Hot-melt type renewable phenolic resin and preparation method thereof, hot-melt type renewable phenolic resin-based ablation-resistant composite material and preparation method and regeneration method of hot-melt type renewable phenolic resin-based ablation-resistant composite material

Abstract

The invention discloses a hot-melt type renewable phenolic resin and a preparation method thereof, and a hot-melt type renewable phenolic resin-based ablation-resistant composite material and a preparation method and a regeneration method thereof. The preparation method comprises the following steps: carrying out a melting reaction on a polyhydroxymethyl phenol compound and a dithiol compound to prepare the hot-melt type renewable phenolic resin; the preparation method comprises the following steps: heating hot-melt renewable phenolic resin so as to form a resin adhesive film through curtain coating, laminating the resin adhesive film and a fiber reinforcement body, passing through a roller, rolling to obtain a molten phenolic resin prepreg, and carrying out hot-press molding on the hot-melt phenolic resin prepreg to obtain the hot-melt renewable phenolic resin-based ablation-resistant composite material. The catalyst can be regenerated through an aprotic polar solvent dissolution-precipitation process. The prepared hot-melt renewable phenolic resin has the advantages of efficient repair, wide and adjustable viscosity range, high thermal decomposition temperature and high char yield, and endows the hot-melt renewable phenolic resin-based ablation-resistant composite material with reproducibility, self-repair property, ablation resistance and good mechanical properties.

Description

TECHNICAL FIELD

[0001] The present application relates to a phenolic resin-based composite material, in particular to a hot-melt renewable phenolic resin, a preparation method thereof, a hot-melt renewable phenolic resin-based ablative-resistant composite material, a preparation method and a regeneration method thereof. BACKGROUND

[0002] Phenolic resin has become a key material for manufacturing the nozzle expansion section of a solid rocket engine due to its good processability, excellent mechanical properties and ablative resistance. With the upgrading of solid rocket engines, higher requirements are put forward for the performance and preparation process of phenolic resin-based ablative-resistant composite materials.

[0003] When the reinforcing fibers are determined, the performance of the phenolic resin-based ablative-resistant composite material mainly depends on the matrix resin and the forming process. The traditional phenolic resin-based ablative-resistant composite material is usually prepared by first impregnating carbon fiber cloth or glass fiber cloth with phenolic resin to form a prepreg, and then winding and curing the prepreg to form a product. However, in the process of impregnating carbon fiber cloth or glass fiber cloth with phenolic resin, a large amount of solvent needs to be introduced in the solution impregnation process, and the volatilization of the solvent is easily affected by environmental factors, resulting in difficulty in strictly controlling the thickness of the prepreg, complicated process, unstable product quality, and difficulty in meeting the development needs of high-performance nozzles, and is not conducive to the health of operators and environmental protection.

[0004] The hot-melt adhesive film process can effectively avoid the problems existing in the solution impregnation process, thereby obtaining a prepreg with stable product quality and uniform glue content. The prepreg prepared by the hot-melt adhesive film process has improved overall mechanical properties and moisture resistance. However, the hot-melt adhesive film process has strict requirements for the resin: (1) the resin can form a continuous adhesive film at room temperature, and the resin film can be arbitrarily bent without falling off and sticking to the hand; (2) at the operating temperature, the resin should maintain a relatively low viscosity to fully impregnate the fibers, so that the glue content and the glue layer thickness are controllable; (3) the prepreg prepared by the resin impregnated fibers should have a certain stickiness on the surface to meet the requirements of the laying process; (4) the reactivity of the resin is controllable to ensure that the adhesive film and the prepreg have good storage stability. In order to meet the above requirements, the hot-melt adhesive film prepared by the resin requires that the molecular weight and its distribution, viscosity and reactivity of the resin are adjustable. In addition, the hot-melt adhesive film process usually requires melting coating at 60-95℃, while ordinary phenolic resin starts to react at 60-70℃, resulting in a sharp rise in viscosity and difficulty in uniform film formation. For thermoplastic phenolic resins with a large molecular weight, a curing agent such as hexamethylenetetramine is often added for crosslinking, but the curing agent is easily precipitated in the prepreg, and after the solvent is volatilized, the resin becomes dry and hard, which cannot be formed into a film and rolled up.

[0005] In recent years, researchers have successively developed various types of hot-melt phenolic resins. For example, Solid Rocket Technology, 2017, 40(3): 380-385, 390, uses toughening agents to make the phenolic resin have suitable viscosity and film-forming properties at the film-forming temperature, and introduces heat-resistant modifiers into the phenolic resin to ensure that the heat resistance of the phenolic resin is not lost while toughening. Chinese patent CN118440638A discloses a resin for hot-melt adhesive film process and its preparation method, as well as a hot-melt adhesive film preparation method and its application, using dihydroxydiphenylmethane and formaldehyde as raw materials. Materials were developed to synthesize a low-viscosity, high-char-rate free-phenol thermosetting phenolic resin. This was achieved by mixing free-phenol thermosetting phenolic resin, thermoplastic phenolic resin, and additives to optimize processability and improve char-rate yield, thus preparing a resin for hot-melt adhesive film processing. Chinese patent CN114380963A discloses a dual-curing high-char-residue phenolic resin and its preparation method. This method improves the ablation resistance of the phenolic resin by introducing high-bond-energy BO and Si-O structures into the phenolic resin structure, and simultaneously controls the viscosity of the modified resin to meet the requirements of the hot-melt adhesive film prepreg preparation process. However, existing hot-melt phenolic resins lack repair and regeneration properties. This leads to high defect rates and large amounts of waste in the manufacturing process of solid rocket motor nozzle expansion sections due to the variety of product sizes and complex processes, resulting in significant economic losses.

[0006] Although traditional thermosetting phenolic resins can be reprocessed and recycled by introducing dynamic bonds, it is often difficult to simultaneously meet the requirements of regeneration performance and high char yield. For example, phenolic resins crosslinked with boric acid or phenylboronic acid are brittle and difficult to form continuous resin films; phenolic resins based on dynamic urethane bond crosslinking have a short pot life, and the introduced isocyanate compounds have poor environmental stability, making them unsuitable for the molding process of hot melt adhesive films.

