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Unlike ethylene glycol, propylene glycol is much lower in toxicity. Both are readily biodegradable.

Propylene glycol is used:

Propylene glycol has properties similar to those of ethylene glycol (monoethylene glycol, or MEG). (Note: Infrequently propylene glycol may also use the acronym MEG, but as an abbreviation of methyl ethyl glycol- the industry standard acronym for propylene glycol is PG or MPG (monopropylene glycol). The industrial norm is to replace ethylene glycol with propylene glycol when safer properties are desired.




Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, liquid. Ethylene glycol is toxic, and ingestion can result in death.


Approximately 60% of ethylene glycol is consumed for antifreeze, and the remainder is mainly used as a precursor to polymers. Because this material is cheaply available, it finds many niche applications.[3]

[edit] Coolant and heat transfer agent

The major use of ethylene glycol is as a medium for convective heat transfer in, for example, automobiles and liquid cooled computers. Ethylene glycol is also commonly used in chilled water air conditioning systems that place either the chiller or air handlers outside, or systems that must cool below the freezing temperature of water. In geothermal heating/cooling systems, ethylene glycol is the fluid that transports heat through the use of a geothermal heat pump. The ethylene glycol either gains energy from the source (lake, ocean, water well) or dissipates heat to the source, depending if the system is being used for heating or cooling.

Due to its low freezing point and tendency to form glasses, ethylene glycol resists freezing. A mixture of 60% ethylene glycol and 40% water does not freeze until temperatures below -45 C.[3] Diethyleneglycol behaves similarly. It is used as a deicing fluid for windshields and aircraft. The antifreeze capabilities of ethylene glycol have made it an important component of vitrification (anti-crystallization) mixtures for low-temperature preservation of biological tissues and organs.

Ethylene glycol disrupts hydrogen bonding when dissolved in water. Pure ethylene glycol freezes at about -12 C, but when intermixed with water molecules, neither can readily form a solid crystal structure, and therefore the freezing point of the mixture is depressed significantly. The minimum freezing point is observed when the ethylene glycol percent in water is about 70%, as shown below. This is the reason pure ethylene glycol is not used as an antifreeze--water is a necessary component as well.

Niche applications

Minor uses of ethylene glycol include the manufacture of capacitors, as a chemical intermediate in the manufacture of 1,4-dioxane and as an additive to prevent corrosion in liquid cooling systems for personal computers. Ethylene glycol is also used in the manufacture of some vaccines, but it is not itself present in these injections. It is used as a minor (12%) ingredient in shoe polish and also in some inks and dyes. Ethylene glycol has seen some use as a rot and fungal treatment for wood, both as a preventative and a treatment after the fact. It has been used in a few cases to treat partially rotted wooden objects to be displayed in museums. It is one of only a few treatments that are successful in dealing with rot in wooden boats, and is relatively cheap. Ethylene glycol may also be one of the minor ingredients in screen cleaning solutions, along with the main ingredient isopropyl alcohol. Ethylene glycol is commonly used as a preservative for specimens in schools, frequently during dissection. It is said to be safer than formaldehyde, but the safety is questionable.[citation needed] Sometimes it is used in killing jars.





Clinical uses

Polyethylene glycol has a low toxicity[6] and is used in a variety of products. It is the basis of a number of laxatives (e.g., macrogol-containing products such as Movicol and polyethylene glycol 3350, or SoftLax, MiraLAX or GlycoLax). It is the basis of many skin creams, as cetomacrogol, and sexual lubricants, frequently combined with glycerin. Whole bowel irrigation (polyethylene glycol with added electrolytes) is used for bowel preparation before surgery or colonoscopy and drug overdoses. It is sold under the brand names GoLYTELY, NuLytely, GlycoLax, Fortrans, TriLyte, Colyte, Halflytely, MiraLAX, Softlax and MoviPrep. When attached to various protein medications, polyethylene glycol allows a slowed clearance of the carried protein from the blood. This makes for a longer acting medicinal effect and reduces toxicity, and it allows longer dosing intervals. Examples include PEG-interferon alpha, which is used to treat hepatitis C, and PEG-filgrastim (Neulasta), which is used to treat neutropenia. It has been shown that polyethylene glycol can improve healing of spinal injuries in dogs.[7] One of the earlier findings that polyethylene glycol can aid in nerve repair came from the University of Texas (Krause and Bittner).[8] Polyethylene glycol is commonly used to fuse B-cells with myeloma cells in monoclonal antibody production. PEG has recently been proved to give better results in constipation patients than tegaserod.[9]


