
Application Note:Research on polypropylene / carbon nanofiber composites indicate that samples with very low fiber aspect ratios (approximately l/d=19) have higher vibration damping properties than those having high fiber aspect ratios. Also, carbon nanofiber that has been heat treated gives the highest damping values when used as reinforcement in polypropylene.Source Data:Discussion:Carbon nanofibers are incorporated into polypropylene composites and are tested for vibration damping properties. Predictions show that composites having very low fiber aspect ratios should have higher damping than those having high fiber aspect ratios, and that the carbon nanofiber aspect ratios of approximately l/d=19 are in the range which yields the highest predicted damping. Storage modulus and loss modulus both increase as the fiber aspect ratio increases. Damping loss factor decreases as the fiber aspect ratio decreases. Top left graph: Plot of loss factor, loss modulus, and storage modulus for VGCF/PP composites as a function of fiber aspect ratio (l/d). The analytical model predicts a maximum loss factor for l/d is less than 50 and the loss modulus reaches a peak at l/d=500. The damping loss factor of the VGCF/PP composites decreases as the fiber aspect ratio increases. Top right graph: Predicted loss factor vs. fiber volume fraction for different fiber aspect ratios. The damping loss factor decreases as the fiber volume fraction increases for short fibers as well as for long fibers. Bottom left graph: Predicted and measured loss factor vs. fiber volume fraction for VGCF/PP composites having l/d=19 (T=21oC). It is seen that adding carbon nanofibers as reinforcement to the polypropylene decreases the damping loss, but increases the storage modulus (bottom right graph). The highest measured loss factor is obtained at the lowest fiber volume fraction. This coincides with the fact that the damping in composites is matrix dominated. Also, the carbon nanofiber having a graphitized surface (heat treated) gives the highest damping values if used as reinforcement in polypropylene. Bottom right graph: Predicted and measured storage modulus vs. fiber volume fraction for VGCF/PP composites having l/d=19 (T=21oC). The trend of the stiffness is opposite to the trend of the loss factor, i.e., as the fiber volume fraction increases the composite stiffness increases. The fiber surface treatment of the carbon nanofibers has an effect on the storage modulus of the carbon nanofiber/polypropylene composites. 