Description:FIELD OF INVENTION
[0001] The present disclosure relates to a field of engineering and biomedicine. The present disclosure relates to a composite material. The present disclosure also relates to a method of preparation of a composite material. The composite material of the present disclosure has enhanced mechanical strength, responsive shape memory, and tailored rheological properties, paving the way for innovative use of the material in various industrial and technological sectors.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention or that any publication specifically or implicitly referenced is prior art.
[0003] In the domains of contemporary engineering and biomedicine, the development of novel materials that have enhanced properties and are environmentally sustainable is pivotal. The shape memory materials with biodegradable characteristics are now coming to light as an enticing material as they possess unique ability to endure reversible shape/structural changes in response to external stimuli, in addition to their biocompatibility. These captivating materials have different applications, such as, smart fabrics, biomedical implants, drug delivery systems, etc. [Nagahama et al., Biomacromolecules, 2009, 10(7), 1789–1794]. Traditional Shape memory polymers (SMPs) predominantly have non-biodegradable components, which may harm the environment and limit their applications in the industries where biodegradability is important. The synthesis and fabrication of biodegradable SMPs from renewable materials through sustainable methods has welcomed deep attention in recent years. These materials have a great potential to meet essential social needs and abridge the environmental impact of conventional polymer systems. Furthermore, the introduction of biodegradability into shape memory materials offers novel rooms to manoeuvre ecofriendly technology that could expedite the transformation to an adorning economy [Hartmann et al., Adv. Mater., 2021, 33(19), 2004413].
[0004] The epoxy resins are considered to be vital materials for an extensive variety of industrial applications because of their remarkable corrosion resistance, mechanical strength and adhesive properties. Diglycidyl ether of bisphenol A (DGEBA) is the core epoxy formulation that have been used for a long time. Nowadays, greener alternatives are emerging as a result of increasing environmental awareness and unsustainable nature of petrochemical derived materials [Appl. Mech., 2021, 2(2), 419–430]. Bioepoxies derived from biomass and plant oils are a functional and versatile alternative for traditional epoxies. The lower toxicity and biocompatibility of bioepoxies bring them as potential high-performance materials for a wide range of applications. Bioepoxy resins have the potential to be a key component in facilitating the shift to highly environment-friendly and sustainable economy as long as research and innovation in biomaterials continue to progress [Capretti et al., Polymers (Basel)., 2023, 15(24), 4733].
[0005] Polycaprolactone (PCL) manifest excellent shape memory characteristics along with its biocompatibility, which give rise to a potential material for a wide variety of implementations including biomedicine, robotics, smart fabrics, etc. The semi-crystalline structure and the phase changes occurring reversibly in PCL results in the shape memory capabilities. PCL can regain its original shape after a temporary distortion when subjected to a temperature greater than its glass transition temperature (Tg). The shape memory ability of this material can be flexibly tuned as per the applications via modifying its crystallinity, preparation conditions and molecular weight [Hada et al., Food, Medical, Environ. Appl. Nanomater., 2022, 413–433].
[0006] The PCL/Epoxy compositions have been immensely researched as they hold remarkable shape memory characteristics and outstanding mechanical properties. N. Lorwanishpaisarn et al. [Polym. Test., 2020, 81, 106159] studied shape memory and self-healing properties of epoxy (EP) and PCL combinations with cashew nut shell liquid (CNSL) as a natural curing agent. There was a great enhancement in shape memory response to chemical and thermal stimuli with increasing the concentration of PCL in the EP-CNSL matrix. All specimens exhibited complete form recovery in response to temperature changes, and the time required for recovery decreased as the PCL content increased. When PCL was added, the immersion period required for complete shape recovery in methanol and water were significantly lowered. Furthermore, by heating, the EP-CNSL matrix containing 20 wt% of PCL exhibited remarkable self-healing capability. In another work by I. Razquin et al. [Molecules, 2020, 25(7), 1-16], PCL incorporated epoxy composites were cured using a traditional diamine, 4,4′-diaminodiphenylmethane (DDM) and disulfide-containing diamine, 4,4´- dithioaniline (DSS). The materials’ recyclability and shape memory properties were examined. The mixture was plasticized by the PCL, which enabled the epoxy glass transition to be tailored. Additionally, the original shape can be removed, and a new shape can be created in the DDS cured composites as a result of the disulfide exchange reaction. This approach resulted in the development of permanent shape memory materials that could be reprogrammed.
[0007] The advanced shape memory properties of PCL/Epoxy system are really interesting and intriguing, thus we decided to analyze the effect of PCL in tuning the properties of bio-epoxies. As mentioned above, PCL/Epoxy systems have been extensively studied, the scope of this current research is broadened by the limited works on the effect of PCL on bioepoxy.
[0008] In view of the above, there is a need to develop a novel composite material to overcome the drawbacks of the prior arts.

