Non-ionics are a major group of surfactants that find application in all areas of detergents and cosmetics. They function as detergents, emulsifiers, wetting agents, solubilisers, foaming agents, and foam stabilisers. Below is a detailed overview by Norman Lowe, Senior Technical Consultant HPC and Industrial at HARKE UK & Ireland.

 

Why are they called non-ionic?

As the name suggests, non-ionics do not form ‘ions’ in solution. This is because they go into solution by forming hydrogen bonds with water molecules.

These bonds are heat sensitive, meaning that as you heat the solutions, the bonds break down, eventually leading to the product coming out of solution. This is called the cloud point (or reverse cloud point). The cloud point can serve as an indicator for the non-ionic being used, acting as an identifier. Furthermore, the wetting power, particularly of ethoxylates and alkoxylates, is at its ‘optimum’ at the cloud point. This is important when formulating rinse aids in auto dishwashing, for example, and Clean-In-Place (CIP) cleaners.

Another key advantage of non-ionics is their compatibility with both anionic and cationic surfactants.

 

Types of non-ionic surfactants

 

Fatty Alcohol Ethoxylates

Fatty alcohol ethoxylates are possibly the largest group of non-ionic surfactants in today’s market. These are based on either natural or synthetic fatty alcohols, reacted with various levels of Ethylene Oxide to yield a wide range of properties.

These properties can be broadly classified using the HLB (Hydrophilic-Lipophilic Balance) scale, which ranges from 1 to 20. It is roughly calculated by taking the percentage of ethylene oxide in the molecule (by molecular weight) divided by 5.

• Low HLBs (e.g., 3 to 6) denote water-in-oil emulsification.
• Medium HLBs (e.g., 6 to 12) denote oil-in-water emulsification.
• Optimum Detergent HLB is around 12 to 14.
• High HLBs (e.g., 16 to 20) indicate wetting/solubilising agents.

This is a rough guide but is helpful when deciding which ethoxylate to use in a specific application.

It is important to know the origin of the fatty alcohol used, as this has a direct bearing on the physical and chemical properties of the ethoxylates:

Synthetic Fatty Alcohols

These typically have chain lengths from C₉ to C₁₄ (for the detergent industry) and are made by three main processes, all starting with ethylene gas (CH₂=CH₂) and chain growth through oligomerization:

• SHOP (Shell Higher Olefin Process): The main advantage is that it produces even-numbered straight chains, which improves the speed of biodegradability. The commercial chain lengths (e.g., C₁₂-C₁₈ alpha olefins) are separated and processed into alcohols. The remaining olefins are further processed and then reacted using Hydroformylation (OXO process) to form the fatty aldehyde, which is hydrogenated to give the fatty alcohol of the right commercial chain lengths.
• Ziegler: In a similar way to SHOP processed fatty alcohols, ethylene is oligomerised, but using triethyl aluminium as the catalyst. This produces a trialkyl aluminium product which is oxidised to produce 3 moles of the fatty alcohol. This again produces a straight-chain, even-numbered fatty alcohol.
• OXO Process: Reaction of an alpha olefin with hydrogen and carbon monoxide, with a Cobalt catalyst, produces a fatty aldehyde, which is then reduced to the fatty alcohol. This process yields both linear and branched-chain alcohols.

Natural Fatty Alcohols

These are produced by the reduction of fatty methyl esters with high-pressure hydrogen. The esters are produced from triglycerides and can be either broad or narrow cut. All natural alcohols are straight-chained and even-numbered.

These various fatty alcohols can then be reacted with ethylene oxide and propylene oxide to give the fatty alcohol alkoxylates with differing properties and applications. As a rule, ethoxylates based on straight-chain alcohols have higher melting points than those based on branched-chain alcohols. The properties of ethylene oxide and propylene oxide adducts depend on the ratio of EO to PO for their specific characteristics.

