Kinetics of crosslinking reaction of low density polyethylene and linear low density polyethylene using dicumyl peroxide as initiator

Abstract

The kinetics of crosslinking reaction of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) using dicumyl peroxide (DCP) as the initiator and tetrakis [methylene 3-(3’,5’-di-t-butyl-4’-hydroxyl)propanoate] (Irganox 1010) as the inhibitor were studied using Brabender Plasti-Corder (BPC) and Differential Scaning Calorimeter (DSC). The crosslinking reaction in the absence of inhibitor was found to be first order with respect to initiator concentration, while in the presence of inhibitor, the reaction was first order with respect to initiator concentration and 0.21-0.31 with respect to inhibitor concentration at 446 K for BPC and 413 K for DSC. In addition, the rate constant in the presence of inhibitor was found to be around three time lower than that in the absence. The activation energy of crosslinking reaction of LDPE and LLDPE were 118 and 112 kJ/mol, respectively for BPC technique and 184 and 176 kJ/mol, respectively for DSC technique. The pre-exponential factor of crosslinking reaction of LDPE and LLDPE were respectively 3.23 x 10¹¹ and 0.82 x 10¹¹ sec⁻¹ for BPC technique and 3.56 x 10¹⁹ and 3.64 x 10¹⁸ sec⁻¹ for DSC technique. The fraction of termination was determined and found that approximately 65% was terminated by combination of polymer radicals, while 35% was terminated by disproportionation and cyclization. The amount of DCP higher than 1.6%w/w used for the crosslinking reaction gave the degree of crosslinking in polymer greater than 80%. When 0.1-0.2%w/w of Irganox 1010 was used in the preparation of compound LDPE or LLDPE containing about 2%w/w DCP, the degree of crosslinking was constant at more than 80%. For the Iragox 1010 concentration greater than 0.2%w/w, the degree of crosslinking decreased with increasing inhibitor concentration.