SILICONE OIL

Polydimethylsiloxanes (PDMS) belong to a group of polymeric organosilicon compounds which are commonly referred to as “silicones”. This report covers PDMS fluids of viscosities 10 to 100,000 centistokes (cs). These are clear, colourless and odourless liquids that have non detectable vapour pressure and are insoluble in water. PDMS will strongly sorb to particulate matter in aquatic systems.

PDMS have a wide range of industrial and domestic applications especially as antifoaming agents, in personal care products, as textile treatment, polishing or release agents. The worldwide production is estimated to be 150,000 tons a year.

Bulk amounts of PDMS waste from industrial use are predominantly recycled or incinerated. Used PDMS fluids contained in consumer waste and certain industrial waste streams are discharged diffusely and can be expected to enter waste water.

PDMS removal during wastewater treatment approaches 100% because of sorption onto sludge solids. Levels of PDMS in effluents range from non-detectable to ppb levels. Surface water levels of PDMS are generally below detection. Sewage sludge concentrations of up to several hundred ppm have been measured. Biodegradation on sludge solids during conventional aerobic and anaerobic treatment has not been observed. PDMS introduced into wastewater treatment systems will enter the environment as a component of sludge.

Sludge disposal include soil amendment, landfill, incineration and ocean disposal. PDMS introduced to the soil environment as a result of sludge amendment of soil is expected to abioticaly degrade to lower molecular siloxanols and possibly volatile oligomers. The breakdown products can bind to soil humic matter, can volatilise and can undergo photoinduced degradation or potentially biodegrade. The fate of PDMS in landfills has not been investigated but processes similar to those that occur in soil may also happen. PDMS combustion products include CO,, H,O, and amorphous silica.

PDMS will be sorbed to aquatic sediments as a result of small amounts discharged to surface waters from wastewater treatement plants or where ever waste water is discharged without treatment and where sludge ocean disposal is practiced. Sediment concentrations can range from trace levels to low ppm levels in areas of high industrial discharge. The fate of PDMS in sediments has not been fully investigated.

Bioconcentration of PDMS in aquatic organisms does not occur and bioaccumulation through the food chain in aquatic and terrestrial organisms has not been demonstrated.

No aquatic toxicity has been ascribed to PDMS.

PDMS of all viscosities display a very low acute toxicity via oral, dermal, inhalational, intraperitoneal, intradermal or subcutaneous routes of administration. Irritancy to the eye is low and no skin sensitising potential has been detected.

The potential routes of human exposure are by ingestion and dermal contact. PDMS are not absorbed through the skin, or from the gastrointestinal tract, from which it is rapidly excreted unchanged in the faeces.

Inhalation exposure normally does not occur due to the very low vapour pressure. Spray applications may give rise to the potential for aerosol exposure. The available toxicological data do not indicate any adverse effects.

Repeated dosage studies with PDMS of different viscosities demonstrated no significant adverse effects to a variety of mammalian species after oral, dermal or inhalative administration. In chronic studies, no adverse effects attributable to the treatment with PDMS were seen with rats, mice, dogs or monkeys.

In vitro genotoxicity studies with bacteria and mammalian cells provided no indications that POMS have a mutagenic or clastogenic potential.

Limited studies with rats and rabbits displayed no clear evidence of a teratogenic effect of PDMS. Oral administration of PDMS to rats prior to mating had no effects on fertility, gestation, peri- and postnatal development. Long term dermal treatment of male monkeys with PDMS did not affect their reproductive performance.

No suppressive or stimulating influence of PDMS on the immune system has been demonstrated in studies on mice. In a study on man there was no evidence of dermal absorption of PDMS after repeated applications.

Overall, the available data indicate that PDMS do not present a health hazard for man. The safety of PDMS has been recognised by their widespread uses in many applications involving human exposure (e.g. food additives, personal care products) for more than 30 years.

Polydimethylsiloxane (PDMS), also known as dimethylpolysiloxane or dimethicone, belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer due to its versatility and properties leading to many applications.

It is particularly known for its unusual rheological (or flow) properties. PDMS is optically clear and, in general, inert, non-toxic, and non-flammable. It is one of several types of silicone oil (polymerized siloxane). Its applications range from contact lenses and medical devices to elastomers; it is also present in shampoos (as it makes hair shiny and slippery), food (antifoaming agent), caulking, lubricants and heat-resistant tiles.

Silicones are synthetic polymers having an inorganic skeleton of alternate silicone and oxygen atoms, the silicone valences not taken up by oxygen being saturated with organic grpoupe and other groups. They occupy an intermediate position between inorganic and organic compounds. Because of this dual nature they have many properties which have made them very useful in many applications. Silicones are produced in several forms including fluids, rubbers and resins. Silicones emulsions are formed from silicone fluids and water with the help of a suitable emulsifier, and find various applications.

The term silicone denotes a polymer with the structural formula (RnSiO(4-n)1/2)m where n is between 0 and 3 and m is 2 or more. It contains a repeating silicone oxygen chain having organic groups R, attached to a significant portion of the silicone atom by silicone carbon bonds. In commercial silicones most of the R groups are methyl, longer alkyl, fluoroalky, phenyl, vinyl and a few others. Silicone fluids the Si-O chain is unbanked.

Silicone fluids are generally, dimethyl polysiloxane, methyl hydrogen polysiloxane or silicones consisting of copolymers of dimethyl siloxane with methyl phenyl, methyl-hydrogen, diphenyl, methyl-alkyl and other siloxanes. Linear poly-dimethyl siloxanes or dimethyl polysiloxanes are the most important of all the silicones. These fluids with hexamethyl disiloxane. For relating low viscosity fluids are manufacured by reacting dimethyl silicone fluids the process is run for several hours at 180oC in glass lined kettles with acid chloride catalysts or at lower temperature with sulphuric acid. Alkaline catalysts are used for the production of high viscosity fluids or gums. Silicone fluids have m.wt. of 2000 to 15000 and viscosities from 10 to 10,000 cps.

Dimethyl silicone fluids are colourless, odorless and nontoxic and are resistant to oxidation and chemicals. They have good lubricating action. They reduce surface tension and have water repellent properties, together with foam inhibition. Inclusion of phenyl groups into the silicone structure increase their thermal and oxidative stability, while lowering the pour point. Thus methyl phenyl silicone fluids have higher viscosity, temperature coefficient and lower pour point and lower flash points than dimethyl silicone fluids of the same viscosity. Fluids with chlorinated phenyl groups attached to silicone, e.g. methyl alkyl fluids where alkyl is octyl to tetradecyl are good lubricants but have higher viscosity temperature coefficients and poorer oxidative stability than methyl fluids.

In general, the dimethyl silicone fluids are soluble in aliphatic and aromatic hydrocarbons and chlorinated hydrocarbons. Lower m. wt. fluids are more soluble than higher fluids. They are insoluble in methanol, ethanol, acetone, ethylene, gylcol, polyglycol ethers, gylcerol cyclohexanol and water. Methyl-phenyl silicones are more soluble than the corresponding dimethyl silicones.