Phytic iron cooperates with straw cellulose-based polyurethane flame-retardant biological composite material, and preparation method and application thereof

Abstract

The application provides a phytic acid iron synergistic straw cellulose-based polyurethane flame-retardant biological composite material and a preparation method and application thereof. The preparation method comprises the following steps: S1, delignification treatment is performed on original straw by mixing the original straw with an alkali solution, to obtain delignified straw; S2, an aqueous PA solution is sprayed to the surface of the delignified straw, and after sufficient absorption, a polyester polyol solution containing Fe2O3 is added, and the mixture is stirred and mixed to obtain a mixture; S3, the mixture is subjected to pressure molding, and after demolding, the phytic acid iron synergistic straw cellulose-based polyurethane flame-retardant biological composite material is obtained by air drying. In the application, phytic acid is used as a biological flame retardant, Fe2O3 is used as a synergistic functional additive, straw cellulose-polyurethane composite material is modified, the inherent cellulose structure of straw is used to promote carbonization and enhance thermal stability, the limit oxygen index of the composite material reaches 27.9%, and the total delayed release amount within 240s is reduced to 48.89m 2 / m 2 .

Description

Technical Field

[0001] This invention relates to the field of bio-based composite functional materials technology, specifically to a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material, its preparation method, and its application. Background Technology

[0002] High-value utilization of agricultural waste (especially crop straw) is a key pathway to achieving sustainable resource management and carbon neutrality. Global annual straw production exceeds 4.1 billion tons, but mainstream disposal methods such as open burning or landfilling lead to environmental pollution and resource depletion. China alone produces 900 million tons of straw annually, yet high-value utilization is still less than 50%, mainly limited to low-value uses such as fertilizer or biomass fuel. These challenges highlight the urgent need to develop bio-derived high-performance materials—that are both high-value utilization of lignocellulosic biomass and functional performance requirements.

[0003] Cellulose, as the most abundant natural biopolymer, is derived not only from traditional raw materials such as wood and cotton, but also from agricultural waste such as straw. It possesses advantages such as renewable sources, biodegradability, and naturally high mechanical strength. However, the inherent flammability of cellulose and its derivatives (including straw cellulose) has become a major obstacle to their application in fire-sensitive fields (such as interior materials, structural panels, and multifunctional composite materials). Therefore, improving the thermal stability and flame retardant properties of cellulose-based materials has become a core objective of materials research. Recent systematic reviews have detailed advanced modification strategies using elements such as phosphorus, nitrogen, and boron, as well as inorganic synergistic treatment technologies, to enhance the charring ability and thermal stability of cellulose and its composites, making flame-retardant cellulose a highly promising bio-based additive in polymer systems.

[0004] Recent experimental studies have demonstrated the diverse applications of cellulose-based materials in enhancing fire resistance. Yang et al. successfully prepared a green, flammable, and flame-retardant straw cellulose nanofiber laminate by synergistically adding flame retardants, significantly improving its mechanical and fire-resistant properties, providing a new option for lightweight, fire-resistant biocomposite materials. Meanwhile, Adil's team developed a high-performance flame-retardant cellulose filament composite material derived from various biological resources, fully demonstrating the multifunctionality of cellulose in reinforcing sustainable composite structures. Furthermore, cellulose nanocrystals modified with phosphoric acid and silane compounds can significantly improve the flame retardancy and mechanical properties of polymer composites, achieving high residual carbon content and self-extinguishing characteristics. These breakthroughs indicate that flame-retardant cellulose, as a bio-based additive, is becoming an ideal choice for multifunctional polymer systems that combine fire safety and sustainability.

[0005] In previous studies, nitrogen- and phosphorus-based flame retardants (especially ammonium polyphosphate) have been commonly used in wood-based materials to enhance their flame retardant properties. For example, Arao et al. demonstrated that adding melamine phosphate and ammonium polyphosphate to wood-plastic composites (WPCs) significantly improved their flame retardancy. Adding 10% by weight of the flame retardant even achieved a self-extinguishing effect. However, these treatments often lead to decreased material strength and increased hygroscopicity due to excessive use of flame retardants. Furthermore, the use of petroleum-based flame retardants (such as ammonium polyphosphate and phosphate esters) has raised environmental concerns, particularly after the disposal of WPCs, due to their potential long-term environmental impact.

