Changes in structural characteristics of LLDPE functionalized with DEM using gamma-irradiation

摘要

This work studies the structural changes produced by gamma-radiation as a source of free radicals for functionalizing linear low-density polyethylene (LLDPE) with diethyl maleate (DEM). The grafting of the DEM onto the LLDPE was carried out in solution using gamma-rays from a ~(60)Co source in air at room temperature, at a dose rate of 4.8 kGy/h and absorbed doses ranging from 15 to 400 kGy. The increase in the dose produced a higher concentration of free radicals and hence a higher grafting degree. The effects of DEM concentration are only perceptible at absorbed doses higher than 50 kGy. For a concentration of 30% DEM, the functionalization degrees ranged from 0.04 to 0.44 mol%. The use of gamma radiation modifies the structural and physical characteristics of the functionalized polyethylene with respect to the unmodified one, because, depending on the dose, the effects of gamma-rays can lead to crosslinking of materials with decreased flowability. The effects of gamma-radiation onto the molecular structure and molecular weight distribution of LLDPE are mitigated by the presence of DEM, due to the competition with the chain scission, branching and crosslinking reactions, for the consumption of the free radicals. The results provided by applying the successive self-nucleation and annealing technique allow reaching an unequivocal conclusion: that the free radicals formed by gamma radiation for the DEM insertion and main chain modifications are preferentially generated in the secondary carbons of the more regular -CH _2- sequences.