Preparation method and application of anhydrous magnesium carbonate based on citrate multistage morphology regulation and control

Abstract

The invention discloses a preparation method and application of anhydrous magnesium carbonate based on citrate multistage morphology regulation and control, and belongs to the technical field of inorganic material preparation and polymer composite materials. Citric acid esters are adopted as a regulating agent, the characteristic that the citric acid esters are gradually hydrolyzed under hydrothermal and alkaline conditions is utilized, carboxyl coordination groups with complexing capacity are released step by step, accurate regulation and control are implemented in the nucleation stage, the growth stage and the crystal face selection exposure stage of the crystal, and the crystal is obtained. Therefore, the anhydrous magnesium carbonate powder which is uniform in particle size, high in crystal form purity, good in dispersity and controllable in morphology is obtained. The anhydrous magnesium carbonate with abundant morphology prepared by the invention is used as a filler to be added into a high polymer material, and by releasing CO2 to dilute combustible gas, forming a compact MgO layer and other flame-retardant mechanisms, excellent flame-retardant performance can be realized under the condition of lower addition amount, so that the anhydrous magnesium carbonate is a novel environment-friendly flame-retardant material with great potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic material preparation and polymer composite materials, and particularly relates to a preparation method of anhydrous magnesium carbonate based on multi-stage morphology regulation of citrate esters and application thereof. BACKGROUND

[0002] Magnesium-based inorganic materials have a broad application prospect in the field of flame-retardant modification of polymer composites due to their abundant resource reserves, environmental friendliness and excellent thermal stability. As a new magnesium-based functional filler, anhydrous magnesium carbonate has good heat insulation and heat absorption capacity and carbonization auxiliary effect, and has great application potential in the field of cable materials such as ethylene-vinyl acetate copolymer (EVA) and flame-retardant polymer materials.

[0003] However, there is no mature commercial product of anhydrous magnesium carbonate at present, and its synthesis is limited by both thermodynamics and process bottlenecks. At normal temperature and pressure, Mg 2+ is easy to combine with OH - or H2O to form magnesium hydroxide or hydrated magnesium carbonate, and the stability is limited. In addition, it is easy to hydrolyze and absorb moisture, so that the preparation process needs to rely on harsh solvent environments such as high temperature and high pressure, which increases energy consumption and equipment cost and hinders the industrialization process.

[0004] The mainstream methods for preparing anhydrous magnesium carbonate at present include high-temperature solid-phase method, CO2 carbonization method and liquid-phase hydrothermal method. The high-temperature solid-phase method needs to be dehydrated at 800-1100℃ and 1-4GPa, which is extremely harsh and has high energy consumption. The CO2 carbonization method can prepare anhydrous magnesium carbonate with special morphology by high-pressure CO2 and catalyst, but the reaction efficiency is low, the product has many impurities and the equipment is complex. The liquid-phase hydrothermal method has mild and controllable conditions, but the reaction time is generally long (6-24 hours), and the morphology regulation mechanism is not clear, so the product consistency is poor.

[0005] In the traditional liquid-phase hydrothermal method, citrate (such as sodium citrate and potassium citrate) is generally used as a crystal face regulator. Since it is completely dissolved at the beginning and directly provides carboxylate ions, it is difficult to precisely control the different growth stages of magnesium carbonate crystals because it quickly forms a complex with magnesium ions. At the same time, the traditional method of directly adding citrate cannot achieve precise stage release during the reaction, and the crystal nucleation and crystal growth process lacks fine control means, resulting in uneven morphology, poor dispersibility and low preparation efficiency of the obtained anhydrous magnesium carbonate crystals.

[0006] Therefore, there is an urgent need for a method for preparing anhydrous magnesium carbonate with high dispersibility and controllable morphology to solve the above problems. SUMMARY

[0007] To solve the above technical problems, the application provides a preparation method of anhydrous magnesium carbonate based on multi-stage morphology regulation of citrate esters and application thereof.

[0008] To achieve the above object, the application provides the following technical scheme.

