Bioactive Thymol in Epoxy Network Toward Durable and Protective Polymeric Coatings

Bioactive Thymol in Epoxy Network Toward Durable and Protective Polymeric Coatings | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Bioactive Thymol in Epoxy Network Toward Durable and Protective Polymeric Coatings Arunkumar Patil, N S Pawar, Pundalik Mali, Madhukar Tayade, Kundan Borse, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7882858/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Thymol a bioactive phytochemical, is becoming an essential component in the synthesis of monomers, pushing forward advances in the design of functional polymers. The complex reaction process begins with thymol interacting with 1,4-Butanediol diglycidyl ether generates the reactive intermediate 3,3′-(butane-1,4-diylbis-oxy) bis(1-(2-isopropyl-5-methylphenoxy) propan-2-ol). This species undergoes further epoxidation to yield 2,2'-(3,12-bis((2-isopropyl-5-methylphenoxy) methyl)-2,5,10,13-tetraoxatetradecane-1,14-diyl) bis(oxirane) (shortly TMTO ). Thymol which is known for its antimicrobial properties synchronously enhances the protective qualities of coatings applied to metal substrates, thereby improving their resistance to environmental degradation. The structural and functional integrity of polymer was evaluated by analytical tools including techniques such as X-ray diffraction (XRD), gel fraction determination, water uptake measurement, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). These investigations unequivocally demonstrated the performance superiority of the thymol-derived epoxy (TMTO) in terms of molecular stability and reactivity. Further refinement of functional characteristics and molecular architecture was conducted using analytical techniques including gas chromatography coupled with mass spectrometry (GC-MS), proton nuclear magnetic resonance (¹H-NMR), and infrared (IR) spectroscopy were employed.. These techniques enabled an in-depth exploration of the cured epoxy's thermal robustness, mechanical durability, and anti-corrosive proficiency. Promoting TMTO as an optimal candidate for next-generation polymeric coatings to high-performance applications. Thymol Anticorrosion antioxidant Curing agent Antimicrobial Bioactive compound Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Thymol, a naturally occurring monoterpene phenol, is primarily present in the essential oil of Thymus vulgaris and other Lamiaceae species. It exhibits potent antimicrobial, antioxidant, and anti-inflammatory properties [ 1 ], and its hydrophobic nature enables efficient penetration of biological membranes, making it a promising candidate for antiseptics, preservatives, and other bioactive formulations [ 1 – 2 ]. Plant secondary metabolites, especially phenolic compounds, are abundant bioactive molecules, encompassing both volatile and non-volatile types. Non-volatile phenolics include tannins, flavonoids, and phenolic acids, while volatile phenolic terpenes, such as thymol and its isomer carvacrol, are found in essential oils from genera like Thymus , Ocimum , Origanum , Satureja , Thymbra , and Monarda [ 3 – 4 ]. Commercially, thymol is synthesized via aromatization of γ-terpinene to p-cymene followed by hydroxylation [ 5 ]. Its broad bioactivities and industrial applications in food, cosmetics, and pharmaceuticals underscore its potential as a natural alternative to synthetic chemicals, though further research is needed to fully assess its safety and long-term effects. Organic coatings are widely used to protect metals from corrosion by acting as a barrier against environmental exposure [ 6 ]. Epoxy resins are especially valued for their mechanical strength, thermal stability, and chemical resistance. Recent enhancements, such as incorporating metal oxides (ZnO, TiO₂) or organic compounds (polyaniline), have improved barrier properties, adhesion, and self-healing capabilities [ 7 – 8 ]. Bio-based coatings are gaining attention for sustainability, with plant oils explored as additives or modifiers. For example, epoxidized soybean oil incorporated into epoxy resin has been shown to improve curing, wettability, and mechanical properties, yielding effective corrosion protection [ 9 ]. Similarly, Li et al. [ 10 ] developed self-healing coatings by embedding tung oil in urea-formaldehyde microcapsules, and Veedu et al. [ 11 ] demonstrated that Ixora leaf extract enhanced epoxy coating corrosion resistance through phytochemical–metal interactions. Epoxy resins are extensively employed in various industrial applications, including coatings, adhesives, and composite materials, due to their remarkable mechanical strength, chemical stability, and long-lasting performance [ 12 – 13 ]. Nevertheless, the majority of conventional epoxy resins are derived from petroleum-based sources. Which are not environmentally friendly and can be harmful to health. To address these concerns, researchers are exploring bio-based alternatives that are safer and more sustainable. One promising natural compound is thymol, a phenolic compound found in thyme oil [ 2 ]. Thymol is known for its antimicrobial, antioxidant, and thermal stability properties, making it a valuable ingredient for developing functional epoxy materials. Its chemical structure allows it to react with epoxy components, forming strong cross-linked networks while also adding bioactive features. To further improve the performance of thymol-based epoxy resins, nanoparticles are introduced into the system. These nanoparticles—such as nano-silica, titanium dioxide (TiO₂), or graphene oxide—act as reinforcing agents. They contribute to improving the mechanical durability, thermal resistance, and barrier performance of the epoxy resin. Moreover, nanoparticles facilitate a more uniform distribution of thymol throughout the matrix and may also contribute to antibacterial and UV-resistant properties, depending on the type used. The combination of thymol and nanoparticles creates a hybrid material that is not only strong and durable but also eco-friendly and multifunctional 14–16]. The present research investigates the preparation and detailed analysis and performance evaluation of thymol-based epoxy resins reinforced with nanoparticles. The goal is to develop a new class of green nanocomposites that combine the benefits of natural bioactive compounds with advanced nanotechnology. This study investigates the development of bio-based epoxy hybrid coatings, with an emphasis on evaluating their corrosion resistance, adhesion, and overall coating characteristics when applied to galvanized steel. A commercially sourced epoxy resin, featuring alkoxy groups along with epoxy functionalities and a hardener, was employed to modify the polymer matrix. The modification was intended to examine how various functional groups affect the performance of the hybrid coatings. Additionally, a novel thymol-based epoxy curing agent was synthesized and incorporated into the epoxy system at five different concentrations (0, 5, 10, 15, and 20 wt%). This approach aimed to assess the influence of the curing agent concentration on the corrosion resistance and adhesion behavior of the resulting coating films. 2. Experimental 2.1 Materials and Methods: The chemicals used in this study were obtained from various suppliers. Methylene dichloride, N,N-Dimethylformamide, tetrahydrofuran, epichlorohydrin, Tetra butyl ammonium bromide (TBAB), and 1,4-butandiol diglycidyl ether were procured from Spectrochem Pvt. Ltd., Kalbadevi Road, Mumbai. Potassium carbonate and potassium tert-butoxide were purchased from Sigma-Aldrich, Gujarat. Thymol was kindly provided by Pratap College, Amalner, Maharashtra. All reagents were of analytical grade and were used as received without additional purification. Fourier Transform Infrared (FTIR) spectroscopy was performed to characterize the samples over a spectral range of 400–4000 cm⁻¹, following ASTM D7371-14, using a Perkin Elmer instrument (USA). Samples were prepared using the Diamond ATR technique to ensure accurate spectral measurements. Thermal stability was evaluated through thermogravimetric analysis (TGA) of TMTO-cured samples using a Q600 thermal analyzer (TA Instruments, USA). Samples were placed in a weighing pan and analyzed under a nitrogen atmosphere, with a heating rate of 5°C/min over the temperature range of 50–600°C. Chemical composition analysis was carried out using gas chromatography-mass spectrometry (GC-MS) on methylene dichloride-diluted samples, performed with a Shimadzu QP 2010 system. Proton nuclear magnetic resonance (¹H NMR) spectra were recorded using a Bruker AV500WB system operating at 400 MHz, with DMSO as the solvent. Differential scanning calorimetry (DSC) was conducted to study thermal behavior using a TA SDT Q600 instrument at a heating rate of 5°C/min. Gel content of UV-cured films was determined according to ASTM D2765-16 by immersing the films in xylene for 24 hours, followed by drying at 65–70°C until a constant weight was achieved. Water absorption of cured films was evaluated as per ASTM D570 standards. Structural characteristics of TMTO-cured films were investigated using X-ray diffraction (XRD) with a Bruker D-8 Advance system to examine the d-spacing patterns. Corrosion resistance of the material applied to galvanized steel plates was assessed using the salt spray method, following ASTM B117 standards, to provide a comprehensive evaluation of durability. 