Description:FIELD OF THE INVENTION
[0001] The present invention relates to a hybrid nanocomposite filler material as reinforcing agent for epoxy composite. Specifically, the present invention relates to a hybrid nanocomposite filler comprising poly(styrene-co-methylacrylate) copolymer and Ag-rGO (silver nanoparticle decorated reduced graphene oxide) nanocomposite (represented as Ag-rGO/P(S-co-MA)), a composite polymer comprising the same. The present invention also relates to photocatalytic methods of preparations thereof and uses thereof.

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] Epoxy-based nanocomposites are a subclass of polymer composites that hold a prominent position in the composite family as a result of their unique properties. Epoxy based nanocomposites find application in diverse fields that include aerospace, automotive industries, as protective coatings (anti-corrosive), furniture, antimicrobial coatings or materials and for biomedical applications.
[0004] One of the biggest downsides of epoxy materials is its brittle nature i.e they easily crack, however addition of various fillers to produce epoxy nanocomposites improves the properties and enable them to withstand the mechanical stress. Nanomaterials, fibres, polymers, particulate matter etc. are generally used for enhancing the toughness of epoxy. The inorganic nanoparticles or carbon-based nano materials like Carbon nano tube (CNT), graphene(GN), graphene oxide (GO), graphene nanoplatelets (GNP) etc. are used as reinforcing fillers with epoxy, the resulting nanocomposites provide good chemical and physical/mechanical properties making them very versatile alternative to traditional structural materials.
[0005] Sir Andre Geim and Konstantin Novoselov through their experimental work produced graphene (2004) and showcased the advantageous properties of the material that eventually also became the Nobel Prize winning contribution in Physics in the year 2010. Since then, there has been a tremendous increase in the scientific publication involving graphene and now we see a rapid increase in the publications with epoxy/graphene-based nanocomposites having diverse and important applications, including the studies involved in our group. They show good strength, higher than common structural metals, but at the same time are lighter than metals. Both graphene and graphene oxide reinforced epoxy have been thoroughly investigated by numerous research groups because of the excellent mechanical, thermal and electrical features exhibited by the resulting epoxy/graphene and epoxy/graphene oxide nano composite material. Graphene oxide is very compatible to epoxy and thus enhances the toughness to a great extent.
[0006] Mohan Raj Krishnan et al. (Journal of Polymeric Materials and Polymeric Biomaterials, 1–12) discloses about (polystyrene-co-polymethylmethacrylate/silver/reduced graphene oxide)-(nano-hydroxyapatite) ((PS-PMMA/Ag/RGO)-(nHA)) nanocomposites as potential bone cement. However, the process adopted is a longer process and requires more time to clear the unreacted components from the system.
[0007] Xinchuan Fan et al. (Coatings 2019, 9(10), 666) discloses the preparation of reduced graphene oxide–epoxy grafted poly(styrene-co-acrylate) composites (GESA) by anchoring different amount of epoxy modified poly(styrene-co-acrylate) (EPSA) onto reduced graphene oxide (rGO) sheets through π–π electrostatic attraction and studied corrosion rates. However, it does not disclose the use of any photo polymerisation reaction to create a hybrid system.
[0008] Saadman Sakib Rahman et al. (Materials Today Communications, Volume 25, December 2020, 101633) discloses the preparation of graphene oxide/poly(styrene-co-methyl methacrylate) nanocomposite using radical polymerisation using AIBN as catalyst in presence of graphene oxide and reported the effect of GO on the microstructural, mechanical, and thermal behaviour of the optimized copolymer.
[0009] To strengthen epoxy composites, metal or metallic oxide nanoparticles were typically utilised. Because of their strong electrical and thermal conductivities and oxidation resistant behaviour, Ag nanoparticles (Ag NPs) are one of the most common metal nanoparticles as a filler for epoxy composite. Among the various epoxy metal nanocomposites, epoxy silver nanocomposite has captured much of research attention. The use of hybrid fillers is one of the proven methods to significantly increase the toughness of epoxies owing to the synergistic effect of hybrid fillers. So, the effect of graphene-based hybrid fillers is considered as highly interesting choice of study.
[0010] Accordingly, the present invention provides a hybrid nanocomposite filler system, an epoxy resin composite material comprising the same and photocatalytic methods of preparation thereof.
[0011] The present invention satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.

OBJECTS OF THE INVENTION
[0012] Objects of the present invention are to provide a hybrid nanocomposite filler system.
[0013] An object of the present invention is to provide a method of preparing the hybrid nanocomposite filler system.
[0014] An object of the present invention is to provide a epoxy composite reinforced with the hybrid nanocomposite filler.
[0015] Another object of the present invention is to provide a method of preparing the epoxy composite reinforced with the hybrid nanocomposite filler.
