Abstract The Fe3O4-functionalized graphene oxide

Abstract
The Fe3O4-functionalized graphene oxide ([email protected]) and waterborne epoxy (WEP) nanocomposites (WEP/[email protected]) fabricated via co-precipitation followed by sulfonation technique, and the effect of functionalized GO on mechanical properties of the nanocomposites also examined. The functionalization of [email protected] was analyzed and confirmed by FTIR, Raman, XRD, and TGA. It was convinced from the field emission scanning electron microscopy and transmission electron microscopy analyses that the covalent functionalization of graphene oxide with Fe3O4 nanoparticles followed by sulfonation with 3-mercaptopropyl trimethoxysilane was favorable to homogeneous dispersion in WEP matrix. Meanwhile, the tight covalent interfaces between WEP and [email protected] promote the stress transfer. As the [email protected] content increases, the tensile strength of WEP increases, but the totaling more than 0.2 wt% [email protected] yield unfavorable results. When the concentration of [email protected] increases to 0.2 wt% of WEP, the tensile strength of the nanocomposite films was found to be 300% higher than that of the blank group. Besides, the DMA shows that the storage modulus and tan? of the WEP/[email protected] remarkably enhanced due to the strong interactions between [email protected] and WEP. It could concluded that the appropriate quantity of [email protected] toting up can significantly improve the mechanical properties of WEP/[email protected] nanocomposites.

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1. Introduction
Waterborne polymers are unusual materials for obtaining stout, fine-isolated and eco-friendly composites. Graphene is a 2D structure nanomaterial having a functional and well-organized self-gathering into the prearranged network. Self-gathering into lyotropic nematic liquid crystalline (LC) phases has been available for graphene oxide (GO) liquid dispersal (1). Graphene mixed polymer nanocomposites are commonly geared up with the aid of solvent assimilation and in situ polymerization process, which leads to more usage of the massive quantity of organic solvents. To attain the excellent steadiness and the possible of LC stage configuration of GO in an aqueous system, waterborne epoxy (WEP) are outstanding resources for obtaining stout, fine-isolated and eco-friendly nanocomposites. Additionally, the liquid system from the WEP matrix helps to maintain appropriate surroundings for the GO to reinstate its properties without any effect. Moreover with the assist of the proper chemistry and chemical bonding properties could able to improve the attachment amid the polymer matrix and the GO network via the oxygen functionalities (2, 3).

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GO has been identified with desirable properties such as large surface area, considerable tensile strength, single layer structure, outstanding physicochemical stability, strong mutual boding ability and high flexibility (4). The enormous accessibility of oxygen-containing functionalities, such as epoxide, hydroxyl, carboxyl, on the surface of the GO networks allows them to modified with various organic and inorganic materials in covalent or non-covalent approaches (5). When GO is discrete in water, the – (COOH) groups and – (OH) groups of GO network can be ionized, and a steady GO colloid will shaped by the electrostatic disgust of pessimistically charged GO network (6). The existence of oxygen functional groups make GO particularly attractive for use in polymer nanocomposites, and therefore polymer containing GO have spurred intense interest due to their beautiful properties (7). The improvement in carbon made nanofillers seeing as the sighting of graphene has established significant development over the decade. It has induced the importance and enrichment of the execution within commercial applications for both textile and engineering hybrid composites (8). Graphene, having a mono-layered network of hexagonally shaped sp2 hybridized carbon materials, has an arrangement of excellent mechanical, electrical and thermal behaviors, such as Young’s modulus and contravention strength, etc., (9).

On the other hand, GO layer in the polymer system can create harsh aggregations, due to their vast surface area, van der Waals’ force of attraction, and sterile filtration in groundwork course (10). This will leads to poor sheet and polymer system interfacial excellence, which restricts their significant advantages in polymer nanocomposites (11). As is imminent, the mechanical behaviors of polymer composites are not only resolute by the inherent possessions and spreading point of fillers, but are also fundamentally reliant on their boundary with the polymer congregation (12). Too many methods, e.g., in-situ polymerization, automatic mixing and solution amalgamation, have been reported to diffuse graphene or its derivatives into a polymer system (13-15). Though the GO/polymer matrix interfacial excellence was yet to be enviable as requisite and only can be led to a gentle alter in the mechanical behaviors for the nanocomposites attached with immaculate GO layers.

