A method for preparing recycled polyester slices using waste polyester fabrics and recycled polyester slices

Abstract

The invention relates to the technical field of recycled polyester, and discloses a method for preparing recycled polyester slices using waste polyester cloth and the recycled polyester slices. The preparation method comprises: alcoholyzing the pretreated waste polyester cloth by ethylene glycol alcoholysis, and obtaining recycled ethylene terephthalate after decolorization; polycondensing the flame retardant monomer with the recycled ethylene terephthalate under catalyst conditions to obtain flame retardant polyethylene terephthalate; melt blending the flame retardant polyethylene terephthalate with the flame retardant, melt extruding, cooling and pelletizing to obtain recycled polyester slices; the recycled polyester slices have excellent flame retardancy and can be used to prepare polyester fiber products with good flame retardancy.

Description

Technical Field

[0001] The invention relates to the technical field of recycled polyester, and in particular to a method for preparing recycled polyester slices by utilizing waste polyester cloth and the recycled polyester slices. Background Art

[0002] Polyester fiber has many excellent properties and is one of the main raw materials for textiles. It is widely used in making various clothing. However, with the rapid development of the polyester textile industry, the amount of waste polyester fabrics has increased year by year. At present, the recycling methods of waste polyester fabrics include landfill, energy recovery, physical recovery and chemical recovery. The landfill method takes up a lot of land space, and polyester fibers are difficult to degrade in the natural environment. The energy recovery method incinerates the recycled waste polyester fabrics, which can generate heat energy, but harmful gases will be generated during the incineration process. The physical recovery method refers to the process of reprocessing waste polyester fabrics into secondary raw materials or products through physical means, but the physical recovery method has high requirements on the composition and purity of the recycled waste polyester fabrics, and is not suitable for the recycling of most mixed colored waste polyester fabrics. The chemical recycling method refers to the depolymerization of the polymer of polyester fiber into monomers through various chemical reactions, and then separation, purification, and repolymerization to form recycled polyester materials. It has the characteristics of high recovery rate and high product purity, and realizes the recycling of waste polyester fabrics.

[0003] Existing technologies such as Chinese patent application CN116284710A disclose a method for preparing polyester chips by chemically recycling waste polyester fibers, wherein the waste polyester fibers are pretreated to obtain polyester recycled materials, which are depolymerized and cooled for crystallization, and solid-liquid separation is performed to obtain polyester monomer BHET particles, which are then subjected to sublimation and desublimation to remove heavy metal ions, pigments and impurities in the polyester monomer BHET, which is beneficial to improving the quality and performance of recycled polyester chips. However, the flame retardancy of the recycled polyester chips prepared by the method has not been improved, which limits the application of the material. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing regenerated polyester slices using waste polyester cloth and the regenerated polyester slices. The regenerated polyester slices have excellent flame retardancy and can be used to prepare polyester fiber products with good flame retardancy.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: a method for preparing recycled polyester slices using waste polyester fabrics, comprising the following steps:

[0006] Step 1, mixing and washing the waste polyester fabric with an aqueous solution of sodium hydroxide, taking it out after washing, and drying it to obtain the pretreated waste polyester fabric; mixing the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate, reacting, filtering after the reaction, taking the filtrate, cooling and crystallizing, filtering by suction, taking the filter cake, and obtaining the crude product of regenerated ethylene terephthalate; mixing and dissolving the crude product of regenerated ethylene terephthalate with water, adding acidified activated carbon, decolorizing, filtering by suction after the decolorization, taking the filtrate, cooling and crystallizing, filtering, taking the filter cake, and drying to obtain regenerated ethylene terephthalate; wherein the acidified activated carbon is prepared by the following steps: mixing the activated carbon with an aqueous solution of nitric acid, reacting, filtering after the reaction, taking the filter cake, washing, and drying to obtain the acidified activated carbon;

[0007] Step 2: Mix the flame-retardant monomer, regenerated ethylene terephthalate and ethylene glycol antimony, perform a pre-polycondensation reaction, perform a final polycondensation reaction after the reaction is completed, and obtain flame-retardant polyethylene terephthalate; wherein the flame-retardant monomer is prepared by the following steps: Step (1): mix benzaldehyde and ethanol, add 5-amino-dimethyl isophthalate, react, cool to room temperature after the reaction is completed, filter, take the filter cake, recrystallize, and dry to obtain a reaction product; mix the reaction product, 1,4-butanediol and tetrapropyl titanate, react, and obtain a comonomer after the reaction is completed; Step (2): mix the comonomer, DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) and methanol, react, filter after the reaction is completed, take the filter cake, wash, and dry to obtain a flame-retardant monomer;

[0008] Step 3, melt-blending flame-retardant polyethylene terephthalate and flame retardant, melt-extrude, cool and pelletize to obtain recycled polyester slices; wherein the flame retardant is prepared by the following steps: step (1), mixing γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol and water, ultrasonically dispersing, reacting, filtering after the reaction, taking the filter cake, washing, and drying to obtain amide magnesium hydroxide; step (2), mixing and dissolving hexachlorocyclotriphosphazene and tetrahydrofuran, adding phenol and anhydrous potassium carbonate, reacting, adding p-hydroxybenzaldehyde after the reaction, continuing the reaction, purifying, and drying to obtain aldehyded cyclotriphosphazene; step (3), mixing aldehyded cyclotriphosphazene, amide magnesium hydroxide and ethanol, reacting, filtering after the reaction, taking the filter cake, washing, and drying to obtain a flame retardant.

[0009] Preferably, in the step 1, the solid-liquid ratio of the waste polyester fabric and the sodium hydroxide aqueous solution is 1:(40-50), and the sodium hydroxide aqueous solution is 1 g / L of sodium hydroxide aqueous solution; the mass ratio of the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate is 10:(60-70):(0.2-0.25); and the reaction conditions are: in a nitrogen atmosphere, at a rotation speed of 100-200 r / min and a temperature of 230-240°C for 5-6 hours.

[0010] Preferably, in the step 1, the mass ratio of the crude product of regenerated ethylene terephthalate, acidified activated carbon and water is 10:(10-12):(30-40); and the decolorization conditions are: decolorization at a temperature of 90-95° C. for 2-3 hours.

[0011] Preferably, in the preparation of the acidified activated carbon in step 1, the mass ratio of the activated carbon to the aqueous nitric acid solution is 1:(10-15), the aqueous nitric acid solution is a 10 mol / L aqueous nitric acid solution; and the reaction conditions are: reacting at a temperature of 30-40°C for 2-3h.

[0012] Preferably, in the step 2, the mass ratio of the flame retardant monomer, the regenerated ethylene terephthalate and the ethylene glycol antimony is (10-12):(88-90):0.4; the pre-polycondensation reaction conditions are: the pre-polycondensation reaction is carried out at a vacuum degree of 10-11 kPa and a temperature of 230-245°C for 0.8-1 h; the final polycondensation reaction conditions are: the final polycondensation reaction is carried out at a vacuum degree of 40-50 Pa and a temperature of 270-280°C for 0.8-1 h.

[0013] Preferably, in the preparation of the flame-retardant monomer in step 2, in step (1): the mass ratio of benzaldehyde, ethanol and 5-amino-dimethyl isophthalate is (6-6.3):(25-35):(12-12.5); when preparing the reaction product, the reaction conditions are: reacting for 6-8h in a nitrogen atmosphere at a temperature of 75-85°C; the mass ratio of the reaction product, 1,4-butanediol and tetrapropyl titanate is 530:(180-190):(3-4); when preparing the comonomer, the reaction conditions are: reacting in a nitrogen atmosphere at a temperature of 180-200°C until the methanol distillate amount is 90-95% of the theoretical amount.

