A technical review on epoxy-nanoclay nanocomposites: Mechanical, hygrothermal and wear properties

Abstract This review offers a summary of the epoxy-nanoclay nanocomposites research that has been performed. Epoxy-nanoclay nanocomposites have an across-the-board variety of aerospace, defense, construction, and automobile applications. Nanoclay is one of the ideal nano-reinforcement for epoxy because of its ease of workability, environmental accessibility, well-versed chemistry, and lower cost. The significant addition of a smaller quantity of nanoclay, mostly ≤5 wt.%, may efficiently improve polymer composites’ properties. This review aims to provide a state-of-the-art overview of epoxy-nanoclay nanocomposites, including their preparation methods, mechanical, hygrothermal, and wear properties. The discussion highlights the nanoclay influence on the properties listed above and the morphology of epoxy-nanoclay nanocomposites.


Epoxy
Epoxy resin is a versatile and widely used synthetic material known for its exceptional adhesion, durability, and chemical resistance.It is a type of thermosetting polymer formed through the reaction of two main components: epoxy resin and a curing agent (also called hardener).Epoxy resins are valued for their wide range of applications across various industries, including construction, electronics, automotive, aerospace, art, and more.Epoxies usually outperform the majority of resin forms with respect to mechanical properties, heat, and chemical resistance and, hence, are almost exclusively used as adhesives, coatings, and matrix material (Cerit et al., 2016;Park & Seo, 2011;Shettar et al., 2019;Unnikrishnan & Thachil, 2006).
Unlike other resins, epoxies are cured with a "hardener" instead of a catalyst.In an "addition reaction" where both products participate in the chemical reaction, the hardener uses an amine to cure the epoxy.This reaction's chemistry indicates that each amine site typically has two epoxy sites bonded to it (Kárpáti et al., 2020;Park & Seo, 2011).
Meanwhile, the amine molecules "co-react" with the epoxy molecules in a predetermined ratio.The correct resin-to-hardener ratio must be obtained to guarantee a full reaction.Unreacted hardener or resin will remain within the matrix if amine and epoxy are not mixed in the predetermined ratios, affecting the final properties after cure (Gebhard et al., 2008;Park & Seo, 2011).Manufacturers typically articulate the components to have an apparent mixing ratio that is simply accomplished by calculating the weight or volume to assist with precisely mixing the epoxy and the hardener.
Other factors, such as cure time, temperature, and mixing ratio, can create vastly distinct macromolecular structures in addition to the hardener's chemical nature.The hardener to epoxy ratio has substantially affected mechanical and thermal properties (Jiang et al., 2015;Pereira & D'Almeida, 2016).

Nanoclay
Nanoclay is a crystalline compound with very fine grain sizes.The most basic structural feature of nanoclay is a sheet, which is likely to be stacked on top of one another like pages of a book (Nazir et al., 2016;Uddin, 2008), shown in Figure 1.
Nanoclay has earned distinction over numerous nanoparticles owing to its ease of workability, environmental accessibility, well-versed chemistry, and lower cost.They are the highly accepted reinforcement fillers for polymer resins (Bitinis et al., 2011;Dantas de Oliveira & Augusto Gonçalves Beatrice, 2019;Guo et al., 2018).The previous literature (Ho et al., 2006;Kini et al., 2019;Lim & Chow, 2011;Yasmin et al., 2006;Zainuddin et al., 2010) shows that higher superficial area and great aspect ratio are the primary characteristics accountable for the nanoclay as reinforcement for polymer matrix.Each layer of nanoclay has 200-600 nanometers of lateral dimensions and a thickness of only some nanometers (Ray, 2014).In order to be organophilic and compatible with organic polymers, the surface of nanoclay should be reformed prior to its use.Organic cations, viz., ammonium or phosphonium ion, are typically used as organic modifiers for nanoclay (Munteniţă et al., 2018).Nanoclay may be diffused in a polymer matrix based on the surface alteration of the nanoclay layers by aminopropyltriethoxysilane.With ammonium salts, commercially available nanoclays are modified.They are often referred to as "organically modified nanoclays or organoclays" (Shettar et al., 2019;Zhang et al., 2016).
The modification process involves introducing organic molecules, usually long hydrocarbon chains, onto the surface of the clay particles.These organic molecules can interact more effectively with organic materials (polymers) due to their similar chemical nature (Sabaa et al., 2020).The organic modification alters the interlayer spacing between the clay layers and makes the clay particles more dispersible in organic solvents or polymer matrices (Abdel-Gawad et al., 2022;Zhu et al., 2019).The most commonly used type of clay for organophilic modification is montmorillonite, which is a type of smectite clay.Montmorillonite has a layered structure, and its layers are held together by weak forces, allowing for easy intercalation of organic molecules (Noskov et al., 2020).

