Comparative Bench Scale Evaluation of Flame Exposure Behavior of Plywood and MDF Coated with Fire-Retardant Paint

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This study evaluates the effectiveness of commercial fire-retardant (FR) coatings on plywood and medium-density fiberboard (MDF). The coatings were characterized using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Fluorescence (XRF), while fire performance was assessed through a bench-scale vertical flame exposure setup developed for comparative evaluation of ignition behavior under localized flame exposure, combined with infrared thermography to monitor surface temperature evolution. FTIR revealed functional groups such as phosphate, melamine, and hydroxyls, while XRF confirmed phosphorus, aluminum, and silicon, all contributing to char formation and flame inhibition. Fire tests showed that FR-coated panels delayed ignition, lowered peak surface temperatures, and in some cases achieved partial self-extinction compared with uncoated or primer-coated boards. Plywood retained structural integrity after exposure, whereas MDF became brittle and flaky, highlighting the role of substrate type in thermal response under localized flame exposure. Overall, FR coatings demonstrated improved resistance to ignition and early-stage thermal development by extending ignition time, reducing heat transfer, and preserving stability. These findings emphasize the value of passive fire protection strategies in delaying ignition onset and reducing early-stage thermal development under localized flame exposure and reducing early-stage thermal degradation in wood-based panel applications and furnishing applications. Wood-based panels Fire-retardant coatings Bech-scale flame exposure Ignition behavior Thermal response Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Passive fire protection is essential for ensuring structural safety, employing materials and systems that are designed to resist or slow down the spread of fire without requiring active measures (Lim et al., 2019 ). Among these solutions, fire-retardant coatings stand out as an option, especially in construction and material engineering. These coatings improve thermal response under localized flame exposure to the surface by creating protective layers when exposed to high temperatures which release water vapor that suppress combustion (Eremina & Korolchenko, 2020 ). Fire retardant materials are used in improving the safety of combustible items by delaying or preventing the spread of flames. Wood-based panel boards are among the most widely used materials in residential, commercial, and industrial applications because of their lightweight structure, good insulating properties, and cost-effectiveness. However, their high susceptibility to ignition and rapid flame spread presents significant safety concerns (Mensah et al., 2023 ). When subjected to flames, wood-based board ignites rapidly, emitting significant amounts of heat and potentially facilitating fire spread. The application of fire-retardant coating on panel board greatly enhances its thermal response under localized flame exposure by postponing ignition and lowering heat release rate. These coatings interfere with the chemical pathways of combustion, thereby lowering thermal hazards and improving evacuation time during fire emergencies (Aqlibous et al., 2020 ; Mensah et al., 2023 ). Despite these advances, the effectiveness of fire-retardant coatings across different types of wood-based panels remains insufficiently documented. Variations in physical and chemical properties among substrates influence the protective performance of coatings, yet comprehensive evaluations under realistic heat exposure scenarios are limited. Bridging this knowledge gap is crucial for optimizing the protective functions of fire-retardant systems and ensuring safer applications of wood-based materials in construction. Accordingly, this study experimentally investigates the thermal resistance and fire-development performance of commercial fire-retardant coatings applied to wood-based boards. Particular attention is given to their behavior under heat exposure, integrating chemical and thermal characterization techniques. The coating’s chemical composition was analyzed using Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Fluorescence (XRF), while its influence on heat transfer and surface temperature was evaluated through Infrared (IR) thermography. On this basis, the study systematically assesses the role of fire-retardant coatings in passive fire protection, providing insights into their effectiveness in mitigating fire risks in wood-based panel applications. 2. Methodology 2.1 Sample preparation A commercially available fire-retardant (FR) paint, primer and wood panel board was locally purchased. The test samples used in this experiment were panels from two different board of medium-density fibre board (MDF) and plywood board (210 mm x 70 mm x 6 mm) each were prepared as shown in Table 1 . All wood panels were disc-sanded on the flat grain using P150 grit paper before the coating application. Two uncoated test samples, labelled as PA and MA were used as reference or control sample, other three test samples were prepared at different coating application for each type of wood-board. Second coatings (PB and MB) using commercial solvent-based primer containing aromatic hydrocarbons, ketones, esters, glycol ethers and LPG as propellant. Third coating (PC and MC) using FR paint and the last coatings system (PD and MD) using the combination of primer and FR. The FR coating was applied as 5 layers using roller paint, with was dried overnight for each layer to ensure uniform thickness. The weight of each sample is recorded before the test. Table 1 Details of test sample. Sample ID Wood panel board type Initial weight (g) Coated system PA Plywood board 37 ± 2 n/a PB 47 ± 2 Primer only PC 44 ± 2 FR paint PD 46 ± 2 Primer + FR MA Medium-density fibreboard (MDF) 101 ± 5 n/a MB 99 ± 5 Primer only MC 103 ± 5 FR paint MD 109 ± 5 Primer + FR 2.2 Fire test method Bench-scale flame exposure tests were conducted using a laboratory-developed vertical flame exposure setup designed for comparative screening of coated and uncoated wood-based panels. The setup can be illustrated in Fig. 1 . A Bunsen burner flame was applied to the lower edge of vertically mounted specimens under controlled and repeatable conditions. The separation distance between the burner opening and the sample edge was maintained at 10 cm to ensure consistent heating conditions. The thermal response of each panel was monitored for 15 minutes using an infrared (IR) thermal imaging camera, which recorded the surface temperature distribution during fire exposure. The method was intended to provide relative comparison of ignition behavior, flame stability and thermal response. After exposure, the samples were cooled under ambient conditions overnight and re-weighed to determine mass loss. Each test was repeated three times for reproducibility and data reliability. The experimental setup also represents a laboratory-scale comparative screening method and does not correspond to a standardized fire classification or regulatory test. The results should be interpreted on a relative basis. 2.3 Analysis and characterization 2.3.1 Fourier Transform Infrared Bay (FTIR) The functional groups present in the fire-retardant coating were analyzed using a Nicolet 400D Fourier Transform Infrared (FTIR) spectrometer. Spectra were recorded in the range of 4000–515 cm⁻¹ to identify characteristic absorption bands associated with the coating components. 2.3.2 X-ray Fluorescence Spectrometer (XRF) The elemental composition of the fire-retardant paint was determined using a Panalytical Axios DY2156 X-ray Fluorescence (XRF) spectrometer. This analysis provided quantitative information on the inorganic elements incorporated into the coating formulation. 2.3.4 Surface Temperature Profiles Thermal distribution on coated wood panels was monitored using Keysight TrueIR, an infrared (IR) thermal imaging camera. Measurements were performed over a temperature range of 0–650°C, with the camera positioned at a distance of 1 m from the heat source. The recorded temperature profiles were then analysed using TrueIR Analysis and Reporting Tool software to evaluate relative surface temperature evolution and apparent thermal response under localized flame exposure. 3. Results and discussion 3.1 FTIR analysis FTIR spectra of the commercial fire-retardant paint were recorded using a Nicolet 400D spectrometer in the range of 4000–515 cm − 1 to identify the functional group and chemical components contributing to its FR properties. The sample, a white opaque liquid, was scanned and the resulting FTIR spectrum is shown in Fig. 2 . The absorption peak observed at 3802 cm − 1 is attributed to the O-H stretching vibration, which indicates the presence of hydroxyl group (Li et al., 2024 ). This peak typically arises from the water content or polyol structure in the formulation. The peaks at 3587cm − 1 , 3462 cm − 1 and 3356 cm − 1 suggest overlapping of N-H and O-H stretching vibrations, commonly associated with melamine-derived structure and amino group (-NH 2 ) present in the paint (Eremina & Korolchenko, 2020 ; Gu et al., 2007 ; Kwang Yin et al., 2019 ). A peak detected at 2193 cm − 1 correspond to C ≡ N stretching, confirming the presence of nitrile groups. This aligns with the melamine or cyanamide-based FR agent known for contributing to thermal stability and intumescent behaviour (produce charring layer). In the region of 1732 cm − 1 , a strong absorption band indicates the C = O stretching vibration typical of ester or carbonyl-containing compounds such as acrylates or polyamide hardeners. Another prominent peak at 1637 cm − 1 is attributed to the N-H bending from primary or secondary amines and may also involve C = N stretching, indicate of melamine or other triazine based structure (Kwang Yin et al., 2019 ; Ullah et al., 2014 ). The peak at 1451 cm − 1 can be assigned to -CH 2 or -CH 3 bending vibrations, possibly from alkyl chains or solvent residues within paint matrix. An absorption at 1241 cm − 1 associated with P = O or P-O-C stretching modes, supporting the presence of phosphate compounds, which are essential components in many FR formulations. Additionally, a distinct absorption at 1153 cm − 1 corresponds to PO 4 3− group, further verifying the existence of phosphate-based FR agents (Zhan et al., 2024 ). 