[0009] The application provides a preparation method of anhydrous magnesium carbonate based on multi-stage morphology regulation of citrate esters, comprising the following steps: dissolving a carbon source, a magnesium source, an alkaline mineralizer and a multi-stage regulation agent of citrate esters in water, and obtaining morphology-controllable anhydrous magnesium carbonate through a hydrothermal reaction.

[0010] Technical principle: the application uses citrate esters as a regulation agent, utilizes the characteristics of gradual hydrolysis of citrate esters under hydrothermal and alkaline conditions, and gradually releases carboxyl coordination groups (-COO-) with complexing ability, so that precise regulation is implemented in the nucleation stage, growth stage and crystal face selection exposure stage of the crystal, thereby obtaining anhydrous magnesium carbonate powder with uniform particle size, high crystal purity, good dispersity and controllable morphology.

[0011] Further, the molar ratio of the magnesium source, the carbon source, the alkaline mineralizer and the multi-stage regulation agent of citrate esters is 1:(0.8-5):(0.2-1.2):(0.005-0.5).

[0012] Further, the multi-stage regulation agent of citrate esters is at least one of trimethyl citrate, triethyl citrate, tributyl citrate, acetylated trimethyl citrate, acetylated triethyl citrate and acetylated tributyl citrate.

[0013] Further, the carbon source is at least one of urea, a carbonate and a bicarbonate; and / or,

[0014] the magnesium source is at least one of magnesium chloride hexahydrate, anhydrous magnesium chloride, magnesium sulfate heptahydrate, anhydrous magnesium sulfate, basic magnesium carbonate, basic magnesium sulfate, basic magnesium chloride and magnesium bicarbonate; and / or,

[0015] the alkaline mineralizer is at least one of sodium hydroxide, potassium hydroxide and ammonia water.

[0016] Further, the temperature of the hydrothermal reaction is 120-220 DEG C, and the time of the hydrothermal reaction is 1-20 hours.

[0017] The application provides morphology-controllable anhydrous magnesium carbonate, which is prepared according to the preparation method described in the above technical scheme.

[0018] Further, the anhydrous magnesium carbonate has a particle size of 0.5-10 microns and a morphology of at least one of cubic, spindle, dumbbell, spherical, leaf-like and flower-like.

[0019] The application further provides application of the morphology-controllable anhydrous magnesium carbonate in improving the flame-retardant performance of a polymer material.

[0020] Further, the morphology-controllable anhydrous magnesium carbonate is incorporated at a volume ratio of 5-65%.

[0021] Further, the polymer material is selected from ethylene-vinyl acetate copolymer, polyvinyl chloride, polyethylene or polypropylene.

[0022] Compared with the prior art, the application has the following advantages and technical effects:

[0023] The preparation method provided by the application has a simple process, mild conditions, low requirements on equipment, and is especially suitable for industrial-grade magnesium salt of Qinghai Salt Lake and the like, is conducive to continuous production on an industrial scale, and realizes diversified and accurate control of the crystal morphology of anhydrous magnesium carbonate, the obtained crystal has uniform particle size, excellent dispersity and high crystal purity.

[0024] The morphology-rich anhydrous magnesium carbonate prepared by the application is added into a polymer material as a filler, and excellent flame-retardant performance is realized at a low addition amount through flame-retardant mechanisms such as release of CO2 to dilute combustible gas and formation of a dense MgO layer, the flame-retardant efficiency is significantly improved, and the flame-retardant effect is better than that of a traditional inorganic flame-retardant system. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which form a part of the present application, are included to provide a further understanding of the application, and are incorporated herein for purposes of illustration. The embodiments of the present application, together with its details, are described and illustrated by these drawings in which:

[0026] Figure 1 SEM and XRD diagrams of AMC-1 prepared for Example 1;

[0027] Figure 2 SEM and XRD diagrams of AMC-2 prepared for Example 2;

[0028] Figure 3 SEM and XRD diagrams of AMC-3 prepared for Example 3;

[0029] Figure 4 SEM and XRD diagrams of AMC-4 prepared for Example 4;

[0030] Figure 5 SEM and XRD diagrams of AMC-5 prepared for Example 5. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be apparently and completely described below with the accompanying drawings and specific embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0032] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with the accompanying drawings and specific embodiments.