Epoxy-nanoclay nanocomposites
Epoxy-nanoclay nanocomposites have been comprehensively researched over the last decade.Epoxynanoclay nanocomposites have attracted a lot of attention in the materials world due to their favorable properties.The nanoclay-filled polymers could display significant enhancement in mechanical, thermal, fire retardancy, and barrier properties (Alsagayar et al., 2015;Kusmono & Mohd Ishak, 2013;Zaïri et al., 2011).However, such fillers have some disadvantages, such as reducing the failure strain (Jumahat et al., 2012).Owing to the fine and homogeneous dispersion in the matrix, the ability to achieve the most beneficial effect in epoxy-nanoclay nanocomposites is derived from the characteristics of nanoclays (Šupová et al., 2011).A small percentage of nanoclay, typically 5 wt.%, may significantly enhance the properties of polymer composites (Jeyakumar et al., 2017;Okada & Usuki, 2006).Further, a rise in the nanoclay wt.% would reduce the properties of the composite due to increased stiffness and agglomeration (Chan et al., 2011;Ho et al., 2006;Kumar et al., 2010).Higher nanoclay addition increases the number of air bubbles in the mix in the course of the mixing process.Hence, for better material properties, the amount of nanoclay must be carefully optimized (Saikia, 2020).
The specific objective of this review is to summarize and synthesize the latest advancements, research findings, and methodologies, contributing to the collective understanding of the field.Most importantly, this review article may be considered as reference material (general knowledge) for beginners/individuals working in a similar field.The main objective of this review is to present a comprehensive and up-to -date assessment of epoxy-nanoclay nanocomposites.This encompasses exploring their preparation techniques and an investigation of their mechanical, hygrothermal, and wear properties.The discourse emphasizes explicitly how nanoclay impacts the aforementioned properties, alongside an investigation into the morphology of epoxy-nanoclay nanocomposites.Many individuals fail to analyse morphology; hence, this article may help beginners to understand the same.

Monomer intercalation method
In this method, the organically modified nanoclay with a known quantity is blended in the epoxy by a mechanical/magnetic stirrer for 2 hours.The mixture is allowed overnight to swell.The mixture is then sonicated for 30 minutes using probe sonication.Then, the mix of nanoclayepoxy and the hardener (curing agent) is meticulously combined, degassed, cast, and cured (Jagtap et al., 2013;Kini et al., 2019).Figure 2 outlines the method schematically.

Solution intercalation method
To synthesize intercalated epoxy-nanoclay nanocomposites, polar solvents viz., water, acetone, and chloroform can be used.In the solvent, organoclay is swollen first.The polymer is then added to the solution, dissolved in the solvent, and intercalated between the nanoclay layers.The last step consists of extracting the solvent typically under vacuum by evaporation (Basturk & Celik Erbas, 2018;Mat Yazik et al., 2020).The schematic overview of the procedure is presented in Figure 3.

Physical and chemical properties
The interaction between organoclays and epoxy involves a complex interplay of chemical, physical, and interfacial forces, producing epoxy-nanoclay nanocomposites.These nanocomposites merge the properties of epoxy resins with the enhanced properties of nanoclays, leading to improved mechanical, wear, and barrier properties.The link or interaction between nanoclay and epoxy occurs through several following mechanisms: (1) Intercalation and Exfoliation: In the initial stages of producing epoxy-nanoclay nanocomposites, the organoclays are typically in a layered structure, with separate clay layers stacked together.The organic modifier on the nanoclays interacts with the epoxy matrix, causing the layers to separate and create gaps.Epoxy molecules can penetrate into these gaps, leading to intercalation (spacing between clay layers) or exfoliation (complete separation of individual layers) (Shanti Kiran et al., 2021, Fakhreddini-Najafabadi et al., 2021).
(2) Chemical Bonding: The organic modifier on the nanoclays can have functional groups that chemically interact with the epoxy molecules.This can lead to chemical bonding between the nanoclays and the epoxy matrix, further enhancing the compatibility and overall performance of the nanocomposite (Basturk & Celik Erbas, 2018).
(3) Van der Waals Forces: Van der Waals forces play a significant role in the interaction between the epoxy matrix and the organoclays.These forces help hold the nanoclays within the epoxy and contribute to the overall strength of the nanocomposite (Purut Koc et al., 2018).
(4) Physical Confinement: Nanoclays within the epoxy matrix can physically restrict the movement of polymer chains.This confinement effect can improve mechanical properties, such as increased stiffness and strength (Surendran et al., 2022).(5) Barrier Effect: The nanoparticle structure of the nanoclays can create a tortuous path for the movement of molecules.This barrier effect is particularly relevant for gas and moisture diffusion, making epoxy-nanoclay nanocomposites suitable for applications requiring enhanced barrier properties (Merah et al., 2022).
(6) Synergistic Effects: The interaction between nanoclays and epoxy can lead to synergistic effects, where the combined properties of the two materials exceed the sum of their individual properties.This can improve mechanical properties (Mylsamy et al., 2019, Anandraj et al., 2022).