OBJECTS OF THE INVENTION
[0009] The primary objective of the present disclosure is to provide a composite material.
[0010] Another objective of the present disclosure is to provide a method of preparation of a composite material.
[0011] Still another objective of the present disclosure is to develop advanced materials with superior mechanical properties and shape memory efficiency.
[0012] Yet another objective of the present disclosure is to develop a fully eco-friendly composite system.

SUMMARY OF THE INVENTION
[0013] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in Detailed Description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0014] An aspect of the present disclosure relates to a composite material comprising: a biodegradable resin; a biodegradable polyester; and a biobased curing agent.
[0015] Another aspect of the present disclosure is it relates to a method of preparation of a composite material comprising: a) dispersing 1 to 25 % w/w (in relative to the biodegradable resin) of biodegradable polyester in a biodegradable resin via ultrasonication to obtain a dispersion; b) dissolving the biobased curing agent in the range of 1:1 to 4:1 resin to hardener mix ratio in a solvent to obtain a biobased curing agent solution; c) adding the biobased curing agent solution of step b) in the dispersion of step a) to obtain a mixture; d) removing of free solvent from the mixture of step c) to obtain a solution; and e) pouring the solution in the mould and cured under condition to obtain a composite material.
[0016] Various objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing FIG..s in which numerals represent features.

BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The following drawings form part of the present specification and are included to further illustrate aspects of the present invention. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0018] FIG.. 1 illustrates The FTIR spectrum of a) Tannic acid, PCL and Uncured bioepoxy resin; b) Cured neat BE sample, 3PCL, 5PCL, 7PCL, 10PCL, 15PCL and 20PCL samples.
[0019] FIG.. 2 illustrates The XRD patterns of BE, 3PCL, 5PCL, 7PCL, 10PCL, 15PCL and 20PCL samples.
[0020] FIG.. 3 illustrates the tensile and flexural properties of the developed samples.
[0021] FIG.. 4 illustrates the SEM images of the fracture surfaces of (1(a-c)) neat BE; (2(a-c)) 3PCL; (3(a-c)) 5PCL; (4(a-c)) 20wt% PCL.
[0022] FIG.. 5 illustrates the TGA curves of developed composites.
[0023] FIG.. 6 illustrates the DSC curves of the developed composites.
[0024] FIG.. 7 illustrates viscosity v/s shear rate plot for the developed composites.
[0025] FIG.. 8 illustrates a) the Newtonian modelling of the samples b) The Bingham and Herschel-Bulkley modelling of the 20PCL sample.
[0026] FIG.. 9 illustrates the storage modulus v/s temperature curves of fabricated composites.
[0027] FIG.. 10 illustrates the tan delta v/s temperature curves of developed samples.
[0028] FIG.. 11 illustrates the shape recovery and shape fixity ratios of developed composites.
[0029] FIG.. 12 illustrates the shape memory behaviour of 5PCL sample.
[0030] FIG.. 13 illustrates the optical images showing the self-healing behaviour of a) BE, b) 3PCL, c) 5PCL, d) 7PCL, e) 10PCL, f) 15PCL, g) 20PCL samples.
[0031] FIG.. 14 illustrates the self-healing efficiency v/s heating time plots of the fabricated samples.

DETAILED DESCRIPTION OF THE INVENTION
[0032] The following is a detailed description of the embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0033] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0034] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0035] In some embodiments, numbers have been used for quantifying weights, percentages, ratios, and so forth, to describe and claim certain embodiments of the invention and are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0036] The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0037] Unless the context requires otherwise, throughout the specification which follows, the word “comprise” and variations thereof, such as “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[0038] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0039] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. Furthermore, the ranges defined throughout the specification include the end values as well, i.e., a range of 1 to 10 implies that both 1 and 10 are included in the range. For the avoidance of doubt, the applicant shall be entitled to any equivalents according to applicable law.
[0040] All methods described herein can be performed in a suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0041] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in or deleted from a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified.
[0042] The description that follows and the embodiments described therein are provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0043] It should also be appreciated that the present disclosure can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.
[0044] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0045] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0046] The term “or,” as used herein, is generally employed in its sense, including “and/or” unless the content clearly dictates otherwise.
[0047] Various terms are used herein to the extent a term used is not defined below; it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0048] An embodiment of the present disclosure is to provide a composite material comprising: a biodegradable resin; a biodegradable polyester; and a biobased curing agent.
[0049] In an embodiment, the biodegradable resin is selected from a group consisting of isosorbide based bio-epoxy, polylactic acid (PLA), polyhydroxyalkanoates (PHA), polybutylene succinate (PBS), polycaprolactone (PCL), starch-based resins, and blends thereof. Preferably, the amount of the biodegradable resin is selected isosorbide based bio-epoxy.
