Incorporation of carbon-based nanoparticles into epoxy adhesives: Enhancing mechanical properties through plasma functionalization and morphology analysis

Abstract

The incorporation of carbon-based nanoparticles into epoxy adhesives is a promising strategy to enhance the mechanical properties of adhesive joints, improving their reliability and competitiveness compared to traditional mechanically fastened joints. This study investigates the effect of plasma functionalization of carbon-based nanoparticles with distinct geometries (carbon nanotubes, graphene, and carbon black) on the thermal and mechanical properties of an epoxy adhesive. Plasma treatment was employed to introduce oxygen and nitrogen functional groups onto the nanoparticle surfaces, enhancing their interaction with the epoxy matrix. Among these nanoparticles, carbon black, although a traditional and widely used material in composites, often presents challenges such as poor dispersion and agglomeration, which can negatively impact adhesive properties. Plasma functionalization addresses these issues by modifying the particle surface, enhancing dispersion and interfacial bonding with the epoxy matrix. Nanocomposites were fabricated using three nanoparticle mass fractions (0.25%, 0.5%, and 1%). X-ray photoelectron spectroscopy (XPS) was used to quantify the functional group concentrations on the nanoparticle surfaces. Tensile tests and electron and scannig microscopy characterizations were conducted to assess the effects of functionalization and nanoparticle concentration on the properties of the adhesive-based nanocomposites. XPS results confirmed the incorporation of oxygen and nitrogen onto the nanoparticle surfaces at the atomic level. Among the evaluated materials, functionalized carbon nanotubes (CNT.f) exhibited the highest nitrogen content, with 0.63 at.% of N 1s and a 37% increase in O 1s concentration compared to untreated CNTs. Nanocomposites containing functionalized CNTs showed reduced nanoparticle agglomeration and enhanced interfacial interaction with the epoxy matrix. As a result, a 21% increase in ultimate tensile strength was achieved with 0.25 wt.% of CNT.f, along with a 19% improvement in elastic modulus using 0.5 wt.% of the same filler. These findings provide valuable insights into the influence of functionalization and nanoparticle morphology on the mechanical behaviour of adhesive systems for advanced composite applications.

Keywords

mechanical properties adhesive nanocomposite carbon-based nanoparticles plasma functionalization adhesive joints

Introduction

The demand for lightweight and high-performance materials has driven the development of more efficient structural solutions, particularly in aerospace and transportation sectors. In this context, ensuring reliable joining of components remains a significant technical challenge. Traditional mechanical fastening methods, such as bolts and rivets, although widely used, require additional machining steps like drilling, which can compromise structural integrity by inducing delamination, material rupture, and stress concentrations.¹

As an alternative, adhesive bonding has emerged as a promising solution, offering improved stress distribution, enhanced fatigue resistance, and significant weight reduction.^2,3 Furthermore, adhesive joints exhibit high versatility, allowing adaptation to different stress types, loads, substrates, and application conditions.^4,5 Among the most commonly used structural adhesives, epoxy resins stand out due to their excellent mechanical properties, broad service temperature range, and strong adhesion to a wide variety of substrates.⁶

In recent years, the incorporation of nanomaterials into epoxy adhesives has gained attention as a promising strategy to enhance the mechanical performance of bonded joints. Carbon-based nanoparticles, such as carbon nanotubes (CNTs), graphene, and carbon black, have demonstrated the potential to improve strength, elasticity modulus, and fracture toughness.^7,8 Although it is a conventional material, the carbon black used in this study exhibits a spherical morphology with a diameter between 64 and 74 nm. Its inclusion is relevant due to its low cost, widespread industrial application, and its role as a reference point for comparison with the distinct geometries of the other nanoparticles investigated.

