Biological flame retardant based on alginic acid as well as preparation method and application of biological flame retardant

Abstract

The invention provides a biological flame retardant based on alginic acid and a preparation method and application thereof.The preparation method comprises the following steps that alginic acid is dissolved in water, an aqueous solution of tetrabutyl ammonium hydroxide is dropwise added under the stirring condition till the pH value reaches 7-9, and alginate-TBA is obtained; the preparation method comprises the following steps: dissolving alginate-TBA in N, N-dimethylformamide containing 2 wt% of tetrabutylammonium fluoride; the preparation method comprises the following steps: adding an alginic acid solution into a reaction kettle, then adding phosphonitrilic chloride trimer and 1, 8-diazabicyclo [5.4. 0] undec-7-ene, after the reaction is finished at 50-70 DEG C, cooling to below 5 DEG C, finally adding 10-20 mL of isopropanol hydrochloride, and stirring to obtain the biological flame retardant based on alginic acid. An acid source and a gas source are introduced into the prepared alginic acid-based biological flame retardant, so that the alginic acid-based biological flame retardant has good flame retardance.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardants, in particular to an alginate-based biological flame retardant and a preparation method and application thereof. Background Art

[0002] Epoxy resin (EP) is flammable and releases a lot of smoke and toxic gases when burning. Its flammability can be reduced by adding flame retardants. Alginate is a natural polysaccharide that can be used as a carbon source for intumescent flame retardants. It has good carbonization properties. Its inherent flame retardant and smoke suppression properties make it a potential environmentally friendly flame retardant material. However, due to the lack of acid and gas sources in its molecules, the flame retardant effect is relatively poor when used alone. Therefore, it is necessary to improve its structure and develop an environmentally friendly bio-flame retardant with excellent flame retardant effect. Summary of the invention

[0003] The invention provides a biological flame retardant based on alginic acid, a preparation method and application thereof, introduces an acid source and a gas source, and has good flame retardancy.

[0004] The technical solution of the present invention is achieved as follows: a method for preparing a bioflame retardant based on alginic acid, comprising the following steps: (1) dissolving alginic acid in water, and adding an aqueous solution of tetrabutylammonium hydroxide (TBAOH) dropwise under stirring until the pH value reaches 7-9, and freeze-drying to obtain alginate-TBA; (2) Dissolve 0.5-1.5 g of alginate-TBA in 25-35 mL of solution C, which is N,N-dimethylformamide (DMF) containing 2 wt % tetrabutylammonium fluoride (TBAF); then add 1.5-2.5 g of hexachlorotriphosphazene (HCCP) and 3.5-4.5 mL of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). After the reaction is completed at 50-70 °C, cool to below 5 °C, and finally add 10-20 mL of isopropanol hydrochloric acid. After stirring for 10-20 min, vacuum filter and wash to obtain alginate-based bioflame retardant (AAFR).

[0005] Furthermore, in step (1), the preparation method of alginic acid is as follows: 7-8 g of alginate is dissolved in 450-550 mL of distilled water, and then 3-4 g of ascorbic acid and 4.5-5.5 mL of pyridine are added to obtain solution A, solution A is placed in a water bath, and nitrogen is passed through, heated to 75-85° C., and then hydrogen peroxide is added to carry out degradation reaction. After the reaction is completed, solution B is added and stirred at 3-5° C. for 8-15 hours, vacuum filtered, washed, and dried to obtain alginic acid; solution B is prepared from 550-650 mL of ethanol, 35-40 mL of concentrated hydrochloric acid, and 90-110 mL of water.

[0006] Furthermore, in step (2), the concentration of isopropyl hydrochloride is 5M (M is mol / L).

[0007] Furthermore, in step (2), the reaction is carried out at 60°C for 8-15 hours, and after the reaction is completed, the reaction is cooled to 0°C.

[0008] Furthermore, in step (2), after vacuum filtration, the product is washed multiple times with ethanol and acetonitrile.

[0009] Furthermore, in step (1), the concentration of the aqueous solution of tetrabutylammonium hydroxide is 4% w / v.

