Flame-retardant PLA composite material with high thermal stability and preparation method thereof

Abstract

The invention provides a flame-retardant PLA composite material with high thermal stability and a preparation method thereof, and relates to the technical field of flame-retardant materials. A preparation method of a flame-retardant PLA composite material with high thermal stability comprises the following steps: S1, adding a magnesium phytate solution into a chitosan solution, adjusting the pH value, stirring, centrifuging, washing and drying to obtain a mixture A; s2, uniformly mixing the mixture A, ammonium polyphosphate and a triazine derivative CFA to obtain a mixture B; s3, stirring and banburying PLA at the temperature of T1 and the rotating speed of R1, then adding the mixture B, stirring and banburying at the temperature of T2 and the rotating speed of R2 to obtain a mixture C, and carrying out hot press molding on the mixture C at the temperature of T3 to obtain the flame-retardant PLA composite material with high thermal stability. The flame-retardant PLA composite material with high thermal stability provided by the invention has excellent thermal stability and flame retardance.

Description

Technical Field

[0001] The invention relates to the technical field of flame retardant materials, and in particular to a high thermal stability flame retardant PLA composite material and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA) is a natural polyester that can be extracted from renewable resources such as corn, potatoes, and wheat straw in nature through direct polycondensation and two-step methods. In addition, polylactic acid can also be directly decomposed into water and carbon dioxide by microorganisms, greatly alleviating the problems of subsequent recycling and environmental pollution of materials. In addition to its environmentally friendly characteristics, polylactic acid has good mechanical properties and processing properties, involving many fields such as food packaging, building materials, medical devices, and biopharmaceuticals.

[0003] In the exploration of polylactic acid modification, due to its high flammability, it is difficult to get involved in the fields of electronics, aerospace, etc. Therefore, polylactic acid is used as the matrix of the modified material, and a reinforcing phase with flame retardant properties is added to it to make it flame retardant and improve its thermal stability, so as to expand the application market of polylactic acid modified materials. In the environment of green and sustainable development, it has good development potential. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a high thermal stability flame retardant PLA composite material and a preparation method thereof.

[0005] The present invention provides a method for preparing a high thermal stability flame-retardant PLA composite material, comprising the following steps:

[0006] S1, adding magnesium phytate solution to chitosan solution, adjusting pH, stirring, centrifuging, washing, and drying to obtain mixture A;

[0007] S2, mixing mixture A, ammonium polyphosphate and triazine derivative CFA uniformly to obtain mixture B;

[0008] S3, stirring and kneading PLA at T1 temperature and R1 speed, then adding mixture B and stirring and kneading at T2 temperature and R2 speed to obtain mixture C, and hot-pressing mixture C at T3 temperature to obtain a high thermal stability flame-retardant PLA composite material.

[0009] Preferably, in S1, the preparation of the magnesium phytate solution comprises: adding a phytic acid solution to a magnesium salt solution, heating under reflux and stirring, and dripping an alkaline solution to adjust the pH to obtain a magnesium phytate solution.

[0010] More preferably, the magnesium salt is selected from one or more of magnesium carbonate, magnesium hydroxide and magnesium chloride.

[0011] More preferably, the mass fraction of the phytic acid solution is 50-90wt%.

[0012] More preferably, the molar ratio of the magnesium salt to the phytic acid is (3-4):1.

[0013] More preferably, the heating temperature is 70-90°C.

[0014] More preferably, the alkaline solution is NaOH solution.

[0015] Preferably, in S1, the preparation of the chitosan solution comprises: stirring chitosan and water evenly, and adjusting the pH to acidic to obtain the chitosan solution.

[0016] More preferably, the mass ratio of chitosan to water is 1:(10-20).

[0017] More preferably, the acidic pH is 2-3.

[0018] More preferably, the acid solution for adjusting pH is selected from one or more of acetic acid, phosphoric acid and hydrochloric acid.

