Technical Bulletins

Selecting Amide Slip Concentrates for Polyethylene Film Applications


The primary function of fatty acid amide additives in the production of polyethylene blown and cast film is to convey slip and antiblock properties to the film surface. In order to make the best use of slip additives in formulating for polyethylene film applications, it is helpful to consider some basic concepts of polymer morphology.

Although LDPE and HDPE are common ethylene-based homopolymers used in film production, their respective manufacturing routes result in very different molecular architectures that help to determine each resins unique surface properties. The high degree of long and short chain branching inherent in LDPE resins give rise to a molecular structure that cannot readily order itself on cooling. As a result, LDPE exhibits a low degree of crystallinity with crystalline regions embedded in a highly amorphous matrix. One consequence is that LDPE resins often display 'sticky' surfaces that tend to 'block' or adhere together under the influence of temperature and pressure. In addition, LDPE surfaces do not slide over one another easily and may adhere to other surfaces during processing or storage. HDPE homopolymer resins are essentially linear in nature with little or no side chain branching. Because they can achieve relatively high levels of crystallinity on cooling, HDPE resins generally exhibit hard, slippery surfaces that resist blocking. UHMW-HDPE resins combine extremely high molecular weights with a high degree of crystallinity producing surfaces that are often referred to as “self lubricating” because of their low inherent coefficient of friction.

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