Cure control for neoprene, fire safety for belts and sheaths

In neoprene compounding, magnesium oxide is not an additive — it is the ingredient that makes the cure controllable. It absorbs the acid released during vulcanization, delays scorch, and together with zinc oxide forms the classic cure package that every CR formula relies on.

01Why CR needs MgO

Chloroprene rubber cures through its chlorine sites, and that reaction releases hydrogen chloride. Left unchecked, the acid attacks the polymer, corrodes the mould and accelerates ageing. MgO neutralises it as it forms — which is why the industry-standard package is 4 phr MgO + 5 phr ZnO.

MgO does a second job at the same time: it acts as a scorch retarder, extending the Mooney scorch time so the compound can be mixed, calendered and shaped without premature crosslinking. The balance is delicate — and it is governed by the activity of the MgO, usually tracked by iodine value.

02High-activity vs. low-activity

• High-activity MgO (high iodine value, fine particle) reacts fast — better scorch safety and higher crosslink density, preferred for CR adhesives and fast cures.

• Low-activity MgO (lower iodine value, coarser) reacts more slowly, giving longer processing windows and lower water absorption.

• Light vs. heavy MgO — bulk density affects dispersion and dosing accuracy in automatic weighing systems.

Choosing the wrong one shows up as scorch, blooming, or batch-to-batch variation in cure time. We supply the full activity range so the recipe can stay fixed across production runs.

03Halogen-free fire safety

For conveyor belts used underground or in enclosed plants, cable sheaths, and rubber seals in transport, Mg(OH)₂ delivers flame retardancy without halogens — low smoke density, no acid gas, and no toxic decomposition products. It also keeps the compound's flexibility better than many mineral alternatives at the same loading.

04Recommended grades