Abstract
Polyetherimide (PEI) foams with graphene nanoplatelets (GnP) were prepared by supercritical carbon dioxide (scCO2) dissolution. Foam precursors were prepared by melt-mixing PEI with variable amounts of ultrasonicated GnP (0.1–2.0 wt %) and foamed by one-step scCO2 foaming. While the addition of GnP did not significantly modify the cellular structure of the foams, melt-mixing and foaming induced a better dispersion of GnP throughout the foams. There were minor changes in the degradation behaviour of the foams with adding GnP. Although the residue resulting from burning increased with augmenting the amount of GnP, foams showed a slight acceleration in their primary stages of degradation with increasing GnP content. A clear increasing trend was observed for the normalized storage modulus of the foams with incrementing density. The electrical conductivity of the foams significantly improved by approximately six orders of magnitude with only adding 1.5 wt % of GnP, related to an improved dispersion of GnP through a combination of ultrasonication, melt-mixing and one-step foaming, leading to the formation of a more effective GnP conductive network. As a result of their final combined properties, PEI-GnP foams could find use in applications such as electrostatic discharge (ESD) or electromagnetic interference (EMI) shielding.
Highlights
Polyetherimide (PEI) is a high-performance thermoplastic that has proven to be a viable candidate in advanced applications in cutting edge sectors, such as aerospace, due to its outstanding properties, including, but not limited to, high mechanical performance, high chemical and inherently high flame resistance, thermal and dimensional stability, low smoke generation, and transparency [1]
The values of the temperature corresponding to a 5% weight loss (T5% weight loss ), the temperature at maximum velocity of degradation (Tmax ), the temperature corresponding to a 35% weight loss (T35% weight loss ), the char residue (CR, in wt %), and the limiting oxygen index (LOI), calculated based on Van Krevelen and Hoftyzer [26] equation: LOI(%) = 17.5 + 0.4CR
The results indicate that two main factors could have affected the viscoelastic response of foams: Their relative density and the amount of graphene nanoplatelets (GnP)
Summary
Polyetherimide (PEI) is a high-performance thermoplastic that has proven to be a viable candidate in advanced applications in cutting edge sectors, such as aerospace, due to its outstanding properties, including, but not limited to, high mechanical performance, high chemical and inherently high flame resistance, thermal and dimensional stability, low smoke generation, and transparency [1]. The properties of PEI-based nanocomposite foams prepared using water vapour-induced phase separation (WVIPS) have been investigated in depth and the effect of carbon-based nanoparticles on the physical properties of these foams has been studied, showing promising results in terms of simultaneously enhancing the mechanical properties and electrical conductivity [3,4,5,6,7] Another foaming technique with characteristics closer to that of industrial foaming processes involves the dissolution of a gas in a polymer precursor in a semisolid-state, i.e., below its melting temperature (semicrystalline polymers) or below its glass transition temperature. This article considers investigating the effects of foaming by scCO2 on the cellular structure, thermal, mechanical, and electrical properties of PEI foams containing variable concentrations of GnP (0.1–2.0 wt %), with the objective of developing novel lightweight materials for advanced applications, such as EMI shielding, ESD, and fuel cells
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