In this context of advances in the use of carbon-based nanomaterials, recent studies on the application of surface-modified nanostructures highlight the significant potential of carbon dots (CDs), nanomaterials with dimensions under 10 nm, water solubility, low toxicity, and high reactive species generation. These properties make CDs suitable for bioadhesives, pressure-sensitive epoxy adhesives, as well as for enhancing the mechanical properties of polymers through covalent bonding with the polymer network.^9–12

Ekrem et al.¹³ achieved a 14% increase in shear strength by incorporating 1 wt% of CNTs into an epoxy adhesive, while Yilmaz and Ekrem¹⁴ reported a 43.7% improvement in tensile strength using a hybrid epoxy adhesive reinforced with nylon nanofibers and 1 wt% graphene, compared to the neat epoxy resin. However, challenges such as nanoparticle agglomeration and weak interfacial adhesion with the matrix hinder the full realization of these benefits.^15,16

Plasma functionalization has emerged as an effective technique to address these limitations. By introducing functional groups, such as oxygen and nitrogen, onto the nanoparticle surfaces, this treatment enhances both dispersion and interfacial interaction with the matrix.¹⁷ Studies have reported significant improvements in mechanical properties, including increased tensile strength and elasticity modulus, in epoxy-based nanocomposites incorporating plasma-treated CNTs.^18,19

Larouche et al.²⁰ functionalized carbon black in a thermal plasma reactor using a helium and nitrogen gas mixture, with plasma generated by direct current and high-frequency sources, achieving a nitrogen incorporation of 6.3 at.%. Alam et al.²¹ used an epoxy resin with CNTs surface-modified through different routes. The results showed a 124% increase in tensile strength with 1% plasma-functionalized CNTs compared to samples with untreated CNTs. Bertóti et al.²² treated graphene with O2 plasma (50 W, 1 min), increasing the oxygen content from 3.61% to 5.23%, attributed to the introduction of hydroxyl groups on the graphene surface.

Although there are several scientific contributions regarding the plasma functionalization of nanoparticles and their application in polymer matrices, no studies have been found to date that comprehensively investigate the effect of different carbon nanoparticles with varied geometries in epoxy adhesive systems. Moreover, the specific combination of gases used for plasma functionalization, in conjunction with an organic compound during the process and the experimental parameters adopted in this study, has not been previously reported in the literature. In this context, this study investigates the incorporation of three different types of nanoparticles into a commercial epoxy adhesive (AH/AR-345), using three mass fractions and a plasma functionalization process. The plasma treatment aimed to enhance the incorporation of oxygen and nitrogen functional groups on the nanoparticle surfaces. The selected nanoparticles, carbon nanotubes (CNT), graphene, and carbon black (CB), are chemically similar but morphologically distinct, allowing an evaluation of how nanoparticle geometry influences the functionalization process and the properties of the resulting nanocomposite. X-ray photoelectron spectroscopy (XPS) was used to determine the concentration of functional groups introduced on the nanoparticle surfaces. The effects of functionalization and nanoparticle concentration on the properties of the adhesive-based nanocomposites were assessed through tensile tests and microscopy characterizations. By the end, this work provides a comprehensive approach to understanding the impact of functionalization and nanoparticle morphology on the mechanical behavior of adhesive systems for advanced composite applications. The findings offer insights into the manufacturing process of composite bonded joints and their potential performance improvements.

Methodology

The methodology includes nanoparticle functionalization, nanocomposite preparation, and material characterization, as illustrated in Figure 1. The methodology begins with the plasma functionalization of the nanoparticles, followed by their incorporation at different mass fractions into the epoxy adhesive, including both pristine and functionalized nanoparticles. Subsequently, Type I specimens (ASTM D638) are fabricated and tested to evaluate the variations in mechanical properties of the different adhesive-based nanocomposites.

Materials

The materials used in this study included three types of carbon-based nanoparticles, multiwalled carbon nanotubes (MWCNTs), graphene, and carbon black, along with a commercial epoxy adhesive. The MWCNTs (TNIM4, 95% purity) were sourced from Chengdu Organic Chemicals Co. Ltd and had a length of 10–30 μm, an internal diameter of 5–10 nm, and an external diameter of 10–30 nm. Graphene (HP10 Powder, 99.5% purity, 0.17 g/cm³ density) was supplied by Hexo Graphene Indústria Química LTDA. Carbon black, with a particle diameter of 64–74 nm and a surface area of 35 m²/g, was manufactured by Orion Engineered Carbons and provided by Caribor Tecnologia da Borracha. The epoxy adhesive (AR/AH-345), with a elasticity modulus of approximately 4.0 GPa and a viscosity of 61, 000 cps, was supplied by E-Composites Comércio de Materiais Compostos LTDA.

