Preparation method of flame-retardant antibacterial PBT (polybutylene terephthalate) modified polyester chip

Abstract

The invention discloses a preparation method of a flame-retardant antibacterial PBT (polybutylene terephthalate) modified polyester chip, and aims to solve the technical problems that when the existing modified polyester chip is modified, a flame retardant and an antibacterial agent are chemically incompatible when being compounded, so that the performance is reduced, and the traditional antibacterial agent is easy to migrate and lose efficacy and insufficient in antibacterial long-term effect. According to the preparation method of the flame-retardant antibacterial PBT modified polyester chip provided by the invention, through a phosphorus-nitrogen-silicon synergistic flame retardant and an antibacterial-flame-retardant composite microcapsule system in combination with a supercritical CO2-assisted dispersion process and a sectional temperature control one-step melt blending technology, the multi-dimensional performance of a PBT material is improved, and the self-extinguishing time is greatly shortened; the polydopamine microcapsule can slowly release a plant source antibacterial agent magnolol, so that the long-acting antibacterial rate is realized; the epoxy compatibilizer and PBT terminal carboxyl are grafted in situ to form a branched structure, so that the interface bonding strength is improved, and the tensile strength loss rate is effectively reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of modified polyester chip preparation, in particular to a preparation method of flame-retardant and antibacterial PBT modified polyester chip. BACKGROUND

[0002] PBT, namely polybutylene terephthalate, as a thermoplastic engineering plastic with excellent comprehensive performance, is widely used in electronic and electrical, automobile parts, household appliances and other fields. However, the traditional PBT material has significant defects in flame retardance and antibacterial property: the limiting oxygen index is only 18%-22%, which belongs to flammable material, and is easy to breed bacteria and mold in long-term use, which cannot meet the needs of high health and safety scenes such as medical devices and food packaging.

[0003] When the traditional flame retardant such as halogen and phosphorus is compounded with the antibacterial agent such as silver ion and quaternary ammonium salt, the interface separation often occurs due to poor chemical compatibility, for example, the silver ion will have oxidation-reduction reaction with the phosphorus flame retardant, reducing the flame retardant efficiency, and the LOI decreases by 10%-15%, and the antibacterial activity, namely the bacteriostatic rate, decreases to below 80%.

[0004] High addition amount of flame retardant and antibacterial agent easily causes mechanical property degradation of the material, such as decrease of tensile strength, and thermal decomposition easily occurs in the processing process. The traditional antibacterial agent such as nano-silver is easy to migrate and lose, and the long-acting antibacterial property is insufficient, and the uneven dispersion caused by nano-particle agglomeration affects the surface smoothness of the material. SUMMARY

[0005] The existing problems in the prior art are that the existing modified polyester chip has poor chemical compatibility when the flame retardant and the antibacterial agent are compounded during modification, resulting in performance degradation, and the traditional antibacterial agent is easy to migrate and lose, and the long-acting antibacterial property is insufficient. In view of the above technical problems, the present application provides a preparation method of flame-retardant and antibacterial PBT modified polyester chip.

[0006] The technical scheme of the present application is: a preparation method of flame-retardant and antibacterial PBT modified polyester chip, comprising the following steps:

[0007] S1, dry PBT matrix and additives are mixed to obtain a mixture, the additives include 12-15wt% phosphorus-nitrogen-silicon synergistic flame retardant, 8-10wt% antibacterial-flame retardant composite microcapsule, 3-5wt% modified montmorillonite and 2-3wt% epoxy-based compatibilizer according to the total mass percentage of the PBT matrix;

[0008] S2, the mixture is put into a twin-screw extruder, the temperature is first controlled at 220-230℃, mixed for 1-2 min; then the temperature is raised to 240-250℃, supercritical CO2 with a pressure of 8-10 MPa is injected into the melt, the injection amount of the supercritical CO2 per minute is 5-8% of the melt volume, and the duration is 2-3 min; finally, the temperature is raised to 250-260℃, the phosphorus-nitrogen-silicon synergistic flame retardant is melted, and the temperature is maintained for 3-5 min, to obtain a PBT composite melt with completed in-situ grafting reaction;

[0009] S3, the PBT composite melt is water-cooled and granulated to obtain a flame-retardant and antibacterial PBT modified chip.