[0007] Therefore, how to prepare hot-melt phenolic resin-based ablation-resistant composite materials with excellent thermal and mechanical properties and endow phenolic resin composite materials with repairability and regenerability is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] The present invention aims to provide a hot-melt regenerable phenolic resin and its preparation method, a hot-melt regenerable phenolic resin-based ablation-resistant composite material and its preparation and regeneration methods. The prepared hot-melt regenerable phenolic resin has the advantages of high efficiency repair, wide and adjustable viscosity range, high thermal decomposition temperature and high char formation rate, and endows the hot-melt regenerable phenolic resin-based ablation-resistant composite material with regenerability, self-healing, ablation resistance and good mechanical properties.

[0009] This invention is achieved through the following technical solution:

[0010] A preparation method of a hot-melt renewable phenolic resin, comprising the following steps: first, according to weight parts, 100 parts of a polyhydroxymethyl phenolic compound and 50-140 parts of a dithiol compound are added into a reaction kettle, under the protection of inert atmosphere, the temperature is lowered to 95-110 DEG C, and the stirring is continued for 80-100 min, and then the temperature is lowered to room temperature, to obtain a hot-melt renewable phenolic resin which is uniform and transparent.

[0011] Further, the polyhydroxymethyl phenolic compound is at least one of 2-hydroxy-5-methylresorcinol, 4-[2-[4-hydroxy-3,5-di(hydroxymethyl)phenyl]propan-2-yl]-2,6-di(hydroxymethyl)phenol, (5-hydroxy-1,3-phenylene)dimethanol and 2-hydroxy-1,3,5-benzenetriol.

[0012] Further, the dithiol compound is at least one of 4,4'-dihydroxydiphenyl disulfide and 3,3'-dihydroxydiphenyl disulfide.

[0013] A hot-melt renewable phenolic resin, characterized in that the number average molecular weight is 600-1000 g / mol, the viscosity at 25 DEG C is 10 4 ~ 10 5 Pa·s.

[0014] A method for preparing a hot-melt renewable phenolic resin-based ablative-resistant composite material by using a hot-melt renewable phenolic resin, comprising the following steps:

[0015] Step 1, the hot-melt renewable phenolic resin is heated to 60-75 DEG C, and is cast into a resin film with a thickness of 65-75 μm, a release paper is covered on the surface of the resin film to prevent adhesion, and then the resin film is wound to obtain a wound resin film which is stored in a refrigerator for standby;

[0016] Step 2, the resin film is laminated with a continuous fiber reinforcement, and is passed through a roller at a roller temperature of 70-80 DEG C and a line speed of 1-3 m / min, and then is wound to obtain a hot-melt phenolic resin prepreg;

[0017] Step 3, the hot-melt phenolic resin prepreg is cut according to the required size and is laminated and laid up, is placed in a hot press, is heated to 80 DEG C, and then is heated to 160-180 DEG C from room temperature at a heating rate of 1-3 DEG C / min, is kept warm until the gel point is reached, is pressurized to 2-4 MPa, and is kept warm and pressurized for 1.5-3 h, is cooled to room temperature, is demolded, and a hot-melt phenolic resin-based ablative-resistant composite material is obtained.

[0018] Further, the fiber reinforcement in step 2 is a carbon fiber cloth or a glass fiber cloth.

[0019] A hot-melt renewable phenolic resin-based ablation-resistant composite material has a mass ablation rate of 0.0263-0.0604 g / s.

[0020] Further, interlaminar damage or cracks can be repaired by a hot-pressing process, wherein: the hot-pressing process is at 165-220 DEG C, under a pressure of 2-4 MPa, and pressure maintaining for 0.5-3 h.

[0021] A regeneration method of a hot-melt renewable phenolic resin-based ablation-resistant composite material, wherein fibers and resins are recovered by a polar aprotic solvent dissolving-out process, and the method comprises the following steps:

[0022] S1, according to weight parts, 1 part of the hot-melt renewable phenolic resin-based ablation-resistant composite material is put into 10-200 parts of a polar aprotic solvent, under the protection of inert gas, heated at 130-150 DEG C for 6-48 h, so that the resin on the surface of the fiber reinforced body is degraded, and the fiber reinforced body and the resin solution are separated;

[0023] S2, the fiber reinforced body is cleaned with anhydrous ethanol to remove residual polar aprotic solvent, and dried to obtain a regenerated fiber reinforced body;

[0024] S3, the polar aprotic solvent in the resin solution is removed by vacuum distillation to obtain a concentrated resin solution, which is dried under vacuum to obtain a regenerated phenolic resin degradation product.

[0025] Further, the polar aprotic solvent is at least one of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

[0026] The present application has the following beneficial technical effects:

[0027] The present application mixes the polyhydroxymethyl phenolic compound and the dithiol compound, then directly melts, through the active hydrogen on the benzene ring in the dithiol compound and the hydroxymethyl in the polyhydroxymethyl phenolic compound condensation reaction, obtains the hot melt type renewable phenolic resin, not only the reaction process does not need solvent and catalyst, has the advantages of safe, simple, efficient, energy saving and environmental protection, and the prepared thermosetting phenolic resin has the advantages of high efficient repair, wide viscosity range, high thermal decomposition temperature and high carbon yield, which is embodied in: first, the reversible conversion between aromatic disulfide bond and sulfur radical endows the dynamic reconstruction of the phenolic resin crosslinking network, so that the phenolic resin can be efficiently repaired or regenerated; second, the sulfur radical in the phenolic resin crosslinking network can capture the free radicals generated in the thermal cracking process, reduce the volatilization of free phenol, so that the phenolic resin has high carbon yield and endows the composite with good ablation resistance; third, by controlling the reaction degree of the phenolic resin, the phenolic resin has a large viscosity at room temperature, so that it can be formed into a film, and under the condition of heating, the dissociation of the dynamic sulfur bond helps to reduce the viscosity, and the disulfide bond also leads to the decrease of the ortho reaction activity of phenolic hydroxyl group, thereby improving the decomposition temperature, that is, the viscosity of the phenolic resin is controllable and the reaction activity is moderate, which can meet the process requirements of hot melt adhesive film, prepreg and composite; fourth, the dynamic disulfide bond enhances the chain segment movement ability at high temperature, so that the resin can reach a higher crosslinking degree, thereby endowing the composite with excellent mechanical properties.