[0006] Compared to petroleum-based flame retardants, phytic acid significantly reduces the ecological footprint, offering environmental advantages. Yin et al. reported that composites using phytic acid as a flame retardant exhibited a 28.8% reduction in limiting oxygen index (Loi) and a 28.3% reduction in peak heat release rate, highlighting its potential as a highly efficient flame retardant. However, the presence of hydrophilic groups in PA-based flame retardants often leads to increased hygroscopicity, which may adversely affect the mechanical properties of the composites, thus hindering their practical application in high-strength materials.

[0007] Therefore, there is an urgent need for a new preparation process that combines the flame retardancy and mechanical properties of composite materials. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material, its preparation method, and its application, thus solving the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the present invention, a method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material is provided, comprising the following steps: S1. Mix the raw straw with an alkaline solution and perform delignification treatment to obtain delignified straw; S2. Spray the aqueous PA solution onto the surface of the delignified straw. After it is fully absorbed, add the polyester polyol solution containing Fe2O3 and stir to mix to obtain a mixture. S3. The mixture is subjected to pressure molding, demolded and air-dried to obtain the phytic acid iron synergistic straw cellulose-based polyurethane flame retardant biocomposite material.

[0010] This invention utilizes the chelating effect between PA and ferric oxide to form a stable composite on cellulose fibers, promoting the formation of a phosphorus-rich protective char layer during combustion, thereby improving thermal stability and reducing flammability. Simultaneously, the iron ions act as a crosslinking agent for cellulose, enhancing the structural integrity of the composite material and catalyzing the conversion of CO to CO2, thus reducing smoke emissions. Furthermore, the phosphate groups of PA interact with the isocyanate functional groups in the polyurethane matrix, enhancing interfacial bonding and overall mechanical integrity.

[0011] Preferably, in step S1, the alkaline solution includes sodium hydroxide and sodium sulfite, wherein the concentration of sodium hydroxide in the alkaline solution is 2~3M and the concentration of sodium sulfite is 0.3~0.5M; The mass ratio of the original straw to the volume ratio of the alkaline solution is 1g:2~3mL.

[0012] Preferably, in step S1, the delignification treatment is performed at a temperature of 80-90°C for 1.5-2 hours.

[0013] Preferably, in step S2, the concentration of the aqueous PA solution is 4~10wt%, and the volume ratio of the aqueous PA solution to the mass ratio of the original straw is 1mL:2~3g.

[0014] Preferably, in step S2, the Fe2O3 content in the Fe2O3-containing polyester polyol solution is 1~2wt%.

[0015] Preferably, in step S2, the polyester polyol in the Fe2O3-containing polyester polyol solution is composed of polytetrahydrofuran ether diol, glycerol and triethanolamine, and the mass ratio of polytetrahydrofuran ether diol, glycerol and triethanolamine is 4:7:1.

[0016] Preferably, in step S2, the stirring speed is 1000~2000 rpm / min, and the stirring time is 3~5 min.

[0017] Preferably, in step S3, the pressure of the pressure molding is 0.5~2MPa, and the time is 50~70min; The relative humidity during the air-drying process is 25-50%.

[0018] According to a second aspect of the present invention, a phytic acid-ferric synergistic straw cellulose-based polyurethane flame-retardant biocomposite material is provided, prepared according to the above-described method.

[0019] According to a third aspect of the present invention, an application of phytic acid iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material in furniture decorative fabrics is provided.

[0020] This invention provides a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material, its preparation method, and its application. It possesses the following beneficial effects: (1) The method provided in this scheme for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material uses phytic acid as a bioflame retardant and Fe2O3 as a synergistic functional additive to modify the straw cellulose-polyurethane composite material. The inherent cellulose structure of straw promotes carbonization and enhances thermal stability, so that the limiting oxygen index of the composite material reaches 27.9% and the total smoke release within 240s is reduced to 48.89m. 2 / m 2 .

