A bio-based flame-retardant coating crosslinked with urushiol glycidyl ether and phytic acid and a preparation method thereof

Abstract

The application discloses a kind of lacquer phenol glycidyl ether and biological base fire-retardant coating of crosslinking with phytic acid and preparation method thereof.Epoxy monomer lacquer phenol glycidyl ether with epoxy reaction activity and rigid aromatic ring skeleton is obtained by using lacquer phenol as raw material and being modified by epoxidation,then self-expanding biological base fire-retardant coating is constructed with phytic acid.Lacquer phenol glycidyl ether is rich in aromatic ring structure as charring agent,phytic acid releases phosphoric acid as acid source to catalyze dehydration and carbonization of matrix and releases water vapor as foaming source to promote carbon layer expansion when heated.Phosphorus hydroxyl of phytic acid and epoxy group of lacquer phenol glycidyl ether occur ring-opening esterification to form phosphorus-oxygen-carbon covalent crosslinking network,realizing efficient fire-retardant with condensed phase fire-retardant mechanism as dominant.The fire-retardant coating prepared by the application has simple components and convenient preparation process,avoiding the dependence on petroleum-based resin and halogen / phosphorus-based synthetic fire retardant of traditional fire-retardant coating,providing a new idea for developing biological base fire-retardant coating.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant coating technology, specifically relating to a bio-based flame retardant coating crosslinked with urushiol glycidyl ether and phytic acid, and its preparation method. Background Technology

[0002] Flame-retardant coatings, as an important type of functional protective material, are widely used for fire protection of flammable substrates such as wood, textiles, cables and wires, and building structures. They play an irreplaceable role in reducing fire risks and ensuring personal and property safety.

[0003] Currently, commercially available flame-retardant coating systems, especially intumescent flame-retardant coatings, mostly use petroleum-based epoxy resins or acrylic resins as film-forming base materials, and are compounded with multi-component intumescent flame retardant systems such as ammonium polyphosphate (APP), pentaerythritol (PER), and melamine (MEL) to achieve a synergistic flame-retardant effect from the acid source, carbon source, and gas source. These systems have numerous components and complex preparation processes, and many components are derived from non-renewable petrochemical resources. The production process involves high energy consumption and volatile organic compound emissions, which contradicts current "dual carbon" goals and green manufacturing concepts. Furthermore, some traditional flame retardants suffer from migration and poor compatibility with the matrix, limiting their long-term protective efficacy.

[0004] With the deepening of the concept of renewable resource utilization, the development of fully bio-based flame-retardant coatings that combine excellent flame-retardant properties with environmental friendliness has become a research hotspot in the field of materials. Urushiol, as the main active ingredient of traditional Chinese lacquer (raw lacquer), is a naturally derived catechol compound. Its molecule has a benzene ring as its backbone, is rich in phenolic hydroxyl groups, and has long-chain unsaturated alkyl side chains, which endow it with excellent weather resistance, chemical corrosion resistance, and film-forming properties.

[0005] Phytic acid is a natural polyphosphate compound widely found in the seeds of grains, beans, and other plants. Its molecule contains six phosphate ester groups, has a high phosphorus content, and is rich in reactive sites. When heated, it can release phosphoric acid substances to catalyze the dehydration of the matrix into char, while the release of water vapor promotes the expansion and foaming of the char layer. It has the dual function of acid source and gas source in intumescent flame retardant systems. In addition, the active phosphoric hydroxyl groups of phytic acid can also undergo ring-opening esterification reaction with the epoxy groups of epoxy resin, and participate in the construction of phosphorus oxycarbon (POC) covalent cross-linking network as a curing agent, thereby imparting flame retardancy to the system while achieving curing and cross-linking.

[0006] There are existing reports on constructing bio-based flame retardant systems using bio-based phenolic epoxy resins or natural polyphenol derivatives such as tannic acid and cashew phenol as curing agents or flame retardant additives. However, such systems may require additional compounding with synthetic flame retardants such as ammonium polyphosphate to achieve the ideal flame retardant rating. Alternatively, due to the relatively simple structure of the bio-based phenols used and the limited content of aromatic rings and char-forming groups, it is difficult to achieve a self-expanding flame retardant effect that combines high oxygen index, UL-94 V-0 rating, and excellent char-forming properties by relying solely on two natural components.

