Low density full water blown polyurethane rigid foam

Abstract

A formulation for preparing a low density, full water blown polyurethane rigid foam includes an isocyanate component; an isocyanate-reactive component comprising from 30-50 wt % of a first polyether polyol having a functionality greater than 5 and an OH value from 350-550 mg/g; from 5 to 25 wt % of a diol having an OH value from 100-300 mg/g; and from 15 to 35 weight percent of a second polyether polyol having a functionality from 3 to 5; further including from 1.5 to 5 wt % of a catalyst selected from dimethylbenzylamine and/or 1,2-dimethyl-imidazole; from greater than 0 to 1 wt % of a trimerization catalyst selected from a glycine salt and/or tris(dimethyl aminomethyl) phenol; greater than 4.1 wt % water as a blowing agent; and any additional constituents selected such that the formulation, excluding the isocyanate component, totals 100 wt % and, the formulation absent the isocyanate component, has a dynamic viscosity from 540 to 864 mPa*s at 20° C. Processing under one-shot conditions can yield a rigid form having a molecular weight per crosslink ratio from 380 to 420. The formulation offers good processability, while the foam shows desirable dimensional stability and mechanical properties at unexpectedly low applied density.