[0014] Preferably, the solvent used in the recrystallization operation comprises ethanol.

[0015] Preferably, in the preparation of the flame-retardant monomer in step 2, in step (2): the mass ratio of the comonomer, DOPO and methanol is 30:(23-25):(65-75); the reaction conditions are: reflux reaction at 65-70° C. in a nitrogen atmosphere for 7-8 hours.

[0016] Preferably, in the step three: the mass ratio of flame retardant polyethylene terephthalate to flame retardant is 100:(3-5); the melt blending conditions are: melt blending at a temperature of 230-240°C; and the melt extrusion conditions are: melt extrusion through a twin-screw extruder at a speed of 180-200r / min and a temperature of 250-255°C.

[0017] Preferably, in the preparation of the flame retardant in step three, in step (1): the mass ratio of γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol and water is (0.5-0.8):4:(30-35):(1-2); the reaction conditions are: reacting at a temperature of 85-95°C for 12-16h.

[0018] Preferably, in the preparation of the flame retardant in step three, in step (2): the mass ratio of hexachlorocyclotriphosphazene, tetrahydrofuran, phenol, anhydrous potassium carbonate and p-hydroxybenzaldehyde is 1:(20-30):(2-3):(8-10):(3-4); the reaction conditions are: reacting at a temperature of 55-60°C for 24-26h; and the continued reaction conditions are: continuing the reaction at a temperature of 55-60°C for 12-16h.

[0019] Preferably, the purification operation includes: adding deionized water 2-3 times the mass of the reaction product to the reaction product after the reaction is completed, filtering, taking the filter cake, adding ethyl acetate 5-8 times the mass of the filter cake to dissolve it, and repeating the precipitation and filtration operation.

[0020] Preferably, in the preparation of the flame retardant in step three, in step (3): the mass ratio of aldehyded cyclotriphosphazene, amide magnesium hydroxide and ethanol is 1:(3-4):(250-300); the reaction conditions are: reacting at a temperature of 75-85°C for 8-10h.

[0021] Preferably, a regenerated polyester slice is prepared by the method for preparing regenerated polyester slice using waste polyester cloth as described above.

[0022] Compared with the prior art, the invention has the following beneficial effects: the invention pre-treats waste polyester fabric, performs alcoholysis by ethylene glycol alcoholysis, and then performs decolorization by acidified activated carbon to obtain regenerated ethylene terephthalate; a flame-retardant monomer is added to the regenerated ethylene terephthalate, a polycondensation reaction occurs under the action of a catalyst, the obtained flame-retardant regenerated polyethylene terephthalate is melt-blended with a flame retardant, and extruded and pelletized, and the obtained regenerated polyester slices have excellent flame retardancy, and polyester fiber products with good flame retardancy can be prepared.

[0023] The ethylene glycol alcoholysis method is one of the important processes for chemical recovery of polyester. The depolymerizing agent is ethylene glycol, and the product is mainly ethylene glycol terephthalate (BHET). The reaction conditions of the ethylene glycol alcoholysis method are mild, ethylene glycol is not easy to volatilize and is easy to recover, and the product ethylene glycol terephthalate can be directly used as a polycondensation monomer in polyester production. In the present invention, waste polyester fabric is subjected to alkaline solution pretreatment to remove surface impurities, and then alcoholysis is performed by the ethylene glycol alcoholysis method to obtain a crude product of regenerated ethylene glycol terephthalate. Since the dye contained in the waste polyester fabric will remain in the crude product crystals of the regenerated ethylene glycol terephthalate during alcoholysis, the present invention adopts acidified activated carbon for decolorization to achieve the purpose of regenerating ethylene glycol terephthalate. The invention relates to an effective decolorization method for crude product of ethylene glycol dicarboxylate; wherein, the acidified activated carbon is prepared by acidifying the activated carbon with a nitric acid aqueous solution, and a large number of oxygen-containing groups such as carboxyl groups are introduced into the activated carbon after acidification, so that the dye and the acidified activated carbon have better binding force, so the acidified activated carbon can more effectively decolorize the crude product of regenerated ethylene glycol terephthalate; the invention mixes 5-amino-dimethyl isophthalate with benzaldehyde, and generates a Schiff base dynamic covalent bond through the amino group and the aldehyde group, and the obtained reaction product is then subjected to an ester exchange reaction with 1,4-butanediol to generate a comonomer with a double-terminal hydroxyethyl ester group, and a phosphine reaction is generated between DOPO and the side Schiff base bond in the comonomer. The flame retardant monomer is obtained by hydrogenation reaction, and the flame retardant monomer containing DOPO flame retardant group and double-terminal hydroxyethyl ester group is obtained; the regenerated polyethylene terephthalate obtained after decolorization is used as a condensation monomer, and a condensation reaction is carried out with the flame retardant monomer under catalyst conditions, so that the flame retardant monomer is copolymerized in the polyethylene terephthalate main chain, thereby improving the flame retardancy of the polyethylene terephthalate. Moreover, since the DOPO flame retardant group is grafted on the polymer side chain, even if the phosphorus-containing group DOPO decomposes during the combustion process, it will not affect the integrity of the polymer main chain structure, so that the anti-melting droplet performance of the polymer is improved. At the same time, the benzene ring structure in the flame retardant monomer can also further improve the flame retardant recycled polyethylene terephthalate. The invention relates to a method for preparing a flame retardant polyester having a thermal oxidation performance and a thermal stability performance of alcohol esters; the invention reacts hexachlorocyclotriphosphazene with phenol and p-hydroxybenzaldehyde to obtain an aldehyde-formylated cyclotriphosphazene grafted with a benzene ring and an aldehyde group; the aldehyde group of the aldehyde-formylated cyclotriphosphazene reacts with an amino magnesium hydroxide surface-modified with an aminosilane coupling agent to produce a Schiff base reaction, so that the organic flame retardant group cyclotriphosphazene is connected with the magnesium hydroxide through a Schiff base bond, which can not only improve the dispersibility of nano magnesium hydroxide in a polymer matrix and make it difficult to agglomerate, but also improve the stability of the organic flame retardant group cyclotriphosphazene, and the obtained flame retardant has better thermal stability and flame retardancy; the flame retardant recycled polyethylene terephthalate is melt-blended with the flame retardant, extruded and pelletized, and recycled polyester slices are obtained;Among them, the unreacted amino groups on the surface of the flame retardant react with the terminal carboxyl groups of the flame-retardant recycled polyethylene terephthalate molecular chain in the molten state to undergo an amidation reaction, grafting the flame retardant onto the chain segments of the flame-retardant recycled polyethylene terephthalate, making the flame retardant have better dispersibility and compatibility, and further improving the flame retardant properties of the recycled polyester chips. ; BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a process flow chart of preparing recycled polyester slices using waste polyester fabrics in the present invention;

[0025] Figure 2 It is a schematic diagram of the reaction for preparing the flame retardant monomer in the present invention;

[0026] Figure 3 It is a bar graph of the limiting oxygen index of Examples 1-5 and Comparative Examples 1-2 in the performance test of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment discloses a method for preparing recycled polyester slices using waste polyester fabric, comprising the following steps:

[0030] Step 1: Mix the waste polyester fabric with 1g / L sodium hydroxide aqueous solution at a solid-liquid ratio of 1:40 for 2h, take it out after washing, and dry it at 50°C for 10h to obtain the pretreated waste polyester fabric; mix the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate at a mass ratio of 10:60:0.2, react for 6h in a nitrogen atmosphere at a speed of 100r / min and a temperature of 230°C, filter after the reaction, take the filtrate, cool and crystallize at 5°C for 10h, filter by suction, take the filter cake, and obtain the crude product of regenerated ethylene terephthalate; mix the crude product of regenerated ethylene terephthalate with water at 90°C and dissolve it, add acidifying agent Activated carbon, the mass ratio of the crude product of regenerated ethylene terephthalate, acidified activated carbon and water is 10:10:30, decolorize at 90°C for 3h, after decolorization, filter by suction, take the filtrate, cool and crystallize at 0°C for 10h, filter, take the filter cake, dry at 50°C for 10h, and obtain regenerated ethylene terephthalate; wherein, the acidified activated carbon is prepared by the following steps: mixing the activated carbon with a 10mol / L nitric acid aqueous solution at a mass ratio of 1:10, reacting at 30°C for 3h, filtering after the reaction, taking the filter cake, adding water 5 times the mass of the filter cake to wash until neutral, and drying at 50°C for 12h to obtain the acidified activated carbon;

[0031] Step 2: Mix the flame retardant monomer, regenerated polyethylene terephthalate and ethylene glycol antimony in a mass ratio of 10:90:0.4, perform a pre-polycondensation reaction at a vacuum degree of 10 kPa and a temperature of 230°C for 1 hour, and after the reaction, perform a final polycondensation reaction at a vacuum degree of 40 Pa and a temperature of 270°C for 1 hour. After the reaction, flame retardant regenerated polyethylene terephthalate is obtained; wherein the flame retardant monomer is prepared by the following steps: Step (1): mix benzaldehyde and ethanol, add 5-amino-dimethyl isophthalate, the mass ratio of benzaldehyde, ethanol and 5-amino-dimethyl isophthalate is 6:25:12, react in a nitrogen atmosphere at a temperature of 75°C for 8 hours, and after the reaction, Cool to room temperature, filter, take the filter cake, add ethanol 5 times the mass of the filter cake for recrystallization, and dry at 50°C for 16 hours to obtain a reaction product; mix the reaction product, 1,4-butanediol, and tetrapropyl titanate in a mass ratio of 530:180:3, react in a nitrogen atmosphere at 180°C until the methanol distillate is 90% of the theoretical amount, and after the reaction is completed, obtain a comonomer; step (2), mix the comonomer, DOPO, and methanol in a mass ratio of 30:23:65, reflux in a nitrogen atmosphere at 65°C for 8 hours, after the reaction is completed, filter, take the filter cake, add methanol 5 times the mass of the filter cake for washing three times, and dry at 60°C for 14 hours to obtain a flame retardant monomer;

[0032] Step 3: melt-blending flame-retardant recycled polyethylene terephthalate and flame retardant at a mass ratio of 100:3 at a temperature of 230°C, melt-extrude through a twin-screw extruder at a speed of 180r / min and a temperature of 250°C, and cool and pelletize to obtain recycled polyester slices; wherein the flame retardant is prepared by the following steps: step (1): mixing γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol, and water at a mass ratio of 0.5:4:30:1, ultrasonically dispersing for 10 minutes, reacting at a temperature of 85°C for 16 hours, filtering after the reaction, taking the filter cake, adding 5 times the mass of the filter cake to wash three times, and drying at a temperature of 80°C for 12 hours to obtain amide magnesium hydroxide; step (2): mixing hexachlorocyclotriphosphazene with tetrahydrofuran to dissolve, adding phenol and anhydrous potassium carbonate, and drying at 55°C. The mixture was reacted at room temperature for 26 hours. After the reaction was completed, p-hydroxybenzaldehyde, hexachlorocyclotriphosphazene, tetrahydrofuran, phenol, anhydrous potassium carbonate and p-hydroxybenzaldehyde were added in a mass ratio of 1:20:2:8:3. The reaction was continued at 55°C for 16 hours. After the reaction was completed, a reaction product was obtained. Deionized water twice the mass of the reaction product was added for precipitation. The filter cake was taken and ethyl acetate five times the mass of the filter cake was added for dissolution. The precipitation and filtration operation was repeated once. The mixture was dried at 50°C for 18 hours to obtain aldehyded cyclotriphosphazene. Step (3) aldehyded cyclotriphosphazene, aminated magnesium hydroxide and ethanol were mixed in a mass ratio of 1:3:250 and reacted at 75°C for 10 hours. After the reaction was completed, the mixture was filtered and the filter cake was taken. The filter cake was washed with ethanol five times the mass of the filter cake and dried at 50°C for 10 hours to obtain a flame retardant.

[0033] Example 2

[0034] This embodiment discloses a method for preparing recycled polyester slices using waste polyester fabric, comprising the following steps:

[0035] Step 1: Mix the waste polyester fabric with 1g / L sodium hydroxide aqueous solution at a solid-liquid ratio of 1:40 for 2h, take it out after washing, and dry it at 55°C for 9h to obtain the pretreated waste polyester fabric; mix the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate at a mass ratio of 10:65:0.23, react for 5.5h in a nitrogen atmosphere at a speed of 150r / min and a temperature of 235°C. After the reaction is completed, filter, take the filtrate, cool and crystallize at 5°C for 10h, filter by suction, take the filter cake, and obtain the crude product of regenerated ethylene terephthalate; mix the crude product of regenerated ethylene terephthalate with water at 90°C and dissolve it, add acidifying agent Activated carbon, the mass ratio of the crude product of regenerated ethylene terephthalate, acidified activated carbon and water is 10:10.5:35, decolorize at 90°C for 3h, after decolorization, filter by suction, take the filtrate, cool and crystallize at 2°C for 11h, filter, take the filter cake, dry at 55°C for 9h, and obtain regenerated ethylene terephthalate; wherein, the acidified activated carbon is prepared by the following steps: mixing the activated carbon with a 10mol / L nitric acid aqueous solution at a mass ratio of 1:12, reacting at 30°C for 3h, filtering after the reaction, taking the filter cake, adding water 6 times the mass of the filter cake to wash until neutral, and drying at 55°C for 11h to obtain the acidified activated carbon;

[0036] Step 2: Mix the flame retardant monomer, regenerated polyethylene terephthalate and ethylene glycol antimony in a mass ratio of 10.5:89.5:0.4, carry out a pre-polycondensation reaction at a vacuum degree of 10 kPa and a temperature of 235°C for 1 hour, and after the reaction is completed, carry out a final polycondensation reaction at a vacuum degree of 45 Pa and a temperature of 275°C for 0.9 hour. After the reaction is completed, flame retardant regenerated polyethylene terephthalate is obtained; wherein the flame retardant monomer is prepared by the following steps: Step (1): mix benzaldehyde and ethanol, add 5-amino-dimethyl isophthalate, the mass ratio of benzaldehyde, ethanol and 5-amino-dimethyl isophthalate is 6.1:30:12.2, react in a nitrogen atmosphere at a temperature of 80°C for 7 hours, and the reaction is completed. Afterwards, cool to room temperature, filter, take the filter cake, add ethanol 6 times the mass of the filter cake for recrystallization, and dry at 55°C for 14 hours to obtain a reaction product; mix the reaction product, 1,4-butanediol, and tetrapropyl titanate in a mass ratio of 530:182:3.2, react in a nitrogen atmosphere at 190°C until the methanol distillate is 92% of the theoretical amount, and after the reaction is completed, obtain a comonomer; step (2), mix the comonomer, DOPO, and methanol in a mass ratio of 30:23.5:68, reflux in a nitrogen atmosphere at 65°C for 7.5 hours, after the reaction is completed, filter, take the filter cake, add methanol 6 times the mass of the filter cake for washing three times, and dry at 65°C for 13 hours to obtain a flame retardant monomer;

