Preparation method of modified starch-based intumescent flame retardant using itaconic acid as a bridge

Abstract

The present invention discloses a modified starch-based single-component intumescent flame retardant using itaconic acid as a bridge, as well as its preparation method and application. A "three-source-in-one" modified starch-based single-component intumescent flame retardant is prepared by a one-pot process using starch, itaconic acid, DOPO, phosphoric acid, and melamine as raw materials. The preparation process of the flame retardant of the present invention is simple and safe, and most of the raw materials are derived from low-cost, green, renewable biomass materials. It is environmentally friendly and highly compatible with polymers. Its application in PLA has little effect on the mechanical properties of the material, can improve the degradation performance of PLA, and has a high flame retardant efficiency, which can effectively suppress its melt droplets and smoke emissions.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer flame retardancy, and particularly relates to the preparation and application of a modified starch-based single-component intumescent flame retardant using itaconic acid as a bridge. Background Art

[0002] Polylactic acid (PLA) is a synthetic polymer material with excellent biocompatibility and biodegradability. It is made from agricultural crops, which are degraded by enzymes to produce glucose, then fermented by lactic acid bacteria to produce lactic acid, and finally polymerized to produce a biodegradable material. In addition to its remarkable biodegradability, PLA also boasts excellent mechanical properties, ease of processing, high transparency, and good biocompatibility. These properties have led to its widespread application in various fields, including electronic packaging, textiles, and medical treatments. However, PLA's flammability and the large amount of droplets it produces during combustion have limited its applications. Therefore, flame retardant modification of PLA has become crucial. Traditional flame retardants for PLA primarily include halogen-based flame retardants, nitrogen-based flame retardants, phosphorus-based flame retardants, and intumescent flame retardants. In recent years, biomass-based intumescent flame retardants have gained increasing attention due to their excellent biocompatibility, environmental friendliness, and ability to achieve effective flame retardancy at low addition levels.

[0003] Starch is one of the most abundant polysaccharides in nature. It is inexpensive and rich in -OH groups, making it suitable for a variety of chemical reactions. The combustion process of starch is similar to thermal degradation, and it is easily catalyzed by acid sources to char, forming a dense carbon layer that protects the matrix, making it a stable carbon source. At the same time, starch combustion decomposes and releases inert gases such as CO2, which inhibits heat and oxygen exchange. However, starch's phosphorylation reaction requires catalysis with a toxic solvent (DMF) and is extremely inefficient.

[0004] Itaconic acid (IA) is the fifth largest organic acid in the world. Its molecular structure contains two carboxyl groups and an unsaturated double bond, making it highly reactive chemically and capable of undergoing addition, esterification, and amidation reactions. Currently, itaconic acid is primarily produced by fermentation, using agricultural byproducts such as starch, sucrose, and sawdust as raw materials, along with nitrogen sources and inorganic salts, for appropriate fermentation. Its annual production is approximately 100,000 tons, making it relatively inexpensive and a renewable resource. Therefore, using itaconic acid as a bridge in the synthesis of modified starch-based single-component intumescent flame retardants can avoid the use of toxic reagents and improve the synthesis efficiency of the flame retardant. It is also of great significance for the commercialization of modified starch-based single-component intumescent flame retardants.

[0005] 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) possesses abundant PH bonds and exhibits vapor-phase flame-retardant properties, making it a popular flame-retardant polymer material used synergistically with other biomass materials. DOPO's flame retardancy is primarily achieved through two pathways: vapor-phase flame retardancy and solid-phase flame retardancy. During chemical vapor-phase flame retardancy, polymer combustion generates a large number of free radicals, such as H· and ·OH. In phosphorus-containing flame retardant systems, the PO·, PO2, and HPO· radicals produced by DOPO's thermal decomposition can capture H· and ·OH, effectively extinguishing the flame. Furthermore, the formation of phosphine oxide radicals in DOPO is more favorable than that of phosphate products, meaning that more phosphorus in DOPO is consumed in the vapor phase. Physical vapor-phase flame retardancy involves the pyrolysis of DOPO, which produces more non-flammable gases (such as H2O and CO2), which dilute O2 and combustible gases. The condensed phase flame retardancy of DOPO is mainly achieved by protecting the polymer surface through the phosphoric acid and polyphosphoric acid produced by the decomposition of some phosphorus-containing compounds, and preventing the molten adhesive layer from oxygen penetration. This process can significantly limit the melt dripping rate of the composite material under high heat conditions, thereby controlling the spread of flame and combustion.

