Plasticised PVC (Plastisol)

PVC was known for decades as a hard, brittle powder nobody could use. In 1926 Waldo Semon at B.F. Goodrich found that certain liquids dissolve it only when hot, and that the hot solution sets on cooling into a soft, rubber-like gel - flexible PVC. **US 1,929,453**, "Synthetic rubber-like composition and method of making same", Semon, assigned to B.F. Goodrich, granted 10. October 1933, claims dissolving "an insoluble polymerized vinyl halide at an elevated temperature" in a liquid that dissolves it only well above room temperature, and gelling it by cooling. One example: 8 parts PVC, 8 parts tricresyl phosphate, 3 parts dibutyl phthalate. **Plastisol is that idea in a bottle**: PVC grains suspended, undissolved, in plasticiser. Heat makes the liquid dissolve the grains and fuse into solid flexible PVC. You bake test films at three temperatures and pull them apart to find where it truly fuses.