[0019] Preferably, in S1, the molar ratio of magnesium ions in the alkaline magnesium phytate solution to chitosan in the acidic chitosan solution is (3-4):1.

[0020] Preferably, in said S1, the pH is 4-5.

[0021] Preferably, in said S2, the mass ratio of the mixture A, ammonium polyphosphate and the triazine derivative CFA is 1:2:(1-6).

[0022] Preferably, in S3, the mass of the mixture B is 15%-25% of the mass of the high thermal stability flame-retardant PLA composite material.

[0023] Preferably, in the S3, the temperature T1 is 160-175°C; the speed R1 is 500-800r / min.

[0024] Preferably, in said S3, T2 temperature is 175-185°C; R2 speed is 1200-1600r / min.

[0025] Preferably, in said S3, the temperature of T3 is 175-185°C.

[0026] Preferably, in S3, the hot pressing pressure is 5-20 MPa, and the hot pressing time is 3-10 min.

[0027] Preferably, in the above S3, the raw materials are dried before the banburying.

[0028] The present invention also provides a high thermal stability flame-retardant PLA composite material prepared by the above preparation method.

[0029] Application of the high thermal stability flame retardant PLA composite material or the high thermal stability flame retardant PLA composite material prepared by the above preparation method in the fields of electronics and aerospace.

[0030] The beneficial effects of the present invention are:

[0031] The present invention uses renewable resources such as phytic acid, chitosan, and metal magnesium ions as main raw materials, and successfully prepares a mixture A containing three elements of C, N, and P through a complex reaction. The mixture A, ammonium polyphosphate, and a triazine derivative CFA are mixed and then subjected to a banburying reaction with PLA to prepare a flame-retardant PLA composite material with high thermal stability.

[0032] There are a large number of phosphate groups containing hydroxyl groups in phytic acid, which can ionize a large number of anions OH in an alkaline solution environment. - , can combine with magnesium ions in magnesium salts to form magnesium phytate, making the flame retardant have high thermal stability and durability; some Mg 2+ The metal oxide MgO formed after combustion further enriches the carbon layer structure, enhances the strength of the carbon layer, stably supports the carbon layer and prevents it from collapsing, which adds another guarantee to the flame retardant efficiency of PLA modified materials. The phosphorus oxygen (P=O, PO) group structure in the molecular structure of mixture A undergoes pyrolysis and phosphorylation reaction, which can promote the formation of the carbon layer, so that it can better and faster play a barrier effect and block the transfer of heat and combustible gases; at the same time, the NH3 group in the molecular structure will also produce some inert gas when heated, which will also delay the pyrolysis reaction to a certain extent. In addition, the chair structure in mixture A will also jointly increase the residual amount of flame retardant at 800℃. The addition of mixture A improves the carbonization and thermal stability of flame-retardant PLA composite materials.

[0033] The triazine ring structure of the triazine derivative CFA in the flame retardant contains a large amount of N element, which will release non-combustible gases such as N2 and NO2 during the thermal degradation process, which can not only make the carbon layer expand and form fine pores in the carbon layer, but also show a good shielding effect in the condensed phase. The triazine ring structure improves the strength of the carbon layer, so that the carbon layer does not collapse, effectively preventing the erosion of internal materials by heat or combustible gases; it can also dilute the concentration of combustible gases in the external environment, and the internal and external combination can improve the flame retardant properties of flame-retardant PLA composites. The addition of triazine derivative CFA has the effect of improving the flame retardancy of flame-retardant PLA composites in both the gas phase and the condensed phase.

[0034] The invention fully mixes a mixture A, ammonium polyphosphate and a triazine derivative CFA with a PLA matrix through methods such as melt blending and hot pressing molding to obtain a high thermal stability flame-retardant PLA composite material, successfully improving the heat resistance and fire resistance of the PLA material. In addition, due to the synergistic effect of the mixture A, ammonium polyphosphate and the triazine derivative CFA, the prepared high thermal stability flame-retardant PLA composite material forms a high-strength, high-quality carbon skeleton, and has excellent thermal stability and flame retardant properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a digital photo of the carbon residue of the high thermal stability flame-retardant PLA composite material prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is described in detail through specific embodiments.

