A lignin fiber composite material and a method for producing the same

Abstract

The present application belongs to the field of composite materials, and discloses a lignin fiber composite material and a preparation method thereof, which comprises the following components in parts by weight: lignin fiber 30-50 parts, composite matrix resin 25-45 parts, nano-enhanced particles 5-12 parts, interface modifier 3-7 parts, toughening agent 4-9 parts, graphene aerogel 2-6 parts, and basalt fiber 3-8 parts; the present application provides a lignin fiber composite material and a preparation method thereof by combining a multi-element reinforcing system design (lignin fiber / basalt fiber / graphene aerogel / nano silicon dioxide) and an interface modification technology, and solves the problems of poor interface compatibility and insufficient mechanical properties of traditional lignin fiber asphalt composite materials.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a lignin fiber composite material and its preparation method. Background Technology

[0002] Lignin fiber, as a renewable biomass resource, boasts advantages such as wide availability, low cost, and environmental friendliness, leading to increasing attention on its application in asphalt pavement composite materials. However, traditional lignin fiber asphalt composite materials face the following technical bottlenecks:

[0003] First, the surface polarity of lignin fibers is relatively high, resulting in poor interfacial compatibility with the non-polar asphalt matrix. This leads to the fibers easily detaching from the asphalt, significantly reducing the road surface's rutting resistance and durability.

[0004] Secondly, the reinforcing effect of single fiber reinforcing phase is limited, and the mechanical properties of composite materials, such as high-temperature shear strength and low-temperature crack resistance, are difficult to meet the requirements of high-grade pavement engineering.

[0005] Third, the existing preparation process lacks effective control over the synergistic effect of multi-scale reinforcements, making it difficult to optimize the comprehensive performance of composite materials (such as resistance to fatigue cracking and resistance to water damage).

[0006] In existing technologies, lignin fiber composites are usually prepared by simple fiber surface treatment and single bitumen modification. However, there is insufficient research on the construction of multi-dimensional reinforcement systems (such as nanoparticle-microfiber-aerogel multi-level reinforcement) and the synergistic effect of interface modifiers, resulting in limited improvement in the strength of composite materials. In particular, under complex load and temperature and humidity alternating environments, interface debonding and material degradation are prominent problems.

[0007] Therefore, in response to the demand for high-performance and long-life composite materials in asphalt pavement engineering, this invention proposes a lignin fiber composite material and its preparation method that combines a multi-reinforcement system design (lignin fiber / basalt fiber / graphene aerogel / nano silica) with interface modification technology, thereby solving the key problems of poor interfacial compatibility and insufficient mechanical properties of traditional lignin fiber asphalt composite materials. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a lignin fiber composite material and its preparation method that combines a multi-component reinforcement system design (lignin fiber / basalt fiber / graphene aerogel / nano silica) with interface modification technology, thereby solving the problems of poor interfacial compatibility and insufficient mechanical properties of traditional lignin fiber asphalt composite materials.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] The technical solution provided by this invention is: a lignin fiber composite material, comprising the following components by weight: 30-50 parts lignin fiber, 25-45 parts composite matrix resin, 5-12 parts nano-reinforcing particles, 3-7 parts interface modifier, 4-9 parts toughening agent, 2-6 parts graphene aerogel, and 3-8 parts basalt fiber.

[0011] The composite matrix resin is a mixture of polypropylene resin and epoxy resin in a mass ratio of 2:1 to 3:1.

[0012] The nano-reinforcing particles are nano-silica particles with a particle size of 50-100 nm, whose surface has been treated with γ-methacryloxypropyltrimethoxysilane.

[0013] The interface modifier is sodium lignosulfonate modified with tannic acid;

[0014] The toughening agent is hydroxyl-terminated liquid nitrile rubber.

[0015] Furthermore, the lignin fiber is agricultural straw lignin fiber, which is soaked in a 5%-10% sodium hydroxide solution for 2-4 hours, washed with water until neutral, and then dried.

[0016] Furthermore, the preparation method of graphene aerogel is as follows: react graphene oxide dispersion with ascorbic acid at 60-80℃ for 2-3 hours, and then freeze-dry to obtain the aerogel with a specific surface area of ​​500-800m² / g.

[0017] Furthermore, the basalt fiber is soaked in a 3%-5% KH550 silane coupling agent solution for 1-2 hours and then dried at 80-100℃.

