Preparation method of amino acid metal ion complex surface modified ammonium polyphosphate flame retardant

Abstract

The invention discloses a preparation method of an amino acid metal ion complex surface modified ammonium polyphosphate flame retardant, and the method comprises the following steps: generating an amino acid metal ion complex from amino acid and metal salt through chelation, and carrying out ion exchange reaction between the amino acid metal ion complex and ammonium polyphosphate to obtain the surface modified ammonium polyphosphate flame retardant. After the amino acid metal ion complex surface modified ammonium polyphosphate flame retardant and a wood-plastic composite material are subjected to melt blending, the flame retardance, smoke suppression, mechanical property and ultraviolet aging resistance of the composite material can be remarkably improved; the method is cheap in raw materials, simple and environment-friendly in process and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of flame retardant technology for composite materials, specifically a method for preparing a surface-modified ammonium polyphosphate flame retardant using an amino acid metal ion complex. Background Technology

[0002] Wood-plastic composites (WPC) are an innovative and environmentally friendly material composed of plastic as the base matrix and wood flour or other plant fibers as fillers. This unique combination gives WPC the natural texture of wood and the processing properties of plastic, making it widely used in construction, home furnishings, and outdoor facilities. However, the flammability of WPC poses a serious threat to human life and property. To address this issue, the most common method is to add flame retardants to wood-plastic composites to enhance their fire resistance. Ammonium polyphosphate (APP), as a halogen-free flame retardant, is widely used in flame-retardant polymer materials. However, APP suffers from poor compatibility and low flame-retardant efficiency. Current technologies often involve surface modification of APP using silane coupling agents or quaternary ammonium salts, but these methods suffer from drawbacks such as residual toxicity of the modifiers, complex processes, or high costs.

[0003] With increasing awareness of health and environmental safety, the development of environmentally friendly, renewable, efficient, and non-toxic flame retardants is becoming a research focus in the flame retardant field. Biomass materials are abundant and diverse natural materials with advantages such as sustainability, wide availability, and relatively low cost. Many biomass materials, due to their unique chemical composition and structure, exhibit excellent char formation, non-flammable gas release, and free radical capture capabilities when exposed to flame. Among them, amino acids, as natural nitrogen-containing compounds, are completely biodegradable, aligning with green chemistry principles. Amino acids are rich in nitrogen (such as glycine, glutamic acid, and arginine), and decompose during combustion to generate inert gases such as NH3 and N2, diluting oxygen and inhibiting free radical chain reactions. Furthermore, some metal ions (such as Zn2+, Ca2+, Ni2+, Co2+, Cu2+, and Mn2+) can not only be used as catalysts for resin crosslinking reactions to improve the thermal stability of composite materials, but also as catalysts for dehydrogenation reactions, promoting char formation, forming a dense char layer, isolating oxygen and heat, and slowing the spread of combustion. Therefore, it is feasible to synthesize amino acid-metal ion complexes by utilizing the chelation principle of amino acids and metal ions, and then modify the surface of APP by ion exchange reaction to prepare a surface-modified ammonium polyphosphate flame retardant based on amino acid-metal ion complexes, and use it to improve the flame retardant properties of wood-plastic composites. Summary of the Invention

[0004] The purpose of this invention is to provide a halogen-free, environmentally friendly amino acid metal ion complex surface-modified ammonium polyphosphate flame retardant and to apply it to wood-plastic composites. By rationally designing the composition and structure of the flame retardant, the mechanical properties of wood-plastic composites are improved while ensuring effective flame retardancy, and excellent antibacterial and UV aging resistance are also imparted to the wood-plastic composites.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One method for preparing an amino acid-metal ion complex surface-modified ammonium polyphosphate flame retardant:

[0007] Step 1: Add an inorganic metal ion salt solution to the amino acid solution, adjust the pH value, heat and react for a period of time, add an organic solvent to crystallize, filter, wash and dry to obtain the amino acid metal ion complex.

