on the mechanical, surface and interfacial properties of the fibres was determined and correlated. It was shown that a relationship exists between the ability of the surface to transfer loads and its oxygen content. Finally, the influence of the non-axisymmetry on the interfacial parameters obtained in the fragmentation tests was assessed.

Role of sulfur in the production of carbon fibers in the vapor phase

Abstract Iron particles do not grow filaments in a methane atmosphere profusely enough to make a continuous reactor practical. Adding small quantities of sulfur to the iron vastly increases filament formation. We show that this is because the sulfur liquefies the iron particle, enhancing filament nucleation. With continued increases in sulfur, the number of filaments produced continues to increase, but quality, measured by length and straightness, decreases. We attribute this to higher sulfur concentration in the catalyst particle moving the melting point above the eutectic, thus decreasing the efficiency of filament lengthening.

Production and Assessment of Polycarbonate Composites Reinforced with Vapour-Grown Carbon Fibres

Abstract Vapour-grown carbon fibres were produced from methane in a flow reactor. The fibres were compounded with poly-carbonate in a co-rotating twin-screw extruder and the composites were subsequently injection moulded. The rheological characteristics of the polycarbonate composites reinforced with these vapour-grown carbon fibres were determined by using capillary and rotational rheometry. The tensile properties of the injection-moulded specimens were marginally better than those of the un-reinforced polycarbonate, but the impact resistance was severely diminished by the addition of the carbon fibres. This was attributed to the presence of polycyclic aromatic hydrocarbons on the surface of the fibres, that may impair the impact resistance of polycarbonate by chemical stress cracking.

Transport properties of polymer-vapour grown carbon fibre composites

Abstract DC electrical resistivity and thermal conductivity of polypropylene (PP) filled with vapour grown carbon fibre (VGCF) was studied. This was done for a wide range of fibre content and compared to systems produced under the same conditions in which a conventional carbon fibre was used as filler. The composites studied exhibit characteristic percolating behaviour. Because of the low degree of graphite perfection in the VGCF used in this work, the fraction of VGCF required to achieve percolation was higher than expected. Non-linear I – V characteristics and time dependent electrical resistivity effects are only observed in PP filled with VGCF. Several mechanisms must be called upon to explain the observed electrical behaviour of the PP/VGCF composite. The thermal conductivity of the composites is in agreement with the effective medium theories.

Effects of plasma oxidation on the surface and interfacial properties of carbon fibres/ polycarbonate composites

Two types of carbon fibres, ultra-high modulus (pitch-based) and high strength (PAN-based), were submitted to an oxygen plasma treatment. Single filament tests were performed to evaluate the effects of the treatment on the mechanical properties of the fibres. Weibull analysis of the tensile data revealed no substantial changes in the tensile strength after fibre oxidation. Fragmentation tests performed on carbon fibre/polycarbonate composites showed that the plasma treatment increases significantly the interfacial shear strength. This demonstrates the ability of the cool plasma oxidation to enhance the adhesion of carbon fibres to polycarbonate. The possible influences of the structural and chemical properties of the carbon surfaces upon the final response of the interface were investigated using inverse gas chromatography (IGC) at infinite dilution. The increase of surface functional groups induced by the plasma treatment seems to be the main reason for the improvement of the interfacial adhesion.

Studies of deactivation of metals by carbon deposition

Abstract Studies of carbon deposition from aliphatic and aromatic hydrocarbons over metal catalysts were carried out over the temperature range 700–1025 K using a microbalance coupled with a tubular reactor. The influence of the nature of the reactor wall on the rate of carbon formation, as well as the effect of hydrogen in preventing deactivation of the catalysts, was investigated. A general reaction scheme is proposed to explain the relationships between the different types of carbon formed on the catalysts.

Frontiers in the science and technology of polymer recycling

Preface. 1. Introduction. 2. Fundamental Issues Pertinent to Polymer Recycling. 3. Reprocessing of Single Type Polymers. 4. Reprocessing of Mixture of Polymers. 5. Recovery of Chemicals and Energy. 6. The Way Forward. Index.

The use of a three-point support flexural test to predict the stiffness of anisotropic composite plates in bending

Abstract Anisotropic polymeric matrix composite discs supported on three points were subjected to a non-destructive bending test to study their behaviour in complex flexural loading situations. The results show that the flexural behaviour of the composites depends on several factors, such as fibre orientation, laminate stacking, surface waviness and moulding temperature. The experimental data were compared with those obtained from the finite element program software Algor . Differences up to 13% were found between the experimental and simulated values of the flexural stiffness. In spite of that, it was concluded that the non-destructive test used is a useful tool to predict the behaviour of anisotropic composites and to validate the results obtained from computer FEM analysis.

The effect of morphology on the properties of vapour-grown carbon fibres

In the present work, mechanical properties of a batch of VGCF with various morphologies have been studied.

A novel technique for the interfacial characterisation of glass fibre–polypropylene systems

Abstract In the present work, a new technique was developed to determine the interfacial properties of two opaque glass fibre/polypropylene (GF/PP) systems via fragmentation tests on single filament model composites. Fragmentation tests usually require the fibre inside the composites to be completely aligned in the loading direction. Since PP matrices are non-transparent, it is not possible to guarantee a priori this condition. Hence, a novel technique was developed to determine the inclination of the filaments embedded in the composites. The fibre–polymer systems were also evaluated by comparing their interfacial properties with the overall mechanical properties determined on pultruded GF/PP composites. The present work shows that the knowledge of the interfacial properties is important, not only to compare alternative fibre/matrix systems, but also to assess whether the level of adhesion in these systems is adequate to fabricate composites with good mechanical properties.