[0018] The solvent of the KH550 silane coupling agent solution is selected from ethanol and water, and the volume ratio of ethanol to water is 8-9:1-2.

[0019] The purpose of the soaking is to hydrolyze the KH550 silane coupling agent and graft it onto the surface of the basalt fiber, thereby enhancing the interfacial bonding between the fiber and the composite matrix resin.

[0020] Furthermore, the surface treatment method for nano-silica particles is as follows: reacting them with an ethanol solution of γ-methacryloxypropyltrimethoxysilane at 60-80℃ for 2-3 hours, followed by filtration and drying.

[0021] A method for preparing a lignin fiber composite material includes the following steps:

[0022] S1: Soak lignin fibers in a 5%-10% sodium hydroxide solution for 2-4 hours, wash with water until neutral, and then dry at 80-100℃ until the moisture content is ≤5%;

[0023] S2: Mix nano-silica particles with an ethanol solution of γ-methacryloxypropyltrimethoxysilane, stir and react at 60-80℃ for 2-3 hours, filter and dry to obtain modified nanoparticles.

[0024] S3: Immerse the basalt fiber in a 3%-5% KH550 silane coupling agent solution for 1-2 hours, then remove and dry at 80-100℃;

[0025] S4: Graphene oxide dispersion was reacted with ascorbic acid at 60-80℃ for 2-3 hours, and then freeze-dried to obtain graphene aerogel.

[0026] S5: Add the lignin fiber pretreated in S1, the composite matrix resin, the modified nanoparticles obtained in S2, the interface modifier, the toughening agent, the basalt fiber treated in S3, and the graphene aerogel obtained in S4 to a high-speed mixer and mix at 100-200℃ for 5-10 minutes to obtain a mixture.

[0027] S6: The mixture obtained in S5 is fed into a twin-screw extruder with a length-to-diameter ratio of 30-40:1 and melt-blended at 180-220°C. The screw speed is controlled at 200-300 r / min. The vacuum degree is maintained at -0.08 to -0.06 MPa during blending, and then extruded and granulated.

[0028] S7: Preheat the granules at 190-230℃ for 5-10 minutes, mold them under 10-20MPa pressure, and demold them after cooling to room temperature at a cooling rate of 5-10℃ / min.

[0029] Furthermore, the melt blending temperature of the twin-screw extruder in S6 consists of 180-190℃ in the feeding section, 190-210℃ in the compression section, and 210-220℃ in the homogenization section.

[0030] Furthermore, in the S7 compression molding process, the pressure during the preheating stage is 2-5 MPa, and the pressure during the compression molding stage is gradually increased to 10-20 MPa and maintained for 5-15 minutes.

[0031] The beneficial effects of this technical solution are:

[0032] (1) Lignin fiber and basalt fiber form a hybrid reinforcement network of "natural fiber-mineral fiber". The former forms hydrogen bond with the resin with abundant hydroxyl groups, while the latter provides rigid support with high-strength basalt mineral structure. The two intertwine to construct a micron-level mechanical load-bearing skeleton, which increases the tensile strength of the composite material by 40%-60% compared with the single fiber reinforcement system. Nano-silica particles (50-100nm) are uniformly dispersed in the resin matrix and fiber interface, which inhibits crack propagation through "pinning effect". The unique three-dimensional porous structure of graphene aerogel (specific surface area 500-800m² / g) not only acts as a nano-scale reinforcement to transfer load, but also converts impact energy into multiple crack propagation energy through the stress scattering effect of nano-scale pores, which increases the impact strength by 35%-50%. The gradient distribution of multi-scale reinforcement (nanoparticles-micron fibers-aerogel) realizes the full-scale mechanical property optimization from interface to matrix to macro structure.

[0033] (2) Sodium lignosulfonate modified with tannic acid is an amphiphilic interface modifier. In its molecular structure, the sulfonic acid group is bonded to the hydroxyl group on the surface of lignin fiber through ionic bonds, while the tannic acid benzene ring structure is entangled with the molecular chain of the resin matrix through π-π conjugation, forming a dual interface of "chemical bond-physical entanglement". This increases the interfacial shear strength from 25-30N in traditional modification methods to 50-60N, significantly reducing fiber pull-out and interface debonding. At the same time, after the basalt fiber is treated with KH550 silane coupling agent, the amino groups (-NH2) grafted on the surface are cured with epoxy resin to form covalent bonds, further enhancing the chemical bonding force between the mineral fiber and the composite resin. This constructs a strong coupling interface layer of "fiber-interface modifier-matrix", fundamentally solving the compatibility problem between lignin fiber and non-polar resin.

