Flame-retardant-plasticizing environment-friendly plasticizer for polyvinyl chloride and preparation method of flame-retardant-plasticizing environment-friendly plasticizer

Abstract

The invention provides a preparation method and application of a flame-retardant-plasticizing-self-repairing polyester plasticizer for polyvinyl chloride, and belongs to the technical field of polymer functional materials and polyvinyl chloride modification. According to the method, binary acid and dihydric alcohol are used as basic raw materials, a polyester main chain is constructed through esterification and polycondensation under the action of a catalyst, and a phosphorus-nitrogen flame-retardant structural unit and a reversible disulfide bond structure are cooperatively constructed in polyester molecules by introducing a binary acid monomer containing a DOPO-hydrazide structure and 4, 4 '-diaminodiphenyl disulfide. The molecular structure of the obtained polyester plasticizer simultaneously has a flexible aliphatic chain segment, an internal flame-retardant group and a dynamic reversible covalent bond, and has good plasticizing performance, flame-retardant performance and structure reconstruction capability. When the plasticizer is blended with polyvinyl chloride resin for use, the flexibility and processability of the material can be maintained, the flame-retardant safety of the material can be improved, rearrangement and self-repairing of a microstructure can be realized under a heating condition, and the plasticizer is suitable for the field of polyvinyl chloride materials with comprehensive requirements on flame retardance, flexibility and service stability.

Description

Technical Field

[0001] This invention belongs to the field of polymer material additives and polyvinyl chloride (PVC) modification technology, and relates to a flame-retardant and plasticizing environmentally friendly plasticizer for polyvinyl chloride and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Polyvinyl chloride (PVC) is widely used in wires and cables, building decoration, transportation interiors, films, and hoses due to its low cost, good chemical resistance, and good processing performance. To meet the performance requirements of flexible products during molding, processing, and use, plasticizers are typically introduced into the PVC system to lower the glass transition temperature and improve the material's flexibility and processing properties. Currently, commonly used plasticizers are mostly small-molecule compounds such as phthalates or citrates. These plasticizers are prone to precipitation or migration during use, and under thermal aging, long-term loads, or the influence of external media, they may lead to decreased material flexibility, reduced mechanical properties, and low stability in use. Furthermore, some small-molecule plasticizers also raise environmental and health safety concerns in practical applications, limiting their use in fields with high safety requirements.

[0004] On the other hand, flexible PVC has high requirements for flame retardant performance in applications such as cable protection and aerospace interiors. Although PVC itself has certain flame retardant properties, plasticizers and additives introduced during the plasticizing process may adversely affect the flame retardant performance of the system. Currently, flame retardant modification of PVC is often carried out by adding flame retardants, but this method often has problems such as large addition amounts, limited compatibility with the matrix, easy migration, or impact on the mechanical properties and processing stability of the material, thus restricting the improvement of the overall performance of the material to a certain extent.

[0005] Based on the above problems, in recent years, a research approach has emerged that integrates flame-retardant units with plasticizing structures into reactive plasticizers, aiming to improve flame retardancy while maintaining material flexibility. However, these approaches generally suffer from drawbacks such as complex synthesis routes, high costs, or decreased plasticizing efficiency due to the introduction of rigid flame-retardant structures. Furthermore, even when both flame retardancy and plasticizing properties are achieved, microcracks and structural damage caused by repeated bending, insertion, or assembly stress during actual service of flexible PVC remain difficult to mitigate effectively. Under thermal aging and continuous load conditions, these micro-defects easily expand and evolve into macro-failures, manifesting as reduced material strength, decreased elongation, or even premature failure. Existing methods, such as increasing the degree of crosslinking or introducing repair components, often adversely affect material processing performance and system stability, making it difficult to balance flexibility, flame retardancy, and long-term service reliability.

