A flame-retardant polyethylene terephthalate composite material, its preparation method and application

Abstract

The present invention relates to a flame-retardant polyethylene terephthalate composite material, its preparation method and application, belonging to the technical field of preparation of flame-retardant composite materials. The composite material is prepared from polyethylene terephthalate (PET), metal-organic framework porous material (MOFs), reduced graphene oxide (rGO) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Based on the biocompatibility of MOFs and PET, the mechanical properties of the modified PET are basically unaffected; at the same time, the porous MOFs and the rGO with a layered structure can act as physical barriers to effectively reduce the release of flue gas and the volatilization of combustible gases; the PO· radicals generated by DOPO during the pyrolysis of PET can capture H· and OH·, thereby contributing to the inhibition of flame development. Compared with pure PET, the peak heat release rate and total heat release rate of this material are greatly decreased, and the limiting oxygen index is greatly increased, and the vertical burning test can reach V-0 level.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of flame - retardant composite materials, and relates to a flame - retardant polyethylene terephthalate composite material, a preparation method thereof and an application thereof. Background Art

[0002] Polyethylene terephthalate (PET) is widely used in textile and clothing materials, packaging materials, engineering plastics and other fields because of its excellent comprehensive performance and good cost performance. However, the limiting oxygen index (LOI) of PET is relatively low, only 20% - 22%, so it has the characteristic of being easy to burn. When PET burns, obvious melting - drop phenomenon will occur, which can carry the heat generated during combustion away from the substrate, not only easily causing secondary injuries, but also aggravating the spread of fire. Therefore, it is of great significance to conduct research on flame - retardant modification of PET materials.

[0003] Common flame retardants such as phosphorus - based, halogen - based, boron - based, halogen - phosphorus - based, nitrogen - based, silicon - based, phosphorus - nitrogen - based, etc. can improve the flame - retardant performance of PET to a certain extent, but they have disadvantages such as low flame - retardant efficiency, and at the same time, they are prone to phenomena such as deterioration of the thermal stability and mechanical properties of the materials. In recent years, more and more scientific researchers have deeply developed and applied metal - organic framework porous materials (MOFs) as flame retardants. MOFs are a new type of inorganic - organic hybrid porous material formed by self - assembly with metal ions as the center and connected by coordination bonds with organic ligands. Their application in the field of flame retardancy has the following prominent advantages: (1) The organic ligands have strong designability. By selecting appropriate organic ligands or modifying the organic ligands, flame - retardant elements such as phosphorus, nitrogen, sulfur and groups with carbonization functions can be introduced into the MOF structure; (2) The porous structure of MOFs is retained in the initial stage of combustion, which can adsorb and filter pyrolysis products and reduce smoke release; (3) The metal oxides generated after the pyrolysis of MOFs can catalyze carbonization to form a stable and dense carbon layer, reducing the release of toxic gases; (4) MOFs have uniform morphology and size, and the organic framework structure has good biocompatibility with polymers (such as PET), and has little impact on the mechanical properties of polymers.

[0004] Although MOFs have great advantages compared with common halogen, phosphorus, nitrogen and other flame retardants, their flame - retardant effect is still limited when used alone as a flame retardant. Therefore, on the premise of ensuring not to damage the mechanical properties of PET materials, in order to further improve the flame - retardant effect on it, the present invention has developed a new type of flame retardant based on MOFs. Summary of the Invention

[0005] In view of this, one of the objectives of the present invention is to provide a method for preparing a flame-retardant polyethylene terephthalate composite material; another objective of the present invention is to provide a flame-retardant polyethylene terephthalate composite material; and a third objective of the present invention is to provide an application of the flame-retardant polyethylene terephthalate composite material in polyester flame-retardant materials.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] 1. A method for preparing a flame-retardant polyethylene terephthalate composite material, the method is as follows:

[0008] (1) Preparation of MOFs@rGO: Dispersed graphene oxide (GO) in deionized water, then added a divalent metal salt soluble in water to form a mixture, added 2-methylimidazole methanol solution to the mixture and mixed evenly, and then added hydrazine hydrate and reacted until the temperature reached 100 °C, centrifuged, washed, and dried to obtain MOFs@rGO;

[0009] (2) Preparation of MOFs@rGO@DOPO: Dispersed the MOFs@rGO in step (1) in tetrahydrofuran, then added a tetrahydrofuran solution of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), reacted at 45-55 °C for 4.5-5.5 h, filtered, washed, and dried to obtain MOFs@rGO@DOPO;

[0010] (3) Preparation of the flame-retardant polyethylene terephthalate composite material: Mixed polyethylene terephthalate and the MOFs@rGO@DOPO in step (2), and then melted and extruded in a twin-screw extruder to obtain the composite material.

