Developing Insulating Polymeric Foams: Strategies and Research Needs from a Circular Economy Perspective

Insulating polymeric foams have an important role to play in increasing energy efficiency and therefore contributing to combating climate change. Their development in recent years has been driven towards the reduction of thermal conductivity and achievement of the required mechanical properties as main targets towards sustainability. This perception of sustainability has overseen the choice of raw materials, which are often toxic, or has placed research efforts on optimizing one constituent while the other necessary reactants remain hazardous. The transition to the circular economy requires a holistic understanding of sustainability and a shift in design methodology and the resulting research focus. This paper identifies research needs and possible strategies for polymeric foam development compatible with Circular Product Design and Green Engineering, based on an extensive literature review. Identified research needs include material characterization of a broader spectrum of polymer melt-gas solutions, ageing behavior, tailoring of the polymer chains, detailed understanding and modeling of the effects of shear on cell nucleation, and the upscaling of processing tools allowing for high and defined pressure drop rates.

Manufacture and model calculation of porcelain-like microcellular low-density polystyrene foam

It is a well known that nucleation by gases in the supercritical state lead to high-density nanocellular foams, but the aim of this article was to find a route to microcellular low-density closed-cell foam with expected low heat conductivity and high mechanical properties. Polystyrene was impregnated with carbon dioxide or propane at room temperature and 70 bar pressure. Pentane served as a reference substance. The samples were investigated by electron microscopy. The specimens comprising carbon dioxide and propane showed bubbles surrounded by a ring of lamellas. The samples were foamed in hot bathes of silicone, of saturated NaNO3 water solution, and in water vapor under stretching conditions at 100℃ or 110℃. The foaming was registered continuously on a balance by buoyancy experimentally and calculated in diffusion as well as viscosity-controlled foaming models. A microcellular foam with 35 kg/m3 density, 1.5 µm or 1500 nm cell diameter, 5.5 MPa tear strength, and 0.027 W/m.K heat conductivity was obtained, which looked like porcelain. The continuous manufacture of low-density carbon dioxide or propane foam by extrusion did not lead to microcellular foam, because the necessary high-pressure, low-temperature nucleation conditions could not be performed.