[0006] This invention utilizes the unsaturated double bond of itaconic acid to react with DOPO, and then uses the two carboxyl groups of itaconic acid to undergo esterification and amidation reactions with starch and melamine phosphate, respectively, to produce a modified starch-based single-component intumescent flame retardant that integrates acid, carbon, and gas sources. This novel flame retardant has appropriate carbon, nitrogen, and phosphorus content, high flame retardancy, and can effectively suppress smoke and prevent secondary combustion caused by molten droplets. Its raw materials are renewable and green, with low cost and no need for toxic solvents. It has high commercial value and broad application prospects and economic value. Summary of the Invention

[0007] The present invention aims to provide a modified starch-based single-component intumescent flame retardant using itaconic acid as a bridge, a preparation method thereof, and an application thereof. The flame retardant prepared thereby has the advantages of using renewable materials, good thermal stability, strong compatibility with PLA, high flame retardant efficiency, and anti-drip and anti-smoke properties. It has broad application prospects and application value in PLA.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A modified starch-based single-component intumescent flame retardant using itaconic acid as a bridge is prepared via a one-pot process using starch, itaconic acid (IA), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), phosphoric acid, and melamine as raw materials. The synthesis route is as follows:

[0010] .

[0011] The preparation of the modified starch-based single-component intumescent flame retardant comprises the following steps:

[0012] (1) Add starch to deionized water and stir magnetically at room temperature to obtain a starch suspension;

[0013] (2) Slowly adding itaconic acid and DOPO into anhydrous ethanol and stirring to react to obtain a DOPO-modified itaconic acid solution;

[0014] (3) adding melamine to deionized water, stirring evenly to obtain a suspension, and then adding phosphoric acid to react to obtain a melamine phosphate solution;

[0015] (4) adding the starch suspension obtained in step (1) dropwise into the DOPO-modified itaconic acid solution obtained in step (2), and reacting by stirring to obtain a DOPO-modified starch suspension with itaconic acid as a bridge;

[0016] (5) The melamine phosphate solution obtained in step (3) is added dropwise to the DOPO modified starch suspension obtained in step (4), and after stirring and reacting, aging at room temperature, vacuum filtration, washing, drying, and crushing, a modified starch-based single-component intumescent flame retardant with itaconic acid as a bridge is obtained.

[0017] Furthermore, the starch in step (1) is one or more of soluble starch and water-soluble starch.

[0018] Furthermore, the molar ratio of itaconic acid to DOPO used in step (2) is 1:1.

[0019] Furthermore, the stirring reaction in step (2) is carried out at a temperature of 90° C. and for 2 h.

[0020] Furthermore, the molar ratio of melamine to phosphoric acid used in step (3) is 1:(1-2).

[0021] Furthermore, the reaction temperature in step (3) is 70-100°C and the reaction time is 2 h.

[0022] Furthermore, the amount of the DOPO-modified itaconic acid solution in step (4) is converted based on a molar ratio of DOPO to starch of 1:(1-2).

[0023] Furthermore, the stirring reaction in step (4) is carried out at a temperature of 120° C. and for a time of 1.0-2.0 h.

[0024] Furthermore, the amount of the melamine phosphate solution in step (5) is converted based on a molar ratio of melamine to DOPO of 1:1.

[0025] Furthermore, the stirring reaction in step (5) is carried out at a temperature of 70-100°C and for a time of 2 h.

[0026] Furthermore, the aging time in step (5) is 12-24 h.

[0027] Furthermore, the drying temperature in step (5) is 70-100°C and the drying time is 12-24 hours.

