Hydration-induced reinforcement of rigid polyurethane–cement foams: mechanical and functional properties

Mechanical and functional properties of a newly proposed hybrid foam based on rigid polyurethane foam and Portland cement for application in the building field are herein reported. The hybrid is characterized by the co-continuity of the two phases, hydrated cement and polyurethane, which cooperate in a synergistic way to the properties of the resulting material. Furthermore, the closed-cell foam structure gives the material properties typical of porous materials: in particular, the hybrid foam evidences thermal insulation, sound absorption and acoustic insulation, high impact energy and low density typical of polymeric foams. At the same time, the hybrid foam exhibits water vapor permeability, improvement of thermal stability, high compressive mechanical behavior, and adhesion to concrete and mortars typical of inorganic binders such as cement. The materials were obtained by mixing cement powder with polyurethane foam precursors, i.e., methylene di(phenyl-isocyanate), polyol polyether and catalysts, and silicone surfactants. Water was used as blowing reagent. The resulting compounds were foamed in flat closed molds. The cement phase was then allowed to hydrate in accelerated conditions, i.e., in water at 60 °C for 72 h. Mechanical, morphological, and functional characterization showed that the hydrated cement particles interacted with each other, forming an inorganic network within the polymeric matrix (co-continuity), thus ''hydration-induced reinforcement of polymer-cement'' hybrid foam, in contraposition with the term ''composite foam