Ultra-high-molecular-weight functional siloxane additives in polymers. Effects on processing and properties

Two new types of solid siloxane additives for plastics are described which give improved benefits compared to previous silicone additives. Ultra-high- molecular-weight (UHMW) siloxanes are used in the new additives; traditiona l silicone plastic additives have used much lower molecular-weight silicone s. The siloxane is converted into solid forms, either masterbatch pellets o r 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 pe llets at higher siloxane concentrations than previously possible, e. g., up to 50%. They impart improved processing and release, lower coefficient of friction, and broader performance latitude compared to conventional lower-m olecular-weight silicones. These benefits can be delivered at reduced silox ane levels with increased concentration at the surface interface with a new functionalized UHMW siloxane which provides unique surface segregation cha racteristics. Ultra-high-molecular-weight siloxanes have been formulated into powders tha t can also act as processing aids and mechanical property modifiers for hig hly 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.