Rheological Study of Linear High Density Polyethylenes Modified with Organic Peroxide

CLAUDIO JAVIER PÉREZ; GUILLERMO CASSANO; ENRIQUE M. VALLÉS; MARCELO DANIEL FAILLA; LIDIA MARÍA QUINZANI

POLYMER

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2002 vol. 43 p. 2711 - 2720

0032-3861

Four high density polyethyleneswere modified using different concentrations of an organic peroxide in order tochange their molecular structure. The effect of the presence of vinyl groups inthe original polymer molecules and of the peroxide concentration used in themodification process were analyzed.  Allthe concentrations of peroxide used in this study were below the criticalconcentration that produces a macroscopic molecular network.  The weight-average molecular weight of all thepolyethylenes augments and the molecular weight distribution gets wider as theconcentration of peroxide increases. These results support the general belief that the chain-linkingreactions dominate the modification process. Evidence of the important role played by the vinyl groups is found notonly in the change of the width of the chromatograms but also in the positionof their maximums.  The vinyl-containingpolymers display the largest molecular changes for a given peroxidecontent.  The magnitude of the viscousand elastic moduli of the polyethylenes goes up as the concentration ofperoxide used increases showing the effect of the generated large molecules.  The linear viscoelastic response of themodified polymers is thermo-rheologically complex.  This complexity can be associated with thegeneration of branched molecules.  Forsimilar molecular weights and peroxide concentration, the flow activationenergy displayed by the polyethylenes with larger concentration of vinyl groupsis larger.  This result suggest that amuch more complex molecular structure is formed in the presence of vinylgroups.  The dynamic moduli of the polymerswere analyzed using the generalized viscoelastic model.  The spectrum of relaxation times wasdetermined for each polymer and analyzed as a function of the peroxide concentration.