[0008] Step 2: Add a certain amount of the amino acid metal ion complex obtained in step (1) to the ammonium polyphosphate dispersion, heat and react for a period of time, then filter, wash, dry, grind and sieve to obtain the amino acid metal ion complex surface-modified ammonium polyphosphate flame retardant.

[0009] The amino acid solution in step 1 is an aqueous solution of amino acids, wherein the mass ratio of amino acids to water is 1:8-15; the amino acid solution is an aqueous solution of amino acids, wherein the mass ratio of amino acids to water is 1:8-15; the amino acid is one or more of lysine, arginine, aspartic acid, glutamic acid, serine, and glycine; the inorganic metal ion salt solution is one or more of copper sulfate, copper chloride, copper acetate, copper nitrate, zinc sulfate, zinc chloride, zinc acetate, zinc nitrate, cobalt sulfate, cobalt chloride, cobalt nitrate, ferric sulfate, ferric chloride, ferric nitrate, manganese sulfate, and manganese chloride aqueous solution; the molar ratio of the amino acid to the metal ion in the inorganic metal salt is 1-4:1; the pH value is 5-7; the reaction heating temperature is 70-120℃, and the reaction time is 2-6 hours; the organic solvent includes one or more of methanol, ethanol, propanol, and chloroform.

[0010] The degree of polymerization of the ammonium polyphosphate in step 2 is 500–1200; the ammonium polyphosphate dispersion is one or more of deionized water, methanol, and ethanol; the mass ratio of the amino acid metal ion complex to the ammonium polyphosphate is 1:1–4; the reaction heating temperature is 60–100°C, and the reaction time is 2–8 hours.

[0011] Secondly, the flame retardant prepared by the above method is used to prepare flame-retardant wood-plastic composite materials, specifically:

[0012] The flame retardant, corn stalks, and polypropylene were dried at 80°C for 24 hours to remove any residual moisture. The flame retardant, corn stalks, and polypropylene were weighed according to the mass ratio. After uniform mixing, the mixture was melt-blended and granulated using a twin-screw extruder. The resulting granules were then pulverized and added to a special mold, and hot-pressed using a flat vulcanizing machine to prepare the flame-retardant wood-plastic composite material.

[0013] The mass ratio of the flame retardant, corn stalks, and polypropylene is 1–3:2–4:5–7; the melt blending temperature is 160–185°C; the hot pressing temperature is 140–190°C; the hot pressing pressure is 1.0–3 MPa; and the hot pressing time is 5–25 min.

[0014] The beneficial effects of this invention are:

[0015] This invention significantly improves the flame-retardant properties of ammonium polyphosphate by introducing amino acids and metal ions, while reducing its hygroscopicity and compatibility with organic substrates, thus improving the material's mechanical and processing properties. Furthermore, the use of bio-based materials gives this flame retardant a significant advantage in environmental friendliness, reducing dependence on petroleum-based chemicals and lowering potential environmental pollution risks. Experimental results show that the modified ammonium polyphosphate exhibits significantly improved flame-retardant properties and good stability at high temperatures, meeting the needs of modern flame-retardant materials. Attached Figure Description

[0016] Figure 1 SEM images of ammonium polyphosphate (a), amino acid metal ion complex (b), and surface-modified ammonium polyphosphate with amino acid metal ion complex (c).

[0017] Figure 2 FTIR images of ammonium polyphosphate, amino acid metal ion complexes, and surface-modified ammonium polyphosphate with amino acid metal ion complexes.

[0018] Figure 3 Vertical combustion diagrams of the WPC composite materials prepared in Comparative Examples 1-2 and Examples 1-3.

[0019] Figure 4 Stress-strain curves of WPC composite materials prepared in Comparative Examples 1-2 and Examples 1-3.

[0020] Figure 5 Tensile strength diagrams of the WPC composite materials prepared in Comparative Examples 1-2 and Examples 1-3.

