rus
Issue #5/2025
M.T.A. Al-Khalidi, A.N.Blokhin
STUDY OF THE EFFECT OF MODIFYING ALKYD ENAMEL PAINT ON ITS HEAT RESISTANCE, UV RESISTANCE, AND CHEMICAL RESISTANCE PROPERTIES
STUDY OF THE EFFECT OF MODIFYING ALKYD ENAMEL PAINT ON ITS HEAT RESISTANCE, UV RESISTANCE, AND CHEMICAL RESISTANCE PROPERTIES
https://doi.org/10.22184/1993-8578.2025.18.5.276.284
Although the use of nano-additives can improve the corrosion resistance of some organic coatings, it can lead to deterioration of other coating properties, such as resistance to thermal changes, ultraviolet radiation and chemicals. In this paper, the effect of carbon nanotubes coated with silicon oxide nanoparticles on the resistance to thermal changes, ultraviolet radiation and chemicals of alkyd enamel coating is investigated. To study these properties, a heat resistance test according to ASTM D573, a UV resistance test according to ASTM G155 and a chemical resistance test according to ASTM D5402-93 (1999) were conducted. The experimental results showed that the addition of nano-fillers led to an increase in resistance to chemicals with an increase in the mass concentration of nano-fillers to 0.349%, however, after this limit, the effect of chemicals on the paint increased, and the additive did not lead to a deterioration in resistance to thermal changes and ultraviolet radiation.
Although the use of nano-additives can improve the corrosion resistance of some organic coatings, it can lead to deterioration of other coating properties, such as resistance to thermal changes, ultraviolet radiation and chemicals. In this paper, the effect of carbon nanotubes coated with silicon oxide nanoparticles on the resistance to thermal changes, ultraviolet radiation and chemicals of alkyd enamel coating is investigated. To study these properties, a heat resistance test according to ASTM D573, a UV resistance test according to ASTM G155 and a chemical resistance test according to ASTM D5402-93 (1999) were conducted. The experimental results showed that the addition of nano-fillers led to an increase in resistance to chemicals with an increase in the mass concentration of nano-fillers to 0.349%, however, after this limit, the effect of chemicals on the paint increased, and the additive did not lead to a deterioration in resistance to thermal changes and ultraviolet radiation.
INTRODUCTION
Metal corrosion is a serious problem for many industries, especially in construction industry, as it significantly affects on safety of facilities and structures, not to mention the high costs associated with maintenance and repair work on these facilities [1, 2]. Therefore, scientists have endeavoured to find solutions to limit occurrence of this phenomenon.
The methods used to reduce corrosion of metals are diverse and these methods can be divided into several groups such as protective coatings [3], cathodic protection [4], alloying [5], surface pre-oxidation [6] and the use of anti-corrosion agents (inhibitors) [7].
Speaking of anticorrosion coatings, it is necessary to mention nanoanti-corrosion coatings, as advances in nanotechnology have enabled development of this category of coatings. Anticorrosion nanocoatings take advantage of specific properties possessed by materials consisting of nanoparticles, and their properties are very different from those when such substances are in bulk form [8].
It should be noted that although these nano additives improve corrosion resistance of the coating matrix, it must be ensured that they do not cause deterioration of other properties such as resistance to thermal changes, UV radiation and the action of chemicals, since exposure to these factors can lead to serious defects in the coating layer, which in turn leads to a weakening of the barrier effect of the coating layer and corrosive agents ingress onto the metal surface.
The aim of this work is to study the effect of modification of alkyd enamel coating on its heat resistance, UV resistance and chemical resistance.
