Description:TECHNICAL FIELD
The present disclosure relates to a field of synthesis of sustainable foam materials. Moreover, the present disclosure relates to a method for synthesizing a flexible and self-healing bio-based vitrimer epoxy foam.
BACKGROUND
The petroleum-based polymer foams, such as polystyrene and polyurethane foams, have been widely used for packaging and insulation purposes due to their lightweight nature, affordability, and excellent insulating properties. However, the petroleum-based polymer foams pose significant environmental challenges due to their non-biodegradable nature and extremely slow degradation rates. As a result, the accumulation of non-degradable foam waste in landfills and the environment has become a pressing concern, as these can persist for many years without breaking down.
To address the environmental issues, there is a growing need to develop sustainable alternatives to petroleum-based polymer foams. The sustainable alternatives aim to provide comparable functionality while minimizing environmental impact. Efforts to develop alternatives to the polystyrene and the polyurethane in the realm of sustainable alternatives have been ongoing. However, existing solutions encounter sustainability and cost-effectiveness hurdles, impeding their widespread adoption. While some bio-based sustainable alternatives have been explored, they often lack the necessary properties and performance for their concerned applications. Additionally, concerns about production costs and scalability limit their practicality.
Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks.

SUMMARY
The present disclosure provides a method for synthesizing a bio-based vitrimer epoxy foam. The present disclosure provides a solution to the technical problem how to produce a flexible and self-healing epoxy foam using sustainable and environmentally friendly materials. An aim of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provide an improved method that not only synthesises the bio-based flexible vitrimer epoxy foam that is cost-effective but the method that may be easily adopted. Thus, the method of the present disclosure manifests a technical advancement as well as economic benefits.
One or more objectives of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.
In one aspect, the present disclosure provides the method for synthesizing the bio-based vitrimer epoxy foam. The method includes epoxidizing a fatty acid by reacting the fatty acid with a cation exchange resin catalyst and hydrogen peroxide to obtain an epoxidized fatty acid. Furthermore, the method includes synthesizing a hardener comprising an amino-alkyl derivative by a condensation reaction of enolic molecules, formaldehyde, and an amine containing a disulfide bond. The amino-alkyl derivative comprises a benzoxazine-disulfide moiety. Furthermore, the method includes curing the epoxidized fatty acid with the synthesized hardener to synthesize the bio-based vitrimer epoxy foam comprising a crosslinked epoxy vitrimer network having a polybenzoxazine-disulfide moiety. The dynamic covalent disulfide bonds undergo exchange reactions at elevated temperatures to provide self-healing and reprocessability properties to the bio-based vitrimer epoxy foam.
The method of the present disclosure for synthesizing bio-based vitrimer epoxy foam has several significant technical effects.
The utilization of bio-based materials derived from renewable sources, such as the fatty acids, in the production of epoxy foams reduces dependence on fossil fuels and promotes environmental sustainability by mitigating the carbon footprint associated with petroleum-based alternatives. Additionally, the use of renewable sources decreases reliance on finite resources and minimizes the greenhouse gas emissions. The presence of dynamic covalent bonds of disulfide within the crosslinked epoxy vitrimer network grants the bio-based epoxy foam self-healing properties. The self-healing capability enables the bio-based vitrimer epoxy foam to autonomously repair damages, extending its longevity and enhancing its durability, thus reducing the need for frequent replacements. Furthermore, the bio-based vitrimer epoxy foam can be reshaped, remolded, or recycled without compromising its structural integrity. The feature of remolding facilitates reprocessing, minimizes waste generation, and optimizes resource utilization, thereby enhancing overall sustainability and reducing environmental impact. The method allows for precise control over the bio-based vitrimer epoxy foam’s properties, enabling the tailoring of characteristics such as density, flexibility, and strength to meet specific application requirements. The customization capability enhances the versatility and usability of the bio-based vitrimer epoxy foam, ensuring optimal performance in diverse industrial settings. The dynamic covalent bonds contribute to improved mechanical properties, including strength, toughness, and resilience, while also enhancing thermal stability and chemical resistance. Moreover, the relatively simple synthesis process contributes to cost-effectiveness by minimizing production costs and resource requirements. Consequently, the bio-based vitrimer epoxy foam emerges as a viable and competitive alternative to traditional petroleum-based polymer foams, offering comparable performance at a lower cost. The cost-effectiveness of the bio based vitrimer epoxy foam enhances accessibility and affordability, driving its adoption in diverse markets and applications.
The method of the present disclosure is thus a sustainable approach and has potential to significantly reduce the environmental impact of plastic disposal.
In another aspect, the present disclosure provides the bio-based vitrimer epoxy foam composition comprising ten parts by weight of an epoxidized castor oil. The composition further comprises one part by weight of a hardener. The hardener comprises a benzoxazine-disulfide moiety having dynamic covalent disulfide bonds, and is a reaction product of enolic molecules, formaldehyde, and an amine containing a disulfide bond, synthesized through a condensation reaction, wherein the bio-based vitrimer epoxy foam comprises a crosslinked epoxy vitrimer network having the polybenzoxazine-disulfide moiety. The dynamic covalent disulfide bonds undergo exchange reactions at elevated temperatures to provide self-healing and reprocessability properties to the bio-based vitrimer epoxy foam.
The bio-based vitrimer epoxy foam composition of the present disclosure has same technical effects as described above for the method.
It is to be appreciated that all the aforementioned implementation forms can be combined. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.
Additional aspects, advantages, features, and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart depicting a method for synthesizing a bio-based vitrimer epoxy foam, in accordance with an embodiment of the present disclosure;
FIG. 2A is a flowchart for epoxidizing the fatty acid, in accordance with an embodiment of the present disclosure;
FIG. 2B is a graph depicting Fourier Transform Infrared (FTIR) spectrum of the epoxidized fatty acid;
FIGs. 3A and 3B collectively depict a flowchart for preparing the hardener, in accordance with an embodiment of the present disclosure;
FIG. 3C is a graph depicting FTIR spectrum of the hardener, in accordance with an embodiment of the present disclosure;
FIGs. 4A, 4B and 4C collectively depict a flowchart for reaction of the epoxidized fatty acid and the hardener, in accordance with an embodiment of the present disclosure;
FIG. 5A is a graph depicting FTIR spectrum of the bio-based vitrimer epoxy foam and epoxidized fatty acid, in accordance with an embodiment of the present disclosure;
FIG. 5B is a graph depicting FTIR spectrum of the bio-based vitrimer epoxy foam and the hardener, in accordance with an embodiment of the present disclosure;
FIG. 6A is diagram illustrating thermostability of the bio-based vitrimer epoxy foam, in accordance with the present disclosure;
FIG. 6B is a diagram illustrating characterization graph obtained using differential Scanning calorimetry (DSC), in accordance with present disclosure;
FIGs. 7A, 7B, 7C and 7D are graphs illustrating behaviour of the bio-based vitrimer epoxy foam behaviour under creep; and
FIG. 8 is diagram illustrating behaviour of the bio-based vitrimer epoxy foam behaviour under cyclic load, in accordance with the present disclosure.