Consequently, to take overall benefit of the latent of graphene or GO, a proper boundary intend is imperative for mounting the towering performance of nanocomposites (11). There is decidedly less notable work has been attempted to enrich the mechanical and thermal properties of GO-based epoxy nanocomposites (16-20). Nevertheless, very few works have been published on the role of waterborne epoxy (WEP) nanocomposites to enhance mechanical and thermal properties along with the existence of functionalized GO (21). The aggregation and restocking of GO layers in WEP are not accessible to avoid, and it is the main reason for the poor performance of graphene oxide based nanocomposites.

To avoid the aggregation of GO in the polymer matrix, we espouse the nanoparticles (NPs)-bedecked GO sheets to accomplish great distribution. There are vast varieties of NPs existing for ornamentation, such as zinc oxide, silica, aluminum, whereas minimal report exists on the magnetic Fe3O4 NPs ornamented GO layers fabricated into the polymer. Intrinsically, Fe3O4 NPs are dissimilar from other metal oxides and are eco-friendly resources with specific mechanical behaviors, trouble-free groundwork process, squat equipped expenditure, and excellent anticorrosive properties, which have been broadly applicable in the pasture of electrode kinds of stuff, catalyst activity, pigments and anticorrosive properties (22). Also, magnetic Fe3O4 NPs based nanocomposite demonstrate a competent technique for the severance in research method, when they introduced into the matrix system, which is environmentally adequate and has provided a qualified superior adhesion with matrix (23-25).
Magnetic NPs, particularly iron oxide, due to more considerable surface energy may cause agglomeration swiftly and switch to bulkier form (26). Thus, surface covering and its sustaining via an organosiloxane agent (27), supramolecule (28), polymer (29), or level with one more metal oxide or noble metal, correspondingly (30, 31), are the better conventional process to preclude agglomeration. When Fe3O4 NPs incorporated on the surface of the GO layers can be possible to prevent the agglomeration of magnetite Fe3O4 NPs (32, 33). In situ amalgamation of Fe3O4 in the existence of GO ([email protected]) is an incredibly immense nanofiller for mechanical investigation with polymer composites due to the truth that GO itself can endure alteration by a variety of agents (34).

In case of mechanical analysis, restocking of graphene relies upon layer is a crucial concern and tend to reduce mechanical and thermal properties. To avoid this issue, the as-synthesized GO should be able to disperse well in the polymer matrix. Moreover, in the current work, we trust that sustaining Fe3O4 nanoparticles can also be the primary source of pillaring of GO through Fe3O4 NPs. Altogether, here, GO, and Fe3O4 are helping each other to avoid aggregation. Besides, GO is structure forming agent and sustaining agent for Fe3O4 NPs. The as-prepared [email protected] hybrid undergoes a sulfonation process through post-alteration with the help of 3-mercaptopropyl trimethoxysilane (MPTMS) and flowed oxidation with the presence of hydrogen peroxide (H2O2) to enrich the dispersion ability with the polymer matrix. This as-prepared [email protected] hybrid nanocomposite, for the first trial, was introduced as a filler to study the mechanical behavior of WEP nanocomposites. Post-alteration by using MPTMS can also direct to promote steadiness of Fe3O4 over the GO network. Since MPTMS gifted of attaching thiol groups (-(SO3H) to both on Fe3O4 and on the GO skin through their availability of substantial oxygen functionalities groups.
2. Experimental
2.1 Materials
The following materials used in the experiment purchased from Sigma Aldrich, USA. Natural flake graphite, (? 98%) concentrated sulfuric acid (Conc.H2SO4), 30% hydrogen peroxide (H2O2), 37% hydrochloric acid (HCl), potassium nitrate (KNO3). Blue star technology, China supplied 25% ammonium solution (NH3 H2O), potassium permanganate (KMnO4), anhydrous ethanol (AR grade), FeCl2 4H2O, FeCl3 6H2O, methanol, 3-mercaptopropyl trimethoxysilane (MPTMS), glacial AcOH, waterborne epoxy (WEP) resin (E51), and an amine-based curing agent. All other remaining reagents used in this study were an analytical grade and double distilled water (DI).

