A high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system and its preparation and recycling method

Abstract

The present invention relates to a high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system and a preparation and recycling method thereof. A hyperbranched phosphate / borate hybrid polymer (abbreviated as hyperbranched polyborophosphate, HBPPB) is prepared by a one-step solvent-free and catalyst-free green synthesis method, and copolymerized with petroleum-based bisphenol A epoxy resin and an anhydride curing agent to obtain a high-strength, high-toughness, well-transparent and flame-retardant recyclable epoxy resin system. Since the HBPPB end groups contain a large number of active hydroxyl groups, it can copolymerize with epoxy resin and introduce multiple dynamic interactions into the epoxy resin crosslinking network, namely borate / phosphate structures, ester bonds and multiple hydrogen bonds. The epoxy resin system constructed in this way can not only achieve the degradation, recycling and reuse of traditional petroleum-based thermosetting epoxy resins, but also has simple preparation, low cost, can improve the strength and toughness of the resin, endow it with additional values such as flame retardancy, smoke suppression and transparency, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of advanced polymer materials science, and relates to a high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system and a preparation and recycling method thereof. Background Art

[0002] Epoxy resins are widely used in the fields of aerospace, electronics and electrical appliances, transportation, etc. due to their good heat resistance, chemical corrosion resistance, excellent electrical properties, mechanical properties and good processing properties. At present, most of the epoxy resins on the market are bisphenol A diglycidyl ether (DGEBA), which are produced from epichlorohydrin and bisphenol A. These raw materials are mostly downstream products of petroleum and coal. However, both petroleum and coal are non-renewable resources. Especially due to the accelerating consumption in recent years, the shortage of resources has led to high prices of petroleum-based polymers. Compared with thermoplastic materials, the three-dimensional cross-linked network formed by the curing of thermosetting polymers cannot be reshaped or reprocessed, so it is more difficult to degrade and recycle, and can only be treated by incineration, landfill, etc., causing serious environmental pollution and resource waste. At present, recyclable epoxy mainly constructs Vitrimer polymers with dynamic structures such as ester bonds, imine bonds, and disulfide bonds through the design of epoxy monomers or curing agents. Its synthesis process is complex, the development cost is high, and the mechanical strength is insufficient; another type is to design and synthesize new modifiers containing dynamic structures and copolymerize and blend them, but the instability of dynamic covalent bonds inevitably sacrifices their thermal stability and mechanical properties, making it difficult to achieve the integration of degradation and functions. Therefore, there is an urgent need to develop a new multifunctional epoxy resin material with excellent molding process, high strength and toughness, and degradability.

[0003] Patent CN201810387204.3 synthesized a sulfur-containing hyperbranched epoxy monomer, which was cured with bisphenol A type epoxy E-51 and 4,4-diaminodiphenylmethane to obtain a degradable epoxy resin. However, the synthesis process of the above epoxy monomer is complicated (at least 4 steps), and the yield of the hyperbranched epoxy monomer is low, which affects its large-scale industrial production. Moreover, a large amount of organic solvents and formaldehyde are used in the reaction and recovery processes, which will not only cause serious harm to the human body, but also produce a large amount of waste liquid pollution, which is not conducive to environmental protection. Patent CN201811589511.6 prepared a recyclable hyperbranched epoxy resin with an epoxy modifier containing a s-triazine-based multi-ester group. There are also problems such as complex process and difficulty in separating the catalyst and dehydrating agent in the product. Patent CN202011330625.6 reported a class of curing agents containing borate-bridged groups, and a moldable and recyclable epoxy resin can be obtained by room temperature curing with bisphenol A epoxy resin and tertiary amine accelerator. The advantage of room temperature curing in this patent is obvious, but it will lead to poor heat resistance of the resin and it is difficult to meet the application requirements in many fields. Patent CN201910762065.2 involves a recyclable epoxy resin prepared from a hyperbranched polysiloxane containing amino and hydroxyl groups. The synthesis method of this patent is simple, but it is difficult to achieve the integration of functions such as toughness, flame retardancy, and transparency of the epoxy resin.

