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The original article on &#;Surfactants&#; (a contraction of the three words &#;Surface Active Agents&#;) was written in the fall of i. Although the general topic of surfactants has not changed in nearly 6 years, several new chemistries have surfaced, and there wasn&#;t nearly as much emphasis on bio-based or green chemistry back then, as there is today. In addition, if you are new to coatings you should also be looking at ancillary markets such as personal care and cosmetics. Prospector has an excellent expert in Belinda Carli. See her article entitled &#;How to Select Natural Surfactants&#;ii. A natural surfactant has to have both the head and tail groups to come from truly natural sources. Personal care surfactants often have the same chemistry as paint surfactants, but perhaps different names or slightly different functions. Another article that pulls it all together is &#;breaking that tension with surfactants&#;iii
Thirty percent of global respondents are willing to pay a premium for products that deliver on social accountability claims (Nielsen, ). Bio-based surfactants are designated by the new EN. The chemical industry is now able to use a transparent definition and division which also enables to communicate in a comparable way to the end-user. Companies such as BASF, Ethox, Solvay and Locus Fermentation Solutions, among many others, are producing more bio surfactants.
Surfactants are materials that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid. In the general sense, any material that affects the interfacial surface tension can be considered a surfactant, but in the practical sense, surfactants may act as wetting agents, emulsifiers, foaming agents, and dispersants, among others.
Surfactants play an important role as dispersing, emulsifying, cleaning, wetting, foaming and anti-foaming agents in many practical applications and products, including: paints, emulsions adhesives, inks, biocides (sanitizers), shampoos, toothpastes, firefighting (foams), detergents, insecticides, deinking of recycled papers, ski waxes, spermicides (nonoxynol-9). This is an article about paint, which means surfactants that are used in paint, emulsions, wetting agents, and in many items used in paint that are dispersed or emulsified.
The dynamics of surfactant adsorption is of great importance for practical applications such as in emulsifying or coating processes as well as foaming, where bubbles or drops are rapidly generated and need to be stabilized. As the interface is created, the adsorption is hindered by the diffusion of the surfactant to the interface, which can result in the kinetics being limited. These energy barriers can be due to steric or electrostatic repulsions; steric repulsions form the basis of how dispersants work. Surface rheology of surfactant layers, is important to the stability of foams and emulsions.
In the bulk aqueous phase, surfactants form masses, such as micelles, where the hydrophobic tails form the core and the hydrophilic heads are immersed in the surrounding liquid. Other types of structures can also be formed, such as spherical micelles or lipid bilayers. The shape of the molecules depends on the balance in size between hydrophilic head and hydrophobic tail. A measure of this is the HLB, Hydrophilic-lipophilic Balance. Higher HLB surfactants (>10) are hydrophilic (&#;water loving&#;) and form O/W (Oil-in-water) emulsions. Lipophilic surfactants possess low HLB values (1-10) and form W/O (water-in-oil) emulsions. Dish detergents, surfactants for emulsion polymerization, and the following example (SLS = Sodium Lauryl Sulfate) are high HLB surfactants.
Most surfactants&#; &#;tails&#; are fairly similar, consisting of a hydrocarbon chain, which can be branched, linear, or aromatic. Fluorosurfactants have fluorocarbon chains. Siloxane surfactants have siloxane chains. Recent advances in surfactant technology have seen the development of mixed chains or/and complex structures. One example of mixed chain/complex structures is N,N-dimethyldodecylamine oxide (DDAO) and sodium decyl-, sodium dodecyl- and sodium tetra-decylsulfate (abbreviated as SDeS, SDS and STS, respectively).
There are 4 types of surfactants with a brief review of each as follows. These classifications are based upon the composition of the polarity of the head group: nonionic, anionic, cationic, amphoteric.
A non-ionic surfactant has no charge groups in its head. The head of an ionic surfactant carries a net charge. If the charge is negative, the surfactant is more specifically called anionic; if the charge is positive, it is called cationic. If a surfactant contains a head with two oppositely charged groups, it is termed zwitterionic. Commonly encountered surfactants of each type are listed as follows. A complete compendium can be found on www.ULProspector.com.
