Description:FIELD OF INVENTION
[001] The present disclosure belongs to the technical field of a polymer composites. Particularly, the present disclosure relates to a bioepoxy composite. The present disclosure also provides a method of preparation of a bioepoxy composite. Further, the present disclosure also provides a method of fabricating bioepoxy coating on a substrate.

BACKGROUND OF THE INVENTION
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] The ever-increasing demand for sustainable and high-performance materials has catalysed significant advancements in the field of polymer composites. Bioepoxy composites are widely used in structural and functional applications due to their strong mechanical properties, chemical stability, and long-term durability. However, their inherent brittleness restricts their performance, making it essential to introduce appropriate fillers to improve their mechanical strength, thermal stability, and wear resistance [Ogbanna et al., Polymer-Plastics Technology and Materials, 2022, 61, 937-974].
[004] Graphene and its derivatives, such as graphene nanoplatelets (GNPs) and graphene oxide (GO), have attracted considerable attention as reinforcements in epoxy systems [Akter et al., Polymers, 2024, 16(11), 1483; Zhang et al., Composites Part A: Applied Science and Manufacturing, 2021, 147, 106479]. GNPs, with their two-dimensional structure, large surface area, and exceptional mechanical, thermal, and electrical properties, have shown great potential in enhancing the stiffness, toughness, and thermal conductivity of polymer composites [Jang et al., Composites Communications, 2022, 31, 101110]. Moreover, graphene enhances the corrosion resistance of epoxy coatings by creating a highly impermeable barrier that restricts the penetration of corrosive agents. Their excellent electrical conductivity and strong interfacial bonding with the epoxy matrix further contribute to the uniform distribution of stress, reducing microcrack formation and improving long-term durability in harsh environments. Ou et al. [Journal of Materials Research and Technology, 2024, 28, 4626-4638] investigated the role of graphene in enhancing the anticorrosion performance of epoxy powder coatings. Graphene powder, prepared via liquid-phase exfoliation and freeze drying, was incorporated into the epoxy matrix in small amounts (0.0125–0.05 wt%). Electrochemical impedance spectroscopy, Tafel polarization, and salt spray tests revealed that graphene significantly improved the corrosion resistance of the coatings by reducing micropores and increasing structural compactness. The formulation with 0.025 wt% graphene exhibited the highest impedance modulus after prolonged exposure to a 3.5% NaCl solution, demonstrating its effectiveness in providing a durable protective barrier against corrosion.
[005] Metal-organic frameworks (MOFs) have gained considerable interest as porous materials with diverse applications in polymer composites. These crystalline materials consist of metal ions linked to organic ligands, providing high surface area, tunable porosity, and functional groups that can interact with polymer matrices [Zhu et al., Chem. Soc. Rev., 2014, 43, 5468-5512]. In epoxy composites, MOFs have been explored for their potential to enhance mechanical strength, thermal stability, wear resistance, and corrosion protection. Their large surface area promotes efficient stress transfer and thermal insulation, while their structural adaptability allows for the development of composites with tailored properties [Roy et al., RSC Adv., 2014, 4, 52338-52345]. HKUST-1 is a copper-based metal-organic framework composed of copper ions coordinated with benzene-1,3,5-tricarboxylate ligands, forming a highly porous structure. Its large surface area and well-defined pore network make it suitable for applications in gas storage, catalysis, and polymer composites [Zhao et al., Journal of Alloys and Compounds, 2024, 974, 172897]. In epoxy-based systems, HKUST-1 can enhance mechanical strength, thermal stability, and barrier properties due to its strong interfacial interactions and high adsorption capacity [Beigmoradi et al., Analytical and Bioanalytical Chemistry Research, 2023, 10, 363-373].
[006] Thus, there is an urgent need to develop novel composite along with improved mechanical, thermal, tribological, and corrosion-resistant properties.

OBJECTS OF THE INVENTION
[007] Primary object of the present disclosure is to provide a composite that overcomes one or more limitations associated with the conventional composites.
[008] An objective of the present disclosure is to provide a bioepoxy composite.
[009] Another objective of the present disclosure is to provide a method of preparation of a bioepoxy composite.
[0010] Still another objective of the present disclosure is to provide a method of fabricating bioepoxy coating on a substrate.
[0011] Other objects of the present disclosure will be apparent from the description of the invention herein below.

SUMMARY OF THE INVENTION
[0012] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0013] Accordingly, in one aspect, the present disclosure provides a bioepoxy composite comprises: an epoxy matrix; and a GNP/HKUST-1 coreshell nanoparticles (GMC), wherein the GNP/HKUST-1 coreshell nanoparticles are incorporated in the epoxy matrix in the range of 0.1 to 2 wt%.
[0014] Another aspect of the present disclosure relates to a method of preparation of a bioepoxy composite comprising: a) taking a GNP/HKUST-1 coreshell nanoparticles; b) dispersing the GNP/HKUST-1 coreshell nanoparticles in an epoxy matrix to obtain a dispersion; c) adding a bio-based curing agent in a solvent to obtain a curing agent solution; d) adding the curing agent solution of step c) in the dispersion of step b) followed by removing the free solvent to obtain a solution; and e) pouring the solution into the mould followed by curing to obtain a bioepoxy composite.
[0015] Further aspect of the present disclosure relates to a method of fabricating of bioepoxy coating on a substrate comprising: pre-treating a substrate with a solvent by degreasing to eliminate surface contaminants followed by sanding with sandpaper to obtain a pre-treated substrate; and coating 0.1 to 2 wt% of bioepoxy composite as defined above to the pre-treated substrate with brush coating method followed by curing to obtain a coated substrate.
[0016] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.

