Polyphosphazene modified polycarbodiimide flame-retardant anti-hydrolysis agent as well as preparation method and application thereof

Abstract

The invention 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 an inflammable material and is easy to age under a hydrothermal condition. In order to solve the problems, the invention provides the polyphosphazene modified polycarbodiimide flame-retardant hydrolysis-resistant agent, the molecular structure of the polyphosphazene modified polycarbodiimide flame-retardant hydrolysis-resistant agent contains a cyclic crosslinking type polyphosphazene microsphere structure PHB and a polymeric carbodiimide structure PCDI, the PCDI structure and the PHB microsphere structure are linked through an isocyanate group and a hydroxyl group, and the polyphosphazene modified polycarbodiimide flame-retardant hydrolysis-resistant agent is obtained. The flame-retardant hydrolysis-resistant agent PHB-PCDI is used as an additive of a PET composite material, so that the flame retardance and hydrolysis resistance of the PET composite material can be remarkably improved, and the flame-retardant hydrolysis-resistant agent PHB-PCDI is not easy to migrate out in the subsequent use process due to the high molecular weight and high cross-linked structure of the flame-retardant hydrolysis-resistant agent PHB-PCDI, and has long-term effectiveness.

Description

Technical Field

[0001] The 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. It is considered one of the most important polymer materials at this stage because of its many advantages. However, the limiting oxygen index of PET is only about 22%, and a large number of molten droplets will be produced during the combustion process, causing secondary damage and expanding the spread of the fire. In addition, PET materials are very sensitive to water, and long-term contact with water will cause performance degradation and affect use. Therefore, it is very important to improve the flame retardant and hydrolysis resistance of PET at this stage.

[0003] As a new type of organic phosphorus flame retardant skeleton material, cyclotriphosphazene has a stable structure, is easy to produce, and has excellent thermal stability and flame retardant properties, so it is widely used in the field of flame retardancy. However, cyclotriphosphazene produces hydrogen chloride gas when burned, which can cause secondary damage to the human body, and is easily hydrolyzed, resulting in a decrease in the mechanical properties of the material, so it needs to be modified.

[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 to inhibit their catalytic action. Carbodiimide is the most commonly used anti-hydrolysis agent for polyester materials at present, and is divided into monomeric and polymeric types. Carbodiimide can capture the terminal carboxyl groups in the chain segments, and react at room temperature to obtain ureide structures, thereby inhibiting the progress of hydrolysis reactions. Because there will be isocyanate groups that do not participate in the reaction in polycarbodiimide, the reaction activity it possesses will cause the storage of carbodiimide to be unstable, so the present invention uses the hydroxyl groups on polyphosphazene to end-cap the isocyanate groups, while improving the storage stability of carbodiimide, constructing a flame retardant anti-hydrolysis agent having 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 prone to hydrolysis and aging. In view of the above problems, the present invention provides a polyphosphazene modified polycarbodiimide flame retardant and anti-hydrolysis agent, and the preparation method thereof comprises 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, and after the reaction is completed, ring-crosslinked polyphosphazene microspheres, namely PHB microspheres, are obtained;

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

[0009] (2) Synthesis of PCDI:

[0010] Polymeric carbodiimide (PCDI) was 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 to the benzene ring in the PHB structure react with the free isocyanate groups on PCDI at high temperature to form a capping reaction. After the reaction, polyphosphazene-modified polycarbodiimide, namely PHB-PCDI, is obtained.

[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) comprises acetonitrile or tetrahydrofuran.

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

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

[0020] Preferably, the temperature required for the isocyanate condensation method in step (2) is comprised between 170°C and 200°C.

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

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

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

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

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

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

[0027] 1) Dissolve 4,4'-dihydroxydiphenyl sulfone in a solvent, then begin to drop an acid-binding agent, and ultrasonically disperse the reaction system uniformly; the dosage ratio of 4,4'-dihydroxydiphenyl sulfone to the acid-binding agent and the solvent in the reaction is 0.25g:2g:40mL-1.0g:3g:50mL;

[0028] 2) dissolving hexachlorocyclotriphosphazene in a solvent, and then adding the solvent to the reaction system formed in step (1), stirring and reacting at 50° C.-60° C. for 6 h-8 h. After the reaction is completed, centrifuging, washing and drying the reaction solution to obtain PHB; the ratio of hexachlorocyclotriphosphazene to the solvent in the reaction is 0.35 g:40 mL-0.35 g:50 mL.

