Lightweight, good insulators and cheap to produce — especially when fossil fuel prices are low — foam materials derived from petroleum or natural gas are routinely used to lag buildings, protect fragile goods during shipping and build lightweight structures.
The disadvantage, of course, is reliance on fossil fuels. So, researchers in Germany are turning their attention to raw materials derived from renewable sources in an effort to manufacture more sustainable foams.
Based at the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut (WKI), Braunschweig, Germany, the researchers have developed what they describe as a very promising approach to creating foam from wood particles.
“Our wood foam can be used in exactly the same way as conventional plastic foams, but is an entirely natural product made from sustainable raw materials,” explains professor Volker Thole, department head for process technology and system technology for wood-based materials at Fraunhofer WKI.
Figure 1. Manufacturing of the new foam relies on chemical processes similar to those at play when bread is baked. Source: Fraunhofer WKI.
Another of its advantages is that, unlike conventional foam products, wood foam can be easily recycled after use. For instance, if used as packaging material, it can be simply discarded in the paper recycling bin.
The scientists produce the foam by first grinding wood very finely until the tiny wood particles become a viscous mass. They then add gas to this suspension to expand it into a frothy foam and allow it to harden. The hardening process is aided by natural substances contained in the wood itself.
This new manufacturing technique is based on specific chemical processes. “It’s similar to the way dough rises and sets when bread is baked in an oven,” Thole explains. The resulting wood foam is a lightweight material that can be formed into rigid boards or flexible sheets. Just like other wood-based products, they can be easily sawed or cut to the desired dimensions.
In terms of home insulation applications, the new foam doesn’t suffer from the deformation that is a problem in existing wood-based insulation materials such as wood-fiber sheets and wood-fiber wool.
“Thin sheets of fiber insulation have a tendency to gradually collapse under their own weight due to the accumulation of moisture, especially in the middle. This adversely affects their insulating properties,” says Thole.
In contrast, he stresses, the wood foam developed at WKI is every bit as good as conventional plastic foams in this regard: “We analyzed our foam products in accordance with the applicable standards for insulation materials and obtained very promising results, not only in terms of their thermal insulation properties but also with respect to their mechanical and hydrodynamic properties.”
In other words, the wood foam insulates well, and is resistant to pressure and humidity.
The scientists are currently experimenting with different types of wood to determine which tree species provide the best raw material for this application. Furthermore, they are working to identify suitable processes for mass-producing wood foams on an industrial scale. The wood-based foam products are expected to be ready for commercialization within a few years.
Such is the potential of this novel material that it already has won a 2015 GreenTec Award in the “Construction and Living” category. The GreenTec Awards are Europe’s largest environmental and business prize. Every year, they honor innovative products and projects that lead the way toward a more environmentally friendly future. Criteria for selection include a project’s contribution to environment protection, its level of innovation, and whether the idea generates a positive publicity effect for future sustainability.
Fraunhofer WKI also is focused on preparing wood and other renewable materials for use in wood-polymer composites (WPCs). Today, these are commonly used for decking.
Industrial WPC formulations on the European market normally contain about 70% wood flour, 20–25% thermoplastic polymer and 5–10% additives. The additives, including coupling agents, UV stabilizers, pigments, lubricants, biocides and foaming agents, are intended to improve the machinability and performance of the composite.
WPCs are primarily produced by extrusion, injection molding or compression molding. Various thermoplastics are used as polymer matrices.
In this work, the researchers focus on optimizing particle size, formulation development — including wood, natural fibers, polymers, biopolymers, polymer blends and additives — together with durability testing, and the use of recycled WPCs and other materials.
The organization has set up a testing center in Giessen, Germany, for monitoring quality and testing specifications for new WPC decking materials.