Composite insulation paper based on dopamine modified PPTA fiber and wood fiber pulp and preparation method thereof

Abstract

The invention discloses insulation paper based on compounding of dopamine modified PPTA fibers and wood fiber pulp and a preparation method of the insulation paper, and belongs to the technical field of composite insulation paper. PPTA fibers are subjected to surface pretreatment and then modified with dopamine, then the dopamine modified PPTA fibers and wood fiber pulp are mixed, after the mixed pulp is dissociated and formed, wet paper sheets are subjected to calendaring treatment and drying and then continue to be subjected to multiple times of calendaring treatment, and finally the wet paper sheets are impregnated with mineral insulating oil and drained to obtain a final target product. The prepared composite insulation paper comprises 75%-95% of wood fiber pulp (SWP); and 5%-25% of dopamine modified PPTA fiber (MKP). The dielectric constant of the paper is reduced by adding the PPTA fibers, molecular polarization is reduced by the dopamine modified PPTA fibers, the dielectric property is remarkably improved, meanwhile, fiber interface bonding is enhanced by dopamine modification, a more stable fiber network and a more stable hydrogen bond network are formed, and the mechanical strength is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite insulating paper, and in particular to an insulating paper based on dopamine-modified PPTA fibers and wood fiber pulp and a preparation method thereof. Background Art

[0002] In the fields of power equipment, electronic devices, and new energy equipment, as a core functional component, the performance of insulating materials directly affects the safety, reliability, and energy efficiency level of system operation.

[0003] Traditional wood fiber insulating materials (such as insulating paper made from sulfate wood pulp) are still widely used in equipment such as transformers, cables, and circuit breakers. However, their dielectric constant and dielectric loss are relatively high, which easily causes partial discharge. At the same time, their mechanical strength is relatively low and they are prone to deformation. To improve the performance, researchers have tried to blend synthetic fibers (such as aramid and polyester) with wood fibers to prepare composite insulating paper. However, practical applications have shown that due to the poor chemical compatibility between wood fibers and synthetic fibers, the mechanical properties decline. Although pure synthetic insulating paper has excellent performance, its production cost is high, and the concentration of chlorine-containing organic compounds emitted during the production process is relatively high, and its environmental performance is poor.

[0004] Therefore, there are significant technical bottlenecks in the current mainstream insulating material system, and it is urgent to develop a new composite insulating medium with high mechanical strength, excellent dielectric properties, and environmental friendliness. Summary of the Invention

[0005] The purpose of the present invention is to provide an insulating paper based on dopamine-modified PPTA fibers and wood fiber pulp and a preparation method thereof to solve the problems in the background art, and to prepare a composite insulating paper with a low dielectric constant and high mechanical strength, which is suitable for power equipment such as oil-immersed transformers.

[0006] To achieve the above purpose, the present invention provides an insulating paper based on dopamine-modified PPTA fibers and wood fiber pulp, which includes the following components by mass percentage: 75% - 95% of wood fiber pulp (SWP); 5% - 25% of dopamine-modified PPTA fibers (MKP).

[0007] The present invention also provides a preparation method for the above-mentioned insulating paper based on dopamine-modified PPTA fibers and wood fiber pulp, which includes the following steps: S1. Pretreatment of PPTA fibers Clean and dry the PPTA fibers successively with acetone and absolute ethanol; S2. Dopamine modification of PPTA fibers The pretreated PPTA fibers are immersed in a dopamine hydrochloride solution, magnetically stirred at 30 °C for 4 h, rinsed with deionized water, and naturally dried to obtain dopamine-modified PPTA fibers; S3. Preparation of composite insulating paper The dopamine-modified PPTA fibers are mixed with wood fiber pulp. The mixed slurry is dispersed in deionized water and dissociated at a speed of 75000 r / min, filtered through a sieve to form a wet paper sheet, placed in a flat calender for calendering to remove moisture, and then vacuum dried. After taking out, it is continuously calendered multiple times to obtain a composite insulating paper; S4. Impregnation treatment The composite insulating paper is immersed in mineral insulating oil, fully impregnated, taken out and drained to obtain the final target product.

