# Transmission Reduction for UV and IR Radiation with Dyed Lyocell Knitted Textiles
## 3 Results
### Transmission Spectra of Knitted Fabrics of 100% Lyocell and Lyocell with TiO\({}_{2}\)  
Knitted fabrics made of Lyocell fibers and Lyocell fibers spin-doped with 2% TiO\({}_{2}\) served as the basis for further tests. Figure 3 shows the transmission spectra of these raw materials without further dye application as reference measurements. The addition of TiO\({}_{2}\) to the fiber material reduces the transmission in the UV range (below 380 nm) drastically. This absorption behavior of the TiO\({}_{2}\) is determined by its band gap energy [66]. However, a reduction in transmission was also observed over the entire measured spectrum, which can be explained by the reflective properties of the TiO\({}_{2}\) white pigment particles. Please remark, in addition to its use as a UV absorber, TiO\({}_{2}\) is one of the most important white pigments with a high reflectivity for visible light. These knitted fabrics were dyed with the selected dyes Drimaren Yellow and Solophenyl Bordeaux. After dyeing, the optical transmission was investigated. A dye concentration of 1.5% of Drimaren Yellow or Solophenyl Bordeaux was chosen, as the solution tests showed that higher concentrations are more effective. Photographic images of dyed Lyocell  
Figure 3: Comparison of transmission spectra of Lyocell knitted fabric with and without TiO\({}_{2}\). The doped Lyocell fibers contain 2 wt-% TiO\({}_{2}\). knitted fabrics are presented in Figure 4. The intensive dark yellow-orange and dark violet coloration is presented. Figure 5 shows the spectra of the transmission measurements. The influence of the dyeing on the transmission can be determined. In the case of Drimaren Yellow, the transmission is reduced to almost zero in the entire UV range and the spectral range of visible light up to around 480 nm. With increasing wavelength, the transmission increases and approaches the values of the undyed samples for both the pure Lyocell and the Lyocell fabrics containing TiO\({}_{2}\). In the case of Solophenyl Bordeaux, the effect of reducing transmission for visible light is even more pronounced and a slight increase in transmission is determined for the spectral range starting at around 560 nm. Overall, dyeing with Solophenyl Bordeaux reduces the transmission for visible range significantly to values below 10%. For the spectral range of near-infrared light up to 920 nm, also a reduction in transmission is observed. An influence of added TiO\({}_{2}\) in the fiber only becomes obvious from a wavelength of around 600 nm and  
Figure 4: Photographic images of dyed Lyocell knitted fabrics (dyeing with Drimaren Yellow HF-CD on top; dyeing with Solophenyl 3 BLE Bordeaus below)—**(left)**: knit from Lyocell yarn; **(right)**: knit from Lyocell yarn spin-doped with TiO\({}_{2}\). Figure 5: Transmission spectrum of knitted fabrics dyed with Drimaren Yellow HF-CD or Solophenyl 3 BLE Bordeaux made of 100% Lyocell and Lyocell with TiO\({}_{2}\). reduces the transmission by at least 5% from here on. The dyed samples were examined colorimetrically and the LCH values were determined (Table 2). The presence of TiO\({}_{2}\) in the fiber material increases the brightness (L*) compared to the pure Lyocell fiber material (compare also photographic images in Figure 1). TiO\({}_{2}\) is a bright white pigment with a high refractive index of 2.7, so the increase of brightness of the fiber materials in the presence of embedded TiO\({}_{2}\) particles is expected [67]. This brightening effect remains in a similar order of magnitude for the dyed samples. The Hue values (h) confirm the optical impression of the color tone [46; 68]. The samples dyed with Drimaren Yellow show an orange color tone (a* \(\approx\) 35, b* \(\approx\) 64) with h \(\approx\) 60. The textiles dyed with Solophenyl Bordeaux have an h-value of about 350 and show a violet color tone (a* \(\approx\) 30, b* \(\approx\) \(-\)3) (see Figure 4). Washing of the samples resulted in small changes in the values.