2.2. Synthesis of thymol-based resin: 2.2.1 Synthesis of 3,3'-(butane-1,4-diylbis(oxy)) bis(1-(2-isopropyl-5-methylphenoxy) propan-2-ol) [TBMP]: The synthetic route for TBMP is illustrated in Scheme-1. In a clean and dry round-bottom flask, 2.0 g (0.0133 mol) of thymol was dissolved in 12 mL of N,N-dimethylformamide (DMF). Subsequently, 1.07 g (0.005 mol) of 1,4-butandiol diglycidyl ether (BDGE) was added. Potassium carbonate powder (4.59 g, 0.033 mol) was employed as a base, and tetrabutylammonium bromide (TBAB, 0.002 g, 0.1%) was introduced as a phase-transfer catalyst. The reaction was conducted under a dry nitrogen atmosphere to maintain optimal conditions. The mixture was initially stirred at 25–30°C for 10–15 minutes, then gradually heated to 85–90°C and maintained at this temperature for 6–8 hours to ensure reaction completion. Progress of the reaction was monitored using thin-layer chromatography (TLC) with a 4:6 ethyl acetate/n-hexane mobile phase (Rf values: SM = 0.35, TBMP = 0.2). Upon completion, the product was extracted with ethyl acetate, and the organic phase was washed with water. Removal of the solvent under reduced pressure at 35–40°C yielded 5.7 g of TBMP as a yellow liquid, corresponding to an excellent yield of 85–90%. The 1 H NMR spectrum of TBMP in CDCl₃ showed characteristic signals: a doublet at 1.19–1.21 ppm (a, a’, 12H) corresponding to the methyl protons of the isopropyl groups on the aromatic rings; 1.65–1.69 ppm (b, b’, 4H) for the methylene protons of the aliphatic chain; a singlet at 2.3 ppm (c, c’, 6H) for methyl groups attached to the aromatic rings; 2.66–2.68 ppm (d, d’, 2H) for hydroxyl protons; a multiplet at 3.2–3.3 ppm (e, e’, 2H) representing the methine protons of the isopropyl groups; a doublet at 3.53–3.59 ppm (f, f’, 4H) corresponding to -CH2- protons linked to the aliphatic -O- chain; a doublet at 4.0–4.11 ppm (g, g’, 4H) due to -CH2 protons adjacent to phenolic hydroxyl groups; a multiplet at 4.15–4.22 ppm (h, h’, 2H) assigned to -CH protons attached to hydroxyl groups; a doublet at 6.67 ppm (i, i’, 2H) and another doublet of doublets at 6.75–6.77 ppm (j, j’, 2H) corresponding to aromatic protons; and a doublet at 7.08–7.10 ppm (k, k’, 2H) also due to aromatic protons. 2.2.2 Synthesis of 2,2'-(3,12-bis((2-isopropyl-5-methylphenoxy) methyl)-2,5,10,13-tetraoxatetradecane-1,14-diyl) bis(oxirane) (TMTO): The synthetic pathway for 2,2'-(3,12-bis((2-isopropyl-5-methylphenoxy)methyl)-2,5,10,13-tetraoxatetradecane-1,14-diyl) bis(oxirane) (TMTO) is illustrated in Scheme 2 . In a clean, dry round-bottom flask, TBMP (2.0 g, 0.004 mol) and epichlorohydrin (1.94 g, 0.021 mol) were combined in the presence of potassium tert-butoxide powder (1.34 g, 0.012 mol) as the base, with tetrabutylammonium bromide (TBAB, 0.002 g, 0.1%) acting as a phase-transfer catalyst. The reaction was carried out in tetrahydrofuran (16 mL) at 5–10°C. Subsequently, the reaction mixture was heated to 40–45°C and stirred for 10–12 hours. Reaction progress was monitored by thin-layer chromatography (TLC) using a 3:7 mixture of ethyl acetate and n-hexane as the mobile phase (Rf values: starting material 0.2, TMTO 0.4). After completion, the solvent was removed under reduced pressure at 35–40°C. The residue was diluted with ethyl acetate and water, and the pH was adjusted to 6–7 using 2 N HCl. The organic layer was washed with water to remove inorganic impurities, and the solvent was evaporated under vacuum at 35–40°C to yield TMTO as a pale-yellow liquid (2.2 g, 86.5% yield). The ^1H NMR spectrum of TMTO in DMDO-d6 showed characteristic peaks corresponding to its structure. The doublet at 1.18–1.21 ppm (a, a’, 12H) corresponds to the methyl protons of the isopropyl groups on the aromatic rings, while the multiplet at 1.58–1.59 ppm (b, b’, 4H) arises from CH2-CH2 protons of the aliphatic chain. A singlet at 2.3 ppm (c, c’, 6H) is attributed to the methyl groups attached to the aromatic rings. The doublets of doublets at 2.59–2.61 ppm (d, d’, 2H) and 2.76–2.78 ppm (e, e’, 2H) correspond to CH2 protons adjacent to the O-CH2 of the epoxy ring, whereas the multiplet at 3.13–3.15 ppm (f, f’, 2H) is due to the CH proton bonded to the O-CH of the epoxy ring. Signals at 3.20–3.26 ppm (g, g’, 2H) represent the CH protons of the isopropyl groups, and the doublet at 3.47–3.49 ppm (h, h’, 4H) corresponds to CH2 protons of the O-CH2 aliphatic chain. The multiplet at 3.51–3.54 ppm (i, i’, 2H) is assigned to CH protons bonded to oxygen near the epoxy ring, and the multiplet at 3.52–3.59 ppm (j, j’, 4H) corresponds to the CH2-CH2 protons of the aliphatic chain linked to oxygen. The doublet at 3.90–3.93 ppm (k, k’, 4H) arises from CH2-CH2 protons adjacent to oxygen, and the signals at 3.99–4.11 ppm (l, l’, 4H) are due to CH2 groups connected to the phenoxy moiety. Aromatic protons appear as a doublet at 6.74–6.76 ppm (m, m’, 2H), a singlet at 6.79 ppm (n, n’, 2H), and a doublet at 7.08–7.10 ppm (o, o’, 2H). 2.2.3 Preparation of TMTO bio-based coating formulation ( Scheme 3 ) The TMTO bio-based curing agent was prepared by blending it with varying weight percentages of bisphenol A-based epoxy resin (YD128), an initiator, and accurately measured amounts of the hardener triethylenetetramine (TETA, 0.1 mol%) along with cerium oxide (CeO₂) nanoparticles (2.0 mol%). The detailed formulation is presented in Table 1 and Scheme 3 . These mixtures were then applied onto galvanized steel panels (7.5 cm × 9.5 cm) to form a uniform coating. In parallel, free-standing TMTO-cured bio-based polymer films were fabricated by casting the formulations into thin, transparent Teflon molds. Both the coated panels and the polymer films were subsequently cured in an oven at 50–55°C for 12–16 hours under ambient air conditions to ensure complete polymerization. Table 1 Formulation of epoxy resin with TMTO curing agent Sr. No. Ingredients TMTO curing agents’ weight % (0.1 mole % of TETA initiator) 1 Epoxy resin 100 98 93 88 83 78 2 TMTO Curing agent 0 0 5 10 15 20 3 Cerium oxide (CeO 2 ) 0 2 2 2 2 2 3 Total 100 100 100 100 100 100 3. Results and discussion 3.1 FTIR Analysis of TBMP and TMTO The FTIR spectrum of TBMP is presented in Fig. 1 ( Supporting Information ). A prominent absorption band at 3411.59 cm⁻¹ corresponds to the O-H stretching, which arises from the epoxy ring opening reaction between thymol and BDGE. The band observed at 2927.25 cm⁻¹ is attributed to the C-H stretching of the oxygen-bound groups, while the peak at 2867.69 cm⁻¹ is associated with the stretching vibrations of aromatic and aliphatic C-H groups. Peaks at 1611.94 cm⁻¹ and 1505.46 cm⁻¹ indicate the C = C stretching within the aromatic ring. The FTIR spectrum of TMTO is depicted in Fig. 2 ( Supporting Information ). The absorption at 2923.52 cm⁻¹ arises from C-H stretching of oxygen-linked groups, and the band at 2867.78 cm⁻¹ corresponds to aromatic and aliphatic C-H stretching. The aromatic C = C stretching is observed at 1611.54 cm⁻¹ and 1505.49 cm⁻¹. The strong band at 1169.77 cm⁻¹ is assigned to the C-O-C stretch of the oxirane ring. Notably, the O-H band present in TBMP at 3411.59 cm⁻¹ disappears in TMTO, confirming the successful synthesis of TMTO. 3.2 GC-MS Analysis of TBMP and TMTO The GC-MS spectrum of TBMP, shown in Fig. 3 ( Supporting Information ), confirms its structure. The data indicate that thymol reacts with BDGE through a ring-opening addition to form TBMP. The base peak at m/z = 503.5 (positive mode) corresponds to the TBMP intermediate, which has a molecular weight of 530.6. The GC-MS spectrum of TMTO (Fig. 4 , Supporting Information ) displays a molecular ion peak at m/z = 637.4 (M + 23, positive mode), representing the sodium adduct of TMTO, consistent with a molecular weight of 614.4. 3.3 ¹H NMR Analysis of TBMP The ¹H NMR spectrum of TBMP in CDCl₃ (Fig. 5, Supporting Information ) shows a doublet at 1.19–1.21 ppm (12H) corresponding to -CH₃ protons of the isopropyl groups on the aromatic ring. Signals at 1.65–1.69 ppm (4H) correspond to CH₂-CH₂ protons of the aliphatic chain. A singlet at 2.3 ppm (6H) arises from -CH₃ protons attached to the aromatic ring. The -OH proton of the hydroxyl group appears as a doublet at 2.66–2.68 ppm (2H). Multiplets at 3.2–3.3 ppm (2H) correspond to -CH protons of the isopropyl groups, and doublets at 3.53–3.59 ppm (4H) represent -CH₂ protons attached to -O-CH₂ of the aliphatic chain. Peaks at 4.0–4.11 ppm (4H) and 4.15–4.22 ppm (2H) are attributed to -CH₂ and -CH protons linked to phenolic OH groups. Aromatic protons appear as a doublet at 6.67 ppm (2H), a doublet of doublets at 6.75–6.77 ppm (2H), and a doublet at 7.08–7.10 ppm (2H). 3.4 ¹H NMR Analysis of TMTO The ¹H NMR spectrum of TMTO in DMSO-d₆ (Fig. 6, Supporting Information ) shows a doublet at 1.18–1.21 ppm (12H) corresponding to -CH₃ protons of the isopropyl groups. Multiplets at 1.58–1.59 ppm (4H) arise from CH₂-CH₂ protons of the aliphatic chain. A singlet at 2.3 ppm (6H) is attributed to -CH₃ protons attached to the aromatic ring. Doublets of doublets at 2.59–2.61 ppm and 2.76–2.78 ppm (2H each) correspond to CH₂ protons adjacent to O-CH₂ in the epoxy ring. Multiplets at 3.13–3.15 ppm (2H) and 3.20–3.26 ppm (2H) correspond to -CH protons of the epoxy-linked chain and isopropyl groups, respectively. Doublets at 3.47–3.49 ppm (4H) and multiplets at 3.51–3.54 ppm (2H) and 3.52–3.59 ppm (4H) correspond to -CH₂ and -CH protons of the aliphatic chain and epoxy ring. Peaks at 3.90–3.93 ppm (4H) and 3.99–4.11 ppm (4H) are attributed to -CH₂ groups linked to the aliphatic and phenoxy groups. Aromatic protons appear as a doublet at 6.74–6.76 ppm (2H), a singlet at 6.79 ppm (2H), and a doublet at 7.08–7.10 ppm (2H). 