The vision behind FoamWood was inspired by biomimicry thinking. In other words, we started by looking at natural cellular structures to understand and replicate its beneficial properties.
We were particularly inspired by wood and its cellular, foam-like structures. This interest was then followed by an extensive laboratory scale research on the flow and control of foams made with bio-based particles (NFC, fibers). Which resulted in the FoamWood device: a machine that produces continuously and efficiently bio-based foams (FoamWood) with little cost and promising applications.
When taking a closer look at this very familiar material two properties stood out: wood’s load-bearing and insulation capacities. Both result from wood’s structures of elongated cells forming a unique large-scale structure with dual properties: in one direction wood is very strong, allowing it to carry large loads, while in the other, it is a good thermal insulator.
Also knowing that foams possess similar cellular structures, we wanted to explore how to create a bio-based foam with the same kind of elongated (anisotropic) structures found in wood. To that end, the challenge was to control the average foams’ bubble shape which tends to be spherical or hexagonal as they always relax to a symmetric shape once drying.
The research path
The team of scientists behind the project used their extensive knowledge of the preparation of wet foams to start the exploration process. More specifically, they started investigating the interfacial tension between the liquid and gas phases of foams.
Such exploration was based on the understanding of how lower tension levels allow the additional surfaces (formed by the thin films between the bubbles) to be maintained by the bubble structure, which may be achieved by the addition of surface-active materials such as surfactants or particles.
The team also explored novel methods to retain the shape of the bubble structure once the liquid is removed from the foam; as the two most well-known methods (quick oven baking and freeze-drying) have issues with the efficiency of the process itself and the scalability of production, respectively.
To find better solutions our approach focused on some peculiarly behaving materials. The special rheological properties of these materials allowed us to increase relaxation time so the foam could dry while maintaining the shape of the bubbles. This novel process allows for scalable and flexible production of such foam materials never accomplished before. Through Optical Coherence Tomography (OCT), Scanning Electron Microscopy (SEM), and mechanical testing we have confirmed that our method can produce anisotropic foams. Not to mention, our process may also be tuned in such a way that the necessary shrinkage occurring during the drying process favors a certain direction, further enhancing the anisotropy.
Years of research then resulted in the main innovation behind this project: the FoamWood manufacturing continuous process. It can be adjusted to customer-defined parameters to produce bio-based anisotropic foams made of readily available materials and minimize the amount of raw material.
The FoamWood process was designed in modules. Each of them can be customized separately to best fit customers production volumes and needs. The more foam nozzles a device has, the larger are the foam volumes it can produce. Consequently, the sizes of the other modules must be adjusted to fit the production volume. The simplicity and modularity of this method make it also suitable for decentralized production.
A key aspect of the innovation is the use of a cellulose based carrier fluid which acts as a binder and a mould to create anisotropic rod-like structures. One of the most interesting effects of the carrier fluid is the reduction of the energy consumption during the drying process. Independent of the additives the energy needed for water removal is significantly reduced, especially if compared to other foam forming processes.
The FoamWood method can produce a variety of foams using different raw materials and settings, each resulting in a different set of properties. At this point we conclude that almost any fiber based raw material that creates a network structure can be used with our method. Still, among the suitable foam mixes we believe the most interesting ones to be made fully with bio-based (and biodegradable) non-toxic ingredients. Nonetheless, we keep our eyes open for new materials and applications such as conductive carbon and suitable battery technology applications.
The FoamWood new continuous method produces foams with elongated and closed bubbles structures, which create an anisotropic film structure. Such characteristics give the final material high directional strength and insulating and shock proofing properties.
As a result, FoamWood has a superior directional strength (per density) in comparison to other bio-based foams. Due to the material’s elongated bubbles our foams are harder and stronger even if compared to cardboard.
our research shows
that FoamWood presents
great load-bearing strength
in one direction and
great thermal insulation
on the other.
Our team got to understand well how FoamWood behaves as a material. By examining the foam structure using Optical Coherence Tomography (OCT) and Scanning Electron Microscopy (SEM) we could confirm an average 1:2 aspect ratio between the length of the bubbles on the stronger direction and the insulating direction, confirming the anisotropy of FoamWood.
And through compression and acoustic emission (AE) experiments, we confirmed that along the elongated bubbles’ direction the strength was up to 64 times higher than the other direction. The strength difference between the orientations is significantly larger by a factor of 10 than other anisotropic cellulose foams.
To learn more about our research results, please check the scientific articles below:
From © The Royal Society of Chemistry 2020:
Crossover from mean-field compression to collective phenomena in low-density foam-formed fiber material