[0037] Unless otherwise specified, the materials, reagents, etc. used in the following examples and comparative examples can be obtained from commercial sources.

[0038] Example 1

[0039] A method for preparing a high thermal stability flame-retardant PLA composite material comprises the following steps:

[0040] S1. Dissolve 0.06 mol MgCl2·6H2O in water to obtain a magnesium salt solution, add 0.02 mol 70% phytic acid solution to the magnesium salt solution, uniformly heat to 80°C, reflux and stir at this temperature for 4 hours, and after the solution is cooled to room temperature, drop 5 mol / l NaOH solution thereto until the pH is 4 to obtain a magnesium phytate solution; dissolve 0.02 mol chitosan in water, drop an acid solution to adjust the pH to 2, the acid solution is a mixture of acetic acid and phosphoric acid in a volume ratio of 8:1 to obtain a chitosan solution; slowly pour the magnesium phytate solution into the chitosan solution, adjust the pH to 4, stir continuously until a white flocculent precipitate is produced, then centrifuge at a speed of 4000 r / min, retain the precipitate and wash it three times with distilled water, put it in an oven at 80°C and vacuum dry it for 48 hours to obtain a mixture A;

[0041] S2, 4.43 g of mixture A, 8.87 g of ammonium polyphosphate, and 6.67 g of triazine derivative CFA were mixed to obtain mixture B;

[0042] S3. 80 g of PLA was stirred and kneaded at 175° C. and 600 r / min for 5 min, and then mixture B was added and stirred and kneaded at 175° C. and 1400 r / min for 15 min to obtain mixture C. Mixture C was hot-pressed at 180° C. and 10 MPa for 5 min to obtain a flame-retardant PLA composite material with high thermal stability.

[0043] Example 2

[0044] A method for preparing a high thermal stability flame-retardant PLA composite material comprises the following steps:

[0045] S1. Dissolve 0.06 mol MgCl2·6H2O in water to obtain a magnesium salt solution, add 0.02 mol 70% phytic acid solution to the magnesium salt solution, uniformly heat to 80°C, reflux and stir at this temperature for 4 hours, and after the solution is cooled to room temperature, drop 5 mol / l NaOH solution thereto until the pH is 4 to obtain a magnesium phytate solution; dissolve 0.02 mol chitosan in water, drop an acid solution to adjust the pH to 2, the acid solution is a mixture of acetic acid and phosphoric acid in a volume ratio of 8:1 to obtain a chitosan solution; slowly pour the magnesium phytate solution into the chitosan solution, adjust the pH to 4, stir continuously until a white flocculent precipitate is produced, then centrifuge at a speed of 4000 r / min, retain the precipitate and wash it three times with distilled water, put it in an oven at 80°C and vacuum dry it for 48 hours to obtain a mixture A;

[0046] S2, 3.33 g of mixture A, 6.67 g of ammonium polyphosphate, and 10 g of triazine derivative CFA were mixed to obtain mixture B;

[0047] S3. 80 g of PLA was stirred and kneaded at 175° C. and 600 r / min for 5 min, and then mixture B was added and stirred and kneaded at 175° C. and 1400 r / min for 15 min to obtain mixture C. Mixture C was hot-pressed at 180° C. and 10 MPa for 5 min to obtain a flame-retardant PLA composite material with high thermal stability.

