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Exploring the Impact of Nanoclay on Epoxy Nanocomposites: A Comprehensive Review

Daksh Shelly

Varun Singhal

Surinder Singh

Tarun Nanda

⁴

Rajeev Mehta

^5,6

Seul-Yi Lee

^1,* and

Soo-Jin Park

^7,*

Department of Chemistry, Inha University, 100 Inharo, Incheon 22212, Republic of Korea

Department of Mechanical Engineering, GLA University, Mathura 281406, India

Surface Engineering for Advanced Materials (SEAM), Swinburne University of Technology, Hawthorn, VIC 3122, Australia

⁴

Mechanical Engineering Department, Thapar Institute of Engineering & Technology, Patiala 147001, India

⁵

Chemical Engineering Department, Thapar Institute of Engineering & Technology, Patiala 147001, India

⁶

TIET Virginia Tech Center of Excellence in Emerging Materials (CEEMS), Thapar Institute of Engineering & Technology, Patiala 147001, India

⁷

Department of Mechanical Engineering, College of Engineering, Kyung Hee University, Yongin 17104, Republic of Korea

Authors to whom correspondence should be addressed.

J. Compos. Sci. 2024, 8(12), 506; https://doi.org/10.3390/jcs8120506

Submission received: 24 September 2024 / Revised: 11 November 2024 / Accepted: 25 November 2024 / Published: 2 December 2024

(This article belongs to the Section Nanocomposites)

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Abstract

This review provides a comprehensive exploration of the current research landscape surrounding nanoclay-reinforced epoxy composites. A primary challenge in developing these nanocomposites is the hydrophilic nature of pristine clay, which hinders its dispersion within the epoxy matrix. To address this issue, organic modifiers are frequently employed to enhance clay compatibility and facilitate effective incorporation into the nanocomposite structure. The unique properties of nanoclay make it a particularly attractive reinforcement material. The performance of nanoclay/epoxy nanocomposites is largely determined by their morphology, which is influenced by various factors including processing methods, clay types, modifiers, and curing agents. A thorough understanding and control of these parameters are essential for optimizing nanocomposite performance. These advanced materials find extensive applications across multiple industries, including aerospace, defense, anti-corrosive coatings, automotive, and packaging. This review offers an in-depth analysis of the processing techniques, mechanical properties, barrier capabilities, and thermal characteristics of nanoclay-reinforced epoxy nanocomposites. Additionally, it explores their diverse industrial applications, providing a holistic view of their potential and current use. By examining the multifaceted landscape of epoxy/clay nanocomposites, this review illuminates the intricate relationships between fabrication methods, resulting properties, and potential industrial applications. It serves as a comprehensive resource for researchers and practitioners seeking to advance the development and application of these innovative materials.

Keywords:

epoxy; nanoclay; nanocomposite; performance; application

1. Introduction

The dawn of polymer nanocomposites research in the late 1980s marked a pivotal moment in materials science. Originating in academic laboratories and commercial research organizations, these innovative materials are now poised to dominate 21st century applications due to their unique ability to combine properties and exhibit design characteristics absent in traditional composites. Nanocomposites are defined as materials with at least one phase having dimensions in the nanoscale range [1,2,3]. They are classified into four distinct categories based on the dimensionality of their nanofillers:

Zero-dimensional nanofillers: This category includes quantum dots, and nanoclusters, all with dimensions entirely within the nanoscale. These have garnered significant attention due to their small size and unique physical/chemical properties.

One-dimensional nanomaterials: Materials like nanowires, nanotubes, nanofibers, and nanorods fall into this category, with two dimensions at the nanoscale. They have attracted considerable interest from both industry and academia due to their versatile applications.

Two-dimensional structures: These materials, such as graphene, have only one dimension reduced to the nanoscale. They have recently gained prominence due to their exciting benefits, including unique surface chemistry, high aspect ratio, and large surface area.

Three-dimensional nanofillers: Composed of combinations of zero-, one-, and two-dimensional nanomaterials, these complex structures, like metal–organic frameworks and zeolites, represent a significant focus of current research. In these materials, surfaces and interfaces are no longer seen as defects but as integral components of the material’s structure and function [4,5,6].

The commercial potential of polymer nanocomposites was first realized by Toyota, which pioneered their use in automotive applications [7]. Nanocomposites offer several advantages over conventional composites (Figure 1a):

Lower filler content: Nanocomposites typically require less than 5% filler content, compared to the >10% needed in traditional composites. This results in better processability, more control in fabrication, and improved properties.

Reduced viscosity and density: The lower filler content in nanocomposites leads to lower viscosity, making them easier to process, and lower overall density, which is crucial for many applications [2].

The exceptional properties of nanocomposites stem from the extraordinarily high surface-to-volume ratio or aspect ratio of their nanofillers, which provides a greater surface area for binding with the polymer matrix. This unique structure leads to a range of enhanced properties, including heightened durability [8], a greater elastic modulus [9], reduced gas permeability [10], enhanced flame retardancy and flammability [11], and improved corrosion protection [12], among other benefits [13,14,15,16,17]. As research in this field continues to advance, nanocomposites are poised to revolutionize materials science and engineering, offering unprecedented opportunities for innovation across diverse industries and applications.

2. Nanocomposite Constituents

There are primarily three functional components that make up nanocomposites.

2.1. Matrix

In functional polymer nanocomposites, the polymer matrix serves as the cornerstone. The primary function of the polymer matrix in functional polymer nanocomposites is to serve as a continuous phase that effectively binds the nano- and micro-scale reinforcements, thereby enhancing the overall properties of the composite. It provides structural integrity, ensuring uniform stress distribution throughout the material, which in turn improves tensile strength, toughness, and impact resistance. Additionally, the polymer matrix contributes significantly to thermal stability by enhancing dimensional stability and resilience to temperature fluctuations, all while maintaining high-temperature performance. This matrix also bolsters the material’s barrier properties, making it more impermeable to gases, moisture, and other substances, thus offering superior protection. By integrating various nanoparticles, the polymer matrix enables the composite material to exhibit advanced mechanical, thermal, and barrier properties, making it suitable for cutting-edge applications. The selection of an appropriate matrix depends on the specific application requirements of the nanocomposites. Commercially, polymer matrices are generally classified into three types: (i) thermoset polymers, (ii) thermoplastic polymers, and (iii) elastomers.

Thermoset polymers are characterized by chemical bonding that forms cross-links between molecules, creating a rigid, three-dimensional network structure (Figure 1b). Once these cross-links are established during the curing or polymerization process, the material cannot be melted by heat. However, if the cross-link density is low, the material may become pliable at elevated temperatures [18,19]. Thermoplastic polymers, on the other hand, consist of molecules that are not chemically linked but are held together by secondary bonds or weak intermolecular forces such as hydrogen or van der Waals bonds (Figure 1c). When exposed to heat and pressure, these secondary bonds can be temporarily disrupted, allowing the molecules to flow and reposition themselves. Upon cooling, the molecules solidify into a new configuration, with the secondary bonds restored [18,19]. Elastomers are a distinct type of polymer known for their viscoelasticity, meaning they exhibit both viscosity and elasticity but have relatively weak intermolecular interactions. These materials can be stretched significantly and will return to their original shape once the force is removed, a property known as high elasticity or resilience. Due to their unique combination of flexibility, durability, and impact absorption, elastomers are integral to industries ranging from automotive to medical devices, where these properties can be tailored to meet specific needs [20]. The characteristics of various polymer matrices are given in Table 1. The choice of matrix material in nanocomposites is primarily determined by the specific conditions and requirements of the intended application. Factors such as temperature range, operating environment, desired mechanical properties, and recyclability play a crucial role in selecting the most suitable matrix material.

Table 1. Characteristics of various polymer matrices [21].

Matrix Material	Density (g/cm³)	Glass Transition Temperature (°C)	Tensile Strength (MPa)	Flexural Strength (MPa)	Compressive Strength (MPa)
Epoxy	1.15–1.3	37–127	27–200	74–325	116–404
Vinyl ester	1.03–1.15	55–145	16–95	60–163	82
Unsaturated polyester	1.1–1.2	94–125	22–85	67–113	104–131
High density polyethylene	0.94–1.0	−113–−133	13–51	25–40	20
Polypropylene	0.84–0.91	−9–−15	26–32	41	40
Poly(ethylene terephthalate)	1.3–1.4	76–88	24–41.4	69–78	80
Polyurethane	1.10–1.25	−19–−60	7.6–66	20–120	–
Ethylene-propylene diene terpolymer	0.85–0.90	−48–−69	8.8–25	18–23	–

2.2. Reinforcement

The secondary or dispersed phase reinforcements, ranging from the nano to macro dimensions, play a crucial role in enhancing the performance of multifunctional polymer nanocomposites. These reinforcements, typically harder or stiffer than the matrix, bear the applied stresses through an interface, and their effectiveness is largely dependent on strong interfacial adhesion with the matrix. These fillers significantly contribute to thermal stability by protecting the polymer from degradation at high temperatures, serving as physical barriers to heat diffusion, and extending the operational temperature range of the material. The synergistic effect of nanofillers further enhances heat conductivity, stability, and resistance to thermal degradation. In addition to their thermal benefits, these reinforcements create a complex network within the polymer matrix, which impedes the diffusion of gases, liquids, and moisture, thereby reducing the overall permeability of the material. The performance of these nanocomposites is ultimately determined by the degree of filler dispersion throughout the matrix, with uniform distribution being key to maximizing the material’s properties [2,18,22]. A wide variety of materials are used as reinforcements, including nanoclay (silicate layers), carbon nanotubes, nanowires, nanowhiskers, and nanofibers. The characteristics of various reinforcements are given in Table 2. Figure 1d provides an illustration of the shapes of these materials and their corresponding surface area-to-volume ratios, which are critical factors in their functionality. Among these, nanoclay, particularly in the form of silicate layers, has garnered significant attention in the field of polymer nanocomposites due to its remarkable properties. These include resilient intercalation chemistry, a high aspect ratio, a large active surface area (ranging from 700 to 800 m²/g), easy availability, and cost-effectiveness. These attributes make nanoclay an especially valuable reinforcement material in the development of advanced polymer nanocomposites [1,2,18].

Table 2. Characteristics of various reinforcements [23,24,25].

Material	Density (g/cm³)	Tensile Strength (GPa)	Young’s Modulus (GPa)
Nanoclay	2.0–2.7	0.05–0.19	180–380
Graphene	2.7	130.5	1000
Single-walled/multi-walled carbon nanotubes	0.7–1.7	100–200	1000
Carbon fiber	1.75	3.5	230
Kevlar fiber	1.44	3.6	60
Glass fiber	2.6	3.4	22

2.3. Interface

The structural integrity and performance of nanocomposites arise from the sophisticated interplay between their constituent elements—specifically, the nano/micro fillers and the polymer matrix—with particular emphasis on their interfacial interactions. To fully grasp these interactions, it is essential to distinguish between two fundamental concepts: the interface and the interphase. The interface, traditionally defined in fiber composites, represents the two-dimensional surface formed at the common boundary between the reinforcing fiber and matrix. This surface serves as the critical junction for load transfer and exhibits unique physical and mechanical properties distinct from either the fiber or matrix components. However, this classical definition has evolved with our understanding of composite materials. The interphase presents a more comprehensive concept, encompassing not only the geometrical surface of the fiber-matrix contact but also extending into a three-dimensional region of finite volume (Figure 2). Within this region, chemical, physical, and mechanical properties undergo either continuous or stepwise transitions between the characteristics of the bulk fiber and matrix materials. This transition zone extends from a point within the fiber, through the interface, and into the matrix, incorporating all volumes modified during the composite’s consolidation or fabrication process. The interphase serves as a crucial determinant of the composite’s overall behavior, exhibiting distinct physical and chemical properties that deviate from the bulk polymer due to filler influences. A well-developed interphase facilitates efficient stress transfer between matrix and fillers, leading to enhanced mechanical properties, including improved tensile strength and fracture toughness. The interphase creates a stabilizing effect by restricting polymer molecule movement during degradation processes. It functions as an effective barrier, limiting the diffusion of liquids and gases through the composite structure [26,27,28,29].

Figure 2. A graphic representation of the elements of the 3-D phase transition between the fiber and matrix [30].

The development and characteristics of this interfacial region result from a complex interplay of variables, including nanofiller morphology (size and shape), surface chemistry of the fillers, processing conditions during fabrication, and matrix–filler compatibility. Through the careful optimization of these parameters, researchers can engineer the interphase to effectively modulate stress transfer, thermal conductivity, and other critical properties, thereby enhancing the nanocomposite’s overall performance. This ability to manipulate interfacial characteristics at the nanoscale represents a powerful tool in materials engineering, opening new avenues for developing materials with unprecedented property combinations. As the field advances, the strategic manipulation of the interphase continues to be a central focus in nanocomposite research. This emphasis reflects its crucial role in achieving breakthrough performance metrics across diverse applications, from aerospace to electronics. The ongoing investigation of filler–matrix interface dynamics remains fundamental to developing next-generation nanocomposite materials that can meet increasingly demanding performance requirements [2,19,25,30].

