Preparation method and application of composite halogen-free flame-retardant polyester with high phosphorus content

Abstract

The invention relates to the field of high polymer materials, and provides a preparation method and application of composite halogen-free high-phosphorus-content flame-retardant polyester aiming at the problems of non-uniform component dispersion and poor anti-dripping effect of the composite flame-retardant polyester. The preparation method comprises the following steps: mixing dihydric alcohol, terephthalic acid, a catalyst, esterification liquid of the reaction type phosphorus flame retardant and the reaction type nitrogen flame retardant, sequentially carrying out esterification reaction and polycondensation reaction to obtain a melt, and treating the melt to obtain the composite halogen-free high-phosphorus-content flame-retardant polyester. The invention also provides application of the flame-retardant polyester. According to the invention, the reactive phosphorus flame retardant participates in the polyester polymerization process, so that the influence on the molecular regularity of polyester is small, and the crystallization behavior and post-processing performance of slices are not influenced; the apparent viscosity of the polyester is improved by the modified nitrogen flame retardant, the polycondensation time is greatly shortened, and the polyester with lasting flame-retardant effect and good anti-dripping effect is obtained by compounding multiple halogen-free flame retardants.

Description

Technical Field

[0001] The invention relates to the field of polymer materials, and in particular to a preparation method and application of a composite halogen-free high-phosphorus content flame-retardant polyester. Background Art

[0002] PET is a material widely used in production and life, and is favored for its good mechanical properties and spinnability. However, its flammable properties have become a safety hazard that cannot be ignored. PET is a flammable material with a limiting oxygen index of 21-23%, which means that PET is extremely easy to burn under high temperature and sufficient oxygen. PET burns quickly, and a large amount of heat and smoke will be generated during the combustion process, and even melt dripping will occur, all of which will increase the risk of fire. Therefore, the flame retardant modification of PET materials and the research on flame retardants have become important topics with great practical significance and application prospects.

[0003] Early flame retardants usually used halogen flame retardants, which had good flame retardant effects. However, they would release toxic and carcinogenic substances during the combustion process, causing harm to human health and the natural environment. Therefore, halogen-free flame retardants have attracted people's attention. Among them, phosphorus-containing flame retardants have a wide range of applications and development prospects due to their high flame retardant efficiency, low smoke toxicity, heat release rate and good carbonization. However, a single phosphorus-based flame retardant is often difficult to achieve the flame retardant effect requirements, so it is often necessary to use a phosphorus-based and nitrogen-based compound. The nitrogen-based flame retardants that are currently well used are mainly melamine and its derivatives, dicyandiamide, biurea, and guanidine compounds.

[0004] The sublimation endothermic enthalpy of melamine is -963 kJ / kg. For a substrate with a specific heat capacity of 2.1 kJ / (kg / ℃), when it contains 20% melamine, the sublimation of melamine will cause its temperature to drop by 115℃. This cooling effect can prevent the polymer from being ignited. In addition, the sublimated melamine and its degradation product nitrogen can also dilute the combustibles and isolate the polymer from contact with air. At the same time, the sublimated melamine can capture free radicals in the flame zone, so the gas phase flame retardant efficiency of melamine is relatively high.

[0005] Patent CN116218153A discloses a flame-retardant polyester chip and its preparation method. The flame-retardant chip prepared by the blending method can achieve a certain flame-retardant effect, but due to the blending method, the flame-retardant components in the flame-retardant chip have problems such as uneven dispersion and short flame-retardant effect. Patent CN116162343A discloses melamine cyanurate-coated aluminum diethylphosphinate intumescent flame-retardant thermoplastic polyurethane and its preparation method. The flame-retardant chip is prepared by melamine cyanurate (MCA) and aluminum diethylphosphinate (ADP), and the anti-drip effect is average. Summary of the invention

