A polyphosphazene modified polycarbodiimide flame-retardant hydrolysis-resistant agent, a preparation method and application thereof

Abstract

The application relates to the field of plastic modification, in particular to a polyphosphazene modified polycarbodiimide flame-retardant hydrolysis-resistant agent and a preparation method thereof. PET belongs to flammable materials, and is prone to aging under hydrothermal conditions. In view of the above problems, the application provides a polyphosphazene modified polycarbodiimide flame-retardant hydrolysis-resistant agent, which contains a ring-crosslinked polyphosphazene microsphere structure PHB and a polymerized polycarbodiimide structure PCDI in a molecular structure, the PCDI structure is linked with the PHB microsphere structure through isocyanate groups and hydroxyl groups, the flame-retardant hydrolysis-resistant agent PHB-PCDI obtained by the application is used as an additive of a PET composite material, can significantly improve the flame retardance and hydrolysis resistance of the PET composite material, and the high molecular weight and high crosslinking structure of the flame-retardant hydrolysis-resistant agent make the flame-retardant hydrolysis-resistant agent not easy to migrate out in the subsequent use process, and the flame-retardant hydrolysis-resistant agent has long-acting property.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic modification, and in particular to a polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent and a preparation method thereof. Background Art

[0002] PET is a non-toxic, corrosion-resistant, and dimensionally stable compound. Due to its numerous advantages, it is currently considered one of the most important polymer materials. However, PET's limiting oxygen index is only around 22%, which produces a large amount of molten droplets during combustion, causing secondary damage and expanding the spread of fire. Furthermore, PET is highly sensitive to water, and prolonged contact with water can degrade its performance, hindering its use. Therefore, improving PET's flame retardancy and hydrolysis resistance is crucial.

[0003] As a novel framework material for organophosphorus flame retardants, cyclotriphosphazene (CPP) is widely used in flame retardant applications due to its stable structure, ease of production, and excellent thermal stability and flame retardancy. However, CPP generates hydrogen chloride gas during combustion, which can cause secondary harm to the human body. It also readily hydrolyzes, resulting in a decrease in the material's mechanical properties, necessitating modification.

[0004] At present, the method of alleviating PET hydrolysis is mainly to reduce the terminal carboxyl concentration of polyester materials by adding anti-hydrolysis agents, thereby inhibiting their catalytic action. Carbodiimide is the most commonly used anti-hydrolysis agent for polyester materials and is divided into monomeric and polymeric types. Carbodiimide can capture the terminal carboxyl groups in the chain segments and react to form urea structures at room temperature, thereby inhibiting the progress of the hydrolysis reaction. Because there are isocyanate groups that do not participate in the reaction in polycarbodiimide, the reactivity thereof can cause the storage instability of carbodiimide. Therefore, the present invention uses the hydroxyl groups on the polyphosphazene to block the isocyanate groups, thereby improving the storage stability of the carbodiimide and constructing a flame retardant anti-hydrolysis agent with both a ring-crosslinked polyphosphazene structure and a carbodiimide structure. Summary of the Invention

[0005] The problem in the prior art is that PET is a flammable material and is susceptible to hydrolysis and aging. To address the above problems, the present invention provides a polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent, the preparation method of which includes the following steps:

[0006] (1) Synthesis of PHB microspheres:

[0007] 4,4'-dihydroxydiphenyl sulfone reacts with hexachlorocyclotriphosphazene in a reaction solvent under the action of an acid-binding agent. After the reaction is completed, ring-crosslinked polyphosphazene microspheres, namely PHB microspheres, are obtained.

[0008] The H atom of the hydroxyl group in the molecular structure of 4,4'-dihydroxydiphenyl sulfone and the part of Cl atom connected with the phosphorus atom in the molecular structure of hexachlorocyclotriphosphazene undergo nucleophilic substitution reaction under the action of an acid-binding agent, and the mass ratio of hexachlorocyclotriphosphazene to 4,4'-dihydroxydiphenyl sulfone in the reaction is 0.35:0.25-0.35:1.0.

[0009] (2) Synthesis of PCDI:

[0010] Polymeric carbodiimide (PCDI) is synthesized by isocyanate condensation method with tetramethylxylylene diisocyanate (TMXDI) as raw material under the action of high temperature and catalyst.