[0033] The present application provides a preparation method of anhydrous magnesium carbonate based on multi-stage morphology regulation of citrate esters, comprising the following steps: dissolving a carbon source, a magnesium source, an alkaline mineralizer and a citrate ester multi-stage regulator in water, and obtaining morphology-controllable anhydrous magnesium carbonate through a hydrothermal reaction.

[0034] In a preferred embodiment, the molar ratio of the magnesium source, the carbon source, the alkaline mineralizer and the citrate ester multi-stage regulator is 1:(0.8-5):(0.2-1.2):(0.005-0.5), and is further preferably 1:(1.5-2):(1-1.2):(0.05-0.2).

[0035] In a preferred embodiment, the citrate ester multi-stage regulator is at least one of trimethyl citrate, triethyl citrate, tributyl citrate, acetylated trimethyl citrate, acetylated triethyl citrate and acetylated tributyl citrate, and is further preferably at least one of trimethyl citrate, triethyl citrate, tributyl citrate and acetylated triethyl citrate. The citrate ester has high chemical stability at room temperature, and can gradually hydrolyze to release carboxyl and hydroxyl functional groups in an alkaline hydrothermal environment. This "thermal sensitive release" property makes citrate ester an ideal multi-stage crystal morphology regulator. Specifically, the ester bond of the ester gradually breaks under alkaline hydrothermal conditions, and slowly releases the carboxyl coordination group with complexing ability with the reaction process, dynamically regulates the growth behavior of anhydrous magnesium carbonate crystals in the nucleation stage, the crystal growth stage and the crystal face termination stage, and significantly improves the morphology uniformity of the product. On the other hand, as the key coordination functional group after hydrolysis of citrate ester, the carboxyl group (-COOH or -COO-) can effectively coordinate with magnesium ions, thereby realizing selective growth of specific crystal faces and precise control of crystal size. The hydrophobic property of the ester molecule can also improve the crystal nucleus density in the initial stage, avoid excessive agglomeration of the crystal grains, make the particle size of the anhydrous magnesium carbonate material more uniform and controllable, and further improve the dispersibility and synergistic effect of the anhydrous magnesium carbonate material as a flame-retardant filler.

[0036] In preferred embodiments, the carbon source is selected from at least one of urea, carbonates and bicarbonates; the carbonates are selected from sodium carbonate and / or potassium carbonate; the bicarbonates are selected from at least one of sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate.

[0037] In preferred embodiments, the magnesium source is selected from at least one of magnesium chloride hexahydrate, magnesium chloride anhydrous, magnesium sulfate heptahydrate, magnesium sulfate anhydrous, basic magnesium carbonate, basic magnesium sulfate, basic magnesium chloride and magnesium bicarbonate, further preferably at least one of magnesium chloride hexahydrate, magnesium chloride anhydrous and basic magnesium chloride.

[0038] In preferred embodiments, the alkaline mineralizing agent is selected from at least one of sodium hydroxide, potassium hydroxide and ammonia.

[0039] In preferred embodiments, the citrate-based multi-level morphology control agent can also be used in combination with traditional morphology control agents, the selection of the type of traditional morphology control agent is determined according to the target particle morphology, exposed crystal surface and reaction environment; the traditional morphology control agent includes but is not limited to: (1) planar nucleating agent or template agent, selected from flaky inorganic materials, aromatic polycarboxylic acids and their anhydrides or natural polymer materials, exemplary: montmorillonite, flaky aluminum hydroxide, graphene, pyromellitic acid, pyromellitic anhydride, 1,4,5,8,-naphthalene tetracarboxylic acid, 1,4,5,8,-naphthalene tetracarboxylic anhydride, tannic acid, lignin, tannic acid derivatives, lignin derivatives; (2) spherical particle template agent, exemplary: nano-silicon dioxide, PMMA microspheres, starch microparticles, PS latex particles; (3) surfactant or small molecule auxiliary agent, selected from non-ionic surfactants, cationic surfactants, anionic surfactants, zwitterionic surfactants or organic small molecules; the non-ionic surfactant is selected from polyethylene glycol, polyvinyl alcohol, polysorbate or octylphenol polyoxyethylene ether; the cationic surfactant is selected from cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide or cetylpyridinium chloride; the anionic surfactant is selected from sodium dodecyl sulfate, sodium laurate, fatty acid salt or sodium N-dodecanoyl glutamate; the zwitterionic surfactant is selected from betaine or amino acid derivatives; the organic small molecule is selected from ethylene glycol, glycerol, tartaric acid, glucose or oxalic acid.

