Processing aids melt fracture, preventing

Fluoropolymers (e.g., copolymers of vinylidene fluoride and hexafluoropropylene) and silicone-based (e.g., poly-dimethylsiloxanes) additives are often referred to as processing aids, preventing melt-fracture, for example, the so-called sharkskin. Fluoropolymers are applied in concentrations between 0.01% and 0.1%. 

When antiblocking agents are incorporated into PE films, other important properties of the polymer are also affected. These include an increase in stiffness, a decrease in the coefficient of friction, and an increase in haze. Interaction effects with processing aids can also result, especially with fluorocarbon elastomers that are added to prevent melt fracture in the blowing process of films. Worker exposure to dust generated by these additives can be hazardous if impurities such as crystalline silica or asbestos are present. 

Lubricants and process aids can be either (a) internal, whereby they act in the resin phase to increase melt flow and throughput, prevent shear burning, and resist melt fracture (by reducing viscosity at high shear rate), or (b) external, whereby they act at the interface between resin and other materials to improve release of the composite, promote dispersion of fillers, resist melt fi"acture, and/or reduce friction between resin and process equipment. 

Talc is commonly added to film resins to prevent blocking in the resulting film. Concentrations from 1,000 to 10,000 ppm are commonly used. Luzenac America offers selected talc products that provide the optimal coag>romlse between film property retention and antiblock performance. A surface modified product is also offered where melt fracture or interactions with fluorocarbon processing aids needs to be minimized. 

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