Quantitative assessment of dispersion stability and processing parameters in graphene-enhanced unsaturated polyester resins: Effect of mixing techniques

Recent advances in cost-effective graphene mass production highlight its potential for industrial applications, along with the challenges of achieving and controlling uniform dispersion at a large scale. State-of-the-art approaches such as functionalization, solvent mixing, and sonication are costly for large-scale use. As for dispersion analysis, microscopy techniques such as scanning electron microscopy and transmission electrical microscopy are still commonly employed, while emerging quantitative methods, including electrical conductivity measurements, micro-CT, and machine learning, remain time-intensive and are limited to fully-cured nanocomposites. This study aims to evaluate three mixing techniques-mechanical mixing, high shear mixing, and probe sonication-for dispersing an industrial mass-produced graphene powder in an unsaturated polyester resin. Their impact on processing parameters is examined using thermal and rheology analysis. Furthermore, dispersion states throughout the processing window are quantified for the first time. Results indicate that graphene addition inhibits resin curing, delaying gelation and increasing peak temperatures. Mechanical mixing exhibited the lowest dispersion efficiency with dispersion indices of 62.87%, 65.15%, and 66.37% at 0.25, 0.5, and 0.75 Wt.% graphene, respectively. Probe sonication was most effective at lower concentrations (66.65% and 68.20% at 0.25 and 0.5 Wt.%), while high shear mixer excelled at 0.75 Wt.% graphene (69.11%) due to increased viscosity. The dispersion states remained stable during curing, as the resin's higher viscosity restricted nanofiller mobility.Highlights Graphene delays resin curing (5.8%-40%) by radical scavenging and hindrance. Objective method for quantitative graphene dispersion across processing window. Better dispersion obtained using high shear mixer at higher graphene content. High resin viscosity stabilizes graphene dispersion, limits mobility in curing.