[0021] (2) The phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material provided in this solution forms an integrated network through the hydrogen bonding between phytic acid and straw cellulose matrix and the chelation between phytic acid and Fe2O3. It has moderate tensile, bending and hygroscopic properties, but significantly improves the limiting oxygen index and reduces smoke release. The flame-retardant performance is significantly improved and it is suitable for non-load-bearing furniture decorative fabrics. Attached Figure Description

[0022] Figure 1 The stress-strain curves of the composite materials prepared in Example 1 and Comparative Examples 1-2 of this invention are shown. Figure 2 This is a schematic diagram showing the tensile strain and tensile strength of the composite materials prepared in Example 1 and Comparative Examples 1-2 of the present invention; Figure 3 This is a schematic diagram showing the flexural modulus and flexural strength of the composite materials prepared in Example 1 and Comparative Examples 1-2 of the present invention; Figure 4 This is a schematic diagram showing the fracture load and internal bond strength of the composite materials prepared in Example 1 and Comparative Examples 1-2 of the present invention; Figure 5 This is a schematic diagram showing the weight percentage gain of the composite materials prepared in Example 1 and Comparative Examples 1-2 of the present invention under moisture exposure; Figure 6 The expansion rates of the composite materials prepared in Example 1 and Comparative Examples 1-2 of this invention after 2 hours, 24 hours, 2 days, and 7 days of moisture exposure are shown. Figure 7 This is a schematic diagram of the contact angle of the composite materials prepared in Example 1 and Comparative Examples 1-2 of the present invention; Figure 8 The Louis values ​​of the composite materials prepared in Example 1 and Comparative Examples 1-2 of this invention; Figure 9 Thermogravimetric curves of the composite materials prepared in Example 1 and Comparative Examples 1-2 of this invention; Figure 10 The XRD patterns of the composite materials prepared in Example 1 and Comparative Examples 1-2 of this invention are shown below. Figure 11 The FTIR spectra of the composite materials prepared in Example 1 and Comparative Examples 1-2 of this invention before combustion are shown. Figure 12 The FTIR spectra of the composite materials prepared in Example 1 and Comparative Examples 1-2 of this invention after combustion are shown below. Figure 13 These are schematic diagrams of microscopic analysis of the composite materials prepared in Examples 1 and 1-2 of the present invention, wherein (a) is a three-dimensional perspective view of the SC / PA / Fe composite material; (b) a three-dimensional rendered interaction diagram showing polyurethane, PA-Fe chelate and delignified straw (straw is set to semi-transparent); (c) the corresponding cross-section of the SC / PA / Fe composite material obtained at half height; (d) SEM image of the unburned SC / PA / Fe composite material; (e) SEM image of the unburned SC / PA composite material; (f) SEM image of the unburned SC composite material; (g) SEM image of the SC / PA / Fe composite material after combustion; (h) SEM image of the SC / PA composite material after combustion; and (i) SEM image of the SC composite material after combustion. Detailed Implementation

[0023] To better illustrate the content of this invention, the following description is provided in conjunction with specific embodiments.

[0024] All chemicals used in this invention were commercially purchased and used directly without additional purification.

[0025] The original straw was selected from marigold straw, with a length of 8-10mm and a width of 2-4mm, and was purchased from farmland in Sihai Town, Yanqing County, Beijing. Sodium hydroxide and sodium sulfite were purchased from Sinopharm Chemical Reagent Co., Ltd. in Shanghai, China. The aqueous PA solution was purchased from Grantham Life Sciences, UK, product code CK9311 (CAS 83863). Ferric oxide was purchased from Thermo Fisher Scientific, Inc., USA. The polytetrahydrofuran ether diol was purchased from BASF in Ludwigshafen, Germany. Glycerin was purchased from Shanghai Aladdin Biotechnology Co., Ltd. Triethanolamine was purchased from Merck Group in Darmstadt, Germany.

[0026] Example 1 Step 1: Preheat an aqueous solution containing 2.5M sodium hydroxide and 0.4M ammonium sulfite to 85°C, then spray it onto 200g of marigold stalks at a flow rate of 5mL / min for 90min while maintaining the temperature at 85°C for delignification treatment. After the treatment is complete, rinse the straw three times with deionized water, and then dry it in an oven at 65°C for 10h to obtain delignified straw. Step 2: Spray 100 mL of 10% phytic acid aqueous solution onto the surface of the lignin-de-lignosed straw at a flow rate of 3 mL / min, then roll it at 20 rpm for 10 min to ensure full absorption. Next, spray 100 g of 1% Fe2O3-containing polyester polyol solution (the polyester polyol is composed of polytetrahydrofuran ether diol, glycerol and triethanolamine in a mass ratio of 4:7:1) onto the surface of the lignin-de-lignosed straw. Stir at 5000 rpm for 5 min, then at 3000 rpm for 10 min to obtain the mixture. Step 3: Transfer the mixture to a hydraulic press equipped with a 150×150mm steel plate, and mold it at 1MPa and room temperature for 60 minutes. After demolding, let it stand for 48 hours at a relative humidity of 50% to obtain phytic acid iron synergistic straw cellulose-based polyurethane flame retardant biocomposite material, denoted as SC / PA / Fe composite material.

