Flame-retardant recyclable plant fiber reinforced epoxy composite material and preparation method thereof

Abstract

The invention relates to a flame-retardant recyclable plant fiber reinforced epoxy composite material and a preparation method thereof, and belongs to the technical field of flame retardance. The preparation method comprises the following steps: (1) carrying out a reaction on N, N, N ', N'-tetraepoxypropyl-4, 4 '-diaminodiphenylmethane (TGDDM) and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), so as to obtain an epoxy precursor DOPO-TGDDM, and carrying out a reaction on the epoxy precursor DOPO-TGDDM and 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), so as to obtain an epoxy precursor DOPO-TGDDM; and (2) carrying out hot pressing curing on the DOPO-TGDDM and an anhydride curing agent, so as to prepare the polyester type epoxy glass polymer (vitrimer) pre-cured sheet. And (3) alternately stacking the epoxy vitrimer pre-cured sheets and plant fiber cloth, putting the stacked epoxy vitrimer pre-cured sheets and the plant fiber cloth into a hot press, and carrying out hot pressing to obtain the plant fiber reinforced epoxy composite material. The prepared plant fiber reinforced epoxy composite material has excellent intrinsic flame retardance, smoke suppression performance and degradability and recoverability.

Description

Technical Field

[0001] The invention relates to the field of flame retardant technology, and more particularly to a flame retardant recyclable plant fiber reinforced epoxy composite material and a preparation method thereof. Background Art

[0002] Plant fiber reinforced epoxy composite is a kind of plant fiber reinforced composite material. It is not only light and high-strength, but also exhibits good physical properties such as sound absorption, heat insulation, electromagnetic wave absorption and damping noise reduction. These properties make it widely used in automotive interiors, aviation doors, building pipes and other fields. However, the interface compatibility between plant fibers and epoxy resin matrix is ​​poor, resulting in reduced mechanical properties and durability of the composite material. At the same time, the composite material is highly flammable and there is a fire hazard during use. In addition, the epoxy resin matrix is ​​difficult to recycle and degrade, and the composite material will bring serious environmental pollution problems after the service ends. Therefore, the development of plant fiber reinforced epoxy composite materials with strong interface effects, flame retardant and recyclable has become a key issue to be solved.

[0003] The interfacial compatibility of plant fiber reinforced epoxy composites can be improved by plant fiber surface modification, epoxy resin matrix modification and interfacial compatibilization modification. Among them, surface modification enhances the bonding force between fiber and resin by introducing reactive groups, matrix modification optimizes mechanical properties and wettability with the help of nanofillers, and interfacial compatibilizers enhance interfacial bonding ability through chemical or physical effects. In addition, the improvement of flame retardancy of such composites has also received widespread attention. Common methods include grafting flame retardants on the surface of plant fibers, directly adding flame retardants and using intrinsic flame retardant epoxy resin matrix. Among them, although the first two can improve flame retardancy, they often face the problem of limited grafting rate or decreased mechanical properties, while the intrinsic flame retardant epoxy resin matrix can maintain the mechanical properties of the material while improving flame retardancy. In recent years, the introduction of epoxy vitrimer has provided a new strategy for the recyclability of plant fiber reinforced epoxy composites. Since the proposal of epoxy vitrimer, researchers have endowed epoxy resin chemical bonds with reversible reconstruction capabilities by introducing dynamic covalent bonds such as disulfide bonds, imine bonds, and siloxane bonds, making them processable. They have also successfully prepared biodegradable and recyclable plant fiber-reinforced epoxy composites, providing new ideas for the high performance and sustainable development of such composite materials.

[0004] Although significant progress has been made in the research of plant fiber reinforced epoxy composites, how to construct plant fiber reinforced epoxy composites with strong interface effects, flame retardancy and recyclability is a difficult point in current research, and related technologies are still relatively limited. In addition, the performance of recyclable epoxy resins after chemical recycling and remodeling is often relatively low, and how to achieve high-value utilization of degradation liquid is also a technical problem that needs to be solved urgently. Summary of the invention

[0005] The present invention aims at the shortcomings in the current epoxy resin material field and provides a flame retardant and recyclable plant fiber reinforced epoxy composite material and a preparation method thereof. The composite material has excellent mechanical properties, flame retardancy and degradability and recyclability.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing a flame retardant recyclable plant fiber reinforced epoxy composite material comprises the following steps:

[0008] Step 1: N,N,N',N'-tetracyclyl-4,4'-diaminodiphenylmethane (TGDDM) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) are reacted to prepare epoxy resin A;

[0009] Step 2: Evenly mix the epoxy resin A and the acid anhydride curing agent, and heat and cure them in a mold to obtain a precured sheet;

[0010] Step 3: Alternately stack the precured sheets and the plant fiber cloth, and place them in a hot press for hot pressing to obtain a plant fiber reinforced epoxy composite material.