Tensile properties
The tensile properties of the epoxy-nanoclay nanocomposites are determined by the microstructure through which the nanoclay layers in the epoxy resin are distributed.The good dispersion of the nanoclay particles in the resin usually results in enhanced tensile modulus and strength.As presented in Tables 1 (a) and (b), the tensile strength and modulus seem to enhance; with a rise in nanoclay wt.%, the tensile module's rising trend is more noticeable.The effect of nanoclay addition on the tensile modulus is largely owing to the disseminated nanoclay layer's greater aspect ratio and modulus (Sand Chee & Jawaid, 2019).This will offer a broad interfacial relation between nanoclay and the matrix.Table 1 (c) presents the drastic drop in the tensile strain before failure for epoxy-nanoclay nanocomposite, indicating a decline in epoxy resin ductility.At a higher nanoclay weight percentage, tensile strength improvement is very marginal.In some cases, tensile strength is reduced compared to pure epoxy because of the lack of adhesion between the matrix and the nanoclay.The reduction in strength is caused by the non-homogeneous dispersal of nanoclay at a higher weight percentage, which has caused agglomeration and stress concentration sites (Ozsoy et al., 2015;Saharudin et al., 2020).

Flexural strength
As per the literature and Table 2, the addition of nanoclay enhances the flexural strength of virgin epoxy, and at 2 wt.% of nanoclay, the maximum flexural strength is obtained.Epoxy-nanoclay nanocomposite's flexural strength increase is attributed to enriched interfacial properties.The surrounding matrix is strengthened and stiffened by nanoclay.As seen from Figure 1, the morphology of nanoclay "layers or stacks" is enormously vital in improving the tensile strength and resulting in a decline in flexural strength beyond 2 wt.% of nanoclay.Flexural properties are significantly matrix-dominated in comparison with tensile properties.The nanoclay agglomeration is harmful to the nanocomposite's strength because of decreased aspect ratio, followed by poor bonding among matrix and nanoclay, which causes the flexural strength to decrease at higher nanoclay content (Harshita et al., 2018).

Compression strength
As presented in Table 3 and limited literature, the compressive strength of epoxy is bettered by the addition of nanoclay.Compressive strength is inversely proportional to porosity.Specimens with low porosity exhibited greater compressive strength.The addition of nanoclay improves the crosslinking density of epoxy and reduces the porosity in the epoxy-nanoclay nanocomposite.

Impact strength
It is very clear from literature and Table 4 that epoxy-nanoclay nanocomposites show improved impact strength in comparison to pure epoxy.This signifies the fact that the addition of nanoclay in nanocomposite imparts both toughening and strengthening (Ratna et al., 2003).The nanoclay can have an effective toughening influence that works as effective crack stoppers and provides a tortuous path of propagation of the crack that leads to better impact strength (Kusmono & Mohd Ishak, 2013).

Micro-hardness
Note that the improvement in hardness of up to 5 wt.% of nanoclay loading, as shown in Table 5 is more important.The higher hardness values for 5 wt.% loaded epoxy-nanoclay nanocomposite are believed to benefit partially from the inherent nanoclay hardness.Nanoclays may enforce better resistance under indentation to epoxy.However, the improvement in hardness is minimal in additional nanoclay (more than 5 wt.%), indicating that higher filler quantity causes poor dispersion and agglomeration (Zabihi et al. 2018).