3. Polymer Matrix Nanocomposites

Polymer nanocomposites have emerged as a revolutionary category of materials, capturing the attention of both industry and academia in recent years [31,32,33,34,35,36,37,38]. Since the pioneering research conducted at Toyota Laboratories [39], these innovative materials have been the subject of extensive studies, driven by their unique properties and vast potential applications. At its core, a polymer nanocomposite is an interfacial combination of a polymer matrix and a solid phase, with at least one dimension of the solid phase falling within the nanoscale range (typically 0.1 nm to 100 nm). This solid phase can comprise three-, two-, one-, or zero-dimensional nanofillers, each offering distinct properties and benefits. While various polymer matrices are available, including vinyl polymers, nylon, polyamides, and phenolics, epoxy resin stands out due to its exceptional characteristics, such as low viscosity, minimal shrinkage during curing, and high strength [7,40]. Among the wide array of synthetic and natural fillers, montmorillonite clay has gained particular prominence. Its outstanding aspect ratio, extensive surface area, easy accessibility, and cost-effectiveness make it a preferred choice for many applications. This preference for nanoscale fillers marks a significant departure from conventional composites, which typically rely on micrometer-sized fillers with substantially higher densities (2–4 g/cm³) compared to polymer matrices (0.8–1.2 g/cm³). The shift to nanofillers brings remarkable advantages. Traditional composites (composites reinforced with micro-fillers) often require high filler content (30–60%) to achieve desired reinforcing effects, resulting in increased weight and reduced processability. In contrast, nanocomposites demonstrate enhanced thermo-mechanical characteristics with minimal filler addition (<5 wt.%). This efficiency is attributed to the vastly increased surface area at the polymer–nanofiller interface, leading to improved strength, modulus, barrier resistance, and flame retardancy. The versatility and superior performance of polymer nanocomposites have led to their adoption across a wide spectrum of industries, from packaging to aerospace [2,40].

4. Materials for Polymer Nanocomposites

4.1. Epoxy Resin

Epoxy resins have emerged as the predominant matrix material in high-performance composite systems, distinguished by their unique molecular architecture and versatile processing capabilities [41]. The fundamental chemistry of these materials centers on their epoxide groups, which undergo ring-opening polymerization with curing agents to form extensively crosslinked networks. This molecular transformation from small monomeric units to complex three-dimensional structures is key to developing their exceptional properties [42]. The cured epoxy systems exhibit an impressive array of characteristics, including superior bonding strength, dimensional stability, and customizable hardness ranges. These properties become particularly pronounced when epoxies are combined with fiber reinforcement, resulting in composite materials that offer an optimal balance of light weight, high mechanical strength, and excellent stiffness [43]. Such property combinations, along with their inherent resistance to corrosion and fatigue, have made epoxy-based composites indispensable in demanding applications across aerospace, rail transportation, and medical equipment sectors [44].

A critical factor in the industrial adoption of epoxy systems is their curing behavior, which significantly influences both production economics and final material properties. The curing process, typically the rate-limiting step in composite manufacturing, has been the focus of extensive optimization efforts [45]. Several strategies have been developed to accelerate curing, i.e., (i) external energy input to enhance molecular mobility [46,47], (ii) chemical structure modification through reactive group incorporation [48], and (iii) process optimization for improved component interaction [42]. However, the relationship between curing kinetics and material properties presents a complex optimization challenge. While rapid curing can boost production efficiency, it may adversely affect mechanical properties [49]. This is because the curing process involves intricate chemical transformations that determine not only the rate of network formation but also the ultimate strength and toughness of the material [50,51]. The curing rate directly influences crosslink density, which in turn affects multiple mechanical properties, e.g., tensile and compressive strength, impact resistance, internal stress distribution, and dimensional stability. Accelerated curing can lead to increased internal stresses, potentially causing material shrinkage and cracking [52,53]. Conversely, slower curing, while potentially beneficial for property development, increases production time and associated costs. Understanding these tradeoffs has driven research into curing kinetics, focusing on reaction dynamics and mechanisms [54]. This knowledge enables the optimization of both material formulation and processing conditions to achieve an ideal balance between mechanical properties and manufacturing efficiency.

A distinctive advantage of epoxy systems is their environmentally conscious curing process, which produces no volatile byproducts. However, this benefit must be balanced against safety considerations, particularly regarding skin sensitization and contact dermatitis risks from uncured resins. This necessitates strict adherence to safety protocols and appropriate PPE usage during handling and processing. Despite these precautionary requirements, epoxy resins continue to dominate various industrial sectors due to their exceptional performance characteristics, processing versatility, and broad applicability [55,56,57,58,59,60].

4.2. Nanoclay

Clay is a complex material composed primarily of layered silicates, specifically aluminum phyllosilicates. These silicates incorporate various metal oxides, including those of alkali and alkaline earth metals, calcium, and other elements. Trace amounts of organic compounds are also present [61]. The fundamental structure of clay consists of stacked silicate layers, each comprising sheets of silica and alumina in varying proportions. These layers are separated by variable interlayer distances, which contribute to clay’s unique properties. The ratio of silica to alumina condensation within these sheets determines the specific type of clay mineral. This ratio can be classified into three main categories: (i) 1:1, (ii) 2:1, or (iii) 2:2. This structural diversity accounts for the wide range of clay types found in nature, each with distinct characteristics and applications [2,25].

5. Structure, Characteristics, and Surface Modification of Nanoclay (Montmorillonite)

Clay minerals are classified based on their sheet structure, with three main types: 1:1, 2:1, and 2:2. The 1:1 type, also known as two-sheet or dimorphic minerals, consists of alternating tetrahedral silica and octahedral alumina sheets in equal proportions. Examples of this type include halloysite and perlite. The 2:1 type, referred to as three-sheet or trimorphic minerals, features a more complex structure. In this arrangement, a single alumina sheet is sandwiched between two silica sheets, resulting in a three-layer configuration. Common examples of 2:1 type clay minerals include montmorillonite (MMT), saponite, and hectorite. The 2:2 category, sometimes called metamorphic or four-sheet minerals, represents the most complex structure. These minerals comprise two silica sheets alternating with two alumina sheets, creating a four-layer arrangement. Chlorite is a notable example of this type [2,25,62].

Montmorillonite, hectorite, and saponite are the three 2:1 phyllosilicates most frequently used in polymer nanocomposites. The unique chemical formulas for these layer silicates, which contribute to their specific properties and applications, are detailed in Table 3. This combination of nanoscale thickness and variable lateral dimensions, along with their specific chemical compositions, makes these clay minerals particularly versatile and effective in enhancing the properties of polymer nanocomposites [63,64,65]. Montmorillonite stands out among the 2:1 phyllosilicate material as the preferred choice for fabricating polymer clay nanocomposites. This preference stems from its remarkable ability to undergo extensive interlayer expansion and swelling. This unique property facilitates the penetration and intercalation of polymers between the montmorillonite layers, significantly enhancing the performance of the resulting nanocomposite materials. The structure of montmorillonite, illustrated in Figure 3a, reveals its complex crystal arrangement. It consists of three primary layers: a central octahedral alumina sheet sandwiched between two tetrahedral silica sheets, all held together by triclinic bonds. A key feature of this structure is the partial substitution of aluminum atoms in the octahedral sheets with magnesium atoms. This substitution creates a valence difference, resulting in a negative charge distribution across the crystal lattice. To maintain electrical neutrality, this negative charge is balanced by alkali and alkaline earth cations, predominantly sodium (Na+), which reside within the interlayer spaces or galleries. This intricate structure, combined with the presence of these exchangeable cations, contributes to montmorillonite’s exceptional swelling capacity and its ability to interact effectively with polymers, making it an invaluable component in the development of advanced nanocomposite materials.

Table 3. Chemical compositions of frequently employed 2:1 phyllosilicates ^a [25,66].

2:1 Phyllosilicate	General Formula
Montmorillonite	M_x(Al_4–xMg_x)Si₈O₂₀(OH)₄
Hectorite	M_x(Mg_6–xLi_x)Si₈O₂₀(OH)₄
Saponite	M_xMg₆(Si_8–xAl_x)O₂₀(OH)₄

^a M: monovalent cation; X: degree of isomorphous substitution (between 0.5 and 1.3).

Montmorillonite naturally occurs in a layered structure, where the combined thickness of a single layer and its adjacent interlayer gallery is known as the D-spacing or basal spacing. The exceptional properties of clay, which contribute to significant improvements in nanocomposite materials, stem from three key characteristics: its nanoscale layer thickness of approximately 1 nm, high aspect ratio, and expansive active surface area (reaching up to 800 m²/g) [11,42,56,57]. These silicate layers function as minute reinforcing elements with extensive internal surfaces. However, this characteristic also leads to a tendency for the layers to cluster rather than distribute uniformly throughout the matrix [58]. The layers have an inherent propensity to self-organize into stacked configurations, maintaining consistent van der Waals gaps between them. These empty spaces are referred to as galleries or interlayers [55,56,59,60]. At a structural level, silicate layers can be described as parallel lamellae arranged in stacks [61]. This unique layered arrangement, combined with the nanoscale dimensions and high surface area, is fundamental to the enhanced properties observed in clay-based nanocomposites. The ability to manipulate these stacked structures and interlayer spaces is crucial in harnessing the full potential of montmorillonite in various applications.

Unmodified clay is typically only compatible with hydrophilic polymers, limiting its applications. To enhance its versatility and compatibility with organic polymers, the clay’s surface is often subjected to organic modification and silanization. The organic modification involves exchanging the inorganic cations naturally present in the clay with organic modifiers, commonly alkylammonium, sulfonium, or phosphonium ions (Figure 3b) [63,64]. The introduction of alkylammonium cations into nanoclay serves two crucial purposes. It expands the interlayer spacing by reducing the surface energy of the inorganic material. It introduces reactive functional groups that can either interact directly with the polymer matrix or initiate the polymerization of monomers. Both effects contribute to strengthening the bond between clay particles and the surrounding polymer, thereby enhancing the overall interface quality in the nanocomposite [66,67,68]. Among these modifiers, alkyl ammonium ions are most frequently used due to their ability to easily replace the ions in the clay gallery [25]. The impact of this modification is significant. While the thickness of a single clay platelet is approximately 0.94 nm, the D-spacing of dehydrated, unmodified montmorillonite is about 0.96 nm [69]. Organic modification, particularly with longer-chain surfactants, can substantially increase this D-spacing. This expanded interlayer distance is crucial as it weakens the electrostatic attraction between clay platelets, allowing polymer molecules to penetrate the galleries more easily. The choice of organic modifier is thus essential in nanocomposite formation. Longer-chain surfactants generally create greater separation between clay layers, facilitating better polymer infiltration and dispersion within the clay structure [2,70,71].

The silane treatment of nanoclays represents a crucial surface modification strategy that significantly enhances the compatibility and performance of clay–polymer nanocomposites. The process fundamentally alters the clay’s surface characteristics, transforming its inherently hydrophilic nature to a more organophilic state that better interfaces with polymer matrices. These silane agents possess a unique dual functionality, represented by the general chemical formula R₃Si–X, where one end facilitates bonding with organic matrices while the other end interacts with inorganic surface of nanoclay. The mechanism of silane modification occurs through a series of well-defined chemical reactions. Initially, the Si–OR bonds undergo rapid hydrolysis in aqueous solutions, generating reactive silanol (Si–OH) groups. These silanol groups then interact with the hydroxyl groups present on the nanoclay surface through condensation reactions. During the subsequent drying phase, the condensation process continues, resulting in the formation of a robust polysiloxane network on the nanoclay surface. Concurrently, the X functional groups oriented outward from the modified clay surface become available for reaction with the polymer matrix, establishing stable covalent bonds upon contact. This creates a strong chemical bridge between the polymer matrix and nanoclay through primary bonds, significantly enhancing interfacial adhesion. Moreover, the presence of the silane layer around individual nanoclay platelets effectively reduces platelet–platelet interactions, disrupting their natural stacking sequence. This steric hindrance, combined with the enhanced organic compatibility, facilitates the superior dispersion of clay platelets at the nanoscale, ultimately leading to improved nanocomposite properties [72,73,74].

6. Morphologies of Polymer Clay Nanocomposite Systems

The creation of a nanocomposite through the combination of a polymer and nanoclay is not guaranteed, but rather depends on several key factors: the characteristics of the polymer and clay, the processing protocol, and the interface between the matrix and filler. Generally, clay–polymer nanocomposites can be categorized into three distinct groups [25,75,76].

6.1. Phase-Separated Micro-Composite or Immiscible Nanocomposite

In this structure, the polymer fails to penetrate the interlayer or gallery between clay layers (Figure 4a–c). The nanoclay remains non-uniformly distributed in the polymer, with clay layers maintaining their original aggregated state. The D-spacing remains identical to the pristine clay, resulting in properties similar to conventional composites [2,25].

6.2. Intercalated Nanocomposites

This structure forms when one or a few polymer chains enter the interlayer or gallery, causing the silicate layers to maintain an ordered multilayer structure but with enlarged d-spacing (Figure 4d–f). The D-spacing typically ranges between 20 and 30 Å, leading to improved properties compared to phase-separated microstructures [63,64,77].