[0011] Preferably, the preparation method of the graphene oxide in step (1) is as follows:

[0012] Mixed graphite powder and NaNO3, added concentrated sulfuric acid to obtain a mixed solution, placed the mixed solution in an ice-water bath, then added KMnO4 and reacted fully, and then reacted at 35-45 °C for 25-35 min to obtain a reaction mixture. Added deionized water to the reaction mixture and then added H2O2 until no bubbles were generated, filtered while it was hot to obtain a precipitate, and the precipitate was washed, centrifuged, and dried with deionized water and hydrochloric acid respectively to obtain graphene oxide.

[0013] Preferably, the mass-volume ratio of the graphite powder, NaNO3, concentrated sulfuric acid, and KMnO4 is 3:1.5:80:12-12:6:300:45, g:g:ml:g.

[0014] Preferably, the water-soluble divalent metal salt in step (1) is any one of Ni(NO3)2·6H2O, Zn(NO3)2·6H2O or Co(NO3)2·6H2O.

[0015] Preferably, the molar mass ratio of graphene oxide, water-soluble divalent metal salt, 2-methylimidazole and hydrazine hydrate in step (1) is 0.6:0.0165:0.0825:1.3416~1:0.024:0.12:1.8576, g:mol:mol:g.

[0016] Preferably, the mass ratio of MOFs@rGO and DOPO in step (2) is 0.2:0.1~0.8:0.1.

[0017] Preferably, the mass ratio of polyethylene terephthalate and MOFs@rGO@DOPO in step (3) is 98:2.

[0018] Preferably, the temperature of the twin-screw extruder in step (3) is 255~265°C and the screw speed is 40~45 rpm.

[0019] 2. The flame-retardant polyethylene terephthalate composite material prepared by the preparation method.

[0020] 3. The application of the flame-retardant polyethylene terephthalate composite material in the preparation of polyester flame-retardant materials.

[0021] The beneficial effects of the present invention are as follows: The present invention provides a flame-retardant polyethylene terephthalate composite material. The composite material is prepared from polyethylene terephthalate (PET), metal-organic framework porous material (MOFs), reduced graphene oxide (rGO), and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Among them, based on the biocompatibility of MOFs and PET, the mechanical properties of the modified PET are basically not affected; at the same time, the porous structure of MOFs is retained in the initial stage of combustion, which can adsorb and filter pyrolysis products and reduce smoke release; the rGO with a layered structure can act as a physical barrier during combustion, which helps to inhibit the volatilization of combustible gases during the combustion process of PET; the PO· free radicals generated by DOPO during the pyrolysis process of PET can capture active free radicals such as H· and OH·, thus helping to inhibit the development of the flame. Each component complements each other, and greatly improves its flame retardancy on the premise of not damaging the mechanical properties of PET. Compared with pure polyethylene terephthalate, by adding a novel flame retardant MOFs@rGO@DOPO, the peak heat release rate (pHRR) of this material can be reduced to more than 39%, the total heat release rate (THR) can be reduced to more than 16%, the limiting oxygen index (LOI) can be increased to more than 24.7%, and the vertical burning test (UL-94) can reach V-0 level.

[0022] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Detailed implementation manners

[0023] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0024] Example 1

[0025] A flame-retardant polyethylene terephthalate composite material, calculated by mass percentage, the material consists of 98% polyethylene terephthalate and 2% Co-ZiF@rGO@DOPO. The preparation method is as follows:

[0026] (1) Preparation of graphene oxide: Weigh 6 g of graphite powder and 3 g of NaNO3 and mix them. Then add 150 ml of concentrated sulfuric acid to form a mixed solution. Place this mixed solution in an ice-water bath and slowly add 24 g of KMnO4 under stirring. After reacting for 1 h, transfer it to a 40 °C warm-water bath and continue reacting for 30 min. Then slowly add 250 ml of deionized water and stir for 25 min. After stirring evenly, add H2O2 to reduce the excess oxidant until no bubbles are generated. Filter while it is hot to obtain a precipitate. Wash the precipitate 5 times with deionized water and 5% hydrochloric acid. After centrifugation, dry it thoroughly in a vacuum drying oven at 60 °C to obtain graphene oxide;