[0004] The present invention synthesizes a polyborate / phosphate hybrid with a hyperbranched structure (abbreviated as hyperbranched polyborophosphate, HBPPB) by a one-step green synthesis method of solvent-free and catalyst-free A2+B3+C3 transesterification polycondensation, and copolymerizes it with bisphenol A epoxy resin and anhydride curing agent, so that multiple dynamic interactions can be introduced into the epoxy resin crosslinking network, namely the borate / phosphate bonds in the HBPPB structure, the ester bonds formed by the reaction of HBPPB with anhydride, and the multiple hydrogen bonds between the hydroxyl groups in the crosslinking network. The epoxy resin system constructed in this way can be degraded, recycled and reused through the low-temperature immersion degradation process of N,N-dimethylacetamide (DMAc) solvent. The production process has low energy consumption and little pollution. In addition, the mechanical properties of the epoxy resin prepared by the present invention are significantly improved, and it can also maintain excellent transparency and molding process, and endow it with the functions of flame retardancy and smoke suppression, meeting the needs of the national high-end manufacturing industry for high-performance recyclable epoxy resin materials, and having broad application prospects. Summary of the Invention

[0005] Technical Problems to be Solved

[0006] To avoid the deficiencies of the prior art, the present invention provides a high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system and a preparation and recycling method thereof. In order to solve the problems of the difficult degradation, recycling, and reuse of petroleum-based epoxy resins, reduce the development cost of high-performance resins, and simultaneously achieve the integration of functions such as toughness and flame retardancy. The present invention prepares a high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system by a simple method.

[0007] Technical solution

[0008] A high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system, characterized by comprising 1 to 20 parts by mass of hyperbranched polyborophosphate HBPPB, 80 to 100 parts by mass of bisphenol A epoxy resin, 60 to 80 parts by mass of acid anhydride curing agent, and 1 to 2 parts by mass of tertiary amine accelerator.

[0009] The HBPPB is synthesized by an A2+B2+C3 transesterification polycondensation reaction using trifunctional borate ester, trifunctional phosphate ester, and diol as raw materials, and the phosphorus and boron element sites in its branched structure are randomly distributed.

[0010] The trifunctional borate ester includes but is not limited to: tributyl borate, triethyl borate, or other types of trifunctional borate esters.

[0011] The diol includes but is not limited to: ethylene glycol, 1,3-propanediol, 1,4-butanediol, or other types of diols.

[0012] The bisphenol A epoxy resin includes but is not limited to domestic epoxy resins of grades E-51 and E-44.

[0013] The acid anhydride curing agent includes but is not limited to acid anhydride curing agents such as succinic anhydride, phthalic anhydride, methyltetrahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

[0014] The tertiary amine accelerator includes but is not limited to the domestic tertiary amine curing accelerator DMP-30 for epoxy resins.

[0015] A preparation method of the high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system, characterized by the following steps:

[0016] Step 1: HBPPB is obtained by feeding trifunctional borate ester, trifunctional phosphate ester, and diol monomer in a molar ratio of 1:1:3 to 5, reacting at 120 to 190 °C for 10 to 12 hours under nitrogen protection, without solvent and without catalyst to obtain HBPPB;

[0017] Step 2: Add 1 - 20 parts by mass of HBPPB into 80 - 100 parts of bisphenol A epoxy resin, and pre - polymerize at 80 - 100 °C for 15 - 30 min; Add 60 - 80 parts of anhydride curing agent and stir for 30 - 60 min, then add 1 - 2 parts of tertiary amine accelerator. After stirring evenly, pour it into a mold, and degas in a vacuum at 80 °C for 1 h and then cure.

[0018] Step 3: The curing process is carried out according to 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h, and then the epoxy resin is obtained.

[0019] A recycling method for the high - strength, high - toughness, high - transparency and flame - retardant recyclable epoxy resin system, characterized in that: the epoxy resin system is soaked at room temperature in N,N - dimethylacetamide (DMAc) solvent, filtered to obtain a filter cake, and after being knocked, ground, pulverized and dried, an epoxy resin degradation product is obtained.