[0007] The patent "Dual-epoxy functional lacquer phenolic phosphorus-containing flame retardant and its preparation method and application" requires a multi-step reaction to prepare DOPO modified flame retardant additives. These additives only provide flame retardancy and lack the ability to cure and form films. The formulation also requires the addition of petroleum-based epoxy resin and amine curing agents, making it difficult to build a fully bio-based self-expanding flame retardant system. Another flame retardant scheme involves phytic acid, cashew phenol glycidyl ether, and melamine. However, powdered melamine is poorly dispersed in liquid resin, easily forming defective coatings. The patent "A bio-based intumescent flame retardant for thermoplastic vulcanized rubber TPV and its synthesis method and application" requires the separate synthesis of the flame retardant before physical blending into the substrate, resulting in a lengthy process. Furthermore, this product is only suitable for thermoplastic rubbers like TPV and cannot be directly applied to thermosetting flame retardant coating systems.

[0008] Therefore, developing a high-performance, low-environmental-impact, self-expanding, fully bio-based flame-retardant coating system that does not require the addition of synthetic flame retardants such as ammonium polyphosphate is an urgent problem to be solved in this field. Summary of the Invention

[0009] The purpose of this invention is to address the limitations of existing bio-based flame retardant coating systems, which are characterized by complex components, reliance on synthetic flame retardants, and difficulty in achieving a balance between excellent flame retardant performance and char formation efficiency using only natural components. This invention provides a bio-based flame retardant coating crosslinked with urushiol glycidyl ether and phytic acid, and its preparation method.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A bio-based flame-retardant coating crosslinked with urushiol glycidyl ether and phytic acid, wherein the bio-based flame-retardant coating comprises, by weight 100%, the following components: Urushiol glycidyl ether (UGE): 70.82~83.06 wt%; the urushiol glycidyl ether is prepared by epichlorohydrin epoxidation modification of urushiol, and the molecule contains epoxy groups, catechol hydroxyl groups and long-chain unsaturated alkyl structures. Phytic acid (PA): 16.94~29.18 wt%, wherein the phytic acid is a 70% aqueous solution of phytic acid; The molar ratio of the active phosphorohydroxyl group in phytic acid to the epoxy group in urushiol glycidyl ether is 0.5~1.0.

[0011] Furthermore, the preparation method of the urushiol glycidyl ether is as follows: urushiol, epichlorohydrin and tetrabutylammonium bromide are reacted at 60°C for 3 hours, then 20% sodium hydroxide aqueous solution is added dropwise, and the reaction is continued at 60°C for 2 hours. After the reaction is completed, the crude product is cooled to room temperature, washed with water, filtered, and dried to obtain urushiol glycidyl ether with an epoxy value of 0.261 mol / 100g.

[0012] Furthermore, the mass ratio of urushiol, epichlorohydrin, tetrabutylammonium bromide, and 20% sodium hydroxide aqueous solution is 12.82:15.11 to 60.44:1.04:16, preferably 12.82:38.02:1.04:16.

[0013] Furthermore, the bio-based flame retardant coating has an oxygen index of ≥30%, a vertical burning rating of UL-94 V-0, and a char rate of ≥20%.

[0014] A method for preparing the above-mentioned bio-based flame-retardant coating includes the following steps: (1) Dissolve urushiol glycidyl ether in propylene glycol methyl ether, then slowly add phytic acid, and stir at 70°C for 2 h to obtain a flame retardant coating composition. (2) The flame retardant coating composition obtained in step (1) is coated on the surface of the substrate or placed in a mold for curing to obtain a bio-based flame retardant coating.

[0015] Furthermore, the curing process described in step (2) is to maintain the temperature at 80 ℃ for 1 h, then raise the temperature to 130 ℃ for 1 h, and finally raise the temperature to 180 ℃ for 3 h.

[0016] Furthermore, the substrate mentioned in step (2) is the surface of a wood substrate or the surface of a tinplate.

