A bio-based flame-retardant-water-resistant-moldable starch composite material and a preparation method thereof

Abstract

The application discloses a kind of bio-based flame-retardant-water-resistant-plastic starch composite materials and preparation method, belong to starch modification technical field.First, the hydrophobicity of starch is improved by esterification modification through maleic anhydride;Then, the bio-based flame retardant APA is synthesized by using phytic acid and arginine;Finally, the flame retardant is melt-blended with modified starch, polybutylene adipate terephthalate (PBAT) and glycerol to obtain a full bio-based composite material with good flame retardance, water resistance and plasticity.The material prepared by the application realizes efficient phosphorus-nitrogen synergistic flame retardation, significant water resistance and good mechanical toughness simultaneously under the premise of maintaining excellent processability and biodegradability through molecular design and multi-component synergy, overcomes the technical bottlenecks of poor flame retardance, easy brittle fracture and poor water resistance of traditional starch-based materials, and widens its application in packaging, agricultural mulch and other fields with high requirements for flexibility and safety.

Description

Technical Field

[0001] This invention relates to the field of starch modification technology, and in particular to a bio-based flame-retardant, water-resistant, and plastic starch composite material and its preparation method. Background Technology

[0002] Starch-based plastics are a class of biodegradable materials with natural starch as the main component. They are characterized by a wide range of raw material sources, low cost, and good biodegradability, and have been widely used in packaging bags, agricultural mulch films, and other fields in recent years. This material is typically produced by melt blending starch with plasticizers (such as glycerol and sorbitol) to obtain thermoplastic starch (TPS). It can also be blended with biodegradable polymers such as polylactic acid (PLA) and polybutylene adipate / terephthalate (PBAT) to improve mechanical and processing properties.

[0003] However, starch-based plastics suffer from high flammability and poor thermal stability, posing certain combustion safety hazards during transportation, storage, and use, especially in applications such as agricultural mulch films and packaging bags where they are easily ignited by open flames. Furthermore, pure starch materials are highly hygroscopic, and their mechanical properties are prone to degradation in high humidity or outdoor environments, limiting their long-term performance. Therefore, in recent years, researchers have focused on developing flame-retardant starch-based plastics to improve the material's safety and environmental adaptability.

[0004] Existing flame retardant modification methods include: additive flame retardant compounding, chemical modification, nanocomposite and synergistic flame retardant methods, and multilayer structure and surface coating methods.

[0005] Among them, bio-based phosphorus-based flame retardants (such as phytic acid, choline phytate, and lignin phosphate) have become an important research direction for starch-based flame-retardant plastics due to their renewability and low toxicity. Studies have shown that such bio-based flame-retardant systems can significantly improve the limiting oxygen index (LOI), reduce the heat release rate (PHRR), and possess good environmental compatibility. However, these materials still face the following technical challenges: (1) When the flame retardant content is high, it can easily lead to increased material brittleness and decreased elongation, making it difficult to meet the flexibility requirements of film products; (2) Flame retardants are mostly hydrophilic components, which are easy to absorb moisture or migrate, resulting in the flame retardant effect decaying over time; (3) The material has poor thermal stability during industrial processing such as extrusion and blown film, and the flame retardant is not evenly dispersed, making it difficult to achieve large-scale continuous production; (4) Inorganic or high-carbon residual components introduced into the flame retardant system may affect biodegradability.

[0006] Based on the above problems, there is an urgent need to develop a bio-based flame-retardant, water-resistant, and plastic starch composite material and its preparation method. Summary of the Invention

[0007] The purpose of this invention is to provide a bio-based flame-retardant, water-resistant, and plastic starch composite material and its preparation method. Through molecular design and multi-component synergy, while maintaining excellent processability and biodegradability, the material simultaneously achieves efficient phosphorus-nitrogen synergistic flame retardancy, significant water resistance, and good mechanical toughness. This overcomes the technical bottlenecks of traditional starch-based materials, such as poor flame retardancy, easy cracking, and poor water resistance, and broadens its application in packaging, agricultural mulch films, and other fields with high requirements for flexibility and safety.