3.2 XRF result X-ray fluorescence (XRF) spectroscopy was conducted to identify the elemental composition of the commercial FR paint, providing complementary data to support the functional group analysis obtained from the FTIR. Table 2 shows the presence of several key elements, with significant implications for the FR properties and formulation of the paints. Table 2 XRF component detection in Greenlack waterborne fire-retardant. Compound Value (%) Al 2.673 Si 1.789 S 0.368 P 0.259 Ca 0.176 K 0.059 Br 0.015 Pt 0.012 The detection of phosphorus at 0.259% strongly supports the presence of phosphate-based compound as observed in the FTIR spectrum. Peaks at 1153 cm − 1 and 1241 cm − 1 in the FTIR were assigned to PO 4 3− stretching and P = O or P-O-C bonds, indicating incorporation of ammonium polyphosphate (APP) or others phosphate salts, which are widely used in intumescent fire-retardant systems (Kim et al., 2021 ; Li et al., 2024 ; Ullah et al., 2014 ; Zhan et al., 2024 ). The presence of aluminium (Al, 2.673%) is significant, as aluminium compounds such as aluminium hydroxide (ATH) or aluminium phosphate are commonly used as FR or synergists. ATH, in particular, decomposes endothermically to release water, diluting combustible gases and absorbing heat. This complements the O-H related FTIR peaks (3462–3802 cm − 1 ), indicate hydroxyl-rich compounds (Li et al., 2024 ). Silicon with a contribution of 1.798% may originate from silicate additives or silicone-based resins, often used to enhance thermal stability, water repellence, or adhesion in FR paints. Although not distinctly observed in FTIR due to overlapping bands, their presence is consistent with the known use of silica resins in high-performance coatings (Zhan et al., 2024 ). The presence of sulfur (0.368%) and calcium (0.176%) may be attributed to the use of inorganic FR synergist that help improve thermal barrier properties. This is typically used alongside phosphate and alumina to reinforce the protective char structure (Zhan et al., 2024 ). Other than that, with trace amount, three elemental was detected which are potassium (K), bromine (Br) and platinum (Pt). 3.3 Experimental observations The experimental setup allowed for continuous visual inspection of the test sample during testing. In this way, it was possible to visually examine the behaviour of uncoated and coated test sample under fire exposure. Fire-resistance performance on the plywood and MDF samples was assessed based on thermal response indicators including time-to-ignition (TTI), time-to-extinction (TTE) and observable flame characteristics. Table 3 reports the TTI and TTE of all test samples. TTI was defined as the elapsed time from flame application to the onset of the sustained flame observed visually, accompanied by a rapid and continuous increase in surface temperature recorded by infrared thermography, while TTE is duration from ignition until the flame is disappearing or fully extinguished. Table 3 Time-based fire performance (average value). Sample ID Time-to-ignition (min) Time-to-extinction (min) PA ~ 1.6 ~ 13.5 PB ~ 1.0 ~ 14.7 PC ~ 2.0 ~ 3.6 PD ~ 0.9 ~ 10.3 MA ~ 1.9 ~ 15.0 MB ~ 0.8 ~ 15.0 MC ~ 1.9 ~ 7.3 MD ~ 1.1 ~ 13.8 The analysis of TTI and TTE provides critical insight into their safety performance during fire incidents. These parameters are especially significant when considering the use of such material in residential, commercial and public buildings, where fire safety and human evacuation are paramount. TTI indicates how rapidly a material reacts to a heat source and is closely linked to the critical timeframe available for individuals to notice and respond to a fire. Coatings that prolong ignition, like exceeding 1.5 minutes able to offer an essential buffer for early fire detection systems (such as smoke alarms). This delay in ignition grants occupants additional time to become aware of danger and initiate evacuation before conditions worsen. Conversely, TTE measures the duration that the material continues to support flames. Materials with extended extension time such as material labelled PB, MA and MB, which can maintain combustion for as long as 14 minutes, present a greater risk for fire spread and heat build-up, potentially hindering rescue efforts and escalating structural damage. In contrast, materials with fire-retardant coating, highlighted as PC, not only ignite at a later stage but also extinguish more rapidly and steadily, significant more effective flame suppression. Flame behaviour is also a main factor in fire dynamics. The flame condition of uncoated samples and primer coated samples (PA, PB, MA and MB) were characterized by rapid flame spread, bright orange colour and complete consumption of the substrate. These sample kept burning for the whole duration of the test and no flame extinction was recorded for any of the samples during the fire test. Primer coated surfaces show slightly slower spread due to minor sealing effect but ultimately provide no-fire-retardant benefit. FR coated samples (PC, PD, MC and MD) on the other hands, exhibited unstable flames with evidence of partially self-extinction before complete combustion. This observation reflects the ability of FR layers to suppress flame propagation and smother the combustion process via char formation and gas release. Figure 3 shows the condition of plywood for uncoated samples (left) and primer-coated samples (right) at minute of 5 during the fire exposure. 3.4 Evolution of the temperature within samples The thermal response of different wood substate, namely plywood and medium-density fiberboard (MDF), was studied under varying coating systems to assess their thermal response under localized flame exposure characteristic and implications for fire safety. These substrates were tested in four conditions of uncoated, primer-coated, FR coated and combination-coated (primer followed by FR paint). The evolution of temperature during fire exposure was captured using a thermal infrared camera over a duration of 15 minute. Figure 4 presents the temperature profile for plywood and MDF. The uncoated samples (PA and MA) represent the reference baseline. The general trend across all samples reveals a rapid rise in temperature during the first 3 minutes, followed by a peak and subsequent gradual decline. This trend indicates the onset of combustion followed by activation of decomposition processes. For plywood samples, the coating labelled PD (combination-coated) exhibited the highest peak of temperature, at around the fourth minute (minute of 4), suggesting insufficient early-stage thermal resistance. In contrast, PA and PC demonstrated more favourable thermal behaviour, with lower peak temperatures and smother temperature decline. This behaviour reflects a more efficient and stable formation of the protective layer, effectively insulating the substate and delaying thermal degradation. Among the plywood sample, PC emerged as the most thermal stable coating, likely due to a balanced formulation that promotes surpass combustion and minimizes heat transfer. In the MDF group, a similar trend was observed, with coating MD reaching the highest and most sustained temperature, indicating reduced fire protection performance. Notably, coating MA exhibited as control sample presented a relatively low peak temperature and steady decline implying this material alone is a good heat insulating material. However, comparing to the MC, significant performance on delaying time for reached temperature of 400℃ from 1 minute to 2 minutes indicate a good implication of fire-retardant coating to reduce the thermal conductivity properties. Comparatively, MDF samples generally exhibited higher peak temperatures and slower temperature reduction than plywood samples, which may be attributed to the denser structure and higher resin content of MDF that influences its thermal properties and combustion behaviour. Figure 5 report the maximum temperature achieved for all samples. The thermal behaviour of uncoated samples in Fig. 6 (a), serves as critical reference point in evaluating the fire performance of surface-treated materials. Both plywood and MDF displayed rapid temperature increases, at approximately 400℃ within the first minutes of exposure. This early temperature surge reflects the inherent flammability of untreated lignocellulosic material. However, it is noticeable that plywood sample tended to reach the peak slightly faster than MDF, due to its layered structure and lower density, which facilitates faster heat penetration. Conversely, MDF, being denser and more homogenous, exhibited a marginal delay in temperature rise and withstood higher temperature before decomposition, supporting natural insulation. This inherent differences in substrate behaviour significantly influences the interaction with surface coatings. In the case of coating only with primer (Fig. 6 (b)), a