[0006] In order to overcome the problems of uneven dispersion of composite flame-retardant polyester components and poor anti-drip effect, the present invention provides a preparation method and application of a composite halogen-free high-phosphorus content flame-retardant polyester, wherein not only a reactive phosphorus-based flame retardant is involved in the polyester polymerization process, which has little effect on the molecular regularity of the polyester itself and does not affect the crystallization behavior and post-processing performance of the slices; but also a modified nitrogen-based flame retardant is provided, which can increase the apparent viscosity of the polyester and greatly shorten the polycondensation time. A plurality of halogen-free flame retardants are compounded to obtain a polyester with a long-lasting flame retardant effect and a good anti-drip effect.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing a composite halogen-free high-phosphorus content flame-retardant polyester comprises the following steps: (1) mixing a diol, a carboxyl-containing reactive phosphorus-based flame retardant and anhydrous sodium acetate, and heating the mixture to react to obtain an esterified liquid of the reactive phosphorus-based flame retardant; (2) mixing melamine salt and formaldehyde, adjusting the pH to alkaline, heating and reacting to obtain a prepolymer of a reactive nitrogen-based flame retardant, and filtering, washing, drying and grinding the prepolymer to obtain a micron-sized reactive nitrogen-based flame retardant; (3) mixing diol, terephthalic acid, a catalyst, the esterification liquid of the reactive phosphorus-based flame retardant in step (1), and the reactive nitrogen-based flame retardant in step (2), and sequentially performing esterification reaction and polycondensation reaction to obtain a melt, and treating the melt to obtain a composite halogen-free high-phosphorus content flame-retardant polyester.

[0008] Preferably, the temperature of the heating reaction in step (1) is 165-200°C. In order to obtain a phosphorus-based reactive flame retardant with a phosphorus content of about 50,000 ppm, the esterification temperature must be controlled at 165-200°C and the esterification rate must be controlled at more than 90%. If the esterification temperature is too low, the esterification rate will be reduced, affecting the subsequent masterbatch preparation; if the temperature is too high, the diol will self-polymerize, and the diethylene glycol content of the system will increase, which will affect the quality of the polyester. If the esterification temperature is too low or too high, it is not conducive to the quality of the polyester.

[0009] Preferably, the reactive phosphorus-based flame retardant in step (1) is one or both of 2-carboxyethylphenylphosphite (CEPPA) and [(6-oxo-6H-dibenzo[1,2]oxaphosphorin-6-yl)methyl]succinic acid (DDP).

[0010] Preferably, the diol in step (1) is a mixture of one or more of ethylene glycol, propylene glycol, butylene glycol, pentanediol and 1,4-cyclohexanedimethanol.

[0011] Preferably, in step (1), the molar ratio of diol to reactive phosphorus-based flame retardant is 3:(6-8). Anhydrous sodium acetate accounts for 0.5% of the total mass of the reaction system.

[0012] More preferably, the mass ratio of CEPPA to ethylene glycol is 3:7, and the heating reaction temperature is 175-185°C.

[0013] Preferably, step (1) is carried out in a reactor, and when the amount of water discharged from the reaction reaches 95-98% of the theoretical value, heating is stopped, diol is added to the reaction system for dilution, and discharge is started when the temperature in the reactor drops below 120° C. to obtain the esterified liquid of the reactive phosphorus-based flame retardant.

[0014] Preferably, the melamine salt in step (2) is one or both of melamine cyanurate and melamine polyphosphate, and more preferably melamine cyanurate.

[0015] Preferably, in step (2), the pH is adjusted to 9-10, the temperature of the heating reaction is 75-95° C., and the reaction time is 2-3 h.

[0016] Preferably, the grinding time in step (2) is 25-35 minutes, the filtering, washing, drying and grinding process of the prepolymer is repeated 1-2 times, and the micron-sized particles are 1-5 μm in diameter, so as to obtain a micron-sized nitrogen-based flame retardant with more uniform size and more stable properties.

[0017] Preferably, in step (3), the molar ratio of the diol to terephthalic acid is 1:(1.2-1.5), the amount of the catalyst added is 100-1000 ppm of the total mass of the copolyester, the amount of the esterification liquid of the reactive phosphorus-based flame retardant is 0.5-2% of the total mass of the copolyester, and the amount of the reactive nitrogen-based flame retardant is 1-3% of the total mass of the copolyester.

[0018] Preferably, the phosphorus content of the esterified liquid of the reactive phosphorus flame retardant accounts for 15000-25000ppm of the total mass of the copolyester. High phosphorus content generally refers to phosphorus accounting for more than 10000ppm of the total mass of the copolyester, because the reactive phosphorus flame retardant contains macromolecular structures such as benzene rings, which have large steric hindrance, making it difficult to prepare flame-retardant polyester with high phosphorus content. In the present invention, the carboxyl-containing reactive phosphorus flame retardant is pre-esterified with ethylene glycol, so that the steric hindrance between the reactive phosphorus flame retardant and the polyester is greatly reduced, the degree of polymerization of the flame retardant and the matrix is ​​increased, and the preparation of flame-retardant polyester with high phosphorus content can be achieved.

