A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6

Abstract

The invention belongs to the technical field of waste PA6 recycling, and relates to a method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, wherein CaF2@SiO2 and PA6 are compounded in a mixed solvent by a dissolution precipitation method to obtain PA6@CaF2@SiO2 fluorescent powder; the mixed solvent is composed of methanol and ethanol; the preparation process of CaF2@SiO2 is as follows: firstly, CaF2 and tannic acid solution are uniformly mixed, then SiO2 is added and mixed uniformly to obtain a CaF2 / SiO2 dispersion, then a phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution is added to the CaF2 / SiO2 dispersion and mixed uniformly, and CaF2@SiO2 is obtained by post-processing. The invention realizes the effective recycling of waste PA6 and endows the composite powder with good dimensional stability and fluorescent function.

Description

Technical Field

[0001] The invention belongs to the technical field of waste PA6 recycling and relates to a method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6. Background Art

[0002] PA6 (polyamide 6, also known as nylon 6) is a high molecular polymer formed by the ring-opening polymerization of ε-caprolactam. With the development of the textile industry, the demand for PA6 continues to increase, and its application areas have gradually expanded to multiple industries such as electronics, automobiles, packaging, and building materials, becoming one of the important materials. However, this has also led to a significant increase in the amount of PA6 waste. Therefore, the recycling of PA6 has significant social significance.

[0003] There are three ways to recycle PA6: energy recycling, physical recycling, and chemical recycling. Energy recycling converts waste PA6 into heat energy by incinerating it, but this process releases harmful gases, leading to secondary pollution. Although chemical recycling can more thoroughly depolymerize PA6 into caprolactam monomers, its widespread application is limited due to harsh conditions, high equipment requirements, and high production costs. Physical recycling mainly uses the melt regeneration method to melt PA6 into slices, but this method often leads to a decrease in the performance of the recycled material, and it can only be downgraded for use.

[0004] As a material with excellent performance and diverse functions, polymer powder materials are widely used in biomedicine, 3D printing, coatings and adhesives, composite materials, medicine and medical devices, electronic optics and other fields due to their unique physical and chemical properties. Dimensional stability and fluorescence function are crucial for polymer powder materials. For polymer powder materials, dimensional stability is directly related to their processing performance, product quality and service life. The fluorescence function is a special property of polymer powder materials, which enables the material to emit fluorescence when irradiated with excitation light. This property has wide application value in biomedicine, material science, environmental monitoring and other fields.

[0005] Nylon powder is a widely used type of polymer powder material. Preparing waste PA6 into powder material is a potential solution to the PA6 recycling problem. However, PA6 is a polymer connected by repeated amide groups, so it is easy to form hydrogen bonds with water molecules, making PA6 highly hygroscopic. If it is used in the laser sintering process of 3D printing, it will also face the problem of poor dimensional stability. In addition, PA6 itself does not have additional functionality.

[0006] Reference 1 (Controllable preparation of polyamide 12@ SiO2 composite powders [J]. Polymer Composites, 2019, 40 (3): 1251 - 1257.) heats a specific ratio of silica sol, PA12 particles and a mixed solvent (methanol to ethanol volume ratio of 3:1) to 165°C in a reactor and maintains this temperature for 3 hours, then cools to room temperature at a rate of 1°C / min. During this process, the nano-SiO2 in the silica sol is evenly dispersed in the solvent, and as the temperature increases, PA12 completely dissolves in the solvent. During cooling, due to the decrease in the solvent's solubility, PA12 gradually precipitates and aggregates and precipitates on the SiO2 surface to obtain a composite powder.

[0007] Reference 2 (A nanosilica / nylon-12 composite powder for selective lasersintering [J]. Journal of Reinforced Plastics and Composites, 2009, 28 (23): 2889-2902.) First, SiO2 was modified with a silane coupling agent to give it an amino group on its surface, and then the modified SiO2 was dispersed in a solvent to form a suspension. After PA12 was completely dissolved in a mixed solvent consisting of ethanol, butanone and water, PA12 was precipitated on the surface of the modified SiO2 to obtain a composite powder through a cooling process. In this process, the amino groups on the surface of the modified SiO2 reacted with the carboxyl groups of the PA12 macromolecular chain to undergo an amidation reaction, which not only promoted the deposition of PA12 on the modified SiO2, but also significantly enhanced the interaction between the two.