Morphological studies
According to morphological studies, a significant difference can be noted between the fractured surfaces of both pure epoxy and epoxy-nanoclay nanocomposites.The pure epoxy (Figure 4(a)) displays a completely smooth surface, indicating growth and spread of cracks reflecting lower fracture toughness.Compared with pure epoxy, the epoxy-nanoclay nanocomposite's SEM micrograph (Figure 4(b)) showed a substantially rougher surface.Nanoclay instinctively hinders and delays the crack propagation in epoxy-nanoclay nanocomposites.The surface of epoxy-nanoclay nanocomposites has a typical river-surface-form, with cracks that are fine, abrupt, twisty, erratic in shape, and spread out in different directions (Li et al., 2011).A clear indication of improved fracture toughness is provided by the river-surface-form (Domun et al., 2015).
SEM micrographs also showed that, due to the cross-linking effect and enhanced nanoclayepoxy bonding, nanoclay addition could change the crack forming mechanism.The nanoclay will interweave the epoxy chains and eventually create effective barriers to avoid crack propagation (Chan et al., 2011).An increasing network is formed by cross-linking reactions, and the movement of the chain segments is reduced.These are the critical factors for improving the epoxy-nanoclay nanocomposite's strength (Bindu Sharmila et al., 2014).

Moisture uptake
In the case of epoxy-nanoclay nanocomposites, with an increase in nanoclay weight percentage, the maximum moisture uptake decreases steadily.It is witnessed that all epoxy-nanoclay nanocomposites exhibit typical moisture uptake behavior of polymers.The tendency of water molecules to penetrate into the epoxy system may be responsible for moisture uptake.The water dispersion in epoxy is due to the polymer's nature, which exhibits an intense interaction with water.Water molecules in the epoxy establish a strong bond with "hydrophilic functional groups," viz., hydroxyl, or amine (Sugiman et al., 2016).The nanoclay addition to the epoxy lowers the mean free pathway for water molecules to traverse in the epoxy system (Figure 5), resulting in lower moisture uptake (Rao et al., 2018;Rull et al., 2015;Zabihi et al., 2018).
Al-Qadhi et al. (Al-Qadhi et al., 2013) reported that the nanoclay addition also reduces the maximum moisture uptake and the highest decrease is about 22% for epoxy-nanoclay nanocomposites containing 5 wt.% of nanoclay.Further increase in nanoclay wt.% leads to the nanoclay agglomeration and micro-voids.The effectiveness of nanoclay as a barrier is decreased when agglomerated since the moisture molecules move around the entire aggregated nanoclay instead of moving around each nanolayer.

Hygrothermal aging effect on mechanical properties
Absorbed moisture under hygrothermal aging conditions generally degrades the epoxy's functional and mechanical properties.Moisture content in a polymer matrix induces physical and chemical changes and influences mechanical properties by various mechanisms, viz., plasticization, hydrolysis, crazing, and/or swelling (Banea et al., 2018;Dogan & Arman, 2019;Prolongo et al., 2012;Shettar et al., 2018).Shettar et al. (Shettar et al., 2019) found that after soaking neat epoxy in cold water for 70 days, the tensile and flexural strengths decreased by 25% and 23.7%, respectively.Whereas tensile and flexural strengths of epoxy-nanoclay nanocomposites with 2 wt.% of nanoclay under water soaking declined by 14.8% and 14.34%, respectively.Similarly, aforesaid strengths of epoxy-nanoclay nanocomposites with 4 wt.% of nanoclay decreased by 13.9% and 13.2%, respectively, under cold water soaking, as compared to dry specimens.The incorporation of nanoclay decreased the loss percentage in tensile and flexural strengths.
In yet another work, Shettar et al. (Shettar et al., 2020) described that artificial aging in the hygrothermal chamber (at 40°C with 60% relative humidity for 180 days) declined the tensile and flexural strengths of neat epoxy by 21% and 22%, respectively.For aged epoxy-nanoclay nanocomposites with nanoclay have decreased the percentage of reduction in the tensile and flexural strengths by 12% and 13%, respectively, at 2 wt.% of nanoclay and 10% and 12%, respectively, at 4 wt.% of nanoclay as compared to unaged epoxy-nanoclay nanocomposites.Al-Qadhi et al. (Al-Qadhi et al., 2014) described that the tensile strength decrease caused by water absorption is smaller for epoxy-nanoclay nanocomposites than for pure epoxy.The tensile strength decreased by 4% for epoxy-nanoclay nanocomposite, which is less as compared to 9% for pure epoxy.
The nanoclay addition into the epoxy diminished the overall effect of hygrothermal aging conditions.Nanoclay particles have very high aspect ratios, in addition to being hard substances.In a moisture-absorbed epoxy, the nanoclay particles create endurance to polymer chain mobility, resulting in lower degradation of mechanical properties compared to pure epoxy (Hamim & Singh, 2014;Merah & Mohamed, 2019;Shettar et al., 2019;Wolf et al., 2018).