modest change in thermal behaviour was observed. Surprisingly, notably accelerated ignition and promoted stable heat retention, with some samples exhibiting significantly higher surface temperatures and prolonged heat retention during flame exposure within the first 3 minutes. This behaviour can be directly linked to the chemical composition of primer, which includes high proportions of flammable solvent of hydrocarbon chain. These compounds serve as readily available fuel sources in the context of fire triangle, the carbon content of the primer, have enhanced initial heat absorption and consequently promoted combustion, significantly reducing the ignition time and increasing the heat release rate (Puspitasari et al., 2019 ; Stewart et al., 2021 ). While primer may contribute to temporary heat retention due to surface charring, it does not actively inhibit combustion and may in fact pose a fire hazard in early-stage fire development. These results suggest that primers coating provides an aesthetically appearance but it only prone to worsening flammability. Significant improvements were observed in the samples coated with FR paint only. The samples showed lower peak temperature and slower thermal progression over a longer duration as seen in Fig. 6 (c). The presence of FR additives in the coating of phosphorus, aluminium and etc likely promoted the formation of protective layers, inhibiting combustion process and actings as thermal insulator effectively interrupt the fire triangle (Kandola & Horrocks, 1996 ). The delayed and more stable temperature rise in MDF compared to plywood reinforces the role of material density, with benefiting from both its structural compactness and the fire-resistance properties. This result also aligns with fire safety standards and allows more time for evacuation and firefighting intervention (Jaafar et al., 2023 ). Additionally, the consistent temperature declines after peak in both samples indicates improved fire suppression and partially self-extinguishing properties. In comparison, combination-coated samples (Fig. 6 (d)), demonstrated the highest peak temperature, exceeding 600℃ and prolonged heat retention in both materials, which may indicate heat entrapment or potential flammability of the combined coating system. The layered chemical load and reduced thermal dissipation create a scenario where surface ignition may be slightly delayed, but internal pyrolysis progresses rapidly, leading to an intense and sustained combustion phase. Notably, the coating sustained peak temperatures beyond typical flashover levels well past minute 3, exceeding durations commonly associated with early-stage tenability limits reported in fire safety literature, and thus raises a substantive safety concern (Jaafar et al., 2023 ). The distinctive temperature profile observed in combination-coated samples can be primarily attributed to the interplay between the FR and primer layers, where both chemical composition and thermal behaviour play critical roles. While the FR layer is designed to suppress combustion through mechanisms such as char formation, gas phase inhibition and thermal insulation, its performance can be significantly compromised by the presence of underlying primer layer that is rich in volatile organic compound (VOCs). The primer, composed of flammable constituents of ketones, esters, aromatics and LPG act as a fuel-rich interface that facilitates the release of combustible vapors during heating ultimately undermining the effectiveness of the FR layer. Moreover, the primer undergoes continuous thermal degradation, releasing heat steadily and absorbing residual energy once the FR layer has degraded (Puspitasari et al., 2019 ). This leads to prolonged heat retention and elevated post-ignition temperatures. Rather than acting synergistically, the layers may interfere with each other, with the primer contributing both fuel and latent heat. This explains the consistently higher peak temperatures and slower cooling rates observed in combination-coated samples compared to FR-only coatings. Therefore, without proper chemical compatibility, multi-layer systems may experience thermal instability, reducing overall fire protection performance. Overall, it can be summarizing that FR coated samples exhibited the most delayed onset of full fire development, followed sequentially by the combination-coated samples, with the uncoated and primer-coated samples demonstrating the fastest progression to fully ignition. 3.5 Post-exposure analysis Following fire exposure, the samples were allowed to cool under ambient conditions and were left in open air for at least one night to assess post-exposure material stability. Notable differences were observed in post-fire integrity between plywood and MDF samples. MDF samples, irrespective of coating configuration, become extremely fragile after overnight exposure. The material transformed into a flaky, ash-like texture that disintegrated easily upon handling, making accurate post-exposure dimensional measurement impractical, as illustrated in Fig. 7 . This behavior indicates that, despite limited surface flame involvement in some cases, the internal structural integrity of MDF was irreversibly compromised by thermal exposure. In contrast, plywood samples retained their overall geometry and remained structurally coherent after overnight air-drying. The car layer formed on plywood surfaces, particularly in FR and combined coated samples, remains adherent and mechanically stable, enabling post-exposure inspection and dimensional analysis. This difference is attributed to the layered veneer structure of plywood, which provides mechanical restraint and limits significant loss during thermal degradation, in contrast to homogenous fibre-resin matric of MDF that is more susceptible to binder decomposition and fibre separation. The observation was also supported by the average weight loss as presented in Table 4 . As summarized in Table 4 , average weight loss for plywood ranged from 36.21% to 51.12%, while MDF experienced higher mass loss, reaching up to 92.56% in certain configurations. The inability to obtain dimensional measurements for MDF samples reflects the extent of post-exposure disintegration rather than experimental uncertainty. Table 4 Average weight and dimension lost post-fire test. Sample Average weight loss (%) Dimension loss (%) PA 40.69 24.62 PB 51.12 18.62 PC 36.21 20.50 PD 50.75 20.98 MA 87.69 Can’t be measured MC 84.97 Can’t be measured MC 83.62 Can’t be measured MD 92.56 Can’t be measured These findings highlight that post-fire stability and residual material integrity are strongly substrate-dependent and may not be inferred solely from surface flame behavior of temperature evolution during exposure. The results emphasize the importance of considering post-exposure mechanical coherence when evaluating the practical performance of coated wood-based panels under localized flame exposure. 4. Conclusions This study describes an exploratory investigation into the thermal performance of different coating samples applied to wood-based boards with varying material properties. FTIR analysis revealed the presence of key fire-retardant functional groups such as phosphate, melamine, and hydroxyls, which play an important role in forming a stable and insulating layer during thermal exposure. These results were further supported by XRF analysis, which confirmed the presence of phosphorus, aluminum, silicon, and other flame-resistant elements that contribute to the overall flame-retardancy mechanism. Fire exposure testing using the bench scale fire exposure setup showed good agreement with the analytical results, particularly in relation to time-to-ignition, time-to-extinction, and flame behavior. Coated samples, especially those treated with fire-retardant coatings, consistently delayed ignition, resisted flame spread, and in some cases demonstrated partial self-extinction compared to uncoated or primer-coated samples. Temperature profile analysis also supported these findings, where coated samples displayed slower heat development and reduced peak surface temperatures. In contrast, combination-coated samples retained higher temperatures for longer durations, raising concerns about heat retention and prolonged combustion. Post-exposure evaluation highlighted the importance of substrate selection in fire protection design. Plywood samples maintained their structural integrity after air-drying, showing minimal warping and forming a strong char layer, whereas MDF samples became brittle, flaky, and structurally compromised. These results emphasize that both coating formulation and material type play a critical role in passive fire protection. Overall, the use of fire-retardant coatings has been shown to improve resistance to ignition and early-stage fire development at the material level by delaying ignition, lowering peak temperatures, and preserving the structural stability of wood-based panels. Future work should investigate long-term durability under environmental conditions, as well as scale-up testing under real fire scenarios to further validate these findings. Declarations Funding statement - Not Available. Author Contribution **Nur Ain Idrus** : Conceptualization, Data Curation, Formal Analysis, Investigation, Methodology, Writing—original draft preparation; **Nur Shahidah Ab Aziz** : Conceptualization, Resources, Supervision, Validation, Writing- review and editing. Acknowledgement The author would like to express sincere appreciation to University Teknologi MARA (UiTM) for providing the facilities, resources, and academic environment necessary for the successful completion of this research. Specifically, the author acknowledges the support provided by the Faculty of Chemical Engineering, UiTM Shah Alam. This study was self-funded. Data Availability The dataset(s) supporting the conclusions of this article are included within the article. 