6.3. Exfoliated Nanocomposites

Exfoliated nanocomposites occur when the polymer readily enters the interlayer or gallery, effectively separating the clay platelets (Figure 4g–i). This results in uniform distribution of clay within the polymer matrix, with d-spacing increasing to 100 Å or more. This structure exhibits the best properties among the three types and is the most sought-after by researchers [63,66,78].

While these three categories are commonly used, most nanocomposites fall somewhere in between. The lack of thorough investigation into morphological variations when comparing nanocomposite systems often leads to ambiguity in structure–property relationships. To address this, a more nuanced classification system has been proposed, distinguishing between ordered, disordered, or partially exfoliated and ordered and disordered intercalated structures. These classifications are based on the degree of variation in layer spacing and orientation. Ordered exfoliation refers to nanoclay platelets arranged in a parallel, ordered manner throughout the matrix. Disordered exfoliation occurs when the organized structure of nanoclay platelets is completely disrupted, resulting in a homogeneous, random arrangement of individual platelets. Partial exfoliation represents an intermediate structure between intercalated and exfoliated states. The morphology of polymer nanocomposites is highly complex, with microscopic scale morphology potentially impacting the nanocomposite’s mechanical and physical characteristics if the clay platelet distribution is non-uniform [65,79,80]. Consequently, identifying structures at both the microscale and nanoscale is crucial for establishing relationships between morphology, processing, structure, and property [65]. This structural identification is typically accomplished through XRD and TEM analyses, as illustrated in Figure 4.

7. Fabrication of Clay–Polymer Nanocomposites

The fabrication methods for clay–polymer nanocomposites can be broadly classified into four categories, as illustrated in Figure 5a [25,81,82].

Figure 5. (a) Classification of processing of clay–polymer nanocomposites, (b) melt intercalation synthesis of clay–polymer composites, (c) in situ template synthesis of clay–polymer composites, and (d) in situ polymerization synthesis of clay–polymer composites [83].

7.1. Intercalation of Polymer or Prepolymer from Solution

Pioneered by the Toyota research team for polyimide nanocomposites, this method involves exfoliating clay platelets into individual sheets using a solvent capable of dissolving the polymer [84,85]. The mild interlayer forces allow easy separation of platelets in suitable solvents like chloroform or toluene/acetone. After the clay absorbs the solvent and swells, the polymer is introduced and intercalated between silicate layers. Upon solvent evaporation, the polymer becomes sandwiched between reassembled clay sheets, forming the nanocomposite. This technique has been successfully used for water-soluble polymers like poly(ethylene vinyl alcohol) and poly(ethylene oxide) [1,86,87,88].

7.2. Melt Intercalation

As shown in Figure 5b, melt intercalation occurs when clay platelets are combined with a molten polymer matrix. The resulting nanocomposite morphology (intercalated or exfoliated) depends solely on the compatibility between clay platelets and the polymer. This solvent-free method is environmentally friendly and compatible with industrial polymer processes, making it suitable for polymers that cannot be processed using other techniques. It is commonly used for polyethylene terephthalate and nylon 6 nanocomposites. The use of supercritical carbon dioxide during processing can enhance mechanical properties [66,84,89,90,91,92,93].

7.3. In Situ Template Synthesis

This method involves forming clay platelets within a polymer matrix by integrating a solution/gel containing both clay building blocks and the polymer (Figure 5c). The polymer aids in nucleation and growth of inorganic host crystals, which become trapped within the platelets. While commonly used for double-layer hydroxide nanocomposites, this method has limitations due to high temperatures required for clay synthesis, which can decompose the polymer. It is advantageous for large-scale production and its straightforward procedure [1,94,95].

7.4. In Situ Intercalative Polymerization

Formerly used for clay–polyamide nanocomposites, this technique involves polymerization within intercalated clay sheets (Figure 5d). Modified clay layers swell when exposed to liquid monomers or monomer solutions, leading to polymerization between clay layers and increased d-spacing. Polymerization can be initiated by heat, radiation, or organic catalysts fixed through cationic exchange. This method often yields exfoliated nanocomposites due to careful reagent selection and creates a strong interface between polymer and clay platelets. It is particularly suitable for clay–thermoset (epoxy, polyester, etc.) nanocomposites [1,63,94,96,97].

Each of these methods offers unique advantages and is chosen based on the specific polymer–clay system and the desired nanocomposite properties.

8. Epoxy Clay Nanocomposites

Epoxy clay nanocomposites are advanced materials that combine epoxy as the matrix and clay (silicate layers) as reinforcement. These systems have found a wide range of applications due to their unique properties. In this section, we will explore epoxy clay nanocomposites in depth, examining their various features, mechanisms, curing agents, processing techniques, characteristics, and applications.

8.1. Exfoliation Mechanism in Epoxy Clay Nanocomposite Systems

Exfoliated nanocomposites exhibit superior homogeneity compared to their intercalated counterparts. In these systems, clay platelets are effectively dispersed and randomly arranged, fostering strong bonding between the clay layers and the epoxy resin. This enhanced bonding significantly improves the nanocomposites’ thermal, mechanical, and barrier properties. Achieving a high degree of exfoliation requires consideration of several factors: nanoclay structure, modifier chain length and number, curing agent type, curing conditions (viscosity, temperature, duration), and functionality of the resin matrix. Typically, exfoliated nanocomposites are produced using clay modified with primary/secondary alkyl ammonium or quaternary surfactants as modifiers. These modifiers are chosen for their hydroxyl groups, which effectively interact with the clay due to their high Brønsted acidity. Increasing the alkyl ammonium chain length can shift the structure from intercalated to exfoliated. However, exfoliation remains a challenging process due to high matrix viscosity, strong nanoclay agglomeration tendency, and large lateral dimensions of clay layers (1 mm or larger) [98,99,100,101,102].

Park’s group [103] proposed that elastic forces are the primary driver behind clay platelet exfoliation in clay–epoxy nanocomposites. This concept is grounded in the recoil theory of polymers. Cross-linked epoxy chains attempt to recoil but are resisted by neighboring clay platelets due to attractive electrostatic interactions between quaternary ammonium ions and negatively charged platelets, and Van der Waals forces between organic fragments of the molecules. This resistance prevents the cross-linked epoxy chains from relaxing. As the epoxy resin’s conformational entropy increases, it reaches a threshold where attractive forces balance entropic elastic forces. Beyond this critical point, elastic forces overcome the attractive force, causing neighboring clay platelets to separate. The exfoliation process occurs at all curing rates, but fast-curing reactions allow epoxy chains to accumulate significantly more elastic energy than slow-curing processes. Achieving a balance between polymerization within and external to the gallery is crucial for producing exfoliated nanoclay–epoxy nanocomposites. Figure 6a illustrates the various forces acting on two neighboring clay layers: (i) viscous and attractive forces (electrostatic attraction and van der Waals) hinder exfoliation, and (ii) elastic force from conformational entropy promotes clay layer separation. If attractive and viscous forces cannot overcome elastic forces, an intercalated structure forms instead of exfoliation. In uncured systems, exfoliation is not possible due to the small size of epoxy moieties in interlayer galleries, resulting in minimal entropic separation force [103,104,105,106,107,108]. The exfoliation process typically begins with the removal of outer/surface layers from tactoids, as these have lower ionic bonding energy compared to inner layers (Figure 6b). Full exfoliation is achieved when all layers separate from all tactoids [84,103,109]. This complex interplay of forces and mechanisms underlies the formation and properties of epoxy clay nanocomposites, making them a fascinating and valuable class of materials for various applications.

8.2. Influence of Various Curing Agents on Morphology of Clay/Epoxy Nanocomposites

The choice of curing agent, or hardener, plays a crucial role in determining the properties and structure of clay–epoxy nanocomposites. Typically, amine and anhydride-based curing agents are employed, each imparting unique characteristics to the final nanocomposite. Anhydride-based hardeners: These hardeners often lead to exfoliated morphology in clay–epoxy nanocomposites. Their liquid state allows for easy dispersion within the interlayers or galleries between nanoclay platelets, promoting exfoliation [110,111]. The morphology resulting from amine-based hardeners depends on their specific type: aliphatic amines result in exfoliated morphology and more reactive than cyclo aliphatic amines. Cyclo aliphatic amines lead to intercalated morphology and are less reactive than aliphatic amines. In aromatic diamines cases, the morphology depends on their reactivity and electro-negativity. The exfoliation of clay platelets is influenced by both the diffusion rate and reactivity of the curing agent [87]. Kong et al. studied the exfoliation behavior of epoxy/clay nanocomposites by adjusting curing temperatures and electro-negativities of aromatic diamine hardeners. The intercalated morphology is obtained with epoxy/1,3-phenylenediamine and epoxy/4,4-methylenedianiline systems because they are highly reactive, which makes gel formation faster in the extra gallery region. On the other hand, exfoliated morphology is obtained with the epoxy/4,4-diaminodiphenyl sulfone system because its reactivity is low, and gel formation is slow in interlayers or galleries, providing enough time for intragallery polymerization [112]. The study demonstrates that the reactivity of the curing agent significantly influences the final nanocomposite structure. Highly reactive hardeners tend to promote faster gel formation outside the clay galleries, leading to intercalated structures. Conversely, less reactive hardeners allow more time for polymerization within the galleries, facilitating exfoliation. This intricate relationship between curing agent properties and nanocomposite morphology underscores the importance of careful hardener selection in designing clay–epoxy nanocomposites with desired structures and properties.

8.3. Influence of Various Processing Techniques on Morphology of Clay–Epoxy Nanocomposites

The dispersion of clay platelets in the epoxy matrix significantly influences the nanocomposite’s morphology and properties. Various processing methods have been employed, including mechanical mixing, ball milling, ultrasonication, and combinations thereof [13,14,15,32,113,114,115,116].

Mechanical mixing: Ho et al. achieved intercalated morphology (Figure 7a) at all clay concentrations using mechanical mixing, with optimal tensile strength and Vicker’s hardness at 5 wt.% [117]. Kusmono et al. reported exfoliated morphology (Figure 7b) up to 3 wt.% clay content, beyond which intercalated structures formed due to clay agglomeration [118].

Ultrasonication vs. mechanical mixing: Bashar et al. found ultrasonication superior to mechanical mixing for clay dispersion. Ultrasonication achieved partially exfoliated morphology up to 2 wt.% clay, while mechanical stirring resulted in intercalated structures. The exfoliated nanocomposites exhibited better mechanical properties [14].

High-shear mixing and combined techniques: Chen et al. achieved full clay exfoliation in epoxy using high-shear mixing followed by ultrasonication (Figure 7c) [102]. Al-Qadhi and his group utilized high-shear mixing to fabricate clay–epoxy and observed disordered intercalated or exfoliated morphology. It was observed that diffusivity decreased by about 51% at 1 wt.% of clay, and the highest water uptake declined by 22% at 5 wt.% of clay content. Another research has shown that 2 wt.% clay/epoxy nanocomposite and pristine epoxy have water uptakes of 1.98% and 2.2%, respectively, over the 0.9% and 1% for crude oil, suggesting that the water uptake of these materials is over twice as high as that of crude oil [13,119]. Zunjarrao compared high-speed shear mixing and ultrasonic mixing, finding exfoliated structures at all compositions (0.5–6 wt.% clay) with high shear mixing, while ultrasonication achieved exfoliation only up to 4 wt.% clay [120].

Three-roll milling: Yasmin et al. found three-roll milling highly effective in achieving well-exfoliated morphology (Figure 7d) in clay/epoxy nanocomposites, with increased clay loading boosting tensile modulus but decreasing tensile strength [116].

Slurry compounding: A novel two-stage approach involving solvent exchange and silanization achieved highly exfoliated morphology using pristine clay with minimal organic modifier. This method improved glass transition temperature, fracture toughness, and tensile modulus [121,122].

A comprehensive evaluation of clay dispersion methodologies reveals distinct advantages and limitations across various techniques. Mechanical mixing stands out as a straightforward and cost-effective approach, particularly effective in achieving intercalated morphologies when working with lower clay concentrations in polymer matrices. Moving up the sophistication scale, ultrasonication demonstrates marked improvements over conventional mechanical mixing, frequently resulting in partial exfoliation of clay platelets and enhanced material properties. More advanced processing techniques, including high-shear mixing, three-roll milling, and slurry compounding, have proven exceptionally effective in generating sophisticated morphological structures, characterized by disordered intercalation or complete exfoliation, ultimately leading to superior mechanical, thermal, and barrier properties in the final nanocomposites. Perhaps most significantly, the implementation of hybrid processing approaches, which strategically combine multiple dispersion techniques, has consistently demonstrated superior results compared to single-method approaches, yielding optimized clay dispersion, improved interfacial interaction, and enhanced overall performance characteristics. This synergistic effect suggests that carefully designed combination methods may represent the optimal pathway for developing high-performance polymer–clay nanocomposites.