Nanoparticles plasma functionalization

The carbon-based nanoparticles were pre-mixing with 10% by mass of urea in solid phase. This process was performed using a mortar and pestle until a visually homogeneous mixture was obtained by Steffen.¹⁷ The treatment was conducted in a home made reactor (Figure 2), in capacitive coupling mode (CCP) using a dielectric barrier discharge (DBD) configuration. A gas mixture of argon and nitrogen in an 80:20 ratio was used for the plasma process. The treatment was applied for 30 min, with a real power of 35 W and a radio frequency (RF) source operating at 13.56 MHz.

The nanoparticle and urea mixture was evenly spread on the surface of the vacuum chamber, forming a layer with a thickness not exceeding 3 mm. After placing the sample into the reactor, the chamber was evacuated to a base pressure of approximately 4.0 × 10⁻² Torr. Nitrogen was then gradually introduced until the system pressure reached 2.8 × 10⁻¹ Torr, followed by the introduction of argon until a final pressure of 9.0 × 10⁻¹ Torr was achieved. The system was allowed to stabilize for 15 min to ensure uniform gas flow and pressure. Once stabilized at approximately 1 Torr, the RF source was activated, and the real power was gradually increased to 35 W. This power level was maintained for 30 min to carry out the plasma functionalization process. At the end of the treatment, the RF source was turned off, the argon flow was closed, and the nitrogen flow was fully opened for an additional 5 min, completing the plasma functionalization process.

Nanocomposite preparation

The nanocomposites were individually prepared by incorporating only one type of nanoparticle per formulation into Component A of the adhesive (AR-345) using a torque rheometer (Thermo Scientific Haake Rheomix 600) at 23°C and 100 rpm for 10 min. Following this, the catalyst (AH-345) was manually mixed into the adhesive for 4 min in a 100A : 45B mass ratio.

The resulting homogeneous mixture was carefully transferred into silicone molds (Five samples of each composition) (Figure 3(a)) designed according to ASTM D638 Type I specifications, using a spatula to ensure even filling. The samples were cured at room temperature for 24 h before being demolded (Figure 3(b)) and subsequent prepared for testing. Samples were labeled based on their composition as (Adhesive/mass fraction/type of nanoparticle), with “.f” appended to indicate functionalized nanoparticles. The abbreviations used for the nanoparticles were CNT (carbon nanotubes), NF (carbon black), and Gr (graphene). Table 1 provides a summary of the composition and processing details for all developed samples.

Table 1.

Samples code.

Sample code
Ad/0.25/CNT	Ad/0.25/CB	Ad/0.25/Gr
Ad/0.5/CNT	Ad/0.5/CB	Ad/0.5/Gr
Ad/1.0/CNT	Ad/1.0/CB	Ad/1.0/Gr
Ad/0.25/CNT.f	Ad/0.25/CB.f	Ad/0.25/Gr.f
Ad/0.5/CNT.f	Ad/0.5/CB.f	Ad/0.5/Gr.f
Ad/1.0/CNT.f	Ad/1.0/CB.f	Ad/1.0/Gr.f

Fourier transform infrared spectroscopy (FTIR)

FTIR spectroscopy analyses were carried out using a Bruker INVENIO-S FTIR spectrophotometer (CMU/UDESC/CCT). Spectra were recorded in the range of 4000–400 cm⁻¹ with a resolution of 4 cm⁻¹, using the transmission mode with KBr pellets. A total of 32 scans were accumulated for each sample.

X-ray photoelectron spectroscopy (XPS)

The XPS analysis was performed using a commercial K-Alpha spectrometer (CMU/UDESC/CCT), manufactured by Thermo Scientific, with a base pressure below 5 × 10⁻⁸ mBar. The Al K_α line (hν = 1486.6 eV) was used as the ionization source, and the analyzer pass energy was set to 200 eV for survey spectra and 50 eV for high-resolution spectra. Some nanoparticles underwent a washing process to remove unreacted urea. The samples were immersed in methanol and subjected to magnetic stirring for 12 h, followed by vacuum filtration using a PVDF membrane with 0.22 µm pores. The collected material was then dried in an oven at 70°C for 1 h.