[0010] Note: The halogen-free formula meets the RoHS standard, avoids the release of toxic gases such as dioxins, and matches the solvent usage and reaction time, resulting in high product purity and suitability for industrial production.

[0011] Further, the preparation method of the phosphorus-nitrogen-silicon synergistic flame retardant in S1 is as follows: DOPO derivative, aminated POSS, and zinc nitrate are mixed in a mass ratio of 5-6:3-4:1-2, dissolved in tetrahydrofuran, and the mass of the tetrahydrofuran is 3-4 times the total mass of the DOPO derivative, aminated POSS, and zinc nitrate; under nitrogen protection, the mixture is reacted at 80-85℃ for 6-8h, then a 0.5-1mol / L zinc nitrate solution is added, the mass of the zinc nitrate solution is 1-2 times the total mass of the DOPO derivative, aminated POSS, and zinc nitrate, and the mixture is stirred at 60-65℃ for 2-3h, and then dried to obtain the phosphorus-nitrogen-silicon synergistic flame retardant.

[0012] Note: The reactive phosphorus-nitrogen compound in the phosphorus-nitrogen-silicon synergistic flame retardant, i.e. DOPO, provides gas-phase flame retardation and releases PO· free radicals, the aminated cage-type silsesquioxane, i.e. POSS, forms a dense carbon layer to achieve solid-phase flame retardation, and Zn 2+ complexation with the POSS amino group achieves antibacterial function.

[0013] Further, the core material of the antibacterial-flame-retardant composite microcapsule in S1 is composed of magnolol and aluminum hypophosphite in a mass ratio of 4-5:5-6.

[0014] Note: Magnolol is a plant-derived antibacterial agent with an inhibition rate of greater than 99.5%, and aluminum hypophosphite is a halogen-free flame retardant. After optimization of the ratio of the two, the flame-retardant and antibacterial efficiencies are synergistically improved, the plant-derived antibacterial agent replaces heavy metals such as nano-silver, and the environmental toxicity is reduced, which is green and sustainable.

[0015] Further, the preparation method of the antibacterial and flame-retardant composite microcapsule S1 comprises the following steps: mixing the core material with Tris buffer solution in a mass ratio of 1:10-20, wherein the pH value of the Tris buffer solution is 8.5-9, then adding 5-10% of dopamine monomers based on the mass of the core material, stirring at room temperature for 24-36 h, and then centrifuging and drying to obtain the antibacterial and flame-retardant composite microcapsule.

[0016] Description: The polydopamine shell protects the core material from decomposition during processing, i.e., the decomposition temperature needs to be greater than 300℃.

[0017] Further, the thickness of the dopamine monomers attached to the surface of the core material is 50-100 nm, and the particle size of the antibacterial and flame-retardant composite microcapsule is 1-5 μm.

[0018] Description: The thickness of the nanoscale shell is 50-100 nm, which can provide sufficient protection and does not affect the processing fluidity, and the microcapsule particle size of 1-5 μm matches the PBT matrix, which can avoid agglomeration.

[0019] Further, the temperature of the supercritical CO2 S2 is 31-40℃.

[0020] Description: The diffusion coefficient of supercritical CO2 is 10 times higher than that of conventional melt, which can promote the intercalation and exfoliation of montmorillonite, and there is no solvent residue.

[0021] Further, the epoxy-based compatibilizer S1 is glycidyl methacrylate.

[0022] Description: The epoxy group is grafted in situ with the terminal carboxyl group of PBT to form a branched structure, and the interfacial bonding strength is improved.

[0023] Further, the preparation method of the modified montmorillonite S1 comprises the following steps: mixing sodium-based montmorillonite with cetyltrimethylammonium bromide in a mass ratio of 1:0.5-1, then stirring in a 70-80℃ water bath for 4-6 h, centrifuging and washing 3-5 times, and then vacuum drying at 60-80℃ for 12-13 h to obtain the modified montmorillonite.

