Meaning
Lubricating additives based on fluoroelastomers modify interfacial friction during the extrusion of polyolefins to prevent melt fracture and reduce energy consumption. These fluoropolymer processing aids operate by coating the die walls to create a slip layer that lowers shear stress at the metal interface. Such additives mitigate sharkskin defects and die buildup while allowing for higher output rates without degrading the physical properties of the finished polymer.
Extrusion Mechanics
Low levels of additive molecules migrate to the die surface during the initial start-up phase of a production run. This surface modification permits the transition from stick-slip flow to continuous wall slip at lower pressures. Extruders maintained at specific temperature ranges provide the energy necessary for the rapid formation of this film.
Frequent adjustments to the dosage levels ensure that the protective layer remains intact throughout long production campaigns.
Economic Variables
Virgin resin streams require precise concentrations of these agents to stabilize the processing window and avoid unnecessary maintenance shutdowns. Recycled polymer streams often contain contaminants that interfere with the slip layer, necessitating higher additive loading to achieve the same surface finish on the final part. Production managers must calculate the cost of the additive against the savings gained from reduced head pressure and the elimination of surface defects in finished films.
Operational Limits
Tooling geometry directly influences the effectiveness of these materials. Complex die designs that feature stagnation points demand higher additive concentrations to prevent localized degradation and gel formation within the channel. Changes in shear rates or melt temperatures during processing force the chemical equilibrium of the slip layer to shift, often causing a temporary increase in surface irregularities until the system stabilizes under new conditions.
Proper application of these additives dictates the boundary between smooth output and costly rework due to structural surface failure.