DESCRIPTION OF THE FIGURES
[0017] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0018] FIG. 1 illustrates a) XRD Patterns and b) FTIR spectrums of GNP, HKUST-1 and GMC.
[0019] FIG. 2 illustrates FESEM Images of a) HKUST-1; b) Graphene nanoplatelets; c) GMC.
[0020] FIG. 3 illustrates TGA curve of HKUST-1, GNP and GMC.
[0021] FIG. 4 illustrates XRD patterns of neat cured bioepoxy (BE) and developed bioepoxy nanocomposites.
[0022] FIG. 5 illustrates plot of (a) tensile strength and flexural strength; (b) fracture toughness of developed composites
[0023] FIG. 6 illustrates SEM images of the fracture surfaces of (a) of GNP/BE sample (b) MOF/BE, (c) GMC/BE composites.
[0024] FIG. 7 illustrates (a) DSC and (b) TGA curves of the developed composites
[0025] FIG. 8 illustrates a) comparative analysis of recovery ratios under thermal and NIR-driven heating, along with shape fixity ratio; b) schematic representation of thermoresponsive shape memory of GMC/BE sample.
[0026] FIG. 9 illustrates a) wear Rate and b) friction coefficient after wear test of developed samples.
[0027] FIG. 10 illustrates (A) contact angle images of a) BE, b) GNP/BE, c) MOF/BE, d) GMC/BE and (B) contact angle of developed samples.
[0028] FIG. 11 illustrates tafel polarization curves of developed coatings.
[0029] FIG. 12 illustrates OCP Plots of developed coatings
[0030] FIG. 13 illustrates the bode plots of developed composite coatings.

DETAILED DESCRIPTION OF THE INVENTION
[0031] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0032] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0033] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the usage of the phrases “in one embodiment” or “in an embodiment” at various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0034] In some embodiments, numbers have been used for quantifying weights, percentages, ratios, and so forth, to describe and claim certain embodiments of the invention and are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0035] The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0036] Unless the context requires otherwise, throughout the specification which follows, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0037] As used herein, the terms “blend”, and “mixture” are all intended to be used interchangeably.
[0038] As used herein, the terms “GNP/HKUST-1 coreshell nanoparticles”, and “GMC” are all intended to be used interchangeably.
[0039] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0040] The terms “weight percent”, “vol-%”, “percent by weight”, “% by weight”, and variations thereof, as used herein, refer to the concentration of a substance as the weight of that substance divided by the total weight of the composition and multiplied by 100. It is understood that, as used here, “percent”, “%”, and the like are intended to be synonymous with “weight percent”, “vol-%”, etc.
[0041] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. Furthermore, the ranges defined throughout the specification include the end values as well, i.e., a range of 1 to 10 implies that both 1 and 10 are included in the range. For the avoidance of doubt, the applicant shall be entitled to any equivalents according to applicable law.
[0042] All methods described herein can be performed in a suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0043] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified.
[0044] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0045] It should also be appreciated that the present disclosure can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.
[0046] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0047] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0048] The term “or”, as used herein, is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[0049] Various terms are used herein. To the extent a term used is not defined below, it should be given the broadest definition persons in the pertinent art have given to that term as reflected in printed publications and issued patents at the time of filing.
[0050] The present disclosure is based on the premise that GNP/HKUST-1 coreshell nanoparticles are incorporated in the epoxy matrix. The incorporation of these fillers enhances fracture toughness by improving load transfer and crack deflection mechanisms. The tribological studies confirm that reinforced composites exhibit lower wear rates and reduced friction compared to pristine bioepoxy, ensuring better durability under sliding conditions. Electrochemical analysis reveals that GMC-incorporated epoxy coatings offer superior corrosion resistance by forming an effective barrier against electrolyte penetration. Additionally, surface wettability is significantly altered, with reinforced composites showing increased hydrophobicity, which further contributes to their protective performance. The shape memory properties of these composites are also enhanced, particularly in GMC-based systems, which exhibit efficient thermal and NIR-induced recovery. The combined improvements in mechanical, thermal, tribological, and corrosion-resistant properties establish GMC-reinforced bioepoxy composites as promising materials for advanced applications requiring multifunctional performance.
[0051] An embodiment of the present disclosure is to provide a bioepoxy composite comprises: an epoxy matrix; and a GNP/HKUST-1 coreshell nanoparticles, wherein the GNP/HKUST-1 coreshell nanoparticles are incorporated in the epoxy matrix in the range of 0.1 to 2 wt%.
[0052] In some embodiments, the epoxy matrix is selected from a group comprising of bisphenol-A diglycidyl ether (DGEBA), bisphenol-F diglycidyl ether (DGEBF), epoxidized soybean oil, isosorbide based bioepoxy and combination thereof. Preferably, the epoxy matrix is isosorbide based bioepoxy.
[0053] In some embodiments, the composite has an X-ray powder diffraction pattern (CuKα) comprising peaks at 2-theta about 17° and 40°, wear rate ranging from 0.60 × 10-2 mm3/Nm to 0.70 × 10-2 mm3/Nm, friction coefficient ranging from 0.30 to 0.32, and tensile strength ranging from 35 to 45 MPa. Preferably, the wear rate is 0.65 × 10-2 mm3/Nm, friction coefficient is 0.31, and tensile strength is 40 MPa.
[0054] Another embodiment of the present disclosure is to provide a method of preparation of a bioepoxy composite comprising: a) taking a GNP/HKUST-1 coreshell nanoparticles; b) dispersing the GNP/HKUST-1 coreshell nanoparticles in an epoxy matrix to obtain a dispersion; c) adding a bio-based curing agent in a solvent to obtain a curing agent solution; d) adding the curing agent solution of step c) in the dispersion of step b) followed by removing the free solvent to obtain a solution; and e) pouring the solution into the mould followed by curing to obtain a bioepoxy composite.
