Versatile Method to Produce Wood Particle Foams for Building Insulation

Lightweight foams are excellent thermal insulators due to their structure, which traps layers of air pockets and results in low thermal conductivity. Modern buildings overwhelmingly use insulative foams derived from petrochemical sources, which not only contribute greenhouse gases during manufacturing but also end up in a landfill at the end of their life. Alternatives to petrochemical-based foams, such as mineral wool, have been linked to health concerns. As a result of these environmental and health concerns, the appetite for bio-based and environmentally-friendly materials is growing and may be awarded through building sustainability certifications like LEED or BREEAM [1].<br/><br/>Materials that are truly sustainable must be considered holistically, from their feedstock source to their manufacturing process to their end-of-life stage. Some examples of bio-based insulative foams are cellulose- and pulp-based foams, which are moving towards being fully sustainable but still require relatively high amounts of processing energy to transform them from their raw feedstock form. One feedstock source that is often overlooked is forest residues, materials generated by the forestry industry that have little to no economic value and includes bark, dead trees, off-cuts, and small-diameter trees. Due to their poor mechanical qualities, they are often used for low-value products [2].<br/><br/>We previously showed that we can circumvent the poor macro-scale mechanical properties of forest residue wood by milling the feedstock to &lt; 1 mm and recombining the wood particles as a lightweight, high bio-based content foam [3]. This previous work focused on pine beetle-killed wood, which refers to trees that have been killed by mountain pine beetles and may contribute to high-intensity fires if left in the forest [4]. To produce these foams, waste wood particles are foamed in water with surfactant and a water-soluble polymer binder and then oven dried [5], a relatively facile and low-energy method of solid foam production. The resulting foams have mechanical (density ca. 0.12 g cm⁻³) and thermal (thermal conductivity ca. 0.042 W m⁻¹ K⁻¹) properties that are competitive with conventional petrochemical-based foams. The promising performance of our foams is attributed to their low density and hierarchical pore structure consisting of polyhedral cells templated by air bubbles and natural honeycomb pores from the wood cell walls [3]. The end-of-life stage is also considered, as the foams are able to be re-wetted, re-foamed, and re-dried while maintaining their original properties.<br/><br/>Our current research pushes this method further by exploring different waste wood feedstocks, different particle sizes, and the replacement of our surfactant and polymer binder with bio-based materials alternatives. Verifying the potential of alternative waste wood feedstocks and particle sizes is important for scalability and adaptability, while alternative surfactants and binders are important to create a fully bio-based product with no negative environmental impact. In most cases the thermal and mechanical properties of these alternative foams are competitive and have the potential to replace petrochemical-based foams. The alternative foams that do not meet ASTM or building standards may still be able to pass if the milling procedure is tweaked to allow for higher aspect ratio particles, which may result in more comingling of the wood particles and binder and produce a more cohesive solid foam structure.<br/><br/>[1] Schiavoni et al. <i>Renew. Sust. Energ. Rev., </i>2016, 62, 988<br/>[2] Kizha & Han. <i>Biomass Bioenergy</i>, 2016, 93, 97<br/>[3] Ferreira et al. <i>Mater. Adv., </i>2023, 4(2), 641<br/>[4] Kurz et al. <i>PNAS, </i>2008, 105(5), 1551<br/>[5] Tiwary & Chen. Canada Patent WO 2022/073126, 2022