[0019] Preferably, the diol in step (3) is a mixture of one or more of ethylene glycol, propylene glycol, butylene glycol, pentanediol, and 1,4-cyclohexanedimethanol; the catalyst is selected from antimony trioxide, antimony glycol, antimony acetate, calcium acetate, zinc acetate, zinc oxide, sodium acetate, tetrabutyl titanate, tetraisopropyl titanate, tetraisooctyl titanate, and one or more of organic amine compounds. More preferably, the diol is ethylene glycol and the catalyst is antimony glycol.

[0020] Preferably, the esterification reaction in step (3) is carried out at a temperature of 180-250°C and a pressure of 0-0.40 MPa. More preferably, the temperature is 210-245°C.

[0021] Preferably, after the esterification reaction in step (3), an oxide flame retardant synergist is added to the reaction system, wherein the oxide flame retardant synergist is a mixture of one or more of silicon dioxide, titanium dioxide, zinc oxide, calcium oxide, magnesium oxide, titanium pentoxide, and aluminum oxide. Silicon dioxide is more preferred.

[0022] Preferably, the polycondensation reaction in step (3) includes a pre-shrinkage reaction and a final shrinkage reaction, wherein the pre-shrinkage reaction is performed at a temperature of 240-280°C and a pressure of 0.1-3 KPa; the final shrinkage reaction is performed at a temperature of 270-285°C and a pressure of 30-250 Pa. More preferably, the pre-shrinkage reaction is performed at a temperature of 255-270°C and a pressure of 0.2-2 KPa; the final shrinkage reaction is performed at a temperature of 275-285°C and a pressure of 50-250 Pa.

[0023] Preferably, the melt in step (3) is allowed to stand, discharged, and pelletized to obtain the composite halogen-free and high-phosphorus content flame-retardant polyester.

[0024] The invention also discloses the application of the prepared composite halogen-free high-phosphorus content flame-retardant polyester. The composite halogen-free high-phosphorus content flame-retardant polyester is dried under vacuum at 70-120° C. and then spun to prepare the composite halogen-free high-phosphorus content flame-retardant polyester fiber.

[0025] Preferably, the drying step is: first heating to 70°C and drying for 2 hours, keeping at 70°C for 2 hours, then heating to 110°C and drying for 2 hours, and continuing drying at 110°C for 8-10 hours, and then the drying is completed.

[0026] Therefore, the beneficial effects of the present invention are: (1) The reactive phosphorus-based flame retardant containing carboxyl groups can significantly reduce the steric hindrance between the flame retardant and the polyester by pre-esterification with ethylene glycol, thereby increasing the degree of polymerization between the flame retardant and the polyester matrix. This process does not have an adverse effect on the subsequent processing performance.

[0027] (2) Reactive phosphorus-based flame retardants directly participate in the polyester polymerization process and are grafted onto the polyester molecular chain, serving as the intrinsic flame retardant functional component of polyester, thereby reducing the migration and precipitation of flame retardants.

[0028] (3) Hydrogen bonds or chemical bonds are generated between the melamine salt and the reactive phosphorus flame retardant in the polyester system, forming a flame retardant interconnected network, which can increase the adsorption force between molecules during combustion and reduce the generation of droplets.

[0029] (4) The present invention improves the flame retardant performance in the following aspects: First, the carboxyl-containing phosphorus-based reactive flame retardant used in the method is used as the main flame retardant component. Phosphoric acid is formed during the combustion process as a dehydrating agent and promotes carbonization; phosphoric acid can absorb heat and prevent CO from being oxidized to CO2; a thin glassy or liquid protective layer is formed on the surface of the condensed phase, thereby reducing oxygen diffusion and heat and mass transfer between the gas phase and the solid phase, inhibiting the carbon oxidation process, and reducing the thermal decomposition of the phosphorus-containing flame retardant, resulting in the following changes: phosphorus-based flame retardant → metaphosphoric acid → phosphoric acid → polymetaphosphoric acid, polymetaphosphoric acid is a stable compound that is not easy to volatilize and has strong dehydration properties, forming a dense carbon layer to isolate the polymer surface from the air; at the same time, when the polymer burns, the phosphorus-containing compound produces PO· free radicals, which will capture the active H· or HO· in the flame area,· reducing the concentration of H· or HO· in the flame, that is, PO·+H·=HPO, so that the combustion chain reaction cannot continue. Therefore, the phosphorus-based reactive flame retardant used in this method can be used as both an acid source and a gas source in the intumescent flame retardant. Second, the nitrogen-based flame retardant used in this method, on the one hand, generates non-combustible gases such as N2, CO2, and H2O through combustion and thermal decomposition, dilutes the concentration of combustible gases, reduces the temperature of the material surface, and inhibits the chain reaction; on the other hand, when heated, nitrogen-based flame retardants (such as melamine salts) can cross-link with each other to form a carbon layer on the surface of the material, which plays a role in isolating heat and oxygen and inhibiting smoke, thereby achieving an anti-melting droplet effect. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below through specific embodiments.