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Synergistic effects of kaolin clay on intumescent fire retardant coating composition for fire protection of structural steel substrate. Polymer Degradation and Stability , 110 , 91-103. Zhan, W., Li, L., Chen, L., Kong, Q., Chen, M., Chen, C., Zhang, Q., & Jiang, J. (2024). Biomaterials in intumescent fire-retardant coatings: a review. Progress in Organic Coatings , 192 , 108483. Additional Declarations No competing interests reported. Supplementary Files GraphicalAbstract.docx Cite Share Download PDF Status: Published Journal Publication published 28 Apr, 2026 Read the published version in Journal of the Indian Academy of Wood Science → 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8501365","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":571284101,"identity":"66b57d25-17b1-4e8a-9b40-92937945b4a1","order_by":0,"name":"NUR AIN IDRUS","email":"","orcid":"","institution":"Universiti Teknologi MARA","correspondingAuthor":false,"prefix":"","firstName":"NUR","middleName":"AIN","lastName":"IDRUS","suffix":""},{"id":571284103,"identity":"898df326-68ac-473f-9d54-370e8ae31544","order_by":1,"name":"NUR SHAHIDAH AB 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13:53:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8501365/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8501365/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s13196-026-00412-w","type":"published","date":"2026-04-28T15:57:49+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":100012052,"identity":"91f86925-d575-42e0-a6e8-e059c9eba543","added_by":"auto","created_at":"2026-01-12 06:12:55","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":7015511,"visible":true,"origin":"","legend":"","description":"","filename":"JIAWSWoodBoardPanelCoatingsubmitted.docx","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/d176072c5b31e72e4b180cc9.docx"},{"id":100361247,"identity":"64dcd682-8514-421c-b7d8-a2b927206a3d","added_by":"auto","created_at":"2026-01-16 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07:46:10","extension":"xml","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":68818,"visible":true,"origin":"","legend":"","description":"","filename":"6bb2998ef694447e80b3fd09393dabc41structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/5a0d08f0250b08d353b646e2.xml"},{"id":100361744,"identity":"80ebd5ea-b91d-472a-b5b1-0777da7f13ea","added_by":"auto","created_at":"2026-01-16 07:45:40","extension":"html","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":76921,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/be3d0d764b0aad056c1b5721.html"},{"id":100361737,"identity":"03c25d66-39ea-449c-b27d-7f363a331680","added_by":"auto","created_at":"2026-01-16 07:45:40","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":342316,"visible":true,"origin":"","legend":"\u003cp\u003eBench scale fire exposure setup with vertical orientation.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/c7bc3b14d0ab7e1f6d36415c.png"},{"id":100361756,"identity":"37f54b99-829e-4f20-ba27-efbba5d627bc","added_by":"auto","created_at":"2026-01-16 07:45:41","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":240757,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra on formulation of commercial fire-retardant.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/d559b6a86c4e5b3c14c084b1.png"},{"id":100012055,"identity":"0552c938-1958-430b-a604-44da9d1d1a8d","added_by":"auto","created_at":"2026-01-12 06:12:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":307908,"visible":true,"origin":"","legend":"\u003cp\u003eFlaming condition of MDF samples during fire testing.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/859baf53b8ea88dfbfd0f0b4.png"},{"id":100012054,"identity":"7669bce3-3f08-4bdf-9375-edd8fadf8d1d","added_by":"auto","created_at":"2026-01-12 06:12:55","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":120958,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature profile of different coating system: (a) plywood, (b) MDF.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/a21cd009c72bd46beb24d06c.png"},{"id":100012062,"identity":"d2ec0a5c-ffce-4e97-b9f7-4a3e1c37f6d4","added_by":"auto","created_at":"2026-01-12 06:12:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":34478,"visible":true,"origin":"","legend":"\u003cp\u003eMaximum temperature of each sample.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/f96a7b0bf03f6c03321a98c8.png"},{"id":100012070,"identity":"85cbd5b0-38b2-45ed-8359-3e560c7f6a9c","added_by":"auto","created_at":"2026-01-12 06:12:56","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":335598,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature profile of each coating system (a) Uncoated (b) Primer only (c) FR only and (d) Combination of primer and FR.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/ced4ec6d8b15de6e8b1907f3.png"},{"id":100012053,"identity":"827a9df6-9441-4178-bdaf-402d4cc6c274","added_by":"auto","created_at":"2026-01-12 06:12:55","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":412754,"visible":true,"origin":"","legend":"\u003cp\u003ePost fire-exposure condition (left to right: PA, MA, PB, MB, PD, MD)\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/f58aeba345a7538275206a87.png"},{"id":108437974,"identity":"42900f32-5e6a-4c53-9d59-e8dc3e842d58","added_by":"auto","created_at":"2026-05-04 16:05:10","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2115972,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/257871d4-2232-4c9d-9b65-a1a480bf5bd3.pdf"},{"id":100012044,"identity":"8c182685-bb67-4f25-969d-fd7626544879","added_by":"auto","created_at":"2026-01-12 06:12:55","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1617052,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-8501365/v1/deef275f0e9d6bd30a6af491.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eComparative Bench Scale Evaluation of Flame Exposure Behavior of Plywood and MDF Coated with Fire-Retardant Paint\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003ePassive fire protection is essential for ensuring structural safety, employing materials and systems that are designed to resist or slow down the spread of fire without requiring active measures (Lim et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Among these solutions, fire-retardant coatings stand out as an option, especially in construction and material engineering. These coatings improve thermal response under localized flame exposure to the surface by creating protective layers when exposed to high temperatures which release water vapor that suppress combustion (Eremina \u0026amp; Korolchenko, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Fire retardant materials are used in improving the safety of combustible items by delaying or preventing the spread of flames.\u003c/p\u003e \u003cp\u003eWood-based panel boards are among the most widely used materials in residential, commercial, and industrial applications because of their lightweight structure, good insulating properties, and cost-effectiveness. However, their high susceptibility to ignition and rapid flame spread presents significant safety concerns (Mensah et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). When subjected to flames, wood-based board ignites rapidly, emitting significant amounts of heat and potentially facilitating fire spread. The application of fire-retardant coating on panel board greatly enhances its thermal response under localized flame exposure by postponing ignition and lowering heat release rate. These coatings interfere with the chemical pathways of combustion, thereby lowering thermal hazards and improving evacuation time during fire emergencies (Aqlibous et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Mensah et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite these advances, the effectiveness of fire-retardant coatings across different types of wood-based panels remains insufficiently documented. Variations in physical and chemical properties among substrates influence the protective performance of coatings, yet comprehensive evaluations under realistic heat exposure scenarios are limited. Bridging this knowledge gap is crucial for optimizing the protective functions of fire-retardant systems and ensuring safer applications of wood-based materials in construction.\u003c/p\u003e \u003cp\u003eAccordingly, this study experimentally investigates the thermal resistance and fire-development performance of commercial fire-retardant coatings applied to wood-based boards. Particular attention is given to their behavior under heat exposure, integrating chemical and thermal characterization techniques. The coating\u0026rsquo;s chemical composition was analyzed using Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Fluorescence (XRF), while its influence on heat transfer and surface temperature was evaluated through Infrared (IR) thermography. On this basis, the study systematically assesses the role of fire-retardant coatings in passive fire protection, providing insights into their effectiveness in mitigating fire risks in wood-based panel applications.\u003c/p\u003e"},{"header":"2. Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Sample preparation\u003c/h2\u003e \u003cp\u003eA commercially available fire-retardant (FR) paint, primer and wood panel board was locally purchased. The test samples used in this experiment were panels from two different board of medium-density fibre board (MDF) and plywood board (210 mm x 70 mm x 6 mm) each were prepared as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. All wood panels were disc-sanded on the flat grain using P150 grit paper before the coating application. Two uncoated test samples, labelled as PA and MA were used as reference or control sample, other three test samples were prepared at different coating application for each type of wood-board. Second coatings (PB and MB) using commercial solvent-based primer containing aromatic hydrocarbons, ketones, esters, glycol ethers and LPG as propellant. Third coating (PC and MC) using FR paint and the last coatings system (PD and MD) using the combination of primer and FR. The FR coating was applied as 5 layers using roller paint, with was dried overnight for each layer to ensure uniform thickness. The weight of each sample is recorded before the test.\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\u003eDetails of test sample.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample ID\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWood panel board type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInitial weight (g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCoated system\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003ePlywood board\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e37\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003en/a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e47\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePrimer only\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e44\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFR paint\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e46\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePrimer\u0026thinsp;+\u0026thinsp;FR\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eMedium-density fibreboard (MDF)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e101\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003en/a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e99\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePrimer only\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e103\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFR paint\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e109\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePrimer\u0026thinsp;+\u0026thinsp;FR\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 \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Fire test method\u003c/h2\u003e \u003cp\u003eBench-scale flame exposure tests were conducted using a laboratory-developed vertical flame exposure setup designed for comparative screening of coated and uncoated wood-based panels. The setup can be illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A Bunsen burner flame was applied to the lower edge of vertically mounted specimens under controlled and repeatable conditions. The separation distance between the burner opening and the sample edge was maintained at 10 cm to ensure consistent heating conditions. The thermal response of each panel was monitored for 15 minutes using an infrared (IR) thermal imaging camera, which recorded the surface temperature distribution during fire exposure. The method was intended to provide relative comparison of ignition behavior, flame stability and thermal response. After exposure, the samples were cooled under ambient conditions overnight and re-weighed to determine mass loss. Each test was repeated three times for reproducibility and data reliability. The experimental setup also represents a laboratory-scale comparative screening method and does not correspond to a standardized fire classification or regulatory test. The results should be interpreted on a relative basis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Analysis and characterization\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1 Fourier Transform Infrared Bay (FTIR)\u003c/h2\u003e \u003cp\u003eThe functional groups present in the fire-retardant coating were analyzed using a Nicolet 400D Fourier Transform Infrared (FTIR) spectrometer. Spectra were recorded in the range of 4000\u0026ndash;515 cm⁻\u0026sup1; to identify characteristic absorption bands associated with the coating components.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2 X-ray Fluorescence Spectrometer (XRF)\u003c/h2\u003e \u003cp\u003eThe elemental composition of the fire-retardant paint was determined using a Panalytical Axios DY2156 X-ray Fluorescence (XRF) spectrometer. This analysis provided quantitative information on the inorganic elements incorporated into the coating formulation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.3.4 Surface Temperature Profiles\u003c/h2\u003e \u003cp\u003eThermal distribution on coated wood panels was monitored using Keysight TrueIR, an infrared (IR) thermal imaging camera. Measurements were performed over a temperature range of 0\u0026ndash;650\u0026deg;C, with the camera positioned at a distance of 1 m from the heat source. The recorded temperature profiles were then analysed using TrueIR Analysis and Reporting Tool software to evaluate relative surface temperature evolution and apparent thermal response under localized flame exposure.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 FTIR analysis\u003c/h2\u003e \u003cp\u003eFTIR spectra of the commercial fire-retardant paint were recorded using a Nicolet 400D spectrometer in the range of 4000\u0026ndash;515 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to identify the functional group and chemical components contributing to its FR properties. The sample, a white opaque liquid, was scanned and the resulting FTIR spectrum is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe absorption peak observed at 3802 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the O-H stretching vibration, which indicates the presence of hydroxyl group (Li et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This peak typically arises from the water content or polyol structure in the formulation. The peaks at 3587cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 3462 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3356 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e suggest overlapping of N-H and O-H stretching vibrations, commonly associated with melamine-derived structure and amino group (-NH\u003csub\u003e2\u003c/sub\u003e) present in the paint (Eremina \u0026amp; Korolchenko, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Gu et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Kwang Yin et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). A peak detected at 2193 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to C\u0026thinsp;\u0026equiv;\u0026thinsp;N stretching, confirming the presence of nitrile groups. This aligns with the melamine or cyanamide-based FR agent known for contributing to thermal stability and intumescent behaviour (produce charring layer). In the region of 1732 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, a strong absorption band indicates the C\u0026thinsp;=\u0026thinsp;O stretching vibration typical of ester or carbonyl-containing compounds such as acrylates or polyamide hardeners. Another prominent peak at 1637 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is attributed to the N-H bending from primary or secondary amines and may also involve C\u0026thinsp;=\u0026thinsp;N stretching, indicate of melamine or other triazine based structure (Kwang Yin et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ullah et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe peak at 1451 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e can be assigned to -CH\u003csub\u003e2\u003c/sub\u003e or -CH\u003csub\u003e3\u003c/sub\u003e bending vibrations, possibly from alkyl chains or solvent residues within paint matrix. An absorption at 1241 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e associated with P\u0026thinsp;=\u0026thinsp;O or P-O-C stretching modes, supporting the presence of phosphate compounds, which are essential components in many FR formulations. Additionally, a distinct absorption at 1153 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponds to PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e group, further verifying the existence of phosphate-based FR agents (Zhan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 XRF result\u003c/h2\u003e \u003cp\u003eX-ray fluorescence (XRF) spectroscopy was conducted to identify the elemental composition of the commercial FR paint, providing complementary data to support the functional group analysis obtained from the FTIR. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the presence of several key elements, with significant implications for the FR properties and formulation of the paints.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eXRF component detection in Greenlack waterborne fire-retardant.