ANALYSIS OF PROPERTIES AND SYNTHESIS OF HYDROGELS ENRICHED WITH MINERAL FERTILIZERS BASED ON NATURAL POLYMERS

ABSTRACT

In this work, hydrogels enriched with highly swelling mineral fertilizers were synthesized on the basis of natural polymer carboxymethylcellulose. The physicochemical properties of the synthesized hydrogel were studied. The methodology of the synthesis process was also investigated. In the analysis of the synthesized hydrogel, it was found that the hydrogel absorbs salt solutions of different concentrations affecting its swellability. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the synthesized hydrogel were carried out. In addition, the results obtained by infrared spectroscopy (IR) were analyzed. The degree of swelling of the synthesized hydrogel was compared with conventional hydrogels. The advantages of hydrogels enriched with mineral fertilizers are presented.

АННОТАЦИЯ

В данной работе на основе природного полимера карбоксиметилцеллюлозы синтезированы гидрогели, обогащенные высоконабухающими минеральными удобрениями. Изучены физико-химические свойства синтезированного гидрогеля. Также исследована методология процесса синтеза. При анализе синтезированного гидрогеля было установлено, что гидрогель поглощает растворы солей различной концентрации, что влияет на его набухаемость. Были проведены термогравиметрический анализ (ТГА) и дифференциальный термический анализ (ДТА) синтезированного гидрогеля. Кроме того, были проанализированы результаты, полученные с помощью инфракрасной спектроскопии (ИК). Степень набухания синтезированного гидрогеля сравнивалась с обычными гидрогелями. Представлены преимущества гидрогелей, обогащенных минеральными удобрениями.

Keywords: hydrogel, carboxymethylcellulose, methylenebisacrylamide, sodium hydroxide, infrared spectroscopy, thermogravimetric analysis, differential thermal analysis, degree of swelling.

Ключевые слова: гидрогель, карбоксиметилцеллюлоза, метиленбисакриламид, гидроксид натрия, инфракрасная спектроскопия, термогравиметрический анализ, дифференциально-термический анализ, степень набухания.

Introduction. At present, as a result of increasing demand for water resources in our republic, the need for water-saving polymeric substances capable of retaining water and delivering it to plants through the root system in a timely manner is sharply increasing. At present, there are different types of such polymers, differing from each other in composition and functional purpose. Hydrogels are three-dimensional polymers capable of absorbing and retaining large amounts of water, which are obtained by cross-linking natural and synthetic polymers with the help of binders.

Research methodology. Materials and reagents used: carboxymethylcellulose - basic polymer, n,n-methylenebisacrylamide - crosslinking agent, ammonium persulfate - initiator for the reaction, urea and potassium chloride - nitrogen and potassium fertilizer filler, sodium hydroxide for neutralization. Heating oven with controlled temperature, heat-resistant beaker of 500 ml volume, stirrer.

Synthesis method: First, a 5% solution of CMC was prepared and stirred continuously until completely dissolved at 70°C. The solution was then poured into a wide glass container and dried completely at 85-90°C. The resulting film was pulverized and prepared for use in hydrogel synthesis. The obtained film substance was thoroughly pulverized. Then the crushed CMC was placed in a beaker, distilled water was added in an amount of 30% of the total mass of the raw material and mixed, then neutralized with 18% sodium hydroxide solution. Neutralized mixture is heated to 70 ° C and with constant stirring added binder n,n-methylenebisacrylamide, then as an initiator added a small amount of ammonium persulfate and continue the process of stirring. One hour after the addition of the initiator, a gel-like substance begins to form, at which point a pre-crushed mixture of urea and potassium chloride is added in an amount of 18% by weight of the initial polymer, and the process continues for another 20 minutes. After completion of the process, the finished hydrogel is placed in a special container, dried to a constant mass and ready for use. One hour after the addition of the inhibitor, a gel-like substance begins to form, while 18% of the weight of the initial polymer was added from a pre-crushed mixture of urea and potassium chloride and the process continued for another 20 minutes.

