Core-shell Nanoparticles Based on Polystyrene and Poly(n-butyl acrylate) Functionalized with Itaconic Acid for Baroplastic Processing

Abstract

Core-shell polymer nanoparticles with poly(n-butyl acrylate) core and polystyrene shell can be produced by emulsion polymerization. These materials exhibit baroplastic behavior that allows them to be processed at low temperatures by compression molding or extrusion. In this work, core-shell copolymers of poly(n-butyl acrylate) cores and polystyrene shells were synthesized in a two-stage emulsion polymerization. The addition of itaconic acid as functional monomer in the core polymerization was carried out in order to study its influence on polymer processing and mechanical properties. The copolymers were characterized by dynamic light scattering (DLS), transmission electronic microscopy (TEM), infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The functional monomer incorporation was confirmed by DSC and quantified by titration. The poly(n-butyl acrylate) and polystyrene proportions had a direct influence on the polymer processing and mechanical properties. Copolymers with polystyrene contents higher than 50% presented baroplastic behavior and they could be processed at room temperature by compression molding and extrusion. The presence of itaconic acid did not affect polymer processing and significantly improved tensile resistance, increasing its toughness.

Keywords:
Core-shell; N-butyl acrylate; Styrene; Functionalization; Itaconic acid; Baroplastic; Mechanical properties

1. Introduction

Baroplastic copolymers are composed of two polymeric phases: a rigid, at high-Tg phase and a rubbery, at low-Tg phase¹,². The rigid polymeric domain is responsible for the mechanical properties and the rubbery domain provides the necessary flexibility for molding³. They also can be flow and shape under pressure without melting (even room temperature)⁴-⁶.

For the traditional polymers processing, a high temperature, generally above 200 °C, is needed to melt the polymers. The high temperature application could cause a large energy consumption, polymers thermal degradation and it also limits the recycling ability⁷. Thus, the application of baroplastics have some green advantages over conventional thermoplastics.

Block copolymers and core-shell nanoparticles are suitable structures for baroplastic processing. However, core-shell copolymers have better mechanical properties, being comparable to commercial thermoplastic elastomers⁸.

Baroplastic are prepared by emulsion polymerization. This technique allows the use of a wide variety of monomers, as well as the incorporation of functionalities in the core-shell particles.

Industrial emulsion polymerization usually formulates materials using monomers that are relatively water insoluble, such as styrene (St), n-butyl acrylate (nBA), 2- ethylhexyl acrylate (2-EHA), and a small amount of carboxylic monomers such as acrylic (AA), methacrylic (MAA), itaconic (IA) and fumaric (FA) acids⁹. These carboxylic monomers are typically incorporated to improve the coloidal stability of the latexes outer surface particles, providing both steric and electrostatic stabilizations¹⁰,¹¹. Polar or ionic functional groups in carbon chains or hydrophobic groups in polar chains are some examples. The heterogeneity of the chains confers greater reactivity, separation, or association of phases¹². Small carboxylic acids amount in industrial formulations used essentially as bonding agents and for adjusting the latex viscosity by varying the degree of neutralization⁹ and superior tolerance to the addition of mineral fillers¹³. The incorporation of the carboxylated monomer also depending on the pH. Santos et al.¹⁴ evaluated the influence of pH on the copolymerization of styrene and n-butyl acrylate in the presence of acrylic and methacrylic acids. The authors concluded that the incorporation of methacrylic acid is favored due to its greater hydrophobicity in relation to acrylic acid.

Smaller particle size, in emulsion polymerization still had higher Young’s modulus and tenacity. This behavior is called ‘nano effect’ and it is used to understand these fantastic phenomena, such as improved materials mechanical properties¹⁵.

Lee et al.⁶ produced phase transitions of polystyrene-b-poly(n-butyl methacrylate) (PS-b-PnBMA) and a deuterated polystyrene-b-poly(n-hexyl methacrylate) (dPS-b-PnHMA) blocks. Excellent baroplasticity was observed in nearly symmetric blends of PS-b-PnBMA/dPS-b-PnHMA, leading to the most outstanding pressure coefficients transitions. The authors explained that it was possible demonstrated that the entropic compressibility for the miscible blends is a baroplastic indicator, characterized by the negative volume change on mixing (DVmix) at transitions.