[0008] If PA6 can be precipitated onto SiO2 or modified SiO2 to form composite powders, as described in References 1 and 2, it will provide a new idea for the recycling of waste PA6. However, the methods described in References 1 and 2 only improve the dimensional stability of the composite powders and do not give them additional functions. Summary of the invention

[0009] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, comprising compounding CaF2@SiO2 and PA6 in a mixed solvent by a dissolution precipitation method to obtain PA6@CaF2@SiO2 fluorescent powder;

[0012] The mixed solvent is composed of methanol and ethanol. At room temperature and pressure, the solubility of PA6 is limited to highly polar organic solvents, such as formic acid, m-cresol and trifluoroacetic acid, but it cannot be dissolved in organic reagents such as DMF (N,N-dimethylformamide), ethanol, methanol and acetone. Since the principle of the dissolution precipitation method requires PA6 to be able to dissolve and precipitate in the selected solvent with changes in temperature, good solvents such as formic acid that can easily dissolve PA6 at room temperature are not suitable for achieving the precipitation of PA6 through simple temperature changes, because their solubility at room temperature is too strong. On the contrary, the use of a mixed solvent of methanol and ethanol becomes a more suitable choice. This mixed solvent is insoluble in PA6 at room temperature, but can dissolve PA6 under high temperature conditions. This characteristic makes it easy to achieve the dissolution and precipitation process of PA6 by controlling the temperature change, thereby meeting the operating requirements of the dissolution precipitation method.

[0013] The preparation process of CaF2@SiO2 is as follows: adding phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution into CaF2 / SiO2 dispersion and mixing evenly, and then post-processing (washing with ethanol 5 times and drying at 60°C) to obtain CaF2@SiO2;

[0014] The preparation process of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution is as follows: firstly, phytic acid and polyvinyl alcohol are mixed evenly, and then mannitol and aminoterephthalic acid are added and mixed evenly to obtain the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution;

[0015] The preparation process of CaF2 / SiO2 dispersion is: firstly, mix CaF2 and tannic acid solution evenly, then add SiO2 and mix evenly, so as to obtain CaF2 / SiO2 dispersion. If all raw materials are mixed together directly, it will be not conducive to the combination of SiO2 and CaF2.

[0016] In order to solve the problem that the prior art cannot give the composite powder a fluorescent function, the present invention attempts to compound CaF2 and SiO2 to form CaF2@SiO2 (i.e., composite particles of CaF2 and SiO2), and uses CaF2@SiO2 as the core to precipitate PA6 on the surface of CaF2@SiO2 by a dissolution precipitation method; CaF2 is an inorganic compound that is poorly soluble in water and slightly soluble in inorganic acids. It often exists in the form of fluorite or fluorspar in nature, with various colors, including gray, yellow, green, purple, etc., and sometimes colorless and transparent. It is brittle and has a significant fluorescent function. Using CaF2@SiO2 as the core, it is theoretically possible to simultaneously improve the dimensional stability of PA6 and give it a fluorescent function;

[0017] However, CaF2@SiO2 not only needs to have a certain attraction to the PA6 macromolecular chain, but also needs to be able to exist stably during the dissolution and precipitation process. If CaF2 and SiO2 are directly compounded, CaF2 and SiO2 will form a "soft agglomeration" to combine by the electrostatic force and van der Waals force between the particles, and the force is weak, especially in the high temperature mixed solvent during the dissolution and precipitation process, this combination is easily destroyed;

[0018] In order to solve this problem, the present invention uses tannic acid as an adhesive to combine CaF2 and SiO2. Tannic acid can form a tannic acid film on the surface of CaF2@SiO2. Relying on the adhesion of tannic acid, the bonding mode between CaF2 and SiO2 will change from "soft agglomeration" to "hard agglomeration". In addition to electrostatic force and van der Waals force, there are also chemical bonds and hydrogen bonds, so it is not easy to be destroyed; however, the tannic acid film is easily peeled off during the dissolution and precipitation process, resulting in the separation of CaF2 and SiO2. Therefore, the present invention attempts to continue to wrap a protective polymer film on the surface of the tannic acid film to solve this problem;

[0019] In view of the fact that the tannic acid film and CaF2@SiO2 will consume part of the hydroxyl groups due to the attachment of hydrogen bonds, the present invention selects phytic acid and aminoterephthalic acid to construct a protective polymer film. Phytic acid and aminoterephthalic acid have a large number of hydroxyl groups and benzene ring structures, which can form stronger hydrogen bonding with the tannic acid film and simultaneously produce π-π stacking. However, although aminoterephthalic acid and phytic acid can form a strong force with the tannic acid film, they will be more strongly dissolved by methanol / ethanol and diffuse into the solution.