[0055] In some embodiments, the GNP/HKUST-1 coreshell nanoparticles are prepared by steps comprising: a1) dissolving Cu(NO3)2·3H2O (5.24 mmol) and 1,3,5-benzenetricarboxylic acid (2.76 mmol) in dimethyl sulfoxide to obtain a precursor solution; a2) adding 1 to 5% v/v of the precursor solution in the methanol with stirring for a time period ranging from 5 to 15 min to obtain a crystalline precipitate; a3) washing the crystalline precipitate with methanol to obtain HKUST-1; a4) dispersing of 1 to 5 % w/v of HKUST-1 in DMF with sonication for a time period of 20 to 40 minutes to obtain a HKUST-1 dispersion; a5) dispersing of 1 to 5% w/v of GNP in DMF with sonication for a time period of 20 to 40 minutes to obtain a GNP dispersion; a6) mixing of the HKUST-1 dispersion and the GNP dispersion with stirring for a time period in the range of 2 to 5 hours to obtain a solution; and a7) processing the solution by pouring into an autoclave at a temperature ranging from 60 to 100 °C for a time period ranging from 20 to 30 hours followed by rinsing with centrifugation and drying at a temperature ranging from 60 to 100 °C to obtain a GNP/HKUST-1 coreshell nanoparticles.
[0056] In a preferred embodiment, the amount of precursor solution in the methanol in step a2) is ranging from 1 to 4% v/v or 1 to 3% v/v. More preferably, the amount is 2% v/v.
[0057] In a preferred embodiment, the amount of HKUST-1 in DMF in step a4) is ranging from 1 to 4% w/v or 1 to 3% w/v. More preferably, the amount is 2% w/v.
[0058] In a preferred embodiment, the amount of GNP in DMF in step a5) is ranging from 1 to 4% w/v or 1 to 3% w/v. More preferably, the amount is 2% w/v.
[0059] In a preferred embodiment, the sonication in step a4) and a5) is carried out for a time period of 30 minutes.
[0060] In a preferred embodiment, the mixing in step a6) is carried out with stirring for a time period of 2 to 4 hours. Preferably, the time period is 3 hours.
[0061] In a preferred embodiment, the autoclave in step a7) is carried out for a temperature ranging from 70 to 90 °C for a time period ranging from 22 to 26 hours. More preferably, the temperature is 80 °C for a time period of 24 hours.
[0062] In a preferred embodiment, the drying in step a7) is carried out for a temperature ranging from 70 to 90 °C. More preferably, the temperature is 80 °C.
[0063] In some embodiments, the GNP/HKUST-1 coreshell nanoparticles are dispersed in the epoxy matrix in the range of 0.1 to 2 wt% and the amount of the bio-based curing agent in the ratio of 0.5:1 (raw hydroxyl:epoxide groups).
[0064] In some embodiments, the bio-based curing agent is selected from a group comprising of tannic acid, citric acid, sebacic acid, maleic acid and combination thereof. Preferably, the bio-based curing agent is tannic acid.
[0065] In some embodiments, the solvent is selected from a group comprising of ethanol, acetone, isopropanol, methanol, ethyl acetate, water, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and combination thereof. Preferably, the solvent is ethanol.
[0066] In some embodiments, the curing in step e) is carried out at a temperature ranging from 100 to 200 °C for a time period ranging from 10 to 20 hours. Preferably, the temperature is 150 °C for a time period of 15 hours.
[0067] Still another embodiment of the present disclosure is to provide a method of fabricating of bioepoxy coating on a substrate comprising: pre-treating a substrate with a solvent by degreasing to eliminate surface contaminants followed by sanding with sandpaper to obtain a pre-treated substrate; and coating 0.1 to 2 wt% of bioepoxy composite as defined above to the pre-treated substrate with brush coating method followed by curing to obtain a coated substrate.
[0068] In some embodiments, the substrate is selected from a group comprising of low-carbon A36 steel (Mild steel), carbon steel, low alloy steel and combination thereof. Preferably, the substrate is low-carbon A36 steel (Mild steel).
[0069] In some embodiments, the solvent is selected from a group comprising of acetone, ethanol, methanol and combination thereof. Preferably, the solvent is acetone.
[0070] In some embodiments, the curing is carried out at a temperature ranging from 100 to 200 °C for a time period ranging from 10 to 20 hours. Preferably, the temperature is 150 °C for a time period of 15 hours.
[0071] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person skilled in the art.
EXAMPLES
[0072] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
Example 1:
(A) Preparation of HKUST-1
[0073] To synthesize HKUST-1, following steps were carried out. Initially, a precursor solution was prepared by dissolving Cu(NO3)2·3H2O (1.22 g, 5.24 mmol) and 1,3,5-benzenetricarboxylic acid (0.58 g, 2.76 mmol) in 5 g of dimethyl sulfoxide (DMSO). Subsequently, 200 μL of this precursor solution was gradually added to 10 mL of methanol with continuous stirring over a period of 10 minutes. The crystalline precipitate formed was then collected through centrifugation and washed multiple times with methanol.
(B) Preparation of HKUST1-GNP Core shell hybrids
[0074] The GNP/HKUST-1 coreshell hybrids were synthesized via solvothermal method. 0.1 g each of GNP and HKUST-1 were dispersed in 5 mL of DMF and sonicated for 30 minutes. Following ultrasonication, the GNP and HKUST-1 dispersions were combined and stirred for 3 hours. The entire solution was poured into an autoclave with a Teflon liner and kept in an oven for 24 hours at 80°C. After cooling to ambient temperature, the compound was rinsed using centrifugation and dried at 80°C.
