PSI - Issue 68

Krastena Nikolova et al. / Procedia Structural Integrity 68 (2025) 845–853 K. Nikolova et al. / Structural Integrity Procedia 00 (2025) 000–000

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3. Results and discussion 3.1. FT-IR analysis FT-IR spectroscopy was used to assess the intermolecular interactions between the chitosan, pectin, alginate and Hydroxypropyl Methylcellulose and the oil from tea three. The chitosan-containing film displayed a characteristic band between 3000 and 3050 cm -1 , which is due to the OH and NH 2 stretching – Fig. 1. The band around 1635 cm -1 is attributed to C-O acetyl group stretching, and the one around 1255 cm-1 – to CS tension bands (Chan-Matú et al., 2021).The OH and CH group bending vibration in chitosan is around 1400 cm -1 (Myong Kim et al., 2006). The band around 850 cm -1 is caused by the glycoside bond in chitosan (Islam and Yasin 2012, Pawlak and Mucha 2003, Zivanovic et al. 2007, Souza et al. 2011, Dilamian et al. 2013). The addition of tea three oil leads to a significant increase in the intensity of the bands around 850 cm -1 . This is attributed to the symmetrical spatial arrangement of the oil in the polymer matrix (Rambabu et al. 2019). The presence of oil molecules affects the spatial arrangement in the polymer chain. A characteristic band around 1736 cm -1 can be observed in the film sample of chitosan and oil from tea three. This can be conceptualized with the presence of phenolic compounds in the essential oil, which in turn affects the C=O carbonyl stretching vibration (Talón et al. 2017) The addition of oil from tea three to the chitosan film leads to a shift of the bands around 2096 cm -1 and 3050 cm -1 to higher wavenumbers - 2116 cm -1 and 3650 cm -1 respectively. This tendency has been observed by other authors in the literature (Stoica et al. 2015).

Fig. 1. FT-IR spectra of chitosan-based films.

Fig. 2. FT-IR spectra of alginate-based films.

The alginate-containing film displays the following characteristic absorption bands (Bhatia et al. 2022): C-H alkyl group stretching around 2950 cm -1 ; C=C group stretching around 1600 cm -1 ; O-H bending vibration around 1400 cm 1 . Apart from these absorption bands a sharp peak around 950 cm -1 – 1110 cm -1 can also be observed. The latter could be attributed to the C-O-C stretching from the glycoside bonds. This band is also attributed to the C-N stretching and N-H bending vibrations by Jafari et al. (2023). Other authors explain this peak with the binding between galacturonic carbohydrate moieties (Shahbazi 2018; Avila-Sosa et al. 2016, Ramírez et al. 2012, Guillen & Cabo 2000, Mishra et al. 2011, Rezvanian et al. 2016). The asymmetric vibration of carboxylate groups gives rise to an absorption band around 1600 cm -1 . This can be seen in the chitosan and oil from tea three film, but with lower intensity. As with the chitosan film an absorption band around 1736 cm -1 can be observed, most probably due to the phenolic compounds present in the film. Other authors explain this band with the presence of ester groups (Kurita et al. 2008) The vibrations at 2170 cm -1 are due to monosubstituted terminal alkyne С=С (Nandiyanto et al. 2019). The addition of essential oil from tea three