3.4 Mechanical Properties of Bio-based Epoxy Resin 3.4.1 Thermal Characteristics of TMTO-Epoxy Films The thermal stability of the cured epoxy samples was examined using thermogravimetric analysis (TGA), as illustrated in Fig. 1 . The residual char content of the cured films increases with higher TMTO concentrations, showing 15% and 20% TMTO samples possess greater char formation than those containing 5% and 10% TMTO. TGA data indicate that all the coated films undergo a single-step degradation process, resulting in roughly 50% weight loss occurring up to 400°C. The onset of degradation is observed at approximately 290°C, primarily due to the breakdown of aliphatic hydrocarbon segments within the cured epoxy and its cross-linked network. Notably, samples containing 15% and 20% TMTO demonstrate improved thermal resistance, with degradation temperatures rising to 415°C and 420°C, respectively, surpassing the thermal stability of the films with lower TMTO content and those without TMTO. Moreover, the sample, containing the highest TMTO and CeO₂ content, demonstrated superior stability with decomposition onset near 290°C and over 30% residue at 600°C. These results show improving flame retardancy and thermal endurance of epoxy matrices, making them promising candidates for high-temperature protective coatings [ 17 ]. Figure 2 illustrates the thermal behaviour of TMTO-modified epoxy systems across various formulations. Differential Scanning Calorimetry (DSC) was employed to assess the glass transition temperature (Tg) of the cured coatings. A progressive reduction in Tg was observed with increasing TMTO content, indicating enhanced molecular mobility within the polymer network. As shown in Fig. 2 , each formulation displayed a distinct single Tg, confirming homogeneous phase behaviour. This thermal softening effect imparts valuable flexibility and energy degeneracy characteristics, making these coatings particularly well-suited for applications such as flexible adhesives, electronic encapsulants, and protective layers subjected to thermal or mechanical stress [ 17 ]. Their capacity to absorb strain and reduce vibrations positions them as promising alternatives in environments where conventional rigid epoxies may underperform. 3.4.2 Determination of Gel Content and Water Absorption The degree of photopolymerization in the resin, with and without the addition of TMTO, was evaluated through the gel content analysis using solvent extraction. Figure 3 presents the relationship between gel content and various TMTO concentrations. For this test, the cured polymer films were carefully peeled off from the Teflon substrate. Samples of known initial weight were immersed in methyl ethyl ketone at room temperature for 48 hours. Following extraction, the films were removed and dried at 70°C until a constant weight was obtained. The results indicated a steady increase in gel content with higher TMTO loading, implying the formation of a denser and more stable cross-linked polymer network, which contributes to improved coating characteristics [ 18 ]. Figure 3 illustrates a direct trend in water absorption behaviour, showing a decline as TMTO concentration rises. This reduction is attributed to the increased crosslinking within the polymer network, which minimizes free volume and restricts water infiltration. TMTO-based coating material effectively limits water entry, thereby enhancing the coating’s resistance. Furthermore, the aromatic structure within the epoxy resin backbone imparts hydrophobic characteristics, enhancing water resistance through cross-link formation [ 19 ]. Consequently, coatings containing a higher proportion of curing agents demonstrate reduced water absorption. 3.4.3 X‑ray diffraction (XRD) of TMTO cured films The X-ray diffraction (XRD) patterns of dried TMTO films were evaluated, as given in Fig. 4 . The analysis revealed that the control sample (TM2), which did not contain thymol or cerium oxide, exhibited a broad halo, indicating an amorphous structure. In contrast, sample TM1, which included cerium oxide nanoparticles, displayed sharp diffraction peaks at approximately 28.5°, 33.0°, 47.4°, and 56.3° 2θ. These peaks correspond to the (111), (200), (220), and (311) planes of crystalline CeO₂. Samples TM3 to TM6, which contained increasing concentrations of thymol (5–20 wt%), showed a gradual reduction in peak intensity and broadening. This suggests a decrease in crystallinity, likely due to the amorphous nature of thymol [ 20 ][ 21 ]. The XRD results confirm that cerium oxide nanoparticles introduce a crystalline phase into the epoxy matrix, while higher concentrations of thymol disrupt this order. These structural changes also impact the thermal behavior of films. While CeO₂ enhances thermal resistance, thymol reduces it, as it has a lower decomposition temperature and interferes with the dispersion of nanoparticles. Additionally, the observed decrease in the glass transition temperature (Tg) with thymol addition supports the idea of matrix plasticization, which may enhance flexibility and enable controlled release of thymol. Overall, these findings highlight how thymol modifies the structural order and tunes the thermal response of the composite. 3.4.4 Scanning Electron Microscopy Analysis (SEM) Figure 5 presents the SEM micrographs depicting the morphology of the coating matrix. The morphological evolution of the epoxy coating was investigated through SEM imaging, highlighting the combined effect of TMTO incorporation and cerium oxide nano powder dispersion. At 0% TMTO, the surface appears relatively smooth and lacks textural complexity. With progressive inclusion of TMTO at 5%, 10%, and 15%, the surface begins to display enhanced microstructural uniformity and increased nanopatterning, indicative of improved polymer chain crosslinking and cohesive interfacial bonding. The introduction of cerium oxide nano powder further amplifies these effects by acting as an active nanofiller, facilitating homogeneous phase dispersion and impeding agglomeration. Its presence contributes to a denser, more refined surface architecture by filling micro voids and enhancing interfacial compatibility within the matrix. By the time 20% TMTO is reached, the SEM micrographs show a highly ordered, layer-by-layer nanostructure with pronounced surface gratings—suggestive of harmonious strengthening from both the curing agent and the nano powder. This dual-modifier system not only optimizes surface topography but also implies superior mechanical integrity and environmental resistance. The observed morphological improvements position the composite system as a strong candidate for high-performance coating and protective applications. 3.4.5 Anticorrosion Performance Analysis: After 650 hours of salt spray exposure, the coated specimens with TMTO-based epoxy coatings were examined for their anticorrosion behaviour, as illustrated in Fig. 6 . The extent of corrosion beneath the coatings was evaluated in accordance with ASTM B117 standards, and the results are summarized in Table 2 . The reference coating exhibited clear evidence of degradation, including rust formation, blistering, and partial detachment of the film. The appearance of darkened areas near the scribed region indicates moisture ingress through the coating. These findings provide important insights into the material’s performance and highlight areas for potential improvement. The observed corrosion and rusting in the reference sample can be attributed to the interaction of water, oxygen, and aggressive ions such as H+, OH−, and Cl−, which promote blistering and surface damage. Conversely, the TMTO-incorporated coatings displayed markedly enhanced corrosion resistance, primarily due to the formation of a stable oxide layer on the metal surface, as previously verified by DSC analysis. Table 2 Adhesion test result according to ASTM B117 Corrosion test result according to ASTM B117 Sr. No. Coatings Before salt spray After salt spry 1 0% TMTO 5B 5B 5 2 5% TMTO 5B 4B 7 3 10% TMTO 5B 4B 7 4 15% TMTO 5B 4B 8 5 20% TMTO 5B 4B 8 Samples cured using thymol-derived agents exhibit a significant improvement in corrosion resistance. This enhancement is mainly attributed to the development of a stable oxide film on the metal surface, as previously verified through SEM analysis. The thymol-based TMTO curing agent facilitates the formation of this protective oxide layer, effectively acting as a barrier against corrosive attack. Hence, the incorporation of this curing agent represents a promising approach for enhancing the long-term durability of metal coatings. In regions where scratches occur, greater water ingress can result in blister formation near the damaged sites. Nevertheless, the presence of the stable oxide film and the strong interfacial adhesion between the coating and the metal substrate help minimize blistering compared to coatings cured without TMTO . 3.4.6 Antimicrobial Behaviour of Thymol-Epoxy Resin: The biological activity of polymeric materials is strongly influenced by their molecular architecture. Key structural parameters such as chain length, the density and type of functional groups, hydrophilic–hydrophobic balance, as well as surface charge (cationicity) play pivotal roles in determining their interaction with biological systems. These characteristics govern not only the physicochemical behaviour of the material but also its ability to inhibit microbial growth and adhere to biological surfaces. In recent years, epoxy-based systems have gained attention for their potential in antimicrobial and bioactive applications. Among these, TMTO (thymol-derived monoepoxide) has emerged as a promising bi-functional curing agent. Its symmetrical molecular structure and dual epoxy functionality enable it to serve both as a cross-linking agent and a bioactive component. The concept of using the curing agent itself as a functional template introduces a novel strategy in epoxy design. This approach not only facilitates efficient network formation but also imparts biological functionality to the cured material. Such dual-purpose systems are particularly valuable in applications requiring both structural integrity and antimicrobial performance, such as biomedical coatings, flexible adhesives, and encapsulants for sensitive electronics. Supporting literature highlights the effectiveness of phenolic epoxides in biological applications. For example, curing a mixture of mono-epoxidized thymol and di-epoxy resorcinol with an iodonium salt under photopolymerization conditions yields epoxy co-networks exhibiting notable antimicrobial activity. The inclusion of phenolic compounds like thymol has been shown to enhance antibacterial performance, with studies reporting significant reduction in bacterial adhesion. These findings underscore the potential of phenol-derived epoxy systems in developing next-generation functional coatings and materials for hygienic and biomedical use. Table 3 shows that epoxy resins with symmetrical thymol-based structures work better at fighting bacteria. This is likely because their balanced design helps them interact more effectively with bacterial cell membranes, causing damage that leads to cell death. As demonstrated in Fig. 7 and