[0037] Step 3: melt-blending flame-retardant recycled polyethylene terephthalate and flame retardant at a mass ratio of 100:3.5 at a temperature of 230°C, melt-extrude through a twin-screw extruder at a speed of 190r / min and a temperature of 253°C, cool and pelletize to obtain recycled polyester slices; wherein the flame retardant comprises the following steps: step (1): mixing γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol and water at a mass ratio of 0.55:4:31:1.3, ultrasonically dispersing for 15 minutes, reacting at a temperature of 90°C for 14 hours, filtering after the reaction, taking the filter cake, adding 6 times the mass of the filter cake to wash three times, and drying at a temperature of 85°C for 11 hours to obtain amide magnesium hydroxide; step (2): mixing hexachlorocyclotriphosphazene with tetrahydrofuran to dissolve, adding phenol and anhydrous potassium carbonate, and heating at a temperature of 55°C. The mixture was reacted at 400 °C for 25 h. After the reaction, p-hydroxybenzaldehyde, hexachlorocyclotriphosphazene, tetrahydrofuran, phenol, anhydrous potassium carbonate and p-hydroxybenzaldehyde were added in a mass ratio of 1:25:2.3:8.5:3.3. The reaction was continued at 55 °C for 15 h. After the reaction, a reaction product was obtained. Deionized water twice the mass of the reaction product was added for precipitation. The product was filtered. The filter cake was taken and ethyl acetate six times the mass of the filter cake was added for dissolution. The precipitation and filtration operation was repeated once. The product was dried at 55 °C for 15 h to obtain aldehyded cyclotriphosphazene. Step (3) aldehyded cyclotriphosphazene, aminated magnesium hydroxide and ethanol were mixed in a mass ratio of 1:3.3:260. The mixture was reacted at 80 °C for 9 h. After the reaction was completed, the product was filtered. The filter cake was taken and ethanol six times the mass of the filter cake was added for washing. The product was dried at 55 °C for 9 h to obtain a flame retardant.

[0038] Example 3

[0039] This embodiment discloses a method for preparing recycled polyester slices using waste polyester fabric, comprising the following steps:

[0040] Step 1: Mix the waste polyester fabric with 1g / L sodium hydroxide aqueous solution at a solid-liquid ratio of 1:45 and wash for 1.5h. After washing, take it out and dry it at 55°C for 9h to obtain the pretreated waste polyester fabric; mix the pretreated waste polyester fabric, ethylene glycol and potassium carbonate at a mass ratio of 10:65:0.23, react for 5.5h in a nitrogen atmosphere at a speed of 150r / min and a temperature of 235°C. After the reaction is completed, filter and take the filtrate, cool and crystallize at 8°C for 11h, filter and take the filter cake to obtain a crude product of regenerated ethylene terephthalate; mix and dissolve the crude product of regenerated ethylene terephthalate with water at 90°C, add acidifying agent Activated carbon, the mass ratio of the crude product of regenerated ethylene terephthalate, acidified activated carbon and water is 10:11:35, decolorize at 92°C for 2.5h, after decolorization, filter by suction, take the filtrate, cool and crystallize at 2°C for 11h, filter, take the filter cake, dry at 55°C for 9h, and obtain regenerated ethylene terephthalate; wherein, the acidified activated carbon is prepared by the following steps: mixing the activated carbon with a 10mol / L nitric acid aqueous solution at a mass ratio of 1:13, reacting at 35°C for 2.5h, filtering after the reaction, taking the filter cake, adding water 6 times the mass of the filter cake to wash until neutral, and drying at 55°C for 11h to obtain the acidified activated carbon;

[0041] Step 2: Mix the flame retardant monomer, regenerated polyethylene terephthalate and ethylene glycol antimony in a mass ratio of 11:89:0.4, carry out a pre-polycondensation reaction at a vacuum degree of 10.5 kPa and a temperature of 240°C for 0.9 h, and after the reaction, carry out a final polycondensation reaction at a vacuum degree of 45 Pa and a temperature of 275°C for 0.9 h. After the reaction, flame retardant regenerated polyethylene terephthalate is obtained; wherein the flame retardant monomer is prepared by the following steps: Step (1): mix benzaldehyde and ethanol, add 5-amino-dimethyl isophthalate, the mass ratio of benzaldehyde, ethanol and 5-amino-dimethyl isophthalate is 6.2:30:12.3, react in a nitrogen atmosphere at a temperature of 80°C for 7 h, and the reaction result is After the reaction is completed, the mixture is cooled to room temperature, filtered, and the filter cake is taken. Ethanol 6 times the mass of the filter cake is added for recrystallization, and the mixture is dried at 55°C for 14 hours to obtain a reaction product; the reaction product, 1,4-butanediol, and tetrapropyl titanate are mixed in a mass ratio of 530:185:3.5, and the mixture is reacted in a nitrogen atmosphere at a temperature of 190°C until the methanol distillation amount is 93% of the theoretical amount. After the reaction is completed, a comonomer is obtained; step (2), the comonomer, DOPO, and methanol are mixed in a mass ratio of 30:24:70, and the mixture is refluxed in a nitrogen atmosphere at a temperature of 68°C for 7.5 hours. After the reaction is completed, the mixture is filtered, the filter cake is taken, and methanol 6 times the mass of the filter cake is added for washing three times, and the mixture is dried at 65°C for 13 hours to obtain a flame retardant monomer;

[0042] Step 3: melt-blending flame-retardant recycled polyethylene terephthalate and flame retardant at a mass ratio of 100:4 at a temperature of 235°C, melt-extrude through a twin-screw extruder at a speed of 190 r / min and a temperature of 253°C, and cool and pelletize to obtain recycled polyester slices; wherein the flame retardant comprises the following steps: step (1): mixing γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol, and water at a mass ratio of 0.6:4:33:1.5, ultrasonically dispersing for 15 minutes, reacting at a temperature of 90°C for 14 hours, filtering after the reaction, taking the filter cake, adding water 6 times the mass of the filter cake to wash three times, and drying at a temperature of 85°C for 11 hours to obtain amide magnesium hydroxide; step (2): mixing hexachlorocyclotriphosphazene with tetrahydrofuran to dissolve, adding phenol and anhydrous potassium carbonate, and drying at a temperature of 58°C The mixture was reacted for 25 hours at room temperature. After the reaction was completed, p-hydroxybenzaldehyde, hexachlorocyclotriphosphazene, tetrahydrofuran, phenol, anhydrous potassium carbonate and p-hydroxybenzaldehyde were added in a mass ratio of 1:25:2.5:9:3.5. The reaction was continued at 58°C for 14 hours. After the reaction was completed, a reaction product was obtained. Deionized water 2.5 times the mass of the reaction product was added for precipitation. The filter cake was taken and ethyl acetate 6 times the mass of the filter cake was added for dissolution. The precipitation and filtration operation was repeated once. The mixture was dried at 55°C for 15 hours to obtain aldehyded cyclotriphosphazene. Step (3) aldehyded cyclotriphosphazene, aminated magnesium hydroxide and ethanol were mixed in a mass ratio of 1:3.5:280 and reacted at 80°C for 9 hours. After the reaction was completed, the mixture was filtered and the filter cake was taken. Ethanol 6 times the mass of the filter cake was added for washing. The mixture was dried at 55°C for 9 hours to obtain a flame retardant.

