Environment-friendly flame retardant melamine phosphite as well as preparation method and application thereof

Abstract

The invention relates to an environment-friendly flame retardant melamine phosphite as well as a preparation method and application thereof, belongs to the technical field of flame retardants, and aims to overcome the defects and deficiencies in the prior art, melamine, phosphorous acid (and salts thereof) and a modifier are used as raw materials to prepare the melamine phosphite. The preparation method disclosed by the invention has the beneficial effects that (1) the preparation method is simple to operate, low in production cost and easy for batch production; (2) the flame retardant has the advantages of flame retardance when an acid source, a gas phase and a condensation phase are in the same time, corrosion resistance, low smoke, low toxicity, difficulty in moisture absorption, high temperature resistance and the like; (3) the flame retardant can be well dispersed in a matrix, has good flame retardant property and is not easy to separate out; and (4) the melamine phosphites with different particle sizes are obtained through screening, so that the requirements of different polymer products on the particle sizes are met.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardants, and in particular relates to a method for preparing halogen-free environmentally friendly flame retardant melamine phosphite. Background Art

[0002] Polymer materials, due to their many excellent properties, are playing an increasingly important role in daily life and production. However, fires caused by their flammability and low ignition point have brought heavy losses to people, so the research on polymer flame retardant materials is very necessary. At present, in terms of global production and usage, flame retardants have become plastic additives second only to plasticizers. Due to the expansion of the application field of flame retardant materials and the needs of human living environment, the synthesis and flame retardant technology of new flame retardants with multiple flame retardant effects (gas phase, condensed phase flame retardant) and low smoke and low toxicity have become two major topics of concern for polymer flame retardant materials today.

[0003] When polyurethane materials burn, the thick smoke can suffocate people and seriously pollute the environment, but studies have found that when melamine is used as a flame retardant and smoke suppressant for polyurethane, its smoke suppression effect is very good. Phosphite is a new domestic inorganic phosphorus flame retardant. It has good dispersibility and good affinity with organic matrices. It helps to exert the excellent properties of organic materials and avoid local stress causing material damage and failure. Compared with the flame retardant aluminum hypophosphite, it has the advantages of stability, non-flammability, high expansion rate, and better flame retardant effect. It has a wide market for single or compound use as a flame retardant.

[0004] Melamine is used as an additive flame retardant in polyurethane foam. If a good flame retardant effect is to be achieved, a large amount of addition is often required. A large amount of addition is bound to affect other properties of the polymer. Therefore, melamine is usually used in combination with other flame retardants. Liu Xinmin et al. used melamine for flame retardant polyurethane rigid foam plastics in the development of composite board polyurethane rigid foam. It was found that the amount of melamine reached 50wt% and still did not meet the flame retardant requirements, but affected the compressive strength of the material. However, when melamine was used in combination with flame retardants such as dimethyl methylphosphonate and trichloroethyl phosphate, the amount of 15% could meet the flame retardant requirements, indicating that there is a synergistic effect between melamine and other flame retardants. In addition, the thermal decomposition temperature of melamine is relatively low compared to the resin processing temperature, which is easy to cause the decomposition of melamine during the processing process, and the flame retardant effect is also reduced. Phosphite mainly plays a flame retardant role in the acid source and condensed phase, and the amount of gas decomposed is small, and the flame retardant effect in the gas phase is limited. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies in the prior art, the present invention uses melamine, phosphorous acid (and its salts) and a modifier as raw materials to prepare melamine phosphite.

[0006] The preparation method of environmentally friendly flame retardant melamine phosphite specifically comprises the following steps:

[0007] (1) Synthesis of melamine phosphite:

[0008] a. Dissolve phosphorous acid or its salt in deionized water, turn on heating and stirring to obtain a concentration of 30-50wt% phosphorous acid or its salt solution;

[0009] The phosphorous acid or its salt in step a is phosphorous acid (H3PO3) and its various phosphites, such as sodium phosphite (Na2HPO3) and ammonium phosphite ((NH4)2HPO3), preferably the concentration of phosphorous acid and its salt solution is 30% to 50%; the heating temperature is set at 70-80°C, and the stirring speed is 12-17r / min.