Transmission electron microscope (TEM)

The distribution and dispersion of the nanoparticles in the polymer matrix were characterized by transmission electron microscopy (TEM). The transmission electron microscope used was a Jeol JEM-2100 (CMU/UDESC-CCT). The samples were microtomed into sections with a thickness of 70 nm using the RCM Power Tome X ultramicrotome, with a diamond knife, at room temperature.

Tensile test

To determine the Young’s modulus (E) and the ultimate tensile strength (σ_r), a tensile test was performed using the INSTRON EMIC 23–100 universal testing machine (UDESC-CCT), equipped with a 100 kN load cell, a testing speed of 5 mm/min, at room temperature, and fitted with an extensometer. The test was conducted according to ASTM D638 Type I standard. The cross-sectional area of each specimen was individually calculated for the correct application in the stress calculation.

Scanning electron microscope (SEM)

The fracture behavior of the specimens was analyzed by scanning electron microscopy (SEM) using a JEOL JCM 700 benchtop microscope (CMU/UDESC/CCT).The fractured surface was coated with gold.

Results and discussion

The initial analyses refer to the FTIR spectra of all nanoparticles before and after functionalization (Figure 4). For carbon nanotubes, the band at 3440 cm⁻¹ is attributed to the stretching and in-plane bending vibrations of O–H bonds, associated with carboxylic groups or adsorbed water. The bands at 2920 and 2850 cm⁻¹ are related to C–H stretching vibrations. The band at 1635 cm⁻¹ corresponds to the vibration of conjugated C=C bonds, typically found in non-graphitic aromatic domains, and may also include the bending mode of the N–H bond from amine groups. The region between 3500 and 3000 cm⁻¹, in addition to O–H stretching, may also involve the symmetric and asymmetric stretching modes of N–H bonds from urea. The band at 1417 cm⁻¹ can be associated with the deformation of C–N, C–O, or N–H bonds, while the band at 1162 cm⁻¹ is attributed to C–O stretching. The overlap of these bands may hinder the precise identification of nitrogen-containing groups by FTIR alone.^23–25

For carbon black, the peak at 3440 cm⁻¹ also corresponds to O-H groups. The band at 1630 cm⁻¹ arises from the stretching vibration of C=C bonds, while the peak at 1384 cm⁻¹ is attributed to C-H bending modes. The band at 2360 cm⁻¹, more pronounced in the functionalized CB, is associated with the stretching vibrations of nitrogen-containing bonds.²⁶ For graphene, the characteristic bands of O–H and C=C groups appear at 3440 cm⁻¹ and 1640 cm⁻¹, respectively. Bending vibrations at 1585 cm⁻¹ confirm the presence of NH₂ groups, while O–H group vibrations are also observed at 1400 cm⁻¹.²⁷

To complement the FTIR analysis and deepen the investigation of the surface chemical composition—especially regarding functional groups that may overlap or remain undetected—X-ray photoelectron spectroscopy (XPS) was employed. It can be observed (Table 2) that the untreated nanoparticles display predominant atomic concentrations of C 1s, due to the aromatic carbon bonds in their compositions, and a low atomic concentration of O 1s, possibly originating from impurities in the nanoparticle production process.²⁸ The XPS results revealed percentage increases in O 1s and N 1s for all the functionalized samples. Carbon black (CB), after functionalization, showed a 14% increase in the O 1s percentage (1.65 at.%) and an atomic percentage of N 1s of 0.55 at.%. Graphene, on the other hand, exhibited 0.52 at.% of N 1s and an 18% increase in the O 1s atomic percentage (1.86 at.%). Among the functionalized nanoparticles, carbon nanotubes (CNT.f) exhibited the highest nitrogen content, with a N 1s value of 0.63 at.% and a 37% increase in O 1s content (2.59 at.%) compared to pristine CNTs. These results are consistent with the findings of Yatim et al.,²⁹ who reported that oxygenated functional groups, such as carboxyl (-COOH) and hydroxyl (-OH), create active sites that enhance nitrogen incorporation during plasma treatment.

Table 2.

Atomic percentage of C 1s, O 1s, and N 1s for pristine and functionalized nanoparticles.