[0006] Therefore, there is an urgent need to develop a functional plasticizer that can simultaneously achieve plasticizing, flame retardant and self-healing functions in PVC systems, so as to improve its flame retardant safety and long-term service stability while maintaining the material's processing performance and flexibility. Summary of the Invention

[0007] This invention aims to solve the problems of single function, difficulty in balancing flame retardancy and flexibility, and difficulty in recovering damage to materials during service in existing plasticizer systems for polyvinyl chloride. It provides a method for preparing a polyester plasticizer with flame retardant, plasticizing and self-healing functions and its application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for preparing a flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride, comprising: In the presence of an esterification catalyst and a capping agent, at least one dicarboxylic acid and a diol are esterified. After the reaction is completed, a dicarboxylic acid containing a DOPO-hydrazide structure and 4,4′-diaminodiphenyl disulfide are added, and the mixture is heated to carry out a compression polymerization reaction to obtain the product.

[0009] This invention improves the flame retardant safety of PVC materials by synergistically introducing phosphorus-nitrogen flame retardant structural units and dynamic reversible bond structures into the molecular structure of polyester plasticizers, while ensuring the flexibility and processing performance of PVC materials. It also endows the materials with structural reconstruction and self-repair capabilities under heating conditions, thereby enhancing the long-term service stability of flexible PVC materials.

[0010] In a second aspect, the present invention provides a flame-retardant, plasticizing, and self-healing polyester plasticizer prepared by the above-described method.

[0011] The polyester plasticizer molecule of the present invention simultaneously possesses: (1) Flexible segments provided by aliphatic dicarboxylic acids and diols; (2) A phosphorus-nitrogen synergistic flame-retardant structure provided by DOPO-acylhydrazide dicarboxylic acid; (3) A reversible S–S disulfide network provided by 4,4′-diaminodiphenyl disulfide.

[0012] A third aspect of the present invention provides the application of the above-described flame-retardant, plasticizing, and self-healing polyester plasticizer in the preparation of PVC materials.

[0013] When this plasticizer is blended with polyvinyl chloride, it can simultaneously improve the flexibility and flame retardancy of the material, and endow the material with heat-triggered self-healing and reprocessing capabilities, so that the limiting oxygen index (LOI) of the resulting material reaches the range of 28–32%, and the flame retardancy rating can reach UL-94 V-0 or equivalent.

[0014] Polyester plasticizers containing S–S dynamic bonds can achieve microcrack healing and interfacial stress relaxation through disulfide bond exchange at 60–120 °C, thereby improving the fatigue resistance and long-term mechanical stability of polyvinyl chloride materials.

[0015] Beneficial effects of the present invention (1) By introducing flexible aliphatic segments, phosphorus-nitrogen synergistic flame retardant units containing DOPO-hydrazide structure and reversible disulfide bond structure into the main chain of polyester plasticizer, the resulting polyester plasticizer has plasticizing, flame retardant and structural reconfigurable properties at the molecular level. This reduces the compatibility decline and migration risk caused by adding various additives to obtain the multifunctionality of the material, and realizes the integrated structural design of multifunctionality.

[0016] (2) The polyester plasticizer uses aliphatic polyester segments as the main structure, which can effectively reduce the glass transition temperature of PVC and improve the chain segment mobility, thereby giving the material good flexibility and processing fluidity; at the same time, the DOPO-hydrazide structure introduced into the molecule can promote the char formation of the condensed phase and inhibit the thermal decomposition reaction through the phosphorus-nitrogen synergistic effect during combustion, so that the PVC material can achieve flexibility while maintaining a high flame retardancy level.

[0017] (3) The present invention introduces a 4,4′-diaminodiphenyl disulfide structure into the polyester main chain to construct a reversible S–S dynamic covalent bond network in the material system. Under heating conditions of 60–120 °C, the disulfide bonds can undergo a reversible exchange reaction, which promotes the rearrangement of molecular chain segments and the reconstruction of local network structure. This can alleviate and repair the microcracks, interface defects and stress concentration areas generated in the PVC material during use, and improve the structural stability and mechanical retention rate of the material under repeated deformation and long-term service conditions.