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

[0030] In the reaction vessel, tetramethylxylene diisocyanate (TMXDI) is added, the temperature is raised to 180°C in an oil pan, and the catalyst 3-methyl-1-phenyl-2-phosphocyclopentene-1-oxide (MPPO) is added under stirring. During the reaction, N2 is introduced regularly to purge the CO2 generated during the reaction and effectively isolate the oxygen and moisture in the air. Finally, the added catalyst and the remaining unreacted TMXDI are distilled off under reduced pressure at 180°C and 1mbar to obtain the anti-hydrolysis agent PCDI. The mass ratio of tetramethylxylene diisocyanate to 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) PHB is added to tetrahydrofuran and stirred at a constant temperature of 50°C to 60°C for 0.5h to 1.0h; during the reaction, the solid-liquid ratio of PHB to tetrahydrofuran is 0.25g:50mL to 0.5g:60mL;

[0033] (2) Add the prepared PCDI to tetrahydrofuran, and stir 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, mix the PHB dispersed in tetrahydrofuran in the previous step with PCDI evenly, and stir 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 performance 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, and the PCDI structure is linked to the PHB microsphere structure through 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, so they will form a dense carbon layer on the surface when the material burns. The carbon layer blocks the heat and energy transfer and isolates the oxygen in the air, thereby delaying the thermal degradation of the material and improving the flame retardant properties of PET.

[0038] (3) After the polycarbodiimide is synthesized, a small amount of unreacted isocyanate has reactive activity, which affects the storage stability of the polycarbodiimide. First, the isocyanate selected in the present invention is tetramethylxylylene diisocyanate, and the two methyl groups it carries have a shielding effect on the -NCO group, reducing the occurrence of other side reactions; the present invention reacts part of the isocyanate with the hydroxyl group to generate carbamate, which can also play 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 is described in detail below with reference to the examples. However, it should be understood that the following examples are only 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 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 dispersed uniformly by ultrasonication; the dosage ratio of 4,4'-dihydroxydiphenyl sulfone to the acid-binding agent and the solvent in the reaction was 0.6g:3g:50mL.

[0045] Dissolve hexachlorocyclotriphosphazene in acetonitrile solvent, then add it to the reaction system formed in step (1), stir and react at 60° C. for 6 hours. After the reaction is completed, centrifuge, wash and dry the reaction solution to obtain PHB. The ratio of hexachlorocyclotriphosphazene to the solvent in the reaction is 0.35 g:50 mL.

[0046] (2) Synthesis of PCDI:

[0047] In a 250mL four-necked glass flask, add 5g of tetramethylbenzene diisocyanate (TMXDI), heat to 180°C in an oil pan, and add 0.05g of catalyst 3-methyl-1-phenyl-2-phosphopentene-1-oxide (MPPO) under stirring. During the reaction, N2 is introduced regularly to purge the CO2 generated during the reaction and effectively isolate oxygen and moisture in the air. Finally, the added catalyst and the remaining unreacted TMXDI are distilled off under reduced pressure at 180°C and 1mbar to obtain the anti-hydrolysis agent PCDI.

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

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

[0050] The PCDI prepared in step (2) was added to tetrahydrofuran, and the mixture was 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 evenly mixed with PCDI, and the mixture was 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 2258cm -1 The antisymmetric stretching vibration absorption peaks at 942 cm-1 and 942 cm-2 are -N=C=N- and -N=C=O groups, respectively. -1 There is an absorption peak representing the PO-Ar bond at 1186 and 881 cm -1 The strong peaks at represent the absorption peaks of P=N and PN, which illustrate the formation of polyphosphazene structure and carbodiimide structure, indicating the successful synthesis of PHB-PCDI.

[0052] Specific applications

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

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

[0055] Example 2

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

[0057] Example 3

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

[0059] Example 4

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

[0061] Comparative Example 1

[0062] Comparative Example 1 is the same as Example 1, except that PHB-PCDI is not added in Comparative Example 1, and pure PET material is obtained after banburying.

[0063] Comparative Example 2

[0064] Comparative Example 2 is the same as Example 2, except that, in Comparative Example 2, the PHB-PCDI added during the preparation of the PET / PHB-PCDI composite material is replaced with hexachlorocyclotriphosphazene of equal mass.