The optimal processing method depends on various factors, including clay concentration, clay type (modified or unmodified), desired properties, and specific processing conditions (time, temperature). Selecting the appropriate technique requires careful consideration of these factors to achieve the best results for a given application. This comprehensive overview of processing techniques highlights the versatility and effectiveness of various methods in tailoring clay–epoxy nanocomposite properties to meet specific performance requirements.

8.4. Performance of Clay–Epoxy Nanocomposites

Clay–epoxy nanocomposites have garnered significant attention due to their remarkable performance enhancements, even at low clay concentrations of 1–5%. These nanocomposites exhibit improved mechanical, thermal, and barrier properties, largely attributed to the high aspect ratio of nanoclay particles, which facilitates extensive interfacial contact with the epoxy resin.

8.4.1. Mechanical Performance

The mechanical performance of these nanocomposites is primarily influenced by the dispersion quality of clay platelets within the epoxy matrix. Generally, properties such as impact strength, tensile characteristics, and fracture toughness improve with increasing clay content, up to an optimal range of 1–3 wt%. Beyond this threshold, property deterioration often occurs due to clay aggregation. The tensile modulus typically demonstrates a linear increase with clay content, owing to the higher modulus and aspect ratio of the nanoclay particles.

Studies have shown that temperature can significantly affect the nanocomposite’s performance. In a study by Yang et al., the mechanical properties of these nanocomposites were evaluated at both ambient and cryogenic (77 K) temperatures. The maximum tensile strength was observed at a 1% clay loading (Figure 8a). At 77 K, the nanocomposite demonstrated enhanced tensile strength due to thermal shrinkage, resulting from the significant difference in thermal expansion coefficients between the modified nanoclay and epoxy, leading to improved interfacial bonding. Additionally, the tensile modulus was higher at 77 K, as both the epoxy and silicate layers exhibited increased modulus values at lower temperatures. However, the impact strength increased only up to 1 wt.% clay loading at ambient temperature, while at 77 K, the impact strength decreased with further clay addition due to the formation of clay agglomerates (Figure 8b) [123]. Mohan’s research further highlighted the influence of curing temperature on the mechanical properties of epoxy nanocomposites. The study found that both curing temperature and nanoclay loading significantly affect the mechanical performance. A curing temperature of 120 °C resulted in a greater d-spacing between clay layers compared to lower temperatures, with maximum tensile strength observed at 2–3 wt.% clay loading. However, beyond this range, the formation of clay agglomerates led to a deterioration in tensile strength [124].

Researchers have developed three-phase models to predict the Young’s modulus of these nanocomposites effectively. Luo and Daniel’s three-phase model, incorporating epoxy, exfoliated clay, and clay agglomerates, effectively predicts Young’s modulus by accounting for various factors, such as the matrix’s Poisson’s ratio and modulus, exfoliation ratio, ratio of clay platelets to aggregates, intragallery modulus, and d-spacing. This model’s predictions closely align with experimental data and key findings: the exfoliation ratio is critical for modulus enhancement, improved dispersion increases composite modulus, and larger d-spacing and high cluster aspect ratios significantly boost stiffness. Additional studies have shown that clay loading of up to 5 wt.% can increase stiffness by nearly 50% over neat epoxy [125,126]. Microhardness improves with rising clay content until reaching an optimal limit, beyond which a decrease is noted due to reduced reinforcement from the silicate layers [127]. However, increasing clay content generally results in decreased impact strength, as observed by Miyagawa’s group [128,129]. Fracture toughness improved by 25% by adding 5 wt.% of clay in epoxy composite [130]. The fracture toughness, elongation at break, and tensile strength improved by 93%, 64%, and 38%, respectively, at an optimum clay content of 1 wt.% [131].

Many authors revealed that fracture toughness, impact strength, and tensile strength decayed with a rise in clay percentage. There were many reasons behind that, like clay agglomerates, the mixture’s viscosity increased, difficulty in degassing and lower filler surface area (resulted in weak interfacial bonding) [2,25,132,133]. Optimizing clay content is crucial, as excessive amounts can lead to agglomeration and subsequent property deterioration. The potential of clay–epoxy nanocomposites for enhancing mechanical properties is significant. However, achieving optimal performance requires careful consideration of various factors, including clay content, processing conditions, and dispersion methods. By understanding and managing these variables, researchers and engineers can design nanocomposites with tailored properties to meet specific performance requirements across a wide range of applications.

8.4.2. Thermal Performance

Clay–epoxy nanocomposites are renowned for their exceptional thermal stability and flame retardancy, making them highly suitable for applications that demand enhanced thermal properties. These nanocomposites leverage the unique characteristics of nanoclay to enhance thermal resistance through multiple mechanisms. Nanoclay acts as a barrier to volatile elements generated during degradation, creating a labyrinth effect that slows the exit of these products. Additionally, it contributes to char formation after thermal degradation, further improving fire resistance [134,135,136,137].

Figure 8. (a,b) Influence of modified clay loading on tensile and impact strength at ambient and at 77 K temperature [123], (c,d) TGA curves of epoxy-containing various loading of hydrated/dehydrated sepiolite [138], (e) illustration of a zigzag pathway of a liquid/gas through clay–epoxy nanocomposites.

Modified clays generally outperform pristine clays in reducing burning rates, highlighting the value of clay surface modification in enhancing thermal properties. Kaya et al. reported that the burning rate of nanocomposites containing 10 wt.% pristine and modified clay decreased by 38% and 58%, respectively. Interestingly, unmodified clay did not affect the glass transition temperature (T_g), whereas modified clay led to an increase in T_g due to better dispersion [139]. Research has shown mixed results, with some studies reporting increases in T_g [140,141] while others note decreases [13,142]. This variability is attributed to several factors, including the morphology of the nanocomposite, the interfacial adhesion between the epoxy and clay, and the type of surfactant used for clay modification. Polar surfactants tend to have minimal impact on T_g, while non-polar surfactants often lead to a decrease due to weaker interfacial bonding and potential plasticization effects [140,143,144,145].

Research has shown that the type and preparation of clay significantly influences the thermal performance of these nanocomposites. In a study by Zotti et al., the effects of dehydrated (ANIDRA) and hydrated (IDRA) clay on the fire performance and degradation of epoxy composites were closely examined. The researchers found that both types of nanoclay had a minimal impact on the overall degradation behavior of the epoxy composite (Figure 8c,d). The nanoclay remained chemically inert during the degradation process, and its presence did not significantly alter the formation of char. However, the fire performance differed between the two types: with 10 wt.% ANIDRA nanoclay, the peak heat release rate was reduced by 27%, while with 10 wt.% IDRA nanoclay, the reduction was 17%. Although the total heat emitted remained similar to that of the reference sample, the highest IDRA nanoclay loading extended the burning time and further reduced the peak heat release rate, thereby lowering the fire hazard. Nevertheless, ANIDRA clay demonstrated superior fire performance compared to IDRA [138].

The dispersion quality of nanoclay within the epoxy matrix plays a crucial role in determining thermal stability. Uniformly distributed nanoclay tends to offer better thermal resistance, with some studies reporting a 15 °C increase in the maximum degradation temperature compared to virgin epoxy [146]. The thermal stability of the nanocomposite is also influenced by the type of epoxy resin used. Aromatic epoxy resins form adducts that exhibit superior thermal stability compared to those formed by aliphatic epoxy resins, resulting in a higher initial decomposition temperature (T_onset) of 250 °C for aromatic adducts [147]. Fire resistance can be further enhanced by curing the epoxy–clay nanocomposite with specific agents, such as methyl tetrahydrophthalic anhydride, which creates a protective layer through ablative reassembly and the nanoclay’s chemical structure. Incorporating other additives like graphene alongside nanoclay can also improve the fire resistance of epoxy-based carbon fiber composites [148,149].

The clay content, type, modification, and dispersion quality all play critical roles in determining the final thermal characteristics of the nanocomposite. Clay–epoxy nanocomposites represent a promising avenue for enhancing the thermal stability and flame retardancy of materials. Their ability to significantly improve these properties, even at low clay concentrations, makes them attractive for applications in aerospace, automotive, and construction industries where fire safety is paramount. As research in this field continues to evolve, it promises to unlock new possibilities for high-performance, thermally resistant materials across a wide range of applications.

8.4.3. Barrier Properties

Incorporating nanoclay into epoxy composites significantly enhances their barrier properties by creating a complex network, or “labyrinth path” (Figure 8e) that makes the epoxy matrix less permeable to gases and liquids. This improved barrier performance arises because the nanoclay layers disrupt the diffusion pathways, effectively increasing the length and complexity of the route that permeants must traverse. The effectiveness of nanoclay in improving barrier properties is influenced by several factors, including clay type, modification, dispersion quality, and loading percentage. Modified clays, which transform from hydrophilic to organophilic, generally outperform unmodified clays in resisting water uptake. This transformation is crucial in applications where moisture resistance is paramount [150].

Researchers have employed various models to predict and understand the barrier properties of these nanocomposites. Neilson’s equation [151], later modified by Bharadwaj [152] to include an orientation factor, has proven valuable in estimating gas permeability. These theoretical frameworks help bridge the gap between experimental observations and predictive modeling, enabling more efficient material design. In a study of modified nanoclay/epoxy nanocomposites, oxygen gas permeability was reduced by 30% at a clay loading of 3.5 vol.% compared to neat epoxy. Similarly, water uptake decreased in modified clay composites due to the transformation of the clay’s nature from hydrophilic to organophilic by the organic modifier [153]. Conversely, unmodified clay, with its inherently hydrophilic silicate layers, exhibited increased water uptake. Interestingly, water uptake in these nanocomposites increased with clay loading up to 1 wt.% but plateaued beyond this concentration [154]. Further research highlighted the nanocomposite’s resistance to various solvents. A study on methyl ethyl ketone resistance revealed that clay–epoxy nanocomposites had lower solvent uptake than pristine epoxy, due to the obstruction of diffusion pathways by the clay layers [155]. Moisture permeability also decreased with increased clay loading, particularly when the clay was homogeneously dispersed, enhancing the nanocomposite’s resistance to moisture [156].

Different types of Cloisite clays (e.g., 30B, 15A, NaMMT, 10A) were tested for their barrier properties, with Cloisite 10A and 30B outperforming others due to their homogenous dispersion and partially exfoliated morphology. This underscores the importance of achieving optimal dispersion during nanocomposite preparation [157]. A clay–epoxy nanocomposites excel in barrier properties, their impact on mechanical characteristics under wet conditions is nuanced. Water absorption can lead to a plasticization effect, resulting in a decline in flexural properties. However, this same effect can enhance fracture toughness and impact strength due to increased matrix flexibility. This complex interplay highlights the need for careful consideration of the intended application environment when designing these materials [158]. Bagherzadeh and his group used electrochemical impedance spectroscopy and salt spray techniques to examine the nanocomposites’ water uptake and anti-corrosive potentials. When compared to pure epoxy coating, the results demonstrated a reduction in water absorption and an improvement in the barrier and anti-corrosive properties of epoxy-based nanocomposite coating. Water absorption is reduced by around 70% when a nanocomposite coating with a 1 weight percent clay loading is applied. The anti-corrosive qualities of nanocomposite coatings 1 and 5 wt.% clay content change significantly, as evidenced by the results of salt spray and electrochemical impedance spectroscopy, which demonstrate that the barrier qualities improve with increasing clay concentration. The coating worked best at concentrations of 3 and 5 wt.% clay [159].

Clay–epoxy nanocomposites offer significant improvements in barrier properties against a wide range of permeants, making them attractive for applications in protective coatings, packaging materials, and corrosion-resistant structures. However, the complex relationship between clay content, dispersion, and various properties underscores the need for careful optimization to achieve desired performance characteristics. Future research opportunities lie in further refining clay modification techniques, exploring synergistic effects with other additives, and developing more accurate predictive models. By tailoring nanocomposite formulations through meticulous selection of clay types, modifications, and dispersion processes, researchers and engineers can maximize the benefits of these advanced materials, paving the way for their application in increasingly diverse and demanding environments.

8.4.4. Applications

The incorporation of nanoclay reinforcement in epoxy resin has led to substantial improvements in mechanical, thermal, and barrier properties, making these materials invaluable in high-precision sectors.

Aerospace, aviation, automotive, and defense industries have been at the forefront of adopting epoxy–clay nanocomposites. These materials excel in both structural and functional applications, finding use in adhesives, tooling, sealants, casting, electronics, construction, laminates, and composites [72,160,161,162,163,164,165,166,167,168]. Njuguna et al. highlighted the utilization of carbon- or glass fiber-reinforced clay–epoxy nanocomposites in automotive and aeronautical applications, showcasing their versatility [169]. The fatigue fracture propagation characteristics of epoxy nanocomposites are particularly relevant in engineering components subjected to cyclic stress. Research has shown that reinforcing carbon fiber/epoxy composites with 3 wt.% nanoclay results in a significant improvement in fatigue life, attributed to the strong interfacial adhesion between the composite system’s various constituents [170].

