Coefficient of friction (COF) measurements and AFM of LLDPE films containing erucamide and behenamide indicated that COF reduction is not necessarily dependent on additive coverage of the film surface. A film containing 1010 ppm erucamide yielded a kinetic COF of 0.2 without complete surface coverage, whereas a 1080 ppm behenamide film exhibited a saturated surface and higher COF. AFM showed distinct differences in crystal formation between the surface-segregated additives, with erucamide exhibiting a plate-like structure.

Many polymer films are produced by extruding the polymer in a cast-or blown-film process. Often an additive is preblended into the polymer and, once the film is formed, the additive migrates to the film surface(s). Erucamide is a migratory additive that is commonly placed in polyolefin films to reduce their coefficient of friction (COF). The aim of this study was to examine the relationship between erucamide surface concentration and COF of LLDPE films. The erucamide surface concentration was varied in two ways. In one set of experiments, a film containing 5,000 ppm of erucamide was surface-washed with solvent and/or aged at room temperature for specific time periods. In another set, films with different erucamide bulk loadings were aged for 7 days to achieve different equilibrium surface concentrations. The surface concentration was measured by using surface washing, and the bulk loading was quantified by using microwave extraction. A plot of COF as a function of surface concentration showed that all of the results fell on a single curve, regardless of the method used to regulate the erucamide surface concentration. At a surface concentration of ϳ0.5 g/cm 2 , the kinetic COF began to plateau to a value less than or equal to ϳ0.2 for this erucamide-LLDPE system. J. VINYL ADDIT. TECHNOL., 11:9 -12, 2005.