[0028] Furthermore, the stirring rate in steps (1) to (5) is 200-500 rpm.

[0029] The modified starch-based single-component intumescent flame retardant can be applied to PLA. Specifically, the modified starch-based single-component intumescent flame retardant is added to PLA in an amount of 5% to 15% of the mass of the PLA.

[0030] The significant advantages of the present invention are:

[0031] (1) The modified starch-based single-component intumescent flame retardant with itaconic acid as a bridge of the present invention uses starch, one of the most abundant polysaccharides in nature, as its main raw material. The raw material source is wide and green and environmentally friendly. The synthesis of the flame retardant is completed in the aqueous phase, the preparation process is simple, and it is easy to achieve industrial production.

[0032] (2) The present invention uses itaconic acid as a bridge, utilizes its unsaturated double bond to undergo addition reaction with DOPO, and utilizes its two carboxyl groups to undergo esterification reaction and amidation reaction with starch and melamine phosphate, respectively, to obtain a modified starch-based single-component intumescent flame retardant that integrates acid source, carbon source and gas source. The flame retardant is pure white and has no effect on the appearance of the PLA composite material after processing.

[0033] (3) The modified starch-based single-component intumescent flame retardant of the present invention has appropriate C, N, and P contents and high flame retardant efficiency. When the modified starch-based single-component intumescent flame retardant is added in an amount of 10 wt% in PLA, the flame retardant grade can reach UL94 V-0, and it can effectively prevent molten dripping and thick smoke emissions. In addition, the modified starch-based single-component intumescent flame retardant has strong compatibility with polymers and has little effect on the mechanical properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FT-IR images of the modified starch-based one-component intumescent flame retardant prepared in Examples 1 and 2, starch (SST), and melamine (MEL).

[0035] Figure 2 This is the SEM image of the char layer of the flame retardant sample prepared by adding the flame retardant obtained in Example 1 after combustion.

[0036] Figure 3 This is the SEM image of the char layer of the flame retardant specimen prepared by adding the flame retardant obtained in Example 2 after combustion.

[0037] Figure 4 This is the SEM image of the carbon layer of the combustion specimen prepared by adding the flame retardant obtained in the comparative example and the starch mixture after combustion.

[0038] Figure 5 This is the SEM image of the char layer after combustion of the combustion specimen prepared by adding only starch.

[0039] Figure 6 This is the SEM image of the carbon layer after combustion of pure PLA combustion specimen.

[0040] Figure 7 This is a graph showing the 90-day degradation data changes of degradation specimens prepared by adding the flame retardant obtained in Example 1, starch and pure PLA. DETAILED DESCRIPTION

[0041] A modified starch-based single-component intumescent flame retardant using itaconic acid as a bridge, the preparation of which comprises the following steps:

[0042] (1) Add starch to deionized water and stir magnetically at room temperature to obtain a starch suspension;

[0043] (2) Itaconic acid and DOPO were slowly added to anhydrous ethanol at a molar ratio of 1:1 and stirred at 90 °C for 2 h to obtain a DOPO-modified itaconic acid solution (DOPOIA solution);

[0044] (3) Add melamine to deionized water and stir evenly to obtain a suspension. Then add phosphoric acid at 70-100 °C and react for 2 h to obtain a melamine phosphate solution.

[0045] (4) Add the starch suspension obtained in step (1) dropwise to the DOPO-modified itaconic acid solution obtained in step (2), and react at 120°C with stirring for 1.0-2.0 h to obtain a DOPO-modified starch suspension with itaconic acid as a bridge;

[0046] (5) adding the melamine phosphate solution obtained in step (3) dropwise into the DOPO modified starch suspension with itaconic acid as a bridge obtained in step (4), stirring and reacting at 70-100 °C for 2 h to obtain a DOPO / melamine / phosphate modified starch suspension;

[0047] (6) The suspension obtained in step (5) is allowed to stand for 12-24 h, then filtered and washed three times, dried in a vacuum oven at 70-100 °C for 12-24 h, and then crushed into powder using a high-speed crusher to obtain a modified starch-based single-component intumescent flame retardant with itaconic acid as a bridge.

