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Siloxane Assets and Attributes


Dow Corning revolutionized the plastics additive industry by introducing ultra-high molecular weight siloxane polymers as the basis of its standard additives. These unique additives are far more effective than conventional lower molecular weight silicones as process aids and surface lubricants. So, they provide greatly enhanced effects, and also overcome many of the limitations of the lower molecular weight materials. This page details the history of the highly beneficial use of Dow Corning silicone materials as additives to thermoplastic resins.

The first commercial use of silicone materials as additives to thermoplastic resins was the use of silanes to promote crosslinking of polyethylene and to improve the compatibility of mineral fibers. The Sioplas process for crosslinking polyethylene, which was developed and patented by Midland Silicones, has since been further developed by others.

The first use of polysiloxane polymers was also in filler treatment, especially with silica and titania. The low molecular weight polydimethylsiloxanes used for this treatment are less expensive than silanes and yield broadly similar results unless very high surface areas are required.

During the early 1970's, higher molecular weight polydimethylsiloxanes began to be used as separate additives to thermoplastics.

Other types of polysiloxanes have also been used as additives, but because they are more expensive than basic dimethyl materials, they are normally restricted to smaller, higher value applications. Phenyl-containing siloxanes, for example, have been used in styrenic polymers for medical applications and where outstanding clarity is required.

While all of these silicone polymers are good lubricants, they have two intrinsic disadvantages:

  • Because they are liquid at room temperature, they present handling difficulties to an industry accustomed to solid raw materials.

  • When added directly into a polymer melt, they induce screw-slip at higher concentrations

Masterbatches can partially overcome these problems, but the second issue has effectively limited silicone concentrations to about 10%. While this is sufficient for a few specific applications, it is not high enough for broad spectrum use.

Fortunately, by using an ultra-high molecular weight siloxane as the basis of its standard masterbatches, Dow Corning has overcome this concentration problem by making 25-50% masterbatches. At the same time, ultra high molecular weight siloxane additives are even more effective than conventional lower molecular weight siloxanes as process aids and surface lubricants, thus providing greatly enhanced effects.

Dow Corning Multibase has developed two special solid forms of plastic additives:

1. Siloxane masterbatches
2. Siloxane powders

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Siloxane Masterbatches and Siloxane Powders

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