[0027] (2) Preparation of Co-ZIF@rGO: Take 0.6 g of the graphene oxide obtained in step (1), disperse it ultrasonically in 110 ml of deionized water for 1 h, then transfer it to a flask. Add 55 ml of 0.3 mol / L Co(NO3)2·6H2O aqueous solution and stir at room temperature for 2 h. Then add 55 ml of 1.5 mol / L 2-methylimidazole methanol solution and stir for 12 h. After the stirring is completed, add 1.3 ml of hydrazine hydrate and continue stirring for 2 h until the temperature rises to 100 °C to obtain a reaction product. The reaction product is separated by centrifugation to precipitate, and then washed 3 times each with deionized water and ethanol. Freeze-dry it at -80 °C for 4 h to obtain Co-ZIF@rGO;

[0028] (3) Preparation of Co-ZIF@rGO@DOPO: Ultrasonically disperse 0.2 g of Co-ZIF@rGO obtained in step (2) in 20 ml of tetrahydrofuran, then add 10 ml of 0.01 g / ml DOPO tetrahydrofuran solution, and react at 50 °C for 5 h to obtain a reaction mixture. Filter the reaction mixture to collect the precipitate, wash the precipitate 5 times with tetrahydrofuran, and then dry it at 80 °C for 4 h to obtain Co-ZIF@rGO@DOPO;

[0029] (4) Preparation of flame-retardant polyethylene terephthalate composite material: Crush and mix PET and Co-ZIF@rGO@DOPO obtained in step (3) in a high-speed crusher (the mass ratio of Co-ZIF@rGO@DOPO to PET is 2:98). After mixing evenly, place it in an oven at 140 °C for 12 h to remove moisture. After drying, place it in a twin-screw extruder and melt-extrude it at 260 °C with a screw speed of 40 rpm. Finally, use a precision micro-injection molding machine to inject the processed sample into different sizes (the temperatures of the injection molding machine are 245 °C in zone 1, 245 °C in zone 2, and 230 °C in zone 3).

[0030] Example 2

[0031] A flame-retardant polyethylene terephthalate composite material. By mass percentage, the material consists of 98% polyethylene terephthalate and 2% Zn-ZiF@rGO@DOPO. The preparation method is as follows:

[0032] (1) Preparation of graphene oxide: Weigh 3 g of graphite powder and 1.5 g of NaNO3 and mix them. Then add 80 ml of concentrated sulfuric acid to form a mixed solution. Place the mixed solution in an ice-water bath and slowly add 12 g of KMnO4 under stirring. After reacting for 1 h, transfer it to a 40 °C warm-water bath and continue reacting for 30 min. Then slowly add 130 ml of deionized water and stir for 25 min. After stirring evenly, add H2O2 to reduce the excess oxidant until no bubbles are generated. Filter while it is hot to obtain a precipitate. Wash the precipitate 5 times with deionized water and 5% hydrochloric acid, and after centrifugation, dry it thoroughly in a 60 °C vacuum drying oven to obtain graphene oxide;

[0033] (2) Preparation of Zn-ZIF@rGO: Take 1.0 g of the graphene oxide from step (1), disperse it ultrasonically in 180 ml of deionized water for 1 h, then transfer it to a flask. Add 80 ml of 0.3 mol / L Zn(NO3)2·6H2O aqueous solution and stir at room temperature for 2 h. Then add 80 ml of 1.5 mol / L 2-methylimidazole methanol solution and stir for 12 h. After the stirring ends, add 1.8 ml of hydrazine hydrate and continue stirring for 2 h to raise the temperature to 100 °C to obtain a reaction product. The reaction product is separated by a centrifuge to precipitate, and then washed 3 times each with deionized water and ethanol, and freeze-dried at -80 °C for 4 h to obtain Zn-ZIF@rGO;

[0034] (3) Preparation of Zn-ZIF@rGO@DOPO: Ultrasonically disperse 0.5 g of the Zn-ZIF@rGO from step (2) in 20 ml of tetrahydrofuran, then add 20 ml of 0.005 g / ml DOPO tetrahydrofuran solution, and react at 50 °C for 5 h to obtain a reaction mixture. Filter the reaction mixture to collect the precipitate, wash the precipitate 5 times with tetrahydrofuran, and then dry it at 80 °C for 4 h to obtain Zn-ZIF@rGO@DOPO;

[0035] (4) Preparation of flame-retardant polyethylene terephthalate composite material: PET and Zn-ZIF@rGO@DOPO in step (3) are pulverized and thoroughly mixed in a high-speed pulverizer (where the mass ratio of Zn-ZIF@rGO@DOPO to PET is 2:98). After being evenly mixed, it is placed in an oven at 140 °C for 12 h to remove moisture. After drying, it is placed in a twin-screw extruder and melt-extruded at 255 °C with a screw speed of 45 rpm. Finally, the processed sample is injection-molded into different sizes using a precision micro-injection molding machine (the temperatures of the injection molding machine are 245 °C in zone 1, 245 °C in zone 2, and 230 °C in zone 3).