Özdemir et al.¹⁶ synthesized styrene-n-butyl acrylate block copolymers by emulsion polymerization. Copolymers of cationic type were obtained in all cases with glass transition temperature from 40 to 51 °C. The copolymers in emulsion were almost monodisperse with average molecular diameter between 30.7 nm and 45 nm. According to the authors, the materials produced showed potential for use in paper coverings.

Tang et al.¹³ also synthesized a core-shell latex nanoparticles consisting of poly(n-butyl acrylate) (PnBA) core, poly(methyl methylacrylate) (PMMA) shell and graphene oxide (GO), by a two stage emulsion polymerization technique. Powdery materials were obtained with low-Tg soft core by a high-Tg hard shell. Thin films were processed by compression molding at room temperature due to the pressure-induced miscibility of microphase-separated baroplastics. The authors concluded that baroplastic pressure induced processing, at low temperature, reduces energy consumption, thermal degradation and processing time during plastic processing and it also improves the recyclability.

Qiao et al.⁷ synthetized a poly(n-butyl acrylate-co-styrene) core-shell. It was introduced strong hydrogen bond of agar into poly(n-butyl acrylate-co-styrene) matrix Their results showed that the tensile strength and Young’s modulus as high as 8.4 and 350.6 MPa, respectively, was obtained. This result reinforces the strong hydrogen interactions obtained between agar and baroplastic. In addition, the baroplastics can be repeatedly processed at 100 °C at the same condition with a small loss of mechanical properties. Lv et al.¹⁷ also introduced hydrogen bond by complexing poly(n-butyl acrylate-co-styrene) with poly(acrylic acid) and poly(ethylene oxide). These hydrogen bonds produced materials with mechanical strength of 5.6 MPa and Young’s modulus of 10 MPa.

Despite these studies, a few studies on the behavior of itaconic acids in block copolymers processing have been reported in the literature. Kinetic studies conducted by Lock et al.¹⁸ showed that itaconic acid induces the decomposition of potassium persulfate, reducing monomeric conversion. Oliveira et al.¹⁹ studied the role of itaconic acid in the emulsion copolymerization of methyl methacrylate and n-butyl acrylate. They demonstrated that itaconic was distributed differently throughout the three phases of the emulsion (particle inside, particle surface and serum), with these differences depending on the solubility of the itaconic acid. Mendizábal et al.²⁰ synthesized core-shell copolymers based on polystyrene and poly (n-butyl acrylate) functionalized with itaconic or methacrylic acid. The authors found that the incorporation of itaconic acid is lower when compared to methacrylic acid, and the degree of incorporation is pH-dependent. It was also observed that the copolymers toughness increases depending on the functional monomer’s concentration. The presence of itaconic acid also increases the core-shell copolymers tenacity.

Therefore, the objective of this work is to evaluate the influence of monomer composition and functionalization with itaconic acid on the mechanical and baroplastic processing properties of core-shell copolymers based on polystyrene and poly(n-butyl acrylate).

2. Experimental

2.1. Materials

Styrene (S), purity level: commercial (DOW, Brazil); n-butyl acrylate (nBA), purity level: 99.5% minimum (BASF S.A., Brazil); itaconic acid (IA), purity level: 99% minimum (Sigma Aldrich); methyl alcohol, degree of purity: P.A. (Isofar Ltda., Brazil); tetrahydrofuran (THF), degree of purity: P.A. (Isofar Ltda., Brazil); sodium lauryl sulfate (SLS), purity level: 95% minimum (Cognis, Brazil); potassium persulfate (KPS), purity level: 98% minimum (Laporte Chemicals, Brazil); ethyl alcohol, degree of purity: P.A. (Vetec Química Fina Ltda, Brazil); isopropyl alcohol degree of purity: P.A. (Vetec Química Fina Ltda, Brazil); thymol blue, degree of purity: P.A. (Vetec Química Fina Ltda, Brazil); potassium hydroxide (KOH), degree of purity: P.A. (Vetec Química Fina Ltda, Brazil) were utilized as received.

2.2. Polymer synthesis and coagulation

Poly(n-butyl acrylate)(core) and poly(styrene)(shell) latices were synthesized by two-step emulsion polymerization. The formulations are listed in Table 1.

Table 1
Composition of by two-step emulsion polymerization.