[0028] The prepared hot melt type phenolic resin is added into a hot melt prepreg machine to prepare a resin adhesive film, the resin adhesive film is combined with a fiber reinforcement to obtain a hot melt phenolic resin prepreg, and finally a hot melt type phenolic resin based ablation resistant composite material is obtained by using a hot pressing process, which has excellent ablation resistance, mechanical properties, self-repairing properties and regenerative properties, and can meet the performance requirements of solid rocket engine composite materials.

[0029] The hot melt type renewable phenolic resin based ablation resistant composite material prepared by the present application not only can repair the defects and cavities of the resin adhesive film through the hot pressing process, but also can realize the recycling and regeneration of the resin adhesive film and the fiber through the polar aprotic solvent dissolution-precipitation process, thereby reducing the economic loss caused by the waste of products and the next product in the preparation process of the nozzle expansion section of the solid rocket engine. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the Fourier transform infrared spectrum FTIR diagram of the hot melt type renewable phenolic resin prepared in Example 1;

[0031] Figure 2 is the gel permeation chromatogram GPC diagram of the hot melt type renewable phenolic resin prepared in Example 1;

[0032] Figure 3is a viscosity-temperature curve of the hot-melt renewable phenolic resin prepared in Example 1 under isokinetic temperature rising;

[0033] Figure 4 is a viscosity-time curve of the hot-melt renewable phenolic resin prepared in Example 1 under constant temperature of 65℃;

[0034] Figure 5 is a thermogravimetric curve of the cured product of the hot-melt renewable phenolic resin prepared in Example 1;

[0035] Figure 6 is a schematic diagram of the regeneration process of the hot-melt renewable phenolic resin-based ablation-resistant composite material prepared in Example 1. DETAILED DESCRIPTION

[0036] The present application will be further described in conjunction with specific examples, which are an explanation rather than a limitation of the present application.

[0037] In Examples 1-8, the thickness of the resin film is 65-75 μm.

[0038] As shown in Figure 6 Examples 1-8, the fiber reinforcement and the resin are separated by a polar aprotic solvent dissolution-precipitation process, the recovered renewable phenolic resin degradation product can continue to be used for the synthesis of hot-melt renewable phenolic resin, and the recovered regenerated carbon fiber cloth or glass fiber cloth can continue to be used as a fiber reinforcement, thereby realizing the regeneration of the hot-melt renewable phenolic resin-based ablation-resistant composite material.

[0039] Example 1

[0040] Step 1, according to parts by weight, 100 parts of 2-hydroxy-5-methyl resorcinol and 85 parts of 4,4'-dihydroxydiphenyl disulfide are added to a reaction kettle with a condensation reflux device, and stirred at 115℃ under inert atmosphere protection until a uniform solution is formed, then the temperature inside the reaction kettle is slowly reduced to 105℃, and the stirring is continued for 90 min, the reaction product is poured out, and cooled to room temperature to obtain a uniform transparent hot-melt renewable phenolic resin, which is denoted as HPDS-1, and the structural formula is as follows:

[0041]

[0042] Step 2, HPDS-1 is added to the double rollers of a hot-melt pre-impregnation machine, heated to 65℃, and cast into a resin film, a release paper is covered on the surface of the resin film to prevent adhesion, and then wound to obtain a wound resin film, which is stored in the freezer for standby;

[0043] Step 3, stack the resin film with the carbon fiber cloth, pass through the roller at a roller temperature of 70℃, at a line speed of 3m / min, and then wind up to obtain a hot-melt phenolic resin prepreg;

[0044] Step 4, cut the hot-melt phenolic resin prepreg according to the required size and stack and lay up, place in a hot press, close the hot press, first heat to 80℃, then heat from room temperature to 165℃ at a heating rate of 1℃ / min, keep warm until the gel point is reached, slowly pressurize to 2MPa, keep warm and pressurized for 2h, turn off the hot press, wait until it cools to room temperature, open the hot press, demold, and obtain a hot-melt phenolic resin-based ablative composite material, recorded as HPDS-1-based ablative composite material;

[0045] Step 5, recover the carbon fiber cloth and resin through a polar aprotic solvent dissolution-precipitation process, the specific process is as follows:

[0046] Step 5.1, according to the weight parts, put 1 part of HPDS-1-based ablative composite material into 50 parts of N,N-dimethylformamide, heat at 140℃ for 12h under inert gas protection, so that the resin on the surface of the carbon fiber cloth is degraded, and the carbon fiber cloth and the resin solution are separated;

[0047] Step 5.2, use anhydrous ethanol to clean the carbon fiber cloth to remove residual N,N-dimethylformamide, dry in a blast oven at 55℃ to obtain regenerated carbon fiber cloth;

[0048] Step 5.3, use a method of reduced pressure distillation to remove N,N-dimethylformamide in the resin solution at 95℃ to obtain a concentrated resin solution, dry in a vacuum drying oven at 85℃ to obtain regenerated phenolic resin degradation product.

[0049] 1), in order to verify the repairability of the HPDS-1-based ablative composite material prepared in Example 1, heat the HPDS-1-based ablative composite material with interlaminar damage and cracks to 180℃, and pressurize at 2MPa for 1h, and it is found that the damage is completely repaired.

