Apr. 29, 2024
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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“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.
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;
These companies supply their products to other companies to be incorporated into end-user products often in very small quantities.
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.
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.
Consumers continue to demand more and more “natural” formulations, leading formulators to continue to brainstorm ways to meet this demand. With strict regulations on what can be labeled “natural,” this can be a challenge. How do you know what materials to select? I’ve put together a short video that provides some tips on how to select natural surfactants.
Hi, I’m Belinda Carli, the Director of the Institute of Personal Care Science. And today, I’m going to guide you through natural surfactant selection.
Surfactants are composed of a water-loving head group and an oil-loving tail group. To be a truly natural surfactant, both the head and tail groups need to come from truly natural sources. In the past, most surfactants have been synthetically sourced for at least the head or the tail portion. But now, there is an increasing amount of selection for formulators to choose from. In order to make your selections, you first need to understand how surfactants work and some of the key things consumers look for.
So first, let’s talk about how surfactants clean. Surfactants are segregated into classes based on charge. You have your anionic surfactants which have a negative charge, your nonionic surfactants which have no charge, and amphoteric surfactants which have either a positive or negative charge depending on the pH environment. This video is going to focus on truly natural solutions, and at the moment, amphoterics just aren’t available in this category. So we’re going to focus on anionic and nonionic selections instead.
Anionic surfactants are the best at cleaning, and this is because they clean using charged repulsion. The skin and the hair is negatively charged. So, when you introduce an anionic surfactant, it will form around the oil or dirt that’s adhering to the skin or the hair, and then negative charge will lift the oil or dirt from the surface through ionic repulsion. And this is relatively strong for the surface you’re cleaning.
Nonionic surfactants, on the other hand, do not carry charge. So, they rely on disjointing pressure to force the soil from the surface. This is why anionic surfactants tend to give you a better clean, but they can also be more potentially irritating to the skin because of their better cleansing ability. And there’s more nonionic choices out there. Nonionic surfactants have also got a relatively good mildness profile, but they just simply don’t clean as well. And this is why I would use combinations in formulas.
Contrary to popular belief, you don’t actually need a lot of foam to clean a surface properly. You technically only need enough surfactant to lift all the oil and dirt from the surface. Foam is really just air trapped by the surfactant. But consumers expect to see a relatively high level of foam to think that the product is cleaning or working effectively. So, one of the first things you need to formulate for when making your surfactant formula is a good foam profile. The first thing we’re going to do then is compare various natural surfactants based on their foaming ability.
In order to test the foaming profile of these surfactants, what I did was created 7% active solutions and have put them into these convenient little self-foaming pumps. I’ve also prepared a 7% active solution of sodium lauryl ether sulfate which we’re using as our test standard because everyone knows how well that foams. So next, you see, I’ve dispensed one pump from the self-foaming bottle onto a watch glass. And then we’re going to look at the foam that is generated and how quickly it degrades. And this will give us indication of the best foaming agents from the surfactants selected.
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So now, what you can see here is the sodium lauryl ether sulfate plates, these two here, and you can see how this foam is degrading compared to the other samples. The K-Noa foam here, for example, the foam has all but dissipated. While over here, the Plantacare 810 has still got a very creamy, dense-looking foam. The OlivOil Fruttoside has a much more open foam and the Plantacare 2000UP also has a much denser foam profile. This is a really great way of comparing the foaming profiles of the materials as well as how they degrade.
So, it’s been a half an hour now. Remember these were our sodium lauryl ether sulfate benchmark samples. And if we compare the foam, we can see that the densest foam profiles are still the Plantacares and OlivOil Glutamate. The OlivOil Fruttoside has compared well with the sodium lauryl ether sulfate while the Plantacares and OlivOil Glutamate have actually kept their foam profile denser and better than the sodium lauryl ether sulfate benchmark samples.
So, now we’ve compared how they foam, the other important thing, of course, is how well they clean. Let’s evaluate that now. What I’m going to do, I’m going to apply a small amount of an oil-based zinc oxide dispersion onto my hand. Now, two reasons for doing this. One, the zinc oxide is visible, it’s a particle. The other thing is it’s an oil-based product. So, it’s also going to be a little difficult for a foaming product to remove. It’s also gonna help protect my skin barrier between applications. So, let’s take a look at how well each of these materials cleans a specified amount of this zinc oxide oil-based dispersion with one pump from these dispensers again.
So what I have here is 0.25 grams of the oil-based zinc oxide dispersion. I’m going to apply each one of these one by one onto my hand and then use one pump of the 7% active solutions to clean. You’ll be able to see how well they clean. I’ll be evaluating also for the after feel on my skin, which unfortunately you won’t be able to see but I will be able to tell you when I finish testing all eight of these products. So I’m going to start first with the sodium lauryl ether sulfate, our benchmark sample, and then I’ll be comparing each of these natural surfactants against its performance and the after feel.
