Molecular Flexibility
Freedom of movement of individual macromolecular segments within a polymer determines the elasticity and barrier properties of a protective coating. High polymer chain mobility allows the coating to stretch during the creasing and folding of the paperboard, which prevents structural fracture. This microscopic behavior is directly related to the glass transition temperature of the polymer.
Thermal Influence
At temperatures above the glass transition point, the polymer chains have enough thermal energy to rotate and slide past one another easily. This state allows the material to deform elastically under mechanical stress and to absorb energy without cracking. However, if the operating temperature drops below this transition point, the mobility is restricted and the coating behaves like a brittle glass.
Barrier Performance
In barrier applications, restricted movement of the chains is desirable to prevent the diffusion of water vapor and gas molecules through the coating layer. Therefore, formulators must carefully balance this property, ensuring the polymer has sufficient chain mobility to survive the folding process but remains rigid enough to provide an effective barrier during storage. This balance is often achieved by blending different polymers or by adjusting the amount of plasticizer in the formulation to meet the specific requirements of the packaging application.