Morphological studies
Hygrothermal aging has an adverse effect on epoxy and nanocomposite.As displayed in Figure 6(b), aged epoxy's fracture surface has a grid of micro-cracks spreading through it in comparison to unaged epoxy (Figure 6(a)).Moisture absorption in epoxy during hygrothermal aging causes craze inception and dissemination, resulting in micro-cracks.As compared to unaged epoxy-nanoclay nanocomposite (Figure 6(c)), aged epoxy-nanoclay nanocomposite's fracture surface (Figure 6(d)) has smaller riversurface-patterns.Since shear yielding requires less energy to shape a new layer/surface, and the fracture toughness of aged specimens (both epoxy and nanocomposite) is lower than that of unaged samples, the presence of shear leaps can be seen in aged SEM micrographs (Figures 6(b,d)).
Liu et al. (Liu et al., 2017) reported that, with an increase in hygrothermal aging time, size, length, and width of cracks and slits within the epoxy increases.The cracks and slits that form early are unevenly distributed.The distribution of cracks and slits becomes more uniform as hygrothermal aging progresses.This is because hygrothermal aging causes resin expansion, decomposition, and degradation, resulting in internal structural destruction.The absorption of water molecules is linked to the creation of cracks and slits.The polymer expands due to the water molecules.As water molecules are distributed unevenly, the material's expansion stress is uneven, resulting in uneven cracks and slits.

Wear properties
The wear property of a material is equally as important in any given application as its mechanical properties.Wear is described as the loss of material when it is exposed to the contact surface's relative motion.The five basic forms of wear with polymer composites are fretting, erosion, fatigue, adhesive and abrasive wear (Brostow et al., 2010;Jumahat et al., 2016).Aradhya & Renukappa (Aradhya & Renukappa, 2020) and Rashmi et al. (Rashmi et al., 2011) reported that, when compared to pure epoxy, epoxy-nanoclay nanocomposites have a lower wear volume loss.The two surfaces of all the asperities are in contact with each other at the start of sliding.The asperities deform when shear forces are applied.The nanoclay protrude from the sample's surface, and the epoxy matrix eventually wears away, leaving only nanoclay in contact with the counter surface.The wear rate decreases as the sliding distance increases, and the nanoclay wear out the steel countersurface.Nanoclay adhere to the matrix due to extreme hardness of the countersurface, and surplus filler intensity is seen on the exposed surface of composite after prolonged sliding.Shear stress, coefficient of friction, and temperature at contact can all be reduced by the rolling effect of nanoparticles while sliding.
Jumahat et al. (Jumahat et al., 2016) described that the wear properties of nanocomposite are enhanced by adding nanoclay to epoxy at a concentration of up to 3 wt.%.The addition of nanoclay to a concentration of 5 wt.% decreased the wear properties of nanocomposite because the nanoclay particles agglomerated in the epoxy, making surface removal easier.The addition of nanoclay to epoxy improves thermal stability, resulting in less surface removal.

Morphological studies
Shettar et al. (Shettar et al., 2020) reported that worn surfaces of epoxy-nanoclay nanocomposite (Figure 8) are smoother as compared to the worn surface of pure epoxy (Figure 7).The addition of nanoclay has considerably reduced the material removal from the specimen.Fatigue wear, which occurs more often at higher temperatures, is what causes surface damage.The surface is damaged by the micro-cracks.The integrity of the surface is preserved in the matrix with the addition of nanoclay, preventing crack propagation in the epoxy.Abrasive wear and adhesive wear, two different types of wear mechanisms, are shown in Figures 7 and 8  refers to the surface being cut and ploughed by hard particles.The material is transferred from one surface to the next during adhesive wear, where adhesive bonds are created, established, and ultimately broken.It is crucial to keep in mind that wear is typically brought on by a number of mechanisms rather than just one.
Esteves et al. (Esteves et al., 2013) presented that, on epoxy-nanoclay nanocomposites, wear mechanisms include the creation of cracks perpendicular to the sliding path (Figures 5 & 6), material waves induced by adhesion and subsequent plastic deformation, and debris separation by delamination, all of which are caused by matrix's brittle behaviour.The lower nanoclay concentrations provide the best response in terms of wear resistance.

