Silicone oil
Silicone oils (actually Diorganopolysiloxanes; polymerized siloxanes with organic side chains) are from the group of silicones and synthetic silicon- based oils, which, in contrast to mineral oils or vegetable oils, have no organic, ie carbon-based, but siloxane chain molecules as the basic structure. This is characterized by the periodically alternating arrangement of silicon and oxygen atoms with the general formula [ R1R2SiO ] n. At the free outer electrons of silicon hanging radicals R which are mostly organic radicals, but can also be halogens. So silicone oils have both an organic and an inorganic fraction.
Properties
Silicone oils are clear, colorless, non-toxic, inert, odorless, chemically inert, thermally stable over a wide range, hydrophobic liquids with a molecular mass of ( 162-150000 ) g / mol, a density of 0.76 to 1.07 g/cm3 and viscosities from 0.6 to 1,000,000 mPa · s Further, they are excellent electrical insulators, silicone fluids have a low surface tension of 21.5 mN / m (at 25 ° C) or less. They are also in the air permanently heat resistant up to 180 ° C. Your pour point, depending on the viscosity at ( -80 to -40 ) ° C. Silicone fluids include between -60 ° C and to 200 ° C to lubricating properties. Lubricity is lower than that of mineral oils and other lubricants. They do not tend to gum up. Silicone fluids are soluble in benzene, toluene, aliphatic and chlorinated hydrocarbons. They are not very resistant to strong inorganic acids and bases. Like all silicones, they are very good gas permeable.
The representative with the simplest structure is polydimethylsiloxane, which is unbranched and each R is a methyl group.
Industrial and technical use
There are many uses of silicone oils. Some of the most important:
- In refrigeration during freeze -drying silicone oils are used because of their excellent thermal conductivity as heat transfer fluid, and because of their non-combustibility in thermal baths of laboratories, the so-called oil baths, used as heat carrier.
- Because of their low surface tension some silicone oils have a foam-inhibiting effect and are typically correspond in industrial plants, such as fermenters or distillation units for applications where foaming can have critical consequences.
- Silicone oil is an excellent blowing agent in the oil diffusion pump.
- Silicone fluids play an important role as an electrical insulating materials ( dielectrics), (eg transformers).
- Special plasticine, as Bouncing Putty ( Silly Putty), half composed of silicone oil, while the other half consists of boric acid.
- In vehicle silicone fluids of higher viscosity are axle and / or used as a fluid for the torque transmission with an automatic speed compensation in viscous couplings and (in conjunction with ) the central differential.
In addition, silicone oils can be used as hydraulic fluid, as a mold release agent, as an ingredient for special inks, for waterproofing of glass (eg, in the pharmaceutical industry ), ceramics, textiles, leather, etc., cleaning and polishing additive for automotive coatings, metals, leather and furniture, prevention of Ausschwimmens of pigments in pigmented coatings, as manometer, collectors in flotation processes, damping means are used.
Medical and cosmetic applications
Due to the properties of the silicone oil, and medical products and cosmetics are made from silicone oils. The application range is very wide.
- Silicone oils, are often used as a lubricant. Example can be found on the majority of units in commercial condoms thin silicone oil films.
- Because of their aforementioned foam-inhibiting effect they are at Tensidvergiftungen, ie the ingestion of surfactants administered to counteract the in the digestive tract forming foam and the resulting swelling.
- Also a positive effect on the basis of an existing medicament in the use of polydimethylsiloxanes has been achieved on the skin for lice infestation.
Furthermore, silicone oils are used as an ingredient of cosmetics, detergents and cleaning products, skin cream, ointment bases, massage oils, implants and means for hairstyle stabilizing and as a carrier for fragrances.
Food industry
The defoaming effect plays a significant role in the food industry. So silicone oils are added in the preparation of jams and fruit juices, in order to suppress the formation of undesirable foams. Also admixtures in frying oils make foaming at Frittiervorgängen much more controllable.
The maximum concentrations of the silicone oil is polydimethylsiloxane ( food additive E900 ), as follows:
- Jam, marmalade, jelly ( max. 10 mg / kg)
- Frying oils and fats (up to 10 mg / kg)
- Fruit and vegetable preserves (up to 10 mg / kg)
- Chewing gum ( max. 100 mg / kg)