Influence of nanoscale fibres and discs on intrinsic modulus and packing fraction of polymeric particulate composites and suspensions

Abstract

There appear to be three potential response regions in the processing of polymeric suspensions or composites containing non-spherical particles such as fibres or discs. Two apparent maximums as a function of concentration should be manifested for the viscosity of a suspension or the modulus of a composite with fibrous or disc particles. The first maximum is attained as the concentration approaches the maximum random packing fraction associated with a specific fibre or disc aspect ratio α. The second maximum occurs at a much higher concentration associated with the maximum aligned packing fraction at which viscosity processing would be practical. This two-maximum processing response has been confirmed theoretically and experimentally for both discs and fibres. However, experimental measurements have also shown that if shear stress is very high, the first maximum does not occur owing to induced preferential orientation of the fibres and/or discs. A new variable, the 'sphericity' s (as a function of α, defined as the surface/volume ratio of a non-spherical particle relative to that of a sphere of equivalent volume, is introduced. A modification of the Kerner equation, based on a simple function of s, is proposed to predict the intrinsic modulus of non-spherical particles. For composites with non-spherical particles, a modification of the generalised modulus - viscosity model employing a simple function of s is found to be give an effective fit for modulus and viscosity data over the whole concentration range.