(C) Preparation of Bioepoxy composites
[0075] Bioepoxy nanocomposites incorporated with 1 wt% of GNP, HKUST-1 and GNP/HKUST-1 coreshell nanoparticles were developed by dispersing the nanofiller in the epoxy matrix via ultrasonication. The amount of bio-based curing agent to be taken was calculated in accordance with the ratio of 0.5: 1 (raw hydroxyl: epoxide groups). The bio-based curing agent was first dissolved in 10 mL of ethanol and added to the BE/nanofiller dispersions. The free solvent was removed by employing a vacuum pump. The solution was poured into the mould and cured at 150℃ for 15 hours.
(D) Fabrication of bioepoxy coatings
[0076] Low-carbon A36 steel, a widely used structural material in civil and transportation engineering, served as the substrate for this study. Four distinct coating systems; BE, 1wt% GNP/BE, 1wt% MOF/BE, 1wt%GMC/BE dispersions were selected to evaluate their effectiveness in corrosion protection. To prepare the specimens, they were first degreased using acetone to eliminate surface contaminants. This was followed by sanding with sandpaper (40-60 grit) to achieve the desired surface roughness. The coatings were applied using the brush coating method on mild steel plates of size 20 mm × 20 mm × 1 mm for anticorrosion analysis. The coated samples were then cured at 150°C for 15 hours. A digital vernier caliper was used to measure the coating thickness, which was approximately 100 µm.
(E) Characterization of synthesized GMC coreshell particles
[0077] In the XRD characterization (FIG. 1a), the peak at 27° in Graphene Nanoplatelets (GNP) corresponds to the (002) plane of graphite, indicating the presence of stacked graphene layers. For HKUST-1, the peak at 12° corresponds to its characteristic crystalline structure. The XRD pattern of the GMC composite reveals a shift of the prominent (002) peak of GNP from 27° to 20°, indicating a disturbance in the graphitic layer stacking due to the formation of the core–shell structure. This downshift suggests an increase in the interlayer spacing of GNP, which is likely caused by shell formation of graphene nanoplatelets over the MOF surface. In the GNP@HKUST-1 core-shell composite, the additional peaks at 17°, 32.5°, and 40° indicate the formation of a new crystalline phase or interactions between GNP and HKUST-1. These peaks are not merely additive features of the individual components but suggest a structural reorganization resulting from the intimate interaction between GNP and the HKUST-1 framework during the coreshell formation. In the IR spectrum of GNP (FIG. 1b), peaks at 3460 cm⁻¹ correspond to O-H stretching from adsorbed water or hydroxyl groups, 2364 cm⁻¹ to CO2 adsorption, 1642 cm⁻¹ to C=C stretching in graphene, and 1386 cm⁻¹ to C-OH bending. For HKUST-1, peaks at 3400 cm⁻¹ represent O-H stretching, 1370 cm⁻¹ indicate C-O vibrations, and 730 cm⁻¹ correspond to C-H out-of-plane bending. In the core-shell composite (GNP@HKUST-1), the spectrum shows O-H stretching at 3338 cm⁻¹ (shifted due to interaction), C=C stretching at 1506 cm⁻¹ (from GNP), C-OH bending at 1385 cm⁻¹, and C-H out-of-plane bending at 754 cm⁻¹. These shifts highlight the interaction and integration of functional groups in the core-shell structure.
[0078] The FESEM images (FIG. 2) provide a detailed visualization of the morphological features of HKUST-1, GNP, and GMC particles. HKUST-1 exhibits a distinct crystalline structure, characteristic of its metal-organic framework (MOF) composition. GNP appears as ultrathin, layered nanosheets with a high aspect ratio, reflecting its graphitic nature. In the GMC particles, a core-shell structure is evident, where GNP uniformly coats the surface of HKUST-1. This encapsulation indicates strong interfacial interactions between the components, contributing to enhanced structural stability and functional properties. The GNP shell is expected to improve overall stability, conductivity, and surface characteristics, making the composite suitable for advanced applications.
[0079] Thermogravimetric analysis (TGA) (FIG. 3) was conducted to evaluate the thermal stability of GNP, HKUST-1, and GMC particles. The results indicate that GNP exhibits remarkable thermal stability, retaining its structure even at high temperatures. This stability is attributed to the presence of strong C=C bonds in its graphitic framework, which resist thermal degradation. In contrast, HKUST-1 undergoes significant weight loss at lower temperatures, primarily due to the release of physically adsorbed and coordinated water, followed by the decomposition of its organic linkers. The GMC particles, which incorporate both HKUST-1 and GNP, display a distinct thermal behaviour that combines the properties of the individual components. The presence of GNP as a protective shell around HKUST-1 contributes to enhanced thermal resistance, effectively delaying the decomposition of the MOF core. This core-shell interaction improves the overall thermal stability of the composite, making it a promising material for applications requiring high-temperature resilience.
[0080] The XRD patterns of neat cured bioepoxy and its composites with GNP, MOF, and GMC are shown in FIG. 4 exhibit broad diffraction peaks, indicating the predominantly amorphous nature of the epoxy matrix. The absence of distinct crystalline peaks from the fillers suggests their uniform dispersion within the polymer network. Additionally, strong interfacial interactions between the epoxy matrix and the fillers may lead to a partial suppression of the inherent crystallinity of the reinforcements, thereby maintaining the overall amorphous character of the composites. The absence of new diffraction peaks further confirms that the addition of GNP, MOF, and GMC does not induce any major phase transformation or crystallisation in the bioepoxy system. These results confirm that the structural integrity of the epoxy matrix is retained while integrating the nanofillers, ensuring effective reinforcement without disrupting the matrix morphology.
