PHYSICAL-MECHANICAL AND IR SPECTRAL ANALYSIS OF MODIFIED POLYETHYLENE COATING FOR MAIN PIPES COATING

УДК 678.742:539.3

Abstract

In this study, the infrared (IR) spectroscopic analysis and mechanical properties of polyethylene (PE) composites modified with melamine cyanurate (MCA) and gossypol (GBNCO)-based nitrogen-containing oligomer were investigated.The composites were prepared by extrusion by adding 2 wt.% MCA and a gossypol-based nitrogen-containing oligomer to the PE matrix. IR spectroscopic analysis showed the appearance of new absorption regions at 1743 cm-1, corresponding to carbonyl groups, and at 1656 cm-1, corresponding to nitrogen-containing cyclic structures. The observed spectral changes confirm the physicochemical interaction between PE and the introduced modifiers, including the formation of hydrogen bonds and weak covalent interactions. These interactions contributed to changes in the supramolecular structure of the polymer matrix. Mechanical tests showed that the composite containing 2 wt.% GBNCO and MCA has the highest relative elongation value of 183% gThe improvement in properties can be explained by the plasticizing effect induced by the additives and the optimized intermolecular interactions. The results obtained show that GBNCO and MCA-based additives are effective modifiers for controlling the structural and mechanical properties of polyethylene composites. Furthermore, the developed modified polymer materials can serve as a promising basis for obtaining protective metal coating systems with improved performance characteristics.

Аннотация

В настоящей работе исследованы механические свойства и результаты ИК-спектроскопического анализа полиэтиленовых (ПЭ) композитов, модифицированных меламинциануратом (МЦА) и азотсодержащим олигомером на основе госсипола (АOHОГ). Композиты получали методом экструзии, вводя в полиэтиленовую матрицу 2 мас.% МЦА и азотсодержащего олигомера на основе госсипола. ИК-спектроскопический анализ показал появление новых полос поглощения при 1743 см^-1, соответствующих карбонильным группам, и при 1656 см^-1, соответствующих азотсодержащим циклическим структурам. Наблюдаемые спектральные изменения подтверждают физико-химическое взаимодействие между ПЭ и введенными модификаторами, включая образование водородных связей и слабых ковалентных взаимодействий. Эти взаимодействия способствовали изменениям в надмолекулярной структуре полимерной матрицы. Механические испытания показали, что композит, содержащий 2 мас.% АOHОГ и МЦА, имеет наивысшее значение относительного удлинения- 183%. Улучшение свойств можно объяснить пластифицирующим эффектом добавок и оптимизацией межмолекулярных взаимодействий. Полученные результаты показывают, что добавки на основе АOHОГ и МЦА являются эффективными модификаторами для управления структурно-механическими свойствами полиэтиленовых композитов. Кроме того, разработанные модифицированные полимерные материалы могут служить перспективной основой для получения защитных покрытий для металлов с улучшенными эксплуатационными характеристиками.

Keywords: composite coating, modified polyethylene, epoxy layer, inhibitor, metal pipe, IR spectrum, corrosion .

Ключевые слова: композитное покрытие, модифицированный полиэтилен, эпоксидный слой, ингибитор, металлическая труба, ИК-спектр, коррозия.

1. Introduction

 Polyethylene is one of the most widely used polymers due to its high chemical resistance, ease of processing, and low cost. However, its low resistance to thermal and photo-oxidation, as well as its flammability, limits its use in many engineering applications. For this reason, modifying PE with various organic and inorganic modifiers is considered an effective strategy for expanding its functional properties. Infrared (IR) spectroscopy is one of the most important tools in this field, as it allows for the observation of changes occurring in the molecular structure of polyethylene during the modification process, such as the appearance or disappearance of functional groups, the degree of oxidation, and changes in double bonds [1,2].

In an experiment conducted by Soudmand et al., FTIR spectroscopy was used to study the bonding characteristics within ultra-high molecular weight PE (UHMWPE) /nano-zeolite nanocomposites. [4].