[0010] b. Disperse melamine in aqueous solution at a dispersion ratio of 30 to 50 wt %, and then add 30-50 parts by weight of melamine aqueous solution to the phosphorous acid or its salt solution in step a in batches. Generally, the weight of each batch is 10-17 g. Adding in batches can prevent agglomeration and ensure complete reaction. Continue to add materials after each transparent reaction and continue stirring the reaction under heating conditions;

[0011] In step b, melamine is dispersed in aqueous solution to avoid agglomeration of melamine, and the heating temperature is kept consistent with that in step a.

[0012] c. After the reaction is about 1.5h, add 1-5 parts by weight of the modifier and continue stirring until the reaction is transparent;

[0013] The modifier includes, but is not limited to, mineral modifiers such as stearic acid, silane coupling agent, titanate, Tween-80, etc., and the concentration of the modifier is 1wt%-5wt%. The total reaction time is 1.5h-3h, preferably 3h, and the modifier is added in the middle of the reaction.

[0014] d. After the reaction is completed, the obtained solution is completely cooled, filtered, and washed until the pH value is neutral to obtain a white precipitate;

[0015] e. Place the white precipitate in an oven and bake it to dry to obtain melamine phosphite;

[0016] The baking temperature is 90°C-240°C, preferably 110°C, and the drying time is 2h-8h, preferably 5h.

[0017] f. Controlling the content of crystal water in melamine phosphite through baking process;

[0018] Step f: The baking temperature is 150° C.-240° C. and the baking time is 3 h-8 h. The temperature and time are adjusted according to different requirements for the crystal water content.

[0019] g. Grinding and sieving the product to obtain melamine phosphite of different particle sizes.

[0020] A melamine phosphite flame retardant material prepared according to the above preparation method.

[0021] The present invention also provides an application of melamine phosphite: the efficacy of melamine phosphite is verified, and a thermal weight loss experiment, a combustion performance test, a glow wire test, and the influence of melamine phosphite on the mechanical properties of the product are carried out. The application of melamine phosphite in polyurethane and polypropylene is explored.

[0022] The invention innovatively synthesizes melamine phosphite, which plays a flame retardant role in the acid source, gas phase and condensed phase at the same time, and is used to improve the flame retardant and thermal stability of melamine in polyurethane and the like.

[0023] In addition, the present invention also provides the use of melamine phosphite added to polymer resins such as polypropylene, polystyrene, nylon 6 / 66, and epoxy resin.

[0024] Compared with the prior art, the present invention has the following advantages and effects:

[0025] (1) The present invention adopts a one-step method to prepare melamine phosphite, and the preparation method is simple to operate, has low production cost, and is easy to mass produce;

[0026] (2) The melamine phosphite prepared by the present invention has the advantages of having an acid source, a gas phase and a condensed phase, being flame retardant at the same time, being corrosion resistant, having low smoke, being low in toxicity, not being easy to absorb moisture and being resistant to high temperatures;

[0027] (3) The present invention adds a modifier during the preparation process to improve the dispersion of crystals. As a polymer flame retardant additive, it can be well dispersed in the matrix, has good flame retardant properties, and is not easy to precipitate;

[0028] (4) The melamine phosphite material prepared by the present invention is novel and enriches the polymer flame retardant system;

[0029] (5) Melamine phosphite with different particle sizes is obtained by screening to meet the particle size requirements of different polymer products. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the thermogravimetric test diagram of melamine phosphite;

[0031] Figure 2 SEM test images (a1 and a2) and photos (a3) ​​of the specimens added to the PP material with PAPP+MPP replaced by melamine phosphite after combustion;

[0032] Figure 3 is a particle size distribution diagram of melamine phosphite; DETAILED DESCRIPTION

[0033] Example 1

[0034] Weigh 70g of phosphorous acid and add it to a 1L round-bottom flask containing 200ml of deionized water. Place the round-bottom flask in an oil bath and turn on heating and stirring. The temperature is controlled at 80°C. Weigh 70g of melamine, add the melamine to 100ml of deionized water to disperse it, and then add the melamine dispersion to the phosphorous acid mixed solution in batches. Continue to add it after the solution becomes transparent each time. Keep the mixed solution temperature at 80°C and continue stirring for 0.5h. Add 3g of silane coupling agent and continue stirring for 1h. The transparent time gradually becomes longer, and the suspension gradually becomes viscous. Replenish water and heat to 100°C. The reaction is transparent and ends. After the mixed solution is completely cooled, filter and wash the precipitate repeatedly until the pH is neutral to obtain a white precipitate. Place the precipitate in an oven and bake it at 90°C for 8h. Adjust the baking temperature to 150°C and bake it for 2h to obtain melamine phosphite with a moisture content of 3%. The melamine phosphite is ground and sieved to obtain a product with a particle size D50 of 3-7 microns.