2.2 Synthesis of GO
GO preparation was carried out with the aid of reported literature (35) along with little alteration. In brief, 3 g of graphite powder mixed into 150 ml of Conc.H2SO4 at lower than 5 °C (ice bath) cold environment followed by the accumulation of 3.6 g of KNO3 and the reaction system maintained for 30 min, and then 18 g of KMnO4 was introduced at a snail’s pace under energetic stirring. Then, the reaction set up lasted for 6 h at 35 °C by stirring, followed by 250 ml of DI water added to the reaction medium and again the medium was stirred for 10 h at less than 5°C (ice bath) cold environment. Finally, the reaction was clogged with the mixing of 80 ml H2O2 and 600 ml DI water mixture, followed by washing with 1% HCl and DI water more than a few times till the final GO attained pH = 7. Then, the wet GO dried in space drier at 60 °C overnight. Lastly, the obtained GO (about 2 g) was dissolved in 400 ml of DI water and sonicated for 60 min for further processing.

2.3 Preparation of [email protected]

The synthesis method of magnetically detachable graphene oxide ([email protected]) ground worked by the earlier report of J. Mondal et al. (36) in the company of minor modifications. Therefore, FeCl3•6H2O (0.013 mol) and FeCl2•4H2O (0.0065 mol) mixed with 100 ml solution of DI water containing 3 ml of the glacial acetic acid mixture under mechanical stirring. Then, 10 ml of sonicated GO solution was added to the reaction mixture slowly, and the reaction temperature rose to 80°C. Subsequently, 20 ml of ammonia solution (25 wt %) was introduced to the reaction medium under the vital stirring and permitted to maintain the same for 15 min. In the end, the black impetuous was composed with the aid of an outer magnet and flushed by DI water and MeOH more than a few times, followed by dehydrated in an oven for few hours at 70°C.

2.4 Synthesis of [email protected] nanohybridThe amalgamation of [email protected] nanohybrid was geared up by according to the literature report of E. Doustkhah, S. Rostamnia et al. (25) with minor variations. To sum up, 0.5 g of as-prepared [email protected] detached in 20 ml of Methanol and measured quantity of (1.5 ml) of MPTMS was added together the reaction system. Then, the set up was permitted to stir dynamically for a day. Finally, the product was claimed with an unending magnet, washed with DI water, and dried at 50°C. Afterward, the dried product was redispersed in 10 ml of DI water and stirred energetically. 10 ml of H2O2 (30 %) was introduced to the reaction dropwise for the 30 min at room temperature. The set up was permitted to process the same for a day, and then, the reaction was clogged and alienated from the combination and washed with DI water followed by drying.

2.5 Preparation of WEP nanocomposites
The desired quantity of as-synthesized GO was discrete well in DI water with the aid of sonication at room temperature for 1 h. The GO suspension initially mixed with the pre-calculated amine based waterborne curing agent, and professionally stirred for 30 min and followed by sonication for 30 min to ensure harmonized dispersal. Then the WEP resin was added to the GO dispersed curing agent mixture with constant stirring to shape the same medium and was degassed in a vacuum oven at room temperature for 15 min. The stoichiometric weight ratio of epoxy and hardener was 2:1. The curing process of the blends performed with the help of Teflon coated plates at 60°C for 24 h. For assessment, the samples nominated as WEP (neat epoxy) and WEP/[email protected] ([email protected] and WEP nanocomposites) were also geared up in the similar route followed for WEP/GO.