The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those skilled in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.
Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.
DETAILED DESCRIPTION OF EMBODIMENTS
The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.
FIG. 1 is a flowchart depicting a method for synthesizing a bio-based vitrimer epoxy foam, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, there is shown a flowchart of a method 100. In some implementations, the method 100 is executed by a skilled person. The method 100 may include steps 102 to 106.
At step 102, the method 100 includes epoxidizing a fatty acid by reacting the fatty acid with a cation exchange resin catalyst and hydrogen peroxide to obtain an epoxidized fatty acid. The term ‘epoxidizing’ refers to a chemical reaction in which the fatty acid undergoes the process of addition of an epoxy group i.e., oxirane ring to the structure of the fatty acid. The process involves bonding an oxygen atom to a double bond, creating an epoxide functional group. The epoxidizing reactions are used to transform unsaturated compounds, like alkenes or fatty acids, into their respective epoxides. In the process of epoxidizing the fatty acid, the cation exchange resin catalyst is utilized to facilitate the reaction between the fatty acid and hydrogen peroxide, resulting in the formation of the epoxidized fatty acid. The cation exchange resin catalyst acts as a mediator, enabling the interaction between the fatty acid and hydrogen peroxide by selectively binding and releasing cations involved in the reaction. The catalytic action promotes the conversion of the fatty acid into its epoxidized form, thereby achieving the desired chemical transformation efficiently and selectively. In some implementations, the cation exchange resin catalyst is a Seralite SRC 120. The high catalytic activity of the Seralite SRC 120 ensures efficient conversion of the fatty acids into epoxidized fatty acids, facilitating the desired chemical transformation. Further, the excellent selectivity of the Seralite SRC 120 promotes the specific epoxidation reaction while minimizing undesired side reactions. The Seralite SRC 120 may be regenerated after use, extending its lifespan and reducing overall costs associated with catalyst procurement.
In an implementation, the epoxidizing of the fatty acid includes mixing the fatty acid, the cation exchange resin catalyst, a glacial acetic acid, toluene to obtain a fatty acid mixture. Before mixing, each reactant is prepared for the reaction. The fatty acid (for e.g., castor oil), is measured out in the desired quantity. Similarly, the cation exchange resin catalyst is sourced commercially. In some examples, the fatty acid may be oleic acid, palmitoleic acid, linoleic acid, linolenic acid, arachidonic acid, ricinoleic acid, alpha eleostearic acid, licanic acid and their triglycerides. The fatty acid may further include triolein, linolein, ricinolein (castor oil) etc. The glacial acetic acid and toluene are also measured out as solvents. All reactants are combined in a vessel. After adding the reactants to the reaction vessel, the mixture is stirred vigorously to ensure homogeneity. The stirring helps in dispersing the reactants and catalyst evenly throughout the fatty acid mixture.
In another implementation, the epoxidizing of the fatty acid further includes heating the fatty acid mixture at a temperature ranging from 50 to 65 degrees Celsius. The heating of the fatty acid mixture lowers the activation energy barrier for the reaction that facilitates faster conversion of the fatty acid into its epoxide form. By carefully controlling the reaction temperature within the specified range, higher selectivity towards the formation of the desired epoxide product is achieved that minimizes the formation of unwanted byproducts. The chosen temperature range is striking a balance between reaction efficiency and safety considerations.
In some implementations, the epoxidizing of the fatty acid further includes adding hydrogen peroxide dropwise to the fatty acid mixture for 7 to 9 hours to form a reaction mixture. Dropwise addition of the hydrogen peroxide ensures that the oxidizing agent (i.e., hydrogen peroxide) is continuously available throughout the reaction period. The continuous availability maximizes reactivity and efficiency of the hydrogen peroxide in converting the fatty acid to respective epoxide forms.
In some implementations, the epoxidizing the fatty acid further includes neutralizing and washing the reaction mixture with a 2M sodium carbonate aqueous solution. During the epoxidation process, acidic byproducts may be formed due to side reactions. The acidic impurities may affect the purity and stability of the epoxidized fatty acid. Adding the sodium carbonate solution helps neutralize the acidity by reacting with the acidic species.
At step 104, the method 100 further includes synthesizing a hardener including an amino-alkyl derivative by a condensation reaction of enolic molecules, formaldehyde, and an amine containing a disulfide bond. The amino-alkyl derivative includes a benzoxazine-disulfide moiety. The hardener is compound which reacts with the epoxidized fatty acid to catalyse the reaction for formation of the bio-based vitrimer epoxy foam. When mixed with epoxidized fatty acid, the hardener undergoes a chemical reaction, typically through crosslinking, that transforms the liquid epoxy fatty acid into a solid and durable polymer material with desirable mechanical and thermal properties. The condensation refers to a chemical reaction in which two or more molecules combine to form a larger molecule, usually with the elimination of a small molecule such as water, alcohol, or ammonia. The amino-alkyl derivative is a compound derived from an amine molecule (i.e. molecule containing a nitrogen atom) that is attached to an alkyl group (i.e. a hydrocarbon chain). The amino-alkyl derivative is formed by replacing one or more hydrogen atoms in the alkyl group with an amino group (-NH2). Enolic molecules are organic compounds that contain an enol functional group (-C=C-OH) along with a carbonyl group (such as -C=O). The benzoxazine-disulfide moiety refers to a specific molecular structure that combines two distinct components: a benzoxazine group and a disulfide bond. The benzoxazine group is a heterocyclic ring system composed of a benzene ring fused to an oxazine ring i.e., a six-membered ring containing one oxygen and one nitrogen atom. The benzoxazine moiety is known for its ability to undergo ring-opening polymerization, which results in the formation of polybenzoxazine materials with desirable properties such as high thermal stability, low flammability, and excellent mechanical properties. The disulfide bond, also known as a disulfide bridge or disulfide linkage, is a covalent bond formed between two sulphur atoms. The combination of the benzoxazine group and the disulfide bond in the "benzoxazine-disulfide moiety" results in a unique molecular structure that can impart specific properties to the materials derived from it. The presence of the benzoxazine group can provide thermal stability and mechanical strength, while the disulfide bond can introduce dynamic covalent bonds, enabling potential self-healing or remolding capabilities.