[0010] Furthermore, 45-55 mL of 30% hydrogen peroxide is added to the degradation reaction, and the degradation reaction time is 1-3 h.

[0011] A biological flame retardant based on alginic acid is prepared by adopting the preparation method.

[0012] The invention discloses an application of a bio-flame retardant based on alginate in the preparation of flame-retardant epoxy resin.

[0013] Beneficial effects of the present invention: The alginate-based bioflame retardant prepared by the present invention uses -TBA as an acid source and hexachlorotriphosphazene as a gas source, has good flame retardancy, and when the temperature reaches 800°C, the residual carbon content reaches 27.63%.

[0014] The present invention adds AAFR as a flame retardant to the epoxy resin. When the addition amount of AAFR reaches 20%, the limiting oxygen index of the EP composite material reaches 30.3%, and the vertical combustion test reaches V-0 level; the results of the thermogravimetric test show that the residual carbon content of the epoxy resin composite material added with 15% AAFR heated to 700°C in an air atmosphere is 24.33%, which is much higher than 9.49% of pure EP. The carbon layer of the epoxy resin composite material added with AAFR is dense and thick. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 is the TGA curve of AAFR; Figure 2 is the TGA curve of EP composite material; Figure 3is the heat release rate curve of EP composite material; Figure 4 is the total heat release curve of EP composite material; Figure 5 is the CO release rate curve of EP composite material; Figure 6 is the CO2 release rate curve of EP composite material; Figure 7 is the smoke generation rate curve of EP composite material; Figure 8 is the total smoke generation curve of EP composite material; Fig. 9 Figure 2 shows the carbon residue of EP composites after cone calorimetry test. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] A method for preparing a bioflame retardant based on alginic acid comprises the following steps: (1) 7.5 g of high molecular weight alginate was dissolved in 500 mL of distilled water (1.5% w / v), and then 3.5 g of ascorbic acid and 5 mL of pyridine were added to obtain solution A. Solution A was placed in a water bath, nitrogen was introduced, and the solution was heated to 80°C. After heating, 50 mL of 30% hydrogen peroxide was added to start degradation. After 2 h of reaction, solution B was added and stirred at 4°C for 12 h. The product was vacuum filtered, washed with ethanol and acetone, and dried in air to obtain alginate. Solution B was prepared from 600 ml of ethanol, 38 ml of concentrated hydrochloric acid, and 100 ml of water. The concentration of concentrated hydrochloric acid was 37 wt%. (2) re-dissolving the alginate prepared in step (1) in 80 ml of water, placing and immersing a pH probe under constant stirring, and then adding a dilute solution of tetrabutylammonium hydroxide (4% w / v) dropwise until the pH reaches 7-9, and freeze-drying the resulting low molecular weight alginate-TBA solution to obtain alginate-TBA; (3) Dissolve 1 g of alginate-TBA (6 mmol of alginate) in 30 mL of solution C, which is N,N-dimethylformamide containing 2 wt % of tetrabutylammonium fluoride; then add 2.1 g of hexachlorotriphosphazene and 4 ml of 1,8-diazabicyclo[5.4.0]undec-7-ene, and react at 60 °C for 12 h. Cool to 0 °C, slowly add 15 ml of 5 M hydrochloric acid isopropanol, stir for 15 min, vacuum filter, and wash with ethanol and acetonitrile 3 times to obtain alginate-based bioflame retardant (AAFR).

[0019] The AAFR was subjected to thermogravimetric testing at a heating rate of 20°C / min in air. The test results are shown in Figure 1 As shown. Figure 1 It can be seen that when the temperature reaches 800°C, the amount of residual carbon reaches 27.63%. After it is added to the EP composite material as a flame retardant, more flame retardant components will be produced during the combustion process to act on the composite material, and more residual carbon will be formed to wrap the composite material, and the flame retardant effect will be better.

