Preparation and recovery method of tough recyclable phenolic resin-based bamboo-plastic composite material

Abstract

The invention belongs to the technical field of polymer composite materials, and relates to a preparation and recovery method of a tough recyclable phenolic resin-based bamboo-plastic composite material. The preparation method comprises the following steps: mixing 100 parts by weight of thermoplastic phenolic resin, 10-50 parts by weight of raw materials for dynamic covalent bond construction, 1-10 parts by weight of a curing agent and 100-200 parts by weight of an organic solvent, heating, sealing and stirring until the materials are dissolved, and uniformly mixing to obtain a recyclable phenolic resin solution; uniformly stirring 100 parts by weight of recoverable phenolic resin solution and 10-100 parts by weight of bamboo powder to prepare a resin-bamboo powder blending material, heating to recover the organic solvent, drying to a constant weight, crushing and sieving to obtain a composite material mould pressing raw material; and carrying out a hot-pressing curing process on the composite material mould pressing raw material to obtain the tough recyclable phenolic resin-based bamboo-plastic composite material. The problems that a traditional phenolic resin material is high in brittleness and difficult to recycle after being cured are solved.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, and specifically relates to a method for preparing and recycling a strong and recyclable phenolic resin-based bamboo-plastic composite material. Background Technology

[0002] Phenolic resin, as one of the earliest industrially synthesized resins, is widely used in aerospace, transportation, construction, wood processing, and molding compounds due to its excellent mechanical strength, durability, temperature resistance, corrosion resistance, and flame retardancy. However, phenolic resin suffers from two major problems during application: high brittleness and non-recyclability. High brittleness mainly stems from the highly cross-linked three-dimensional network structure formed after curing traditional phenolic resin; while non-recyclability arises from the fact that this highly cross-linked network structure is a covalent network, which is irreversible. High brittleness makes phenolic resin extremely susceptible to damage upon impact, thus limiting its application scenarios and safety. The stable structure of traditional phenolic resin after curing makes it difficult to recycle and reuse like thermoplastics after disposal. Incineration or landfill disposal results in significant resource waste and environmental pollution. Therefore, developing recyclable phenolic resin materials with good toughness has significant practical value.

[0003] To improve the toughness of phenolic resins, there are generally two main methods: chemical copolymerization and physical blending. CN113637286A introduces toughening agents such as hydroxyl POSS into the phenolic resin matrix, thereby improving the toughness of phenolic resin-based composite materials. However, this method is prone to insufficient bonding between the toughening agent and the phenolic resin matrix, thus affecting the mechanical properties of the material. CN115873544A utilizes benzoic acid to modify the abundant carboxyl groups on the surface of nano-SiO2, which interact with the hydroxyl groups of the phenolic resin to form a three-dimensional network structure. At the same time, some modified phenol with toughening chains is added to synthesize phenolic resin, improving the mobility and flexibility of the network chain molecules, which greatly improves the toughness of the phenolic resin. However, this toughening method, which adjusts the cross-linking structure through chemical reactions, requires high precision in optimizing the formulation and process adjustment. In the recycling and reuse of phenolic resin, the mainstream methods include physical and chemical methods. Physical methods involve mechanically processing the cured resin and composite materials to destroy them. However, the products obtained by this method are irreversible and destructive to the properties and structure of the materials themselves. Moreover, the recycled products can only be used as filler mixtures and cannot achieve complete recycling. Chemical methods involve treating the materials through pyrolysis, solvents, etc., to obtain various monomers for the synthesis of new materials. However, the structure of cured phenolic resin is extremely stable, and it is not easy to depolymerize it through pyrolysis or solvents. Special high-temperature pyrolysis equipment or solvents are usually required in the laboratory, making it difficult to put it into actual production.

[0004] Therefore, it is very important to develop a tough and recyclable phenolic resin-based composite material that can solve the problems of high brittleness and difficulty in recycling of traditional phenolic resin-based composite materials after curing, which easily leads to impact damage and waste of resources and environmental pollution. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing and recycling a strong and recyclable phenolic resin-based bamboo-plastic composite material. This method solves the problems of traditional phenolic resin-based bamboo-plastic composite materials being brittle after curing, difficult to recycle, easily causing impact damage to the composite material, and resulting in resource waste and environmental pollution.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a strong, recyclable phenolic resin-based bamboo-plastic composite material, comprising the following steps: 100 parts by weight of thermoplastic phenolic resin, 10-50 parts by weight of raw material for dynamic covalent bond construction, 1-10 parts by weight of curing agent, 100-200 parts by weight of organic solvent and 1-5 parts by weight of catalyst are mixed, heated and sealed and stirred until dissolved, and after uniform mixing, a phenolic resin mixed solution is obtained, wherein the thermoplastic phenolic resin is ordinary thermoplastic phenolic resin. 100 parts by weight of phenolic resin mixed solution are mixed with 10 to 100 parts by weight of bamboo powder to make resin-bamboo powder blend. The organic solvent is recovered by heating, dried to constant weight, and crushed and sieved to obtain composite molding raw material. A strong and recyclable phenolic resin-based bamboo-plastic composite material is prepared by hot pressing of the composite molding raw material.