In an implementation, the synthesizing of the hardener includes mixing the enolic molecules, formaldehyde, the amine containing the disulfide bond, and a solvent mixture of acetone and water in equal parts to obtain a pre-hardener reaction mixture. The enolic molecules, formaldehyde, and the amine containing the disulfide bond are mixed together in a vessel to obtain a blend. The equal parts of acetone and water ensure are added to the blend in order to obtain the pre-hardener reaction mixture. The pre-hardener reaction mixture is stirred thoroughly to ensure uniform distribution of the ingredients and to facilitate the reaction. The pre-hardener reaction mixture undergoes a chemical reaction. In an example, the enolic molecule may be polyphenol. In some examples, polyphenols may be selected from catechin, epicatechin, epigallocatechin-3-gallate (EGCG), genistein, quercetin, kaempferol, rutin, malvidin, cyanidin, delphinidin, apigenin, peonidin, anthocyanins, isoflavones, flavanols. The anthocyanins further include pelargonidin, petunidin, and rosinidin. The isoflavone may include puerarin and cladrin. The flavanol includes kaempferol, myticetin, isorhamnetin and theaflavin. Further, the amine containing the disulfide bond may be primary or secondary amine.
In an implementation, the hardener is a benzoxazine-disulfide compound formed by a Mannich condensation reaction of the enolic molecules, formaldehyde, and the amine containing the disulfide bond. The Mannich condensation reaction is organic reaction which consists of an amino alkylation of an acidic pronucleophile i.e. a compound containing an active hydrogen atom with formaldehyde and a secondary amine. In an example, the enolic molecule (for e.g. EGCG) reacts with formaldehyde to form an intermediate hydroxymethylated enol. The primary amine (for e.g. cystamine dihydrochloride) attacks the hydroxymethylated enol, leading to the formation of an iminium ion intermediate. The iminium ion intermediate then undergoes an intramolecular nucleophilic addition by the phenolic hydroxyl group, resulting in the formation of the benzoxazine ring structure containing the disulfide linkage. The hardener is formed in a one-pot reaction, with the disulfide bond being incorporated into the final structure due to the use of cystamine dihydrochloride as the amine source.
In an implementation, the synthesizing of the hardener further includes heating the pre-hardener reaction mixture for 5 to 24 hours at a temperature ranging from 70 to 100 degrees Celsius to obtain a final reaction mixture. In some examples, pre-hardener reaction mixture is heated for six hours at 80 degrees Celsius. The parameters during mixing of pre-hardener reaction mixture, such as temperature and time period of the mixing, may vary depending on the specific application requirements. The parameters may be adjusted to optimize the mixing process and achieve the desired properties and characteristics of the resulting material. The controlled heating process facilitates ensuring the formation of high-quality hardener compounds. Maintaining the pre- hardener reaction mixture at a specified temperature range allows for optimal conditions for the desired chemical reactions, leading to the production of the hardener with desired properties such as strength, stability, and compatibility with other materials.
In an implementation, the synthesizing of the hardener further includes washing the final reaction mixture with distilled water and a 1N sodium hydroxide aqueous solution. Washing with distilled water helps to remove water-soluble impurities, unreacted starting materials, and by-products that may be present in the final reaction mixture. The sodium hydroxide adjusts the pH of the final reaction mixture, which is important for the stability and functionality of the hardener. In an example, after washing the final reaction mixture with distilled water and 1N NaOH solution, the entire reaction mixture is transferred to a separating funnel. The separating funnel is closed with a stopper and allowed to stand for some time to allow the two immiscible layers i.e., an aqueous layer and an organic layer to separate them completely based on difference in their densities. The denser aqueous layer settles at the bottom, while the less dense organic layer floats on top. The stopcock at the bottom of the separating funnel is carefully opened to drain out the denser aqueous layer into a separate container. Once the aqueous layer is drained out, the stopcock is closed. The organic layer remaining in the separating funnel can then be drained out into another container by opening the top portion of the funnel. If an emulsion forms between the two layers, making separation difficult, additional techniques like adding salt or gentle swirling may be employed to break the emulsion and facilitate separation.
In an implementation, the synthesizing of the hardener further include drying the washed final reaction mixture to obtain the hardener comprising the benzoxazine-disulfide moiety, wherein the dynamic covalent disulfide bonds present in the benzoxazine-disulfide moiety of the hardener act as a single Covalent Adaptable Network. In an example, the drying of the washed the final reaction mixture may be performed using vacuum oven, air drying, desiccant drying, inert gas purging, lyophilization microwave drying, vacuum concentration. In some examples drying is performed in the vacuum oven for two hours.
At step 106, the method 100 further includes curing the epoxidized fatty acid with the synthesized hardener to synthesize the bio-based vitrimer epoxy foam comprising a crosslinked epoxy vitrimer network having a polybenzoxazine-disulfide moiety. The dynamic covalent disulfide bonds undergo exchange reactions at elevated temperatures to provide self-healing and reprocessability properties to the bio-based vitrimer epoxy foam.
The epoxidized fatty acid contains epoxy rings (oxirane groups) that can react with amine groups. The hardener contains the benzoxazine-disulfide moiety, which has amine groups. When the epoxidized fatty acid and the hardener are mixed, the epoxy groups undergo a ring-opening reaction with the amine groups, forming covalent bonds and creating a crosslinked network structure. The benzoxazine portion of the hardener undergoes a ring-opening polymerization reaction during the curing process. The reaction forms a highly crosslinked and thermally stable polybenzoxazine disulfide moiety structure within the epoxy network. The disulfide (-S-S-) bonds act as dynamic covalent bonds, capable of undergoing exchange reactions at elevated temperatures. At the elevated temperatures the disulfide bonds in the network may undergo associative and dissociative exchange reactions. In the associative and dissociative exchange reactions, the disulfide bonds may break and reform with other sulphur atoms, resulting in a reorganization of the crosslinked epoxy vitrimer network structure.
When the bio-based vitrimer epoxy foam is damaged, the exchange reactions of the disulfide bonds are triggered at elevated temperatures. The broken disulfide bonds may reform with other sulphur atoms, effectively healing the damage by reconstructing the crosslinked epoxy vitrimer network structure. At higher temperatures, the exchange reactions of the disulfide bonds become more frequent and widespread. This allows the crosslinked epoxy vitrimer network structure to temporarily break down and flow like a viscous liquid. In viscous liquid state, the material may be reshaped, remolded, or reprocessed into a new form. Upon cooling, the crosslinked epoxy vitrimer network structure reforms, solidifying the material in its new shape. The self-healing and reprocessability properties arise due to dynamic nature of the disulfide bonds and their ability to undergo reversible exchange reactions at elevated temperatures. The polybenzoxazine structure provides thermal stability and chemical resistance, while the epoxy network serves as the base matrix.