[0016] Yet another object of the present invention is to provide a finished product produced from the epoxy composite reinforced with the hybrid nanocomposite filler.

SUMMARY OF THE INVENTION
[0017] This summary is provided to introduce a selection of concepts in a simplified form that is further described below in the 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.
[0018] Aspects of the present invention relate to a hybrid nanocomposite for epoxy composite. Specifically, the present invention relates to a hybrid nanocomposite filler comprising poly(styrene-co-methylacrylate) copolymer and Ag-rGO (silver nanoparticle decorated reduced graphene oxide) nanocomposite (represented as Ag-rGO/P(S-co-MA)), a composite polymer comprising the same. The present invention also relates to photocatalytic methods of preparations thereof and uses thereof.
[0019] In an aspect, the present invention provides a method of preparing the Ag-rGO/P(S-co-MA) by photocatalytic method, comprises:
a) mixing Ag-rGO in ethanol by sonication to obtain a uniformly dispersed solution;
b) adding styrene and methyl acrylate to ethanol to obtain a reaction mixture;
c) adding the uniformly dispersed solution of Ag-rGO from step a) to the reaction mixture of step b), followed by irradiating the same using blue LED with vigorous stirring for 4-8 h to obtain to obtain Ag-rGO/(P(S-co-MA) in ethanol; and
d) removing ethanol by vacuuming for 10-30 min to obtain Ag-rGO/(P(S-co-MA).
[0020] In an aspect, the ratio of styrene and methyl acrylate 1:1.1, respectively.
[0021] In an aspect, the amount of Ag-rGO is 0.025 wt%.
[0022] In an aspect, the P(S-co-MA)-Ag-rGO hybrid nanocomposite filler improves fracture toughness of epoxy composite by 45% to 104% compared to neat epoxy composite, in a concentration-dependent manner of Ag-rGO/P(S-co-MA).
[0023] In an aspect, the polymer composite is prepared from epoxy resin monomers.
[0024] In an aspect, the present invention provides a method of preparing the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite by photocatalytic method, comprises:
a) mixing Ag-rGO in ethanol by sonication to obtain a uniformly dispersed solution;
b) adding styrene and methyl acrylate to ethanol to obtain a reaction mixture;
c) adding the uniformly dispersed solution of Ag-rGO from step a) to the reaction mixture of step b), followed by irradiating the same using blue LED with vigorous stirring for 4-8 h;
d) adding an epoxy monomer resin to the components from step c), followed by vigorous stirring to obtain an epoxy resin-Ag‑rGO/P(S‑co‑MA) mixture;
e) adding a curative agent (hardener) to the epoxy resin-Ag‑rGO/P(S‑co‑MA) mixture, followed by stirring to obtain Ag‑rGO/P(S‑co‑MA)/Epoxy Composite in ethanol; and
f) removing ethanol by vacuuming for 10-30 min to obtain Ag-rGO/(P(S-co-MA).
[0025] In an aspect, the epoxy monomer resin is Diglycidyl Ether of Bisphenol A (DGEBA)-based epoxy resin, diglycidyl ether of bisphenol-A, diglycidyl ether of bisphenol-F, epoxy novolac resin, or a combination thereof.
[0026] In an aspect, the curative agent (hardener) is Diethylene Toluene diamine (DETDA), aromatic polyamine, and having at least one substituent on the same which is selected from an aliphatic substituent, at an ortho position with respect to an amino group.
[0027] In an aspect, the ratio of epoxy monomer resin and the curative agent (hardener) is 1:0.1 to 0.1:1, respectively.
[0028] In an aspect, the ratio of epoxy monomer resin and the curative agent (hardener) is 1:0.244, respectively.
[0029] In an aspect, the amount of Ag/r-GO is 0.25 to 0.50 wt% with respect to the weight of epoxy monomer resin.
[0030] In an aspect, the amount of styrene is 10 to 20 wt% with respect to the weight of epoxy monomer resin.
[0031] In an aspect, the amount of Methyl acrylate is 9 to 19 wt% with respect to the weight of epoxy monomer resin.
[0032] In an aspect, the stirring in step c) is effected for 6 h.
[0033] In an aspect, the stirring in step d) is effected 20 min at 80 °C.
[0034] In an embodiment of the present invention, the method further comprises the step of pouring the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite into moulds, followed by curing the same using hot air oven with precuring at 60-150 °C for 2 h and kept at a temperature of 160-200 °C for duration of 2 h for post curing.
[0035] In another aspect, the present invention provides a finished product comprising the Ag‑rGO/P(S‑co‑MA) hybrid nanocomposite filler prepared by the method as disclosed herein.