[0036] Example 3

[0037] A flame-retardant polyethylene terephthalate composite material, calculated by mass percentage, consists of 98% polyethylene terephthalate and 2% Ni-ZiF@rGO@DOPO. Its preparation method is as follows:

[0038] (1) Preparation of graphene oxide: Weigh 12 g of graphite powder and 6 g of NaNO3 and mix them, then add 300 ml of concentrated sulfuric acid to form a mixed solution. Place this mixed solution in an ice-water bath and slowly add 45 g of KMnO4 under stirring. After reacting for 1 h, transfer it to a warm water bath at 40 °C and continue to react for 30 min. Then slowly add 450 ml of deionized water and stir for 25 min. After stirring evenly, add H2O2 to reduce the excess oxidant until no bubbles are generated. Filter while it is hot to obtain a precipitate. The precipitate is washed 5 times with deionized water and 5% hydrochloric acid, and after centrifugation, it is fully dried in a vacuum drying oven at 60 °C to obtain graphene oxide;

[0039] (2) Preparation of Ni-ZIF@rGO: Take 0.8 g of graphene oxide in step (1), place it in 150 ml of deionized water and ultrasonically disperse it for 1 h, then transfer it to a flask. Then add 70 ml of 0.3 mol / L Ni(NO3)2·6H2O aqueous solution and stir at room temperature for 2 h. Then add 70 ml of 1.5 mol / L 2-methylimidazole methanol solution and stir for 12 h. After the stirring ends, add 1.6 ml of hydrazine hydrate and continue to stir for 2 h to raise the temperature to 100 °C to obtain a reaction product. The reaction product is separated by centrifugation to precipitate and washed 3 times each with deionized water and ethanol, and then freeze-dried at -80 °C for 4 h to obtain N-ZIF@rGO;

[0040] (3) Preparation of Ni-ZIF@rGO@DOPO: 0.8 g of Ni-ZIF@rGO obtained in step (2) was ultrasonically dispersed in 50 ml of tetrahydrofuran, then 25 ml of a tetrahydrofuran solution of DOPO with a concentration of 0.004 g / ml was added, and the mixture was reacted at 50 °C for 5 h to obtain a reaction mixture. The reaction mixture was filtered to collect the precipitate, and the precipitate was washed 5 times with tetrahydrofuran and then dried at 80 °C for 4 h to obtain Ni-ZIF@rGO@DOPO;

[0041] (4) Preparation of flame-retardant polyethylene terephthalate composite: PET and Ni-ZIF@rGO@DOPO obtained in step (3) were pulverized and thoroughly mixed in a high-speed pulverizer (the mass ratio of Ni-ZIF@rGO@DOPO to PET was 2:98). After being mixed evenly, they were placed in an oven at 140 °C for 12 h to remove moisture. After drying, they were placed in a twin-screw extruder and melt-extruded at 255 °C with a screw speed of 40 rpm. Finally, the processed samples were injection-molded into different sizes using a precision micro-injection molding machine (the temperatures of the injection molding machine were 245 °C in zone 1, 245 °C in zone 2, and 230 °C in zone 3).

[0042] The peak heat release rate (pHRR) and total heat release rate (THR) of the PET composites and pure PET in Comparative Examples 1 to 3 at a test time of 100 s, as well as the limiting oxygen index (LOI) and vertical burning (UL 94) of the PET composites and pure PET in Examples 1 to 3 were compared. The experimental results are shown in Table 1.

