Organic Peroxide-Initiated Crosslinking Study of Cable Compounds

摘要

One of the most widely used crosslinking methods for wire and cable compounds in electrical applications is radical reaction by organic peroxides to enhance both dimensional stability at elevated temperatures and physical integrity under high electrical stress of the compounds. A moving die rheometer (MDR) has been a useful instrument to investigate the various crosslinking stages and crosslinking kinetics of the peroxide based thermal vulcanization of compounds with organic peroxide. In this study, we obtained the dynamic properties of polyethylene compounds with dicumyl peroxide (one peroxy group) and a,a'-bis(tert-butylperoxy)-diisopropylbenzene (two peroxy groups) from 150 °C to 200°C. It was found that the thermal decomposition of the peroxide follows the first order free-radical decomposition reaction and therefore, half-lives at various temperatures can be estimated from the kinetic data. The compound containing dicumyl peroxide crosslinked faster than the compound with a,a'-bis(tert-butylperoxy)-diisopropylbenzene, but it would also generate scorch faster at the lower temperature range. The activation energy of the compounds with dicumyl peroxide was estimated slightly higher than that of α,α'-bis(tert-butylperoxy)-diisopropylbenzene. For another kinetic study approach, the time dependent torque from the MDR is assumed to be equivalent to the modulus of the compounds during the crosslinking process, and described by the concept of a non-equilibrium thermodynamic fluctuation theory of characteristic exponential decay behavior. It was found that the activation energy of relaxation for crosskinking of dicumyl peroxide is slightly lower than that of a,a'-bis(tert-butylperoxy)-diisopropylbenzene in polyethylene. The understanding of these concepts can help to achieve an improved balance of processability and cure performance for potential new compounds in wire and cable applications.