So, now we’ve compared on the cleaning ability, the foam ability, and the after feel. And now you’re probably gonna say, “Belinda, what do we do with this information?” Well, now, we make our selections based on a good cleansing surfactant. We want to build a good foam profile and we want to make sure, of course, it cleans well with a nice after feel. And this is exactly why we put combinations of surfactants together.
Other factors you need to consider are mildness, price, and how the product is to be used. Because, obviously, the products that had the highest foaming and cleansing ability are best for areas like the hair, which you need to get over a lot of surface tension of the air to hair to be able to clean it effectively. Those with a lower foaming profile, you could, of course, use for facial care products where a high foam isn’t necessarily the biggest requirement. However, a mild skin feel would be.
Last and by no means least is thickening your surfactant. Now, you need to thicken your surfactant formula so that a consumer can pour the product into their hand or a wash cloth without it running readily out of the hand. And you would have seen from the samples I made if they would in a self-foaming dispenser, they were actually quite liquid solutions. So, we need to thicken them.
Now, when you have a charged surfactant, you can thicken with salt. It’s also the combination of surfactants that will help build viscosity. But we’re going to help our surfactants along and use some viscosity modifiers – again, natural viscosity modifiers – to help build the viscosity in the formulations I’m going to show you. We’re also going to add refattening agents. Now, there’s relatively few truly natural refattening agents available on the market at the moment. Going back a few years ago, there were pretty much none. They were mostly ethoxylated. And what these refattening agents do is they actually help provide some conditioning benefits to the skin or the hair. But because they are partially surfactant molecules themselves, they wash readily from the skin or hair without greasy residue.
It’s best not to add straight lipids, or if you do, less than 1%. Because if you add straight lipids into a surfactant formula, the lipids actually go into the surfactant micelle. It reduces their foaming and cleansing power. But when you use refattening or superfatting agents, because they are amphiphilic, they have water-loving and oil-loving portions, they actually go into the surfactant micelle structure rather than need to be stabilized within the micelle itself. And in this way, they don’t impact foam or cleansing ability but still add to the conditioning profile.
In a moment, I’m going to show you some formulation examples and talk you through why I’ve made the selections I have. But remember, another really important additive that you should put into your formulations, are some hydrolyzed proteins or similar natural ingredients. Now, double check this carefully if you are aiming for a COSMOS-compliant formula or an all-natural formulation philosophy because some of them may have some synthetic constituents. But hydrolyzed proteins are actually excellent additives to your foaming products because they help improve mildness and structurally, on the skin or hair, can help protect moisture losses and repair minor damages when they are applied to the skin or the hair and the excess washed away.
So now, let’s get formulating. Now, as I’ve mentioned, these natural surfactants are notoriously hard to thicken, but I’m going to show you now how you can create a luxuriously thick and gentle shampoo or body wash product using these natural materials. And for this, I’m starting with the OlivOil Fruttoside mixed with Plantacare 810UP. To this, I’m going to add a superfatting agent, the TEGOSOFT LSE 65 K Soft. Now, this is a really good natural superfatting agent. You can also use Lamesoft PO 65 by BASF. These materials are really good to provide conditioning benefits to the formula. So this formula we’re creating here, the Fruttoside has an especially soft and gentle conditioning effect on the skin and the hair. So this would be a very gentle formulation for either a body wash or for a dry hair shampoo. Now, I’m going to add the superfatting agent to the surfactants first.
When mixing your surfactants in the lab, it’s very important you don’t create a vortex. Otherwise, you’d just be sucking in air, which will leave you with a beaker full of bubbles. And, of course, in manufacturing, that’s highly undesirable to be left with a vat full of bubbles as well.
Now next, I’m going to add some essential oils and some vitamin E. Now, I’m adding in at this point because I want the essential oils and vitamin E being lipid soluble substances to be mixed into micelles that form with the concentrated surfactant mixture here. If I add them after the water has been added, there’ll then be a majority of water in the formulation, while at this point there is still a majority of surfactant present. And this will help the essential oils and vitamin E to be captured into the micelles and solubilized better in the formulation.
Now, once a homogenous mix has formed, we can now add the water. So we’re really just aiming for a homogenous mixture at this point. As you can see, it is still water thin, extremely thin. So now, we’re going to use gums to thicken. But before we can use gums to thicken this product, we need to check and adjust the pH because that can also have an impact on the formulation.
So first, I’m going to add the preservative because that will also impact on the pH, and then I’m going to adjust the pH of this formula to 5 to 5.3, and that is mainly to suit the preservative that I’m using but it also makes a skin-friendly and compatible pH.
