Rheological Parameter
Evaluation of the shear modulus in high molecular weight polymer melts within the temperature range between the glass transition and the terminal flow region characterizes the elasticity of the entangled polymer network. In rheological testing of polymer melts, the rubbery plateau modulus quantifies the molecular weight between entanglements. The plateau appears because the dense network of chains acts like a temporary crosslinked network.
This value dictates the elastomeric behavior of the material during high-speed processing.
Entanglement Network
Density of physical entanglements per unit volume dictates how the polymer melt behaves when subjected to rapid deformation during melt-extrusion coating of paperboard. A higher rubbery plateau modulus indicates a more densely entangled polymer melt, which prevents excessive neck-in and edge-weave on the coating line. The property is sensitive to the molecular weight distribution and the presence of long-chain branching.
When the chain branching is optimized, the polymer melt resists draw resonance and maintains a stable web width. This stability ensures uniform barrier thickness across the paperboard substrate.
Converting Performance
Extrusion coating of packaging substrates depends on the melt strength and elasticity of the polymer to prevent film breakage. Utilizing the rubbery plateau modulus allows formulation chemists to design polymer blends that withstand the extreme drawing forces of the lamination nip. It assists in predicting how the polymer behaves at high line speeds.