[0011] (3) Synthesis of PHB-PCDI:

[0012] A large number of hydroxyl groups connected with benzene rings in the structure of PHB and free isocyanate groups on PCDI undergo end-capping reaction under high temperature, and polyphosphazene modified polycarbodiimide, namely PHB-PCDI, is obtained after the reaction is completed.

[0013] The structural formula of PHB-PCDI is:

[0014]

[0015] The structural formula of R is:

[0016]

[0017] Preferably, the solvent for the nucleophilic substitution reaction in step (1) includes acetonitrile, tetrahydrofuran.

[0018] Preferably, the acid-binding agent in step (1) includes triethylamine, pyridine, potassium carbonate.

[0019] Preferably, the mass ratio of hexachlorocyclotriphosphazene to 4,4'-dihydroxydiphenyl sulfone in step (1) is 0.35:0.25-0.35:1.0.

[0020] Preferably, the temperature required for the isocyanate condensation method in step (2) includes 170-200°C.

[0021] Preferably, the catalyst for the isocyanate condensation method in step (2) includes 3-methyl-1-phenyl-2-phospholene-1-oxide, 1-methyl-1-oxo-2-phospholene.

[0022] Preferably, the mass ratio of tetramethylxylylene diisocyanate to catalyst in step (2) is 5-6:0.04-0.05.

[0023] Preferably, the solvent for the end-capping reaction in step (3) includes tetrahydrofuran, toluene.

[0024] Preferably, the mass ratio of PHB to PCDI in step (3) is 0.25-0.5:1.2-1.5.

[0025] Preferably, the end-capping reaction in step (3) is stirring at 50-60°C for 6-10h.

[0026] Preferably, the method of step (1) comprises the following steps:

[0027] 1) Dissolve 4,4'-dihydroxy diphenyl sulfone in a solvent, then start adding an acid-binding agent, and uniformly disperse the reaction system by ultrasonic; the amount ratio of 4,4'-dihydroxy diphenyl sulfone to the acid-binding agent and the solvent in the reaction is 0.25g:2g:40mL-1.0g:3g:50mL;

[0028] 2) Dissolve hexachlorocyclotriphosphazene in a solvent, then add it to the reaction system formed in step (1), and stir at 50-60°C for 6-8h; after the reaction is completed, centrifuge, wash, and dry the reaction solution to obtain PHB; the amount ratio of hexachlorocyclotriphosphazene to the solvent in the reaction is 0.35g:40mL-0.35g:50mL.

[0029] Preferably, the synthesis method of PCDI in step (2) comprises the following steps:

[0030] In a reaction vessel, add tetramethylxylylene diisocyanate (TMXDI), heat the oil bath to 180°C, and add the catalyst 3-methyl-1-phenyl-2-phospholene-1-oxide (MPPO) under stirring. During the reaction, periodically introduce N2 to blow away the CO2 generated during the reaction and effectively isolate oxygen and moisture in the air. Finally, distill the added catalyst and the remaining unreacted TMXDI under reduced pressure at 180°C and 1mbar to obtain the hydrolysis-resistant agent PCDI. The mass ratio of tetramethylxylylene diisocyanate to the catalyst is 5-6:0.04-0.05.

[0031] Preferably, the synthesis method of PHB-PCDI in step (3) comprises the following steps:

[0032] (1) Add PHB to tetrahydrofuran, and stir at 50-60°C for 0.5-1.0h; in the reaction, the solid-liquid ratio of PHB to tetrahydrofuran is 0.25g:50mL-0.5g:60mL;

[0033] (2) The prepared PCDI is added to tetrahydrofuran and stirred at a constant temperature of 50°C-60°C for 0.5h-1.0h. The amount ratio of PCDI to tetrahydrofuran is 1.2g:50mL-1.5g:60mL. Then, the PHB dispersed in tetrahydrofuran in the previous step is mixed evenly with PCDI and stirred at a constant temperature of 50°C-60°C for 6h-10h. After the reaction is complete, PHB-PCDI is obtained.

[0034] The flame retardant and anti-hydrolysis agent PHB-PCDI obtained by the present invention is used as an additive for PET composite materials, and can significantly improve the flame retardancy and anti-hydrolysis properties of the PET composite materials.