[0021] Figure 6 Flexural strength diagrams of the WPC composite materials prepared in Comparative Examples 1-2 and Examples 1-3.

[0022] Figure 7Stress-strain curves of WPC composite materials prepared in Comparative Examples 1-2 and Examples 1-3 after UV aging for 600 h.

[0023] Figure 8 Tensile strength diagrams of WPC composite materials prepared in Comparative Examples 1-2 and Examples 1-3 after UV aging for 600 hours. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Implementation Example 1: Dissolve 5g of glutamic acid in 60g of deionized water, stir to dissolve, and then add zinc nitrate solution, where Zn... 2+ The amount of substance was 0.05 mol, and the pH was adjusted to 6.5. The reaction was carried out at 90 °C for 4 h, followed by the addition of ethanol to precipitate crystals. After filtration and drying, the zinc glutamate complex was obtained.

[0026] A zinc glutamate complex and ammonium polyphosphate with a degree of polymerization of 800 were mixed at a mass ratio of 1:2 and dispersed in an ethanol solution. The mixture was reacted at 80°C for 5 hours. After filtration and drying, a zinc glutamate complex-modified ammonium polyphosphate flame retardant was obtained.

[0027] A mixture of zinc glutamate complex-modified ammonium polyphosphate flame retardant, corn stalks, and polypropylene at a mass ratio of 2:3:6 was melt-blended and granulated at 175°C using a twin-screw extruder. The granules were then pulverized and hot-pressed at 170°C and 2 MPa for 15 minutes using a flatbed vulcanizing machine to obtain a flame-retardant wood-plastic composite material.

[0028] Implementation Example 2

[0029] Dissolve 4g of arginine in 60g of deionized water, stir to dissolve, and then add copper sulfate solution, where Cu... 2+ The amount of substance was 0.04 mol, and the pH was adjusted to 7.0. The reaction was carried out at 90 °C for 4 h, followed by the addition of ethanol to precipitate crystals. After filtration and drying, the arginine copper complex was obtained.

[0030] Arginine copper complex and ammonium polyphosphate with a degree of polymerization of 1200 were mixed at a mass ratio of 1:3 and dispersed in an ethanol solution, and reacted at 70°C for 6 hours. After filtration and drying, the arginine copper complex-modified ammonium polyphosphate flame retardant was obtained.

[0031] Arginine copper complex surface-modified ammonium polyphosphate flame retardant, corn stalks, and polypropylene were mixed in a mass ratio of 2:2:6, melt-blended and granulated at 180°C using a twin-screw extruder. The granules were then pulverized and hot-pressed at 180°C and 2.5 MPa for 10 minutes using a flat vulcanizing machine to obtain a flame-retardant wood-plastic composite material.

[0032] Implementation Example 3

[0033] Dissolve 4.5g of lysine in 50g of deionized water, stir to dissolve, and then add copper sulfate solution, where Cu... 2+ The amount of substance was 0.035 mol, and the pH was adjusted to 6.0. The reaction was carried out at 95 °C for 3 h, followed by the addition of ethanol to precipitate crystals. After filtration and drying, the lysine copper complex was obtained.

[0034] Lysine copper complex and ammonium polyphosphate with a degree of polymerization of 1000 were mixed at a mass ratio of 1:3, dispersed in an ethanol solution, and reacted at 75°C for 6 hours. After filtration and drying, a lysine copper complex surface-modified ammonium polyphosphate flame retardant was obtained.

[0035] Flame-retardant wood-plastic composite material was prepared by mixing lysine copper complex surface-modified ammonium polyphosphate flame retardant, corn stalks, and polypropylene in a mass ratio of 3:4:7, followed by melt blending and granulation at 180°C using a twin-screw extruder. The granules were then pulverized and hot-pressed at 175°C and 3.0 MPa for 15 minutes using a flat vulcanizing machine.