Many long chain alcohols exhibit some surfactant properties. Some examples of non-ionic surfactants include:
Trade name Structure/name Applications Triton&#; X-100 Polyoxyethylene glycol octylphenol ethers: C8H17&#;(C6H4)&#;(O-C2H4)1&#;25&#;OH Wetting agent &#; coatings Nonoxynol-9 Polyoxyethylene glycol alkylphenol ethers: C9H19&#;(C6H4)&#;(O-C2H4)1&#;25&#;OH Spermacide Polysorbate Polyoxyethylene glycol sorbitan alkyl esters Food ingredient Span® Sorbitan alkyl esters Polishes, cleaners, fragrance carriers Poloxamers, Tergitol&#;, Antarox® Block copolymers of polyethylene glycol and polypropylene glycol Various
Anionic surfactants contain anionic functional groups at their head, such as sulfonate, phosphate, sulfate and carboxylates. Alkyl sulfates include ammonium lauryl sulfate, sodium lauryl and the related alkyl-ether sulfates sodium laureth sulfate, also known as sodium lauryl ether sulfate (SLES), and sodium myreth sulfate. These are the most common surfactants and comprise the alkyl carboxylates (soaps), such as sodium stearate. The stearates comprise >50% of the global usage of surfactants. Many of these find utilization in emulsion polymerization. Other anionic surfactants include dioctyl sodium sulfosuccinate (DOSS), linear alkylbenzene sulfonates (LABs), as well as alkyl-aryl ether phosphates.
Trade name Structure/name Applications Pentex 99 Dioctyl sodium sulfosuccinate (DOSS) Wetting agent &#; coatings, toothpaste PFOS Perfluorooctanesulfonate (PFOS) Scotchguard&#;, Skydrol&#; Calsoft® Linear alkylbenzene sulfonates Laundry detergents, dishwasher detergents Texapon® Sodium lauryl ether sulfate Shampoos, bath products Darvan® Lignosulfonate Concrete plasticizer, plasterboard, DMSO N/A Sodium stearate Handsoap, HI&I products
Cationic surfactants are comprised of a positively charged head. Most of cationic surfactants find use as anti-microbials, anti-fungals, etc. in household, institutional and industrial cleaners (Benzalkonium chloride (BAC), Cetylpyridinium chloride (CPC), Benzethonium chloride (BZT)). The cationic nature of the surfactants is not typically consistent with the world of non-ionic and anionic charges, and they disrupt cell membranes of bacteria and viruses. Permanently charged quaternary ammonium cations include: Alkyltrimethylammonium salts: cetyl trimethylammonium bromide (CTAB) and cetyl trimethylammonium chloride (CTAC).
Zwitterionic (amphoteric) surfactants have both cationic and anionic centers attached to the same molecule. The anionic part can be variable and include sulfonates, as in the sultaines CHAPS (3-[(3-Cholamidopropyl)dimethylammonio]-1-propanesulfonate). Betaines such as cocamidopropyl betaine have a carboxylate with the ammonium. The cationic part is based on primary, secondary, or tertiary amines or quaternary ammonium cations. Zwitterionic surfactants are often sensitive to pH and will behave as anionic or cationic based on pH. Fast dry (&#;coacervation&#;) latex traffic paints are based on this concept, with a drop in pH triggering the latex in the paint to coagulate.
[i] Surface Active Agents (Surfactants): Types and Applications (ulprospector.com)
[ii] How to select natural surfactants for personal care products (ulprospector.com)
[iii] Surfactants in paints: how they work and current market trends | Prospector (ulprospector.com)
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When we talk about cleaning products, we often talk about surfactants. Discover all the surfactants available, the problems associated with them and ways to formulate natural hygiene products.
By definition, surfactants are molecules with both an affinity for: water (hydrophilic part) and oil (lipophilic part). In other words, surface-active molecules allow the mixing of two phases which do not have, at the beginning, any affinity for each other. This particularity allows them to ensure a cleaning function by clinging to the fatty substances, which are then carried away in the rinsing water. They thus play the role of emulsifier and washing agent at the same time.
Surfactants can be used as :
Each surfactant has several of these properties, but they are not all present with the same intensity in the same molecule. Some surfactants are more detergent, wetting and foaming, while others can be more emulsifying or solubilizing.
There is therefore a wide variety of surfactants on the market, suitable for the formulation of all kinds of products: soaps, shower gels, shampoos, creams, make-up remover&#; Most surfactants are of synthetic origin but some, increasingly used, are of natural origin.
From a chemical point of view, surfactants are classified into 4 groups: anionic, cationic, amphoteric and non-ionic. These groups are defined according to the positive or negative charge of their hydrophilic part (attracted by water).
Anionic :
The anionic surfactant is the most common. More expensive, it has a good detergent and foaming activity.
Cationic :
Cationic surfactants have an affinity with keratin (found in hair in particular), on which they form a smooth film. This type of surfactant is mainly used in after-shampoo care.