[0007] Preferably, the hot pressing process preparation steps are as follows: The composite molding raw material is preheated at 100℃~120℃ for 10min~30min; then hot-pressed at 1MPa~5MPa and 120℃~150℃ for 30min~60min; and then hot-pressed again at 150℃~200℃ and 5MPa~20MPa for 1h~3h. Heating is then stopped, and the material is held under pressure and cooled to room temperature to obtain a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material. Only through hot pressing can a composite material with superior strength and toughness be prepared.

[0008] Preferably, the heating temperature for preparing the phenolic resin mixed solution and the heating temperature for preparing the composite molding raw material are both 50℃~70℃.

[0009] Preferably, the raw material for constructing the dynamic covalent bond is one of phenylboronic acid, tris(ethylene glycol)divinyl ether, toluene diisocyanate, polyetheramine, or thioctic acid. This is used to construct different types of dynamic covalent bonds with ordinary thermoplastic phenolic resins, such as borate bonds, acetal bonds, urethane bonds, imine bonds, disulfide bonds, etc.

[0010] Preferably, the curing agent is hexamethylenetetramine; the catalyst is one of triethylamine, p-toluenesulfonic acid, tin octoate, glacial acetic acid, or dibutyltin dilaurate.

[0011] Preferably, the organic solvent is one of ethanol, ethyl acetate, acetone, or tetrahydrofuran. The organic solvents given herein facilitate the dissolution of thermoplastic phenolic resins and raw materials for constructing dynamic covalent bonds.

[0012] This invention provides a method for preparing a strong and recyclable phenolic resin-based bamboo-plastic composite material.

[0013] This invention provides a method for recycling a strong and recyclable phenolic resin-based bamboo-plastic composite material, comprising the following steps: 100 parts by weight of pulverized tough and recyclable phenolic resin-based bamboo-plastic composite material are mixed with 200-500 parts by weight of recycled solvent. The mixture is heated and stirred in a sealed manner at 50℃-90℃ until the tough and recyclable phenolic resin-based bamboo-plastic composite material is fully dissolved or no longer dissolves. Then, the solvent is removed and recycled at the same temperature to obtain pre-recycled material with solvent removed. The pre-recycled material is then vacuum dried at 50℃-70℃ to obtain solid block recycled material. After crushing the solid block recycled material, a composite molding raw material that can be used for secondary molding is obtained.

[0014] Preferably, the recovered solvent is one of ethanol, ethyl acetate, acetone or tetrahydrofuran.

[0015] This invention provides applications of strong and recyclable phenolic resin-based bamboo-plastic composites in aerospace, transportation, construction, wood processing, and molding compounds.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: Compared to traditional phenolic resins primarily based on covalent crosslinking, this invention adds a curing agent, raw materials for dynamic covalent bond construction, and a catalyst to thermoplastic phenolic resin. Under the action of the curing agent, a covalent crosslinking network is obtained; under the catalytic action of the catalyst, a dynamic covalent bond network is constructed. Based on this, bamboo materials are blended and composited with the resin, and then hot-pressed to prepare a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material. This phenolic resin-based bamboo-plastic composite material is constructed using a dynamic covalent bond and a synergistic covalent bond crosslinking mechanism, enabling it to break and reassemble under specific stimulus-response conditions, thus achieving the recyclability of phenolic resin. Simultaneously, by adding bamboo materials to partially replace phenolic resin, not only can the mechanical strength and toughness of the phenolic resin be improved, but production costs can also be reduced. Replacing plastic with bamboo extends the service life and carbon fixation cycle of the composite material, reducing plastic pollution.

[0017] Furthermore, the phenolic resin-based bamboo-plastic composite material prepared by this invention is constructed by dynamic covalent bonds and covalent bond synergistic crosslinking. The dynamic covalent bonds can break and recombine under specific stimulus response conditions (solvent, temperature, alkaline environment, acid environment, etc.), and the recycling process is simple. Some covalent bonds are still retained. Therefore, the composite material prepared in the second stage still has excellent mechanical properties. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation and recycling process of a strong, recyclable phenolic resin-based bamboo-plastic composite material developed based on dynamic covalent bonds, according to the present invention.

