**3. Results and Discussion**

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The gelation time was determined by the loss of stickiness time [27].

The water absorption of hydrogel film samples in cold water was carried out ac-

Antibacterial properties were determined by the inhibition time of the active growth zones of *Aspergillus niger* (A. niger) molds on the surface of HESBHM in a nutrient medium using an electronic microscope, the Digital Microscope HD color CMOS

The method described in ISO 846:1997 was used to measure the degree of biodeg-

*3.1. Rheological and Physical Studies of the Mechanism of Hybrid Modification of Hydroxypropyl Methylcellulose Hydrogels with Humic Acids 3.1. Rheological and Physical Studies of the Mechanism of Hybrid Modification of Hydroxypropyl Methylcellulose Hydrogels with Humic Acids*

The HESBHM conditional viscosity and conductivity dependence of hydroxypropyl methylcellulose on different humic acid contents is shown in Figure 1. The HESBHM conditional viscosity and conductivity dependence of hydroxypropyl methylcellulose on different humic acid contents is shown in Figure 1.

**Figure 1.** The HESBHM conditional viscosity (ν, s), conductivity dependence, and conductivity (μ, mkS/cm) of hydroxypropyl methylcellulose on the different humic acid contents. **Figure 1.** The HESBHM conditional viscosity (ν, s), conductivity dependence, and conductivity (µ, mkS/cm) of hydroxypropyl methylcellulose on the different humic acid contents.

From the data in the Figure 1 it can be seen that there is an increasing HESBHM conditional viscosity and specific electrical conductivity with an increase in humic acid content: from 1200 to 1650 s and from 1630 to 2950 mkS/cm, respectively. Such changes indicate the following effects in terms of modification by humic acids on the structure From the data in the Figure 1 it can be seen that there is an increasing HESBHM conditional viscosity and specific electrical conductivity with an increase in humic acid content: from 1200 to 1650 s and from 1630 to 2950 mkS/cm, respectively. Such changes indicate the following effects in terms of modification by humic acids on the structure formation processes of HESBHM:


The formation of a larger number of agglomerates in the HESBHM is clearly visible from the microscopic studies results (Figure 2): unmodified hydroxypropyl cellulose-sodium alginate systems are homogeneous solutions without visible streaks and The formation of a larger number of agglomerates in the HESBHM is clearly visible from the microscopic studies results (Figure 2): unmodified hydroxypropyl cellulosesodium alginate systems are homogeneous solutions without visible streaks and inhomogeneities both on the surface and in the volume. At the same time, with an increase in humic acid content, the appearance of visible streaks and inhomogeneities both on the surface and in the volume in the HESBHM occurs.

inhomogeneities both on the surface and in the volume. At the same time, with an increase in humic acid content, the appearance of visible streaks and inhomogeneities both

on the surface and in the volume in the HESBHM occurs.

**Figure 2.** Microscopic studies of HESBHM: (**A**) pure hydroxypropyl methylcellulose and sodium alginate hydrogel; (**B**) hydroxypropyl methylcellulose and sodium alginate hydrogel + 5% wt. of humic acid; (**C**) hydroxypropyl methylcellulose and sodium alginate hydrogel + 10% wt. of humic acid; (**D**) hydroxypropyl methylcellulose and sodium alginate hydrogel + 15% wt. of humic acid. **Figure 2.** Microscopic studies of HESBHM: (**A**) pure hydroxypropyl methylcellulose and sodium alginate hydrogel; (**B**) hydroxypropyl methylcellulose and sodium alginate hydrogel + 5% wt. ofhumic acid; (**C**) hydroxypropyl methylcellulose and sodium alginate hydrogel + 10% wt. of humic acid; (**D**) hydroxypropyl methylcellulose and sodium alginate hydrogel + 15% wt. of humic acid.

