Boron-phosphorus synergistic starch-based single-component intumescent flame retardant as well as preparation method and application thereof

Abstract

The invention discloses a boron-phosphorus synergistic starch-based single-component intumescent flame retardant as well as a preparation method and application thereof. Starch, phytic acid, boric acid, allantoin and the like are used as raw materials, and the boron-phosphorus synergistic starch-based single-component intumescent flame retardant integrating an acid source, a carbon source and a gas source is designed and prepared. The flame retardant provided by the invention is simple and convenient in preparation process and high in safety, most of the raw materials of the flame retardant are derived from green renewable biomass materials with low cost, and the flame retardant has environment-friendly characteristic and excellent polymer compatibility. The synergistic effect of the phytic acid boron component in a flame-retardant system can be fully exerted by regulating and controlling the ratio of boron to phosphorus, when the flame retardant is applied to a polylactic acid (PLA) material, the influence on the mechanical property of the PLA is small, the PLA can be endowed with excellent flame retardance, the molten drop phenomenon and a large amount of dense smoke in the combustion process of the PLA can be effectively inhibited, and the biodegradation speed of the PLA can be increased.

Description

Technical Field

[0001] This invention belongs to the field of biomass-based polymer flame retardant technology, specifically relating to a boron-phosphorus synergistic starch-based single-component intumescent flame retardant, its preparation method, and its application. Background Technology

[0002] Polylactic acid (PLA) is a biodegradable polymer material made from renewable biomass and has become one of the core options for replacing traditional petroleum-based plastics. PLA is produced from starchy crops such as corn and cassava through bio-fermentation and chemical polymerization processes. After disposal, it can completely degrade into carbon dioxide and water in the natural environment. Due to its excellent machinability and controllable degradation characteristics, it has been widely used in packaging, medical, electronics, automotive interiors, and 3D printing. However, PLA has inherent flammability and produces a large amount of molten dripping during combustion, which greatly limits its applications. Therefore, efficient flame-retardant modification of PLA is crucial. Compared to traditional halogenated, phosphorus-based, nitrogen-based, and intumescent flame retardants, biomass-based flame retardants are ideal choices for improving the flame-retardant properties of PLA due to their high efficiency, low toxicity, and environmental friendliness.

[0003] Starch, one of the most abundant natural high-molecular-weight polysaccharides, boasts advantages such as renewable source, low price, and complete biodegradability. Rich in carbon, starch readily dehydrates and carbonizes upon heating, rapidly forming a dense and strongly adhering char layer. This layer effectively insulates against heat and oxygen, inhibiting the release of flammable gases, thus serving as a stable char source. Simultaneously, starch combustion decomposes and releases inert gases such as CO2, further suppressing heat-oxygen exchange. However, the flame-retardant effect of pure starch is limited; modification of starch can further improve its flame-retardant efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a boron-phosphorus synergistic starch-based single-component intumescent flame retardant, its preparation method, and its application. The prepared flame retardant is based on biomass-based materials and not only has excellent thermal stability, high compatibility with PLA, and significant flame retardant effect, but also simultaneously achieves anti-dripping and smoke suppression functions, thus possessing broad application potential and practical value in PLA-related fields.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A boron-phosphorus synergistic starch-based single-component intumescent flame retardant is prepared from starch, phosphoric acid, boric acid, allantoin, and other raw materials via a one-pot synthesis method. The synthetic route is as follows: The preparation of the boron-phosphorus synergistic starch-based single-component intumescent flame retardant includes the following steps: (1) Weigh an appropriate amount of starch and disperse it in deionized water. Stir magnetically at room temperature to obtain a starch suspension. (2) Boric acid and phytic acid are stirred evenly in a certain molar ratio, and then placed in a muffle furnace at a certain temperature for a certain time to obtain boron phytate blocks, which are then ball-milled into powder and prepared into a 5wt% boron phytate solution. (3) Add an appropriate amount of allantoin to deionized water and stir until homogeneous to obtain an allantoin suspension; (4) Add the boron phytate solution obtained in step (2) to the starch suspension obtained in step (1) and stir to obtain a boron phytate modified starch suspension. (5) Add the allantoin solution obtained in step (3) to the phytate boron modified starch suspension obtained in step (4), stir and react, age at room temperature, vacuum filter and wash, dry and pulverize to obtain the boron phosphorus synergistic starch-based single-component intumescent flame retardant.

[0006] Furthermore, the starch mentioned in step (1) is one or more of soluble starches.

