Thermal diffusivity measurements of vapour grown carbon fibre composites, using the optical beam deflection technique

Carbon fibres are used widely as reinforcements for polymeric matrices in h igh-tech applications by virtue of their good mechanical, electrical and th ermal properties. Vapour grown carbon fibres (VGCF) are a new type of fibre s whose technological applications, namely reinforcements for thermoplastic matrix composites, are yet to be developed. Due to their potentially low c ost and high production rates, VGCFs show promising new possibilities in th is area. Recently, in industry worldwide, the potential of VGCFs in thermal and electrical applications such as solid-state batteries and electrostati c painting of high volume automotive plastic parts is increasingly being re cognised. As a result, easy and non-destructive measurement of thermal and electrical properties of VGCF-based composites has become an important issu e for use in industrial applications. In this study the optical beam deflec tion technique was used for the evaluation of the thermal diffusivity of va pour grown carbon fibres (VGCF) - polymer composites. It is shown that, for low diffusivities, simple approaches such as the "phase method" or the "ze ro crossing method" are not valid and a multiparameter fitting to the ampli tude values has to be used instead. The thermal diffusivity of the composites, measured along the direction of the fibre preferential orientation, increases with fibre content. This incr ease is not very marked, possibly due to poor adhesion between fibre and ma trix. (C) 1999 Elsevier Science S.A. All rights reserved.