2.6 Characterization
STOE-STADV diffractometer was used to perform the X-ray diffraction (XRD) pattern for analyzing the as-synthesized GO and [email protected] hybrid. The parameter which maintained with Cu radiation (? = 15.4 nm) at 40 kV ad 40 mA.

A Perkin Elmer spectrophotometer (USA) instrument was taken to approve the Fourier transform infrared (FTIR) spectrum of GO and [email protected] hybrid. The average scanning rate of 64 scans and the range starting from 4000 to 400 cm-1, with the aid of KBr at a decree of 4 cm-1. The well-dried samples taken for analysis.
Raman spectrum was recorded for GO and [email protected] hybrid at 537 nm laser excitation with the help of Raman Microscope (Renishaw, Invia).

The as-prepared samples of GO and [email protected] hybrid morphology study were carried out with the help of Transmission Electron Microscopy (TEM) with the assist of JEM-2010 (JEOL, Japan) with the accelerating voltage of 200 kV. The sample preparation for TEM analysis was 0.05 ml of micelle solution on a copper electron microscopy grid used.

Energy disperses X-ray spectrometer (EDS) supported Field emission scanning electron microscope (FESEM) with the made of (FESEM) (JSM-7500F, SU8010/EDX, and Japan) was engaged to investigate the surface morphologies on GO and [email protected] hybrid. The analyzed samples were dried well before performing the test.

TA instruments STA449C (USA) was used to analyze the thermal properties of the synthesized GO and [email protected] hybrid. The amount of sample taken for analysis was around 10 mg, and the heating rate was maintained at 10 °C per min from 25 °C to 800 °C in the presence of a nitrogen atmosphere.

The mechanical property investigated with the help of electron universal testing machine (Instron5567), based on ISO527-2/1A:1993 standard followed. The tested samples dimensions are (gauge distance 45 mm, length 150 mm, preferred thickness 4 mm) strictly followed. TA instruments (DMA Q800, USA) was used to examine the dynamic mechanical measurements with the support of the double cantilever model. The experiment was carried out from the temperature starting from 25 °C to 180 °C with the temperature variation rate of 5 °C per min at the frequency of 1 Hz.

3. Results and discussion
3.1 Characterization of GO) and functional graphene oxide ([email protected])
In general, the preparation route for the [email protected] hybrid has started from the oxidation assisted graphite to graphene oxide (GO). The co-precipitation of Fe2+ and Fe3+ ions under base medium over totaling of the ammonia solution at 80 °C can be the main reason for sustaining Fe3O4 nanoparticles on the GO network. The MPTMS treatment on the [email protected] was able to create a thiol functionalities on the hybrid materials and those thiol groups are undergoes oxidation reaction in the existence of H2O2 at space temperature to develop sulfonic acid groups on the [email protected] surface of hybrid. The graphical methodology of the preparation route of the [email protected] hybrid displayed in Scheme 1.The XRD pattern investigation of GO and [email protected] hybrid exposed in Figure 1. The notable peaks has identified with the spectrum obtained for [email protected] (red curve in Figure 1) at 2? = 30.21° (220), 35.71° (311), 43.31° (400), 53.70° (422), 57.35° (511), and 62.72° (440) exemplify the inimitability of iron oxides in the hybrid (37). The pattern is fit and well matched with the archetypal description of a cubic magnetite configuration (JCPDS No. 75-0033). There are no diffraction signals of GO sheets in [email protected] hybrid while comparing with XRD pattern obtained for unmodified GO (black curve in Figure 1), which can be explained in the previous literature (38). There are few possible reasons described for the disappearance of carbon peaks in the XRD spectrum (Figure 1). The high signals of iron oxides may lead to diminishing the weak carbon peaks, and the Fe3O4 NPs may shrink the agglomeration of the GO nanosheets, which cause much fewer-layered GO nanosheets may be the main reason for diminishing of carbon peaks in the [email protected] hybrid material.

