Surfactants
Surfactants are molecules that reduce the surface tension of water, helping it to spread out more uniformly. In essence, surfactants make water “wetter”. A drop of water on a very non-polar surface such as a freshly waxed car or on a plastic surface will bead up due to water’s surface tension. Essentially, the water would rather interact with itself than with the non-polar surface. Adding surfactants to water reduces the surface tension and allows water to relax or wet-out and cover a larger surface area.
Beyond surface tension reduction, surfactants serve a vital role in the cleaning process. Surfactants molecules are made up of two parts: a hydrophilic (water-loving) head and hydrophobic (water-hating) tail. This dual functionality allows surfactants to work along the interface of water molecules and soiled surfaces. In cleaning products, the surfactant’s hydrophobic tails naturally aligns away from the water and attempts to cling to the surface. This action forces the surfactant underneath layers of soil and grime, loosening and lifting the soils from the surface. This cleaning process, known as roll-up, increases cleaning efficiency and decreases scrubbing time. Furthermore, as the cleaning solution rolls up bits of dirt and soil, the surfactant’s hydrophobic tails cling to the soil particles, suspending the soils and helping to prevent them from settling back on the surface. Once the soil is suspended, the surface is simply wiped or rinsed and allowed to dry.
Almost all commercially produced cleaning products contain surfactants. The combination of wetting and roll-up helps to make cleaning easier and more effective. Whether running dinner plates through the dishwasher or cleaning the mirror in a bathroom, the power of surfactants means less scrubbing and better overall cleaning.
For more technical information on surfactants click here.
Solvents
A solvent is any substance that dissolves another substance. For example, water is called the “universal solvent” because most materials dissolve in water to some degree. However, when it comes to cleaning, water alone is not always enough. Oily, greasy stains and soils have limited solubility in plain water, so other materials such as surfactants and solvents are added to improve performance. Some solvents, such as short chain alcohols and glycol ethers, readily dissolve in water, creating a water-based solution that effectively penetrates and breaks down oily soils. Other solvents, such as d-limonene and pine oil, require the use of special surfactants called hydrotropes that will solubilize and stabilize these solvents in an aqueous dilution to help deliver their performance benefit.
Solvents play an important role in the cleaning process. They break up stains, dissolve soil particles, and help prevent grimy residue from returning on freshly scrubbed surfaces. Solvents are present in many common cleaning products, including:
- Spot treatments for carpet
- Degreasers
- Furniture dusting/polishing aids
- Tub and tile cleaner
- Glass cleaners
Solvents are also added to cleaning products for reasons other than soil removal. Solvents are used to ensure a cleaner remains properly mixed and stable during storage. Without solvents, a product may become cloudy and separate over time. Solvents are also used to adjust viscosity, making the cleaning product thicker or thinner as desired. Lastly, solvents help surfaces dry faster, preventing water spots on just-cleaned surfaces or preventing streaks on freshly cleaned glass, mirrors, and furniture.
For more technical information on solvents click here.
Chelants
Water that contains high concentrations of dissolved magnesium and calcium ions is referred to as hard water. According to the United States Geological Survey, 85% of American homes have hard water. Hard water can negatively impact cleaning product performance. A chelants, sometimes referred to as a sequestrant, is a specialized molecule designed to bind to positively charged magnesium and calcium ions in solution. By binding to these ions, chelants prevent them from forming insoluble precipitates such as hard water scale and soap scum, that can accumulate on surfaces and are difficult to remove. Chelants can also bind other metal ions such as iron and manganese, preventing the formation of deposits such as iron oxide (rust) and manganese dioxide.
Chelants are found in laundry detergents, autodish detergents, and other concentrated hard surface cleaners. The chelants help the cleaners maintain a high level of performance even in hard water. One of the most common chelants is EDTA (ethylenediamine tetra acetic acid). Alternatives to EDTA include phosphates, NTA (nitrilotriacetic acid), citrates, silicates, polymers of acrylic, maleic acid and others.
Finally, chelants are effective in removing stains because they remove the metal ions that crosslink and stabilize stain structures. With the metal ions gone, the remainder of the stain is easier to clean.
Hard water can seem like an inconvenience, but it is a natural occurrence in most homes across the nation. With the aid of chelants, hard water buildup is easily removed and the resulting powerful shower spray or shining shower wall are left to enjoy.
For more technical information on chelants click here.
