Strain Rate Dependent Behavior of Carbon Nanofiber Filled Polypropylene
In this study, vapor-grown carbon nanofibers were mechanically dry-mixed with polypropylene powder and extruded into filaments with a single screw extruder. Then tensile tests were performed on the single filament at a strain rate range from 0.02/min to 2/min. Results indicate that both neat and nanophased polypropylene were strain rate-strengthening material. The tensile modulus and yield strength both increased with increasing strain rate. Results also show that infusing polypropylene with nanofibers increases tensile modulus and yield strength, but decreases ductility. The thermal properties of neat and nanophased polypropylene were characterized by TGA and DSC. TGA thermograms showed that the nanoparticle-infused systems are more thermally stable, and DSC results indicated that CNFs can slightly increase melting temperature and crystallinity. Finally, based on the tensile test results, a nonlinear constitutive equation was developed to describe strain rate-sensitive behavior of neat and nanophased polypropylene.