The following reactions occur in this process:

Analysis of the synthesized hydrogel: The synthesized hydrogel was subjected to infrared spectroscopic, thermogravimetric and differential thermal analysis.

IR spectroscopic analysis. The synthesized hydrogel was swollen in water, then dried and ground for IR analysis using SHIMADZU FTIR. The results obtained were analyzed and the peaks characteristic of the corresponding functional groups were identified. The IR spectrum was analyzed as follows.

Figure 1. Infrared spectrum of the synthesized hydrogel

IR spectrum analysis and identification of functional groups: 3271.72 cm^-1 - O-H and N-H valence vibrations indicating the presence of hydrophilic groups in the hydrogel composition. 2914.44 cm^-1 - aliphatic C-H valence vibrations (indicating the presence of polysaccharides and organic components). 2308.97 cm^-1 is the absorption peak of CO₂, indicating its formation by some cross-linking reactions in the hydrogel. 1716.05 cm^-1 - valence vibrations of C=O (carbonyl group), confirming the participation of formaldehyde or urea in the reaction. 1593.20 cm^-1 - N-H strain vibrations indicating the presence of amine or amide groups 1411.98 cm^-1 - C-N valence vibrations, which is evidence of polymer crosslinking processes. 1076.32 cm^-1 - valence vibrations of C-O-C ester groups, which may be present in CMC (carboxymethylcellulose). 1014.56 cm^-1 - valence vibrations of C-O, confirming the presence of polysaccharides and other oxygen-containing groups. 789.86 cm^-1, 657.37 cm^-1, 595.60 cm^-1 - valence vibrations of KCl or other inorganic components indicating the presence of natural mineral components (potassium chloride and others) in the hydrogel composition.

Conclusion: The presence of O-H and N-H valence vibrations means that the hydrogel has hydrophilic properties. C-O-C and C-O valence vibrations confirm the presence of CMC components and polysaccharides. KCl and other inorganic vibrations are natural minerals within the hydrogel.

TGA and DTA analysis of the synthesized hydrogel: the crushed synthesized hydrogel was heated to 600 °C in an inert argon atmosphere and the mass loss and energy absorption were determined.

Figure 2. TGA and DTA analysis of the hydrogel prepared on the basis of carboxymethylcellulose and N,N-methylenebisacrylamide

From the above TGA and DTA analysis, it can be seen that when the synthesized hydrogel was heated to 600 °C in argon atmosphere, a two-fold mass loss and a one-fold energy absorption were observed, the reasons for which are given below.

A twofold mass loss was observed during TGA.

Table 1.

TGA analysis of hydrogel containing urea and potash fertilizer

If we pay attention to the above table, we can notice that the mass loss is insignificant: this mass is mainly due to water and urea in the hydrogel composition, and at the second mass loss the decomposition of the hydrogel molecule occurs with the formation of hydrolyzed polyacrylonitrile, which corresponds to the fraction of gases released during its decomposition.

If we consider the DTA analysis, there is one peak in the analysis at which energy absorption is observed.

Table 2.

DTA analysis of hydrogel containing urea and potassium fertilizers

If we pay attention to the table, energy absorption was observed at a sufficiently high temperature, with energy absorbed to split the hydrogel molecule into its constituents.

Table 3.

Analysis of the results of TGA and DTA curves of hydrogel containing NPK-fertilizers

Analyzing the TAG and DTA curves, the following conclusion was made: the mass loss at temperatures up to 200 °C was caused by the evaporation of water and urea from the hydrogel. Between 200 °C and 300 °C, a fairly high stability of the hydrogel was observed, with very little mass loss and mainly due to the removal of impurities from the added fertilizers. At temperatures above 300 °C, the mass loss increases significantly due to the breakdown of the hydrogel molecule and the release of various gases from the hydrogel. As can be seen from the table, the hydrogel loses more mass in the range of 300-500 °C, which means the complete decomposition of the hydrogel in this interval. Above 500 °C, the mass loss is due to gases released by the decomposition of the remaining residue and carbonization of the remaining organic matter.