[0017] This invention creatively selects urushiol, which has a natural catechol structure and a long-chain aromatic skeleton, as a char-forming agent precursor. Uurushiol glycidyl ether is obtained through epoxidation and then combined with phytic acid rich in phosphate groups to construct a self-expanding flame-retardant system. In this system, UGE, with its high aromatic ring density, imparts excellent thermal stability and density to the char layer, acting as a char-forming agent. Phosphate substances generated by the thermal decomposition of phytic acid catalyze the dehydration and char formation of the system and induce water vapor release and foaming. Simultaneously, its active phosphoric hydroxyl groups undergo ring-opening esterification with the UGE epoxy groups to form a POC covalent cross-linked network, constructing a dual-action mechanism that combines chemical cross-linking and intumescent flame-retardant functions. This allows the coating to achieve excellent flame-retardant performance under the dominance of the condensed phase flame-retardant mechanism, which is difficult to achieve using other relatively simple plant phenolic epoxy resins or conventional flame-retardant compound systems alone.

[0018] The significant advantages of this invention are as follows: (1) The present invention uses only two natural biomass-derived components, urushiol glycidyl ether and phytic acid, to construct a flame-retardant coating system. There is no need to add synthetic intumescent flame retardants such as ammonium polyphosphate and melamine. The system has simple components and a high degree of bio-based composition, which effectively reduces the coating's dependence on petroleum-based raw materials and synthetic flame-retardant additives. The dual functions of chemical cross-linking film formation and self-expanding flame retardancy can be achieved through the synergistic effect of the two biomass components, making it more green and environmentally friendly.

[0019] (2) The flame retardant coating obtained by the present invention achieves the best comprehensive performance when the phytic acid to UGE epoxy equivalent ratio is about 0.8 (UP-0.8), the oxygen index (LOI) can reach 33.6%, the vertical combustion reaches UL-94 V-0 level, the char rate can reach up to 24.41%, and the total heat release (THR), effective heat of combustion (EHC) and peak heat release rate (pHRR2) are significantly lower than those of other coatings in the system. It achieves the unity of excellent flame retardant performance and char formation efficiency, and can meet the growing demand of the flame retardant coating market for high-performance and green products.

[0020] (3) The flame-retardant coating obtained by the present invention forms a dense condensed phase flame-retardant carbon layer after curing. The formation of phosphorus oxygen carbon (POC) covalent cross-linking network effectively improves the thermal stability of the carbon layer, which can meet the fire protection requirements of flammable substrates such as wood materials and textiles, and has important industrial application prospects.

[0021] (4) Phytic acid serves as both a curing agent and a phosphorus source. Its phosphorus hydroxyl groups can directly react with the UGE epoxy groups to form a POC covalent cross-linking network, achieving the dual functions of curing and flame retardancy. The aromatic structure in UGE is conducive to the formation of a stable char layer, improving the integrity and thermal stability of the char layer. The two work together to promote the formation of a continuous and dense phosphorus-rich char layer, thereby effectively blocking the transfer of heat and oxygen and reducing the release of combustible volatiles, achieving a highly efficient flame retardant mechanism dominated by the condensed phase. Attached Figure Description

[0022] Figure 1 Fourier transform infrared spectra of urushiol glycidyl ether (UGE), phytic acid (PA), and flame-retardant coating (UP-1.0).

[0023] Figure 2 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the flame-retardant coating prepared in Example 4.

[0024] Figure 3 The flame-retardant coating prepared in Example 4 31 p-NMR spectrum Figure 4 The images show the DSC test results of the flame-retardant coatings prepared in Examples 1-6.

[0025] Figure 5 The TGA test results are for the flame-retardant coatings prepared in Examples 1-6.

[0026] Figure 6 The graph shows the trend of the oxygen index (LOI) of the flame-retardant coatings prepared in Examples 1-6.

[0027] Figure 7 Cone calorimetry curves of pure poplar (PW) and the flame-retardant coatings prepared in Examples 1, 4, and 6.

[0028] Figure 8 For comparative analysis of the physical performance of UP-0.8-MEL.

[0029] Figure 9 Scanning electron microscope (SEM) images of the char layer after combustion of pure poplar (PW) and the flame-retardant coating prepared in Example 4. Detailed Implementation

[0030] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0031] The substrate pretreatment method used in the embodiments is as follows: After cleaning the tinplate substrate with acetone, anhydrous ethanol and deionized water to remove surface oil, it is dipped in a 1 wt% solution of silane coupling agent KH-560 (a mixed solution of anhydrous ethanol and water in a volume ratio of 9:1). After hydrolysis for 45-60 min, it is taken out and cured by stepwise temperature increase from 80 ℃ / 30 min to 120 ℃ / 30 min to obtain a pretreated substrate for later use.