FTIR investigation demonstrated in the Figure 2a and b. The major peaks are showing for GO representing to C=C in-plane stretching vibration, C=O stretching, O-H deformation, epoxy C-O stretching vibration, adsorbed water molecules and alkoxy C-O extending which can be corresponding to the peaks at 1629, 1728,3400, 1225 and 1400 cm-1 respectively (39). This observed peaks of GO undoubtedly confirmed the GO formation and also the existence of hydroxyl; epoxy and carboxylic functionalities are present in the synthesized GO networks. The [email protected] hybrid FTIR spectra (Figure 2b) shows matching peaks with GO, to the stretching vibration of carbonyl (C-O) at 1400 cm-1 and the broad peaks at 3400 cm-1, which is representing stretching modes of the hydroxyl groups (OH) on the surface of the [email protected] hybrid (40). The peaks representing at 1095 and 1629 cm-1 attributed to the existence of S=O groups and the aromatic stretch of C=C (41). At the end there are two peaks has been identified and matched at 445 and 584 cm-1 which represent the metal iron Fe-O bonds of Fe3O4 (42).

Raman spectrum was used to identify the attachment between the GO and [email protected] hybrid and displayed in Figure 3a and b. The primary two peaks at 1355 and 1599 cm-1 represent the understandable mountains of D and G bands of carbon for both the materials (43). The following two peaks established the existence of GO sheets. On the other hand, aromatic carbons (hybridization of sp2) ascribed by G band and oxygen-containing carbon associated with D band respectively (44). In the case of [email protected] hybrid Raman spectrum was showing two different parts; such as there are few peaks assigned at 668 and 376 cm-1 ascribed to the metal irons are anchored on the surface of the GO network (45), and broadband at 1355 cm-1, which represents to the corresponding D band. Also, the D band intensity reduced, and G band disappeared in the [email protected] hybrid. The disappearance of G band, because of the metal irons are overcome the GO sheets concentration, and G band was diminishing due to its comparatively inferior intensity compared to D band. On the other hand, while oxidation takes place with the aid of H2O2 thiol groups leads to reacts with a portion of Csp2.

The ID/IG ratio shows increasing intensity, it relates to the higher degree of disarray within the GO network and the high degree of oxidation. On the contrary, the diminishing of G band relies on the shift charge from the metal irons (Fe3O4), which is pragmatic is under the anxiety (46).
Figure 4a and b, representing the morphology analysis for FESEM images of GO and [email protected] hybrid material respectively. According to figure 4a, the synthesized GO shows a crinkly emblematical arrangement on the surface. In the case of Figure 4b, GO surface was occupied by Fe3O4 NPs, which identified as black dots on the GO surface. Luckily, Fe3O4 NPs are uniformly anchored on the surface of the GO and helps to form a layer like structure hybrid. The uniform distribution of magnetite NPs on the GO and the layer-like structure demonstrate that possibly appropriate [email protected] hybrid formation. The same statement proved with the help of TEM analysis.

The elemental analysis of [email protected] hybrid material was investigated with the aid of Electron dispersive Scanning Electron Microscopy (EDS-SEM) to identify the associated atoms present in the hybrid. Based on this examination the hybrid material was mainly associated with the following elements such as O, C, S, and Fe, and the analysis graph mentioned in supplementary documents (Figure S1). The obtained weight % of the atoms is available in details with the Table 1. This analysis result shows that the supported particles confirmed that GO modified by Fe3O4 NPs, and the thiol groups anchored on the surface of GO and Fe3O4 NPs.

TEM treatment scrutinized for GO, [email protected] hybrid, and the results displayed in Figure 6a and b. For the GO surface in the TEM image demonstrate that wrinkled or crumple emblematical structure, and these results are correlated and matched with the GO SEM analysis as well. Besides, the GO model showed multi-sheets like structure, which is not suitable for good dispersion in the polymer matrix (Figure 6a). The effects, of Fe3O4 ornamentation on the GO network, revealed that the GO surface neatly designed and modified by the Fe3O4 NPs (Figure 6b). The modification takes place, due to the excellent interfacial interactions flanked by GO and Fe3O4 NPs, and it helps to maintain 2D morphology of GO. More importantly, the [email protected] hybrid is showing very thin and limited agglomeration of layered configuration in TEM (Figure 6b). The slim and single-sheets structure is more liable to achieve outstanding discrete in polymer matrix compared with multi-sheets configuration (47, 48). According to the TEM analysis, the as-synthesized [email protected] hybrid is well suitable to utilize the nanofiller for WEP matrix.

