Development of Activated Carbon-Modified Polymer Composites for Application in Hydroponic SystemsAbstract
Contemporary agriculture faces the challenge of reconciling productivity and sustainability, making hydroponics a promising alternative. However, the lack of biodegradable materials that combine mechanical performance, stability, and compatibility with nutrient solutions limits its expansion. In this context, this study proposes innovative composites based on poly (butylene adipate-co-terephthalate) (PBAT), functionalized with activated carbon (AC) and the cationic surfactant CTAB, targeting applications in hydroponic systems. The formulations (PBAT, PBAT/5AC, PBAT/5AC/1CTAB, and PBAT/5AC/2CTAB) were processed by extrusion and injection and characterized by mechanical testing (ASTM D638), thermogravimetric analysis (TGA/DTG), scanning electron microscopy (SEM), and contact angle (ASTM D7334-08). CTAB acted as a functionalizing agent, improving CA dispersion and reducing agglomerates, which resulted in gains of 15.53% in the modulus of elasticity and 4.05% in tensile strength, in addition to greater surface hydrophilicity. Despite lower thermal stability, the properties obtained favor the adhesion of aqueous solutions, making the composites promising for sustainable substrates and components in hydroponic cultivation.
Keywords:
Activated carbon; PBAT and biodegradable
1. Introduction
Modern agriculture faces significant challenges related to productivity and environmental protection, exacerbated by climate change that affects soil fertility and increases the presence of pathogens, nematodes and erosion1. New agricultural techniques, such as hydroponics, emerge as viable alternatives to conventional practices, offering efficiency in water use and food production, as well as reducing the need for chemicals in cultivation2,3.
Hydroponics involves growing plants in artificial mediums, such as controlled environments with artificial lighting through LEDs and precise irrigation, protecting crops from pests and harsh weather conditions. Controlled environment agriculture (CEA) systems range from small urban farms to large commercial operations, adaptable to different crops and growing conditions4.
Hydroponic systems can be classified as open or closed. In open systems, the nutrient solution is used only once and then discarded, which can cause contamination of the water with nitrogen and phosphorus. In closed systems, the nutrient solution is recycled, reducing water consumption and optimizing the use of nutrients, although they present a risk of spreading pathogens if the solution is not properly disinfected5. One of the main concerns in the implementation of closed hydroponic systems is precisely this possible spread of pathogens in roots and plants. To prevent this problem, methods such as sand filtration, filter membranes, heat treatment, chlorination, UV radiation, ozonation, and hydrogen peroxide can be applied6.
An effective strategy to improve the quality of crop production and optimize nutrient uptake, while minimizing environmental impacts, is the use of controlled-release fertilizers (CRFs)7. These products are designed to release nutrients gradually, following the nutritional needs of crops throughout their development. Its formulation involves coating the active soluble nutrient with a membrane that acts as a diffusion barrier8.
An emerging approach to controlled-release systems involves the use of polymeric composites, especially biodegradable ones. These materials, consisting of macromolecules, can be enzymatically degraded into low molecular weight structures, which are subsequently absorbed by microorganisms and converted into biomass, CO2 and water. Biopolymers such as poly (lactic acid) (PLA), poly(hydroxybutyrate) (PHB), poly(caprolactone) (PCL) and poly (butylene adipate-co-terephthalate) (PBAT) have high potential in several areas, including medicine, electronics, packaging and, most notably, agriculture9.
Aliphatic polyesters stand out for the presence of ester bonds in the molecular chain, sensitive to hydrolysis, which makes them easily biodegradable. However, polymers such as poly(caprolactone) (PCL) and poly(hydroxybutyrate) have limited mechanical and thermal performance. In contrast, aromatic polyesters, such as polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), have excellent mechanical properties but high resistance to microbial degradation10. In this context, poly (butylene adipate-co-terephthalate) (PBAT) stands out among aliphatic-aromatic copolymers for combining biodegradability, conferring good mechanical properties from the aromatic units11,12.
Despite its advantages, pure PBAT has a high production cost and lower properties than conventional plastics such as polyethylene (PE)13. To overcome these limitations, the incorporation of low-cost fillers emerges as an effective strategy, reducing the final price and improving properties, ensuring the biodegradability of composites12.