[0007] Furthermore, the molar ratio of phytic acid to boric acid used in step (2) is 1:4-1:6; Furthermore, the calcination temperature in step (2) is 160-200℃ and the calcination time is 4-12 h.

[0008] Furthermore, the molar ratio of allantoin to starch used in step (3) is 1:1 to 1:2; Furthermore, the stirring temperature in step (3) is 60-80 ℃ and the stirring time is 1 h.

[0009] Furthermore, in step (4), the molar ratio of the amount of boron phytate solution used to starch is converted from 1:5 to 1:10. Furthermore, the temperature of the stirring reaction in step (4) is 120-160℃ and the time is 2-4 h.

[0010] Furthermore, the temperature of the stirring reaction in step (5) is 60-80 °C, and the time is 1-2 h; Furthermore, the aging time described in step (5) is 12-24 h; Furthermore, the drying temperature in step (5) is 70-100 °C and the time is 12-24 h.

[0011] Furthermore, the stirring speed in steps (1)-(5) is 300-500 rpm.

[0012] The boron-phosphorus synergistic starch-based single-component intumescent flame retardant can be applied to PLA materials. Specifically, it is melt-blended with PLA, extruded and granulated, and then injection molded. The amount added accounts for 5% to 15% of the mass of PLA.

[0013] Boron phytate (BPA) is a compound formed by the complexation of phytic acid and boron. Its molecular structure contains numerous active functional groups, including incompletely coordinated phosphate hydroxyl groups (-OH), coordinated P=O bonds, and boron-oxygen coordination bonds. These functional groups provide sites for further complexation with metal ions or participation in chemical reactions, while also imparting polar characteristics to the molecule. By adjusting the molar ratio of boron to phosphorus, not only can the synergistic flame-retardant effect between B and P be fully utilized, but the processing characteristics of different substrates can also be adapted, reducing the damage of flame retardants to the mechanical properties of the substrate and achieving a balance between flame retardancy and practicality.

[0014] Allantoin molecules contain four nitrogen atoms, with a nitrogen content of 32.6%. These nitrogen atoms are covalently bonded to the urea ring and urea group. At high temperatures, it slowly decomposes, releasing non-flammable gases such as ammonia and nitrogen. These gases dilute the concentration of oxygen and combustible gases in the combustion zone, while simultaneously inhibiting flame spread, meeting the core requirement of "gas-phase flame retardancy" for nitrogen sources in flame retardants. Nitrogenous substances (such as NH3) produced by the decomposition of allantoin can react with phosphoric acid and polyphosphoric acid from the decomposition of phosphorus-based flame retardants, generating phosphazene compounds with higher thermal stability. This enhances the catalytic char formation effect and reduces the release of toxic gases. Simultaneously, nitrogen can combine with carbon sources (such as starch) to optimize the char layer structure and improve the heat and oxygen insulation capabilities of the char layer, achieving a dual enhancement of "gas-phase flame retardancy + condensed-phase flame retardancy."

[0015] This invention achieves phytic acid borate by adjusting the molar ratio of phytic acid and boric acid, and utilizes the incompletely coordinated phosphate hydroxyl groups (-OH) on phytic acid to undergo boron esterification and hydrogen bonding with starch and allantoin, resulting in a boron-phosphorus synergistic starch-based single-component intumescent flame retardant that integrates carbon, acid, and gas sources. The raw materials for this novel flame retardant are mostly derived from low-cost, green, and renewable biomass materials. The synergistic effect of boron and phosphorus significantly improves flame retardant efficiency, effectively reducing smoke emissions during combustion and preventing the risk of secondary combustion caused by molten drippings. Furthermore, this flame retardant is low-cost, easy to mass-produce, and has high commercial feasibility, possessing enormous potential in expanding application scenarios and transforming economic value.

[0016] The significant advantages of this invention are: (1) The boron-phosphorus synergistic starch-based single-component intumescent flame retardant of the present invention is mostly derived from biomass, with starch (one of the typical polysaccharides in nature) as the main raw material. The raw materials are widely available and meet environmental protection requirements. Moreover, the flame retardant is synthesized in an aqueous system, and the preparation process is simple and easy to achieve industrial mass production.

[0017] (2) This invention utilizes the incompletely coordinated phosphate hydroxyl groups (-OH) on boron phytate to undergo boron esterification and hydrogen bonding with starch and allantoin, resulting in a boron-phosphorus synergistic starch-based single-component intumescent flame retardant that integrates carbon, acid, and gas sources. By controlling the ratio of boron to phosphorus to construct a boron-phosphorus synergistic system, PLA is endowed with excellent flame retardancy, which can effectively suppress dripping and excessive smoke during combustion. When the addition amount of PLA is 7wt%, the flame retardancy rating can reach UL94V-0.