[0050] In an embodiment, the amount of the biodegradable resin is taken as per requirement to achieve the desired amount of the composite material. In some embodiment the amount is taken in the range of 10 to 100 g. In an embodiment, the biodegradable resin is taken in 70 g.
[0051] In an embodiment, the biodegradable polyester is selected from a group consisting of polycaprolactone, polyglycolide, polylactic acid and combination thereof. Preferably, the biodegradable polyester is polycaprolactone.
[0052] In an embodiment, the biodegradable polyester is present in the range of 1 to 25 % w/w in relative to the biodegradable resin. Preferably, the biodegradable polyester is present in the range of 3 to 20 % w/w in relative to the biodegradable resin.
[0053] In an embodiment, the biobased curing agent is selected from a group consisting of tannic acid, citric acid, sebacic acid, maleic acid and combination thereof. Preferably, the biobased curing agent is tannic acid.
[0054] In an embodiment, the biobased curing agent is present in the range of 1:1 to 4:1 resin to hardener mix ratio. Preferably, the biobased curing agent is present in 1:1, 2:1, 4:1 resin to hardener mix ratio. More preferably, the biobased curing agent is present in 2:1 resin to hardener mix ratio.
[0055] Another embodiment of the present disclosure is to provide a method of preparation of a composite material comprising: a) dispersing 1 to 25 % w/w (in relative to the biodegradable resin) of biodegradable polyester in a biodegradable resin via ultrasonication to obtain a dispersion; b) dissolving the biobased curing agent in the range of 1:1 to 4:1 resin to hardener mix ratio in a solvent to obtain a biobased curing agent solution; c) adding the biobased curing agent solution of step b) in the dispersion of step a) to obtain a mixture; d) removing of free solvent from the mixture of step c) to obtain a solution; and e) pouring the solution in the mould and cured under condition to obtain a composite material.
[0056] In an embodiment, the solvent is selected from a group consisting of ethanol, acetone, isopropanol, methanol, ethyl acetate, water, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and combinations thereof. Preferably, the solvent is ethanol. In an embodiment, the condition in step e) includes temperature in the range of 140 to 160 °C for a period in the range of 10 to 20 hrs. Preferably, the condition in step e) includes temperature of 150 °C for a period of 15 hrs.
[0057] The present disclosure explores the fabrication and characterization of bioepoxy/PCL combination cured with a biomaterial tannic acid. The multifunctional properties of this trio system are not reported yet. The present disclosure reveals the magnificent shape memory behaviour shown by the trio composite in response to both thermal and chemical stimuli. The dynamic mechanical and thermal analysis were employed to understand the effect of PCL concentration and tannic acid curing, which further reveals the strong cross linking and dynamic networks formed in this system. This unique composite material exhibit shape memory in response to heat as well as solvents including methanol and acetone. Apart from this, the fabricated composites have remarkable self-healing efficiency because of the PCL’s effect and unique dynamic bond exchange mechanism, allowing them to recuperate from physical damage. This study emphasizes the potential of these advanced materials for various applications that demand adaptive and long-lasting performance, including biomedical devices, smart textiles, etc.
[0058] The present disclosure particularly chosen tannic acid as bio-based curing agent and a procured biobased epoxy resin. To enhance the biocharacter, polycaprolactone as a third component has been incorporated. This formulation is not reported yet. Moreover, the chemo-responsive and thermal shape memory of these materials have studied which can be considered as the foremost novelty of this work. Thus, the essential feature of the present invention lies in the use of tannic acid, which not only enhances the sustainability of the material but also significantly improves its mechanical performance, responsiveness, and healing properties, making it ideal for advanced smart material applications.
[0059] In accordance with an embodiment, an isosorbide based bioepoxy resin was used. Tannic acid (CAS number: 1401-55-4) and Polycaprolactone (average Mn 80,000) were purchased from Sigma Aldrich.
[0060] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person skilled in the art.

EXAMPLES
[0061] The present invention is further explained in the form of the following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.
Example 1:
(A) Preparation of composite material
[0062] Bioepoxy composites incorporated with 3 wt%, 5 wt%, 7 wt%, 10 wt%, 15 wt% and 20 wt% of PCL were developed by dispersing the nanofiller in the epoxy matrix via ultrasonication. The neat sample is designated as BE while the 3 wt%, 5 wt%, 7 wt%, 10 wt%, 15 wt% and 20 wt% of PCL incorporated samples were named as 3PCL, 5PCL, 7PCL, 10PCL, 15PCL, 20PCL respectively. The amount of tannic acid to be taken was calculated in accordance with the ratio of 0.5: 1 (raw hydroxyl: epoxide groups). The tannic acid was first dissolved in ethanol and added to the BE/PCL dispersions. The free solvent was removed by employing a vacuum pump. The solution was poured into the mould and cured at 150°C for 15 hours.
