Polymers 2024 , 16 , 110
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Next, the impact of different crosslinkers on the morphology of the prepared paper samples was evaluated via SEM (Figure 4). The reference sample exhibits the presence of CaCO 3 between the cellulose fibers with uneven distribution. The PEG/SiO 2 and PEG/TiO 2 paper samples (Figure 4B,C) show a more even distribution of CaCO 3 particles along cellulose fibers compared to the reference sample. In the material with PEG/SiO 2 , the amount of CaCO 3 between the fibers is much higher compared to the reference sample. Paper samples with h-BN and h-BN-OH exhibit agglomerated CaCO 3 particles. This may lead to increased permeability of CaCO 3 through cellulose fibers, which will result in a reduced content of calcium carbonate in the sample.
Figure 4. SEM images of ( A ) reference paper and paper containing different crosslinkers: ( B ) PEG/SiO 2, ( C ) PEG/TiO 2 , ( D ) PEG/h-BN, and ( E ) PEG/h-BN-OH. Figure 5 presents the Raman spectra of paper samples (reference, PEG/SiO 2 ,PEG/TiO 2 , PEG/h-BN, and PEG/h-BN-OH). Cellulose is a linear polymer made up of repeating glu- cose units linked by β -1,4-glycosidic bonds. It exhibits a high degree of crystallinity, with both crystalline and amorphous regions in its structure. Raman spectroscopy is sensi- tive to various vibrational modes present in cellulose. The main Raman-active modes for cellulose fibers include C-C and C-O bonds. These vibrations are observed around 1095 cm − 1 , offering valuable information about the molecular bonds within the cellulose structure [21,22]. Next, out-of-plane ring bending (C-C-C and C-O-C), observed in the range of 400 to 600 cm − 1 , provides insights into the spatial arrangement and flexibility of the cel- lulose rings. Additionally, Raman peaks associated with deformations in the CH 2 andCH 3 groups are prominent in the range of 1300 to 1470 cm − 1 [23] (orange zones). Furthermore, Raman spectroscopy studies revealed the distinctive peaks of CaCO 3 corresponding to two different forms: calcite (green zones) and vaterite (blue zones). The peak at 1085 cm − 1 signifies calcite, while the peaks at 1080 and 1090 cm − 1 represent vaterite, specifically
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