OBTAINING A NEW TYPE OF HYDROGEL BY POLYMERIZING FARPAN WITH FORMALIN AND VARIOUS ADDITIVES

ABSTRACT

The article presents the results of research on obtaining hydrogels from local raw materials. Hydrolyzed polyacrylonitrile (FarPAN) of Ferganaazot JSC, formaldehyde, sulfuric acid, organic acid and mineral fertilizers were used as initial products. The kinetics of the degree of swelling of the hydrogel and the influence of sulfuric acid on the process of polymerization of FarPAN with formalin was studied by IR spectroscopy.

АННОТАЦИЯ

Приведены результаты исследования получению гидрогелей нового типа из местного сырья. В качестве исходных продуктов использованы гидролизованный полиакрилонитрил (ФарПАН) АО «Ферганаазот», формальдегид, серная кислота, органическая кислота и минеральные удобрения. Исследована кинетика и степень набухания синтезированных гидрогелей. Методом ИК-спектроскопии изучено влияние серной кислоты на процесс полимеризации ФарПАНа с формалином.

Keywords: hydrolyzed polyacrylonitrile, formaldehyde, sulfuric acid, ammophos, NPK, humin, hydrogel, IR spectroscopy.

Ключевые слова: гидролизованный полиакрилонитрил, формальдегид, серная кислота, аммофос, NPK, гумин, гидрогель, ИК-спектроскопия.

Introduction. Global warming has set a number of urgent tasks for the world community, the main of which is the problem of irrigating crops in annually expanding arid areas with insufficient water supply. One of the effective solutions to this problem is the use of polymer hydrogels with high water-holding capacity. The wide practical application of hydrogels in agriculture makes it possible not only to achieve significant savings in water for irrigating plants, but also to reduce the consumption of fertilizers. In addition, the use of hydrogels contributes to the rational use of fresh water on the planet and the reduction of the harmful effects of fertilizers on the soil. An analysis of the relevant literature has shown that most of the hydrogels available on the market are made from polyacrylamide and polyacrylonitrile. However, they are not completely biodegradable, therefore they are themselves considered potential soil pollutants [1, 2].

Hydrogels are a group of polymeric materials whose hydrophilic structure makes them capable of holding large amounts of water in their three-dimensional networks. Widespread use of these products in a range of industrial and environmental applications is considered to be of paramount importance. Natural hydrogels have gradually been replaced by synthetic ones over time due to their higher water absorption capacity, long service life, and wide variety of raw chemical resources. The volume of scientific literature devoted to the study of hydrogels is expanding every year. In order to review and analyze the technological aspects covering this growing interdisciplinary area of research, publications and technical reports on hydrogel products are analyzed from an engineering point of view.

Statement of the problem of research and development. In a number of published works, on the basis of the main physicochemical characteristics, a classification of hydrogels was carried out, and the technical possibilities of their practical use were also studied. An updated category of latest generation hydrogel materials was also presented in some detail [3–6]. In previous works, the authors presented the results of studies of a number of reactions of FARPAN with various reagents containing hydrophilic groups in their composition [7-12].

In this article, the process of polymerization of FarPAN with formalin in the presence of sulfuric acid, as well as various additives, was studied. Thanks to a whole complex of scientific research, it was possible to synthesize a new effective and highly swellable polymer hydrogel based on locally available starting materials.

Analysis of the experiment and the results obtained. As a polymer product, hydrolyzed polyacrylonitrile (FarPAN) produced by Ferganaazot JSC was used, as well as other substances - formalin, organic acid (OA) and mineral additives. All of these materials are affordable, natural and non-toxic. The synthesis of hydrogels of a new type was carried out by the interaction of FarPAN with formalin with the addition of sulfuric acid. The reactions were carried out at a temperature of 75-80°C for 4 hours. in a 500 ml flask using a thermostatically controlled water bath. The synthesized hydrogels after cooling to room temperature were solid particles of various colors.

The main physicochemical parameters of the obtained hydrogels with various additives are given in Table. one.

Table 1.

Basic physical and chemical characteristics of gels

It should be noted that the unequal coloration of hydrogels is due to the use of different initial raw materials and components of different nature (Fig. 1).

Figure. 1. Appearance of hydrogels.

As is known, the degree of swelling is one of the most important physicochemical characteristics of hydrogels. The conducted studies of the swelling kinetics of various synthesized samples of hydrogels showed their unequal water-absorbing capacity (Fig. 2). Thus, it was found that sample No. 2 has the highest degree of swelling. The initial weight is 1 g. of this sample after swelling for 237 min. amounted to 17 gr., while the weight of sample No. 5 after swelling after 174 min. was equal to 12 gr.

To determine the effect of sulfuric acid on the polymerization of FARPAN with formalin, an IR spectroscopic analysis of the synthesized samples was carried out. IR spectra data were recorded on a ShimadzuIR-100 instrument (Japan).

Figure 2. Kinetics of swelling of hydrogels

The IR spectra of the obtained hydrogels show a broad peak of the О-Н wave at the level of 2926 and 2854 cm^-1, while the wave number of 1109 cm^-1 indicates the presence of the C-O group in the structure. The IR spectrum for phosphoric acid shows the presence of O-H groups at the peak wave number of 2926 cm^-1, while the wave number of 1707 cm^-1 indicates the presence of the C=O group, while the C=C groups have a wave number of 1647 cm^-1. The hydrogel contained formalin-crosslinked polyacrylonitrile in the main chain with side chains carrying carboxamide and phosphate functional groups, as evidenced by 3 new peaks at 1354, 1421 and 1147 cm^-1 (Fig. 3). These peaks are explained by C=O stretching in carboxamide functional groups, as well as symmetric and asymmetric stretching modes of carboxylate groups. During the interaction of acids, most of the nitrile groups are converted into carboxamide and carboxylate groups. Analysis of the IR spectra of the synthesized hydrogel samples showed the absence of a wave number indicating the presence of C=C groups in the product. This proves that the graft copolymerization reaction between FARPAN in the presence of sulfuric acid was successful and occurs in the urea group on acrylonitrile.

Scope of the results. The results of IR spectroscopic analysis showed that the OH group of sulfuric acid reacts with the carbamide group of FARPAN during the polymerization of hypan with formalin. The reaction of cross-linking with formalin between the polymer chain leads to the formation of a three-dimensional network, the cross-linking is also formed due to the cross-linking agent - formalin. The research results showed that the swelling of the synthesized hydrogel increases due to the presence of free hydroxyl groups of sulfuric acid, as well as urea groups.

Figure 3. Infrared spectra of the synthesized hydrogel

The main physical and chemical properties of new hydrogels have been studied, the swelling kinetics have been studied, and their IR spectra have been analyzed. A new type of hydrogels has been obtained with high water-retaining properties and the ability to retain mineral fertilizers. Hydrogels are environmentally friendly and contain the main nutritional and mineral components necessary for the growth and development of crops.

Conclusions. A comprehensive study of the properties of synthesized hydrogels based on available local raw materials and materials indicates the fundamental possibility of their successful use in agriculture in arid regions with insufficient water supply, as well as their effective use in hilly agricultural areas where it is difficult to carry out the necessary agrotechnical measures (irrigation, application of mineral fertilizers, etc.). etc.).

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