Fractural performance of epoxy nanocomposites reinforced with carbon aerogels in different structures
Introduction
In recent decades, polymer nanocomposites have received much attention due to their unique properties. Increasing the surface area due to the transfer from microparticles to nanoparticles, low concentration of required filler for significant changes in the mechanical properties of nanocomposites has caused increasing attention to this category of materials [1], [2], [3]. Generally, the dispersion of nanoparticles and the optimal adhesion between the matrix and the particles play very important roles in determining the mechanical properties of polymer nanocomposites [4], [5], [6].
Epoxy resins are subset of thermoset resins and constitute polymer matrixes. There is a great interest in epoxy resins due to the different groups of epoxy for extensive reactions and outstanding properties of cross-linked polymers. These properties include high strength, very low creep, and excellent resistance to chemical agents, weather and heat. Disadvantages of thermoset polymers are their low final strain at rupture, which leads to low impact resistance and reduced fracture toughness [7], [8], [9], [10]. According to the studies reported so far, many methods have been proposed to improve the toughness of epoxy resins. Among these methods is the combination of epoxy resin with nanofillers and the production of polymer nanocomposites [11], [12], [13]. Chandrasekaran et al. [14] used Aerographite (AG) to reinforce the epoxy matrix. Their composites showed 133% improvement in energy absorption per unit volume, and 19% increase in fracture toughness (KIC). The mechanisms pull-out of arms of AG tetrapod, interface and inter-graphite failure have improved the toughness of composites. Salimian et al. [15] used silica aerogel to increase the toughness of epoxy nanocomposites by 126%. They attributed the toughness improvement to the mechanisms: pinning, crack deflection, debonding and plastic deformation. Park et al. [16] treated multi-walled carbon nanotubes (MWCNTs) surface with chemical functionalization and used them to make epoxy nanocomposites. Nanocomposites containing modified MWCNTs showed better fracture toughness than unmodified MWCNTs. Examination of the fracture surface of the samples showed increment in river lines and the fracture surface, and considerable increase in the fracture toughness of nanocomposites, which resulted due to the good dispersion of the modified particles throughout the matrix.
The aerogel word is used for sol-gel materials in which the liquid component of the gel is replaced with a gas, leaving a solid nanostructure without the collapse of pores, so that 90–99% of its volume is occupied by air. As a result, aerogels are highly porous solids with a high specific surface area and extremely low density [17]. Therefore, these materials are used for various applications. In general, due to the porous structure of aerogels, these materials are proposed as a new alternative for reinforcement of polymer nanocomposites in very low weight quantities. Thus, by placing these materials in the polymer bed and trapping the chains inside the pores, a high interaction between the polymer and the filler can be achieved [18]. Among the types of aerogels, carbon aerogels were widely welcomed due to their extremely high specific surface area and strong mechanical properties. Carbon nanotubes (CNTs) are one of the best candidates for making carbon aerogels due to their unique properties e.g. small size, low density, high aspect ratio, and considerable stiffness and strength. Due to the CNTs aspect ratio, carbon aerogels with high porosity and specific surface area can be produced from them or their combination with carbon particles, as a new nanomaterial for engineering applications [19], [20], [21], [22].
The KIC (fracture toughness) and GIC (fracture energy) parameters are used to investigate the fracture mechanics of nanocomposites. KIC is the degree of resistance of the material to crack propagation and GIC is defined as the amount of energy required to form 1 m2 of new surface [23]. In general, measurement of fracture parameters is evaluated both directly and indirectly. The direct method is based on calculations that eventually arrive at the true value of the parameters, while the indirect method provides an estimate of the actual value of the parameters [24].
In this work, epoxy nanocomposites were produced using two different types of carbon aerogels as reinforcements in various weight percentages (0.1, 0.3, and 0.5 wt%). Carbon aerogels were different in specific surface area and total pore volume. Three-point bending and impact test methods were used to evaluate the fracture parameters to compare direct and indirect methods, respectively. SEM and AFM observations were used to investigate the fractography and topography of the nanocomposites, respectively. The purpose of this study was to investigate the effect of physical structure of aerogels in different contents on fracture parameters using direct and indirect measurements. The results showed that only by changing the physical structure of the filler and very low weight percentages and creating physical intermingles between the filler and the matrix, the fracture toughness of nanocomposites has increased significantly.