[0020] The degradation product is stirred evenly with bisphenol A epoxy resin, anhydride curing agent and tertiary amine accelerator, and recycled according to 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h.

[0021] Beneficial effects

[0022] A high - strength, high - toughness, high - transparency and flame - retardant recyclable epoxy resin system and its preparation and recycling method proposed by the present invention are aimed at the recycling problem of currently widely used petroleum - based epoxy resins. For the development of bio - based degradable epoxy resins, there are deficiencies such as complex processes, low mechanical properties, and difficulty in functionalizing simultaneously. The present invention prepares a hyperbranched phosphate / borate hybrid polymer (referred to as hyperbranched polyborophosphate, HBPPB) with a hyperbranched structure by a one - step solvent - free and catalyst - free green synthesis method, and copolymerizes it with petroleum - based bisphenol A epoxy resin and anhydride - type curing agent to obtain a high - strength, high - toughness, good - transparency and flame - retardant recyclable epoxy resin system. Due to the large number of active hydroxyl groups at the end of HBPPB, it can copolymerize with epoxy resin and introduce multiple dynamic interactions into the epoxy resin cross - linked network, namely borate / phosphate structure, ester bond and multiple hydrogen bonds. The epoxy resin system constructed in this way can not only achieve the degradation, recycling and reuse of traditional petroleum - based thermosetting epoxy resins, but also has simple preparation, low cost, can improve the strength and toughness of the resin, and endow it with additional values such as flame retardancy, smoke suppression and transparency, and has broad application prospects.

[0023] The technical solution of the present invention has the following advantages and beneficial effects compared with the prior art:

[0024] 1. In the present invention, the preparation of HBPPB adopts a one - step solvent - free and catalyst - free green synthesis method, which has low raw material cost, easy - to - control reaction process, does not require complex post - treatment and purification steps, has good economic benefits and is environmentally friendly.

[0025] 2. The recyclable epoxy resin system prepared by the present invention has excellent processability, and can also improve the strength and toughness of the cured resin, and has good transparency.

[0026] 3. By introducing phosphorus and boron flame-retardant elements in the present invention, the cured resin has good flame retardancy and smoke suppression properties.

[0027] 4. The degradation method used in the present invention has low energy consumption, and it can be degraded by soaking at room temperature for 48 h or heating at 95 °C for 8 h in N,N-dimethylacetamide (DMAc) solvent.

[0028] 5. The degraded epoxy resin in the present invention can still be recycled, and the recycled and reprocessed epoxy resin still has good mechanical properties, comparable to those before modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : Infrared spectrum (a) and distillate spectrum (b) of hyperbranched polyborophosphate in the example

[0030] Figure 2 : Transparency (a), impact strength (a) and flexural strength (b) of epoxy resin samples with different contents of HBPPB; Degradability (d) of epoxy resin in DMAc solvent; Digital photos (e) of recycled epoxy resin samples and their mechanical properties (f)

[0031] Figure 3 : Cone calorimeter test of epoxy resin with different contents of HBPPB: Heat release rate (a), total heat release (b), smoke release rate (c), total smoke release (d), CO and CO2 release (e), fire growth rate FGR and fire performance index FPI (f) (Note: In EP-X, X represents the mass fraction of HBPPB)

[0032] Figure 4 : Synthesis and structural example of hyperbranched polyborophosphate HBPPB DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be further described in conjunction with the examples and the drawings:

[0034] Preparation method of high-strength, high-toughness, highly transparent and flame-retardant recyclable epoxy resin system:

[0035] Add 9 - 20 parts by mass of HBPPB to 70 parts of bisphenol A epoxy resin, and pre-polymerize at 80 - 100 °C for 15 - 30 min; add 56 parts of anhydride curing agent and stir for 30 - 60 min, then add 1 part of DMP-30 accelerator. After stirring evenly, pour it into a mold and degas in a vacuum at 80 °C for 1 h. The curing process is carried out according to 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h to obtain the epoxy resin of the present invention. Among them, HBPPB is obtained by feeding trifunctional borate ester, trifunctional phosphate ester and diol monomer in a molar ratio of 1:1:3 - 5, and reacting at 120 - 190 °C for 10 - 12 hours under the conditions of nitrogen protection, no solvent and no catalyst.

