*3.4. Bioactive Compound Preparation*

The carvacrol (Sigma Aldrich, Hamburg, Germany) was used as an antimicrobial compound. The ratio between the polymer and carvacrol was 2:1. The freeze–dried gels were immersed into a carvacrol solution and immersion was realized by diffusion mechanism. All the liquid was adsorbed into a polymer matrix.

#### *3.5. Characterization of PITAU–Alg Gels*

#### 3.5.1. FT–IR Spectra

FT–IR spectra of the synthesized samples (S1, S2, S3) were recorded on a Vertex Bruker Spectrometer (Germany) in an absorption mode ranging from 400 to 4000 cm−<sup>1</sup> . The samples were grounded with potassium bromide (KBr) powder and compressed into a disc for analysis. The spectra were generated at 4 cm−<sup>1</sup> resolution with an average of 64 scans.

#### 3.5.2. SEM Studies

The microstructural architecture of the samples was analyzed using SEM microscopy. The freeze-dried samples were examined by using a scanning electron microscope (Quanta 200). According to the cross–sectional SEM pictures, the hydrogels displayed a continuous and porous configuration acquired after freeze-drying.

#### 3.5.3. Thermal Analysis

Thermogravimetric behavior of the samples was studied in dynamic conditions using a STA 449 F1 Jupiter apparatus (Netzsch, Germany) in a nitrogen atmosphere with a 10 ◦C min−<sup>1</sup> heating rate, in the temperature range of 30–650 ◦C. Samples of 10–15 mg were placed in Al2O<sup>3</sup> crucibles, and Al2O<sup>3</sup> was used as reference material. The gases appearing by the thermal degradation of the samples were analyzed using an online connected spectrophotometer FT–IR (Vertex 70) equipped with an external module TGA– IR and Aëolos QMS 403C mass spectrometer. The acquisition of FT–IR spectra in 3D was

executed with OPUS 6.5 software, with spectra recorded at 600–4000 cm−<sup>1</sup> intervals, at a resolution of 4 cm−<sup>1</sup> . The QMS 403C spectrometer worked at 10–5 mbar vacuum and electron impact ionization energy of 70 eV. The data acquisition was achieved in the range *m*/*z* = 1–200 with a measurement time of 0.5 s for one channel, resulting in a time/cycle of 100 s.