Table 3 , the antimicrobial activity was evaluated using the disc diffusion method of TMTO-based curing agents against three bacterial strains and one fungal strain. The molecular profiles of these agents showed notable differences compared to the standard reference. The antimicrobial responses varied across the samples: Sample C exhibited moderate inhibition of Gram-negative bacteria and fungi. Sample D displayed strong, broad-spectrum antimicrobial activity. Sample E was particularly effective against fungal strains. Sample F showed moderate activity against Gram-negative bacteria. All tested samples showed positive results against Staphylococcus aureus , Escherichia coli , and Rhizopus oryzae . Compared to the blank control, the coating formulations significantly inhibited microbial growth. These outcomes suggest that the TMTO-based coatings hold promise as effective antimicrobial surfaces. Table 3 Antimicrobial disc diffusion assay results of curing agent. Entry Gram-positive bacteria Gram-negative bacteria Fungi S.A. MTCC96 E.C. MTCC739 R.O. MTCC1009 A 1000 µg/mL 1000 µg/mL 1000 µg/mL B 125 µg/mL 1000 µg/mL 1000 µg/mL C 1000 µg/mL 250 µg/mL 250 µg/mL D 250 µg/mL 62.5 µg/mL 62.5 µg/mL E 1000 µg/mL 1000 µg/mL 250 µg/mL F 1000 µg/mL 100 µg/mL 500 µg/mL STREPTOMYCIN - 50 µg/mL - AMPICILLIN 100 µg/mL - - NYSTATIN - - 100 µg/mL Boldfaced values indicate the active compounds; S.A., Staphylococcus aureus ; E.C., Escherichia coli ; R.O., Rhizopus oryzae ; MTCC, microbial-type culture collection Conclusion In this work, an epoxy resin system was modified using a bio-derived curing agent synthesized from thymol to evaluate its thermal stability, corrosion resistance, and other physicochemical characteristics. The gel content and water absorption analyses revealed that the degree of photopolymerization in the cured composites increased notably with higher concentrations of the thymol-based curing agent. X-ray diffraction (XRD) analysis confirmed a fully amorphous structure after curing, signifying the successful incorporation of the TMTO curing agent into the epoxy matrix and its uniform dispersion within the polymeric soft domains. Salt spray testing demonstrated that samples containing the maximum proportion of curing agent exhibited the most effective corrosion protection. Overall, the increasing interest in bio-based curing agents provides opportunities for chemical industries to develop fully sustainable epoxy networks. Thymol, a naturally occurring phenolic compound, can be utilized to produce bio-based curing agents capable of substituting conventional aliphatic and aromatic hardeners. Such agents hold significant potential as eco-friendly alternatives to petroleum-based systems, enabling the fabrication of entirely bio-based epoxy materials. The integration of TMTO curing agents into epoxy formulations resulted in coatings with superior film quality, along with enhanced thermal, mechanical, and antimicrobial performance compared to conventional epoxy resins, owing to their distinct curing mechanisms. Declarations Data Availability: The data that support the findings of this study are available on within the article. Declaration for conflict of interest The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Authors contribution: AP: Experimental investigation, validation, and formal analysis, Writing - Review & Editing NSP: formal analysis and validation; Writing - Review & Editing. PM: Resources and data curation, MT: conceptualization and supervision; KB: conceptualization and supervision; VP: Writing - Review & Editing, visualisation and supervision. Acknowledgement : Dr. Vikas Patil is thankful to UGC for his position through the Faculty Recharge Program. Funding Declarations : The work has no funding received. References Kowalczyk A, Przychodna M, Sopata S, Bodalska A, Fecka I (2020) Thymol and thyme essential oil—new insights into selected therapeutic applications. Molecules 25(18):4125 Salehi B et al (2018) Thymol, thyme, and other plant sources: Health and potential uses. Phyther Res 32(9):1688–1706 Moein MR, Zomorodian K, Pakshir K, Yavari F, Motamedi M, Zarshenas MM (2015) Trachyspermum ammi (L.) sprague: chemical composition of essential oil and antimicrobial activities of respective fractions. J Evid Based Complement Altern Med 20(1):50–56 Marchese A et al (2016) Antibacterial and antifungal activities of thymol: A brief review of the literature. 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J Fire Sci - J FIRE SCI 29:259–296. 10.1177/0734904110395469 Malik M, Kaur R (Feb. 2018) Mechanical and Thermal Properties of Castor Oil–Based Polyurethane Adhesive: Effect of TiO2 Filler. Adv Polym Technol 37(1):24–30. https://doi.org/10.1002/adv.21637 Ifijen IH, Maliki M (2023) A comprehensive review on the synthesis and photothermal cancer therapy of titanium nitride nanostructures. Inorg Nano-Metal Chem 53(4):366–387 Idumah CI (Jun. 2020) Emerging advancements in flame retardancy of polypropylene nanocomposites. J Thermoplast Compos Mater p. 0892705720930782. 10.1177/0892705720930782 Mali P, Sonawane NS, Patil V, Lokhande G, Mawale R, Pawar N (2021) Morphology of wood degradation and flame retardants wood coating technology: an overview, Int. Wood Prod. J. , pp. 1–20, Dec. 10.1080/20426445.2021.2011552 Kumar B, Agumba DO, Pham DH, Kim HC, Kim J (2022) Recent progress in bio-based eugenol resins: From synthetic strategies to structural properties and coating applications. J Appl Polym Sci 139(2):51532 Donley MS, Mantz RA, Khramov AN, Balbyshev VN, Kasten LS, Gaspar DJ (2003) The self-assembled nanophase particle (SNAP) process: a nanoscience approach to coatings. Prog Org Coat 47(3):401–415. https://doi.org/10.1016/j.porgcoat.2003.08.017 Kaur R, Kumar M (2020) Addition of anti-flaming agents in castor oil based rigid polyurethane foams: studies on mechanical and flammable behaviour. Mater Res Express 7(1):15333. 10.1088/2053-1591/ab68a2 Schemes Schemes 1 to 3 are available in the Supplementary Files section. Supplementary Files Scheme1.png Scheme2.png SupportingInformation.docx Scheme3.png Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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14:08:01","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":1745662,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7882858/v1/ec4f9eb8dcf6556cc41d2a18.docx"},{"id":96758957,"identity":"8ad66917-51d5-4205-aafd-07869f56dcf7","added_by":"auto","created_at":"2025-11-25 18:36:30","extension":"png","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":43126,"visible":true,"origin":"","legend":"","description":"","filename":"Scheme3.png","url":"https://assets-eu.researchsquare.com/files/rs-7882858/v1/841cfafd8721de1316e5b6a1.png"}],"financialInterests":"","formattedTitle":"Bioactive Thymol in Epoxy Network Toward Durable and Protective Polymeric Coatings","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThymol, a naturally occurring monoterpene phenol, is primarily present in the essential oil of \u003cem\u003eThymus vulgaris\u003c/em\u003e and other Lamiaceae species. It exhibits potent antimicrobial, antioxidant, and anti-inflammatory properties [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], and its hydrophobic nature enables efficient penetration of biological membranes, making it a promising candidate for antiseptics, preservatives, and other bioactive formulations [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Plant secondary metabolites, especially phenolic compounds, are abundant bioactive molecules, encompassing both volatile and non-volatile types. Non-volatile phenolics include tannins, flavonoids, and phenolic acids, while volatile phenolic terpenes, such as thymol and its isomer carvacrol, are found in essential oils from genera like \u003cem\u003eThymus\u003c/em\u003e, \u003cem\u003eOcimum\u003c/em\u003e, \u003cem\u003eOriganum\u003c/em\u003e, \u003cem\u003eSatureja\u003c/em\u003e, \u003cem\u003eThymbra\u003c/em\u003e, and \u003cem\u003eMonarda\u003c/em\u003e [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Commercially, thymol is synthesized via aromatization of γ-terpinene to p-cymene followed by hydroxylation [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Its broad bioactivities and industrial applications in food, cosmetics, and pharmaceuticals underscore its potential as a natural alternative to synthetic chemicals, though further research is needed to fully assess its safety and long-term effects.\u003c/p\u003e\u003cp\u003eOrganic coatings are widely used to protect metals from corrosion by acting as a barrier against environmental exposure [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Epoxy resins are especially valued for their mechanical strength, thermal stability, and chemical resistance. Recent enhancements, such as incorporating metal oxides (ZnO, TiO₂) or organic compounds (polyaniline), have improved barrier properties, adhesion, and self-healing capabilities [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Bio-based coatings are gaining attention for sustainability, with plant oils explored as additives or modifiers. For example, epoxidized soybean oil incorporated into epoxy resin has been shown to improve curing, wettability, and mechanical properties, yielding effective corrosion protection [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Similarly, Li et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] developed self-healing coatings by embedding tung oil in urea-formaldehyde microcapsules, and Veedu et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] demonstrated that Ixora leaf extract enhanced epoxy coating corrosion resistance through phytochemical\u0026ndash;metal interactions.