[0040] In preferred embodiments, the temperature of the hydrothermal reaction is 120-220°C, further preferably 160-180°C; the time of the hydrothermal reaction is 1-20 hours, further preferably 2-6 hours; the hydrothermal reaction is carried out under stirring, and the stirring speed is 20-150 r / min.

[0041] In a preferred embodiment, the hydrothermal reaction is followed by steps of filtering, washing and drying; the washing agent is deionized water, the washing is performed for three times; the drying is performed at a temperature of 80 DEG C for 12 hours.

[0042] The application provides a morphology-controllable anhydrous magnesium carbonate.

[0043] In a preferred embodiment, the anhydrous magnesium carbonate has a particle size of 0.5-10 microns and a morphology of at least one of a cubic shape, a spindle shape, a dumbbell shape, a spherical shape, a leaf-like shape and a flower shape.

[0044] The application also provides an application of the morphology-controllable anhydrous magnesium carbonate in improving the flame-retardant performance of a polymer material.

[0045] In a preferred embodiment, the morphology-controllable anhydrous magnesium carbonate is incorporated at a volume ratio of 5-65%, and is further preferably incorporated at a volume ratio of 25-35%.

[0046] In a preferred embodiment, the polymer material is selected from ethylene-vinyl acetate copolymer (EVA), polyvinyl chloride (PVC), polyethylene (PE) or polypropylene (PP).

[0047] In the embodiment of the application, room temperature refers to 25 DEG C + / - 2 DEG C.

[0048] Unless otherwise specified, the raw materials in the embodiment of the application are obtained through a commercial channel.

[0049] Embodiment 1

[0050] A preparation method of anhydrous magnesium carbonate based on multi-stage morphology regulation of citrate esters, the specific steps are as follows:

[0051] Urea, magnesium chloride hexahydrate, sodium hydroxide and acetylated triethyl citrate (ATEC) are sequentially dissolved in 40 mL of deionized water at a molar ratio of 2:1:1:0.25, and are subjected to magnetic stirring for 20 min, and are then transferred to a 100 mL reaction kettle, and are subjected to a hydrothermal reaction at a temperature of 180 DEG C and a rotation speed of 30 r / min for 5 h, and after the reaction is completed, are subjected to filtering, washing for three times and drying at 80 DEG C for 12 h, to obtain spindle-shaped anhydrous magnesium carbonate crystals with smooth surfaces, regular morphologies and uniform particle sizes, which are denoted as AMC-1.

[0052] Figure 1 The SEM and XRD images of AMC-1 prepared in Embodiment 1 are shown in Figures 1 and 2. Figure 1 As can be seen, the AMC-1 prepared in Embodiment 1 has a spindle shape, and has smooth surfaces, regular morphologies and uniform particle sizes, the long axis of the spindle-shaped surface is about 5.4 microns, and the short axis is about 1.3 microns.

[0053] Example 2

[0054] A preparation method of anhydrous magnesium carbonate based on multi-level morphology regulation of citrate esters, the specific steps are:

[0055] Urea, magnesium chloride hexahydrate, sodium hydroxide and trimethyl citrate (TMC) were sequentially dissolved in 40 mL of deionized water in a molar ratio of 1.5:1:1:0.4, and then transferred to a 100 mL reaction kettle after magnetic stirring for 20 min. The hydrothermal reaction was carried out at a temperature of 180℃ and a rotation speed of 60 r / min for 5h. After the reaction was completed, the product was filtered and washed three times, and then dried at 80℃ for 12h to obtain dumbbell-shaped anhydrous magnesium carbonate crystals with uniform particle size, denoted as AMC-2.