One of the best investigations to confirm the compound transformation is Thermogravimetric analysis. GO, and the [email protected] hybrid test was carried out under the N2 atmosphere, and the results demonstrated in Figure 7a and b. For GO plots (Figure 7a) proved that the initial weight loss started at lesser than 100 °C, which is clearly showing that adsorbed water molecules are begun fading (49). Also, the interior weight thrashing has been taken place at about 175 °C is associated with the availability of rich-oxygen functionalities to acquiesce carbon monoxide, carbon-di-oxide, and haze (50). The water molecules are bonded firmly with the GO network, due to the massive availability of oxygen functionalities with hydrophilic behavior.

Conversely, the oxygen functionalities eradication was started at the temperature of about 280 °C to continue up to 800 °C, since the steady weight loss started at the point of 280 °C. Compared with the GO (175 °C), the significant weight loss began for [email protected] hybrid (Figure 7b) at 424 °C, confirmed that most of the oxygen-functionalities are occupied by the Fe3O4 NPs and (-SO3H) groups to enrich the thermal steadiness of GO. Besides, the core weight loss of [email protected] hybrid noticed at 400 °C and 500 °C, it’s because of the diminishing of incorporated Fe3O4 NPs and thiol groups on the surface of the hybrid material. On the other hand, the residual char of modified GO is 3.8 %, when compared; with tidy GO it’s 30% lower on the state of the same mass. This consequence reveals that the as-prepared [email protected] hybrid material network is having very less amount of carbon, due to the incorporation of Fe3O4 NPs and thiol groups on the GO surface.

3.2 Characterization of WEP nanocomposites
The fracture surface morphology was investigated to examine the reason behind the mechanical property enrichment on WEP nanocomposites. Here we have scrutinized the fracture surface of the tidy WEP, WEP/GO, and WEP/[email protected] after tensile strength analysis with the help of FESEM study. The resulted images are displayed in Figure 7, to look at the nanocomposites samples microstructures and bonding flanked by the composites layers and matrix. There is a considerable delicacy, and weak confrontation surface on the cracked area was revealing that the tidy WEP can be secure to break and colossal crack instigation on Figure 7a.