The excellent moisture-barrier properties of epoxy–clay nanocomposites have expanded their utility across diverse domains. They are particularly valuable in packaging, coatings, and as a matrix for fiber-reinforced plastic pipes used in water transportation [13]. In environments prone to moisture, nanoclay–epoxy nanocomposites have proven invaluable for adhesively bonded joints. Their application in these scenarios helps reduce moisture absorption and mitigate the loss of load capacity, enhancing the overall durability and performance of the bonded structures [171,172].

The diverse applications of nanoclay-reinforced epoxy nanocomposites span multiple industries. In aeronautics, they are used in engineering components, while in electronics, they are integral to the production of electrical components and high-tension insulators. Their adhesive properties make them ideal for bonding various substrates in construction and manufacturing, and they are also employed in floor tooling, stamping dies, and patterns [154,173,174,175]. In the food and beverage industry, clay–epoxy nanocomposites have found a niche application in the production of multilayer PET bottles for beer and soft drinks, as well as food packaging sheets. By reducing carbon dioxide loss and oxygen absorption, these materials significantly extend the shelf life and maintain the freshness of beverages [176].

As research in this field continues to advance, the potential applications for epoxy/clay nanocomposites are likely to expand further, promising innovative solutions across an even broader spectrum of industries and technological domains.

9. Conclusions

Epoxy nanocomposites reinforced with nanoclay represent a revolutionary leap in 21st century materials science. These nanocomposites demonstrate remarkable property enhancements with the incorporation of merely a small fraction of nanoclay (<5%). Among various morphologies, exfoliated nanocomposites stand out for their superior characteristics, showcasing the potential of nanoscale engineering in polymer nanocomposite systems.

The intricate relationship between nanocomposite morphology and performance cannot be overstated. A complex interplay of factors—including processing methods, clay modifier selection, curing agent choice, and curing temperature—governs the final structure and properties of these nanocomposites. This delicate balance underscores the need for meticulous optimization to unlock the full potential of epoxy clay nanocomposites.

As we look to the future, the trajectory of epoxy clay nanocomposite research promises exciting possibilities. Ongoing investigations are likely to yield more sophisticated materials with enhanced properties and expanded capabilities. Their ability to deliver significant property improvements with minimal filler content, coupled with their adaptability to various industrial needs, positions them as key players in the generation of materials.

Author Contributions

Conceptualization, D.S., V.S. and T.N.; data curation, D.S., V.S. and S.S.; investigation, D.S. and S.S.; methodology, D.S., S.S., T.N. and R.M.; project administration, D.S., T.N. and R.M.; validation, D.S., T.N., R.M., S.-Y.L. and S.-J.P.; writing—original draft, D.S. and V.S.; writing—review and editing, D.S., S.S., T.N., R.M., S.-Y.L. and S.-J.P.; supervision, T.N. and R.M.; visualization, T.N., R.M. and S.-Y.L.; funding acquisition, S.-J.P. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2022M3J7A1062940, 2023R1A2C1004109, and 2022R1I1A1A01070007). Also, this was supported by Korea Energy (No. 2024-Research and Development in Field Technology, Yeongheung-01).

Data Availability Statement

The cited literature is the principal source for the data used in this study. It is possible to obtain the datasets mentioned in this study by consulting the sources that were indicated in the related references.

Conflicts of Interest

The authors declare that they have no competing interests.