Preservatives
Consumers who purchase cleaning products expect to receive and use a quality product that remains useable for several months after the initial purchase date. Accordingly, when developing a new cleaning product, a key consideration is how long the product will remain stable on the store shelves and in consumer households. Many consumer products are designed to be stable for at least two years following manufacture.
In order to meet this time frame, most products contain low levels of materials called preservatives. Preservatives are chemicals added to a product to help prevent decay and spoilage of the product that render the product un-useable and possibly dangerous.
Preservatives are used in almost all liquid cleaners and some dry products as well. Preservatives help to ensure the long-term stability of products sitting on store shelves and kept for use in homes.
Preservatives added to formulated products inhibit bacterial and fungal growth. Bacteria and fungi exist almost everywhere and grow wherever they find conditions favorable for growth. Unless formulated cleaning products provide extreme conditions, such as pH extremes or very low water content, these products are prone to microbial growth. As cleaning products are formulated to become milder to surfaces and users, the cleaning products inevitably provide favorable conditions for growing microbes that naturally contaminate the product. This growth-positive environment increases the need for cleaning product preservation.
Microbial contamination in a cleaning product leads to numerous problems including the development of malodors, development of abnormal appearance including precipitate, flocculant, color changes, opacity changes and decreased cleaning performance. Performance impacts are the result of the microbes feeding on the product’s surfactants and other active components. The loss of formulation stability may also be due to pH changes from microbial metabolism, and/or the microbes consuming the components required to keep products homogeneous. Microbial contamination can also lead to problems with the product packaging including pressurization that bulges the container, corrosion of metal containers such as aerosol cans, and, in extreme examples, clogging of the product delivery mechanisms by biofilm.
In addition to these aesthetic and product performance concerns, there is also the risk that the contaminated product can be a reservoir of unknown microbial contamination leading to rapid contamination of a freshly cleaned surface.
Preservatives, however, should not be confused with antimicrobial active ingredients used to create disinfectants and sanitizers. Preservatives are included only in amounts sufficient to protect the product itself from microbial contamination; the preservative will not provide any efficacy in a product once diluted to use dilution. Examples of commonly used preservatives are isothiazolones, bronopol, and aldehydes which include formaldehyde releasers and glutaraldehyde. Current trends include a move towards more sustainable options.
For more technical information on preservatives click here.
Microbial Based Cleaners
Cleaning products generally separate soils from fabrics or surface substrates by dissolving or suspending the soil in a water or solvent liquid solution that is carried away when the solution is rinsed off. The cleaning action of the primary formulation components is supplemented by additives to optimize the performance of the cleaners.
Microbial based cleaners are products that are designed to incorporate bacterial spores. Spores are used because these can survive in the concentrated cleaning product. Once the primary cleaning has taken place and the cleaning solution has been wiped or rinsed from the surface, a small residual amount of cleaning solution and soil will almost certainly remain on the surface. This is especially true of porous surfaces such as unsealed wood, grout and concrete. Once the bulk of the cleaning solution has been removed, any bacterial spores remaining on the surface will germinate and begin to digest the residual soil trapped in the pores of the surface. These growing bacteria produce enzymes specific to the soil present. These enzymes act to break down organic soils into smaller particles which the bacteria use as food. In this manner, the growing bacteria remove any residual soil and leave a cleaner surface.
It is important to recognize that bacteria are ubiquitous, which means they exist almost everywhere in our environment. Most bacteria are considered non-pathogenic and so do not cause illness in humans and pets. Many bacteria are considered as essential to good health. It is only a small percentage of bacteria that are associated with disease. It is therefore important to use only non-pathogenic bacteria in microbial based cleaners.
For more technical information on microorganisms click here.
Acids & Bases
One of the most critical parameters for the success of an aqueous (water-based) cleaning solution is the pH of the solution. In the most rudimentary terms, pH is a measure of how acidic or basic a solution is. To understand pH in cleaning solutions, however, we need to understand pH in more technical terms. Scientifically speaking, pH is the negative log of the concentration of hydronium ions (H3O+), ranging from 0 to 14, with neutral at the mid-point of 7.
Water dissociates according to equation 1. The water dissociation constant, Kw, governs this dissociation according to equation 2, where the square brackets indicate concentration in moles per liter of hydronium and hydroxide (OH–) ions. The value of Kw for pure water is 1.0 x 10-14, thus when there are no impurities present, the concentration of hydronium ions is equal to the concentration of hydroxide ions, and both concentrations are 1.0 x 10-7. The negative log of this is 7, thus pure water has a pH of 7.