Furthermore, the IR spectra of the original humic acid, original hydroxypropyl methylcellulose, and hydroxypropyl methylcellulose systems (5% by mass) were investigated by IR analysis (Figure 3 and Table 2). It was found that these functional groups determine the humic acid's ability to act as a hybrid modifier in relation to hydroxypropyl methylcellulose. Among the most characteristic humic acid spectral bands are: phenolic –OH hydroxyl groups at 3380–3400 cm−<sup>1</sup> , aliphatic bands C–H at 2920–2940 cm−<sup>1</sup> , symmetric νCOO– carboxyl and νCO (phenolic), and νOH (aliphatic) at 1100 cm−<sup>1</sup> . The IR spectra of the hydroxypropyl methylcellulose–5% wt. of humic acid, characteristic bands from hydroxypropyl methylcellulose and humic acid are clearly observed, for example, a hydroxyl band at 3100–3600 cm−<sup>1</sup> , a methyl band at 2750–2900 cm−<sup>1</sup> , an aromatic C–C band at 1400 and 1600 cm−<sup>1</sup> , a carboxyl band at approximately 1500–1650 cm−<sup>1</sup> , and the C–O band at 1000–1150 cm−<sup>1</sup> [29]. Compared with the IR spectra of hydroxypropyl methylcellulose and humic acid, there was a significant difference in the IR spectrum of the hydroxypropyl methylcellulose–5 wt% system of humic acid: a band of carboxyl groups of hydroxypropyl methylcellulose systems–5% by mass of humic acid at 1595 cm−<sup>1</sup> shifts to wave numbers 1625–1650 cm−<sup>1</sup> . Additionally, it can be seen that there were increases in the formation of hydrogen bonds due to modification, as evidenced by the shift of the hydroxyl band at 3100–3600 cm−<sup>1</sup> and C–O band at 1000–1150 Furthermore, the IR spectra of the original humic acid, original hydroxypropyl methylcellulose, and hydroxypropyl methylcellulose systems (5% by mass) were investigated by IR analysis (Figure 3 and Table 2). It was found that these functional groups determine the humic acid's ability to act as a hybrid modifier in relation to hydroxypropyl methylcellulose. Among the most characteristic humic acid spectral bands are: phenolic –OH hydroxyl groups at 3380–3400 cm−<sup>1</sup> , aliphatic bands C–H at 2920–2940 cm−<sup>1</sup> , symmetric νCOO– carboxyl and νCO (phenolic), and νOH (aliphatic) at 1100 cm−<sup>1</sup> . The IR spectra of the hydroxypropyl methylcellulose–5% wt. of humic acid, characteristic bands from hydroxypropyl methylcellulose and humic acid are clearly observed, for example, a hydroxyl band at 3100–3600 cm−<sup>1</sup> , a methyl band at 2750–2900 cm−<sup>1</sup> , an aromatic C–C band at 1400 and 1600 cm−<sup>1</sup> , a carboxyl band at approximately 1500–1650 cm−<sup>1</sup> , and the C–O band at 1000–1150 cm−<sup>1</sup> [29]. Compared with the IR spectra of hydroxypropyl methylcellulose and humic acid, there was a significant difference in the IR spectrum of the hydroxypropyl methylcellulose–5 wt%. system of humic acid: a band of carboxyl groups of hydroxypropyl methylcellulose systems–5% by mass of humic acid at 1595 cm−<sup>1</sup> shifts to wave numbers 1625–1650 cm−<sup>1</sup> . Additionally, it can be seen that there were increases in the formation of hydrogen bonds due to modification, as evidenced by the shift of the hydroxyl band at 3100–3600 cm−<sup>1</sup> and C–O band at 1000–1150 cm−<sup>1</sup> to the side by 50–100 cm−<sup>1</sup> .

.

cm−1 to the side by 50–100 cm−<sup>1</sup>

**Figure 3.** IR spectra of humic acids, hydroxypropyl methylcellulose, and hydroxypropyl methylcellulose–humic acids system: 1—hydroxypropyl methylcellulose; 2—humic acids; 3—hydroxypropyl methylcellulose +5% wt. humic acids, 4: hydroxypropyl methylcellulose +10% **Figure 3.** IR spectra of humic acids, hydroxypropyl methylcellulose, and hydroxypropyl methylcellulose– humic acids system: 1—hydroxypropyl methylcellulose; 2—humic acids; 3—hydroxypropyl methylcellulose +5% wt. humic acids, 4: hydroxypropyl methylcellulose +10% wt. humic acids.


**Table 2.** IR spectral characteristics of humic acids, hydroxypropyl methylcellulose, and hydroxypropyl methylcellulose–humic acids system. **Table 2.** IR spectral characteristics of humic acids, hydroxypropyl methylcellulose, and hydroxypropyl methylcellulose–humic acids system.

