A heat-degradable thermosetting resin, and a preparation method and application thereof

Abstract

The application belongs to the technical field of thermosetting resin preparation, and particularly relates to a thermosetting resin capable of being heated and degraded for recycling, a preparation method and application thereof. The structural formula of the thermosetting resin is shown in formula I, II, III and IV. The thermosetting resin capable of being heated and degraded for recycling is prepared by using ester-based alkyne and di-oxime compounds. The thermosetting resin is selectively and quantitatively broken under relatively mild heat treatment conditions by using the thermal reversible characteristics of enoxyl bond, and high-purity original monomers are efficiently depolymerized and recycled. The monomer recovery rate can reach more than 88%, high-value closed-loop recycling is realized, and the resource utilization rate is greatly improved. In the preparation process, no inert gas protection is needed, and no harsh catalyst is needed, which greatly reduces the energy consumption and equipment requirements, and the recycling process is more energy-saving, safe and low in cost. Meanwhile, the alkyne-oxime click reaction has the characteristics of high efficiency, high atom utilization rate, no by-product and mild reaction conditions, which is beneficial to material preparation and recycling.

Description

Technical Field

[0001] This application belongs to the field of thermosetting resin preparation technology, specifically relating to a thermosetting resin that can be heated, degraded, and recycled, its preparation method, and its application. Background Technology

[0002] Thermosetting resins, such as epoxy resins, phenolic resins, and unsaturated polyesters, have become indispensable key materials in aerospace, electronics, automotive manufacturing, and composite materials fields due to their excellent mechanical properties, thermal stability, dimensional stability, and chemical resistance. While their three-dimensional cross-linked network structure endows materials with superior properties, it also presents a significant environmental challenge: once cured, they cannot be remelted or dissolved in solvents by heating, making traditional physical recycling difficult. This results in the vast majority of waste thermosetting resin products being disposed of through landfill or incineration, causing not only serious waste of resources but also environmental pollution and carbon emissions. With the urgent global pursuit of sustainable development and a circular economy, achieving green and efficient recycling and reuse of polymer materials, especially thermosetting resins, has become one of the core challenges facing materials science and environmental engineering. Against this backdrop, thermal degradation recycling technology has shown great potential. This technology selectively breaks the chemical bonds in the cross-linked network of thermosetting resins under controlled conditions by applying external heat energy, thereby degrading them into low-molecular-weight oligomers, monomers, or high-value-added chemicals. These degradation products can serve as valuable raw materials for the resynthesis of resins or the preparation of other high-value materials, truly turning waste into treasure and forming a closed-loop resource system.

[0003] Currently, while the thermal degradation technology for thermosetting resins shows promise, it still faces a series of serious challenges. The core issue lies in the significant contradiction between the high energy costs (typically requiring extremely high temperatures and inert atmospheres) and low economic returns: poor selectivity in the degradation process leads to complex and difficult-to-separate products, making it difficult to recover monomers for high-value purposes, often resulting in them being relegated to low-value fuels or chemicals. Simultaneously, the use of catalysts can easily trigger new problems such as deactivation, pollution, and equipment corrosion, while harmful gases and solid residues generated during degradation may cause secondary pollution. Ultimately, these factors collectively result in the poor universality and insufficient environmental friendliness of existing technologies, leaving a significant gap before large-scale industrial application. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a thermosetting resin that can be heated, degraded, and recycled, as well as its preparation method and application. Specifically, the following technical solution is adopted:

[0005] In a first aspect, the present invention provides a thermosetting resin that can be heated, degraded, and recycled, having the structural formula shown in Formula I, II, III, or IV:

[0006] Formula I;

[0007] Formula II;

[0008] Formula III;

[0009] Formula IV;

[0010] Wherein, R1 is selected from , , Any one of them; R2 is selected from Any one of CH3.

[0011] As a further preferred embodiment, the structural formula of the heat-degradable and recyclable thermosetting resin is selected from any one of the following formulas 1-4;

[0012] Formula 1;

[0013] Formula 2;

[0014] Formula 3;

[0015] Formula 4.

[0016] This invention provides a thermosetting resin that can be heated, degraded, and recycled, obtained by the method described herein. The crosslinking network of this resin is constructed via oxime bonds. These are chemical bonds that undergo reverse reactions or specific breakage under heating stimulation (typically at 100-200 °C, far below traditional pyrolysis temperatures). Upon heating, the oxime bonds break efficiently and selectively along a predetermined path, like a "zipper," and quantitatively and in high yield recover the original ester-alkyne and oxime monomers. This achieves true closed-loop recycling, with the recovered monomers possessing high purity and quality, allowing for direct use in resin resynthesis, resulting in significant economic value.