In the other hand, the introduced nanofillers are well-discrete, and the rough surface exhibited in the GO, and [email protected] hybrids mixed WEP nanocomposites as exposed in Figure 7b, 7d, 7f, 7h (WEP/GO) and 7c, 7e, 7g, 7i (WEP/[email protected]), respectively. The escalating fracture surface irregularity and homogenous circulation of nanofillers were experiential in WEP/GO nanocomposites, with the augmentation of GO fillers from 0.1 to 0.3 % accordingly. For WEP/[email protected] nanocomposites also shows the same morphology with the increment of filler content from 0.1 to 0.3 %, particularly on the loading percentage of 0.2 wt%, nanocomposites are exposing high roughness and consistency dispersal achieved for the nanocomposites. This can recognize that, the bonding flanked by fillers (GO and [email protected]) and WEP matrix connected through covalent nature, and the well-bonded nanocomposites are helping to achieve the better mechanical properties. Figure 7d is demonstrating, the moderately weak interfacial connection between WEP matrix and GO, it leads to the uneven cracking gaps as well as less roughness (see the red circle in the Figure 7d) on the WEP/GO nanocomposites. Such aggregations of GO and deprived sheet/matrix connection may origin a stress concentration all through the rupture process, impairing stress shift from the form to the sheets. Relatively, the fractured surface of WEP/[email protected] nanocomposites (Figure 7e), exposed uniform breaking gap and fine-homogeneous distribution of fillers with WEP matrix. The smooth cracking may be, due to covalent bonding between the liners and WEP matrix and the better dispersion of the [email protected] hybrids in the matrix system. The better distribution and the better mechanical property obtained with the help of GO functionalization with Fe3O4 NPs followed by MPTMS.
3.3 Mechanical properties of WEP nanocomposites
The WEP/GO and WEP/[email protected] nanocomposites tensile strength test performed, and the analyses plot (stress-strain) displayed in Figure 8. The loading quantity of GO containing 0.2 wt %, revealed higher than 90% enrichment compared with neat WEP. Further, the decreasing strategy was observed, increasing the filler (GO) content from 0.2 to 0.5 wt%, the tensile strength decreasing from 90% to 55% respectively, which is far better than tidy WEP nanocomposites. The tensile strength decreases due to the higher loading of GO content may cause to agglomeration in the nanocomposites. Therefore, there are few reasons, for derisory and non-incessant development of tensile properties of the GO-based WEP nanocomposites, such as GO nanosheets aggregation and non-uniform dispersion (51). This is the main reason for the frail mixing of nanofiller and destitute compatibility among the GO layer and the matrix region. The squat load transfer competence at the interfaces due to the weak interfacial connection.
The essential enriched mechanical properties exposed in the case of WEP/[email protected] nanocomposites. Three times better tensile strength was achieved with the little amount of filler ([email protected], 0.2 wt %) content with WEP nanocomposites, compared with pure WEP nanocomposites. The tensile strength was decreasing with increasing the filler ([email protected]) content in the matrix, as like WEP/GO nanocomposites. The totaling of [email protected] filler from 02 to 0.5 % shows the tensile strength decreases from 37 MPa to 28 MPa compared to precise WEP. Based on the mechanical analysis report of 0.2 wt% [email protected] filler mixed WEP nanocomposites was exposed notable improvement in the tensile strength (about three times better results compared with tidy WEP) highlighting that the as-synthesized magnetite graphene oxide anchored sulfonic acid hybrids have the remarkable capability in the intensification of WEP. Although, the introduction as a filler of graphite sheets are exposed noteworthy enhancement in mechanical properties, due to its vast surface area. The increasing mechanical interlocking flanked by the furrowed façade of graphite layers and the WEP matrix and excellent adhesion characters are the main reason for enrichment in mechanical properties (52, 53).

On the other hand, incorporation of Fe3O4 NPs and thiol groups on the GO surface leads to improve the dispersion nature in a matrix system, since the modifications can increase the distance between the two layers of GO, and helps to inhibit the restocking and agglomeration of GO layers. The covalent bonding, during curing process because of availability of amine functionality in the curing agents with the fillers (GO and [email protected]) afford a rich-amine milieu close to the layers for epoxide groups of WEP. Consequently, the interfacial dealing flanked by different components becomes stronger. In the interim, the long malleable incorporation chains act as a notable character in load shifting from graphite sheets to the matrix.
The DMA properties of pure WEP and its nanocomposites (WEP/GO and WEP/[email protected] with different filler contents) demonstrated in Figure 9 and Table 2. The incorporation of GO and [email protected] can improve the storage modulus and (Tan Delta) Tg. Particularly, with the totaling 0.2 wt % content both the fillers (GO and [email protected]), exhibits extraordinary improvements in DMA properties for WEP nanocomposites. Figure 9b revealed that, the storage modulus of WEP/[email protected] nanocomposites. The loading content of [email protected] 0.2 wt % exposed that outstanding storage modulus for WEP composites. But, in the case of GO toting up to 0.2 wt % fails to attain the storage modulus same as modified GO-based WEP nanocomposites (WEP/[email protected]).