910 out-of-phase δCH (aromatic) Such changes in the IR spectra are evidence that humic acids react with hydroxy-Such changes in the IR spectra are evidence that humic acids react with hydroxypropyl methylcellulose through the multipoint interaction of their carboxyl groups with the hydroxyl groups of the polymer, with the formation of such a structure (Figure 4) [18].

1005 νCO

propyl methylcellulose through the multipoint interaction of their carboxyl groups with the hydroxyl groups of the polymer, with the formation of such a structure (Figure 4) [18]. Based on the research described above, a general scheme and mechanism for the formation in systems of hydroxypropylcellulose-sodium alginate hybrid modification with humic acids due to the formation of a more rigid network, the enhancement of agglomeration processes, additional supramolecular interactions between functional groups, and an increase in the number of hydrogen bonds are proposed. In fact, the given structure of the hydroxypropyl

wt. humic acids.

R1 "

> methylcellulose–humic acid system indicates that it is formed by the mechanism of matrix synthesis within the framework of the hybrid modification of the polymer. HPMC-HA

*3.2. Study of the Effect of Hybrid Modification of Hydroxypropyl Methylcellulose with Humic* 

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R2 " R2 R1 "

R2 "

R1

HA HPMC

"

**Figure 4.** The structure of the hydroxypropyl methylcellulose–humic acid system, which is formed by the mechanism of matrix synthesis: НА- humic acids, НPMC—hydroxypropyl methylcellulose. **Figure 4.** The structure of the hydroxypropyl methylcellulose–humic acid system, which is formed by the mechanism of matrix synthesis: HA—humic acids, HPMC—hydroxypropyl methylcellulose.

### Based on the research described above, a general scheme and mechanism for the formation in systems of hydroxypropylcellulose-sodium alginate hybrid modification *3.2. Study of the Effect of Hybrid Modification of Hydroxypropyl Methylcellulose with Humic Acids on a Set of Characteristics of Biodegradable Hydrogel Films Acids on a Set of Characteristics of Biodegradable Hydrogel Films*

with humic acids due to the formation of a more rigid network, the enhancement of agglomeration processes, additional supramolecular interactions between functional groups, and an increase in the number of hydrogen bonds are proposed. In fact, the given structure of the hydroxypropyl methylcellulose–humic acid system indicates that it is formed by the mechanism of matrix synthesis within the framework of the hybrid We have determined that hybrid modification by humic acid changes the most important characteristics of HESBHM: water absorption, gelation time, time of mold appearance, and degree of biodegradability. The graphical dependence of these indicators HESBHM based on hydroxypropyl methylcellulose and the humic acid content of humic acids is shown in Figure 5. We have determined that hybrid modification by humic acid changes the most important characteristics of HESBHM: water absorption, gelation time, time of mold appearance, and degree of biodegradability. The graphical dependence of these indicators HESBHM based on hydroxypropyl methylcellulose and the humic acid content of humic acids is shown in Figure 5.

**Figure 5.** Graphical dependence of water absorption and gelation time of HESBHM based on hydroxypropyl methylcellulose and the humic acid content.

From Figure 4, it can be seen that the hybrid modification of hydroxypropyl methylcellulose with humic acids by mechanism matrix synthesis when receiving biodegradable hydrogel films allows for a reduction in their water absorption by reducing the time of gelation.

The mold appearance time and the degree of biodegradation of HESBHM based on hydroxypropyl methylcellulose and the humic acid content are shown in Table 3.

**Table 3.** Characterization of the mold appearance time and the degree of biodegradation of HESBHM based on hydroxypropyl methylcellulose and the humic acid content.


In general, it was found that the hybrid modification with humic acids according to the mechanism of matrix synthesis of biodegradable hydrogel films based on hydroxypropyl methylcellulose allows for a reduction in their water absorption and gives them antibacterial properties, which is confirmed by the data on the mold appearance time in the films, while preserving their biodegradation properties. It is important to note that the optimal humic substances content for hydroxypropyl cellulose–sodium alginate systems is no more than 15% wt. With this content in terms of humic acids, good antibacterial properties are achieved, due to the complete inhibition of mold formation and sufficiently high levels of water absorption, and the gelation time of hydrogel films are ensured due to an additional supramolecular multipoint interaction occurring between functional groups in addition to hydrogen bonds.