[0036] Comparative Example 1

[0037] Corn stalks and polypropylene were mixed at a mass ratio of 4:6, melt-blended and granulated at 180°C using a twin-screw extruder. The granules were then crushed and hot-pressed at 180°C and 2.5 MPa for 10 minutes using a flat vulcanizing machine to obtain a pure wood-plastic composite material.

[0038] Comparative Example 2

[0039] The ammonium polyphosphate flame retardant, corn stalks, and polypropylene were mixed in a mass ratio of 2:2:6, melt-blended and granulated at 180°C using a twin-screw extruder. The granules were then pulverized and hot-pressed at 180°C and 2.5 MPa for 10 minutes using a flatbed vulcanizing machine to obtain the flame-retardant wood-plastic composite material.

[0040] from Figure 1 The SEM images show that ammonium polyphosphate (a), the amino acid metal ion complex (b), and the surface-modified ammonium polyphosphate with the amino acid metal ion complex (c) exhibit different morphologies. Figure 2FTIR analysis revealed typical characteristic peaks for APP, including the P=O stretching vibration peak at 880 cm⁻¹, the PO stretching vibration peak at 1014 cm⁻¹, the NH bending vibration peak at 1256 cm⁻¹, and the C=O stretching vibration peak at 1700 cm⁻¹. For amino acid metal ion complexes, NH bond stretching vibration peaks were observed at 3361 and 3301 cm⁻¹, COO⁻ stretching vibration peaks at 1665 and 1354 cm⁻¹, and a new characteristic peak for amino-metal ion coordination appeared at 442 cm⁻¹. For surface-modified ammonium polyphosphate of amino acid metal ion complexes, the COO⁻ stretching vibration peak shifted from 1665 cm⁻¹ to 1623 cm⁻¹, while a symmetric deformation vibration peak at 1477 cm⁻¹ attributed to α-amino groups appeared, indicating cation exchange between ammonium polyphosphate and the amino acid metal ion complex. These results demonstrate the successful preparation of surface-modified ammonium polyphosphate of amino acid metal ion complexes.

[0041] The flame retardant properties of the WPC composites prepared in Comparative Examples 1-2 and Examples 1-3, tested using a cone calorimeter, oxygen index meter, and horizontal / vertical combustion tester, are shown in Table 1. In Comparative Example 1, the peak heat release rate (pHRR), total heat release (THR), and total smoke release (TSP) of pure WPC reached as high as 529 kW / m², 133 MJ / m², and 1116 m², respectively. In Comparative Example 2, the pHRR, THR, and TSP of the WPC composite with only APP added were 318 kW / m², 101 MJ / m², and 1458 m², respectively. Although the pHRR and THR decreased significantly, the TSP increased significantly, indicating that APP does not have a smoke-suppressing effect. For Examples 1-3, the pHRR, THR, and TSP of all WPC composites with added amino acid metal ion complex surface-modified ammonium polyphosphate flame retardants decreased, with the highest reductions to 223 kW / m², 98 MJ / m², and 364 m², respectively. This indicates that the amino acid metal ion complex surface-modified ammonium polyphosphate flame retardant prepared in this invention can impart excellent flame retardant and smoke suppression properties to WPC. Furthermore, oxygen index and vertical burning tests show that the oxygen index of the WPC composites prepared in Examples 1-3 can reach approximately 30%, and all can achieve UL-94V-0 rating (…). Figure 3 It exhibits good flame retardant properties.