[0048] Wherein, the starch in step (1) is one or more of soluble starch and water-soluble starch.

[0049] The molar ratio of melamine to phosphoric acid used in step (3) is 1:(1-2).

[0050] The amount of DOPO-modified itaconic acid solution used in step (4) is calculated based on the molar ratio of DOPO to starch being 1:(1-2).

[0051] The amount of melamine phosphate solution used in step (5) is calculated based on a molar ratio of melamine to DOPO of 1:1.

[0052] The stirring rate in steps (1) to (5) is 200-500 rpm.

[0053] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0054] Example 1

[0055] Weigh 9 g (0.05 mol) of soluble starch into a beaker, add deionized water, and stir at room temperature to form a starch suspension. In another beaker, weigh 4.5 g (0.05 mol) of melamine into the beaker, add 80 mL of deionized water, and stir at room temperature. Slowly add 5.8 mL of phosphoric acid (0.05 mol) from a graduated cylinder to the melamine solution. Stir magnetically to allow for complete reaction to yield a melamine phosphate solution. Weigh 10.8 g (0.05 mol) of DOPO and 6.050 g (0.05 mol) of itaconic acid into a three-necked flask equipped with a magnetic stirrer, a reflux condenser, 80 mL of anhydrous ethanol, and nitrogen. Stir at 300 rpm, raise the temperature to 90°C, and react for 2 h to yield a DOPOIA solution. Slowly add the prepared starch suspension dropwise to the DOPOIA solution, then raise the temperature to 120°C and react for 2 h. The temperature was lowered to 90°C under stirring at 500 rpm, and the prepared melamine phosphate was slowly added dropwise to the three-necked flask using a separatory funnel for 2 h. After the reaction, the resulting product was allowed to settle for 24 h, then filtered and washed three times with anhydrous ethanol, dried in a vacuum oven at 80°C for 48 h, and then crushed into powder using a high-speed crusher to obtain the flame retardant DOPOIASST-1.

[0056] Example 2

[0057] Weigh 9 g (0.05 mol) of water-soluble starch into a beaker, add deionized water, and stir at room temperature to form a starch suspension. In another beaker, weigh 4.5 g (0.05 mol) of melamine into the beaker, add 80 mL of deionized water, and stir at room temperature. Slowly add 11.6 mL of phosphoric acid (0.1 mol) from a graduated cylinder to the melamine solution. Stir magnetically to allow for complete reaction to yield a melamine phosphate solution. Weigh 10.8 g (0.05 mol) of DOPO and 6.050 g (0.05 mol) of itaconic acid into a three-necked flask equipped with a magnetic stirrer, a reflux condenser, 80 mL of anhydrous ethanol, and nitrogen. Stir at 300 rpm, raise the temperature to 90°C, and react for 2 h to yield a DOPOIA solution. Slowly add the prepared starch suspension dropwise to the DOPOIA solution, then raise the temperature to 120°C and react for 2 h. The temperature was lowered to 90°C under stirring at 500 rpm, and the prepared melamine phosphate was slowly added dropwise to a three-necked flask using a separatory funnel for 2 h. After the reaction, the resulting product was allowed to settle for 24 h, then filtered and washed three times with anhydrous ethanol, dried in a vacuum oven at 80°C for 48 h, and then crushed into powder using a high-speed crusher to obtain the flame retardant DOPOIASST-2.

