A Beginner's Guide to Surfactants - Essentially Natural

This week we are leading into a new blog series, on all the things you can make with surfactants. I've gone through a real phase of fascination with these foamy DIY friends, but thought it would be helpful to first explain what they are and how they work before diving into recipes.

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Are Surfactants Toxic?

Surfactants may conjure up a chemically, unnatural image in one's mind, but there are quite a few that are in fact naturally derived and absolutely safe for use in natural products. Natural surfactants are great because they have a huge variety of applications, are biodegradable and environmentally safe, are easily pH adjustable to suit your needs and are gentle and non-irritant. The surfactants we will work with are derived from sustainably sourced plant sugars and enzymes and many are even ECOCERT approved, meaning you can use them to make organic products. Surfactants are used in everything from household cleaners, to shampoos, shower gels and baby washes.

To properly understand surfactants, here is a quick chemistry lesson:

What Are Surfactants?

'Surfactant' is shorthand for 'surface active agent', and as you may gather from this, they are active on the surface of the water-air/oil interface.

Much like soap, surfactants are made up of molecules that are amphiphilic, having both hydrophobic ('water-hating'; you can also think of them as lipophilic/'fat-loving') and hydrophilic ('water-loving' and 'fat-hating') ends. Remember that water and oil don't mix so you can think of them essentially as opposites; if one end of the molecule likes water, it simultaneously won't like fats/oils and vice versa.

How Do Surfactants Work?

Surfactant molecules position themselves with their hydrophobic ends pointing up and away from the water surface, while their hydrophilic end point into the water (you can picture them as sailboats on the ocean, with the hydrophobic sails in the air and the hydrophilic hull in the water). This breaks the surface tension on the water, making it easier for cleaning to happen, as there is no longer a distinction between the water and oil (ie. they can now mix and spread, aiding in cleaning and washing away).

Another thing to keep in mind is that all molecules have a charge, so surfactant molecules do too. Surfactants are classified as:

• Anionic (negative charge)
• Cationic (positive charge)
• Amphoteric (can be attracted to either positive or negative charge)
• Non-Ionic (no charge)

You want to generally stick to the rule of like-with-like, so don't go mixing cationic and anionic surfactants as they may not work so well together.

How Do I use Surfactants?

At Essentially Natural we sell only naturally derived, sulfate free products so this excludes most anionic surfactants such as sodium lauryl sulfate and sodium laureth sulfate which although lather and clean extremely well, are very harsh. We do stock one anionic liquid surfactant, sodium lauroyl sarcosinate, which is naturally derived.

Non-ionic surfactants work well with other surfactants so can be used in blends which are highly effective, but naturally derived.

Amphoteric surfactants are typically used with other surfactants to reduce harshness and support foam.

Here is a quick guide to the surfactants we stock:

Decyl glucoside

1. Liquid
2. Non- ionic
3. pH: 11.5-12.5
4. Active matter: 51%

Decyl glucoside is ECOCERT approved, a rich and quick-forming foam, but short lasting with low viscosity.

Coco glucoside

1. Liquid
2. Non-ionic
3. pH: 11.5-12.5
4. Active matter: 55%

Coco glucoside is ECOCERT approved, a pearliser/opacifier and gas properties in between those of decyl and lauryl glucoside

Lauryl glucoside

1. Viscous liquid to paste-like if crystallisation occurs
2. Non-ionic
3. pH: 12
4. Active matter: 50%

Lauryl glucoside is slow forming, but the most stable foam. Suitable for higher viscosity products.

Lauryl betaine

1. Liquid
2. Amphoteric
3. pH: 5-8
4. Active matter: 28 - 33%

Lauryl Betaine has antistatic and conditioning properties.

Sodium cocoyl isethionate (better known simply as SCI)

1. Solid
2. Anionic
3. pH: 5-6.5
4. Active matter: 87%

SCl has a rich lather with easy and complete rinse-off. Excellent tolerance of hard water and leaves no soap scum with it mostly used in shampoo and conditioner bars, and syndet bars.

Sodium C14-16 alpha olefin sulfonate (Hostapur OS liquid)

1. Liquid
2. Anionic
3. pH: 6-8
4. Active matter: 40%

Hostapur OS liquid has high foam and is versatile for use in household cleaners as well as personal care products.

