Rigid polyurethane (PUR) foam is valued across construction, appliances and the automotive industry for its thermal and acoustic insulation, but its highly cross-linked chemistry has long complicated end-of-life recycling. A mechanical approach is drawing attention because it turns post-use foam into a fine powder that can serve as a reactive filler in adhesives rather than as inert waste.

Rigid PUR foam is built from isocyanates, isocyanurates and polyfunctional polyols, and it often contains flame retardants. Those components give the material high chemical stability, which is an advantage in service but a barrier at disposal.

Chemical recycling methods such as depolymerization face high energy demand, low yields and difficult separation of impurities, limiting large-scale industrial adoption. Landfill and incineration are also problematic: the foam biodegrades poorly, and incineration can release hydrogen cyanide and nitrogen oxides, according to the research.

Unlike flexible foam, rigid PUR foam has a glass transition temperature close to ambient conditions, allowing it to be mechanically degraded through micronization. Research shows that milling waste rigid PUR foam into a fine powder can physically reduce waste volume and produce a material that can be reincorporated into adhesive systems as an active filler.

The central innovation is to treat recovered PUR powder as a reactive ingredient rather than an ordinary filler. In one-component PUR prepolymer adhesives, replacing part of the polyol component with recycled powder, at a 20% substitution rate for example, maintained adhesive performance and significantly increased shear strength in wood bonding, the research shows.

For flexible adhesives, strength gains reached up to 10 times; for rigid adhesives, the increase was about twofold. The results suggest that the powder can participate in curing chemistry instead of merely adding bulk.