References

Camargo, P.H.C.; Satyanarayana, K.G.; Wypych, F. Nanocomposites: Synthesis, structure, properties and new application opportunities. Mater. Res. 2009, 12, 1–39. [Google Scholar] [CrossRef]
Azeez, A.A.; Rhee, K.Y.; Park, S.J.; Hui, D. Epoxy clay nanocomposites—Processing, properties and applications: A review. Compos. Part B Eng. 2013, 45, 308–320. [Google Scholar] [CrossRef]
Kalendova, A.; Kupkova, J.; Urbaskova, M.; Merinska, D. Applications of Clays in Nanocomposites and Ceramics. Minerals 2024, 14, 93. [Google Scholar] [CrossRef]
Wang, R.; Xiong, Y.; Yang, K.; Zhang, T.; Zhang, F.; Xiong, B.; Hao, Y.; Zhang, H.; Chen, Y.; Tang, J. Advanced progress on the significant influences of multi-dimensional nanofillers on the tribological performance of coatings. RSC Adv. 2023, 13, 19981–20022. [Google Scholar] [CrossRef]
Wu, W.; Liu, L.; Goksen, G.; Demir, D.; Shao, P. Multidimensional (0D-3D) nanofillers: Fascinating materials in the field of bio-based food active packaging. Food Res. Int. 2022, 157, 111446. [Google Scholar] [CrossRef]
Byakodi, M.; Shrikrishna, N.S.; Sharma, R.; Bhansali, S.; Mishra, Y.; Kaushik, A.; Gandhi, S. Emerging 0D, 1D, 2D, and 3D nanostructures for efficient point-of-care biosensing. Biosens. Bioelectron. X 2022, 12, 100284. [Google Scholar] [CrossRef]
Crosby, A.J.; Lee, J.Y. Polymer nanocomposites: The “nano” effect on mechanical properties. Polym. Rev. 2007, 47, 217–229. [Google Scholar] [CrossRef]
Muralishwara, K.; Sudhakar, Y.N.; Kini, U.A.; Sharma, S.; Gurumurthy, B.M. Moisture absorption and spectroscopic studies of epoxy clay nanocomposite. Polym. Bull. 2022, 79, 5587–5611. [Google Scholar] [CrossRef]
Fakhreddini-Najafabadi, S.; Torabi, M.; Taheri-Behrooz, F. An investigation on the effects of synthesis on the mechanical properties of nanoclay/epoxy. J. Mater. Res. Technol. 2021, 15, 5375–5395. [Google Scholar] [CrossRef]
Ardebili, A.; Alaei, M.H.; Kaveh, A.; Jam, J.E. Permeability and mechanical properties of nanoclay/epoxy liner used in type IV liquid oxygen vessel: Experimental and numerical study. Iran. Polym. J. 2024, 33, 1351–1367. [Google Scholar] [CrossRef]
Geng, J.; Qin, J.; He, J. Preparation of Intercalated Organic Montmorillonite DOPO-MMT by Melting Method and Its Effect on Flame Retardancy to Epoxy Resin. Polymers 2021, 13, 3496. [Google Scholar] [CrossRef]
Xavier, J.R.; Vinodhini, S.P.; Srinivasan, N. Effects of Incorporating Silanized Nanoclay on the Barrier, Hydrophobic and Mechanical Properties of Epoxy Resin in Chloride Environment. Ind. Eng. Chem. Res. 2022, 61, 6973–6986. [Google Scholar] [CrossRef]
Al-Qadhi, M.; Merah, N.; Gasem, Z.M. Mechanical properties and water uptake of epoxy–clay nanocomposites containing different clay loadings. J. Mater. Sci. 2013, 48, 3798–3804. [Google Scholar] [CrossRef]
Bashar, M.; Mertiny, P.; Sundararaj, U. Effect of Nanocomposite Structures on Fracture Behavior of Epoxy-Clay Nanocomposites Prepared by Different Dispersion Methods. J. Nanomater. 2014, 2014, 312813. [Google Scholar] [CrossRef]
Bindu Sharmila, T.K.; Ayswarya, E.P.; Abraham, B.T.; Sabura Begum, P.M.; Thachil, E.T. Fabrication of partially exfoliated and disordered intercalated cloisite epoxy nanocomposites via in situ polymerization: Mechanical, dynamic mechanical, thermal and barrier properties. Appl. Clay Sci. 2014, 102, 220–230. [Google Scholar] [CrossRef]
Vijayan, P.P.; Harikrishnan, M.G.; Puglia, D.; Vijayan, P.P.; Kenny, J.M.; Thomas, S. Solvent Uptake of Liquid Rubber Toughened Epoxy/Clay Nanocomposites. Adv. Polym. Technol. 2016, 35, 21531. [Google Scholar] [CrossRef]
Kim, S.-H.; Park, S.-J.; Lee, S.-Y.; Park, S.-J. Amine functionalization on thermal and mechanical behaviors of graphite nanofibers-loaded epoxy composites. J. Mater. Sci. Technol. 2023, 151, 80–88. [Google Scholar] [CrossRef]
Callister, W.D.; Rethwisch, D.G.; Blicblau, A.; Bruggeman, K.; Cortie, M.; Long, J.; Hart, J.; Marceau, R.; Mitchell, R. Materials Science and Engineering: An Introduction; John Wiley & Sons: New York, NY, USA, 2007; Volume 7. [Google Scholar]
Harris, B. Engineering Composite Materials; IoM: London, UK, 1999. [Google Scholar]
Alarifi, I.M. A comprehensive review on advancements of elastomers for engineering applications. Adv. Ind. Eng. Polym. Res. 2023, 6, 451–464. [Google Scholar] [CrossRef]
Wypych, G. Handbook of Polymers; Elsevier: Amsterdam, The Netherlands, 2022. [Google Scholar]
Huang, C.; Qian, X.; Yang, R. Thermal conductivity of polymers and polymer nanocomposites. Mater. Sci. Eng. R Rep. 2018, 132, 1–22. [Google Scholar] [CrossRef]
Abdalla, S.; Al-Marzouki, F.; Al-Ghamdi, A.A.; Abdel-Daiem, A. Different Technical Applications of Carbon Nanotubes. Nanoscale Res. Lett. 2015, 10, 358. [Google Scholar] [CrossRef]
Srinivasa, M.; Rammohan, Y.; Sadashiva, M.; Santhosh, N. Effect of shock waves on the hardness of graphene reinforced aluminium composites. J. Polym. Compos. 2020, 8, 32–38. [Google Scholar]
Alexandre, M.; Dubois, P. Polymer-layered silicate nanocomposites: Preparation, properties and uses of a new class of materials. Mater. Sci. Eng. R Rep. 2000, 28, 1–63. [Google Scholar] [CrossRef]
Smaradhana, D.F.; Surojo, E.; Alnursyah, R. An Overview of Interface/Interphase Modification in Functional Composites. In Proceedings of the 6th International Conference and Exhibition on Sustainable Energy and Advanced Materials, Surakarta, Indonesia, 16–17 October 2019. [Google Scholar]
Tal, N.Y.; Timor, Y.; Dodiuk, H.; Kenig, S. Polymer/Nanoparticle Interface in Polymer Nanocomposites: A Critical Review. Rev. Adhes. Adhes. 2021, 9, 368–400. [Google Scholar]
Snipes, J.S.; Robinson, C.T.; Baxter, S.C. Effects of scale and interface on the three-dimensional micromechanics of polymer nanocomposites. J. Compos. Mater. 2011, 45, 2537–2546. [Google Scholar] [CrossRef]
Pitsa, D.; Danikas, M.G. Interfaces features in polymer nanocomposites: A review of proposed models. Nano 2011, 6, 497–508. [Google Scholar] [CrossRef]
Kim, J.-K.; Mai, Y.-W. Engineered Interfaces in Fiber Reinforced Composites; Elsevier: Amsterdam, The Netherlands, 1998. [Google Scholar]
Olad, A.; Azar, R.H.; Babaluo, A.A. Investigation on the mechanical and thermal properties of intercalated epoxy/layered silicate nanocomposites. Int. J. Polym. Mater. 2012, 61, 1035–1049. [Google Scholar] [CrossRef]
Lim, S.; Chow, W. Fracture toughness enhancement of epoxy by organo-montmorillonite. Polym.-Plast. Technol. Eng. 2011, 50, 182–189. [Google Scholar] [CrossRef]
Kinloch, A.; Taylor, A. Mechanical and fracture properties of epoxy/inorganic micro-and nano-composites. J. Mater. Sci. Lett. 2003, 22, 1439–1441. [Google Scholar] [CrossRef]
Martinez, P.; Nutt, S. Flax–Reinforced Vitrimer Epoxy Composites Produced via RTM. J. Compos. Sci. 2024, 8, 275. [Google Scholar] [CrossRef]
Mezeix, L.; Gupta, P.; Bouvet, C.; Wongtimnoi, K. Mechanical Characterization of Recyclable and Non-Recyclable Bio-Epoxy Resins for Aerospace Applications. J. Compos. Sci. 2024, 8, 191. [Google Scholar] [CrossRef]
Ravindran, B.; Agathocleous, T.; Oswald-Tranta, B.; Fauster, E.; Feuchter, M. Impact Characteristics and Repair Approaches of Distinct Bio-Based Matrix Composites: A Comparative Analysis. J. Compos. Sci. 2024, 8, 126. [Google Scholar] [CrossRef]
Anidha, S.; Mozhuguan Sekar, S.; Natarajan, E.; Muthukkumar, M.; Markandan, K.; Ang, C.K.; Franz, G. Preliminary Investigations and Support for the Mechanical and Dynamic Characteristics of a Natural Rubber Reinforcement in E-Glass/CNT/Epoxy Composite. J. Compos. Sci. 2024, 8, 140. [Google Scholar] [CrossRef]
Puttaswamygowda, P.H.; Sharma, S.; Ullal, A.K.; Shettar, M. Synergistic Enhancement of the Mechanical Properties of Epoxy-Based Coir Fiber Composites through Alkaline Treatment and Nanoclay Reinforcement. J. Compos. Sci. 2024, 8, 66. [Google Scholar] [CrossRef]
Papadopoulos, L.; Terzopoulou, Z.; Vlachopoulos, A.; Klonos, P.A.; Kyritsis, A.; Tzetzis, D.; Papageorgiou, G.Z.; Bikiaris, D. Synthesis and characterization of novel polymer/clay nanocomposites based on poly (butylene 2,5-furan dicarboxylate). Appl. Clay Sci. 2020, 190, 105588. [Google Scholar] [CrossRef]
Kotsilkova, R. Performance of Thermoset Nanocomposites; Smithers Rapra Technology Limited Shawbury: Shropshire, UK, 2007. [Google Scholar]
Shundo, A.; Aoki, M.; Yamamoto, S.; Tanaka, K. Cross-Linking Effect on Segmental Dynamics of Well-Defined Epoxy Resins. Macromolecules 2021, 54, 5950–5956. [Google Scholar] [CrossRef]
Liang, M.; Liu, X.; Liu, D.; Li, X.; Hu, X.; Feng, C.; Li, T.-T.; Lin, J.-H.; Chang, B.; Chen, J. A review of the curing rate and mechanical properties of epoxy resin on polymer matrix composites. J. Polym. Res. 2024, 31, 337. [Google Scholar] [CrossRef]
Heng, Z.; Wang, L.; Chen, F.; Zhou, J.; Zhang, H.; Zhang, X.; Sun, T.; Ling, Y.; Xia, S.; Liang, M.; et al. In-situ constructing ultra-high-aspect-ratio core–shell nanostructures to achieve high-performance epoxy thermosets and their carbon fiber reinforced epoxy composites. Chem. Eng. J. 2022, 448, 137707. [Google Scholar] [CrossRef]
Gu, H.; Ma, C.; Gu, J.; Guo, J.; Yan, X.; Huang, J.; Zhang, Q.; Guo, Z. An overview of multifunctional epoxy nanocomposites. J. Mater. Chem. C 2016, 4, 5890–5906. [Google Scholar] [CrossRef]
Lorenz, N.; Müller-Pabel, M.; Gerritzen, J.; Müller, J.; Gröger, B.; Schneider, D.; Fischer, K.; Gude, M.; Hopmann, C. Characterization and modeling cure- and pressure-dependent thermo-mechanical and shrinkage behavior of fast curing epoxy resins. Polym. Test. 2022, 108, 107498. [Google Scholar] [CrossRef]
Vázquez, L.S.; López-Beceiro, J.; Díaz-Díaz, A.-M.; Álvarez-García, A.; Pereira, M.; Artiaga, R. Comparison by thermal analysis of Joule-cured versus oven-cured composites. J. Therm. Anal. Calorim. 2024, 149, 10487–10495. [Google Scholar] [CrossRef]
Guan, C.; Zhan, L.; Sun, F.; Yao, S.; Zhong, S.; Wang, B. Study on the heating mechanism and macro/micro properties of composite materials under microwave curing. Polym. Compos. 2024, 45, 1405–1421. [Google Scholar] [CrossRef]
Morancho, J.M.; Ramis, X.; Fernández-Francos, X.; Konuray, O.; Salla, J.M.; Serra, À. Dual curing of an epoxy resin with dicarboxylic acids. J. Therm. Anal. Calorim. 2020, 142, 607–615. [Google Scholar] [CrossRef]
Patel, A.; Kravchenko, O.; Manas-Zloczower, I. Effect of Curing Rate on the Microstructure and Macroscopic Properties of Epoxy Fiberglass Composites. Polymers 2018, 10, 125. [Google Scholar] [CrossRef]
Guo, H.; Wang, B.; Fu, X.; Li, N.; Li, G.; Zheng, G.; Wang, Z.; Liu, C.; Chen, Y.; Weng, Z.; et al. A New Strategy to Improve the Toughness of Epoxy Thermosets—By Introducing Poly(ether nitrile ketone)s Containing Phthalazinone Structures. Materials 2023, 16, 2878. [Google Scholar] [CrossRef]
Li, S.; Chen, D.; Yuan, Y.; Gao, C.; Cui, Y.; Wang, H.; Liu, X.; Liu, M.; Wu, Z. Influence of flexible molecular structure on the cryogenic mechanical properties of epoxy matrix and carbon fiber/epoxy composite laminate. Mater. Des. 2020, 195, 109028. [Google Scholar] [CrossRef]
Yamamoto, S.; Kuwahara, R.; Tanaka, K. Effects of Chemistry of Silicon Surfaces on the Curing Process and Adhesive Strength for Epoxy Resin. ACS Appl. Polym. Mater. 2022, 4, 6038–6046. [Google Scholar] [CrossRef]
Qu, C.; Zhang, X.; Wang, D.; Fan, X.; Li, H.; Liu, C.; Feng, H.; Wang, R.; Guo, K.; Tian, Y.; et al. Residual stress and thermal properties of rubber-modified epoxy systems for semiconductor package. J. Appl. Polym. Sci. 2022, 139, 51786. [Google Scholar] [CrossRef]
Ma, H.; Zhang, X.; Ju, F.; Tsai, S.-B. A Study on Curing Kinetics of Nano-Phase Modified Epoxy Resin. Sci. Rep. 2018, 8, 3045. [Google Scholar] [CrossRef]
Babayan, E.; Nguyen, H. Epoxy Matrix Toughened with Polyimide Thermoplastic Resin. European Patent 0455755, 10 August 1990. [Google Scholar]
May, C. Epoxy Resins: Chemistry and Technology; Routledge: London, UK, 2018. [Google Scholar]
Ashcroft, W.; Ellis, B. Chemistry and Technology of Epoxy Resins. Ellis, B., Ed.; Blackie Academic & Professional: London, UK, 1993; pp. 37–71. [Google Scholar]
Kumar, S.; Krishnan, S.; Mohanty, S.; Nayak, S.K. Synthesis and characterization of petroleum and biobased epoxy resins: A review. Polym. Int. 2018, 67, 815–839. [Google Scholar] [CrossRef]
Capricho, J.C.; Fox, B.; Hameed, N. Multifunctionality in Epoxy Resins. Polym. Rev. 2020, 60, 1–41. [Google Scholar] [CrossRef]
Ligon-Auer, S.C.; Schwentenwein, M.; Gorsche, C.; Stampfl, J.; Liska, R. Toughening of photo-curable polymer networks: A review. Polym. Chem. 2016, 7, 257–286. [Google Scholar] [CrossRef]
Abulyazied, D.E.; Ene, A. An Investigative Study on the Progress of Nanoclay-Reinforced Polymers: Preparation, Properties, and Applications: A Review. Polymers 2021, 13, 4401. [Google Scholar] [CrossRef]
Ke, Y.; Stroeve, P. Polymer-Layered Silicate and Silica Nanocomposites; Elsevier: Amsterdam, The Netherlands, 2005. [Google Scholar]
Pavlidou, S.; Papaspyrides, C. A review on polymer–layered silicate nanocomposites. Prog. Polym. Sci. 2008, 33, 1119–1198. [Google Scholar] [CrossRef]
Paul, D.R.; Robeson, L.M. Polymer nanotechnology: Nanocomposites. Polymer 2008, 49, 3187–3204. [Google Scholar] [CrossRef]
Liu, J.; Boo, W.-J.; Clearfield, A.; Sue, H.-J. Intercalation and exfoliation: A review on morphology of polymer nanocomposites reinforced by inorganic layer structures. Mater. Manuf. Process. 2006, 21, 143–151. [Google Scholar] [CrossRef]
Ray, S.S.; Okamoto, M. Polymer/layered silicate nanocomposites: A review from preparation to processing. Prog. Polym. Sci. 2003, 28, 1539–1641. [Google Scholar]
Blumstein, A. Polymerization of adsorbed monolayers. II. Thermal degradation of the inserted polymer. J. Polym. Sci. Part A Gen. Pap. 1965, 3, 2665–2672. [Google Scholar] [CrossRef]
Krishnamoorti, R.; Vaia, R.A.; Giannelis, E.P. Structure and dynamics of polymer-layered silicate nanocomposites. Chem. Mater. 1996, 8, 1728–1734. [Google Scholar] [CrossRef]
Fornes, T.; Paul, D. Modeling properties of nylon 6/clay nanocomposites using composite theories. Polymer 2003, 44, 4993–5013. [Google Scholar] [CrossRef]
Heinz, H.; Vaia, R.; Krishnamoorti, R.; Farmer, B. Self-assembly of alkylammonium chains on montmorillonite: Effect of chain length, head group structure, and cation exchange capacity. Chem. Mater. 2007, 19, 59–68. [Google Scholar] [CrossRef]
Paul, D.; Zeng, Q.; Yu, A.; Lu, G. The interlayer swelling and molecular packing in organoclays. J. Colloid Interface Sci. 2005, 292, 462–468. [Google Scholar] [CrossRef]
Shelly, D.; Nanda, T.; Mehta, R. Addition of compatibilized nanoclay to GFRCs for improved izod impact strength and tensile properties. Proc. Inst. Mech. Eng. Part L J. Mater. Des. Appl. 2021, 235, 2022–2035. [Google Scholar] [CrossRef]
Bruce, A.N.; Lieber, D.; Hua, I.; Howarter, J.A. Rational interface design of epoxy–organoclay nanocomposites: Role of structure-property relationship for silane modifiers. J. Colloid Interface Sci. 2014, 419, 73–78. [Google Scholar] [CrossRef]
Asgari, M.; Sundararaj, U. Silane functionalization of sodium montmorillonite nanoclay: The effect of dispersing media on intercalation and chemical grafting. Appl. Clay Sci. 2018, 153, 228–238. [Google Scholar] [CrossRef]
LeBaron, P.C.; Wang, Z.; Pinnavaia, T.J. Polymer-layered silicate nanocomposites: An overview. Appl. Clay Sci. 1999, 15, 11–29. [Google Scholar] [CrossRef]
Zeng, Q.; Yu, A.; Lu, G.; Paul, D. Clay-based polymer nanocomposites: Research and commercial development. J. Nanosci. Nanotechnol. 2005, 5, 1574–1592. [Google Scholar] [CrossRef]
Kim, G.-M.; Lee, D.-H.; Hoffmann, B.; Kressler, J.; Stöppelmann, G. Influence of nanofillers on the deformation process in layered silicate/polyamide-12 nanocomposites. Polymer 2001, 42, 1095–1100. [Google Scholar] [CrossRef]
Varlot, K.; Reynaud, E.; Kloppfer, M.; Vigier, G.; Varlet, J. Clay-reinforced polyamide: Preferential orientation of the montmorillonite sheets and the polyamide crystalline lamellae. J. Polym. Sci. Part B Polym. Phys. 2001, 39, 1360–1370. [Google Scholar] [CrossRef]
Weon, J.-I.; Sue, H.-J. Effects of clay orientation and aspect ratio on mechanical behavior of nylon-6 nanocomposite. Polymer 2005, 46, 6325–6334. [Google Scholar] [CrossRef]
Chee, S.S.; Jawaid, M.; Sultan, M.T.H.; Alothman, O.Y.; Abdullah, L.C. Effects of nanoclay on physical and dimensional stability of Bamboo/Kenaf/nanoclay reinforced epoxy hybrid nanocomposites. J. Mater. Res. Technol. 2020, 9, 5871–5880. [Google Scholar] [CrossRef]
Kim, S.W.; Jo, W.H.; Lee, M.S.; Ko, M.B.; Jho, J.Y. Preparation of clay-dispersed poly(styrene-co-acrylonitrile) nanocomposites using poly(ϵ-caprolactone) as a compatibilizer. Polymer 2001, 42, 9837–9842. [Google Scholar] [CrossRef]
Beyer, G. Nanocomposites—A new class of flame retardants. Plast. Addit. Compd. 2009, 11, 16–21. [Google Scholar] [CrossRef]
Uysal Unalan, I.; Cerri, G.; Marcuzzo, E.; Cozzolino, C.A.; Farris, S. Nanocomposite films and coatings using inorganic nanobuilding blocks (NBB): Current applications and future opportunities in the food packaging sector. RSC Adv. 2014, 4, 29393–29428. [Google Scholar] [CrossRef]
Hussain, F.; Hojjati, M.; Okamoto, M.; Gorga, R.E. Review article: Polymer-matrix Nanocomposites, Processing, Manufacturing, and Application: An Overview. J. Compos. Mater. 2006, 40, 1511–1575. [Google Scholar] [CrossRef]
Yano, K.; Usuki, A.; Okada, A.; Kurauchi, T.; Kamigaito, O. Synthesis and properties of polyimide–clay hybrid. J. Polym. Sci. Part A Polym. Chem. 1993, 31, 2493–2498. [Google Scholar] [CrossRef]
Rehab, A.; Salahuddin, N. Nanocomposite materials based on polyurethane intercalated into montmorillonite clay. Mater. Sci. Eng. A 2005, 399, 368–376. [Google Scholar] [CrossRef]
Kornmann, X.; Lindberg, H.; Berglund, L.A. Synthesis of epoxy–clay nanocomposites: Influence of the nature of the clay on structure. Polymer 2001, 42, 1303–1310. [Google Scholar] [CrossRef]
