The Science behind Polyethylene glycols: Understanding its Applications and Benefits
Polyethylene glycols (PEGs) are a versatile group of compounds that have gained immense popularity in various industries, including pharmaceuticals, cosmetics, and food. These compounds are synthetic polymers that are produced by the polymerization of ethylene oxide, resulting in a range of molecular weights and properties. PEGs are widely used due to their excellent solubility, biocompatibility, and lubricant properties, making them an essential ingredient in many products. However, understanding the science behind PEGs can be complex, as their properties vary depending on their molecular weight and the application they are used for. In this article, we will delve into the science behind PEGs, explore their various applications, and highlight their benefits in different industries. Irrespective of your professional role as a scientist, a marketing executive, or a consumer, this article will provide you with a comprehensive understanding of the science behind PEGs and how they can benefit you.
Fig. 1.1 - Types of Polyethylene glycol
The chemistry of PEGs
PEGs is chemically a polyether denoted as synthetic polymers that are produced by the polymerization of ethylene oxide. Ethylene oxide is a highly reactive epoxide that can polymerize with itself or other hydroxyl-containing compounds to form Polyethylene glycols. The common structure of PEG can be expressed as H−(O−CH2−CH2)n−OH. PEG is a hydrophilic molecule, having low toxicity, and flexibility.
The molecular weight and properties of PEGs depend on the number of ethylene oxide units that are polymerized. Polyethylene glycols were named based on the number of units of ethylene glycol (PEG-4, PEG-8), earlier but now are based on their molecular weights (eg PEG 200, PEG 400).
PEGs are classified based on their molecular weight. Low molecular weight PEGs have a molecular weight of up to 700 g/mol, while high molecular weight PEGs can have a molecular weight of up to 20,000 g/mol. PEGs with molecular weights above 20,000 g/mol are also called polyethylene oxides (PEOs).
The properties of PEGs depend on their molecular weight. Low molecular weight PEGs are in the liquid state, water-soluble, have a low viscosity, and are used as solvents, lubricants, and emulsifiers. High molecular weight PEGs exist as waxy solids, water-soluble, have a higher viscosity, and are used as thickeners, binders, and gelling agents.
Properties and characteristics of PEGs
PEGs have several properties and characteristics that make them useful in various industries. One of the most important properties of PEGs is their excellent solubility in water and many organic solvents. This property makes PEGs useful as solvents, emulsifiers, and dispersants in pharmaceuticals, personal care products, and food. In the later discussion, we will elaborate on each specific PEG type manufactured at Esteem with their probable uses.
PEGs are also biocompatible, which means they are not toxic to living cells. This property makes PEGs useful in pharmaceuticals and medical devices. PEGs are also used as lubricants and surfactants due to their low toxicity and low surface tension. Polyethylene glycols or PEGs because of their neutral, nontoxic, and water soluble nature are used in drug delivery systems and can form micelles which are biocompatible and biodegradable.
Another property of PEGs is their ability to reduce friction and increase lubrication. This property makes PEGs useful in personal care products such as lotions, creams, and hair conditioners. PEGs also have a low melting point, which makes them useful as solidifiers and binders in food and pharmaceuticals. Pharmaceutical and cosmetics use PEGs with smaller molecular weights. The lower the molecular weight, it helps the active compounds to penetrate the skin. In cosmetic application, polyethylene glycols (PEGs) can function in three different ways: as emollients which helps to soften and lubricate the skin; as emulsifiers which help mix water- and oil-based ingredients thoroughly, and as delivery vehicles that help transport other ingredients deeper into the skin.
Applications and benefits of PEGs in different industries
PEGs have a wide range of applications in various industries. One of the main benefits of using PEGs is their excellent solubility in water and many organic solvents. This property make it useful in the pharmaceutical industry, as solvents, emulsifiers, and stabilizers in drug formulations. PEGs are also used as coatings and binders in tablets and capsules. Another benefit of using PEGs is their biocompatibility. PEGs are not toxic to living cells, which makes them useful in pharmaceuticals, personal care products, and medical devices. For example, PEGs are used in medical devices such as catheters and implantable devices to reduce friction and increase lubrication, which reduces tissue damage and inflammation.
In the personal care industry, PEGs are used as emulsifiers, surfactants, and thickeners in lotions, creams, and shampoos. PEGs are also used as humectants and lubricants in skin care products and hair conditioners. PEGs are also used in cosmetics as a thickener in makeup products.In the food industry, PEGs are used as emulsifiers, stabilizers, and thickeners in processed foods. PEGs are also used as mold release agents and solidifiers in food products such as cheese and confectionery.
