What is Polyethylene Glycol?

by Lucy Bell-Young

Polyethylene glycol (PEG) is a polyether compound that has a variety of uses and appearances depending on its molecular weight. Polyethylene Glycol is made by polymerising ethylene glycol, the main ingredient in antifreeze solutions, and has a strong presence in the medical industry.

How is PEG Made?

Like most polyethers, polyethylene glycol is made by polymerising (combining with) monomers. It does this by forming ether links between them, which have a chain-like molecular structure.

In the case of PEG, ethylene oxide is reacted with ethylene glycol. An acidic or basic catalyst is then used to catalyse the reaction. When ethylene glycol polymerises, the reaction creates a variety of products. Each of these contain a different number of ethylene glycol units and are referred to as PEGs.

Characteristics of Polyethylene Glycol

PEG refers to an extremely diverse range of polyethers that are available in a variety of molecular weights. The characteristics of polyethylene glycol are similarly varied as its appearance is respective to its molecular weight. In general, polyethylene glycol is:

  • Non-Toxic
  • Odourless
  • Colourless
  • Not volatile
  • Inert

Polyethylene glycol is also extremely soluble in water and most organic solvents, like benzene, chloroform and carbon tetrachloride. The physical appearance of PEG changes depending on its molecular weight:

  • Low molecular weight PEG appears as an opaque liquid
  • Average molecular weight PEG appears as a semisolid
  • High molecular weight PEG appears as a white crystalline solid. It can also come in the form of flakes or powder, and is often waxy

In terms of chemistry, the difference between low and high molecular PEG weights is the length of their chains.

For example, PEG 400 means that there is an average weight of 400 daltons. This means that there are approximately 9 ether repetitions that form the polyethylene glycol molecule. PEG 4000, on the other hand, will have a considerably longer chain because it will have more ether repetitions in its structure.

Close up of a lab technician holding a small glass jar of colourless liquid

5 Uses of Polyethylene Glycol

Its non-toxic properties, solubility and ability to be rapidly removed make polyethylene glycol suited to a wide range of applications. It plays a huge role in medical and pharmaceutical industries, but is also used in everything from food processing and polyutherane manufacturing to cleaners and detergents. Here are 5 of its most notable applications:

  1. Laxative

The most common medical use of polyethylene glycol is as a laxative. This is because of its ability to use osmosis to pull water into the stool when inside the intestines. This softens the stool and makes it easier to pass. PEG’s capacity to apply osmotic pressure is also utilised in biochemistry tests.

  1. Whole Bowel Irrigation

Whole bowel irrigation is a medical process that is employed in order to empty the gastrointestinal tract. This is usually done before colonoscopies or bowel surgeries. PEG and added electrolytes are used during this process to help prepare the bowel.

  1. Pharmaceuticals

PEG is used in many pharmaceutical applications because of its non-toxicity and high solubility. It is the basis of many skin creams and lubricants, where it is often combined with glycerin. It is also used in ointments, medical solvents and even fragrances.

Solid-grade PEG is the favourite when it comes to making film coatings for tablets. It behaves as an excellent plasticiser by preventing the coating film from rupturing or sustaining damage.

  1. Lubricants

Polyethylene glycol is not only used as a lubricant in cosmetics. Low molecular weight PEG is used as an effective lubricant with printing ink, while most available types of PEG utilise their lubricant skills in the metal parts and textiles industries.

Polyethylene glycol is not only non-toxic but also non-corrosive. This means that it can be used with metals, plastics, rubbers and fabrics without causing any staining or damage. PEG can also be cleaned away very easily with water because of its high solubility.

  1. Binding & Dispersing Agent

Among PEGs many uses are its ability to function as a binding agent and dispersing agent across many industries. When manufacturing moulds in ceramics or casting, polyethylene glycol is used as a binding agent to ensure that the mould retains its shape and structure. As a dispersant, PEG improves the separation of particles in order to prevent clumping.

In toothpaste, polyethylene glycol acts as both a binding and dispersing agent by keeping the xanthan gum evenly distributed and preventing the paste from forming any clumps in the tube.

Polyethylene glycol is used in many more applications that span a variety of different industries. PEG is also used in:

  • Textile auxiliaries
  • Surfactants
  • Polyutherane manufacturing
  • Thickening agents
  • Hydraulic fluids
  • Anti-dusting agents
  • Electroplating (as brighteners)
  • Cleaners and detergents
  • Anti-foaming agents
  • Food industries
  • Humectants

Is PEG Toxic?

While its cousin, ethylene glycol, is toxic to humans, PEG has been “recognised as safe” by the FDA and is classified as non-toxic. With that being said, polyethylene glycol does, like every chemical, have its drawbacks that should be kept in mind when using it directly.

The main issue surrounding PEGs toxicity is the fact that it contains ethylene glycol, a potential carcinogen and toxic substance. Depending on how it has been manufactured, PEG could also contain contaminants like lead, arsenic or 1,4-dioxane. Therefore, it is also worth doing your research before handling pure polyethylene glycol.

Different types and colours of medical pills and capsules

At ReAgent, our online chemical shop has polyethylene glycol available in a range of molecular weights. We also offer flexible packaging options to ensure that we meet the needs of your business. Check out our online shop today, or get in touch to find out more about what we can offer you.


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