[0056] Figure 2 The SEM and XRD images of AMC-2 prepared in Example 2 are shown in Figures 2a and 2b, respectively. Figure 2 As can be seen from the figures, the AMC-2 prepared in Example 2 has a dumbbell-shaped morphology and uniform particle size, with a long axis of about 8.3μm.

[0057] Example 3

[0058] A preparation method of anhydrous magnesium carbonate based on multi-level morphology regulation of citrate esters, the specific steps are:

[0059] Sodium bicarbonate, urea, anhydrous magnesium chloride, potassium hydroxide and tributyl citrate (TBC) were sequentially dissolved in 50 mL of deionized water in a molar ratio of 0.5:1:1:1:0.4, and then transferred to a 100 mL reaction kettle after magnetic stirring for 20 min. The hydrothermal reaction was carried out at a temperature of 160℃ and a rotation speed of 20 r / min for 5h. After the reaction was completed, the product was filtered and washed three times, and then dried at 80℃ for 12h to obtain flower-shaped anhydrous magnesium carbonate crystals, denoted as AMC-3.

[0060] Figure 3 The SEM and XRD images of AMC-3 prepared in Example 3 are shown in Figures 3a and 3b, respectively. Figure 3 As can be seen from the figures, the AMC-3 prepared in Example 3 has a flower-shaped morphology and a particle size of about 4.8μm.

[0061] Example 4

[0062] A preparation method of anhydrous magnesium carbonate based on multi-level morphology regulation of citrate esters, the specific steps are:

[0063] Urea, magnesium chloride hexahydrate, sodium hydroxide and acetylated triethyl citrate (ATEC) were sequentially dissolved in 800 mL of deionized water in a molar ratio of 1.5:1:1:0.25, and magnetically stirred for 20 min, and then transferred to a 2 L reaction kettle, and subjected to a hydrothermal reaction at a temperature of 180℃ and a rotation speed of 150 r / min for 2 h. After the reaction was completed, the product was filtered, washed three times, and dried at 80℃ for 12 h to obtain an anhydrous magnesium carbonate crystal in the shape of a shuttle, which was denoted as AMC-4.

[0064] Figure 4 SEM and XRD images of the AMC-4 prepared in Example 4. As can be seen from Figure 4 the AMC-4 prepared in Example 4 has a shuttle-shaped morphology, with a long axis of about 1.5 μm and a short axis of about 0.5 μm.

[0065] Example 5

[0066] A preparation method of an anhydrous magnesium carbonate based on multi-stage morphology control of citrate esters, comprising the following steps:

[0067] Urea, magnesium chloride hexahydrate, sodium hydroxide, triethyl citrate (TEC) and pyromellitic dianhydride were dissolved in 40 mL of deionized water in a molar ratio of 1.5:1:1:0.01:0.04, and magnetically stirred for 20 min, and then transferred to a 100 mL reaction kettle, and subjected to a hydrothermal reaction at a temperature of 160℃ and a rotation speed of 30 r / min for 6 h. After the reaction was completed, the product was filtered, washed three times, and dried at 80℃ for 12 h to obtain an anhydrous magnesium carbonate crystal in the shape of a leaflet, which was denoted as AMC-5.

[0068] Figure 5 SEM and XRD images of the AMC-5 prepared in Example 5. As can be seen from Figure 5 the AMC-5 prepared in Example 5 has a leaflet-shaped morphology, with a long axis of about 3.7 μm and a short axis of about 1.4 μm.