2 H2O H3O+ + OH- – (1)
Kw = [H3O+] [OH-] – (2)
If we add an acid to pure water, the concentration of hydronium ions goes up, let us assume to 10-5, thus the pH would be 5. Similarly, if we add a base to pure water, the concentration of hydroxide ions goes up, again let us assume to 10-5, and thus the concentration of hydronium ions would go down to 10-9 (remember we must satisfy equation 2) and the pH would be 9. So, if we add an acid to water the pH goes down, and if we add a base to water the pH goes up. Obviously, the more acid or base we add to the solution the more the pH moves away from 7, and more reactive the solutions become.
So, what happens when our aqueous cleaning solution encounters a soil like a calcium carbonate deposit caused by hard water? If our solution pH is basic (also called alkaline), there is no reaction between the soil and the solution. Hydroxide ion will not react with calcium carbonate. However, if our solution pH is acidic, there is an immediate reaction according to equations 3 and 4, and we can easily see the bubbling as carbon dioxide gas is formed.
CaCO3 + 2 H3O+ Ca2+ + H2CO3 + 2 H2O – (3)
H2CO3 H2O + CO2(g) – (4)
Similarly, many inorganic soil deposits react with acid but do not react with alkalinity, thus the common approach to dealing with inorganic soils is to use acidity and the products used on inorganic soils tend to be acidic. This includes products such as descalers/hard water deposit removers, toilet bowl cleaners and rust removers.
So, what happens if our soil is organic, such as dietary fat? These materials are triacyl glycerols and contain ester groups which can be hydrolyzed under both acidic and alkaline conditions. Despite this, we typically use alkalinity to remove fatty soils, rather than acidity, because the products of ester hydrolysis are the fatty acid and the glycerol. Glycerol is readily water soluble and is easily rinsed from the surface being cleaned. However, the water solubility of the fatty acid is highly dependent upon pH. If the solution pH is below the fatty acid pKa, typically in the range of 4-5, the fatty acid will be protonated and relatively water insoluble. If the solution pH is above the fatty acid pKa the fatty acid will be deprotonated and relatively water soluble. Similarly, other organic soils can react with both alkalinity and acidity, but we prefer to use alkalinity due to the water solubility of the reaction products. Thus, products where the typical soil encountered is organic tend to be alkaline. This includes products such as oven cleaners, degreasers, all-purpose cleaners, and laundry detergents.
Enzymes
The chemical reactions essential for life can all be performed in the laboratory under conditions such as refluxing solvents, high temperatures, extremes of pH, excesses of certain reagents, and long reaction times. However, these conditions do not exist within a living organism. To survive, an organism must be able to perform these same chemical reactions efficiently under the relatively mild conditions found within a living cell. The solution to this apparent dichotomy is the use of enzymes.
Enzymes are biological catalysts. These long chain proteins are composed on the 20 naturally occurring amino acids. Each enzyme is specific for a single reaction. The 3-dimensional structure of the enzyme gives the enzyme its functionality and specificity. The reactant(s) fit together with the enzyme in what is often referred to as a “lock and key mechanism”. Once the desired reaction has occurred, the product(s) of the reaction disengage from the enzyme. As with all catalysts, enzymes are not consumed in the reaction, so the same enzyme molecule can be used multiple times for the same reaction. It is this ability to allow reactions to occur under relatively mild conditions and the fact that the enzyme is not consumed or altered during the process, which makes enzymes so desired in cleaning products. A small amount of enzyme can contribute a significant boost to cleaning performance.
There are three common classes of enzymes which are used in cleaning products: proteases cleave the amide bonds of proteins, creating smaller peptides and single amino acids; lipases cleave the ester bonds of fats (triacyl glycerols), creating free fatty acids and glycerol; and amylases cleave long chain carbohydrates into smaller oligosaccharides. In each case, the smaller reaction products are more water soluble than the initial material, and thus the enzyme contributes to soil removal from the surface being cleaned.
It should be noted that the use of enzymes is not compatible with harsh cleaning chemicals like hypochlorites and caustics because these strong chemicals can attack the enzyme resulting in loss of its 3-dimensional structure and thus its catalytic ability. Fortunately, the use of enzymes not only requires milder conditions, but also allows for comparable, and in some cases superior, cleaning results under these same conditions.
For more technical information on enzymes click here.