[0034] (3) The twin-screw extruder adopts a deep mixing structure with an aspect ratio of 30-40:1. Through a three-stage temperature control process of resin melting in the feeding section (180-190℃), shear dispersion in the compression section (190-210℃), and component compatibility in the homogenization section (210-220℃), combined with a vacuum degree of -0.08 to -0.06MPa to remove volatiles, the size of nanoparticle aggregates is reduced from 500nm in the traditional process to below 100nm, and the fiber dispersion uniformity is improved by 30%. In the compression molding process, the low pressure (2-5MPa) in the preheating stage promotes resin wetting of the fiber surface, and the pressure is gradually increased to 10-20MPa in the compression stage to eliminate internal pores. Combined with a gradient cooling rate of 5-10℃ / min to control the resin crystallinity, a composite material with a density of ≥98% is finally obtained. The porosity is reduced by 60% compared with the existing technology, and the bending strength and fatigue resistance are significantly improved.

[0035] (4) The core raw material, lignin fiber, is derived from agricultural straw waste. Graphene aerogel is prepared by ascorbic acid reduction (avoiding the use of toxic reducing agents). The overall process energy consumption is reduced by 25% compared with traditional thermosetting composite materials, which is in line with the global green manufacturing trend. At the same time, the synergistic use of basalt fiber and lignin fiber reduces the amount of expensive resin (the composite matrix resin accounts for 25-45%) while maintaining high performance. The material cost is reduced by 30%-40% compared with pure resin-based composite materials, which has significant economic and environmental benefits. Attached Figure Description

[0036] Figure 1 This is a table of component data for various embodiments of the lignin fiber composite material and its preparation method proposed in this invention;

[0037] Figure 2 This is a table of preparation parameter data for a lignin fiber composite material and its preparation method proposed in this invention;

[0038] Figure 3 This is a comparative table of experimental data for embodiments of the lignin fiber composite material and its preparation method proposed in this invention;

[0039] Figure 4 This table compares the lignin fiber composite material proposed in this invention and its preparation method with existing technologies. Detailed Implementation

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

[0041] The specific implementation process is as follows:

[0042] Example 1:

[0043] Please see Figure 1-4 The present invention provides a technical solution: a lignin fiber composite material and its preparation method, comprising the following components by weight: 40 parts of pretreated lignin fiber, 30 parts of composite matrix resin (PP:EP=2:1), 8 parts of modified nano silica particles, 5 parts of interface modifier, 6 parts of toughening agent, 4 parts of graphene aerogel, and 5 parts of treated basalt fiber.

[0044] The preparation method is as follows:

[0045] S1: Lignin Fiber Pretreatment: 40g of corn stalk lignin fiber was added to 500mL of 8% sodium hydroxide solution (prepared using analytical grade sodium hydroxide) and soaked at room temperature (25℃) for 3 hours, stirring once every hour during the soaking process. After soaking, the fiber was washed several times with deionized water until the pH of the washing solution was 7, which was measured using a pH meter (model PHS-3C). Then, the fiber was placed in a forced-air drying oven (model DHG-9145A) and dried at 90℃ for 12 hours. After drying, the moisture content was measured using a moisture meter (model MB25), and the result was 4.2%.

[0046] S2: Nanoparticle modification: 8g of 80nm nano-silica (model AEROSIL200) was mixed with 160mL of 2wt% γ-methacryloxypropyltrimethoxysilane ethanol solution (ethanol was analytical grade, silane coupling agent was chemically pure), and placed in a reaction vessel equipped with a stirrer. The mixture was reacted at 70℃ and 150r / min for 2.5 hours. After the reaction, the mixture was filtered using a Buchner funnel. The filtered particles were then placed in a vacuum drying oven (model DZF-6020) and dried at 60℃ and a vacuum of -0.08MPa for 12 hours.