[0019] Figure 2 These are infrared spectra of bamboo-plastic composite samples based on different phenolic resins, where NR represents pure phenolic resin; H5.5B60NR represents the non-recyclable phenolic resin bamboo-plastic composite prepared in Comparative Example 1; and P15H5.5B60NR represents the recyclable phenolic resin bamboo-plastic composite prepared in Example 1 based on borate ester modification.

[0020] Figure 3 This describes the dissolution and recovery of phenolic resin-based bamboo-plastic composite materials in solution in Comparative Example 1 and Examples 1-5.

[0021] Figure 4 These are actual images of the original hot-pressed samples and recycled samples of Comparative Example 1 and Examples 1 to 5 of phenolic resin-based bamboo-plastic composite materials. Detailed Implementation

[0022] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0023] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in Examples 1 to 15, preferred embodiments are described to avoid redundancy. However, this invention is not limited to these embodiments and can be implemented in other ways within the scope of the technical solutions defined in the appended claims. All raw materials, reagents, instruments, and equipment used in the following embodiments of this invention can be purchased commercially or prepared using existing methods.

[0024] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Example 1 A method for preparing a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: Preparation of molding raw materials: 100g of thermoplastic phenolic resin (NR), 15g of phenylboronic acid (PBA), 5.5g of hexamethylenetetramine (HTMA), and 2g of triethylamine were mixed with 100g of anhydrous ethanol. The mixture was sealed and stirred at 60℃ to dissolve the resin, and the solution was homogeneous to obtain a recyclable phenolic resin solution. 40g of bamboo powder was added to 100g of the recyclable phenolic resin solution and stirred until homogeneous to prepare a resin-bamboo powder blend. The ethanol solvent in the blend was then removed by stirring under a 60℃ water bath and condensed for recovery. Subsequently, the sample was dried to constant weight in a vacuum oven at 60℃. The resulting solid sample was pulverized and passed through a 100-mesh sieve to obtain the composite molding raw material.

[0026] 2) Hot pressing Take 50g of composite molding material and spread it evenly in a steel mold. Preheat at 110℃ for 20min; then pre-press at 130℃ and 3MPa for 40min; finally cure at 180℃ and 15MPa for 2h. After holding the pressure and cooling, demold to produce a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material.

[0027] A method for recycling a strong and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: The recovered, tough, recyclable phenolic resin-based bamboo-plastic composite material was pulverized. Using ethanol solution as the recovery solution, 100g of the pulverized material was mixed with 300g of ethanol solution. The mixture was stirred at 600 rpm in a sealed container at 60°C for 12 hours until the phenolic resin powder was fully dissolved or stopped dissolving. After thorough mixing, the solvent was further removed and recovered at 60°C. The remaining sample was then vacuum-dried at 60°C to remove the remaining solvent. The resulting material was pulverized to obtain the recycled composite material raw material. The same molding process was then used to prepare the tough, recyclable phenolic resin-based bamboo-plastic composite material, defined as Recycling Example 1. The preparation and recycling process is as follows: Figure 1 As shown, the dissolution of the comparative and example samples is as follows: Figure 3 As shown, macroscopic photographs of the samples formed by one-time hot pressing and two-time hot pressing are as follows. Figure 4 As shown.

[0028] Example 2 A method for preparing a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: Preparation of molding raw materials: 100g of thermoplastic phenolic resin (NR), 15g of phenylboronic acid (PBA), 2.5g of hexamethylenetetramine (HTMA), and 2g of triethylamine were mixed with 100g of anhydrous ethanol. The mixture was sealed and stirred at 60℃ to dissolve the resin, and the solution was homogeneous to obtain a recyclable phenolic resin solution. 40g of bamboo powder was added to 100g of the recyclable phenolic resin solution and stirred until homogeneous to prepare a resin-bamboo powder blend. The ethanol solvent in the blend was then removed by stirring under a 60℃ water bath and condensed for recovery. Subsequently, the sample was dried to constant weight in a vacuum oven at 60℃. The resulting solid sample was pulverized and passed through a 100-mesh sieve to obtain the composite molding raw material.

[0029] 2) Hot pressing Take 50g of composite molding material and spread it evenly in a steel mold. Preheat at 110℃ for 20min; then pre-press at 130℃ and 3MPa for 40min; finally cure at 180℃ and 15MPa for 2h. After holding the pressure and cooling, demold to produce a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material.