[0043] Example 4

[0044] This embodiment discloses a method for preparing recycled polyester slices using waste polyester fabric, comprising the following steps:

[0045] Step 1: Mix the waste polyester fabric with 1g / L sodium hydroxide aqueous solution at a solid-liquid ratio of 1:50 and wash for 2h, take it out after washing, and dry it at 55°C for 9h to obtain the pretreated waste polyester fabric; mix the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate at a mass ratio of 10:68:0.24, react for 5h in a nitrogen atmosphere at a speed of 200r / min and a temperature of 240°C, filter after the reaction, take the filtrate, cool and crystallize at 8°C for 11h, filter with suction, take the filter cake, and obtain the crude product of regenerated ethylene terephthalate; mix the crude product of regenerated ethylene terephthalate with water at 90°C and dissolve it, add acidifying agent, The mass ratio of the crude product of regenerated ethylene terephthalate, acidified activated carbon and water is 10:11.5:38, and the product is decolorized at 95°C for 2h. After the decolorization is completed, the product is filtered, the filtrate is taken, cooled and crystallized at 2°C for 11h, filtered, the filter cake is taken, and dried at 55°C for 9h to obtain regenerated ethylene terephthalate; wherein the acidified activated carbon is prepared by the following steps: the activated carbon is mixed with a 10mol / L nitric acid aqueous solution at a mass ratio of 1:13, reacted at 35°C for 3h, filtered after the reaction, the filter cake is taken, washed with water 6 times the mass of the filter cake until it is neutral, and dried at 55°C for 11h to obtain the acidified activated carbon;

[0046] Step 2: Mix the flame retardant monomer, regenerated polyethylene terephthalate and ethylene glycol antimony in a mass ratio of 11.5:88.5:0.4, carry out a pre-polycondensation reaction at a vacuum degree of 11 kPa and a temperature of 240°C for 0.8 h, and after the reaction is completed, carry out a final polycondensation reaction at a vacuum degree of 45 Pa and a temperature of 270°C for 1 h. After the reaction is completed, flame retardant regenerated polyethylene terephthalate is obtained; wherein the flame retardant monomer is prepared by the following steps: Step (1): mix benzaldehyde and ethanol, add 5-amino-dimethyl isophthalate, the mass ratio of benzaldehyde, ethanol and 5-amino-dimethyl isophthalate is 6.25:33:12.4, react in a nitrogen atmosphere at a temperature of 80°C for 7 h, and the reaction is completed. Afterwards, cool to room temperature, filter, take the filter cake, add ethanol 6 times the mass of the filter cake for recrystallization, and dry at 55°C for 14 hours to obtain a reaction product; mix the reaction product, 1,4-butanediol, and tetrapropyl titanate in a mass ratio of 530:188:3.8, react in a nitrogen atmosphere at 190°C until the methanol distillate is 94% of the theoretical amount, and after the reaction is completed, obtain a comonomer; step (2), mix the comonomer, DOPO, and methanol in a mass ratio of 30:24.5:73, reflux in a nitrogen atmosphere at 70°C for 7.5 hours, after the reaction is completed, filter, take the filter cake, add methanol 6 times the mass of the filter cake for washing three times, and dry at 65°C for 13 hours to obtain a flame retardant monomer;

[0047] Step 3: melt-blending flame-retardant recycled polyethylene terephthalate and flame retardant at a mass ratio of 100:4.5 at a temperature of 235°C, melt-extrude through a twin-screw extruder at a speed of 200 r / min and a temperature of 255°C, cool and pelletize to obtain recycled polyester slices; wherein the flame retardant is prepared by the following steps: step (1): mixing γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol and water at a mass ratio of 0.7:4:34:1.8, ultrasonically dispersing for 15 minutes, reacting at a temperature of 90°C for 14 hours, filtering after the reaction, taking the filter cake, adding water 6 times the mass of the filter cake to wash three times, and drying at a temperature of 85°C for 11 hours to obtain amide magnesium hydroxide; step (2): mixing hexachlorocyclotriphosphazene with tetrahydrofuran to dissolve, adding phenol and anhydrous potassium carbonate, and drying at a temperature of 60°C. The mixture was reacted at 400 °C for 25 h. After the reaction, p-hydroxybenzaldehyde, hexachlorocyclotriphosphazene, tetrahydrofuran, phenol, anhydrous potassium carbonate and p-hydroxybenzaldehyde were added in a mass ratio of 1:28:2.8:9.5:3.8. The reaction was continued at 60 °C for 13 h. After the reaction, a reaction product was obtained. Deionized water 3 times the mass of the reaction product was added for precipitation. The filter cake was taken and ethyl acetate 6 times the mass of the filter cake was added for dissolution. The precipitation and filtration operation was repeated once. The mixture was dried at 55 °C for 15 h to obtain aldehyded cyclotriphosphazene. Step (3) aldehyded cyclotriphosphazene, aminated magnesium hydroxide and ethanol were mixed in a mass ratio of 1:3.8:290 and reacted at 80 °C for 9 h. After the reaction was completed, the mixture was filtered. The filter cake was taken and ethanol 6 times the mass of the filter cake was added for washing. The mixture was dried at 55 °C for 9 h to obtain a flame retardant.

[0048] Example 5

[0049] This embodiment discloses a method for preparing recycled polyester slices using waste polyester fabric, comprising the following steps:

[0050] Step 1: Mix the waste polyester fabric with 1g / L sodium hydroxide aqueous solution at a solid-liquid ratio of 1:50 and wash for 1h, take it out after washing, and dry it at 60°C for 8h to obtain the pretreated waste polyester fabric; mix the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate at a mass ratio of 10:70:0.25, react for 5h in a nitrogen atmosphere at a speed of 200r / min and a temperature of 240°C, filter after the reaction, take the filtrate, cool and crystallize at 12°C for 12h, filter by suction, take the filter cake, and obtain the crude product of regenerated ethylene terephthalate; mix the crude product of regenerated ethylene terephthalate with water at 90°C and dissolve it, add acid The mass ratio of the crude product of ethylene terephthalate, acidified activated carbon and water is 10:12:40, and the product is decolorized at 95°C for 2h. After the decolorization is completed, the product is filtered by suction, the filtrate is taken, and the product is cooled and crystallized at 4°C for 12h. The product is filtered, the filter cake is taken, and the product is dried at 60°C for 8h to obtain regenerated ethylene terephthalate; wherein the acidified activated carbon is prepared by the following steps: the activated carbon is mixed with a 10mol / L nitric acid aqueous solution at a mass ratio of 1:15, and the product is reacted at 40°C for 2h. After the reaction is completed, the product is filtered, the filter cake is taken, and water 8 times the mass of the filter cake is added to wash the product until it is neutral, and the product is dried at 60°C for 10h to obtain the acidified activated carbon;