[0047] S3: Basalt fiber treatment: Immerse 5g of basalt fiber (monofilament diameter 12μm) in 100mL of 4% KH550 silane coupling agent solution (ethanol:water volume ratio = 9:1, both analytical grade) at room temperature for 1.5 hours; after removal, rinse 3 times with analytical grade ethanol, and then dry in an oven (model 101-2AB) at 80℃ for 2 hours;

[0048] S4: Preparation of graphene aerogel: Take 200 mL of graphene oxide dispersion with a concentration of 5 mg / mL (prepared by Hummers method), and use an ultrasonic cleaner (model KQ-500DE) to sonicate for 30 minutes until uniformly dispersed; add 200 mg of ascorbic acid (analytical grade) and stir evenly, transfer to a reaction vessel, and react in a 65℃ water bath for 2.5 hours; after the reaction is completed, the product is quickly frozen to -80℃, and then placed in a freeze dryer (model LGJ-18S) and dried at -50℃ and a vacuum degree of 10 Pa for 48 hours. After drying, the aerogel is crushed to a particle size of 1-2 mm for later use.

[0049] S5: Premixing treatment: Add the above-treated lignin fibers, 30g PP-HM-150 polypropylene resin particles, 15g E-51 epoxy resin particles, modified nanoparticles, 5g interface modifier powder, 6g hydroxyl-terminated liquid nitrile rubber (model CTBN-1300X8), treated basalt fiber segments (length 5-10mm) and 4g graphene aerogel particles to a high-speed mixer (model SHR-10A) and mix for 8 minutes at 150℃ and 300r / min.

[0050] S6: Melt Blending: The premixed material is fed into a twin-screw extruder (length-to-diameter ratio 35:1). The extruder temperature is set as follows: feeding section 185℃, compression section 200℃, homogenization section 215℃, screw speed 250r / min, and vacuum degree is maintained at -0.07MPa during the blending process. After the extrudate is water-cooled and stretched (cooling water temperature 20℃), it is pelletized using a pelletizer.

[0051] S7: Compression molding: The composite material granules are dried in a forced-air drying oven at 80℃ for 2 hours, and then transferred to a flat vulcanizing machine (model XLB-D400×400×2). First, it is preheated at 210℃ for 8 minutes (preheating stage pressure 3MPa), then the pressure is gradually increased to 15MPa and held for 15 minutes. After cooling to room temperature at a cooling rate of 8℃ / min, it is demolded to obtain a lignin fiber composite material board with a size of 100mm×100mm×3mm.

[0052] Example 2:

[0053] Please see Figure 1-4 The present invention provides a technical solution: a lignin fiber composite material and its preparation method, comprising the following components by weight: 30 parts of pretreated lignin fiber, 45 parts of composite matrix resin (PP:EP=3:1), 5 parts of modified nano silica particles, 7 parts of interface modifier, 4 parts of toughening agent, 6 parts of graphene aerogel, and 3 parts of treated basalt fiber.

[0054] The preparation method is as follows:

[0055] S1: Lignin Fiber Pretreatment: 30g of corn stalk lignin fiber was added to 300mL of 10% sodium hydroxide solution (prepared using analytical grade sodium hydroxide) and soaked at room temperature (25℃) for 2 hours, stirring once every 0.5 hours. After soaking, the fiber was washed several times with deionized water until the pH of the washing solution was 7, and the pH was measured using a pH meter (model PHS-3C). Then the fiber was placed in a forced-air drying oven (model DHG-9145A) and dried at 100℃ for 10 hours. After drying, the moisture content was measured using a moisture meter (model MB25), and the result was 3.8%.

[0056] S2: Nanoparticle modification: 5g of 90nm nano-silica (model AEROSILR972) was mixed with 100mL of 2wt% γ-methacryloxypropyltrimethoxysilane ethanol solution (ethanol was analytical grade, silane coupling agent was chemically pure), and placed in a reaction vessel equipped with a stirrer. The mixture was reacted at 60℃ and 150r / min for 3 hours. After the reaction, the mixture was filtered using a Buchner funnel. The filtered particles were then placed in a vacuum drying oven (model DZF-6020) and dried at 60℃ and a vacuum of -0.08MPa for 12 hours.

[0057] S3: Basalt fiber treatment: Immerse 3g of basalt fiber (monofilament diameter 13μm) in 50mL of 5% KH550 silane coupling agent solution (ethanol:water volume ratio = 9:1, both analytical grade) at room temperature for 1 hour; after removal, rinse 3 times with analytical grade ethanol, and then dry in an oven (model 101-2AB) at 80℃ for 2 hours;

[0058] S4: Preparation of graphene aerogel: Take 300 mL of graphene oxide dispersion with a concentration of 5 mg / mL (prepared by Hummers method), and use an ultrasonic cleaner (model KQ-500DE) to sonicate for 30 minutes until uniformly dispersed; add 300 mg of ascorbic acid (analytical grade) and stir evenly, transfer to a reaction vessel, and react in an 80℃ water bath for 2 hours; after the reaction, quickly freeze the product to -80℃, and then put it into a freeze dryer (model LGJ-18S) and dry it at -50℃ and a vacuum degree of 10 Pa for 48 hours. After drying, break the aerogel to a particle size of 1-2 mm for later use.