[0024] Description: CTAB intercalation expands the interlayer spacing of montmorillonite from 1.2 nm to 2.0-2.5 nm, improves the dispersion of fillers, and montmorillonite and aluminum hypophosphite synergistically enhance the densification of the carbon layer.

[0025] Further, the water-cooling pelletizing method of S3 is as follows: the PBT composite melt is introduced into a circulating water cooling tank with water temperature of 20-25 DEG C, cooled and shaped for 30-90s, then introduced into a pelletizer, the rotating speed of the pelletizer is adjusted to 300-400 rpm, cylindrical slices with uniform particle size are obtained by cutting, then centrifugal dewatering is carried out at a rotating speed of 800-1000 rpm for 2-3 min, surface moisture is removed, finally, the slices are placed into a hot air circulating drying box at 80-90 DEG C for drying for 4-6 h, and then flame-retardant and antibacterial PBT modified slices are obtained.

[0026] Description: The water cooling rate is less than 50 DEG C / s, which can avoid slice deformation, and the slices can prevent subsequent hydrolysis after drying.

[0027] The beneficial effects of the present application are as follows: the present application realizes multi-dimensional performance improvement of PBT material by using phosphorus-nitrogen-silicon synergistic flame retardant and antibacterial-flame-retardant composite microcapsule system, combining supercritical CO2 assisted dispersion process and segmented temperature control one-step melt blending technology, using DOPO derivative to release phosphorus-containing free radicals to interrupt gas phase combustion chain reaction, using silicon-oxygen skeleton of amino POSS to form a dense carbon layer in solid phase, using phosphorus-nitrogen-silicon synergistic effect to make the limiting oxygen index jump and greatly reduce the self-extinguishing time; Zn 2+ complexed on the amino group of POSS, instant bacteria inhibition is realized by destroying the bacterial cell membrane and inhibiting enzyme activity, polydopamine microcapsules can release plant source antibacterial agent magnolol to realize long-acting antibacterial rate; epoxy-based compatibilizer is grafted in situ with PBT terminal carboxyl group to form a branched structure, the interface bonding strength is improved, the tensile strength loss rate is effectively reduced, supercritical CO2 assisted stripping modified montmorillonite is realized, the interlayer spacing is expanded, and the impact strength is effectively improved; aluminum hypophosphite and DOPO replace bromine-based flame retardant to meet the RoHS standard, and toxic gas release is avoided. DETAILED DESCRIPTION

[0028] In order to further illustrate the manner of carrying out the present application and the effects achieved by the present application, the technical solutions of the present application will be described in detail below with reference to experiments.

[0029] Example 1:

[0030] A preparation method of flame-retardant and antibacterial PBT modified polyester slices, comprising the following steps:

[0031] S1, dry PBT matrix is mixed with additives to obtain a mixture, the additives include 14wt% phosphorus-nitrogen-silicon synergistic flame retardant, 9wt% antibacterial-flame retardant composite microcapsule, 4wt% modified montmorillonite and 2.5wt% epoxy-based compatibilizer; the phosphorus-nitrogen-silicon synergistic flame retardant is prepared by covalent bonding and ionic complexation reaction of reactive phosphorus-nitrogen compound, aminated POSS and zinc salt; the core material of the antibacterial-flame retardant composite microcapsule is a mixture of plant source antibacterial agent and aluminum hypophosphite, and the shell layer is biobased polydopamine; the modified montmorillonite is modified by intercalation agent;

[0032] The preparation method of the phosphorus-nitrogen-silicon synergistic flame retardant is: mixing DOPO derivative, aminated POSS and zinc nitrate in a mass ratio of 5:3:1, dissolving in tetrahydrofuran, the mass of tetrahydrofuran is 3.5 times the total mass of DOPO derivative, aminated POSS and zinc nitrate; under nitrogen protection, 82.5℃ for 7h, then add 0.75mol / L zinc nitrate solution, the mass of the zinc nitrate solution is 1.5 times the total mass of DOPO derivative, aminated POSS and zinc nitrate, stir at 62.5℃ for 2.5h, dry to obtain phosphorus-nitrogen-silicon synergistic flame retardant;

[0033] The core material of the antibacterial-flame retardant composite microcapsule is composed of magnolol and aluminum hypophosphite in a mass ratio of 4:5.5;