(B) Characterization techniques
(i) IR analysis of Bioepoxy/PCL composites
[0063] The infrared (IR) spectrum of tannic acid exhibits distinct peaks at 3552 cm⁻¹ for O-H stretching, 1765 cm⁻¹ for C=O stretching, 1615 cm⁻¹ for aromatic C=C stretching, 1457 cm⁻¹ for C-H bending, 1192 cm⁻¹ for C-O stretching, and 761 cm⁻¹ for C-H bending. The IR spectrum of PCL possess peaks at 2944 and 2869 cm⁻¹ which corresponds to the C-H stretching. In addition, there is a peak at 1722 cm⁻¹ related to C=O stretching. The spectrum also exhibits another peak at 1234 cm⁻¹ and 1166 cm⁻¹ respective to C-O-C and C-O stretching. The uncured bioepoxy resin exhibits prominent peaks at 3050 cm⁻¹ for aromatic C-H stretching, 2966 cm⁻¹, 2927 cm⁻¹, and 2869 cm⁻¹ indicating aliphatic C-H stretching, 1602 cm⁻¹ for aromatic C=C stretching, 1508 cm⁻¹ for C=C stretching, 1462 cm⁻¹ (C-H bending), 1030 cm⁻¹ indicating C-O stretching, 910 cm⁻¹ for epoxy ring and 829 cm⁻¹ for C-C bond stretching (FIG.. 1a).
[0064] The IR spectra show consistent peaks for cured bioepoxy systems. These peaks include 3778 cm⁻¹ and 3662 cm⁻¹ for O-H stretching, 2923 cm⁻¹ and 2858 cm⁻¹ for C-H stretching, 1724 cm⁻¹ for C=O stretching, 1607 cm⁻¹ for aromatic C=C stretching, 1504 cm⁻¹ for C=C stretching, 1243 cm⁻1 for C-O-C stretching, 1175 and 1034 cm⁻1 for C-O stretching, and 825 and 757 cm⁻1 for C-H bending. The peak corresponding to the epoxide group is absent after the curing process which confirms the ring opening reaction. The peaks remain consistent regardless of the content of PCL in the systems. The existence of these peaks in the hardened systems signifies effective cross-linking and the establishment of a stable network structure (FIG.. 1b).
[0065] The presence of peaks at 1724 cm⁻1 in the cured systems suggests the establishment of ester bonds. This observation is significant because it indicates the significant role of tannic acid in the curing process, as a cross-linking agent. Tannic acid, due to its many hydroxyl groups, has the ability to chemically interact with the epoxy groups of the resin resulting in the creation of ester bonds. This process is crucial for the remarkable characteristics of the cured bioepoxy composites. Furthermore, the existence of ester peaks in all cured systems consistently indicates the possibility of a transesterification reaction. Transesterification enhances the dynamic aspect of the polymer network, allowing the material to undergo stress relaxation and reconFIG.uration, which are characteristics of vitrimeric like materials.
(ii) XRD of Bioepoxy/PCL composites
[0066] The XRD patterns of composites shown in FIG.. 2 with different amounts of PCL- incorporated bioepoxy elucidate the quality of dispersion and miscibility between epoxy matrix and PCL. Normally, PCL exhibits notable crystallinity, thus have peaks at 21.9° and 24.2° corresponding to the (110) and (200) planes of the orthorhombic crystal structure, respectively. If the composite has preserved the crystalline structure of PCL, it is possible to recognize the peaks of PCL in the composite’s XRD pattern. However, the intensities of these peaks may be lowered due to the presence of the amorphous epoxy matrix. Typically, the absence of distinct peaks of PCL in the XRD patterns of composites suggests that the crystallinity of PCL polymer is completely interrupted by the epoxy matrix. In the FIG.ure., a couple peaks observed around 18° and 45°, indicates the scattering of the cured epoxy network and the revelation of its amorphous nature. The absence of new peaks in XRD pattern of the composites confirms that there is no phase separation between the polymers. Thus, in all the composite samples, PCL is exhibiting good dispersion and miscibility with epoxy matrix.
(iii) Mechanical characteristics of Bioepoxy/PCL composites
[0067] The flexural strength refers to the greatest extent of stress that a material can endure before it fails during a bending test. An elevation in flexural strength signifies enhanced durability and robustness against bending. Flexural properties of PCL consolidated bioepoxy composites are demonstrated in FIG.. 3. The flexural strength of fabricated composites shows a notable increase as the PCL concentration rises up to 5 wt%. At this point, it reaches a maximum value of 66.97 MPa. The enhanced performance can be due to the increased toughness and efficient reinforcement offered by the PCL. Nevertheless, when the PCL content crosses the optimum, several adverse consequences including inadequate interfacial bonding, and excessive plasticization, begin to predominate. The combination of these factors leads to a significant decrease in the flexural strength of the composite, reaching a minimum value of 0.55 MPa at a PCL weight percentage of 20. Hence, the diminution in flexural strength observed at elevated PCL concentrations can be ascribed to the unfavourable impact of excessive PCL on the interfacial bonding, microstructure, and mechanical characteristics of the composite. Similarly, the tensile strength of the developed samples shows an increasing trend with increasing PCL content up to 5 wt% of PCL. When the PCL content reaches 5 wt%, the tensile strength reaches a value of 43.89 MPa. But, when the PCL content further increases, the tensile strength decreases. At 5 wt% PCL, the phase morphology is balanced, with strong interfacial bonding between the PCL and the epoxy. This leads to efficient load transfer and improves tensile attributes for the composite. The tensile characteristics of the developed samples are shown below (FIG.. 3).
