December 03, 2020 4 min read
The washing of clothes in the household is an essential part of personal and family hygiene. Laundry not only cleans the garments from stains and unpleasant odors but also acts as a disinfectant for clothes. Disinfecting clothes from germs gets more important as cold and wet weathers of the late fall and early winter fall upon us, increasing the chances of catching an airborne pathogen. The airborne pathogens may be viruses, bacteria, and fungi, and are transmitted by small particulates dispersed in the air (aerosols). Looking at it in that way, clothing (scarfs, sweaters, hoodies, etc.) acts as an aerosol filter in everyday life.
The air that surrounds us passes through the clothes and sticks any microscopic particles it carries along to the textile fibers. As a result, the garments we wear gradually loose their perceived freshness and acquire various smells. Imagine standing close to an open fire or a smoker for a few minutes. The clothes quickly absorb the smoke particles and carry their odor until it's washed away. The same thing happens with airborne germs. The germ-carrying particles can be picked up from an atmosphere of a stuffy room or captured by clothes when one covers a sneeze or a cough with a garment (for example, a scarf) or a clothed body part (for example, an elbow). Once trapped in the clothes, the germs may remain active for days unless sanitized. Their transmission can be carried out by repetitive use of clothes, cross-contamination through contact with other garments, or laundry sorting before washing.
When one thinks of disinfecting a fabric, it is natural to imagine high temperatures and chlorine-containing bleach. Despite being effective at cleaning and killing the pathogens, such washing conditions tend to destroy delicate fabrics of high-end clothes made of wool, fine cotton, or viscose. That does not mean that it is impossible to sanitize clothes made of delicate materials. A bit of knowledge about the chemistry of regular and germ killing laundry detergents and the evidence-based effectiveness of various washing conditions could help us to identify best-washing practices at home even for the most capricious garments.
A typical laundry detergent (for example, Dash® All in 1 PODS) is composed of a mixture of soaps and various surfactants, both anionic and non-anionic. The surfactants clean clothes by dissolving fats and removing dust and germ particles by wrapping around them and detaching them from the textile fibers. However, removal alone might not be complete and does not imply the deactivation of germs. The addition of bleach is needed to further enhance the potency of the cleaning.
Commonly used chlorine bleaches (for example, Clorox®) contain sodium hypochlorite salt (NaClO). The hypochlorite is an oxidizer that works by reacting with molecules in its environment and producing oxygen or chlorine, depending on the reaction conditions. The hypochlorite does not distinguish between “bad” molecules (ones that compose germs and dirt) and “good” molecules (the ones that compose fabric and its colors). For these reasons, bleach whitens the fabric and may damage the colors if used incorrectly. In addition, chlorine-based bleach is generally incompatible with wool. Wool is made of proteins, and proteins are long chains of interconnected amino acids. Chlorine bleach solutions are typically basic (pH > 7) and that, in combination with the oxidizing power, breaks wool proteins into fragments, irreversibly damaging the fabric. The finer the fabric, the bigger the damage. Fine fabrics feature thinner fibers and expose larger surface areas than coarse fabrics, making fine fabrics more reactive towards aggressive chemicals.
Active oxygen bleach (AOB) detergents provide an alternative to chlorine-based bleach. It is common for an AOB laundry disinfectant to contain two principal components: the one that carries active oxygen and another that activates it during the washing. For example, in the case of a popular AOB Napisan®, that would be sodium percarbonate salt and TAED (tetraacetylethylenediamine), respectively. The activation means the production of peroxides, such as hydrogen peroxide or peracetic acid and is especially helpful for washing in cold or warm (30-40 °C) water. These peroxides are potent oxidizers that destroy outer membranes of microorganisms and produce molecular oxygen in the process. Thus, AOB-containing products are good laundry disinfectants. Although they may be aggressive towards some fabrics, especially at high temperatures and high concentrations, AOB-based detergents are more forgiving than chlorine bleach.
In 2013, the International Scientific Forum on Home Hygiene produced an evidence-based report on the germicidal efficiency of various washing conditions in a domestic setting, as well as recommended washing practices to achieve and maintain good hygiene. Below are the seven tips distilled from the report and applicable to the clothing worn normally, such as daily wear that gets in contact with skin and outerwear. Regardless of the tips, make sure to consult both care instructions for the clothing and directions on the detergent and bleach before use.
Dmitry Baranov is a research chemist specialized in nanomaterials and nanotechnologies