Migration and performance of erucamide slip additive in high-density polyethylene bottle caps

Diffusion of erucamide and their morphology on surface characteristics of high-density polyethylene (HDPE) screw caps depend on storage conditions. Erucamide performance relies on its amount, distribution, and consistency on the surface of HDPE. Specific application and removal torques can be achieved by controlling the amount of erucamide on the surface. The surface amount and the torque increased to an optimum level at 38 and 50 °C within 120 hours of incubation, while they remained unchanged for lower temperatures. Erucamide diffused to the surface and formed flat plate-like crystal structures at similar time and temperature. These flat-plates can slide over each other and provide the slip required to decrease the torque. An increase in contact angle demonstrated that hydrophobic hydrocarbon-chains of amide slip additives were oriented toward the air interface. An optimum surface amount of erucamide for proper sealing torque could be produced at a different combination of storage time and temperature.