[0051] Step 2: Mix the flame retardant monomer, regenerated polyethylene terephthalate and ethylene glycol antimony in a mass ratio of 12:88:0.4, perform a pre-polycondensation reaction at a vacuum degree of 11 kPa and a temperature of 245°C for 0.8 h, and after the reaction, perform a final polycondensation reaction at a vacuum degree of 50 Pa and a temperature of 280°C for 0.8 h. After the reaction, flame retardant regenerated polyethylene terephthalate is obtained; wherein the flame retardant monomer is prepared by the following steps: Step (1): mix benzaldehyde and ethanol, add 5-amino-dimethyl isophthalate, the mass ratio of benzaldehyde, ethanol and 5-amino-dimethyl isophthalate is 6.3:35:12.5, react in a nitrogen atmosphere at a temperature of 85°C for 6 h, and react After completion, cool to room temperature, filter, take the filter cake, add ethanol 8 times the mass of the filter cake for recrystallization, and dry at 60°C for 12 hours to obtain a reaction product; mix the reaction product, 1,4-butanediol, and tetrapropyl titanate in a mass ratio of 530:190:4, react in a nitrogen atmosphere at 200°C until the methanol distillate is 95% of the theoretical amount, and after the reaction is completed, obtain a comonomer; step (2), mix the comonomer, DOPO, and methanol in a mass ratio of 30:25:75, reflux in a nitrogen atmosphere at 70°C for 7 hours, after the reaction is completed, filter, take the filter cake, add methanol 8 times the mass of the filter cake for washing three times, and dry at 70°C for 12 hours to obtain a flame retardant monomer;

[0052] Step 3: melt-blending flame-retardant recycled polyethylene terephthalate and flame retardant at a mass ratio of 100:5 at a temperature of 240°C, melt-extrude through a twin-screw extruder at a speed of 200 r / min and a temperature of 255°C, and cool and pelletize to obtain recycled polyester slices; wherein the flame retardant is prepared by the following steps: step (1): mixing γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol, and water at a mass ratio of 0.8:4:35:2, ultrasonically dispersing for 20 minutes, reacting at a temperature of 95°C for 12 hours, filtering after the reaction, taking the filter cake, adding water 8 times the mass of the filter cake to wash three times, and drying at a temperature of 90°C for 10 hours to obtain amide magnesium hydroxide; step (2): mixing hexachlorocyclotriphosphazene with tetrahydrofuran to dissolve, adding phenol and anhydrous potassium carbonate, and drying at 60°C. The mixture was reacted at room temperature for 24 hours. After the reaction was completed, p-hydroxybenzaldehyde, hexachlorocyclotriphosphazene, tetrahydrofuran, phenol, anhydrous potassium carbonate and p-hydroxybenzaldehyde were added in a mass ratio of 1:30:3:10:4. The reaction was continued at 60°C for 12 hours. After the reaction was completed, a reaction product was obtained. Deionized water 3 times the mass of the reaction product was added for precipitation. The filter cake was taken and ethyl acetate 8 times the mass of the filter cake was added for dissolution. The precipitation and filtration operation was repeated once. The mixture was dried at 60°C for 12 hours to obtain aldehyded cyclotriphosphazene. Step (3) aldehyded cyclotriphosphazene, aminated magnesium hydroxide and ethanol were mixed in a mass ratio of 1:4:300 and reacted at 85°C for 8 hours. After the reaction was completed, the mixture was filtered and the filter cake was taken. Ethanol 8 times the mass of the filter cake was added for washing. The mixture was dried at 60°C for 8 hours to obtain a flame retardant.

[0053] Comparative Example 1

[0054] This comparative example discloses a method for preparing recycled polyester slices using waste polyester fabric, comprising the following steps:

[0055] Step 1: Mix the waste polyester fabric with 1g / L sodium hydroxide aqueous solution at a solid-liquid ratio of 1:40 for 2h, take it out after washing, and dry it at 50°C for 10h to obtain the pretreated waste polyester fabric; mix the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate at a mass ratio of 10:60:0.2, react for 6h in a nitrogen atmosphere at a speed of 100r / min and a temperature of 230°C, filter after the reaction, take the filtrate, cool and crystallize at 5°C for 10h, filter by suction, take the filter cake, and obtain the crude product of regenerated ethylene terephthalate; mix the crude product of regenerated ethylene terephthalate with water at 90°C and dissolve it, add acidifying agent Activated carbon, the mass ratio of the crude product of regenerated ethylene terephthalate, acidified activated carbon and water is 10:10:30, decolorize at 90°C for 3h, after decolorization, filter by suction, take the filtrate, cool and crystallize at 0°C for 10h, filter, take the filter cake, dry at 50°C for 10h, and obtain regenerated ethylene terephthalate; wherein, the acidified activated carbon is prepared by the following steps: mixing the activated carbon with a 10mol / L nitric acid aqueous solution at a mass ratio of 1:10, reacting at 30°C for 3h, filtering after the reaction, taking the filter cake, adding water 5 times the mass of the filter cake to wash until neutral, and drying at 50°C for 12h to obtain the acidified activated carbon;

[0056] Step 2: regenerated polyethylene terephthalate and ethylene glycol antimony are mixed in a mass ratio of 100:0.4, and pre-polycondensed at a vacuum degree of 10 kPa and a temperature of 230° C. for 1 hour. After the reaction is completed, a final polycondensed reaction is carried out at a vacuum degree of 40 Pa and a temperature of 270° C. for 1 hour. After the reaction is completed, regenerated polyethylene terephthalate is obtained;

[0057] Step 3: melt-blending recycled polyethylene terephthalate and flame retardant at a mass ratio of 100:3 at a temperature of 230°C, melt-extrude through a twin-screw extruder at a speed of 180r / min and a temperature of 250°C, and cool and pelletize to obtain recycled polyester slices; wherein the flame retardant comprises the following steps: step (1): mixing γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol, and water at a mass ratio of 0.5:4:30:1, ultrasonically dispersing for 10 minutes, reacting at a temperature of 85°C for 16 hours, filtering after the reaction, taking the filter cake, adding water 5 times the mass of the filter cake to wash three times, and drying at a temperature of 80°C for 12 hours to obtain amide magnesium hydroxide; step (2): mixing hexachlorocyclotriphosphazene and tetrahydrofuran to dissolve, adding phenol and anhydrous potassium carbonate, and drying at a temperature of 55°C The mixture was reacted for 26 hours at room temperature. After the reaction was completed, p-hydroxybenzaldehyde, hexachlorocyclotriphosphazene, tetrahydrofuran, phenol, anhydrous potassium carbonate and p-hydroxybenzaldehyde were added in a mass ratio of 1:20:2:8:3. The reaction was continued at 55°C for 16 hours. After the reaction was completed, a reaction product was obtained. Deionized water twice the mass of the reaction product was added for precipitation. The filter cake was taken and ethyl acetate five times the mass of the filter cake was added for dissolution. The precipitation and filtration operation was repeated once. The mixture was dried at 50°C for 18 hours to obtain aldehyded cyclotriphosphazene. Step (3) aldehyded cyclotriphosphazene, aminated magnesium hydroxide and ethanol were mixed in a mass ratio of 1:3:250 and reacted at 75°C for 10 hours. After the reaction was completed, the mixture was filtered and the filter cake was taken. The filter cake was washed with ethanol five times the mass of the filter cake and dried at 50°C for 10 hours to obtain a flame retardant.

