Polymers 2024 , 16 , 110
8of 12
corresponding to the Ag internal mode derived from the v 1 symmetric stretching mode of the carbonate ion in each material. The v 4 in-plane bending mode of carbonate is observed at 712cm − 1 for calcite and 739–749 cm − 1 for vaterite. It is noteworthy that the characteristic peak for vaterite was not detected in the case of PEG/h-BN and PEG/hBN-OH. However, the reason of the lack of this peak is not clear.
Figure 5. Raman spectra of reference paper and paper with different crosslinkers (PEG/SiO 2 , PEG/TiO 2 , PEG/h-BN, and PEG/h-BN-OH). Figure 6 shows the X-ray diffraction patterns of the reference, PEG/SiO 2 , PEG/TiO 2 , PEG/h-BN, and PEG/h-BN-OH paper samples. In the patterns of all samples, two char- acteristic phases were identified, i.e., cellulose and calcium carbonate (CaCO 3 ). The three observed peaks (broad peaks) at 2 θ =16 ◦ , 22 ◦ , and35 ◦ correspond to cellulose. However, a series of reflections at 2 θ equal to ~23 ◦ , 29.4 ◦ , 36 ◦ , 39.4 ◦ , 43.2 ◦ , 47.5 ◦ , and48.5 ◦ are charac- teristic for CaCO 3 (ICDD no. 00-005-2586). The XRD diffractograms also show two peaks (low intensity) at ~30.9 ◦ and 31.6 ◦ , which can be attributed to other calcium carbonate polymorphs (e.g., aragonite and vaterite) (ICDD no. 01-075-9984, 00-024-0030). The reflec- tions, which correspond to the calcium carbonate, are narrow and intense (compared to the cellulose peaks, the peaks are wider and of lower intensity), which indicates the high crystallinity of the used CaCO 3 . A lack of a significant effect of the fillers on the intensity and location of individual reflections was found, which may be attributed to the small amount of the additives. To define the thermal behavior of the paper samples, thermogravimetric analysis (TGA) was applied. The TGA results for the reference and the PEG/SiO 2 , PEG/TiO 2 , PEG/h-BN, and PEG/h-BN-OH papers are presented in Figure 7. For all samples, three significant weight decreases are noticeable. First, weight loss is observed at 90 ◦ Cand is attributed to the evaporation of the adsorbed water or moisture present in the samples. Furthermore, two stages of cellulose degradation are observed. The first decomposition stage starts at 250 ◦ C. Cellulose consists of glucose molecules linked together by β -1,4- glycosidic bonds [24]. During this stage, glycosidic bonds break, resulting in the release of volatile products and various volatile organic compounds, such as acetic acid and levoglucosan [25,26]. Next, a second decomposition stage starting at 350 ◦ C is observed. During this stage, additional volatile products are formed as cellulose decomposes. Carbon dioxide (CO 2 ) and carbon monoxide (CO) are released at this stage as a result of the
Made with FlippingBook Digital Proposal Creator