POLYETHYLENES MODIFIED BY IRRADIATION AND ORGANIC PEROXIDE TREATMENT : RHEOLOGICAL STUDY

C. J. PÉREZ; E.M. VALLÉS; L.M. QUINZANI; M.D. FAILLA

LATIN AMERICAN APPLIED RESEARCH

PLAPIQUI(UNS-CONICET)

Lugar: Bahia Blanca; Año: 2003 vol. 33 p. 109 - 114

0327-0793

A series of polyethylenes were obtained by chemical modification of two commercial high-densitypolyethylenes using an organic peroxide and by irradiation. The rheological behavior of these materials is analyzed as a function of the molecular structure of the polymers and the concentration/dose used in the modification processes. The peroxide concentrations and irradiation dosis considered are below the critical quantities that produce macroscopic molecular networks. The two original high-density polyethylenes have similar vinyl concentration but different molecular weights. The molecular structure of the polymers are strongly affected by the modification process and by the concentration/dose used in that process. It was observed that the molecular weights of the modified polyethylenes increase, and the molecular weight distribution gets wider, as the peroxide concentration or irradiation dose increases. These results are a consequence of the large molecular weight molecules generated during the chain-linking modification processes. By the time traces of gel begin to appear in the modified samples, the peroxide modified materials display larger molecular weights and smaller vinyl concentrations than the irradiated ones. Both the viscous and elastic moduli of the polyethylenes increase as the concentration of peroxide and irradiation dose increase showing the effect of the generated large molecules. All the modified polymers show a complex thermo-rheological behavior which it may be associated to the presence of  long-branched macromolecules. The flow activation energy of the polymers increase as the concentration/dose increases. The polymers obtained using the organic peroxide display the largest rate of change of the flow activation energy within the range of concentration/dose analyzed