A method for constructing a self-healing network of insulating paper based on cellulose nanocrystal reinforcement phase

Abstract

The present invention discloses a method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase, and relates to the technical field of insulating materials for power equipment. The steps are as follows: (1) preparing dissociated cellulose pulp; (2) reacting the dissociated cellulose pulp with furfural and a solid acid catalyst to obtain a furan-modified pulp suspension; (3) dehydrating, washing, and freeze-drying the dissociated cellulose pulp to obtain cellulose nanocrystals (CNC); (4) preparing maleimide; (5) reacting CNC with maleimide to obtain maleimide-functionalized cellulose nanocrystals (CNC-Mal); (6) adding the CNC-Mal suspension to the furan-modified pulp suspension to prepare wet paper, hot pressing, and drying to obtain cellulose insulating paper with self-healing function. The present invention combines maleimide-functionalized cellulose nanocrystals and furan-modified cellulose for the first time to construct insulating paper with self-healing ability, thereby extending the service life of transformers and reducing maintenance costs and downtime risks.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating materials for power equipment, and in particular to a method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase. Background Art

[0002] Oil-immersed transformers are subject to a variety of factors during operation, which can cause damage to the cellulose insulation paper within. Mechanical, thermal, electrical, and environmental factors can all affect the cellulose insulation paper. Mechanical and thermal stresses can cause microcracks in the paper, while electrical stress can easily lead to electrical damage such as electrical treeing. These damages not only degrade the mechanical properties of the paper but also its insulation performance, thereby affecting the normal operation of the transformer. In particular, defects such as microcracks and electrical treeing can gradually expand under the influence of an electric field, ultimately causing insulation breakdown and seriously threatening the safety and reliability of the transformer.

[0003] Maintaining the integrity of the internal insulation system is crucial to ensuring the long-term stable operation of power transformers. Once damaged, insulating paper is often difficult to repair and replace. This not only results in equipment downtime, but also increases maintenance costs and the risk of power outages. Therefore, developing self-healing insulating paper materials that can proactively repair defects such as microcracks and electrical dendrites upon damage is crucial for improving transformer reliability and extending its service life. Self-healing insulating paper can effectively restore mechanical strength and insulation performance, reduce failures caused by damage, and reduce the frequency of maintenance and replacement, thereby ensuring stable transformer operation and reliable power supply.

[0004] Self-healing technology has been preliminarily studied in the field of insulating materials, such as insulating coatings and insulating cables. Self-healing technology has successfully achieved automatic repair of materials after damage through various mechanisms, such as microcapsules, self-healing polymers and dynamic covalent bonds. It is also very feasible to apply self-healing technology to the construction of cellulose insulating paper. Cellulose insulating paper is an environmentally friendly and readily available material, and cellulose nanocrystals (CNC) have become an ideal reinforcing phase material due to their excellent mechanical properties and biocompatibility. By compounding cellulose nanocrystals with cellulose insulating paper to construct a network structure with self-healing capabilities, the mechanical strength and self-healing properties of the insulating paper can be effectively improved, thereby achieving protection for the internal insulation system of the power transformer. Summary of the Invention

[0005] To address the above shortcomings, the present invention provides a method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase, which solves the problem of microcracks and electrical dendrites easily occurring in cellulose insulating paper in oil-immersed transformers. The specific technical solution is as follows:

[0006] A method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase comprises the following steps:

[0007] (1) Preparing a furan-modified pulp suspension: dissociated cellulose pulp and anhydrous N,N-dimethylformamide are stirred in a nitrogen atmosphere, and after ultrasonication, furfural and a solid acid catalyst are added for reaction, cooled, and the mixed solution is placed in a centrifuge for high-speed centrifugation to remove the solid acid, thereby obtaining a furan-modified pulp suspension;

[0008] (2) Preparation of cellulose nanocrystals: Dehydrate the dissociated cellulose pulp, mechanically stir it in water, wash it to a neutral pH, freeze-dry it, and collect the cellulose nanocrystal powder for storage and future use;

[0009] (3) Preparation of maleimide-functionalized cellulose nanocrystals: suspending the cellulose nanocrystals in anhydrous N,N-dimethylformamide, adding maleimide and 4-dimethylaminopyridine, cooling in an ice bath, then slowly adding dropwise an anhydrous N,N-dimethylformamide solution containing N,N'-dicyclohexylcarbodiimide, stirring at room temperature, precipitating with an acid solution, dialyzing, and finally freeze-drying to obtain the maleimide-functionalized cellulose nanocrystals;

[0010] (4) Preparation of self-repairing cellulose insulating paper: first, the maleimide-functionalized cellulose nanocrystals are added to deionized water and stirred to obtain a maleimide-functionalized cellulose nanocrystal suspension, and then the maleimide-functionalized cellulose nanocrystal suspension is slowly added to the furan-modified cellulose pulp suspension obtained in step (1), stirred to fully mix, and then poured into a paper sheet former to be filtered into wet paper, and then the wet paper is hot-pressed, vacuumed, and vacuum-dried, and finally the dried and formed insulating paper is calendered to obtain the self-repairing cellulose insulating paper.