[0008] To achieve the above objectives, this invention provides a method for preparing a bio-based flame-retardant, water-resistant, and plastic starch composite material, comprising the following steps: (1) Maleic anhydride modification of starch: Dry starch and maleic anhydride powder are mixed evenly and reacted at 80±5℃ for 2-4 hours. After the reaction is completed, the product is cooled, washed with acetone, and dried to obtain maleic anhydride modified starch. The mechanism of this step is as follows: The chemical modification of starch by maleic anhydride is mainly achieved through nucleophilic ring-opening esterification of the anhydride carbonyl group by a hydroxyl group. The primary hydroxyl group at the C6 position reacts most readily due to its low steric hindrance. After ring-opening, the anhydride forms a starch-maleic ester structure, retaining a carboxyl group that can further participate in condensation, thereby initiating intra- or inter-chain crosslinking under specific conditions. Water competitively hydrolyzes maleic anhydride, significantly reducing esterification efficiency; therefore, anhydrous conditions are crucial for improving grafting degree. Overall, this reaction effectively introduces polar groups and modulates the structure and interfacial compatibility of starch, providing a chemical basis for improving its performance in composite materials and flame-retardant systems.

[0009] (2) Preparation of flame retardant APA: Arginine was dissolved in deionized water, and phytic acid solution was added under stirring, wherein the molar ratio of phytic acid to arginine was 1:3.5-4.5. The reaction was carried out at 80±5℃ for 2-4 hours. After the reaction was completed, the white solid flame retardant APA was obtained by freeze drying. (3) Melt blending: The maleic anhydride modified starch obtained in step (1), the flame retardant APA obtained in step (2), polybutylene terephthalate-adipate ester PBAT and glycerol are mixed and melt blended at 120-140℃ for 3-8 minutes to obtain a bio-based flame retardant-water resistant-plastic starch composite material.

[0010] Preferably, in step (1), the mass ratio of dried starch to maleic anhydride is 4:1-10:1.

[0011] Preferably, in step (1), after the reactants are cooled, acetone is added, stirred, and then filtered. The mixture is washed three times with acetone and then dried in a vacuum oven at 50°C until constant weight is achieved.

[0012] Preferably, in step (2), the molar ratio of phytic acid to arginine is 1:4.

[0013] Preferably, in step (3), the ratio of the mass of maleic anhydride modified starch to the mass of glycerol is 70:30-100:30.

[0014] Preferably, in step (3), the total mass of maleic anhydride modified starch (SA-MA) and glycerol (Gly) added is in the mass ratio of polybutylene terephthalate to poly(butylene adipate) 50:50-70:30.

[0015] Preferably, in step (3), the added mass of flame retardant APA is 10%-30% of the total mass of maleic anhydride modified starch, polybutylene terephthalate-adipate and glycerol.

[0016] Preferably, in step (3), the composition ratio of the melt blend by mass parts is: 35-54 parts of maleic anhydride modified starch; 11.5-21 parts of glycerol; 30-50 parts of polybutylene terephthalate-adipate; and 10-30 parts of flame retardant APA.

[0017] The present invention also provides a bio-based flame-retardant, water-resistant, and plastic starch composite material prepared by the above preparation method.

[0018] Therefore, the present invention employs the above-mentioned bio-based flame-retardant, water-resistant, and plastic starch composite material and its preparation method, and the specific beneficial effects are as follows: 1. This invention utilizes the ionic interaction between natural phytic acid (PA) and arginine (Arg) to construct a novel fully bio-based flame retardant, APA, achieving "phosphorus-nitrogen synergistic" flame retardancy: at high temperatures, phosphorus-rich phytic acid acts as a highly efficient acid source, promoting rapid dehydration of the material to form a dense and stable expanded char layer, isolating heat and oxygen; simultaneously, nitrogen-rich arginine acts as an ideal gas source, decomposing and releasing non-combustible gases, expanding the char layer. Furthermore, the dense hydrogen bond network between APA molecules further enhances char formation ability, thus efficiently inhibiting combustion through a dual mechanism of gas-phase dilution and condensed-phase char formation, providing an environmentally friendly and highly efficient comprehensive flame retardant solution.