[0068] The degree of PCL dispersion within the resin matrix has a substantial impact on the enhancement of the cured epoxy’s mechanical properties. FIG.. 4 depicts the SEM images of fractured surfaces of neat, 3wt%, 5wt%, 20wt% PCL incorporated bioepoxy samples, respectively. The FIG.. 4(1(a-c)-3(a-c)) illustrates that PCL is distributed uniformly throughout the BE matrix. When there are no cavities, it signifies that the PCL and epoxy matrix have bonded properly. As estimated by the observations, it is evident from FIG.. 4(4(a-c)) that there is a small volume of PCL that is not chemically bonded to the matrix. As a consequence, the mechanical strength experiences an initial increase up to 5 wt% PCL, followed by a subsequent decrease as the weight percentage of PCL increases further, owing to the excessive PCL.
(iv)Thermal Properties of PCL/BE composites
[0069] The thermogravimetric analysis (TGA) results of PCL-incorporated bioepoxy composites are depicted in the FIG.. 5. Examination of the TGA thermograms reveals that the presence of PCL has a negative impact on the thermal stability of epoxy. The neat sample and the composite samples start to degrade around 240°C. The negative influence of PCL on thermal stability of fabricated composites can be attributed to the inferior thermal stability of PCL compared to the epoxy matrix. Furthermore, inadequate interfacial bonding promotes thermal deterioration of the composites. The plasticizing effect of PCL reduces glass transition temperature (Tg) of the developed materials, while increasing polymer chain mobility, hence accelerating thermal breakdown. The pristine, 3PCL, 5PCL, 7PCL, 10PCL, 15PCL and 20PCL samples show a residual weight percentage of 14.63%, 13.04%, 8.09%, 12.07%, 11.64%, 12.24% and 12.07%, respectively. A lower residual weight at higher temperatures subsequent to the degradation process would indicate the diminished char yield in the PCL/epoxy composites in comparison to the pristine epoxy samples. The char-forming capability of PCL is inferior to that of epoxy resins. In the course of thermal decomposition, epoxy resins commonly generate a crosslinked char structure which serves as a protective barrier against additional degradation of the material underneath. However, the formation of a solid char structure is hindered by PCL, resulting in a diminished char yield in the composite.
[0070] Differential Scanning Calorimetry (DSC) graphs of bioepoxy composites are portrayed in FIG.. 6. The glass transition temperature (Tg) of neat, 3, 5, 7, 10, 15 and 20 wt% PCL/BE composites are obtained as 54°C, 72.2 °C, 65°C, 61.9 °C, 50°C, 50°C and 47.6°C respectively. When the PCL content is increased to 3 wt%, the composites exhibit a higher Tg value compared to the neat epoxy sample. This indicates that the interaction between PCL and the bioepoxy may have increased the composite’s rigidity or cross-linking up to this concentration. When the PCL concentration exceeds 3 weight percent, the Tg begins to decrease. This may be the result of the plasticizing effect of PCL, which decreases Tg by increasing the flexibility and mobility of the polymer chains. Additionally, the observed reduction in Tg at elevated PCL concentrations may suggest that PCL disrupts the epoxy network, resulting in a composite with enhanced flexibility. Interestingly similar to vitrimers another inflection is observed around the temperature range 202-213°C, which can be attributed to the topology freezing transition temperature (Tv). Hence this confirms the vitrimer-like characteristics of the system PCL/bio- epoxy system. This temperature remains relatively consistent across a variety of PCL concentrations, but it exhibits minor increases at higher loadings, particularly at 15 and 20 wt%, where it is recorded at 213°C. This implies that the stability of the composite network may be marginally improved by a higher PCL content. The effect of PCL in altering the Tg and Tv of bioepoxy composites is underscored by the observed thermal behaviour, which maintains a balance between rigidity at lower concentrations and flexibility at higher concentrations.