[0032] After sanding the poplar surface with 400-grit sandpaper and drying it, a pre-treated wood substrate surface is obtained.

[0033] The preparation method of urushiol glycidyl ether used in the examples is as follows: In a reactor equipped with a thermometer, magnetic stirrer, and condenser, 12.82 g of urushiol, 38.02 g of epichlorohydrin, and 1.04 g of tetrabutylammonium bromide were added sequentially. The reaction system was heated to 60 °C, and after stirring for 3 h, 16 g of 20 wt% sodium hydroxide aqueous solution was slowly added dropwise, and stirring was continued for another 2 h. After cooling to room temperature, the crude product was washed three times with ethyl acetate and saturated sodium chloride solution (each time at 3-4 h intervals), and finally dried with anhydrous sodium sulfate to obtain urushiol glycidyl ether (UGE). Its epoxy value was determined to be approximately 0.261 mol / 100 g by the hydrochloric acid-acetone method. The structure of urushiol glycidyl ether is as follows: .

[0034] The phytic acid used in the examples was a commercially available 70% phytic acid aqueous solution, and all other raw materials were commercially available products. All tests were conducted in accordance with the relevant national or industry standards, and the parameter settings of the testing instruments were performed according to the equipment manufacturer's recommended conditions.

[0035] The coating composition is prepared as follows: first, dissolve urushiol glycidyl ether in propylene glycol methyl ether (PM), and add 70% phytic acid aqueous solution dropwise to the above solution at 70°C. Stir and mix evenly to obtain the flame retardant coating composition to be coated. Propylene glycol methyl ether is used as a processing aid and is volatilized and removed during the heating and curing process after coating. It is not included in the composition of the cured coating product.

[0036] The polytetrafluoroethylene mold used in the example has a volume of 125×13×1mm. 3 .

[0037] Example 1 UP-0.5 2.5 g of urushiol glycidyl ether was dissolved in 0.80 g of propylene glycol methyl ether. Then, 0.51 g of phytic acid (70% aqueous solution, i.e., the molar ratio of the active phosphorohydroxyl group of phytic acid to the epoxy group of UGE was 0.5) was added dropwise at 70 °C. The mixture was stirred at 70 °C for 2 h. The resulting mixed coating was then applied to the surface of a pretreated wood substrate (coating amount: 0.05 g / cm³). 2 (The same below) The surface of the tinplate is filled with a portion of the material, which is then poured into a polytetrafluoroethylene mold and cured according to a stepped heating program (80 ℃ / 1 h→130 ℃ / 1 h→180 ℃ / 3 h) to obtain a flame-retardant coating, denoted as UP-0.5.

[0038] Example 2 UP-0.6 2.5 g of urushiol glycidyl ether was dissolved in 0.85 g of propylene glycol methyl ether. 0.62 g of phytic acid (70% aqueous solution, i.e., the molar ratio of the active phosphoric hydroxyl group of phytic acid to the epoxy group of UGE was 0.6) was added dropwise at 70 °C. The mixture was stirred at 70 °C for 2 h. The resulting mixed coating was applied to the surface of pretreated wood substrate and tinplate, and a portion was poured into a polytetrafluoroethylene mold. The mixture was cured according to a stepped heating program (80 °C / 1 h → 130 °C / 1 h → 180 °C / 3 h) to obtain a flame-retardant coating, denoted as UP-0.6.

[0039] Example 3 UP-0.7 2.5 g of urushiol glycidyl ether was dissolved in 0.90 g of propylene glycol methyl ether. 0.72 g of phytic acid (70% aqueous solution, i.e., the molar ratio of the active phosphoric hydroxyl group of phytic acid to the epoxy group of UGE was 0.7) was added dropwise at 70 °C. The mixture was stirred at 70 °C for 2 h. The resulting mixed coating was applied to the surface of a pretreated wood substrate and a tinplate surface, and a portion of it was poured into a polytetrafluoroethylene mold and cured according to a stepped heating program (80 °C / 1 h → 130 °C / 1 h → 180 °C / 3 h) to obtain a flame-retardant coating, denoted as UP-0.7.

