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Solvents PDF Print E-mail

Water is the most common solvent and dissolves very many substances. It can also emulsify many more with the help of surfactants, as for instance in water-based paints or PVA glue, or whenever we use soap or detergent for washing. In such emulsions the dispersed substance is present in the form of microscopic particles and it will depend on their size and nature whether they will settle out in the long run.

There are many kinds of solvents for different uses.

Those derived from petroleum
These products are formed by distilling petroleum into fractions of different boiling ranges and then by further refining. All these products are flammable. They are mixtures of hydrocarbons. Included are benzene-type chemicals: these are poisonous and are absorbed through the skin.
Petrol (gasoline, motor spirit)---a fuel used for cars. Its boiling range is 70o--200oC: about 20--40 per cent are benzene-type (aromatic) chemicals. In Australia lead was added to petrol in the past but this has now been discontinued. (See Car exhaust gases, Motor fuel .)
Kerosene---a fuel used in diesel and jet engines and for heating. It has a higher boiling range (175o--300oC) than petrol. It contains about 20 per cent of benzene-type chemicals and burns with a luminous flame in lamps. It is a good solvent for grease and tar. It is very poisonous to drink.
White spirit---this is used as lighter fluid and for cleaning (dry-cleaning solvents). It has a boiling range of 150o--200oC.
Mineral turps---an intermediate product containing about 45 per cent of aromatic (benzene) type compounds. It is readily absorbed through the skin (see Benzene below). A useful solvent for oil paints. An odourless solvent for artists' oil paints is now available.
Petroleum spirit (petroleum ether, shellite)---this is used as a paint thinner and cleaning agent. It has a lower boiling range than petrol (30o--130oC) and may contain benzene-type chemicals.

Other flammable solvents
Acetone---a highly flammable general solvent used in nail polish remover, in varnishes, paint thinners, aeroplane lacquers and cellulose glues. A similar more toxic but less volatile solvent is methylethylketone (MEK). Both can affect the nervous system if inhaled in high concentrations and should be used only with good ventilation.
Alcohol (ethyl alcohol, ethanol, methylated spirits)---this is best known as the intoxicating agent in beverages. It is also used as an antiseptic and solvent. For commercial use, it is sold as methylated spirits. In this product the alcohol is 'denatured' by the addition of a few per cent of methyl alcohol, dinitronium benzoate, methylisobutyl ketone and fluorescein dye. This makes methylated spirits poisonous and gives it a bad taste.
Benzene, toluene, xylene---these occur in coal tar and in petroleum and their boiling points increase and volatility decreases in the order given: for this reason, xylene is usually the preferred solvent. They are classed as aromatic solvents and are used in rubber cements, some glues, resins and fats. They are more hazardous than other hydrocarbon solvents because they are chemically very stable and are eliminated from the body very slowly. This means they accumulate in the body and even low-level chronic exposure can lead to liver damage and, possibly, cancer. The acute effect of exposure to benzene can be headaches, a reduced red blood corpuscle count and damage to the bone marrow. All aromatic solvents act as narcotics and prolonged or repeated exposure can lead to permanent brain damage. These solvents can be absorbed by inhalation or through the skin and after any contact they should be washed off with soap and water. See also the main entry for Benzene.

Chlorinated organic solvents
Most of these solvents are non-flammable (an advantage compared to the petroleum-based solvents). However, all are toxic because they dissolve in fatty tissues and affect the nervous system. Chronic exposure affects the liver. Those solvents with the lowest boiling point are eliminated most quickly from the body. They all remove fat from the skin and are absorbed through it. They are listed below in the order of increasing boiling point (40o--120oC).
Methylene chloride (dichloromethane)---used in paint strippers and for degreasing. Very effective for softening paints and plastics.
Chloroform---this is a solvent for resins and fats. Better known as a powerful anaesthetic, chloroform is not used in that capacity now because it can cause liver damage and cancer.
Trichloroethane---(also known as methylchloroform or 1,1,1 trichloroethane) is used in typing correction fluids. It may be fatal or cause permanent brain damage if inhaled in high concentrations. Trichloroethane is used as an industrial solvent and like the CFCs it damages the ozone layer. See also the main entry for Trichloroethane.
Dichloroethane (ethylene dichloride)---used as a solvent for lacquers.
Perchloroethylene (tetrachloroethylene)---this is the most common dry-cleaning solvent. See also the main entry for Perchloroethylene.
Trichloroethylene---used in some paint strippers and for industrial degreasing. It is also used in anaesthesia.

Ethylene glycol, glycol ethers, glycol esters
This is a family of synthetic solvents based on ethylene glycol and its polymers. They range from volatile liquids boiling at 85oC to involatile ones boiling at 240oC, and from thin liquids to an almost syrupy consistency. Many are completely miscible with water. Their solvent properties also cover a wide range and they are used in paints, lacquers, resins, cosmetics, printing inks, cleaning fluids, and as de-icing additives in aviation fuel. The high molecular weight members of the family are used in food as thickeners and solvents, and as detergents.
Ethylene glycol (egl) is used as antifreeze in cars and as clutch and brake fluid. Its ether and ester derivatives (such as egl-monomethylether, egl-monoethyletheracetate) are known as Cellosolve solvents and are excellent solvents for paints and resins.
Ethylene glycol polymers and their ether and ester derivatives (such as diethyleneglycol dimethylether or diethyleneglycol monoethylether acetate) have a lower vapour pressure and are also used as solvents.

The lower molecular weight (m.w.) members of the family are all highly toxic and it has been shown that women using the solvents have twice as many miscarriages as other women. In the USA, the permitted exposure limit for the lowest molecular weight ethers and esters is 0.1 ppm; in Australia the limit (time-weighted average---TWA) varies between five and 25 ppm. The limits for the higher m.w. members of the family are much higher e.g. 100 ppm for dipropylene glycol in Australia.

The very high molecular weight glycols, ethers and esters are not toxic and are used as solvents and thickeners in cosmetics, pharmaceuticals and detergents. The solvents all rapidly diffuse through the skin and through ordinary rubber gloves.

Health effects
All types of solvents remove protective fats and oils from the skin and leave it more easily damaged. Contact with the liquids should be avoided and special nitrile rubber or VITON gloves should be worn when handling them. It is important to assure good ventilation when working with products containing these solvents or to wear a respirator with an adequate filter. (See also Protective clothing, Material Safety Data Sheets.)

There is increasing evidence that exposure to many solvents can have chronic and delayed effects as well as acute effects. These include effects on the reproductive system of both men and women. The risk of miscarriage can be doubled or tripled if a woman is heavily exposed to solvents during the first trimester of pregnancy or if the father has been exposed before the child was conceived.

Recommended procedures for all solvents:
1. Choose solvents that are the least flammable and least volatile (e.g. mineral turpentine).
2. Avoid chlorinated solvents if possible.
3. Choose water-based products wherever possible.
4. Ensure good ventilation.
5. Avoid skin contact with all solvents.
6. Wear protective clothing and thoroughly wash off splashes of solvent.

 
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