[0030] A method for recycling a strong and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: The recovered, tough, recyclable phenolic resin-based bamboo-plastic composite material was pulverized. Using ethanol solution as the recovery solution, 100g of the pulverized material was mixed with 300g of ethanol solution and stirred at 60°C for 12 hours at 600 rpm until the phenolic resin powder was fully dissolved or stopped dissolving. The mixture was then stirred until homogeneous, and then further stirred at 60°C to remove and recover some of the solvent. The remaining sample was then vacuum-dried at 60°C to remove the remaining solvent, pulverized, and the recovered composite material raw material was obtained. The same molding process was then used to prepare the tough, recyclable phenolic resin-based bamboo-plastic composite material, defined as Recycling Example 2. The preparation and recycling process is as follows: Figure 1 As shown, the dissolution of the comparative and example samples is as follows: Figure 3 As shown, macroscopic photographs of the samples formed by one-time hot pressing and two-time hot pressing are as follows. Figure 4 As shown.

[0031] Example 3 A method for preparing a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: Preparation of molding raw materials: 100g of thermoplastic phenolic resin (NR), 20g of phenylboronic acid (PBA), 5.5g of hexamethylenetetramine (HTMA), and 2g of triethylamine were mixed with 100g of anhydrous ethanol. The mixture was sealed and stirred at 60℃ to dissolve the resin, and a recyclable phenolic resin solution was obtained. 40g of bamboo powder was added to 100g of the recyclable phenolic resin solution and stirred evenly to prepare a resin-bamboo powder blend. The ethanol solvent in the blend was then removed by stirring under a 60℃ water bath and condensed for recovery. Subsequently, the sample was dried to constant weight in a vacuum oven at 60℃. The resulting solid sample was pulverized and passed through a 100-mesh sieve to obtain the composite molding raw material.

[0032] 2) Hot pressing Take 50g of powder and spread it evenly in a steel mold. Preheat at 110℃ for 20min; then pre-press at 130℃ and 3MPa for 40min; finally cure at 180℃ and 15MPa for 2h. After holding the pressure and cooling, demold to produce a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material.

[0033] A method for recycling a strong and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: The recovered, tough, recyclable phenolic resin-based bamboo-plastic composite material was pulverized. Using ethanol solution as the recovery solution, 100g of the pulverized material was mixed with 300g of ethanol solution and stirred at 60°C for 12 hours at 600 rpm until the phenolic resin powder was fully dissolved or stopped dissolving. The mixture was then stirred until homogeneous, and then further stirred at 60°C to remove and recover some of the solvent. The remaining sample was then vacuum-dried at 60°C to remove the remaining solvent, pulverized, and the recovered composite material raw material was obtained. The same molding process was then used to prepare the tough, recyclable phenolic resin-based bamboo-plastic composite material, defined as Recovery Example 3. The preparation and recovery process is as follows: Figure 1 As shown, the dissolution of the comparative and example samples is as follows: Figure 3 As shown, macroscopic photographs of the samples formed by one-time hot pressing and two-time hot pressing are as follows. Figure 4 As shown.

[0034] Example 4 A method for preparing a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: (1) Preparation of molding raw materials 100g of thermoplastic phenolic resin (NR), 15g of toluene diisocyanate (TDI), 5.5g of hexamethylenetetramine (HTMA), and 2g of tin octoate were mixed with 100g of acetone and stirred under nitrogen at 60°C until dissolved and homogeneous, yielding a recyclable phenolic resin solution. 40g of bamboo powder was added to 100g of the recyclable phenolic resin solution and stirred until homogeneous, forming a resin-bamboo powder blend. The blend was then stirred under a 60°C water bath to remove the ethanol solvent, which was then condensed and recovered. Subsequently, the sample was dried to constant weight in a vacuum oven at 60°C. The resulting solid sample was pulverized and passed through a 100-mesh sieve to obtain the composite molding raw material.

[0035] 2) Hot pressing Take 50g of composite molding material and spread it evenly in a steel mold. Preheat at 110℃ for 20min; then pre-press at 130℃ and 3MPa for 40min; finally cure at 180℃ and 15MPa for 2h. After holding the pressure and cooling, demold to produce a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material.