[0035] As a compound flame retardant, in the halogen-free flame retardant PP (PAPP system), melamine phosphite replaces part of the PAPP+MPP and is added to the PP material, and the flame retardancy reaches UL94 (V0). Comparing the flame retardant performance test before and after compounding, the results are shown in Table 1 below:

[0036]

[0037] Afterflame time (T1+T2 / S): the duration of afterflame;

[0038] LOI: Limiting Oxygen Index. A high index indicates that the material is not easy to burn, and a low index indicates that the material is easy to burn. It is generally believed that an oxygen index <22% is a flammable material, an oxygen index between 22% and 27% is a combustible material, and an oxygen index >27% is a flame retardant material.

[0039] UL94 plastic flame retardant grade V0: After two 10-second burning tests on the sample, the flame goes out within 30 seconds. No burning objects can fall.

[0040] From the test data in Table 1, it can be seen that when PAPP+MPP, which replaces part of the melamine phosphite, is added to the PP material, the limiting oxygen index increases from 28% to 29%, the flammability of the material decreases, the horizontal afterflame burning time increases by 1 second, and the flame retardant grade UL94 reaches V0 level.

[0041] Figure 1 The thermogravimetric test diagram of the melamine phosphite of Example 1 is shown. From the diagram, it can be seen that it starts to decompose at 260°C and decomposes in large quantities in the range of 500°C, producing phosphates and flame-retardant ammonia substances and their gases.

[0042] Figure 2 The SEM test images (a1 and a2) and the photos (a3) ​​after burning of the sample strips of the melamine phosphite replacement part of Example 1 added to the PP material are shown. According to the SEM of the residue after burning of the sample strips, during the combustion process, the flame retardant forms a porous protective layer in the condensed phase and the residual carbon layer, and at the same time plays a flame retardant role in the gas phase and the condensed phase, preventing oxygen from contacting the combustibles. The flame retardant mechanism analysis is: during combustion, phosphoric acid will further dehydrate to form metaphosphoric acid, and metaphosphoric acid will further polymerize to form polymetaphosphoric acid. In this process, not only the covering layer generated by phosphoric acid has a covering effect, but also because polymetaphosphoric acid is a strong acid and a strong dehydrating agent, it will dehydrate the polymer and carbonize it, change the mode of the polymer combustion process and form a carbon film on its surface to isolate the air, and the ammonia, water vapor and other flame retardant gases produced by decomposition not only dilute the concentration of oxygen and combustibles in the gas phase, but also capture the hydrogen atom free radicals in the flame to inhibit the combustion, thereby exerting a stronger flame retardant effect. This proves that the flame retardant mechanism of the product is mainly the synergistic flame retardancy of acid source, condensed phase and gas phase, and it is an intumescent flame retardant system.

[0043] Figure 3 The following is a data chart showing the effect of adding different amounts of modifier on the particle size of melamine phosphite. The particle size data of melamine phosphite without modifier and melamine phosphite with 1% to 5% modifier added are shown in Figure 2. Figure 3 As shown in the chart, Figure 3 The corresponding samples are shown in Table 2 below:

[0044]

[0045]

[0046] Table 2

[0047] Comparing the D50 and D97 data of the particle size of melamine phosphite with different modifier addition amounts, it can be seen that after adding the modifier, the particle size of melamine phosphite is significantly reduced: D50 is reduced from 6.2μm to 3.6-4.6μm, and the particle size distribution is more uniform: D97 is reduced from 31μm to 15-22μm. Among them, when the modifier content is 3%, the particle size is the smallest and the particle size distribution is the most uniform. The above data show that the modifier can adjust the particle size of melamine phosphite crystals to improve its dispersibility. The smaller the particle size and the more uniform the distribution, the better the dispersibility of the crystal.