[0020] The prepared AAFR is used as a flame retardant to prepare a flame retardant epoxy resin material (abbreviated as: EP composite material). The EP composite material includes AAFR, E-44 epoxy resin and curing agent. The curing agent is m-phenylenediamine. The mass ratio of E-44 epoxy resin to curing agent is 9:1. First, heat the epoxy resin to soften it, then add AAFR to mix, and finally add the curing agent. After fully mixing, pour it into the mold and cure it. The mass percentages of AAFR are 0%, 5%, 10%, 15%, and 20% respectively.

[0021] Test the limiting oxygen index of EP composite materials: The limiting oxygen index test uses LZB-6 oxygen index tester, mixes nitrogen and oxygen, and tests under the condition of passing mixed gas. By adjusting the ratio of oxygen to nitrogen, the combustion conditions under different oxygen concentrations are tested to determine its limiting oxygen index. If the burning time of the sample after being ignited exceeds 180s, it means that the oxygen concentration is too high. The oxygen concentration is adjusted until the sample burns for exactly 180s.

[0022] The EP composite material is tested vertically, and UL-94 is tested using the CFZ-1 vertical combustion instrument. The sample is clamped vertically in the test instrument, cotton is placed under the sample, and the sample is ignited with an igniter for 10 seconds, and then removed. The flame retardant performance of the material is judged based on the burning time and extinguishing of the sample after ignition. According to the national standard GB / T 2408-2008, UL-94 is divided into four levels: Fail, V-2, V-1, and V-0.

[0023] Table 1 Combustion performance of EP composites with different flame retardant additions Serial number UL-94 Is it dripping? LOI / % EP Fail yes 22.0 EP-5% Fail no 25.1 EP-10% V-2 no 27.4 EP-15% V-0 no 29.5 EP-20% V-0 no 30.3 As shown in Table 1, the LOI value of pure EP material without adding flame retardant is 22.0%. A large amount of black smoke is generated during the combustion process, and a small amount of molten droplets are generated, which does not reach the grade in the UL-94 test. When a certain amount of AAFR is added, the limiting oxygen index of the EP composite material increases, no molten droplets are generated, and the generated black smoke is reduced. As the content of AAFR increases, the limiting oxygen index of the EP composite material increases. When the addition amount of AAFR reaches 15%, the limiting oxygen index of the composite material reaches 29.5%, the UL-94 test grade reaches V-0, and the amount of black smoke is significantly reduced, meeting the flame retardant requirements.

[0024] Thermogravimetric test of EP composite materials: Thermogravimetric analysis was tested using an HCT-2 microcomputer differential thermal balance. The composite material was cut into fine particles with a blade, 5-10 mg was weighed and placed in a crucible, and the temperature was raised in a nitrogen atmosphere at a rate of 20°C / min in the range of 25-700°C. The test results are shown in the figure. Figure 2 shown.

[0025] Depend on Figure 2 It can be seen that the initial decomposition temperature of the epoxy resin composite material with the addition of AAFR is slightly reduced, but the maximum weight loss rate temperature does not change much. When the temperature reaches 700°C, the residual carbon rate of the epoxy resin before adding the flame retardant is only 9.49%. With the addition of AAFR, the residual carbon rate gradually increases. When the addition amount of AAFR is 15%, the residual carbon rate can reach 24.33%.

[0026] Cone calorimetry testing of flame retardant epoxy materials. Figure 3 As shown in the figure, EP rapidly releases heat after ignition, reaching a peak of 1214.68 KW / m at 154s. 2 After AAFR is added to EP, the peak appears lower than that of pure EP and the time is earlier. This is mainly because the addition of AAFR prompts the EP composite material to form a stronger carbon layer during the combustion process, which continuously insulates heat.

[0027] like Figure 4 As shown in Figure 2, the total heat released by EP is as high as 152.34MJ / m 2 The total heat release of EP-15 is 134.70 MJ / m 2 The total heat release of EP-20 is 118.16MJ / m 2 , which shows that AAFR can play a flame retardant role to a certain extent.