[0059] S5: Premixing treatment: Add the above-treated lignin fibers, 45g PP-HM-150 polypropylene resin particles, 15g E-51 epoxy resin particles, modified nanoparticles, 7g interface modifier powder, 4g hydroxyl-terminated liquid nitrile rubber (model CTBN-1300X8), treated basalt fiber segments (length 5-10mm) and 6g graphene aerogel particles to a high-speed mixer (model SHR-10A) and mix for 5 minutes at 200℃ and 300r / min.

[0060] S6: Melt Blending: The premixed material is fed into a twin-screw extruder (length-to-diameter ratio 35:1). The extruder temperature is set as follows: feeding section 180℃, compression section 190℃, homogenization section 210℃, screw speed 200r / min, and vacuum degree is maintained at -0.08MPa during the blending process. After the extrudate is water-cooled and stretched (cooling water temperature 20℃), it is pelletized using a pelletizer.

[0061] S7: Compression molding: The composite material granules are dried in a forced-air drying oven at 80℃ for 2 hours, and then transferred to a flat vulcanizing machine (model XLB-D400×400×2). First, it is preheated at 190℃ for 10 minutes (preheating stage pressure 2MPa), then the pressure is gradually increased to 20MPa and held for 15 minutes. After cooling to room temperature at a cooling rate of 5℃ / min, it is demolded to obtain a lignin fiber composite material board with a size of 100mm×100mm×3mm.

[0062] Example 3:

[0063] Please see Figure 1-4 The present invention provides a technical solution: a lignin fiber composite material and its preparation method, comprising the following components by weight: 50 parts of pretreated lignin fiber, 25 parts of composite matrix resin (PP:EP=2.5:1), 12 parts of modified nano silica particles, 3 parts of interface modifier, 9 parts of toughening agent, 2 parts of graphene aerogel, and 8 parts of treated basalt fiber.

[0064] The preparation method is as follows:

[0065] S1: Lignin Fiber Pretreatment: 50g of corn stalk lignin fiber was added to 600mL of 5% sodium hydroxide solution (prepared using analytical grade sodium hydroxide) and soaked at room temperature (25℃) for 4 hours, stirring once every hour during the soaking process. After soaking, the fiber was washed several times with deionized water until the pH of the washing solution was 7, which was measured using a pH meter (model PHS-3C). Then, the fiber was placed in a forced-air drying oven (model DHG-9145A) and dried at 80℃ for 15 hours. After drying, the moisture content was measured using a moisture meter (model MB25), and the result was 4.5%.

[0066] S2: Nanoparticle modification: 12g of 70nm nano-silica (model AEROSILR812S) was mixed with 240mL of 2wt% γ-methacryloxypropyltrimethoxysilane ethanol solution (ethanol was analytical grade, silane coupling agent was chemically pure), and placed in a reaction vessel equipped with a stirrer. The mixture was reacted at 75℃ and 150r / min for 2 hours. After the reaction, the mixture was filtered using a Buchner funnel. The filtered particles were then placed in a vacuum drying oven (model DZF-6020) and dried at 60℃ and -0.08MPa for 12 hours.

[0067] S3: Basalt fiber treatment: Immerse 8g of basalt fiber (monofilament diameter 10μm) in 160mL of 3% KH550 silane coupling agent solution (ethanol:water volume ratio = 9:1, both analytical grade) at room temperature for 2 hours; after removal, rinse 3 times with analytical grade ethanol, and then dry in an oven (model 101-2AB) at 100℃ for 2 hours;

[0068] S4: Preparation of graphene aerogel: Take 100 mL of graphene oxide dispersion with a concentration of 5 mg / mL (prepared by Hummers method), and use an ultrasonic cleaner (model KQ-500DE) to sonicate for 30 minutes until uniformly dispersed; add 100 mg of ascorbic acid (analytical grade) and stir evenly, transfer to a reaction vessel, and react in a 70℃ water bath for 3 hours; after the reaction, quickly freeze the product to -80℃, and then put it into a freeze dryer (model LGJ-18S) and dry it at -50℃ and a vacuum degree of 10 Pa for 48 hours. After drying, break the aerogel to a particle size of 1-2 mm for later use.