[0036] In yet another aspect, the present invention provides a finished product comprising the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite prepared by the method as disclosed herein. In an embodiment, the epoxy composite reinforced with P(S-co-MA)-Ag-rGO may be used in laminated circuit board, electronic component encapsulations, surface coatings, adhesives, furniture, aerospace components, automotive industries, as protective coatings (anti-corrosive), furniture, antimicrobial coatings or materials and for biomedical applications.
[0037] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 relates to the schematic representation of preparing Poly(styrene-co-methylacrylate) reinforced Ag-rGO nanocomposite by Polymerisation of styrene and methyl acrylate using Ag-rGO.
[0039] FIG. 2 relates to the FTIR spectrum of copolymer formed from styrene and methyl acrylate monomers
[0040] FIG. 3 relates to the Phase Contrast Microscopic image of a GO, b P(S-co-MA)-Ag-rGO polymer composite
[0041] FIG. 4 relates to the 1H-NMR of P(S-co-MA)-Ag-rGO polymer composite.
[0042] FIG. 5 relates to the FE-SEM a Ag-rGO, b GO, c EDS-Ag-rGO hybrids, d EDS -GO, e EDS-Ag003 epoxy composite sample
[0043] FIG. 6 relates to the critical stress intensity factor (KIC) for different loading of Ag-rGO/P(S-co-MA)/Epoxy composites
[0044] FIG. 7 relates to the TGA curves of a Neat, b Ag001, c Ag003 and d Ag004 prepared as exemplary embodiments.
[0045] FIG. 8 relates to the DSC graphs of a Neat, b Ag001, c Ag003 and d Ag004 prepared as exemplary embodiments.
[0046] FIG. 9 relates to the Images of antimicrobial studies against a S. aureus for all 5 samples, b Escherichia coli for all 5 samples, c Candida albicans for all 5 samples (Neat, Ag001, Ag002, Ag003, Ag004 prepared as exemplary embodiments.)

DETAILED DESCRIPTION OF THE INVENTION
[0047] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention.
[0048] 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.
[0049] 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.
[0050] In some embodiments, numbers have been used for quantifying weight 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. 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.
[0051] Various terms as used herein are shown below. To the extent a term used in a claim 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.
[0052] 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.
[0053] Unless the context requires otherwise, throughout the specification which follow, 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.”
[0054] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[0055] All methods described herein can be performed in any 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.
[0056] 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.
[0057] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present invention. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.
[0058] It should also be appreciated that the present invention 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.
[0059] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0060] 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.
[0061] Embodiments of the present invention relate to a hybrid nanocomposite for epoxy composite. Specifically, the present invention relates to a hybrid nanocomposite filler comprising poly(styrene-co-methylacrylate) copolymer and Ag-rGO (silver nanoparticle decorated reduced graphene oxide) nanocomposite (represented as Ag-rGO/P(S-co-MA)), a composite polymer comprising the same. The present invention also relates to photocatalytic methods of preparations thereof and uses thereof.
[0062] In an embodiment of the present invention, the photocatalytic property of Ag-rGO composite is used for the preparation of Poly(styrene-co-methylacrylate)(P(S-co-MA)) and the resultant hybrid composite, P(S-co-MA)-Ag-rGO as a filler for epoxy toughening application.
[0063] In some embodiments of the present invention, the P(S-co-MA)-Ag-rGO nanocomposite may have a size of at least about 50 nm to 1000 nm.
[0064] In an embodiment, the present invention provides a method of preparing the Ag-rGO/P(S-co-MA) by photocatalytic method, comprises:
e) mixing Ag-rGO in ethanol by sonication to obtain a uniformly dispersed solution;
f) adding styrene and methyl acrylate to ethanol to obtain a reaction mixture;
g) adding the uniformly dispersed solution of Ag-rGO from step a) to the reaction mixture of step b), followed by irradiating the same using blue LED with vigorous stirring for 4-8 h to obtain to obtain Ag-rGO/(P(S-co-MA) in ethanol; and
h) removing ethanol by vacuuming for 10-30 min to obtain Ag-rGO/(P(S-co-MA).
[0065] In an embodiment, the ratio of styrene and methyl acrylate 1:1.1.
[0066] In an embodiment, the amount of Ag-rGO is 0.025 wt%.
[0067] In an embodiment of the present invention, the stirring is effected for 6 h.
[0068] In an embodiment of the present invention, the vacuum is effected for 20 min.
[0069] In an embodiment of the present invention, the P(S-co-MA)-Ag-rGO hybrid nanocomposite filler improves fracture toughness of epoxy composite by 45% to 104% compared to neat epoxy composite, in a concentration-dependent manner of Ag-rGO/P(S-co-MA).
