Polyethylene glycol (PEG), or PEG glycol, is a chemical widely used in various fields due to its unique properties. Composed of repeating units of ethylene glycol, PEG comes in different forms depending on its molecular weight and specific applications. Highly valued in the cosmetics industry , it is often combined with plant extracts to improve the texture and effectiveness of formulations. This first part introduces the fundamental characteristics of PEG, exploring its chemical composition, properties, and how it differs from similar compounds.
1. Definition and fundamental properties of PEG
Definition of polyethylene glycol
Polyethylene glycol (PEG) belongs to the polyether family, characterized by a linear structure formed by repeating ethylene glycol units. It is often designated by its average molecular weight, such as PEG-400 or PEG-6000, which reflects the average number of constituent units. This variability allows PEG to be adapted to specific uses, ranging from cosmetics to the pharmaceutical industry.
Physicochemical properties
PEG possesses remarkable physicochemical properties that explain its success in many sectors:
- Solubility : PEG is water-soluble and miscible with many organic solvents, which facilitates its incorporation into various formulations.
- Chemical stability : It is stable against acids, bases, and oxidants, while remaining resistant to thermal degradation under normal conditions.
- Molecular weight and viscosity : The viscosity of PEG increases with its molecular weight, thus offering flexibility in the choice of grades for specific applications.
Differences between PEG and PPG
Polyethylene glycol (PEG) and polypropylene glycol (PPG) share similar structures, but their properties differ:
- Hydrophilicity vs. hydrophobicity : PEG is hydrophilic, making it ideal for applications requiring compatibility with water, while PPG is hydrophobic.
- Applications : PEG is commonly used in moisturizing and pharmaceutical formulations, while PPG is more commonly used in industrial products and lubricants.
2. Synthesis and manufacturing of PEG
Manufacturing process
PEG is synthesized from ethylene oxide, a reactive organic compound, in the presence of water, ethylene glycol, or diethylene glycol. The process relies on ring-opening polymerization, catalyzed by acidic or basic agents.
- Acid catalysis : Used to produce PEGs with specific molar mass distributions, it offers better control over the oligomers formed.
- Basic catalysis : Promotes a rapid reaction and is often used to produce PEGs with lower molecular weights.
Molecular mass control
The molecular mass of PEG is a key parameter that influences its physical properties and its use.
- Low molecular weights (<600 g/mol) : These PEGs are liquid and widely used as solvents, excipients, or moisturizing agents.
- Intermediate molecular weights (600 to 1000 g/mol) : These PEGs exhibit increased viscosity, suitable for applications as thickeners in cosmetics.
- High molecular weights (>1000 g/mol) : These PEGs are solid and find applications in industrial and pharmaceutical formulations where a stable structure is required.
Manufacturing of specific grades
To meet the diverse requirements of industries, several grades of PEG are developed:
- Medical grades : Requiring high purity to ensure safety and efficacy in pharmaceutical formulations and vaccines.
- Industrial grades : Focused on versatility and suitable for applications such as solvents or bonding agents.
- Cosmetic grades : Optimized for skin compatibility and used as moisturizers or emulsifiers.
Importance of derivatization
Some PEGs undergo derivatization to improve their functionality, for example by increasing their biodegradability or adapting their chemical reactivity. These processes make it possible to produce PEGs tailored to specific needs, such as PEGs derived for controlled-release drug delivery systems.
3. Industrial applications of PEG
Medical and pharmaceutical sector
PEG occupies a central place in the medical and pharmaceutical fields due to its biocompatibility and hydrophilic properties.
- Excipients and laxatives : When used as an excipient in drug formulations, PEG promotes the solubility of active ingredients. As an osmotic laxative (e.g., PEG-3350), it works by increasing the volume of water in the intestines to facilitate bowel movements.
- mRNA vaccines : PEG is an essential component in mRNA vaccines, where it stabilizes the lipid nanoparticles carrying messenger RNA, thereby improving their efficacy and bioavailability.
- Paramedical applications : Used in hydroalcoholic gels and medical lubricants, PEG contributes to the texture and hydration of these products.
Cosmetics industry
Thanks to its moisturizing properties and compatibility with many ingredients, PEG is widely used in cosmetic .
- Surfactants and emulsifiers : PEG acts as a binding agent between aqueous and oily phases, facilitating the stability of creams, lotions and shampoos.
- Moisturizers and softeners : Due to its hydrophilicity, PEG helps maintain skin hydration and improve the softness of formulations.
- Penetration activator : It improves the penetration of active ingredients in topical dermatological products, optimizing their effectiveness.
Chemistry and agri-food
PEG plays a key role in the chemical and food thanks to its solubilizing and stabilizing properties.
- Polymer solvent : Used to dissolve salts and organic compounds, PEG is essential in certain complex chemical reactions.
- Food additives : As an additive, it improves the texture and stability of products, while being safe for human consumption.
Other industrial sectors
PEG is also used in a variety of fields that exploit its flexibility and unique properties.
- Textile industry : PEG acts as a surfactant for surface treatments of fibers.
- Archaeology : Used for the preservation of waterlogged wood, PEG helps to stabilize fragile structures.