[0034] The preparation method of the antibacterial-flame retardant composite microcapsule is: mixing the core material with Tris buffer in a mass ratio of 1:15, the pH value of the Tris buffer is 8.5, then adding 7.5% dopamine monomer based on the mass of the core material, stirring at room temperature for 30h, then centrifuging and drying to obtain antibacterial-flame retardant composite microcapsule; the adhesion thickness of dopamine monomer on the surface of the core material is 75nm, and the particle size of the antibacterial-flame retardant composite microcapsule is 3μm;

[0035] The epoxy-based compatibilizer is glycidyl methacrylate;

[0036] The preparation method of the modified montmorillonite is: mixing sodium-based montmorillonite and cetyltrimethylammonium bromide in a mass ratio of 1:0.75, then stirring in a 75℃ water bath for 5h, washing by centrifugation for 4 times, and then vacuum drying at 70℃ for 11h to obtain modified montmorillonite;

[0037] S2, the mixture is put into a twin-screw extruder, the temperature is first controlled at 225℃, and mixed for 1.5 min; then the temperature is raised to 245℃, supercritical CO2 with a pressure of 9 MPa is injected into the melt, the injection amount of the supercritical CO2 per minute is 6.5% of the melt volume, and the duration is 2.5 min; finally, the temperature is raised to 255℃, the phosphorus-nitrogen-silicon synergistic flame retardant is melted, and the duration is 4 min, to obtain a PBT composite melt after the completion of the in-situ grafting reaction; the temperature of the supercritical CO2 is 35℃;

[0038] S3, the PBT composite melt is introduced into a circulating water cooling tank with a water temperature of 22.5℃, cooled and shaped for 60 s, then introduced into a granulator, the rotation speed of the granulator is adjusted to 350 rpm, and cylindrical granules with uniform particle size are obtained by cutting, then centrifugal dewatering is performed at a rotation speed of 900 rpm for 2.5 min to remove surface moisture, and finally placed into a hot air circulating drying box at 85℃ for drying for 5 h, to obtain flame-retardant and antibacterial PBT modified granules.

[0039] Example 2: This example is basically the same as Example 1, except that the mass ratio of the DOPO derivative, the aminated POSS and the zinc nitrate mixed during preparation of the phosphorus-nitrogen-silicon synergistic flame retardant is 5:4:1.

[0040] Example 3: This example is basically the same as Example 1, except that the mass ratio of the DOPO derivative, the aminated POSS and the zinc nitrate mixed during preparation of the phosphorus-nitrogen-silicon synergistic flame retardant is 6:3:1.

[0041] Example 4: This example is basically the same as Example 1, except that the mass ratio of the DOPO derivative, the aminated POSS and the zinc nitrate mixed during preparation of the phosphorus-nitrogen-silicon synergistic flame retardant is 3:2:1.

[0042] Example 5: This example is basically the same as Example 1, except that the core material of the antibacterial-flame-retardant composite microcapsule is composed of magnolol and aluminum hypophosphite at a mass ratio of 4:6.

[0043] Example 6: This example is basically the same as Example 1, except that the core material of the antibacterial-flame-retardant composite microcapsule is composed of magnolol and aluminum hypophosphite at a mass ratio of 4.5:5.5.

[0044] Example 7: This example is basically the same as Example 1, except that the core material of the antibacterial-flame-retardant composite microcapsule is composed of magnolol and aluminum hypophosphite at a mass ratio of 1:1.

[0045] Example 8: This example is basically the same as Example 1, except that the mixed materials are fed into the twin-screw extruder, the temperature is first controlled at 220°C, and mixed for 1 min; then the temperature is raised to 240°C, supercritical CO2 with a pressure of 8 MPa is injected into the melt, the injection amount of the supercritical CO2 per minute is 5% of the melt volume, and the duration is 2 min; finally, the temperature is raised to 250°C, the phosphorus-nitrogen-silicon synergistic flame retardant is melted, and the duration is 3 min, to obtain a PBT composite melt with completed in-situ grafting reaction; the temperature of the supercritical CO2 is 31°C.

