Desenvolvimento de compósitos PU / PAni / grafite eletricamente condutores para aplicações tribológicas

Abstract

Conducting polymer market is expected to grow 8.4% annually from 2016 to 2021. Typical applications of those materials include electrostatic dissipative (ESD) packages, ESD bearings, biomedical devices and electrostatic paints. Intrinsic conductive polymers (ICPs) display the ability to conduct electricity through its macromolecules. ICPs are gaining market share steadily against extrinsic conductive polymers (ECPs). ECPs are polymeric composites with conductive fillers. However, ICPs do not present suitable mechanical properties for tribological applications. They could, nonetheless, be used as fillers in an insulating matrix, making a blend that could be able to withstand tribological uses. Recent advances in graphene production technologies, such as carbon nanotubes and graphite nanoplatelets, allowed the development of novel materials using small fractions of conductive fillers. Therefore, it is possible to obtain conductive materials without significant losses of mechanical properties. This work aims to develop and evaluate novel conductive composites, using a commercial polyurethane (PU) matrix filled with graphite nanoplatelets (GNPs) and polyaniline (Pani), which is an ICP of high scientific and technological interest. GNPs present high aspect ratio due to its micrometric diameter and nanometric thickness, which is necessary for low electrical percolation thresholds. GNPs were obtained through ultrasound exfoliation of a commercial expanded graphite (EG). Polyaniline synthesis was carried as traditionally reported in the literature, with partial modification by addition of sulfonic acid followed by fine grinding. All particles were analyzed with scanning electron microscopy, laser diffraction granulometry, X-ray diffraction and infrared spectroscopy with Fourier transform. Tribological characterization of PU and its blends and composites was carried with ball-on-plate reciprocating tests on a tribometer, under different loads and speeds. Wear width was measured through optical micrographs of the worn surface. Volume electrical conductivity was evaluated with a potentiostat/galvanostat. GNP and Pani composites were obtained with 0 to 10wt% GNP filling and 0 to 30% Pani filling. Materials with a minimum of 8wt% GNP and 10wt% Pani exhibited conductivity of 10−7 S m−1 and 10−6 S m−1, respectively. Those values are in the semiconductor range. Mean kinetic coefficient of friction dropped 30.2% with 1.3wt% GNP filling. Polyaniline did not affect wear or friction behavior up to 1.3wt% filling. Wear width was shown to be a function of normal load and composition. Results show the novel 4wt% GNP filled composite can be used in tribological applications with ESD needs. Other composites, such as those with 10wt% GNP or 10wt% Pani, can be used in other applications. However, those are not suited for tribological applications.