[0018] (4) The preparation method of the present invention is simple, practical and easy to promote. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 The mechanical properties of the flame retardant plasticizer prepared in Example 1 of this invention are compared with those of Comparative Examples 1 and 2.

[0021] Figure 2 The limiting oxygen index diagrams are shown for the flame retardant plasticizers prepared in Examples 1 and 2 of this invention and for Comparative Examples 1 and 2. Detailed Implementation

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or product instructions. Similarly, unless otherwise specified, the test methods of this invention are performed in accordance with conventional methods in the art or industry-standard methods or practices. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0024] This invention provides a method for preparing a flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride, comprising: In the presence of an esterification catalyst and a capping agent, at least one diacid and a diol are esterified. After the reaction is completed, a diacid containing a DOPO-hydrazide structure and 4,4′-diaminodiphenyl disulfide are added, and the mixture is heated to carry out a compression polymerization reaction to obtain a polyester plasticizer whose main chain contains flexible aliphatic segments, a phosphorus-nitrogen synergistic flame retardant structure, and reversible disulfide bonds.

[0025] Preferably, the molar ratio of the dicarboxylic acid to the diol is 1:0.5~1.3, which is more conducive to the complete esterification reaction and provides a flexible structure for the polyester molecular chain.

[0026] Preferably, the dicarboxylic acid is selected from one or more of succinic acid, azelaic acid, sebacic acid, and mixtures thereof; Preferably, the diol is selected from one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and 2,2,4-trimethyl-1,3-pentanediol.

[0027] Preferably, the esterification catalyst is phosphoric acid, p-toluenesulfonic acid, or tetrabutyl titanate, and when the amount of the esterification catalyst added is 0.05~0.3wt% of the total mass of the diacid and diol, it exhibits good esterification polycondensation catalytic activity.

[0028] Preferably, the end-capping agent is 2-ethylhexanol; the molar ratio of the end-capping agent to the diacid is 0.05~0.4:1, which can effectively control the termination structure of the polyester molecular chain and the processing flowability of the product.

[0029] In some embodiments, the diacid monomer containing the DOPO-hydrazide structure is introduced into the reaction system as a functionalized monomer before polyester polycondensation, followed by polyester esterification and polycondensation reactions, with the reaction temperature controlled at 180°C to 190°C.

[0030] Preferably, the amount of the DOPO-hydrazide-containing dicarboxylic acid accounts for 8-20 mol% of the total acid equivalent (i.e., the amount is based on the sum of the carboxyl equivalents provided by all dicarboxylic acids participating in the polycondensation reaction). The DOPO-hydrazide-containing dicarboxylic acid undergoes an addition reaction with an unsaturated dicarboxylic acid to obtain a phosphorus-containing dicarboxylic acid, which then undergoes a condensation reaction with a diamine compound to introduce a nitrogen-containing group, thereby forming a flame-retardant dicarboxylic acid monomer containing both phosphorus and nitrogen structures.

[0031] More preferably, the phosphorus-containing dicarboxylic acid obtained by the addition reaction of DOPO with itaconic acid, maleic acid or fumaric acid is then subjected to a condensation reaction with the diamine compound ethylenediamine to introduce a nitrogen-containing group and form a dicarboxylic acid monomer with a PN cooperating structure. The molecule simultaneously contains a DOPO structure, a nitrogen-containing functional group and at least two carboxyl end groups.

[0032] Preferably, the amount of 4,4′-diaminodiphenyl disulfide accounts for 2-8 mol% of the carboxyl equivalent. The 4,4′-diaminodiphenyl disulfide participates in the construction of the polyester backbone during polycondensation, introducing a dynamic covalent disulfide bond structure of –Ar–S–S–Ar– into the polyester molecule, enabling the resulting polyester plasticizer to possess network reconstruction and self-repair capabilities under heating conditions.