[0011] Furthermore, in step (1) and step (2), the preparation method of the dissociated cellulose pulp is: first, the cellulose pulp board is decomposed into small pieces and then soaked in deionized water, and then the pieces are disintegrated in a pulper after soaking, and then the pieces are beaten in a beater to a beating degree of 40-50°SR, and finally the beaten pulp is dissociated and water is added to make the pulp concentration of 5-10%, thereby obtaining the dissociated cellulose pulp.

[0012] Furthermore, in step (1), the volume ratio of the dissociated cellulose pulp to anhydrous N,N-dimethylformamide is 2-4:1; the amount of furfural added is 10-20wt% of the mass of the dissociated cellulose pulp, and the amount of the solid acid added is 1-5wt% of the mass of the dissociated cellulose pulp.

[0013] Furthermore, in step (1), the stirring time is 1-2 hours, the ultrasonic time is 2-4 hours, the reaction temperature is 90-110° C., and the reaction time is 18-24 hours.

[0014] Furthermore, in step (2), the water temperature for mechanical stirring is 45-55° C., and the stirring time is 1-2 h.

[0015] Furthermore, in step (2), the storage temperature of the cellulose nanocrystal powder is 4-6°C.

[0016] Furthermore, in step (3), the preparation method of the maleimide is: first dissolving maleic anhydride in an acetic acid solution, then adding an acetic acid solution dissolved with β-alanine and stirring at room temperature for 3-5 hours, then adding acetic acid, heating to 100-115°C and stirring for 10-15 hours, cooling, extracting with toluene and purifying to obtain the maleimide.

[0017] Furthermore, in step (3), the cooling temperature in the ice bath is 0° C., and the stirring time at room temperature is 20-24 h.

[0018] Furthermore, in step (4), the mass ratio of the maleimide-functionalized cellulose nanocrystals to deionized water is 1:10-20.

[0019] Furthermore, the mass ratio of the maleimide-functionalized cellulose nanocrystal suspension to the furan-modified cellulose pulp suspension is 1:5-10.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. To address the problem of microcracks and electrical dendrites easily occurring in cellulose insulating paper in oil-immersed transformers, the present invention proposes, based on experiments, a method for constructing a self-healing network for insulating paper using a cellulose nanocrystal reinforcement phase, based on the Diels-Alder reversible reaction. The method's dynamic characteristics enable the insulating paper to self-heal microcracks and electrical dendrites without the need for external maintenance, thereby improving the reliability of the transformer's solid insulation and extending its service life.

[0022] 2. The present invention mainly prepares insulating paper with a self-repairing functional network by furan-modifying the long chain of cellulose and adding maleimide-functionalized cellulose nanocrystals. The furan group and the maleimide group can undergo a reversible Diels-Alder reaction to form a self-repairing network in the insulating paper, giving the insulating paper a self-repairing function. The reinforcing effect of cellulose nanocrystals can ensure the stability of the insulating paper structure during the repair process, and ensure the mechanical strength and insulation performance of the insulating paper after repair of microcracks and electrical tree damage. This has important theoretical guidance significance and practical application value for promoting the development of insulating materials, improving the operational reliability of transformers, extending their service life, and ensuring the stable operation of new power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments.

[0024] Figure 1 This is a flow chart of the method for constructing a self-healing network of insulating paper according to the present invention;

[0025] Figure 2 This is a reaction mechanism diagram of the self-healing network of the present invention;

[0026] Figure 3 A diagram of the manufacturing equipment for the insulating paper of the present invention;

[0027] Figure 4 This is a comparison chart of the polymerization degree of the insulating paper prepared in the embodiment of the present invention and ordinary cellulose insulating paper. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0029] Example 1

[0030] This embodiment provides a method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase, and the specific steps are as follows:

[0031] (1) Preparation of dissociated cellulose pulp: 100g of insulating pulp board was decomposed into 1cm 2 Soak the square pieces in 1 L of deionized water for 5 hours. Place them in a pulper for 10 minutes, then beat them in a beater to a beating degree of 40° SR. Dissociate the beaten pulp and add an appropriate amount of deionized water to a pulp concentration of 5% to obtain dissociated cellulose pulp.