Fig. 1.2 - 3D structure of Polyethylene glycol
The following sections describe the detailed uses for each PEG type manufactured in Esteem.
PEG 200 (Polyethylene Glycol 200)
PEG 200 (Polyethylene Glycol 200) is a colorless, non-volatile, hygroscopic liquid. It is soluble in water, and organic solvents like acetone, alcohol, benzene, and other glycols. Due to it low molecular weight and properties PEG-200 has a wide range of potential uses. PEG 200 is used as a defoaming agent, lubricant and viscosity modifier in many different products. PEG-200 is used as a coating for fresh fruit to preserve their freshness, as a solvent in metal working fluids, heat transfer fluids, as a binder and modifier in latex paints, and as a humectant in inks and abrasives. PEG 200 also finds use in formulations of resins, adhesives, as antistatic agent, in chemical intermediates, release agent and plasticizers. Specific industries like agriculture, cosmetics, detergents, health and medicine, textiles also rely on PEG-200 for its emulsifying property.
PEG 400 (polyethylene glycol 400)
PEG 400 (polyethylene glycol 400) is a low-molecular-weight grade of polyethylene glycol. It is a clear, colorless, viscous liquid. PEG-8 is also known as Polyethylene Glycol 400, where 400 represents the average molecular weight of the compound. Due in part to its low toxicity, PEG 400 is widely used in a variety of pharmaceutical formulations. For example PEG 400 help dissolve a large number of substances that do not readily dissolve in water by forming complexes with active substances. Therefore PEG 400 functions as solubilising agents for these active substances and excipients in liquid and semi-solid preparations. Polyethylene glycols 400 functions as viscosity modifiers and stabilizers for liquid pharmaceutical preparations and ointments. PEG 400 is soluble in water, acetone, alcohols, benzene, glycerin, glycols, and aromatic hydrocarbons, and is slightly soluble in aliphatic hydrocarbons. The low-molecular-weight formulations of Polyethylene glycols (e.g. PEG 400), find use in HP design jet printers as a solvent for ink and lubricant for the print heads.
PEG 600 (polyethylene glycol 600)
Polyethylene glycol 600 exist as clear colorless liquid with approx. mol weight of 630-670.
PEG 800 (polyethylene glycol 800)
PEG 800 exist as milky white paste with approx. mol weight of 720-880. Its freezing point ranges between 20-25oC. PEG 800 belong to the category of non-ionic surfactants and has similar applications as other low molecular weight PEG polymers.
PEG 1500 (polyethylene glycol 1500)
PEG 1500 with a hydroxyl number of 70-85 mg KOH/g typically exists as white to off white flaky solid with approx. mol weight of 1300-1600. The solubility of a 5% solution is clear and colourless, and hence find use in cosmetic and drug delivery applications.
PEG 3350 (polyethylene glycol 3350)
Polyethylene glycol 3350 is used to treat occasional constipation. Polyethylene glycols 3350 is in a class of medications called osmotic laxatives. It works by causing water to be retained with the stool. This increases the number of bowel movements and softens the stool so it is easier to pass. Polyethylene glycol 3350 is a laxative solution that increases the amount of water in the intestinal tract to stimulate bowel movements. Polyethylene glycol 3350 is used as a laxative to treat occasional constipation or irregular bowel movements. Esteem Industries subsidiary Avesta Pharma manufactures PEG/Macrogol 3350 for supply to US, Europe and Canadian markets.
PEG 4000 (polyethylene glycol 4000)
Polyethylene glycol 4000 (commonly refered to as PEG 4000) typically exists as white to off white flaky solid with a hydroxyl number of 28-36 mg KOH/g and approx. mol weight of 3100-4010. The solubility of a 5% solution is clear and colourless. These Polyethylene glycols polymers are used in a wide variety of products including bath products, shaving products, skin care products, makeup, skin cleansing products, shampoo, hair conditioners and deodorants. Esteem Industries manufactures technical grade while its subsidiary Avesta Pharma manufactures PEG/Macrogol 4000 for supply to European markets.
