Dulal, Nabeen, et al. Journal of colloid and interface science. 2017 Nov 1;505:537-45.
Polymer screw caps are manufactured from high-density polyethylene (HDPE1) as one piece by injection molding. The inherent friction of HDPE closures creates rotational resistance (torque) on the production line and on consumers' hands. Manufacturers add slip agents to HDPE and store lids to allow the slip agent to migrate to the surface to reduce friction. Slip agents are added to polyethylene prior to extrusion or injection molding to ensure sealing and removal properties with uniform and rapid torque. Commonly used slip agents erucamide and benzamide can improve production line efficiency, improve melt flow, and prevent product loss caused by sticking to machinery.
Experimental
High-density polyethylene seals are produced with erucamide and benzamide respectively and stored until the required torque is produced. The surface composition of the samples was determined using spectroscopic analysis and gas chromatography. The distribution of additives was observed under optical microscopy, scanning electron microscopy and atomic force microscopy. The surface energy, crystallinity and applied torque of the composites were measured using contact angle, differential scanning calorimeter and torque tester respectively.
Results and discussion
Each slip additive produces a characteristic amide peak at 1645 cm-1 in the infrared spectrum and oxygen and nitrogen peaks in the X-ray photoelectron spectrum, indicating their presence on the surface. Erucamide forms a flat scale-like structure and benzamide forms a tooth-like structure. The torque reducing surface erucamide and phenylacetamide were 15.7 µg/cm2 and 1.7 µg/cm2 respectively.