[0058] Comparative Example

[0059] Weigh 4.5 g (0.05 mol) of melamine into a beaker and add 80 mL of deionized water. Stir at room temperature. Slowly add 5.8 mL of phosphoric acid (0.05 mol) from a graduated cylinder to the melamine solution. Stir magnetically to allow for complete reaction to yield a melamine phosphate solution. Weigh 10.8 g (0.05 mol) of DOPO and 6.050 g (0.05 mol) of itaconic acid into a three-necked flask equipped with a magnetic stirrer, a reflux condenser, 80 mL of anhydrous ethanol, and nitrogen. Stir at 300 rpm. Raise the oil bath temperature to 90°C and react for 2 h to yield a DOPOIA solution. Under stirring at 500 rpm, the prepared melamine phosphate was slowly added dropwise into a three-necked flask using a separatory funnel and reacted for 2 h. After the reaction, the obtained product was allowed to settle for 24 h, then filtered and washed three times, and dried in a vacuum oven at 80 °C for 48 h. It was then crushed into powder using a high-speed crusher to obtain the flame retardant DOPOIAMEL.

[0060] Application Examples

[0061] 90 parts by mass of PLA were weighed and mixed with 10 parts by mass of the flame retardant prepared in the example, 8 parts by mass of the flame retardant prepared in the comparative example, 2 parts by mass of soluble starch, and 10 parts by mass of a single soluble starch. The mixture was then extruded into pellets using a twin-screw extruder and injection molded to produce standard vertical flame (UL-94) test bars (length × width × thickness = 130 mm × 10 mm × 3.2 mm), dumbbell-shaped test bars (length × width × thickness = 150 mm × 20 mm × 10 mm), and standard mechanical properties test bars for testing. Pure PLA pellets were also injection molded for comparison.

[0062] The combustion performance and mechanical properties of the prepared vertical combustion specimens, limiting oxygen index specimens, standard compression specimens and composite materials were tested. The test results are shown in Table 1.

[0063] Table 1 Flame retardant and mechanical properties test results

[0064]

[0065] As shown in the test results in Table 1, the vertical burning test grade of pure PLA is NR, the LOI value is 19.8%, and the residual carbon rate is only 2.1%. The samples in which the comparative flame retardant is mixed with starch or starch is used alone for flame retardancy have a limited improvement in flame retardancy compared to pure PLA, and the severe droplet problem is not significantly improved. However, the samples using the flame retardant of the embodiment all have a vertical burning test grade of V-0, an LOI value increased to above 28.7%, and a residual carbon rate of above 8.2% after full combustion. This proves that the flame retardant of the present invention has good compatibility when used in PLA, and the flame retardant effect of the burning strip is significantly improved.

[0066] Furthermore, compared to pure PLA (tensile strength of 58.2 MPa), samples in which the comparative flame retardant was mixed with starch or starch alone showed a significant decrease in tensile strength (42.9 MPa and 40.3 MPa, respectively). In contrast, samples using the example flame retardant showed a slightly smaller decrease in tensile strength (46.1 MPa and 47 MPa, respectively), despite having a better flame retardant effect. This demonstrates that the flame retardant prepared using the one-pot method of the present invention not only has a higher flame retardant efficiency but also effectively maintains the original mechanical properties of PLA.

[0067] Figure 1 The FT-IR spectra of the modified starch-based single-component intumescent flame retardant prepared in Examples 1 and 2, starch (SST), and melamine (MEL). From the spectra of DOPOIASST-1 and DOPOIASST-2, it can be seen that the FT-IR spectra at 1114.54 cm -1 、1175.01 cm -1The vibration absorption peak corresponding to POC (aromatic ring) indicates that DOPO was successfully modified onto itaconic acid; at 1658 cm -1 The characteristic peak of C=N appeared at the position of 1030 cm, proving that melamine was also successfully modified onto itaconic acid; -1 The peak at 3600-3300 cm may be the absorption peak of COC in the starch structure. -1 There is a broad peak at , which may be the absorption peak of the hydroxyl group in starch. In summary, the infrared test confirmed the successful synthesis of the flame retardant.

[0068] Figure 2 、 3 The SEM images of the char layer after combustion of PLA strips containing modified starch-based flame retardants prepared using flame retardants from Examples 1 and 2 are shown. As can be seen from the images, the char layer is dense and compact, free of holes, effectively insulating against heat transfer and providing excellent flame retardancy.

