# Transmission Reduction for UV and IR Radiation with Dyed Lyocell Knitted Textiles
## 1 Introduction  
The skin is often named the largest organ of the human body [1, 2]. It protects against a variety of environmental influences, regulates heat balance, and is an important sensory organ [3, 4]. Physical environmental influences, such as ultraviolet (UV) radiation and infrared (IR) radiation, can have a major impact [5, 6, 7]. UV radiation covers the spectral range of non-visible electromagnetic radiation in the wavelength range from 100 nm to 400 nm. The UV portion of the sun's electromagnetic spectrum is about 6% and is mainly related to the spectral range of the sun from 280 nm to 400 nm [8]. Moreover, artificial light sources for indoor and outdoor illumination can emit a significant amount of UV light [9, 10, 11]. Infrared radiation (IR radiation) is defined as the part of the electromagnetic spectrum in the wavelength range of 700 nm to 1 mm. The human skin is exposed to IR radiation from the sun and artificial sources [12]. Of particular interest is the near-infrared range, also known asIR-A radiation (700 nm to 1400 nm), as this radiation is richer in energy and the penetration depth of the radiation into the skin is particularly high [13]. Frequent exposure to UV and infrared radiation can cause significant damage to the skin, such as sunburn, premature skin aging, and promotion of the development of carcinomas [14; 15; 16; 17; 18; 19]. For this, materials able to support protection against UV and infrared radiation can contribute significantly to human health and wellbeing [20; 21; 22]. The use of sun creams to protect against UV radiation is well established. However, the protective properties of these cosmetic products are not permanent and are inferior to a functionalized textile in terms of applicability and benefit [23; 24]. In addition to the research on radiation-protective materials, a recent field of research is the development of photoactive materials active under illumination with visible light. These materials show strong potential for applications for disinfection and degradation of pollutants [25; 26; 27; 28]. Nowadays, developments in the sustainability of textile production processes are of high importance because textile production is responsible for 5 to 10% of greenhouse gas emissions [29]. Due to this the carbon and water footprint for textile products are intensively investigated during the last years [30; 31; 32]. The functionalization of fibers by doping during the spinning process, in-situ growth of metal and metal-organic components, and coating processes on textile fabrics are intensively investigated [23; 33; 34; 35; 36; 37; 38]. In comparison, the achievement of a UV/IR absorbing effect via the coloring of textiles in civilian use has so far been little researched. In the summer months, the intensity of the sun's rays are particularly high, and many activities take place outdoors. To protect against radiation, light and comfortable textiles made of appropriate materials are an adequate solution and often advantageous compared to cosmetic products. Knitted fabrics made of Lyocell, a cellulose regenerate fiber, are suitable [39]. Compared to cotton, the regenerated fiber has a higher water absorption capacity, which has a positive effect on wearable comfort when sweating [40; 41]. A known problem of Lyocell fibers is the so-called \"washing greying\" (fibrillation), which becomes noticeable after the washing process in the form of a greyish film on the fabric surface and negatively influences the fabric's appearance [42]. However, fibrillation can be reduced by additives such as cross-linking agents or by selecting suitable reactive dyes [43; 44]. Textile manufacturing and finishing generally offer a variety of options for reducing transmission in the UV and IR spectral ranges [45; 46; 47]. By this, protective properties against UV and IR light can be implemented. Swimwear, outdoor clothing, and technical textiles, for example, warnings and sunshades, focus on reducing the transmission of UV radiation [48; 49].