Amphoteric :
Contact us to discuss your requirements of Advantages of Calcium Dodecyl Benzene Sulfonate over Traditional Surfactants. Our experienced sales team can help you identify the options that best suit your needs.
This type of surfactant is mainly composed of betaine. They are generally used in shampoos, conditioners and detangling hair care products since they have detangling and smoothing properties.
Non-ionic:
This type of surfactant is widely used in make-up removal products (micellar waters, lotions or milks). Their foaming power is however less powerful, but allows to create a light foam.
Anionic: Anionic surfactants are known to be drying and among the most irritating. However, it is important to remember that conventional soap contains an anionic surfactant, which is created naturally during the saponification process. This is the mixture of vegetable oil and soda. However, this one remains natural and biodegradable, which is not the case of the most widespread anionic surfactant: the SLS or Sodium Laureth Sulfate. This powerful surfactant has a very foaming power, which belongs to the large family of &#;Sulfates&#;.
Cationic : Cationic surfactants are often known to be irritating to the eyes. Another constraint for formulators: cationic and anionic surfactants cannot be mixed, as their opposite charges attract each other forming insoluble complexes.
Amphoteric: Amphoteric surfactants are milder and less irritating than anionic surfactants, but have little foaming. These surfactants are rather well tolerated by the skin and do not sting the eyes. On the other hand, they are suspected of being endocrine disruptors, i.e. interacting with the hormonal system.
Non-ionic: Non-ionic surfactants are less aggressive on the skin than anionic surfactants, which are better tolerated. Even though they are gentler, some non-ionic surfactants can disrupt the hormonal system.
Surfactants can be found in solid (powder) or liquid form (more or less fluid depending on the surfactant). The industry proposes mostly the liquid form because it facilitates the integration of the ingredient in liquid formulas which represent the majority of the market (shower gels, shampoos, creams, make-up removers&#;). However, since the rise of solid cosmetics (solid shower gel, solid make-up remover, solid shampoo), suppliers are offering more and more surfactants in powder or flake form. But for formulators, these surfactants are more complex to use because they are more concentrated and more reactive to interactions with other ingredients in the formula.
Surfactants of natural origin are the compromise between price, efficiency and environmental impact. Globally, synthetic surfactants are derived from petrochemicals and are therefore relatively polluting because they are not very biodegradable and release chemical compounds that are sometimes more toxic than the initial product when they break down. However, there are alternatives made from renewable raw materials (vegetable such as copra, palm or rapeseed, sugars, amino acids, &#;), which present less risk to health and are more environmentally friendly.
Glutamates
The family of glutamates includes a set of surfactants made from fatty acids of coconut oil and an amino acid, glutamate. They are very soft surfactants, recreated from vegetable oils and sugar. These surfactants are non-toxic and fully biodegradable.
Saponin
Saponin is a substance extracted from soapwort (herbaceous plant) or Panama wood (exotic tree). These plants or trees belong to the genus Sapindus, from the Latin sapo (soap) and indus (India). The extract of the soap tree (Sapindus trifoliatus) was exploited by the indigenous peoples of northwestern North America for hundreds of years. The soap nuts from this tree were crushed or whipped into a thick lather and used as a detergent. Some manufacturers still offer this type of 100% natural cleaning agent.
There are other vegetable emulsifiers such as soy lecithin, sunflower or rapeseed, or even proteins such as casein derivatives, which are very interesting for their emulsifying properties and their affinity with the skin.
On the whole, these soft and natural surfactants are expensive, they can cost 10 to 15 times more than classic petrochemical surfactants. They are rarely used in hygiene products because they are considered as &#;first necessity&#;. They are sold mainly in supermarkets at prices affordable to the general public.
From a formulation point of view, the two main difficulties encountered with these surfactants of natural origin (compared to synthetic surfactants), are:
Surfactants are often criticized and pointed out by the press. More and more consumers are studying the labels of their cosmetic products to track down undesirable ingredients.
Sulfated surfactants
Sulfates or sulfated surfactants have a powerful detergent action. They are commonly used for industrial floor and engine cleaning. They are an ingredient of choice for manufacturers because of their advantages: low cost, foaming, good for conservation and stabilized formulas wash.
What we reproach it: Sulfates are too &#;stripping&#; to be used daily. They destroy the lipidic film of the skin or the scalp, preventing it from being reformed from one washing to another. They therefore contribute to skin dehydration and an imbalance in sebum production, as the skin overreacts, causing blackheads and greasy roots.