[0020] To solve this problem, the present invention also introduces polyvinyl alcohol into the protective polymer film. Polyvinyl alcohol will not dissolve in methanol or ethanol, so it has a certain degree of resistance to solvent erosion and can provide protection for the tannic acid film. In the process of forming the protective polymer film, if polyvinyl alcohol, phytic acid and aminoterephthalic acid are blended, phytic acid is more likely to aggregate with small molecular compounds such as aminoterephthalic acid, thereby causing the mixture to form an uneven network structure, thereby affecting the formation of the coating. For this reason, the present invention first constructs a network structure of phytic acid and polyvinyl alcohol to ensure good resistance to the mixed solvent. In order to embed aminoterephthalic acid into the network structure, the present invention achieves this by adding mannitol. Mannitol can pry the phytic acid / polyvinyl alcohol network structure. When in a high temperature environment, the interaction between phytic acid and polyvinyl alcohol is weakened, and the molecular movement of mannitol is accelerated. Since mannitol has multiple hydroxyl groups, it can carry aminoterephthalic acid into the macromolecular network of phytic acid / polyvinyl alcohol through intermolecular action. After cooling, mannitol / aminoterephthalic acid is embedded in phytic acid / polyvinyl alcohol through hydrogen bonding, forming a protective polymer film that can be combined with the tannic acid film through hydrogen bonding and π-π stacking.

[0021] As the preferred technical solution:

[0022] In the method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 as described above, during the preparation of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution, the mass ratio of phytic acid, mannitol, aminoterephthalic acid, and polyvinyl alcohol is 3:2~2.5:3:2; the temperature of the first mixing is 60~65°C, and the time is 1~1.5h; the temperature of the second mixing is 80~90°C, and the time is 1.5~2h.

[0023] As described above, a method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, a preparation process of CaF2 / SiO2 dispersion, the mass fraction of tannic acid in the tannic acid solution is 10~15wt%, the mass ratio of CaF2 to tannic acid solution is 1:30~40, and the mass ratio of CaF2 to SiO2 is 1:0.4~0.5; the temperature of the first mixing is 60~70℃, and the time is 1~1.2h; the temperature of the second mixing is 60~70℃, and the time is 1~1.5h.

[0024] As described above, in the method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, during the preparation of CaF2@SiO2, the mass ratio of phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution to CaF2 / SiO2 dispersion is 2.5~3:102.5~103; the mixing temperature is 80~85°C and the mixing time is 1~1.5h.

[0025] In the method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 as described above, the volume ratio of methanol to ethanol in the mixed solvent is 85:15.

[0026] The method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 as described above, the specific process of preparing PA6@CaF2@SiO2 fluorescent powder from PA6 is: mixing CaF2@SiO2, PA6, and a mixed solvent, heating to 145~150°C and keeping warm for 1~2 hours, cooling to 25~30°C at a cooling rate of 0.2~1°C / min, and post-treating (washing with deionized water, vacuum drying at 60°C for 24 hours) to obtain PA6@CaF2@SiO2 fluorescent powder.

[0027] Methanol and ethanol are both poor solvents for PA6 at room temperature. PA6 can only be dissolved at higher temperatures. When the temperature used is too low, it cannot be completely dissolved. If the temperature is too high, the PA6 macromolecular chain will break. Therefore, 145~150℃ is used as the dissolution temperature; the insulation time is 1~2h, which can ensure that PA6 can be completely dissolved.

[0028] In the method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 as described above, the mass ratio of PA6 to CaF2@SiO2 is 12~10:1. Under such a ratio, CaF2@SiO2 can be used as a core to control the average particle size of the composite powder to a suitable size; the mass ratio of the mixed solvent to PA6 is 7~8:1. Under such a ratio, the macromolecular chains of the dissolved PA6 in the mixed solvent are distributed more freely and can be more uniform during the precipitation process.