RESEARCH METHODS
Materials
In this study, commercial alkyd enamel PF-115 (Factor LLC, Russia) was used as a polymer matrix to form the modified nanocomposite coatings. Nanofillers were multi-walled carbon nanotubes of Taunit-M series (NanoTechCentre LLC, Tambov, Russia) coated with silicon oxide. To increase dispersibility of nanotubes in the polymer matrix, a non-ionogenic surfactant Triton X-100 (PanEco LLC, Russia) was used. Tetraethylorthosilicate (Reactive Express, Moscow, Russia) was used as a precursor for the synthesis of silicon oxide. The solvent was commercial white spirit (Leroy Merlin, Russia), AISI 303 sheet steel from which the substrate for protective coating was made. The coating was applied to the substrate by airbrush (Nasedal, China).
Methods
Preparation of the modified coating was carried out by synthesising the nanomodified coating in two steps. In the first step, carbon nanotubes (CNTs) were subjected to oxidation in concentrated nitric acid to prepare oxygen-containing functional groups on the surface. The obtained oxidised CNTs (50 g) were dispersed in ethanol-ammonia solvent (35:1). To the obtained suspension, 6.25 mL of tetraethoxysilane (TEOS) was added, initiating the process of hydrolysis and condensation to form silicon dioxide particles on the surface of nanotubes. After 9 hours of stirring at room temperature, the product was thoroughly washed and dried.
At the second stage, the obtained CNTs coated with silicon dioxide were distributed in a mixture of white spirit – alkyd enamel paint (with a ratio of 1:9, respectively), stirred, then applied by airbrush to the previously prepared metal substrates. To obtain different concentrations of nanofillers, the modified paint volume was mixed with paint diluted with white spirit and unmodified paint (the dilution ratio was also 1:9). Table 1 shows mass concentration of nanofillers in the dried coating layer.
Heat resistance test (ASTM D573)
The purpose of testing coatings for thermal resistance is to evaluate their ability to maintain their integrity and protective properties when exposed to high temperatures, as well as to verify the absence of thermal degradation [9]. To carry out the coating resistance test to heat, a sample is first prepared, which is a metal substrate painted with a modified coating.
After complete drying of the applied layer, the samples were placed in a drying cabinet, where they were heated to a temperature close to the actual operating conditions (50 °C) and kept at this temperature for 10 minutes, then cooled to room temperature and remained at this temperature for 10 minutes. The samples are then cooled in a refrigerator to (–5 °C) and held for 10 minutes and then removed from the refrigerator to allow the temperature to rise to room temperature, after which they are again held for 10 minutes. The heating and cooling cycle is repeated ten times. After that, the changes in the surface of the coating are evaluated. At this stage it is inspected for any signs of damage, peeling, cracking or other defects.
Chemical resistance test (ASTM D5402 – 93(1999))
ASTM D5402-93 (1999) is a standard methodology developed by the American Society for Testing and Materials (ASTM) for evaluating solvent resistance of organic coatings. This standard specifies a method for determining solvent resistance of organic coatings such as paints, varnishes and lacquers. The method involves wiping a coated surface with a cotton cloth or cotton swab moistened with a specified solvent for a specified number of movements or for a specified duration. After solvent exposure, the coating is tested for softening, swelling, stickiness, colour change or other signs of damage or alteration. This test method is commonly used in coatings industry to evaluate performance and durability of coatings, especially those applied where exposure to solvents is expected, such as automotive finishes or industrial coatings. It helps manufacturers and users to assess suitability of coatings for specific applications and provides valuable information for quality control and product development [10].
In this test, different solvents were used to wipe the samples.
White spirit, ethanol and acetone were used as solvents. After exposure to the solvent, the damage of the coating layer was assessed.
During the test procedure, the number of double wipings was 25 times for each type of solvent and for each sample, and after the wiping was completed, and thickness of the coating after wiping was measured and compared with thickness before wiping. A visual inspection of the fabric was also carried out for traces of dye.
Prior to testing, the specimens were aged for one month and tested at 23 °C and 50% humidity.