[0032] (2) Preparation of maleimide: Dissolve 20 g of maleic anhydride in 200 mL of acetic acid solution, add 10 g of β-alanine dissolved in 200 mL of acetic acid solution, and stir at room temperature for 3 hours. Then add 200 mL of acetic acid, heat to 115°C, and stir for 10 hours. After cooling, extract with 400 mL of toluene and purify to obtain white solid maleimide.

[0033] (3) Preparation of a furan-modified pulp suspension: Dissociated cellulose pulp (5% concentration, 1 L volume) was stirred with 500 mL of anhydrous N,N-dimethylformamide (DMF) under a nitrogen atmosphere for 1 hour and ultrasonicated for 4 hours. 15 g of furfural and 2 g of a solid acid catalyst were added and reacted at 110°C for 24 hours. After cooling to room temperature, the mixed solution was placed in a centrifuge and subjected to high-speed centrifugation to remove the solid acid, thereby obtaining a furan-modified pulp suspension.

[0034] (4) Preparation of maleimide-functionalized cellulose nanocrystals: The dissociated cellulose pulp was dehydrated, mechanically stirred in 55°C water for 2 hours, washed until the pH was neutral, and the cellulose nanocrystal (CNC) powder was collected by freeze drying and stored at 5°C. 5g of CNC was suspended in 100mL of DMF, 5g of maleimide and 0.5g of 4-dimethylaminopyridine (DMAP) were added, and the mixture was cooled to 0°C in an ice bath. 100mL of a 10% wt DMF solution (containing 0.6g of N,N'-dicyclohexylcarbodiimide (DCC)) was slowly added dropwise. After stirring at room temperature for 24 hours, the mixture was precipitated with an acid solution and dialyzed. Finally, the mixture was freeze dried to obtain maleimide-functionalized cellulose nanocrystals (CNC-Mal).

[0035] (5) Preparation of cellulose insulating paper with self-repairing functional network: Add 10g CNC-Mal to 100mL deionized water and stir with a stirrer for 30 minutes to obtain a CNC-Mal suspension. Slowly add the CNC-Mal suspension to the furan-modified cellulose insulating paper pulp suspension. Pour the mixed insulating paper pulp suspension into a paper sheet former and filter it into wet paper. Hot press the wet paper on a hot press, evacuate it with a vacuum filter, and then vacuum dry it in a dryer. Place the dried and formed insulating paper into a flat vulcanizer for calendering to obtain cellulose insulating paper with a self-repairing functional network.

[0036] Example 2: This example differs from Example 1 in that: in the step of preparing dissociated cellulose pulp, an appropriate amount of deionized water is added to bring the pulp concentration to 10%; in the step of preparing the furan-modified pulp suspension, the dissociated cellulose pulp concentration is 10%, the volume is 1L, the volume of anhydrous N,N-dimethylformamide is 250mL, and the volume ratio of the two is 4:1. The amount of furfural added is 20g (20wt% of the mass of the dissociated cellulose pulp), and the amount of solid acid added is 5g (5wt% of the mass of the dissociated cellulose pulp); in the step of preparing the cellulose insulating paper with a self-healing functional network, the amount of CNC-Mal used is 10g, the volume of deionized water is 200mL, and the mass ratio of the two is 1:20.

[0037] Example 3: This example differs from Example 1 in that, in the step of preparing dissociated cellulose pulp, an appropriate amount of deionized water is added to bring the pulp concentration to 10%. In the step of preparing the furan-modified pulp suspension, the dissociated cellulose pulp concentration is 10%, the volume is 1 L, and the volume of anhydrous N,N-dimethylformamide is 500 mL, with a volume ratio of 2:1. The amount of furfural added is 20 g (20 wt% of the dissociated cellulose pulp mass), and the amount of solid acid added is 5 g (5 wt% of the dissociated cellulose pulp mass).

[0038] Example 4: This example differs from Example 1 in that in the step of preparing the furan-modified pulp suspension, the amount of furfural added is 20 g (20 wt% of the mass of the dissociated cellulose pulp), and the amount of solid acid added is 5 g (5 wt% of the mass of the dissociated cellulose pulp);

[0039] Example 5: This example differs from Example 1 in that, in the step of preparing the furan-modified pulp suspension, the concentration of the dissociated cellulose pulp is 5%, the volume is 1 L, the volume of anhydrous N,N-dimethylformamide is 250 mL, and the volume ratio of the dissociated cellulose pulp to anhydrous N,N-dimethylformamide is 4:1. The amount of furfural added is 10 g (10 wt% of the mass of the dissociated cellulose pulp), and the amount of solid acid added is 1 g (1 wt% of the mass of the dissociated cellulose pulp). In the step of preparing the cellulose insulating paper with a self-healing functional network, the amount of CNC-Mal used is 10 g, the volume of deionized water is 200 mL, and the mass ratio of the two is 1:20.