In this context, activated carbon (AC) stands out as a promising material due to its high surface area and considerable adsorption capacity. In conventional cultivation systems, AC can act as sources of nutrients or agrochemicals, promoting their gradual release through adsorption. In addition to its low cost, the material has wide application in sectors including deodorization, water and wastewater treatment, and in capacitor enhancement14-16. Recently, research has demonstrated the potential of AC as an additive in functional polymeric composites, aiming to improve mechanical properties and adsorption capacity17,18. However, their high hydrophobicity requires the use of surfactants to increase wettability and ensure efficient performance in aqueous media19. In these formulations, surfactants act at the interface between polymer matrix and filler, reducing interfacial energy and promoting compatibility between components due to their amphiphilic nature20.
This interaction favors the homogeneous dispersion of the fillers in the polymeric matrix, preventing the formation of agglomerates that cloud compromise the properties of the composite. In addition, surfactants increase interfacial adhesion, promoting more efficient stress transfer between the filler and the polymer, which results in better mechanical properties21. The choice of surfactant depends on the chemical nature of both the filler and the polymer matrix, and anionic, cationic or non-ionic agents can be used. Among the examples frequently used in systems containing inorganic fillers, such as clays and carbonaceous particles, cetyltrimethylammonium bromide (CTAB) stands out22,23, Sodium Lauryl Sulfate (SDS)24 e o Tween 8019. This approach makes it possible to obtain materials with optimized performance for different technological applications.
Given this context, the present study aims to develop biodegradable controlled-release polymeric composites using poly (butylene adipate-co-terephthalate) (PBAT) as a matrix, combined with activated carbon and the cationic surfactant CTAB. The proposal aims to produce injection-molded composites that combine good mechanical properties and high adsorption capacity, intended for application in hydroponic cultivation systems.
2. Material and Methods
2.1. Materials
The commercial polymer Ecoflex® F Blend C1200, produced by BASF, which is based on poly(butylene adipate-co-terephthalate) – PBAT, was used as a polymeric matrix. In addition, other additives were incorporated, including cetylthiethylammonium bromide (CTAB), CAS 57-09-0, a cationic surfactant manufactured by Êxodo Científica, and activated carbon (AC) in particulate form P.A., CAS 7440-44-0, from the company Dinâmica.
2.2. Preparation of polymeric composites
In a step prior to incorporation into the polymer matrix, the activated carbon was screened using a 50 mesh sieve with an opening of 300 μm. Next, the commercial polymer, together with the additives, was dried in an oven at 60 °C for a period of 24 hours. After the drying procedure, the materials were mixed beforehand by manual tumbling at room temperature and processed in a single-screw extruder, model AX-16 (L/D=26), from AX Plásticos. The temperature profile was set at 140 °C in the first zone, 145 °C in the second zone, and 150 °C in the third zone, with a screw rotation speed of 44 rpm. The composite mixtures were not cooled in a water bath and were later subsequently pelletized.
The compositions were established considering the processing conditions, since contents above 5% by mass of activated carbon made the extrusion unfeasible due to the operational limitations of the single-screw extruder used. Thus, it was not possible to incorporate larger amounts of activated carbon and surfactants into the formulations. The samples were named PBAT, PBAT/5AC, PBAT/5AC/1CTAB, PBAT/5AC/2CTAB, as shown in Table 1.
2.3. Preparation of injected specimens.
The systems obtained were subjected to a drying process at 60 °C for a period of 24 hours and then injected into a mold containing cavities with standardized dimensions for performing mechanical tensile testing, in accordance with ASTM D638. The injection was performed using a Eurostec BL32 ER-I thermoplastic injection molding machine, available at the Polymer Laboratory of the Materials Engineering Undergraduate program at the Federal University of Piauí, located in Teresina/PI.
The mold temperature during the injection process was set at 45 °C, as detailed in the temperature profile shown in Table 2.
3. Characterizations
3.1. Scanning Electron Microscopy (SEM)
The surface morphology of the test specimens was analyzed using Scanning Electron Microscopy (SEM) at magnifications ranging from 60x to 3230x, using a TESCAN VEGA 3 microscope. The micrographs obtained by SEM were acquired at an acceleration voltage of 20 kV. The analyses were performed at the Renewable Energy Center, CT-Gas, located in the state of Rio Grande do Norte. Cross-sectional analysis of the specimens was adopted for morphological characterization. This choice was justified by the fact that, during the mechanical tests, the specimens did not show complete rupture. Thus, it was necessary to make a cut in the region of greatest deformation in order to allow adequate analysis of the interface and distribution of the composite components using SEM.
