There are four main types of surfactants, with the first three used the most in laundry detergents, and their actions depend on their interactions with ions. Ions are charged particles due to the gain or loss of electrons. Ions can be positive such as calcium, Ca2+, or negative such as chloride, Cl-.
Anionic surfactants are negatively charged in solution. However, they do not work as well by themselves in hard water. This is because hard water has many positively charged ions present such as calcium (Ca2+) and magnesium (Mg2+). Since anionic surfactants are negative they are attracted to the positive ions and bind, making them unable to bind to other molecules in solution.
Nonionic surfactants have no charge. Therefore, they are not as easily impaired under hard water conditions, since they are not attracted to the positive ions.
Cationic surfactants are positively charged in solution. They help the anionic surfactant molecules pack in at the water/dirt interface thereby allowing the anionic surfactants to pull more dirt away.
Amphoteric or zwitterionic surfactants are both positively and negatively charged. These surfactants are very mild and are often found in gentler cleansers such as hand soaps, shampoos, and cosmetics.
Read on to learn about some other ingredients that help detergents do their job.
Researchers at Wright State University examined the extent to which mites and mite allergens were removed when washing clothes in water alone and with detergents. Interestingly, they found that both methods were equally effective in removing mite allergens. The researchers suggest that washing in water alone is equally effective as washing with detergent because allergens and mites are water-soluble, so contact with water removes them.
Although surfactants are at the heart of laundry detergent’s ability to clean fabrics, other ingredients can help detergents clean better, brighten clothes or smell better. As described previously, some types of surfactants typically do not work well in hard water due to the excess positive ions present. Additives called builders can help detergents to work better under hard water conditions. Builders accomplish this feat by removing calcium (Ca2+) and magnesium (Mg2+) ions in hard water by binding to them. This allows the surfactants, especially anionic surfactants, to bind to more grime, rather than the positively charged ions in the wash water. Builders also are bases, so they work to neutralize acid and can help disrupt chemical bonds. Another benefit of adding builders to laundry detergents is that manufacturers can use less surfactant since the builders make the surfactant more efficient. Some examples of builders include sodium tripolyphosphate (STTP) and zeolites.
Detergents can also include components that make clothes whiter or brighter. The most common whitening agents are bleaches. Bleaches contain peroxides, which can oxidize fabrics [source: EPA]. Fluorescent whiteners and brighteners are also added to some laundry detergents because they minimize the yellowing of fabrics. These additives work by absorbing ultraviolet light and emitting back visible blue light, which can mask the yellow that may make colors appear faded and whites appear dingy.