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

Abstract

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.

Vinyl ester resin modified with silicone‐based additives. I. Mechanical properties

“…The addition of 1 wt % of the same siloxane powder increased the impact strength by approximately 100% over the fireretardant system, which restored mechanical properties lost from the use of the fire-retardant additives. 20 The effect of silicone powder as a processing aid in poly(phenylene oxide) (PPO) has also been demonstrated by dynamic mechanical analysis. PPO is very difficult to process by conventional methods in the molten state and, for commercial applications, is blended with high-impact polystyrene to give a processable resin.…”

“…20 -23 These powders can be further modified by the attachment of organoreactive sites, such as epoxy and methacrylic functional groups, to enhance the compatibility of the powders with various organic resins. 20,23 The siloxane powders, when compounded into an organic resin with mixing equipment, can break into smaller sizes. The additives have the capability of improving the processability and mechanical properties and show synergistic behavior with conventional flame-retardant additives.…”

Vinyl ester resin modified with silicone‐based additives: II. Flammability properties

“…10 -13 These additives are a combination of ultra high molar mass polydimethylsiloxane with fumed silica filler and other additives. The resulting additive is a free flowing agglomerate, with a particle size range of 6 to 600 m. 10,12,13 These powders can be further modified to present chemical groups, such as epoxy and methacrylate, to enhance compatibility of the powders with various organic resins. 12 The siloxane powders, when compounded into an organic resin using some types of mixing equipments, can break down into smaller sizes.…”

“…The resulting additive is a free flowing agglomerate, with a particle size range of 6 to 600 m. 10,12,13 These powders can be further modified to present chemical groups, such as epoxy and methacrylate, to enhance compatibility of the powders with various organic resins. 12 The siloxane powders, when compounded into an organic resin using some types of mixing equipments, can break down into smaller sizes. The additives have the capability of improving processability and mechanical properties, and show synergistic behavior with conventional flame retardant additives.…”

“…14 The effect of a siloxane powder as a processing aid in polypropylene was demonstrated by torque rheometry. 12 Polypropylene containing typical fire retardants is very difficult to process because of the high filler content and nonlubricating nature of the additives. With the addition of 1% of methacrylate-functionalized silicone powder, the extrusion torque was reduced over 50%.…”