3.2. Tensile strength
The composites produced were subjected to analysis using a DL 30000 EMIC universal testing machine, which is equipped with a 50 kN load cell and belongs to the Materials Engineering Course of the Federal University of Piauí. For each composition, five test specimens were analyzed, whose dimensions comply with the ASTM D638 technical standard.
3.3. Thermogravimetric Analysis (TGA/DTG)
The samples were analyzed using an SDT Q600 V20.9 thermoscale, available at the Renewable Energy Center, CT-Gas, located in the state of Rio Grande do Norte. The equipment operated under a nitrogen flow, in a temperature range varying from 30 to 600 °C, with a heating rate of 10° C.min-1. The analysis was performed on the composites processed in this study, with the aim of determining the degradation temperature and mass loss associated with each thermal event of the compositions developed.
3.4. Contact angle
The analysis contact angle analysis was conducted to evaluate the wettability of the surfaces of the test specimens, which were produced by injection molding. This procedure followed the guidelines established in the ASTM D7334-08, using the sessile drop method. Measurements were taken at room temperature, in which a 16 μL drop of distilled water was deposited on the surface of the specimen using a micrometric dispenser. The images obtained were analyzed based on the average of five measurements taken at different sections of the sample, using ImageJ Software (Open License). The analysis was performed at the Polymer Laboratory, located at the Federal University of Piauí, in Teresina-PI.
3.5. Statistical analysis
The experimental data were analyzed using Origin 2024 Statistical Software (student license). Single-factor analysis of variance (ANOVA) was used to identify significant differences between the mean values, considering a confidence level of 95% (P < 0.005).
4. Results and Discussion
4.1. Morphology
To analysis the morphology of the pure polymer and composites, scanning electron microscopy (SEM) tests were performed and the surface of the test specimens was evaluated, as shown in Figures 1 and 2.
Scanning Electron Microscopy of the surfaces obtained for the samples: a. pure PBAT; PBAT/5AC; PBAT/5AC/1CTAB and PBAT/5AC/2CTAB.
Scanning Electron Microscopy of the cross-section obtained for the samples: a. Pure PBAT; PBAT/5AC; PBAT/5AC/1CTAB and PBAT/5AC/2CTAB.
In Figure 1a, the micrograph of the pure PBAT sample reveals a smooth and homogeneous surface, typical characteristics of polymers in their pure state, with no particulates detected. Wongphan et al.25 observed similar behaviors in their study when analyzing the morphology of pure PBAT.
In Figure 1b, the incorporation of activated carbon as a filler enabled the identification of agglomerates on the surface of the composites, as shown in the image, evidencing the presence of the filler in all compositions containing activated carbon. The same identification was recorded in the work of Correia et al.26.
In Figures 1c and 1d, it can be observed that the progressive increase in the concentration of CTAB surfactant in the composition results in a reduction and greater uniformity of the particulates on the surface of the composites. This behavior suggests that the surfactant facilitated the uniform dispersion of activated carbon particles in the PBAT matrix, promoting a homogeneous distribution of reinforcements in the matrix. This behavior corroborates the results described by Alves et al.27, which demonstrated that the presence of surfactants favors the dispersion of particles in polymeric matrices, preventing agglomeration and promoting a homogeneous distribution of reinforcements.
Pure PBAT has a smooth surface without cavities (Figure 1a), while compositions with activated carbon exhibited increased in surface roughness due to the formation of ellipsoidal cavities aligned in the direction of stretching (Figures 1b, 1c and 1d), as described by Kargarzadeh et al.28. During the stretching process, activated carbon particles can generate shear zones and stress concentrations, acting as points of weakness in the polymer matrix29. This effect is influenced by factors such as viscosity, elastic modulus, interfacial adhesion, and surface energy of the matrix and particles30. The initial detachment at the interface facilitates the growth of these cavities during elongation, which can impair or, in some cases, improve the mechanical properties of the composites, depending on the characteristics of the material and the processing conditions31,32
Figure 2 shows the SEM micrographs obtained the cross-sections of the test specimens, showing the internal morphology of the materials after mechanical cutting. In micrograph Figures 2a, a homogeneous and continuous surface can be observed, characteristic of a polymeric matrix without significant addition of fillers, indicating good structural cohesion and absence of visible defects.