[0008] Preferably, in S1, at 75 °C, the PPTA fibers are washed with acetone for 24 h.

[0009] Preferably, in S1, the temperature of vacuum drying is 100 °C and the drying time is 3 h.

[0010] Preferably, in S2, the concentration of the dopamine hydrochloride solution is 2 g / L and the pH value is 8.5.

[0011] Preferably, in S3, the dopamine-modified PPTA fibers and wood fiber pulp are mixed at a mass ratio of 5%:95%, 10%:90%, 20%:80%.

[0012] Preferably, in S3, the temperature of vacuum drying is 105 °C and the drying time is 12 min.

[0013] Preferably, in S3, the calendering treatment is carried out at 120 °C and 12 MPa, 3 min each time.

[0014] Preferably, in S3, the paper thickness of the composite insulating paper is 130 ± 5 μm and the grammage is 125 ± 5 g / m 2 .

[0015] Therefore, an insulating paper based on the composite of dopamine-modified PPTA fibers and wood fiber pulp and its preparation method provided by the present invention have the following beneficial effects: 1) Low dielectric constant and dielectric loss The addition of PPTA fibers reduces the dielectric constant of the paper. The dopamine-modified PPTA fibers reduce the polarity of the fibers, enhance the interfacial bonding between the PPTA fibers and the wood fibers, and reduce the interfacial polarization effect, thereby significantly reducing the power frequency 50 Hz dielectric constant (3.28) and dielectric loss (0.33%) of the oil-impregnated composite insulating paper.

[0016] 2) High mechanical properties The dopamine modification self - polymerizes on the fiber surface to form a polydopamine layer, introducing active groups (such as hydroxyl groups and amino groups), enhancing the chemical bonding and physical adsorption with wood fibers, strengthening the interfacial bonding strength, forming a more stable fiber network and hydrogen - bond network, and significantly improving the tensile strength of the composite insulating paper (38.4% higher than the unmodified sample).

[0017] 3) Low cost and environmental friendliness Based on natural wood fiber pulp, it has the advantages of low cost, renewable and environmental friendliness. A small amount of PPTA fibers (poly - p - phenylene terephthalamide) have high strength, high modulus and low dielectric constant. As the reinforcing phase, it reduces the production cost while maintaining the renewability and environmental friendliness of the material.

[0018] 4) Excellent thermal properties The dopamine modification improves the thermal stability of the composite insulating paper, making it suitable for applications in high - temperature environments.

[0019] The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments. Description of the drawings

[0020] Figure 1 It is a flow chart for preparing the insulating paper based on dopamine - modified PPTA fibers and wood fiber pulp according to the present invention. Detailed implementation manners

[0021] The technical solutions of the present invention will be further described below through the accompanying drawings and embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Any other changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principle of the present invention should be equivalent replacement methods and are all included in the protection scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application and all belong to the protection scope of the present invention.

[0022] Referring to "embodiments" in this text means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The term "embodiment" that appears in various positions in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0023] Unless otherwise defined, the technical terms used herein have the same meanings as those commonly understood by those skilled in the technical field to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0024] Unless otherwise specified in the present invention, the reagents, instruments, equipment, etc. used are all the reagents, instruments and equipment commonly used by those skilled in the art in this field.

[0025] Table 1 shows the basic information parameters and sources of the raw materials used in the following examples and comparative examples.

[0026] Table 1 Basic Information Parameters of Raw Materials

[0027] The following Table 2 shows the basic information of the key equipment used in the preparation process of the composite insulating paper.

[0028] Table 2 Key Equipment Information

[0029] Example 1 As Figure 1 shown, this example provides a preparation method of an insulating paper based on the composite of dopamine-modified PPTA fibers and wood fiber pulp, which specifically includes the following steps: 1) Pretreatment of PPTA fibers: Wash the PPTA fibers with acetone at 75°C for 24 hours to remove surface attachments, then wash with anhydrous ethanol to remove dust and oil on the fiber surface, and finally place them in a vacuum oven and dry at 100°C for 3 hours.

