Effect of fiber length distribution on dynamic viscosity of model suspensions

Investigation of flow properties of suspensions and polymers and their flow behavior in various geometries, are essential in developing and understanding the processing and technology for polymers and polymer composites. In industrial applications, the chopped fibers in a matrix are far from being monosized and often one finds a distribution of fiber length in the matrix. In this work, the effect of fiber length distribution on the dynamic viscosity of model suspensions at room temperature, was investigated. A model suspension was prepared by mixing the appropriate amount of chopped nickel coated graphite fibers with two different lengths in a viscous silicon oil. Rheometries RDSII with cone and plate geometry, was utilized to conduct Dynamic Mechanical Analysis (DMA) spectroscopy on carefully prepared and characterized suspensions. The average fiber lengths were 1/16 and 1/32 in. and the composition of each suspension was 95% by volume oil and 5% fibers. The response of these experiments was a set of plots of dynamic viscosity versus strain rate. The composition of the suspension had an effect on the measured viscosities. An increase in viscosity was observed with an increase in the proportion of long fibers to short fibers. The suspensions of high long-fiber content lacked a Newtonian viscosity region.