Meaning
Processing and operational mechanisms reduce active surface concentrations of lubricating fatty acid amides from converted polymer films and moulded articles. Across polyolefin manufacturing and conversion, slip agent depletion occurs when low-molecular-weight additives migrate out of the bulk, volatilise under heat, transfer into contacting media, or degrade through oxidative exposure. This concentration loss elevates the dynamic and static coefficients of friction across plastic surfaces, impairing high-speed film movement and package conveying.
The phenomenon terminates when surface migration ceases entirely, or when the polymer bulk exhausts its reservoir of free, non-entangled additive molecules.
Exhaustion Mechanisms
Fatty acid amides like erucamide and oleamide possess limited thermodynamic solubility within semi-crystalline polyethylene and polypropylene matrices. Post-extrusion cooling drives these small polar molecules out of the crystalline lattice toward the film surface where they form a lubricating monolayer. Depletion initiates when high web processing temperatures evaporate this surface layer into production exhaust hoods.
Physical wiping during film winding, slitting, and converting mechanically strips the external slip film away. Bulk adsorption onto porous inorganic additives, including talc, calcium carbonate, or silica anti-block particles, traps migrating molecules internally and stops them from ever reaching the plastic boundary.
Processing Disruptions
Converting operations suffer immediate production downtime when surface friction rises uncontrollably. High-speed form-fill-seal machines experience web jams, improper pouch tracking, and severe stretching when film lines lose surface lubricity. In injection moulding, low active slip concentrations cause part sticking inside deep-draw cores, resulting in pin push-out defects and cosmetic surface scuffing during ejection.
Corona treatment applied to films to enhance printing ink adhesion oxidises migrating amides, converting lubricating double bonds into polar functional groups that ruin slip performance.
Datasheet Divergence
Raw material supplier datasheets report nominal slip additive dosing measured on fresh, unaged virgin pellets immediately following pelletisation. Processing converters rarely achieve these theoretical friction values after thermal conversion and warehouse storage. Elevated warehouse storage temperatures accelerate surface blooming, leading to rapid evaporative loss and inter-layer transfer within tightly wound rolls.
Regrind incorporation aggravates depletion because repetitive extrusion cycles thermally degrade virgin erucamide into sticky secondary amines and carboxylic acids. Recycled resin moulders must monitor surface friction continuously across production shifts, dosing supplementary masterbatch to replace depleted slip agents rather than relying on original resin specification values.