[0031] In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or are commonly used in the art. The methods in the embodiments, unless otherwise specified, are all conventional methods in the art.

[0032] Overall embodiment A method for preparing a composite halogen-free high-phosphorus content flame-retardant polyester comprises the following steps: (1) Preparation of esterified liquid of reactive phosphorus-based flame retardant A diol and a carboxyl-containing reactive phosphorus flame retardant (selected from CEPPA and DDP) are mixed in an alcohol-acid molar ratio of 3:(6-8), anhydrous sodium acetate accounting for 0.5% of the total mass of the reaction system is added, and the mixture is reacted in a reactor at 165-200° C. When the amount of reaction water reaches 95-98% of the theoretical value, heating is stopped, diol is added to the reaction system for dilution, and material is discharged when the temperature in the reactor drops below 120° C. to obtain an esterified liquid of the reactive phosphorus flame retardant.

[0033] (2) Preparation of reactive nitrogen flame retardants Melamine salt (selected from melamine cyanurate and melamine polyphosphate) and formaldehyde are mixed, the pH is adjusted to 9-10 with sodium hydroxide solution, and the reaction is carried out at 75-95° C. for 2-3 hours to obtain a prepolymer of a reactive nitrogen-based flame retardant. The prepolymer is filtered, washed, dried, and ground for 25-35 minutes; the above-mentioned filtering, washing, drying, and grinding operation process are repeated 1-3 times to obtain a reactive nitrogen-based flame retardant with a particle size of 1-5 μm.

[0034] (3) Preparation of composite halogen-free high phosphorus content flame-retardant polyester Mixing diol, terephthalic acid, a catalyst, the esterification liquid of the reactive phosphorus-based flame retardant in step (1), and the reactive nitrogen-based flame retardant in step (2), wherein the molar ratio of diol to terephthalic acid is 1:(1.2-1.5), the amount of the catalyst added is 100-1000ppm of the total mass of the copolyester, the amount of the esterification liquid of the reactive phosphorus-based flame retardant used is 0.5-2% of the total mass of the copolyester, the phosphorus element in the esterification liquid of the reactive phosphorus-based flame retardant accounts for 15000-25000ppm of the total mass of the copolyester, and the amount of the reactive nitrogen-based flame retardant used is 1-3% of the total mass of the copolyester; The above raw materials are first subjected to esterification reaction at 180-250° C. and 0-0.40 MPa, an oxide flame retardant synergist is added, and then a polycondensation reaction is carried out. The polycondensation reaction is divided into a pre-condensation reaction and a final polycondensation reaction. The pre-condensation reaction is carried out at a temperature of 240-280° C. and a pressure of 0.1-3 KPa; the final polycondensation reaction is carried out at a temperature of 270-285° C. and a pressure of 30-250 Pa. The melt is obtained by polycondensation reaction, and the melt is subjected to standing, discharging and pelletizing to obtain composite halogen-free and high-phosphorus content flame-retardant polyester.

[0035] Example 1 A method for preparing a composite halogen-free high-phosphorus content flame-retardant polyester, comprising the following steps: (1) Adding ethylene glycol and 2-carboxyethylphenyl hypophosphorous acid in an alcohol-acid molar ratio of 3:7 into a reaction kettle, and then adding anhydrous sodium acetate accounting for 0.5% of the total mass of the reaction system; turning on the stirring motor, and controlling the motor frequency at 50 Hz; gradually increasing the temperature in the reaction kettle, and when the temperature in the kettle rises to 180° C., adjusting the water outlet rate, controlling the water outlet speed, and stopping heating after the water outlet reaches 98% of the theoretical value, adding diol for dilution, and discharging after the internal temperature is cooled to 120° C., thereby obtaining an esterified liquid of a reactive phosphorus-based flame retardant.