Jeon, H.G.; Jung, H.T.; Lee, S.W.; Hudson, S.D. Morphology of polymer/silicate nanocomposites High density polyethylene and a nitrile copolymer. Polym. Bull. 1998, 41, 107–113. [Google Scholar] [CrossRef]
Lim, S.-H.; Dasari, A.; Wang, G.-T.; Yu, Z.-Z.; Mai, Y.-W.; Yuan, Q.; Liu, S.; Yong, M.S. Impact fracture behaviour of nylon 6-based ternary nanocomposites. Compos. Part B Eng. 2010, 41, 67–75. [Google Scholar] [CrossRef]
Ferreira, J.A.M.; Reis, P.N.B.; Costa, J.D.M.; Richardson, B.C.H.; Richardson, M.O.W. A study of the mechanical properties on polypropylene enhanced by surface treated nanoclays. Compos. Part B Eng. 2011, 42, 1366–1372. [Google Scholar] [CrossRef]
Timmaraju, M.V.; Gnanamoorthy, R.; Kannan, K. Influence of imbibed moisture and organoclay on tensile and indentation behavior of polyamide 66/hectorite nanocomposites. Compos. Part B Eng. 2011, 42, 466–472. [Google Scholar] [CrossRef]
Su, F.-H.; Huang, H.-X.; Zhao, Y. Microstructure and mechanical properties of polypropylene/poly (ethylene-co-octene copolymer)/clay ternary nanocomposites prepared by melt blending using supercritical carbon dioxide as a processing aid. Compos. Part B Eng. 2011, 42, 421–428. [Google Scholar] [CrossRef]
Vaia, R.A.; Giannelis, E.P. Polymer Melt Intercalation in Organically-Modified Layered Silicates: Model Predictions and Experiment. Macromolecules 1997, 30, 8000–8009. [Google Scholar] [CrossRef]
Tomasko, D.L.; Han, X.; Liu, D.; Gao, W. Supercritical fluid applications in polymer nanocomposites. Curr. Opin. Solid State Mater. Sci. 2003, 7, 407–412. [Google Scholar] [CrossRef]
Zanetti, M.; Lomakin, S.; Camino, G. Polymer layered silicate nanocomposites. Macromol. Mater. Eng. 2000, 279, 1–9. [Google Scholar] [CrossRef]
Yalcin, B.; Cakmak, M. Superstructural hierarchy developed in coupled high shear/high thermal gradient conditions of injection molding in nylon 6 nanocomposites. Polymer 2004, 45, 2691–2710. [Google Scholar] [CrossRef]
Okamoto, M.; Morita, S.; Kotaka, T. Dispersed structure and ionic conductivity of smectic clay/polymer nanocomposites. Polymer 2001, 42, 2685–2688. [Google Scholar] [CrossRef]
Park, J.H.; Jana, S.C. Mechanism of exfoliation of nanoclay particles in epoxy–clay nanocomposites. Macromolecules 2003, 36, 2758–2768. [Google Scholar] [CrossRef]
Wu, C.L.; Zhang, M.Q.; Rong, M.Z.; Friedrich, K. Tensile performance improvement of low nanoparticles filled-polypropylene composites. Compos. Sci. Technol. 2002, 62, 1327–1340. [Google Scholar] [CrossRef]
Chin, I.-J.; Thurn-Albrecht, T.; Kim, H.-C.; Russell, T.P.; Wang, J. On exfoliation of montmorillonite in epoxy. Polymer 2001, 42, 5947–5952. [Google Scholar] [CrossRef]
Ke, Y.; Lü, J.; Yi, X.; Zhao, J.; Qi, Z. The effects of promoter and curing process on exfoliation behavior of epoxy/clay nanocomposites. J. Appl. Polym. Sci. 2000, 78, 808–815. [Google Scholar] [CrossRef]
Dean, D.; Walker, R.; Theodore, M.; Hampton, E.; Nyairo, E. Chemorheology and properties of epoxy/layered silicate nanocomposites. Polymer 2005, 46, 3014–3021. [Google Scholar] [CrossRef]
Chen, C.; Tolle, T.B. Fully exfoliated layered silicate epoxy nanocomposites. J. Polym. Sci. Part B Polym. Phys. 2004, 42, 3981–3986. [Google Scholar] [CrossRef]
Wang, Q.; Song, C.; Lin, W. Study of the exfoliation process of epoxy–clay nanocomposites by different curing agents. J. Appl. Polym. Sci. 2003, 90, 511–517. [Google Scholar] [CrossRef]
Tolle, T.B.; Anderson, D.P. Morphology development in layered silicate thermoset nanocomposites. Compos. Sci. Technol. 2002, 62, 1033–1041. [Google Scholar] [CrossRef]
Brown, J.M.; Curliss, D.; Vaia, R.A. Thermoset-layered silicate nanocomposites. Quaternary ammonium montmorillonite with primary diamine cured epoxies. Chem. Mater. 2000, 12, 3376–3384. [Google Scholar] [CrossRef]
Lan, T.; Kaviratna, P.D.; Pinnavaia, T.J. On the nature of polyimide-clay hybrid composites. Chem. Mater. 1994, 6, 573–575. [Google Scholar] [CrossRef]
Lan, T.; Kaviratna, P.D.; Pinnavaia, T.J. Mechanism of clay tactoid exfoliation in epoxy-clay nanocomposites. Chem. Mater. 1995, 7, 2144–2150. [Google Scholar] [CrossRef]
United States Department of Commerce. Microstructure of Ceramic Materials. In Proceedings of the American Ceramic Society Symposium, Pittsburgh, PA, USA, 27–28 April 1963. [Google Scholar]
Jiankun, L.; Yucai, K.; Zongneng, Q.; Xiao-Su, Y. Study on intercalation and exfoliation behavior of organoclays in epoxy resin. J. Polym. Sci. Part B Polym. Phys. 2001, 39, 115–120. [Google Scholar] [CrossRef]
Xu, W.B.; Bao, S.P.; He, P.S. Intercalation and exfoliation behavior of epoxy resin/curing agent/montmorillonite nanocomposite. J. Appl. Polym. Sci. 2002, 84, 842–849. [Google Scholar] [CrossRef]
Kong, D.; Park, C.E. Real time exfoliation behavior of clay layers in epoxy–clay nanocomposites. Chem. Mater. 2003, 15, 419–424. [Google Scholar] [CrossRef]
Isik, I.; Yilmazer, U.; Bayram, G. Impact modified epoxy/montmorillonite nanocomposites: Synthesis and characterization. Polymer 2003, 44, 6371–6377. [Google Scholar] [CrossRef]
Bakar, M.; Białkowska, A.; Molenda, J.; Piasek, J. Preparation and properties evaluation of thermoplastic modified epoxy nanocomposites. J. Macromol. Sci. Part B 2012, 51, 1159–1171. [Google Scholar] [CrossRef]
Lu, H.; Liang, G.; Ma, X.; Zhang, B.; Chen, X. Epoxy/clay nanocomposites: Further exfoliation of newly modified clay induced by shearing force of ball milling. Polym. Int. 2004, 53, 1545–1553. [Google Scholar] [CrossRef]
Yasmin, A.; Abot, J.L.; Daniel, I.M. Processing of clay/epoxy nanocomposites by shear mixing. Scr. Mater. 2003, 49, 81–86. [Google Scholar] [CrossRef]
Ho, M.-W.; Lam, C.-K.; Lau, K.-t.; Ng, D.H.; Hui, D. Mechanical properties of epoxy-based composites using nanoclays. Compos. Struct. 2006, 75, 415–421. [Google Scholar] [CrossRef]
Kusmono, Wildan, M.W.; Mohd Ishak, Z.A. Preparation and properties of clay-reinforced epoxy nanocomposites. Int. J. Polym. Sci. 2013, 2013, 690675. [Google Scholar]
Al-Qadhi, M.; Merah, N.; Gasem, Z.; Abu-Dheir, N.; Aleem, B.A. Effect of water and crude oil on mechanical and thermal properties of epoxy-clay nanocomposites. Polym. Compos. 2014, 35, 318–326. [Google Scholar] [CrossRef]
Zunjarrao, S.; Sriraman, R.; Singh, R. Effect of processing parameters and clay volume fraction on the mechanical properties of epoxy-clay nanocomposites. J. Mater. Sci. 2006, 41, 2219–2228. [Google Scholar] [CrossRef]
Wang, K.; Chen, L.; Wu, J.; Toh, M.L.; He, C.; Yee, A.F. Epoxy nanocomposites with highly exfoliated clay: Mechanical properties and fracture mechanisms. Macromolecules 2005, 38, 788–800. [Google Scholar] [CrossRef]
Wang, K.; Wang, L.; Wu, J.; Chen, L.; He, C. Preparation of highly exfoliated epoxy/clay nanocomposites by “slurry compounding”: Process and mechanisms. Langmuir 2005, 21, 3613–3618. [Google Scholar] [CrossRef] [PubMed]
Yang, J.-P.; Yang, G.; Xu, G.; Fu, S.-Y. Cryogenic mechanical behaviors of MMT/epoxy nanocomposites. Compos. Sci. Technol. 2007, 67, 2934–2940. [Google Scholar] [CrossRef]
Mohan, T.; Kanny, K.; Velmurugan, R. Epoxy—Clay nanocomposites—Effect of curing temperature in mechanical properties. Int. J. Plast. Technol. 2009, 13, 123–132. [Google Scholar] [CrossRef]
Daniel, I.; Miyagawa, H.; Gdoutos, E.; Luo, J. Processing and characterization of epoxy/clay nanocomposites. Exp. Mech. 2003, 43, 348–354. [Google Scholar] [CrossRef]
Luo, J.-J.; Daniel, I.M. Characterization and modeling of mechanical behavior of polymer/clay nanocomposites. Compos. Sci. Technol. 2003, 63, 1607–1616. [Google Scholar] [CrossRef]
Lam, C.-K.; Cheung, H.-y.; Lau, K.-t.; Zhou, L.-m.; Ho, M.-w.; Hui, D. Cluster size effect in hardness of nanoclay/epoxy composites. Compos. Part B Eng. 2005, 36, 263–269. [Google Scholar] [CrossRef]
Miyagawa, H.; Foo, K.H.; Daniel, I.M.; Drzal, L.T. Mechanical properties and failure surface morphology of amine-cured epoxy/clay nanocomposites. J. Appl. Polym. Sci. 2005, 96, 281–287. [Google Scholar] [CrossRef]
Miyagawa, H.; Drzal, L.T. The effect of chemical modification on the fracture toughness of montmorillonite clay/epoxy nanocomposites. J. Adhes. Sci. Technol. 2004, 18, 1571–1588. [Google Scholar] [CrossRef]
Qi, B.; Zhang, Q.; Bannister, M.; Mai, Y.-W. Investigation of the mechanical properties of DGEBA-based epoxy resin with nanoclay additives. Compos. Struct. 2006, 75, 514–519. [Google Scholar] [CrossRef]
Wang, M.; Fan, X.; Thitsartarn, W.; He, C. Rheological and mechanical properties of epoxy/clay nanocomposites with enhanced tensile and fracture toughnesses. Polymer 2015, 58, 43–52. [Google Scholar] [CrossRef]
Zhao, C.; Qin, H.; Gong, F.; Feng, M.; Zhang, S.; Yang, M. Mechanical, thermal and flammability properties of polyethylene/clay nanocomposites. Polym. Degrad. Stab. 2005, 87, 183–189. [Google Scholar] [CrossRef]
Peeterbroeck, S.; Alexandre, M.; Jérôme, R.; Dubois, P. Poly (ethylene-co-vinyl acetate)/clay nanocomposites: Effect of clay nature and organic modifiers on morphology, mechanical and thermal properties. Polym. Degrad. Stab. 2005, 90, 288–294. [Google Scholar] [CrossRef]
Zhu, J.; Uhl, F.M.; Morgan, A.B.; Wilkie, C.A. Studies on the mechanism by which the formation of nanocomposites enhances thermal stability. Chem. Mater. 2001, 13, 4649–4654. [Google Scholar] [CrossRef]
Ray, S.S.; Bousmina, M. Biodegradable polymers and their layered silicate nanocomposites: In greening the 21st century materials world. Prog. Mater. Sci. 2005, 50, 962–1079. [Google Scholar]
Becker, O.; Varley, R.J.; Simon, G.P. Thermal stability and water uptake of high performance epoxy layered silicate nanocomposites. Eur. Polym. J. 2004, 40, 187–195. [Google Scholar] [CrossRef]
Zanetti, M.; Camino, G.; Thomann, R.; Mülhaupt, R. Synthesis and thermal behaviour of layered silicate–EVA nanocomposites. Polymer 2001, 42, 4501–4507. [Google Scholar] [CrossRef]
Zotti, A.; Borriello, A.; Ricciardi, M.; Antonucci, V.; Giordano, M.; Zarrelli, M. Effects of sepiolite clay on degradation and fire behaviour of a bisphenol A-based epoxy. Compos. Part B Eng. 2015, 73, 139–148. [Google Scholar] [CrossRef]
Kaya, E.; Tanoğlu, M.; Okur, S. Layered clay/epoxy nanocomposites: Thermomechanical, flame retardancy, and optical properties. J. Appl. Polym. Sci. 2008, 109, 834–840. [Google Scholar] [CrossRef]
Miyagawa, H.; Rich, M.J.; Drzal, L.T. Amine-cured epoxy/clay nanocomposites. I. Processing and chemical characterization. J. Polym. Sci. Part B Polym. Phys. 2004, 42, 4384–4390. [Google Scholar] [CrossRef]
Ying, Z.; Xianggao, L.; Bin, C.; Fei, C.; Jing, F. Highly exfoliated epoxy/clay nanocomposites: Mechanism of exfoliation and thermal/mechanical properties. Compos. Struct. 2015, 132, 44–49. [Google Scholar] [CrossRef]
Liu, T.; Tjiu, W.C.; Tong, Y.; He, C.; Goh, S.S.; Chung, T.S. Morphology and fracture behavior of intercalated epoxy/clay nanocomposites. J. Appl. Polym. Sci. 2004, 94, 1236–1244. [Google Scholar] [CrossRef]
Triantafillidis, C.S.; LeBaron, P.C.; Pinnavaia, T.J. Homostructured mixed inorganic–organic ion clays: A new approach to epoxy polymer–exfoliated clay nanocomposites with a reduced organic modifier content. Chem. Mater. 2002, 14, 4088–4095. [Google Scholar] [CrossRef]
Becker, O.; Varley, R.; Simon, G. Morphology, thermal relaxations and mechanical properties of layered silicate nanocomposites based upon high-functionality epoxy resins. Polymer 2002, 43, 4365–4373. [Google Scholar] [CrossRef]
Chen, K.H.; Yang, S.M. Synthesis of epoxy–montmorillonite nanocomposite. J. Appl. Polym. Sci. 2002, 86, 414–421. [Google Scholar] [CrossRef]
Chung, S.K.; Wie, J.J.; Park, B.Y.; Kim, S.C. Synthesis of Reactive Organifier for the Epoxy/layered Silicate Nanocomposite and the Properties of the Epoxy Nanocomposites. J. Macromol. Sci. Part A 2008, 46, 205–214. [Google Scholar] [CrossRef]
Gârea, S.-A.; Nicolescu, A.; Deleanu, C.; Iovu, H. New nanocomposites based on epoxy resins reinforced with modified montmorillonite. Int. J. Polym. Anal. Charact. 2010, 15, 497–508. [Google Scholar] [CrossRef]
Ávila, A.F.; Yoshida, M.I.; Carvalho, M.G.R.; Dias, E.C.; de Ávila Junior, J. An investigation on post-fire behavior of hybrid nanocomposites under bending loads. Compos. Part B Eng. 2010, 41, 380–387. [Google Scholar] [CrossRef]
Camino, G.; Tartaglione, G.; Frache, A.; Manferti, C.; Costa, G. Thermal and combustion behaviour of layered silicate–epoxy nanocomposites. Polym. Degrad. Stab. 2005, 90, 354–362. [Google Scholar] [CrossRef]
Merah, N.; Ashraf, F.; Shaukat, M.M. Mechanical and Moisture Barrier Properties of Epoxy–Nanoclay and Hybrid Epoxy–Nanoclay Glass Fibre Composites: A Review. Polymers 2022, 14, 1620. [Google Scholar] [CrossRef]
Nielsen, L.E. Models for the Permeability of Filled Polymer Systems. J. Macromol. Sci. Part A Chem. 1967, 1, 929–942. [Google Scholar] [CrossRef]
Bharadwaj, R.K. Modeling the Barrier Properties of Polymer-Layered Silicate Nanocomposites. Macromolecules 2001, 34, 9189–9192. [Google Scholar] [CrossRef]
Mittal, V. Epoxy—Vermiculite Nanocomposites as Gas Permeation Barrier. J. Compos. Mater. 2008, 42, 2829–2839. [Google Scholar] [CrossRef]
Khanbabaei, G.; Aalaie, J.; Rahmatpour, A.; Khoshniyat, A.; Gharabadian, M.A. Preparation and Properties of Epoxy-Clay Nanocomposites. J. Macromol. Sci. Part B 2007, 46, 975–986. [Google Scholar] [CrossRef]
Zaarei, D.; Sarabi, A.A.; Sharif, F.; Gudarzi, M.M.; Kassiriha, S.M. Using of p-Phenylenediamine as Modifier of Montmorrilonite for Preparation of Epoxy-Clay Nanocomposites: Morphology and Solvent Resistance Properties. Polym.-Plast. Technol. Eng. 2010, 49, 285–291. [Google Scholar] [CrossRef]
Kim, J.-K.; Hu, C.; Woo, R.S.C.; Sham, M.-L. Moisture barrier characteristics of organoclay–epoxy nanocomposites. Compos. Sci. Technol. 2005, 65, 805–813. [Google Scholar] [CrossRef]
Kint, D.P.R.; Seeley, G.; Gio-Batta, M.; Burgess, A.N. Structure and Properties of Epoxy-Based Layered Silicate Nanocomposites. J. Macromol. Sci. Part B 2005, 44, 1021–1040. [Google Scholar] [CrossRef]
Alamri, H.; Low, I.M. Effect of water absorption on the mechanical properties of nano-filler reinforced epoxy nanocomposites. Mater. Des. 2012, 42, 214–222. [Google Scholar] [CrossRef]
Bagherzadeh, M.R.; Mahdavi, F. Preparation of epoxy–clay nanocomposite and investigation on its anti-corrosive behavior in epoxy coating. Prog. Org. Coat. 2007, 60, 117–120. [Google Scholar] [CrossRef]
Nanda, T.; Singh, K.; Shelly, D.; Mehta, R. Advancements in multi-scale filler reinforced epoxy nanocomposites for improved impact strength: A review. Crit. Rev. Solid State Mater. Sci. 2021, 46, 281–329. [Google Scholar] [CrossRef]
Shelly, D.; Nanda, T.; Mehta, R. Addition of compatibilized nanoclay and UHMWPE fibers to epoxy based GFRPs for improved mechanical properties. Compos. Part A Appl. Sci. Manuf. 2021, 145, 106371. [Google Scholar] [CrossRef]
Shelly, D.; Nanda, T.; Mehta, R. Novel epoxy-based glass fiber reinforced composites containing compatibilized para-aramid fibers and silanized nanoclay for improved impact strength. Polym. Compos. 2022, 43, 1357–1370. [Google Scholar] [CrossRef]
Shelly, D.; Nanda, T.; Mehta, R. Synergistic effect of compatibilized nanoclay/polyethylene fibers on the impact strength of epoxy-glass fiber nanocomposites. Polym. Compos. 2023, 44, 6528–6541. [Google Scholar] [CrossRef]
Shelly, D.; Nanda, T.; Mehta, R. Reinforcement of compatibilized nanoclay/Inviya fibers to epoxy-based glass fiber nanocomposites for high-impact strength applications. Arch. Civ. Mech. Eng. 2023, 23, 84. [Google Scholar] [CrossRef]
Shelly, D.; Lee, S.-Y.; Park, S.-J. Compatibilization of ultra-high molecular weight polyethylene (UHMWPE) fibers and their composites for superior mechanical performance: A concise review. Compos. Part B Eng. 2024, 275, 111294. [Google Scholar] [CrossRef]
Raturi, M.; Singh, B.J.; Shelly, D.; Singh, K.; Nanda, T.; Mehta, R. Tensile behaviour and characterization of epoxy-clay-poly (ethylene terephthalate) nanocomposites. Mater. Res. Express 2019, 6, 115014. [Google Scholar] [CrossRef]
Nanda, T.; Sharma, G.; Mehta, R.; Shelly, D.; Singh, K. Mechanisms for enhanced impact strength of epoxy based nanocomposites reinforced with silicate platelets. Mater. Res. Express 2019, 6, 065061. [Google Scholar] [CrossRef]
Shelly, D.; Singh, K.; Nanda, T.; Mehta, R. Addition of nanomer clays to GFRPs for enhanced impact strength and fracture toughness. Mater. Res. Express 2018, 5, 105013. [Google Scholar] [CrossRef]
Njuguna, J.; Pielichowski, K.; Alcock, J.R. Epoxy-Based Fibre Reinforced Nanocomposites. Adv. Eng. Mater. 2007, 9, 835–847. [Google Scholar] [CrossRef]
Khan, S.U.; Munir, A.; Hussain, R.; Kim, J.-K. Fatigue damage behaviors of carbon fiber-reinforced epoxy composites containing nanoclay. Compos. Sci. Technol. 2010, 70, 2077–2085. [Google Scholar] [CrossRef]
Kim, D.-H.; Kim, H.-S. Waterproof characteristics of nanoclay/epoxy nanocomposite in adhesively bonded joints. Compos. Part B Eng. 2013, 55, 86–95. [Google Scholar] [CrossRef]
Sancaktar, E.; Kuznicki, J. Nanocomposite adhesives: Mechanical behavior with nanoclay. Int. J. Adhes. Adhes. 2011, 31, 286–300. [Google Scholar] [CrossRef]
Feldman, D. Polymer Nanocomposite Barriers. J. Macromol. Sci. Part A 2013, 50, 441–448. [Google Scholar] [CrossRef]
Ianchis, R.; Rosca, I.D.; Ghiurea, M.; Spataru, C.I.; Nicolae, C.A.; Gabor, R.; Raditoiu, V.; Preda, S.; Fierascu, R.C.; Donescu, D. Synthesis and properties of new epoxy-organolayered silicate nanocomposites. Appl. Clay Sci. 2015, 103, 28–33. [Google Scholar] [CrossRef]
Unuabonah, E.I.; Taubert, A. Clay–polymer nanocomposites (CPNs): Adsorbents of the future for water treatment. Appl. Clay Sci. 2014, 99, 83–92. [Google Scholar] [CrossRef]
Chaudhry, Q.; Scotter, M.; Blackburn, J.; Ross, B.; Boxall, A.; Castle, L.; Aitken, R.; Watkins, R. Applications and implications of nanotechnologies for the food sector. Food Addit. Contam. Part A 2008, 25, 241–258. [Google Scholar] [CrossRef]