[0042] from Figure 4-6It can be seen that the tensile and flexural strengths of the WPC composite material with only APP added in Comparative Example 2 are lower than those of pure WPC in Comparative Example 1, while the tensile and flexural strengths of the WPC composite materials with amino acid metal ion complex surface-modified ammonium polyphosphate flame retardant added in Examples 1-3 are higher than those of pure WPC in Comparative Example 1. This indicates that APP deteriorates the mechanical properties of WPC, and the modified APP flame retardant prepared in this invention can improve the tensile and flexural strength of WPC. Furthermore, as... Figure 7-8 As shown, after 600 hours of aging treatment, the tensile strength of the WPC composites prepared in Comparative Examples 1-2 and Examples 1-3 decreased by 16.5%, 34.9%, 9.7%, 7.3%, and 12.1%, respectively, indicating that the surface-modified ammonium polyphosphate with amino acid metal ion complexes can improve the UV aging performance of WPC. This demonstrates that the surface-modified ammonium polyphosphate with amino acid metal ion complexes prepared by the method of this invention not only has good flame retardant effects but also improves the mechanical properties and UV aging resistance of WPC.

[0043] Table 1. pHRR, THR, TSP, LOI, and UL-94 ratings of the materials.

[0044]

[0045] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0046] 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 an amino acid metal ion complex surface-modified ammonium polyphosphate flame retardant, characterized in that... Includes the following steps: (1) Add an inorganic metal ion salt solution to the amino acid solution, adjust the pH value, heat the reaction for a period of time, add an organic solvent to crystallize, filter, wash and dry to obtain the amino acid metal ion complex. (2) A certain amount of the amino acid metal ion complex obtained in (1) is added to the ammonium polyphosphate dispersion, heated and reacted for a period of time, and then filtered, washed, dried, ground and sieved to obtain the amino acid metal ion complex surface modified ammonium polyphosphate flame retardant.

2. Step 1 of the preparation method according to claim 1, characterized in that: The amino acid solution is an aqueous solution of amino acids, wherein the mass ratio of amino acids to water is 1:8-15; the amino acid is one or more of lysine, arginine, aspartic acid, glutamic acid, serine, and glycine; the inorganic metal ion salt solution is one or more of the aqueous solutions of copper sulfate, copper chloride, copper acetate, copper nitrate, zinc sulfate, zinc chloride, zinc acetate, zinc nitrate, cobalt sulfate, cobalt chloride, cobalt nitrate, ferric sulfate, ferric chloride, ferric nitrate, manganese sulfate, and manganese chloride; the molar ratio of the amino acid to the metal ion in the inorganic metal salt is 1-4:1; the pH value is 5-7; the reaction heating temperature is 70-120℃, and the reaction time is 2-6 hours; the organic solvent includes one or more of methanol, ethanol, propanol, and chloroform.

3. Step 2 of the preparation method according to claim 1, characterized in that: The degree of polymerization of the ammonium polyphosphate is 500-1200; the ammonium polyphosphate dispersion is an ethanol solution of ammonium polyphosphate; the ammonium polyphosphate dispersion is one or more of deionized water, methanol and ethanol; the mass ratio of the amino acid metal ion complex to the ammonium polyphosphate is 1:1-4; the reaction heating temperature is 60-100℃, and the reaction time is 2-8h.

4. The application of an amino acid metal ion complex surface-modified ammonium polyphosphate flame retardant prepared by the method of preparing phosphorus-nitrogen type flame retardants according to claims 1-3 in flame-retardant wood-plastic composites, characterized in that: The flame retardant, corn stalks, and polypropylene were dried at 80°C for 24 hours to remove any residual moisture. The flame retardant, corn stalks, and polypropylene were weighed according to the mass ratio. After uniform mixing, the mixture was melt-co-granulated using a twin-screw extruder. The resulting granules were added to a special mold and hot-pressed using a flat vulcanizing machine to prepare the flame-retardant wood-plastic composite material.

5. The preparation method according to claim 4, characterized in that: The mass ratio of the flame retardant, corn stalks, and polypropylene is 1–3:2–4:5–7; the melt blending temperature is 160–185 °C; the hot pressing temperature is 140–190 °C; the hot pressing pressure is 1.0–3 MPa; and the hot pressing time is 5–25 min.

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