[0030] 2) Dopamine-modified PPTA fibers: Immerse the pretreated PPTA fibers in a 2 g / L dopamine hydrochloride solution with a pH value of 8.5, and magnetically stir at 30°C for 4 hours to form a polydopamine layer by self-polymerization of dopamine on the fiber surface, then rinse with deionized water and dry naturally for standby.

[0031] 3) Mix wood fiber pulp: Mix dopamine-modified PPTA fibers and wood fiber pulp according to a mass ratio of 20%:80%.

[0032] 4) Pulp dissociation and forming: Disperse the mixed pulp in 2000 mL of deionized water, dissociate at a speed of 75000 r / min, and filter and form on a 400-mesh stainless steel sieve to obtain wet paper sheets.

[0033] 5) Calendering treatment of wet paper sheets: Place them in a flat calender and calender at 120°C and 12 MPa for 3 min to remove excess moisture.

[0034] 6) Vacuum drying: Vacuum dry at 105 °C for 12 min.

[0035] 7) Multi-pass calendering: Conduct multi-pass calendering at 120 °C and 12 MPa, 3 min each time.

[0036] 8) Impregnation with mineral insulating oil: Immerse the prepared composite insulating paper in mineral insulating oil (KI25X), and drain to obtain the finished composite insulating paper.

[0037] Example 2 This example provides a method for preparing an insulating paper based on the composite of dopamine-modified PPTA fibers and wood fiber pulp. The specific preparation method is the same as that of Example 1. The difference from Example 1 is only that in step 3), dopamine-modified PPTA fibers and wood fiber pulp are mixed in a mass ratio of 10%:90%. The rest are the same as those in Example 1 and will not be repeated here.

[0038] Example 3 This example provides a method for preparing an insulating paper based on the composite of dopamine-modified PPTA fibers and wood fiber pulp. The specific preparation method is the same as that of Example 1. The difference from Example 1 is only that in step 3), dopamine-modified PPTA fibers and wood fiber pulp are mixed in a mass ratio of 5%:95%. The rest are the same as those in Example 1 and will not be repeated here.

[0039] Comparative Example 1 Use ordinary kraft paper as the comparative insulating paper.

[0040] Comparative Example 2 Use the composite insulating paper of unmodified dopamine-modified PPTA fibers and wood fiber pulp as the comparative unmodified composite insulating paper. The mass ratio of PPTA fibers to wood fiber pulp is 5%:95%.

[0041] Comparative Example 3 Use the composite insulating paper of unmodified dopamine-modified PPTA fibers and wood fiber pulp as the comparative unmodified composite insulating paper. The mass ratio of PPTA fibers to wood fiber pulp is 10%:90%.

[0042] Comparative Example 4 Use the composite insulating paper of unmodified dopamine-modified PPTA fibers and wood fiber pulp as the comparative unmodified composite insulating paper. The mass ratio of PPTA fibers to wood fiber pulp is 20%:80%.

[0043] The following methods are used to test the dielectric constant, dielectric loss, tensile strength, and thermal properties of the insulating papers of Examples 1-3, Comparative Examples 1-2, and traditional insulating papers.

[0044] 1. Dielectric Constant and Dielectric Loss Testing Method The dielectric property test is completed by a Novo-control broadband dielectric spectrometer (Novocontrol GmbH, Germany). The specific steps are as follows: (1) Specimen preparation: Cut the composite insulating paper sample into circular pieces with a diameter of 35 mm. After vacuum drying at 90 °C for 48 hours, immerse them in pre-treated KI25X mineral insulating oil, which has been pre-treated by vacuum dehydration and degassing at 60 °C for 48 hours; (2) Test conditions: Apply a test voltage of 3 V in the frequency range of 10 -1 -10 7 Hz, and record the power frequency dielectric constant and the tangent value of the dielectric loss angle.

[0045] 2. Mechanical Property Testing Method Use an AT-L-1 type tensile testing machine (Jinan Animet Instrument Co., Ltd.) to measure the tensile strength. The specific steps are as follows: (1) Specimen specifications: Prepare strip specimens with a width of 15 mm according to the ISO 1924-2:1994 and GB / T 12914-2008 standards; (2) Test parameters: Set the clamp spacing to 100 mm, stretch at a constant rate of 250 ± 50 mm / min, keep the test environment temperature at 25 °C, record the maximum tension value when the specimen breaks, and ensure that the fracture time is controlled within the range of 20 ± 5 seconds.