[0050] 2), according to the JC / T 773-2010 standard, test the interlaminar shear performance of the HPDS-1-based ablative composite material, the sample size is long x wide x high = 30mm x 15mm x 3mm, the span is 15mm, and the parallel samples are not less than 5; according to the GJB323B-2018 standard, test the ablative performance of the HPDS-1-based ablative composite material, the sample is a cylinder with a diameter of 30mm and a thickness of 10mm, the ablative angle is 90°, the parallel samples are not less than 5, and the oxygen-ethyne ablation is used, the ablation time is 20s; the mechanical properties and ablative resistance of the HPDS-1-based ablative composite material prepared in Example 1 are shown in Table 1;

[0051] Table 1 Mechanical properties and ablation resistance of HPDS-1 based ablation-resistant composite materials

[0052]

[0053] 3) The HPDS-1 resin prepared in Example 1 was subjected to FTIR testing, and the results are as follows: Figure 1 As shown, the peak of hydroxymethylation has basically disappeared, at 2850 cm⁻¹. -1 and 2923cm -1 The vibrational absorption peak at 516 cm⁻¹ indicates that the hydrogen atom on the benzene ring of 4,4'-dihydroxydiphenyl disulfide reacts with the hydroxymethyl group of 2-hydroxy-5-methyl-m-phthalimide to form a methylene group. -1 The absorption peak at this point is for SS, indicating that the cured resin retains disulfide bonds.

[0054] 4) The HPDS-1 resin prepared in Example 1 was analyzed by gel permeation chromatography using polystyrene as a standard, and the results were as follows: Figure 2 The standard curve shown indicates that the number-average molecular weight of HPDS-1 is 688 g / mol, the weight-average molecular weight is 827 g / mol, and the polydispersity index (PDI) is 1.2. It can be seen that, compared with ordinary commercially available thermosetting phenolic resins, the hot-melt regenerable phenolic resin prepared in Example 1 has a lower molecular weight and a very narrow molecular weight distribution, which can meet the process requirements of hot-melt resin molds, prepregs, and composite materials. Furthermore, the very narrow molecular weight distribution is beneficial to improving the thermal stability and char formation rate of the hot-melt regenerable phenolic resin.

[0055] 5) The viscosity of the HPDS-1 resin prepared in Example 1 was tested using a rheometer, wherein: as Figure 3 As shown, under the test conditions of a temperature range of 25–175℃, a heating rate of 2℃ / min, a fixed shear strain of 1%, and a fixed frequency of 1Hz, the viscosity of HPDS-1 resin at 25℃ is 3.6 × 10⁻⁶. 4 Pa·s; as Figure 4 As shown, at a film-forming temperature of 65°C, the viscosity can be maintained within the range of 5–20 Pa·s, which is conducive to film formation, for a long time (>60 min).

[0056] 6) The HPDS-1 resin prepared in Example 1 was subjected to thermogravimetric analysis (TGA). The heating rate was 10 °C / min, the protective gas was nitrogen, and the flow rate was 50 mL / min. The results are as follows: Figure 5 As shown, the cured HPDS-1 resin exhibits excellent thermal stability, with a char rate of 64.7% at 800℃, indicating that it can be used as a matrix for ablation-resistant composite materials.

[0057] Example 2

[0058] Step 1, according to parts by weight, 100 parts of 2-hydroxy-5-methyl resorcinol and 65 parts of 4,4'-dihydroxydiphenyl disulfide are added to a reaction kettle with condensation reflux device, under the protection of inert atmosphere, fully stirred at 125℃ until a uniform solution is formed, then the temperature inside the reaction kettle is slowly reduced to 110℃, continue to stir for 100 min, pour out the reaction product, cool to room temperature to obtain a uniform transparent hot melt renewable phenolic resin, recorded as HPDS-2, the number average molecular weight is 1000 g / mol, the viscosity at 25℃ is 1 x 10 5 Pa·s;

[0059] Step 2, HPDS-2 is added to the double roller of the hot melt pre-impregnation machine, heated to 70℃, cast into a resin film, and then covered with release paper on the surface of the resin film to prevent adhesion, then wound to obtain a wound resin film, and stored in the freezer for standby;

[0060] Step 3, the resin film is laminated with carbon fiber cloth, passed through the roller at a roller temperature of 75℃ and a line speed of 2.5 m / min, and then wound to obtain a hot melt phenolic resin prepreg;

[0061] Step 4, the hot melt phenolic resin prepreg is cut according to the required size and stacked and laid up, and placed in a hot press, the hot press is closed, first heated to 80℃, then heated from room temperature to 170℃ at a heating rate of 2℃ / min, and kept at the gel point, slowly pressurized to 3 MPa, and kept at temperature and pressure for 2 h, the hot press is closed, and the hot press is opened after cooling to room temperature, and the mold is removed to obtain a hot melt phenolic resin-based ablative composite material, recorded as HPDS-2-based ablative composite material;

[0062] Step 5, the carbon fiber cloth and the resin are recovered by polar aprotic solvent dissolution-precipitation process, the specific process is as follows:

[0063] Step 5.1, first, according to a mass ratio of 9:1, N,N-dimethylformamide and dimethyl sulfoxide are mixed to obtain a mixed solvent, then 1 part of HPDS-2-based ablative composite material is put into 100 parts of mixed solvent under the protection of inert gas at 145℃ for 24 h, so that the resin on the surface of the carbon fiber cloth is degraded, and the carbon fiber cloth and the resin solution are separated;

[0064] Step 5.2, the carbon fiber cloth is washed with anhydrous ethanol to remove residual N,N-dimethylformamide and dimethyl sulfoxide, and dried in a 55℃ air oven to obtain regenerated carbon fiber cloth;

[0065] Step 5.3, remove N,N-dimethylformamide and dimethyl sulfoxide in the resin solution by distillation under reduced pressure at 100℃, to obtain a concentrated resin solution, and dry in a vacuum drying oven at 85℃ to obtain the regenerated phenolic resin degradation product.

[0066] 1) In order to verify the repairability of the HPDS-2-based ablative composite material prepared in Example 2, the HPDS-2-based ablative composite material with interlaminar damage and cracks was heated to 200℃, and the pressure was maintained at 3MPa for 1.5h, and it was found that the damage was completely repaired.

[0067] 2) According to the standard of GJB 323B-2018, the ablation performance of the HPDS-2-based ablative composite material was tested, and the mass ablation rate was 0.0392g / s.