(F) Mechanical properties of developed composites
[0081] The mechanical properties of the fabricated composites are shown in FIG. 5. The mechanical performance of the GMC-incorporated system does not exhibit a significant overall enhancement. The incorporation of GMC into epoxy composites enhances tensile properties compared to GNP and MOF-reinforced systems. This improvement is due to strong interfacial bonding and efficient stress transfer between the filler and the epoxy matrix. The unique structure of GMC, which includes graphene components, contributes to higher stiffness and load-bearing capacity. A well-integrated filler network allows for better load distribution under tensile stress, leading to an increase in tensile strength and modulus compared to other reinforced systems. However, in terms of flexural properties, GMC-incorporated composites do not show significant enhancement. MOF-reinforced systems exhibit superior flexural performance due to the knee effect, where their porous and rigid structure effectively dissipates energy and redistributes stress. In contrast, the relatively rigid nature of GMC may limit strain accommodation under bending, reducing its efficiency in improving flexural strength. This suggests that while GMC aids in tensile performance, its contribution to flexural reinforcement is less pronounced.
[0082] A notable concern is the decrease in fracture toughness for the GMC-incorporated system compared to both GNP and MOF-reinforced composites, as well as the pristine epoxy. This reduction can be attributed to the intrinsic brittleness of GMC, which may lead to premature crack initiation and propagation. While the filler is well dispersed for tensile loading, its interaction with crack propagation mechanisms may not be sufficient to enhance fracture resistance. Unlike GNP and MOF systems, where mechanisms like crack bridging and energy dissipation improve toughness, the GMC-incorporated system lacks effective toughening pathways, making it more susceptible to brittle failure.
[0083] The SEM analysis of fracture surfaces (FIG. 6) provides insights into the failure mechanisms of the composites. The pristine epoxy system exhibits a relatively smooth surface, indicative of brittle fracture with minimal energy dissipation during crack propagation. The absence of reinforcement mechanisms results in lower fracture toughness. In the GNP-incorporated composite, the fracture surface reveals notable particle pull-out, creating a more tortuous crack path. This process enhances energy dissipation, improving fracture resistance. While the interfacial bonding between GNP and the matrix is not ideal, it still facilitates this energy-absorbing pull-out effect. For the MOF-incorporated composites, the fibrous structures observed on the fracture surface are indicative of polymer fibrillation, where the matrix undergoes localized plastic deformation during crack propagation. The presence of MOF particles likely promotes this mechanism by altering stress distribution and enhancing interfacial adhesion, resulting in improved energy dissipation through fibril formation. These structures suggest a crack-bridging mechanism, where the fillers partially hinder crack growth, leading to greater energy dissipation and improved fracture toughness. Conversely, the GMC-incorporated system presents a smoother fracture surface, similar to the pristine epoxy. This indicates limited energy dissipation, as there is no significant filler pull-out or crack-bridging effect. Although the core-shell morphology of GMC fillers aids in stress distribution, it does not significantly enhance the energy absorption mechanisms necessary for toughness improvement. Overall, the results establish a clear correlation between fracture surface characteristics and mechanical performance. The pristine and GMC composites, with smoother surfaces, exhibit lower fracture toughness due to restricted energy dissipation. In contrast, the GNP and MOF systems demonstrate features like particle pull-out and crack bridging, which contribute to superior fracture resistance by increasing energy absorption during failure.
(G) Thermal properties of fabricated composites
[0084] The Tg values from DSC analysis (FIG. 7a) for the pristine epoxy and composites reinforced with GMC, GNP, and MOF fillers are 54°C, 52°C, 58°C, and 65°C, respectively, highlighting the influence of filler incorporation on the thermal characteristics of the epoxy matrix. The pristine epoxy exhibits a Tg of 54°C, representing the inherent thermal stability of the unmodified polymer network. The composite containing GMC fillers show a slightly lower Tg of 52°C, suggesting that the presence of core-shell structured GMC particles influences the polymer network. This slight reduction may be attributed to a decrease in cross-linking density, likely due to weaker interfacial interactions between the GMC fillers and the epoxy matrix. The lower network rigidity increases polymer chain mobility, making the composite more flexible than the pristine epoxy. The GNP-reinforced composite displays an increased Tg of 58°C, signifying enhanced thermal stability. The strong interfacial bonding between GNPs and the epoxy matrix restricts polymer chain mobility, reinforcing the matrix and contributing to a more rigid structure. The high aspect ratio and planar geometry of GNPs promote stress transfer and structural reinforcement, not only improving Tg but also enhancing fracture toughness. The ability of GNPs to deflect cracks and create energy-dissipating mechanisms contribute to the superior toughness of this system. Among all composites, the MOF-incorporated system exhibits the highest Tg at 65°C, indicating a significant restriction of polymer chain mobility. The porous framework and surface chemistry of MOF fillers facilitate strong interactions with the epoxy matrix, leading to a highly reinforced structure with enhanced thermal stability. However, despite the high Tg, the fracture toughness of MOF composites remains lower than that of GNP-reinforced systems, as the crack-deflection and pull-out mechanisms observed in GNP composites contribute more effectively to energy dissipation during fracture.
[0085] The thermogravimetric analysis (TGA) (FIG. 7b) results reveal that all the composites maintain comparable thermal stability, demonstrating that the inclusion of different fillers; GMC, GNP, and MOF does not significantly affect their overall degradation profiles. Despite the variations these fillers introduce in the Tg, their influence on the resistance to thermal decomposition remains minimal. The uniform thermal stability suggests that the fillers are well integrated within the bioepoxy matrix without triggering premature degradation or altering the decomposition pathway. Additionally, the absence of major shifts in degradation temperatures implies that these fillers do not act as thermal stabilizers or accelerants, reinforcing the reliability of the composites for applications requiring consistent performance under elevated temperatures.