[0011] The tertiary amine and hydroxyl structures in DOPO-TGDDM can catalyze the transesterification of epoxy resin, thereby achieving the degradability and recyclability of the material without the need for additional catalysts. At the same time, the degraded liquid can be reused as a flame retardant coating. In addition, plant fibers can achieve interfacial fusion with epoxy resin through transesterification, thereby improving interfacial bonding strength, and are a highly promising polymer material.

[0012] Preferably, the reaction conditions in step 1 are: under nitrogen conditions, N,N,N',N'-tetracyclyl-4,4'-diaminodiphenylmethane and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are added to a flask equipped with a magnetic stirring and condensation reflux device, and reacted at 150-170°C for 6-10 h.

[0013] The beneficial effects brought about by adopting the above-mentioned optimization include: more complete reaction and high product purity: at a higher temperature of 150-170° C. and a sufficient reaction time of 6-10 h, N,N,N',N'-tetracyclyl-4,4'-diaminodiphenylmethane and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide can fully react, effectively improving the yield and purity of the target product.

[0014] The reaction system is stable and controllable: the reaction is carried out under nitrogen protection, which effectively inhibits the occurrence of oxidation side reactions and ensures the stability and repeatability of the reaction.

[0015] It is conducive to large-scale preparation: it adopts solvent-free reaction, is simple and controllable, suitable for industrial production, and has good process feasibility.

[0016] Preferably, the molar ratio of the N,N,N',N'-tetracyclyl-4,4'-diaminodiphenylmethane to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(0.5-1.5).

[0017] The beneficial effects brought about by adopting the above-mentioned optimization include: regulating the product structure and optimizing the performance balance: flexibly regulating according to the different requirements of the reaction system for the phosphorus content, thereby achieving coordination and unity among heat resistance, mechanical properties and flame retardant properties.

[0018] Preferably, the anhydride curing agent described in step 2 includes: glutaric anhydride, methyltetrahydrophthalic anhydride, maleic anhydride, phthalic anhydride, nadic anhydride, itaconic anhydride, methylnadic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, one or a mixture of two or more thereof.

[0019] The beneficial effects brought about by adopting the above-mentioned optimization include: enhancing the versatility and process adaptability of the system: different types of acid anhydrides can be selected or used in combination according to application requirements, so as to achieve performance regulation and be suitable for a variety of application scenarios and process routes.

[0020] Preferably, in step 2, the molar ratio of the epoxy group of the epoxy resin A to the anhydride of the anhydride curing agent is 1:(0.5-1).

[0021] The beneficial effects brought about by adopting the above-mentioned preferred embodiments include: achieving a reasonable ratio of reactive functional groups and promoting efficient curing: the epoxy group and the acid anhydride group can fully react within this molar ratio range, avoiding insufficient crosslinking due to insufficient acid anhydride and preventing side reactions caused by excessive acid anhydride, thereby improving curing efficiency and product stability.

[0022] Preferably, the uniform mixing condition in step 2 is: stirring at 100-150° C. for 1-2 min.

[0023] Preferably, the heating and curing conditions in step 2 are: curing at 150-180° C. for 5-15 min.

[0024] Preferably, the hot pressing conditions in step 3 are: curing at 150° C. for 3 h under 10 MPa, and then curing at 180° C. for 3 h.

[0025] The beneficial effects brought about by adopting the above-mentioned preferred method include: improving the mixing efficiency of the system and ensuring uniform mixing of the components: stirring at 100-150°C for 1-2 min helps to reduce the viscosity of the reaction mixture, allowing the epoxy resin and the acid anhydride curing agent to be quickly and fully mixed to avoid local uneven concentration, thereby laying a good foundation for the subsequent curing reaction.