[0033] Preferably, the method for preparing the dicarboxylic acid containing the DOPO-hydrazide structure includes: adding DOPO with itaconic acid, maleic acid or fumaric acid to obtain a phosphorus-containing dicarboxylic acid, and then performing a condensation reaction with a diamine compound ethylenediamine to obtain the final product.

[0034] Preferably, the esterification reaction is carried out at 150-160°C for 3-4 hours; Preferably, the conditions for the reduced-compression polymerization reaction are reduced-compression polymerization at 180-190°C for 1.5-2 hours.

[0035] More specifically, including: A diacid and one or more diols are added to a reaction vessel, protected by nitrogen gas, and heated with stirring. Esterification is carried out in the presence of a catalyst until no more water is released. Subsequently, the temperature is increased further, and a polycondensation reaction is carried out under reduced pressure to obtain a polyester prepolymer with terminal hydroxyl groups. Adipic acid, azelaic acid, and sebacic acid are used as the diacid components, and ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, pentanediol, or 2,2,4-trimethyl-1,3-pentanediol are used. The polycondensation stage is carried out under vacuum to obtain a polyester prepolymer with suitable molecular weight and terminal hydroxyl structure.

[0036] In the polyester polycondensation stage, a diacid monomer containing a DOPO-hydrazide structure and 4,4′-diaminodiphenyl disulfide are introduced into the reaction system to participate in the main chain construction. This introduces phosphorus-nitrogen synergistic flame-retardant structural units and –Ar–S–S–Ar– dynamic covalent bond structural units into the polyester main chain, resulting in a flame-retardant, plasticizing, and self-healing polyester plasticizer. The diacid monomer containing the DOPO-hydrazide structure accounts for 2–5 mol% of the total acid equivalent; the 4,4′-diaminodiphenyl disulfide accounts for 0.5–10 mol% of the total hydroxyl / carboxyl equivalent, thus achieving adjustable flame-retardant and self-healing properties.

[0037] The modified polyester and PVC powder were mixed at a mass ratio of 2:1, dissolved in 80 mL of tetrahydrofuran, and stirred at 60°C for 2 hours to form a transparent homogeneous solution. This solution was poured into a glass mold and dried in a vacuum drying oven to obtain a flame-retardant polyester-plasticized PVC composite film.

[0038] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0039] In the following examples, the preparation method of the dicarboxylic acid monomer containing the DOPO-hydrazide structure includes: under nitrogen protection, 0.10 mol of 9,10-dihydro-9-oxo-10-phosphaphenanthrene-10-oxide (DOPO) and 0.10 mol of maleic anhydride are added to 150 mL of anhydrous toluene, heated to 105 °C and stirred for 4 h. After the reaction is completed, the mixture is cooled to room temperature, and the reaction solution is poured into excess n-hexane to precipitate a solid. The solid is filtered and dried under vacuum at 60 °C to obtain the DOPO-anhydride addition intermediate. Subsequently, 0.20 mol of the obtained intermediate is dispersed in 250 mL of anhydrous tetrahydrofuran, and 0.10 mol of hydrazine hydrate (N2H4·H2O, content 80 wt%) is slowly added dropwise at 0–5 °C for 30 min. After the addition is completed, the temperature is raised to 40 °C and the reaction is stirred for 3 h. After the reaction was completed, the system was poured into excess deionized water and the pH was adjusted to 2–3 with dilute hydrochloric acid to allow the product to be fully precipitated. After filtration, the product was washed with deionized water until neutral and finally dried under vacuum at 60 °C for 12 h to obtain a dicarboxylic acid monomer containing the DOPO-acylhydrazine structure.

[0040] Example 1: (1) Add 0.10 mol adipic acid and 0.12 mol 1,4-butanediol to a 250 mL three-necked flask, purge with nitrogen, add 0.25 wt% p-toluenesulfonic acid (total mass of adipic acid and 1,4-butanediol) as an esterification catalyst, and add 0.07 mol 2-ethylhexanol as a capping agent. Heat to 150 °C for esterification reaction for 3 h. After no more water is precipitated from the system, heat to 180 °C. Polyester prepolymer PEA was obtained by reducing pressure and polymerizing for 2 h under 0.08 MPa conditions.