[0069] Figure 4 This is a SEM image of the char layer of a combustion specimen prepared by adding a mixture of the flame retardant obtained in the comparative example and starch. As can be seen from the image, although the char layer is dense after full combustion, some holes have appeared, which is not conducive to isolating heat and oxygen, and the flame retardant effect is poor.

[0070] Figure 5 This is an SEM image of the char layer after combustion of a sample prepared with only starch added. As can be seen from the image, it has large holes, which cannot isolate heat transfer and has almost no flame retardant effect.

[0071] Figure 6 This is a SEM image of the char layer of pure PLA strips after combustion. As can be seen from the image, the char layer after full combustion of pure PLA is fluffy and porous, which is not conducive to isolating heat and oxygen, and has almost no flame retardant effect.

[0072] The mass of the degradation specimens prepared by adding the flame retardant obtained in Example 1, starch and pure PLA before and after degradation was recorded, and the mass change rate was calculated and plotted as Figure 7 . As can be seen from the results in the figure, the mass of different materials increases in the initial stage. It is speculated that this may be because the material absorbs water in the soil, resulting in an increase in mass. About 30 days after degradation, the degradation rates of the three began to diverge. Among them, the mass loss rate of the spline with the addition of the flame retardant of Example 1 was the largest, followed by the spline with the addition of starch. The degradation rate of the pure PLA spline was much lower than the two. By 90 days, the pure PLA spline had only degraded by 0.002%, the spline with the addition of starch had degraded by 0.008%, and the spline with the addition of the flame retardant of Example 1 had degraded by 0.13%, and its degradation rate was greatly improved. In summary, it can be seen that the addition of the flame retardant of the present invention can accelerate the degradation rate of PLA.

[0073] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a modified starch-based single-component intumescent flame retardant using itaconic acid as a bridge, characterized in that: The following steps are involved: (1) Add starch to deionized water and stir magnetically at room temperature to obtain a starch suspension; (2) Slowly adding itaconic acid and DOPO into anhydrous ethanol and stirring to react to obtain a DOPO-modified itaconic acid solution; (3) adding melamine to deionized water, stirring evenly to obtain a suspension, and then adding phosphoric acid to react to obtain a melamine phosphate solution; (4) adding the starch suspension obtained in step (1) dropwise into the DOPO-modified itaconic acid solution obtained in step (2), and reacting by stirring to obtain a DOPO-modified starch suspension with itaconic acid as a bridge; (5) The melamine phosphate solution obtained in step (3) is added dropwise to the DOPO modified starch suspension obtained in step (4), and after stirring and reacting, aging at room temperature, vacuum filtration, washing, drying, and crushing, a modified starch-based single-component intumescent flame retardant with itaconic acid as a bridge is obtained.

2. The preparation method according to claim 1, wherein: The starch in step (1) is one or more of soluble starch and water-soluble starch.

3. The preparation method according to claim 1, wherein: The molar ratio of itaconic acid to DOPO used in step (2) is 1:1; the stirring reaction temperature is 90° C. and the time is 2 h.

4. The preparation method according to claim 1, wherein: The molar ratio of melamine to phosphoric acid used in step (3) is 1:(1-2); the reaction temperature is 70-100°C and the reaction time is 2 h.

5. The preparation method according to claim 1, wherein: The amount of DOPO-modified itaconic acid solution used in step (4) is calculated based on the molar ratio of DOPO to starch being 1:(1-2); the stirring reaction temperature is 120°C and the time is 1.0-2.0 h.

6. The preparation method according to claim 1, wherein: The amount of melamine phosphate solution used in step (5) is converted based on a molar ratio of melamine to DOPO of 1:1; the stirring reaction temperature is 70-100°C and the time is 2 h; the aging time is 12-24 h; and the drying temperature is 70-100°C and the time is 12-24 h.

7. A modified starch-based single-component intumescent flame retardant using itaconic acid as a bridge, prepared by the method of any one of claims 1 to 6.

8. Use of the modified starch-based single-component intumescent flame retardant according to claim 7 in PLA, characterized in that: The modified starch-based single-component intumescent flame retardant is added to PLA in an amount of 5% to 15% of the mass of the PLA.

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