[0069] Example 6

[0070] A preparation method of an AMC / EVA flame-retardant composite material, comprising the following steps:

[0071] The anhydrous magnesium carbonate crystals prepared in Examples 1-3 were mixed into ethylene-vinyl acetate copolymer (EVA) at a volume ratio of 25 vol% and 35 vol% (i.e. the volume ratio of the anhydrous magnesium carbonate crystals in the AMC / EVA flame-retardant composite material was 25 vol% or 35 vol%) respectively, and then uniformly mixed in a torque rheometer at a temperature of 170°C, a rotation speed of 30 r / min and a time of 15 min to obtain a mixed product. The mixed product was hot-pressed into a sheet by a flat vulcanizing instrument at a sheeting temperature of 150°C, a pressure of 10 MPa, a preheating time of 10 min and a sheeting time of 10 min, and finally an AMC / EVA flame-retardant composite material with a thickness of 3 mm was obtained.

[0072] The flame-retardant properties of the AMC / EVA flame-retardant composite material prepared in Example 6 were tested by vertical combustion (UL-94 grade), limiting oxygen index (LOI) and cone calorimeter test, and the results are shown in Table 1.

[0073] Table 1

[0074]

[0075] The results in Table 1 show that when the amount of the anhydrous magnesium carbonate crystals of each morphology prepared in Examples 1-3 added into ethylene-vinyl acetate copolymer (EVA) reaches 35 vol%, the LOI value is significantly improved and exceeds 25%, the UL-94 grade reaches V-2 level, and the peak heat release rate is less than 180 kW / m 2 , which reflects the good flame-retardant effect of the special morphology anhydrous magnesium carbonate prepared in the present application.

[0076] The above merely provides the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions easily conceived by those skilled in the art within the technical scope disclosed in the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing anhydrous magnesium carbonate based on multi-stage morphology control of citrate esters, characterized in that: The following steps are involved: A carbon source, a magnesium source, an alkaline mineralizer and a citrate multi-stage regulator are dissolved in water, and subjected to a hydrothermal reaction to obtain anhydrous magnesium carbonate with controllable morphology.

2. The method for preparing anhydrous magnesium carbonate based on multi-stage morphology control of citrates according to claim 1, wherein The molar ratio of the magnesium source, the carbon source, the alkaline mineralizer and the citrate multi-stage regulating agent is 1:(0.8-5):(0.2-1.2):(0.005-0.5).

3. The method for preparing anhydrous magnesium carbonate based on multi-stage morphology control of citrates according to claim 1, wherein The citric acid ester multi-stage control agent is selected from at least one of trimethyl citrate, triethyl citrate, tributyl citrate, acetylated trimethyl citrate, acetylated triethyl citrate and acetylated tributyl citrate.

4. The method for preparing anhydrous magnesium carbonate based on multi-stage morphology control of citrates according to claim 1, wherein The carbon source is selected from at least one of urea, carbonate and bicarbonate; and / or, The magnesium source is at least one selected from magnesium chloride hexahydrate, anhydrous magnesium chloride, magnesium sulfate heptahydrate, anhydrous magnesium sulfate, basic magnesium carbonate, basic magnesium sulfate, basic magnesium chloride and magnesium bicarbonate; and / or, The alkaline mineralizer is selected from at least one of sodium hydroxide, potassium hydroxide and ammonia water.

5. The method for preparing anhydrous magnesium carbonate based on multi-stage morphology control of citrates according to claim 1, wherein The temperature of the hydrothermal reaction is 120 to 220° C., and the time of the hydrothermal reaction is 1 to 20 hours.

6. A morphology-controlled anhydrous magnesium carbonate, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 5.

7. The morphology-controlled anhydrous magnesium carbonate according to claim 6, wherein The anhydrous magnesium carbonate has a particle size of 0.5 to 10 μm and a morphology of at least one of cubic, spindle, dumbbell, spherical, leaf-like, and flower-like.

8. Use of the morphology-controllable anhydrous magnesium carbonate according to any one of claims 6 to 7 in improving the flame retardant properties of polymer materials.

9. The use according to claim 8, characterized in that The anhydrous magnesium carbonate with controllable morphology is added in a volume ratio of 5 to 65%.

10. The use according to claim 8, characterized in that The polymer material is selected from ethylene-vinyl acetate copolymer, polyvinyl chloride, polyethylene or polypropylene.

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