Rheology of polypropylene filled with short-glass fibers: From low to concentrated filled composites

Dynamic flow properties of two commercial short glass fiber reinforced polypropylene were carefully investigated. Rotational rheometry was employed to analyze the effect of the particle size distribution, the sizing and the fiber content on the flow properties. This experimental study allowed the examination of large fiber volume fractions up to 60 vol%, allowing the evidence of different phenomena. As generally known, the more the fiber level, the higher is the reinforcement effect on the matrix. The higher the average aspect ratio, the higher is the probability of creating a fiber network. Thus, higher aspect ratio leads to lower values of percolation threshold (4). It was found that, small variations of the particle size distribution strongly affect the flow behavior of the composites. Dynamic frequency sweeps put in evidence the different concentration transitions regimes viz., dilute to semi-dilute and concentrated to nematic regimes. Finally, the elastic characteristic time has been found to increase when increasing the fiber content. This was in agreement with the behavior of the relative viscosity as a function of the filler level.