SSA study of early polyethylenes degradation stages. Effects of attack rate, of average branch length, and of backbone polymethylene sequences length distributions

C. J. PÉREZ; M. D. FAILLA; J.M. CARELLA

POLYMER DEGRADATION AND STABILITY

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2013 vol. 98 p. 177 - 183

0141-3910

Low-density polyethylenes have been attacked by free radicals in the presence of oxygen to promotechains scission, aiming at showing effects of the molecular structure on the thermal behavior asdetermined by using a Successive Self-Nucleation and Annealing (SSA) technique. Three types of lowdensitypolyethylenes were used: a hydrogenated polybutadiene (HPB), as a model for a statistical linearethyleneebutene copolymer, a linear ethyleneebutene copolymer (LLDPE) with short branches notrandomly distributed along the main chains, and a low-density polyethylene (LDPE) with randomlyplaced long and short branching. All the polymers were subjected to thermal oxidation in air. Additionally,the LDPE and HPB were exposed to gamma irradiation in air, while the HPB was also degradedwith an organic peroxide. By virtue of the thermally activated oxidation, the three polymers show signsof molecular scission evidenced by the appearance of endotherms in the high temperature range of thefinal SSA thermogram. These endotherms are associated with the melting of thicker crystals formed bylonger polymethylene sequences that were not available for crystallization in the original polymer.Similar indication of chain scission was detected in some of the irradiated HPB. In the case of the irradiatedLDPE or the HPB modified with peroxide, the main effect observed was crosslinking that wasidentified by a reduction of the area of the higher melting endotherms in the final SSA thermogram.