A process involves adding a peroxide masterbatch to a molten blend of a fluorocarbon elastomer and a thermoplastic material. The peroxide masterbatch contains greater than or equal to 5% weight percent organic peroxide, further contains a fluorocarbon elastomer, and typically also contains a crosslinker containing at least two sites of olefinic unsaturation. The fluorocarbon elastomer in the molten blend and in the peroxide masterbatch may be the same or different. After the peroxide masterbatch is added to the molten blend, the combination is mixed at a temperature and for a time sufficient to effect cure of the fluorocarbon elastomers. By using a masterbatch, a faster and more uniform dispersion of peroxide curative is possible due to pre-dispersion of peroxide in the elastomer phase, which leads to shaped articles having improved mechanical properties.