[0029] According to the method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, the yield of PA6@CaF2@SiO2 fluorescent powder is 70~80% ( ), the average particle size is 50~70μm, and the shrinkage rate is 1.28~1.31%.

[0030] Beneficial effects:

[0031] (1) The present invention composites CaF2@SiO2 with PA6 through a dissolution precipitation method to prepare PA6@CaF2@SiO2 fluorescent powder, which not only achieves the effective recycling of waste PA6, but also gives the composite powder good dimensional stability and fluorescent function, providing a new idea for the recycling of waste polymer materials.

[0032] (2) The present invention successfully solves the problem of easy separation of CaF2 and SiO2 during the dissolution and precipitation process by introducing tannic acid as a binder and combining it with a protective polymer film constructed from phytic acid, polyvinyl alcohol and aminoterephthalic acid, thereby ensuring the stability and integrity of the composite particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the SEM image of the PA6@CaF2@SiO2 fluorescent powder of Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0035] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0036] Shrinkage: After conditioning the powder at 23°C and 50% humidity for 24 hours, measure using a vernier caliper in accordance with ASTM D955.

[0037] The source of PA6 in the following embodiments: PA6 waste silk (manufacturer: Wujiang Fuhua Weaving Co., Ltd., Suzhou City, Jiangsu Province) was first immersed in a soap solution with a concentration of 2g / L, and the bath ratio was controlled to be 1:30-50, and then the PA6 waste silk was soaked and washed at 25-35°C for 1h, and then dried at 25-35°C for 20-24h to obtain the raw material PA6.

[0038] Example 1

[0039] A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, the specific steps are as follows:

[0040] (1) Preparation of raw materials;

[0041] Phytic acid: CAS number is 83-86-3;

[0042] Polyvinyl alcohol: CAS number is 9002-89-5;

[0043] Mannitol;

[0044] Aminoterephthalic acid;

[0045] CaF2;

[0046] Tannic acid solution: mass fraction is 15wt%, solvent is water;

[0047] SiO2;

[0048] PA6;

[0049] Mixed solvent: composed of methanol and ethanol, with a volume ratio of methanol to ethanol of 85:15;

[0050] (2) preparing phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution and CaF2 / SiO2 dispersion respectively;

[0051] The preparation process of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution is as follows: firstly, phytic acid and polyvinyl alcohol are mixed at 60° C. for 1 hour, and then mannitol and aminoterephthalic acid are added and mixed at 90° C. for 2 hours to obtain a phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution; wherein the mass ratio of phytic acid, mannitol, aminoterephthalic acid and polyvinyl alcohol is 3:2.5:3:2;

[0052] The preparation process of the CaF2 / SiO2 dispersion is as follows: first, CaF2 and tannic acid solution are mixed at 60°C for 1 hour, and then SiO2 is added and mixed at 60°C for 1.5 hours to obtain the CaF2 / SiO2 dispersion; wherein the mass ratio of CaF2 to tannic acid solution is 1:30, and the mass ratio of CaF2 to SiO2 is 1:0.4;

[0053] (3) Preparation of CaF2@SiO2;

[0054] The phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution was added to the CaF2 / SiO2 dispersion, mixed at 80°C for 1 hour, and post-treated to obtain CaF2@SiO2; wherein the mass ratio of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution to the CaF2 / SiO2 dispersion was 2.5:103;

[0055] (4) Preparation of PA6@CaF2@SiO2 fluorescent powder;

[0056] CaF2@SiO2, PA6 and mixed solvent were mixed, heated to 150°C for 1 hour, cooled to 25°C at a cooling rate of 1°C / min, and post-treated to obtain PA6@CaF2@SiO2 fluorescent powder; wherein the mass ratio of PA6 to CaF2@SiO2 was 12:1, and the mass ratio of the mixed solvent to PA6 was 7:1.

[0057] The yield of PA6@CaF2@SiO2 fluorescent powder is 70%; the SEM of the final PA6@CaF2@SiO2 fluorescent powder is as follows Figure 1 As shown; the average particle size of PA6@CaF2@SiO2 fluorescent powder is 50μm and the shrinkage rate is 1.28%.