In some implementations, the curing of the epoxidized fatty acid with the synthesized hardener comprises mixing the epoxidized fatty acid and the hardener to obtain a mixture. The mixing process begins by measuring out the desired amounts of the epoxidized fatty acid and the hardener according to the desired formulation. Once the quantities are determined, the epoxidized fatty acid and hardener are combined in a suitable container or vessel. In an example, the mixing may be done manually using stirring rods or spatulas, or it may be achieved using mechanical mixers or homogenizers for larger-scale production. During mixing, it's essential to ensure thorough blending of the epoxidized fatty acid and hardener to promote uniform distribution of the components throughout the mixture. This ensures that all reactive sites within the epoxidized fatty acid are exposed to the hardener, facilitating the curing process.
In some implementations, the curing of the epoxidized fatty acid with the synthesized hardener further comprises subjecting the mixture to a stimulus to initiate a competitive nucleophilic attack by the amine and hydroxyl groups of the hardener on epoxide groups of the epoxidized fatty acid to form the bio-based vitrimer epoxy foam comprising the crosslinked epoxy vitrimer network. The vitrimers are a class of polymers that can undergo controlled topological rearrangement of their crosslinks through stimuli, allowing for reprocessing and recycling. The stimulus provides the energy required to overcome the activation barrier for the nucleophilic attack. In an implementation, the stimulus is thermal energy. In other words, the stimulus is in a form of heat that is applied to the mixture. In another implementation, the stimulus is ultraviolet (UV) radiation. In some implementation, the stimulus may be any form of energy, as per application requirement. The amine and hydroxyl groups of the hardener act as nucleophiles and attack the electrophilic epoxide groups of the epoxidized fatty acid. As nucleophilic attack occurs, the amine and hydroxyl groups open the oxirane rings, forming new covalent bonds with the carbon atoms of the epoxide groups. The reaction leads to the formation of crosslinks between the epoxidized fatty acid molecules, creating a three-dimensional network structure.
In some implementations, the competitive nucleophilic attack occurs via an SN2 mechanism, and the amine and hydroxyl groups of the hardener attack less substituted carbons of the epoxide groups in the epoxidized fatty acid. In an SN2 reaction, the nucleophile (i.e. amine or hydroxyl groups of the hardener) attacks the electrophilic carbon atom of the oxirane ring of the epoxidized fatty acid from the backside, leading to the formation of a new covalent bond and the opening of the oxirane ring. The nucleophilic attack by the amine and hydroxyl groups of the hardener preferentially occurs at the less substituted carbons of the epoxide groups in the epoxidized fatty acid. This means that the nucleophiles tend to attack the carbon atom of the oxirane ring that has fewer substituents (e.g., hydrogen atoms or alkyl groups) attached to it.
The method 100 is based bio-based materials derived from renewable sources, such as the fatty acids, reduces dependence on fossil fuels. The shift promotes environmental sustainability by mitigating the carbon footprint associated with petroleum-based alternatives. Further, the dynamic covalent bonds of benzoxazine and disulfide within the crosslinked epoxy vitrimer network grant the foam self-healing capabilities. The self-healing property enables the bio-based vitrimer epoxy foam to autonomously repair damages. By undergoing self-healing, the bio-based vitrimer epoxy foam extends its longevity and enhances its durability, ensuring prolonged functionality and reducing the need for frequent replacements.
In some implementations, self-healing of the synthesized bio-based vitrimer epoxy foam is initiated by heating the synthesized bio-based vitrimer epoxy foam at 120 degrees Celsius to 180 degrees Celsius for a duration of 5 hours to10 hours. The heat triggers the mobility of the polymer chains within the bio-based vitrimer epoxy foam. As a result, any damage present in the bio-based vitrimer epoxy foam is exposed to this increased mobility. The increased mobility of the polymer chains allows them to reconfigure and rearrange themselves. This reconfiguration process helps the damaged regions of the bio-based vitrimer epoxy foam to effectively heal by closing the gaps. The duration of heating allows the polymer chains to undergo the necessary reconfiguration and bonding to restore the integrity of the bio-based vitrimer epoxy foam.
In an implementation, the self-healing of the synthesized bio-based vitrimer epoxy foam is initiated by exposing the synthesized bio-based vitrimer epoxy foam to the ultraviolet (UV) radiation. The UV radiation activates one or more reactive components within the foam. Such components may include photo initiators or functional groups that are sensitive to UV light. Upon exposure to UV radiation, the activated components within the foam undergo chemical reactions. These reactions may involve the formation of free radicals or other reactive species.
The bio-based vitrimer epoxy foam can be reshaped, remolded, or recycled without compromising its structural integrity. This facilitates reprocessing, reduces waste generation, and optimizes resource utilization, enhancing its overall sustainability and reducing environmental impact. The method 100 for synthesizing the bio-based vitrimer epoxy foam allows for precise control over its properties. By adjusting formulation and processing parameters, characteristics such as density, flexibility, and strength may be tailored to meet specific application requirements. This customization capability enhances the versatility and usability of the bio-based epoxy foam, ensuring optimal performance in diverse industrial settings. Additionally, the presence of dynamic covalent bonds contributes to improved mechanical properties, including strength, toughness, and resilience, while enhancing thermal stability and chemical resistance. This makes the bio-based vitrimer epoxy foam suitable for demanding applications across various industries. Its enhanced performance ensures reliable operation in challenging environments, increasing its utility and value. The relatively simple synthesis process contributes to cost-effectiveness by minimizing production costs and resource requirements. Consequently, the bio-based vitrimer epoxy foam emerges as a viable and competitive alternative to traditional petroleum-based polymer foams, offering comparable performance at a lower cost. Its cost-effectiveness enhances accessibility and affordability, driving adoption in diverse markets and applications.
In some implementations, the bio-based vitrimer epoxy foam composition includes ten parts by weight of an epoxidized castor oil; and one part by weight of a hardener. The hardener includes a benzoxazine-disulfide moiety having dynamic covalent disulfide bonds, and is the reaction product of enolic molecules, formaldehyde, and the amine containing the disulfide bond, synthesized through the condensation reaction. The bio-based vitrimer epoxy foam includes the crosslinked epoxy vitrimer network having the polybenzoxazine-disulfide moiety. The dynamic covalent disulfide bonds undergo exchange reactions at elevated temperatures to provide self-healing and reprocessability properties to the bio-based vitrimer epoxy foam.