[0046] 3. Thermal Property Testing Method Characterize the thermal stability through a TGA / DSC1 / 1600LF synchronous thermal analyzer (Mettler Toledo, Switzerland), specifically including: (1) Test process: Under the protection of nitrogen at a flow rate of 50 mL / min, program the temperature from 25 °C to 800 °C at a heating rate of 7 °C / min; (2) Data analysis: Record the sample mass loss curve and determine the thermal decomposition characteristic temperature of the material through the derivative thermogravimetry (DTG) curve.

[0047] Analyze the test results.

[0048] The test results of the dielectric constant are shown in Table 3 below.

[0049] Table 3 Test Results of Dielectric Constant

[0050] It can be seen from the data in Table 3 that with the increase of the mass fraction of Kevlar fiber, the dielectric constant and dielectric loss of the composite insulating paper show a significant downward trend. Preferably, when the content of Kevlar fiber (PPTA fiber) is 20wt%, the dielectric constant of the composite insulating paper under power frequency conditions (50Hz) can be reduced to 3.34, which is 18.53% lower than that of traditional kraft paper (dielectric constant 4.1, 50Hz), and the dielectric loss is reduced to 0.38%. Furthermore, the dielectric constant and dielectric loss of the Kevlar fiber-wood fiber composite system surface-modified by dopamine are significantly lower than those of the unmodified system. When the PPTA fiber content after dopamine treatment is 20%, the dielectric constant of the composite insulating paper is reduced to 3.28 and the dielectric loss is reduced to 0.33%.

[0051] Under the action of the power frequency electric field, the polarization behavior of the composite insulating paper is mainly dominated by the orientation polarization of the polymer molecular chain segments. Through the dopamine modification treatment, the improvement of the fiber interface bonding strength effectively increases the molecular chain rotation barrier, inhibits the rotation polarization of the polar molecular chain segments under the action of the electric field, and thus reduces the dielectric polarization response. This technical feature enables the modified composite insulating paper to achieve the coordinated optimization of the dielectric constant while maintaining low dielectric loss, meeting the stringent requirements of high-voltage equipment on the dielectric properties of insulating materials.

[0052] The mechanical properties test results are shown in Table 4 below.

[0053] Table 4 Mechanical properties test results

[0054] It can be seen from the data in Table 4 that in the Kevlar fiber composite system, the tensile strength and elongation at break show controllable adjustable characteristics with the increase of fiber content. When the Kevlar fiber content is 20wt%, the tensile strength of the composite insulation paper is 71.7MPa, which is 38.4% higher than that of the unmodified system, and the tensile strength retention rate can reach 87.9% of the kraft paper benchmark value; at the same time, the elongation at break is increased to 3.03%, which is significantly optimized compared with the unmodified system (2.92%).

[0055] Dopamine modification treatment effectively inhibits fiber interface slip and stress concentration by enhancing the interfacial bonding strength between Kevlar fiber and wood fiber. Specifically, the modified composite insulating paper exhibits linear elastic deformation characteristics at the initial strain stage (<1%). When the strain exceeds the critical threshold, the fiber network dissipates mechanical energy through cooperative deformation, thereby delaying crack propagation. This technical feature enables the material to have both high tensile strength and toughness matching characteristics when subjected to winding vibration and electrodynamic shock, meeting the stringent requirements of transformer windings for the mechanical reliability of insulating paper.

[0056] The thermal performance test results are shown in Table 5 below.

[0057] Table 5 Thermal Performance Test Results

[0058] As can be seen from the data in Table 5, when the Kevlar fiber content is 20wt%, the initial fiber decomposition temperature of the dopamine-modified composite insulating paper is increased by 2.2 °C compared with the unmodified system, and the temperature corresponding to the maximum decomposition rate of cellulose is increased by about 2 °C compared with the kraft paper reference value.

