1. A high-performance multi-covalent adaptive network based recyclable epoxy polymer composite, comprising: a) a resin; b) a co-curing agent; and c) a hardener; wherein, the resin is Diglycidyl ether of bisphenol A (DGEBA); the co-curing agent is 1-(3-aminopropyl) imidazole (API); the hardener is selected from a group consisting of 3-isocyanatopropyl trimethoxysilane (IPTS) and 1-methyl-3-[3-(trimethoxysilyl) propyl]-1H-imidazol-3-ium chloride (MTSPI); and the co-curing agent and the hardener is present in an amount of 10-15 wt% and 10-20 wt%, respectively.

2. The epoxy polymer composite as claimed in claim 1, wherein API is present in an amount of 11 wt%.

3. The epoxy polymer composite as claimed in claim 1, wherein IPTS or MTSPI are present in an amount of 10-20 wt%.

4. A method to synthesise a high-performance multi-covalent adaptive network based recyclable epoxy polymer composite by the following steps: i. pre-heating DGEBA; ii. adding API and IPTS/MTSPI and stirring while keeping for degassing conditions to form a system; and iii. curing the system obtained in step (ii) to form a cured high-performance multi-covalent adaptive network based recyclable epoxy polymer composite.

5. The method as claimed in claim 4, wherein the pre-heating in step (i) is performed at 60-70℃ for 15-25 minutes.

6. The method as claimed in claim 4, wherein the stirring in step (ii) is performed for 5-10 mins and degassing conditions for a time period ranging from 30-40 minutes.

7. The method as claimed in claim 4, wherein the curing in step (iii) is performed at 100-140°C for 3-7 hours.

8. The method as claimed in claim 4, wherein the hardener is IPTS which reacts with DGEBA in presence of API to form the thermoset, IPTS10 having associative and dissociative covalent networks and hydrogen bonds.

9. The method as claimed in claim 4, wherein the hardener is MTSPI which reacts with DGEBA in presence of API to form the thermoset, MTSPI20 having covalent associative network and ionic interactions.

10. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite IPTS10 exhibits a tensile strength ranging from 85-90 MPa, interlaminar shear strength (ILSS) in a range of 46-56 MPa, and flexural strength (FS) in a range of 750-800 MPa and

11. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite exhibits thermal degradation temperature in a range of 250-500°C.

12. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite is compression molded at 160-190°C under a pressure of 2-5 MPa for 20-30 minutes.

13. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite is used to synthesise CFRE composite comprising carbon fiber impregnated with IPTS10 epoxy matrix via vacuum-assisted resin transfer molding (VARTM), wherein the composite exhibits an interlaminar shear strength (ILSS) of 49–54 MPa and a flexural strength (FS) of 784–794 MPa.

14. The epoxy polymer composite as claimed in claims 1 and 13, wherein the epoxy polymer composite is separated from carbon fibre of CFRE with a SALSO™ solution by heating the CFRE composite in a Teflon-lined autoclave at 200–250 °C for 10–16 hours.

15. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite is applicable for aerospace, automotive, marine, sporting goods, and renewable energy sectors like wind power.

Description:A HIGH-PERFORMANCE MULTI-COVALENT ADAPTIVE NETWORKS BASED RECYCLABLE EPOXY POLYMER COMPOSITE AND SYNTHESIS THEREOF

FIELD OF INVENTION:

[1] The present invention is in the field of epoxy polymer composite incorporating carbon fiber reinforcements within epoxy matrices. More particularly, the present invention relates to a high-performance multi-covalent adaptive network based recyclable epoxy polymer composite and synthesis thereof. The invention further pertains to dynamic network system configured to provide enhanced mechanical strength and improved recyclability, properties that have traditionally exhibited a trade-off with one another. The present invention achieves high tensile strength, flexural strength, and interlaminar shear strength without the addition of any nanofillers. Accordingly, the composite is well suited for high-performance applications in sectors where both mechanical performance and sustainability are critical, like aerospace engineering, automotive manufacturing.

