Cure Terms Glossary

Scorch

In conventional usage, scorch means heat-induced discolouration - and the word is used in exactly this sense to cover visible degradation in slabstock (polyurethane) foam manufacture. Given that this is an exotherm-driven process, and that the product is thermally insulating, avoiding scorch in the centre of the block is always a challenge in high throughput operations.

Scorch has a quite specific meaning in rubber technology where it is the term for premature vulcanisation of the mix before the final shaping can be accomplished. Scorch inhibits flow and results in scrap. Since the raw polymers are highly viscous, the work required for mixing generates substantial heat. Thus the act of mixing in the curatives can trigger the vulcanisation itself.

The challenge of the rubber technologist is to introduce adequate process safety into the cure formulation. The tendency to scorch is therefore routinely characterised - usually by monitoring viscosity at typical processing temperatures and noting the time (scorch time) to a given viscosity increment.