Compositions	Step one (g)	Step two (g)
Destilled water	630.0	16.80 - 58.80
Sodium lauryl sulfate	3.78	2.52 – 8.82
Potassium persulfate	0.63	0.42 – 1.47
Butyl acrilate	63.00	0.00
Itaconic acid	0.00 - 63.00	0.00
Styrene	0.00	42.00 – 147.00

Firstly, the polymerization of n-butyl acrylate and itaconic acid (functionalized sample) was carried out in batch at 60°C and 500 rpm. The reactor was pressurized with nitrogen and evacuated before heating began. After 1 hour of reaction, pre-emulsified styrene and potassium persulfate in 15% m.v. sodium lauryl sulfate solution was added continuously for 3 hours at an average flow rate of 0.6 g/min. The feeding was carried out through a metallic cylinder, kept under constant nitrogen pressure, and connected to the reactor inlet valve. The pre-emulsion transfer from the cylinder to the reactor was carried out by pressure difference. The cylinder was placed on a scale to monitor the flow, which was controlled by opening the reactor valve. The polymerizations were carried out in a glass reactor equipped with a supervision system, agitation controller and temperature indicator (Figure 1). The reaction temperature was controlled by the Haake thermostatic bath. To maximize the incorporation of itaconic acid, phosphoric acid was added, keeping the medium pH equal to or less than 3.0; value below the pH of functional monomer first ionization (pK₁=3.85)¹⁸,¹⁹,²¹.

Figure 1
Reactor system for polymerization reactions.

Latice conversion was determined by gravimetry. Samples were removed from the reactor every hour and added to tared aluminum capsules. 1 g of latex and ethanol (to deactivate free radicals) were added to each capsule. The capsules were then taken to the infrared chamber, where they were dried until they reach constant weight. The conversion of the non-volatile functional monomer was determined by titration. The latices were coagulated with ethanol and the precipitate was washed twice with a mixture of ethanol/distilled water in a volumetric ratio of 1:1 to remove emulsifier and monomers residues. To obtain homogeneous clots, the latex was added continuously to the ethanol using a decantation funnel. Agitation was controlled at 300 rpm during coagulation and clots washing. The clots were filtered and subsequently dried at 60°C, for 24 hours, in a drying oven with air circulation.

2.3. Baroplastics characterization

The particle size was determined by light scattering, at 25°C, in a Zetasizer Nano equipment (Malvern Instruments, ZEN3600 model), with a 633 nm laser supply. The latices were dispersed in deionized water to avoid interaction between particles.

The particles morphology was analyzed by transmission electron microscopy (TEM) (Jeol, 1011). Latex samples were treated with 2% m.v. osmium tetroxide for 1 hour and dehydrated in methanol. Next, they were embedded in epon resin at 60°C for 48 hours. Sections of 70 nm were cut using an ultramicrotome and deposited on copper grids for observation under an electron microscope operated at 100 kV.

Glass transition temperatures were determined by differential scanning calorimetry (DSC) at a heating rate of 20 °C/min.

The functionalized samples were qualitatively analyzed by infrared spectrometry (Perkin-Elmer, Spectrum One). The functionalized samples films were obtained by pouring a polymer solution in chloroform into a KBr cell. The itaconic acid content incorporated into the polymer was determined by non-aqueous titration, being an adaptation of the procedure reported in the literature¹⁴,¹⁸. Approximately 1 g of the precipitated polymer was dissolved in 50 mL of THF and a KOH solution in methanol at 0.1 N was used as titrant. A solution of thymol blue in isopropyl alcohol at 0.3% m.v. was used as an indicator. The acidity of the solvent was determined by a blank test. For each sample, two titrations were performed and the average between the two determinations was expressed as the result. The calculated relative standard deviation is ± 4.5%.

The samples were processed in presses at 25°C and 150kgf/cm² for 5 min. Compression molding was carried out in a two-plate mold, with dimensions of 7.5 x 15 x 0.15 cm, in a hydraulic press. Extrusion molding was carried out in a piston-type mold (Figure 2c and 2g) in a 4-rod Carver electric press.

Figure 2
CS-D core-shell copolymer before (a) and after (b) its compression molding. CS-D core-shell copolymer extrusion (c) and extruded material (d). Compression molded CS-A core-shell copolymer test specimen (e). CS-1 core-shell copolymer before and after compression molding (f). Extrusion of CS-5 core-shell copolymer (g) and extruded material (h).

