Evaluation of the unraveling state of polymer fiber lumps in powder matrix by using image analysis

An image analyzing technique was applied to evaluate the dispersion state of chopped aramid fiber (average diameter 12 μm and aspect ratio 83.3) in a matrix. In order to observe the fiber distribution in the fluffy fiber—powder mixtures just after the mixing operation, the mixture samples were pre-pressed to one-fifth in volume at constant pressure and formed into a disk shape using molding epoxy resin. In the range of fiber—powder ratios necessary to obtain unraveled fiber, the total number of exposed fibers in the cross-section of the molded test piece was proportional to the initial fiber concentration in spite of the degree of dispersal. The experimental values agreed well with the estimated number of fibers based on the simplified arrangement model. Therefore, it was shown that the variation of dispersion state versus mixing time could be discussed based on the coefficient of variation, CV. In addition, it was ascertained that the bulk density of the unraveled sample, ρ0, of the fiber–powder mixture was an effective index expressing the degree of dispersion.