[0036] A method for recycling a strong and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: The recovered, tough, recyclable phenolic resin-based bamboo-plastic composite material was pulverized. Using ethanol solution as the recovery solution, 100g of the pulverized material was mixed with 300g of ethanol solution and stirred at 60°C for 12 hours at 600 rpm until the phenolic resin powder was fully dissolved or no longer dissolved. The mixture was then stirred until homogeneous, and then further stirred at 60°C to remove and recover some of the solvent. The remaining sample was then vacuum-dried at 60°C to remove the remaining solvent, pulverized, and the recovered composite material raw material was obtained. The same molding process was then used to prepare the tough, recyclable phenolic resin-based bamboo-plastic composite material, defined as Recovery Example 4. The preparation and recovery process is as follows: Figure 1 As shown, the dissolution of the comparative and example samples is as follows: Figure 3 As shown, macroscopic photographs of the samples formed by one-time hot pressing and two-time hot pressing are as follows. Figure 4 As shown.

[0037] Example 5 A method for preparing a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: Preparation of molding raw materials: 100g of thermoplastic phenolic resin (NR), 15g of tris(ethylene glycol)divinyl ether (TEGDVE), 5.5g of hexamethylenetetramine (HTMA), and 2g of p-toluenesulfonic acid were mixed with 100g of anhydrous ethanol. The mixture was sealed and stirred at 60℃ to dissolve the ethanol. Once homogeneous, a recyclable phenolic resin solution was obtained. 40g of bamboo powder was added to the recyclable phenolic resin solution and stirred until homogeneous to prepare a resin-bamboo powder blend. The ethanol solvent in the blend was then removed by stirring in a 60℃ water bath and condensed for recovery. Subsequently, the sample was dried to constant weight in a vacuum oven at 60℃. The resulting solid sample was pulverized and passed through a 100-mesh sieve to obtain the composite molding raw material.

[0038] 2) Hot pressing Take 50g of composite molding material and spread it evenly in a steel mold. Preheat at 110℃ for 20min; then pre-press at 130℃ and 3MPa for 40min; finally cure at 180℃ and 15MPa for 2h. After holding the pressure and cooling, demold to produce a strong, tough, and recyclable phenolic resin-based bamboo-plastic composite material.

[0039] A method for recycling a strong and recyclable phenolic resin-based bamboo-plastic composite material includes the following steps: The recovered, tough, recyclable phenolic resin-based bamboo-plastic composite material was pulverized. Using ethanol solution as the recovery solution, 100g of the recovered bamboo-plastic composite powder was mixed with 300g of ethanol solution. The mixture was stirred at 600 rpm at 60°C for 12 hours in a sealed container until the phenolic resin powder was fully dissolved or no longer dissolved. After thorough stirring, the mixture was further stirred at 60°C to remove and recover some of the solvent. The remaining sample was then vacuum-dried at 60°C to remove the remaining solvent. The resulting material was pulverized to obtain the recovered composite raw material. The same molding process was then used to prepare the tough, recyclable phenolic resin-based bamboo-plastic composite material, defined as Recovery Example 5. The preparation and recovery process is as follows: Figure 1 As shown, the dissolution of the comparative and example samples is as follows: Figure 3 As shown, macroscopic photographs of the samples formed by one-time hot pressing and two-time hot pressing are as follows. Figure 4 As shown.

[0040] Example 6 The difference between Example 6 and Example 1 is that the amount of phenylboronic acid is changed to 10g, the amount of hexamethylenetetramine (HTMA) is changed to 1g, the amount of triethylamine is changed to 1g, and the amount of anhydrous ethanol is changed to 200g, while the other steps and parameters remain unchanged.

[0041] Example 7 The difference between Example 7 and Example 1 is that the amount of phenylboronic acid is changed to 50g, the amount of hexamethylenetetramine is changed to 10g, the amount of triethylamine is changed to 5g, and the amount of anhydrous ethanol is changed to 150g, while the other steps and parameters remain unchanged.

[0042] Example 8 The difference between Example 8 and Example 1 is that phenylboronic acid is replaced with lipoic acid, anhydrous ethanol is replaced with ethyl acetate, and triethylamine is replaced with dibutyltin dilaurate, while the other steps and parameters remain unchanged.

[0043] Example 9 The difference between Example 9 and Example 1 is that the amount of bamboo powder added is changed to 10g, while the other steps and parameters remain the same.

[0044] Example 10 The difference between Example 10 and Example 1 is that the amount of bamboo powder added is changed to 100g, while the other steps and parameters remain the same.

[0045] Example 11 The difference between Example 11 and Example 1 is that the hot pressing process curing step is changed, while the other steps and parameters remain the same.

[0046] 50g of powder is spread evenly in a steel mold and heated at 100℃ for 10 minutes to obtain a pre-treated composite material for molding. Then, it is hot-pressed at 120℃ and 1MPa for 30 minutes. Finally, it is hot-pressed at 150℃ and 5MPa for 1 hour, and after holding the pressure and cooling, it is demolded to produce a strong and recyclable phenolic resin-based bamboo-plastic composite material.