[0041] (2) Add a diacid monomer containing a DOPO-hydrazide structure to the system. The amount of the monomer is based on the sum of the carboxyl equivalents provided by all the diacids participating in the polycondensation reaction. The amount added accounts for 10 mol% of the total acid equivalent. At the same time, add 4,4′-diaminodiphenyl disulfide. The amount of 4,4′-diaminodiphenyl disulfide accounts for 3 mol% of the carboxyl equivalent of the reaction system based on the functional group equivalent. Continue the polycondensation reaction for 1 h to obtain a polyester plasticizer containing both a phosphorus-nitrogen synergistic flame retardant structure and an –Ar–S–S–Ar– dynamic disulfide bond structure in the main chain. The plasticizer is named PEA-PN-SS.

[0042] (3) Take the obtained polyester plasticizer and PVC powder and mix them at a mass ratio of 2:1. Add 80 mL of THF and stir at 60℃ for 2 h to form a homogeneous solution. Cast, dry and press into sheets to obtain a flame-retardant-plasticized-self-healing PVC composite film with a thickness of about 0.4 mm.

[0043] Example 2: (1) Add 0.10 mol sebacic acid and 0.11 mol 1,6-hexanediol to a reaction flask, purge with nitrogen, add 0.20 wt% phosphoric acid as a catalyst (based on the total amount of sebacic acid and 1,6-hexanediol), and add 0.065 mol 2-ethylhexanol as a capping agent. Esterify at 150 ℃ for 3 h, then raise the temperature to 180 ℃. Polyester prepolymer PHA was obtained by reducing pressure and polymerizing for 2 h under 0.09 MPa conditions.

[0044] (2) Add a diacid monomer containing DOPO-hydrazide structure (accounting for 8 mol% of the total acid equivalent) and 4,4′-diaminodiphenyl disulfide (accounting for 5 mol% of the carboxyl equivalent), and continue the polycondensation reaction for 1 h to obtain the polyester plasticizer PHA-PN-SS.

[0045] (3) Take the obtained polyester plasticizer and PVC powder and mix them at a mass ratio of 2:1. Add 80 mL of THF and stir at 60℃ for 2 h to form a homogeneous solution. Cast, dry and press into sheets to obtain a flame-retardant-plasticized-self-healing PVC composite film with a thickness of about 0.4 mm.

[0046] Example 3: (1) Add 0.10 mol adipic acid and 0.12 mol neopentyl glycol to a reaction flask, purge with nitrogen, add 0.30 wt% tetrabutyl titanate as a catalyst (based on the total amount of adipic acid and neopentyl glycol), and add 0.08 mol 2-ethylhexanol as a capping agent. Esterify at 150 °C for 3 h, then raise the temperature to 180 °C. Flexible polyester PNA was obtained by polycondensation at 0.08 MPa for 2 h.

[0047] (2) Add a diacid monomer containing DOPO-hydrazide structure (accounting for 12 mol% of the total acid equivalent) and 4,4′-diaminodiphenyl disulfide (accounting for 2 mol% of the carboxyl equivalent), and continue the polycondensation reaction for 1 h to obtain polyester plasticizer PNA-PN-SS.

[0048] (3) Take the obtained polyester plasticizer and PVC powder and mix them at a mass ratio of 2:1. Add 80 mL of THF and stir at 60℃ for 2 h to form a homogeneous solution. Cast, dry and press into sheets to obtain a flame-retardant-plasticized-self-healing PVC composite film with a thickness of about 0.4 mm.