[0019] 2. This invention constructs an integrated performance balance strategy of "flame retardancy-flexibility-water resistance," solving the industry problem of mutual constraints among flame retardancy, mechanical flexibility, and water resistance. First, by esterifying starch with maleic anhydride, hydrophobic groups are introduced into its molecular chain, improving the material's water resistance and significantly enhancing the interfacial compatibility between hydrophilic starch and the hydrophobic polymer PBAT. Second, glycerol is used to simultaneously plasticize the modified starch and PBAT, forming a synergistic effect with the hydrogen bond network of the flame retardant APA. This ensures that while achieving high flame retardancy, the elongation at break can exceed 260%, achieving the optimal balance between flame retardancy and mechanical toughness.

[0020] 3. This invention embodies the concept of green design, constructing a complete fully bio-based, biodegradable composite material system. Through scientific component proportioning and melt blending processes, maleic anhydride-modified starch, bio-based flame retardant APA, biodegradable polyester PBAT, and glycerol function individually while also working synergistically. Through multiple mechanisms such as interfacial compatibility, hydrogen bonding, plasticization, and PN synergistic flame retardancy, the components synergistically achieve a comprehensive improvement in flame retardancy, water resistance, processability, and mechanical toughness, opening up a new technological path for the development of high-performance, environmentally friendly starch plastics.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 The infrared spectrum of the maleic anhydride-modified starch prepared in step (1) of Example 1; Figure 2 The infrared spectrum of the flame retardant APA prepared in step (2) of Example 1; Figure 3 The graph shows the combustion heat release rate of the products prepared in Examples 1, 2, and Comparative Examples 1 to 3; Figure 4 The graph shows the total heat of combustion release of the products prepared in Examples 1, 2, and Comparative Examples 1 to 3. Figure 5 The mechanical properties of the products prepared in Examples 1, 2, and Comparative Examples 1 to 3 are shown in the diagram.

[0023] Figure 6 The graphs show the water absorption rate of the products prepared in Examples 1, 2, and Comparative Examples 1 to 4. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] The present invention will be further described below through specific embodiments. However, it should be understood that these embodiments are only for more detailed description and should not be construed as limiting the present invention in any way, that is, not intended to limit the scope of protection of the present invention.

[0026] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] Example 1 This embodiment provides a bio-based flame-retardant, water-resistant, and plastic starch composite material, the preparation method of which includes the following steps: (1) Weigh 5g of maleic anhydride and grind it into a fine powder in a mortar. Add 20g of dry corn starch to the mortar, mix it with the maleic anhydride powder, and grind it evenly. Transfer the mixture to a 250ml conical flask, place it in a hot water bath at 80℃, and stir continuously and slowly for 3 hours. Stop heating after the set reaction time is reached. After the reaction material cools, add a certain amount of acetone, stir for a certain time, and then filter. Finally, wash the mixture three times with acetone, place it in a vacuum oven at 50℃ and dry it to constant weight to obtain maleic anhydride-modified starch.

[0028] The infrared spectrum of starch modified with maleic anhydride is shown below. Figure 1 As shown in the figure, the -OH tensile vibration peak of SA-MA (3200-3570 cm⁻¹) -1 The narrower value compared to the SA spectrum indicates successful esterification substitution. At 1720 cm⁻¹ -1 The significant merging of the stretching vibration peaks of the ester carbonyl and carboxyl carbonyl groups was observed, which further indicates that the esterification was successful.

