The effect of co-agent on the peroxide cross-linking of LDPE

Peroxide cross-linking of polyethylene is one of the most important methods for the production of cross-linked polyethylene (PEX). The kinetic study of the crosslinking reaction of low density polyethylene (LDPE) in the presence of 2,4-diphenyl-4-methyl-1-pentene (MSD), pentaerythritol triacrylate (PETA) and divinylbenzene (DVB) as the co-agent and dicumyl peroxide(DCP) as the cross-linking agent was carried out by differential scanning calorimeter (DSC, non-isothermal condition), rheometer and internal mixer (isothermal condition). The reaction was first order and independent of DCP and the co-agent concentration. The activation energy and In k(o) (In k(o) defined as the intercept of DeltaH vs. 1/T) did not change with DCP concentration but energy of activation decreased with co-agent and the highest decrement was observed with respect to MSD. The overall reaction rate constant (with constant value of DCP) increased with temperature due to the faster decomposition rate of peroxide at higher temperatures. By comparison of the three methods used, it was found that the different results obtained were in good agreement with each other. However, because of the higher shear rate and mechanical stress experienced in the internal mixer, the measured overall reaction rate constants were of higher values with respect to those obtained from other methods.