Tensile tests (Instron, 5581)(load cell capacity = 50kN) were carried out at a stretching speed of 50 mm/min. For each polymer sample, 3 or 5 dumbbell specimens were used, taken from the pressed samples, according to the ASTM D 412 method²². For each series of specimens, the median was calculated and expressed as the result.

3. Results and Discussion

Firstly, non-functionalized core-shell copolymers were synthesized and the influence of composition on processing and mechanical properties was evaluated.

3.1. Synthesis and characterization of non-functionalized core-shell copolymers

Table 2 shows the characteristics of the core-shell lattices obtained by emulsion polymerization.

Table 2
Effect of monomers composition on the conversion and particle size of core-shell obtained.

Core-shell copolymer	N-butyl acrylate (core) (% w)	Styrene (shell) (% w)	Conversion (%)	Particle sizea (nm) Core/core-shell
CS-A	30	70	100	72/99
CS-B	35	65	99	77/99
CS-C	40	60	96	78/98
CS-D	45	55	94	77/92
CS-E	50	50	97	66/80
CS-F	55	45	95	68/80
CS-G	60	40	97	77/88

• ^a
  Determined by light scattering

The average size of the core particles is in the range of 70 to 80 nm and the final particles had sizes in the range of 80 to 100 nm. The increase in the average diameter of the particles in the second stage of polymerization suggests that the polystyrene has covered the core particles, but it is not enough to determine the morphology. Therefore, TEM analysis was carried out with the aim of to prove the final morphology of the particles. Figure 3 presents a micrograph of the CS-D latex particles, where the core-shell morphology can be clearly observed. The core, poly(n-butyl acrylate) appears dark in color because it has been dyed by osmium tetroxide²³.

Figure 3
CS-D core-shell copolymer TEM image (146,000X magnification).

Samples of copolymers with PS contents above 50% presented a powdery appearance, while the other samples presented high stickiness. This characteristic led to the formation of large lumps upon coagulation, which greatly hampered drying. Figure 4 shows the CS-A and CS-G copolymers. The difference in appearance between the two samples suggests that copolymers with PS contents greater than 50% have the core particles completely covered by the rigid polystyrene shell. Copolymers with less than 50% PS have the particles partially covered by the shell, leaving the rubbery core exposed and, consequently, have high stickiness⁸.

Figure 4
CS-A (a) and CS-G (b) core-shell copolymers samples.

Gel formation was expected due to the high conversions obtained and the use of potassium persulfate as a polymerization initiator. As reported in the literature, these factors contribute to gel formation in n-butyl acrylate polymerizations, which are susceptible to intermolecular chain transfer to the polymer and termination by the combination of two macro-radicals²³-²⁶. In n-butyl acrylate and styrene copolymers, the gel fraction decreases as the styrene content increases²⁷. Resources available for molar mass control and gel formation were not utilized because high molar mass copolymers have better mechanical properties in relative to their lower molar mass analogues. The samples were demonstrated in Figure 5, by differential scanning calorimetry results (DSC)²⁸. Furthermore, González-León⁸ demonstrated that high molar mass shell-core copolymers can be processed at room temperature and their molded objects have good mechanical properties. The DSC thermogram of the CS-D copolymers presented two glass transition temperatures (T_g), indicating the presence of two polymeric domains in the same sample. The lowest temperature transition observed at -52°C corresponds to the core Tg, composed of poly(n-butyl acrylate). The transition observed at 100°C corresponds to the shell Tg, composed of polystyrene.

Figure 5
DSC curve of CS-D core-shell copolymer.

3.2. Non-functionalized core-shell copolymers processing

As previously mentioned, core-shell copolymers with PS contents lower than 50% showed high stickiness. This characteristic made processing very difficult and the samples were not molded. Thus, only core-shell copolymers with contents above 50% PS were processed at room temperature, making it possible to mold them only by applying pressure. Figure 2a and 2b shows the CS-D copolymer molded at 150 kgf/cm² for 5 minutes at 25 °C.

Room temperature processing is possible due to PS and PnBA induced miscibility pressure. The proposed mechanism is that the rubbery phase (PnBA) acquires mobility under pressure and drags the rigid phase (PS), enabling the copolymer flow and providing cohesion to the molded object²⁸,²⁹. The molded samples transparency and shape are evidence that the core-shell copolymer can flow under pressure, exhibiting baroplastic behavior. The core-shell copolymers extrusion was verified using a two-parts mold composed: a piston and a chamber with a 0.7 mm orifice, through which the copolymer can flow when subjected to pressure of 140 kgf/cm² (Figure 2c and 2d). The transparency of the extruded material demonstrates the miscibility between the copolymer phases and its ability to be molded by extrusion.