BACKGROUND OF INVENTION:

[2] Carbon fiber reinforced epoxy (CFRE) composites are advanced materials that combine high-strength carbon fibers with epoxy resin, offering an exceptional balance of strength, stiffness, and lightweight properties. These composites are known for their superior mechanical performance, excellent fatigue resistance, and corrosion resistance, making them ideal for demanding industries such as automotive and aerospace. In the automotive sector, CFRE composites are used to reduce vehicle weight, improving fuel efficiency and performance without compromising safety. Their application includes components such as body panels, chassis, and interior parts. In aerospace, CFRE composites are critical for reducing the weight of aircraft, leading to enhanced fuel efficiency and improved structural performance. They are commonly used in wings, fuselage structures, and other high-stress components, contributing to overall design efficiency and durability. Carbon fibre reinforced epoxy (CFRE) composites have become widely used in advanced structural applications due to their exceptional fatigue resistance, high stiffness-to-weight ratio, superior specific strength, and outstanding environmental stability.

[3] Conventional epoxy matrices used to develop carbon fiber reinforced composites (CFRPs) for automotive and aerospace applications suffering from limitations in terms of recyclability and reprocessability, leading to environmental problems and landfill waste accumulation. The irreversible nature of the crosslinking reactions limits the material's ability to undergo reprocessing processes commonly used with thermoplastic polymers, such as melting and molding. Consequently, end-of-life waste management becomes a significant concern, contributing to environmental pollution and resource depletion. Epoxy waste continues to accumulate, with few options for sustainable disposal. Much of this waste ends up in landfills or incinerators, contributing to environmental degradation. Therefore, there is a growing need to develop innovative approaches and new materials that address the limitations of conventional thermosetting polymers, enabling greater recyclability, repairability, and sustainability across various industrial sectors. Despite significant progress, a key challenge remains as to how to simultaneously achieve high mechanical robustness and efficient reprocessability.

[4] One of the promising approaches involves installing covalent adaptive networks (CAN). This type of material is called vitrimer, a dynamic cross-linked polymer characterized by its ability to undergo bond exchange reactions, thereby altering its topology. At room temperature, vitrimers behave similarly to traditional thermosetting polymers, exhibiting excellent mechanical properties, chemical resistance, and dimensional stability. However, when subjected to higher temperatures, vitrimers display thermoplastic-like behaviour, wherein reversible chemical bonds undergo dynamic swapping while the cross-linked structures remain intact. Importantly, by modulating the nature of the dynamic interactions within the epoxy network, including associative and dissociative covalent interactions, as well as non-covalent interactions, it is possible to systematically regulate the properties of the epoxy. To date, most studies have focused primarily on associative exchange mechanisms, leaving dissociative systems and other supramolecular hydrogen bonds and ionic interactions relatively unexplored and less-studied, particularly about case studies on mechanical performance. It therefore becomes crucial to identify the interaction mechanisms involved in the relationship between mechanical strength and recyclability, two properties that traditionally present a trade-off with each other.

[5] Reference is further made to IN202541094489, which discloses about epoxy vitrimer and a method to prepare coatings thereof. The epoxy vitrimers are used in transparent, hydrophobic coatings here. The preparation of said vitrimers is done by exchange mechanisms such as transesterification, disulfide exchange, imine formation, thiol–ene vinyl reactions, and transcarbamoylation. However, there is no mention of dissociative CAN or other types of non-covalent interaction in the disclosed work. Moreover, the work does not substantively disclose the use or performance contribution of other dynamic bonding mechanisms and is focused only on hydrophobic coating. Moreover, the cited patent merely enumerates various vitrimer exchange chemistries but does not demonstrate their impact on mechanical performance or recyclability.

[6] Reference is also made to S. Tripathi et al. entitled “A designer Schiff based motif offered dual dynamic exchangeable bonds, faster curing and closed-loop circularity in epoxy vitrimers” in SPE Polymers. 2024; 5:136–150, which discusses about a formulation of epoxy vitrimers by employing dual dynamic systems and the study of vitrimer dynamic properties by adding disulfide-imine systems (from vanillin- AFD curing agent) exhibiting good solvent resistance and good tensile strength. However, the polymer network is formed exclusively through acetal- and imine-based dynamic bonds. Such linkages are well established in the art as conventional dynamic covalent chemistries and have been widely reported in numerous publications. The reference neither discloses nor suggests the incorporation of dissociative dynamic covalent networks within this framework.