[0068] Example 3

[0069] Step 1, according to the weight parts, 100 parts of 2-hydroxy-5-methyl resorcinol and 50 parts of 4,4'-dihydroxydiphenyl disulfide were added to a reaction kettle with condensation reflux device, and stirred under inert atmosphere protection at 130℃ until a uniform solution was formed, then the temperature inside the reaction kettle was slowly reduced to 110℃, and the stirring was continued for 100min, the reaction product was poured out, and cooled to room temperature to obtain a uniform transparent hot melt type renewable phenolic resin, which was recorded as HPDS-3, and the number average molecular weight was 714g / mol, and the viscosity at 25℃ was 5.2x10 4 Pa·s;

[0070] Step 2, HPDS-3 was added to the double roller of the hot melt pre-impregnation machine, heated to 75℃, and cast into a resin film, and then covered with release paper on the surface of the resin film to prevent adhesion, and then wound to obtain a wound resin film, which was stored in the freezer for standby;

[0071] Step 3, the resin film was laminated with carbon fiber cloth, and the roller temperature was 80℃, the line speed was 1m / min, and the hot melt phenolic resin prepreg was obtained by winding.

[0072] Step 4, the hot melt phenolic resin prepreg was cut according to the required size and stacked and laid up, and placed in a hot press, the hot press was closed, the temperature was first raised to 80℃, and then the temperature was raised to 180℃ at a rate of 3℃ / min from room temperature, and the temperature was maintained until the gel point was reached, and the pressure was slowly increased to 4MPa, and the temperature and pressure were maintained for 3h, the hot press was closed, and the hot press was opened after cooling to room temperature, and the mold was removed to obtain a hot melt type phenolic resin based ablative composite material, which was recorded as HPDS-3 based ablative composite material.

[0073] Step 5, the carbon fiber cloth and resin were recovered by polar aprotic solvent dissolution-precipitation process, the specific process was as follows:

[0074] Step 5.1, first mix N,N-dimethylformamide and N,N-diethylformamide according to mass ratio 9:1 to obtain mixed solvent, then put 1 part of HPDS-3 based ablation-resistant composite into 100 parts of mixed solvent according to weight, heat at 150℃ for 30h under inert gas protection to degrade the resin on the surface of carbon fiber cloth, separate the carbon fiber cloth and resin solution;

[0075] Step 5.2, clean the carbon fiber cloth with anhydrous ethanol to remove residual N,N-dimethylformamide and N,N-diethylformamide, dry in a blast oven at 55℃ to obtain regenerated carbon fiber cloth;

[0076] Step 5.3, remove N,N-dimethylformamide and N,N-diethylformamide in the resin solution by vacuum distillation at 100℃ to obtain concentrated resin solution, dry in a vacuum drying oven at 85℃ to obtain regenerated phenolic resin degradation product.

[0077] 1), in order to verify the repairability of the HPDS-3 based ablation-resistant composite prepared in Example 3, the HPDS-3 based ablation-resistant composite with interlaminar damage and cracks was heated to 220℃, and the pressure was maintained at 4MPa for 3h, and it was found that the damage was completely repaired.

[0078] 2), according to the standard of GJB 323B-2018, the ablation performance of the HPDS-3 based ablation-resistant composite was tested, and the mass ablation rate was 0.0517g / s.

[0079] Example 4

[0080] Step 1, according to weight, 90 parts of 2-hydroxy-5-methyl-m-xylenediol, 10 parts of (5-hydroxy-1,3-phenylene) dimethanol and 125 parts of 4,4'-dihydroxydiphenyl disulfide were added to a reaction kettle with condensation reflux device, stirred under inert atmosphere protection at 115℃ until a uniform solution was formed, then the temperature inside the reaction kettle was slowly reduced to 105℃, and the stirring was continued for 90min, the reaction product was poured out, and cooled to room temperature to obtain a uniform transparent hot melt type renewable phenolic resin, which was recorded as HPDS-4, and the number average molecular weight was 657g / mol, and the viscosity at 25℃ was 2.9x10 4 Pa·s;

[0081] Step 2, HPDS-4 was added to the double rollers of the hot melt pre-impregnation machine, heated to 65℃, and cast into a resin film, and then covered with release paper on the surface of the resin film to prevent sticking, then wound to obtain a roll of resin film, and stored in the freezer for standby;

[0082] Step 3, stack the resin film with the carbon fiber cloth, pass through the roller at a roller temperature of 70℃, at a line speed of 3m / min, and then wind up to obtain a hot-melt phenolic resin prepreg;

[0083] Step 4, cut the hot-melt phenolic resin prepreg according to the required size and stack and lay up, place in a hot press, close the hot press, first heat to 80℃, then heat from room temperature to 165℃ at a heating rate of 1℃ / min, keep warm until the gel point is reached, slowly pressurize to 2MPa, keep warm and pressurized for 2h, turn off the hot press, wait for cooling to room temperature, open the hot press, demold, and obtain a hot-melt type phenolic resin based ablative composite material, recorded as HPDS-4 based ablative composite material;

[0084] Step 5, recover the carbon fiber cloth and resin by polar aprotic solvent dissolution-precipitation process, the specific process is as follows:

[0085] Step 5.1, first mix N,N-dimethylformamide and N,N-dimethylacetamide according to a mass ratio of 4:1 to obtain a mixed solvent, then put 1 part of HPDS-4 based ablative composite material into 80 parts of mixed solvent under inert gas protection, heat at 130℃ for 36h to degrade the resin on the surface of the carbon fiber cloth, separate the carbon fiber cloth and the resin solution;

[0086] Step 5.2, wash the carbon fiber cloth with anhydrous ethanol to remove residual N,N-dimethylformamide and N,N-dimethylacetamide, dry in a blast drying oven at 55℃ to obtain regenerated carbon fiber cloth;

[0087] Step 5.3, remove N,N-dimethylformamide and N,N-dimethylacetamide in the resin solution by vacuum distillation at 95℃ to obtain a concentrated resin solution, dry in a vacuum drying oven at 85℃ to obtain regenerated phenolic resin degradation product.

[0088] 1), in order to verify the repairability of the HPDS-4 based ablative composite material prepared in Example 4, heat the HPDS-4 based ablative composite material with interlaminar damage and cracks to 175℃, pressurize at 2MPa for 1.5h, and find that the damage is completely repaired.

