Mechanical degradation of mica during processing with polypropylene

Abstract Mechanical degradation of reinforcing fillers during processing is a problem that has been seldom studied due to a lack of particle size determination techniques. Using phlogopite mica as an example, a method allowing a rapid and accurate characterization of flake size and aspect ratio will be described. The influence of several parameters on the mechanical degradation of mica flakes in a mica/polypropylene system has been studied using a laboratory roller blade mixer. The degradation was found to occur in two stages. The first stage takes place immediately after the addition of mica, where the average flake size decreases very rapidly by as much as 20 percent. In the second stage, the particle size remains essentially constant with the time of mixing at low concentrations (2 percent wt); at higher concentrations (40 percent wt) there is a slow reduction in the flake size. The influence of other parameters such as system viscosity, mode of mica addition, silane treatment, and the initial particle size is also discussed.