[0017] Secondly, the present invention provides a method for preparing the above-mentioned heat-degradable and recyclable thermosetting resin, comprising the following steps:

[0018] An ester-based acetylene monomer compound and a dioxime compound are dissolved in an organic solvent, and then an alkaline catalyst is added to react them to obtain the thermosetting resin that can be heated, degraded, and recycled.

[0019] This invention utilizes the click reaction of ester-based alkynes and oximes to prepare thermosetting resins that can be thermally degraded and recycled. The degradation process requires only moderate heating temperatures (typically even lower with solvent assistance), eliminating the need for inert gas protection and demanding catalysts. This significantly reduces energy consumption and equipment requirements, making the recycling process more energy-efficient, safe, and cost-effective. Furthermore, this click reaction of alkynes exhibits high efficiency, high atom utilization, no byproducts, and mild reaction conditions, facilitating material preparation and recycling.

[0020] As a further preferred embodiment, the content ratio of the ester-activated alkyne group in the ester-based alkyne monomer compound to the oxime hydroxyl group in the dioxime compound is 1:1.05-1.2;

[0021] The amount of alkaline catalyst used is such that the ratio of oxime hydroxyl content in the oxime compound is 1%-3%:1.

[0022] In the preparation process of this invention, the ratio of ester-based alkyne monomer compounds and dioxime compounds is calculated based on the reactive groups. By adding an excess of oxime hydroxyl groups, the exchange of dynamic bonds is ensured. The total content of oxime hydroxyl groups is 1.05-1.2 times that of the ester-activated alkyne groups in the ester-activated alkyne monomer compounds, and the amount of base (catalyst) is 1%-3% of the total content of oxime hydroxyl groups.

[0023] As a further preferred embodiment, the ester-based alkyne monomer compound is at least one of the following structural formulas:

[0024] .

[0025] As a further preferred embodiment, the dioxime compound is at least one of the following structures:

[0026]

[0027] As a further preferred embodiment, the solvent is at least one selected from dichloromethane, tetrahydrofuran, ethyl acetate, chloroform, and acetone.

[0028] As a further preferred embodiment, the alkaline catalyst is at least one of triethylenediamine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and tetrabutylammonium bromide.

[0029] Thirdly, the present invention provides the application of the above-mentioned heat-degradable and recyclable thermosetting resin in the preparation of recyclable composite materials.

[0030] As a further preferred embodiment, the recyclable composite material includes carbon fiber thermosetting composite material or thermosetting resin for wind turbine blades.

[0031] The beneficial effects of this invention are as follows:

[0032] This invention utilizes ester-based alkynes and dioxime compounds to prepare thermosetting resins that can be thermally degraded and recycled. Taking advantage of the thermally reversible nature of oxime bonds, the resin crosslinking network can selectively and quantitatively break down under relatively mild heat treatment conditions (e.g., 120 °C), efficiently depolymerizing and recovering high-purity original monomers. The monomer recovery rate can reach over 88%, achieving true high-value closed-loop recycling and greatly improving resource utilization. Compared to the high temperatures (>400 °C) required for the degradation of traditional thermosetting resins... The degradation temperature required by this invention is significantly reduced compared to harsh chemical conditions (such as ℃) and no catalyst or inert atmosphere protection is required. The entire process has low energy consumption and no harmful byproducts, making it an environmentally friendly green recycling process. The cross-linked network constructed through acetylene oxime click chemistry exhibits excellent mechanical strength, thermal stability, and solvent resistance at room temperature, fully meeting the requirements of practical applications. It ensures that the material can be degraded by simple heating after use, successfully resolving the contradiction between "stable use" and "easy recycling". The entire process from resin synthesis to degradation and recycling does not require complex equipment or special conditions. The degradation products are pure and easy to separate, greatly simplifying subsequent processing steps, reducing recycling costs, and providing a practical and feasible technical path for the large-scale recycling and reuse of thermosetting resins. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The figures shown are tensile curves of the materials prepared in Examples 1-4 and Comparative Example 1.

[0035] Figure 2 The diagram shown is a schematic diagram of the thermal degradation of the material prepared in Example 1;

[0036] Figure 3 The diagram shown is a schematic diagram of the recycling of the initial resin film prepared in Example 1;

[0037] Figure 4 The figures shown are TGA curves of the materials prepared in Examples 1-4 and Comparative Example 1.

[0038] Figure 5 The diagram shows the degradation kinetics of the material prepared in Example 1.

