Scorch Safety: Understanding t5, ts2 and t35
How to read scorch numbers off a Mooney or rheometer curve, and what safety margin to require from a supplier.
Scorch — premature crosslinking during processing — stops a production line and scraps material. It is also entirely predictable if you ask for the right numbers.
The numbers
- •t5 (Mooney scorch) — minutes for viscosity to rise 5 units above the minimum at the test temperature. A common specification minimum.
- •ts2 (rheometer) — time to 2 units of torque rise above minimum at cure temperature.
- •t35 — minutes to rise 35 units, sometimes used alongside t5 to judge how sharply scorch accelerates once it starts.
What margin to ask for
The processing safety you need depends on how much heat history the compound sees before it reaches the mould: mixing dump temperature, mill passes, extrusion, calendering and any storage in a warm warehouse. As a working rule, the compound's t5 at the actual processing temperature should be several times the total hot residence time in the process.
Common causes of a sudden scorch problem
- •Accelerator level increased without changing the activator package.
- •Masterbatch stored warm, or stored too long before the final mix.
- •A change of carbon black supplier changing the surface chemistry and hence cure interaction.
- •Ambient temperature rising in summer with no adjustment to the mix cycle.
If scorch appears suddenly on a previously stable compound, check storage conditions and ingredient lot changes before reformulating. ## Need the documents or today's price? Send us the grade, quantity and destination port — we return a quotation with COA and MSDS attached. Email manager@fipolymer.com or use the inquiry form on this site.