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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2.2. Formulation of empty polysaccharide films Chitosan, pectin, and sodium alginate films were prepared in an identical manner as follows. 1% of the polysaccharide was dissolved overnight at room temperature in deionized water containing 0.15 % (v/v) glycerol and 0.5 % (v/v) Tween 20. The the solution was casted in glass Petri dishes (d = 100 mm), and dried in an oven (Faithful Technology Park, Cangzhou, China) at 30 °C for 12 h. 1 g HPMC and 0.15 g glycerol were mixed with 100 mL deionized water, using a magnetic stirrer at 80 °C for 1 h. Then the solution was cooled down room temperature, cast on a glass petri dishes (d =100 mm), and dried in an oven at 30 °C for 12 h. The resulting dry films were stored in a desiccator at a relative humidity of 55% for further use. 2.3. Preparation of tea tree oil (TTO) emulsion The tea tree oil (TTO) emulsion was prepared using 10% w/w TTO, 10% w/w Tween 20, used as an emulsifier, and 80% w/w deionized water. The compounds were stirred for 3 min at 3000 rpm and a temperature of 25 °C with the use of a PV-1 Vortex Mixer (Grant Instruments, Chelmsford, UK). The resulting mixture was ultrasonicated for 3 min using UP100H—Compact Ultrasonic Laboratory Device (Hielscher Ultrasonics GmbH, Teltow Germany. 2.4. Preparation of polysaccharide films loaded with TTO emulsion The prepared TTO emulsion was added to the 1 % solutions of polysaccharides described in point 2.2 and sonicated for 5 min. Then the final emulsion was degassed for 30 min in an ultrasound bath (BANDELIN electronic GmbH & Co. KG, Berlin, Germany), cast in glass Petri dishes (d = 100 mm), and dried in the same way, as the empty films. 2.5. FT-IR spectroscopy Using a Thermo Fischer Nicolet iS50 spectrometer, the infrared spectra of films made from pectin, HPMC, chitosan, alginate, and these with TTO contained in them were recorded. An ATR module with a diamond crystal was used to record the infrared spectra of the film's constituent parts, and a typical magnetic film holder was used to record the film's spectra in transmission mode. 2.6. SEM Philips 515, digitized scanning electron microscope was used for studying the surface morphology of the films. A preliminary preparation of the samples was applied and a very thin gold-paladium coatings have been deposited on their surfaces. The visualization was held at 8 kV accelerating voltage. 2.7. Mechanical testing The tensile properties of the films were examined using an LS1 universal testing machine (Lloyd Instruments Ltd., Bognor Regis, UK) according to standard ASTM D882-91 (2017). Film strips (width: 10 mm, length: 100 mm, instrument gap: 50 mm) were fastened with rubber sealed pneumatic clumps and subjected to a load with a constant deformation rate of 1 mm/s up to breaking. The tensile modulus, the stress and strain at the break were analyzed. 2.8. Statistical Analysis The experimental results were statistically analyzed by the ANOVA function of Statistica software (TIBCO Software Inc. ver. 14, Palo Alto, CA, USA).