Over the past few years, the use of surfactants in the global market has experienced steady growth. The global surfactant market is in a phase of transformation, diversification or consolidation. The application of different types of surfactants in different fields is described below.
Pharmaceuticals and cosmetics
Over the past few decades, the use of surfactants in medicine has received intense attention. Surfactants have been studied as pharmaceutical excipients for many years because of their unique functional properties. Synthetic surfactants have been widely used as emulsifiers and wetting agents in the petroleum, food and pharmaceutical industries. Surfactants are used in the preparation of ointments, cold creams, cleansers, creams, shaving creams so that they are easily removed from the skin when washed with water. Many reviews, books, and recently published articles have highlighted the use of surfactants. Lukic et al. introduced the synthesis of new surfactants and their application in cosmetics. Quaternary ammonium surfactants (cationic surfactants containing N+, QAS) have received much attention in the biomedical field since 1935 for their broad-spectrum antibacterial, antiviral, and antifungal activities. But QAS is not easy to biodegrade and is toxic to aquatic organisms. Therefore, the demand for the synthesis of more environmentally friendly surfactants is increasing. At this time, amino acid surfactants emerged as a promising new antimicrobial agent for inhibiting bacterial resistance. HLB value, cationic charge density and amino acid sequence on polar head group directly affect antimicrobial activity. Many proteins are unstable at storage and transport temperatures. Over the past 10 years, the biggest challenge for pharmaceutical products containing proteins has been maintaining the structural stability of proteins during purification, processing, and storage. Surfactants directly affect protein stability by binding to proteins. Ionic surfactants bind to protein molecules mainly through electrostatic and hydrophobic action, while non-ionic surfactants bind to protein molecules through hydrophobic action. Unlike ionic surfactants, non-ionic surfactants play a critical role in protein stabilization in commercial formulations. However, the mechanism of this stabilizing effect remains unclear. Katz et al. reported that amino acid-based nonionic surfactants are promising protein drug stabilizers. Kishore et al. recently described the interaction between nonionic surfactants and proteins in biotherapy formulations. Polysorbitan esters (PS) are common non-ionic surfactants that are commonly used in biopharmaceutical products, especially to protect proteins against interfacial stresses. A recent review describes the trend of polysorbate esters and their degradation products used in biopharmaceutical formulations.
Detergents and cleaners
More than 50 million tons of detergent are used worldwide each year in various forms (powder, liquid, stick, paste, block, molded parts, etc.) for household laundry products, household cleaners, industrial cleaners, cosmetics, etc. Surfactants are one of the most basic ingredients in the formulation of detergents and other cleaning agents. The role of cleaners is mainly to clean the surface of the material by removing hydrophobic oily molecules (such as non-covalent bonded lipids) and dust particles, because water alone cannot remove greasy dirt stuck on the cloth. Surfactants are usually used to remove these oily dirt from the surface of the cloth, as surfactants effectively dissolve these oily molecules by forming micelles. The hydrophobic tail of the surfactant is tightly attached to the oily dirt, while the hydrophilic head group is oriented towards the water. Oils or lipids are dispersed into water, for example to form oil-in-water emulsions. In this case, the dirt can be washed away. The application of surfactants has been greatly expanded and is no longer limited to the original soaps and detergents (personal cleaners, washing powders, dishwashing agents, household cleaners). Anionic surfactants are often used as wetting agents in industrial applications, especially when wetting fluids are applied to waxy or "waxy" surfaces. The two main surfactants currently used in the detergent industry are linear alkylbenzene sulfonate (LAS) and alkylphenol polyoxyethylene ether (APE). Anionic surfactants are the most important ingredients in laundry detergents, while cationic surfactants are commonly used in hair care products because cationic surfactants make hair softer, silky and shiny. In addition, cationic surfactants exert their wetting ability in dry washes and are used as oil wetting agents. Long alkyl quaternary ammonium compounds are a kind of cationic surfactants commonly used in detergents as fabric softeners. A large class of nonionic surfactants consists of a hydrophilic ethoxy chain composed of several ethoxy units (EO). It should be pointed out that such non-ionic surfactants with good washing properties usually have a EO number of 7 to 12. Polyoxyethylene ether surfactants are widely used in various detergent formulations, such as shampoo, dishwashing agent, hand washing products and other formulations. Cleaning agents come in four main forms: soaps, synthetic detergents, lipid-free lotions, and antibacterial agents.
Recently, there has been a lot of interest in the production of environmentally friendly, low-cost modern synthetic cleaners. Binici et al. recently reported that sunflower stem powder is a harmless natural detergent that can remove a large number of difficult stains. Surfactants can also be used as viscosifiers and foaming agents. Highly surface-active fatty acid salt compounds containing at least 8 carbon atoms are used in large quantities as detergents. Table 1 lists some of the more common surfactants and their potential applications in medicine and cleaning.
bioremediation
bioremediation refers to the process of biological transformation of organic compounds by living microorganisms. Bioremediation is a widely adopted new waste treatment technology that can remove or neutralize environmental pollutants in contaminated sites. Compared with the earlier established chemical method, surfactant-assisted bioremediation is a more effective and convenient method to remove toxic heavy metals. In the presence of SDS and TX-100, the highly toxic Cr(VI) was effectively reduced to the relatively less toxic Cr(III) by oxidation of a bioorganic compound in a wallalgae water extract. In the presence of these surfactants, the aqueous extract of mango leaves also has a strong bioremediation effect and has a detoxification effect on Cr(VI) in polluted wastewater. In recent years, saponin, a natural surfactant, has been successfully extracted from Sapindusmukorossi for bioreactor of more Cr(VI) in sewage. Biorepair of Cr(VI) was accelerated by adding TX-100 and SDS surfactants to bagasse water extract. In most cases, SDS is the best accelerator for efficient and maximum reduction of high-priced metal ions in contaminated water. With the development of micellar enhanced ultrafiltration processes, the application of surfactants or micellar aggregates in the separation of heavy metal ions in water has become increasingly popular, in which the charge of the surfactant is opposite to the target toxic ions. Bioadsorption of Cr(VI) with water extract of Albizia alebbeck wood chips is a very cost-effective method for the purification of high-priced chromium wastewater. SDS and TX-100 micellar aggregates can efficiently assist the bioremediation process and increase the removal rate through micellar catalysis.
