Rheological behaviors of randomly crosslinked low density polyethylene and its gel network

Dicumy peroxide (DCP) modification of low density polyethylene (LDPE) below gel point (GP) produces modified LDPE (mLDPE) with wide molecular weight distributions while the random crosslinking beyond GP yields crosslinked LDPE (XLPE). Molecular weight distributions of mLDPE below GP and the sol-fractions of XLPE above GP were investigated. The sol-fractions in XLPE were extracted to prepare XLPE gels of different crosslinking densities. Both XLPE and the gels were subjected to shear action for studying dynamic rheology and relaxation modulus in the linearity region for revealing the role of entanglements and dangling chains to viscoelasticity of the randomly crosslinked network. The results revealed that the sol-fractions with molecular weight much higher than entanglement molecular weight contributed to equilibrium modulus in addition to the gel network, which lowered the DCP dosage for appearance of critical gel behavior of XLPE in comparison with the XLPE gel. However, rheological method yielded critical DCP dosages for appearance of apparent gel behaviors far beyond the chemical GP from the extraction experiment. The sol-fraction residing in the network gave rise to additional contribution to relaxation modulus of XLPE, shortening network relaxation time and improving equilibrium modulus.