Other uses

PEG is used in a number of toothpastes as a dispersant; it binds water and helps keep gum uniform throughout the toothpaste. It is also under investigation for use in body armor[15] and tattoos to monitor diabetes.[16]

Low mol weight (PEG 400) is used in Hewlett-Packard designjet printers as a ink dissolvent and lubricant for the print heads.

PEG is a commonly used precipitant for protein crystallization. X-ray diffraction of protein crystals can reveal the atomic structure of proteins.

Polymer segments derived from PEG polyols impart flexibility to polyurethanes for applications such as elastomeric fibers (spandex) and foam cushions.

Since PEG is a flexible, water-soluble polymer, it can be used to create very high osmotic pressures (tens of atmospheres). It also is unlikely to have specific interactions with biological chemicals. These properties make PEG one of the most useful molecules for applying osmotic pressure in biochemistry experiments, particularly when using the osmotic stress technique.[citation needed]

PEO (poly (ethylene oxide)) can serve as the separator and electrolyte solvent in lithium polymer cells. Its low diffusivity often requires high temperatures of operation, but its high viscosity even near its melting point allows very thin electrolyte layers. While crystallization of the polymer can degrade performance, many of the salts used to carry charge can also serve as a kinetic barrier to the formation of crystals. Such batteries carry greater energy for their weight than other lithium ion battery technologies.

When working with phenol in a laboratory situation, PEG 300 can be used on phenol skin burns to deactivate any residual phenol.

Poly (ethylene glycol) is also commonly used as a polar stationary phase for gas chromatography, as well as a heat transfer fluid in electronic testers.

PEG is traditionally also one of the main ingredients in Paintball fill because it is thick and flexible. However, as early as 2006, some Paintball manufacturers have been substituting PEG with cheaper alternatives.[citation needed]

PEG has also been used to preserve objects which have been salvaged from underwater, as was the case with the warship Vasa in Stockholm.[17], and the Mary Rose in England. It replaces water in wooden objects, which makes the wood dimensionally stable and prevents warping or shrinking of the wood when it dries. Additionally, PEG is used when working with green wood as a stabilizer and to prevent shrinkage. [18]

PEG is often used (as an internal calibration compound) in mass spectrometry experiments, with a characteristic fragmentation pattern.

In the field of microbiology, PEG precipitation is used to concentrate viruses and PEG is also used to induce complete fusion (mixing of both inner and outer leaflets) in liposomes reconstituted in vitro.

PEG is also used in lubricant eye drops. PEG derivatives such as narrow range ethoxylates are used as surfactants.

Dimethyl ethers of PEG are the key ingredient of Selexol, a solvent used by coal-burning, integrated gasification combined cycle (IGCC) power plants to remove carbon dioxide and hydrogen sulfide from the gas waste stream.

PEG has been used as the hydrophilic block of amphiphilic block copolymers used to create some polymersomes.[19]

Gene therapy vectors (such as viruses) can be PEG-coated to shield them from inactivation by the immune system and to de-target them from organs where they may build up and have a toxic effect.[20] The size of the PEG polymer has been shown to be important, with large polymers achieving the best immune protection.

PEG is used as an excipient in pharmaceutical products. Lower molecular weight variants are used as solvents in oral liquids and soft capsules whereas solid variants are used as ointment bases, tablet bindings, film coatings and lubricants.[21]






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