[0039] Figure 6The diagram shows a comparison of the activation energies of the materials prepared in Examples 1-4 and Comparative Example 1. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] Example 1

[0042] A method for preparing a heat-degradable and recyclable thermosetting resin, the preparation route of which is as follows:

[0043]

[0044] Specifically, the following steps are included:

[0045] 2.6 mmol of tri(methyl propynate)methylpropane, 2.15 mmol of benzoyl dioxime, and 2.15 mmol of p-benzoquinone dioxime were added to 4 mL of tetrahydrofuran. After mixing and stirring, 1 mol% of triethylenediamine (DABCO) was added, and the mixture was stirred for 5 min. The solution was then poured into a polytetrafluoroethylene (PTFE) film (length*width*height = 5 cm*5 cm*2 cm) and cured at room temperature for 24 h to obtain a thermosetting resin that can be recycled by heating.

[0046] Example 2

[0047] A method for preparing a heat-degradable and recyclable thermosetting resin, the preparation route of which is as follows:

[0048]

[0049] Specifically, the following steps are included:

[0050] 2.6 mmol of dodecyl ester yne, 0.87 mmol of tris(methyl propynate) methyl propane, 2.15 mmol of benzoyl dioxime, and 2.15 mmol of p-benzoquinone dioxime were added to 4 mL of tetrahydrofuran. After mixing and stirring, 1 mol% of triethylenediamine (DABCO) was added, and the mixture was stirred for another 5 min. The solution was then poured into a polytetrafluoroethylene (PTFE) film (length*width*height = 5 cm*5 cm*2 cm) and cured at room temperature for 24 h to obtain a thermosetting resin that can be recycled by heating.

[0051] Example 3

[0052] A method for preparing a heat-degradable and recyclable thermosetting resin, the preparation route of which is as follows:

[0053]

[0054] Specifically, the following steps are included:

[0055] 2.6 mmol of dodecyl ester yne, 0.87 mmol of tri(methyl propynate) methyl propane, and 4.3 mmol of benzoyl dioxime were added to 4 mL of tetrahydrofuran. After mixing and stirring, 1 mol% of triethylenediamine (DABCO) was added, and the mixture was stirred for 5 min. The solution was then poured into a polytetrafluoroethylene (PTFE) film (length*width*height = 5 cm*5 cm*2 cm) and cured at room temperature for 24 h to obtain a thermosetting resin that can be recycled by heating.

[0056] Example 4

[0057] A method for preparing a heat-degradable and recyclable thermosetting resin, the preparation route of which is as follows:

[0058]

[0059] Specifically, the following steps are included:

[0060] 2.6 mmol of dodecyl ester yne, 0.87 mmol of tri(methyl propynate) methyl propane, and 4.3 mmol of p-benzoquinone dioxime were added to 4 mL of tetrahydrofuran. After mixing and stirring, 1 mol% of triethylenediamine (DABCO) was added, and the mixture was stirred for another 5 min. The solution was then poured into a polytetrafluoroethylene (PTFE) film (length*width*height = 5 cm*5 cm*2 cm) and cured at room temperature for 24 h to obtain a thermosetting resin that can be recycled by heating.

[0061] Comparative Example 1

[0062] A method for preparing a heat-degradable and recyclable thermosetting resin, the preparation route of which is as follows:

[0063]

[0064] Specifically, the following steps are included:

[0065] 2.6 mmol of p-phenyl ester yne, 0.87 mmol of tris(methyl propynate) methyl propane, and 4.3 mmol of p-benzoquinone dioxime were added to 4 mL of tetrahydrofuran. After mixing and stirring, 1 mol% of triethylenediamine (DABCO) was added, and the mixture was stirred for another 5 min. The solution was then poured into a polytetrafluoroethylene (PTFE) film (length*width*height = 5 cm*5 cm*2 cm) and cured at room temperature for 24 h to obtain a thermosetting resin that can be recycled by heating.

[0066] The thermosetting resins prepared by heat degradation and recovery in Examples 1-4 and Comparative Example 1 were subjected to performance tests, as follows:

[0067] (1) Tensile tests were performed on each embodiment and Comparative Example 1 in accordance with GB / T 528-2009 standard. The test conditions were 25℃ and a tensile rate of 3N / min.

[0068] (2) Thermogravimetric analysis was performed on each example and Comparative Example 1 in accordance with GB / T 27761-2011 standard, and the temperature was increased from 25 °C to 750 °C at a heating rate of 30 °C / min on a TGAQ50.

[0069] (3) Stress relaxation experiments were conducted on each embodiment and comparative example in accordance with GBT1685-2008 standard at 60℃-90℃, and activation energy curves were obtained through the treatment.

[0070] The results are shown in Table 1 and Figures 1-6 As shown.

[0071] Table 1

[0072]

[0073] From the table above and Figure 1 As can be seen, by adjusting the rigid structure and flexible segments, the mechanical properties of samples in Examples 1-4 gradually increased from the initial 7 MPa to 18 MPa, while their degradation rates remained at 97% or higher, showing virtually no significant change. However, Comparative Example 1 exhibited poorer mechanical properties and a slightly lower degradation rate. This indicates that the degradable material can have its mechanical properties optimized through component adjustment while maintaining excellent degradation capabilities. Furthermore, the tensile properties of the hot-pressed recovered sample were essentially consistent with the original sample, demonstrating that the material possesses good recyclability.