The &#;SCI&#; surfactant
Sodium cocoyl isethionate, otherwise known as &#;SCI&#;, is a mild surfactant commonly used in solid cosmetics, especially in solid shampoos. This surfactant has multiple advantages for formulators: inexpensive, foaming, natural origin and conditioner for hair.
The problem with this surfactant is more in its manufacture than in its use. One of the components necessary to its manufacture (the ethylene oxide) is toxic for the man and the environment. This is why not all solid shampoos that use it can be certified organic.
The &#; CAPB &#; surfactant
Cocamidopropry Betaine (CAPB) is an amphoteric surfactant derived from Coconut oil &#; most often from Copra oil &#; and Dimethylaminopropylamine (DMAPA) or Dimethylamine (DMA). It is an ingredient that has both a natural and petrochemical fraction. It is often used in shower gels and shampoos as a secondary surfactant. Cocamidopropry Betaine softens more aggressive surfactants like anionics. It has experienced an effervescence following the various controversies on sulfated surfactants.
What it is accused of: Due to the presence of residues of Dimethylaminopropylamine in the manufacturing process, various cases of skin allergies have been reported in recent years, particularly among certain professionals (hair salons). A North American study concludes that the allergy rate is around 6%. These allergies most often result in eczema and various contact dermatitis on the face, neck and scalp.
Cocamidopropyl betaine could react with other components to form more toxic or carcinogenic molecules. Thus, amines and esters can react and develop nitrosamines, highly carcinogenic substances. However, to date, we have very little information on the possible toxicity of this ingredient on humans.
Cosmébio
It&#;s a professional association dedicated to natural and organic cosmetics that uses the COSMOS referential. This referential is the most demanding and it can be used internationally. The organization has a very clear-cut opinion on the ICS. It denounces an unfinished ecological approach, putting health and the environment at risk.
Cosmébio&#;s argument is that beyond the format of the cosmetic, a product composition that includes certain surfactants, such as sodium cocoyl isethionate (SCI) goes against a responsible approach. This surfactant, derived from coconut oil, is widely used in the solid cosmetics market. It is used to make the product foam. It is often marketed as a &#;green&#; ingredient despite its prohibition in the natural and organic certification, because of its manufacturing process which uses ethoxylation.
Cosmébio says:
&#;The dangers associated with ethylene oxide for humans: a highly irritating and corrosive carcinogen for the skin and eyes. It therefore presents a direct risk to the worker in contact with this substance.&#;
The association adds that ethoxylation is a heavy process carried out in conditions of extreme temperatures and pressures. This process is also very polluting: it involves ethylene oxide which is very reactive and toxic.
Its toxicity is indirectly found in nature if the good practices of use are not respected. Moreover, the ethoxylated derivatives obtained can contaminate the environment with the presence of toxic impurities (1,4-dioxane, ethylene oxide, etc.) for micro-organisms and fish.
&#;Even if the final ingredient can be considered natural and gentle on the planet, what is the point if all the harm has been done since its creation?&#;, Cosmébio calls out and launching a &#;call to reason to manufacturers&#;.
Slow Cosmetics
Slow Cosmetique is an association that aims to bring together brands that make the effort to offer ecological, healthy and reasonable products throughout the design chain. The respect of the specifications of this association allows the brands to obtain a &#;Slow Cosmetic Label&#; and are thus referenced on the eponymous online sales platform (slow-cosmetique.com).
The Slow Cosmetics Association does not tolerate the presence of sulfated compounds such as ammonium or sodium laureth sulfates in the formulas of its labeled brands. Nevertheless, sulfated surfactants of the sodium or ammonium lauryl sulfate type, accepted by organic certifications (Ecocert, Natrue&#;) are therefore also tolerated by the Label. However, they must be present in an isolated or exceptional way in a range of products. It&#;s the same for the sodium coco sulfate.
Conclusion
Today, 70% of surfactants are still essentially derived from petrochemicals. But the cosmetics industry is looking for new ingredients that meet the expectations of users, i.e. ingredients from natural resources and respecting health and the environment.
The European surfactants market amounts to 2.5 million tons, and has good growth prospects in this post-COVID period (which has greatly stimulated concerns about personal hygiene and environmental cleanliness).
The challenge for manufacturers will be to find the right compromise between affordability, efficiency, naturalness and respect for the environment.
Also read our expert file on &#;How is a natural cosmetic product formulated?&#;.
Are you interested in learning more about Anionic Surfactant Manufacturing? Contact us today to secure an expert consultation!