Polyurethane foams co-blown by water and alkylated polyethylenimine-CO2 adducts: An additive or antagonistic effect?

Recently developed CO2 adducts of alkylated polyethylenimines (PEIs) can replace traditional, ozone-depleting, and/or global warming halogen-containing blowing agents of polyurethanes (PUs). Meanwhile, water is the most common chemical blowing agent that is cheap and also environment neutral. Herein, the co-blowing performances of the two types of blowing agents were investigated. For the polyether polyol or castor oil derived polyol foaming systems, which were blended just before foaming, the consequent co-blown foams surprisingly did not possess lower densities than the control foams blown solely by water, showing an antagonistic effect in blowing performance. The relatively large particles (e.g. tens of micrometers) of the hydrophilic PEI-CO2 blowing agents absorbed water from the foaming mixtures, preventing the trapped water from chemically blowing PUs. After the foams were set, the absorbed water gradually diffused out to react with the residual isocyanate groups, which no longer contributed to PU foaming. Differently, after aging the castor oil derived polyol foaming mixtures (without water and isocyanate components that were added before PU foaming), the dispersed PEI-CO2 particles decreased in size down to nanoscale (about 20–180 nm). These nanoparticles were small enough for out-diffusion of the absorbed water, which generated foaming CO2 in time. The densities of the resultant foams could be lowered to the theoretical values. The additive effect with water could enhance the application freedom of the climate-friendly alkylated PEI-CO2 blowing agents.