Temperature, time, pressure, and CO2concentration dependence of rheological properties for poly(methyl methacrylate)/expanded graphite composites

Abstract

The effects of temperature, pressure, and supercritical carbon dioxide (scCO2) concentration are investigated on the rheological behavior of poly(methyl methacrylate)/expanded graphite (PMMA/EG) composites with 1, 4, and 7 wt. % EG. The validity of the time-temperature superposition and time-pressure-scCO2 concentration superposition principles for the PMMA/EG composites is explored. At atmospheric pressure, the time–temperature superposition principle holds for the composites with 1 and 4 wt. % EG but fails for that with 7 wt. % EG. This is demonstrated by the rheological master curves and the van Gurp–Palmen plots. The scanning electron microscopy micrographs, the Cole–Cole plots, and weighted relaxation spectra reveal that the composite with a higher content (7 wt. %) of EG exhibits a stronger interfacial interaction between the PMMA chains and EG layers and delayed chains’ relaxation. The viscosity evolution with testing time for the PMMA/EG composite samples during time sweep testing demonstrates that the EG layers hinder the dissolution of scCO2 into the PMMA matrix to some extent. Different from the time–temperature superposition principle, the time–pressure–scCO2 concentration superposition principle is valid for all the prepared PMMA/EG composite samples. This is because the dissolved scCO2 at the PMMA matrix-EG layer interfaces reduces the interfacial interaction between the PMMA chains and EG layers and weakens the effect of the EG layers on the chains’ relaxation.