[0029] (2) Dissolve 8.8 g of arginine (Arg) in 200 ml of deionized water with constant stirring, and then stir magnetically for 10 min. Add 11.8 g of 70% phytic acid solution (PA) dropwise to the above solution at a uniform rate, wherein the molar ratio of PA to Arg is 1:4. The resulting mixture is continuously stirred and heat-treated at 80 °C for 3 h. After the reaction is completed, freeze-dry in a freeze dryer for 48 h to obtain white solid flame retardant APA.

[0030] The infrared spectrum of flame retardant APA is as follows: Figure 2 As shown, the raw material phytic acid is at 3500cm -1 The strong, broad peak (-OH stretching peak) in the vicinity is significantly weakened and the peak shape narrows in the product APA, indicating that phytic acid -OH participates in proton transfer, indirectly proving the formation of ionic bonds.

[0031] (3) Maleic anhydride-modified starch, polybutylene terephthalate (PBAT), and glycerol were used as base materials. The total mass ratio of PBAT to glycerol and modified starch was 40:60, and the mass ratio of glycerol to maleic anhydride-modified starch was 30:70. Flame retardant APA was added at 20% of the mass of the base materials. In this step, PBAT was first melted at 130°C, then the mixture of maleic anhydride-modified starch and glycerol was added, and finally the flame retardant APA was added and melt-blended for 5 minutes to obtain a white, plastic starch composite material.

[0032] Example 2 (Flame retardant dosage) In this embodiment, the same steps (1) and (2) as in Example 1 were used to prepare maleic anhydride modified starch and flame retardant APA. The difference is that in step (3), maleic anhydride modified starch, PBAT and glycerol were used as base materials. The mass ratio of maleic anhydride modified starch to glycerol was 70:30, and the mass ratio of PBAT to the total mass of maleic anhydride modified starch and glycerol was 60:40. Then, 30% of the mass of the base material was added to the flame retardant APA. At 130°C, PBAT was first poured in and melted, then the mixture of maleic anhydride modified starch and glycerol was added, and finally the flame retardant APA was added and melted and mixed for 5 minutes to obtain a white plastic starch composite material.

[0033] Comparative Example 1 In this comparative example, corn starch, PBAT and glycerol were mixed. The mass ratio of glycerol to corn starch was 70:30, and the total mass ratio of glycerol and corn starch to PBAT was 60:40. At 130°C, PBAT was first poured in and melted, and then the mixture of corn starch and glycerol was added and melted and blended for 5 minutes to obtain a transparent plastic starch composite material.

[0034] Comparative Example 2 In this comparative example, maleic anhydride-modified starch, PBAT, and glycerol were mixed. The preparation of maleic anhydride-modified starch was the same as in Example 1. The mass ratio of glycerol to modified starch was 70:30, and the mass ratio of the total mass of glycerol and maleic anhydride-modified starch to PBAT was 60:40. At 130°C, PBAT was first poured in and melted, and then the mixture of maleic anhydride-modified starch and glycerol was added and melt-blended for 5 minutes to obtain a white plastic starch composite material.

[0035] Comparative Example 3 In this comparative example, the same steps (1) and (2) as in Example 1 were used to prepare maleic anhydride-modified starch and flame retardant APA. The difference is that in step (3), maleic anhydride-modified starch, PBAT and glycerol were used as base materials. The mass ratio of maleic anhydride-modified starch to glycerol was 70:30, and the mass ratio of PBAT to the total mass of maleic anhydride-modified starch and glycerol was 60:40. Then, 10% of the mass of the base materials was added to the flame retardant APA. At 130°C, PBAT was first poured in and melted, then the mixture of maleic anhydride-modified starch and glycerol was added, and finally the flame retardant APA was added and melt-blended for 5 minutes to obtain a white plastic starch composite material.

[0036] Comparative Example 4 In this comparative example, corn starch and glycerol were mixed at a mass ratio of 30:70. After melting and blending at 130°C for 5 minutes, a transparent, plastic starch material was obtained.