[0036] Recovery method of high-strength, high-toughness, high-transparency flame-retardant recyclable epoxy resin system:

[0037] Take 10 g of cured resin and carry out a degradation reaction in DMAc. Among them, when the mass content of HBPPB in the epoxy / anhydride resin system is greater than 9%, obvious degradation can be observed. The sample is soaked at 95 °C for more than 8 h or soaked at room temperature for more than 2 days. Filter the solution to obtain a filter cake, and after knocking, grinding and drying, obtain the epoxy resin degradation product; take 10 g of the degradation product, add 30 g of bisphenol A epoxy resin, 24 g of anhydride curing agent and 0.3 g of tertiary amine accelerator, stir evenly at 80 °C, and carry out the same curing process as above to achieve its recovery.

[0038] The resin system is composed of 1 - 20 parts by mass of hyperbranched polyborophosphonate (HBPPB), 80 - 100 parts of bisphenol A epoxy resin, 60 - 80 parts of anhydride curing agent, and 1 - 2 parts of tertiary amine accelerator. Among them, hyperbranched polyborophosphonate is synthesized by A2 + B3 + C3 transesterification polycondensation reaction. Taking tributyl borate, triethyl phosphate, and 1,3-propanediol as examples, the synthesis and structural formula of HBPPB are as follows; the cured resin system is copolymerized by mixing the synthesized hyperbranched polyborate ester with bisphenol A epoxy resin and anhydride curing agent in a certain proportion, adding a small amount of curing accelerator 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), and preparing by heating, curing and demolding. The synthesis and structural example of hyperbranched polyborophosphonate HBPPB are shown in the appendix Figure 4 。

[0039] Among them, the synthesized HBPPB has a large number of active hydroxyl groups at the terminal positions, which can not only undergo ring-opening reactions with the epoxy groups in bisphenol A epoxy monomers, but also react with the anhydride groups in the curing agent. In the constructed hyperbranched polymer / epoxy Vitrimer network, in addition to containing borate and phosphate dynamic bonds, there are also a large number of ester bonds and multiple hydrogen bonds, providing the necessary conditions for its degradation and recycling. In addition, the relatively large intramolecular cavity of the hyperbranched polymer is conducive to the entry of small molecule solvents to induce the reconstruction and degradation of the dynamic network. In addition, the organic / inorganic hybrid B-O-C / P-O-C chain segments and multiple hydrogen bonds are beneficial to simultaneously enhance the strength and toughness of the epoxy resin. The introduction of flame retardant elements such as boron and phosphorus can endow the epoxy resin with good flame retardancy and smoke suppression properties.

[0040] Example 1:

[0041] Add 15 parts by mass of HBPPB to 70 parts of bisphenol A epoxy resin (E-51), and pre-polymerize at 80 °C for 15 min; add 56 parts of methyltetrahydrophthalic anhydride and stir for 30 min, add 1 part of DMP-30 accelerator, stir evenly and pour into a mold, and degas in a vacuum at 80 °C for 1 h. The curing process is carried out according to 120 °C / 2 h + 150 °C / 3 h + 180 / 2 h to obtain an epoxy resin cured product with a HBPPB content of about 12%. Among them, HBPPB is prepared by feeding tributyl borate, triethyl phosphate, and 1,3-propanediol in a molar ratio of 1:1:4.375, and reacting at 120-190 °C for 10-12 hours under the conditions of nitrogen protection, no solvent, and no catalyst.

[0042] Take 10 g of the cured resin and carry out a degradation reaction in DMAc. Soak it at room temperature for more than 2 days, and it is found that the epoxy resin is significantly degraded. Filter the solution to obtain a filter cake, and the epoxy resin degradation product can be obtained after knocking, grinding, pulverizing, and drying; take 10 g of the degradation product, add 30 g of bisphenol A epoxy resin, 24 g of anhydride curing agent, and 0.3 g of tertiary amine accelerator, and its recycling can be realized after curing.

