Hybrid foam combines strengths of wood and metal
Back in 2014, we heard how scientists from Germany's Fraunhofer Institute for Wood Research had developed a wood-based foam that could be used as eco-friendly insulation. Now, they've combined it with metal to create a composite that has a much wider range of potential applications.
The original foam is made by grinding down wood particles to the point that they form a slimy substance, adding gas to that slime to make it frothy, and then allowing it to dry – the wood used could conceivably be waste from the forestry industry.
Taking the form of rigid panels or flexible mats (pictured below), the finished product is reportedly well-suited to use as building insulation that's more environmentally-friendly than conventional petroleum-based foam, and that doesn't settle over time like some looser alternatives.
Samples of the original wood-based foam (Credit: Fraunhofer WKI / Manuela Lingnau)
To make the new wood/metal foam, a team led by Dr. Frauke Bunzel started by creating open-cell metal "sponges" via a casting process. The wood-fiber froth was then added to them – the sponges were repeatedly mechanically tapped, with the vibrations causing the viscous froth to trickle down through them, filling all of their cavities. It was then left to dry.
Known as HoMe foam (a German acronym for wood-metal), the result is a lightweight composite that still offers the thermal and acoustic insulation properties of the wood foam, but that has much higher bending strength than either the wood foam or the metal sponges alone. This characteristic allows it to also provide structural support. Additionally, it can conduct electricity.
It is now hoped that the HoMe foam could be sandwiched inside of existing materials or used in the form of stand-alone panels, with suggested applications including use as acoustic mats in cars' engine compartments, or as insulting plates in the vehicles' floors. The scientists are currently refining the processes of creating the wood foam and getting it into the metal sponges, with an eye toward soon entering commercial-scale production.