As you can see, even with very significant pH adjustment, it’s still not building any sort of viscosity to this formula. As I mentioned, using natural surfactants makes them notoriously hard to thicken. So we’re now going to use a natural gum to help build viscosity and gel this product.
Now, I’m gonna be adding a significant portion of gum to this formula. So I first need to slurry it so that I can add it effectively to the formula. Now, I’m adding it after I’ve adjusted pH for a couple of reasons. The first is, as you could see while I was testing pH, I was stirring the product quite vigorously, and in the lab that could introduce a lot of bubbles and foam if I had my gum in the product because the gum will help trap air and hold the air in a bubble. So that’s obviously not suitable in a lab setting. And also, because this will build viscosity, which will make it a lot harder to stir the product homogenously for pH adjustment. And that’s more important in a large batch in the manufacturing sense. So, we adjust the pH first, and that also helps us see if pH is going to have any impact on viscosity, which could reduce the amount of gum we need. Now, in this example – and I’m using this particular as an example – so I can show you how to thicken even the most difficult to thicken natural formulations.
And there you have it, a beautifully thick natural surfactant with lovely soft conditioning benefits for either the body or the hair.
Now, I want to show you an alternative system. And one of the reasons I want to show you this surfactant blend is because there is a big misconception out in the marketplace that natural means it’s safer or less irritating, and that’s actually not correct. The irritancy potential or the safety profile of a surfactant formula really has to do with the chemicals you use in it. Whether or not they’re natural or not is not actually the reasoning behind a reduced irritancy profile. So, in this particular formula, I’m going to be showing you a formulation using SugaNate 160 NC. This is sodium laurylglucosides hydroxypropyl sulfonate.
Now, unfortunately, because of the sulfonation in this product, it’s not eligible to be suitable for COSMOS formula, but this is actually one of the least irritating products that you could use. It’s absolutely not irritating to eyes, this raw material.
So, I’m going to show you this formula, and in this formula, I’m also going to use some cocamidopropyl hydroxysultaine [Cola Teric CBS-HP]. I’m using a sultaine in this formula as an amphoteric because it avoids issues with California Proposition 65, which of course effects a lot of your cocamidopropyl betaines. So, in this formula, slightly different materials using, but I really I want to emphasize the point that even if you’re trying to create natural formulas, you shouldn’t disclude some of the materials that are maybe not COSMOS-certified or suitable because natural does not mean it’s safer or milder. And, in fact, this is a very, very mild formula that I’m creating here, suitable for use even with babies. And you’re even going… you’re going to also see with this formula how much easier it is to thicken a product when I’m using amphoterics and anionics compared to relying a lot on your nonionic glycosides.
So first, I have measured out water here, and through this I am going to add Glucamate CCO thickener. This is a really effective thickening agent in surfactant products when there are amphoterics and anionics present.
Now, I’m just going to stir to combine this. You’ll see it will go cloudy. And then I am going to add the amphoteric material and then the anionic material, and you’ll see the viscosity of this formula build.
So, you can see, even with the amphoteric added, viscosity has started to build straight away. The Glucamate CCO thickener being a very efficient viscosity modifier.
So you can see a honey-like consistency from this surfactant build even when using materials that would otherwise be quite difficult to thicken. Now, I would need to add preservative, essential oils or fragrance, and adjust pH. Just be careful when you are creating formulas with more natural surfactant choices because you can lose viscosity very rapidly with some preservative or essential oil choices. So, just be aware of that, when you’re selecting preservatives or essential oils, they may have a big impact on its viscosity and turn what is a nice honey-like consistency product into a watery product even with a thickener present.
Now, one final material I want to introduce you to is Rhodapex ESB-17 NAT. Now, this is sodium lauryl ether sulfate, but it’s actually all biodegradable source, so the carbon entities here are all plant sourced. And even the ethoxylation steps have been carried out using sugar cane-derived materials. So, what I’m going to illustrate here is that we need to keep our options open as formulators. Now, obviously, if we’re saying a no-sulfate formula or a sulfate-free formula, we can’t use this material. But otherwise, this is a fantastic anionic surfactant, and you’ll see just how much easier it is to thicken when I formulate with it.
And there you have it, how to make the best natural surfactant selections and put them together in a formula to suit your specific formulation needs. Remember to check that paperwork carefully and don’t claim something is truly natural if it’s actually not.
And remember, mildness, foaming profile, and performance, as well as that after feel is what matters most to your consumer. If they are looking for natural, they’re usually prepared to pay a little bit more for it, but they won’t repeat purchase if they’re not happy with how it’s foamed, performed, or feels after use. Happy formulating.
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