Meaning
Thermodynamic parameter defining the minimum energy barrier that a penetrant or additive molecule must overcome to jump between free volume gaps within a polymer matrix. Calculating activation energy diffusion allows resin specifiers to predict temperature-dependent migration rates of plasticizers or slip agents. The parameter applies to solid and molten polymers under Fickian transport, whereas non-Fickian or swelling-induced penetrant movement falls outside its standard kinetic boundary.
Thermal Dependence
Temperature fluctuations alter the thermal energy available to penetrants, causing exponential changes in transport speed according to Arrhenius behavior. When a moulded container experiences hot-fill conditions or warm ambient storage, activation energy diffusion dictates how rapidly smaller molecules traverse the container wall into the packaged contents. High values indicate a strong sensitivity to heat, meaning small temperature increases lead to pronounced surges in additive leaching.
Migration Mechanism
Molecular movement relies on the transient formation of localized free volume pockets created by segmental motion in polymer chains. Lower activation energy diffusion values occur in flexible polymers with low glass transition temperatures where chain mobility is high. Semi-crystalline resins like polyethylene present higher barriers because crystalline domains force penetrants through tortuous pathways.
Barrier Performance
Molded wall thickness and cooling rates during injection molding alter final crystallinity and density. Rapid chilling in the mold preserves higher amorphous fraction, lowering activation energy diffusion and increasing potential additive migration. Molders adjust cycle times to achieve optimal crystalline structure for stringent shelf-life requirements.
