A silicone oil is any liquid polymerized siloxane with organic side chains. The most important member is polydimethylsiloxane. These polymers are of commercial interest because of their relatively high thermal stability and their lubricating properties.
Polymer backbone of silicone oil consists of alternating silicon oxygen atoms. According to the chemical structure, the silicone oil series can be divided into methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen-containing silicone oil, methylphenyl silicone oil, methyl chlorophenyl silicone oil, methyl ethoxy silicone oil, methyl propyl silicone oil, methyl vinyl silicone oil, methyl hydroxyl silicone oil, ethyl hydrogen-containing silicone oil, hydroxyl hydrogen-containing silicone oil, cyanogen-containing silicone oil and so on. Silicone oil can be prepared by dimethyl cyclosiloxanes and hexamethyldisiloxane conducted telomerization under the presence of catalysts. Its viscosity was increased by the number of silicone chain sections in the molecule, from the easily flowing liquid to a thick semi-solid. It is generally colourless or pale yellow, odourless, non-toxic, non-volatile liquid. It has excellent heat resistance power, electrical insulation, weather resistance, hydrophobicity, physiologically inert & smaller surface tension.
Silicone oil is used as a long-term release agent in the contour machining of plastic and rubber as well as in food production. It is also used as high and low temperature lubricant between various materials, manufacturing the additives of lubricating plastics. glass, ceramics, metal, cement and other products which when treated with dimethylsilicone oil are not only hydrophobic, but also corrosion resistance, mildew proof, surface smooth. It is widely used as heat carrier and efficient defoamers in the chemical, pharmaceutical, cosmetics materials, food and other sectors, quakeproof damping material in precision machinery and instrumentation, high-temperature resistance dielectric liquid in the electric appliance and electronics industry. It also widely used as polishing agent of automotive, furniture, floor, as well as hydraulic oil of pumps, brakes , cylinders and so on.
Experimental & Results:
Silicon & other trace elements were quantatively estimated by Perkin Elmer optima 7000 DV ICP-OES. Thermogravimetry analysis was done using Perkin Elmer STA 6000 TG/DSC instrument. The samples were also studied by Thermo Scientific Nicolet IS10 Fourier Transmission Infra-red Spectrometry.Viscosity of the samples were measured using Red Wood Viscometer.
a) ICP-OES Analysis: The samples were acid digested using acid digestion vessel.Calibration curves were made using reagent blank & analysed standard of pure standard liquid CRM of required strength. The following figures show the calibration curves made for analyzing different element in ICP and their spectrum details. The table shows silicon and trace element concentration analysed in ICP for five different grades of silicone oil samples received at laboratory.
b) TG/DSC Analysis: Analysis was performed at a heating rate of 10°C /min in pure nitrogen gas atmosphere upto 350°C & after that in zero air upto 700°C. From TG/DSC curves, it was observed that there was loss which took place upto 350°C (approximately).Volatile matters were volatilized at this temperature. Again loss was observed within 350°C to 700°C. It indicates the presence of different volatile matters which decompose at different temperature zone.
c) FTIR Analysis: The samples were dissolved in pure xylene. 10% sample solutions were prepared & scanned was carried out from the region of 4000 cm-1 to 400 cm-1. The region was zoomed form 3000 cm-1 to 1000 cm-1. Same treatment was done using 5% i.e diluted sample solution. The following figures show the FTIR spectrum of each of the 5% silicone oil solution.
It was observed from the FTIR scan of all the five silicone oil samples that Aliphatic –CH3 asymmetric stretching (2975-2950 cm-1), stretching frequency of carbon carbon triple bond are absent. Stretching of Isopropyl group (1390-1380 cm-1), C=C stretching (2000-1540 cm-1), -SiH3 symmetric stretching (2153-2142 cm-1) , Si-C stretching (1280-1255 cm-1) are present.Small quantity of Si-O-Si (1130-1000 cm-1) & Si-O-C stretching (1110-1000 cm-1) are also present.
d) Viscosity Measurement: Viscosity of four Silicone Oil (except Silicone Oil 5 as it is semi-solid) was measured at 40°C.
It was found from FTIR study that few hydrocarbon groups are present. TG/DSC study indicates that those volatile hydrocarbons are volatilized into two steps, one is at approximately 350°C & other 350°C – 700°C. It can be concluded that those silicon oils which show more loss contain more hydrocarbons.