[0074] from Figure 2The results show that the degradation process of Example 1 at 120 °C exhibited the following characteristics: slight swelling occurred after 1 h of heating; significant swelling occurred after 3 h, attributed to the diffusion of solvent molecules into the material; partial degradation began after 6 h; and complete degradation was achieved after 12 h. These results demonstrate that the material can be completely degraded by heating.

[0075] Figure 3 The diagram shown is a schematic diagram of the recycling of the initial resin film prepared in Example 1; it can be seen that the material has good recycling performance and retains almost no change in performance after recycling.

[0076] Figure 4 The TGA curves for Examples 1-4 and Comparative Example 1 are shown. All samples exhibit two-stage thermal decomposition behavior: (i) in the range of 150–200 °C, the curve decreases due to the breaking of olefinic bonds; (ii) significant decomposition of the main chain occurs above 300 °C. Notably, the 5% weight loss temperature of all networks is approximately 220 °C, indicating considerable thermal stability among the different samples.

[0077] Figure 5 The degradation kinetics curve for Example 1 is shown. The curve indicates that the degradation time significantly decreased from 12 hours to 8 hours when the temperature increased from 150°C to 170°C. Half-life (t) 1 / 2 The degradation time (50%) is defined as the time it takes for a material to degrade to 50%. According to pseudo-first-order kinetics calculations, this time is 4 hours, 2.5 hours, and 1.6 hours at 150℃, 160℃, and 170℃, respectively. Clearly, an increase of only 20℃ in temperature significantly accelerates the degradation rate. This is mainly because the increased temperature accelerates the chain motion of molecules and the rate of molecular bond breaking.

[0078] Figure 6 The diagram shows a comparison of the activation energies of Examples 1-4 and Comparative Example 1. As shown, Comparative Example 1 has the highest activation energy, indicating a higher temperature at which degradation is achieved, making it less prone to degradation under normal circumstances. The other examples can undergo thermal degradation at lower temperatures. From a chemical kinetics perspective, the rate constant of the degradation process follows the Arrhenius equation regarding the reaction activation energy. A lower activation energy means that reactant molecules can more easily cross the energy barrier to transform into products at room temperature, thus significantly increasing the rate of the degradation reaction and rapidly breaking chemical bonds.

[0079] The embodiments of this application have been described above with reference to the accompanying drawings. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the core ideas of this application. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A thermosetting resin that can be heated, degraded, and recycled, characterized in that, Its structural formula is shown in Equation I, Equation II, Equation III, or Equation IV: Formula I; Formula II; Formula III; Formula IV; Where R1 is -(CH2) 12 -; R2 is phenyl or -CH3.

2. The thermosetting resin that can be heated, degraded, and recycled according to claim 1, characterized in that, The structural formula of the heat-degradable and recyclable thermosetting resin is selected from any one of the following formulas 1-4; Formula 1; Formula 2; Formula 3; Formula 4.

3. The method for preparing the thermosetting resin that can be heated, degraded, and recycled according to any one of claims 1-2, characterized in that, Includes the following steps: An ester-based acetylene monomer compound and a dioxime compound are dissolved in an organic solvent, and then an alkaline catalyst is added to react them to obtain the thermosetting resin that can be heated, degraded, and recycled.

4. The preparation method according to claim 3, characterized in that, The ratio of the content of the ester-activated alkyne group in the ester-based alkyne monomer compound to the content of the oxime hydroxyl group in the dioxime compound is 1:1.05-1.2; The amount of alkaline catalyst used is such that the ratio of oxime hydroxyl content in the oxime compound is 1%-3%:

1.

5. The preparation method according to claim 4, characterized in that, The ester-based alkyne monomer compound is at least one of the following structural formulas: 。 6. The preparation method according to claim 4, characterized in that, The dioxime compound is at least one of the structures shown below: 。 7. The preparation method according to claim 3, characterized in that, The solvent is at least one of dichloromethane, tetrahydrofuran, ethyl acetate, chloroform, and acetone.

8. The preparation method according to claim 3, characterized in that, The alkaline catalyst is at least one of triethylenediamine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene, and tetrabutylammonium bromide.

9. The use of the thermosetting resin that can be heated and degraded for recycling according to any one of claims 1-2 in the preparation of recyclable composite materials.

10. The application according to claim 9, characterized in that, The recyclable composite material includes carbon fiber thermosetting composite material or thermosetting resin for wind turbine blades.

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