What is Propylene Glycol?

Propylene glycol is a chemical made by reaction of propylene oxide with water. For more than five decades propylene glycol has had an unsurpassed reputation for safe use in a wide range of consumer products, including foodstuffs, animal feed, cosmetics and pharmaceuticals, as well as industrial applications.

Features

With its unique combination of properties propylene glycol fulfils various roles in different environments. It

  • serves as a solvent
  • connects and stabilises insoluble fluids (emulsifier)
  • helps to bind and transport other substances (excipient)
  • holds and dissolves active ingredients equally in a medium
  • attracts/holds water/moisture (hygroscopic)
  • reduces the freezing point
  • increases the boiling point
  • offers outstanding stability with high flash and boiling points

The propylene glycol molecule is chemically neutral, i.e. it usually does not react with other substances. This is a particularly helpful property when seeking to combine contrasting chemical elements, for example in a perfume, to create a single, homogeneous fluid.

By emulsifying the active ingredients, which otherwise would not mix, the propylene glycol creates a stable homogeneous fluid that will allow the intended final product, be it a face cream or shampoo, for example, to do its job.

Production

In the traditional production process propylene glycol is made from propylene oxide reacted with water.

The resulting mixture of mono-, di- and tri-glycols is distilled to purify the different grades before being stored and distributed to customers.

Propylene glycol is typically produced in two grades: technical or industrial grade, and USP/EP grade. The latter designates the requirements for the US Pharmacopiea and the European Pharmacopoeia, but this grade is also the grade for use in food, feed and personal care applications.

The production of propylene glycol USP/EP is seamlessly monitored and controlled through a track-and-trace system from the base material throughout the production process up to the point of delivery. The high product quality standards, and compliance with stringent hygiene conditions, qualifies propylene glycol USP/EP (pharmaceutical grade) for use in health-sensitive applications.

Markets

Propylene glycol enables a large variety of consumer and industrial applications: In food and beverage, feed, cosmetics and pharmaceutical applications, propylene glycol USP/EP (pharmaceutical grade) is used, for example, to dissolve flavouring in drinks, to keep animal feed moist, to homogeneously emulsify oily and watery elements in creams, sprays and liquids, or as solvent (excipient) for the active ingredients in medicines.

In industrial applications propylene glycol is used as an intermediate to make other chemical substances, such as the unsaturated polyester resins which are used in bath and kitchenware, pipes or windmill blades. It is also used to manufacture plastics, resins, paints and coatings, and plays an important role as an ingredient of formulations for heat transfer fluids, liquid detergents or aircraft de-icing.

Safety

The use and effects of propylene glycol have been thoroughly researched. It has been used safely for more than 50 years, including adoption in health-sensitive applications such as food, cosmetics and pharmaceuticals, where the molecule mainly serves as non-active ingredient or carrier of other substances.

Studies demonstrate that propylene glycol has a very low degree of toxicity. In the body under conditions of normal low exposure, propylene glycol is quickly metabolised and excreted.

For the environment, studies show that propylene glycol is readily biodegradable and hence does not persist nor does it bio-accumulate – it is readily biodegradable.

Accordingly, there is

  • no official hazard classification or labelling of propylene glycol, and
  • propylene glycol is not listed “negatively” in any country of the EU

In addition, all members of the sector group representing the producers of propylene glycol within Cefic are committed to Responsible Care®, a voluntary initiative of the chemical industry aimed at continuous improvement of their health, safety and environmental performance in handling chemicals.

Propylene glycol is known to be used as a carrier liquid in electronic cigarettes. Upon use of the electronic cigarettes, an artificial smoke is generated among others by fine droplets or mist of propylene glycol. While propylene glycol is a very safe compound, the producers of propylene glycol and members of Cefic’s PO/PG sector group do not support the use of propylene glycol in electronic cigarettes, nor in artificial (theatrical) fogs due to possible effects on the eye, nose, throat, and respiratory tract membranes as well as the absence of information on potential long term effects from prolonged inhalation of (fine) droplets of propylene glycol.

Regulatory

Several international authorities investigated the safety of propylene glycol. Both the Organisation for Economic Cooperation and Development (OECD), and the Canadian Centre for Occupational Health and Safety, have published risk assessments that indicate the very low toxicity of propylene glycol.

Pharmaceuticals

If propylene glycol is used in pharmaceuticals applications, strict specifications for quality as laid out in the European Pharmacopoeia, have to be followed. The 8th edition of this official document of the European Directorate for the Quality of Medicines (EDQM) was published in 2013; it is used in more than 37 countries in Europe. In the US, propylene glycol is listed as GRAS – Generally Recognized as Safe – for use in food and pharmaceuticals in the US-Pharmacopoeia (Ref21CFR), the official FDA (US Food & Drug Administration) document.

Food

The European authorities responsible for consumer health have approved the use of propylene glycol with food:

  • in direct food contact (Dir95/2/EC and amendments) as food additive E1520. In 2011 Propylene Glycol was included in te Union list of food additives approved for us in food additives, food enzymes, food flavouring and nutrients (EU Regulation 1130/2011);
  • in indirect food contact (Dir2002/72/EC and amendments) relating to plastic materials and articles intended to come into contact with food, such as packaging material.