In contrast, Figures 2b and 2c reveal more irregular surfaces, with marks suggesting the presence of additives or dispersed particles, as well as possible matrix-filler interfaces. The roughness observed is indicative of heterogeneous interaction and possible influence on mechanical behavior.
Figure 2d highlights the presence of cavities and adhesion failures (indicated by arrows and circles), attributed to particle extraction during cutting or poor dispersion during processing. Such discontinuities can act as stress concentration points, compromising the mechanical integrity of the composites.
The morphological results point to the direct influence of the dispersion and adhesion of the fillers within the matrix, which are determining factors for the final performance of the material, corroborating the importance of a strict control in the formulation and mixing process.
4.2. Mechanical Properties
Figure 3 shows the mechanical behaviors obtained in the tensile test of the test specimens of the pure polymer (PBAT) compositions and their composites PBAT/5AC, PBAT/5AC/1CTAB and PBAT/5AC/2CTAB.
Mechanical properties (modulus of elasticity and tensile strength) of PBAT, PBAT/5AC, PBAT/5AC/1CTAB, PBAT/5AC/2CTAB compositions.
The composition of pure PBAT had an average elasticity modulus of 67.8 ± 1.71 MPa and a tensile strength of 17.73 ± 0.46 MPa. The addition of 5% activated carbon (PBAT/5AC) resulted in a significant increase of 7.3% in the modulus of elasticity, which reached 74.00 ± 2.98 MPa. Regarding tensile strength, an increase of 7.05% was observed, reaching an average value of 18.98 ± 0.25 MPa33.
In compositions that include activated carbon and the surfactant CTAB, the results show variations depending on the amount used. The PBAT/5AC/1CTAB composition showed the greatest increase in the modulus of elasticity, with an increase of 15.53%, reaching a value of 78.16 ± 1.43 MPa. In Addition, a 4.05% improvement in tensile strength was observed, with an average value of 18.53 ± 0.18 MPa. In contrast, the PBAT/5AC/2CTAB composition showed a significant reduction in tensile strength values compared to all other compositions, although the modulus of elasticity increased by 13.51%, reaching 76.96 ± 3.55 MPa.
The increase in the modulus of elasticity of the composites can be attributed to the reinforcing effect provided by activated carbon (AC), combined with the good interface adhesion between the AC and the polymer matrix34,35.
As reported by Das et al36, the increase in the modulus of polymer/biochar composites can be attributed to the high surface area of biochar, which facilitates stress transfer between its particles and the polymer matrix. This mechanism results in reduction deformation and improvement modulus. In addition, the increase in modulus can be explained by the greater adhesion between the polymer matrix and the load material, which minimizes the presence of gaps on the interfacial surfaces.
Idrees et al.37, report in their study that the incorporation of biochar in concentrations of 5% w/w in a PET matrix resulted in a significant increase in tensile strength compared to pure polymer. This behavior may be associated with the efficient interface between the components promoted by the porous structure of biochar, which restricts the mobility of polymeric chains due to the presence of solid particulates in the matrix.
Abreu et al.38 investigated the use of CTAB in polymeric blends its effects on dispersion and functionalization in multi-walled carbon nanotubes (MWNT's) and observed that the PVP/CTAB blend showed a synergistic effect at certain polymer concentrations, resulting in improved MWNT's dispersion efficiency compared to using the components individually.
When the surfactant concentration was increased to 2% in the PBAT/5AC/2CTAB composition, a significant reduction in the tensile strength of the composite was observed. This decrease can be attributed to the physicochemical characteristics of CTAB, which has a high melting point and strong polarity. This implies that, during composites processing, the surfactant does not melt properly with the polymer matrix. Instead, it retains its original structure, forming agglomerates that can act as defects within the PBAT matrix. These agglomerates create zones of stress concentration, weakening the cohesion between the matrix and the AC reinforcement, resulting in lower load transfer efficiency within the composite39.
Thus, the formation of CTAB agglomerates compromises the homogeneity of the material and reduces its mechanical properties, especially tensile strength, which counteracts the positive effect observed in the composition with 1% CTAB. Therefore, the behavior of the PBAT/5AC/2CTAB composition can be attributed to poor dispersion surfactant at high concentrations, which compromises the structural integrity of the composite and results in a reduction in its mechanical strength.