Among natural and biosynthesized additives, gossypol (a pigment from the cotton plant) and its derivatives are distinguished by their strong antioxidant activity [5, 6, 7]. It has been found that gossypol-based oligomers, particularly derivatives obtained with epichlorohydrin (GECH), significantly improve the mechanical and thermal properties of the material when incorporated into a polyethylene matrix [8, 9]. A key feature of these compounds is that they contain nitrogen atoms, which imparts anti-corrosion and flame-retardant properties in addition to their antioxidant capabilities [10]. The mechanism of action of gossypol derivatives in PE is explained by their ability to scavenge free radicals and to form cross-linked bonds by altering the supramolecular structure of the polymer. Research indicates that the degree of cross-linking in low-density PE stabilized in the presence of technical gossypol (TG) increases, which enhances the strength of the composite [11,12].

Another relevant direction for modifying PE is increasing its fire resistance. Melamine cyanurate (MCA) is gaining significant attention as a halogen-free and environmentally safe fire-retardant additive [13, 14, 15]. The mechanism of action of MCA in PE is based on its endothermic decomposition and the release of inert gases, resulting in the formation of a dense and stable coal layer on the polymer surface [16]. In particular, synergistic mixtures of MCA with other flame retardant additives (e.g., piperazine pyrophosphate or ammonium polyphosphate) can provide PE composites with UL-94 V-0 levels and a high limiting oxygen index (LOI) [13,14]. In this regard, in recent years, the combined use of nitrogen-containing gossypol oligomers and melamine cyanurate has been considered a promising solution to satisfy several requirements, such as extending the service life of polyethylene (antioxidant properties) and ensuring its fire safety (fire resistance).

2.1. Synthesis of a complex inhibitor consisting of melamine cyanurate and gossypol

To prepare a modified polyethylene composite material, melamine cyanurate was initially synthesized. A heat-resistant glass container, a glass rod, porcelain lime, a laboratory mixer, and analytical scales were used in the experiment. Melamine and cyanic acid were taken in a 1:3 mass ratio, placed in a heat-resistant glass container, and thoroughly mixed. The mixture was heated at 70°C for 30 minutes. Then the reaction medium was cooled to 50°C, and the resulting product was filtered and washed. The final product was dried at a temperature of 100°C. At the next stage of preparing the composite material, the synthesized melamine cyanurate was crushed and mixed with other components in a specific ratio. Crushed gossypol was placed in a special container. Gossipol was heated to the melting point and melamine cyanurate was added to it. The process was carried out at a temperature of 165°C for 1 hour.At this stage, a complex inhibitor consisting of a nitrogen-containing oligomer based on melamine cyanurate and gossypol was synthesized.

2.2. Obtaining a modified polyethylene composite

A complex inhibitor consisting of melamine cyanurate and gossypol was thermally mixed with polyethylene in various proportions using an extruder. As a result, modified polyethylene materials were obtained. The melamine cyanurate-based modifier included in the modification served to improve the thermal stability, mechanical strength and fire resistance properties of the material.

2.3. Fourier Transform Infrared Spectroscopy

The chemical and structural properties of the composite materials were studied using Fourier Transform Infrared (FTIR) spectroscopy on a SHIMADZU IRTracer-100. The spectra were recorded in the range of 4000-400 cm-1 with a resolution of 4 cm-1 and a set of 32 scans for each sample.

