# Alternative Fiber-Based Paperboard Adhesion Evaluation with T- and Y-Peel Testing
## 2 Materials and Methods  
### Paperboard Samples  
For the presented research, three different paperboards (that can be used for packaging production) made of alternative fiber sources were produced: (1) **JK**--240 g/m\({}^{2}\) paperboard made of the invasive plant Japanese knotreed's fibers (_Reynoutria japonica_); (2) **SD**--240 g/m\({}^{2}\) paperboard made of residual sawdust; and (3) **BL**--240 g/m\({}^{2}\) paperboard made of black locust fibers (_Robinia pseudoacacia_), an invasive alien plant harvested or collected in Slovenia.  
Japanese knotreed and black locust plants were firstly harvested, dried, and cut into small pieces. After grinding them into 0.5 mm particles, the chemical analyses were performed. The ash content (TAPPI 211 method), hexane and ethanol extractives (TAPPI 204), cellulose ([PERSON] method), hemicellulose (chlorite method), and lignin (TAPPI 222) were determined prior to further preparation [22]. The results of the analyses are presented in Table 1.  
After chemical analysis, the delignification process of biomass was performed using the Kraft procedure. The biomass was treated with 50% NaOH. The reaction temperature was 160 \({}^{\circ}\)C and delignification time 3 h at constant mixing. After delignification, the pulp was separated from the black liquor, screened, and cleaned.  
The JK and BL fiber properties were analyzed using a Valmet F55 fiber analyzer (Valmet, Espoo, Finland), which analyzes fibers based on automated image analysis (Table 2).  
In the case of the SD sample, sawdust was incorporated as a filler into the paperboard structure produced from commercially available wood-based Kraft cellulose fibers.  
The paperboard samples were machine-produced on a pilot paper machine (Pulp and Paper Institute, Slovenia) which works with a Fourdrinier principle, has a width of 60 cm, and has all the features of an industrial machine regarding fiber bonding and paper production.  
The pulp was prepared in a combination with commercially available Kraft wood-based cellulose fibers (Table 2). All papers had similar starch and surface sizing components, the freeness of the pulp was 25\({}^{\circ}\) SR for all samples, so the variability in the paperboard properties was mostly due to the fiber properties, filler content, paperboard formation, and porosity properties. Their properties are presented in Table 2; their appearance in Figure 1.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline  & **Alternative Fiber** & **JK** & **BL** \\ \hline \multirow{6}{*}{Chemical structure *} & Ash (\%) & 2.5 & 0.3 \\ \cline{2-4}  & Hexane extractives (\%) & 0.4 & 0.3 \\ \cline{2-4}  & Ethanol extractives (\%) & 1.1 & 4.7 \\ \cline{2-4}  & Cellulose (\%) & 35 & 41 \\ \cline{2-4}  & Hemicellulose (\%) & 36.6 & 34.7 \\ \cline{2-4}  & Lignin (\%) & 26.8 & 21.9 \\ \hline \hline \end{tabular}  
* The chemical structure may vary depending on seasonal and location influences.  
\end{table}
Table 1: Chemical analyses of Japanese knotowed (JK) and black locust (BL) [22].  
Figure 1: The appearance of tested paperboards produced from alternative fibers: JK—Japanese knotowed, SD—sawdust, and BL—black locust samples.