[0040] Example 4 UP-0.8 2.5 g of urushiol glycidyl ether was dissolved in 0.95 g of propylene glycol methyl ether. 0.82 g of phytic acid (70% aqueous solution, i.e., the molar ratio of the active phosphoric hydroxyl group of phytic acid to the epoxy group of UGE was 0.8) was added dropwise at 70 °C. The mixture was stirred at 70 °C for 2 h. The resulting mixed coating was applied to the surface of a pretreated wood substrate and a tinplate surface, and a portion of it was poured into a polytetrafluoroethylene mold and cured according to a stepped heating program (80 °C / 1 h → 130 °C / 1 h → 180 °C / 3 h) to obtain a flame-retardant coating, denoted as UP-0.8.

[0041] Example 5 UP-0.9 2.5 g of urushiol glycidyl ether was dissolved in 1.00 g of propylene glycol methyl ether. 0.92 g of phytic acid (70% aqueous solution, i.e., the molar ratio of the active phosphoric hydroxyl group of phytic acid to the epoxy group of UGE was 0.9) was added dropwise at 70 °C. The mixture was stirred at 70 °C for 2 h. The resulting mixed coating was applied to the surface of a pretreated wood substrate and a tinplate surface, and a portion of it was poured into a polytetrafluoroethylene mold and cured according to a stepped heating program (80 °C / 1 h → 130 °C / 1 h → 180 °C / 3 h) to obtain the flame retardant coating UP-0.9.

[0042] Example 6 UP-1.0 2.5 g of urushiol glycidyl ether was dissolved in 1.05 g of propylene glycol methyl ether. 1.03 g of phytic acid (70% aqueous solution, i.e., the molar ratio of the active phosphoric hydroxyl group of phytic acid to the epoxy group of UGE was 1.0) was added dropwise at 70 °C. The mixture was stirred at 70 °C for 2 h. The resulting mixed coating was applied to the surface of a pretreated wood substrate and a tinplate surface, and a portion of it was poured into a polytetrafluoroethylene mold and cured according to a stepped heating program (80 °C / 1 h → 130 °C / 1 h → 180 °C / 3 h) to obtain a flame-retardant coating, denoted as UP-1.0.

[0043] Comparative Example 1 UP-0.8-MEL To further compare the differences between the flame retardant system constructed using melamine and the present invention, 5 wt% melamine powder was added to Example 4 (UP-0.8), while keeping the rest of the preparation process the same, to obtain a flame retardant coating, denoted as UP-0.8-MEL.

[0044] The performance of the cured samples prepared in the examples and comparative examples was then tested, and the specific methods are as follows: Infrared spectroscopy analysis was performed using a Nicolet iS50 infrared spectrometer, with a wavelength range of 4000-500 cm⁻¹. -1 Spectral resolution 4 cm -1 .

[0045] X-ray photoelectron spectroscopy analysis was performed using a Thermo Scientific K-Alpha X-ray photoelectron spectrometer to conduct high-resolution scanning of the cured coating surface.

[0046] 31 P nuclear magnetic resonance (NMR) spectra were acquired using a Bruker AVANCE III HD 400 MHz NMR spectrometer in DMSO-d6 solvent.

[0047] The Oxygen Index (LOI) test was conducted according to ASTM D2863.

[0048] Vertical burning (UL-94) testing is conducted in accordance with ASTM D3801.

[0049] The cone calorimetry test was conducted according to ISO 5660 standard at 35 kW / m². 2 Under external heating radiation intensity, a sample coated on poplar wood with dimensions of 100 mm × 100 mm × 10 mm was tested. Before the test, the sample was wrapped with aluminum foil except for the irradiated surface.

[0050] Thermogravimetric analysis was performed using a TG209F3 thermogravimetric analyzer (NETZSCH, Germany). The flame retardant coating (~10 mg) was placed in an alumina ceramic crucible and heated from 30 °C to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere.

[0051] Differential scanning calorimetry (DSC) tests were performed using a TA Q2000 instrument under constant nitrogen gas flow. Samples were first heated from room temperature to 200 °C at a heating rate of 10 °C / min, held isothermally for 5 minutes to eliminate the previous thermal history, then cooled and reheated at the same rate. The glass transition temperature (Tg) was taken from the midpoint of the second heating scan. Thermogravimetric analysis (TGA) was performed using a STA449F3 thermal analyzer. The flame-retardant coating was heated from 30 °C to 600 °C at a heating rate of 10 °C / min under a nitrogen atmosphere.