[0058] Example 2

[0059] A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, the specific steps are as follows:

[0060] (1) Preparation of raw materials;

[0061] Phytic acid: CAS number is 83-86-3;

[0062] Polyvinyl alcohol: CAS number is 9002-89-5;

[0063] Mannitol;

[0064] Aminoterephthalic acid;

[0065] CaF2;

[0066] Tannic acid solution: mass fraction is 10wt%, solvent is water;

[0067] SiO2;

[0068] PA6;

[0069] Mixed solvent: composed of methanol and ethanol, with a volume ratio of methanol to ethanol of 85:15;

[0070] (2) preparing phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution and CaF2 / SiO2 dispersion respectively;

[0071] The preparation process of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution is as follows: firstly, phytic acid and polyvinyl alcohol are mixed at 65° C. for 1.5 hours, and then mannitol and aminoterephthalic acid are added and mixed at 80° C. for 1.5 hours to obtain a phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution; wherein the mass ratio of phytic acid, mannitol, aminoterephthalic acid and polyvinyl alcohol is 3:2:3:2;

[0072] The preparation process of the CaF2 / SiO2 dispersion is as follows: first, CaF2 and tannic acid solution are mixed at 70°C for 1.2 hours, and then SiO2 is added and mixed at 70°C for 1 hour to obtain the CaF2 / SiO2 dispersion; wherein the mass ratio of CaF2 to tannic acid solution is 1:40, and the mass ratio of CaF2 to SiO2 is 1:0.5;

[0073] (3) Preparation of CaF2@SiO2;

[0074] The phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution was added to the CaF2 / SiO2 dispersion, mixed at 85°C for 1.5 hours, and post-treated to obtain CaF2@SiO2; wherein the mass ratio of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution to the CaF2 / SiO2 dispersion was 3:102.5;

[0075] (4) Preparation of PA6@CaF2@SiO2 fluorescent powder;

[0076] CaF2@SiO2, PA6 and mixed solvent are mixed, heated to 145°C and kept warm for 2 hours, then cooled to 30°C at a cooling rate of 0.2°C / min, and post-treated to obtain PA6@CaF2@SiO2 fluorescent powder; wherein the mass ratio of PA6 to CaF2@SiO2 is 10:1, and the mass ratio of the mixed solvent to PA6 is 8:1.

[0077] The yield of PA6@CaF2@SiO2 fluorescent powder is 80%; the average particle size of the final PA6@CaF2@SiO2 fluorescent powder is 70μm and the shrinkage rate is 1.31%.

[0078] Example 3

[0079] A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, the specific steps are as follows:

[0080] (1) Preparation of raw materials;

[0081] Phytic acid: CAS number is 83-86-3;

[0082] Polyvinyl alcohol: CAS number is 9002-89-5;

[0083] Mannitol;

[0084] Aminoterephthalic acid;

[0085] CaF2;

[0086] Tannic acid solution: mass fraction is 12.5wt%, solvent is water;

[0087] SiO2;

[0088] PA6;

[0089] Mixed solvent: composed of methanol and ethanol, with a volume ratio of methanol to ethanol of 85:15;

[0090] (2) preparing phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution and CaF2 / SiO2 dispersion respectively;

[0091] The preparation process of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution is as follows: firstly, phytic acid and polyvinyl alcohol are mixed at 62° C. for 1.25 h, and then mannitol and aminoterephthalic acid are added and mixed at 85° C. for 1.75 h to obtain a phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution; wherein the mass ratio of phytic acid, mannitol, aminoterephthalic acid and polyvinyl alcohol is 3:2.25:3:2;

[0092] The preparation process of the CaF2 / SiO2 dispersion is as follows: first, CaF2 and tannic acid solution are mixed at 65°C for 1.1h, and then SiO2 is added and mixed at 65°C for 1.25h to obtain the CaF2 / SiO2 dispersion; wherein the mass ratio of CaF2 to tannic acid solution is 1:35, and the mass ratio of CaF2 to SiO2 is 1:0.45;

[0093] (3) Preparation of CaF2@SiO2;

[0094] The phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution was added to the CaF2 / SiO2 dispersion, mixed at 83°C for 1.25h, and post-treated to obtain CaF2@SiO2; wherein the mass ratio of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution to the CaF2 / SiO2 dispersion was 2.75:102.75;

[0095] (4) Preparation of PA6@CaF2@SiO2 fluorescent powder;

[0096] CaF2@SiO2, PA6 and mixed solvent were mixed, heated to 147°C and kept warm for 1.5 hours, then cooled to 27°C at a cooling rate of 0.6°C / min, and post-treated to obtain PA6@CaF2@SiO2 fluorescent powder; wherein the mass ratio of PA6 to CaF2@SiO2 was 11:1, and the mass ratio of the mixed solvent to PA6 was 7.5:1.