Figure 1. (a) Comparison of conventional composites and polymer nanocomposites, (b) schematic representation of thermoset polymer, (c) schematic representation of thermoplastic polymer, and (d) surface-to-volume ratios of frequently used particle reinforcements and shapes.

Figure 3. (a) Structure of sodium montmorillonite [64] and (b) organic modification of nanoclay [2].

Figure 4. Types of nanoclay dispersion in polymers and their associated TEM, XRD, and schematic micrographs (a–c) phase-separated/immiscible, (d–f) intercalated, and (g–i) exfoliated morphologies [64].

Figure 6. (a) Diagram depicts the intercalated/exfoliation procedure, illustrating the forces exerted on a pair of nanoclay platelets, modified nanoclay, epoxy intercalated state, and the forces acting on two-particle tactoids, (b) figure illustrating the correlation between the energy of ionic bonding and the positioning of the clay platelets within the tactoids [103].

Figure 7. (a,b) XRD patterns of pristine epoxy, nanoclay, and their nanocomposites [117,118]; (c) TEM micrographs of 3 wt.% nanoclay reinforced epoxy nanocomposite [102]; and (d) TEM micrographs of epoxy nanocomposite containing 5 wt.% and 10 wt.% nanoclay [116].

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MDPI and ACS Style

Shelly, D.; Singhal, V.; Singh, S.; Nanda, T.; Mehta, R.; Lee, S.-Y.; Park, S.-J. Exploring the Impact of Nanoclay on Epoxy Nanocomposites: A Comprehensive Review. J. Compos. Sci. 2024, 8, 506. https://doi.org/10.3390/jcs8120506

AMA Style

Shelly D, Singhal V, Singh S, Nanda T, Mehta R, Lee S-Y, Park S-J. Exploring the Impact of Nanoclay on Epoxy Nanocomposites: A Comprehensive Review. Journal of Composites Science. 2024; 8(12):506. https://doi.org/10.3390/jcs8120506

Chicago/Turabian Style

Shelly, Daksh, Varun Singhal, Surinder Singh, Tarun Nanda, Rajeev Mehta, Seul-Yi Lee, and Soo-Jin Park. 2024. "Exploring the Impact of Nanoclay on Epoxy Nanocomposites: A Comprehensive Review" Journal of Composites Science 8, no. 12: 506. https://doi.org/10.3390/jcs8120506

APA Style

Shelly, D., Singhal, V., Singh, S., Nanda, T., Mehta, R., Lee, S. -Y., & Park, S. -J. (2024). Exploring the Impact of Nanoclay on Epoxy Nanocomposites: A Comprehensive Review. Journal of Composites Science, 8(12), 506. https://doi.org/10.3390/jcs8120506

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