Treating footwear against Covid
Gloria Lillo-Dangla, Ana M. Torró-Palau & Elena Orgilés-Calpena – INESCOP
The pandemic caused by covid-19 burst into our lives unexpectedly, affecting in a remarkable way the activity of different industries, including footwear and its components. Once the crisis caused by the first wave of the pandemic was overcome, the footwear sector, used to reacting to adversities, focused on measures that allowed the reactivation of production and the commercialisation of products in a safe way.
As the highly infectious nature and ease of transmission of coronavirus, as well as its survival in common objects and on their surfaces became known, hygiene became an essential measure to prevent contagion. In this sense, footwear was no exception. The in-store sale of footwear, therefore, needed to be carried out in such a way that the consumer's shopping experience was safe and satisfactory. The same applied to online sales where disinfection of the products sold and returned had to be guaranteed.
In a very short time, a wide variety of products appeared that claimed to offer companies solutions and technologies for the disinfection of footwear, leaving those companies‘ choice of sanitising products or systems potentially both tricky and risky. On the one hand, there were liquid sanitising systems applied directly on to the product after use, which had been previously authorised by the Spanish Ministry of Health as effective against SARS-Cov-2. On the other hand, there were radiation-based systems such as ozone or UV, the disinfectant effectiveness of which had already been proven against other microorganisms.
Given the wide availability of solutions and technologies available for the sanitation of products and surfaces, companies did not have an easy choice. Faced with this situation, INESCOP made its capabilities, knowledge and resources available to the Government, as well as companies and other users, in order to offer a suitable response. As a direct result of this, the COVIDSHOE project was launched in March 2020, at the outbreak of the pandemic and when there was still not much information about it. Funded by IVACE (Valencian Institute of Business Competitiveness) and the ERDF (European Union Regional Development Fund), its main objective was the effective sanitisation of footwear in order to fight coronavirus.
In the development of this project, two possible actions were considered. One was to evaluate the effects of different sanitising treatments on the aesthetic, mechanical and functional properties of footwear, as the effect of a continuous application of these treatments on the materials involved was unknown. The other was the development of new materials with viricidal (ability to destroy viruses) properties included in the nature of the material to prevent the possible contagion caused by people’s movement, especially in places where contamination could be high.
Sanitising treatments
Three types of sanitising treatment were used for this study, all of which are considered to be effective viricides against SARS-COV-2 by the Spanish Ministry of Health. First, liquid products sprayed on the surface of various materials were used, with the application of up to 96 sprays. Those used were:• Sodium hypochlorite (4.5% active chlorine)
• Alkyldimethylbenzyl ammonium chloride (1.6%)
• Biphenyl-2-ol (0.4%)/Ethyl alcohol (30.6%)• Didecyldimethylammonium chloride (2.7%)
The other type of treatment tried was UV radiation with a wavelength of 254 nm with up to 240 hours of continuous exposure, as well as daily exposures of 45 minutes for 10 days. Ozone was also used as a sanitising treatment, with up to 72 hours of application.
To apply these treatments, different types of footwear were selected (flip-flops, trainers, men's and women's footwear), as well as dark, light and translucent soling materials including thermoplastic rubber (TR), polyvinyl chloride (PVC), styrene-butadiene rubbers (SBR) of different hardnesses, thermoplastic polyurethane (TPU), and copolymers of vinyl acetate (EVA). Different types of upper materials were also tested including leather (patent leather, split leather, metallised leather, finished leather), fabrics (woven, 3D knitted and coagulated fabrics) and ornaments (buckles, different metal pieces), covering the whole range of materials used in footwear.
After each application of the corresponding treatments, the materials were checked for any visual alteration. In addition, the evolution of their mechanical properties (hardness, density, abrasion, tear, tensile properties, elongation, flexing, etc.) was also analysed. They were further subjected to ageing (light, temperature and humidity) and chemical analysis (REACH regulation) to ensure that no substances harmful to users or the environment were generated. The results obtained regarding the effect of the various sanitising treatments on the different upper and soling materials commonly used in footwear manufacturing were compiled in a digital guide to be available to companies.
The general conclusion from this study is that excessive or uncontrolled exposure to some treatments could lead to staining, loss of colour or brightness, and even microcracks affecting the mechanical properties of materials or footwear. Therefore, and based on these results, it is advisable to preferably use alcohol-based viricides specific for footwear, being able to spray soles up to 100 times and being careful with patent or finished leathers that could ‘dry out’ after more than 70 sprays, always bearing in mind that their mechanical properties could be weakened.
Ammonium salt-based products can also be used specifically on textile materials and soles can be sprayed up to 100 times. Patent and metallic leathers should also be treated with the same care. However, special attention must be paid to products based on ammonium salts that are not specifically for textiles or footwear as they can damage soles and some finishes, causing them to lose their qualities/properties.
Development of viricidal materials
Regarding the development of footwear materials with viricidal properties, work was conducted on the addition of different percentages of viricidal agents to footwear materials, incorporating them into the formulation of both soling and upper materials in the form of microcapsules. Antimicrobial tests were carried out on these materials using different bacteria and viruses. The results obtained were very satisfactory, proving in some cases that the samples with an additive showed a positive antimicrobial effect that was not observed in those without.
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