(H) Shape Memory Properties of Fabricated Composites
[0086] The shape memory characteristics of these composites (FIG. 8) reveal the substantial impact of the incorporated fillers on both shape fixity and shape recovery. The GMC-reinforced system exhibits the highest shape fixity ratio of 97.5%, demonstrating its remarkable ability to retain a deformed shape upon cooling. This enhanced performance can be attributed to the unique core-shell structure of the GMC fillers, which aids in maintaining deformation under thermal conditions. In comparison, the pristine bioepoxy (BE) system shows a lower fixity ratio of 91%, reflecting its limited capacity to preserve temporary shapes in the absence of reinforcing fillers. The GNP and MOF composites present intermediate fixity ratios of 92.54% and 94.39%, respectively, indicating their ability to improve fixity through enhanced filler-matrix interactions and increased rigidity. Regarding shape recovery upon thermal activation, all composite systems exhibit recovery to different extents. The GMC-filled composite outperforms the others, achieving a recovery ratio of 86.7%, surpassing the MOF and GNP composites, which display recovery ratios of 81.21% and 83.6%, respectively. This suggests that GMC fillers facilitate efficient energy storage and release, enabling superior shape recovery. The pristine epoxy exhibits the lowest recovery ratio of 78%, underscoring its poor responsiveness to thermal stimuli. Under near-infrared (NIR) irradiation, shape recovery is observed exclusively in the GNP and GMC composites, with recovery ratios of 89% and 88.9%, respectively. This behavior can be attributed to the exceptional photothermal properties of GNP and GMC fillers, which effectively absorb NIR light and convert it into localized heat, triggering the shape recovery process. Conversely, the pristine and MOF composites fail to exhibit any recovery under NIR exposure, indicating their lack of photothermal responsiveness.
(I) Tribological Characteristics of Fabricated Composites
[0087] The tribological performance of the developed composites illustrated in FIG. 9, demonstrates a notable enhancement in both wear resistance and friction reduction with the inclusion of reinforcing fillers. The pristine bioepoxy (BE) system exhibits the highest wear rate of 1.39 × 10-2 mm3/Nm, indicating its susceptibility to material loss under applied load and continuous sliding conditions. In comparison, all filler-incorporated composites show a significant reduction in wear rate, with the GMC-reinforced system achieving the lowest wear rate of 0.65 × 10-2 mm3/Nm, highlighting its superior resistance to material degradation.
[0088] A similar trend is observed in the friction coefficient, where the pristine system records the highest value of 0.37, indicating increased resistance to motion. The introduction of fillers contributes to a progressive decline in the friction coefficient, with the GMC-incorporated composite exhibiting the lowest value of 0.31, suggesting an improved tribological response. This reduction in friction is particularly beneficial for applications requiring enhanced durability and operational efficiency. The exceptional wear resistance of the GMC system can be attributed to the distinctive core-shell morphology of the GMC fillers, which likely function as a self-lubricating component during sliding. This lubrication effect reduces direct asperity contact between the opposing surfaces, minimizing friction and material detachment. Furthermore, the presence of GMC fillers facilitates uniform load distribution, thereby mitigating localized stress concentrations that could otherwise lead to excessive wear. The ability of the GMC-reinforced composite to sustain a stable tribological performance under sliding conditions suggest its potential for prolonged durability and reduced material loss.
[0089] For GNP- and MOF-incorporated composites, the wear rates are also significantly lower than that of the pristine system, owing to the reinforcing effect of these fillers. The planar structure of GNPs enhances interfacial interactions and strengthens the matrix, resulting in a more robust material capable of withstanding wear. Similarly, the rigid framework of MOF particles contributes to improved load-bearing capacity, reducing frictional wear and extending material longevity. However, despite these enhancements, neither system matches the exceptional wear resistance demonstrated by the GMC composite. The pristine bioepoxy system, in contrast, lacks the structural reinforcement provided by the fillers, leading to uncontrolled material removal and surface degradation under sliding conditions. The absence of reinforcing phases results in poor tribological properties, making it highly susceptible to wear.
[0090] These results emphasize the role of filler morphology and interfacial interactions in influencing tribological behaviour. The GMC-incorporated composite emerges as the most promising system, offering the best combination of low wear rate and reduced friction, making it highly suitable for applications demanding superior wear resistance and extended material lifespan.
(J) Contact Angle Studies on Fabricated Composites
[0091] The contact angle measurements (FIG 10) illustrate the impact of different fillers on the wettability of the composite surfaces. The pristine bioepoxy (BE) system exhibits a contact angle of 72.63°, indicating a moderately hydrophilic nature. This behaviour is typical of unmodified bioepoxy, where the presence of polar functional groups contributes to partial wetting by water. The incorporation of fillers leads to an increase in the contact angle, demonstrating a shift towards hydrophobicity. The graphene nanoplatelet (GNP)-reinforced composite shows a contact angle of 75.70°, which can be attributed to the hydrophobic characteristics of graphene. The presence of nonpolar graphitic domains reduces the material’s affinity for water, limiting its ability to spread on the surface. Additionally, the planar structure of GNPs may introduce minor changes in surface roughness, further affecting wettability. A similar trend is observed in the MOF-incorporated composite, where the contact angle increases to 76.97°. This suggests that the MOF particles contribute to a slight reduction in surface wettability. The structural attributes of MOFs, particularly their porous nature and interaction with the epoxy matrix, likely influence the composite’s surface energy, leading to an increase in hydrophobicity. The GMC-incorporated composite exhibits the highest contact angle, reaching 85.20°, indicating the most hydrophobic surface among all systems. This increase in water repellence is likely due to the combined effect of MOF and GNP fillers. The core-shell structure of GMC may further enhance this behaviour by modifying surface roughness and reducing the material’s affinity for water. The progressive increase in contact angle with filler incorporation highlights the influence of filler chemistry and morphology on surface wettability. These modifications in hydrophobicity suggest potential applications in coatings and protective materials where reduced water absorption and enhanced moisture resistance are required.
