Siloxanes - Consumption, Toxicity and Alternatives - Miljøstyrelsen

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Fate of the siloxanes
The major part of the siloxanes will, either by the application or later by
washing of the products on which the polish is applied, be released to wastewater
or to the ground.
A minor part of the siloxanes (e.g. the cyclic dimethylsiloxanes) may be released
to the air by the application.
2.2.6 Mechanical fluids and heat transfer fluids
Silicones fluids are widely applied for the following applications:
• Lubricants and grease;
• Lubricating fluids for metal processing;
• Hydraulic fluids;
• Heat transfer fluids;
• Dielectric fluids (mainly dielectric fluids for fire-resistant transformers).
The siloxanes may be formulated into grease (with filler material) or emulsions
(mixed with water). For many applications the siloxanes only account
for a few per cent of the products.
Silicone fluids and greases are widely used in the automotive and the aircraft
industries - from hydraulic damping and brake fluids to lubricate bearings,
locks, linkages, instruments, etc. Silicone fluids and greases are generally applied
when high temperatures, solvents or corrosive materials would destroy
petroleum-based lubricants. (Will et al. 2003)
Consumption
Based on Will et al. 2003, the total consumption of silicones for mechanical
fluids can be estimated at 110 t/year. In the market report, however, this includes
also antifoaming agents and water repellants for textiles.
Products within this application area are to a large extent registered in the
Danish Product Register. According to the database retrieval, the total consumption
of siloxanes with these products was about 35 tonnes, the main part
used in lubricants. The data only indicate a minor consumption of siloxanes
with metal-working fluids, but a large part of the siloxane-containing fluids for
this application may not be included in the register.
Siloxanes used
For all applications mentioned in Table 2.5, poly(dimethylsiloxane) is the
main substance used according to the Product Register. It is, however,
doubtful to what extent this name is used synonymously with all derivatives of
dimethylsiloxane in the absence of exact knowledge on the siloxanes compound,
when the companies are notifying on the content of the products.
According to Will et al. (2003) phenyl methyl siloxanes and fluorosiloxanes
are more widely used for these application areas than the simple dimethylsiloxane
fluids.
Fate of the siloxanes
Siloxanes used for this application area are mainly disposed of as chemical
waste. For some applications direct releases to soil and discharges to wastewater
may occur.