[0058] Comparative Example 2

[0059] This comparative example discloses a method for preparing recycled polyester slices using waste polyester fabric, comprising the following steps:

[0060] Step 1: Mix the waste polyester fabric with 1g / L sodium hydroxide aqueous solution at a solid-liquid ratio of 1:40 for 2h, take it out after washing, and dry it at 50°C for 10h to obtain the pretreated waste polyester fabric; mix the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate at a mass ratio of 10:60:0.2, react for 6h in a nitrogen atmosphere at a speed of 100r / min and a temperature of 230°C, filter after the reaction, take the filtrate, cool and crystallize at 5°C for 10h, filter by suction, take the filter cake, and obtain the crude product of regenerated ethylene terephthalate; mix the crude product of regenerated ethylene terephthalate with water at 90°C and dissolve it, add acidifying agent Activated carbon, the mass ratio of the crude product of regenerated ethylene terephthalate, acidified activated carbon and water is 10:10:30, decolorize at 90°C for 3h, after decolorization, filter by suction, take the filtrate, cool and crystallize at 0°C for 10h, filter, take the filter cake, dry at 50°C for 10h, and obtain regenerated ethylene terephthalate; wherein, the acidified activated carbon is prepared by the following steps: mixing the activated carbon with a 10mol / L nitric acid aqueous solution at a mass ratio of 1:10, reacting at 30°C for 3h, filtering after the reaction, taking the filter cake, adding water 5 times the mass of the filter cake to wash until neutral, and drying at 50°C for 12h to obtain the acidified activated carbon;

[0061] Step 2: Mix the flame retardant monomer, regenerated polyethylene terephthalate and ethylene glycol antimony in a mass ratio of 10:90:0.4, perform a pre-polycondensation reaction at a vacuum degree of 10 kPa and a temperature of 230°C for 1 hour, and after the reaction, perform a final polycondensation reaction at a vacuum degree of 40 Pa and a temperature of 270°C for 1 hour. After the reaction, flame retardant regenerated polyethylene terephthalate is obtained; wherein the flame retardant monomer is prepared by the following steps: Step (1): mix benzaldehyde and ethanol, add 5-amino-dimethyl isophthalate, the mass ratio of benzaldehyde, ethanol and 5-amino-dimethyl isophthalate is 6:25:12, react in a nitrogen atmosphere at a temperature of 75°C for 8 hours, and after the reaction, Cool to room temperature, filter, take the filter cake, add ethanol 5 times the mass of the filter cake for recrystallization, and dry at 50°C for 16 hours to obtain a reaction product; mix the reaction product, 1,4-butanediol, and tetrapropyl titanate in a mass ratio of 530:180:3, react in a nitrogen atmosphere at 180°C until the methanol distillate is 90% of the theoretical amount, and after the reaction is completed, obtain a comonomer; step (2), mix the comonomer, DOPO, and methanol in a mass ratio of 30:23:65, reflux in a nitrogen atmosphere at 65°C for 8 hours, after the reaction is completed, filter, take the filter cake, add methanol 5 times the mass of the filter cake for washing three times, and dry at 60°C for 14 hours to obtain a flame retardant monomer;

[0062] Step 3: melt-blending flame-retardant recycled polyethylene terephthalate and nano magnesium hydroxide at a mass ratio of 100:3 at 230° C., melt-extrude through a twin-screw extruder at a speed of 180 r / min and a temperature of 250° C., cool and pelletize to obtain recycled polyester chips.

[0063] In the above embodiments and comparative examples: the waste polyester fabric comes from recycled dyed polyester fabric, and the mass fraction of polyester is 90-100%; the activated carbon comes from Sinopharm Chemical Reagent Co., Ltd., with the product number 10006619 and the model is analytically pure; the benzaldehyde comes from Xi'an Tianmao Baoding Biotechnology Co., Ltd., with the model analytically pure, CAS number: 100-52-7; the 5-amino-dimethyl isophthalate comes from Hubei Shineng Chemical Technology Co., Ltd., with the CAS number: 99-27-4; the DOPO comes from Wuhan Kamik Technology Co., Ltd., with the product name 9, 10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, CAS No.: 35948-25-5; nano magnesium hydroxide comes from Hangzhou Hengna New Materials Co., Ltd., particle size 50nm, CAS No.: 1309-42-8; hexachlorocyclotriphosphazene comes from Hubei Chengfeng Chemical Co., Ltd., CAS No.: 940-71-6; phenol comes from Shandong Duoju Chemical Co., Ltd., CAS No.: 108-95-2; p-Hydroxybenzaldehyde comes from Hubei Wei's Chemical Reagent Co., Ltd., CAS No.: 123-08-0.

[0064] Test example

[0065] The comprehensive performance test was conducted on the regenerated polyester slices prepared in Examples 1-5 and Comparative Examples 1-2. The specific test results are shown in Table 1:

[0066]

[0067] The tests of the various indicators in Table 1 are based on the following standards: the intrinsic viscosity is determined by GB / T 14190-2017 "Test method for fiber-grade polyester (PET) chips"; the limiting oxygen index is determined by ISO4589-1981 "Plastic oxygen index method for determining flammability"; the vertical burning grade is determined by ASTM D3801 "Test method for measuring vertical burning of solid plastics".

[0068] It can be seen from the test results in Table 1 that the regenerated polyester slices prepared by the present invention have excellent flame retardancy and can be used to prepare polyester fiber products with good flame retardancy.

[0069] The invention pre-treats waste polyester fabric, performs alcoholysis by ethylene glycol alcoholysis, and then performs decolorization by acidified activated carbon to obtain regenerated ethylene terephthalate; prepares a flame-retardant monomer containing DOPO flame-retardant groups and double-terminal hydroxyethyl ester groups, and co-condenses the monomer with regenerated ethylene terephthalate to obtain flame-retardant regenerated polyethylene terephthalate; wherein, since the DOPO flame-retardant group is grafted on the polymer side chain, even if the phosphorus-containing group DOPO decomposes during the combustion process, it will not affect the integrity of the polymer main chain structure, so that the anti-melting droplet performance of the polymer is improved, and the benzene ring structure in the flame-retardant monomer can also further improve the thermal oxidation performance and thermal stability of the flame-retardant regenerated polyethylene terephthalate; the invention combines the aldehyde group of the aldehyde-formylated cyclotriphosphazene with the aminosilane coupling agent The surface-modified aminated magnesium hydroxide undergoes a Schiff base reaction, so that the organic flame retardant group cyclotriphosphazene is connected to the magnesium hydroxide through a Schiff base bond, which can not only improve the dispersibility of nano magnesium hydroxide in the polymer matrix and make it less likely to agglomerate, but also improve the stability of the organic flame retardant group cyclotriphosphazene, and the obtained flame retardant has better thermal stability and flame retardancy; the flame retardant recycled polyethylene terephthalate is melt-blended with the flame retardant, extruded and pelletized to obtain recycled polyester chips; wherein, the unreacted amino groups on the surface of the flame retardant undergo an amidation reaction with the terminal carboxyl groups of the flame retardant recycled polyethylene terephthalate molecular chain in a molten state, and the flame retardant is grafted onto the chain segments of the flame retardant recycled polyethylene terephthalate, so that the flame retardant has better dispersibility and compatibility, and the flame retardant performance of the recycled polyester chips is further improved.

[0070] In Comparative Example 1, the flame-retardant monomer is not co-condensed with the recycled polyethylene terephthalate, and the nitrogen element and DOPO flame-retardant group in the flame-retardant monomer are lacking to improve the flame retardant ability of the matrix, so the flame retardant performance of Comparative Example 1 is reduced; in Comparative Example 2, the surface of nano-aluminum hydroxide is not modified, and the compatibility of nano-aluminum hydroxide and flame-retardant recycled polyethylene terephthalate is poor, and it is easy to agglomerate, which affects the flame retardant effect, and the flame retardant effect of the cyclotriphosphazene structure is lacking, so the flame retardant performance of Comparative Example 2 is reduced.