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.673\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.789\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.368\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.259\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.176\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.059\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBr\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.015\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.012\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe detection of phosphorus at 0.259% strongly supports the presence of phosphate-based compound as observed in the FTIR spectrum. Peaks at 1153 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1241 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the FTIR were assigned to PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e stretching and P\u0026thinsp;=\u0026thinsp;O or P-O-C bonds, indicating incorporation of ammonium polyphosphate (APP) or others phosphate salts, which are widely used in intumescent fire-retardant systems (Kim et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Ullah et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Zhan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe presence of aluminium (Al, 2.673%) is significant, as aluminium compounds such as aluminium hydroxide (ATH) or aluminium phosphate are commonly used as FR or synergists. ATH, in particular, decomposes endothermically to release water, diluting combustible gases and absorbing heat. This complements the O-H related FTIR peaks (3462\u0026ndash;3802 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), indicate hydroxyl-rich compounds (Li et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSilicon with a contribution of 1.798% may originate from silicate additives or silicone-based resins, often used to enhance thermal stability, water repellence, or adhesion in FR paints. Although not distinctly observed in FTIR due to overlapping bands, their presence is consistent with the known use of silica resins in high-performance coatings (Zhan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe presence of sulfur (0.368%) and calcium (0.176%) may be attributed to the use of inorganic FR synergist that help improve thermal barrier properties. This is typically used alongside phosphate and alumina to reinforce the protective char structure (Zhan et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Other than that, with trace amount, three elemental was detected which are potassium (K), bromine (Br) and platinum (Pt).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Experimental observations\u003c/h2\u003e \u003cp\u003eThe experimental setup allowed for continuous visual inspection of the test sample during testing. In this way, it was possible to visually examine the behaviour of uncoated and coated test sample under fire exposure. Fire-resistance performance on the plywood and MDF samples was assessed based on thermal response indicators including time-to-ignition (TTI), time-to-extinction (TTE) and observable flame characteristics. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e reports the TTI and TTE of all test samples. TTI was defined as the elapsed time from flame application to the onset of the sustained flame observed visually, accompanied by a rapid and continuous increase in surface temperature recorded by infrared thermography, while TTE is duration from ignition until the flame is disappearing or fully extinguished.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTime-based fire performance (average value).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample ID\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTime-to-ignition (min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTime-to-extinction (min)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e~\u0026thinsp;1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e~\u0026thinsp;13.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e~\u0026thinsp;1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e~\u0026thinsp;14.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e~\u0026thinsp;2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e~\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e~\u0026thinsp;0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e~\u0026thinsp;10.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e~\u0026thinsp;1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e~\u0026thinsp;15.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e~\u0026thinsp;0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e~\u0026thinsp;15.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e~\u0026thinsp;1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e~\u0026thinsp;7.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e~\u0026thinsp;1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e~\u0026thinsp;13.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe analysis of TTI and TTE provides critical insight into their safety performance during fire incidents. These parameters are especially significant when considering the use of such material in residential, commercial and public buildings, where fire safety and human evacuation are paramount. TTI indicates how rapidly a material reacts to a heat source and is closely linked to the critical timeframe available for individuals to notice and respond to a fire. Coatings that prolong ignition, like exceeding 1.5 minutes able to offer an essential buffer for early fire detection systems (such as smoke alarms). This delay in ignition grants occupants additional time to become aware of danger and initiate evacuation before conditions worsen.\u003c/p\u003e \u003cp\u003eConversely, TTE measures the duration that the material continues to support flames. Materials with extended extension time such as material labelled PB, MA and MB, which can maintain combustion for as long as 14 minutes, present a greater risk for fire spread and heat build-up, potentially hindering rescue efforts and escalating structural damage. In contrast, materials with fire-retardant coating, highlighted as PC, not only ignite at a later stage but also extinguish more rapidly and steadily, significant more effective flame suppression.\u003c/p\u003e \u003cp\u003eFlame behaviour is also a main factor in fire dynamics. The flame condition of uncoated samples and primer coated samples (PA, PB, MA and MB) were characterized by rapid flame spread, bright orange colour and complete consumption of the substrate. These sample kept burning for the whole duration of the test and no flame extinction was recorded for any of the samples during the fire test. Primer coated surfaces show slightly slower spread due to minor sealing effect but ultimately provide no-fire-retardant benefit. FR coated samples (PC, PD, MC and MD) on the other hands, exhibited unstable flames with evidence of partially self-extinction before complete combustion. This observation reflects the ability of FR layers to suppress flame propagation and smother the combustion process via char formation and gas release. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the condition of plywood for uncoated samples (left) and primer-coated samples (right) at minute of 5 during the fire exposure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Evolution of the temperature within samples\u003c/h2\u003e \u003cp\u003eThe thermal response of different wood substate, namely plywood and medium-density fiberboard (MDF), was studied under varying coating systems to assess their thermal response under localized flame exposure characteristic and implications for fire safety. These substrates were tested in four conditions of uncoated, primer-coated, FR coated and combination-coated (primer followed by FR paint). The evolution of temperature during fire exposure was captured using a thermal infrared camera over a duration of 15 minute. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents the temperature profile for plywood and MDF. The uncoated samples (PA and MA) represent the reference baseline. The general trend across all samples reveals a rapid rise in temperature during the first 3 minutes, followed by a peak and subsequent gradual decline. This trend indicates the onset of combustion followed by activation of decomposition processes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor plywood samples, the coating labelled PD (combination-coated) exhibited the highest peak of temperature, at around the fourth minute (minute of 4), suggesting insufficient early-stage thermal resistance. In contrast, PA and PC demonstrated more favourable thermal behaviour, with lower peak temperatures and smother temperature decline. This behaviour reflects a more efficient and stable formation of the protective layer, effectively insulating the substate and delaying thermal degradation. Among the plywood sample, PC emerged as the most thermal stable coating, likely due to a balanced formulation that promotes surpass combustion and minimizes heat transfer.\u003c/p\u003e \u003cp\u003eIn the MDF group, a similar trend was observed, with coating MD reaching the highest and most sustained temperature, indicating reduced fire protection performance. Notably, coating MA exhibited as control sample presented a relatively low peak temperature and steady decline implying this material alone is a good heat insulating material. However, comparing to the MC, significant performance on delaying time for reached temperature of 400℃ from 1 minute to 2 minutes indicate a good implication of fire-retardant coating to reduce the thermal conductivity properties. Comparatively, MDF samples generally exhibited higher peak temperatures and slower temperature reduction than plywood samples, which may be attributed to the denser structure and higher resin content of MDF that influences its thermal properties and combustion behaviour. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e report the maximum temperature achieved for all samples.