[0026] Precisely control the degree of reaction to form a stable semi-cured state: Curing at 150-180°C for 5-15 minutes can cause the epoxy resin and the anhydride curing agent to undergo a preliminary cross-linking reaction to form a semi-cured sheet with a certain strength and thermal stability, which is convenient for subsequent hot pressing operations and avoids premature complete curing that may cause processing difficulties.

[0027] The cross-linking structure and material properties are optimized by hot pressing in stages: first, hot pressing and curing at 150°C and 10MPa for 3 hours can ensure that the system is gradually cross-linked and stress released at a lower temperature to form a preliminary network structure; then curing at 180°C for another 3 hours can help further deep cross-linking, improve the density and thermal stability of the material, and give the material excellent mechanical properties and dimensional stability.

[0028] Another object of the present invention is to provide a flame retardant and recyclable plant fiber reinforced epoxy composite material prepared by the preparation method of the flame retardant and recyclable plant fiber reinforced epoxy composite material.

[0029] The resin can be degraded by immersing the composite material in ethylene glycol and heating it at 150-180°C for 2-5 hours. The degradation liquid and the plant fiber are separated after filtering. The degradation liquid can be used as a flame retardant coating after being concentrated.

[0030] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The epoxy precursor synthesis method of the present invention is simple and easy to operate, does not require a solvent, and does not require a complicated post-processing step.

[0032] (2) The synthetic epoxy precursor contains a tertiary amine structure, which can promote the epoxy curing reaction without the need to add additional curing accelerators.

[0033] (3) The prepared plant fiber reinforced epoxy composite material has excellent intrinsic flame retardancy, smoke suppression and biodegradability.

[0034] (4) The prepared plant fiber reinforced epoxy composite material has good biodegradability and recyclability, and no additional catalyst is required. The degraded liquid can be reused as a flame retardant coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0036] Figure 1 is the H-NMR spectrum of DOPO-TGDDM;

[0037] Figure 2 is a flow chart for the preparation of composite materials;

[0038] Figure 3 It is a photo of the appearance of the composite material;

[0039] Figure 4 is the temperature-loss factor curve of the composite material;

[0040] Figure 5 Digital photos of composite materials tested in UL-94;

[0041] Figure 6 is the heat release rate curve of the composite material;

[0042] Figure 7 is the total heat release curve of the composite material;

[0043] Figure 8 is the total smoke generation curve of the composite material;

[0044] Fig. 9 is the stress relaxation curve of the epoxy resin matrix involved in the embodiments and comparative examples;

[0045] Fig.10 are digital photos of the composite material in Example 1 before and after chemical degradation;

[0046] Fig.11 This is the application of the composite material degradation liquid in Example 1 as a flame retardant coating. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] Example 1

[0049] This embodiment provides a method for preparing a flame retardant recyclable plant fiber reinforced epoxy composite material, comprising the following steps:

[0050] 1. First, synthesize the epoxy precursor DOPO-TGDDM. Under nitrogen conditions, add 4,4'-diaminodiphenylmethane tetraglycidylamine TGDDM (100 g, 0.2367 mol) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO (51.16 g, 0.2367 mol) into a flask equipped with a magnetic stirring and condensation reflux device, react at 155 ° C for 7 hours, and then cool down to obtain the final product DOPO-TGDDM.

[0051] 2. The above 12 g of DOPO-TGDDM and 3.25 g of glutaric anhydride were melt-mixed and stirred at 150° C. for 1 min, poured into a mold and cured at 150° C. for 10 min to obtain a precured sheet.

[0052] 3. The above three pre-cured sheets and two flax fiber cloths are alternately stacked and placed in a mold, and cured at 150°C for 3 h and 180°C for 3 h under 10 MPa.

[0053] The material has been tested to have a tensile strength of 92 MPa and a glass transition temperature of 132.9°C. It meets the UL 94 vertical burning test V-0 level. The limiting oxygen index (LOI) is 31.5%. The peak heat release rate (PHRR) in the cone calorimetry test is 257kW / m 2 , the total heat release (THR) is 45.6 MJ / m 2 , the total smoke generation (TSP) is 13.8 m 2 .

[0054] The composite material was immersed in ethylene glycol and completely degraded at 180°C for 2 h. The plant fiber and the degradation liquid were separated after filtration. The degradation liquid was concentrated and coated on the wood. It was reheated and cured to be used as a flame retardant coating. When applied with a thickness of 200 μm, it could block continuous burning of a butane torch at 1300°C for more than 9 minutes without flame spread. Pure wood could only last for two minutes with obvious flame spread.