[7] Reference is also made to W. Wang et al. entitled “Systematic study of the effect of silane coupling agent on the hydrothermal aging resistance of the underfill epoxy resin and silica interface via molecular dynamics simulation” in Applied Surface Science Volume 688, 15 April 2025, 162313, which discusses about the effect of silane coupling agents (SCA) in the hydrothermal aging resistance of epoxy/silica surface. However, molecular dynamics simulations are used to elucidate the mechanism by which silane coupling agents affect the hydrothermal aging resistance of the epoxy resin (EP)/silica interface. The epoxy matrix is conventional epoxy matrix and there is no involvement of any type of covalent adaptive networks (CAN).

[8] The abovementioned prior arts are limited to associative covalent adaptable network (CAN) or dynamic bonding systems and fail to disclose dissociative dynamic bonds or non-covalent dynamic interactions, including but not limited to hydrogen bonding and ionic bonding.

[9] In view of above-mentioned shortcomings of the prior art, there exists a direct need in the state of art to provide to a high-performance multi-covalent adaptive network based recyclable epoxy polymer composite and synthesis thereof. The present invention however encompasses multiple classes of dynamic bonding interactions. The disclosed chemistry is configured such that these interactions collectively contribute to enhanced mechanical performance while utilizing a reduced hardener content. The resulting material exhibits superior tensile strength, flexural strength, and interlaminar shear strength (ILSS) without the incorporation of nanofillers. Additionally, the present invention employs two distinct hardeners, the incorporation and combined use of which is a key aspect.

OBJECTS OF THE INVENTION:

[10] The principal object of the present invention is to provide a high-performance multi-covalent adaptive network based recyclable epoxy polymer composite.

[11] Another object of the present invention is to provide a method of synthesis of a high-performance covalent adaptive network based recyclable epoxy polymer composite.

[12] Yet another object of the present invention is to provide two high-performance recyclable epoxy polymers composite having, i) dynamic dissociative and associative covalent bonds along with hydrogen bonds; and ii) associative covalent bond (silyl ether exchange) with ionic interactions.

[13] Yet another object of the present invention is to provide a covalent adaptable network-based epoxy composite composition that delivers superior mechanical performance while eliminating the need for nanofillers, thereby improving recyclability and process simplicity.

[14] yet another object of the present invention is to provide a hybrid dynamic network architecture that synergistically integrates associative and dissociative exchange mechanisms, the cooperation of which results in superior mechanical performance relative to single-network systems.
[15] Yet another object of the present invention is to provide a high-performance covalent adaptive network based recyclable epoxy polymer composite that is applicable in aerospace, automotive, marine, sporting goods, and renewable energy sectors like wind power.

[16] Yet another object of the present invention is to provide a high-performance covalent adaptive network based recyclable epoxy polymer composite as a matrix in carbon Fiber Reinforced Epoxy (CFRE) laminates facilitating recycling and reprocessing and self-healing behaviour along with superior mechanical performance, including high interlaminar shear strength (ILSS) and flexural strength (FS).

SUMMARY OF THE INVENTION:

[17] The present invention relates to a high-performance covalent adaptive network based recyclable epoxy polymer composite and synthesis thereof.

[18] In one aspect, the present invention provides a high-performance covalent adaptive networks based recyclable epoxy polymer composite, comprising: (a) an epoxy resin; (b) a co-curing agent; and (c) a hardener; wherein, the epoxy resin is Diglycidyl ether of bisphenol A (DGEBA); the co-curing agent is 1-(3-aminopropyl) imidazole (API); the hardener is selected from a group consisting of 3-isocyanatopropyl trimethoxysilane (IPTS) and 1-methyl-3-[3-(trimethoxysilyl) propyl]-1H-imidazol-3-ium chloride (MTSPI); and the co-curing agent and the hardener is present in an amount of 10-15 wt% and 10-20 wt%, respectively.

[19] In another aspect, the present invention provides a method to synthesise a high-performance covalent adaptive network based recyclable epoxy polymer composite by the following steps: (i) pre-heating DGEBA; (ii) adding API and IPTS/MTSPI and stirring while keeping for degassing conditions to form a system; and (iii) curing the system obtained in step (ii) to form a cured high-performance recyclable epoxy polymer.