UV resistance test (for applications in metal structures)
To evaluate ability of pigment materials to retain their properties and colour under prolonged exposure to solar UV radiation, a UV resistance test was conducted [11]. To test for UV resistance, paint samples, which are coated sheets, are prepared. After complete drying of the samples, they are placed in ASTM G 155-04a Xenon Arc Weatherometer Test Chamber (ANSI Z97.1-2009, DAXIAN, China). The test parameters are selected according to Table X3.1 of Standard G 155 – 04a Cycle 3 [12]. It should be noted that the coated specimens were placed inside the chamber of the UV light source so that they are exposed to UV light uniformly. After exposing the samples to the UV light source, the changes that occurred in the coating structure are analysed. Particular attention is paid to signs of discolouration, deterioration, flaking or other defects. The results are compared to the requirements of ASTM G155 to determine if the coatings meet the required UV resistance standards.
The UV source was a lamp (8.5 kW xenon lamp (lifetime 2600 h, water-cooled)).
RESULTS
Heat resistance test
The results of the heat resistance test indicate that no noticeable changes were observed in the specimens, indicating that the specimens successfully passed this test. Figure 1 shows the specimens after 10 heating and cooling cycles.
These results can be explained by the fact that adding the nanofillers to the coating led, on the one hand, to improvement in its thermal conductivity and, on the other hand, to improvement in the heat diffusion in it, which led to an improvement in the thermal expansion and contraction of the coating layer during heating and cooling, which is more consistent with the thermal expansion coefficient of the substrate, and, on the other hand, and addition of nanofillers improved the mechanical properties of the paint layer, which improved its resistance to tensile stresses arising from the difference in the rate of expansion and contraction rates between the metal substrate and the coating layer.
Chemical resistance test
The test results showed that as the nanofiller content in the coating layer increased up to a concentration of 0.349% by weight, thickness of the sample coating layer decreased, but after the specified nanofiller concentration, the coating thickness began to increase. It should be noted that acetone had the strongest effect on the paint layer, followed by white spirit, and ethanol had almost no effect. Table 2 shows the change in coating thickness. These results can be interpreted as follows. Increasing the nanofiller content in the coating layer to concentration of 0.349% by weight leads to an increase in density of the coating layer because the nanoparticles occupy pores within the polymer matrix, which limits ability of solvents to penetrate the coating layer and thus reduce interaction surface area between the solvent and the polymer affected by the solvent. However, after applying of specified concentration of nanofiller, the nanoparticles start to agglomerate as a result of the decrease in the average distance between them, due to which the Van der Waals forces become greater than ability of the surfactant to disperse the nanoparticles and promotes the nanotubes agglomeration, causing distortions and defects in the coating matrix, resulting in an increase on interaction surface area between the solvent and the polymer. This occurs for several reasons, the first is that agglomeration of nanoparticles causes cracks in the polymer matrix, resulting in additional contact area between polymer and solvent. Secondly, nanoparticle agglomeration weakens adhesion of the ink to the substrate, allowing solvent to penetrate between the coating layer and the metal substrate.
As for the effects of various solvents, this can be attributed to the fact that pentagram/alkyd enamel paints contain organic polymers that tend to dissolve or soften when exposed to acetone, which dissolves the binders of the paint, causing it to break down and become easier to remove.
As for white spirit, it is less polar than acetone, and although it is effective in removing the freshly applied coating, but is not able to break the bonds formed after full curing of alkyd enamel, which explains the lack of its effect on the coating layer.
Ethanol is a weaker solvent than acetone and white spirit. It is less polar and less aggressive in its ability to break down organic compounds. As a result, ethanol had little effect on the coatings in all samples.
UV resistance test
The results of the UV resistance test of the coating showed that no significant negative changes were observed in any of the samples tested, and the changes were limited to a slight colour change as shown in Fig.2. Also, no changes in coating adhesion were observed compared to samples not exposed to UV light.
The high UV resistance of the coating can be attributed by combination of several factors. Firstly, the enamel used as a coating (pentaphthalic/alkyd) contains chemical stabilisers that help to mitigate the effects of UV rays. These stabilisers act as antioxidants or UV absorbers, which neutralises harmful free radicals produced by UV rays and prevents them from spreading into the coating layer.