The high ratio of the epoxidized castor oil ensures a higher crosslink density within the final vitrimer network of the bio-based vitrimer epoxy foam. A higher crosslink density means that there are more covalent bonds formed between the molecules of epoxidized castor oil and the hardener, resulting in a denser and more interconnected network structure. The increased crosslink density contributes to improvements in the mechanical properties and thermal stability of the bio-based vitrimer epoxy foam. With more crosslinks present, the foam exhibits enhanced strength, stiffness, and resistance to deformation under mechanical stress. Additionally, the denser network structure provides better thermal stability, allowing the foam to withstand higher temperatures without undergoing significant degradation.
FIG. 2A is a flowchart for epoxidizing the fatty acid, in accordance with an embodiment of the present disclosure. FIG. 2A is described in conjunction with FIG. 1. With reference to FIG. 2A, there is shown a flowchart 200A that includes a series of operations from 202A to 204A.
At operation 202A, the fatty acid 202 is fed in the vessel. In the illustrated example, the fatty acid 202 is a castor oil. The chemical structure of the castor oil is shown in a block of the operation 202A. After that, at operation 204A, the castor oil is mixed with glacial acetic acid, toluene, and hydrogen peroxide is added dropwise for 8 hours. As a result, at operation 206A, the epoxidized castor oil 206 is prepared. The chemical structure of the epoxidized fatty acid 206 is shown in a block of the operation 204A.
FIG. 2B is a graph depicting Fourier Transform Infrared (FTIR) spectrum of the epoxidized fatty acid, in accordance with an embodiment of the present disclosure. FIG. 2B is described in conjunction with FIGs 1 and 2A. With reference to FIG. 2B, there is shown a graphical representation 200B depicting an exemplary FTIR spectra of the epoxidized fatty acid 206 prepared using the method 100 (shown in FIG. 1). Specifically, the graphical representation 200B depicts the absorption of infrared light by the epoxidized fatty acid 206 (for example castor oil) at different wavelengths, typically measured in wavenumbers. Wavenumber is expressed in reciprocal centimetre (cm-1) in an abscissa axis. Transmittance is expressed in arbitrary units in an ordinate axis.
The graphical representation 200B includes a curve 202B depicting the FTIR spectrum that indicate the absorption of infrared light. Each peak or band in the curve 202B corresponds to the vibration of specific chemical bonds within the epoxidized fatty acid 206. The curve 202B includes a section 204B. The section 204B displays a distinctive feature known as the oxirane ring's symmetrical axial bending at 1244 cm-1, C-O-C stretching at 1045 cm-1. Further section 206B represents bending in the plane of the C-O-C at 844 cm-1. The section 204B and 206B indicate fatty acid epoxidation.
FIGs. 3A and 3B collectively depict a flowchart for preparing the hardener, in accordance with an embodiment of the present disclosure. FIGs. 3A and 3B are described in conjunction with FIGs 1, 2A and 2B. With reference to FIGs. 3A and 3B, there is shown a flowchart 300 that includes a series of operations 302A to 304A.
At operation 302A, Epigallocatechin gallate (ECGC), cystamine dihydrochloride, and mixture of acetone and water are added together to form a mixture that is later immersed in a temperature-controlled bath. After that, at operation 304A, the mixture of the ECGC, cystamine dihydrochloride, and mixture of acetone and water is stirred at a predetermined temperature for 5 to 24 hours to obtain the hardener 302. In other words, a three-component reaction that is carried out in which an enolic molecule (here, polyphenol) reacts with a mixture of formaldehyde and primary or secondary amine in the presence of acid to produce the hardener comprising an amino-alkyl derivative.
FIG. 3C is a graphical representation depicting FTIR spectrum of the hardener, in accordance with an embodiment of the present disclosure. FIG. 3C is described in conjunction with FIGs. 1, 2A, 2B, 3A and 3B. With reference to FIG. 3C, there is shown a graphical representation 300C depicting an exemplary FTIR spectra of the hardener 302 prepared by the series of operations 302A to 302B (shown in FIGs. 3A and 3B). Specifically, the graphical representation 300C depicts the absorption of infrared light by the hardener at different wavelengths, typically measured in wavenumbers. Wavenumber is expressed in reciprocal centimetre (cm-1) in an abscissa axis. Transmittance is expressed in arbitrary units in an ordinate axis.
The graphical representation 300C includes a curve 302C depicting the FTIR spectrum that indicate the absorption of infrared light. Each peak or band in the curve 302C corresponds to the vibration of specific chemical bonds within the hardener. The curve 302C includes a section 304C, a section 306C and a section 308C. The section 304C, the section 306C and the section 308C include peaks that indicates the synthesis of the benzoxazine as observed in the graphical representation 300C. The section 304C indicates CH2 wagging of the oxazine ring observed at 1315 cm-1. The section 306C represents C–N–C asymmetric stretching vibrations observed at 1140 cm-1. The section 308C represents characteristic oxazine peak observed at 936 cm-1 i.e. the typical C–H out-of-plane bending vibrations of the benzene structure in the benzoxazine ring.
FIGs. 4A and 4B collectively depict a flowchart for reaction of the epoxidized fatty acid and the hardener, in accordance with an embodiment of the present disclosure. FIGs. 4A and 4B are described in conjunction with FIGs. 1, 2A, 2B, 3A, 3B and 3C. With reference to FIGs. 4A and 4B, there is shown a flowchart 400A that includes a series of operations 402A to 404A.
At operation 402A, the epoxy groups (C-O-C) of the epoxidized castor oil 206 react with the functional groups (such as amine groups) present in the hardener 304. At operation 404A, in the presence of heat, the amine (-NH2) and hydroxyl (-OH) groups present in the hardener molecule act as nucleophiles and attack the less-substituted carbon atoms of the epoxide rings in the ECO molecule. This nucleophilic attack follows an SN2 (bimolecular nucleophilic substitution) mechanism, leading to the opening of the epoxide rings and the formation of covalent linkages between the ECO and hardener molecules. At operation 406A, as the hardener molecule contains multiple nucleophilic sites (amine and hydroxyl groups), it can react with multiple epoxide rings on different ECO molecules. This leads to the formation of the bio-based vitrimer epoxy foam 402 having a crosslinked network, where the hardener 302 acts as a crosslinking agent, connecting multiple ECO molecules through the opened epoxide rings.