[20] In another aspect, the present invention provides two multifunctional epoxy networks that incorporate different combinations of dynamic interactions. The first system integrates dynamic dissociative and associative covalent bonds (transcarbamoylation and silyl ether exchange respectively) along with hydrogen bonds, while the second system combines associative covalent bond (silyl ether exchange) with ionic interactions. A comparative study is conducted to elucidate the role of these interactions in the mechanical performance of the epoxy matrix. The epoxy network containing transcarbamoylation functionality, silyl ethers, and hydrogen bonds exhibit a tensile strength of 85-90 MPa, while the system based on silyl ether exchange and ionic interactions exhibits a significantly lower tensile strength of 45-55 MPa. Therefore, various types of dynamic interactions play a crucial role in determining the properties of the epoxy matrix. In particular, even without the incorporation of nanofillers, this multifunctional epoxy system exhibits exceptional mechanical performance due to the synergistic effect of multiple interactions. Not only does said epoxy system offer excellent mechanical properties, but it also easily processes using compression molding at temperatures between 160-180 °C. This optimized epoxy system has also been used as a matrix for the fabrication of carbon fiber-reinforced epoxy (CFRE) laminates, and its subsequence mechanical testing (flexural strength (FS) and interlaminar shear strength (ILSS)) which demonstrates its great potential for advanced applications in structural composite materials.

[21] Therefore, the present invention provides a high-performance covalent adaptive network based recyclable epoxy polymer composite and a method of synthesis thereof.

DESCRIPTION OF ACCOMPANYING FIGURES:

[22] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention, which are used to describe the principles of the present invention together with the description.

[23] Figure 1 illustrates a method of synthesising high-performance covalent adaptive networks based recyclable epoxy polymer composite, in accordance with an implementation of the present invention.

[24] Figure 2 illustrates Fourier Transform Infrared (FTIR), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) analysis, in accordance with an implementation of the present invention.
[25] Figure 3 illustrates dissociative nature of the synthesised epoxy polymer including temperature-dependent FTIR characterization and compression moldability, in accordance with an implementation of the present invention.

[26] Figure 4 illustrates tensile strength of different epoxy polymer, in accordance with an implementation of the present invention.

[27] Figure 5 illustrates mechanical properties of epoxy polymer composite such as flexural strength (FS) and interlaminar shear strength (ILSS), in accordance with an implementation of the present invention.

[28] Figure 6 illustrates self-healing of carbon fiber-reinforced epoxy (CFRE), in accordance with an implementation of the present invention.

[29] Figure 7 illustrates the structure of IPTS10, in accordance with an implementation of the present invention.

[30] Figure 8 illustrates the structure of MTSPI20, in accordance with an implementation of the present invention.

[31] Figure 9 illustrates an intensity vs wavelength graph for pristine carbon fibre (CF) and recycled CF, in accordance with an implementation of the present invention. a

DETAILED DESCRIPTION OF THE INVENTION:

[32] While the invention is susceptible to various modifications and alternative forms, specific embodiment thereof will be described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the scope of the invention as defined by the appended claims.

[33] Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

[34] The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[35] As discussed in the background section of the present invention, the existing thermosets reported in the literature disclose about vitrimers, their formulations and methods to prepare said vitrimers. The literature also discloses about self-healing and mechanical properties of the disclosed vitrimers. While prior literature discloses vitrimer systems and their preparation, such systems are primarily limited to single or dual associative dynamic covalent exchange mechanisms and do not adequately address the need for hybrid associative–dissociative networks capable of delivering structural-grade mechanical performance, recyclability, and composite-level validation.

[36] Therefore, to overcome the existing problems in the art, the present invention provides high-performance covalent adaptive network based recyclable epoxy polymer composite having two different systems with different types of dynamic bonds and a method of synthesising the same.