(v) Rheological Properties of PCL/BE composites
[0071] The rheological behaviour of bioepoxy and its composites with varying concentrations of PCL exhibits distinct patterns in viscosity v/s shear rate graph (FIG.. 7). The viscosity of bioepoxy and the composites containing 3, 5, and 7 PCL remains relatively constant regardless of varying shear rates, suggesting a Newtonian-like behaviour. This implies that the PCL is well-dispersed in the epoxy matrix at these lower concentrations, without substantially affecting the viscosity of the fluid. Conversely, the sample containing 10 PCL exhibits shear-thinning behaviour until a shear rate of 1 s-1, after which the viscosity remains unchanged. This initial decrease in viscosity can be ascribed to the orientation of PCL chains in the direction of flow, which reduces internal resistance to flow. The system exhibits a behaviour that is comparable to a Newtonian fluid with a constant viscosity once the chains are completely oriented. Similarly, the 15PCL incorporated sample exhibits shear-thinning up to a shear rate of 6.81 s-1, followed by a constant viscosity, indicating a threshold shear rate at which the internal structure stabilizes under flow. The viscosity of the composite continuously decreases with an increasing shear rate at the highest concentration of 20PCL, without reaching an equilibrium level within the observed range. This persistent shear-thinning behaviour indicates that the composite is undergoing significant structural changes, as the PCL induces deeper network disruptions and alignment under shear. The decrease in viscosity is indicative of a more complex internal transformation process. Thus, higher PCL loadings can impact the shear- dependent flow properties of the composites. These observations emphasize the critical role of PCL concentration in modifying the rheological characteristics of bioepoxy composites. Lower concentrations maintain Newtonian-like behaviour, while higher concentrations introduce shear-thinning effects as a result of polymer chain dynamics under shear.
Modelling of Rheological Properties
[0072] The rheological characteristics of bioepoxy composites have been methodically modelled to investigate their behaviour under varying shear rates, which has been obtained by introducing varying concentrations of polycaprolactone (PCL) (FIG.. 8). All the composites closely followed the Newtonian model, 20PCL samples, as demonstrated by their high adjusted R² values.
[0073] Contrarily, the 20PCL samples exhibited non-Newtonian behaviour, which were confirmed by the application of more complex rheological models. The Bingham and Herschel-Bulkley models were considered for this sample. The Herschel-Bulkley model demonstrated a superior fit, as evidenced by the higher adjusted R² values in comparison to the Bingham model. This suggests that the 20PCL sample validate shear-thinning behaviour, which is more accurately denoted by the Herschel-Bulkley model.
[0074] These results emphasize the substantial influence of PCL concentration on the rheological characteristics of the composites. Newtonian flow characteristics are maintained at lower concentrations, whereas complex flow behaviours that are consistent with the Herschel- Bulkley model are introduced at higher concentrations. This behaviour is indicative of the complex interplay between polymer chains under shear. These observations are quantitatively supported by the adjusted R² values, which are detailed in the table 1, which ensures the reliability of the rheological models that have been used.

Table 1: Adjusted R2 values from the model fitting.
Models Adjusted R2 values
BE 3PCL 5PCL 7PCL 10PCL 15PCL 20PCL
Newtonian model 0.9997 0.9996 0.9961 0.9936 0.9979 0.9982 0.8920
Bingham model - - - - - - 0.8920
Herschel model - - - - - - 0.9992

(vi) Dynamic Mechanical Analysis of PCL/BE composites
[0075] The storage modulus of the composite is considerably improved by the incorporation of PCL into the bioepoxy matrix (FIG.. 9). This effect is particularly prominent at 5 wt% of PCL. The synergistic interaction between the rigid epoxy network and the flexible PCL chains is responsible for a remarkable increase of 322% in storage modulus for 5 wt% PCL incorporated BE samples with respect to neat BE samples. PCL effectively reinforces the epoxy at this optimal concentration, resulting in a robust composite structure that is better able to withstand deformation under stress. But the storage modulus begins to decrease as the PCL content exceeds 5 wt%. This decrease can be attributed to the disruption in the uniformity of epoxy matrix by the excessive incorporation of PCL, resulting in the subsequent decrease in the composite’s overall structural strength. Consequently, the mechanical performance of the composite material is improved by a moderate addition of PCL; however, the structural consistency and efficiency of the composite material may be compromised by an excessive amount of PCL.
[0076] A comprehensive explanation of the viscoelastic properties of PCL/BE composites is provided by the tan delta versus temperature curves (FIG.. 10) derived from dynamic mechanical analysis (DMA). The Tg gradually increases as the PCL concentration increases, reaching a maximum of 7 wt%. This initial increase in Tg indicates that the PCL effectively enhances the intermolecular interactions within the bioepoxy matrix up to this concentration, resulting in a more rigid composite structure. Nevertheless, a decrease in Tg is observed when PCL exceeds 7 wt%. This trend suggests that the polymer begins to function as a plasticizer at higher PCL loadings, resulting in a decrease in the Tg and an increase in the composite’s flexibility. In addition, the DMA analysis shows an inflection at elevated temperatures, which is in accordance with Tv value obtained from the DSC. This inflection indicates the point at which the material’s network topology becomes dynamic, enabling the reconFIG.uration of polymer chains and stress relaxation. Thus, DMA also supports the vitrimer-like characteristics of the PCL/Epoxy system.
