Rheometric studies on the process of polyethylene or its copolymers' crosslinking in the presence of peroxides. Part III. Effects of the concentration and type of peroxide on the process rate

Kinetics of the processes of low density polyethylene (PE-LD) crosslinking in the presence of three commercial organic peroxides: dicumyl (Di-Cup R), t-butylcumyl (Interox BCUP) or 2,5-dimethyl-2,5-di-(t-butylperoxy)-hexyne (Interox DYBP) ones were compared using rheometric method. Ranges of the peroxides themselves decompositions temperatures were determined using TA-TG and DSC methods. All of them underwent thermal decompositions in the range of temperature 170-200 °C (Table 1, Figs. 1 and 2). Rheometric studies on PE-LD crosslinking process were carried out in the range of temperature 170-200 °C in the presence of peroxides used in concentrations from 1.0 to 3.0 wt. %. Scheme of crosslinking process with the model of kinetic equation resulted from it, related to non-branched chain reactions, were assumed in kinetic considerations. All this enabled to determine the kinetic equation coefficients [equation (12), Table 31 from characteristic parameters of rheometric curves (Table 2) and then to determine rate constants of torque changes (k(x)) in the crosslinking process (Table 4) as well as activation energies (E(a)) of the processes activated with one of three chosen peroxides (Table 5). Dicumyl peroxide appeared to be most effective in the crosslinking process in the temperature range investigated. It allowed reaching the highest values of maximal torque (M(max)) during the shortest time and E(a) of the process was 119.2 kJ/mol. E(a), values of crosslinking processes in the presence of the other peroxides were significantly higher, while M(max) values were in those cases approximately twice lower than M(max) values reached in the presence of dicumyl peroxide.