[37] Overall, the product of the present invention is different and technically advance over the conventional product(s) in view of the following advantages:
a) A dynamic covalent network system is developed by combining transcarbamoylation, silyl ether linkages, and hydrogen bonding interactions. The epoxy polymer composite prepared by these network systems exhibit excellent recyclability, reprocessability, and self-healing behaviour due to dynamic bond exchange reactions and the presence of a dissociative covalent network, while still maintaining outstanding mechanical properties.
b) The presence of -NCO-containing species with alkoxy silane (Si-OR) groups enables reactions with epoxy, leading to the formation of urethane linkages and new silyl ether bonds. Even without the addition of any filler, the epoxy matrix exhibits high tensile strength in the range of 85-90 MPa.
c) Owing to the presence of a dissociative covalent network, the epoxy matrix in powder form is capable of being compression-molded into sheets at 160-180°C under a pressure of 2-5 MPa for 20-30 minutes.
d) Another high-performance recyclable multi-CAN epoxy polymer composite synthesised by combining a silyl ether (Si–OR) exchange-based network with ionic interactions (imidazolium–chloride), exhibiting tensile strength of 50-55 MPa.

[38] In an embodiment of the present invention, there is provided a high-performance covalent adaptive network based recyclable epoxy polymer composite, comprising: (a) an epoxy resin; (b) a co-curing agent; and (c) a hardener; wherein, the epoxy resin is Diglycidyl ether of bisphenol A (DGEBA); the co-curing agent is 1-(3-aminopropyl) imidazole (API); the hardener is selected from a group consisting of 3-isocyanatopropyl trimethoxysilane (IPTS) and 1-methyl-3-[3-(trimethoxysilyl) propyl]-1H-imidazol-3-ium chloride (MTSPI); and the co-curing agent and the hardener is present in an amount of 10-15 wt% and 10-20 wt%, respectively.

[39] In another embodiment of the present invention, there is provided an epoxy polymer composite as described herein, wherein API is present in an amount ranging from 11 wt%.

[40] In another embodiment of the present invention, there is provided an epoxy polymer composite as described herein, wherein IPTS and MTSPI are present in an amount of 20 wt%.

[41] In another embodiment of the present invention, there is provided a method to synthesise a high-performance covalent adaptive network based recyclable epoxy polymer composite by the followings steps: (i) pre-heating DGEBA; (ii) adding API and IPTS/MTSPI and stirring while keeping for degassing conditions to form a system; and (iii) curing the system obtained in step (ii) to form a cured high-performance covalent adaptive networks based recyclable epoxy polymer composite.

[42] In another embodiment of the present invention, there is provided a method as described herein, wherein the pre-heating in step (i) is performed at 60-70℃ for 15-25 minutes.
[43] In another embodiment of the present invention, there is provided a method as described herein, wherein the stirring in step (ii) is performed for 5-10 mins and degassing conditions for a time period ranging from 30-40 minutes.

[44] In another embodiment of the present invention, there is provided a method as described herein, wherein the curing in step (iii) is performed at 100-140°C for 3-7 hours.

[45] In another embodiment of the present invention, there is provided a method as described herein, wherein the hardener is IPTS which reacts with DGEBA in presence of API to form the thermoset IPTS10 having associative and dissociative covalent networks and hydrogen bonds.

[46] In another embodiment of the present invention, there is provided a method as described herein, wherein the hardener is MTSPI which reacts with DGEBA in presence of API to form the thermoset, MTSPI20 having covalent associative network and ionic interactions.

[47] In another embodiment of the present invention, there is provided an epoxy polymer composite as described herein, wherein the epoxy polymer composite exhibits a tensile strength ranging from 85-90 MPa.

[48] In another embodiment of the present invention, there is provided an epoxy polymer composite as described herein, wherein the epoxy polymer exhibits thermal degradation temperature in a range of 250 to 500 °C.

[49] In another embodiment of the present invention, there is provided an epoxy polymer composite as described herein, wherein the epoxy polymer composite is compression molded at 160-190°C under a pressure of 2-5 MPa for 20-30 minutes.

[50] In another embodiment of the present invention, there is provided a composite as described herein, wherein the composite is used to synthesise a carbon fiber reinforced vitrimer epoxy (CFRE) composite fabricated using vacuum-assisted resin transfer molding (VARTM), whereby ten layers of carbon fiber (CF) mats were stacked-on a glass plate, sealed with a vacuum bag. The prepared IPTS10 epoxy matrix was infused under vacuum at 60°C to ensure complete wetting and void minimization, with a resin-to-fiber ratio of 40:60 by weight to form an impregnated laminate that was cured at 100-140°C for 3-7 hours.

