Influence of process parameters on the morphology, rheological and dielectric properties of three-roll-milled multiwalled carbon nanotube/epoxy suspensions

The influence of process parameters on the morphology, rheological and dielectric properties of multiwalled carbon nanotubes (MWCNT)/epoxy suspensions processed by three-roll milling has been investigated. Two apron roll speeds, 180 rpm (low) and 270 rpm (high); two different number of passes, 1 (low) and 5 (high); and two MWCNT loadings 0.01 (low) and 0.1 wt.% (high) were examined. Results obtained from rheological and dielectric measurements indicate that milling at the lower roll speed of 180 rpm leads to better enhancement of rheological and dielectric properties compared to milling at 270 rpm. The results also indicate that a higher number of passes is more favorable for improved rheological and dielectric properties. The relationship between the microstructure and the properties of the suspensions has been explained using the exfoliation-rupture MWCNT agglomerate dispersion mechanism. Milling at 180 rpm was observed to promote exfoliation of MWCNT agglomerates, whereas milling at 270 rpm promoted rupture. Agglomerate statistics carried out on micrographs of the suspensions provided circumstantial evidence that milling at the lower speed indeed promoted exfoliation over rupture, while milling at the higher speed promoted rupture. This technique of combining rheological and dielectric measurements could be an invaluable tool for monitoring MWCNT agglomerate dispersion changes, and hence tuning nanocomposite properties.