# Evaluation of Recycled Paperboard Properties and Characteristics
## 3 Results and Discussion
### Colorimetric Characteristics of Recycled Paperboards  
As revealed above, recycled fiber paperboards have high absorbency; therefore, it is necessary to choose a printing method that does not involve moisture. The inkjet digital printing method is suitable for this purpose because it has a number of advantages:  
* low cost and simplicity, with the possibility of easily changing the press parameters;
* the nature of multi-color reproduction is similar to other printing methods;
* does not require printing forms, which is environmentally beneficial;
* high speed of the printing process and the possibility of producing small circulations;
* any kind of paper and paperboard can be used;
* no intermediate image information carrier is needed, allowing ink to be applied directly to the material. For printing on recycled paperboard, UV-curable inks are the best choice because they dry quickly, have a high gloss, and are solvent-free, making them more environmentally friendly. In addition, UV inks have a high viscosity suitable for fast absorption by macroporous recycled paperboards. Color gamut is defined as all the colors that can be reproduced by the inks used. In addition to inks, the whiteness of the paperboard affects the color gamut. Therefore, before giving a colorimetric evaluation of imprints, it is necessary to compare the parameters of the whiteness of the samples. The average whiteness values of the recycled paperboards were calculated according to the CIE, Berger, and Stensby formulae; the results are presented in Table 3.  
In all three groups, namely WCIE, WB, and WS, as well as within the groups of uncoated and coated paperboards, the differences between the obtained values of whiteness were \begin{table}
\begin{tabular}{c c c c|c c c c} \hline
**Whiteness** & \multicolumn{3}{c}{**Uncoated**} & \multicolumn{3}{c}{**Coated**} \\ \cline{2-9}
**Formula** & **Sample** & **Ladoga** & **HM** & **Umka** & **MCB** & **MCM** & **Neva** \\ \hline CIE & \(18.22\pm 3.05\) \({}^{\mathrm{a}}\) & \(81.19\pm 0.46\) \({}^{\mathrm{b}}\) & \(70.07\pm 0.58\) \({}^{\mathrm{c}}\) & \(89.99\pm 0.57\) \({}^{\mathrm{d}}\) & \(88.30\pm 0.59\) \({}^{\mathrm{e}}\) & \(88.75\pm 1.23\) \({}^{\mathrm{d}}\), \({}^{\mathrm{e}}\) & \(78.94\pm 0.94\) \({}^{\mathrm{f}}\) \\ [PERSON] & \(28.02\pm 1.48\) \({}^{\mathrm{a}}\) & \(80.56\pm 1.10\) \({}^{\mathrm{b}}\) & \(70.12\pm 0.61\) \({}^{\mathrm{c}}\) & \(90.51\pm 1.22\) \({}^{\mathrm{d}}\) & \(88.69\pm 0.53\) \({}^{\mathrm{e}}\) & \(89.23\pm 0.35\) \({}^{\mathrm{d}}\), \({}^{\mathrm{e}}\) & \(78.03\pm 0.74\) \({}^{\mathrm{f}}\) \\ [PERSON] & \(53.78\pm 1.38\) \({}^{\mathrm{a}}\) & \(92.65\pm 1.47\) \({}^{\mathrm{b}}\) & \(84.77\pm 0.54\) \({}^{\mathrm{c}}\) & \(95.44\pm 0.51\) \({}^{\mathrm{d}}\), \(94.97\pm 0.11\) \({}^{\mathrm{d}}\) & \(96.48\pm 0.87\) \({}^{\mathrm{e}}\) & \(88.45\pm 0.74\) \({}^{\mathrm{f}}\) \\ \hline \end{tabular}
\end{table} 
Table 3: Average whiteness values of the recycled paperboards calculated by CIE, Berger, and Stensby formulae. statistically significant (\(p<0.05\)). Pairwise comparisons of whiteness values within the groups (each type of whiteness separately for coated and uncoated cardboards) were assessed using the Tukey test (Table 3). An insignificant difference in whiteness was detected for paperboards Umka, MCB, and MCM from the coated group. Each of them had a multiple pigment coating (Table 1), which led to increased whiteness. Neva also had a coating on the top, but only double-layered. As a result, the whiteness values for this sample were the lowest in the group of uncoated paperboards. Expectedly, the paperboards with a coated ply demonstrate a greater whiteness than uncoated ones. However, all samples have a yellow tint of different intensity due to the presence of secondary fibers in their composition.