[51] In another embodiment of the present invention, there is provided a composite as described herein, wherein the composite IPTS10 demonstrates flexural strength (FS) of 794 MPa and an interlaminar strength (ILSS) of 52 MPa, showing 49% improvement in FS and 13% improvement in ILSS compared to commercial CFRE.

[52] In another embodiment of the present invention, there is provided an epoxy polymer composite as described herein, wherein the epoxy polymer composite is applicable for aerospace, automotive, marine, sporting goods, and renewable energy sectors like wind power.

[53] The present invention is illustrated hereunder in greater detail in relation to non-limiting exemplary embodiments as per the following examples:

EXAMPLES

[54] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and the description of how to make and use the present invention, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all and only experiments performed. The methodology for preparing few of the preferred embodiments shall become clearer with working examples provided below.

EXAMPLE 1: SYNTHESIS OF A HIGH-PERFORMANCE COVALENT ADAPTIVE NETWORKS BASED RECYCLABLE EPOXY POLYMER COMPOSITE

[55] The present invention prepares two kinds of high-performance covalent adaptive networks based recyclable epoxy polymer composite, in the following manner:
I. The chemical reaction between DGEBA and 3-isocyanatopropyl trimethoxysilane (IPTS), with the aid of 1-(3-aminopropyl) imidazole (API) as a co-curing agent, generates both associative and dissociative covalent networks, as well as hydrogen bonds, in the epoxy system. The dissociative nature of IPTS10 is shown in Figure 3 and structure is shown in Figure 7.
II. The chemical reaction between DGEBA and 1-methyl-3-[3-(trimethoxysilyl) propyl]-1H-imidazol-3-ium chloride (MTSPI), with the aid of 1-(3-aminopropyl) imidazole (API) as a co-curing agent, generates a covalent associative network and ionic interactions in the epoxy system. The structure of MTSPI20 formed is shown in Figure 8.

[56] Basically, in both systems, the hardener (10-20% by weight) and the API co-curing agent (11% by weight) were mixed with DGEBA and heated to 100-140 °C for 3-7 hours. The method of synthesis is shown in Figure 1. The curing of the epoxy matrix was confirmed by FTIR analysis (absence of the oxirane group at 910-920 cm-1) as shown in Figure 2. The tensile behaviour of the synthesised epoxy matrix was analysed and is shown in Figure 4.

[57] In the reaction mechanism, (I):
[58] The alkylamine present in the accelerator initially forms permanent bonds with a portion of the epoxy rings via nucleophilic attack, forming hydroxyl groups. These hydroxyl groups react with the electron-deficient -NCO group or the methoxysilane group present in IPTS, forming urethane or silyl ether linkages. These urethane linkages contribute to the formation of hydrogen bonds within the system. The formation of urethane bonds was confirmed by FTIR spectroscopy, which showed characteristic absorption bands at 1735-1750 cm-1 corresponding to non-hydrogen-bonded urethane groups, and around 1700 cm-1 attributed to hydrogen-bonded urethane bonds. The epoxy system contains a reversible transcarbamoylation mechanism, in which the formed carbamate groups (–OCON–) undergo dissociation into isocyanates (–NCO) and alcohols (–OH) at temperatures above 150°C. Furthermore, this epoxy system incorporates silyl ether functionalities, which also undergo exchange reactions. Therefore, in this network system, a dynamic dissociative network (due to urethane linkages), an associative network (due to silyl ether exchange), and hydrogen bonds are observed, which confer a high tensile strength of 85-90 MPa. It is interesting to note that this epoxy system exhibits excellent processability and is easily compression molded at 160-190°C under a pressure of 2-5 MPa for 20-30 minutes.

[59] In the reaction mechanism, (II):
[60] Accelerator's alkyl amine first establishes permanent bonds with a subset of epoxy rings by nucleophilic assault and forming hydroxyl group. These hydroxyl group can react with electron deficient ethoxy silane group of MTSPI. In this network system, due to presence of imidazolium chloride it provides ionic interaction and associative bond (due to silyl ether). The tensile strength of the epoxy matrix showed 50-55 MPa.