[0035] The present invention has the following beneficial effects:

[0036] (1) The present invention provides a novel flame retardant and anti-hydrolysis agent PHB-PCDI, wherein the molecular structure of the flame retardant and anti-hydrolysis agent PHB-PCDI contains a ring-crosslinked polyphosphazene microsphere structure PHB and a polycarbodiimide structure PCDI. The PCDI structure and the PHB microsphere structure are linked by an isocyanate group and a hydroxyl group. The flame retardant and anti-hydrolysis agent PHB-PCDI obtained by the present invention is used as an additive for PET composite materials, which can significantly improve the flame retardancy and anti-hydrolysis properties of the PET composite materials.

[0037] (2) The polyphosphazene PHB microspheres synthesized in the present invention have a size between 300-500 nm and a strong weak interaction with PET. Therefore, when the material burns, a dense carbon layer is formed on the surface. The carbon layer blocks the transfer of heat and energy and isolates oxygen in the air, thereby delaying the thermal degradation of the material and improving the flame retardant properties of PET.

[0038] (3) After the synthesis of polycarbodiimide, a small amount of unreacted isocyanate has reactive activity, thus affecting the storage stability of the polycarbodiimide. First, the isocyanate selected in the present invention is tetramethylxylylene diisocyanate, which has two methyl groups that have a shielding effect on the -NCO group, reducing the occurrence of other side reactions. In the present invention, part of the isocyanate reacts with the hydroxyl group to form carbamate, which also plays a shielding role, effectively reducing the reactive activity of the remaining isocyanate and protecting the generated carbodiimide. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 : Infrared spectrum of PHB-PCDI obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be described in detail below with reference to the following examples. However, it should be understood that the following examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope of the present invention.

[0041] Example 1

[0042] A polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent, the preparation method of which is as follows:

[0043] (1) Synthesis of PHB microspheres:

[0044] 4,4'-dihydroxydiphenyl sulfone was dissolved in acetonitrile solvent, and then the acid-binding agent triethylamine was added dropwise, and the reaction system was ultrasonically dispersed uniformly; the amount ratio of 4,4'-dihydroxydiphenyl sulfone to the acid-binding agent and solvent in the reaction was 0.6g:3g:50mL.

[0045] Hexachlorocyclotriphosphazene is dissolved in acetonitrile solvent, and then added to the reaction system formed in step (1). The mixture is stirred at 60° C. for 6 h. After the reaction is completed, the reaction solution is centrifuged, washed, and dried to obtain PHB. The ratio of hexachlorocyclotriphosphazene to solvent in the reaction is 0.35 g:50 mL.

[0046] (2) Synthesis of PCDI:

[0047] In a 250 mL four-necked glass flask, 5 g of tetramethylxylene diisocyanate (TMXDI) was added. The mixture was heated to 180°C in an oil pan, and 0.05 g of the catalyst 3-methyl-1-phenyl-2-phosphole-1-oxide (MPPO) was added with stirring. During the reaction, nitrogen was regularly introduced to purge the generated CO2 and effectively isolate the atmosphere from oxygen and moisture. Finally, the catalyst and any remaining unreacted TMXDI were removed under reduced pressure at 180°C and 1 mbar to produce the hydrolysis inhibitor PCDI.

[0048] (3) Synthesis of PHB-PCDI:

[0049] PHB was added to tetrahydrofuran and stirred at 60°C for 1.0 h. The ratio of PHB to tetrahydrofuran was 0.3 g:50 mL.

[0050] The PCDI prepared in step (2) was added to tetrahydrofuran and stirred at a constant temperature of 60°C for 1.0 h. The amount ratio of PCDI to tetrahydrofuran was 1.2 g:50 mL. The PHB dispersed in tetrahydrofuran in the previous step was then mixed evenly with PCDI and stirred at a constant temperature of 60°C for 10 h. After the reaction was complete, PHB-PCDI was obtained.

[0051] Figure 1 This is the infrared spectrum of PHB-PCDI obtained in Example 1. In the spectrum, at 2977 and 2929 cm -1 The peak at 2118cm belongs to the stretching vibration peak of -CH3 and -CH2; -1and 2258 cm -1 anti-symmetrical stretching vibration absorption peaks of -N=C=N and -N=C=O groups, respectively; an absorption peak representing P-O-Ar bond appeared at 942 cm -1 -1 strong peaks at 1186 and 881 cm -1 representing P=N and P-N absorption peaks, which indicated the formation of polyphosphazene structure and carbodiimide structure, indicating the successful synthesis of PHB-PCDI.