Secondly, nanoparticles play a crucial role in enhancing UV resistance, as multi-walled carbon nanotubes coated with silicon particles are able to absorb UV radiation and convert it into harmless heat, instead of this radiation interacting with free radicals and destroying the polymer matrix structure, which effectively protects the paint layer from UV damage.
In addition, these nanoparticles can improve the mechanical properties of the coating layer, making it more resistant to UV-induced degradation.
CONCLUSIONS
In this paper, the effect of modification of alkyd enamel paint on the properties of heat resistance, UV stability and chemical resistance of the coating was studied. The study came to the following results:
The results of the heat resistance test indicate that no noticeable negative changes were observed in the samples, indicating that the samples successfully passed this test;
The results of chemical resistance tests showed that as nanofiller content in the coating layer increased to concentration of 0.349% by weight, thickness of the coating layer decreased, as the reduction in paint layer thickness reached 8.2 micrometres for acetone (the strongest tested material);
The UV resistance test of the coating showed no significant change except for a slight change in colour.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Metal corrosion is a serious problem for many industries, especially in construction industry, as it significantly affects on safety of facilities and structures, not to mention the high costs associated with maintenance and repair work on these facilities [1, 2]. Therefore, scientists have endeavoured to find solutions to limit occurrence of this phenomenon.
The methods used to reduce corrosion of metals are diverse and these methods can be divided into several groups such as protective coatings [3], cathodic protection [4], alloying [5], surface pre-oxidation [6] and the use of anti-corrosion agents (inhibitors) [7].
Speaking of anticorrosion coatings, it is necessary to mention nanoanti-corrosion coatings, as advances in nanotechnology have enabled development of this category of coatings. Anticorrosion nanocoatings take advantage of specific properties possessed by materials consisting of nanoparticles, and their properties are very different from those when such substances are in bulk form [8].
It should be noted that although these nano additives improve corrosion resistance of the coating matrix, it must be ensured that they do not cause deterioration of other properties such as resistance to thermal changes, UV radiation and the action of chemicals, since exposure to these factors can lead to serious defects in the coating layer, which in turn leads to a weakening of the barrier effect of the coating layer and corrosive agents ingress onto the metal surface.
The aim of this work is to study the effect of modification of alkyd enamel coating on its heat resistance, UV resistance and chemical resistance.
RESEARCH METHODS
Materials
In this study, commercial alkyd enamel PF-115 (Factor LLC, Russia) was used as a polymer matrix to form the modified nanocomposite coatings. Nanofillers were multi-walled carbon nanotubes of Taunit-M series (NanoTechCentre LLC, Tambov, Russia) coated with silicon oxide. To increase dispersibility of nanotubes in the polymer matrix, a non-ionogenic surfactant Triton X-100 (PanEco LLC, Russia) was used. Tetraethylorthosilicate (Reactive Express, Moscow, Russia) was used as a precursor for the synthesis of silicon oxide. The solvent was commercial white spirit (Leroy Merlin, Russia), AISI 303 sheet steel from which the substrate for protective coating was made. The coating was applied to the substrate by airbrush (Nasedal, China).
Methods
Preparation of the modified coating was carried out by synthesising the nanomodified coating in two steps. In the first step, carbon nanotubes (CNTs) were subjected to oxidation in concentrated nitric acid to prepare oxygen-containing functional groups on the surface. The obtained oxidised CNTs (50 g) were dispersed in ethanol-ammonia solvent (35:1). To the obtained suspension, 6.25 mL of tetraethoxysilane (TEOS) was added, initiating the process of hydrolysis and condensation to form silicon dioxide particles on the surface of nanotubes. After 9 hours of stirring at room temperature, the product was thoroughly washed and dried.
