Chemical-thermal disinfection of textiles

Disinfection of textiles in the washing process (including clothing) is the process of removing microorganisms such as bacteria, fungi, viruses, mycobacteria, spores using biocidal preparations intended for this purpose, using automatic washing machines.

Activities related to washing clothes and textiles have been with us for hundreds of years. The first mention of washing using laundry equipment dates back to 1851, when the first washing machine was built by the American James King. This invention was a global phenomenon, and its creation was intended to speed up and improve the work involved in cleaning materials. However, this device was significantly different from the automatic washing machines known today. The basic task of the washing process is to refresh textiles and remove stains caused by use. However, the definition of laundry has evolved somewhat over the years. It is no longer a process just for refreshment. The broadly understood washing process has also received a new function: thermal disinfection. Over the years, awareness of bacteria, fungi and viruses occurring in the environment has increased significantly.

Currently, scientists know a number of pathogens that are highly tolerant to temperature changes. Therefore, they are resistant to high temperatures. So what if high temperature is not enough? Chemical-thermal disinfection products come to the rescue, i.e. washing powders or liquids with the addition of a biocidal substance.

Biocidal products in the washing process

The biocidal products market is still developing. In addition to the most popular types of preparations, i.e. agents for disinfecting hands and surfaces by spraying, new products appear, including the discussed products for chemical-thermal disinfection. Products of this type are most often in the form of liquid, powder, gel or capsules. However, it is not the form that is most important here, but the addition of an active substance whose task is to remove harmful microorganisms from the fabric surface. Among the substances added to washing liquids, compounds from the group of quaternary ammonium salts (DDAC / ABDAC) are very popular. Due to their gentleness and disinfection effectiveness, they are an efficient combination with non-ionic and anionic surfactants used in standard powders.

Test standard

In 2015, a research methodology was developed to assess the effectiveness of the chemical-thermal disinfection process of textiles. The PN-EN 16616 standard is a carrier methodology describing the procedure for testing biocides to combat harmful pathogens during washing. The basic task of the methodology is to assess whether a given active substance contained in a washing product is effective in the intended disinfection process. The second extremely important element are the practical conditions of use of the detergent, which should be reproduced in a laboratory test.

At this stage, temperature, contact time and the presence of load substances should be taken into account to simulate real conditions. The laundry device on which the tests are performed must meet the requirements strictly specified in the methodology (point 5.3.2.18 Washing machine and machine preparation) “Chemical-thermal disinfection of textiles – Test method and requirements (phase 2, stage 2).” If the actual conditions of use of the product differ from the requirements contained in the methodology, the manufacturer’s task is to determine the effective dose of the disinfectant during the test.

Application of the methodology

Chemical-thermal disinfection of textiles can be used wherever maintaining a high level of hygiene seems to be particularly important. Of course, we are talking about hospitals, health care facilities, rehabilitation offices, social welfare homes and clinics. Taking care of the disinfection process is also important from the point of view of nurseries, kindergartens, schools and the entire industrial area. This includes maintaining the sterility of clothing of employees of plants working with food, dietary supplements or pharmaceutical technologies. A standard washing process using products without biocidal substances may prove to be insufficient.

Registration requirements for biocidal products

In accordance with the requirements of the Office for Registration of Medicinal Products, Medical Devices and Biocidal Products in Poland, a biocidal product used for laundry disinfection registered in the so-called national procedure should have tests according to discussed methodology PN-EN 16616 and optionally according to PN-EN 14476 “Chemical disinfectants and antiseptics. Quantitative suspension method for determining the virucidal effect of chemical disinfectants and antiseptics used in the medical area. Test method and requirements”, as well as PN-EN 14348 “Chemical disinfectants and antiseptics – Quantitative suspension method for determining the tuberculocidal effect of chemical disinfectants and aseptic agents used in the medical area, including tools disinfection. Test method and requirements”.

The European procedure, however, is characterized by slightly broader requirements described by the European Chemicals Agency (ECHA) in the guide “Guidance on the Biocidal Products Regulation Volume II Efficacy – Assessment and Evaluation (Parts B+C) Version 3.0 April 2018”. In the case of the European procedure, in addition to the PN-EN 16616 methodology, the product should have tests according to: PN-EN 13727, PN-EN 13624, PN-EN 14348 and regarding the declaration of virucidal effectiveness according to PN-EN 14476.

Reference strains and testing procedure

The reference strains indicated in the methodology are: Pseudomonas aeruginosa, Escherichia coli (K12), Staphylococcus aureus, Enterococcus hirae, Enterococcus faecium in terms of bacteria; Candida albicans, Aspergillus brasiliensis for fungi and Mycobacterium avium and Mycobacterium terrae in the context of testing the tuberculocidal effectiveness. It is also possible to use optional strains, e.g. viruses. However, it should be remembered that if additional microorganisms are used, they should be incubated under optimal growth conditions (temperature, time, atmosphere, media).

The research procedure involves preparing a support made of cotton fabric. The carrier is covered with pathogenic microorganisms containing centrifuged sheep blood, dried and then placed in cotton bags. Once placed in the laundry machine, they are ready for the disinfection process. The process is carried out at a temperature < 60 °C or ≥ 60 °C and applies only to the actual stage. It is also possible to test after the so-called washing/pre-soaking, which is intended to pre-clean the tested textiles. However, this requires including appropriate information in the product’s instructions for use. After the washing stage is completed, we transfer the carriers to test tubes and then carry out the actual part of the test, i.e. testing. After completing the analyses, we calculate the reduction factor.

Products tested at temperatures < 60 °C are considered effective when, after three test repetitions, the reduction factor of bacteria and mycobacteria is more than 7 logarithms. In the case of fungi, the minimum reduction rate must reach > 6 log. Tests performed at conditions ≥ 60 °C should achieve an analogous value greater than 7 logarithms. For both strains of bacteria, fungi and mycobacteria, as well as additional test microorganisms adapted to the practical function of the product. Moreover, no microorganisms should be detected in 100 ml of washing/disinfectant liquid.

Summary

Research according to PN-EN 16616 methodologies require the use of a special laundry device and the participation of a specialized laboratory crew. This test is a kind of niche in the laboratory services market due to the need for qualified staff. Laboratories with technical facilities and offering test data will help in selecting the research scope necessary to meet the manufacturer’s needs.