Two new types of solid silomne additives for plastics are described which give improved benefits compared to previous silicone additives. Ultra-high-molecularweight (UHMW) siloxanes are used in the new additives: traditional silicone plastic additives have used much lower molecular-weight silicones. The siloxane is converted into solid forms, either masterbatch pellets or powders, that are easy to feed, or mix, into plastics during compounding, extrusion, or injection molding.Ultra-high-molecular-weight siloxanes can be compounded into masterbatch pellets at higher siloxane concentrations than previously possible, e. g., up to 500h.They impart improved processing and release, lower coefficient of friction, and broader performance latitude compared to conventional lower-molecular-weight silicones. These benefits can be delivered at reduced siloxane levels with increased concentration at the surface interface with a new functionalized UHMW siloxane which provides unique surface segregation characteristics. Ultra-high-molecular-weight siloxanes have been formulated into powders that can also act as processing aids and mechanical property modifiers for highly filled polymers such as fire-retardant systems. This paper uses polyolefins as a model. However, many of the effects shown in polyolefins have also been seen in other resin systems.
Various silicone process aid candidates were evaluated and compared to alternative process aids for their effect on surface properties of extruded linear low density polyethylene (LLDPE). Their performance was influenced by the silicone polymer structure and the concentration of the silicone polymer in the polyethylene resin. An increase in the polarity of functional groups on the silicone polymer resulted in an increase in the effect on surface properties of extruded LLDPE. Silicone concentrations in the range 220 to 3520 ppm in the polyethylene resin gave significant reduction in surface roughness caused by melt fracture during extrusion. Concentrations of 10000 ppm or less gave coefficient of friction values of 0.3 or below. Beneficial effects on extruder parameters, such as the reduction of extrusion pressure, current, and output were also observed.
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