[0055] Example 2

[0056] This embodiment provides a method for preparing a flame retardant recyclable plant fiber reinforced epoxy composite material, comprising the following steps:

[0057] 1. First, synthesize the epoxy precursor DOPO-TGDDM.

[0058] 2. The above 13.43 g of DOPO-TGDDM and 3.6 g of glutaric anhydride were melt-mixed and stirred at 150° C. for 1 min, poured into a mold and cured at 150° C. for 10 min to obtain a precured sheet.

[0059] 3. The above 4 pre-cured sheets and 3 flax fiber cloths are alternately stacked and placed in a mold, and cured at 150°C for 3 h and 180°C for 3 h under 10 MPa.

[0060] The material has been tested to have a tensile strength of 112 MPa and a glass transition temperature of 116.6°C. It meets the UL 94 vertical burning test V-0 level. The limiting oxygen index (LOI) is 30.5%. The peak heat release rate (PHRR) in the cone calorimetry test is 301kW / m 2 , the total heat release (THR) is 49.2 MJ / m 2 , the total smoke generation (TSP) is 12.4 m 2 .

[0061] The composite material was immersed in ethylene glycol and completely degraded at 180 °C for 2 h, and the degraded liquid could be used as a flame-retardant coating.

[0062] Comparative Example 1

[0063] 1. Melt and mix 10 g of E51 (bisphenol A epoxy resin, epoxy value 0.51 mol / 100 g), 2.91 g of glutaric anhydride and 0.2 g of 2,4,6-tris(dimethylaminomethyl)phenol (curing accelerator) at 150°C for 1 min, pour into a mold and cure at 150°C for 10 min to obtain a precured sheet.

[0064] 2. The above three pre-cured sheets and two flax fiber cloths are alternately stacked and placed in a mold, and cured at 150°C for 3 h and 180°C for 3 h under 10 MPa.

[0065] The material has been tested to have a tensile strength of 52 MPa and a glass transition temperature of 49.1°C. It has no rating in the UL 94 vertical burning test. It has a limiting oxygen index (LOI) of 24.6% and a peak heat release rate (PHRR) of 653 kW / m in the cone calorimetry test. 2 , the total heat release (THR) is 107.0 MJ / m 2 , the total smoke generation (TSP) is 19.9 m 2 .

[0066] Comparative Example 2

[0067] 1. Melt 10 g of TGDDM and 5.4 g of glutaric anhydride at 150°C and stir for 1 min. Pour into a mold and cure at 150°C for 10 min to obtain a precured sheet.

[0068] 2. The above three pre-cured sheets and two flax fiber cloths are alternately stacked and placed in a mold, and cured at 150°C for 3 h and 180°C for 3 h under 10 MPa.

[0069] The material has been tested to have a tensile strength of 59 MPa and a glass transition temperature of 89.2°C. The UL 94 vertical burning test has no rating and is accompanied by a large amount of droplets. The limiting oxygen index (LOI) is 24.2%. The peak heat release rate (PHRR) in the cone calorimetry test is 826 kW / m 2 , the total heat release (THR) is 98.6 MJ / m 2 , the total smoke generation (TSP) is 17.4 m 2 .

[0070] Comparative Example 3

[0071] 1. Melt 5 g of TGDDM, 5 g of E51 and 4.16 g of glutaric anhydride at 150°C and stir for 1 min. Pour into a mold and cure at 150°C for 10 min to obtain a precured sheet.

[0072] 2. The above three pre-cured sheets and two flax fiber cloths are alternately stacked and placed in a mold, and cured at 150°C for 3 h and 180°C for 3 h under 10 MPa.

[0073] The material has been tested to have a tensile strength of 57 MPa and a glass transition temperature of 67 °C. It has no rating in the UL 94 vertical burning test. The limiting oxygen index (LOI) is 25.1%. The peak heat release rate (PHRR) in the cone calorimetry test is 793 kW / m 2 , the total heat release (THR) is 101 MJ / m 2 , the total smoke generation (TSP) is 18.1 m 2 .