[0046] Example 9: This example is basically the same as Example 1, except that the mixed materials are fed into the twin-screw extruder, the temperature is first controlled at 230°C, and mixed for 2 min; then the temperature is raised to 250°C, supercritical CO2 with a pressure of 10 MPa is injected into the melt, the injection amount of the supercritical CO2 per minute is 8% of the melt volume, and the duration is 3 min; finally, the temperature is raised to 260°C, the phosphorus-nitrogen-silicon synergistic flame retardant is melted, and the duration is 5 min, to obtain a PBT composite melt with completed in-situ grafting reaction; the temperature of the supercritical CO2 is 40°C.

[0047] Example 10: This example is basically the same as Example 1, except that the additives include 12 wt% of the phosphorus-nitrogen-silicon synergistic flame retardant, 8 wt% of the antibacterial-flame-retardant composite microcapsule, 3 wt% of the modified montmorillonite, and 2 wt% of the epoxy-based compatibilizer, based on the total mass percentage of the PBT matrix.

[0048] Example 11: This example is basically the same as Example 1, except that the additives include 15 wt% of the phosphorus-nitrogen-silicon synergistic flame retardant, 10 wt% of the antibacterial-flame-retardant composite microcapsule, 5 wt% of the modified montmorillonite, and 3 wt% of the epoxy-based compatibilizer, based on the total mass percentage of the PBT matrix.

[0049] Comparative Example 1: With reference to Example 1, the raw material does not use the phosphorus-nitrogen-silicon synergistic flame retardant, but uses decabromodiphenyl ether accounting for 15 wt% of the total mass of the PBT matrix.

[0050] Comparative Example 2: With reference to Example 1, the raw material does not add the antibacterial-flame-retardant composite microcapsule.

[0051] Comparative Example 3: With reference to Example 1, supercritical CO2 is not injected in S2.

[0052] Comparative Example 4: With reference to Example 1, the additives include 15 wt% of decabromodiphenyl ether and 4 wt% of unmodified montmorillonite, based on the total mass percentage of the PBT matrix.

[0053] To investigate the flame-retardant and antibacterial properties of PBT modified chips in some examples and control examples, the main materials were determined according to the experimental formulation, and samples were obtained for testing. The limiting oxygen index (LOI) was based on ASTM D2863, and the sample size was controlled to be 100 × 6.5 × 3 mm. 3 The method used was the oxygen concentration gradient method; UL94 vertical combustion was performed according to ASTM D3801, with sample dimensions controlled at 125×13×1.6mm. 3 The microcapsule was ignited twice, and the dripping and self-extinguishing times were recorded. The TGA char rate was determined using Netzsch STA 449F3, under a nitrogen atmosphere, with the temperature increased at 10℃ / min to 800℃, and the char mass was recorded. The antibacterial rate was determined using ISO 22196, with E. coli inoculated for 24 hours using colony counting. The microcapsule thermal stability was determined using TGA to test the core material decomposition temperature, compared to the processing temperature (260℃). Tensile strength was determined using ASTM D638, Type I specimens, at a tensile rate of 50 mm / min. Impact strength was determined using ASTM D256, notched specimens, with a pendulum energy of 5.5 J. SEM / XRD was used to observe dispersibility using JEOL JSM-7800F, and Rigaku SmartLab was used to measure the montmorillonite interlayer spacing. The test results are shown in Tables 1-5. Specific investigations are as follows:

[0054] 1. To investigate the effects of the proportions of DOPO derivatives, POSS, and zinc nitrate in the phosphorus-nitrogen-silicon synergistic flame retardant on flame retardant efficiency and thermal stability.

[0055] Table 1. Performance test results of samples from Examples 1-4 and Control Example 1

[0056]

[0057] As shown in Table 1, a comparison of Examples 1-4 reveals that when the ratio of DOPO derivative, aminated POSS, and zinc nitrate in the phosphorus-nitrogen-silicon synergistic flame retardant of this scheme is 3:2:1, the LOI and char residue are the highest, while the smoke density is the lowest. The synergistic effect of the phosphorus-nitrogen-silicon tri-component in Example 4 significantly enhances the char layer density and gas-phase flame retardant efficiency. A comparison between Examples 2 and 3 shows that the increase in the proportion of POSS leads to a slight decrease in LOI from 36.2% to 35.8%, but the char residue remains above 30%, indicating that the silicon-oxygen skeleton of POSS contributes more to solid-phase flame retardancy.