[0052] Specific application

[0053] Preparation of PET / PHB-PCDI composite material:

[0054] The PET pellets were dried at 120°C for 12h, then PHB-PCDI was added in PET and blended evenly using an internal mixer, the temperature of the internal mixer was set to 260-270°C, and the rotation speed was set to 40-60r / min, to obtain a PET / PHB-PCDI composite material with PHB-PCDI content of 0.25wt%.

[0055] Example 2

[0056] Example 2 was the same as Example 1, except that the amount of PHB-PCDI added in PET in Example 2 was 0.5wt%.

[0057] Example 3

[0058] Example 3 was the same as Example 1, except that the amount of PHB-PCDI added in PET in Example 3 was 1.0wt%.

[0059] Example 4

[0060] Example 4 was the same as Example 1, except that the amount of PHB-PCDI added in PET in Example 4 was 2.0wt%.

[0061] Comparative Example 1

[0062] Comparative Example 1 was the same as Example 1, except that no PHB-PCDI was added in Comparative Example 1, and pure PET material was obtained after internal mixing.

[0063] Comparative Example 2

[0064] Comparative Example 2 was the same as Example 2, except that the PHB-PCDI added in the preparation process of PET / PHB-PCDI composite material in Comparative Example 2 was replaced by the same amount of hexachlorocyclotriphosphazene.

[0065] Comparative Example 3

[0066] Comparative Example 3 is the same as Example 1, except that, in Comparative Example 3, the PHB-PCDI added during the preparation of the PET / PHB-PCDI composite material is replaced with PHB of equal mass.

[0067] Comparative Example 4

[0068] Comparative Example 4 is the same as Example 2, except that, in Comparative Example 4, the PHB-PCDI added during the preparation of the PET / PHB-PCDI composite material is replaced with PHB, and the amount of PHB added to PET is 0.5 wt%.

[0069] Comparative Example 5

[0070] Comparative Example 5 is the same as Example 3, except that, in Comparative Example 5, the PHB-PCDI added during the preparation of the PET / PHB-PCDI composite material is replaced with PHB, and the amount of PHB added to the PET is 1.0 wt%.

[0071] Comparative Example 6

[0072] Comparative Example 6 is the same as Example 4, except that, in Comparative Example 6, the PHB-PCDI added during the preparation of the PET / PHB-PCDI composite material is replaced with PHB, and the amount of PHB added to PET is 2.0 wt%.

[0073] Comparative Example 7

[0074] Comparative Example 7 is the same as Example 2, except that, in Comparative Example 7, the PHB-PCDI added during the preparation of the PET / PHB-PCDI composite material is replaced with PCDI of equal mass.

[0075] Comparative Example 8

[0076] Comparative Example 8 is the same as Example 4, except that, in Comparative Example 8, the PHB-PCDI added during the preparation of the PET / PHB-PCDI composite material is replaced with PCDI of equal mass.

[0077] Comparative Example 9

[0078] Comparative Example 9 is the same as Example 3, except that, in Comparative Example 9, the PHB-PCDI added during the preparation of the PET / PHB-PCDI composite material is replaced with a mixture of PHB and PCDI of equal mass in a mass ratio of 0.5 g:1.0 g.

[0079] Comparative Example 10

[0080] Comparative Example 10 is the same as Example 3, except that in Comparative Example 10, the PHB-PCDI added in the preparation of the PET / PHB-PCDI composite is replaced by a mixture of PHB and PCDI in a mass ratio of 0.3 g: 1.2 g.

[0081] Comparative Example 11

[0082] Comparative Example 11 is the same as Example 3, except that in Comparative Example 11, the raw material used for the synthesis of PCDI is no longer tetramethylxylylene diisocyanate, but another diisocyanate, dicyclohexylmethane diisocyanate, which has a higher -NCO reactivity.

[0083] Performance Test

[0084] The PET composites obtained in Examples 1-4 and Comparative Examples 1-11 were subjected to relevant performance tests, and the specific test results are shown in Tables 1 and 2.

[0085] Limiting Oxygen Index: tested according to the standard ASTM D 2863-97, using a TM606 digital oxygen index tester;

[0086] Vertical Burning: tested according to the standard UL 94-2013, using a vertical burning tester;

[0087] Aging Experiment: the material was prepared into a dumbbell-shaped sample, and was immersed in a constant-temperature water at 60°C for hydrolytic aging test. After the aging was completed, the tensile strength of the sample was tested. The tensile strength was tested according to the standard GB / T 1040, using an electronic universal material testing machine.