Animal Feed

As of October 2010 propylene glycol is an approved animal feed material according to EU Regulation 892/2010. It is listed in the Catalogue of Approved Feed Materials (EU Regulation 575/2011, no. 13.11.1) and in theEU Register of Feed Materials. Consequently, the renewal of the authorisation of propylene glycol as animal feed additive (E – no. 490) due end 2010 was no longer pursued.  Previous restrictions such as maximum allowed concentrations or
use in cat food* as well as the requirement for technical functions for certain application approvals are no longer valid.

* Western European producers of propylene glycol in Cefic do not support its use in cat food: when fed with propylene glycol containing feed, cats show an increase in Heinz body formation, which are deformities of erythrocytes and shorten the life time of the red blood cells.  This effect is unique to cats. For more information
click 
here.

Cosmetics

In 1994, the Cosmetics Industry Safety Panel (of CTFA, Cosmetic, Toiletry and Fragrance Association, known today as “The Personal Care Products Council”) confirmed propylene glycol to be safe for use in cosmetic articles, even at higher concentrations than those actually used in consumer products.

EU Regulation (EC) No 1223/2009 on Cosmetic Products works on the principle of a “negative” list which defines substances that are prohibited or restricted for use in cosmetics. Propylene Glycol is not on this list.

REACH

The Regulation (EC) No 1907/2006 concerning Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) requires producers and importers of chemical substances in quantities of above 1 ton per year to register with the European Chemicals Agency (ECHA). The registration dossier contains detailed information on the intrinsic properties, a risk assessment of the substance and a detailed use mapping. Exposure scenarios do not have to be provided, because Propylene Glycol is not classified.

The Propylene Glycol Producers in the EU have worked together in a Consortium to jointly address the registration requirements of Propylene Glycol. For further details on this please visit the following webpage:Propylene Oxide-Propylene Glycols REACH managed by REACHCENTRUM.

Please be aware that the registration is valid for the molecule Propylene Glycol (CAS No 57-55-6) with a defined and in the Consortium agreed substance identification, which is different from the quality specifications necessary for industrial vs. pharmaceutical applications.

CLP

The EU has adopted the UN Globally Harmonised System (GHS) of Classification and Labelling of Chemicals and transferred into the EC Regulation 1272/2008 on the Classification, Labelling and Packaging of substances and mixtures (CLP). It replaces Directive 67/548/EEC (substances) and Directive 1999/45/EC (preparations). Propylene Glycol remains not classified as hazardous under the CLP Regulation.

In 1994, the Cosmetics Industry Safety Panel (of CTFA, Cosmetic, Toiletry and Fragrance Association, known today as “The Personal Care Products Council”) confirmed propylene glycol to be safe for use in cosmetic articles, even at higher concentrations than those actually used in consumer products.

Science

Chemically, propylene glycol has a very simple structure:

The two parts of the molecule, the alcohol groups (“OH”, likes water) and the hydrocarbon backbone (“CH”, likes oil), represent fundamental chemical characteristics. Their behaviour both in industrial processes, as well as in the human body or in the environment, is well understood.

Humans are exposed to propylene glycol primarily through oral intake or skin contact. It is expected to be readily absorbed by oral exposure whereas uptake through the skin is very low. Once in the body, under conditions of normal low exposure, propylene glycol is quickly metabolised and excreted.The half-life of propylene glycol in the blood stream is about 2-4 hours. It is primarily metabolised to lactate which is further metabolized to pyruvate, carbon dioxide and water. Lactate also contributes to glucose formation through gluconeogenic pathways. Very large exposures to propylene glycol may result in lactic acidosis and hyperosmotic changes in the blood.

Studies show that propylene glycol has a very low degree of toxicity.  It is a low concern for acute toxicity by ingestion, skin contact, and inhalation, although transient signs of altered nervous system function (commonly observed with short-chain glycol exposure) are observed with oral exposure to high levels. Additionally blood pH and osmotic changes may occur with high levels of propylene glycol that over-load normal metabolism. Propylene glycol is non-irritating to the skin and eye, and exhibits a very low skin sensitization potential. Long-term studies in rodents conducted with high oral doses found no evidence of adverse effects. Ingestion by cats, however, results in species-specific haematological changes. High aerosol concentrations inhaled by rats caused minor nasal and ocular signs that may have been due to mild irritation or drying effects of propylene glycol on mucous membranes. Tests conducted in bacteria, mammalian cells, and in animals demonstrate propylene glycol is not utagenic/ genotoxic. Long term toxicity studies conducted in rodents and dogs demonstrate that this substance is not a carcinogen. Studies conducted in rodents with high oral doses indicate monopropylene glycol is not toxic to reproduction or development.

In the environment, tests have shown that propylene glycol is a low concern. The Log Kow value for propylene glycol is low, indicating a tendency to partition to aqueous phases and a low potential for bioaccumulation.  In addition, propylene glycol is readily biodegradable in both fresh water and seawater and is not expected to be persistent in the environment. Several acute aquatic toxicity studies covering three trophic levels (including marine organisms) plus chronic test data (fresh water invertebrates) are available and together these indicate that propylene glycol is of low concern for ecotoxicological hazard.

Source: http://www.propylene-glycol.com/