[0037] The combustion heat release rate of the products prepared in Examples 1 and 2 and Comparative Examples 1 and 3 was detected, and the results are as follows: Figure 3 As shown, the results indicate that, compared with Comparative Examples 1 and 2 without flame retardant, the heat release rate curves of Examples 1, 2, and 3 with added flame retardant APA exhibit two significant characteristics: two heat release rate peaks, and the peak values ​​of both peaks are significantly reduced. The maximum heat release rate of Comparative Example 1 is 215.7 W / g, that of Comparative Example 2 is 223.5 W / g, that of Comparative Example 3 is 172.3 W / g, that of Example 2 is 115.2 W / g, and that of Example 1 is 151.5 W / g. The peak heat release rate of Example 1 is reduced by 29.9% and 32.2% compared with Comparative Examples 1 and 2, respectively; the first heat release peak is significantly earlier. The above results indicate that maleic anhydride-modified starch has little effect on the combustion performance of plastic starch composites; the flame retardant APA is activated in the early stage of material heating, causing the polymer to undergo strong catalytic char formation and cross-linking reactions, thereby constructing a continuous and dense char layer barrier, which effectively inhibits the escape of internal combustibles and the transfer of external heat.

[0038] The total heat release of combustion of the products prepared in Examples 1 and 2 and Comparative Examples 1 and 3 was detected, and the results are as follows: Figure 4As shown, the total heat release value of the composite material in Comparative Example 1 was 17.8 KJ / g, the total heat release value of the composite material in Comparative Example 2 was 17.9 KJ / g, the total heat release value of the composite material in Comparative Example 3 was 12.9 KJ / g, the total heat release value of the composite material in Example 2 was 10.9 KJ / g, and the total heat release value of the composite material in Example 1 was 10.9 KJ / g. These results indicate that the total heat release values ​​of the composite materials in Comparative Example 1 and Comparative Example 2 are similar, further demonstrating that maleic anhydride-modified starch has a relatively small impact on the combustion performance of the composite materials. The total heat release value of the composite material with added flame retardant APA was lower than that of both Comparative Example 1 and Comparative Example 2, and the total heat release value of Example 2 was similar to that of Example 1, decreasing by 38.9% and 39.4% respectively compared to Comparative Example 1 and Example 2, indicating that the flame retardant APA significantly improved the flame retardant performance of the composite material.

[0039] The mechanical properties of the products prepared in Examples 1 and 2 and Comparative Examples 1 and 3 are as follows: Figure 5 As shown, the results indicate that Comparative Example 2 exhibits the highest tensile strength and elongation at break, demonstrating the excellent toughening and reinforcing effect of PBAT. The results of Comparative Example 3, Example 2, and Example 1 show that the tensile strength of the materials decreased after the introduction of the flame retardant APA, mainly due to the stress concentration effect of APA particles in the matrix. Notably, at an addition of 20% (Example 1), the material maintained highly efficient flame retardant properties while its elongation at break (262%) was comparable to Comparative Example 1 and significantly higher than that of Example 2 (102%) with an addition of 30%. These results demonstrate that by controlling the addition of flame retardant APA to approximately 20 wt%, an optimal balance between flame retardancy and flexibility was successfully achieved. Too low an addition (Comparative Example 3, 10%) resulted in insufficient flame retardant effect, while too high an addition (Example 2, 30%) led to excessive embrittlement of the material.

