Amorphous-to-crystalline transition of polyetheretherketone-carbon nanotube composites via resistive heating

The purpose of this study was to investigate increasing crystalline structure in polyetheretherketone (PEEK) via resistive heating. Multi-walled carbon nanotubes (MWCNT) were thoroughly mixed with PEEK powder, hot-pressed into a solid composite, then immediately quenched in ice water. Duplicate specimens were then reheated at 300 °C. 'Quenched' and 'heat treated' samples represented comparative minimum and maximum volume fraction crystallinity used in this study, respectively. Dynamic mechanical analysis, electrical conductivity measurements, scanning electron microscopy, optical microscopy, differential scanning calorimetry (DSC), and resistive heating tests were performed to characterize the composite properties as a function of MWCNT volume fraction. Results showed dispersion within the PEEK matrix is inherently limited by the powder-press technique. Nonetheless, MWCNT volume fractions as low as 1 vol% are above the percolation threshold and 5 vol% allow PEEK to be resistively heated above the glass transition temperature. DSC results of the quenched and reheated samples indicate that the MWCNTs do not inherently inhibit crystalline formation. Reheating the quenched samples via resistive heating is shown to increase the crystalline volume fraction. This study is the first to show an amorphous to crystalline phase transformation of PEEK via resistive heating, opening the possibility of changing mechanical properties and/or elastic deformation range in situ.