# Transmission Reduction for UV and IR Radiation with Dyed Lyocell Knitted Textiles
## 4 Discussion  
The aim of the current investigation was to realize a textile material with reduced transmission for UV light and near-infrared light. For this, knitted fabrics from different Lyocell fibers are produced and dyed. It has been shown that the dyes examined are capable of reducing transmission in general (see Figures 2 and 4). This statement is especially valid for UV light. As expected, the reduction of transmission was dependent on the type of dye. The best results were achieved on textiles dyed with Solophenyl Bordeaux 3 BLE. In comparison, transmission measurements for samples dyed with Drimaren Yellow HF-CD exhibit less advantageous results. While the measurement results in the UV range (see Table 3) can be easily classified on the basis of comparable studies [69; 70]. In comparison, the evaluation of the measurement results in the NIR range is more difficult due to a smaller number of reference data. The behavior of dyes available on the market and frequently used with regard to absorption/reflection properties is relatively unexplored in the IR range and the number of publications, especially with reference to the dye classes mentioned, is low. One reference pointed for a certain classification of the results is the known high reflectivity of indanthrene dyes, whose transmission results serve as a reference point for an assessment in the NIR range [71]. It has been shown that the dyes Solophenyl Bordeaux 3 BLE and Drimaren Yellow HF-CD show a comparable behavior in the NIR range as the dye Indanthren Yellow 5 GF. Solophenyl Bordeaux 3 BLE also shows a significant reduction in transmission values in parts of the NIR range [700 nm to 900 nm], which did not occur in this form with any of the other dyes tested. Compared to the transmission reduction for UV light, the dye has a smaller effect with regard to a reduction in the IR range and a reduction in transmission seems to be more difficult to achieve. Furthermore, it was observed that an increase in dye concentration, and thus a decrease in brightness, leads to a decrease in transmission for \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **UPF** & **UVR Protection Category (See Table 1)** \\ \hline
100\% Lyocell & 6 & bad \\ Lyocell with TiO\({}_{2}\) & 43 & excellent \\
100\% Lyocell, Drimaren Yellow & 40 & excellent \\
100\% Lyocell, Drimaren Yellow, washed & 27 & very good \\ Lyocell with TiO\({}_{2}\), Drimaren Yellow & 69 & excellent \\ Lyocell with TiO\({}_{2}\), Drimaren Yellow, washed & 59 & excellent \\
100\% Lyocell, Solophenyl Bordeaux & 67 & excellent \\
100\% Lyocell, Solophenyl Bordeaux, washed & 42 & excellent \\ Lyocell with TiO\({}_{2}\), Solophenyl Bordeaux & 73 & excellent \\ Lyocell with TiO\({}_{2}\), Solophenyl Bordeaux, washed & 37 & very good \\ \hline \hline \end{tabular}
\end{table} 
Table 4: UPF of different samples, also an evaluation of sample properties according to the UVR protection category is given. near-infrared radiation. For UV light, the transmission was already significantly decreased by the tested dyes at low concentrations, so an increase in the dye concentration did not lead to further improvements (see Figure 2). The color achieved and the reduction of transmission in the non-visible wavelength ranges (here UV and NIR) is a consequence of the chemical structure of the dyes. However, similar or spectroscopically identical color shades can be achieved by different dye structures. It is often assumed that the darker a color is, the better the protective effect. Based on this statement, the color black should be particularly suitable for reducing transmittance, but this cannot necessarily be confirmed [16]. When comparing the UPF values determined, which ultimately reflect the transmission, with the color values (LCh) (Table 2), Sologhenyl Bordeaux 3 BLE, the darkest shade, has the highest UPF value (Table 3). Excellent UPF values are also achieved in textiles dyed with Drimaren Yellow HF-CD (Table 3).