A process for the production of sulfur foam containing at least 50 weight percent sulfur, which comprises: A. heating sulfur in a first zone to a temperature above about 100.degree. C to obtain molten sulfur and reacting the molten sulfur with an organic protonic acid which is reactive with molten sulfur so as to incorporate the organic acid with sulfur to form a sulfur-organic acid adduct containing unreacted protonic acid groups; B. passing said sulfur adduct in liquid state out of said first zone and into a separate mixer; and C. mixing and reacting in said mixer a polyisocyanate with the unreacted acid groups of said sulfur adduct to thereby, upon removal of the polyisocyanate-acid group reaction product from the mixer, release gas and generate a foam. Preferably the sulfur adduct is formed by reacting sulfur with a plasticizer as well as the acid. The plasticization resulting from phenol reacting with sulfur is particularly preferred, and preferably the liquid phenolmodified sulfur-acid adduct is reacted with polyisocyanate in the mixer within a residence time of 0.1 to 3.0 seconds and within a temperature range of 110.degree. to 140.degree. C.
Gar Lok Woo; John M. Dale; Allen C. Ludwig