[0097] The yield of PA6@CaF2@SiO2 fluorescent powder is 75%; the average particle size of the final PA6@CaF2@SiO2 fluorescent powder is 60μm and the shrinkage rate is 1.3%.

[0098] Example 4

[0099] A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, the specific steps are as follows:

[0100] (1) Preparation of raw materials;

[0101] Phytic acid: CAS number is 83-86-3;

[0102] Polyvinyl alcohol: CAS number is 9002-89-5;

[0103] Mannitol;

[0104] Aminoterephthalic acid;

[0105] CaF2;

[0106] Tannic acid solution: mass fraction is 13wt%, solvent is water;

[0107] SiO2;

[0108] PA6;

[0109] Mixed solvent: composed of methanol and ethanol, with a volume ratio of methanol to ethanol of 85:15;

[0110] (2) preparing phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution and CaF2 / SiO2 dispersion respectively;

[0111] The preparation process of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution is as follows: firstly, phytic acid and polyvinyl alcohol are mixed at 60° C. for 1 hour, and then mannitol and aminoterephthalic acid are added and mixed at 90° C. for 2 hours to obtain a phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution; wherein the mass ratio of phytic acid, mannitol, aminoterephthalic acid and polyvinyl alcohol is 3:2.5:3:2;

[0112] The preparation process of the CaF2 / SiO2 dispersion is as follows: first, CaF2 and tannic acid solution are mixed at 60°C for 1 hour, and then SiO2 is added and mixed at 60°C for 1.5 hours to obtain the CaF2 / SiO2 dispersion; wherein the mass ratio of CaF2 to tannic acid solution is 1:30, and the mass ratio of CaF2 to SiO2 is 1:0.4;

[0113] (3) Preparation of CaF2@SiO2;

[0114] The phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution was added to the CaF2 / SiO2 dispersion, mixed at 80°C for 1 hour, and post-treated to obtain CaF2@SiO2; wherein the mass ratio of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution to the CaF2 / SiO2 dispersion was 3:102.5;

[0115] (4) Preparation of PA6@CaF2@SiO2 fluorescent powder;

[0116] CaF2@SiO2, PA6 and mixed solvent were mixed, heated to 150°C and kept for 1 hour, then cooled to 25°C at a cooling rate of 1°C / min, and post-treated to obtain PA6@CaF2@SiO2 fluorescent powder; wherein the mass ratio of PA6 to CaF2@SiO2 was 10:1, and the mass ratio of the mixed solvent to PA6 was 7:1.

[0117] The yield of PA6@CaF2@SiO2 fluorescent powder is 80%; the average particle size of the final PA6@CaF2@SiO2 fluorescent powder is 67μm and the shrinkage rate is 1.3%.

[0118] Example 5

[0119] A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, the specific steps are as follows:

[0120] (1) Preparation of raw materials;

[0121] Phytic acid: CAS number is 83-86-3;

[0122] Polyvinyl alcohol: CAS number is 9002-89-5;

[0123] Mannitol;

[0124] Aminoterephthalic acid;

[0125] CaF2;

[0126] Tannic acid solution: mass fraction is 15wt%, solvent is water;

[0127] SiO2;

[0128] PA6;

[0129] Mixed solvent: composed of methanol and ethanol, with a volume ratio of methanol to ethanol of 85:15;

[0130] (2) preparing phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution and CaF2 / SiO2 dispersion respectively;

[0131] The preparation process of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution is as follows: firstly, phytic acid and polyvinyl alcohol are mixed at 60° C. for 1 hour, and then mannitol and aminoterephthalic acid are added and mixed at 90° C. for 2 hours to obtain a phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution; wherein the mass ratio of phytic acid, mannitol, aminoterephthalic acid and polyvinyl alcohol is 3:2.5:3:2;