[0036] (2) Melamine cyanurate and formaldehyde are mixed, sodium hydroxide solution is added dropwise to adjust the pH to 9, the temperature is raised to 80°C and the reaction time is 2 hours to obtain a prepolymer of a reactive nitrogen flame retardant. The prepolymer is filtered, washed, and dried, and then placed in a grinder. Deionized water accounting for 1 / 6 of the mass of melamine is added, and the prepolymer is ground in the grinder at 20°C for 35 minutes until the dispersed particle size of the nitrogen flame retardant is about 200 μm, the thermal stability is qualified, and no obvious sedimentation occurs after being placed for 12 hours, thereby obtaining a nitrogen reactive flame retardant dispersion. The prepolymer is then filtered, dried, and ground to obtain a modified reactive nitrogen flame retardant with a particle size of 5 μm.

[0037] (3) Add ethylene glycol and terephthalic acid in an alcohol-acid molar ratio of 1:1.3 to a reactor, then add the esterification liquid of the reactive phosphorus-based flame retardant obtained in step (1), control the phosphorus content in the overall polyester to 7000 ppm (by mass), add the reactive nitrogen-based flame retardant obtained in step (2), control the mass of melamine salt in the overall polyester to 2%, add ethylene glycol antimony catalyst, and add an amount of 200 ppm of the overall polyester mass; carry out esterification reaction at 235° C. and 0.3 MPa, and after the esterification is completed, add 0.3% of nano-silicon dioxide by mass of the overall polyester; carry out low vacuum pre-shrinkage reaction at 270° C. and 0.5 KPa to discharge excess diol; after the pre-shrinkage is completed, carry out high vacuum final shrinkage reaction at 275° C. and 100 Pa to obtain a product melt, and then let the melt stand, discharge, and pelletize to obtain a composite halogen-free high-phosphorus content flame-retardant polyester.

[0038] Example 2 The difference from Example 1 is that the amount of modified phosphorus-based reactive flame retardant esterification liquid used in step (3) is different, and the phosphorus content in the overall polyester is controlled at 10000 ppm (mass percentage).

[0039] Example 3 The difference from Example 1 is that the amount of modified phosphorus-based reactive flame retardant esterification liquid used in step (3) is different, and the phosphorus content in the overall polyester is controlled at 15000 ppm (mass percentage).

[0040] Example 4 The difference from Example 1 is that the amount of modified phosphorus-based reactive flame retardant esterification liquid used in step (3) is different, and the phosphorus content in the overall polyester is controlled at 19000 ppm (mass percentage).

[0041] Comparative Example 1 The difference from Example 1 is that no flame retardant component is added, that is, pure polyester is prepared.

[0042] Comparative Example 2 The difference from Example 1 is that no reactive nitrogen flame retardant is added, that is, a polyester containing only phosphorus flame retardant is prepared, and the phosphorus content in the overall polyester is still controlled at 7000 ppm (mass percentage).

[0043] Comparative Example 3 The difference from Example 1 is that no reactive phosphorus-based flame retardant is added, that is, the polyester prepared contains only nitrogen flame retardant, and the mass of melamine salt in the overall polyester is still controlled at 2%.

[0044] Comparative Example 4 The difference from Example 1 is that after the esterification in step (3) is completed, no nano-silicon dioxide is added.

[0045] Comparative Example 5 The difference from Example 1 is that the reaction temperature of step (1) is controlled at 205° C. to prepare a phosphorus-based flame retardant.

[0046] Comparative Example 6 The difference from Example 1 is that the reaction temperature of step (1) is controlled at 145° C. to prepare a phosphorus-based flame retardant.

[0047] The difference between Comparative Example 7 and Example 1 is that 2-carboxyethylphenylphosphorous acid is not subjected to the pre-esterification treatment of step (1) and is directly added to the polyester to participate in the reaction.