[0028] like Figure 5As shown in the figure, the peak value of EP-20 is very low in the whole process, with the maximum peak value of 0.063%, while the maximum peak value of pure EP is 0.26%, which shows that the addition of AAFR greatly improves the thickness and hardness of the carbon layer, and can slow down the generation of CO gas during the combustion of EP composite materials.

[0029] The CO2 release rate is Figure 6 As shown in the figure, the maximum peak of pure EP is 17.52%, and the maximum peak of EP-20 is 4.58%. The addition of AAFR can reduce the release rate of CO2 and delay combustion to a certain extent.

[0030] The smoke generation rate and total smoke production of EP composite materials are shown in Figure 2. Figure 7 and 8 As shown, the peak smoke rate of pure EP (0.3m 2 / s) is the highest among all the tested samples, and the peak value of EP-20% is 0.24m 2 / s, the addition of AAFR reduces the peak smoke generation rate. From the total smoke generation chart, it can be seen that the total amount of smoke generated during EP combustion is 5304.66m 2 , the smoke production of EP-20% is 3925.35m 2 , significantly reducing smoke generation.

[0031] The carbon residue of pure EP and EP composite materials after cone calorimetry test is shown in Figure 2. Fig. 9 As shown, after burning, only a small amount of residual carbon remains in the pure EP material, and the carbon layer has poor density and loose structure, resulting in poor flame retardancy of the EP material.

[0032] The EP composite material with AAFR added has an increased amount of residual carbon, fewer cracks in the carbon layer, and is flat and dense. When continuously heated, it can effectively isolate heat and air.

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a bioflame retardant based on alginic acid, characterized in that: The following steps are involved: (1) dissolving alginic acid in water, and adding an aqueous solution of tetrabutylammonium hydroxide dropwise under stirring until the pH value reaches 7-9, and freeze-drying to obtain alginate-TBA; (2) Dissolve 0.5-1.5 g of alginate-TBA in 25-35 mL of solution C, which is N,N-dimethylformamide containing 2 wt % tetrabutylammonium fluoride; then add 1.5-2.5 g of hexachlorotriphosphazene and 3.5-4.5 mL of 1,8-diazabicyclo[5.4.0]undec-7-ene. After the reaction is completed at 50-70°C, cool to below 5°C, and finally add 10-20 mL of isopropanol hydrochloride. After stirring for 10-20 minutes, vacuum filter and wash to obtain a bioflame retardant based on alginate.

2. The preparation method according to claim 1, characterized in that: In step (1), the preparation method of alginic acid is as follows: 7-8 g of alginate is dissolved in 450-550 mL of distilled water, and then 3-4 g of ascorbic acid and 4.5-5.5 mL of pyridine are added to obtain solution A, solution A is placed in a water bath, and nitrogen is passed through, heated to 75-85° C., and then hydrogen peroxide is added to perform a degradation reaction. After the reaction is completed, solution B is added, and stirred at 3-5° C. for 8-15 hours, vacuum filtered, washed, and dried to obtain alginic acid; solution B is prepared from 550-650 mL of ethanol, 35-40 mL of concentrated hydrochloric acid, and 90-110 mL of water.

3. The preparation method according to claim 1, characterized in that: In step (2), the concentration of isopropanol hydrochloride is 5M.

4. The preparation method according to claim 1, characterized in that: In step (2), the reaction is carried out at 60°C for 8-15 hours. After the reaction is completed, the mixture is cooled to 0°C.

5. The preparation method according to claim 1, characterized in that: In step (2), after vacuum filtration, the product is washed multiple times with ethanol and acetonitrile.

6. The preparation method according to claim 1, characterized in that: In step (1), the concentration of the aqueous solution of tetrabutylammonium hydroxide is 4% w / v.

7. The preparation method according to claim 2, characterized in that: Add 45-55 mL of 30% hydrogen peroxide to carry out degradation reaction, and the degradation reaction time is 1-3 hours.

8. A bioflame retardant based on alginate, prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the alginate-based bioflame retardant according to claim 8 in the preparation of flame-retardant epoxy resin.

Images