[0049] Example 4: (1) Add 0.10 mol azelaic acid and 0.12 mol 1,3-propanediol to a three-necked flask, purge with nitrogen, add 0.20 wt% p-toluenesulfonic acid as a catalyst (based on the total amount of azelaic acid and 1,3-propanediol), and add 0.07 mol 2-ethylhexanol as a capping agent. Esterify at 150 °C for 3 h, then raise the temperature to 180 °C. Polyester PRA was obtained by reducing pressure and polymerizing for 2 h under 0.08 MPa conditions.

[0050] (2) Add a diacid monomer containing DOPO-hydrazide structure (accounting for 15 mol% of the total acid equivalent) and 4,4′-diaminodiphenyl disulfide (accounting for 6 mol% of the carboxyl equivalent), and continue the polycondensation reaction for 1 h to obtain the polyester plasticizer PRA-PN-SS.

[0051] (3) Take the obtained polyester plasticizer and PVC powder and mix them at a mass ratio of 2:1. Add 80 mL of THF and stir at 60℃ for 2 h to form a homogeneous solution. Cast, dry and press into sheets to obtain a flame-retardant-plasticized-self-healing PVC composite film with a thickness of about 0.4 mm.

[0052] Example 5: (1) 0.10 mol sebacic acid, 0.10 mol 1,4-butanediol and 0.02 mol 2,2,4-trimethyl-1,3-pentanediol were added to a reaction flask, protected by nitrogen gas, and 0.25 wt% phosphoric acid was added as a catalyst (based on the total amount of sebacic acid and 1,4-butanediol), and 0.075 mol 2-ethylhexanol was added as a capping agent to carry out esterification-polymerization reaction. Polycondensation was carried out at 180℃ under reduced pressure for 2 h to obtain polyol structure polyester PEAB.

[0053] (2) Add a diacid monomer containing DOPO-hydrazide structure (accounting for 20 mol% of total acid equivalent) and 4,4′-diaminodiphenyl disulfide (accounting for 8 mol% of carboxyl equivalent), and continue the polycondensation reaction for 1 h to obtain polyester plasticizer PEAB-PN-SS.

[0054] (3) Take the obtained polyester plasticizer and PVC powder and mix them at a mass ratio of 2:1. Add 80 mL of THF and stir at 60℃ for 2 h to form a homogeneous solution. Cast, dry and press into sheets to obtain a flame-retardant-plasticized-self-healing PVC composite film with a thickness of about 0.4 mm.

[0055] Comparative Example 1: The procedure was carried out according to Example 1, but without the addition of 4,4′-diaminodiphenyl disulfide; only a dicarboxylic acid monomer containing a DOPO-hydrazide structure was introduced to obtain a polyester plasticizer PEA-PN without dynamic disulfide bonds. It was then blended with PVC under the same conditions to form a film.

[0056] Comparative Example 2: The procedure was carried out according to Example 1, but without adding a dicarboxylic acid monomer containing a DOPO-hydrazide structure; only 4,4′-diaminodiphenyl disulfide was introduced to obtain the polyester plasticizer PEA-SS. It was then blended with PVC under the same conditions to form a film.

[0057] like Figure 1 As shown, the mechanical properties of the plasticizer prepared in the embodiments of the present invention, compared with those of Comparative Examples 1 and 2, in the PVC system were tested. The mechanical property testing was conducted in accordance with GB / T 1040.1-2006. The results show that the overall stress level of the sample corresponding to the flame-retardant polyester plasticizer of the present invention is significantly better than that of Comparative Examples 1 and 2, and the elongation at break is also better. The tensile strength of the material corresponding to Example 1 can reach about 23 MPa, and the fracture strain is close to 400%, showing excellent mechanical strength and flexibility matching. In contrast, although Comparative Example 1 has a certain plasticizing property, its tensile strength is relatively low; while Comparative Example 2 has good flexibility, its stress support capacity is limited, and its overall comprehensive performance is insufficient. The above results indicate that the polyester plasticizer synthesized in the present invention, due to the simultaneous introduction of flexible aliphatic segments and polar functional structures in its molecular backbone, has good compatibility with the PVC matrix and effective plasticizing effect, thereby significantly improving the mechanical properties of the composite material.