[0070] In an embodiment, the present invention provides a polymer composite reinforced with P(S-co-MA)-Ag-rGO.
[0071] In an embodiment of the present invention, the polymer composite is prepared from epoxy resin monomers.
[0072] In an embodiment, the present invention provides a method of preparing the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite by photocatalytic method, comprises:
g) mixing Ag-rGO in ethanol by sonication to obtain a uniformly dispersed solution;
h) adding styrene and methyl acrylate to ethanol to obtain a reaction mixture;
i) adding the uniformly dispersed solution of Ag-rGO from step a) to the reaction mixture of step b), followed by irradiating the same using blue LED with vigorous stirring for 4-8 h;
j) adding an epoxy monomer resin to the components from step c), followed by vigorous stirring to obtain an epoxy resin-Ag‑rGO/P(S‑co‑MA) mixture;
k) adding a curative agent (hardener) to the epoxy resin-Ag‑rGO/P(S‑co‑MA) mixture, followed by stirring to obtain Ag‑rGO/P(S‑co‑MA)/Epoxy Composite in ethanol; and
l) removing ethanol by vacuuming for 10-30 min to obtain Ag-rGO/(P(S-co-MA).
[0073] In an embodiment of the present invention, the epoxy monomer resin is selected from but not limited to Diglycidyl Ether of Bisphenol A (DGEBA)-based epoxy resin, diglycidyl ether of bisphenol-A, diglycidyl ether of bisphenol-F, epoxy novolac resin, or a combination thereof.
[0074] In an embodiment of the present invention, the curative agent (hardener) is selected from but not limited to Diethylene Toluene diamine (DETDA), aromatic polyamine, and having at least one substituent on the same which is selected from an aliphatic substituent, at an ortho position with respect to an amino group.
[0075] In an embodiment of the present invention, the ratio of epoxy monomer resin and the curative agent (hardener) is 1:0.1 to 0.1:1, respectively. Preferably, the ratio of epoxy monomer resin and the curative agent (hardener) is 1:0.244, respectively.
[0076] In an embodiment of the present invention, the amount of Ag/r-GO is 0.01 to 1.0 wt% with respect to the weight of epoxy monomer resin. For example 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1.0 wt% with respect to the weight of epoxy monomer resin. Preferably, 0.01 to 0.50 wt% with respect to the weight of epoxy monomer resin.
[0077] In an embodiment of the present invention, the amount of styrene is 5-50 wt% with respect to the weight of epoxy monomer resin. For example 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 wt% with respect to the weight of epoxy monomer resin. Preferably, 10 to 20 wt% with respect to the weight of epoxy monomer resin.
[0078] In an embodiment of the present invention, the amount of Methyl acrylate is 1-20 wt% with respect to the weight of epoxy monomer resin. For example 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20 wt% with respect to the weight of epoxy monomer resin. Preferably, 9-19 wt% with respect to the weight of epoxy monomer resin.
[0079] In an embodiment of the present invention, the stirring in step c) is effected for 6 h.
[0080] In an embodiment of the present invention, the stirring in step d) is effected 20 min at 80 °C.
[0081] In an embodiment of the present invention, the vacuum in step f) is effected for 20 min.
[0082] In an embodiment of the present invention, the method further comprises the step of pouring the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite into moulds, followed by curing the same using hot air oven with precuring at 60-150 °C for 2 h and kept at a temperature of 160-200 °C for duration of 2 h for post curing.
[0083] In an embodiment, the present invention provides a finished product comprising the Ag‑rGO/P(S‑co‑MA) hybrid nanocomposite filler prepared by the method as disclosed herein.
[0084] In an embodiment, the present invention provides a finished product comprising the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite prepared by the method as disclosed herein. In an embodiment, the epoxy composite reinforced with P(S-co-MA)-Ag-rGO may be used in laminated circuit board, electronic component encapsulations, surface coatings, adhesives, furniture, aerospace components, automotive industries, as protective coatings (anti-corrosive), furniture, antimicrobial coatings or materials and for biomedical applications.
[0085] In an embodiment, the finished product comprising the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite exhibit antimicrobial characteristic.
[0086] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. 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 having ordinary skill in the art.
EXAMPLES
[0087] The present invention is further explained in the form of following examples. However, it is to be understood that the foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.
Materials:
Graphite powder of particle size 60 mesh and purity of 98% was obtained from Loba Chemie Pvt Ltd Company. Potassium permanganate, Hydrogen peroxide (30% solution) Hydrochloric acid, silver nitrate sodium citrate, styrene and methylacrylate were procured from Sigma Aldrich. Diglycidyl Ether of Bisphenol A (DGEBA, YDL680)- based epoxy resin and hardener Diethylene Toluene diamine (DETDA, TH7455) were received from Aditya Birla Epoxy Division.