[0018] (3) By introducing boron element to construct a boron-phosphorus synergistic system, this invention not only has a low impact on the mechanical properties of PLA, but also the boron-containing component can improve the hydrophilicity of the material, enhance water penetration, and increase the biodegradation rate of PLA. Attached Figure Description

[0019] Figure 1 The image shows the FT-IR spectra of the boron-phosphorus synergistic starch-based single-component intumescent flame retardant prepared in Examples 1 and 2, along with boron phytate (BPA) and starch (SST).

[0020] Figure 2 This is a SEM image of the carbon layer after combustion of a pure PLA combustion sample.

[0021] Figure 3 SEM image of the char layer after combustion of a combustion sample prepared by adding starch alone.

[0022] Figure 4 SEM image of the char layer after combustion of a combustion sample prepared by adding the flame retardant obtained in the comparative example.

[0023] Figure 5 SEM image of the char layer after combustion of a flame-retardant sample prepared with the flame retardant obtained in Example 1.

[0024] Figure 6 SEM image of the char layer after combustion of a flame-retardant sample prepared with the flame retardant obtained in Example 2.

[0025] Figure 7 The graph shows the degradation data changes of the degradation strips prepared by adding the flame retardant obtained in Example 1, starch, and pure PLA over 90 days. Detailed Implementation

[0026] 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.

[0027] Example 1 Weigh 13.68 g (0.05 mol) of soluble starch into a beaker, add 200 mL of deionized water, and stir at room temperature to prepare a starch suspension. In another beaker, weigh 4.74 g (0.05 mol) of allantoin, add 100 mL of deionized water, and stir magnetically at 60 °C to ensure complete reaction, obtaining an allantoin suspension. Mix phytic acid and boric acid at a molar ratio of 1:4 at 120 °C until homogeneous, then calcine in a muffle furnace at 160 °C for 12 h. After ball milling into powder, add deionized water to prepare a 5% (w / w) phytate-boron solution. Pour the starch suspension into a three-necked flask equipped with a magnetic stirrer and a reflux condenser, add 160 mL of the 5% (w / w) phytate-boron solution, and react in an oil bath at 120 °C for 2 h with stirring at 300 rpm. The temperature was then lowered to 60°C, and the allantoin suspension was slowly added dropwise to a three-necked flask with stirring at 500 rpm. The reaction was carried out at 60°C for 2 hours. After the reaction was completed, the product was allowed to stand and precipitate for 24 hours. Then, it was washed three times by alternating filtration with anhydrous ethanol and deionized water, and dried in a vacuum oven at 80°C for 48 hours. Finally, it was crushed into powder by a high-speed crusher to obtain flame retardant ASBPA-1.

[0028] Example 2 Weigh 13.68 g (0.05 mol) of soluble starch into a beaker, add 200 mL of deionized water, and stir at room temperature to prepare a starch suspension. In another beaker, weigh 4.74 g (0.03 mol) of allantoin, add 100 mL of deionized water, and stir magnetically at 80 °C to ensure complete reaction, obtaining an allantoin suspension. Mix phytic acid and boric acid in a molar ratio of 1:6 at 120 °C until homogeneous, then calcine in a muffle furnace at 200 °C for 4 hours. After ball milling into powder, add deionized water to prepare a 5% (w / w) phytate-boron solution. Pour the starch suspension into a three-necked flask equipped with a magnetic stirrer and a reflux condenser, add 320 mL of the 5% (w / w) phytate-boron solution, and react in an oil bath at 160 °C for 2 hours with stirring at 300 rpm. The temperature was then lowered to 80°C, and the allantoin suspension was slowly added dropwise to a three-necked flask with stirring at 500 rpm. The reaction was carried out at 80°C for 1 hour. After the reaction was completed, the product was allowed to stand and precipitate for 24 hours. Then, it was washed three times by alternating filtration with anhydrous ethanol and deionized water, and dried in a vacuum oven at 80°C for 48 hours. Finally, it was crushed into powder by a high-speed crusher to obtain flame retardant ASBPA-2.