Sample	C 1s (%)	O 1s (%)	N 1s (%)
CNT pristine	98.11	1.89	0.00
CB pristine	98.17	1.45	0.00
Graphene pristine	98.31	1.58	0.00
CNT + urea (plasma)	96.78	2.59	0.63
CB + urea (plasma)	97.51	1.65	0.55
Graphene + urea (plasma)	97.62	1.86	0.52

High-resolution N 1s spectra confirm the presence of N-C bonds after functionalization in all nanoparticles (Figure 5). The CNT.f samples displayed the largest peak area for N-C bonds, corroborating their higher atomic nitrogen content and demonstrating the effectiveness of the functionalization process for this material.

The O 1s deconvolution for pristine and functionalized CNTs (Figure 6) revealed peaks corresponding to O=C, O-C, O-C=O, and H₂O, with their respective areas determined from high-resolution spectra. For pristine CNTs, the most prominent peak was O-C=O (45.38%), while after functionalization, the predominant peak shifted to O=C (44.59%). This shift indicates the formation of carbonyl (C=O) groups due to interactions with the nanotube walls, as described by Kim et al.³⁰ Additionally, there was a notable decrease in water content, from 10.35% to 6.88%, suggesting that the newly introduced functional groups (O-C and O=C) occupied adsorption sites, thereby demonstrating the plasma treatment’s effectiveness.¹⁷ These findings align with those of Langston and Granata,³¹ who observed that nitric acid treatment increases oxygen content on carbon fibers, promoting the formation of carbonyl (C=O) and carboxyl (O-C=O) groups. This enhancement in in oxygenated functional groups raises the surface energy of carbon materials, improving their reactivity and potential for integration in composite system.

Table 3 summarizes the O 1s bond percentages for all nanoparticles, highlighting the changes observed before and after functionalization. For carbon black (CB), the O 1s deconvolution indicated that, in its pristine state, the O-C bond predominated (51.89%). After plasma treatment, this was replaced by a higher proportion of O-C=O bonds (55.17%), accompanied by a slight increase in O=C contend and a reduction in water content from 12.72% to 9.98%. For pristine graphene, the O=C and O-C=O bonds predominated (42.72% and 41.91%, respectively), with smaller percentage of O-C (9.39%) and H₂O (5.98%). Following plasma treatment, the relative percentages of O=C and O-C=O bonds decreased, offset by an increase in O-C and water content, suggesting the introduction of new functional groups and changes in surface chemistry. These results demonstrate the impact of plasma functionalization on the oxygenated bond distributions of each nanoparticle, highlighting the distinct behavior of bond percentages for each nanoparticle geometry. The success in the atomic insertions of oxygen and nitrogen on the surface demonstrates the effectiveness of the treatment in tailoring surface properties for enhanced compatibility with the polymer matrix.

Table 3.

O 1s % Area for different bonds in the nanoparticles.

Bond	CNT	CNT.f	CB	CB.f	Gr	Gr.f
O=C	29.8	44.59	15.34	19.52	42.72	24.29
O-C	10.65	19.25	51.89	15.34	9.39	26.8
O-C=O	45.38	29.29	20.04	55.17	41.91	32.64
H₂O	10.35	6.88	12.72	9.98	5.98	16.26

The adhesive AR/AH-345, used as the polymeric matrix, contains micro and nanoscale particles, with silica and calcium carbonate likely present as thixotropic and filler agents, as indicated by Ellis.³² TEM analysis was conducted on nanocomposites containing 1 wt.% of nanoparticles. For Ad/1.0/CNT and Ad/1.0/CNT.f samples (Figure 7), plasma functionalization was found to reduced nanotube entanglement without causing significant structural damage.

These observations are consistent with the findings of Steffen¹⁷ and Li et al.,¹⁶ which demonstrated that the introduction of polar functional groups during plasma treatment enhanced electrostatic repulsion between the nanoparticles, thereby mitigating agglomeration and promoting a more homogeneous dispersion within the matrix. For carbon black samples (Ad/1.0/CB and Ad/1.0/CB.f), no significant differences in overall dispersion were observed. However, specific regions showed greater separation between functionalized CB and matrix fillers (Figure 8). This effect is possibly due to repulsive effects from the introduced functional groups, which may reduce particle clustering and promote partial detachment from the surrounding filler particles.