[0058] Compared with Comparative Example 1, the LOI of Example 4 of this scheme is 37.6%, which is significantly higher than the LOI of 29.5% of the bromine system of Comparative Example 1, and the smoke density is reduced significantly. This shows that the halogen-free system of this scheme has dual advantages in flame retardant efficiency and environmental protection.

[0059] 2. Investigating the influence of the core material of antibacterial-flame retardant composite microcapsules on their antibacterial properties:

[0060] Table 2 sample performance test results of examples 5-7, control example 2

[0061]

[0062] As shown in Table 2, by comparing examples 5-7, the antibacterial rate of example 6 is best, which is 99.7%, and the antibacterial rate of example 6 is highest, which is 99.1%, and it can be seen that the increase of aluminum hypophosphite has a positive effect on the long-term antibacterial property.

[0063] The antibacterial rate of example 7 is 99.5%, which is slightly lower than that of example 6, but the antibacterial rate of 180 days is 97.8%, and it can be seen that the functional antagonism of magnolol and aluminum hypophosphite in the core material needs to be balanced.

[0064] As can be seen from the comparison with control example 2, the antibacterial rate of control example 2 without adding microcapsules is 0%, which shows that the core material of antibacterial and flame-retardant composite microcapsules is crucial to the antibacterial property.

[0065] 3, explore the influence of process parameters change of step S2 on mechanical properties:

[0066] Table 3 sample performance test results of examples 1, 8, 9, control example 3

[0067]

[0068] As shown in Table 3, by comparing examples 1, 8, 9, the interlayer spacing of example 9 is the largest, which is 3.5nm, and the impact strength is the largest, which is 8.1kJ / m 2 , and the tensile strength is slightly higher than that of example 1, which is 57MPa, indicating that high pressure CO2 can promote the exfoliation of montmorillonite and enhance the interface bonding between montmorillonite filler and matrix, and the SEM dispersion uniformity of example 9 is 95%, and that of example 8 is 88%, which shows that the CO2 diffusion efficiency under the process parameters of example 9 is better.

[0069] As can be seen from the comparison with control example 3, the interlayer spacing of control example 3 without using supercritical CO2 is only 1.2nm, and the impact strength and tensile strength are low, and the supercritical process has a great influence on the dispersion of fillers.

[0070] 4, explore the influence of additive ratio content change on environmental protection:

[0071] Table 4 sample performance test results of examples 1, 10, 11, control example 3

[0072]

[0073] As shown in Table 4, it can be seen from the comparison of Examples 1, 10 and 11 that: all the examples are not detected dioxin, the biodegradation rate is also greater than 45%, RoHS test passes, that is, heavy metals are not detected, and it can be seen that the halogen-free formula has excellent environmental protection; the adjustment of the content of the additive has no negative effect on the environmental protection, which verifies the stability of the process.

[0074] As can be seen from the comparison with Comparative Example 4: the dioxin release of Comparative Example 4 is 12.5 ng / g, the biodegradation rate is only 8.2%, and RoHS does not pass, the Br content of Comparative Example 4 exceeds the standard, and it can be seen that the bromine system has high environmental toxicity, and the environmental performance of the sample prepared by the additive ratio of the present scheme is better than that of the conventional bromine system.

Claims

1. A method for preparing flame-retardant and antibacterial PBT-modified polyester chips, characterized in that, Includes the following steps: S1. Take the dried PBT matrix and mix it with the additives to obtain a mixture. The additives, based on the total mass percentage of the PBT matrix, include 12-15 wt% of phosphorus-nitrogen-silicon synergistic flame retardant, 8-10 wt% of antibacterial-flame retardant composite microcapsules, 3-5 wt% of modified montmorillonite, and 2-3 wt% of epoxy compatibilizer. S2. The mixture is fed into a twin-screw extruder. First, the temperature is controlled at 220-230℃ and mixed for 1-2 minutes. Then, the temperature is raised to 240-250℃, and supercritical CO2 at a pressure of 8-10 MPa is injected into the melt. The injection rate of supercritical CO2 is 5-8% of the melt volume per minute, and the duration is 2-3 minutes. Finally, the temperature is raised to 250-260℃ to melt the phosphorus-nitrogen-silicon synergistic flame retardant and maintain it for 3-5 minutes to obtain a PBT composite melt that has completed the in-situ grafting reaction. S3. The PBT composite melt is water-cooled and pelletized to obtain flame-retardant and antibacterial PBT modified chips.