The degree of swelling of the synthesized hydrogel was determined: the influence of time, mass ratio of components, amount of binding reagent on the swelling of hydrogel obtained on the basis of CMC, N,N-methylenebisacrylamide, urea and potassium fertilizers was studied. The results obtained are presented in table 1 below.

Table 4.

Effect of time on swellability of hydrogel based on CMC and N,N-methylenebisacrylamide

From the data in the table, it was concluded that the maximum swelling degree of the hydrogels obtained based on CMC, and N,N methylenebisacrylamide, carbide and potassium fertilizer is 578 g/g. In addition, it was found that the swelling time of the obtained hydrogel was found to be slower compared to the other hydrogels. However, despite this disadvantage, a higher degree of swelling could be observed compared to the synthesized hydrogels containing mineral fertilizers. For comparison, the swelling degree of hydrogel derived from hypane and enriched with ammaphos and ammonium polyphosphate is 245 g/g. In short, the physicochemical properties of the synthesized hydrogel do not differ practically from other similar hydrogels.

Conclusion. The results of thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of hydrogel enriched with synthesized mineral fertilizers were obtained and analyzed. According to the analysis results, the obtained hydrogel was found to be resistant to high temperatures, which expands its applications. Using IR spectroscopic analysis, it was confirmed that the reaction did take place and the functional groups that were not involved in the reaction were retained even after the reaction was completed. The significant positive effect of this hydrogel on the degree of swelling can be observed by the high values of this parameter. Mineral fertilizers added to the hydrogel do not bind directly to it, but are located between its three-dimensional networks, forming pores of varying degrees, which causes a high degree of swelling of the synthesized hydrogel. As a result, the synthesized hydrogel in an optimal state can be used in many applications.

References:

1. Ibroximov M.A., Shirinov Sh.D. tarkibida npk saqlagan gidrogellar sintezi va tahlili, development of science volume 2 2025 aprel 143-bet.
2. Amezqueta, S., Subirats, X., Fuguet, E., Rosйs, M., & Rаfols, C. (2020). Octanol-Water Partition Constant. Liquid-Phase Extraction, 183–208. doi:10.1016/b978-0-12-816911-7.00006-2
3. Omirova, R. Z., Bolysbek, A. A., Shirinov, Sh. D., Dzhalilov, A. T. Synthesis and research of polymer hydrogels on the basis of hydrolysed polyacrylonitrile and epichlorhydrin. Rasayan Journal of Chemistry, (2019). 12(4), 2047-2051. [CrossRef]
4. Wang C. Y., Zhao N. U., Huang Y. X., He R., Xu S. C., Yuan W. Z., Chem. Eng. J., 2020, vol. 401 pg. 126100 Google^* Scholar
5. Li L. Y., Zeng Z. H., Chen Z. X., Gao R. Y., Pan L. T., Deng J. J., Ye X. H., Zhang J., Zhang S. J., Mei C. Y., Yu J. J., Feng Y. F., Wang Q. M., Yu A. Y., Yang M., Huang J. H. , ACS Nano, 2020, vol. 14 (pg. 15403-15416) Google* Scholar PubMed
6. Zoratto N., Matricardi P. , Adv. Exp. Med. Biol., 2018, vol. 1059 (pg. 155-188) Google* Scholar PubMed
7. Marapureddy S. G., Hivare P., Sharma A., Chakraborty J., Ghosh S., Gupta S., Thareja P., Carbohydr. Polym., 2021, vol. 269 pg. 118254 Google* Scholar PubMed

*По требованию Роскомнадзора информируем, что иностранное лицо, владеющее информационными ресурсами Google является нарушителем законодательства Российской Федерации – прим. ред.