Cellulose (2020) 27:7215–7225
7221
calculations chemical pretreatment with used DES- system increased the raw material cost from 0.08 to 0.107 € /kg, which is around 34%. We noticed also that both the grinding level of CNF and their loading in the board sheet have a significant impact on the final price of the board. For example, increasing the T3 dosage from 2 to 6 wt% increased the final product price of the board by approximately 160–212%. Overall, the costs associated with using DES-treated CNF were around 30% higher when compared to reference CNF (Figs. S4–S6) recycled board. Because the energy consumption, chemical costs and costs associated with CNF use increased notably when the CNF grinding level increased, the most important mechanical prop- erties of the board were compared to the energy consumption and relative manufacturing price of the strengthened recycled board to analyze the optimal use of CNF as a reinforcement. The tensile strength of the handsheets increased almost linearly as a function of the CNF dosage (Fig. 5). CNF treated with DES enhanced the tensile strength to a greater extent than the addition of reference CNF (Fig. 5), and the highest strength value was obtained with T3. The best tensile strength index was 61% higher (i.e., T3 [6%]) than that of the reference board handsheet (34.0 kNm/kg). Moreover, it was observed that pulp from the DES-pretreatment had better strength properties in comparison to the untreated pulp. However, by considering the total chemical costs associated with the pulp slurry
Fig. 3 Densities of the prepared board handsheets
induced by CNF was very small ( \ 1% unit). Gener- ally, the DES-treated CNF sample resulted in better values than the reference CNF. To evaluate the costs attributed to using CNF as reinforcements in the board handsheet, some prelim- inary calculations were conducted. The estimated price of the electricity was 0.13 € /kWh; the price of recycled boxboard was 0.08 € /kg. Technical grade of urea costs around 200 € /t and choline chloride around 350 € /t (Laitinen et al. 2017). We used in these calculations recycling rate of 10 times and efficiency of chemical recycling 97% and the used consistency of pulp solution during DES-treatment was 5%. Based on
Fig. 4 Tear index ( a ) and strain values ( b ) of prepared board handsheets
123
Made with FlippingBook - Online catalogs