[0071] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing recycled polyester slices using waste polyester fabrics, characterized in that: The following steps are involved: Step 1, mixing the waste polyester fabric with a sodium hydroxide aqueous solution and washing it, taking it out after washing, and drying it to obtain the pretreated waste polyester fabric; The pretreated waste polyester fabric, ethylene glycol and potassium carbonate are mixed and reacted. After the reaction is completed, the filtrate is filtered, the filtrate is cooled and crystallized, and the filter cake is taken to obtain a crude product of regenerated ethylene terephthalate; the crude product of regenerated ethylene terephthalate is mixed and dissolved with water, acidified activated carbon is added, and decolorization is performed. After the decolorization is completed, the filtrate is filtered, the filtrate is taken, the crystallization is cooled, the filter cake is taken, and the filter cake is dried to obtain regenerated ethylene terephthalate; Step 2: Mix the flame-retardant monomer, regenerated ethylene terephthalate and ethylene glycol antimony, perform a pre-polycondensation reaction, perform a final polycondensation reaction after the reaction is completed, and obtain flame-retardant polyethylene terephthalate; wherein the flame-retardant monomer is prepared by the following steps: Step (1): mix benzaldehyde and ethanol, add 5-amino-dimethyl isophthalate, react, and after the reaction is completed, cool to room temperature, filter, take the filter cake, recrystallize, and dry to obtain a reaction product; mix the reaction product, 1,4-butanediol and tetrapropyl titanate, react, and after the reaction is completed, obtain a comonomer; wherein the mass ratio of benzaldehyde, ethanol and 5-amino-dimethyl isophthalate is (6-6.3):(25-35):(12-12.5); when preparing the reaction product, the reaction conditions are: react for 6-8 hours at a temperature of 75-85°C in a nitrogen atmosphere; the structural formula of the reaction product is: ; The mass ratio of the reaction product, 1,4-butanediol and tetrapropyl titanate is 530:(180-190):(3-4); When preparing the comonomer, the reaction conditions are: reacting in a nitrogen atmosphere at a temperature of 180-200° C. until the amount of methanol distilled is 90-95% of the theoretical amount; the structural formula of the comonomer is: ; Step (2), mixing the comonomer, DOPO and methanol, reacting, filtering after the reaction, taking the filter cake, washing and drying to obtain a flame retardant monomer; the structural formula of the flame retardant monomer is: ; Step 3, melt-blending flame-retardant polyethylene terephthalate and flame retardant, melt-extrude, cool and pelletize to obtain recycled polyester slices; wherein the flame retardant is prepared by the following steps: mixing formaldehyde cyclotriphosphazene, amide magnesium hydroxide and ethanol, reacting, filtering after the reaction, taking the filter cake, washing and drying to obtain the flame retardant; the mass ratio of formaldehyde cyclotriphosphazene, amide magnesium hydroxide and ethanol is 1:(3-4):(250-300); the reaction conditions are: reacting at a temperature of 75-85°C for 8-10h.

2. The method for preparing recycled polyester slices using waste polyester fabric according to claim 1, characterized in that: In the step 1, the solid-liquid ratio of the waste polyester fabric and the sodium hydroxide aqueous solution is 1:(40-50), and the sodium hydroxide aqueous solution is 1 g / L of the sodium hydroxide aqueous solution; the mass ratio of the pretreated waste polyester fabric, ethylene glycol, and potassium carbonate is 10:(60-70):(0.2-0.25); the reaction conditions are: in a nitrogen atmosphere, at a speed of 100-200 r / min and a temperature of 230-240° C., the reaction is carried out for 5-6 hours; the mass ratio of the regenerated ethylene terephthalate crude product, the acidified activated carbon, and water is 10:(10-12):(30-40); and the decolorization conditions are: decolorization at a temperature of 90-95° C. for 2-3 hours.

3. The method for preparing recycled polyester slices using waste polyester fabric according to claim 1, characterized in that: The acidified activated carbon in step 1 is prepared by the following steps: mixing the activated carbon with an aqueous nitric acid solution, reacting, filtering after the reaction, taking the filter cake, washing, and drying to obtain the acidified activated carbon; wherein the mass ratio of the activated carbon to the aqueous nitric acid solution is 1:(10-15), and the aqueous nitric acid solution is a 10 mol / L aqueous nitric acid solution; and the reaction conditions are: reacting at a temperature of 30-40°C for 2-3h.

4. The method for preparing recycled polyester slices using waste polyester fabric according to claim 1, characterized in that: In the step 2, the mass ratio of the flame retardant monomer, the regenerated ethylene terephthalate and the ethylene glycol antimony is (10-12):(88-90):0.4; the pre-polycondensation reaction conditions are: the pre-polycondensation reaction is carried out for 0.8-1h at a vacuum degree of 10-11 kPa and a temperature of 230-245°C; and the final polycondensation reaction conditions are: the final polycondensation reaction is carried out for 0.8-1h at a vacuum degree of 40-50 Pa and a temperature of 270-280°C.

5. The method for preparing recycled polyester chips using waste polyester fabric according to claim 1, characterized in that: In the preparation of the flame-retardant monomer in step 2, in step (2): the mass ratio of the comonomer, DOPO and methanol is 30:(23-25):(65-75); the reaction conditions are: reflux reaction at 65-70° C. in a nitrogen atmosphere for 7-8 hours.

6. The method for preparing recycled polyester chips using waste polyester fabric according to claim 1, characterized in that: In the step three, the mass ratio of flame-retardant polyethylene terephthalate to flame retardant is 100:(3-5); the melt blending conditions are: melt blending at a temperature of 230-240°C; and the melt extrusion conditions are: melt extrusion through a twin-screw extruder at a speed of 180-200r / min and a temperature of 250-255°C.

7. The method for preparing recycled polyester chips using waste polyester fabric according to claim 1, characterized in that: The aldehyded cyclotriphosphazene is prepared by the following steps: mixing and dissolving hexachlorocyclotriphosphazene and tetrahydrofuran, adding phenol and anhydrous potassium carbonate, reacting, adding p-hydroxybenzaldehyde after the reaction is completed, continuing the reaction, purifying, and drying after the reaction is completed to obtain the aldehyded cyclotriphosphazene; wherein the mass ratio of hexachlorocyclotriphosphazene, tetrahydrofuran, phenol, anhydrous potassium carbonate, and p-hydroxybenzaldehyde is 1:(20-30):(2-3):(8-10):(3-4); the reaction conditions are: reacting at a temperature of 55-60°C for 24-26h; and the continued reaction conditions are: continuing the reaction at a temperature of 55-60°C for 12-16h.

8. The method for preparing recycled polyester chips using waste polyester fabric according to claim 1, characterized in that: The amination magnesium hydroxide is prepared by the following steps: mixing γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol and water, ultrasonically dispersing, reacting, filtering after the reaction, taking the filter cake, washing, and drying to obtain the amination magnesium hydroxide; wherein the mass ratio of γ-aminopropyltriethoxysilane, nano-magnesium hydroxide, ethanol and water is (0.5-0.8):4:(30-35):(1-2); and the reaction conditions are: reacting at a temperature of 85-95° C. for 12-16 hours.

9. A regenerated polyester slice prepared by the method for preparing regenerated polyester slice using waste polyester fabric as described in any one of claims 1 to 8.

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