[0052] Scanning electron microscopy (SEM) is used to observe the surface morphology of the char layer after a sample has been burned.

[0053] Infrared spectroscopy analysis showed that urushiol glycidyl ether (UGE) was present at 910 cm⁻¹. -1 The presence of characteristic absorption peaks of epoxy groups nearby confirms that some phenolic hydroxyl groups in the urushiol molecule have been converted into glycidyl ether structures. Figure 1 The characteristic peak of epoxy groups in flame-retardant coatings gradually weakens until it disappears, while at 983 cm⁻¹... -1 The appearance of a new characteristic absorption peak of POC nearby confirms that the active phosphorus hydroxyl groups of phytic acid underwent a ring-opening esterification reaction with the epoxy groups of UGE, forming a phosphorus-oxygen-carbon covalently cross-linked structure. X-ray photoelectron spectroscopy (XPS) Figure 2 In Example 4, the flame-retardant coating showed a P 2p characteristic peak at 132.6 eV, attributed to the POC bond. 31 In the nuclear magnetic resonance (NMR) spectrum, the single peak of pure phytic acid solution splits into two peaks as seen in the flame-retardant coating. Figure 3 This further confirms the formation of the condensed phase phosphorus-oxygen-carbon crosslinking network, supporting the flame-retardant coating of this invention, which is dominated by the condensed phase mechanism.

[0054] Table 1 Performance data of flame-retardant coatings in each embodiment

[0055] Table 2. Cone calorimetry data of pure poplar (PW) and Examples 1, 4, and 6

[0056] Experimental results show that with the increase of phytic acid equivalent ratio, the flame retardant performance and thermal stability of the coating exhibit a trend of first increasing and then decreasing. Table 1 shows that the overall performance of the system reaches its optimal level when the phytic acid equivalent ratio is 0.8 (UP-0.8): the oxygen index (LOI) reaches its highest value of 33.6%, and the vertical burning test achieves a V-0 rating; simultaneously, the thermal decomposition temperature (T5%) of the system reaches its highest value of 251.9 ℃, and the glass transition temperature (T... g The temperature reached 98.06 °C. This indicates that, at a phytic acid equivalent ratio of 0.8, the phosphorus-oxygen-carbon (POC) covalent cross-linked network formed in the system was the most dense, exhibited the best thermal stability, and had the most significant condensed phase flame-retardant effect. Figure 4 , 5 6). When phytic acid is in excess (e.g., UP-0.9 and UP-1.0), the strong acidity of the excess phytic acid may cause some epoxy groups to degrade during the curing process, leading to a decrease in crosslinking density and thus reducing T. g T5% and LOI showed varying degrees of decrease.

[0057] Table 2 shows that the ignition time (TTI) of the UP-0.8 coating is 19 s, significantly longer than that of pure wood (10 s), indicating that the heat insulation effect of the coating effectively delays the ignition of the substrate. The conical calorimetric curves exhibit typical bimodal characteristics (PHRR1 and PHRR2), which is an inherent behavior of intumescent flame-retardant coatings: the first peak corresponds to the combustion stage of the coating itself, before the char layer is fully formed, hence PHRR1 is higher than that of pure wood in all coating samples; as the phosphorus-oxygen-carbon cross-linked char layer gradually forms and expands, it forms an effective physical barrier to the substrate, and the heat release rate rapidly decreases to the second peak (PHRR2). The PHRR2 of UP-0.8 is 193.31 kW·m⁻². -2 ) relatively pure wood (296.50 kW·m -2 The carbon layer reduced by 34.8%, indicating that it provided the most significant protection to the substrate. Furthermore, the total heat release of UP-0.8 (THR, 51.60 MJ·m⁻¹) was significantly reduced. -2 ) and effective heat of combustion (EHC, 11.77 MJ·kg -1 The carbon content was reduced by 25.9% and 18.7% respectively compared to pure wood, the charcoal yield (Residue, 24.41%) was significantly higher than that of pure wood (11.46%), and the mass loss rate (MLR, 10.85 g·s⁻¹) was lower. -1 ·m -2 The lowest value among the coating groups is also the lowest, which comprehensively confirms the high flame retardant performance of UP-0.8, which is dominated by the condensed phase char formation mechanism.