[0088] Example 1: Preparation of GO (Graphene oxide)
Modified Hummer's process was used to prepare graphene oxide, with graphite powder as the starting ingredient. Graphite powder (0.5 g) and sodium nitrate (0.5 g) were taken together in a round bottom flask and conc. Sulfuric acid (23.0 mL) was gradually added at 10–15 °C. The resulting reaction mass was stirred for 4 h at 10–15 °C. Thereafter, potassium permanganate (3 g) was added slowly in small portions into the solution and stirred for 1 h. The ice bath was then removed, and the resulting reaction mixture was stirred at 35 °C for 1 h. After 1 h, deionized water (40 mL) was added and the mixture was stirred at 95 °C (jacket temperature) for 2 h. The reaction mass was allowed to attain ambient temperature and then diluted with additional deionized water (100 mL) and stirred for additional 1 h more. The resulting reaction mass was then treated with 30% of hydrogen peroxide (50 mL). The mixture was ultracentrifuged to obtain GO, which was washed with 5% hydrochloric acid followed by copious amounts of water. The washing was repeated several times till the final supernatant liquid (with water wash) turns to a pH of ~ 5. The obtained final supernatant liquid was centrifuged washed and dried to obtain GO.
[0089] Example 2: Preparation of Ag‑rGO Nanocomposites
Ag-rGO nanocomposite was synthesised by the sonochemical, green methodology described by Bozkurt, in which graphene oxide (0.5 g) was dispersed in deionised water (250 mL) by sonication for 0.5 h resulting in a stable GO suspension in water. To the resulting suspension, an aqueous solution of silver nitrate (0.635 g in 250 mL deionized water) was gradually added under stirring. The reaction mass was allowed to stirr at ambient temperature for 0.5 h. To the reaction mixture, sodium citrate (2.575 g) was slowly added and sonicated for 2 h. Ag-rGO nanocomposite was collected as black solid via centrifugation at 6000 rpm. The solid was washed with copious amounts of water, followed by ethanol washings and finally it is dried under vacuum at 60 °C for 24 h.
[0090] Example 3: Preparation of Copolymer Poly(styrene‑co‑methylacrylate)/Ag‑rGO Composite
Poly(styrene-co-methylacrylate) reinforced Ag-rGO nanocomposite was successfully prepared under photochemical conditions. Different ratios of the monomer and Ag-rGO (ref Table 1) were mixed in polar solvent (ethanol) and irradiated under blue LED for 6 h. The synthesis was carried out in a 250 mL conical flask, equipped with a stirring bar and magnetic stirrer. To the conical flask calculated amount of styrene and methyl acrylate (ref Table 1) were added (the commercial reagent was washed with 10% sodium hydroxide and copious amount of water and dried over anhydrous sodium sulfate prior to their usage) along with ethanol (ref Table 1). Desired amount of Ag-rGO was suspended in ethanol, by sonication for 20 min. This uniformly dispersed solution was added to the above reaction mixture. The resulting reaction mass was kept under blue LED with vigorous stirring for 6 h. The reaction mixture in each case was directly used for blending with DEGEBA-DETDA system to prepare DGEBA-DETDA/ P(S-co-MA)-Ag-rGO polymer composite.A small portion of the reaction mass was removed, concentrated under vacuum to remove the solvent, and then analysed by FTIR, 1H-NMR, UV–Visible spectroscopy and phase contrast microscopy. FIG. 1 represents the synthesis process schematically.
[0091] Example 4: Characterization of Copolymer Poly(styrene‑co‑methylacrylate)/Ag‑rGO Composite:
FTIR Spectra of Ag‑rGO/P(S‑co‑MA) Composite:
The FTIR spectrum (FIG. 2) of copolymer formed from styrene and methyl acrylate monomers can be confirmed from the absence of signal at 1710 cm−1 of styrene attributed to –C = C– that appear in the unsaturated monomer spectra. The signal at 1645.46 cm−1 assigned to ester groups of the copolymer. The signal at 1044 cm−1 is owing to the C–O stretching of ester groups. Furthermore, the signal of C = C stretching of the aromatic ring exhibited at 2978.10 cm−1 and the low intensity signal corresponding to the bending of aromatic ring showed up at 1454, 1564 cm−1. Hence the polymerisation of styrene and methyl acrylate is confirmed.
Phase Contrast Microscopy:
The phase contrast microscopy of GO shows that the flakes of GO, and that of Ag-rGO catalysed polymer (P(Sco-MA)-Ag-rGO polymer) composite shows a uniform dispersion of the silver graphene oxide-based system in ethanol (FIG. 3), thus it should potentially have a good dispersion in epoxy as well. It is obvious from the image that there is no significant agglomeration observed and the metallic particles are well dispersed Thus, P(S-co-MA)-g-Ag-rGO nanocomposite can be employed as a functional nanofiller.