FIG. 5A is a graphical representation depicting FTIR spectrum of the bio-based vitrimer epoxy foam and epoxidized fatty acid, in accordance with an embodiment of the present disclosure. FIG. 5A is described in conjunction with FIGs. 1, 2A, 2B, 3A, 3B, 4A and 4B. With reference to FIG. 5A, there is shown a graphical representation 500A depicting an exemplary FTIR spectra of the flexible and the self-healing bio-based vitrimer epoxy foam 402 and the epoxidized fatty acid 206. Specifically, the graphical representation 500A depicts the absorption of infrared light by the flexible and the self-healing bio-based vitrimer epoxy foam 402 and the epoxidized fatty acid 206 at different wavelengths, typically measured in wavenumbers. Wavenumber is expressed in reciprocal centimetre (cm-1) in an abscissa axis. Transmittance is expressed in arbitrary units in an ordinate axis.
The graphical representation 500A includes a curve 502A depicting the FTIR spectrum that indicate the absorption of infrared light by the bio-based vitrimer epoxy foam 402. Each peak or band in the curve 502A corresponds to the vibration of specific chemical bonds within the bio-based vitrimer epoxy foam 402. Further, the graphical representation 500A includes the curve 202B depicting the FTIR spectrum that indicate the absorption of infrared light by the epoxidized fatty acid 206. Each peak or band in the curve 202B corresponds to the vibration of specific chemical bonds within the epoxidized fatty acid 206. The curves 502A and 202B includes the section 206B including a region 504A and a region 506A. The region 506A depicts disappearance of oxirane peak observed at 844 cm-1 which confirms complete curing of the epoxidized fatty acid 206 by the hardener 302 in 14 hours at 150 °C. Further, the region 504B depicts oxirane peak in the epoxidized fatty acid 206.
FIG. 5B is a graphical representation depicting FTIR spectrum of the bio-based vitrimer epoxy foam and the hardener, in accordance with an embodiment of the present disclosure. FIG. 5B is described in conjunction with FIGs. 1, 2A, 2B, 3A, 3B, 4A, 4B and 5A. With reference to FIG. 5B, there is shown a graphical representation 500B depicting an exemplary FTIR spectra of the flexible and the self-healing bio-based vitrimer epoxy foam 402 and the hardener 302. Specifically, the graphical representation 500B depicts the absorption of infrared light by the flexible and the self-healing bio-based vitrimer epoxy foam 402 and the hardener 302 at different wavelengths, typically measured in wavenumbers. Wavenumber is expressed in reciprocal centimetre (cm-1) in an abscissa axis. Transmittance is expressed in arbitrary units in an ordinate axis.
The graphical representation 500B includes a curve 502B depicting the FTIR spectrum that indicate the absorption of infrared light by the bio-based vitrimer epoxy foam 402. Each peak or band in the curve 502B corresponds to the vibration of specific chemical bonds within the bio-based vitrimer epoxy foam 402. Further, the graphical representation 500B includes the curve 302C depicting the FTIR spectrum that indicate the absorption of infrared light by the hardener 302. Each peak or band in the curve 302C corresponds to the vibration of specific chemical bonds within the hardener 302. Each of the curves 502B and 302C include the section 304C and the section 306C. The section 304C includes a region 510B on the curve 502B corresponding to the bio-based vitrimer epoxy foam 402 and a region 512B on the curve 302C corresponding to the hardener 302. The region 510B depicts the elimination of C–N–C peak in the bio-based vitrimer epoxy foam 402 and the region 512B depicts the C–N–C peak in the hardener 302. The section 306C includes a region 514B on the curve 502B corresponding to the bio-based vitrimer epoxy foam 402 and a region 516B on the curve 302C corresponding to the hardener 302. The region 514B depicts elimination of CH2 peak in the bio-based vitrimer epoxy foam 402 and the region 516B depicts CH2 peak in the hardener 302. The elimination of the C–N–C peak and CH2 peak indicates opening of the oxazine ring. The opening of oxazine ring signifies formation of the crosslinked network.
FIG. 6A is diagram illustrating thermostability of the bio-based vitrimer epoxy foam, in accordance with the present disclosure. FIG.6A is described in conjunction with FIGs. 1, 2A, 2B, 3A, 3B, 4A, 4B, 5A and 5B. With reference to the FIG. 6A there is shown a graphical representation 600A showing relationship between weight percent of the bio-based vitrimer epoxy foam and the temperature. The temperature is expressed in degree Celsius in an abscissa axis. Weight per cent is expressed in arbitrary units in an ordinate axis.
The graphical representation 600A includes a curve 602A showing relationship between weight percent of the bio-based vitrimer epoxy foam and the temperature. Further, the graphical representation 600A includes a graphical representation 604A which depicts relationship between 95% weight of the bio-based vitrimer epoxy foam at temperature 213 degrees Celsius. The graphical representation 604A further includes a curve 606A which shows degradation of the bio-based vitrimer epoxy foam at temperature 213 degrees Celsius.
The curve thermal stability of the bio-based vitrimer epoxy foam was evaluated using a Thermogravimetry Analyzer (TGA). The curve 602A depicts the bio-based vitrimer epoxy foam remained stable up to 100 degrees Celsius, beyond which degradation started to occur. Specifically, 5% degradation of the bio-based vitrimer epoxy foam foam was observed at 213 degrees Celsius. Furthermore, entire bio-based vitrimer epoxy foam 402 underwent complete degradation without leaving any residues when subjected to the temperature of 450 degrees Celsius. The complete degradation indicates that the bio-based vitrimer epoxy foam 402 has a limited thermal stability and undergoes significant degradation at elevated temperatures, ultimately resulting in complete decomposition.
FIG. 6B is a diagram illustrating characterization graph obtained using differential Scanning calorimetry (DSC), in accordance with present disclosure. FIG. 6B is described in conjunction with FIGs. 1, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B and 6A.With reference to FIG. 6B there is shown a graphical representation 600B which is obtained after doing characterisation of the bio-based vitrimer epoxy foam 402. The characterization of the bio-based vitrimer epoxy foam is done to determine its Glass Transition Temperature (Tg) by using Differential Scanning Calorimetry (DSC). The graphical representation 600B shows relationship between temperature and the heat flow. The temperature is expressed in degree Celsius in an abscissa axis. Heat flow is expressed in watt per gram in an ordinate axis.