2. The method for preparing flame-retardant and antibacterial PBT modified polyester chips according to claim 1, characterized in that, The preparation method of the phosphorus-nitrogen-silicon synergistic flame retardant described in S1 is as follows: DOPO derivative, aminated POSS, and zinc nitrate are mixed in a mass ratio of 5-6:3-4:1-2 and dissolved in tetrahydrofuran, wherein the mass of the tetrahydrofuran is 3-4 times the total mass of the DOPO derivative, aminated POSS, and zinc nitrate; the reaction is carried out at 80-85℃ for 6-8 hours under nitrogen protection; then a zinc nitrate solution with a concentration of 0.5-1 mol / L is added, wherein the mass of the zinc nitrate solution is 1-2 times the total mass of the DOPO derivative, aminated POSS, and zinc nitrate; the mixture is stirred at 60-65℃ for 2-3 hours; and after drying, the phosphorus-nitrogen-silicon synergistic flame retardant is obtained.

3. The method for preparing flame-retardant and antibacterial PBT modified polyester chips according to claim 1, characterized in that, The core material of the antibacterial-flame retardant composite microcapsule described in S1 is composed of magnolol and aluminum hypophosphite in a mass ratio of 4-5:5-6.

4. The method for preparing flame-retardant and antibacterial PBT modified polyester chips according to claim 3, characterized in that, The preparation method of the antibacterial-flame retardant composite microcapsules described in S1 is as follows: the core material is mixed with Tris buffer at a mass ratio of 1:10-20, the pH value of the Tris buffer is 8.5-9, then 5-10% of the mass of the core material of dopamine monomer is added, the mixture is stirred at room temperature for 24-36 hours, and then centrifuged and dried to obtain the antibacterial-flame retardant composite microcapsules.

5. The method for preparing flame-retardant and antibacterial PBT modified polyester chips according to claim 4, characterized in that, The dopamine monomer has an adhesion thickness of 50-100 nm on the core material surface, and the antibacterial-flame retardant composite microcapsules have a particle size of 1-5 μm.

6. The method for preparing flame-retardant and antibacterial PBT modified polyester chips according to claim 1, characterized in that, The temperature of the supercritical CO2 described in S2 is 31-40℃.

7. The method for preparing flame-retardant and antibacterial PBT modified polyester chips according to claim 1, characterized in that, The epoxy compatibilizer in S1 is glycidyl methacrylate.

8. The method for preparing flame-retardant and antibacterial PBT modified polyester chips according to claim 1, characterized in that, The modified montmorillonite described in S1 is prepared by mixing sodium montmorillonite and hexadecyltrimethylammonium bromide at a mass ratio of 1:0.5-1, stirring in a water bath at 70-80℃ for 4-6 hours, centrifuging and washing 3-5 times, and then vacuum drying at 60-80℃ for 12-13 hours to obtain modified montmorillonite.

9. The method for preparing flame-retardant and antibacterial PBT modified polyester chips according to claim 1, characterized in that, The water-cooled pelletizing method described in S3 is as follows: The PBT composite melt is introduced into a circulating water cooling tank at a water temperature of 20-25℃ and cooled and shaped for 30-90 seconds. Then, it is introduced into a pelletizer, and the pelletizer speed is adjusted to 300-400 rpm to cut cylindrical slices with uniform particle size. Then, it is centrifuged at a speed of 800-1000 rpm for 2-3 minutes to remove surface moisture. Finally, it is placed in a hot air circulating drying oven at 80-90℃ for 4-6 hours to dry, thereby obtaining flame-retardant and antibacterial PBT modified slices.

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