[0048] Example 3

[0049] A method for preparing a high thermal stability flame-retardant PLA composite material comprises the following steps:

[0050] S1. Dissolve 0.06 mol MgCl2·6H2O in water to obtain a magnesium salt solution, add 0.02 mol 70% phytic acid solution to the magnesium salt solution, uniformly heat to 80°C, reflux and stir at this temperature for 4 hours, and after the solution is cooled to room temperature, drop 5 mol / l NaOH solution thereto until the pH is 4 to obtain a magnesium phytate solution; dissolve 0.02 mol chitosan in water, drop an acid solution to adjust the pH to 2, the acid solution is a hydrochloric acid solution, to obtain a chitosan solution; slowly pour the magnesium phytate solution into the chitosan solution, adjust the pH to 4, stir continuously until a white flocculent precipitate is produced, then centrifuge at a speed of 4000 r / min, retain the precipitate and wash it three times with distilled water, put it in a 90°C oven and vacuum dry it for 36 hours to obtain a mixture A;

[0051] S2, 2.22 g of mixture A, 4.45 g of ammonium polyphosphate, and 13.3 g of triazine derivative CFA were mixed to obtain mixture B;

[0052] S3. 80 g of PLA was stirred and kneaded at 175° C. and 600 r / min for 4 min, and then mixture B was added and stirred and kneaded at 180° C. and 1400 r / min for 20 min to obtain mixture C. Mixture C was hot-pressed at 180° C. and 10 MPa for 5 min to obtain a flame-retardant PLA composite material with high thermal stability.

[0053] Comparative Example 1

[0054] A method for preparing a PLA composite material comprises the following steps:

[0055] S1. Dissolve 0.06 mol MgCl2·6H2O in water to obtain a magnesium salt solution, add 0.02 mol 70% phytic acid solution to the magnesium salt solution, uniformly heat to 80°C, reflux and stir at this temperature for 4 hours, and after the solution is cooled to room temperature, drop 5 mol / l NaOH solution thereto until the pH is 4 to obtain a magnesium phytate solution; dissolve 0.02 mol chitosan in water, drop an acid solution to adjust the pH to 2, the acid solution is a mixture of acetic acid and phosphoric acid in a volume ratio of 8:1 to obtain a chitosan solution; slowly pour the magnesium phytate solution into the chitosan solution, adjust the pH to 4, stir continuously until a white flocculent precipitate is produced, then centrifuge at a speed of 4000 r / min, retain the precipitate and wash it three times with distilled water, put it in an oven at 80°C and vacuum dry it for 48 hours to obtain a mixture A;

[0056] S2. 80 g of PLA was stirred and kneaded at 175° C. and 600 r / min for 5 min, and then 20 g of mixture A was added and stirred and kneaded at 175° C. and 1400 r / min for 15 min, and then hot-pressed at 180° C. and 5 MPa for 5 min to obtain a PLA composite material.

[0057] Comparative Example 2

[0058] A method for preparing a PLA composite material comprises the following steps:

[0059] 80 g of PLA was stirred and kneaded at 175° C. and 600 r / min for 5 min, and then 20 g of ammonium polyphosphate was added and stirred and kneaded at 175° C. and 1400 r / min for 15 min, and then hot-pressed at 180° C. and 5 MPa for 5 min to obtain a PLA composite material.

[0060] Comparative Example 3

[0061] A method for preparing a PLA composite material comprises the following steps:

[0062] 80g PLA was stirred and kneaded at 175°C and 600r / min for 5min, then 20g triazine derivative CFA was added and stirred and kneaded at 175°C and 1400r / min for 15min, and then hot pressed at 180°C and 5MPa for 5min to obtain a PLA composite material.

[0063] Comparative Example 4

[0064] A method for preparing a PLA composite material comprises the following steps:

[0065] S1. Dissolve 0.06 mol MgCl2·6H2O in water to obtain a magnesium salt solution, add 0.02 mol 70% phytic acid solution to the magnesium salt solution, uniformly heat to 80°C, reflux and stir at this temperature for 4 hours, and after the solution is cooled to room temperature, drop 5 mol / l NaOH solution thereto until the pH is 4 to obtain a magnesium phytate solution; dissolve 0.02 mol chitosan in water, drop an acid solution to adjust the pH to 2, the acid solution is a mixture of acetic acid and phosphoric acid in a volume ratio of 8:1 to obtain a chitosan solution; slowly pour the magnesium phytate solution into the chitosan solution, adjust the pH to 4, stir continuously until a white flocculent precipitate is produced, then centrifuge at a speed of 4000 r / min, retain the precipitate and wash it three times with distilled water, put it in an oven at 80°C and vacuum dry it for 48 hours to obtain a mixture A;

