Improved properties of carbon nanotube/polymer nanocomposites using a supercritical CO₂ aided melt blending method

Improvements in carbon nanotube (CNT) dispersion and subsequent mechanical properties of CNT/poly(phenylsulfone) (PPSF) composites were obtained by applying the supercritical CO₂ (scCO₂) aided melt blending technique that has been used in our laboratory for nanoclay/polymer composite preparation. The preparation process relied on rapid expansion of the CNTs followed by melt blending using a single-screw extruder. Scanning electronic microscopy (SEM) results revealed that the CNTs exposed to scCO₂ have a more dispersed structure. Further optimization of the nanotube expansion process will be investigated in order to completely disentangle the nanotube bundles before the melt compounding step. Microscopy results showed improved CNT dispersion in the polymer matrix and more uniform networks formed with the use of scCO₂, which indicated that CO₂ expanded CNTs are easier to disperse into the polymer matrix during the blending procedure. The CNT/PPSF composites prepared with scCO₂ aided melt blending and conventional melt blending showed similar tensile strength and elongation at break. The Young's modulus of the composite prepared by means of conventional direct melt blending failed to increase beyond the addition of 1 wt% CNT, but the scCO₂ aided melt blending method provided continuous improvements in Young's modulus up to the addition of 7 wt% CNT. Due to their high cost, it is desirable to see these improvements at lower nanotube concentrations. Efforts at controlling orientation of the nanotubes, and future work on nanocomposites of polar polymers with polar functionalized nanotubes will seek to rectify this.