[0043] Example 2:

[0044] Add 12 parts by mass of HBPPB to 70 parts of bisphenol A epoxy resin (E-51), and pre-polymerize at 80 °C for 15 min; add 56 parts of methyltetrahydrophthalic anhydride and stir for 30 min, then add 1 part of DMP-30 accelerator. After stirring evenly, pour it into a mold and degas in a vacuum at 80 °C for 1 h. The curing process is 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h to obtain an epoxy resin cured product with a HBPPB content of about 9%. Among them, HBPPB is prepared by feeding tributyl borate, triethyl phosphate, and 1,3-propanediol in a molar ratio of 1:1:4.375, and reacting at 120-190 °C for 10-12 hours under the conditions of nitrogen protection, no solvent, and no catalyst.

[0045] Take 10 g of the cured resin and carry out a degradation reaction in DMAc. Soak it at room temperature for more than 2 days, and it is found that the epoxy resin is significantly degraded. Filter the solution to obtain a filter cake, which can be obtained as an epoxy resin degradation product after knocking, grinding and pulverizing, and drying; take 10 g of the degradation product, add 30 g of bisphenol A epoxy resin, 24 g of acid anhydride curing agent and 0.3 g of tertiary amine accelerator, and its recycling can be realized after curing.

[0046] Example 3:

[0047] Add 8 parts by mass of HBPPB to 70 parts of bisphenol A epoxy resin (E-51), and pre-polymerize at 80 °C for 15 min; add 56 parts of methyltetrahydrophthalic anhydride and stir for 30 min, then add 1 part of DMP-30 accelerator. After stirring evenly, pour it into a mold and degas in a vacuum at 80 °C for 1 h. The curing process is 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h to obtain an epoxy resin cured product with a HBPPB content of about 6%. Among them, HBPPB is prepared by feeding tributyl borate, triethyl phosphate, and 1,3-propanediol in a molar ratio of 1:1:4.375, and reacting at 120-190 °C for 10-12 hours under the conditions of nitrogen protection, no solvent, and no catalyst.

[0048] Take 10 g of the cured resin and carry out a degradation reaction in DMAc. Soak it at 95 °C for 8 h or at room temperature for more than 2 days, and no obvious change in the appearance of the sample is observed. It can be seen that when the HBPPB content is low, the epoxy resin is difficult to degrade or degrades slowly in DMAc.

[0049] Example 4:

[0050] Add 4 parts by mass of HBPPB to 70 parts of bisphenol A epoxy resin (E-51), and pre-polymerize at 80 °C for 15 min; add 56 parts of anhydride curing agent and stir for 30 min, then add 1 part of DMP-30 accelerator. After stirring evenly, pour it into a mold and degas in vacuum at 80 °C for 1 h. The curing process is 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h to obtain an epoxy resin cured product with a HBPPB mass content of about 3%. Among them, HBPPB is obtained by feeding tributyl borate, triethyl phosphate, and 1,3-propanediol according to a molar ratio of 1:1:4.375 and reacting at 120-190 °C for 10-12 hours under the protection of nitrogen, without solvent and catalyst.

[0051] Take 10 g of the cured resin and carry out a degradation reaction in DMAc. Soak it at 95 °C for 8 h or soak it at room temperature for more than 2 days, and no obvious change in the appearance of the sample is observed. It can be seen that when the HBPPB content is low, the epoxy resin is difficult to degrade or degrades slowly in DMAc.

[0052] The raw material components and preparation process parameters of the epoxy resin system designed in the present invention are reasonable and can complete the reaction. On the contrary, if the selection of component parameters or the process parameter chain participating in the reaction is unreasonable, the purpose and effect of the present invention cannot be achieved. The following are the counterexamples:

[0053] Counterexample 1:

[0054] Add tributyl borate, triethyl phosphate, and 1,3-propanediol to a three-necked flask according to a molar ratio of 1:1:4.375, stir under the protection of nitrogen, control the reaction temperature between 60-120 °C, and react for 8-12 hours without any distillate. There are still two-phase substances in the flask and the reaction does not occur. This is mainly because the reaction temperature is too low to meet the conditions for transesterification reaction.