[0047] Example 12 The difference between Example 12 and Example 1 is that the hot pressing process curing step is changed, while the other steps and parameters remain the same.

[0048] 50g of powder was spread evenly in a steel mold and heated at 120℃ for 30 minutes. Then it was hot-pressed at 150℃ and 5MPa for 60 minutes. Finally, it was hot-pressed at 200℃ and 20MPa for 3 hours. After holding the pressure and cooling, it was demolded to produce a strong and recyclable phenolic resin-based bamboo-plastic composite material.

[0049] Example 13 The difference between Example 13 and Example 1 is that the 300g ethanol solution in the recycling method of the tough and recyclable phenolic resin-based bamboo-plastic composite material is replaced with 200g acetone, the temperature of sealed heating is replaced with 50°C, and the temperature of vacuum drying is replaced with 50°C. The remaining steps and parameters remain unchanged.

[0050] Example 14 The difference between Example 14 and Example 1 is that the 300g ethanol solution in the recycling method of the tough and recyclable phenolic resin-based bamboo-plastic composite material is replaced with a mixed solution of 500g acetone and anhydrous ethanol, the temperature of sealed heating is replaced with 90°C, and the temperature of vacuum drying is replaced with 70°C. The remaining steps and parameters remain unchanged.

[0051] Example 15 The difference between Example 15 and Example 1 is that phenylboronic acid is replaced with polyetheramine, anhydrous ethanol is replaced with ethyl acetate, and triethylamine is replaced with glacial acetic acid, while the other steps and parameters remain unchanged.

[0052] Comparative Example The difference between the comparative example and Example 1 is that 15g of phenylboronic acid was not added.

[0053] A method for preparing a phenolic resin-based bamboo-plastic composite material includes the following steps: (1) Preparation of ordinary phenolic resin-based bamboo-plastic composite materials Preparation of molding raw materials: 100g of anhydrous ethanol was added to 100g of phenolic resin and 5.5g of hexamethylenetetramine (HTMA), and the mixture was sealed and stirred at 60℃ to dissolve and obtain a phenolic resin solution. 40g of bamboo powder was added to this phenolic resin solution and stirred until homogeneous to prepare a resin-bamboo powder blend. The ethanol solvent in the blend was then removed by stirring in a 60℃ water bath and condensed for recovery. Subsequently, the sample was dried to constant weight in a vacuum oven at 60℃. The resulting solid sample was then pulverized and passed through a 100-mesh sieve to obtain the composite molding raw material.

[0054] (2) Hot pressing Take 50g of powder and spread it evenly in a steel mold. Heat it at 110℃ for 20min. Then pre-cur it at 3MPa pressure and 130℃ under a gradient temperature increase for 40min. Finally, hot-press it at 15MPa pressure and 180℃ for 2h. Stop heating but maintain pressure. Wait for the sample to cool to room temperature with the mold before unloading to make phenolic resin-based bamboo-plastic composite material.

[0055] A method for recycling phenolic resin-based bamboo-plastic composite materials includes the following steps: The recycled phenolic resin-based bamboo-plastic composite waste was pulverized. Using ethanol solution as the recycling solution, 100g of recycled bamboo-plastic composite powder was mixed with 300g of ethanol solution and stirred at 600r / min at 60℃ for 12h in a sealed environment until the phenolic resin powder was fully dissolved or no longer dissolved. After stirring evenly, the solvent was removed and recovered by continuing to stir at 60℃. Subsequently, the remaining sample was vacuum dried at 60℃ to remove the remaining solvent, and then pulverized to obtain the recycled composite material raw material. Phenolic resin-based bamboo-plastic composite materials were then prepared using the same molding process. This was defined as a recycling comparative example.

[0056] All of the examples 1 to 15 described above can prepare strong and recyclable phenolic resin-based bamboo-plastic composite materials. The performance of the preferred strong and recyclable phenolic resin-based bamboo-plastic composite materials prepared in Examples 1 to 5 and the comparative examples is then verified.

[0057] Experimental verification (2) Mechanical properties In accordance with standard GB / T29418-2023, tensile strength, three-point bending strength and impact toughness tests were conducted on the molded specimens of phenolic resin-based bamboo-plastic composite materials of Comparative Example 1, Examples 1 to 5 and Recycled Examples 1 to 5. The results are shown in Table 1.

