Friction and wear properties of PET nanocomposites: The role of matrix morphology, nanoparticles and interface

Tribology of nanoparticle filled polymer systems is of significant interest for the unique behavior that can be obtained. Incorporation of nanofillers has been shown to lead to composites with combined properties of high wear resistance at low loadings as well as reduced friction. The tribology of semi-crystalline polymers is closely connected to the spherulitic and crystalline morphology and as the morphology changes on addition of nanofilers, the tribology can also be expected to change.; In this study, we report the tribological behavior of composites of poly(ethylene) terephthalate (PET) with nanosize Al2O3. Results show that the addition of nanofillers to samples prepared under the same processing conditions increases the wear resistance by as much as 45%. Simultaneously, the coefficient of friction decreases by 24%. Beyond a certain filler content, both properties increased. The addition of nanoparticles changes the crystallization behavior, crystallinity, spherulitic morphology and the supramolecular structure of PET. The decrease in coefficient of friction is attributed to a decrease in crystallinity. The inherent nature of the nanoparticles, however, is to increase the coefficient of friction of the composite. When samples of same crystallinity, but with varying filler content were tested, the coefficient of friction of the nanocomposites was higher than the unfilled polymer. However, the wear rate initially decreased with addition of nanoparticles and then increased beyond an optimum filler content. The decrease in wear rate is attributed to improved adhesion of the transfer film to the counterface with higher filler contents. With increasing nanoparticles loading, there is also an increased tendency of the nanoparticles to agglomerate in the transfer film due to shear as a result of the proximity of the particles. The presence of an optimum filler content is due to competition between increased adhesion of the transfer film and a higher tendency to form abrasive aggregates with increasing filler content.; A procedure was developed for establishing a strong interface between the nanoparticles and the PET matrix. However, the composites with strong interface did not show significantly better properties than composites with weaker interface.