[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 in the preparation process of the PET / PHB-PCDI composite material is replaced by 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 in the preparation process of the PET / PHB-PCDI composite material is replaced by PHB, and the amount of PHB added to 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 in the preparation process of the PET / PHB-PCDI composite material is replaced by 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 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 0.3 g:1.2 g.

[0081] Comparative Example 11

[0082] Comparative Example 11 is the same as Example 3, except that the raw material used for the synthesis of PCDI in Comparative Example 11 is no longer tetramethylxylylene diisocyanate, but another dicyclohexylmethane diisocyanate with greater -NCO reaction activity.

[0083] Performance Testing

[0084] Relevant performance tests were performed on the PET composite materials obtained in Examples 1-4 of the present invention and Comparative Examples 1-11. The specific test results are shown in Tables 1 and 2.

[0085] Limiting oxygen index: According to ASTM D 2863-97 standard, use TM606 digital oxygen index tester for testing;

[0086] Vertical combustion: According to UL 94-2013 standard, the test is carried out using a vertical combustion tester;

[0087] Aging test: The material is prepared into dumbbell-shaped specimens and immersed in 60℃ constant temperature water for hydrolysis aging test. After aging, its tensile strength is tested. The tensile strength is tested according to GB / T 1040 standard using an electronic universal material testing machine.

[0088] Table 1

[0089]

[0090]

[0091] As shown in Table 1, the limiting oxygen index value of pure PET is 22.5%, and t1 and t2 are both greater than 10s, and t1+t2 is greater than 30s, which shows that the flame retardant grade of pure PET is the lowest. When the PHB content is 0.25wt%, the limiting oxygen index of the composite material is 25.1%; compared with the limiting oxygen index of pure PET of 22.5%, when the PHB content is 2.0wt%, the limiting oxygen index of the composite material increases to 28.3%, indicating that when polyphosphazene PHB is added to PET alone, its flame retardant ability increases with the increase of PHB addition. When the addition amount of PHB-PCDI increases from 0.25wt% to 2.0wt%, the limiting oxygen index increases from 25.3% to 28.6%, proving the flame retardant effect of PHB-PCDI. When the addition amount of flame retardant PHB-PCDI is 2wt%, the limiting oxygen index of the composite material is 28.6%, the flame burning time t1 of the sample is only 0.85s, t2 is only 0.88s, the total flame burning time t1+t2 of each group of samples is only 1.73s, and the flame and flameless burning time t2+t3 of each sample after the second flame is only 1.08s. It can be seen that the flame retardancy of the PET composite material obtained by adding PHB-PCDI is better than that of the PET composite material obtained by adding PHB or HCCP to PET.

[0092] Table 2

[0093]

[0094] As can be seen from Table 2, the tensile strength of pure PET and materials with only PHB added has dropped significantly after hydrolysis aging, and the tensile strength retention rate is below 40%. When the addition amount of PHB-PCDI increases from 0.25wt% to 2.0wt%, the tensile strength retention rate of the composite material increases from 43.02% to 56.06%, and the initial tensile strength increases 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 can be seen from 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 will affect 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 the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. 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 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 the polyphosphazene modified polycarbodiimide flame retardant and anti-hydrolysis agent is as follows: (1) Synthesis of PHM microspheres: 4,4'-dihydroxydiphenyl sulfone reacts with hexachlorocyclotriphosphazene in a reaction solvent under the action of an acid-binding agent, and after the reaction is completed, ring-crosslinked polyphosphazene microspheres, namely PHB microspheres, are obtained; (2) Synthesis of PCDI: Using tetramethylbenzene diisocyanate 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 a high temperature. After the reaction is completed, polyphosphazene-modified polycarbodiimide is obtained, which is referred to 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 and potassium carbonate.

6. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: The mass ratio of tetramethylxylylene diisocyanate 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) includes 170° C.-200° C.; the catalyst includes 3-methyl-1-phenyl-2-phosphopentene-1-oxide and 1-methyl-1-oxo-2-phosphopentene.

8. The polyphosphazene-modified polycarbodiimide flame retardant and anti-hydrolysis agent according to claim 2, characterized in that: In step (3), the mass ratio of PHB to PCDI 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 and toluene; the end-capping reaction is stirred at 50° C.-60° C. for 6 h-10 h.

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.

Images