4.3. Thermogravimetric analysis
Figure 4 illustrates the thermogravimetry (TGA) curves and mass derivatives (DTG) corresponding to the compositions containing activated carbon and CTAB. The values obtained from the analysis based on thermal behavior are presented in Table 3.
TGA/DTG curves referring to the thermal analysis of pure PBAT and composites with activated carbon and CTAB.
Thermogravimetry tests were performed to investigate the thermal stability of pure polymer mixtures (PBAT), with an emphasis on the influence of the filler and surfactant in the composite. When analyzing Figure 4, together with Table 3, it is observed that the initial degradation temperature of the pure polymer (PBAT) was recorded at approximately 378.7 °C, with a single mass loss event observed at 399.6 °C. This event is associated with the decomposition by cleavage of the polymer chain in the regions of adipic acid and 1,4-butanediol40,41.
Samples containing 5% activated carbon (PBAT/5AC) showed a slightly higher initial degradation temperature, registering 382.8 °C. The presence of activated carbon, which exhibits greater thermal stability than PBAT, contributes to this improvement. The combination of this component results in a structure that demonstrates heat resistance, evidenced by the increase in initial degradation temperature compared to the pure polymer42.
Pagno et al.43 developed electrospun polymeric membranes from PBAT/PCL blend, incorporating activated carbon derived from the biomass of Brazil nut shells (AC-BCB). Thermogravimetric analysis revealed that the addition of activated carbon promoted a significant increase in the thermal stability of the membranes, raising the onset temperatures of degradation events to approximately 323 °C and 412 °C, respectively, compared to the membranes without the addition of carbon, which had temperatures close to 315 °C and 403 °C, respectively. This result indicated that the presence of AC-BCB favored the thermal resistance of the material, an effect attributed to the physical interaction between the carbon and the polymer matrix
On the other hand, the PBAT/5AC/1CTAB and PBAT/5AC/2CTAB compositions showed the lowest initial degradation temperatures compared to the pure polymer and the PBAT/5AC composite, registering values of 376.9 and 372.4 °C, respectively. In addition, a significantly higher mass loss was observed, reaching 82.7% for the composition with 2% CTAB. Furthermore, the residue at 500 °C increased from 5.8% in pure PBAT to 15.7% in the aforementioned composition, suggesting that the presence of CTAB may result in greater residue formation.
Nunes et al.44 identified that the dispersant agent calcium carbonate (CaCO3) caused a reduction in the thermal stability of PBAT, acting as a catalyst in the depolymerization of the polymer and, consequently, decreasing its stability. With regards to the residue content at 500 °C, as indicated by Baggio et al.45, the increase in surfactant concentration resulted in a decrease in thermal stability. The authors observed that the temperature of 600 °C was not sufficient for the complete thermal decomposition of the surfactant, which influenced the formation of a greater residue.
In their study, Chhetri et al.46 analyzed the thermal degradation behavior of composites formed by LLDPE and CTAB-MoS2. The authors identified that the initial degradation temperature in the compositions was reduced with increasing CTAB/MoS2 content. When the CTAB/MoS2 concentration was increased to 3% by weight, a 20 °C reduction in the degradation temperature was observed. This decrease can be attributed to the decomposition of the CTAB, as well as the high thermal conductivity of the MoS2 filler, which may have facilitated heat transfer. In addition, an increase in residue was observed during the degradation process, similar to that observed in compositions containing carbon and CTAB.
The observations obtained in the thermogravimetric analysis indicated that the thermal stability of composites containing activated carbon and CTAB, showed a slight decrease in the initial degradation temperature, as well as an increase in the formation of residues during the thermal degradation process. However, the addition of additives to the composition did not negatively affect the processing, since PBAT maintains a wide temperature window suitable for the production of manufactured goods for the agricultural industry.
4.4. Contact angle
The contact angle is fundamental for characterization the hydrophobicity of the pure PBAT surface, as well as composites containing activated carbon and the CTAB surfactant, as shown in Figure 5.
Water contact angle measurements for pure PBAT and its composites in the presence or absence of CTAB surfactant.
Samples containing pure polymer have a contact angle of 75.2°± 2.147,48. With the addition of activated carbon, the contact angle increases to 76.82°± 1.9, making the composite more hydrophobic compared to pure PBAT49,50.