(vii) Shape memory properties of PCL/BE composites
(a) Thermo-responsive shape memory effect
[0077] All the developed composites are exhibiting magnificent shape memory characteristics. The shape fixity as well as the shape recovery ratios were greater than 95% in all cases except 20 PCL (FIG.. 11). In case of 20PCL, as the flexibility of the sample got enhanced, thus the shape fixity ratio reduced to 88%. The distinctive thermomechanical properties of PCL are responsible for this improvement. PCL, a semi-crystalline polymer with a comparatively low melting point, contributes to the composite matrix’ flexibility. The material can be shaped by realigning the polymer chains when the composite is deformed at a temperature elevated above the glass transition temperature (Tg). The deformed shape is secured by the crystallized PCL domains, which function as physical cross-links upon cooling. The polymer chains can return to their original conFIG.uration when the crystallized domains melt during reheating, thereby restoring the composite to its original shape. This reversible transformation between the crystalline and amorphous phases of PCL is essential for improved shape memory behaviour. The shape memory behaviour of 5PCL composites is illustrated in FIG.. 12. Furthermore, the shape memory characteristics of the bioepoxy composites are substantially improved by tannic acid. Tannic acid functions as a multifunctional curing agent that introduces dynamic ester bonds within the polymer network and facilitates cross-linking through its numerous hydroxyl groups. This dual functionality is essential for the behaviour of shape memory. The mechanical and thermal stability of the composites is enhanced by the cross- linking induced by tannic acid, which guarantees their ability to retain and regain their original shapes. Furthermore, the material is capable of stress relaxation and reconFIG.uration due to the dynamic character of the ester bonds, which are generated through transesterification reactions. This flexibility is necessary for the composites to deform under stress and revert to their original shape upon the elimination of the stress and the application of heat. Consequently, tannic acid improves the rigidity necessary for preserving shape fixity and the flexibility necessary for shape recovery.
[0078] Thus, the remarkable shape memory characteristics of the PCL-incorporated bioepoxy composites originate from the collaborative interplay between the inflexible bioepoxy matrix and the adaptable PCL phase, strengthened by the dynamic reconFIG.uration abilities by tannic acid unveiled through DMA and DSC analyses. This combination enables the composites to efficiently maintain and restore their shape, rendering them appropriate for diverse sophisticated uses.
(b) Chemo-responsive shape memory effect
[0079] Chemo-responsive shape memory materials have attracted substantial interest because of the ability to alter their shape in accordance with chemical stimulus. The chemo-responsive shape memory PCL/BE composite material is a promising candidate for applications in a wide range of disciplines due to its ability to combine the distinctive characteristics of PCL and bioepoxy resin. The chemo-responsive shape memory behaviour of PCL/BE is analyzed in both methanol and acetone.
[0080] In methanol, 20PCL incorporated BE samples have shown a very fast chemo responsive shape memory behaviour. The samples recovered to original shape by 30 seconds with a recovery ratio of 99%. 15PCL also regained its permanent shape, with a longer time of recovery of 480 seconds. 10PCL and 7PCL are also showing chemo responsive behaviour but are not as much effective as 15PCL and 20PCL samples. 10PCL and 7PCL have shown a shape recovery ratio of 94% and 90% respectively by 1 hour. Pristine BE, 3 PCL and 5 PCL samples did not show any chemo responsiveness towards methanol even after 5 hours of observation.
[0081] Chemo responsive shape memory behaviour of fabricated samples towards acetone was also analyzed. All composite samples were responsive to acetone. The 20PCL sample regained their permanent shape within 62 seconds. 3PCL, 5PCL, 7PCL, 10PCL and15PCL came back to their original shape with recovery ratios of 51%, 85%, 89%, 91% and 95%, respectively within 2 hrs. The pristine sample exhibited only a slight response to acetone. Even after 2 hours of observation, the BE sample recovered only 22% and there were no further changes after 24 hours.
[0082] The chemo responsive shape memory behaviour of the PCL-incorporated bioepoxy composites in response to methanol and acetone can be attributed to the interaction of these solvents with the polymer network, particularly the dynamic ester bonds that are formed during the curing process with tannic acid. Methanol and acetone are polar solvents that have the ability to penetrate the polymer matrix, resulting in plasticization and a reduction in the intermolecular forces within the network. The cross-linked network is disrupted by this solvent interaction, which momentarily increases the chain mobility. Subsequently, the polymer chains can reconFIG.ure. and relax, allowing the composite to revert to its original form.
