Abstract
Carbon nanoparticles tend to form agglomerates with considerable cohesive strength, depending on particle morphology and chemistry, thus presenting different dispersion challenges. The present work studies the dispersion of three types of graphite nanoplates (GnP) with different flake sizes and bulk densities in a polypropylene melt, using a prototype extensional mixer under comparable hydrodynamic stresses. The nanoparticles were also chemically functionalized by covalent bonding polymer molecules to their surface, and the dispersion of the functionalized GnP was studied. The effects of stress relaxation on dispersion were also analyzed. Samples were removed along the mixer length, and characterized by microscopy and dielectric spectroscopy. A lower dispersion rate was observed for GnP with larger surface area and higher bulk density. Significant re-agglomeration was observed for all materials when the deformation rate was reduced. The polypropylene-functionalized GnP, characterized by increased compatibility with the polymer matrix, showed similar dispersion effects, albeit presenting slightly higher dispersion levels. All the composites exhibit dielectric behavior, however, the alternate current (AC) conductivity is systematically higher for the composites with larger flake GnP.
Highlights
The alternate current (AC) electrical conductivity of PP/graphite nanoplates (GnP) nanocomposites was measured with a Quadtech (Sussex, WI, USA) 1920 Precision LCR meter directly on the disks collected from the last flow channel, near to the mixer outlet
Their primary nanoparticles form agglomerates with high cohesive strength, which has practical consequences on the rate and intensity of dispersion in the polymer melt during nanocomposite processing
Different average areas were measured for each GnP type, and it was consistently observed that the nanoparticles functionalized with PP-g-MA formed larger agglomerates
Summary
Polymer matrix-based nanocomposites have attracted intensive research and development effort, due to their potential for developing novel, cost-effective, and high-performance products for advanced engineering applications, for example, in aerospace, automotive, construction, and medicine. The prevalent strategy consists on the chemical oxidation of the graphene surfaces as described by Brodie [13], Staudenmaier [14], and Hummers [15] These procedures disturb the conjugated nature of the graphitic lattice by local bonding of oxygen-containing groups, shifting its hybridization state from sp to sp , as indicated by Raman spectroscopy studies [16,17]. It is well accepted that the dispersion of carbon nanoparticles into polymeric matrices and the electrical percolation threshold of nanocomposites are strongly dependent on nanoparticle surface chemistry [3,21,22], agglomerate density and strength [23,24], size [25], aspect ratio [26], purity [27], alignment [28,29], as well as on polymer type [30] and viscosity [31,32,33]. Dispersion and re-agglomeration were analyzed by microscopy, and the electrical conductivity of the composites was measured
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
