MEKP (Methyl Ethyl Ketone Peroxide, 33% Active)

Methyl Ethyl Ketone Peroxide (MEKP) at 33% active oxygen content is the most widely used peroxide initiator in the composites industry for ambient-temperature cure of unsaturated polyester resins and vinyl ester resins. This standard formulation is a solution of MEKP in a plasticizer diluent, providing consistent reactivity and excellent shelf life when stored correctly. MEKP generates free radicals upon activation by a cobalt accelerator (typically cobalt octoate or naphthenate), triggering styrene co-polymerization and crosslinking of the resin network. The standard grade is designed for hand lay-up, spray-up, and casting applications, offering gel times of 15–30 minutes at 20°C with 1–2% cobalt octoate. It is compatible with most commercially available ortho, iso, and DCPD-based UPRs as well as standard vinyl ester resins. Dosage is typically 1–3% by weight of resin. Proper handling requires segregation from cobalt accelerators, avoidance of contamination, and storage in a cool, dark environment below 25°C. MEKP is classified as an organic peroxide and must be handled according to applicable safety regulations.