3.3. Non-functionalized core-shell copolymers mechanical properties

The core-shell copolymers mechanical properties were evaluated using tensile tests. The CS-E, CS-F and CS-G copolymers were not processed and therefore their mechanical properties were not evaluated. The CS-A and CS-B copolymers, with higher PS contents, were extremely brittle. Their samples were molded by compression, but it was not possible to cut the specimens, which broke when removed from the die or even when subjected to cutting pressure. Figure 2e shows the fragments of the CS-A copolymer specimen. Due to the difficulties of compression molding and cutting of the specimens, only the CS-C and CS-D copolymers had their mechanical properties evaluated.

Figure 6 presents the tensile strength results of the CS-C and CS-D copolymers. Increasing the polystyrene content by 5% considerably increases the breaking stress and reduces elongation. This effect was already expected due to the high influence of composition on the mechanical properties of baroplastic copolymers⁸. As shown in Table 2, the diameters of the CS-C and CS-D cores are almost the same. On the other hand, the average diameter of the CS-C particles is larger than that of the CS-D particles. This indicates that the polystyrene shell is larger. Probably, the increase in the size of the glassy nanophase (polystyrene, Tg = 100°C) caused the reduction in elongation at break (stretching) and the increase in tensile strength (stress). Among the copolymers synthesized, CS-D presents good processability and higher tensile strength. Due to these characteristics, its composition (45% PnBA and 55% PS) was selected to carry out the functionalization study that will be described below.

Figure 6
Tensile results of CS-C and CS-D core-shell copolymers.

3.4. Itaconic acid functionalized core-shell copolymers

As previously mentioned, copolymerization with carboxylated monomers is frequently used in the functionalization of latexes, and the carboxylic groups insertion into the polymer improves its mechanical properties. Following this premise, core-shell copolymers were synthesized in the presence of itaconic acid. The characteristics of the functionalized latexes are shown in Table 3. As with non-functionalized samples, an increase in the particles’ average diameter is observed in the second stage of polymerization.

Table 3
Composition added in the copolymerization and particle size of the functionalized core-shell lattices.

Core-shell copolymer	Core composition (IA/BA)a %m.m.	Shell composition (S)b %m	Particle sizec (nm) Core/core-shell
CS-1	1/45	55	79/100
CS-3	3/45	55	78/96
CS-5	5/46	54	78/98
CS-10	10/47	53	72/92

• ^a
  Itaconic acid/ n-butyl acrylate;
• ^b
  Styrene;
• ^c
  Determined by light scattering.

TEM analysis was carried out to check if the functional monomer presence changes the particles’ final morphology. Figure 7 presents a micrograph of the CS-5 latex particles. It can be seen that the itaconic acid concentrates on the surface of the particles, but does not completely cover them and it is also not present in all of them. Itaconic acid appears intensely colored by osmium tetroxide (black color highlighted). The micrograph suggests that the itaconic acid added in the copolymerization was not fully incorporated into the polymer. Thus, with the aim of qualitatively analyzing the itaconic acid incorporation, infrared spectrometry analysis (FTIR) was carried out.

Figure 7
CS-5 core-shell copolymer TEM image (97200x magnification).

Figure 8 shows the FTIR spectrum of sample CS-10, where characteristic bands of poly(n-butyl acrylate) and polystyrene can be observed³⁰. The band at 1735 cm^-1 (I) corresponds to the C=O bond and the two bands at 1245 and 1164 cm^-1 (II) correspond to the C-O bond, characteristics of poly(n-butyl acrylate). The bands 3080-3030 cm^-1 (III) and 1601 cm^-1 (IV) correspond to the C-H and C=C bonds of aromatics, respectively, indicating the presence of polystyrene. However, the characteristic bands of itaconic acid, corresponding to the O-H bond, which should occur between 3300 and 2500 cm^-1 and close to 920 cm^-1, are not observed.

Figure 8
FTIR spectrum of CS-10 core-shell copolymer.