2. Each sample was mechanically tested 3 times and the maximum result was obtained. Mechanical tests were carried out on an AGS-X universal testing machine. The maximum load capacity of the machine was 10 kN and was used to determine the tensile properties of polymer and composite materials. During the test, the total length of all samples was 7.5 mm and during the test they were fixed in holders, the test length was 55 mm, the width was 5 mm and the thickness was 2.5 mm. The samples were fixed in special clamps and subjected to elongation at a specified speed of 30 mm/min. As a result of the test, the tensile strength of the samples and the relative elongation at break were determined. The measurements were automatically recorded using a computer program and stress-strain diagrams were obtained.

a)                                                                                     b)

Figure 1. a-Physical and mechanical test samples of polyethylene modified with 2% MCA and GBNCO and b- physical-mechanical testing process

All samples had a total length of 7.5 mm, and during the testing process they were clamped in the grips, with a test length of 55 mm, a width of 5 mm, and a thickness of 2.5 mm (Fig. 1).

3. Results and their discussion.

3.1. IQ-spektr measurement

Figure 2 shows the IR spectrum obtained on a SHIMADZU device, showing the main absorption lines characteristic of a sample of pure low-density polyethylene (LDPE). The intense peaks in the spectrum at 2914.44 cm⁻¹ and 2848.86 cm⁻¹ are attributed to the stretching vibrations of the aliphatic –CH₂– groups, confirming the hydrocarbon nature of the polyethylene chain. The absorption at 1462.04 cm⁻¹ is associated with the deformation vibrations of the –CH₂– groups, and is characteristic of the crystalline and amorphous parts of the polymer. The strong peaks in the regions of 729.09 cm⁻¹ and 719.45 cm⁻¹ are attributed to the vibrations of the methylene group, which are diagnostic for polyethylene.

a)                                                                           b)

Figure 2.  IR spectrum: a-PE va b-PE+2% MCA+ GBNCO

The presence of melamine cyanurate in Figure 2b is manifested by additional absorptions at 1743 cm⁻¹ (cyanurate ring bond), 1656 cm⁻¹ (C=N, N–H deformation or triazine ring vibration), 1367, 1078, 1031 cm⁻¹ (C–N, C–O, N–H). The nitrogen-containing oligomer shows the presence of bonds at 1656, 1367 and 775 cm⁻¹ (N–H, C–N). The peaks at 615 and 586 cm⁻¹ are traces of N–H or ring vibrations, confirming the successful introduction of modifiers. In general, the specific absorptions of PE-based melamine cyanurate and nitrogen-containing oligomer are clearly distinguished in the spectrum, which indicates that the material has been modified to enhance its corrosion resistance properties.

3.2. Physical and mechanical tests

These images were used to determine the mechanical stress and relative elongation, mechanical strength, and elastic modulus of the modified polyethylene.

a)                                                               b)

Figure 3. Mechanical stress and elongation properties of modified polyethylene: a-PE and b-PE+2% MCA+ GBNCO

We have visually analyzed the mechanical stress and elongation properties of the modified polyethylene in Figure 3a. Each sample was mechanically tested 3 times and the maximum result was obtained.The first sample consists of only unmodified PE, the maximum stress reached 12.24 MPa and the elongation was 12.5 mm. This shows that PE is very elastic. The second sample, Figure 3b, PE+2% MCA+ GBNCO, has an increased stiffness, the maximum stress reached 8.5 MPa, while the elongation was 10.1 mm. Literature analysis shows that the added fillers or corrosion inhibitors increase the density of the PE coating, which in turn affects its elongation. In the obtained figure, the elongation of the unmodified polyethylene is almost 1.2 times lower than that of the modified polyethylene sample, but the stiffness is higher because the added corrosion inhibitor increases the tensile strength of the coating.

5. Conclusion

This study investigated composite materials based on polyethylene (PE) modified with melamine cyanuret and nitrogen-retaining oligomer. The physical and mechanical properties of the obtained modifications were analyzed.

The results of the relative elongation indicate the following mechanical properties of the PE-based modifications, namely, MCA and GBNCO additives increase the mechanical strength of the polymer material, but a high filler content reduces elasticity. The density of the material and its mass increased, which allows it to be used as a corrosion-protective coating for main pipelines. The optimal result was observed at 2% MCA and GBNCO, the material has strong and moderate elastic properties.

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