(K) Application of Fabricated Composites as Anti-Corrosion Coatings
[0092] Electrochemical impedance spectroscopy (EIS) was conducted using a conventional three-electrode system to evaluate the corrosion resistance of the fabricated composite coatings. In this study, the corrosion behaviour of all fabricated coatings was evaluated in a 3.5 wt% NaCl solution. The Tafel plot of composite coatings is depicted in FIG. 11. Table 1 derived from Tafel plot provides a comprehensive evaluation of the corrosion resistance of the fabricated composite coatings. The corrosion current density (Jcorr) serves as a key parameter in assessing the electrochemical activity of the materials, where lower values indicate enhanced protection. The bare substrate exhibits the highest Jcorr (1.56 × 10-5 A/cm²), confirming its susceptibility to corrosion. In contrast, the GMC/BE composite shows the lowest Jcorr (2.20 × 10-9 A/cm²), demonstrating its superior ability to mitigate corrosion. The corrosion potential (Ecorr) further supports these observations, with more positive values generally associated with improved stability. The bare substrate records the most negative Ecorr (-0.526 V), highlighting its vulnerability, whereas the GMC/BE coating exhibits the most positive potential (0.238 V), suggesting the presence of a robust protective barrier. The polarization resistance (Rp) provides additional insight into the effectiveness of the coatings in impeding charge transfer. A significant increase in Rp indicates better corrosion resistance, with the substrate showing the lowest resistance (634 Ω), while the GMC/BE composite achieves the highest (4.37 × 107 Ω), confirming its ability to limit electrochemical reactions. The corrosion rate (CR) follows a similar pattern, where a lower rate corresponds to reduced material degradation. The bare substrate exhibits the highest CR (0.1807 mmpy), whereas the GMC/BE coating achieves the lowest (2.55 × 10-6 mmpy), demonstrating its efficiency in preventing corrosion. These results highlight the significant improvement in corrosion resistance provided by the composite coatings, with GMC/BE offering the most effective protection, followed by MOF/BE, GNP/BE, and BE coatings. The enhanced performance of these coatings can be attributed to their ability to create a dense and stable barrier, reducing electrochemical interactions with the corrosive environment.
Table 1: Corrosion Parameters Obtained from the Tafel Plot.
Substrate BE GNP/BE MOF/BE GMC/BE
Jcorr (A/cm2) 1.561×10-05 1.51×10-07 1.06×10-08 7.62×10-09 2.20×10-09
Ecorr (V) -0.526042 -0.582919 -0.331122 -0.176359 0.23819
Rp (Ohm) 634.30072 6.37×1004 8.96×1006 1.21×1007 4.37×1007
CR (mmpy) 0.180696 1.75×10-03 1.23×10-05 8.85×10-06 2.55×10-06

[0093] The open circuit potential (OCP) measurements were conducted to evaluate the electrochemical stability of the developed coatings in a 3.5 wt% NaCl solution, and the results are presented in FIG. 12. The bare substrate exhibited the most negative potential, indicating its high susceptibility to corrosion. The BE-coated sample showed a slight improvement; however, its potential remained relatively low, suggesting limited corrosion resistance. In contrast, the incorporation of nanofillers significantly influenced the electrochemical response. The GNP/BE and MOF/BE coatings displayed a shift towards less negative potentials, reflecting their enhanced protective nature. Among all the coatings, the GMC/BE sample exhibited the highest OCP value, indicating superior corrosion resistance. The gradual stabilization of the potential over time further confirmed the electrochemical stability of the coatings. These findings highlight the effectiveness of filler incorporation in improving the barrier properties of the bioepoxy coatings, with the GMC/BE system offering the best corrosion protection.
[0094] The Bode plot presented in FIG. 13 illustrates the impedance modulus (∣Z∣) as a function of frequency for the bare substrate, BE, and nanofiller-incorporated BE coatings. The substrate exhibits the lowest impedance values across the entire frequency range, indicating its poor corrosion resistance. The BE-coated sample demonstrates an increase in impedance compared to the bare substrate, suggesting improved barrier properties. However, the incorporation of nanofillers significantly enhances the impedance response. The GNP/BE coating exhibits a higher impedance than BE but shows a frequency-dependent decline, indicating limited long-term stability. The MOF/BE coating demonstrates a more stable impedance response, highlighting its superior corrosion protection. Among all the coatings, the GMC/BE system exhibits the highest impedance modulus, particularly in the low-frequency region, indicating enhanced charge transfer resistance and superior barrier properties. The results confirm that the incorporation of nanofillers effectively improves the corrosion resistance of bioepoxy coatings, with GMC/BE offering the most robust protection.