[0048] Example 2

[0049] Weigh 50g of phosphorous acid and add it to a 1L round-bottom flask containing 150ml of deionized water. Place the round-bottom flask in an oil bath and turn on heating and stirring. The temperature is controlled at 80°C. Weigh 50g of melamine, add the melamine to 80ml of deionized water to disperse it, and then add the melamine dispersion to the phosphorous acid mixed solution in batches. Continue to add it after the solution becomes transparent each time. Keep the mixed solution temperature at 80°C and continue stirring for 0.5h. Add 3g of sodium stearate and continue stirring for 1h. The transparent time gradually becomes longer, and the suspension gradually becomes viscous. Replenish water and heat to 100°C. The reaction is transparent and ends. After the mixed solution is completely cooled, filter and wash the precipitate repeatedly until the pH is neutral to obtain a white precipitate. Place the precipitate in an oven and bake it at 80°C for 8h. Adjust the baking temperature to 110°C and bake it for 5h to obtain melamine phosphite with a moisture content of 2%. The melamine phosphite is ground and sieved to obtain a product with a particle size D50 of 3-7 microns.

[0050] As a compound flame retardant, in the halogen-free flame retardant PP (PAPP system), it replaces part of PAPP and is added to the PP material, and the flame retardancy reaches UL94 (V0). Comparing the flame retardant performance test before and after compounding, the results are as follows

[0051] As shown in Table 3:

[0052]

[0053] From the test data in Table 3, it can be seen that when PAPP replaced by melamine phosphite is added to the PP material, the limiting oxygen index increases from 28% to 30.4%, the flame retardancy of the material is significantly increased, the vertical and horizontal afterflame burning time increases by 1 second, and the flame retardancy UL94 reaches V0 level.

[0054]

[0055] Table 4

[0056] Table 4 shows the mechanical property test data of melamine phosphite in halogen-free flame retardant PP (PAPP system). From the data in the table, it can be seen that compared with the original flame retardant formula of halogen-free flame retardant PP, after MEOP replaces part of PAPP, the tensile strength, flexural strength and modulus of PP material are slightly reduced, the elongation at break representing the toughness index is increased by 100%, and the notched impact strength is also slightly improved.

Claims

1. A method for preparing an environmentally friendly flame retardant melamine phosphite, characterized in that: The preparation method comprises the following steps: a. Dissolve phosphorous acid or its salt in deionized water, turn on heating and stirring to obtain a concentration of 30-50wt% phosphorous acid or its salt solution; b. The melamine was dispersed in an aqueous solution to obtain a dispersion ratio of 30 to 50 wt% melamine aqueous solution, and then 30-50 parts by weight of the melamine aqueous solution were added in batches to the solution of step a, and stirring and heating were continued; c. Add 1-5 parts by weight of the modifier in the middle of the reaction and continue stirring until the reaction becomes transparent; d. After the reaction is completed, the obtained solution is completely cooled, filtered, and washed until the pH value is neutral to obtain a white precipitate; e. Place the white precipitate in an oven and bake it dry to obtain melamine phosphite.

2. The method for preparing the environmentally friendly flame retardant melamine phosphite according to claim 1, characterized in that: In step a, the phosphorous acid or its salt is phosphorous acid (H3PO3) and its various phosphites, the phosphites are sodium phosphite and ammonium phosphite, and the heating temperature is set at 70-80°C.

3. The method for preparing the environmentally friendly flame retardant melamine phosphite according to claim 1, characterized in that: In step c, the modifier is stearic acid, silane coupling agent, titanate, Tween-80 mineral modifier, and the concentration of the modifier is 1-5wt%.

4. The method for preparing the environmentally friendly flame retardant melamine phosphite according to claim 1, characterized in that: In step e, the baking temperature is 90° C.-240° C., and the drying time is 2 h-8 h, preferably 5 h.

5. The method for preparing the environmentally friendly flame retardant melamine phosphite according to claim 4, characterized in that: The baking temperature in step e is 110° C. and the drying time is 5 h.

6. The method for preparing the environmentally friendly flame retardant melamine phosphite according to claim 1, characterized in that: The preparation method further comprises the following steps: f. Control the content of crystal water in melamine phosphite through baking process, the baking temperature is 150℃-240℃; g. Grinding and sieving to obtain melamine phosphite of different particle sizes.

7. Melamine phosphite prepared by the method for preparing the environmentally friendly flame retardant melamine phosphite according to any one of claims 1 to 6.

8. The use of melamine phosphite prepared by the method for preparing the environmentally friendly flame retardant melamine phosphite according to claim 7, characterized in that: The melamine phosphite is added as a flame retardant to polypropylene, polystyrene, nylon 6 / 66 and epoxy resin polymer resin.

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