- Ink and resin manufacturing : Its chemical stability makes it a key component in the formulation of polyester inks and resins.
Are you looking for an analysis?
4. Advantages and disadvantages of the PEG
Advantages of the PEG
PEG is widely valued for its unique properties that make it indispensable in many industries.
- Chemical versatility : Thanks to its adaptable structure and compatibility with many solvents, PEG can be used in a variety of formulations and processes.
- Low toxicity : It is considered safe for use in pharmaceutical and cosmetic products, being non-reactive and non-irritating when properly formulated.
- Water solubility and liposolubility : These properties allow PEG to play a role in binding between aqueous and oily phases, thus facilitating the stabilization of emulsions.
- Chemical and thermal stability : PEG is resistant to pH variations and high temperatures, making it a reliable material in a variety of industrial conditions.
Disadvantages of PEG
Despite its many advantages, the PEG has certain limitations that must be taken into account.
- Low biodegradability : Although bioeliminable by renal filtration, PEG is not easily broken down in the environment, raising sustainability concerns.
- Environmental impact : The production of PEG from petrochemical resources and its accumulation in aquatic ecosystems can contribute to negative environmental effects.
- Allergic reactions : Although rare, some people may experience allergic reactions to PEG, particularly when used in injectable or topical formulations.
Measures to improve efficiency and reduce impacts
To maximize the benefits of the PEG while minimizing its drawbacks, several approaches are possible:
- Use of renewable resources : The development of processes using bio-based raw materials could reduce the environmental footprint of its production.
- Improving biodegradability : Chemical modification of PEG, for example by adding functional groups, could promote its degradation in the environment.
- Optimized formulation : Judicious use of PEG at minimum effective concentrations can limit its impacts without compromising its performance.
5. Analytical methods for PEG
Standard techniques
Standard PEG analyses involve advanced tools to quantify and characterize its chemical and physical properties.
- Pyrolysis coupled with gas chromatography and mass spectrometry ( GC-MS ) : This technique is used to analyze the thermal degradation of PEG and identify the resulting products. It is particularly useful for quality control in industrial environments.
- High-performance liquid chromatography ( HPLC ) : Suitable for the separation and quantification of PEG oligomers, this method guarantees precise and reproducible analysis. It is often coupled with mass spectrometry (MS) for more detailed component identification.
- Infrared (IR) spectroscopy : Allows confirmation of the chemical structure and detection of any organic or functional impurities.
A brief scientific section: HS-GC-MS screening
The analysis of volatile compounds associated with PEG is carried out using HS-GC-MS (headspace gas chromatography-mass spectrometry) screening.
- Sampling steps : PEG samples are collected in sealed and inert containers to prevent contamination or volatilization of the compounds.
- Principle of the analysis : HS-GC-MS quantifies volatile compounds based on their interaction with PEG. These compounds are first released by heating the sample, then separated and identified by chromatography and mass spectrometry.
- Limit of quantification (LOQ) : The LOQ generally varies between 0.1 and 10 mg/L, depending on the characteristics of the targeted volatile compounds.
Specific methods depending on the application
Depending on the end use of the PEG, specific methods are often employed:
- Derivatization analysis : Used for PEGs involved in complex formulations, this method improves their detection and quantification.
- Capillary electrophoresis : An effective method for separating PEG oligomers according to their molecular mass and charge.
6. Standards and regulations surrounding the PEG
Certifications for medical and pharmaceutical applications
In the medical sector, quality and safety standards are particularly strict.
- ISO 10993 standard : This standard applies to materials used in medical devices, including PEG, by evaluating their biocompatibility to ensure the absence of undesirable side effects.
- Pharmacopoeias : The European and American pharmacopoeias specify the purity, composition, and usage criteria for PEGs in pharmaceutical formulations. This includes rigorous testing to verify the absence of toxic impurities.
- Use in vaccines : PEGs, such as those found in mRNA vaccines, must meet stability and bioavailability standards while complying with FDA and EMA requirements.
Standards in the cosmetics industry
Cosmetic products containing PEG must comply with international regulations to ensure their safety and effectiveness.
- European Regulation (EC) No 1223/2009 : This regulation mandates testing to ensure that PEGs do not pose risks to human health. Formulations must also comply with specific impurity thresholds, particularly for ethylene oxide and dioxane.
- COSMOS label : For organic and natural products, PEG must comply with the criteria of the COSMOS label, limiting the use of petrochemical or non-biodegradable substances.
Regulations for food packaging
The PEG used in materials that come into contact with food is subject to strict controls.
- Regulation (EC) No 1935/2004 : This European legislation ensures that materials do not transfer dangerous substances into food.
- FDA standards : In the United States, the FDA mandates migration tests to ensure that PEGs used in food packaging do not pose any risk to consumers.
Impact of standards on innovation
Regulatory frameworks encourage innovation in PEG development by imposing high quality standards.
- Search for safe formulations : Standards encourage manufacturers to improve the purity of PEGs to avoid adverse effects.
- Sustainable development : Environmental requirements are driving the development of PEGs from renewable resources, thus contributing to a more environmentally friendly industry.
