Rheological Characteristics, Thermodynamics, and Morphologies of Polyethylene Binary Blends

Abstract

Steady and dynamic melt viscoelasticity, thermodynamics and morphologies were investigated for linear/linear, branched/branched and linear/branched polyethylene blends. Elastic parameters such as the first normal stress difference (P11—P22) and storage modulus (G′) have large positive dependence on blend composition and show much higher values than those calculated from the following mixing rule which is valid for linear/linear and branched/branched polyethylene blends at a constant shear rate: P0.4=w1P10.4+w2P20.4. The deviation from this mixing rule is sensitive to shear rate in case of linear/branched polyethylene blends. The Flory–Huggins interaction parameter, χ12, which is calculated from melting temperature depression suggests these blends to be miscible. The rate of crystallization and the spherulite size of linear polyethylene are remarkably reduced by mixing a small amount of branched polyethylene. From observations by SEM and TEM, it has been proved that linear- and branched-polyethylenes in the blend are well mixed in sub-micron order though they separate from each other during crystallization to make their individual lamellar crystals.