Despite the FTIR result indicating the absence of carboxylic groups, the copolymer samples were solubilized in THF and then titrated with KOH in methanol to verify the presence of the functional monomer in the polymer. Through titration it was possible to quantify the itaconic acid content of the samples. The results are shown in Table 4.

Table 4
Conversion, itaconic acid content and Glass transition temperatures in the core-shell copolymers.

Core-shell copolymer	IA Conversion (%)	IA Content (%)	Core Tg (ºC)	Shell Tg (ºC)
CS-1	54.9	0.2	-51	92
CS-3	41.7	0.5	-50	90
CS-5	35.1	0.8	-50	87
CS-10	35.0	1.5	-47	83

• IA – Itaconic acid.

The itaconic acid conversion decreases with higher functional monomer amounts in the medium²⁶. This trend was previously reported in the literature, being attributed to the induced potassium persulfate decomposition by itaconic acid, which results in a lower concentration of initiator available to complete the polymerization¹⁸.

Due to the low conversion of itaconic acid, it is estimated that the CS-10 copolymer, with a higher content of functional groups, would have only 1.5% itaconic acid. The small concentration of carboxylic groups is a plausible explanation for the absence of their characteristic bands in the FTIR spectrum, since the detection limit of the technique is approximately 2%³¹.

Despite being an appropriate methodology, titration can also detect acidic impurities³² and, therefore, is not selective to quantify the functional groups incorporated into the polymer. Therefore, DSC analysis was performed to verify the occurrence of copolymerization with itaconic acid. The results are also listed in Table 4.

The DSC results indicate that both Tg copolymers change depending on the itaconic acid content, confirming the functional monomer incorporation into the polymer. The shell Tg undergoes a more pronounced change in relation to the core Tg, indicating that most of the itaconic acid is located in the shell. This result confirms what was observed by electron microscopy.

3.5. Processing of functionalized core-shell copolymers

The functionalized samples were also analyzed regarding processing and, like the non-functionalized copolymers, they showed transparency after compression molding and extrusion. Figure 2f shows the CS-1 copolymer compression molded at 150 kgf/cm² for 5 minutes at 25°C.

The samples transparency molded by compression and extrusion (Figure 2g and 2h) is evidence that the functionalized core-shell copolymer can flow under pressure, regardless of the functional group’s presence. This behavior indicates that functionalization with itaconic acid does not impair the miscibility of the rubbery phase with the rigid phase.

3.6. Mechanical properties of functionalized core-shell copolymers

Figure 9 shows the tensile tests results. Despite the low conversion of the functional monomer, its presence in the core-shell copolymer leads to an increase in rupture voltage and a reduction in elongation²⁰. This occurs because the carboxylic groups interact with each other³³,³⁴. Among the functionalized samples, it is observed that the increase in the itaconic acid content leads to a significant increase in the rupture voltage. However, the elongation is considered to remain unchanged due to the standard deviation.

Figure 9
Functionalized core-shell copolymers tensile results.

Furthermore, it can be seen that the CS-10 core-shell copolymer showed a small reduction in rupture stress and elongation in relation to CS-5. This suggests that the incorporation of approximately up to 1% itaconic acid increases the material's tensile strength, while levels above this level do not result in improvements.

Figure 10 presents the traction vs elongation curves. The copolymer without CS-D functionality showed soft and weak material behavior, whereas functionalized copolymers are more resistant. It is observed that increased functionality causes a change in mechanical behavior, increasing its tenacity.

Figure 10
Profile of tension vs elongation curves of core-shell copolymers.

4. Conclusion

Core-shell copolymers based on poly(n-butyl acrylate) and polystyrene synthesized by two-step emulsion polymerization exhibit baroplastic behavior and can be molded by compression and extrusion, at room temperature. The proportion of poly(n-butyl acrylate) and polystyrene significantly changed the core-shell copolymers processing and mechanical properties. In copolymers functionalized with itaconic acid, most of the monomer functionality was incorporated into the shell. The addition of itaconic acid small amounts caused significant changes in material mechanical properties, increasing its tenacity.

5. Acknowledgements

The authors thank the National Council for Scientific and Technological Development (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and Carlos Chagas Filho Research Foundation of the State of Rio de Janeiro (FAPERJ) for financial support.

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Publication Dates

• Publication in this collection
  24 Jan 2025
• Date of issue
  2024

History

• Received
  27 May 2024
• Reviewed
  29 Sept 2024
• Accepted
  01 Dec 2024