[0058] like Figure 2As shown, the limiting oxygen index (LOI) of the plasticizer prepared in this embodiment of the invention, along with Comparative Examples 1 and 2, in the PVC system was tested using a JF-3 limiting oxygen index tester according to the GB / T 2408-2021 method. The results showed that the LOI of the samples corresponding to Comparative Examples 1 and 2 were at relatively low levels, while the LOI value of the PVC composite material significantly increased after introducing the polyester plasticizer prepared in this embodiment of the invention, and was within a higher range. This is mainly attributed to the phosphorus-nitrogen synergistic flame-retardant unit containing a DOPO-hydrazide structure introduced into the polyester plasticizer molecule. During combustion, this type of structure can promote the formation of a dense phosphorus-rich carbon layer on the material surface, effectively blocking the transfer of heat and oxygen to the matrix, while inhibiting the release of combustible volatiles, thereby improving the flame-retardant performance of the composite material. The above results demonstrate that this invention, by introducing an intrinsic flame-retardant structural unit into the polyester plasticizer molecule, achieves synergistic regulation of plasticizing function and flame-retardant performance, verifying the rationality of the structural design.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride, characterized in that, include: In the presence of an esterification catalyst and a capping agent, at least one dicarboxylic acid and a diol are esterified. After the reaction is completed, a dicarboxylic acid containing a DOPO-hydrazide structure and 4,4′-diaminodiphenyl disulfide are added, and the mixture is heated to carry out a compression polymerization reaction to obtain the product.

2. The method for preparing the flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride as described in claim 1, characterized in that, The molar ratio of the dicarboxylic acid to the diol is 1:0.5~1.

3.

3. The preparation method of the flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride as described in claim 1, characterized in that, The dicarboxylic acid is selected from one or more of adipic acid, azelaic acid, sebacic acid and mixtures thereof; Alternatively, the diol is selected from one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and 2,2,4-trimethyl-1,3-pentanediol.

4. The preparation method of the flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride as described in claim 1, characterized in that, The esterification catalyst is phosphoric acid, p-toluenesulfonic acid, or tetrabutyl titanate. Alternatively, the amount of the esterification catalyst added is 0.05~0.3 wt% of the total mass of the diacid and diol; Alternatively, the capping agent is 2-ethylhexanol; Alternatively, the molar ratio of the capping agent to the dicarboxylic acid is 0.05 to 0.4:

1.

5. The method for preparing the flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride as described in claim 1, characterized in that, The amount of the dicarboxylic acid containing the DOPO-hydrazide structure accounts for 8-20 mol of the total acid equivalent.

6. The method for preparing the flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride as described in claim 1, characterized in that, The amount of the 4,4′-diaminodiphenyl disulfide is 2-8 mol of carboxyl equivalent.

7. The method for preparing the flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride as described in claim 1, characterized in that, The method for preparing the DOPO-hydrazide-containing dicarboxylic acid includes: adding DOPO with itaconic acid, maleic acid or fumaric acid to obtain a phosphorus-containing dicarboxylic acid, and then performing a condensation reaction with a diamine compound ethylenediamine to obtain the final product.

8. The method for preparing the flame-retardant, plasticizing, and self-healing polyester plasticizer for polyvinyl chloride as described in claim 1, characterized in that, The esterification reaction is carried out at 150-160℃ for 3-4 hours. Alternatively, the conditions for the reduced-compression polymerization reaction are reduced-compression polymerization at 180-190°C for 1.5-2 hours.

9. The flame-retardant, plasticized, and self-healing polyester plasticizer prepared by the method according to any one of claims 1-8.

10. The application of the flame-retardant, plasticizing, and self-healing polyester plasticizer according to claim 9 in the preparation of PVC materials.

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