Section snippets
Materials
CNT-doped carbon aerogel (CNT-CA) and Carbon aerogel (CA) were synthesized according to the methods described elsewhere [25], [26], [27]. Aerogel powders have porosity above 90% and particles diameter of 11.48 ± 4.00 μm. The specific surface area (measured by BET (SBET)), the average pores diameter (Dmean), the total volume of pores (Vt), skeleton densities (ρs) and apparent densities (ρa) of aerogels are presented in Table 1. Epoxy matrix had the following composition: Epoxy bisphenol A resin
Fracture toughness
Three-point bending test was used to determine energy absorption of the samples in static mode. The results are shown in Fig. 1 and Table 3. Fig. 1 (a, b) show force-displacement diagrams of nanocomposites (a) Ep/CA, (b) Ep/CNT-CA and Fig. 1 (c, d) show (KIC) and (GIC) of all the nanocomposites. Fig. 1 (a, b) show that bending properties of all the nanocomposites are improved compared to the pure epoxy matrix. In all the samples, by increasing the content of aerogels, the force and elongation
Conclusions
Epoxy nanocomposites were fabricated using carbon aerogels with different physical structures in different weight percentages (0.1, 0.3, and 0.5 wt%). Carbon aerogels improved fracture toughness (106–143%), fracture energy (241–372%), impact strength (50–58%) and roughness (10.28–14.72 nm) of nanocomposites, compared to the neat epoxy matrix. Examination of the fracture surface of nanocomposites indicated that the known mechanisms: pinning, crack deflection, river lines formation and debonding
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors would like to thank the Ministry of Science, Research and Technology of Iran (MSRT) for financial support of this research. Also, Isfahan University of Technology, and Tarbiat Modares University are acknowledged for the provided laboratory facilities for accomplishment of this research work.
References (43)
- et al.
Influence of microfluidic flow rates on the propagation of nano/microcracks in liquid core and hollow fibers
Theor. Appl. Fract. Mech.
(2018) - et al.
Hollow fiber reinforced polymer composites, in
Fiber Reinforced Composites, Elsevier
(2021) - et al.
Self-healing of densely crosslinked thermoset polymers—a critical review
Prog. Org. Coat.
(2017) - et al.
The effect of agglomeration on the fracture toughness of CNTs-reinforced nanocomposites
Theor. Appl. Fract. Mech.
(2018) - et al.
Effective addition of nanoclay in enhancement of mechanical and electromechanical properties of SWCNT reinforced epoxy: Strain sensing and crack-induced piezoresistivity
Theor. Appl. Fract. Mech.
(2020) - et al.
Interfacial toughening of carbon/epoxy composite by incorporating styrene acrylonitrile nanofibers
Theor. Appl. Fract. Mech.
(2018) - et al.
Interlaminar toughening in carbon fiber/epoxy composites interleaved with CNT-decorated polycaprolactone nanofibers
Compos. Commun.
(2021) - et al.
Fracture, failure and compression behaviour of a 3D interconnected carbon aerogel (Aerographite) epoxy composite
Compos. Sci. Technol.
(2016) - et al.
Fabrication and evaluation of silica aerogel-epoxy nanocomposites: fracture and toughening mechanisms
Theor. Appl. Fract. Mech.
(2018) - et al.
High-performance graphene oxide/carbon nanotubes aerogel-polystyrene composites: Preparation and mechanical properties
Mater. Lett.
(2018)
Impact and after-impact properties of nanocarbon aerogels reinforced epoxy/carbon fiber composite laminates
Compos. Struct.
Properties of single-walled carbon nanotube-based aerogels as a function of nanotube loading
Acta Mater.
Methylene blue removal by carbon nanotube-based aerogels
Chem. Eng. Res. Des.
Synthesis and characterization of powdered CNT-doped carbon aerogels
J. Non-Cryst. Solids
The mechanisms and mechanics of the toughening of epoxy polymers modified with silica nanoparticles
Polymer
Grafting of epoxy chains onto graphene oxide for epoxy composites with improved mechanical and thermal properties
Carbon
Tribological performance of carbon nanotube–graphene oxide hybrid/epoxy composites
Compos. B Eng.
Effect of colloidal silica on the strength and energy absorption of glass fiber/epoxy interphases
Compos. A Appl. Sci. Manuf.
Polymer-matrix nanocomposites, processing, manufacturing, and application: an overview
J. Compos. Mater.
Efficient Improvement in Fracture Toughness of Laminated Composite by Interleaving Functionalized Nanofibers
Polymers
Composite materials: design and applications
Cited by (4)
Exploring the interlaminar toughening potential of carbon nanoparticles: Structural and size effects
2024, Composites CommunicationsThe effects of nano-additives on the mechanical, impact, vibration, and buckling/post-buckling properties of composites: A review
2023, Journal of Materials Research and TechnologyA closed-form solution for thermoelastic stress analysis of perforated asymmetric functionally graded nanocomposite plates
2022, Theoretical and Applied Fracture MechanicsCitation Excerpt :materials were developed by CNT for high and multi-objective performance [15,16]. Comparison of thermal, electrical, and mechanical properties of polymer composites with and without CNT leads to interesting results [17–20]. In the development of composites, Shen [21] used the concept of FGM to aggregate and grade CNT into an isotropic matrix that determined the distribution of CNT using specific rules for the development of mechanical properties.
The influence of CNT-doped carbon aerogels on microstructural, rheological and mechanical properties of epoxy nanocomposites
2021, Composites Science and TechnologyCitation Excerpt :This phenomenon can be attributed to two reasons: 1) The presence of CNTs in the carbon bed (CNTs have high thermal stability), 2) Different structure of CNT-CA aerogel compared to CA. CNT-CA aerogel has the very high special surface area, and more total pores volume, as a result of the aerogel particles being placed in the epoxy matrix, there is more interaction between filler and the matrix and particles provide more barriers to the movement of polymer chains [45]. After completing the analysis, the amount of residual ash is determined and the results are reported in Table 1.