[0069] S5: Premixing treatment: Add the above-treated lignin fibers, 25g PP-HM-150 polypropylene resin particles, 10g E-51 epoxy resin particles, modified nanoparticles, 3g interface modifier powder, 9g hydroxyl-terminated liquid nitrile rubber (model CTBN-1300X8), treated basalt fiber segments (length 5-10mm) and 2g graphene aerogel particles to a high-speed mixer (model SHR-10A) and mix for 10 minutes at 100℃ and 300r / min.

[0070] S6: Melt Blending: The premixed material is fed into a twin-screw extruder (length-to-diameter ratio 35:1). The extruder temperature is set as follows: feeding section 180℃, compression section 210℃, homogenization section 220℃, screw speed 300r / min, and vacuum degree is maintained at -0.06MPa during the blending process. After the extrudate is water-cooled and stretched (cooling water temperature 20℃), it is pelletized using a pelletizer.

[0071] S7: Compression molding: The composite material granules are dried in a forced-air drying oven at 80℃ for 2 hours, and then transferred to a flat vulcanizing machine (model XLB-D400×400×2). First, it is preheated at 230℃ for 5 minutes (preheating stage pressure 5MPa), then the pressure is gradually increased to 10MPa and held for 15 minutes. After cooling to room temperature at a cooling rate of 10℃ / min, it is demolded to obtain a lignin fiber composite material board with a size of 100mm×100mm×3mm.

[0072] Example 4

[0073] Please see Figure 1-4The present invention provides a comparative embodiment of graphene-free aerogel, which, by weight, comprises the following components: 40 parts of pretreated lignin fiber, 30 parts of composite matrix resin (PP:EP=2:1), 8 parts of modified nano silica particles, 5 parts of interface modifier, 6 parts of toughening agent, 0 parts of graphene aerogel, and 5 parts of treated basalt fiber.

[0074] The preparation method is as follows:

[0075] S1: Lignin fiber pretreatment: Same as S1 in Example 1, except that 40g of fiber and 500mL of 8% sodium hydroxide solution were used, and the moisture content after drying was 4.2%;

[0076] S2: Nanoparticle modification: Same as S2 in Example 1, except that 8g of nano silica is used, and the modified particles are ready for use.

[0077] S3: Basalt fiber treatment: Same as S3 in Example 1, except that 5g of basalt fiber is used and used for later use after treatment;

[0078] S4: Preparation of graphene aerogel: This step is omitted in this embodiment, and no graphene aerogel is added;

[0079] S5: Premixing treatment: Add the treated lignin fiber, 30g PP-HM-150 and 15g E-51 resin, modified nanoparticles, 5g interface modifier, 6g toughening agent and 5g basalt fiber to the mixer and mix at 150℃ for 8 minutes (no graphene aerogel).

[0080] S6: Melt blending: Same as S6 in Example 1, except that the extruder temperature is set to 185°C in the feeding section, 200°C in the compression section, and 215°C in the homogenization section, and the screw speed is 250 r / min.

[0081] S7: Compression molding: Same as S7 in Example 1, except that the preheating temperature is 210℃, the molding pressure is 15MPa, and the cooling rate is 8℃ / min.

[0082] Example 5

[0083] Please see Figure 1-4 The present invention provides a comparative embodiment of basalt fiber: by weight, it includes the following components: 40 parts of pretreated lignin fiber, 30 parts of composite matrix resin (PP:EP=2:1), 8 parts of modified nano silica particles, 5 parts of interface modifier, 6 parts of toughening agent, 4 parts of graphene aerogel, and 0 parts of treated basalt fiber.

[0084] The preparation method is as follows:

[0085] S1: Lignin fiber pretreatment: Same as S1 in Example 1, except that 40g of fiber and 500mL of 8% sodium hydroxide solution were used, and the moisture content after drying was 4.2%;

[0086] S2: Nanoparticle modification: Same as S2 in Example 1, except that 8g of nano silica is used, and the modified particles are ready for use.

[0087] S3: Basalt fiber treatment: This step is omitted in this embodiment, and no basalt fiber is added;

[0088] S4: Preparation of graphene aerogel: Same as S4 in Example 1, except that 4g of graphene aerogel is prepared for later use.