[0095] The incorporation of nanofillers significantly enhances the corrosion resistance of epoxy coatings. The corrosion resistance of the coatings is attributed to a combination of barrier protection, electrochemical shielding, and enhanced adhesion. The incorporation of nanofillers such as GNP, MOF, and GMC creates a tortuous path that significantly restricts the penetration of corrosive agents like water, oxygen, and chloride ions. This physical barrier effect is further supported by the electrochemical activity of the fillers, which can influence charge distribution and inhibit localized corrosion. Additionally, the strong interfacial interactions between the fillers and the epoxy matrix improve adhesion to the substrate, reducing the formation of micro voids and defects that could serve as corrosion initiation sites. In some cases, nanofillers like MOFs may also release active corrosion inhibitors, forming a passivating layer on the metal surface. The combined effect of these mechanisms results in a robust protective coating with significantly enhanced corrosion resistance, making it highly effective for long-term applications in harsh environments. These results demonstrate the potential of GMC reinforced epoxy coatings for long-term durability in corrosive environments.

ADVANTAGES OF THE INVENTION
[0096] The GMC-reinforced system stands out for its superior shape fixity, enhanced wear resistance, and excellent corrosion protection due to its unique core-shell structure.
[0097] The shape memory behavior under both thermal and NIR stimuli further highlights the multifunctional potential of these composites, with GNP and GMC composites demonstrating effective NIR-triggered recovery.
[0098] Tribological analysis confirms that filler incorporation reduces wear rate and friction coefficient, with GMC exhibiting the lowest wear rate.
[0099] Additionally, corrosion studies reveal that GMC-based epoxy coatings provide the highest polarization resistance and lowest corrosion rate, ensuring enhanced protection in harsh environments.
, Claims:1. A bioepoxy composite comprises:
an epoxy matrix; and
a GNP/HKUST-1 coreshell nanoparticles,
wherein the GNP/HKUST-1 coreshell nanoparticles are incorporated in the epoxy matrix in the range of 0.1 to 2 wt%.
2. The bioepoxy composite as claimed in claim 1, wherein the epoxy matrix is selected from a group comprising of bisphenol-A diglycidyl ether (DGEBA), bisphenol-F diglycidyl ether (DGEBF), epoxidized soybean oil, isosorbide based bioepoxy and combination thereof.
3. The bioepoxy composite as claimed in claim 1, wherein the composite has an X-ray powder diffraction pattern (CuKα) comprising peaks at 2-theta about 17° and 40°, wear rate ranging from 0.60 × 10-2 mm3/Nm to 0.70 × 10-2 mm3/Nm, friction coefficient ranging from 0.30 to 0.32, and tensile strength ranging from 35 to 45 MPa.
4. A method of preparation of a bioepoxy composite comprising:
a) taking a GNP/HKUST-1 coreshell nanoparticles;
b) dispersing the GNP/HKUST-1 coreshell nanoparticles in an epoxy matrix to obtain a dispersion;
c) adding a bio-based curing agent in a solvent to obtain a curing agent solution;
d) adding the curing agent solution of step c) in the dispersion of step b) followed by removing the free solvent to obtain a solution; and
e) pouring the solution into the mould followed by curing to obtain a bioepoxy composite.
5. The method as claimed in claim 4, wherein the GNP/HKUST-1 coreshell nanoparticles are prepared by steps comprising:
a1) dissolving Cu(NO3)2·3H2O (5.24 mmol) and 1,3,5-benzenetricarboxylic acid (2.76 mmol) in dimethyl sulfoxide to obtain a precursor solution;
a2) adding 1 to 5% v/v of the precursor solution in the methanol with stirring for a time period ranging from 5 to 15 min to obtain a crystalline precipitate;
a3) washing the crystalline precipitate with methanol to obtain HKUST-1;
a4) dispersing of 1 to 5 % w/v of HKUST-1 in DMF with sonication for a time period of 20 to 40 minutes to obtain a HKUST-1 dispersion;
a5) dispersing of 1 to 5% w/v of GNP in DMF with sonication for a time period of 20 to 40 minutes to obtain a GNP dispersion;
a6) mixing of the HKUST-1 dispersion and the GNP dispersion with stirring for a time period in the range of 2 to 5 hours to obtain a solution; and
a7) processing the solution by pouring into an autoclave at a temperature ranging from 60 to 100 °C for a time period ranging from 20 to 30 hours followed by rinsing with centrifugation and drying at a temperature ranging from 60 to 100 °C to obtain a GNP/HKUST-1 coreshell nanoparticles.
6. The method as claimed in claim 4, wherein the GNP/HKUST-1 coreshell nanoparticles are dispersed in the epoxy matrix in the range of 0.1 to 2 wt% and the amount of the bio-based curing agent in the ratio of 0.5:1 (raw hydroxyl:epoxide groups).
7. The method as claimed in claim 4, wherein the bio-based curing agent is selected from a group comprising of tannic acid, citric acid, sebacic acid, maleic acid and combination thereof.
8. The method as claimed in claim 4, wherein the solvent is selected from a group comprising of ethanol, acetone, isopropanol, methanol, ethyl acetate, water, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and combination thereof.
9. The method as claimed in claim 4, wherein the curing in step e) is carried out at a temperature ranging from 100 to 200 °C for a time period ranging from 10 to 20 hours.
10. A method of fabricating of bioepoxy coating on a substrate comprising:
pre-treating a substrate with a solvent by degreasing to eliminate surface contaminants followed by sanding with sandpaper to obtain a pre-treated substrate; and
coating 0.1 to 2 wt% of bioepoxy composite as claimed in claim 1 to the pre-treated substrate with brush coating method followed by curing to obtain a coated substrate.
11. The method as claimed in claim 10, wherein the substrate is selected from a group comprising of low-carbon A36 steel (Mild steel), carbon steel, low alloy steel and combination thereof.
12. The method as claimed in claim 10, wherein the solvent is selected from a group comprising of acetone, ethanol, methanol and combination thereof.
13. The method as claimed in claim 10, wherein the curing is carried out at a temperature ranging from 100 to 200 °C for a time period ranging from 10 to 20 hours.