[0074] Fig. 9It is the stress relaxation curve of the epoxy resin involved in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3. The relaxation time is defined as the time corresponding to the relaxation of the stress (or modulus) of the material to the initial 1 / e. It can be seen from the figure that the epoxy resins involved in Comparative Example 1, Comparative Example 2 and Comparative Example 3 basically have no stress relaxation, while the epoxy resin prepared by using TGDDM-DOPO has obvious stress relaxation behavior. This is because TGDDM-DOPO contains tertiary amine catalysts and hydroxyl structures required for the transesterification reaction, which also makes the composite material prepared using TGDDM-DOPO have excellent biodegradability and recyclability. At the same time, the use of TGDDM-DOPO also promotes the transesterification between plant fibers and epoxy resins to form interface fusion, thereby improving mechanical properties. In addition, the phosphorus element and hydroxyl structure in TGDDM-DOPO can promote the flame retardancy and carbonization of the material, so that the material has excellent smoke suppression properties ( Figure 5 ).

[0075] Since the degradation liquid of the composite material prepared by using TGDDM-DOPO in Example 1 and Example 2 still contains a large amount of flame retardant phosphorus elements, the resin degradation liquid still has excellent intrinsic flame retardancy and high carbonization after concentration and heating and curing. Therefore, the resin degradation liquid can be used as a flame retardant coating ( Fig.11 ), which promoted the high-value utilization of resin degradation liquid.

[0076] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0077] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a flame retardant recyclable plant fiber reinforced epoxy composite material, characterized in that: The steps include: Step 1: N,N,N',N'-tetracyclyl-4,4'-diaminodiphenylmethane and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are reacted to prepare epoxy resin A; Step 2: Evenly mix the epoxy resin A and the acid anhydride curing agent, and heat and cure them in a mold to obtain a precured sheet; Step 3: Alternately stack the precured sheets and the plant fiber cloth, and place them in a hot press for hot pressing to obtain a plant fiber reinforced epoxy composite material.

2. The method for preparing the flame-retardant recyclable plant fiber reinforced epoxy composite material according to claim 1, characterized in that: The reaction conditions in step 1 are as follows: under nitrogen conditions, N,N,N',N'-tetracyclyl-4,4'-diaminodiphenylmethane and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide are added to a flask equipped with a magnetic stirring and condensation reflux device, and the reaction is carried out at 150-170° C. for 6-10 h.

3. The method for preparing the flame-retardant recyclable plant fiber reinforced epoxy composite material according to claim 1, characterized in that: The molar ratio of the N,N,N',N'-tetracyclyl-4,4'-diaminodiphenylmethane to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:(0.5-1.5).

4. The method for preparing the flame-retardant recyclable plant fiber reinforced epoxy composite material according to claim 1, characterized in that: The anhydride curing agent described in step 2 includes: glutaric anhydride, methyltetrahydrophthalic anhydride, maleic anhydride, phthalic anhydride, nadic anhydride, itaconic anhydride, methylnadic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, one or a mixture of two or more thereof.

5. The method for preparing the flame-retardant recyclable plant fiber reinforced epoxy composite material according to claim 1, characterized in that: In step 2, the molar ratio of the epoxy group of the epoxy resin A to the anhydride of the anhydride curing agent is 1:(0.5-1).

6. The method for preparing the flame-retardant recyclable plant fiber reinforced epoxy composite material according to claim 1, characterized in that: The uniform mixing condition in step 2 is: stirring at 100-150° C. for 1-2 min.

7. The method for preparing the flame-retardant recyclable plant fiber reinforced epoxy composite material according to claim 1, characterized in that: The heating and curing conditions in step 2 are: curing at 150-180° C. for 5-15 minutes.

8. The method for preparing the flame-retardant recyclable plant fiber reinforced epoxy composite material according to claim 1, characterized in that: The hot pressing conditions in step 3 are: curing at 150° C. for 3 h under 10 MPa, and then curing at 180° C. for 3 h.

9. A flame retardant recyclable plant fiber reinforced epoxy composite material, characterized in that: The flame retardant recyclable plant fiber reinforced epoxy composite material is prepared by the preparation method of any one of claims 1 to 8.

10. The flame retardant recyclable plant fiber reinforced epoxy composite material according to claim 9, characterized in that: The resin can be degraded by immersing the composite material in ethylene glycol and heating it at 150-180°C for 2-5 hours. The degradation liquid and the plant fiber are separated after filtering. The degradation liquid can be used as a flame retardant coating after being concentrated.

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