[0059] The dopamine modification treatment improves the thermal stability through the following mechanisms: (1) Interface enhancement effect: The interfacial bonding layer formed by dopamine inhibits the thermal expansion mismatch between Kevlar fibers and wood fibers, reducing the generation of interfacial microcracks; (2) Thermal barrier effect: The dense cross-linked structure formed on the surface of the modified fibers hinders the transfer of heat to the interior of the fibers, delaying the initiation temperature of the cleavage of the cellulose main chain; Therefore, by introducing dopamine-modified PPTA fibers, the present invention significantly reduces the dielectric constant and dielectric loss, while improving the mechanical strength. At the same time, the fiber compatibility problem is solved by dopamine modification, and the tensile strength is improved; in addition, by using wood fiber pulp as the substrate, the production cost is reduced and the environmental friendliness is improved. The prepared composite insulating paper has significant advantages in dielectric properties, mechanical properties, cost and environmental friendliness, effectively overcomes the defects and deficiencies of the existing technologies, and has broad application prospects.

[0060] The specific steps and process parameters of the slurry mixing, dissociation, forming, calendering, drying and impregnation treatments disclosed in the present invention ensure the uniformity and performance consistency of the prepared paper.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An insulating paper based on a composite of dopamine-modified PPTA fiber and wood fiber pulp, characterized in that: Calculated by mass percentage, it includes the following components: 75% to 95% of wood fiber pulp; and 5% to 25% of dopamine-modified PPTA fiber.

2. The method for preparing insulating paper based on the composite of dopamine-modified PPTA fiber and wood fiber pulp according to claim 1, characterized in that: The following steps are involved: S1. PPTA fiber pretreatment The PPTA fiber was cleaned with acetone and anhydrous ethanol in sequence and then dried; S2, Dopamine modified PPTA fiber The pretreated PPTA fiber was immersed in a dopamine hydrochloride solution, magnetically stirred at 30°C for 4 hours, then rinsed with deionized water, and dried naturally to obtain the dopamine-modified PPTA fiber; S3. Preparation of composite insulating paper The dopamine-modified PPTA fiber is mixed with wood fiber pulp, the mixed pulp is dispersed in deionized water and dissociated at a speed of 75000r / min, filtered through a screen to obtain a wet paper sheet, placed in a flat calender for calendering to remove moisture, and then vacuum dried, and after being taken out, it is continuously calendered for multiple times to obtain a composite insulating paper; S4. Impregnation treatment The composite insulating paper is immersed in mineral insulating oil, fully immersed, taken out and drained to obtain the final target product.

3. The method for preparing insulating paper based on the composite of dopamine-modified PPTA fiber and wood fiber pulp according to claim 2, characterized in that: In S1, the PPTA fiber was cleaned with acetone at 75°C for 24 h.

4. The method for preparing insulating paper based on the composite of dopamine-modified PPTA fiber and wood fiber pulp according to claim 2, characterized in that: In S1, the vacuum drying temperature is 100°C and the drying time is 3 h.

5. The method for preparing insulating paper based on the composite of dopamine-modified PPTA fiber and wood fiber pulp according to claim 2, characterized in that: In S2, the concentration of dopamine hydrochloride solution is 2 g / L and the pH value is 8.

5.

6. The method for preparing insulating paper based on the composite of dopamine-modified PPTA fiber and wood fiber pulp according to claim 2, characterized in that: In S3, dopamine-modified PPTA fiber and wood fiber pulp are mixed in mass ratios of 5%:95%, 10%:90%, and 20%:80%.

7. The method for preparing insulating paper based on the composite of dopamine-modified PPTA fiber and wood fiber pulp according to claim 2, characterized in that: In S3, the vacuum drying temperature is 105°C and the drying time is 12 minutes.

8. The method for preparing insulating paper based on the composite of dopamine-modified PPTA fiber and wood fiber pulp according to claim 2, characterized in that: In S3, calendering treatment is performed at 120°C and 12 MPa for 3 minutes each time.

9. The method for preparing insulating paper based on the composite of dopamine-modified PPTA fiber and wood fiber pulp according to claim 2, characterized in that: In S3, the thickness of the composite insulation paper is 130±5μm and the weight is 125±5g / m 2 .

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