[0027] Comparative Example 1 Step 1: Preheat an aqueous solution containing 2.5M sodium hydroxide and 0.4M ammonium sulfite to 85°C, then spray it onto 200g of marigold stalks at a flow rate of 5mL / min for 90min while maintaining the temperature at 85°C for delignification treatment. After the treatment is complete, rinse the straw three times with deionized water, and then dry it in an oven at 65°C for 10h to obtain delignified straw. Step 2: Spray 100g of polyester polyol solution (polyester polyol is composed of polytetrahydrofuran ether diol, glycerol and triethanolamine in a mass ratio of 4:7:1) onto the surface of the lignin-de-lignin straw, stir at 5000 rpm for 5 min, and then stir at 3000 rpm for 10 min to obtain a mixture. Step 3: Transfer the mixture to a hydraulic press equipped with a 150×150mm steel plate, and mold it at 1MPa and room temperature for 60 minutes. After demolding, let it stand for 48 hours at a relative humidity of 50% to obtain the rice straw cellulose polyurethane composite material, denoted as SC composite material.

[0028] Comparative Example 2 Step 1: Preheat an aqueous solution containing 2.5M sodium hydroxide and 0.4M ammonium sulfite to 85°C, then spray it onto 200g of marigold stalks at a flow rate of 5mL / min for 90min while maintaining the temperature at 85°C for delignification treatment. After the treatment is complete, rinse the straw three times with deionized water, and then dry it in an oven at 65°C for 10h to obtain delignified straw. Step 2: Spray 100 mL of 10% phytic acid aqueous solution onto the surface of the lignin-de-lignosed straw at a flow rate of 3 mL / min, then roll it at 20 rpm for 10 min to ensure full absorption. Next, spray 100 g of polyester polyol solution (polyester polyol is composed of polytetrahydrofuran ether diol, glycerol and triethanolamine in a mass ratio of 4:7:1) onto the surface of the lignin-de-lignosed straw, stir at 5000 rpm for 5 min, and then stir at 3000 rpm for 10 min to obtain a mixture. Step 3: Transfer the mixture to a hydraulic press equipped with a 150×150mm steel plate, and mold it at 1MPa and room temperature for 60 minutes. After demolding, let it stand for 48 hours at a relative humidity of 50% to obtain a phytic acid bio-based flame retardant modified composite material, denoted as SC / PA composite material.

[0029] Performance testing 1. Mechanical property testing according to Figures 1 to 2 It is evident that, compared to SC composites, SC / PA / Fe composites exhibit reduced overall strength due to the doping of PA and Fe2O3. SC / PA / Fe composites reach a tensile stress of approximately 1.0 MPa at approximately 0.9% strain, while SC reaches approximately 1.65 MPa at approximately 1.15% strain. Although the mechanical properties of SC / PA / Fe are lower than those of conventional wood-based panels, the particleboard types defined by the EN 312 P2 standard are specifically designed for interior finishing and non-load-bearing structural applications where extreme mechanical loads are not required; therefore, materials with moderate tensile and flexural properties are acceptable.

[0030] according to Figure 3 It can be seen that the flexural modulus of the SC / PA / Fe composite material is 115 ± 6 MPa, and the flexural strength is 5.2 ± 0.2 MPa. According to... Figure 4 It is known that the failure load of the SC / PA / Fe composite material is 3048±85 Newtons, while that of the SC material is 4470±90 Newtons, and that of the SC / PA composite material is 2762±70 Newtons. Although the addition of bio-based flame retardants and inorganic fillers slightly reduces some mechanical properties, the composite material can still maintain a failure load of over 3,000 Newtons, fully meeting the requirements for use in furniture inner panels and medium-strength building components.

