What is a glycol ether?
Glycol ethers are liquid solvents. They are produced by reacting ethylene oxide (EO) or propylene oxide (PO) with alcohols. The glycol ether molecules can contain one or more EO or PO molecule in them. Typical alcohols used include methanol, ethanol, propanol, butanol and hexanol. Glycol ethers can then be further reacted (esterified) with acetic acid to produce the equivalent acetate ester form. Therefore a whole family of products with 30 or more possible combinations exists.
What are the properties of glycol ethers?
The 'glycol ethers' are not only a large family of products, they also possess a large range of properties. The main properties are good solubility in water, most organic solvents, and oils. This property makes them very useful for many different applications in industry and also for many products used by the general public. Glycol ethers very often allow the combination of components which would be incompatible without their intervention and therefore are crucial in the formulation of products. For instance, some glycol ethers enable water to be used to dissolve substances that would otherwise remain insoluble. Their use, in low concentrations, can avoid the need to resort to using other solvents that may present safety risks (flammability) and/or environmental risks (evaporation of volatile organic compounds). Glycol ethers can provide the following technical benefits:
- improve the wetting properties of water-based products
- give good long-term stability and shelf-life of products
- work at low concentrations
- have little odour
What are glycol ethers used for?
The use of glycol ethers dates back to the 1930's but their range of applications subsequently expanded, especially during the sixties and seventies. Glycol ethers have a very diverse range of uses. Currently, the most widespread use of glycol ethers is in surface coatings. Many water-based coatings (both for consumers and in industry) would not function without glycol ethers. Glycol ethers are found in applications as diverse as decorative consumer paints and the painting operations of the car manufacturers. Other important coating types include can and wood coatings, coil and anticorrosion coatings. Glycol ethers are also used in adhesives and inks, particularly in screen printing. Other applications include cleaning products, cosmetics, speciality chemical manufacture (including pharmaceuticals), electronics manufacture, leather goods manufacture and hydraulic fluids (e.g. brake fluids). Smaller uses include manufacture of fire fighting foams, agricultural products and in the paper, textile, rubber and construction industries.
What does the European glycol ethers market represent today?
Because of the use of glycol ethers in very varied fields and their important and unique properties, in 2000 the European market for them accounted for approximately 400,000 t.
Do glycol ethers present risks for the environment?
No. All international research and evaluations show that glycol ethers do not accumulate in the environment, because they break down in the air within a few hours by photolysis (= breakdown reaction triggered by sunlight) and they are biodegradable within a few days in the aquatic environment.
Do glycol ethers present risks for people?
It is important to realise that glycol ethers constitute a varied family of more than 30 different solvents. These may have similar physical properties but they do not all have the same technical characteristics or the same toxicity profiles. Some glycol ethers, if ingested or inhaled in very high vapour concentrations, may cause central nervous system depression which may lead to headaches, nausea, dizziness, drowsiness and even coma. Some glycol ethers may cause irritation or eye damage. Glycol ethers are not classified as carcinogens or mutagens and are not expected to cause cancer in humans. Based on effects observed in animal studies, a small number of glycol ethers are classified as "Toxic to reproduction, Category 2" according to the classification criteria laid down in the European Dangerous Substances Directive. These are EGEE (ethylene glycol ethyl ether, 2-ethoxyethanol), EGME (ethylene glycol ethyl ether, 2-methoxyethanol) their acetates (EGEEA and EGMEA) and DEGDME (diethylene glycol dimethyl ether, 2-(2-Methoxyethoxy) ethanol). Extensive research has unravelled the mechanism of the reprotoxic effects observed in animal studies. It is not actually the glycol ether itself that is toxic, but rather one of its breakdown products in the body, a so-called alkoxy acetic acid. It has been found that only small chain alkoxy acetic acids have reprotoxic properties and that the toxicity falls markedly as the size increases. The glycol ethers with more ethylene oxide units or longer alcohols than propanol are completely void of reprotoxic effects. The use of reprotoxic glycol ethers is regulated and restricted. They are effectively forbidden in consumer products. All glycol ethers used in consumer products have been extensively tested and, if used in accordance with the manufacturers' instructions, present no risk to health. Under the right conditions, glycol ethers can be used for professional applications without presenting a risk to health. In most European countries, especially in France, the use of dangerous chemical products in the work place is regulated since many years by the provisions of the Labour Laws. This means that users are obliged to assess the risks at the workplace and to take the required protection measures. Under the most recent chemicals' legislation (REACH; Regulation EC No 1907/2006) this is a requirement for all hazardous chemicals. In addition, EU law requires that legal workplace exposure limits for chemicals, including glycol ethers, are observed.