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe thermal behaviour of uncoated samples in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a), serves as critical reference point in evaluating the fire performance of surface-treated materials. Both plywood and MDF displayed rapid temperature increases, at approximately 400℃ within the first minutes of exposure. This early temperature surge reflects the inherent flammability of untreated lignocellulosic material. However, it is noticeable that plywood sample tended to reach the peak slightly faster than MDF, due to its layered structure and lower density, which facilitates faster heat penetration. Conversely, MDF, being denser and more homogenous, exhibited a marginal delay in temperature rise and withstood higher temperature before decomposition, supporting natural insulation. This inherent differences in substrate behaviour significantly influences the interaction with surface coatings.\u003c/p\u003e \u003cp\u003eIn the case of coating only with primer (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b)), a modest change in thermal behaviour was observed. Surprisingly, notably accelerated ignition and promoted stable heat retention, with some samples exhibiting significantly higher surface temperatures and prolonged heat retention during flame exposure within the first 3 minutes. This behaviour can be directly linked to the chemical composition of primer, which includes high proportions of flammable solvent of hydrocarbon chain. These compounds serve as readily available fuel sources in the context of fire triangle, the carbon content of the primer, have enhanced initial heat absorption and consequently promoted combustion, significantly reducing the ignition time and increasing the heat release rate (Puspitasari et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Stewart et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). While primer may contribute to temporary heat retention due to surface charring, it does not actively inhibit combustion and may in fact pose a fire hazard in early-stage fire development. These results suggest that primers coating provides an aesthetically appearance but it only prone to worsening flammability.\u003c/p\u003e \u003cp\u003eSignificant improvements were observed in the samples coated with FR paint only. The samples showed lower peak temperature and slower thermal progression over a longer duration as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c). The presence of FR additives in the coating of phosphorus, aluminium and etc likely promoted the formation of protective layers, inhibiting combustion process and actings as thermal insulator effectively interrupt the fire triangle (Kandola \u0026amp; Horrocks, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). The delayed and more stable temperature rise in MDF compared to plywood reinforces the role of material density, with benefiting from both its structural compactness and the fire-resistance properties. This result also aligns with fire safety standards and allows more time for evacuation and firefighting intervention (Jaafar et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Additionally, the consistent temperature declines after peak in both samples indicates improved fire suppression and partially self-extinguishing properties.\u003c/p\u003e \u003cp\u003eIn comparison, combination-coated samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d)), demonstrated the highest peak temperature, exceeding 600℃ and prolonged heat retention in both materials, which may indicate heat entrapment or potential flammability of the combined coating system. The layered chemical load and reduced thermal dissipation create a scenario where surface ignition may be slightly delayed, but internal pyrolysis progresses rapidly, leading to an intense and sustained combustion phase. Notably, the coating sustained peak temperatures beyond typical flashover levels well past minute 3, exceeding durations commonly associated with early-stage tenability limits reported in fire safety literature, and thus raises a substantive safety concern (Jaafar et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe distinctive temperature profile observed in combination-coated samples can be primarily attributed to the interplay between the FR and primer layers, where both chemical composition and thermal behaviour play critical roles. While the FR layer is designed to suppress combustion through mechanisms such as char formation, gas phase inhibition and thermal insulation, its performance can be significantly compromised by the presence of underlying primer layer that is rich in volatile organic compound (VOCs). The primer, composed of flammable constituents of ketones, esters, aromatics and LPG act as a fuel-rich interface that facilitates the release of combustible vapors during heating ultimately undermining the effectiveness of the FR layer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMoreover, the primer undergoes continuous thermal degradation, releasing heat steadily and absorbing residual energy once the FR layer has degraded (Puspitasari et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). This leads to prolonged heat retention and elevated post-ignition temperatures. Rather than acting synergistically, the layers may interfere with each other, with the primer contributing both fuel and latent heat. This explains the consistently higher peak temperatures and slower cooling rates observed in combination-coated samples compared to FR-only coatings. Therefore, without proper chemical compatibility, multi-layer systems may experience thermal instability, reducing overall fire protection performance. Overall, it can be summarizing that FR coated samples exhibited the most delayed onset of full fire development, followed sequentially by the combination-coated samples, with the uncoated and primer-coated samples demonstrating the fastest progression to fully ignition.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Post-exposure analysis\u003c/h2\u003e \u003cp\u003eFollowing fire exposure, the samples were allowed to cool under ambient conditions and were left in open air for at least one night to assess post-exposure material stability. Notable differences were observed in post-fire integrity between plywood and MDF samples. MDF samples, irrespective of coating configuration, become extremely fragile after overnight exposure. The material transformed into a flaky, ash-like texture that disintegrated easily upon handling, making accurate post-exposure dimensional measurement impractical, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. This behavior indicates that, despite limited surface flame involvement in some cases, the internal structural integrity of MDF was irreversibly compromised by thermal exposure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, plywood samples retained their overall geometry and remained structurally coherent after overnight air-drying. The car layer formed on plywood surfaces, particularly in FR and combined coated samples, remains adherent and mechanically stable, enabling post-exposure inspection and dimensional analysis. This difference is attributed to the layered veneer structure of plywood, which provides mechanical restraint and limits significant loss during thermal degradation, in contrast to homogenous fibre-resin matric of MDF that is more susceptible to binder decomposition and fibre separation. The observation was also supported by the average weight loss as presented in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. As summarized in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, average weight loss for plywood ranged from 36.21% to 51.12%, while MDF experienced higher mass loss, reaching up to 92.56% in certain configurations. The inability to obtain dimensional measurements for MDF samples reflects the extent of post-exposure disintegration rather than experimental uncertainty.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAverage weight and dimension lost post-fire test.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAverage weight loss (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDimension loss (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e40.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e51.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e36.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e87.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCan\u0026rsquo;t be measured\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e84.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCan\u0026rsquo;t be measured\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e83.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCan\u0026rsquo;t be measured\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e92.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCan\u0026rsquo;t be measured\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThese findings highlight that post-fire stability and residual material integrity are strongly substrate-dependent and may not be inferred solely from surface flame behavior of temperature evolution during exposure. The results emphasize the importance of considering post-exposure mechanical coherence when evaluating the practical performance of coated wood-based panels under localized flame exposure.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis study describes an exploratory investigation into the thermal performance of different coating samples applied to wood-based boards with varying material properties. FTIR analysis revealed the presence of key fire-retardant functional groups such as phosphate, melamine, and hydroxyls, which play an important role in forming a stable and insulating layer during thermal exposure. These results were further supported by XRF analysis, which confirmed the presence of phosphorus, aluminum, silicon, and other flame-resistant elements that contribute to the overall flame-retardancy mechanism.