[0040] Comparing the cellulose nanocrystal-reinforced self-healing insulating paper in the above embodiment with conventional cellulose insulating paper, the insulating paper prepared by the present invention has the ability to repair microcracks and electrical dendrites compared with conventional insulating paper, and the rate of decrease of the degree of polymerization of the insulating paper is effectively reduced. Figure 4 .

[0041] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase, characterized in that: The following steps are involved: (1) Preparation of furan-modified pulp suspension: dissociated cellulose pulp and anhydrous N,N-dimethylformamide are stirred in a nitrogen atmosphere for 1-2 hours, and ultrasonicated for 2-4 hours, and then furfural and solid acid catalyst are added to react at a reaction temperature of 90-110°C for 18-24 hours. The mixture is cooled and placed in a centrifuge for high-speed centrifugation to remove the solid acid, thereby obtaining a furan-modified pulp suspension; The preparation method of the dissociated cellulose pulp comprises: firstly decomposing a cellulose pulp sheet into small pieces and then soaking the pieces in deionized water, then disintegrating the pieces in a pulper, then beating the pieces in a beater until the beating degree is 40-50°SR, finally dissociating the beaten pulp and adding water to make the pulp concentration 5-10%, thereby obtaining the dissociated cellulose pulp; The volume ratio of the dissociated cellulose pulp to anhydrous N,N-dimethylformamide is 2-4:1; the amount of furfural added is 10-20 wt% of the mass of the dissociated cellulose pulp, and the amount of the solid acid added is 1-5 wt% of the mass of the dissociated cellulose pulp; (2) Preparation of cellulose nanocrystals: Dehydrate the dissociated cellulose pulp, mechanically stir it in water, wash it until the pH is neutral, freeze-dry it, and collect the cellulose nanocrystal powder for storage and future use; (3) Preparation of maleimide-functionalized cellulose nanocrystals: first suspending the cellulose nanocrystals in anhydrous N,N-dimethylformamide, then adding maleimide and 4-dimethylaminopyridine, cooling in an ice bath, then slowly adding dropwise an anhydrous N,N-dimethylformamide solution containing N,N'-dicyclohexylcarbodiimide, stirring at room temperature, then performing acid solution precipitation and dialysis, and finally freeze-drying to obtain the maleimide-functionalized cellulose nanocrystals; (4) Preparation of self-repairing cellulose insulating paper: first, the maleimide-functionalized cellulose nanocrystals are added to deionized water and stirred, wherein the mass ratio of the maleimide-functionalized cellulose nanocrystals to deionized water is 1:10-20; a maleimide-functionalized cellulose nanocrystal suspension is obtained, and then the maleimide-functionalized cellulose nanocrystal suspension is slowly added to the furan-modified cellulose pulp suspension obtained in step (1), wherein the mass ratio of the maleimide-functionalized cellulose nanocrystal suspension to the furan-modified cellulose pulp suspension is 1:5-10, and after stirring to fully mix, the mixture is poured into a paper sheet former and filtered into wet paper, and then the wet paper is hot-pressed, vacuumed, and vacuum-dried, and finally the dried and formed insulating paper is calendered to obtain the self-repairing cellulose insulating paper.

2. The method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase according to claim 1, characterized in that: In step (2), the mechanical stirring water temperature is 45-55°C, and the stirring time is 1-2h.

3. The method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase according to claim 1, characterized in that: In step (2), the storage temperature of the cellulose nanocrystal powder is 4-6°C.

4. The method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase according to claim 1, characterized in that: In step (3), the preparation method of the maleimide is as follows: first dissolving maleic anhydride in an acetic acid solution, then adding an acetic acid solution in which β-alanine is dissolved and stirring at room temperature for 3-5 hours, then adding acetic acid, heating to 100-115°C and stirring for 10-15 hours, cooling, extracting with toluene and purifying to obtain the maleimide.

5. The method for constructing a self-healing network of insulating paper based on a cellulose nanocrystal reinforcement phase according to claim 1, characterized in that: In step (3), the cooling temperature in the ice bath is 0°C, and the stirring time at room temperature is 20-24 hours.

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