[0089] 2), according to the standard of GJB 323B-2018, test the ablation performance of the HPDS-4 based ablative composite material, and the mass ablation rate is 0.0304g / s.

[0090] Example 5

[0091] Step 1: According to the weight proportions, 90 parts of 2-hydroxy-5-methylisophthalic acid, 10 parts of (5-hydroxy-1,3-phenylene)diethanol, 60 parts of 4,4'-dihydroxydiphenyl disulfide, and 25 parts of 3,3'-dihydroxydiphenyl disulfide were added to a reactor equipped with a reflux condenser. Under an inert atmosphere, the mixture was stirred thoroughly at 110°C until a homogeneous solution was formed. Then, the temperature inside the reactor was slowly reduced to 105°C, and stirring was continued for 95 minutes. The reaction product was then poured out and cooled to room temperature to obtain a homogeneous and transparent hot-melt regenerable phenolic resin, denoted as HPDS-5, with a number-average molecular weight of 803 g / mol and a viscosity of 7.5 × 10⁻⁶ at 25°C. 4 Pa·s;

[0092] Step 2: Add HPDS-5 to the double rollers of the hot melt prepreg machine, heat to 67°C, and cast into a resin film. Cover the surface of the resin film with release paper to prevent sticking, and then roll it up to obtain a roll of resin film. Store it frozen for later use.

[0093] Step 3: Lay the resin film and carbon fiber cloth together, pass them through the roller at a roller temperature of 75°C and a linear speed of 3m / min, and then rewind them to obtain hot melt phenolic resin prepreg.

[0094] Step 4: Cut the hot-melt phenolic resin prepreg to the required size and lay it in layers. Place it in a hot press, close the hot press, first heat it to 80℃, then heat it from room temperature to 160℃ at a heating rate of 2℃ / min, keep it at the temperature until the gel point is reached, slowly pressurize it to 3MPa, keep it at the temperature and pressure for 2.5h, close the hot press, wait for it to cool to room temperature, open the hot press, demold it, and obtain the hot-melt phenolic resin-based ablation-resistant composite material, which is denoted as HPDS-5-based ablation-resistant composite material.

[0095] Step 5: Recover carbon fiber cloth and resin through a polar aprotic solvent dissolution-precipitation process. The specific process is as follows:

[0096] Step 5.1: First, mix N,N-dimethylformamide and N,N-diethylformamide at a mass ratio of 19:1 to obtain a mixed solvent. Then, according to the weight ratio, put 1 part of HPDS-5-based ablation-resistant composite material into 10 parts of the mixed solvent. Under inert gas protection, heat at 140°C for 48 hours to degrade the resin on the surface of the carbon fiber cloth and separate the carbon fiber cloth and the resin solution.

[0097] Step 5.2: Clean the carbon fiber cloth with anhydrous ethanol to remove residual N,N-dimethylformamide and N,N-diethylformamide, and dry it in a forced-air drying oven at 55°C to obtain recycled carbon fiber cloth.

[0098] Step 5.3, remove N,N-dimethylformamide and N,N-diethylformamide in the resin solution by distillation under reduced pressure at 95℃, to obtain a concentrated resin solution, dry in a vacuum drying oven at 85℃, to obtain the regenerated phenolic resin degradation product.

[0099] 1) In order to verify the repairability of the HPDS-5-based ablative composite material prepared in Example 5, the HPDS-5-based ablative composite material with interlaminar damage and cracks was heated to 180℃, and the pressure was maintained at 2 MPa for 2 h, and it was found that the damage was completely repaired.

[0100] 2) According to the standard of GJB 323B-2018, the ablation performance of the HPDS-5-based ablative composite material was tested, and the mass ablation rate was 0.0373 g / s.

[0101] Example 6

[0102] Step 1, according to the weight parts, 95 parts of 2-hydroxy-5-methyl-m-xylenediol, 5 parts of 2-hydroxy-1,3,5-benzene tri-methanol and 85 parts of 4,4'-dihydroxydiphenyl disulfide were added to a reaction kettle with condensation reflux device, and stirred under inert atmosphere protection at 120℃ until a uniform solution was formed, then the temperature inside the reaction kettle was slowly reduced to 105℃, and the stirring was continued for 90 min, the reaction product was poured out, and cooled to room temperature to obtain a uniform transparent hot melt type renewable phenolic resin, which was recorded as HPDS-6, and the number average molecular weight was 600 g / mol, and the viscosity at 25℃ was 1×10 4 Pa·s;

[0103] Step 2, HPDS-6 was added to the double rollers of the hot melt pre-impregnation machine, heated to 60℃, and cast into a resin film, and then covered with release paper on the surface of the resin film to prevent adhesion, and then wound to obtain a wound resin film, which was stored in the freezer for standby;

[0104] Step 3, the resin film was laminated with carbon fiber cloth, and the roller temperature was 70℃, the line speed was 2.5 m / min, and the hot melt phenolic resin prepreg was obtained by passing through the roller and rewinding.

[0105] Step 4, the hot melt phenolic resin prepreg was cut according to the required size and stacked and laid up, and placed in a hot press, the hot press was closed, the temperature was first raised to 80℃, and then the temperature was raised from room temperature to 170℃ at a rate of 2℃ / min, and the temperature was maintained until the gel point was reached, and the pressure was slowly increased to 4 MPa, and the temperature and pressure were maintained for 1.5 h, the hot press was closed, and the hot press was cooled to room temperature, and the hot press was opened, and the mold was removed, to obtain a hot melt type phenolic resin-based ablative composite material, which was recorded as HPDS-6-based ablative composite material.

[0106] Step 5, the carbon fiber cloth and the resin are recovered by a polar aprotic solvent dissolution-precipitation process, and the specific process is as follows:

[0107] Step 5.1, first, N,N-dimethylformamide and dimethyl sulfoxide are mixed according to a mass ratio of 19:1 to obtain a mixed solvent, then 1 part of HPDS-6-based ablative composite material is put into 200 parts of the mixed solvent, and the carbon fiber cloth surface is degraded under the protection of inert gas at 145°C for 10h, so as to separate the carbon fiber cloth and the resin solution;

[0108] Step 5.2, the carbon fiber cloth is washed with anhydrous ethanol to remove residual N,N-dimethylformamide and dimethyl sulfoxide, and is dried in a blast drying oven at 55°C to obtain regenerated carbon fiber cloth;

[0109] Step 5.3, N,N-dimethylformamide and dimethyl sulfoxide in the resin solution are removed by vacuum distillation at 100°C to obtain a concentrated resin solution, which is dried in a vacuum drying oven at 85°C to obtain regenerated phenolic resin degradation product.