\u003c/p\u003e \u003cp\u003eFire exposure testing using the bench scale fire exposure setup showed good agreement with the analytical results, particularly in relation to time-to-ignition, time-to-extinction, and flame behavior. Coated samples, especially those treated with fire-retardant coatings, consistently delayed ignition, resisted flame spread, and in some cases demonstrated partial self-extinction compared to uncoated or primer-coated samples. Temperature profile analysis also supported these findings, where coated samples displayed slower heat development and reduced peak surface temperatures. In contrast, combination-coated samples retained higher temperatures for longer durations, raising concerns about heat retention and prolonged combustion.\u003c/p\u003e \u003cp\u003ePost-exposure evaluation highlighted the importance of substrate selection in fire protection design. Plywood samples maintained their structural integrity after air-drying, showing minimal warping and forming a strong char layer, whereas MDF samples became brittle, flaky, and structurally compromised. These results emphasize that both coating formulation and material type play a critical role in passive fire protection. Overall, the use of fire-retardant coatings has been shown to improve resistance to ignition and early-stage fire development at the material level by delaying ignition, lowering peak temperatures, and preserving the structural stability of wood-based panels. Future work should investigate long-term durability under environmental conditions, as well as scale-up testing under real fire scenarios to further validate these findings.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding statement -\u003c/h2\u003e \u003cp\u003eNot Available.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003e**Nur Ain Idrus** : Conceptualization, Data Curation, Formal Analysis, Investigation, Methodology, Writing\u0026mdash;original draft preparation; **Nur Shahidah Ab Aziz** : Conceptualization, Resources, Supervision, Validation, Writing- review and editing.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe author would like to express sincere appreciation to University Teknologi MARA (UiTM) for providing the facilities, resources, and academic environment necessary for the successful completion of this research. Specifically, the author acknowledges the support provided by the Faculty of Chemical Engineering, UiTM Shah Alam. This study was self-funded.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe dataset(s) supporting the conclusions of this article are included within the article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAqlibous, A., Tretsiakova-McNally, S., \u0026amp; Fateh, T. (2020). Waterborne intumescent coatings containing industrial and bio-fillers for fire protection of timber materials. \u003cem\u003ePolymers\u003c/em\u003e,\u003cem\u003e\u0026nbsp;12\u003c/em\u003e(4), 757.\u003c/li\u003e\n \u003cli\u003eEremina, T., \u0026amp; Korolchenko, D. (2020). 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Developing a framework for fire safety management plan: the case of Malaysia\u0026apos;s public hospital buildings. \u003cem\u003eInternational journal of building pathology and adaptation\u003c/em\u003e,\u003cem\u003e\u0026nbsp;41\u003c/em\u003e(4), 713-733.\u003c/li\u003e\n \u003cli\u003eKandola, B. K., \u0026amp; Horrocks, A. R. (1996). Complex char formation in flame-retarded fibre-intumescent combinations\u0026mdash;II. Thermal analytical studies. \u003cem\u003ePolymer Degradation and Stability\u003c/em\u003e,\u003cem\u003e\u0026nbsp;54\u003c/em\u003e(2-3), 289-303.\u003c/li\u003e\n \u003cli\u003eKim, Y., Lee, S., \u0026amp; Yoon, H. (2021). Fire-safe polymer composites: flame-retardant effect of nanofillers. \u003cem\u003ePolymers\u003c/em\u003e,\u003cem\u003e\u0026nbsp;13\u003c/em\u003e(4), 540.\u003c/li\u003e\n \u003cli\u003eKwang Yin, J. J., Yew, M. C., Yew, M. K., \u0026amp; Saw, L. H. (2019). Preparation of intumescent fire protective coating for fire rated timber door. \u003cem\u003eCoatings\u003c/em\u003e,\u003cem\u003e\u0026nbsp;9\u003c/em\u003e(11), 738.\u003c/li\u003e\n \u003cli\u003eLi, Y., Cao, C.-F., Chen, Z.-Y., Liu, S.-C., Bae, J., \u0026amp; Tang, L.-C. (2024). Waterborne intumescent fire-retardant polymer composite coatings: a review. \u003cem\u003ePolymers\u003c/em\u003e,\u003cem\u003e\u0026nbsp;16\u003c/em\u003e(16), 2353.\u003c/li\u003e\n \u003cli\u003eLim, J. W., Baalisampang, T., Garaniya, V., Abbassi, R., Khan, F., \u0026amp; Ji, J. (2019).\u0026nbsp;Numerical analysis of performances of passive fire protections in processing facilities. \u003cem\u003eJournal of Loss Prevention in the Process Industries\u003c/em\u003e,\u003cem\u003e\u0026nbsp;62\u003c/em\u003e, 103970.\u003c/li\u003e\n \u003cli\u003eMensah, R. A., Jiang, L., Renner, J. S., \u0026amp; Xu, Q. (2023). Characterisation of the fire behaviour of wood: From pyrolysis to fire retardant mechanisms. \u003cem\u003eJournal of Thermal Analysis and Calorimetry\u003c/em\u003e,\u003cem\u003e\u0026nbsp;148\u003c/em\u003e(4), 1407-1422.\u003c/li\u003e\n \u003cli\u003ePuspitasari, W., Ahmad, F., Ullah, S., Hussain, P., Megat-Yusoff, P. S., \u0026amp; Masset, P. J. (2019). The study of adhesion between steel substrate, primer, and char of intumescent fire retardant coating. \u003cem\u003eProgress in Organic Coatings\u003c/em\u003e,\u003cem\u003e\u0026nbsp;127\u003c/em\u003e, 181-193.\u003c/li\u003e\n \u003cli\u003eStewart, J. R., Phylaktou, H. N., Andrews, G. E., \u0026amp; Burns, A. D. (2021). Evaluation of CFD simulations of transient pool fire burning rates. \u003cem\u003eJournal of Loss Prevention in the Process Industries\u003c/em\u003e,\u003cem\u003e\u0026nbsp;71\u003c/em\u003e, 104495.\u003c/li\u003e\n \u003cli\u003eUllah, S., Ahmad, F., Shariff, A., \u0026amp; Bustam, M. (2014). Synergistic effects of kaolin clay on intumescent fire retardant coating composition for fire protection of structural steel substrate. \u003cem\u003ePolymer Degradation and Stability\u003c/em\u003e,\u003cem\u003e\u0026nbsp;110\u003c/em\u003e, 91-103.\u003c/li\u003e\n \u003cli\u003eZhan, W., Li, L., Chen, L., Kong, Q., Chen, M., Chen, C., Zhang, Q., \u0026amp; Jiang, J. (2024). Biomaterials in intumescent fire-retardant coatings: a review. \u003cem\u003eProgress in Organic Coatings\u003c/em\u003e,\u003cem\u003e\u0026nbsp;192\u003c/em\u003e, 108483.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":true,"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":"Wood-based panels, Fire-retardant coatings, Bech-scale flame exposure, Ignition behavior, Thermal response","lastPublishedDoi":"10.21203/rs.3.rs-8501365/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8501365/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWood-based panel boards are widely used in construction and interior applications for their low cost and favorable mechanical properties, yet their flammability remains a major safety concern. This study evaluates the effectiveness of commercial fire-retardant (FR) coatings on plywood and medium-density fiberboard (MDF). The coatings were characterized using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Fluorescence (XRF), while fire performance was assessed through a bench-scale vertical flame exposure setup developed for comparative evaluation of ignition behavior under localized flame exposure, combined with infrared thermography to monitor surface temperature evolution. FTIR revealed functional groups such as phosphate, melamine, and hydroxyls, while XRF confirmed phosphorus, aluminum, and silicon, all contributing to char formation and flame inhibition. Fire tests showed that FR-coated panels delayed ignition, lowered peak surface temperatures, and in some cases achieved partial self-extinction compared with uncoated or primer-coated boards. Plywood retained structural integrity after exposure, whereas MDF became brittle and flaky, highlighting the role of substrate type in thermal response under localized flame exposure. Overall, FR coatings demonstrated improved resistance to ignition and early-stage thermal development by extending ignition time, reducing heat transfer, and preserving stability. These findings emphasize the value of passive fire protection strategies in delaying ignition onset and reducing early-stage thermal development under localized flame exposure and reducing early-stage thermal degradation in wood-based panel applications and furnishing applications.\u003c/p\u003e","manuscriptTitle":"Comparative Bench Scale Evaluation of Flame Exposure Behavior of Plywood and MDF Coated with Fire-Retardant Paint","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-01-12 06:12:50","doi":"10.21203/rs.3.rs-8501365/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":"d9732a2f-4a74-449d-8ecb-b3e2c2ebe07e","owner":[],"postedDate":"January 12th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-04T16:05:05+00:00","versionOfRecord":{"articleIdentity":"rs-8501365","link":"https://doi.org/10.1007/s13196-026-00412-w","journal":{"identity":"journal-of-the-indian-academy-of-wood-science","isVorOnly":false,"title":"Journal of the Indian Academy of Wood Science"},"publishedOn":"2026-04-28 15:57:49","publishedOnDateReadable":"April 28th, 2026"},"versionCreatedAt":"2026-01-12 06:12:50","video":"","vorDoi":"10.1007/s13196-026-00412-w","vorDoiUrl":"https://doi.org/10.1007/s13196-026-00412-w","workflowStages":[]},"version":"v1","identity":"rs-8501365","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8501365","identity":"rs-8501365","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}