(viii) Self-healing ability
[0083] The FIG.. 13 illustrates the self-healing characteristics of PCL-incorporated BE. At 100 degrees, the damaged region was compelled to fill the void. As shown in FIG.. 14, the heating duration influences the self-healing efficacy of PCL/BE composites. The relationship between time and self-healing efficiency is evidently positive. A self-healing efficiency of 41.4% was exhibited by a pristine BE sample following a 24-hour healing period. Simultaneously, the self- healing efficiency increased dramatically to 94.71% when 5 wt% PCL was incorporated into the BE matrix. The self-healing properties of epoxy/PCL combination were achieved through two distinct processes: (i) the crack surface was closed by the expulsion of strain energy in the plastic zone of SMP, and (ii) the damaged region was filled with PCL through its melting and subsequent flow, which mechanically interconnected with the surrounding matrix. As a result of being heated above Tg, the chain segments were rearranged to occupy the crack area and activated to release strain energy. The results indicated that samples containing 5 wt% PCL subjected to a 24-hour thermal treatment exhibited remarkable self-healing capabilities. Furthermore, by using tannic acid as a curing agent, a dynamic network can be formed within the polymer matrix, allowing it to react to external stimuli like temperature or pH changes. This network makes the material to repair itself by re-establishing fractured bonds at the damaged locations. In addition, tannic acid has the ability to enhance the durability and mechanical strength of the material, thereby enhancing its entire self-healing effectiveness. Self- healing capability was observed to be diminished in samples consolidated with a greater PCL content. Higher concentrations of PCL may result in decreased thermal stability, compromised mechanical properties, and enhanced viscosity. These adverse effects can detrimentally affect the material’s capacity to self-heal efficiently. When PCL is present in excess, the material’s mechanical integrity may be compromised, rendering it more vulnerable to breakage and diminishing the efficacy of its self-healing mechanism.

ADVANTAGES OF THE INVENTION
[0084] The bioepoxy resin, along with bio-based tannic acid and PCL provides a fully eco-friendly composite system.
[0085] The composite material of the present disclosure shows improvement in mechanical properties and shape memory efficiency. With the addition of 5 wt% PCL, the flexural strength of the composite increased by an impressive 520.47%. This result demonstrates the excellent synergy between PCL and the epoxy matrix.
[0086] The composite material of the present disclosure demonstrated remarkable chemo responsive shape memory properties when exposed to methanol and acetone, expanding their range of potential uses. Most of the samples exhibited Newtonian behaviour in the rheological analysis and modelling. However, the 20 wt% PCL composites stood out as it adhered to the Herschel-Bulkley model, suggesting the presence of complex flow dynamics. The shape memory, self-healing and chemo-responsive characteristics and the double inflection observed in DSC and DMA confirm the vitrimer-like characteristics of the PCL/Tannic acid system.
[0087] The composite material of the present disclosure also demonstrated outstanding self-healing capabilities, with the 5 wt% PCL sample attaining an impressive self-healability rate of 94.71%. Developing composites with tuned chemo-responsive behaviour for environmental or industrial applications shows great potential.
 
, Claims:1. A composite material comprising:
a biodegradable resin;
a biodegradable polyester; and
a biobased curing agent.
2. The composite material as claimed in claim 1, wherein the biodegradable resin is selected from a group consisting of isosorbide based bio-epoxy, polylactic acid (PLA), polyhydroxyalkanoates (PHA), polybutylene succinate (PBS), polycaprolactone (PCL), starch-based resins, and blends thereof.
3. The composite material as claimed in claim 1, wherein the biodegradable polyester is selected from a group consisting of polycaprolactone, polyglycolide, polylactic acid and combination thereof.
4. The composite material as claimed in claim 1, wherein the biodegradable polyester is present in the range of 1 to 25 % w/w in relative to the biodegradable resin.
5. The composite material as claimed in claim 1, wherein the biobased curing agent is selected from a group consisting of tannic acid, citric acid, sebacic acid, maleic acid and combination thereof.
6. The composite material as claimed in claim 1, wherein the biobased curing agent is present in the range of 1:1 to 4:1 resin to hardener mix ratio.
7. A method of preparation of a composite material, comprising:
a) dispersing 1 to 25 % w/w (in relative to the biodegradable resin) of biodegradable polyester in a biodegradable resin via ultrasonication to obtain a dispersion;
b) dissolving the biobased curing agent in the range of 1:1 to 4:1 resin to hardener mix ratio in a solvent to obtain a biobased curing agent solution;
c) adding the biobased curing agent solution of step b) in the dispersion of step a) to obtain a mixture;
d) removing of free solvent from the mixture of step c) to obtain a solution; and
e) pouring the solution in the mould and cured under condition to obtain a composite material.
8. The method as claimed in claim 8, wherein the solvent is selected from a group consisting of ethanol, acetone, isopropanol, methanol, ethyl acetate, water, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethylformamide (DMF) and combinations thereof.
9. The method as claimed in claim 8, wherein the condition in step e) includes temperature in the range of 140 to 160 °C for a period in the range of 10 to 20 hrs.