[0031] 2. Water absorption and surface wettability test according to Figure 5 and Figure 6 It was found that the weight percentage gain of all composite materials gradually increased with the extension of soaking time. After 2 hours of water exposure, the WPG value of the SC / PA / Fe composite material reached 6.4%, rising to 7.9% after 24 hours, 8.9% after 3 days, and 9.3% after 7 days, indicating continuous water absorption. In contrast, SC / PA had a higher overall water absorption rate, reaching 11.2% after 7 days, while SC absorbed less water throughout the test, with WPG values ​​ranging from 3.5% to 6.5%. These trends reflect the inherent hydrophilicity of cellulose fibers in straw (a property that dominates the hygroscopic properties of lignocellulose composites) and the influence of PA / Fe modification on water interaction. Correspondingly, the volume expansion rate results showed that all composite materials underwent volume expansion as water penetrated the matrix. The expansion rate of SC / PA / Fe increased from 57.2% after 2 hours to 73.6% after 7 days, which, although lower than 79.2% for SC / PA, was significantly higher than 44.4% for SC. These trends reflect the synergistic effect of polymer penetration and fiber hydrophilicity on the size changes of the composite materials. Surface wettability is characterized by contact angle testing, such as... Figure 7 As shown, the results indicate that the contact angle of the SC / PA / Fe composite material is 66.2°, exhibiting moderate hydrophobicity compared to 61.7° of SC / PA, while the SC material shows higher hydrophobicity (77.6°). The observed moisture absorption response and surface properties suggest that although the water absorption and volume expansion rate of the SC / PA / Fe composite material are increased compared to untreated straw, its physical properties still meet the requirements for furniture and interior decorative panel applications—scenarios requiring controlled moisture absorption behavior and good surface properties.

[0032] 3. Flame retardancy test The flame retardancy of the composite materials prepared in Example 1 and Comparative Examples 1 and 2 was tested using Loewe value, thermogravimetric curves, and structural analysis before and after combustion. Figure 8 It can be seen that the Loewe value of the SC / PA / Fe composite material reaches 27.9%, which is significantly higher than the 19.1% of the unmodified SC and comparable to the 28.4% of the SC / PA composite material. The increased Loewe value of the SC / PA / Fe composite material indicates its enhanced flame retardant properties. Bio-based phosphorus-rich modifiers such as phytic acid improve the flame retardant properties of cellulose composite materials by forming a char layer and creating a barrier effect.

[0033] according to Figure 9It can be seen that the SC / PA / Fe composite material exhibits a lower smoke generation rate and overall smoke release than SC and SC / PA during the 250-second measurement period, indicating the catalytic effect of Fe2O3 and the inherent dehydration and char layer reinforcement properties of cellulose. The carbon-rich matrix provided by cellulose can promote the formation of a more stable char layer during combustion, thereby limiting the formation of combustible volatiles and soot precursors.

[0034] according to Figure 10 As shown, the composite materials prepared in Example 1 and Comparative Examples 1-2 all exhibit broad amorphous characteristics, indicating the dominant position of the typical disordered phase in lignocellulose and polymer materials; according to Figure 11 It can be seen that the characteristic absorption peaks of SC / PA / Fe differ from those of SC and SC / PA, indicating that PA and Fe2O3 have been successfully integrated into the composite matrix. In the SC / PA / Fe spectrum, the peak at approximately 1542 cm⁻¹ can be attributed to the POC and phosphate ester vibrations derived from PA, while the broad absorption peak near 3300 cm⁻¹ corresponds to the OH stretching vibration generated by the interaction between cellulose and PA. Figure 12 It can be seen that the residual carbon in SC / PA / Fe is at 1512 cm⁻¹. -1 1315 cm -1 and 915 cm -1 The graphs show distinct absorption bands at these locations, corresponding to aromatic ring structures, P=O stretching vibrations, and POC bonding, respectively. The presence of aromatic ring absorption bands indicates that aromatization occurred during thermal decomposition, promoting the formation of a carbonaceous network. The P=O and POC absorptions originate from the phosphate groups introduced by PA, indicating the formation of a phosphorus-rich char layer. In contrast, the FTIR spectra of SC and SC / PA after combustion show weaker or indistinct peaks in these regions, indicating a lower degree of solidification of the char layer. These FTIR characteristics suggest that during combustion, SC / PA / Fe forms a thermally stable char layer rich in phosphorus and aromatic structures. This layer enhances its flame-retardant properties by inhibiting heat and mass transfer in the condensed phase.

