Effect of processing variables on the crosslinking of HDPE by peroxide

In this work, the effect of processing variables such as temperature, shear rate, and the content of crosslinking agent on the melt torque behavior in a mixer, the degree of crosslinking, the thermal properties and density of high density polyethylene (HDPE) was investigated. Di-ter-butyl peroxide (DTBP) was used as a crosslinking agent. It was concluded that the crosslinking behavior of HDPE by peroxide was an overall function of temperature, shear rate in terms of mixer rpm, and the peroxide content. Crosslinking termination time was shortened on increasing the reaction temperature, regardless of the mixer rpm. As the mixer rpm increases, the crosslinking reaction time was shortened by the effect of shear heating. As a result, athough the crosslinking reaction termination time of HDPE depends on both the temperature and shear rate at constant peroxide contents the temperature was the more dominant. It was found that there is an optimum peroxide content, here 0.6 phr, to crosslink HDPE. In addition, the crosslinking of HDPE gives rise to a decrease in crystallinity, followed by a decrease in density.