[0089] S5: Premixing treatment: Add the treated lignin fiber, 30g PP-HM-150 and 15g E-51 resin, modified nanoparticles, 5g interface modifier, 6g toughening agent and 4g graphene aerogel to the mixer and mix at 150℃ for 8 minutes (without basalt fiber).

[0090] S6: Melt blending: Same as S6 in Example 1, except that the extruder temperature is set to 185°C in the feeding section, 200°C in the compression section, and 215°C in the homogenization section, and the screw speed is 250 r / min.

[0091] S7: Compression molding: Same as S7 in Example 1, except that the preheating temperature is 210℃, the molding pressure is 15MPa, and the cooling rate is 8℃ / min.

[0092] Example 6

[0093] Please see Figure 1-4 The present invention provides a prior art comparative example, which is single lignin fiber reinforced without interface modifier: by weight, it includes the following components: 50 parts of untreated lignin fiber, 50 parts of polypropylene resin (PP-HM-150), and 0 parts of other components (no composite resin, nanoparticles, interface modifier, toughening agent, graphene aerogel, basalt fiber).

[0094] The preparation method is as follows:

[0095] S1: Lignin fiber treatment: Use 50g of untreated corn stalk lignin fiber directly, without alkali soaking and drying (moisture content about 12%).

[0096] S2: Mixing and molding: Add 50g of lignin fiber and 50g of polypropylene resin granules to a high-speed mixer (model SHR-10A) and mix for 5 minutes at 180℃ and 200r / min.

[0097] S3: Melt blending: The mixture is fed into a single screw extruder (model SJ-30, length-to-diameter ratio 25:1), the extrusion temperature is set to 180℃, the screw speed is 150r / min, and the extrudate is granulated after being water-cooled and stretched.

[0098] S4: Compression molding: Dry the granules in a forced-air drying oven at 80°C for 1 hour, transfer them to a flat vulcanizing machine, and directly compress them at 190°C (without a preheating stage). Maintain a pressure of 10MPa for 10 minutes, and demold after natural cooling to room temperature.

[0099] Please see Figure 1-4 In Example 4, the absence of graphene aerogel resulted in a 19.4% decrease in tensile strength, a 32.7% decrease in interfacial bonding force, and a 38.9% increase in water absorption. This is because the nanoporous structure of graphene aerogel can effectively adsorb the resin matrix, forming a "physical anchoring" effect. At the same time, its high specific surface area enhances the interfacial contact area and reduces the water penetration path.

[0100] In Example 5, without basalt fiber, the bending strength decreased by 15.2% and the impact strength decreased by 24.6%. The basalt fiber and lignin fiber form a "rigid-flexible complementary" fiber network: the basalt fiber (high elastic modulus) bears the main load, and the lignin fiber (good toughness) absorbs the impact energy. The two work together to improve the bending and impact resistance of the composite material.

[0101] Example 6 (Prior Art) did not use an interface modifier, and the interfacial bonding force was only 22N, less than 42% of that in Example 1; the amphiphilic structure of tannic acid-modified sodium lignosulfonate (polar sulfonic acid group affinity for lignin fibers, nonpolar benzene ring affinity for resin matrix) effectively reduced the interfacial tension, significantly improved the compatibility of the two phases through "molecular bridging" and reduced interfacial defects.

[0102] In Examples 1-3, the PP and EP blending ratios were different (2:1 to 3:1). It was found that the strength was highest when PP:EP = 2.5:1 (Example 3). This is because the epoxy groups of epoxy resin (EP) form chemical bonds with the hydroxyl groups on the surface of lignin fibers, while polypropylene (PP) provides good processing fluidity. The blending of the two achieves a balance between "strong interfacial bonding" and "excellent molding performance".

[0103] Example 3 uses a higher extruder homogenization section temperature (220°C) and screw speed (300 r / min), which promotes the uniformity of dispersion of nano-silica and increases the tensile strength to 92.3 MPa;

[0104] Example 2 had a higher molding pressure (20 MPa), but the increased graphene aerogel content (6 parts) made dispersion more difficult and the impact strength decreased slightly, indicating that the optimal match between component ratio and process parameters needs to be found.

[0105] By constructing a four-level reinforcement structure consisting of lignin fiber (bio-based), basalt fiber (inorganic fiber), graphene aerogel (nanocarbon material), and nano silica, a "bio-inorganic-nano" cross-scale reinforcement network was built, breaking through the performance limit of traditional single fiber reinforcement.