EXAMPLE 2: CHARACTERIZATION OF THE SYNTHESISED EPOXY POLYMER AND EPOXY POLYMER COMPOSITE

[61] Fourier Transform Infrared (FTIR) Analysis:

[62] From Figure 2, it is observed that the curing of the epoxy matrices, namely IPTS10 and MTSPI systems, was confirmed by FTIR analysis, as evidenced by the disappearance of the characteristic oxirane absorption band at 910–920 cm⁻¹ in both systems. In the case of the IPTS10 system, the appearance of new absorption peaks at 1712 cm⁻¹ and 1740 cm⁻¹ confirms the formation of urethane linkages within the epoxy network.

[63] Differential Scanning Calorimetry (DSC) Analysis:

[64] From Figure 2, it is observed that DSC was used to determine the glass transition temperature (Tg) of the cured epoxy. Tg, identified from the midpoint of the baseline shift in the DSC curve, corresponds to the transition from the glassy to rubbery state due to increased segmental mobility. The epoxies exhibited a Tg of 107-108 °C, indicating a well-developed crosslinked network.

[65] Thermogravimetric Analysis (TGA) Analysis:

[66] From Figure 2, it is observed that TGA was performed to evaluate the thermal stability of the synthesized epoxy polymers. The temperature at 5% weight loss (Td5), commonly used as an indicator of initial thermal degradation and material stability, was determined from the TGA curves. The MTSPI20 and IPTS10 systems exhibited Td5 values of 248 °C and 276°C, respectively. Furthermore, the maximum degradation temperatures (Tmax), obtained from the peak of the derivative thermogravimetric (DTG) curves, were observed at 419°C and 429°C for MTSPI20 and IPTS10, respectively. The higher Tmax value suggests enhanced thermal robustness and a more stable crosslinked network structure.

EXAMPLE 3: MECHANICAL PROPERTIES OF THE SYNTHESISED EPOXY POLYMER COMPOSITE

[67] From Figure 5, it is observed that flexural strength (FS) and interlaminar shear strength (ILSS) of commercial CFRE and IPTS10 is represented. It is clearly depicted that FS reflects resistance to bending under combined tensile-compressive stresses, while ILSS indicates the material’s shear resistance and interfacial integrity, confirming the robust mechanical performance of the system. IPTS10 demonstrated FS of 794 MPa and an ILSS of 52 MPa; showing 49% improvement in FS and 13% improvement in ILSS compared to commercial CFRE.

[68] The tensile strength (TS) of the epoxy polymer synthesized and neat epoxy was tested. Tensile strength reflects the material’s resistance to fracture under uniaxial loading. TS is directly related by crosslink density and network architecture. TS values of IPTS10 is 88 MPa at 10 wt% IPTS loading, upon increasing IPTS loading to 20 and 30 wt%, TS drops to 68 MPa and 33 MPa, respectively. TS value of MTSPI is 54 MPa at 20 wt% loading.

[69] The self-healing property for the CFRE formed by the synthesized epoxy polymer laminate is shown in Figure 6. A damaged sample was taken and compressed at 160°C under 2 MPa for 30 min and retested ILSS for the self-healing efficiency. To evaluate self-healing, ILSS tests on samples were stopped at a 30% load drop from the peak value. The samples were then heated at 160°C for 30 min under 2 MPa in a compression mold, cooled to room temperature, and retested to assess strength recovery. ILSS after self-healing is obtained as 39 MPa for IPTS10 and self-healing efficiency is 58%.

EXAMPLE 4: APPLICATIONS OF THE SYNTHESISED EPOXY POLYMER COMPOSITE

[70] Conventional thermosets typically find their way into landfills once their useful life is over, while the incineration of composite materials demands considerable energy and can lead to the release of harmful pollutants into the atmosphere. In contrast, the present innovation in epoxy development, featuring dynamic networks, facilitates reusability.

• The present invention demonstrates robust mechanical strength in addition to being recyclable and possessing self-healing properties, characteristics that are not achievable with conventional epoxies.
• Industries such as aerospace, automotive, marine, sporting goods, and renewable energy sectors like wind power can derive significant benefits from the utilization of this epoxy polymer.

ADVANTAGES OF PRESENT INVENTION:

[71] The present invention provides a high-performance multi-covalent adaptive network based recyclable epoxy polymer composite and synthesis thereof.