In graphene-based nanocomposites (Ad/1.0/Gr and Ad/1.0/Gr.f), TEM images (Figure 9) revealed improved dispersion and increased separation from matrix fillers following plasma treatment. This result suggests that functionalization enhanced the electrostatic repulsion between the graphene sheets, reducing aggregation and promoting a more uniform distribution within the matrix. These findings are consistent with those reported by Lee et al.³³

In Figure 10, the samples were grouped by nanoparticle type, with a horizontal line indicating the average elastic modulus (E) of the neat adhesive. All nanocomposites exhibited an increase in stiffness, with the most substantial gains observed in the functionalized samples. This enhanced stiffness is attributed to the improved dispersion and interfacial adhesion of the nanoparticles, which are critical for efficient stress transfer.³⁴ The higher efficiency in nanoparticle dispersion directly influences the mechanical properties of the nanocomposites. Shokrian et al.³⁵ achieved a 10.5% increase in the maximum shear strength using advanced dispersion techniques.

The samples containing functionalized CNTs showed the most consistent improvements, emphasizing the role of oxygenated and nitrogenated groups on interfacial interactions. According to Ma et al.,³⁶ nitrogen-containing groups react with the epoxy matrix, forming covalent crosslinks that strengthen the interface between phases. Regarding ultimate tensile stress, Figure 11 illustrates a consistent increase in all samples compared to the neat adhesive, with the highest values observed in nanocomposites containing 0.25% nanoparticles. The most significant improvement was seen in the samples with functionalized CNTs, which demonstrated a 21% increase in ultimate stress, rising from 37.7 MPa to 45.6 MPa. This highlights the significant role of functionalization in improving matrix interactions and enhancing deformation behavior.

In Figure 12, the same set of samples containing 0.25% of nanoparticles is presented in the form of a Stress-Strain curve. It can be observed that the brittle fracture characteristics of the adhesive remained unchanged with the addition of the nanofiller.

The SEM images reveal the fracture surface characteristics after tensile tests. In the samples containing 1% CNT (Figure 13), plasma functionalization notably reduced both the pore size and quantity, while smoothing the fracture surface edges. These changes are typically associated with crack propagation barriers, such as rigid nanoparticles. Figure 14 further corroborates this observation, showing dispersed nanotubes along the fracture edges (indicated by red markings), consistent with XPS and TEM results.

For the 1% CB samples, no significant changes in fracture morphology were observed. However, in the graphene-based samples (Figure 15), functionalization reduced the pull-out regions of matrix-intrinsic particles (rods) and increased their exposure on the fracture surface. This behavior suggests that functionalization enhanced the interaction between pre-existing matrix fillers and the epoxy, improving adhesion without the need for surface modification of these fillers.

Conclusions

This study aimed to investigate the influence of plasma functionalization on carbon nanoparticles with different geometries on the thermal and mechanical properties of an epoxy adhesive. To this end, pristine and functionalized nanoparticles were incorporated into the epoxy adhesive matrix at different mass fractions, and their properties were analyzed in relation to the effects of functionalization on the matrix/nanoparticle interaction, as well as on the properties of the reinforced adhesive.

The results demonstrate that plasma functionalization induces significant modifications in carbon-based nanoparticles. XPS analysis revealed an increase in oxygen- and nitrogen-containing functional groups, with functionalized carbon nanotubes showing a 37% increase in the O 1s percentage (from 1.89 at.% to 2.59 at.%), and reaching 0.63 at.% for N 1s, enabling greater reactivity and better interaction with the epoxy matrix. TEM analyses confirmed reduced agglomeration in the functionalized samples, particularly for nanotubes and graphene, suggesting better dispersion and electrostatic repulsion.

In mechanical tests, the functionalized nanocomposites exhibited increased stiffness and maximum tensile strength. The samples containing 0.25% functionalized CNTs showed a 21% increase in rupture stress compared to pristine. This gain was attributed to the improved interaction between the matrix and the nanoparticles, facilitated by the functional groups introduced during the functionalization process. SEM images supported these results, revealing more homogeneous fracture surfaces and reduced porosity in the functionalized samples. For graphene, functionalization also improved the interaction between pre-existing adhesive fillers and the matrix, enhancing overall adhesion.