The graphical representation 600B includes a curve 602B which shows characterization of the the bio-based vitrimer epoxy foam 402 done using DSC. The analysis of the plot indicates that glass transition temperature (Tg) of the bio-based vitrimer epoxy foam 402 is 112 degrees Celsius. The observed flexibility of the bio-based vitrimer epoxy foam may be attributed to the presence of eighteen carbon chains (C-18 chains) within the fatty acid, for example, the castor oil, which impart a degree of flexibility to the bio-based vitrimer epoxy foam 402.
Additionally, the bio-based vitrimer epoxy foam 402 maintained its wall thickness due to the rigidity resulting from the reaction between the epoxidized fatty acid and the hardener. This reaction forms a crosslinked network structure, providing structural integrity and preventing the collapse or deformation of the bio-based vitrimer epoxy foam’s walls. As a result, the bio-based vitrimer epoxy foam retains its shape and mechanical properties, contributing to its overall stability and durability.
Example 1
An example illustrating the synthesis of the bio-based vitrimer epoxy foam 402 through a series of steps:
Step 1: Fatty acid (0.1 mol), glacial acetic acid (0.28 mol), 25% catalyst loading of Seralite SRC 120 with respect to triglyceride, and 100ml of toluene were mixed in a round bottom flask fitted with a dropping funnel, reflux condenser, and oil bath with temperature control. The reaction mixture is heated at temperature range of 55-65 degrees Celsius. To this, 30% of hydrogen peroxide added dropwise over a period of 8 hours. The resulting reaction mixture is washed with 2M aqueous sodium carbonate multiple times and solvent was removed using a rotary evaporator, and the resulting solution was dried in a vacuum oven.
Step 2: 100 mL round-bottom flask fitted with a condenser was filled with 0.04 mol of EGCG, 0.1 mol of formaldehyde, and 0.05 mol of cystamine dihydrochloride, and then immersed in a temperature-controlled oil bath. This was mixed with 100 ml of an acetone and water combination in equal parts, and the reaction was stirred for six hours at 80 degrees Celsius. The reaction mixture was rinsed twice with distilled water and 1N NaOH before drying in a vacuum oven for two hours.
Step 3: In the final step, a competitive attack of the amine and hydroxyl group of the hardener on one of the less substituted carbons of the epoxide of castor oil by SN2 mechanism occurs to form a permanent linkage to form a crosslinked network eventually.
By following these steps, the bio-based vitrimer epoxy foam was synthesized.
Characterisation:
Table 1: Mechanical data for behaviour of the bio-based vitrimer epoxy foam behaviour under creep.
Time(min) Stress(kPa) % Strain %Strain Recovery
1 0 0 0 0
2 1 14.6 25 100
3 2 0 0 0
4 3 14.6 25 100
5 19 0 25 100
6 20 14.6 0 0
7 49 0 25 100
8 50 14.6 0 0
9 79 0 25 100
10 80 14.6 0 0
11 99 0 25 100
12 100 14.6 0 0
Table 1 elucidates the mechanical properties of the bio-based vitrimer epoxy foam 402 under creep. In the table 1 relationship between time with the stress applied on the bio-based vitrimer epoxy foam 402, relationship between the time with the strain (%) and relationship between the time and the strain recovery (%) has been shown.
FIGs. 7A, 7B, 7C and 7D are graphical representations illustrating behaviour of the bio-based vitrimer epoxy foam behaviour under creep, in accordance with the present disclosure. FIGs .7A, 7B, 7C, 7D are described in conjunction with FIGs. 1, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, 6A and 6B. With reference to the FIGs. 7A, 7B, 7C and 7D, there is shown behaviour of the bio-based vitrimer epoxy foam 402 when it undergoes compression using parallel plate fixture in dynamic mechanical analyzer. FIG. 7A and FIG. 7B includes the graphical representation showing relationship between stress applied and strain (%) with the time. Time is expressed in minutes in an abscissa axis. Stress is expressed in kilopascal and strain (%) in an ordinate axis.
FIG. 7A and FIG. 7B are obtained based on the data given in Table 1. FIG. 7A includes a graphical representation 700A including a curve 702A and a curve 704A. The curve 702A depicts relationship between stress applied to the bio-based vitrimer epoxy foam 402 and time duration. Further, the curve 704A depicts the strain (%) on the bio-based vitrimer epoxy foam 402. FIG. 7B includes a graphical representation 700B including a curve 702B and a curve 704B. The curve 702B depicts relationship between stress applied to the bio-based vitrimer epoxy foam 402 and time duration. Further, the curve 704B depicts the strain (%) on the bio-based vitrimer epoxy foam 402. FIG.7A is obtained for first five cycles when the bio-based vitrimer epoxy foam 402 undergoes constant load of 15 kPa. FIG. 7B is obtained for the first fifty cycles when the bio-based vitrimer epoxy foam 402 undergoes constant load of 15 kPa.
FIG.7C and FIG.7D are obtained based on the data given in Table 1. FIG. 7C includes a graphical representation 700C. The graphical representation 700C further includes a curve 702C and a curve 704C. The curve 702C depicts stress applied to the bio-based vitrimer epoxy foam 402 and the curve 704C depicts the strain recovery (%) on the bio-based vitrimer epoxy foam 402. FIG. 7D includes a graphical representation 700. The graphical representation 700D further includes a curve 702D and a curve 704D. The curve 702D depicts stress applied to the bio-based vitrimer epoxy foam 402 and the curve 704D depicts the strain recovery (%) on the bio-based vitrimer epoxy foam 402. FIG.7C is obtained for first five cycles when the bio-based vitrimer epoxy foam undergoes a strain recovery. constant load of 15 kPa. FIG. 7D is obtained for the first fifty cycles when the bio-based vitrimer epoxy foam undergoes strain recovery.
The bio-based vitrimer epoxy foam specimen was subjected to a constant load (stress) of 15 kPa, resulting in a deformation of 25% strain. Creep cycles were then conducted over a period of 10 minutes for five cycles. During each cycle, the sample of the flexible and the self-healing bio-based vitrimer epoxy foam was held at 15 kPa stress for 1 minute, followed by the release of stress over the foam with a 1-minute recovery time.
It was observed that over the course of fifty cycles which lasted for 100 minutes, the percentage strain value remained consistent. The phenomenon can be further elucidated using a percentage strain recovery graph. Here, the consistent or increasing trend in the percentage of strain recovery over successive cycles is observed. The consistent trend indicates that the bio-based vitrimer epoxy foam is able to recover its original shape and dimensions after each loading-unloading cycle, demonstrating elastic behaviour and ability to withstand repeated deformation without permanent damage.