1H-NMR:
1H-NMR was recorded for Ag-rGO reinforced copolymer of Styrene and methyl acrylate (FIG. 4) 1H-NMR is recorded using DMSO-d6 as solvent and tetramethylsilane is used as internal reference. The signal at δ 3.3 ppm is due to water/ moisture content in DMSO. The phenyl proton in the poly (styrene -co-methyl acrylate) shows signal at δ 7.25–7.45 ppm (aCH). The signal of methoxy proton of the copolymer poly (styrene -co-methyl acrylate) shows at δ 3.4 ppm (fCH3). The methylene protons show signal at δ 1.3 ppm (bCH2) and δ 1.2 ppm (dCH2). The methylene protons at δ 2.46 ppm for (cCH) and (eCH) are merged with the DMSO residual peak. From these data’s we can demonstrate the structure of the copolymer and also confirm the formation of polymer from the monomer.
[0092] Example 5: Preparation of Ag‑rGO/P(S‑co‑MA)/Epoxy Composite:
DGEBA was added to each of the sample composition (Ag001, Ag002, Ag003, Ag004) of P(S-co-MA) -Ag-rGO polymer nanocomposite (ref Table 1) and was stirred vigorously for 20 min at 80 °C. To above mixtures, curative DETDA was added such that, the overall DGEBA/ DETDA stoichiometry of 1: 0.244 is used in all the prepared sample compositions and stirred for 5 min. Further, samples were kept under vacuum to remove the volatiles and excess solvent for 20 min. The resulting compositions were subsequently poured into moulds, cured using hot air oven with precuring at 140 °C for 2 h and kept at a temperature of 200 °C for duration of 2 h for post curing. In case of the neat sample, the composition excludes the addition of P(Sco-MA)-Ag-rGO polymer nanocomposite and the remaining process remains the same. FESEM analysis of the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite is shown in FIG. 5

Table 1: Composition of materials (in wt% w.r.t DGEBA) used for the modified epoxy composite preparation
S. No. Sample Name Ag/r-GO (wt% w.r.t epoxy resin) Styrene (wt% w.r.t epoxy resin) Methyla Acrylate (wt% w.r.t epoxy resin) Ethanol (mL)
1 Ag001 0.25 10 9.1 12
2 Ag002 0.5 10 9.1 12
3 Ag003 0.25 20 18.2 15
4 Ag004 0.5 20 18.2 15
5 Neat Nil Nil Nil Nil

[0093] Example 6: Characterization of Ag‑rGO/P(S‑co‑MA)/Epoxy Composite:
Fracture Toughness:
All the five samples prepared by adding varying ratios of P(S-co-MA)/Ag-rGO polymer were tested as per ASTM D5045 standard and the critical stress intensity factor was calculated. The bar graph in FIG. 6 shows the comparison of KIC calculated for each of the sample, including the neat sample. From the figure it can be clearly understood that the addition of P(S-co-MA)/Ag-rGO composites helps in boosting the toughness of epoxy due to the combined action of silver, rGO and the copolymer. It is observed that the well dispersed Ag-rGO is capable of enhancing the toughness to a greater extent. There are studies that demonstrate the role of rGO in boosting the toughness of epoxy, and that the highly dispersed rGO could offer better enhancement in toughness compared to less dispersed rGO. Additionally, it has been claimed that incorporating metal nanoparticles like Ag helps in reducing the aggregation of rGO and thus improves the dispersion in epoxy matrix. Metal nanoparticle decoration successfully prevents the re-stacking of rGO sheets, resulting in enhanced dispersion. Generally polystyrene(PS) shows a reaction induced phase separation in epoxy matrix and hence shows enhanced toughness; but it is also observed that when PS is grafted to an epoxyphilic group, it helps in enhancing the compatibility with epoxy matrix and hence obtains higher toughness compared to PS/epoxy composite. Polymethacrylate is miscible with epoxy and are thus expected to enhance the toughness. Here in our study, we have synthesized a copolymer utilizing photocatalytic efficiency of Ag-rGO. Thus, prepared Ag-rGO/ P(S-co-MA) nanocomposites showed excellent dispersion in epoxy and observed an enhancement in toughness of about 102%. Additionally, it is noted that when concentration of polymers and Ag-rGO rises, the toughness increases owing to synergistic effect of rGO, Ag and P(S-co-MA). Sample Ag003 showed the highest KIC of 1.86 MPa.m1/2, where the loading of AgrGO and the monomers were the highest and it showed an increase of about 102% compared to the neat sample (refer Table 2).