\u003c/p\u003e\u003cp\u003eEpoxy resins are extensively employed in various industrial applications, including coatings, adhesives, and composite materials, due to their remarkable mechanical strength, chemical stability, and long-lasting performance [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Nevertheless, the majority of conventional epoxy resins are derived from petroleum-based sources. Which are not environmentally friendly and can be harmful to health. To address these concerns, researchers are exploring bio-based alternatives that are safer and more sustainable. One promising natural compound is thymol, a phenolic compound found in thyme oil [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Thymol is known for its antimicrobial, antioxidant, and thermal stability properties, making it a valuable ingredient for developing functional epoxy materials. Its chemical structure allows it to react with epoxy components, forming strong cross-linked networks while also adding bioactive features. To further improve the performance of thymol-based epoxy resins, nanoparticles are introduced into the system. These nanoparticles\u0026mdash;such as nano-silica, titanium dioxide (TiO₂), or graphene oxide\u0026mdash;act as reinforcing agents. They contribute to improving the mechanical durability, thermal resistance, and barrier performance of the epoxy resin. Moreover, nanoparticles facilitate a more uniform distribution of thymol throughout the matrix and may also contribute to antibacterial and UV-resistant properties, depending on the type used. The combination of thymol and nanoparticles creates a hybrid material that is not only strong and durable but also eco-friendly and multifunctional 14\u0026ndash;16].\u003c/p\u003e\u003cp\u003eThe present research investigates the preparation and detailed analysis and performance evaluation of thymol-based epoxy resins reinforced with nanoparticles. The goal is to develop a new class of green nanocomposites that combine the benefits of natural bioactive compounds with advanced nanotechnology. This study investigates the development of bio-based epoxy hybrid coatings, with an emphasis on evaluating their corrosion resistance, adhesion, and overall coating characteristics when applied to galvanized steel. A commercially sourced epoxy resin, featuring alkoxy groups along with epoxy functionalities and a hardener, was employed to modify the polymer matrix. The modification was intended to examine how various functional groups affect the performance of the hybrid coatings. Additionally, a novel thymol-based epoxy curing agent was synthesized and incorporated into the epoxy system at five different concentrations (0, 5, 10, 15, and 20 wt%). This approach aimed to assess the influence of the curing agent concentration on the corrosion resistance and adhesion behavior of the resulting coating films.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials and Methods:\u003c/h2\u003e\u003cp\u003eThe chemicals used in this study were obtained from various suppliers. Methylene dichloride, N,N-Dimethylformamide, tetrahydrofuran, epichlorohydrin, Tetra butyl ammonium bromide (TBAB), and 1,4-butandiol diglycidyl ether were procured from Spectrochem Pvt. Ltd., Kalbadevi Road, Mumbai. Potassium carbonate and potassium tert-butoxide were purchased from Sigma-Aldrich, Gujarat. Thymol was kindly provided by Pratap College, Amalner, Maharashtra. All reagents were of analytical grade and were used as received without additional purification.\u003c/p\u003e\u003cp\u003eFourier Transform Infrared (FTIR) spectroscopy was performed to characterize the samples over a spectral range of 400\u0026ndash;4000 cm⁻\u0026sup1;, following ASTM D7371-14, using a Perkin Elmer instrument (USA). Samples were prepared using the Diamond ATR technique to ensure accurate spectral measurements. Thermal stability was evaluated through thermogravimetric analysis (TGA) of TMTO-cured samples using a Q600 thermal analyzer (TA Instruments, USA). Samples were placed in a weighing pan and analyzed under a nitrogen atmosphere, with a heating rate of 5\u0026deg;C/min over the temperature range of 50\u0026ndash;600\u0026deg;C.\u003c/p\u003e\u003cp\u003eChemical composition analysis was carried out using gas chromatography-mass spectrometry (GC-MS) on methylene dichloride-diluted samples, performed with a Shimadzu QP 2010 system. Proton nuclear magnetic resonance (\u0026sup1;H NMR) spectra were recorded using a Bruker AV500WB system operating at 400 MHz, with DMSO as the solvent. Differential scanning calorimetry (DSC) was conducted to study thermal behavior using a TA SDT Q600 instrument at a heating rate of 5\u0026deg;C/min. Gel content of UV-cured films was determined according to ASTM D2765-16 by immersing the films in xylene for 24 hours, followed by drying at 65\u0026ndash;70\u0026deg;C until a constant weight was achieved. Water absorption of cured films was evaluated as per ASTM D570 standards.\u003c/p\u003e\u003cp\u003eStructural characteristics of TMTO-cured films were investigated using X-ray diffraction (XRD) with a Bruker D-8 Advance system to examine the d-spacing patterns. Corrosion resistance of the material applied to galvanized steel plates was assessed using the salt spray method, following ASTM B117 standards, to provide a comprehensive evaluation of durability.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Synthesis of thymol-based resin:\u003c/h2\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.2.1 Synthesis of 3,3'-(butane-1,4-diylbis(oxy)) bis(1-(2-isopropyl-5-methylphenoxy) propan-2-ol) [TBMP]:\u003c/h2\u003e\u003cp\u003eThe synthetic route for TBMP is illustrated in Scheme-1. In a clean and dry round-bottom flask, 2.0 g (0.0133 mol) of thymol was dissolved in 12 mL of N,N-dimethylformamide (DMF). Subsequently, 1.07 g (0.005 mol) of 1,4-butandiol diglycidyl ether (BDGE) was added. Potassium carbonate powder (4.59 g, 0.033 mol) was employed as a base, and tetrabutylammonium bromide (TBAB, 0.002 g, 0.1%) was introduced as a phase-transfer catalyst. The reaction was conducted under a dry nitrogen atmosphere to maintain optimal conditions. The mixture was initially stirred at 25\u0026ndash;30\u0026deg;C for 10\u0026ndash;15 minutes, then gradually heated to 85\u0026ndash;90\u0026deg;C and maintained at this temperature for 6\u0026ndash;8 hours to ensure reaction completion.\u003c/p\u003e\u003cp\u003eProgress of the reaction was monitored using thin-layer chromatography (TLC) with a 4:6 ethyl acetate/n-hexane mobile phase (Rf values: SM\u0026thinsp;=\u0026thinsp;0.35, TBMP\u0026thinsp;=\u0026thinsp;0.2). Upon completion, the product was extracted with ethyl acetate, and the organic phase was washed with water. Removal of the solvent under reduced pressure at 35\u0026ndash;40\u0026deg;C yielded 5.7 g of TBMP as a yellow liquid, corresponding to an excellent yield of 85\u0026ndash;90%.\u003c/p\u003e\u003cp\u003eThe \u003csup\u003e1\u003c/sup\u003eH NMR spectrum of TBMP in CDCl₃ showed characteristic signals: a doublet at 1.19\u0026ndash;1.21 ppm (a, a\u0026rsquo;, 12H) corresponding to the methyl protons of the isopropyl groups on the aromatic rings; 1.65\u0026ndash;1.69 ppm (b, b\u0026rsquo;, 4H) for the methylene protons of the aliphatic chain; a singlet at 2.3 ppm (c, c\u0026rsquo;, 6H) for methyl groups attached to the aromatic rings; 2.66\u0026ndash;2.68 ppm (d, d\u0026rsquo;, 2H) for hydroxyl protons; a multiplet at 3.2\u0026ndash;3.3 ppm (e, e\u0026rsquo;, 2H) representing the methine protons of the isopropyl groups; a doublet at 3.53\u0026ndash;3.59 ppm (f, f\u0026rsquo;, 4H) corresponding to -CH2- protons linked to the aliphatic -O- chain; a doublet at 4.0\u0026ndash;4.11 ppm (g, g\u0026rsquo;, 4H) due to -CH2 protons adjacent to phenolic hydroxyl groups; a multiplet at 4.15\u0026ndash;4.22 ppm (h, h\u0026rsquo;, 2H) assigned to -CH protons attached to hydroxyl groups; a doublet at 6.67 ppm (i, i\u0026rsquo;, 2H) and another doublet of doublets at 6.75\u0026ndash;6.77 ppm (j, j\u0026rsquo;, 2H) corresponding to aromatic protons; and a doublet at 7.08\u0026ndash;7.10 ppm (k, k\u0026rsquo;, 2H) also due to aromatic protons.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.2.2 Synthesis of 2,2'-(3,12-bis((2-isopropyl-5-methylphenoxy) methyl)-2,5,10,13-tetraoxatetradecane-1,14-diyl) bis(oxirane) (TMTO):\u003c/h2\u003e\u003cp\u003eThe synthetic pathway for 2,2'-(3,12-bis((2-isopropyl-5-methylphenoxy)methyl)-2,5,10,13-tetraoxatetradecane-1,14-diyl) bis(oxirane) (TMTO) is illustrated in Scheme \u003cspan refid=\"Sch2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In a clean, dry round-bottom flask, TBMP (2.0 g, 0.004 mol) and epichlorohydrin (1.94 g, 0.021 mol) were combined in the presence of potassium tert-butoxide powder (1.34 g, 0.012 mol) as the base, with tetrabutylammonium bromide (TBAB, 0.002 g, 0.1%) acting as a phase-transfer catalyst. The reaction was carried out in tetrahydrofuran (16 mL) at 5\u0026ndash;10\u0026deg;C. Subsequently, the reaction mixture was heated to 40\u0026ndash;45\u0026deg;C and stirred for 10\u0026ndash;12 hours. Reaction progress was monitored by thin-layer chromatography (TLC) using a 3:7 mixture of ethyl acetate and n-hexane as the mobile phase (Rf values: starting material 0.2, TMTO 0.4).\u003c/p\u003e\u003cp\u003eAfter completion, the solvent was removed under reduced pressure at 35\u0026ndash;40\u0026deg;C. The residue was diluted with ethyl acetate and water, and the pH was adjusted to 6\u0026ndash;7 using 2 N HCl. The organic layer was washed with water to remove inorganic impurities, and the solvent was evaporated under vacuum at 35\u0026ndash;40\u0026deg;C to yield TMTO as a pale-yellow liquid (2.2 g, 86.5% yield).\u003c/p\u003e\u003cp\u003eThe ^1H NMR spectrum of TMTO in DMDO-d6 showed characteristic peaks corresponding to its structure. The doublet at 1.18\u0026ndash;1.21 ppm (a, a\u0026rsquo;, 12H) corresponds to the methyl protons of the isopropyl groups on the aromatic rings, while the multiplet at 1.58\u0026ndash;1.59 ppm (b, b\u0026rsquo;, 4H) arises from CH2-CH2 protons of the aliphatic chain. A singlet at 2.3 ppm (c, c\u0026rsquo;, 6H) is attributed to the methyl groups attached to the aromatic rings. The doublets of doublets at 2.59\u0026ndash;2.61 ppm (d, d\u0026rsquo;, 2H) and 2.76\u0026ndash;2.78 ppm (e, e\u0026rsquo;, 2H) correspond to CH2 protons adjacent to the O-CH2 of the epoxy ring, whereas the multiplet at 3.13\u0026ndash;3.15 ppm (f, f\u0026rsquo;, 2H) is due to the CH proton bonded to the O-CH of the epoxy ring.