[0035] 4. Microscopic analysis of composite materials like Figure 13 As shown, according to Figure 13 As shown in Figure (a), a continuous and interpenetrating network structure is formed inside the SC / PA / Fe composite material, indicating that hydrogen bonding and PA-Fe chelation promote the bonding of the components; according to Figure 13 Figures (b) and (c) show that the PU matrix and the PA-Fe region are closely associated with the cellulose-rich straw skeleton, forming an interconnected structure rather than a simple physical mixture; combined with Figure 13As can be seen from the comparison of Figures (d) to (f), the PU matrix in the SC / PA / Fe composite material is deeply embedded in the cellulose network of the straw matrix, and the dispersed PA-Fe regions enhance the interfacial bonding. In contrast, the SC / PA composite material and the SC composite material exhibit lower interfacial integration and more obvious interfacial features. The comparison shows that the combination of PA and Fe2O3 promotes the enhancement of interfacial interaction between the PU matrix and the straw cellulose fibers and the formation of the network structure, thereby improving the overall mechanical properties and flame retardant properties of the composite material.

[0036] After combustion, the residual carbon morphology of the composite materials prepared in Example 1 and Comparative Examples 1-2 showed significant differences, such as... Figure 13 As shown in Figures (g) to (i), the char surface of the SC / PA / Fe composite material after combustion exhibits a dense and continuous carbon paper structure. The residues on the char surface of the SC / PA composite material and the SC composite material after combustion are irregular and loose, indicating that the synergistic effect of PA, Fe2O3 and straw cellulose matrix in the SC / PA / Fe composite material promotes the formation of a stable protective layer during thermal decomposition. This char layer can act as a physical barrier to slow down heat transfer and inhibit the release of combustible volatiles.

[0037] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material, characterized in that: Includes the following steps: S1. Mix the raw straw with an alkaline solution and perform delignification treatment to obtain delignified straw; S2. Spray the aqueous PA solution onto the surface of the delignified straw. After it is fully absorbed, add the polyester polyol solution containing Fe2O3 and stir to mix to obtain a mixture. S3. The mixture is subjected to pressure molding, demolded and air-dried to obtain the phytic acid iron synergistic straw cellulose-based polyurethane flame retardant biocomposite material.

2. The method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material according to claim 1, characterized in that: In step S1, the alkaline solution includes sodium hydroxide and sodium sulfite, wherein the concentration of sodium hydroxide in the alkaline solution is 2~3M and the concentration of sodium sulfite is 0.3~0.5M; The mass ratio of the original straw to the volume ratio of the alkaline solution is 1g:2~3mL.

3. The method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material according to claim 1, characterized in that: In step S1, the delignification treatment is carried out at a temperature of 80~90℃ for 1.5~2h.

4. The method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material according to claim 1, characterized in that: In step S2, the concentration of the aqueous PA solution is 4~10wt%, and the volume ratio of the aqueous PA solution to the mass of the original straw is 1mL:2~3g.

5. The method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material according to claim 1, characterized in that: In step S2, the Fe2O3 content in the Fe2O3-containing polyester polyol solution is 1~2wt%.

6. The method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material according to claim 1, characterized in that: In step S2, the polyester polyol in the Fe2O3-containing polyester polyol solution is composed of polytetrahydrofuran ether diol, glycerol and triethanolamine, and the mass ratio of polytetrahydrofuran ether diol, glycerol and triethanolamine is 4:7:

1.

7. The method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material according to claim 1, characterized in that: In step S2, the stirring speed is 1000~5000 rpm / min, and the stirring time is 3~5 min.

8. The method for preparing a phytic acid-iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material according to claim 1, characterized in that: In step S3, the pressure of the pressure molding is 0.5~2MPa, and the time is 50~70min; The relative humidity during the air-drying process is 25-50%.

9. A phytic acid-ferric synergistic straw cellulose-based polyurethane flame-retardant biocomposite material obtained by the preparation method according to any one of claims 1 to 8.

10. The application of the phytic acid iron synergistic straw cellulose-based polyurethane flame-retardant biocomposite material as described in claim 9 in furniture decorative fabrics.

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