 

Specialty Non-ionics

• Ethoxylates of Acetylenic Diols: These are dihydroxy molecules (two OH groups separated by the triple acetylene bridge: OH-R.C(CH₃)₂.C≡C-C(CH₃)₂.R-OH). They are known as ‘Gemini’ surfactants due to having two chains on either side of an acetylene bridge. They have high wetting properties and are typically low-foaming or defoaming.
• Naturally Derived EO: A recent advance has been the development of naturally derived ethylene oxide. When reacted with a natural fatty alcohol, this means you can now have a fatty alcohol ethoxylate that has a Renewable Carbon Index (RCI) of 100%, meaning all the carbon in the product is renewable from a vegetable source.
• Fatty Acids and Amines: Fatty acids can also be ethoxylated, producing non-ionics with slightly differing properties from the fatty alcohol-based products. Fatty amines can also be ethoxylated, producing non-ionics that have some unique properties, like anti-statics, and enhanced wetting and detergency.

 

Alkoxylates

Fatty alcohols can also be reacted with Propylene Oxide or mixtures of Propylene Oxide and Ethylene Oxide. Propylene oxide is less soluble than Ethylene Oxide, which means the solubility can be adjusted, leading to low-foaming and defoaming properties whilst in some cases enhancing wetting. Block polymers of Ethylene Oxide and Propylene Oxide have wetting and, depending on the relative ratios, low-foaming or solvent properties.

 

Ether Carboxylates

These are the reaction products of alcohol ethoxylates with acyl chlorides (Cl.RCOOH), such as chloroacetic acid. This gives a product with a carboxylate head group (-COOH). While you might assume an anionic character, in solution, these form non-ionic micelles—they do not ionise and are compatible with cationic surfactants. They can be high foaming and good emulsifiers, mild, and dispersants, often used in metalworking, detergents, and cosmetics.

 

Non-EO/PO Surfactants

There are of course surfactants that are non-ionic in character that contain no ethylene or propylene oxide:

• Fatty Amides: Alkanolamines react with fatty acids or esters to form alkanolamides. Examples are Cocamide MEA (Coconut fatty acid with Monoethanolamine) and Cocamide DEA (Coconut fatty acid with Diethanolamine), and similar products using Isopropanolamine, Diisopropanolamine, and various naturally derived fatty acids. These alkanolamides are used as foam stabilisers, viscosity adjusters, and detergent boosters. Certain fatty amides have conditioning properties (e.g., Stearamidopropyl dimethylamine) and are used in hair conditioners as alternatives to cationic surfactants.
• Alkyl Polyglucosides (APGs): These are the reaction products of sugar (usually from sugar beet or sugar cane—glucose) and a fatty acid. Common chain lengths are C₁₀ (decyl) and C₁₂-C₁₄ (cocoyl). Short-chain types (e.g., C₆) find use in high caustic cleaning systems. These products are very mild, good wetting agents, and reasonably high foaming (unless based on a short chain), used in hand dishwash, surface cleaners, shampoos, and body washes.
• Amine Oxides: Reaction product of a tertiary fatty amine (e.g., coco-dimethylamine) with Hydrogen peroxide (H₂O₂). These products are high foaming, have exceptional detergency, and good wetting. They are also stable to high levels of caustic, electrolytes, and hypochlorite bleach. C₁₀ Amine Oxides are relatively lower foaming, while C₁₂-C₁₄ and C₁₄ are high foaming. Higher chain lengths are used in the oil drilling industries and can act as conditioning agents in the cosmetic industry. They also have the ability to shield cationic surfactants in anionic systems, allowing you, for example, to formulate a strong cationic conditioning agent into an anionic-based shampoo. They are used as foam boosters and foam stabilisers in hand dishwash liquids and as detergents in hard surface cleaners.

 

This is an overview of the non-ionic chemical types, and is not definitive – I have simplified some of the data for ease of explanation. At HARKE UK & Ireland, we can supply many of these products. We understand the properties and performance of them in many systems and are experienced in formulating products based on them. 

If you require more information on any of the product types or need help with formulation, please contact us.