[0132] The preparation process of the CaF2 / SiO2 dispersion is as follows: first, CaF2 and tannic acid solution are mixed at 60°C for 1 hour, and then SiO2 is added and mixed at 60°C for 1.5 hours to obtain the CaF2 / SiO2 dispersion; wherein the mass ratio of CaF2 to tannic acid solution is 1:40, and the mass ratio of CaF2 to SiO2 is 1:0.4;

[0133] (3) Preparation of CaF2@SiO2;

[0134] The phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution was added to the CaF2 / SiO2 dispersion, mixed at 80°C for 1 hour, and post-treated to obtain CaF2@SiO2; wherein the mass ratio of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution to the CaF2 / SiO2 dispersion was 3:103;

[0135] (4) Preparation of PA6@CaF2@SiO2 fluorescent powder;

[0136] CaF2@SiO2, PA6 and mixed solvent were mixed, heated to 150°C and kept warm for 1 hour, then cooled to 25°C at a cooling rate of 1°C / min, and post-treated to obtain PA6@CaF2@SiO2 fluorescent powder; wherein the mass ratio of PA6 to CaF2@SiO2 was 12:1, and the mass ratio of the mixed solvent to PA6 was 8:1.

[0137] The yield of PA6@CaF2@SiO2 fluorescent powder is 70%; the average particle size of the final PA6@CaF2@SiO2 fluorescent powder is 66μm and the shrinkage rate is 1.29%.

Claims

1. A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6, characterized in that: CaF2@SiO2, PA6 and a mixed solvent are mixed, heated to 145-150°C and kept for 1-2 hours, then cooled to 25-30°C at a cooling rate of 0.2-1°C / min, and post-treated to obtain PA6@CaF2@SiO2 fluorescent powder; The mixed solvent consists of methanol and ethanol; The preparation process of CaF2@SiO2 is as follows: add phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution into The CaF2 / SiO2 dispersion is mixed evenly and then subjected to post-treatment to obtain CaF2@SiO2; the mixing temperature is 80-85°C and the mixing time is 1-1.5h; The preparation process of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution is as follows: firstly, phytic acid and polyvinyl alcohol are mixed evenly, and then mannitol and aminoterephthalic acid are added and mixed evenly to obtain the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution; the temperature of the first mixing is 60-65° C., and the time is 1-1.5 hours; the temperature of the second mixing is 80-90° C., and the time is 1.5-2 hours; The preparation process of CaF2 / SiO2 dispersion is: first mix CaF2 and tannic acid solution evenly, then add SiO2 and mix evenly to obtain CaF2 / SiO2 dispersion; the temperature of the first mixing is 60-70°C, and the time is 1-1.2h; the temperature of the second mixing is 60-70°C, and the time is 1-1.5h.

2. The method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 according to claim 1, characterized in that: In the preparation process of the phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution, the mass ratio of phytic acid, mannitol, aminoterephthalic acid and polyvinyl alcohol is 3:2 to 2.5:3:

2.

3. The method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 according to claim 1, characterized in that: In the preparation process of CaF2 / SiO2 dispersion, the mass fraction of tannic acid in the tannic acid solution is 10-15wt%, the mass ratio of CaF2 to tannic acid solution is 1:30-40, and the mass ratio of CaF2 to SiO2 is 1:0.4-0.

5.

4. The method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 according to claim 1, characterized in that: During the preparation of CaF2@SiO2, the mass ratio of phytic acid / polyvinyl alcohol / mannitol / aminoterephthalic acid solution to CaF2 / SiO2 dispersion is 2.5-3:102.5-103.

5. The method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 according to claim 1, characterized in that: In the mixed solvent, the volume ratio of methanol to ethanol is 85:

15.

6. The method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 according to claim 1, characterized in that: The mass ratio of PA6 to CaF2@SiO2 is 12-10:1, and the mass ratio of the mixed solvent to PA6 is 7-8:

1.

7. A method for preparing PA6@CaF2@SiO2 fluorescent powder from PA6 according to any one of claims 1 to 6, characterized in that: The yield of PA6@CaF2@SiO2 fluorescent powder is 70-80%, the average particle size is 50-70 μm, and the shrinkage rate is 1.28-1.31%.

Images