[0029] Comparative Example Weigh 13.68 g (0.05 mol) of soluble starch into a beaker, add 200 mL of deionized water, and stir at room temperature to prepare a starch suspension. In another beaker, weigh 4.74 g (0.03 mol) of allantoin, add 100 mL of deionized water, and stir magnetically at 80 °C to ensure complete reaction, obtaining an allantoin suspension. Pour the starch suspension into a three-necked flask equipped with a magnetic stirrer and a reflux condenser, add 13.32 g (0.02 mol) of phytic acid solution, and react in a water bath at 90 °C for 2 hours with stirring at 300 rpm. The temperature was then lowered to 80°C, and the allantoin suspension was slowly added dropwise to a three-necked flask with stirring at 500 rpm. The reaction was carried out at 80°C for 1 hour. After the reaction was completed, the product was allowed to stand and precipitate for 24 hours. Then, it was washed three times by alternating filtration with anhydrous ethanol and deionized water, and dried in a vacuum oven at 80°C for 48 hours. Finally, it was crushed into powder by a high-speed crusher to obtain the flame retardant ASPA.

[0030] Application Examples 93 wt% PLA was used as the matrix, and 7 wt% of flame retardant from Example 1, 7 wt% of flame retardant from Example 2, 7 wt% of comparative flame retardant and 7 wt% of soluble starch were added to it. After thorough mixing, the mixture was extruded, granulated and injection molded using a twin-screw extruder to prepare UL-94 standard vertical burning test specimens (130 mm × 10 mm × 3.2 mm) and dumbbell-shaped mechanical property test specimens (150 mm × 20 mm × 10 mm). Pure PLA granules were separately injection molded as control samples for comparison.

[0031] The prepared samples and composite materials were tested for combustion performance and mechanical properties. The test results are shown in Table 1.

[0032] Table 1. Test results of flame retardant and mechanical properties

[0033] Table 1 shows the test results: pure PLA without any added flame retardant had a vertical burning rating of NR, an LOI value of 19.8%, and a char residue of only 2.1%. When the samples used the comparative flame retardant or only starch as the flame retardant, their flame retardant performance was not significantly improved compared to pure PLA, and the severe dripping phenomenon during combustion did not change significantly. In contrast, the samples with the added flame retardant from the examples not only all achieved a vertical burning rating of V-0, but also had an LOI value exceeding 29.5%, and a char residue exceeding 11.2% after complete combustion. The above data proves that the flame retardant of the present invention can significantly improve the flame retardant effect of PLA during combustion.

[0034] The mechanical property test results in Table 1 show that the tensile strength and elongation at break of pure PLA material are 58.2 MPa and 4.2%, respectively. The tensile strength and elongation at break of the sample with the added comparative flame retardant decrease to 41.6 MPa and 3.9%, respectively, while the sample with only starch added decreases to 41.3 MPa and 3.3%, respectively. However, the sample with the flame retardant of this invention shows only a slight decrease in tensile strength, remaining at 49.1 MPa and 51.3 MPa, respectively, and the elongation at break increases to 4.5% and 4.4%, respectively. Therefore, the flame retardant synthesized by the one-pot method of this invention has good compatibility with PLA, possessing excellent flame retardant performance while retaining the original mechanical properties of PLA material.

[0035] Figure 1 The images show the FT-IR spectra of the modified starch-based single-component intumescent flame retardants prepared in Examples 1 and 2, along with boron phytate (BPA) and starch (SST). In the FT-IR spectrum of SST, the values ​​at 1080, 2928, and 3280 cm⁻¹ are also shown. -1 A characteristic peak reflecting starch structure was observed at 1080 cm⁻¹. -1 The peak at [value missing] represents the asymmetric stretching vibration of the COC bond in the starch backbone, reflecting the skeletal structure of the polysaccharide. An absorption peak for the stretching vibration of the BO bond (1420 cm⁻¹) was observed in the FTIR spectrum of BPA. -1 ), 1050 cm -1 and 1200 cm -1 These represent the symmetric and antisymmetric stretching vibration absorption peaks of -PO4, respectively. In the FTIR spectra of ASBPA-1 and ASBPA-2, 1030 cm⁻¹... -1 1190 cm -1 and 1430 cm -1 The characteristic peaks at these locations correspond to the stretching vibrations of the -PO4 bond and the BO bond in BPA, respectively. The C=O stretching vibration and NH stretching vibration of the allantoin amide group are at 1660 cm⁻¹, respectively. -1 and 3340 cm -1 In summary, the infrared spectrum of ASBPA shows absorption peaks for starch (-OH and COC) and BPA (PO and BO), thus confirming the successful synthesis of the flame retardant.