PEG 6000 (polyethylene glycol 6000)
PEG 6000 (CAS No. 25322-68-3) is a derivative of polyethylene glycol having white to off white color and available in solid flakes or powder form. The melting range for PEG 6000 is between 58-63 oC and the average molecular weight can be within 5000-7000. Due to its lamellar structure, it may find use in pharmaceutical production of pills and tablets as binder or dry lubricant. PEG-6000 also finds use in enbalming of histological and other medical specimens when dissolved in lower glycols in place of paraffin wax. In cosmetics, PEG 6000 due to its binding property finds use in facial makeup and as wetting agents to inhibit soap cracking. The non-ionic property of PEG 6000 can facilitate the even distribution of electrolytes in galvanic baths for copper & nickel electroplating of steel and iron parts when added as a component. It can also function as anti-dusting agent for after-bath talcum powder, lubricant in paper industry, as a tyre mounting agent, as an additive in grease, as plasticiser in synthetic resin, as enhancer of thermal stability in adhesive preparations. In the rubber industry PEG 6000 at loading of 3-20% may function as mold release agent.
PEG 8000 (polyethylene glycol 8000)
PEG 8000 (CAS No. 25322-68-3) is a polyethylene glycol having white to off white color and available in solid flakes or powder form. Its high molecular weight mainly prompts its use in pharmaceutical formulations as solvent for oral, topical and parenteral preparations. The high molecular weight PEG 8000 is soluble in water and organic solvents such as alcohols. It can blend with other PEG molecular weights to achieve the desired viscosity properties. PEG 8000 is quite stable and does not support microbial growth, even in aqueous solutions.
PEG 12000 (polyethylene glycol 12000)
PEG 12000 is a colourless polymer of ethylene oxide with an average molecular weight of 12000. This flaky material melting between 57-64oC is highly water soluble and functions as excellent solubilizers. Like most other PEGs it is soluble in organic solvents, water and aromatic hydrocarbons and has limited solubility in aliphatic hydrocarbons. Therefore it can be used in a wide variety of home care applications like dish wash, fabric and laundry detergents, hard surface cleaning, in waxes and polishes and large scale industrial & institutional applications. Apart from these applications Polyethylene glycols 12000 also functions as a dispersant, in toothpastes, is used to modify therapeutic proteins and peptides to increase their solubility. In analytical applications like gas chromatography, it can function as a polar stationary phase. It is also useful in preserving objects obtained from the ocean. It finds application in blood banking as a potentiator, which is used to detect antigens and antibodies.
PEG 20000 (polyethylene glycol 20000)
PEG 20000 S (CAS No. 25322-68-3) is a solid polyethylene glycol with a mean molecular weight of 20000 available in flake form. The high moleculat weight provides several benefits like excellent solubility in water, low moisture content, highly compatible with hard water, non-volatile non-toxic and generally safe. It belongs to non-hazardous substance or mixture according to Regulation (EC) No. 1272/2008 of the European Union. Considering the safety profiles, studies with drugs like simvastatin for improving their solubility were tested with polyethylene glycol 6000, 12000 and 20000. These studies indicated higher phase solubility of drug and could influence the drug dissolution rate from such dispersion mixtures.
Safety concerns associated with PEGs
Although PEGs are generally considered safe for use in various industries, there are some safety concerns associated with their use. One of the main concerns is the potential for PEGs to be contaminated with ethylene oxide and its derivatives. Ethylene oxide is a known carcinogen and mutagen, and its presence in PEGs can be harmful.
Another safety concern is the potential for PEGs to cause skin irritation and allergic reactions. This is especially true for high molecular weight PEGs, which have a higher viscosity and are more likely to cause skin irritation.
Alternatives to PEGs
Due to the safety concerns associated with PEGs, there has been a growing demand for alternatives. One alternative to PEGs is polyglycerol, which is biodegradable and non-toxic. Polyglycerol has similar properties to PEGs and can be used as a replacement in various industries.
Another alternative to PEGs is poloxamers, which are block copolymers of polyethylene glycol and polypropylene glycol. Poloxamers have similar properties to PEGs and can be used as a replacement in various industries.
Future of PEGs in the market
Despite the safety concerns associated with PEGs, they are still widely used in various industries due to their excellent solubility, biocompatibility, and lubricant properties. However, there has been a growing demand for alternatives to PEGs, which has led to the development of new polymers with similar properties.
The future of PEGs in the market will depend on the development of new polymers that are safer and more environmentally friendly. The demand for biodegradable and non-toxic polymers is expected to increase in the coming years, which will drive the development of new alternatives to PEGs.
Conclusions
As seen in this comprehensive article, PEGs are versatile compounds that have gained immense popularity in various industries due to their excellent solubility, biocompatibility, and lubricant properties. PEGs have a wide range of applications in the pharmaceutical, personal care, and food industries, and their benefits are well-established. However, there are safety concerns associated with their use, which has led to the development of new alternatives. The future of PEGs in the market will depend on the development of new polymers that are safer and more environmentally friendly.