The next step of this project is to evaluate the application of this adhesive in DCB-bonded composite joints, focusing primarily on the interfacial properties under mode I. This will allow us to assess whether the functionalization of the nanoparticles and their different geometries has the potential to enhance the performance of composite joints.

Footnotes

Acknowledgements

The authors acknowledge the financial support of the Santa Catarina State Research and Innovation Foundation (FAPESC number: 2017TR1747, 2023TR563, and 2024TR2327). As well as, Coordination for the Improvement of Higher-Level Personnel (CAPES Finance Code 001), PROMOP (Programa de Bolsas de Monitoria de Pós-Graduação) of the Santa Catarina State University. Ricardo De Medeiros and Daniela Becker acknowledge the financial support of the National Council for Scientific and Technological Development (CNPq process number: 304795/2022-4 and 306823/2021-7). The authors are thankful for the Multi-User Facility infrastructure of Santa Catarina State University’s Technological Sciences Center.

ORCID iD

Ricardo De Medeiros

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors acknowledge the financial support of the Santa Catarina State Research and Innovation Foundation (FAPESC number: 2017TR1747, 2023TR563, and 2024TR2327). As well as, Coordination for the Improvement of Higher-Level Personnel (CAPES Finance Code 001), PROMOP (Programa de Bolsas de Monitoria de Pós-Graduação) of the Santa Catarina State University. Ricardo De Medeiros and Daniela Becker acknowledge the financial support of the National Council for Scientific and Technological Development (CNPq process number: 304795/2022-4 and 306823/2021-7).

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author on request.*

References

Jeevi

Nayak

Abdul Kader

. Review on adhesive joints and their application in hybrid composite structures. J Adhes Sci Technol 2019; 33(14): 1497–1520.

Banea

da Silva

. Mechanical characterization of flexible adhesives. J Adhes 2009; 85(4-5): 261–285.

Beck

da Silva

JAP

da Silva

, et al. Assessing critical fracture energy in mode i for bonded composite joints: a numerical–experimental approach with uncertainty analysis. Proc Inst Mech Eng Part L. 2024; OnlineFirst: 14644207241229601.

Ekrem

Şahin

ÖS

Karabulut

, et al. Thermal stability and adhesive strength of boron nitride nano platelets and carbon nano tube modified adhesives. J Compos Mater 2018; 52(11): 1557–1565.

da Silva

Beck

da Silva

, et al. Parametric study of bonded composite joints under mixed-mode. J Compos Mater. 2024; OnlineFirst: 00219983251343134.

Pocius

. Adhesion and adhesives technology: an introduction. Carl Hanser Verlag GmbH Co KG, 2021.

Khabaz-Aghdam

Behjat

da Silva

, et al. A new theoretical creep model of an epoxy-graphene composite based on experimental investigation: effect of graphene content. J Compos Mater 2020; 54(18): 2461–2472.

Akpinar

Gültekin

Akpinar

, et al. Research on strength of nanocomposite adhesively bonded composite joints. Compos B Eng 2017; 126: 143–152.

Mandal

Panigrahi

Dinesh Kumar

, et al. Unveiling pressure-sensitive adhesiveness of a carbonized polymer dot. Polymer 2022; 254: 125102.

10.

Aggarwal

Sharda

Srivastava

, et al. Carbonized polymer dot-tannic acid nanoglue: tissue reinforcement with concurrent fluorescent tracking, insulin delivery, and reactive oxygen species regulation for normal and diabetic wound healing. Small 2024; 20: e2405531.

11.

Sreenath

Singh

Satyanarayana

et al. Carbon dot–unique reinforcing filler for polymer with special reference to physico-mechanical properties. Polymer 2017; 112: 189–200.

12.

Sreenath

Mandal

Panigrahi

et al. Carbon dots: fluorescence active, covalently conjugated and strong reinforcing nanofiller for polymer latex. Nano-Struct Nano-Objects 2020; 23: 100477.

13.

Ekrem

Koyunbakan

Unal

. Investigation of the mechanical and thermal properties of epoxy adhesives reinforced by carbon nanotubes and silicon dioxide nanoparticles in single-lap joints. J Adhes Sci Technol 2024; 38: 3860–3875.

14.

Yilmaz

Ekrem

. Effect of low velocity impact at different temperatures on hybrid adhesives in aluminium-composite single lap joints. J Compos Mater 2024; 59: 807–820.