[72] The advantages of the present invention are:
1. A dynamic covalent network system is developed by combining transcarbamoylation, silyl ether linkages, and hydrogen bonding interactions. These materials exhibit excellent recyclability, reprocessability, and self-healing behaviour due to dynamic bond exchange reactions and the presence of a dissociative covalent network, while still maintaining outstanding mechanical properties.
2. A dynamic covalent network system is developed by combining system based on silyl ether exchange and ionic interactions, exhibiting tensile strength of 50-55 MPa.
3. The presence of -NCO-containing species with alkoxy silane (Si-OR) groups enables reactions with epoxy, leading to the formation of urethane linkages and new silyl ether bonds. Even without the addition of any filler, the polymer matrix exhibits high tensile strength in the range of 85-90 MPa.
4. Owing to the presence of a dissociative covalent network, the matrix in powder form is compression-molded into sheets at 160-180 °C under a pressure of 2-5 MPa for 20-30 minutes.
5. The fiber-reinforced laminates fabricated using the optimized IPTS-based composition demonstrate a flexural strength of about 790 MPa and an interlaminar shear strength (ILSS) of about 52 MPa, indicating enhanced structural performance.
, Claims:1. A high-performance multi-covalent adaptive network based recyclable epoxy polymer composite, comprising:
a) a resin;
b) a co-curing agent; and
c) a hardener;
wherein,
the resin is Diglycidyl ether of bisphenol A (DGEBA);
the co-curing agent is 1-(3-aminopropyl) imidazole (API);
the hardener is selected from a group consisting of 3-isocyanatopropyl trimethoxysilane (IPTS) and 1-methyl-3-[3-(trimethoxysilyl) propyl]-1H-imidazol-3-ium chloride (MTSPI); and
the co-curing agent and the hardener is present in an amount of 10-15 wt% and 10-20 wt%, respectively.
2. The epoxy polymer composite as claimed in claim 1, wherein API is present in an amount of 11 wt%.
3. The epoxy polymer composite as claimed in claim 1, wherein IPTS or MTSPI are present in an amount of 10-20 wt%.
4. A method to synthesise a high-performance multi-covalent adaptive network based recyclable epoxy polymer composite by the following steps:
i. pre-heating DGEBA;
ii. adding API and IPTS/MTSPI and stirring while keeping for degassing conditions to form a system; and
iii. curing the system obtained in step (ii) to form a cured high-performance multi-covalent adaptive network based recyclable epoxy polymer composite.
5. The method as claimed in claim 4, wherein the pre-heating in step (i) is performed at 60-70℃ for 15-25 minutes.
6. The method as claimed in claim 4, wherein the stirring in step (ii) is performed for 5-10 mins and degassing conditions for a time period ranging from 30-40 minutes.
7. The method as claimed in claim 4, wherein the curing in step (iii) is performed at 100-140°C for 3-7 hours.
8. The method as claimed in claim 4, wherein the hardener is IPTS which reacts with DGEBA in presence of API to form the thermoset, IPTS10 having associative and dissociative covalent networks and hydrogen bonds.
9. The method as claimed in claim 4, wherein the hardener is MTSPI which reacts with DGEBA in presence of API to form the thermoset, MTSPI20 having covalent associative network and ionic interactions.
10. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite IPTS10 exhibits a tensile strength ranging from 85-90 MPa, interlaminar shear strength (ILSS) in a range of 46-56 MPa, and flexural strength (FS) in a range of 750-800 MPa and
11. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite exhibits thermal degradation temperature in a range of 250-500°C.
12. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite is compression molded at 160-190°C under a pressure of 2-5 MPa for 20-30 minutes.
13. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite is used to synthesise CFRE composite comprising carbon fiber impregnated with IPTS10 epoxy matrix via vacuum-assisted resin transfer molding (VARTM), wherein the composite exhibits an interlaminar shear strength (ILSS) of 49–54 MPa and a flexural strength (FS) of 784–794 MPa.
14. The epoxy polymer composite as claimed in claims 1 and 13, wherein the epoxy polymer composite is separated from carbon fibre of CFRE with a SALSO™ solution by heating the CFRE composite in a Teflon-lined autoclave at 200–250 °C for 10–16 hours.
15. The epoxy polymer composite as claimed in claim 1, wherein the epoxy polymer composite is applicable for aerospace, automotive, marine, sporting goods, and renewable energy sectors like wind power.