Sodium lauroyl sarcosinate

1. Liquid
2. Anionic
3. pH: 8 - 9.3
4. Active matter: 29 - 31%

Sodium lauroyl sarcostinate is typically used as a secondary surfactant and in formulations of pH >6.

Cocamidopropyl betaine

1. Liquid
2. Amphoteric
3. pH: 5-6
4. Active matter: 30%

Coco betaine (we will just call it that from now on) is great for supporting other surfactants and lather, and helps bring down pH. It doesn't lather greatly on its own so is most commonly used in conjunction with another surfactant or surfactant blend. It is used on its own when formulating very mild products, such as baby shampoos or for very sensitive skins.

How Do I Choose A Surfactant?

The glucosides are all quite similar to each other, the main molecular difference being the length of their carbon chains. They have slightly varying degrees of foam and longevity, but can generally be substituted for one another in a simple surfactant recipe.

Want more information on Fatty Alcohol Ethoxylates? Feel free to contact us.

• If you are making something specific such as a face wash, go for a quick-foaming, low viscosity surfactant such as decyl glucoside, supported with coco betaine.
• For shampoos, go for a thicker, more stable foamer such as lauryl glucoside, supported with a secondary surfactant and coco betaine.

Calculating ASM

Active surfactant matter or ASM is the amount of actives/concentration found in the surfactant. You want to know the ASM of your surfactants as they are diluted with water. If cocamidopropyl betaine for instance, has a 30% ASM, then it is made up of 30% actives and 70% water.

Products also call for a certain ASM depending on what their use is. If a DIY product calls for 18% ASM then you will need to calculate how much surfactant you need based on which surfactants you choose to use in your formulation.

These are the ASMs of typical products:

• Face wash/facial cleanser - 3-10% ASM depending on how gentle you want it to be
• Shampoo - 10-15% ASM (higher end for more oily type hair, lower for dry hair types)
• Body wash - 15-20% ASM
• Bubble bath - 20-25% ASM

The ASMs of our different surfactants are stated with each in the previous section. So now we need to work out how much of each to use. Let's have a gentle face wash of 6.5% ASM as an example:

We are going to choose Coco glucoside (ASM 55%), Decyl glucoside (ASM 51%), and Cocamidopropyl betaine (ASM 30%) as our surfactant blend. The coco glucoside will be our primary surfactant (the one we will use most of in the recipe), with decyl glucoside and coco betaine as secondary surfactants.

So, now we decide on the share of each to use, keeping in mind it must add to 6.5. Let's decide:

• Coco glucoside - 3
• Decyl glucoside - 2
• Cocamidopropyl betaine - 1.5

To calculate the mililitres of each to use, divide the quota of each by its ASM (or convert the percentage into decimal form, whichever is easiest for you):

• Coco glucoside: 3/55% = 5.45ml
• Decyl glucoside: 2/51% = 3.92ml (can round up to 4ml)
• Coco betaine: 1.5/30% = 5ml

And that is your surfactant recipe! Most of the time the exact amounts are provided in recipes, but ASMs are handy things to know how to calculate if you ever want to formulate your own products.

Surfactants are all around us and we all use natural and synthetic surfactants every day. Our lives depend on natural surfactants which help us to breathe and to digest our food. 15 million tonnes of surfactants are manufactured every year for use in detergents, shampoos, cosmetics, antifoams, recycling of paper, and many specialty chemicals. But what are they and how can we understand them?

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Definition and uses

“Surfactant” is an abbreviated form of “Surface Active Agent”. Surfactants are generally organic molecules with two different functional groups located at either end of the molecule. They are described as Amphiphilic as they have one end which will be hydrophilic (water-loving) and one end which will be hydrophobic (water-hating).

The surfactant will act in a liquid to reduce surface tension and this property can be used by a chemist to create a substance that has the desired properties for their product.

Surfactants have many uses in everyday life. They are used in soaps, detergents, fabric softeners, shampoos, hair conditioners, toothpaste, antifogging chemicals, and cosmetics. They are used in paints, emulsifiers, adhesives, firefighting chemicals, and water treatment. They find uses in biocides, herbicides, insecticides, spermicides, and many specialty chemicals.