Table 2. Fracture toughness (KIC) of prepared samples
S. No. Sample Name Fracture toughness Improvement in fracture toughness (%) wrt neat sample
1 Neat 0.92 ± 0.04 10
2 Ag001 1.34 ± 0.05 45.40%
3 Ag002 1.78 ± 0.07 92.88%
4 Ag003 1.86 ± 0.07 102.15%
5 Ag004 1.65 ± 0.06 79.44%

[0094] Example 7: Thermal Properties
Thermogravimetric (TGA) Analysis
All of the prepared sample specimens were subjected to Thermo gravimetric analysis (TGA). Based on the analysis (FIG. 7), it is obvious that the thermal stability of epoxy is not affected much by the addition of filler. At a temperature of 320ºC, degradation of neat epoxy sample is observed. For Ag001, Ag002, Ag 003 and Ag004 the degradation starts at 323, 324.93, 325.6, 324ºC respectively. Based on these results, it is clear that thermal stability is slightly improved by the addition of hybrid filler. In all cases the about 11% of residue remains after the heating process indicating almost same thermal stability.
DSC Studies
From the DSC analysis shown in FIG. 8, it is clear that addition of nanofillers enhances the Tg value. For neat, Ag001, Ag002, Ag003 and Ag004, the Tg values obtained are 135ºC, 142ºC, 150ºC, 140ºC and 145ºC respectively. In all the cases, the Tg value were greater than neat epoxy sample because of the interaction of filler with the epoxy chain. This means that the epoxy chains are getting confined because of the interaction with the filler, the functionalities present over rGO and methacrylate part in the copolymer having potential H-bonding interaction with the epoxy chains. But comparing Ag001 and Ag002, it is clear that in both cases the content of copolymer is same but the content of Ag-rGO is higher in Ag002, thus owing to the enhanced plasticizing effect of the P(S-co-MA), Tg value is less than Ag002. Due to higher content of Ag-rGO, the plasticizing effect is nullified and the more epoxy chains will get confined to the Ag-rGO part. Similar trend was observed in the case of Ag003 and Ag004.
In comparing the Ag001 and Ag004, similarly Ag002 and Ag004, it is clear that, keeping the Ag-rGO content constant and altering the copolymer content there is a pronounced change in the Tg value. i.e. the Tg value decreases with the enhanced copolymer content owing to its plasticizing effect.
[0095] Example 8: Antibacterial Analysis
Antimicrobial testing for all the samples were done against Staphylococcus aureus, Candida albicans and Escherichia coli. No zonal inhibition was observed for the neat epoxy samples and those with fillers, however, we observed no bacterial growth on the surface of the samples including neat. Below are the images (FIG. 9) indicating no fungal growth on the sample’s surface.

ADVANTAGES OF THE PRESENT INVENTION:
[0096] The present invention provides an environmentally friendly, industrially feasible approach for the production of reinforcing agent comprising of three components that includes silver, reduced graphene oxide and copolymer of styrene and methyl acrylate. The described method further provides effective utilisation of the synergistic effect of above mentioned components for the reinforcing of epoxy composite.
[0097] Polymers, amphiphilic block copolymers and the like are also used for toughening epoxy matrix, but the negative effect of polymer inclusion is that, it leads to a subsequent decrease in tensile strength. Hence the grafting of polymers over nanofillers can be viewed as a successful method in toughening epoxy without compensating its tensile properties. Silver and graphene are known for its catalytic activity, hence Ag-rGO composites are expected to show better photocatalytic property, researchers recently explored the photocatalytic effect of Ag-GN or Ag-GO. The greater charge separation that occurs in presence of light is the reason behind the photocatalytic property of Ag/rGO nanocomposite. However, no prior invention has been reported for the preparation of hybrid composite like, P(S-co-MA)-Ag-rGO under the photolytic conditions and utilised the same as a reinforcing agent in epoxy resin to strengthen the characteristics of epoxy composite for industrial applications.
[0098] In the present invention, the inventors have utilised the photocatalytic property of Ag-rGO composite for the preparation of Poly(styrene-co-methylacrylate)(P(S-co-MA)) and the resultant hybrid composite, P(S-co-MA)-Ag-rGO as a filler for epoxy toughening application. Moreover, to our knowledge, no research has been done on the toughening impact of P(s-co-MA) in epoxy hence, we have utilized AG-rGO/P(s-co-MA) composites as a hybrid filler in epoxy toughening.
, Claims:1. A hybrid nanocomposite filler comprising: poly(styrene-co-methylacrylate) copolymer and Ag-rGO (silver nanoparticle decorated reduced graphene oxide) nanocomposite (Ag-rGO/P(S-co-MA)).
