A new synthesis route to produce isocyanate-free polyurethane foams

Isocyanate is a toxic substance that is one of the main reactants used in the conventional fabrication route for polyurethane foams. This study presents the synthesis of isocyanate-free polyurethane foams from cyclic carbonates and diamines using sodium bicarbonate as the foaming agent. Three different series of foams are synthesised using three types of sodium bicarbonates having different average particle sizes (i.e. 3, 13, and 22 µm) at four content levels (i.e. 5, 10, 15, and 20 wt% with respect to cyclic carbonate). The density, open-cell content, average cell size, normalised standard deviation of the cell size distribution, anisotropy, cell density and cell nucleation density are characterized for all the materials synthesized. In addition, a theoretical study of the expected densities is conducted to compare the theoretical values with the experimental densities obtained for the foams. Finally, the foams previously manufactured with high sodium-bicarbonate content are optimised by modifying the catalyst content from 0.5 to 2.0 wt% with respect to cyclic carbonate, thereby producing foams with lower densities. Nonisocyanate polyurethane foams having densities as low as 142 kg/m3 are fabricated.