[0058] Table 1 Mechanical properties of molded specimens of phenolic resin-based bamboo-plastic composite material As shown in Table 1, the phenolic resin composite material pressed in the comparative example could not be dissolved because no dynamic covalent crosslinking agent was added. In contrast, the strong, recyclable phenolic resin-based bamboo-plastic composite materials prepared in Examples 1-5 could be dissolved. Figure 3 As shown, the phenolic resin-based bamboo-plastic composite materials prepared in Examples 1-5 of this invention did not form complete covalent cross-links, thus they could dissolve in solvents and undergo breakage and recombination. In contrast, the phenolic resin-based bamboo-plastic composite materials prepared in the comparative examples formed complete covalent cross-links and could not undergo breakage, recombination, or dissolution. The comparative examples could not be recycled after crushing, nor could they be pressed into complete composite materials. However, the strong and recyclable phenolic resin-based bamboo-plastic composite materials prepared in Examples 1-5 could not only be recycled after crushing, but also be pressed into complete composite materials, such as… Figure 4 As shown, the strength of the recycled composite material prepared in the comparative example is 0. The strengths of the composite material samples and their recycled samples prepared after adding a modifier capable of constructing dynamic covalent bonds are shown in Table 1. Table 1 shows that the molded specimen prepared from the phenolic resin-based bamboo-plastic composite material in Example 1 exhibits the best comprehensive mechanical properties, with tensile strength, flexural strength, and impact toughness of 26.4 MPa, 84.8 MPa, and 3.6 KJ / m², respectively. 2 Compared to the comparative example, the tensile strength, flexural strength, and impact toughness of the composite material increased by 27.5%, 28.9%, and 56.5%, respectively, demonstrating a significant improvement in overall mechanical properties and toughening effect. The mechanical properties of the one-time molded specimens from Examples 2 to 4 were all superior to the comparative example, especially the impact toughness, which showed a significant improvement of up to 56.5%, indicating that the introduction of dynamic covalent bonds can effectively improve the mechanical properties of the composite material. Furthermore, the introduction of dynamic covalent bond modification also endowed the phenolic resin-based bamboo-plastic composite material with good recyclability. Therefore, it is proven that Examples 1 to 5 can all be successfully recycled and remolded, while the traditional phenolic resin bamboo-plastic composite material prepared in the comparative example cannot be recycled. Example 2 showed the highest performance retention rate after recycling, with secondary recycled tensile strength, flexural strength, and impact toughness of 17.9 MPa, 53.1 MPa, and 2.6 KJ / m, respectively. 2 Compared to Example 2 before recycling, the strength decreased by only 12.5%, 11.7%, and 10.7%, respectively, which is not significant. The relevant properties of the other examples and recycling examples vary due to the different amounts and types of modifiers added. Therefore, by adjusting the amount and type of modifier and the dynamic covalent bond ratio, the mechanical strength of the phenolic resin-based bamboo-plastic composite material can be guaranteed while achieving its recyclability, demonstrating the effectiveness and inventiveness of this invention in solving the problems of brittleness and non-recyclability of phenolic resin.

[0059] The factors affecting the mechanical properties of the strong and recyclable phenolic resin-based bamboo-plastic composites prepared in Examples 1 to 5 were analyzed: (1) The irreversible crosslinking formed by the traditional curing agent HTMA during the curing process of phenolic resin (comparative example) is the main source of the material's mechanical strength, but its high crosslinking density results in insufficient toughness; (2) After introducing different dynamic covalent bonds into the phenolic resin crosslinking network, this type of dynamic covalent crosslinking significantly improves the toughness of the material, but compared with the phenolic resin cured by pure HTMA (comparative example), its mechanical properties are somewhat lost; (3) Bamboo powder, as a component of the composite material, also affects the mechanical properties of the mechanical specimens. In the phenolic resin crosslinking network with a reasonable ratio, the appropriate amount of bamboo powder added as a second phase evenly distributed in the composite material can make the material have better toughness.

[0060] (3) Structural confirmation Figure 2 Infrared spectra of phenolic resin, the strong and recyclable phenolic resin-based bamboo-plastic composite material prepared in Example 1, and the comparative phenolic resin-based bamboo-plastic composite material (comparative sample) were obtained. The interaction between the strong and recyclable phenolic resin-based bamboo-plastic composite material prepared by dynamic covalent bonding and covalent bond synergistic crosslinking was further verified. As shown in the figure, the comparative sample used HTMA as a curing agent, and the 1440 cm⁻¹... -1 CH bending vibration peak at 2850 cm⁻¹ -1 ~2950cm -1 The CH stretching vibration peak in the region was significantly enhanced, indicating that irreversible methylene bridging bonds were formed during the curing reaction. This is the main reason why phenolic resin-based bamboo-plastic composites are difficult to recycle. In Example 1, PBA was used as a modifier. The esterification reaction between PBA and phenolic resin consumed some of the free phenolic hydroxyl groups, resulting in a peak at 3300 cm⁻¹. -1 The intensity of the hydroxyl peak decreased and the peak width narrowed, while PBA itself was 1150 cm⁻¹. -1 The peak at 1340 cm⁻¹, attributed to the β-OH bending vibration, weakened due to reaction consumption. -1 The appearance of newly generated BOC (boronic acid ester bond) stretching vibration peak indicates that the dynamic covalent bond of borate ester was successfully introduced into the phenolic resin, thereby adjusting the irreversible crosslinking density in the resin crosslinking network and realizing the disassembly and recycling of the crosslinking network of phenolic resin-based bamboo-plastic composite material.