[0043] Table 1 Comparison of the peak heat release rate, total heat release rate, limiting oxygen index, and vertical burning of PET composites and pure PET

[0044]

[0045]

[0046] As can be seen from Table 1, by adding 2.0 wt.% of Co-ZIF@rGO@DOPO flame retardant, 2.0 wt.% of Zn-ZIF@rGO@DOPO flame retardant and 2.0 wt.% of Ni-ZIF@rGO@DOPO flame retardant to pure PET respectively, the peak heat release rate (pHRR) of the composite material decreased by 52%, 39% and 46% respectively; the total heat release rate (THR) decreased by 21%, 16% and 18% respectively; the limiting oxygen index (LOI) increased from 22.0% to 29.5%, 24.7% and 27.8% respectively; the vertical burning (UL 94) reached V-0, V-1 and V-0 grades respectively. Compared with pure PET, the peak heat release rate (pHRR) and total heat release rate (THR) of the composite material are greatly reduced, the limiting oxygen index (LOI) is greatly increased, and the flame retardant grade is improved. The lower the peak heat release rate (pHRR) and total heat release rate (THR), the smaller the heat release amount during the combustion of the material, and the smaller the fire hazard formed. And the higher the limiting oxygen index (LOI), the less flammable the material is. Thus, it can be seen that the PET composite materials in Examples 1 to 3 have excellent flame retardant properties.

[0047] In summary, the present invention provides a flame retardant polyethylene terephthalate composite material. The composite material is prepared from polyethylene terephthalate (PET), metal-organic framework porous material (MOFs), reduced graphene oxide (rGO) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Among them, the porous structure MOFs and the layered structure rGO can act as physical barriers during combustion, effectively inhibiting the release of smoke and the volatilization of combustible gases during the combustion of PET; the PO· free radicals generated by DOPO during the pyrolysis of PET can capture active free radicals such as H· and OH·, thus contributing to the inhibition of flame development. Each component complements each other, endowing the PET material with great flame retardancy without damaging the mechanical properties of PET.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a flame-retardant polyethylene terephthalate composite material, characterized in that: The method is as follows: (1) Prepare MOFs@rGO: Disperse graphene oxide in deionized water, then add a water-soluble divalent metal salt to form a mixture. Add a 2-methylimidazole methanol solution to the mixture and mix evenly. Then add hydrazine hydrate and react until the temperature reaches 100 °C. Centrifuge, wash, and dry to obtain MOFs@rGO; (2) Prepare MOFs@rGO@DOPO: Disperse the MOFs@rGO prepared in step (1) in tetrahydrofuran, then add a tetrahydrofuran solution of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and react at 45-55 °C for 4.5-5.5 h. Filter, wash, and dry to obtain MOFs@rGO@DOPO; (3) Prepare a flame-retardant polyethylene terephthalate composite: Mix polyethylene terephthalate and the MOFs@rGO@DOPO prepared in step (2), and then melt and extrude in a twin-screw extruder to obtain the composite; The water-soluble divalent metal salt described in step (1) is any one of Ni(NO3)2·6H2O, Zn(NO3)2·6H2O, or Co(NO3)2·6H2O.

2. The method for preparing the composite material according to claim 1, characterized in that: The preparation method of the graphene oxide described in step (1) is as follows: Mix graphite powder and NaNO3, add concentrated sulfuric acid to obtain a mixed solution. Place the mixed solution in an ice-water bath, then add KMnO4 and react fully. Then react at 35-45 °C for 25-35 min to obtain a reaction mixture. Add deionized water to the reaction mixture, and then add H2O2 until no bubbles are generated. Filter while it is hot to obtain a precipitate. Wash the precipitate with deionized water and hydrochloric acid respectively, centrifuge, and dry to obtain graphene oxide.

3. The method for preparing the composite material according to claim 2, characterized in that: The mass-volume ratio of the graphite powder, NaNO3, concentrated sulfuric acid, and KMnO4 is 3:1.5:80:12-12:6:300:45, g:g:ml:g.

4. The method for preparing the composite material according to claim 1, characterized in that: The molar mass ratio of the graphene oxide, water-soluble divalent metal salt, 2-methylimidazole, and hydrazine hydrate described in step (1) is 0.6:0.0165:0.0825:1.3416-1:0.024:0.12:1.8576, g:mol:mol:g.

5. The method for preparing the composite material according to claim 1, characterized in that: The mass ratio of the MOFs@rGO and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide described in step (2) is 0.2:0.1-0.8:0.

1.

6. The method for preparing the composite material according to claim 1, characterized in that: The mass ratio of the polyethylene terephthalate and MOFs@rGO@DOPO described in step (3) is 98:

2.

7. The method for preparing the composite material according to claim 1, characterized in that: The temperature of the twin-screw extruder described in step (3) is 255-265 °C, and the screw speed is 40-45 rpm.

8. A flame-retardant polyethylene terephthalate composite material prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the flame-retardant polyethylene terephthalate composite material according to claim 8 in the preparation of polyester flame-retardant materials.

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