Thermorheological behavior of peroxide-induced long chain branches linear low density polyethylene

• Performed a correlations between thermorheological behavior and induced branching in LLDPE.
• Determined the changes in gel content, Mw and MWD in terms of processing conditions.
• Found good agreement between induced microstructural changes with SEC and thermorheology data.
• Potential of thermorheological approach for analyzing branching in modified PE was highlighted.

In this article, the correlation between thermorheological behavior and molecular structure of linear low density polyethylene upon peroxide modification was explored. For this purpose, a commercial grade LLDPE (Exxon MobileTM LL4004EL) was reacted with different amounts of dicumyl peroxide (DCP) and their viscoelastic behavior were studied. Moreover, the samples were analyzed by size-exclusion chromatography coupled with a light scattering detector. Increasing the DCP content at roughly constant molar mass led to broadening of molecular weight distribution as well as increasing the number of long-chain branches. The latter consequently resulted in enhanced activation energy and delayed relaxation times of the LLDPE. The thermorheological behavior of peroxide modified samples was investigated and the results showed that the induced long chain branching changes the thermorheological behavior from simple to complex. The plotted results (activation energy versus phase angle) showed constant activation energy at low peroxide level (i.e., increasing the long chain branching) (up to 125 ppm) and a distinct variation from low to high phase angle with increasing the peroxide level. The theromorheological complexity threshold could be determined using these plots. The potential of thermorheological approach as an alternative powerful tool for analyzing LCB issue in peroxide modified LLDPE could be highlighted.