[0061] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification and the scope of protection. Therefore, the scope of protection of this patent should be determined by the appended claims.

[0062] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a strong, tough, recyclable phenolic resin-based bamboo-plastic composite material, characterized in that, Includes the following steps: 100 parts by weight of thermoplastic phenolic resin, 10-50 parts by weight of raw materials for dynamic covalent bond construction, 1-10 parts by weight of curing agent, 100-200 parts by weight of organic solvent and 1-5 parts by weight of catalyst are mixed, heated and sealed and stirred until dissolved, and after being mixed evenly, a phenolic resin mixed solution is obtained. 100 parts by weight of phenolic resin mixed solution are mixed with 10 to 100 parts by weight of bamboo powder to make resin-bamboo powder blend. After heating, drying to constant weight and crushing and sieving, composite material molding raw material is obtained. A strong and recyclable phenolic resin-based bamboo-plastic composite material is prepared by hot pressing of the composite molding raw material.

2. The method for preparing the strong and recyclable phenolic resin-based bamboo-plastic composite material according to claim 1, characterized in that, The hot-pressing process involves the following steps: The composite molding material is preheated at 100℃~120℃ for 10min~30min; then hot-pressed at 1MPa~5MPa and 120℃~150℃ for 30min~60min; then hot-pressed at 150℃~200℃ and 5MPa~20MPa for 1h~3h, heating is stopped and pressure is maintained and cooled to room temperature to obtain a strong and recyclable phenolic resin-based bamboo-plastic composite material.

3. The method for preparing the strong and recyclable phenolic resin-based bamboo-plastic composite material according to claim 1, characterized in that, The raw material for constructing the dynamic covalent bond is one of phenylboronic acid, tri(ethylene glycol)divinyl ether, toluene diisocyanate, polyetheramine, or thioctic acid.

4. The method for preparing the strong and recyclable phenolic resin-based bamboo-plastic composite material according to claim 1, characterized in that, The heating temperature for preparing the phenolic resin mixed solution and the heating temperature for preparing the composite molding raw material are both 50℃~70℃.

5. The method for preparing the strong and recyclable phenolic resin-based bamboo-plastic composite material according to claim 1, characterized in that, The curing agent is hexamethylenetetramine, and the catalyst is one of triethylamine, p-toluenesulfonic acid, tin octoate, glacial acetic acid, or dibutyltin dilaurate.

6. The method for preparing the strong and recyclable phenolic resin-based bamboo-plastic composite material according to claim 1, characterized in that, The organic solvent is one of anhydrous ethanol, ethyl acetate, acetone, or tetrahydrofuran.

7. The tough and recyclable phenolic resin-based bamboo-plastic composite material prepared by the method according to any one of claims 1 to 6.

8. The recycling method for the strong and recyclable phenolic resin-based bamboo-plastic composite material according to any one of claims 7, characterized in that, Includes the following steps: 100 parts by weight of pulverized tough and recyclable phenolic resin-based bamboo-plastic composite material are mixed with 200-500 parts by weight of recycled solvent. The mixture is heated and stirred in a sealed manner at 50-90°C until the tough and recyclable phenolic resin-based bamboo-plastic composite material is fully dissolved or no longer dissolves. Then, the solvent is removed and recycled at the same temperature to obtain pre-recycled material with solvent removed. The pre-recycled material is then vacuum dried to obtain solid block recycled material. After crushing the solid block recycled material, a composite molding raw material that can be used for secondary molding is obtained.

9. The recycling method according to claim 8, characterized in that, The recovered solvent is one of ethanol, ethyl acetate, acetone or tetrahydrofuran.

10. The application of the strong and recyclable phenolic resin-based bamboo-plastic composite material according to claim 7 in aerospace equipment, transportation equipment, building materials, wood processing materials, and molding compounds.

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