At the second stage, the obtained CNTs coated with silicon dioxide were distributed in a mixture of white spirit – alkyd enamel paint (with a ratio of 1:9, respectively), stirred, then applied by airbrush to the previously prepared metal substrates. To obtain different concentrations of nanofillers, the modified paint volume was mixed with paint diluted with white spirit and unmodified paint (the dilution ratio was also 1:9). Table 1 shows mass concentration of nanofillers in the dried coating layer.
Heat resistance test (ASTM D573)
The purpose of testing coatings for thermal resistance is to evaluate their ability to maintain their integrity and protective properties when exposed to high temperatures, as well as to verify the absence of thermal degradation [9]. To carry out the coating resistance test to heat, a sample is first prepared, which is a metal substrate painted with a modified coating.
After complete drying of the applied layer, the samples were placed in a drying cabinet, where they were heated to a temperature close to the actual operating conditions (50 °C) and kept at this temperature for 10 minutes, then cooled to room temperature and remained at this temperature for 10 minutes. The samples are then cooled in a refrigerator to (–5 °C) and held for 10 minutes and then removed from the refrigerator to allow the temperature to rise to room temperature, after which they are again held for 10 minutes. The heating and cooling cycle is repeated ten times. After that, the changes in the surface of the coating are evaluated. At this stage it is inspected for any signs of damage, peeling, cracking or other defects.
Chemical resistance test (ASTM D5402 – 93(1999))
ASTM D5402-93 (1999) is a standard methodology developed by the American Society for Testing and Materials (ASTM) for evaluating solvent resistance of organic coatings. This standard specifies a method for determining solvent resistance of organic coatings such as paints, varnishes and lacquers. The method involves wiping a coated surface with a cotton cloth or cotton swab moistened with a specified solvent for a specified number of movements or for a specified duration. After solvent exposure, the coating is tested for softening, swelling, stickiness, colour change or other signs of damage or alteration. This test method is commonly used in coatings industry to evaluate performance and durability of coatings, especially those applied where exposure to solvents is expected, such as automotive finishes or industrial coatings. It helps manufacturers and users to assess suitability of coatings for specific applications and provides valuable information for quality control and product development [10].
In this test, different solvents were used to wipe the samples.
White spirit, ethanol and acetone were used as solvents. After exposure to the solvent, the damage of the coating layer was assessed.
During the test procedure, the number of double wipings was 25 times for each type of solvent and for each sample, and after the wiping was completed, and thickness of the coating after wiping was measured and compared with thickness before wiping. A visual inspection of the fabric was also carried out for traces of dye.
Prior to testing, the specimens were aged for one month and tested at 23 °C and 50% humidity.
UV resistance test (for applications in metal structures)
To evaluate ability of pigment materials to retain their properties and colour under prolonged exposure to solar UV radiation, a UV resistance test was conducted [11]. To test for UV resistance, paint samples, which are coated sheets, are prepared. After complete drying of the samples, they are placed in ASTM G 155-04a Xenon Arc Weatherometer Test Chamber (ANSI Z97.1-2009, DAXIAN, China). The test parameters are selected according to Table X3.1 of Standard G 155 – 04a Cycle 3 [12]. It should be noted that the coated specimens were placed inside the chamber of the UV light source so that they are exposed to UV light uniformly. After exposing the samples to the UV light source, the changes that occurred in the coating structure are analysed. Particular attention is paid to signs of discolouration, deterioration, flaking or other defects. The results are compared to the requirements of ASTM G155 to determine if the coatings meet the required UV resistance standards.
The UV source was a lamp (8.5 kW xenon lamp (lifetime 2600 h, water-cooled)).
RESULTS
Heat resistance test
The results of the heat resistance test indicate that no noticeable changes were observed in the specimens, indicating that the specimens successfully passed this test. Figure 1 shows the specimens after 10 heating and cooling cycles.
