Extruded Polystyrene Foam: Methyl and Methylene Chloride Gel Let Out at 90 °C (McIntire, Dow 1948, Ex. 2)

Extruded polystyrene foam blown with a mix of methyl chloride and methylene chloride. Polystyrene soaks up both under pressure at 60 °C into a gel. The gel is heated to 90 °C and let out through the bottom valve, where it swells into foam. The gel flowed rapidly and gave small cells that did not shrink or collapse. McIntire found that a hotter gel gives finer cells, because the heat boils off all the chlorides. Methyl chloride is a toxic, flammable gas. Source: O. R. McIntire (Dow), US 2,450,436 (1948), Example 2. Picture: the patent's drawing.