[0055] Counterexample 2:

[0056] First, add 56 parts by mass of anhydride curing agent to 70 parts of bisphenol A epoxy resin (E-51) and mix, and pre-polymerize at 80 °C for 15 min; then add 15 parts of HBPPB and 1 part of DMP-30 accelerator. It is found that the viscosity of the resin increases during stirring, HBPPB agglomerates and precipitates, and a uniform and clear resin solution cannot be obtained. This is due to the change in the feeding process, resulting in the inability to obtain the resin system described in the present invention. It can be seen that the preparation process described in the present invention is crucial for the performance of the cured resin.

[0057] Comparative example:

[0058] Add 56 parts by mass of an anhydride curing agent to 70 parts of bisphenol A epoxy resin (E-51), and pre-polymerize at 80 °C for 15 min; add 1 part of DMP-30 accelerator, stir evenly and pour into a mold, and degas in a vacuum at 80 °C for 1 h. The curing process is 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h, and the pure epoxy resin without HBPPB is obtained as a comparative example.

[0059] Table of Examples:

[0060]

[0061] Perform performance tests on the recyclable epoxy resin system with high strength, toughness, transparency, and flame retardancy prepared in this patent. See the attached drawings in the specification and analyze as follows:

[0062] Infrared spectrum as Figure 1 shown, hyperbranched polyborophosphate (HBPPB) is synthesized from tributyl borate (TBB), triethyl phosphate (TEP), and 1,3-propanediol (PDO) as raw materials. Among them, the spectra of PDO and HBPPB both show stretching vibration absorptions of -OH and -CH2- at around 3360 cm -1 and 2900 cm -1 respectively, indicating that the product contains abundant hydroxyl and methylene groups. In addition, absorption peaks at 1050 cm-1 appear in the spectra of the product HBPPB and the raw materials TEP and TBB, proving the presence of B-O-C and P-O-C groups in its structure. In addition, Figure 1 the infrared spectra of the distillates at different temperatures in b further confirm the occurrence of the reaction. Among them, the distillate at 160 °C is mainly 1-butanol, and the distillate at 190 °C is mainly ethanol, indicating that TBB and PDO preferentially undergo polycondensation reaction to produce by-product 1-butanol at lower temperatures, while TEP and PDO are more likely to react to form ethanol at higher temperatures. Therefore, infrared spectroscopy can confirm that an A2 + B2 + C3 transesterification polycondensation reaction occurs between TBB, TEP, and PDO to synthesize the product HBPPB.

[0063] Figure 2 Transparency (a), impact strength (a), flexural strength (b), degradability in DMAc (d), recycled epoxy resin sample (e), and mechanical properties (f) of epoxy resin samples with different contents of HBPPB: as Figure 2As shown in Figure a, the color of the epoxy resin with different contents of HBPPB gradually becomes lighter as the HBPPB content increases, and the transparency of the samples is significantly improved. In addition, the impact strength and flexural strength of the epoxy resin described in this patent both increase first and then decrease as the HBPPB content increases, indicating that HBPPB has an obvious strengthening and toughening effect on this resin system, mainly due to the unique branched structure and a large number of active hydroxyl groups of HBPPB. It can not only undergo a ring-opening reaction with the epoxy groups in the epoxy resin, but also undergo an esterification reaction with anhydrides. It is easy to aggregate in the resin, and the formed supramolecular / polymer interpenetrating network is not only conducive to dissipating impact energy and toughening, but also can play a strengthening role like a "rivet" on the epoxy resin network itself. As Figure 2 shown in Figure c, when the epoxy resin samples are placed at room temperature in DMAc for 2 days, obvious degradation reactions can occur in 9% HBPPB / EP and 12% HBPPB / EP, while the appearance of the pure epoxy resin hardly changes at all, indicating that the HBPPB / EP epoxy resin described in this patent has good degradation performance in DMAc. After simply filtering, grinding and pulverizing the degraded epoxy resin, and then reprocessing, the recycled epoxy resin samples can be obtained as Figure 2 shown in Figure e, and the corresponding mechanical properties of the recycled resin are as Figure 2 shown in Figure f. It can be seen that its mechanical properties after recycling can still be comparable to those of the original resin.