Manufacturers

Surfactants are often blended into specialty chemicals to help the active ingredient of the product act at the point where it is required so there are many, many, surfactant suppliers in many countries. The manufacture of base surfactants is dominated by large multinational companies such as;

• 3M Company (USA)
• Akzo Nobel BV (Netherlands)
• Arkema S.A. (France)
• Ashland Holdings (USA)
• BASF (Germany)
• Clariant AG (Switzerland)
• Croda International PLC (UK)
• DKS Co Ltd (Japan)

These companies supply their products to other companies to be incorporated into end-user products often in very small quantities.

Types of surfactant

To understand surfactants, we need to look at the ionic charge on the molecules they are made up of. There are four main categories of surfactants which classify them according to their molecular charge: -

Anionic Surfactants have a negative charge on the hydrophilic end. They are great for lifting and suspending solids and oils and other particles with a positive charge. Anionic surfactants are used mainly in detergents and account for over 50% of the world's production of chemical surfactants in industry. Anionic products often produce foams in water. Commonly used anionic surfactant chemicals are sulfates, sulphonates, and gluconates

Cationic Surfactants have a positive charge on the hydrophilic end. They have good antistatic properties and hence are used in fabric softeners. Cationic surfactants are not normally compatible with anionic surfactants as their charged components react with each other. Cationic surfactants have some antimicrobial properties. Cationic surfactants are often amine products.

Non-ionic Surfactants as the name suggests do not carry an ionic charge. Non-ionic surfactants are the second most common form of surfactant accounting for up to 45% of annual world production. They are good for removing organic material from surfaces and are often non-foaming so they are frequently used in tandem with anionic surfactants in laundry detergents and cleaning products. Common chemicals are ethoxylates, alkoxylates, and cocamides.

Zwitterionic or Amphoteric surfactants are molecules with positive and negative charges which cancel each other out. Changes in pH can make one charge more dominant than the other. In acidic environments, a positive charge will dominate and in an alkaline environment, a negative charge will dominate. These types of surfactant are often expensive and they are used in personal care products such as shampoos and cosmetics. Typical chemicals are betaines, amino oxides, and quaternary amine and carboxylic acid combinations.

Surfactants are often used in cleaning products. The mechanism of their action is that the hydrophobic tail attaches to the soil particle and surrounds it forming a micelle. This micelle has hydrophilic tails on its surface so is lifted by the water away from the surface.

In a laundry detergent for instance the chemist may want to remove organic a nonorganic dirt from a surface or fabric. This may require them to blend anionic and other types of surfactants which will require the creation of a “built product”.

A “Built Product” will usually incorporate at least one surfactant, a builder, a hydrotrope, and a carrier. A hydrotrope is a chemical that keeps the mixture stable when in solution. The carrier is usually a solvent or water which keeps the product in solution or suspension.

Builders are chemicals that help lift, disperse or sequester dirt particles. Laundry detergents are typically built products with a mixture of active ingredients designed to give optimal cleaning power by removing organic and nonorganic stains and sometimes including fabric softener and antistatic treatment as well.

Anionic surfactants can have antimicrobial qualities as they can dissolve the hydrophobic outer layers of viruses and bacteria. This has applications in the current world SARS-CoV-2 pandemic. Research has shown that the addition of surfactant to alcohol and soap hand washes can significantly increase the biocidal activity of the product. It can also improve evaporation reducing drying time for hands as well.

Environmental considerations

The use of surfactants has profound effects on the natural environment. Detergents have a very significant effect on fish and other aquatic organisms as they attack the mucous membranes that protect them from virus and bacterial infection. A concentration of 15ppm of detergent is lethal to adult fish and 5ppm will kill their eggs.

A concentration of as little as 2ppm will increase the absorption of pesticides and some other toxic substances in fish. Surfactants have a significant detrimental effect on the breeding success of many aquatic organisms.

These facts mean that any surfactant used should be carefully chosen and safely disposed of. There are discharge consent levels for surfactants when discharging to watercourses and responsible companies will choose surfactants that biodegrade to harmless substances quickly in the natural environment or sewage treatment works.

Further Reading