Appl. Sci. 2025 , 15 , 875
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a JAC SHPD28D laboratory propeller pulp disintegrator (Danex, Katowice, Poland) at 23,000 revolutions, following ISO 5263-1 (2004) [33]. After defibering, the pulps underwent a purification process in a laboratory hydrocyclone with a diameter of 60 mm, operated at a pressure difference of 1.5 bar. Next, the cleaned pulp was subjected to a screening process using a PS-114 membrane screener (Danex, Katowice, Poland) with an amplitude of 25 mm and a frequency of 2 Hz. The screener was equipped with a 0.15 mm gap screen. During this process, the fibrous fraction (designated after the process as sorted pulp) flowed through the sorting plate under the hydrostatic pressure of the water column and the movement of the vibrating membrane beneath the screen plate. After screening, the fibrous fraction was discharged through an overflow spigot into a container below, where it was drained on a sieve. The rejects remained on the sorting plate and were removed after each screening cycle. 2.3. Washing of Wastepaper The washing process involved multi-stage dewatering, during which impurities smaller than the screen openings were removed, including fine fractions, fillers, shorter fibers, and other small particles. This process was performed using a screener equipped with a 180-mesh sieve (90 μ m openings). The pulps were washed with a controlled vol- ume of water while being gently mixed to prevent the formation of a filter layer on the screen plate. 2.4. Preparation of Paper Sheets Laboratory paper sheets were produced from the screened and washed wastepaper pulps. The sheets were formed using a Rapid-Koethen apparatus (Danex, Katowice, Poland) in compliance with PN-EN ISO 5269-2 (2007) [34]. Each sheet had a base weight of 80 g/m 2 , as per ISO 536:2019 [35]. Only sheets with a basis weight within the range of 79–81 g/m 2 were selected for further testing. Prior to testing, the paper samples were conditioned for at least 24 h at a temperature of 23 ◦ C and 50% relative humidity, in accordance with ISO 187:2022 [36]. 2.5. Analysis of the Paper Properties The surface roughness of the paper was measured in accordance with ISO 8791- 2:2013, using the TMI 58-27 Bendtsen Roughness Tester (Kontech, Lodz, Poland) [37]. Air permeability was evaluated using the same device, following the guidelines of ISO 5636-3:2013 [38]. The key strength properties of the paper were assessed using a Zwick 005 Pro-Line test- ing machine (ZwickRoell, Ulm, Germany), in compliance with PN-EN ISO 1924-2:2010 [39], with data acquisition and analysis performed via testXpert III software. The tensile proper- ties of the paper were tested as follows: • I B : breaking length [m]. • F B : tensile force at break [N]. • σ T b : width-related force at break [N · m − 1 ]. • σ T W : force-at-break index [Nm · g − 1 ]. • ε T : strain at break [%]. • W T b : energy absorption [J · m − 2 ]. • W T W : energy absorption index [J · g − 1 ]. • E b : tensile stiffness [N · m − 1 ]. • E w : tensile stiffness index [Nm · g − 1 ]. • E*: Young’s modulus [MPa].
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