[0048] Performance Testing The viscosity test was conducted on the polyesters of the above-mentioned embodiments and comparative examples, and the obtained composite halogen-free high-phosphorus flame-retardant polyester was made into strips and fibers for flame retardant performance test. The preparation method of the strips is: the polyester is dried under vacuum conditions at 80-120°C for 8 h, and after drying, injection molding is performed; according to the requirements of the national standard GB / T2406-2009, the oxygen index test is performed. The preparation method of the fiber is: the polyester is dried under vacuum conditions, specifically, first heated to 70°C and dried for 2 h, kept at 70°C for 2 h, then heated to 110°C and dried for 2 h, and continued to dry at 110°C for 8-10 h. After drying, spinning is performed according to the conventional polyester process to obtain the fiber. The test method refers to GB / T14189-2008, GBT 2408-2008, GBT 5454-1997, and FZ / T50021.

[0049] From the table above we can see that: ① Compared with Comparative Examples 2 and 3, the compound combination of CEPPA and MCA in Example 1 shows obvious advantages. This advantage is mainly reflected in its excellent flame retardant effect. CEPPA provides abundant acid sources during the combustion process, which can combine with silica and work together to significantly enhance the carbonization effect. This enhanced carbonization effect leads to a reduction in the number of droplets, which undoubtedly plays a vital role in improving the flame retardant efficiency.

[0050] On the other hand, MCA releases a large amount of NO, NO2, NH3 and other gases during combustion. The release of these gases not only further enhances the carbonization effect, but also causes the substrate to expand to form an expansion layer. This expansion layer can effectively block oxygen, thereby achieving a good flame retardant effect. This dual effect makes the combination of CEPPA and MCA far superior to CAPPA or MCA alone in flame retardancy.

[0051] In general, the synergistic effect of the combination of CEPPA and MCA during the combustion process makes it have a significant advantage in flame retardant effect. This advantage is mainly reflected in its strong charring ability, the reduction of the number of droplets, and the effective barrier of the expansion layer to oxygen. These factors work together to make the combination of CEPPA and MCA a highly efficient and environmentally friendly flame retardant.

[0052] ② In the comparison between Example 1 and Comparative Example 4, the esterification reaction with the addition of flame retardant synergist silica showed significant advantages in the carbonization effect, while reducing the number of droplets. This result shows that the addition of flame retardant synergist silica has a positive role in improving the carbonization performance of polyester. This advantage can be attributed to the multiple effects of silica, including promoting the formation of a carbon layer and improving its stability and quality. In addition, silica may also inhibit the droplet phenomenon during the combustion of polyester, thereby further improving the safety of combustion. This discovery has important practical value for the production of polyester and the development of flame retardants, and also provides new ideas for research in related fields.

[0053] ③ Comparing Examples 1-4, it can be found that the increase in phosphorus content in polyester shows an obvious positive correlation with its flame retardant effect. In other words, as the phosphorus content in polyester increases, its flame retardant effect becomes better and better. However, it should be noted that in the prior art, since phosphorus-based flame retardants contain macromolecular structures such as benzene rings, their steric hindrance is relatively large, which brings great difficulties to the preparation of high-phosphorus content flame-retardant polyester.

[0054] In the prior art, if the flame retardant is directly added to the polyester reaction system, the polymerization reaction will become increasingly difficult when the phosphorus content exceeds 6000ppm. In addition, due to the low viscosity of the polyester, its melt index will also become extremely poor, which will lead to the lack of spinnability of the polyester.

[0055] In view of the shortcomings of the prior art, the present invention proposes a new method for preparing flame-retardant polyester with high phosphorus content. The core of the method is to pre-esterify the carboxyl-containing reactive phosphorus flame retardant with ethylene glycol. This pre-esterification reaction can greatly reduce the steric hindrance between the carboxyl-containing phosphorus flame retardant and the polyester, thereby increasing the degree of polymerization of the flame retardant and the polyester matrix. Through this method, we have successfully achieved the preparation of flame-retardant polyester with high phosphorus content.

[0056] ④ The difference between Comparative Example 5 and Example 1 is that the esterification temperature of the phosphorus-based reactive flame retardant in Comparative Example 5 is relatively high, resulting in the self-polymerization of ethylene glycol in the reaction system. This self-polymerization reaction causes the diethylene glycol content in the system to exceed the control range, directly affecting the color value of the polyester product. The color value does not meet the standard, which not only affects the quality of the polyester product, but also limits its subsequent use.

[0057] In addition, the self-polymerization reaction of ethylene glycol not only affects the color value of polyester, but also interferes with the subsequent polymerization reaction. Since there are incompletely esterified flame retardants in the reaction system, these unesterified flame retardants are extracted from the system along with small molecular by-products, resulting in a significant reduction in the phosphorus content in the system. This situation not only affects the quality of polyester products, but also greatly reduces the effect of flame retardants.