[0058] In Comparative Example 1, 5 wt% melamine powder was added to the mixture from Example 4 (UP-0.8), while maintaining the same preparation process. Experimental results showed that the melamine powder exhibited poor dispersibility in the UGE-PA system, with significant agglomeration. Particles were visible on the surface of the cured coating, and the pencil hardness was lower than HB. This indicates that directly adding melamine to the UGE-PA liquid system easily affects the coating uniformity and overall performance; therefore, no subsequent flame retardant performance tests were conducted. Figure 8 ).

[0059] Scanning electron microscopy results ( Figure 9The results show that Example 4 (UP-0.8) exhibits a continuous and dense char layer structure after combustion, with uniform pore distribution and no obvious cracks or pore collapse. This indicates that the system at this ratio possesses both good char-forming ability and char layer structural stability, effectively blocking heat and oxygen transfer and inhibiting further combustion of the substrate. Its flame-retardant mechanism lies in the fact that phytic acid decomposes upon heating to generate polyphosphoric acid, which catalyzes the dehydration and carbonization of UGE and promotes the formation of a phosphorus-rich char layer. Simultaneously, the POC cross-linking network improves the integrity and thermal stability of the char layer, forming a continuous and dense heat and oxygen barrier, effectively blocking heat and oxygen transfer and reducing the release of combustible volatiles, thereby significantly reducing the heat release rate and total heat release, achieving excellent flame-retardant performance.

[0060] It should be noted that the above description is merely a preferred embodiment of the present invention, intended to illustrate the principles of the invention, and does not constitute a limitation on the scope of protection of the present invention. For those skilled in the art, appropriate modifications or equivalent substitutions can be made to the technical solutions in the above embodiments without departing from the core ideas of the present invention, and all such modifications should be covered within the scope of protection of the present invention.

Claims

1. A bio-based flame-retardant coating crosslinked with urushiol glycidyl ether and phytic acid, characterized in that, The bio-based flame retardant coating comprises the following components by weight fraction (100%): Urushiol glycidyl ether: 70.82~83.06 wt%; the urushiol glycidyl ether is prepared by epichlorohydrin epoxidation modification of urushiol, and the molecule contains epoxy groups, catechol hydroxyl groups and long-chain unsaturated alkyl structures. Phytic acid: 16.94~29.18 wt%, wherein the phytic acid is a 70% phytic acid aqueous solution; The molar ratio of the active phosphorohydroxyl group in phytic acid to the epoxy group in urushiol glycidyl ether is 0.5~1.

0.

2. The bio-based flame-retardant coating according to claim 1, characterized in that, The preparation method of the urushiol glycidyl ether is as follows: urushiol, epichlorohydrin and tetrabutylammonium bromide are reacted at 60°C for 3 h, then 20% sodium hydroxide aqueous solution is added dropwise, and the reaction is continued at 60°C for 2 h. After the reaction is completed, the crude product is cooled to room temperature, washed with water, filtered and dried to obtain urushiol glycidyl ether with an epoxy value of 0.261 mol / 100 g.

3. The bio-based flame-retardant coating according to claim 2, characterized in that, The mass ratio of urushiol, epichlorohydrin, tetrabutylammonium bromide and 20% sodium hydroxide aqueous solution is 12.82:15.11 to 60.44:1.04:

16.

4. The bio-based flame-retardant coating according to claim 1, characterized in that, The bio-based flame retardant coating has an oxygen index of ≥30%, a UL-94 V-0 rating for vertical burning, and a char rate of ≥20%.

5. A method for preparing a bio-based flame-retardant coating as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Dissolve urushiol glycidyl ether in propylene glycol methyl ether, then slowly add phytic acid, and stir at 70°C for 2 hours to obtain a flame retardant coating composition; (2) The flame retardant coating composition obtained in step (1) is coated on the surface of the substrate or placed in a mold for curing to obtain a bio-based flame retardant coating.

6. The method according to claim 5, characterized in that, The curing process described in step (2) is to maintain the temperature at 80 ℃ for 1 hour, then raise the temperature to 130 ℃ for 1 hour, and finally raise the temperature to 180 ℃ for 3 hours.

7. The method according to claim 5, characterized in that, The substrate mentioned in step (2) is the surface of a wood substrate or the surface of a tinplate.

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