Which are the commercially important glycol ethers?
The most important E series glycol ethers are those derived by reacting ethylene oxide with butanol ('butyl' series). These include EGBE, DEGBE and TEGBE, plus the acetate esters of the first two. Other important E series include EGHE and EGPhE and TEGME. In the P series, the most important are PGME and PGEE plus their acetate esters, and also PGBE.
What are the effects of exposure to glycol ethers?
The main routes of potential exposure are inhalation of vapours or skin absorption of liquid glycol ethers. Some glycol ethers are significantly volatile and will potentially produce the same short-term effects typical of any organic solvent (central nervous system depression) in high enough concentrations. Most glycol ethers can also be absorbed through the skin in significant amounts, although this is still usually a minor route compared to inhalation. Short-term effects of skin exposure may include irritation and eventual skin defattening. There is no convincing evidence that long exposure to glycol ethers produces any adverse effects, but the animal data indicates that some (glycol ethers classified as Category 2 reprotoxins) should be regarded as potentially harmful to the unborn child and male fertility. There is no indication that glycol ethers can produce any adverse effects on the blood in humans.
Do we know all the risks linked to the use of glycol ethers?
Glycol ethers are among the most extensively studied and best-known chemical substances. They have been in wide use for nearly fifty years and so have the advantage of providing us with considerable information through experience of use. In addition, in-depth studies have been carried out to establish their hazards, so that risks associated with their use can be adequately controlled. Industry continues, in cooperation with public authorities and independent research institutes, to collect and generate data on the safe use and new applications of this range of products.
What is the status of the regulations on glycol ethers?
European directive relating to the "restriction on the marketing and use of certain dangerous substances and preparations" (Directive 76/769/EEC) prohibits the provision to the general public of products classified as "Toxic for reproduction" category 1 and 2. Thus, products with a higher content than 0.5% of category 1 or 2 reprotoxic glycol ethers, such as EGEE, EGME and their acetates, were withdrawn from products sold to the general public in 1994. Since 2010 the products containing >=0,1% DEGME cannot be placed on the market for supply to the general public, as paints, paint strippers, cleaning agents, self-shining emulsion or floor sealants, and the products containing >=3% DEGBE shall not be placed on the market for the supply to the general public, as spray paints or spray cleaners in aerosol dispensers.. (See 'regulations' for more details). The Chemicals regulation REACH (1907/2006) obliges manufacturers and importers of substances produced in amounts more than 1tpa to submit a dossier on their substance to the European Chemicals Agency. For those substances that are classified as hazardous, they are also obliged to quantify exposure and risks for themselves and their downstream users and to recommend protection measures where needed. Complementary to this, the EU Directives 80/1107/EEC, on "protection of workers from the risks related to exposure to chemical, physical and biological agents at work", and 89/391/EEC, on "Measures to encourage improvements in the safety and health of workers at work", and their respective daughter directives, in particular 91/322/EEC on "indicative limit values" and 98/24/EC on "the protection of the health and safety of workers from the risks related to chemical agents at work" obliges employers to assess the risks at the workplace and to take the recommended protection measures. These directives also require observation of legal exposure limits. In France these directives led in February 2001 to a decree in the labour laws on special rules for preventing carcinogenic and mutagenic risks and risks of toxicity for reproduction which reinforce the provisions applicable to these types of products. This decree covers, in particular, products classified as "Toxic for reproduction" from category 1 and 2. The glycol ethers listed in category 2 are de facto restricted. This decree provides, among other things, increased protection of pregnant women or nursing mothers, by prohibiting them from working where they could be exposed to such substances.
What steps is the industry taking to improve safety in the use of glycol ethers?
Aware of the potential risks linked to the use of some glycol ethers and concerned to restrict them, the members of OSPA have committed to the following:
- obviously - in accordance with the law - not to sell glycol ethers that are "Toxic for reproduction" Category 1 or 2 for use in products intended for the general public and where exposure at the workplace cannot be adequately controlled;
- to increase the provision of information to users, particularly in cooperation with the public authorities;
- to continue with the programme of monitoring the use of glycol ethers throughout the supply chain;
- to continue to improve scientific knowledge of glycol ethers by cooperating with public and private research bodies;
- to continue the active policy of product improvement and promoting the substitution of certain hazardous glycol ethers when technically possible.