[0088] Table 1

[0089]

[0090]

[0091] As shown in Table 1, the LOI of pure PET is 22.5%, with both t1 and t2 greater than 10 seconds, and t1 + t2 greater than 30 seconds, indicating that pure PET has the lowest flame retardancy. When the PHB content is 0.25wt%, the LOI of the composite is 25.1%. Compared to the LOI of 22.5% for pure PET, the LOI of the composite increases to 28.3% when the PHB content is 2.0wt%. This indicates that when polyphosphazene (PHB) is added to PET alone, its flame retardancy increases with increasing PHB addition. When the PHB-PCDI addition level increases from 0.25wt% to 2.0wt%, the LOI increases from 25.3% to 28.6%, confirming the flame retardant effect of PHB-PCDI. When the flame retardant PHB-PCDI was added at 2 wt%, the composite material had a limiting oxygen index of 28.6%. The flaming combustion time t1 of the sample was only 0.85 s, and t2 was only 0.88 s. The total flaming combustion time t1 + t2 of each sample group was only 1.73 s. After the second flame application, the flaming and flameless combustion time t2 + t3 of each sample was only 1.08 s. This shows that the flame retardancy of the PET composite obtained by adding PHB-PCDI is superior to that of the PET composites obtained by adding PHB or HCCP to PET.

[0092] Table 2

[0093]

[0094] As shown in Table 2, the tensile strength of pure PET and materials with only PHB added decreased significantly after hydrolysis aging, and the tensile strength retention rate was below 40%. When the addition amount of PHB-PCDI increased from 0.25wt% to 2.0wt%, the tensile strength retention rate of the composite material increased from 43.02% to 56.06%, and the initial tensile strength increased from 42.91MPa to 63.57MPa, indicating that PHB-PCDI has excellent hydrolysis resistance, and the greater the addition amount, the better the effect. As shown in Comparative Examples 7 and 8, when PCDI is added alone, the hydrolysis resistance of the composite material is better than that of the composite material with PHB-PCDI added, indicating that the presence of flame retardants affects the mechanical properties of the material, but due to the addition of anti-hydrolysis agents, its effect is greatly weakened.

[0095] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent, characterized in that: The structural formula is: ； The structural formula of R is: .

2. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 1, characterized in that: The preparation method of polyphosphazene modified polycarbodiimide flame retardant and anti-hydrolysis agent is as follows: (1) Synthesis of PHB microspheres: 4,4'-dihydroxydiphenyl sulfone reacts with hexachlorocyclotriphosphazene in a reaction solvent under the action of an acid-binding agent. After the reaction is completed, ring-crosslinked polyphosphazene microspheres, namely PHB microspheres, are obtained. (2) Synthesis of PCDI: Using tetramethylxylylenediisocyanate as raw material, under the action of high temperature and catalyst, the polymeric carbodiimide is synthesized by isocyanate condensation method, which is calculated as PCDI. (3) Synthesis of PHB-PCDI: The PHB microspheres and PCDI undergo a capping reaction in a solvent at high temperature. After the reaction is completed, polyphosphazene-modified polycarbodiimide is obtained, which is calculated as PHB-PCDI.

3. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: The reaction solvent in step (1) includes acetonitrile or tetrahydrofuran.

4. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: In step (1), the mass ratio of hexachlorocyclotriphosphazene to 4,4'-dihydroxydiphenyl sulfone is 0.35:0.25-0.35:1.

0.

5. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: The acid binding agent includes triethylamine, pyridine or potassium carbonate.

6. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: The mass ratio of tetramethylxylylenediisocyanate to the catalyst in step (2) is 5-6:0.04-0.

05.

7. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: The temperature required for the isocyanate condensation method in step (2) ranges from 170°C to 200°C; the catalyst comprises 3-methyl-1-phenyl-2-phosphine-1-oxide or 1-methyl-1-oxo-2-phosphine-1-oxide.

8. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: The mass ratio of PHB to PCDI in step (3) is 0.25~0.5:1.2~1.

5.

9. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: The solvent for the end-capping reaction in step (3) includes tetrahydrofuran or toluene; the end-capping reaction is stirred at 50°C-60°C for 6h-10h.

10. Use of the polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to any one of claims 1 to 9 in PET materials.

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