[0066] S2, 6.67 g of mixture A and 13.33 g of ammonium polyphosphate were mixed to obtain mixture B;

[0067] S3. 80 g of PLA was stirred and kneaded at 175° C. and 600 r / min for 5 min, and then mixture B was added and stirred and kneaded at 175° C. and 1400 r / min for 15 min to obtain mixture C. Mixture C was hot-pressed at 180° C. and 10 MPa for 5 min to obtain a PLA composite material.

[0068] The PLA composite material obtained above was subjected to limiting oxygen index and UL-94 vertical combustion tests, and was subjected to thermogravimetric analysis in a nitrogen atmosphere to record the initial decomposition temperature, maximum decomposition temperature and 800°C residue. The test results are shown in Table 1.

[0069] Table 1

[0070]

[0071] From the data in Table 1, the high thermal stability flame retardant PLA composite material prepared by Example 1-2 has a higher limiting oxygen index, and the flame retardant grade reaches V-0, without dripping phenomenon, indicating that the high thermal stability flame retardant PLA composite material prepared by the present invention has excellent flame retardant properties. As can be seen from Example 3, the content of triazine derivative CFA increases, so that the decomposition temperature decreases, but the residual amount decreases significantly. From the data of Comparative Examples 1-3 and the Examples, it can be seen that the flame retardant properties of the PLA composite material prepared by adding only the mixture A, ammonium polyphosphate or triazine derivative CFA prepared by the present invention are significantly reduced, and there is still a dripping phenomenon, which shows that the addition of a single-component flame retardant is still not ideal for improving the flame retardant properties of PLA. From the data of Comparative Example 4 and the Examples, it can be seen that the PLA composite material prepared without adding triazine derivative CFA has an increased limiting oxygen index, but its decomposition temperature also increases, and the residual amount decreases at the same time, indicating that the flame retardant system in the present invention is more excellent in flame retardant properties than the PLA composite material prepared by Comparative Example 4, indicating that the appropriate addition of CFA has an improving effect on the thermal stability of PLA modified materials.

[0072] The flame retardant raw materials of the present invention work synergistically to help improve the flame retardancy and stability of the material.

[0073] The PLA composite material obtained above was subjected to cone calorimetry test to simulate the external environment of fire, and the flame retardant properties of the PLA composite material were analyzed. The test results are shown in Table 2.

[0074] Table 2

[0075]

[0076]

[0077] It can be seen from the data in Table 2 that the high thermal stability flame-retardant PLA composite material prepared by the present invention has a lower peak value of heat release rate, less time for the maximum heat release rate, a lower total heat release, a lower average effective heat of combustion and a higher residual carbon rate, indicating that the high thermal stability flame-retardant PLA composite material prepared by the present invention can form a dense, high-strength carbon layer, blocking the invasion of heat and combustible gas, and has excellent flame retardant properties. It can be seen from the data of Comparative Example 1 and the embodiment that the P content in the PLA composite material to which mixture A is added alone is less, and the ability of PLA to catalyze carbonization is not obvious, and it is impossible to effectively shield the invasion of heat and combustion media to the internal materials, and the flame retardant performance is poor. It can be seen from the data of Comparative Example 2 and the embodiment that the PLA composite material to which ammonium polyphosphate is added alone has a good improvement effect, but it takes a long time to reach the maximum heat release rate and the total heat release is high. It can be seen from the data of Comparative Example 3 and the embodiment that the PLA composite material to which the triazine derivative CFA is added alone has a larger peak value of heat release rate, indicating that the flame retardant improvement effect of adding the triazine derivative CFA alone for the PLA substrate is not ideal. From the data of Comparative Example 4 and the embodiment, it can be seen that the PLA composite material prepared by the synergistic effect of mixture A and ammonium polyphosphate has a good improvement effect. The two can promote each other to form phosphorylation into carbon, forming a barrier to block the transfer of heat and combustible gas, so as to achieve the effect of delaying or preventing the combustion reaction, and effectively improve the flame retardancy of PLA in the condensed phase. In the high thermal stability flame-retardant PLA composite material of the present invention, the mixture A, ammonium polyphosphate, and triazine derivative CFA have a synergistic effect, and there is an overflow of non-combustible gas, which leads to a reduction in the residual carbon rate. The non-combustible gas produced by decomposition can effectively hinder the erosion of internal materials by heat or combustible gas, and can also dilute the concentration of combustible gas in the external environment, and the internal and external are combined to improve the flame retardant properties of PLA modified materials; the high thermal stability flame-retardant PLA composite material obtained by the synergistic effect of the three has a flame retardant improvement effect in both the gas phase and the condensed phase.

