The foaming process of composites can be strongly influenced by the size, shape, and type of the applied reinforcing materials. In this paper, the structure of foamed polyvinyl chlorides (PVCs) filled with natural additives and 4,4'-diphenylmethane diisocyanate (MDI) were examined by a newly applied ultrasonic technique. The modulus of the composite can be calculated by the longitudinal wave propagation time using this ultrasonic technique. Since the longitudinal waves of ultrasound are strongly influenced by the orientation of the reinforcing materials, the orientation of the composites can be also investigated. Dynamic mechanical analysis (DMA) and bending tests were used to check the changes in modulus, which is comparable to the calculated ultrasonic modulus. Due to the differences in the measurement processes, the ultrasonic and the bending measurements gave opposite results. These opposite results clearly indicate the orientation of the natural filler.

Keywords: polyvinyl chloride composites, ultrasonic measurement, elastic modulus, orientation