[0110] 1), in order to verify the repairability of the HPDS-6-based ablative composite material prepared in Example 6, the HPDS-6-based ablative composite material with interlaminar damage and cracks is heated to 175°C, and the pressure is maintained at 2MPa for 1.5h, and it is found that the damage is completely repaired.

[0111] 2), according to the standard of GJB 323B-2018, the ablative performance of the HPDS-6-based ablative composite material is tested, and the mass ablation rate is 0.0263g / s.

[0112] Example 7

[0113] Step 1, 95 parts of 2-hydroxy-5-methyl-m-xylenediol, 5 parts of 2-hydroxy-1,3,5-benzene tri-methanol, 80 parts of 4,4'-dihydroxydiphenyl disulfide and 15 parts of 3,3'-dihydroxydiphenyl disulfide are added into a reaction kettle with condensation reflux device, and the temperature inside the reaction kettle is slowly reduced to 110°C under the protection of inert atmosphere, and the stirring is continued for 85min, and the reaction product is poured out and cooled to room temperature to obtain a uniform transparent hot melt type renewable phenolic resin, which is recorded as HPDS-7, and the number average molecular weight is 902g / mol, and the viscosity at 25°C is 8.7x10 4 Pa·s;

[0114] Step 2, the HPDS-7 is added into the double rollers of the hot melt pre-impregnation machine, heated to 65°C, and cast into a resin adhesive film, and a release paper is covered on the surface of the resin adhesive film to prevent adhesion, and then the resin adhesive film is wound to obtain a roll of resin adhesive film, which is stored in the refrigerator for standby use;

[0115] Step 3, stack the resin film with the carbon fiber cloth, pass through the roller at a roller temperature of 72℃ and a line speed of 1.5m / min, and then wind up to obtain a hot-melt phenolic resin prepreg;

[0116] Step 4, cut the hot-melt phenolic resin prepreg according to the required size and stack and lay up, place in a hot press, close the hot press, first heat to 80℃, then heat from room temperature to 180℃ at a heating rate of 2℃ / min, keep warm until the gel point is reached, slowly pressurize to 2MPa, keep warm and pressurized for 1.5h, turn off the hot press, wait for cooling to room temperature, open the hot press, demold, and obtain a hot-melt phenolic resin-based ablative composite material, recorded as HPDS-7-based ablative composite material;

[0117] Step 5, recover the carbon fiber cloth and resin by polar aprotic solvent dissolution-precipitation process, the specific process is as follows:

[0118] Step 5.1, first mix N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide according to a mass ratio of 16:3:1 to obtain a mixed solvent, then put 1 part of HPDS-7-based ablative composite material into 150 parts of mixed solvent under inert gas protection, heat at 145℃ for 8h to degrade the resin on the surface of the carbon fiber cloth, and separate the carbon fiber cloth and the resin solution;

[0119] Step 5.2, wash the carbon fiber cloth with anhydrous ethanol to remove residual N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, and dry in a blast drying oven at 55℃ to obtain regenerated carbon fiber cloth;

[0120] Step 5.3, remove N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide in the resin solution by vacuum distillation at 100℃ to obtain a concentrated resin solution, and dry in a vacuum drying oven at 85℃ to obtain regenerated phenolic resin degradation product.

[0121] 1), in order to verify the repairability of the HPDS-7-based ablative composite material prepared in Example 7, the HPDS-7-based ablative composite material with interlaminar damage and cracks was heated to 190℃ at a pressure of 2MPa for 0.5h, and it was found that the damage was completely repaired.

[0122] 2), according to the standard of GJB 323B-2018, the ablative performance of the HPDS-7-based ablative composite material was tested, and the mass ablation rate was 0.0285g / s.

[0123] Example 8

[0124] Step 1, according to parts by weight, 100 parts of 4-[2-[4-hydroxy-3,5-di(hydroxymethyl) phenyl] prop-2-yl]-2,6-di(hydroxymethyl) phenol and 140 parts of 4,4'- dihydroxydiphenyl disulfide are added to a reaction kettle with condensation reflux device, under the protection of inert atmosphere, stirred at 110°C until a uniform solution is formed, then the temperature inside the reaction kettle is slowly reduced to 95°C, continue to stir for 80 min, pour out the reaction product, cool to room temperature to obtain a uniform transparent hot melt renewable phenolic resin, recorded as HPDS-8, the number average molecular weight is 734 g / mol, the viscosity at 25°C is 6.3 x 10 4 Pa·s;

[0125] Step 2, HPDS-8 is added to the double roller of the hot melt pre-impregnation machine, heated to 60°C, cast into a resin film, and then covered with a release paper on the surface of the resin film to prevent adhesion, then wound to obtain a wound resin film, and stored in the freezer for standby;

[0126] Step 3, the resin film is laminated with glass fiber cloth, passed through the roller at a roller temperature of 70°C and a line speed of 2 m / min, and then wound to obtain a hot melt phenolic resin prepreg;

[0127] Step 4, the hot melt phenolic resin prepreg is cut according to the required size and stacked and laid up, placed in a hot press, the hot press is closed, first heated to 80°C, then heated from room temperature to 160°C at a heating rate of 3°C / min, kept at the gel point, slowly pressurized to 2 MPa, kept for 3 h, the hot press is closed, cooled to room temperature, the hot press is opened, demolded to obtain a hot melt phenolic resin-based ablative composite material, recorded as HPDS-8-based ablative composite material;

[0128] Step 5, the glass fiber cloth and the resin are recovered by polar aprotic solvent dissolution-precipitation process, the specific process is as follows:

[0129] Step 5.1, first, according to the mass ratio of 18:1:1, N,N-dimethylformamide, N,N- diethylformamide and N,N-dimethylacetamide are mixed to obtain a mixed solvent, then 1 part of HPDS-8-based ablative composite material is put into 80 parts of mixed solvent, heated at 135°C for 6 h under the protection of inert gas, so that the resin on the surface of the glass fiber cloth is degraded, and the glass fiber cloth and the resin solution are separated;

[0130] Step 5.2, the glass fiber cloth is washed with anhydrous ethanol to remove residual N,N- dimethylformamide, N,N-diethylformamide and N,N-dimethylacetamide, and dried in a blast oven at 55°C to obtain regenerated glass fiber cloth;

[0131] Step 5.3, remove N,N-dimethylformamide, N,N-diethylformamide and N,N-dimethylacetamide in the resin solution by distillation under reduced pressure at 90℃ to obtain a concentrated resin solution, and dry in a vacuum drying oven at 85℃ to obtain the regenerated phenolic resin degradation product.

[0132] 1) In order to verify the repairability of the HPDS-8 based ablative composite material prepared in Example 8, the HPDS-8 based ablative composite material with interlaminar damage and cracks was heated to 165℃, and the pressure was 2MPa, and the pressure was maintained for 0.5h, and it was found that the damage was completely repaired.

[0133] 2) The HPDS-8 resin prepared in Example 8 was subjected to a thermal gravimetric (TGA) test, and the carbon yield at 800℃ was 60.9%, indicating that it can be used as a matrix for ablative composite materials.

[0134] 3) According to the GJB 323B-2018 standard, the ablative performance of the HPDS-8 based ablative composite material was tested, and the mass ablation rate was 0.0604g / s.

Claims

1. A method for producing a hot-melt renewable phenol-aldehyde resin, characterized by, The method comprises the following steps: adding 100 parts of a polyhydroxymethyl phenolic compound and 50-140 parts of a dithiol compound into a reaction kettle according to weight parts, stirring sufficiently under the protection of inert gas at 110-130 DEG C until the materials are uniformly mixed, then reducing the temperature inside the reaction kettle to 95-110 DEG C, continuously stirring for 80-100 min, and cooling to room temperature to obtain a uniform and transparent hot-melt renewable phenolic resin.

2. The method of claim 1, wherein the renewable phenol-formaldehyde resin is a hot-melt type. The polyhydroxymethyl phenolic compound is at least one of 2-hydroxy-5-methyl resorcinol, 4-[2-[4-hydroxy-3,5-di(hydroxymethyl)phenyl]propan-2-yl]-2,6-di(hydroxymethyl)phenol, (5-hydroxy-1,3-phenylene)dimethanol and 2-hydroxy-1,3,5-benzenetriol. ​ 3. The method of claim 1, wherein the renewable phenol-formaldehyde resin is a hot-melt type. The dithiol compound is at least one of 4,4'-dihydroxydiphenyl disulfide and 3,3'-dihydroxydiphenyl disulfide. ​ 4. A hot-melt renewable phenol-formaldehyde resin prepared by the method according to any one of claims 1 to 3, characterized in that, a number average molecular weight of 600 to 1000 g / mol, a viscosity at 25°C of 10 4 to 10 5 Pa s, a gel time at 165°C of 20 to 30 min.

5. A method for preparing a hot-melt renewable phenol-formaldehyde resin-based ablative-resistant composite material using the hot-melt renewable phenol-formaldehyde resin according to claim 4, characterized in that, The method comprises the following steps: Step 1, heating the hot-melt renewable phenolic resin to 60-75 DEG C, casting into a resin adhesive film with a thickness of 65-75 mu m, covering a release paper on the surface of the resin adhesive film to prevent adhesion, and then winding to obtain a wound resin adhesive film, which is stored in a refrigerator for standby; Step 2, laminating the resin adhesive film with a continuous fiber reinforcement, passing through a roller at a roller temperature of 70-80 DEG C and a line speed of 1-3 m / min, and then winding to obtain a hot-melt phenolic resin prepreg; Step 3, cutting and laminating the hot-melt phenolic resin prepreg according to the required size, placing in a hot press, heating to 80 DEG C, then heating from room temperature to 160-180 DEG C at a heating rate of 1-3 DEG C / min, keeping warm until the gel point is reached, pressurizing to 2-4 MPa, keeping warm and pressurizing for 1.5-3 h, cooling to room temperature, demolding, and obtaining a hot-melt phenolic resin-based ablative-resistant composite material.

6. The method of claim 5, wherein the method is characterized by, The fiber reinforcement of step 2 is a carbon fiber cloth or a glass fiber cloth.

7. A hot-melt renewable phenol-formaldehyde resin based ablative composite material prepared according to the method of claim 5, characterized in that, The mass ablation rate is 0.0263-0.0604 g / s.

8. The hot-melt renewable phenol-formaldehyde resin-based ablative-resistant composite material according to claim 7, characterized in that, The interlayer damage or crack can be repaired by a hot pressing process, wherein the hot pressing process is carried out at 165-220 DEG C under a pressure of 2-4 MPa for 0.5-3 h.

9. A method for recycling the hot-melt renewable phenolic resin-based ablative composite material according to claim 7, characterized in that, The fiber reinforcement and the resin are recovered by a polar aprotic solvent dissolution-precipitation process, which comprises the following steps: S1, according to weight parts, 1 part of the hot-melt renewable phenolic resin-based ablative-resistant composite material is put into 10-200 parts of a polar aprotic solvent, heated at 130-150 DEG C for 6-48 h under the protection of inert gas, the resin on the surface of the fiber reinforcement is degraded, and the fiber reinforcement and the resin solution are separated; S2, the fiber reinforcement is washed with anhydrous ethanol to remove the residual polar aprotic solvent, dried, and the regenerated fiber reinforcement is obtained; S3, the polar aprotic solvent in the resin solution is removed by vacuum distillation to obtain a concentrated resin solution, which is dried under vacuum to obtain a regenerated phenolic resin degradation product.

10. The method of claim 9, wherein the recycled thermoset renewable phenolic ablative composite material is characterized by, The polar aprotic solvent is at least one of N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

Images