[0036] Figure 2 This is a SEM image of the char layer after the combustion of a pure PLA sample. As can be seen from the image, the char layer structure after complete combustion of pure PLA is loose and has a large number of pores, which is not conducive to heat and oxygen insulation and has almost no flame retardant effect.

[0037] Figure 3SEM images of the char layer after combustion of a combustion specimen prepared by adding starch alone. The images show that the char layer contains large pores, failing to insulate against heat transfer and exhibiting almost no flame-retardant effect.

[0038] Figure 4 SEM images of the char layer after combustion of the combustion specimens prepared with the flame retardant obtained in the comparative example. As can be seen from the images, although the char layer is dense after complete combustion, some pores appear, which is not conducive to heat and oxygen insulation, resulting in poor flame retardant effect.

[0039] Figure 5 , 6 The images show SEM images of the char layers after combustion of PLA / ASBPA samples prepared with flame retardants from Examples 1 and 2, respectively. As can be seen from the images, the char layer structure is dense and continuous, with no obvious pores observed, indicating a significant improvement in char layer integrity and good flame retardant effect.

[0040] The mass of the degradation samples prepared by adding the flame retardant obtained in Example 1, starch, and pure PLA before and after degradation was recorded, and the rate of mass change was calculated and plotted. Figure 7 As shown in the figure, all three groups of samples exhibited a trend of increasing mass rather than decreasing during the early stages of degradation. This is because the material absorbs water in the soil, leading to increased mass. 30 days is a dividing point; the mass of all three samples begins to decrease, and the degradation rates begin to diverge. By 60 days, the sample with the added flame retardant (Example 1) showed the greatest mass loss, followed by the sample with added starch. The degradation rate of the pure PLA sample was significantly lower than the other two. By 90 days, the pure PLA sample had degraded by only 0.002%, the sample with added starch by 0.007%, while the sample with the added flame retardant (Example 1) degraded by only 0.017%, demonstrating a significant improvement in degradation rate. In summary, the flame retardant ASBPA prepared in this invention can effectively improve the degradation rate of PLA.

[0041] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a boron-phosphorus synergistic starch-based single-component intumescent flame retardant, characterized in that: Includes the following steps: (1) Add starch to deionized water and stir magnetically at room temperature to obtain a starch suspension; (2) Stir phytic acid and boric acid to mix evenly, then calcine in a muffle furnace to obtain boron phytate blocks, ball mill them into powder and prepare a 5wt% boron phytate solution; (3) Add allantoin to deionized water and stir until homogeneous to obtain allantoin suspension; (4) Add the boron phytate solution obtained in (2) to the starch suspension obtained in step (1) and stir to obtain boron phytate modified starch suspension; (5) Add the allantoin suspension obtained in step (3) to the phytate boron modified starch suspension obtained in step (4), stir and react, age at room temperature, vacuum filter and wash, dry and pulverize to obtain the boron-phosphorus synergistic starch-based single-component intumescent flame retardant.

2. The preparation method according to claim 1, characterized in that... The starch mentioned in step (1) is one or more of soluble starches.

3. The preparation method according to claim 1, characterized in that... The molar ratio of phytic acid to boric acid used in step (2) is 1:4-1:6; the calcination temperature is 160-200℃ and the time is 4-12 h.

4. The preparation method according to claim 1, characterized in that... The molar ratio of allantoin to starch used in step (3) is 1:1-1:2; the stirring temperature is 60-80 ℃ and the stirring time is 1 h.

5. The preparation method according to claim 1, characterized in that... In step (4), the molar ratio of boron phytate to starch is calculated as 1:5-1:10; the stirring reaction temperature is 120-160 ℃ and the time is 2-4 h.

6. The preparation method according to claim 1, characterized in that: The stirring reaction in step (5) is carried out at a temperature of 60-80 °C for 1-2 h.

7. The preparation method according to claim 1, characterized in that: The aging time mentioned in step (5) is 12-24 hours.

8. The preparation method according to claim 1, characterized in that: The drying temperature in step (5) is 70-100℃ and the time is 12-24 h.

9. A boron-phosphorus synergistic starch-based single-component intumescent flame retardant prepared by the method according to any one of claims 1 to 8.

10. The application of the boron-phosphorus synergistic starch-based single-component intumescent flame retardant as described in claim 9 in PLA, characterized in that: The boron-phosphorus synergistic starch-based single-component intumescent flame retardant is added to PLA at a rate of 5%-15% of the PLA mass.

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