These results can be explained by the fact that adding the nanofillers to the coating led, on the one hand, to improvement in its thermal conductivity and, on the other hand, to improvement in the heat diffusion in it, which led to an improvement in the thermal expansion and contraction of the coating layer during heating and cooling, which is more consistent with the thermal expansion coefficient of the substrate, and, on the other hand, and addition of nanofillers improved the mechanical properties of the paint layer, which improved its resistance to tensile stresses arising from the difference in the rate of expansion and contraction rates between the metal substrate and the coating layer.
Chemical resistance test
The test results showed that as the nanofiller content in the coating layer increased up to a concentration of 0.349% by weight, thickness of the sample coating layer decreased, but after the specified nanofiller concentration, the coating thickness began to increase. It should be noted that acetone had the strongest effect on the paint layer, followed by white spirit, and ethanol had almost no effect. Table 2 shows the change in coating thickness. These results can be interpreted as follows. Increasing the nanofiller content in the coating layer to concentration of 0.349% by weight leads to an increase in density of the coating layer because the nanoparticles occupy pores within the polymer matrix, which limits ability of solvents to penetrate the coating layer and thus reduce interaction surface area between the solvent and the polymer affected by the solvent. However, after applying of specified concentration of nanofiller, the nanoparticles start to agglomerate as a result of the decrease in the average distance between them, due to which the Van der Waals forces become greater than ability of the surfactant to disperse the nanoparticles and promotes the nanotubes agglomeration, causing distortions and defects in the coating matrix, resulting in an increase on interaction surface area between the solvent and the polymer. This occurs for several reasons, the first is that agglomeration of nanoparticles causes cracks in the polymer matrix, resulting in additional contact area between polymer and solvent. Secondly, nanoparticle agglomeration weakens adhesion of the ink to the substrate, allowing solvent to penetrate between the coating layer and the metal substrate.
As for the effects of various solvents, this can be attributed to the fact that pentagram/alkyd enamel paints contain organic polymers that tend to dissolve or soften when exposed to acetone, which dissolves the binders of the paint, causing it to break down and become easier to remove.
As for white spirit, it is less polar than acetone, and although it is effective in removing the freshly applied coating, but is not able to break the bonds formed after full curing of alkyd enamel, which explains the lack of its effect on the coating layer.
Ethanol is a weaker solvent than acetone and white spirit. It is less polar and less aggressive in its ability to break down organic compounds. As a result, ethanol had little effect on the coatings in all samples.
UV resistance test
The results of the UV resistance test of the coating showed that no significant negative changes were observed in any of the samples tested, and the changes were limited to a slight colour change as shown in Fig.2. Also, no changes in coating adhesion were observed compared to samples not exposed to UV light.
The high UV resistance of the coating can be attributed by combination of several factors. Firstly, the enamel used as a coating (pentaphthalic/alkyd) contains chemical stabilisers that help to mitigate the effects of UV rays. These stabilisers act as antioxidants or UV absorbers, which neutralises harmful free radicals produced by UV rays and prevents them from spreading into the coating layer.
Secondly, nanoparticles play a crucial role in enhancing UV resistance, as multi-walled carbon nanotubes coated with silicon particles are able to absorb UV radiation and convert it into harmless heat, instead of this radiation interacting with free radicals and destroying the polymer matrix structure, which effectively protects the paint layer from UV damage.
In addition, these nanoparticles can improve the mechanical properties of the coating layer, making it more resistant to UV-induced degradation.
CONCLUSIONS
In this paper, the effect of modification of alkyd enamel paint on the properties of heat resistance, UV stability and chemical resistance of the coating was studied. The study came to the following results:
The results of the heat resistance test indicate that no noticeable negative changes were observed in the samples, indicating that the samples successfully passed this test;
The results of chemical resistance tests showed that as nanofiller content in the coating layer increased to concentration of 0.349% by weight, thickness of the coating layer decreased, as the reduction in paint layer thickness reached 8.2 micrometres for acetone (the strongest tested material);
The UV resistance test of the coating showed no significant change except for a slight change in colour.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Readers feedback