Summary
The presence of nanoclays in epoxy matrices can significantly enhance mechanical, hygrothermal, and wear properties through several mechanisms:

Mechanical properties
The nanoclay layers within the epoxy create physical barriers that restrict the movement of polymer chains.The high aspect ratio and large surface area of nanoclays provide numerous sites for load transfer between the epoxy matrix and the nanoclay.Also, the density of cross-linking points reduces the ability of polymer chains to deform under stress.As a result, the nanocomposite becomes stiffer and more deformation-resistant, leading to improved mechanical properties.Also, the nanoclays act as load-bearing entities within the epoxy matrix.Stress is transferred from the polymer matrix to the rigid nanoclays, distributing the load and preventing crack propagation (Figure 2(b), river-surfacepattern).The chemical compatibility achieved through surface modification of the nanoclays enhances the interfacial adhesion between the nanoclays and the epoxy matrix.This strong interface contributes to better stress transfer and load distribution.

Hygrothermal properties
The presence of nanoclays forms a tortuous path (Figure 3) that obstructs the movement of water molecules through the epoxy matrix.This barrier effect reduces the water absorption rate into the nanocomposite, leading to improved dimensional stability and reduced degradation due to moisture.Also, nanoclays can inhibit the propagation of microcracks caused by hygrothermal cycling.Their presence restricts moisture diffusion and minimizes the polymer's expansion and contraction, reducing the likelihood of crack initiation and growth.

Wear properties
The reinforcement provided by nanoclays improves the wear resistance of epoxy-nanoclay nanocomposites.The rigid nanoclay layers effectively resist abrasion and prevent material loss from the surface.Also, the presence of nanoclays can reduce friction due to the smoother and more uniform surface provided by the dispersed nanoclays.This can result in decreased wear and lower energy loss during frictional contact.Nanoclays contribute to load distribution by absorbing and distributing the applied load, reducing stress concentration on specific points, and minimizing wear-induced damage.Additionally, nanoclays, being stiff nanoparticles, can significantly increase the hardness of the nanocomposite.This enhanced hardness reduces wear rates and improves abrasive force resistance.Note that the improvement in hardness of up to 5 wt.% of nanoclay loading, as shown in Table 5 is more important.The higher hardness values for 5 wt.% loaded epoxy-nanoclay nanocomposite arebelieved to benefit partially from the inherent nanoclay hardness.Nanoclays may enforce better resistance under indentation to epoxy.However, the improvement in hardness is minimal in additionalnanoclay (more than 5 wt.%), indicating that higher filler quantity causes poor dispersion and agglomeration (Zabihi et al. (2018).

Conclusion
The addition of nanoclays to epoxy resin improves its physical, mechanical barrier and wear properties.
The most common nano fillers used with epoxy resins are the organically modified montmorillonite clays with filling amounts ranging from 1% to 8%.Low clay contents are shown to result in better epoxy-nanoclay structures.It is proven by several researchers that better epoxy-nanoclay structure results in noticeable improvements in most of the properties of the nanocomposite as compared with the pristine epoxy.Improvements of more than 14% in tensile strength, 57% in tensile modulus, 13% in flexural strength, 15% in compression strength, 80% in impact strength and 26% in micro-hardness for different weight percentage of nanoclay addition are reported.Also, the overall moisture uptake of epoxy-nanoclay nanocomposites decreases by 14% to 25% as compared to neat epoxy.For water absorbed epoxy-nanoclay nanocomposites with nanoclay have decreased the percentage of reduction in the mechanical properties by 10% and 20%.
Morphological studies indicate that the pure epoxy SEM micrograph displays a completely smooth surface, whereas the epoxy-nanoclay nanocomposite's SEM micrograph shows a substantially rougher surface.Nanoclay instinctively hinders and delays the crack propagation in epoxy-nanoclay nanocomposites.The fracture toughness of hydrothermally aged specimens (both epoxy and nanocomposite) is lower than that of unaged samples, and the presence of shear leaps can be seen in aged SEM micrographs.
In short, the enhancement in mechanical, hygrothermal, and wear properties in epoxy-nanoclay nanocomposites can be attributed to the synergistic effects of reinforcement, load transfer, improved interfacial properties, barrier effects, and friction reduction.These mechanisms work together to enhance the overall performance of the nanocomposite material, making it more suitable for demanding applications in various industries.

Figure
Figure 2. Flowchart depicting different steps of monomer intercalation method.

Table 1 .
Percentage of change in tensile properties of epoxy-nanoclay nanocomposites compared with neat/pure/