Table 2: Mechanical data for the bio-based vitrimer epoxy foam behaviour under cyclic load
Loading cycles Time(s) Compressive strength Strain
1st loading 24 7 15
1st unloading 24 0 0.44
2nd loading 24 7 15
2nd unloading 24 0 0.7
9th loading 24 7 15
9th unloading 24 0 1.45
10th loading 24 7 15
10th unloading 24 0 1.45
FIG. 8 is diagram illustrating behaviour of the bio-based vitrimer epoxy foam behaviour under cyclic load, in accordance with the present disclosure. FIG. 8 is described in conjunction with FIGs. 1, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, 6A, 6B, 7A, 7B, 7C and 7D. With reference to the FIG. 8, there is shown a graph 800 showing relationship between the compressive strength and the strain %. The strain (%) is expressed in an abscissa axis. The compressive strength is expressed in kilopascal in an ordinate axis.
FIG. 8 is obtained on the basis of the data given in the Table 2. FIG. 8 comprises a graph 800. The graph 800 includes a loading curve 802A and an unloading curve 804A. In similar manner number of loading and unloading curves may be obtained to obtain the hysteresis curve.
The graphical representation 800 illustrates a hysteresis curve that depicts the loading cycles and the unloading cycles of the bio-based vitrimer epoxy foam. The loading cycles and the unloading cycles were conducted under a constant loading rate of 5N/min for 10 cycles, with each cycle lasting for 24 seconds. During the cyclic loading, the bio-based vitrimer epoxy foam experiences instantaneous loading to a deformation of 15% strain at a compressive strength of 7 kPa. Upon unloading at the same rate, the bio-based vitrimer epoxy foam exhibits elastic behaviour, returning to its original shape with 0% strain. The behaviour indicates that the bio-based vitrimer epoxy foam has good resilience and may recover its shape after being compressed, which is a desirable characteristic for applications requiring repeated loading and unloading cycles without permanent deformation. The hysteresis observed in the graphical representation 800 suggests some energy dissipation during the loading cycles and the unloading cycles, which is typical for viscoelastic materials like polymers.
Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.
, Claims:CLAIMS
We claim:
1. A method (100) for synthesizing a bio-based vitrimer epoxy foam (402), the method comprising:
epoxidizing a fatty acid (202) by reacting the fatty acid (202) with a cation exchange resin catalyst and hydrogen peroxide to obtain an epoxidized fatty acid (206);
synthesizing a hardener (302) comprising an amino-alkyl derivative by a condensation reaction of enolic molecules, formaldehyde, and an amine containing a disulfide bond, wherein the amino-alkyl derivative comprises a benzoxazine-disulfide moiety and
curing the epoxidized fatty acid (206) with the synthesized hardener (302) to synthesize the bio-based vitrimer epoxy foam (402) comprising a crosslinked epoxy vitrimer network having polybenzoxazine-disulfide moiety, wherein the dynamic covalent disulfide bonds undergo exchange reactions at elevated temperatures to provide self-healing and reprocessability properties to the bio-based vitrimer epoxy foam (402).
2. The method (100) as claimed in claim 1, wherein the epoxidizing of the fatty acid (202) comprises:
mixing the fatty acid (202), the cation exchange resin catalyst, a glacial acetic acid, toluene to obtain a fatty acid mixture;
heating the fatty acid mixture at a temperature ranging from 50 to 65 degrees Celsius;
adding hydrogen peroxide dropwise to the fatty acid mixture for 7 to 9 hours to form a reaction mixture; and
neutralizing and washing the reaction mixture with a 2M sodium carbonate aqueous solution.
3. The method (100) as claimed in claim 1, wherein the cation exchange resin catalyst is a Seralite SRC 120.
4. The method (100) as claimed in claim 1, wherein the synthesizing of the hardener (302) comprises:
mixing the enolic molecules, formaldehyde, the amine containing the disulfide bond, and a solvent mixture of acetone and water in equal parts to obtain a pre-hardener reaction mixture;
heating the pre-hardener reaction mixture for 5 to 24 hours at a temperature ranging from 70 to 100 degree Celsius to obtain a final reaction mixture;
washing the final reaction mixture with distilled water and a 1N sodium hydroxide aqueous solution; and
drying the washed final reaction mixture to obtain the hardener (302) comprising the benzoxazine-disulfide moiety. wherein the dynamic covalent disulfide bonds present in the benzoxazine-disulfide moiety of the hardener (302) act as a single Covalent Adaptable Network.
5. The method (100) as claimed in claim 4, wherein the hardener (302) is a benzoxazine-disulfide compound formed by a Mannich condensation reaction of the enolic molecules, formaldehyde, and the amine containing the disulfide bond.
6. The method (100) as claimed in claim 1, wherein the curing of the epoxidized fatty acid (206) with the synthesized hardener (302) comprises:
mixing the epoxidized fatty acid (206) and the hardener (302) to obtain a mixture; and
subjecting the mixture to a stimulus to initiate a competitive nucleophilic attack by the amine and hydroxyl groups of the hardener (302) on epoxide groups of the epoxidized fatty acid (206) to form the bio-based vitrimer epoxy foam (402) comprising the crosslinked epoxy vitrimer network.
7. The method (100) as claimed in claim 6, wherein the competitive nucleophilic attack occurs via an SN2 mechanism, and wherein the amine and hydroxyl groups of the hardener attack less substituted carbons of the epoxide groups in the epoxidized fatty acid (206).
8. The method (100) as claimed in claim 6, wherein the stimulus is thermal energy, and wherein the self-healing of the synthesized bio-based vitrimer epoxy foam (402) is initiated by heating the synthesized bio-based vitrimer epoxy foam (402) at 120 degrees Celsius to 180 degrees Celsius for a duration of 5 hours to10 hours.
9. The method (100) as claimed in claim 6, wherein the stimulus is ultraviolet (UV) radiation, and wherein the self-healing of the synthesized bio-based vitrimer epoxy foam (402) is initiated by exposing the synthesized bio-based vitrimer epoxy foam (402) to the UV radiation.
10. A bio-based vitrimer epoxy foam (402) composition comprising:
ten parts by weight of an epoxidized castor oil; and
one part by weight of a hardener (302), wherein the hardener (302) comprises a benzoxazine-disulfide moiety having dynamic covalent disulfide bonds, and is a reaction product of enolic molecules, formaldehyde, and an amine containing a disulfide bond, synthesized through a condensation reaction,
wherein the bio-based vitrimer epoxy foam (402) comprises a crosslinked epoxy vitrimer network having the polybenzoxazine-disulfide moiety, and wherein the dynamic covalent disulfide bonds undergo exchange reactions at elevated temperatures to provide self-healing and reprocessability properties to the bio-based vitrimer epoxy foam (402).