[0064] Figure 3 Cone calorimeter test of epoxy resins with different contents of HBPPB: heat release rate (a), total heat release (b), smoke release rate (c), total smoke release (d), CO and CO2 release (e), fire growth rate FGR and fire performance index FPI (f): Figure 3 The cone calorimeter test is used to evaluate the flame retardancy and smoke suppression performance of the epoxy resin system. As Figure 3 shown in Figure a, compared with the pure epoxy resin, the peak heat release rate of 9% HBPPB / EP and 12% HBPPB / EP is significantly reduced and delayed, indicating that the phosphorus and boron elements in HBPPB play a good flame retardant effect, and its total combustion heat release ( Figure 3 b) also decreases significantly. Figure 3 Figures c and Figure 3 d represent the smoke release property of the material during combustion. Compared with the pure epoxy resin, the addition of HBPPB can not only reduce the smoke release rate and total smoke release, but also the secondary combustion zone (at 400 s) of the material combustion almost disappears, proving the good smoke suppression property of the resin system described in this patent. In addition, the addition of HBPPB also effectively reduces the release of carbon monoxide, carbon dioxide, etc. during the combustion of the epoxy resin, and the fire safety of the material is significantly improved.

[0065] The above content is a further detailed description of the present invention in combination with specific implementation examples. It cannot be determined that the specific implementation manners of the present invention are limited thereto. Although the implementation examples of the present invention are not disclosed, those skilled in the art can foresee and determine them.

Claims

1. A preparation method of a high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system, characterized in that, The epoxy resin system includes 1 to 20 parts by mass of hyperbranched polyborophosphate HBPPB, 80 to 100 parts of bisphenol A epoxy resin, 60 to 80 parts of anhydride curing agent, and 1 to 2 parts of tertiary amine accelerator; The preparation method of the epoxy resin system includes: Step 1: HBPPB is obtained by feeding trifunctional borate ester, trifunctional phosphate ester, and diol monomer in a molar ratio of 1:1:3 to 5, reacting at 120 to 190 °C for 10 to 12 hours under nitrogen protection, without solvent and without catalyst; Step 2: Add 1 to 20 parts by mass of HBPPB to 80 to 100 parts of bisphenol A epoxy resin, pre-polymerize at 80 to 100 °C for 15 to 30 min; add 60 to 80 parts of anhydride curing agent and stir for 30 to 60 min, add 1 to 2 parts of tertiary amine accelerator, stir evenly and pour into a mold, and degas in a vacuum at 80 °C for 1 h and then cure; Step 3: The curing process is carried out according to 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h to obtain the epoxy resin; The HBPPB is synthesized by transesterification polycondensation reaction using trifunctional borate ester, trifunctional phosphate ester, and diol as raw materials, and the sites of phosphorus and boron elements in its branched structure are randomly distributed; The trifunctional borate ester is tributyl borate or triethyl borate; The trifunctional phosphate ester is triethyl phosphate; The diol is ethylene glycol, 1,3-propanediol, or 1,4-butanediol; The bisphenol A epoxy resin includes epoxy resins of domestic grades E-51 and E-44; The anhydride curing agent includes succinic anhydride, phthalic anhydride, methyltetrahydrophthalic anhydride, or methylhexahydrophthalic anhydride; The tertiary amine accelerator includes the tertiary amine curing accelerator for domestic grade DMP-30 epoxy resin.

2. A method for recycling a high-strength, high-toughness, highly transparent flame-retardant recyclable epoxy resin system prepared by the method according to claim 1, characterized in that: The epoxy resin system is soaked at room temperature in N,N-dimethylacetamide DMAc solvent, filtered to obtain a filter cake, and after knocking, grinding and pulverizing, and drying, an epoxy resin degradation product is obtained.

3. The recovery method according to claim 2, characterized in that: The degradation product is stirred evenly with bisphenol A epoxy resin, anhydride curing agent, and tertiary amine accelerator, and recycled according to 120 °C / 2 h + 150 °C / 3 h + 180 °C / 2 h.

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