\u003c/p\u003e\u003cp\u003eSignals at 3.20\u0026ndash;3.26 ppm (g, g\u0026rsquo;, 2H) represent the CH protons of the isopropyl groups, and the doublet at 3.47\u0026ndash;3.49 ppm (h, h\u0026rsquo;, 4H) corresponds to CH2 protons of the O-CH2 aliphatic chain. The multiplet at 3.51\u0026ndash;3.54 ppm (i, i\u0026rsquo;, 2H) is assigned to CH protons bonded to oxygen near the epoxy ring, and the multiplet at 3.52\u0026ndash;3.59 ppm (j, j\u0026rsquo;, 4H) corresponds to the CH2-CH2 protons of the aliphatic chain linked to oxygen. The doublet at 3.90\u0026ndash;3.93 ppm (k, k\u0026rsquo;, 4H) arises from CH2-CH2 protons adjacent to oxygen, and the signals at 3.99\u0026ndash;4.11 ppm (l, l\u0026rsquo;, 4H) are due to CH2 groups connected to the phenoxy moiety. Aromatic protons appear as a doublet at 6.74\u0026ndash;6.76 ppm (m, m\u0026rsquo;, 2H), a singlet at 6.79 ppm (n, n\u0026rsquo;, 2H), and a doublet at 7.08\u0026ndash;7.10 ppm (o, o\u0026rsquo;, 2H).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e\u003cb\u003e2.2.3 Preparation of TMTO bio-based coating formulation (\u003c/b\u003eScheme \u003cspan refid=\"Sch3\" class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/h2\u003e\u003cp\u003eThe TMTO bio-based curing agent was prepared by blending it with varying weight percentages of bisphenol A-based epoxy resin (YD128), an initiator, and accurately measured amounts of the hardener triethylenetetramine (TETA, 0.1 mol%) along with cerium oxide (CeO₂) nanoparticles (2.0 mol%). The detailed formulation is presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Scheme \u003cspan refid=\"Sch3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. These mixtures were then applied onto galvanized steel panels (7.5 cm \u0026times; 9.5 cm) to form a uniform coating. In parallel, free-standing TMTO-cured bio-based polymer films were fabricated by casting the formulations into thin, transparent Teflon molds. Both the coated panels and the polymer films were subsequently cured in an oven at 50\u0026ndash;55\u0026deg;C for 12\u0026ndash;16 hours under ambient air conditions to ensure complete polymerization.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eFormulation of epoxy resin with TMTO curing agent\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSr. No.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eIngredients\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c8\" namest=\"c3\"\u003e\u003cp\u003eTMTO curing agents\u0026rsquo; weight % (0.1 mole % of TETA initiator)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eEpoxy resin\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e88\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e78\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTMTO Curing agent\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCerium oxide (CeO\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 FTIR Analysis of TBMP and TMTO\u003c/h2\u003e\n \u003cp\u003eThe FTIR spectrum of TBMP is presented in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e (\u003cstrong\u003eSupporting Information\u003c/strong\u003e). A prominent absorption band at 3411.59 cm⁻\u0026sup1; corresponds to the O-H stretching, which arises from the epoxy ring opening reaction between thymol and BDGE. The band observed at 2927.25 cm⁻\u0026sup1; is attributed to the C-H stretching of the oxygen-bound groups, while the peak at 2867.69 cm⁻\u0026sup1; is associated with the stretching vibrations of aromatic and aliphatic C-H groups. Peaks at 1611.94 cm⁻\u0026sup1; and 1505.46 cm⁻\u0026sup1; indicate the C\u0026thinsp;=\u0026thinsp;C stretching within the aromatic ring. The FTIR spectrum of TMTO is depicted in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e (\u003cstrong\u003eSupporting Information\u003c/strong\u003e). The absorption at 2923.52 cm⁻\u0026sup1; arises from C-H stretching of oxygen-linked groups, and the band at 2867.78 cm⁻\u0026sup1; corresponds to aromatic and aliphatic C-H stretching. The aromatic C\u0026thinsp;=\u0026thinsp;C stretching is observed at 1611.54 cm⁻\u0026sup1; and 1505.49 cm⁻\u0026sup1;. The strong band at 1169.77 cm⁻\u0026sup1; is assigned to the C-O-C stretch of the oxirane ring. Notably, the O-H band present in TBMP at 3411.59 cm⁻\u0026sup1; disappears in TMTO, confirming the successful synthesis of TMTO.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 GC-MS Analysis of TBMP and TMTO\u003c/h2\u003e\n \u003cp\u003eThe GC-MS spectrum of TBMP, shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (\u003cstrong\u003eSupporting Information\u003c/strong\u003e), confirms its structure. The data indicate that thymol reacts with BDGE through a ring-opening addition to form TBMP. The base peak at m/z\u0026thinsp;=\u0026thinsp;503.5 (positive mode) corresponds to the TBMP intermediate, which has a molecular weight of 530.6. The GC-MS spectrum of TMTO (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, \u003cstrong\u003eSupporting Information\u003c/strong\u003e) displays a molecular ion peak at m/z\u0026thinsp;=\u0026thinsp;637.4 (M\u0026thinsp;+\u0026thinsp;23, positive mode), representing the sodium adduct of TMTO, consistent with a molecular weight of 614.4.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 \u0026sup1;H NMR Analysis of TBMP\u003c/h2\u003e\n \u003cp\u003eThe \u0026sup1;H NMR spectrum of TBMP in CDCl₃ (Fig. 5, \u003cstrong\u003eSupporting Information\u003c/strong\u003e) shows a doublet at 1.19\u0026ndash;1.21 ppm (12H) corresponding to -CH₃ protons of the isopropyl groups on the aromatic ring. Signals at 1.65\u0026ndash;1.69 ppm (4H) correspond to CH₂-CH₂ protons of the aliphatic chain. A singlet at 2.3 ppm (6H) arises from -CH₃ protons attached to the aromatic ring. The -OH proton of the hydroxyl group appears as a doublet at 2.66\u0026ndash;2.68 ppm (2H). Multiplets at 3.2\u0026ndash;3.3 ppm (2H) correspond to -CH protons of the isopropyl groups, and doublets at 3.53\u0026ndash;3.59 ppm (4H) represent -CH₂ protons attached to -O-CH₂ of the aliphatic chain. Peaks at 4.0\u0026ndash;4.11 ppm (4H) and 4.15\u0026ndash;4.22 ppm (2H) are attributed to -CH₂ and -CH protons linked to phenolic OH groups. Aromatic protons appear as a doublet at 6.67 ppm (2H), a doublet of doublets at 6.75\u0026ndash;6.77 ppm (2H), and a doublet at 7.08\u0026ndash;7.10 ppm (2H).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 \u0026sup1;H NMR Analysis of TMTO\u003c/h2\u003e\n \u003cp\u003eThe \u0026sup1;H NMR spectrum of TMTO in DMSO-d₆ (Fig. 6, \u003cstrong\u003eSupporting Information\u003c/strong\u003e) shows a doublet at 1.18\u0026ndash;1.21 ppm (12H) corresponding to -CH₃ protons of the isopropyl groups. Multiplets at 1.58\u0026ndash;1.59 ppm (4H) arise from CH₂-CH₂ protons of the aliphatic chain. A singlet at 2.3 ppm (6H) is attributed to -CH₃ protons attached to the aromatic ring. Doublets of doublets at 2.59\u0026ndash;2.61 ppm and 2.76\u0026ndash;2.78 ppm (2H each) correspond to CH₂ protons adjacent to O-CH₂ in the epoxy ring. Multiplets at 3.13\u0026ndash;3.15 ppm (2H) and 3.20\u0026ndash;3.26 ppm (2H) correspond to -CH protons of the epoxy-linked chain and isopropyl groups, respectively. Doublets at 3.47\u0026ndash;3.49 ppm (4H) and multiplets at 3.51\u0026ndash;3.54 ppm (2H) and 3.52\u0026ndash;3.59 ppm (4H) correspond to -CH₂ and -CH protons of the aliphatic chain and epoxy ring. Peaks at 3.90\u0026ndash;3.93 ppm (4H) and 3.99\u0026ndash;4.11 ppm (4H) are attributed to -CH₂ groups linked to the aliphatic and phenoxy groups. Aromatic protons appear as a doublet at 6.74\u0026ndash;6.76 ppm (2H), a singlet at 6.79 ppm (2H), and a doublet at 7.08\u0026ndash;7.10 ppm (2H).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Mechanical Properties of Bio-based Epoxy Resin\u003c/h2\u003e\n \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.1 Thermal Characteristics of TMTO-Epoxy Films\u003c/h2\u003e\n \u003cp\u003eThe thermal stability of the cured epoxy samples was examined using thermogravimetric analysis (TGA), as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The residual char content of the cured films increases with higher TMTO concentrations, showing 15% and 20% TMTO samples possess greater char formation than those containing 5% and 10% TMTO. TGA data indicate that all the coated films undergo a single-step degradation process, resulting in roughly 50% weight loss occurring up to 400\u0026deg;C. The onset of degradation is observed at approximately 290\u0026deg;C, primarily due to the breakdown of aliphatic hydrocarbon segments within the cured epoxy and its cross-linked network. Notably, samples containing 15% and 20% TMTO demonstrate improved thermal resistance, with degradation temperatures rising to 415\u0026deg;C and 420\u0026deg;C, respectively, surpassing the thermal stability of the films with lower TMTO content and those without TMTO. Moreover, the sample, containing the highest TMTO and CeO₂ content, demonstrated superior stability with decomposition onset near 290\u0026deg;C and over 30% residue at 600\u0026deg;C. These results show improving flame retardancy and thermal endurance of epoxy matrices, making them promising candidates for high-temperature protective coatings [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e]. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the thermal behaviour of TMTO-modified epoxy systems across various formulations. Differential Scanning Calorimetry (DSC) was employed to assess the glass transition temperature (Tg) of the cured coatings. A progressive reduction in Tg was observed with increasing TMTO content, indicating enhanced molecular mobility within the polymer network. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, each formulation displayed a distinct single Tg, confirming homogeneous phase behaviour. This thermal softening effect imparts valuable flexibility and energy degeneracy characteristics, making these coatings particularly well-suited for applications such as flexible adhesives, electronic encapsulants, and protective layers subjected to thermal or mechanical stress [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e]. Their capacity to absorb strain and reduce vibrations positions them as promising alternatives in environments where conventional rigid epoxies may underperform.