Our plastic industry products that are slip agents; filtering available by resin type, chemistry, end market and processing type.
Figure 1 shows that when a slip agent is mixed with polymer melt, it is absorbed into the polymer amorphous regions where it resides until the polymeric material is in the form of a melt. On cooling, the slip additive becomes incompatible because of its different surface energy and it begins its journey to the material surface. The rate of migration depends on the difference between the surface energies of the polymer and the additive (the larger the difference, the faster the migration). First, a monolayer is formed on the polymer surface, followed by deposition of subsequent layers when new molecules of antislip agent arrive on the surface.
Figure 2 shows that the arrangement of molecules on the surface is not chaotic but it has a structure which results from the affinity of two segments contained in the slip agent. Fatty amides that are described by this mechanism have two structural elements: an amide group and a hydrocarbon chain. The hydrocarbon chain has high affinity to polyethylene, which has very similar properties, and for this reason hydrocarbon chains in the first layer are embedded in polymer with their amide groups facing air. When more slip agent molecules arrive on the surface, they form the second layer on the surface. The molecules of the second layer orient themselves with amide groups facing each other. This is again natural, considering that similar functional groups have affinity to each other, especially because they have both oxygen and hydrogen, which readily form weak hydrogen bonding.
Figure 3 shows the results of an experiment in which polyethylene film containing 1,200 ppm of erucamide was contacted with a metal plate, and after each contact, the coefficient of friction was measured. The coefficient of friction increases after each run but the magnitudes of the increases are gradually diminishing. This prompted proposal of a mechanism explained in Figure 5.9. Film contact with equipment removes some slip agent from the film surface but accumulation of slip agent on a surface of metal parts eventually results in slip agent transfer to the film surface and slip agent loss gradually diminishes.15,16