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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leads to a shift of the band at 2167 cm -1 to 2160 cm -1 , which has been observed previously by other authors for alginate films (Bhatia et al. 2022). In the IR spectrum of the pectin film displays several bands at 2920 cm -1 , 1743 cm -1 , 1623 cm -1 , 1380 cm -1 , 930 cm -1 . The peak at 2920 cm -1 is caused by С-Н stretching vibrations of methyne groups in polymer chains (Nisar et al. 2018). The carboxyl groups characteristic absorbance bands are observed around 1623 cm -1 and 1380 cm -1 (Oliveira et al. 2016) The spectral differences between the pectin and this with pectin and oil from tea three films are probably caused by the different conformations and spatial orientation of the polypeptide chains. The vibrations around 1623 cm -1 and 1743 cm -1 are due to С-О stretching in the deprotonated carboxylate and ester groups. (Chaharbaghi et al. 2017). The decrease in the intensity of these bands is likely caused by chemical interactions between the essential oil components and the pectin.

Fig. 3 FT-IR spectra of HPMC-based films.

Fig. 4. FT-IR spectra of pectin-based films.

3.2. Film morphology Scanning electron microscope images of polymer films before (left hand side) and after oil (right hand side) incorporation in them are shown in Fig. 5. The obtained morphology of these images indicates rather smooth and regular morphology of native films for all films, beside the chitosan-based one. But still, it can be concluded that the formed polymer films are consisted of continues structures formed during the drying step (Sánchez-González et al. 2010). Addition of oil has led to formation of different discontinues in the film structure. In the cases of alginate and pectin films, oil droplets have distributed rather evenly within the polymer matrix, forming a stable emulsion. When these images are compared to other authors publications regarding pectin and alginate films with incorporated oils, it can be concluded that worsening in the morphology at oil concentrations higher than 1% w/v lead to micro pores formation. While in the present study homogenous morphology is present even at higher oil concentrations, probably due to the chosen concentration of Tween 20 in the starting emulsion, resulting in better oil-polymer solution stability (Nisar et al. 2018). About chitosan and HPMC films containing tea tree oil, formation of bigger droplets and even voids in the film structure are present. This observation suggests that for these polymers, during the drying process oil drops started migrating nearer to the drying surface as a result of greater flocculation and coalescence (Sánchez González et al. 2010). It can be concluded that the viscosity of these two polymer solutions wasn’t sufficiently high to stabilize the oil droplets, resulting in higher creaming effect during drying the film (Sanchez-Gonzalez et al. 2010).