Polymers 2024 , 16 , 110
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To determine the ash content in the paper, the guidelines set by the International Organization of Standardization (ISO 1762:2001) were applied. The procedure was through sample ignition at 525 ◦ C. The ash content in the reference and modified papers (PEG/SiO 2 , PEG/TiO 2 , PEG/h-BN, and PEG/h-BN-OH) are presented in Table 2.
Table2. Data obtained from the International Organization of Standardization (ISO) standard (ISO 1762:2001) ash content for all samples.
Ash Content (%)
Reference PEG/SiO 2 PEG/TiO 2 PEG/h-BN
28.1 31.5 25.7 25.1 23.2
PEG/h-BN-OH
Based on the results presented in Table 2, the addition of SiO 2 nanoparticles increased the ash content in the paper significantly. This means that this facile strategy boosts CaCO 3 retention on cellulose fibers by 12.1% in the presence of PEG/SiO 2 as a nanofiller, which can be related to the abundance of active sites available for CaCO 3 bonding. The opposite trend can be observed for PEG/TiO 2 , PEG/h-BN, and PEG/h-BN-OH, where ash content is 8.1, 11.1, and 17.5% lower compared to the reference paper, respectively. In summary, based on the above results, it can be inferred that the addition of porous SiO 2 in the form of a PEG suspension is the most promising crosslinker increasing the affinity of CaCO 3 to cellulose fibers. This conclusion is supported by numerous analyses, such as TGA, and ISO 1762:2001 tests, which showed that the inorganic fillers content after the introduction of PEG/SiO 2 increased by 12.1%, which proves the potential of this facile strategy in practical application in the paper industry. This may be because SiO 2 possesses the largest specific surface area among other crosslinkers (TEM and N 2 adsorption/desorption), increasing affinity to cellulose fibers, resulting in higher inorganic filler content retention. 4. Conclusions In summary, this study investigated the influence of various crosslinkers (TiO 2 , SiO 2 , h-BN, and h-BN-OH) on the inorganic filler content in paper samples. Raman spectroscopy and XRD confirmed that the chemical structure of the samples remained insignificantly changed upon the addition of these compounds. This study further delved into the molecular dynamics of cellulose through various Raman peaks associated with specific vibrational modes. Additionally, Raman spectroscopy identified characteristic peaks for CaCO 3 , distinguishing between calcite and vaterite forms. Moreover, the introduction of h-BN and h-BN-OH led to the formation of agglomerates and uneven distribution of CaCO 3 particles on cellulose fibers, resulting in decreased ash content after testing. Among the crosslinkers, SiO 2 suspended in a PEG solution emerged as a promising candidate due to its excellent affinity to cellulose and high surface area, enhancing inorganic filler content in the paper. These findings contribute to a deeper understanding of how different crosslinkers impact the composition and structure of paper samples and allow the boosting of the content of inorganic compounds in the paper sheet, reducing the contribution of cellulose. Author Contributions: Methodology, K.W. and T.K.; Investigation, W.B.; Writing—original draft, K.M. and K.S.; Visualization, B.Z.; Supervision, E.M.; Project administration, A.G.-K.; Funding acquisition, J.J. and G.M. All authors have read and agreed to the published version of the manuscript. Funding: This research received funding from the National Centre for Research and Development (Poland): POIR.01.01.01-00-0272/19-00. Institutional Review Board Statement: Not applicable.
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