2. The hybrid nanocomposite filler as claimed in claim 1 improves fracture toughness of epoxy composite by 45% to 104% compared to neat epoxy composite, in a concentration-dependent manner of Ag-rGO/P(S-co-MA).
3. A method of preparing the Ag-rGO/P(S-co-MA) as claimed in claim 1 by by photocatalytic method, comprises:
a) mixing Ag-rGO in ethanol by sonication to obtain a uniformly dispersed solution;
b) adding styrene and methyl acrylate to ethanol to obtain a reaction mixture;
c) adding the uniformly dispersed solution of Ag-rGO from step a) to the reaction mixture of step b), followed by irradiating the same using blue LED with vigorous stirring for 4-8 h to obtain to obtain Ag-rGO/(P(S-co-MA) in ethanol; and
d) removing ethanol by vacuuming for 10-30 min to obtain Ag-rGO/(P(S-co-MA).
4. The method as claimed in claim 3, wherein the ratio of styrene and methyl acrylate is 1:1.1, respectively.
5. The method as claimed in claim 3, wherein the amount of Ag-rGO is 0.025 wt.%.
6. The method as claimed in claim 3, wherein the stirring is effected for 6 h.
7. The method as claimed in claim 3, wherein the vacuum is effected for 20 min.
8. An epoxy resin composite reinforced with the hybrid nanocomposite filler comprising the Ag-rGO/P(S-co-MA) (Ag‑rGO/P(S‑co‑MA)/Epoxy Composite) as claimed in claim 1.
9. A method of preparing the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite as claimed in claim 4 by photocatalytic method, comprises:
a) mixing Ag-rGO in ethanol by sonication to obtain a uniformly dispersed solution;
b) adding styrene and methyl acrylate to ethanol to obtain a reaction mixture;
c) adding the uniformly dispersed solution of Ag-rGO from step a) to the reaction mixture of step b), followed by irradiating the same using blue LED with vigorous stirring for 4-8 h;
d) adding an epoxy monomer resin to the components from step c), followed by vigorous stirring to obtain an epoxy resin-Ag‑rGO/P(S‑co‑MA) mixture;
e) adding a curative agent (hardener) to the epoxy resin-Ag‑rGO/P(S‑co‑MA) mixture, followed by stirring to obtain Ag‑rGO/P(S‑co‑MA)/Epoxy Composite in ethanol; and
f) removing ethanol by vacuuming for 10-30 min to obtain Ag-rGO/(P(S-co-MA).
10. The method as claimed in claim 9, wherein the epoxy monomer resin is Diglycidyl Ether of Bisphenol A (DGEBA)-based epoxy resin, diglycidyl ether of bisphenol-A, diglycidyl ether of bisphenol-F, epoxy novolac resin, or a combination thereof.
11. The method as claimed in claim 9, wherein the curative agent (hardener) is Diethylene Toluene diamine (DETDA), aromatic polyamine, and having at least one substituent on the same which is selected from an aliphatic substituent, at an ortho position with respect to an amino group.
12. The method as claimed in claim 9, wherein the ratio of epoxy monomer resin and the curative agent (hardener) is 1:0.1 to 0.1:1, respectively.
13. The method as claimed in claim 9, wherein the ratio of epoxy monomer resin and the curative agent (hardener) is 1:0.244, respectively.
14. The method as claimed in claim 9, wherein the amount of Ag/r-GO is 0.25 to 0.50 wt% with respect to the weight of epoxy monomer resin.
15. The method as claimed in claim 9, wherein the amount of styrene is 10 to 20 wt% with respect to the weight of epoxy monomer resin.
16. The method as claimed in claim 9, wherein the amount of Methyl acrylate is 9 to 19 wt% with respect to the weight of epoxy monomer resin.
17. The method as claimed in claim 9, wherein the stirring in step c) is effected for 6 h.
18. The method as claimed in claim 9, wherein the stirring in step d) is effected 20 min at 80 °C.
19. The method as claimed in claim 9, wherein the vacuum in step f) is effected for 20 min.
20. The method as claimed in claim 9 further comprises the step of pouring the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite into moulds, followed by curing the same using hot air oven with precuring at 60-150 °C for 2 h and kept at a temperature of 160-200 °C for duration of 2 h for post curing.
21. A finished product comprising the Ag‑rGO/P(S‑co‑MA)/Epoxy Composite as claimed in claim 6, or Ag‑rGO/P(S‑co‑MA)/Epoxy Composite prepared by the method as claimed in anyone of claims 7-17.
22. The finished product as claimed in claim 18 is selected from group consisting of laminated circuit board, electronic component encapsulations, surface coatings, adhesives, furniture, aerospace components, automotive industries, protective coatings, anti-corrosive coatings, furniture, antimicrobial coatings or materials for biomedical applications.