15.

Ajayan

Schadler

Braun

. Nanocomposite science and technology. John Wiley & Sons, 2006.

16.

Kröger

Liu

. Nanoparticle geometrical effect on structure, dynamics and anisotropic viscosity of polyethylene nanocomposites. Macromolecules 2012; 45(4): 2099–2112.

17.

Steffen

. Funcionalização de nanotubos de carbono por plasma rádio frequência e sua influência em nanocompósitos de epóxi. Master’s Thesis. Santa Catarina State University - UDESC, Joinville, Santa Catarina, 2017.

18.

Chen

Dai

Magniez

, et al. Improving the mechanical properties of epoxy using multiwalled carbon nanotubes functionalized by a novel plasma treatment. Compos Appl Sci Manuf 2013; 45: 145–152.

19.

Hosur

Rahman

Brundidge-Young

, et al. Mechanical and thermal properties of amine functionalized multi-walled carbon nanotubes epoxy-based nanocomposite. Compos Interfaces 2010; 17(2-3): 197–215.

20.

Larouche

St-Aubin

Balmayer

, et al. Nitrogen functionalization of carbon Black in a thermo-convective plasma reactor. Plasma Chem Plasma Process 2011; 31: 635–647.

21.

Alam

Wan

McNally

. Surface amination of carbon nanoparticles for modification of epoxy resins: plasma-treatment vs. wet-chemistry approach. Eur Polym J 2017; 87: 422–448.

22.

Bertóti

Farah

Bulatko

, et al. Nitrogen implantation into graphene oxide and reduced graphene oxides using radio frequency plasma treatment in microscale. Carbon. 2022; 199: 415–423.

23.

Stobinski

Lesiak

Kövér

et al. Multiwall carbon nanotubes purification and oxidation by nitric acid studied by the ftir and electron spectroscopy methods. J Alloys Compd 2010; 501(1): 77–84.

24.

Mahani

Mekkey

Elsayed

, et al. Structural and ac electrical properties study of solid metal urea complexes. Journal of Advanced Dielectrics 2018; 8: 1850013.

25.

Alam

Islam

Mina

, et al. Structural, mechanical, thermal, and electrical properties of carbon Black reinforced polyester resin composites. J Appl Polym Sci 2014; 131: 40421.

26.

Luo

Wang

, et al. Thermodynamic simulation and experimental investigation of plasma preparation of nanosized carbon using propane. J Nanomater 2019; 2019: 1–13.

27.

Ţucureanu

Matei

Avram

. The effect of the polymeric matrix on the emission properties of yag-based phosphors. J Alloys Compd 2020; 844: 156136.

28.

Benadji

Ikkene

Boudjemaa

, et al. Removal of cr(vi) from aqueous solutions using amino-functionalized carbon nanospheres adsorbents. Water Environ Res 2018; 90: 1925–1937.

29.

Mohamad

Shaaban

Mohd Fairuz

, et al. Effect of functionalised and non-functionalised carbon nanotubes-urea fertilizer on the growth of paddy. Trop Life Sci Res 2018; 29: 17–35.

30.

Kim

, et al. Surface modifications for the effective dispersion of carbon nanotubes in solvents and polymers. Carbon 2012; 50: 3–33.

31.

Langston

Granata

. Influence of nitric acid treatment time on the mechanical and surface properties of high-strength carbon fibers. J Compos Mater 2014; 48: 259–276.

32.

Ellis

. Chemistry and technology of epoxy resins. Blackie Academic & Professional, 1993.

33.

Lee

Wang

Tsai

34.

Han

Meng

Araby

, et al. Mechanical and electrical properties of graphene and carbon nanotube reinforced epoxy adhesives: experimental and numerical analysis. Compos Appl Sci Manuf 2019; 120: 116–126.

35.

Shokrian

Shelesh-Nezhad

Najjar

. Effect of cnt dispersion methods on the strength and fracture mechanism of interface in epoxy adhesive/al joints. J Adhes Sci Technol 2019; 33(13): 1394–1409.

36.

Tang

, et al. Dispersion, interfacial interaction and re-agglomeration of functionalized carbon nanotubes in epoxy composites. Carbon 2010; 48(6): 1824–1834.