Nayab et al.51, observed that adding activated carbon to poly (ether-sufon) (PES) composites membranes increased the contact angle of the compositions with the additive. This behavior is related to the presence of carbon in the membranes, since carbon has highly hydrophobic characteristics. In the PBAT/5AC/1CTAB and PBAT/5AC/2CTAB compositions, a significant reduction in the contact angle was observed, which became 20.1° ± 4.5 and 13.72° ± 5.75, respectively.
During the contact angle test, it was observed that when a drop of water was placed on the surface of the material, the drop slid off. This behavior indicated that the surface, treated with surfactant, had a greater affinity for liquids, demonstrating ease of wettability and interaction with the liquid phase. This observation can be explained by the formation of cationic functional groups on the surface of the compositions, which attract free ions after modification with CTAB. Ji et al.52 observed that modifying activated carbon using CTAB surfactant resulted in significant changes in the surface morphology of the carbon and its adsorption properties. This modification promoted a change in the surface charge of the carbon, favoring the adsorption of positive ions due to the presence of ammonia groups in the surfactant, which, in turn, increased the number of active sites available for the adsorption of pollutants.
In this same study by Zhang et al.53, the addition of CTAB also influenced the wettability of the charcoal, since the presence of cationic surfactants can alter the contact angle, making the surface more wettable, as evidenced in the composites prepared with surfactants. This phenomenon is beneficial for the adsorption of organic compounds, as it promotes increase moisture and the improvement wetting characteristics, allowing for more efficient interaction between the coal and the liquids to be treated54.
Nadeem et al.55 observed in their study that CTAB treated adsorbents have a higher surface area compared to other types of surfactants. This phenomenon can be linked to the characteristic properties of these materials, such as adsorption, wetting, and solubilization. Because they are amphipathic in nature, CTAB-treated surfaces allow for significantly larger surface area, as well as adjustable wetting (water/oil) as needed. This flexibility is due to the ability of the molecules of these substances to organize themselves in an optimal way.
The adsorption and water retention properties of coating materials are crucial factors that directly influence the controlled-release performance in a various system, including those applied to water treatment and hydroponics. In the hydroponic context, polymer compositions, when combined with surfactants, are particularly relevant due to their ability to increase wettability and, possibly, surface area56.
This modification not only facilitates the penetration and retention of substances essential for plant development, but can also play a significant role in water treatment, promoting the capture and removal of contaminants. The combination of these properties is crucial for maximizing the efficiency of the hydroponic system, improving the adsorption and transport of nutrients to the roots, as well as contributing to water purification, ensuring a healthy and balanced environment for plant cultivation.
5. Conclusions
The development of poly (butylene adipate-co-terephthalate) (PBAT) composites reinforced with activated carbon (AC) and functionalized with the cationic surfactant CTAB has shown promising results for applications in hydroponic systems. The inclusion of AC contributed to an increase in the modulus of elasticity, while CTAB played an essential role as a functionalizing agent, favoring the dispersion of carbon particles in the polymeric matrix. This improvement in dispersion resulted in a significant reduction in agglomerates, confirmed by scanning electron microscopy (SEM), and directly reflected in the improved mechanical properties, with increases of 15.53% in the modulus of elasticity and 4.05% in the tensile strength in the composition with 1% CTAB.
In addition, the presence of CTAB altered the surface characteristics, promoting greater hydrophilicity, evidenced by the reduction in the contact angle, an essential factor to favoring the interaction with nutrient solutions in hydroponic systems. Although thermogravimetric analyses (TGA/DTG) revealed a slight reduction in thermal stability, this effect did not compromise the materials viability for the proposed application.
Thus, the results obtained indicate that the developed composites have significant potential for use as substrates or components of hydroponic systems, combining mechanical performance, wettability control and environmental sustainability. As future prospects, it is recommended to investigate the behavior of composites in prolonged contact with nutrient solutions, as well as to evaluate their controlled degradation under real cultivation conditions.
6. Acknowledgments
National Council for Scientific and Technological Development (CNPq), Coordination for the Improvement of Higher Education Personnel (Capes); Piauí State Research Support Foundation (FAPEPI).
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Data Availability
The data that support the findings of this study are available from the corresponding author, Alves, T.S., upon reasonable request.
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Edited by
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Associate Editor: Sandro Amico.Editor-in-Chief: Luiz Antonio Pessan.
The data that support the findings of this study are available from the corresponding author, Alves, T.S., upon reasonable request.
