Polymer Compatibility
Thermodynamic models use a dimensionless quantity to characterize the chemical compatibility between polymers and solvents or between different polymers in a blend. The flory huggins interaction parameter measures the change in free energy when these components are mixed. Low values indicate high solubility and good mixing, while high values point to immiscibility.
Coating Performance
Formulation of barriers and coatings requires careful adjustment of polymer and solvent pairings. When the flory huggins interaction parameter is close to zero, the polymer chains remain highly extended and well-dispersed in the liquid coating. This dispersion allows for even application and uniform film formation during the drying step on paperboard substrates.
If the parameter is too high, the polymer will tend to coil and aggregate, which results in pinholes, uneven thickness and poor overall barrier properties.
Phase Separation
Multilayer flexible packaging often uses blended polymer layers to combine toughness with gas barrier properties. The flory huggins interaction parameter determines whether these blended materials will remain stable or undergo phase separation during the extrusion process. When phase separation occurs, it creates distinct microscopic domains that can scatter light, leading to a hazy appearance that ruins the clarity of the film.
Furthermore, such phase boundaries often act as weak points, which increases the likelihood of delamination under physical stress or when the package is subjected to high moisture during storage.