[0058] ⑤Comparative Example 6 Compared with Example 1, the esterification temperature of the phosphorus-based reactive flame retardant is lower, which results in the esterification rate of the flame retardant failing to reach the expected standard. Since the unesterified flame retardant cannot be successfully connected to the PET molecular chain, the unreacted flame retardant will be drawn away along with the oligomers during the polymerization process. This phenomenon causes the phosphorus content of the entire system to fail to reach the theoretical expected value, which in turn significantly reduces the flame retardant effect.

[0059] ⑥ Compared with Example 1, the polymerization process of polyester was disturbed in Comparative Example 7 due to the addition of unesterified phosphorus flame retardant. This phenomenon is reflected in the decrease in viscosity of polyester chips after the discharge test, and the phosphorus content is far from the theoretical expectation.

[0060] In summary, better effects can only be achieved within the steps, reagents and preferred parameter ranges of the present invention.

[0061] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a composite halogen-free high-phosphorus content flame-retardant polyester, characterized in that: The following steps are involved: (1) mixing a diol, a carboxyl-containing reactive phosphorus-based flame retardant and anhydrous sodium acetate, and heating the mixture to react to obtain an esterified liquid of the reactive phosphorus-based flame retardant; (2) mixing melamine salt and formaldehyde, adjusting the pH to alkaline, heating and reacting to obtain a prepolymer of a reactive nitrogen-based flame retardant, and filtering, washing, drying and grinding the prepolymer to obtain a micron-sized reactive nitrogen-based flame retardant; (3) Mixing diol, terephthalic acid, a catalyst, the esterification liquid of the reactive phosphorus-based flame retardant in step (1), and the reactive nitrogen-based flame retardant in step (2), and sequentially subjecting the mixture to esterification reaction and polycondensation reaction to obtain a melt, and treating the melt to obtain a composite halogen-free high-phosphorus content flame-retardant polyester.

2. The preparation method according to claim 1, characterized in that: The reactive phosphorus-based flame retardant in step (1) is one or two of CEPPA and DDP; and / or; the diol in step (1) is a mixture of one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, and 1,4-cyclohexanedimethanol.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the molar ratio of diol to reactive phosphorus-based flame retardant is 3:(6-8).

4. The preparation method according to claim 1, characterized in that: The melamine salt in step (2) is one or both of melamine cyanurate and melamine polyphosphate.

5. The preparation method according to claim 1, characterized in that: In step (3), the molar ratio of diol to terephthalic acid is 1:(1.2-1.5), the amount of the catalyst added is 100-1000 ppm of the total mass of the copolyester, the amount of the esterification liquid of the reactive phosphorus-based flame retardant is 0.5-2% of the total mass of the copolyester, and the amount of the reactive nitrogen-based flame retardant is 1-3% of the total mass of the copolyester.

6. The preparation method according to claim 1 or 5, characterized in that: In the esterification liquid of the reactive phosphorus-based flame retardant in step (3), the phosphorus element accounts for 15000-25000 ppm of the total mass of the copolyester.

7. The preparation method according to claim 1, characterized in that: The conditions of the esterification reaction in step (3) are a temperature of 180-250°C and a pressure of 0-0.40 MPa.

8. The preparation method according to claim 1, characterized in that: In step (3), after the esterification reaction, an oxide flame retardant synergist is added to the reaction system, wherein the oxide flame retardant synergist is a mixture of one or more of silicon dioxide, titanium dioxide, zinc oxide, calcium oxide, magnesium oxide, titanium pentoxide, and aluminum oxide.

9. The preparation method according to claim 1, 7 or 8, characterized in that: The polycondensation reaction in step (3) includes a pre-condensation reaction and a final condensation reaction. The pre-condensation reaction is performed at a temperature of 240-280°C and a pressure of 0.1-3 KPa; the final condensation reaction is performed at a temperature of 270-285°C and a pressure of 30-250 Pa.

10. Use of the composite halogen-free high-phosphorus content flame-retardant polyester prepared by any preparation method of claims 1-9, drying the composite halogen-free high-phosphorus content flame-retardant polyester in vacuum at 70-120°C and spinning to prepare composite halogen-free high-phosphorus content flame-retardant polyester fiber.

Images