[0078] Figure 1 This is a digital photograph of the residual carbon of the high thermal stability flame-retardant PLA composite material prepared in Example 2 of the present invention. It can be seen that the carbon surface is carbon black, and the surface is more continuous, and the degree of expansion is greatly improved, showing an excellent expansion effect; the high thermal stability flame-retardant PLA composite material releases a large amount of non-combustible gas during the combustion process, but these gases are sufficient to support the expansion of the carbon layer and do not destroy the carbon layer, which is conducive to the formation of fine pores in the carbon layer, indicating that the synergistic effect of the mixture A, ammonium polyphosphate, and triazine derivative CFA can release non-combustible gas in the gas phase to dilute the concentration of combustible gas; at the same time, in the condensed phase, it can also show a better maze effect to isolate the transfer of heat and combustible gas.

[0079] In summary, the high thermal stability flame retardant PLA composite material provided by the present invention has excellent thermal stability and flame retardant properties.

[0080] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a high thermal stability flame-retardant PLA composite material, characterized in that: The following steps are involved: S1, adding magnesium phytate solution to chitosan solution, adjusting pH, stirring, centrifuging, washing, and drying to obtain mixture A; S2, mixing mixture A, ammonium polyphosphate and triazine derivative CFA uniformly to obtain mixture B; S3, stirring and kneading PLA at T1 temperature and R1 speed, then adding mixture B and stirring and kneading at T2 temperature and R2 speed to obtain mixture C, and hot-pressing mixture C at T3 temperature to obtain a high thermal stability flame-retardant PLA composite material.

2. The preparation method according to claim 1, characterized in that: In S1, the preparation of the magnesium phytate solution includes: adding a phytic acid solution to a magnesium salt solution, heating under reflux and stirring, and dripping an alkaline solution to adjust the pH to obtain a magnesium phytate solution.

3. The preparation method according to claim 1, characterized in that: In the above S1, the preparation of chitosan solution includes: stirring chitosan and water evenly, adjusting the pH to acidic, and obtaining chitosan solution.

4. The preparation method according to claim 1, characterized in that: In the S1, the molar ratio of magnesium ions in the alkaline magnesium phytate solution to chitosan in the acidic chitosan solution is (3-4):

1.

5. The preparation method according to claim 1, characterized in that: In the S2, the mass ratio of the mixture A, ammonium polyphosphate and the triazine derivative CFA is 1:2:(1-6).

6. The preparation method according to claim 1, characterized in that: In the S3, the temperature of T1 is 160-175°C; the speed of R1 is 500-800r / min.

7. The preparation method according to claim 1, characterized in that: In the S3, the temperature of T2 is 175-185°C; the speed of R2 is 1200-1600r / min.

8. The preparation method according to claim 1, characterized in that: In the above-mentioned S3, the pressure of hot pressing is 5-20MPa, and the hot pressing time is 3-10min.

9. A high thermal stability flame retardant PLA composite material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 8.

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