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.2 Determination of Gel Content and Water Absorption\u003c/h2\u003e\n \u003cp\u003eThe degree of photopolymerization in the resin, with and without the addition of TMTO, was evaluated through the gel content analysis using solvent extraction. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e presents the relationship between gel content and various TMTO concentrations. For this test, the cured polymer films were carefully peeled off from the Teflon substrate. Samples of known initial weight were immersed in methyl ethyl ketone at room temperature for 48 hours. Following extraction, the films were removed and dried at 70\u0026deg;C until a constant weight was obtained. The results indicated a steady increase in gel content with higher TMTO loading, implying the formation of a denser and more stable cross-linked polymer network, which contributes to improved coating characteristics [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e illustrates a direct trend in water absorption behaviour, showing a decline as TMTO concentration rises. This reduction is attributed to the increased crosslinking within the polymer network, which minimizes free volume and restricts water infiltration. TMTO-based coating material effectively limits water entry, thereby enhancing the coating\u0026rsquo;s resistance. Furthermore, the aromatic structure within the epoxy resin backbone imparts hydrophobic characteristics, enhancing water resistance through cross-link formation [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. Consequently, coatings containing a higher proportion of curing agents demonstrate reduced water absorption.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.3 X‑ray diffraction (XRD) of TMTO cured films\u003c/h2\u003e\n \u003cp\u003eThe X-ray diffraction (XRD) patterns of dried TMTO films were evaluated, as given in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. The analysis revealed that the control sample (TM2), which did not contain thymol or cerium oxide, exhibited a broad halo, indicating an amorphous structure. In contrast, sample TM1, which included cerium oxide nanoparticles, displayed sharp diffraction peaks at approximately 28.5\u0026deg;, 33.0\u0026deg;, 47.4\u0026deg;, and 56.3\u0026deg; 2\u0026theta;. These peaks correspond to the (111), (200), (220), and (311) planes of crystalline CeO₂. Samples TM3 to TM6, which contained increasing concentrations of thymol (5\u0026ndash;20 wt%), showed a gradual reduction in peak intensity and broadening. This suggests a decrease in crystallinity, likely due to the amorphous nature of thymol [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e][\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. The XRD results confirm that cerium oxide nanoparticles introduce a crystalline phase into the epoxy matrix, while higher concentrations of thymol disrupt this order. These structural changes also impact the thermal behavior of films. While CeO₂ enhances thermal resistance, thymol reduces it, as it has a lower decomposition temperature and interferes with the dispersion of nanoparticles. Additionally, the observed decrease in the glass transition temperature (Tg) with thymol addition supports the idea of matrix plasticization, which may enhance flexibility and enable controlled release of thymol. Overall, these findings highlight how thymol modifies the structural order and tunes the thermal response of the composite.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.4 Scanning Electron Microscopy Analysis (SEM)\u003c/h2\u003e\n \u003cp\u003e\u003cstrong\u003eFigure 5\u003c/strong\u003e presents the SEM micrographs depicting the morphology of the coating matrix. The morphological evolution of the epoxy coating was investigated through SEM imaging, highlighting the combined effect of TMTO incorporation and cerium oxide nano powder dispersion. At 0% TMTO, the surface appears relatively smooth and lacks textural complexity. With progressive inclusion of TMTO at 5%, 10%, and 15%, the surface begins to display enhanced microstructural uniformity and increased nanopatterning, indicative of improved polymer chain crosslinking and cohesive interfacial bonding. The introduction of cerium oxide nano powder further amplifies these effects by acting as an active nanofiller, facilitating homogeneous phase dispersion and impeding agglomeration. Its presence contributes to a denser, more refined surface architecture by filling micro voids and enhancing interfacial compatibility within the matrix. By the time 20% TMTO is reached, the SEM micrographs show a highly ordered, layer-by-layer nanostructure with pronounced surface gratings\u0026mdash;suggestive of harmonious strengthening from both the curing agent and the nano powder. This dual-modifier system not only optimizes surface topography but also implies superior mechanical integrity and environmental resistance. The observed morphological improvements position the composite system as a strong candidate for high-performance coating and protective applications.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.5 Anticorrosion Performance Analysis:\u003c/h2\u003e\n \u003cp\u003eAfter 650 hours of salt spray exposure, the coated specimens with TMTO-based epoxy coatings were examined for their anticorrosion behaviour, as illustrated in \u003cstrong\u003eFig.\u0026nbsp;6\u003c/strong\u003e. The extent of corrosion beneath the coatings was evaluated in accordance with ASTM B117 standards, and the results are summarized in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. The reference coating exhibited clear evidence of degradation, including rust formation, blistering, and partial detachment of the film. The appearance of darkened areas near the scribed region indicates moisture ingress through the coating. These findings provide important insights into the material\u0026rsquo;s performance and highlight areas for potential improvement. The observed corrosion and rusting in the reference sample can be attributed to the interaction of water, oxygen, and aggressive ions such as H+, OH\u0026minus;, and Cl\u0026minus;, which promote blistering and surface damage. Conversely, the TMTO-incorporated coatings displayed markedly enhanced corrosion resistance, primarily due to the formation of a stable oxide layer on the metal surface, as previously verified by DSC analysis.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAdhesion test result according to ASTM B117\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCorrosion test result according to ASTM B117\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSr. No.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCoatings\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBefore salt spray\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAfter salt spry\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e0% TMTO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e5% TMTO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e10% TMTO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e15% TMTO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e20% TMTO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4B\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eSamples cured using thymol-derived agents exhibit a significant improvement in corrosion resistance. This enhancement is mainly attributed to the development of a stable oxide film on the metal surface, as previously verified through SEM analysis. The thymol-based \u003cstrong\u003eTMTO\u003c/strong\u003e curing agent facilitates the formation of this protective oxide layer, effectively acting as a barrier against corrosive attack. Hence, the incorporation of this curing agent represents a promising approach for enhancing the long-term durability of metal coatings. In regions where scratches occur, greater water ingress can result in blister formation near the damaged sites. Nevertheless, the presence of the stable oxide film and the strong interfacial adhesion between the coating and the metal substrate help minimize blistering compared to coatings cured without \u003cstrong\u003eTMTO\u003c/strong\u003e.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.6 Antimicrobial Behaviour of Thymol-Epoxy Resin:\u003c/h2\u003e\n \u003cp\u003eThe biological activity of polymeric materials is strongly influenced by their molecular architecture. Key structural parameters such as chain length, the density and type of functional groups, hydrophilic\u0026ndash;hydrophobic balance, as well as surface charge (cationicity) play pivotal roles in determining their interaction with biological systems. These characteristics govern not only the physicochemical behaviour of the material but also its ability to inhibit microbial growth and adhere to biological surfaces. In recent years, epoxy-based systems have gained attention for their potential in antimicrobial and bioactive applications. Among these, \u003cstrong\u003eTMTO\u003c/strong\u003e (thymol-derived monoepoxide) has emerged as a promising bi-functional curing agent. Its symmetrical molecular structure and dual epoxy functionality enable it to serve both as a cross-linking agent and a bioactive component. The concept of using the curing agent itself as a functional template introduces a novel strategy in epoxy design. This approach not only facilitates efficient network formation but also imparts biological functionality to the cured material. Such dual-purpose systems are particularly valuable in applications requiring both structural integrity and antimicrobial performance, such as biomedical coatings, flexible adhesives, and encapsulants for sensitive electronics. Supporting literature highlights the effectiveness of phenolic epoxides in biological applications. For example, curing a mixture of mono-epoxidized thymol and di-epoxy resorcinol with an iodonium salt under photopolymerization conditions yields epoxy co-networks exhibiting notable antimicrobial activity. The inclusion of phenolic compounds like thymol has been shown to enhance antibacterial performance, with studies reporting significant reduction in bacterial adhesion. These findings underscore the potential of phenol-derived epoxy systems in developing next-generation functional coatings and materials for hygienic and biomedical use. Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e shows that epoxy resins with symmetrical thymol-based structures work better at fighting bacteria. This is likely because their balanced design helps them interact more effectively with bacterial cell membranes, causing damage that leads to cell death. As demonstrated in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e and Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, the antimicrobial activity was evaluated using the disc diffusion method of TMTO-based curing agents against three bacterial strains and one fungal strain. The molecular profiles of these agents showed notable differences compared to the standard reference.\u003c/p\u003e\n \u003cp\u003eThe antimicrobial responses varied across the samples:\u003c/p\u003e\n \u003cul\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003eSample C\u003c/strong\u003e exhibited moderate inhibition of Gram-negative bacteria and fungi.\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003eSample D\u003c/strong\u003e displayed strong, broad-spectrum antimicrobial activity.\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003eSample E\u003c/strong\u003e was particularly effective against fungal strains.\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003e\u003cstrong\u003eSample F\u003c/strong\u003e showed moderate activity against Gram-negative bacteria.\u003c/p\u003e\n \u003c/li\u003e\n \u003c/ul\u003e\n \u003cp\u003eAll tested samples showed positive results against \u003cem\u003eStaphylococcus aureus\u003c/em\u003e, \u003cem\u003eEscherichia coli\u003c/em\u003e, and \u003cem\u003eRhizopus oryzae\u003c/em\u003e. Compared to the blank control, the coating formulations significantly inhibited microbial growth. These outcomes suggest that the TMTO-based coatings hold promise as effective antimicrobial surfaces.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\" class=\"fr-table-selection-hover\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAntimicrobial disc diffusion assay results of curing agent.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eEntry\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eGram-positive bacteria\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eGram-negative bacteria\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFungi\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS.A. MTCC96\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eE.C. MTCC739\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eR.O. MTCC1009\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eB\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e125 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eD\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e62.5 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003e62.5\u003c/strong\u003e \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eE\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e250 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eF\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e100 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e500 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eSTREPTOMYCIN\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eAMPICILLIN\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e100 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eNYSTATIN\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e100 \u0026micro;g/mL\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eBoldfaced values indicate the active compounds; S.A., \u003cem\u003eStaphylococcus aureus\u003c/em\u003e; E.C., \u003cem\u003eEscherichia coli\u003c/em\u003e; R.O., \u003cem\u003eRhizopus oryzae\u003c/em\u003e; MTCC, microbial-type culture collection\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work, an epoxy resin system was modified using a bio-derived curing agent synthesized from thymol to evaluate its thermal stability, corrosion resistance, and other physicochemical characteristics. The gel content and water absorption analyses revealed that the degree of photopolymerization in the cured composites increased notably with higher concentrations of the thymol-based curing agent. X-ray diffraction (XRD) analysis confirmed a fully amorphous structure after curing, signifying the successful incorporation of the TMTO curing agent into the epoxy matrix and its uniform dispersion within the polymeric soft domains. Salt spray testing demonstrated that samples containing the maximum proportion of curing agent exhibited the most effective corrosion protection. Overall, the increasing interest in bio-based curing agents provides opportunities for chemical industries to develop fully sustainable epoxy networks. Thymol, a naturally occurring phenolic compound, can be utilized to produce bio-based curing agents capable of substituting conventional aliphatic and aromatic hardeners. Such agents hold significant potential as eco-friendly alternatives to petroleum-based systems, enabling the fabrication of entirely bio-based epoxy materials. The integration of TMTO curing agents into epoxy formulations resulted in coatings with superior film quality, along with enhanced thermal, mechanical, and antimicrobial performance compared to conventional epoxy resins, owing to their distinct curing mechanisms.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability:\u0026nbsp;\u003c/strong\u003eThe data that support the findings of this study are available on within the article.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration for conflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contribution:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAP: Experimental investigation, validation, and formal analysis, Writing - Review \u0026amp; Editing NSP: formal analysis and validation; Writing - Review \u0026amp; Editing. PM: Resources and data curation, MT: conceptualization and supervision; KB: conceptualization and supervision; VP: Writing - Review \u0026amp; Editing, visualisation and supervision.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e: Dr. Vikas Patil is thankful to UGC for his position through the Faculty Recharge Program.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Declarations\u003c/strong\u003e: The work has no funding received.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKowalczyk A, Przychodna M, Sopata S, Bodalska A, Fecka I (2020) Thymol and thyme essential oil\u0026mdash;new insights into selected therapeutic applications. Molecules 25(18):4125\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSalehi B et al (2018) Thymol, thyme, and other plant sources: Health and potential uses. 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Mater Res Express 7(1):15333. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1088/2053-1591/ab68a2\u003c/span\u003e\u003cspan address=\"10.1088/2053-1591/ab68a2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eSchemes 1 to 3 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Thymol, Anticorrosion, antioxidant, Curing agent, Antimicrobial, Bioactive compound","lastPublishedDoi":"10.21203/rs.3.rs-7882858/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7882858/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThymol a bioactive phytochemical, is becoming an essential component in the synthesis of monomers, pushing forward advances in the design of functional polymers. The complex reaction process begins with thymol interacting with 1,4-Butanediol diglycidyl ether generates the reactive intermediate 3,3\u0026prime;-(butane-1,4-diylbis-oxy) bis(1-(2-isopropyl-5-methylphenoxy) propan-2-ol). This species undergoes further epoxidation to yield 2,2'-(3,12-bis((2-isopropyl-5-methylphenoxy) methyl)-2,5,10,13-tetraoxatetradecane-1,14-diyl) bis(oxirane) (shortly \u003cb\u003eTMTO\u003c/b\u003e). Thymol which is known for its antimicrobial properties synchronously enhances the protective qualities of coatings applied to metal substrates, thereby improving their resistance to environmental degradation. The structural and functional integrity of polymer was evaluated by analytical tools including techniques such as X-ray diffraction (XRD), gel fraction determination, water uptake measurement, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). These investigations unequivocally demonstrated the performance superiority of the thymol-derived epoxy (TMTO) in terms of molecular stability and reactivity. Further refinement of functional characteristics and molecular architecture was conducted using analytical techniques including gas chromatography coupled with mass spectrometry (GC-MS), proton nuclear magnetic resonance (\u0026sup1;H-NMR), and infrared (IR) spectroscopy were employed.. These techniques enabled an in-depth exploration of the cured epoxy's thermal robustness, mechanical durability, and anti-corrosive proficiency. Promoting \u003cb\u003eTMTO\u003c/b\u003e as an optimal candidate for next-generation polymeric coatings to high-performance applications.\u003c/p\u003e","manuscriptTitle":"Bioactive Thymol in Epoxy Network Toward Durable and Protective Polymeric Coatings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-25 18:36:26","doi":"10.21203/rs.3.rs-7882858/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"62eb9cd2-2889-4d05-a9bb-316f49414632","owner":[],"postedDate":"November 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-18T22:14:46+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-25 18:36:26","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7882858","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7882858","identity":"rs-7882858","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}