Moreover, the higher loading filler (GO) can destroy the toughness of WEP, since it causes aggregation and poor dispersion in the matrix system. In the case of WEP/[email protected], the excellent interface dealing between WEP and filler ([email protected]) achieved after modification of GO surface with Fe3O4 NPs and MPTMS. The GO functionalization was greatly helping to maintain less agglomeration and homogenous dispersion between filler and matrix system.
Figure 9c and d exposed the tan delta (Tg) plots of fillers (GO and [email protected]) and WEP nanocomposites. The data shows that the better performance was achieved during load apply on polymer nanocomposites and the results associated with incorporated fillers performance (54). The tan delta plots (Figure 9c and d) exposed that, the remarkable improvement of WEP composites, especially for the loading of 0.2 wt % of [email protected] (or GO) obtained the Tg value, not less than 131 °C (or 93 °C) which was far better than pure WEP nanocomposites ( 88 °C). The incorporation of nanofillers (GO and [email protected]) can able to enrich the glass transition temperature by 43 °C (for [email protected]) and 38 °C (for GO). The embedded fillers are making mutually confine mobility with WEP polymer chains appreciably with the intent that the respite can reap up at elevated temperature.

Moreover, the neat WEP nanocomposites Tg value shows higher than that of toting up 0.5 wt % loading of filler (GO). Indifference, hauling up 0.1 wt % loading of filler ([email protected]) to the WEP nanocomposites exhibited that the increase of 6 °C, compared to tidy WEP nanocomposites (without fillers (GO and [email protected]). Utterly, this variation refers to some critical reason for the changing of tan delta value, reliable with consequences of morphology from SEM analysis and tensile properties of nanocomposites. While increasing the loading of filler (GO) content in the matrix, cause the aggregation and restocking of GO sheets, and it leads to deprived dispersion in the model and interfacial interaction of GO and matrix. On the other hand, the well-discrete morphology was obtained for the filler ([email protected]) with matrix nanocomposites even at the higher loading. Few reasonable factors are acting important role for the considerable variation of tan delta value in the case of WEP/GO nanocomposites. The reduced WEP cross-linkage and increased mobility of the polymer segments exhibits, due to the incorporation of GO, because less dispersion can lead to slow down the curing process. Instead, the embedded GO layers may incarcerate matrix system and diminish the chain mobility. Besides, the WEP/GO nanocomposites Tg value decreasing strategy further confirmed with the earlier literature (55), due to the destabilized cross-linking of polymer matrix itself leads to diminishing cross-linking compactness and deprived mechanical behaviors.

In summary, the decreasing strategy of WEP/GO nanocomposites, due to the incorporation of GO increases the mobility in WEP matrix system. For WEP/[email protected] nanocomposites are achieved the remarkable improvement in mechanical properties. In the case of WEP/[email protected], the nail clippings of the grafting chains partake in the curing process of WEP to shape chemical bonds. The sulfonated magnetite GO and epoxide functionalities of WEP matrix, acting major part in continuing the cross-linking network compactness.Table 2 The glass transition temperature (Tg) of neat WEP and its nanocomposites.

Filler content
(wt%) Tg(°C)
WEP 0 88
WEP/GO 0.1 90
0.2 93
0.3 76
0.4 74
WEP/[email protected] 0.1 94
0.2 131
0.3 89
0.5 72
4. Conclusions
A narrative magnetically detachable graphene oxide anchored sulfonic acid hybrid fabricated by co-precipitation reaction followed by sulfonation with the help of MPTMS. After chemical alteration, the well-designed graphite oxide sheets were companionable fighting fit in WEP matrix, which is the most important to an enhanced dispersion and a stronger interface relation between fillers and model. As to the nanocomposites, the improved tensile strength and storage modulus at the loading of 0.2 wt% of well-designed graphene oxide with WEP reveals the notable enhancement of 300 % and 150 %, correspondingly. Much elevated Tg also obtained in the epoxy nanocomposites with the assimilation of [email protected], where about 43 °C elevated Tg is obtained at 0.2 wt% [email protected] compared to the bare WEP. Since, the squat cost, high efficiency, and smooth production of customized GO nanoparticles, the WEP/[email protected] nanocomposites with improved mechanical properties will broaden the application fields of WEP resin. Furthermore, our findings reveal the possibility of industrial use of WEP nanocomposites due to its better performance, and it would be the new path to pull on more research in the currently proposed fields.

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