[0040] The water resistance of the products prepared in Examples 1, 2, and Comparative Examples 1 to 4 is as follows: Figure 6As shown, the results indicate that Comparative Example 4 exhibits high water absorption, with a total water absorption rate of 66.24% after 24 hours of immersion at room temperature, demonstrating the poor water resistance of pure starch materials. The results of Comparative Examples 2 and 3, and Examples 1 to 2, show that the water absorption rate of the materials significantly decreased after the introduction of PBAT, with the total water absorption rate all less than ±5%. This is mainly attributed to the presence of numerous hydrophobic methylene segments and aromatic terephthalate structures in the PBAT molecular backbone. During the mixing process, the long PBAT chains cross-link with starch, encapsulating the hydrophilic components within the hydrophobic network, thereby effectively improving the overall water resistance of the material. Notably, at a 20% addition level (Example 1), while maintaining high flame retardant performance, the absolute value of its water absorption rate (2.47%) decreased by 96.3% compared to Comparative Example 4, and by 43.3% and 17.7% compared to Comparative Examples 3 and 2, respectively. The above results demonstrate that by controlling the flame retardant content to around 20%, the optimal balance between the flame retardancy and water resistance of the material was successfully achieved.

[0041] Therefore, this invention employs the aforementioned bio-based flame-retardant, water-resistant, and plastic starch composite material and its preparation method. Through molecular design and multi-component synergy, while maintaining excellent processability and biodegradability, the material simultaneously achieves highly efficient phosphorus-nitrogen synergistic flame retardancy, significant water resistance, and good mechanical toughness. This overcomes the technical bottlenecks of traditional starch-based materials, such as poor flame retardancy, brittleness, and poor water resistance, and broadens its application in packaging, agricultural mulch films, and other fields with high requirements for flexibility and safety.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a bio-based flame-retardant, water-resistant, and plastic starch composite material, characterized in that: Includes the following steps: (1) Starch maleic anhydride modification: Dry starch and maleic anhydride powder are mixed evenly and reacted at 80±5℃ for 2-4 hours. After the reaction is completed, the product is cooled and washed with acetone and dried to obtain maleic anhydride modified starch. The mass ratio of dry starch to maleic anhydride powder is 4:1-10:

1. (2) Preparation of flame retardant APA: Arginine was dissolved in deionized water, and phytic acid solution was added under stirring, wherein the molar ratio of phytic acid to arginine was 1:3.5-4.

5. The reaction was carried out at 80±5℃ for 2-4 hours. After the reaction was completed, the white solid flame retardant APA was obtained by freeze drying. (3) Melt blending: The maleic anhydride modified starch obtained in step (1), the flame retardant APA obtained in step (2), polybutylene terephthalate and glycerol are mixed in proportion and melt blended at 120-140℃ for 3-8 minutes to obtain a bio-based flame retardant-water resistant-plastic starch composite material. In step (3), the total mass of maleic anhydride modified starch and glycerol added is in the ratio of the mass of polybutylene terephthalate to 50:50-70:

30. In step (3), the added mass of flame retardant APA is 10-30% of the total mass of maleic anhydride modified starch, polybutylene terephthalate-adipate and glycerin.

2. The method for preparing a bio-based flame-retardant, water-resistant, and plastic starch composite material according to claim 1, characterized in that: In step (1), after the reactants are cooled, acetone is added, stirred, and then filtered. The mixture is washed three times with acetone and then dried in a vacuum oven at 50°C until constant weight is achieved.

3. The method for preparing a bio-based flame-retardant, water-resistant, and plastic starch composite material according to claim 1, characterized in that: In step (2), the molar ratio of phytic acid to arginine is 1:

4.

4. The method for preparing a bio-based flame-retardant, water-resistant, and plastic starch composite material according to claim 1, characterized in that: In step (3), the ratio of the mass of maleic anhydride modified starch to the mass of glycerol is 70:30-100:

30.

5. The method for preparing a bio-based flame-retardant, water-resistant, and plastic starch composite material according to claim 1, characterized in that: In step (3), the composition ratio of the melt blend by mass parts is as follows: 35-54 parts of maleic anhydride modified starch; 11.5-21 parts of glycerol; 30-50 parts of polybutylene terephthalate-adipate; and 10-30 parts of flame retardant APA.

6. A bio-based flame-retardant, water-resistant, and plastic starch composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

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