[0106] Tannic acid-modified sodium lignosulfonate, as a novel interface modifier, utilizes the synergistic effect of biomass-derived molecules (tannic acid) and sodium lignosulfonate to achieve bidirectional interface optimization between lignin fibers and resin matrices. No similar modifier has been found in the existing technology.

[0107] The temperature zone control of the twin-screw extruder (gradient heating from feeding section to compression section to homogenization section) and the pressure gradient adjustment of compression molding effectively solve the problems of dispersion and molding density when mixing multiple components, forming a complete preparation process system.

[0108] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific technical solutions or characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A lignin fiber composite material, characterized by, By weight parts, including the following components: lignin fiber 30-50 parts, composite matrix resin 25-45 parts, nano-enhanced particles 5-12 parts, interface modifier 3-7 parts, toughening agent 4-9 parts, graphene aerogel 2-6 parts, basalt fiber 3-8 parts; The composite matrix resin is a polypropylene resin compounded with an epoxy resin at a mass ratio of 2:1 to 3:1; The nano-enhanced particles are nano-silica particles with a surface treated by γ-methacryloxypropyl trimethoxysilane, and the particle size is 50-100 nm; The interface modifier is sodium lignosulfonate modified by tannic acid; The toughening agent is a hydroxyl-terminated liquid butyl nitrile rubber; The lignin fiber is an agricultural straw lignin fiber, which is soaked in a 5%-10% sodium hydroxide solution for 2-4 hours, washed with water to neutral and dried; The basalt fiber is soaked in a 3%-5% KH550 silane coupling agent solution for 1-2 hours and dried at 80-100°C; The solvent of the KH550 silane coupling agent solution is selected from ethanol and water, and the volume ratio of the ethanol to water is 8-9:1-2.

2. The lignin fiber composite material according to claim 1, characterized in that, The preparation method of the graphene aerogel is as follows: graphene oxide dispersion liquid is reacted with ascorbic acid at 60-80°C for 2-3 hours, and then freeze-dried to obtain the graphene aerogel, and the specific surface area of the graphene aerogel is 500-800 m² / g.

3. The lignin fiber composite material according to claim 1, characterized in that, The surface treatment method of the nano-silica particles is as follows: the nano-silica particles are stirred and reacted with an ethanol solution of γ-methacryloxypropyl trimethoxysilane at 60-80°C for 2-3 hours, and then filtered and dried to obtain the nano-silica particles.

4. A method for producing a lignin fiber composite material as claimed in any one of claims 1 to 3, characterized in that, The method comprises the following steps: S1: soaking the lignin fiber in a 5%-10% sodium hydroxide solution for 2-4 hours, washing with water to neutral, and drying at 80-100°C to a water content of ≤5%; S2: mixing the nano-silica particles with an ethanol solution of γ-methacryloxypropyl trimethoxysilane, stirring and reacting at 60-80°C for 2-3 hours, and then filtering and drying to obtain modified nano-particles; S3: soaking the basalt fiber in a 3%-5% KH550 silane coupling agent solution for 1-2 hours, and then drying at 80-100°C after taking out; S4: reacting graphene oxide dispersion liquid with ascorbic acid at 60-80°C for 2-3 hours, and then freeze-drying to obtain graphene aerogel; S5: adding the pretreated lignin fiber of S1, the composite matrix resin, the modified nano-particles of S2, the interface modifier, the toughening agent, the basalt fiber treated in S3, and the graphene aerogel obtained in S4 into a high-speed mixer, and mixing at 100-200°C for 5-10 minutes to obtain a mixture; S6: putting the mixture obtained in S5 into a double-screw extruder with a length-diameter ratio of 30-40:1, and melt blending at 180-220°C, controlling the screw speed at 200-300 r / min, and controlling the vacuum degree at -0.08 to -0.06 MPa during blending, and then extruding and granulating. S7: preheat the material obtained in S6 at 190-230℃ for 5-10 minutes, and then mold it under a pressure of 10-20 MPa, and cool it down to room temperature at a rate of 5-10℃ / min, and then demold it.

5. The method for preparing the lignin fiber composite material according to claim 4, characterized in that, The melt blending temperature of the twin-screw extruder in S6 is composed of 180-190℃ for the feeding section, 190-210℃ for the compression section, and 210-220℃ for the homogenization section.

6. The method for preparing the lignin fiber composite material according to claim 4, characterized in that, In the process of molding in S7, the pressure in the preheating stage is 2-5 MPa, and the pressure in the molding stage is gradually increased to 10-20 MPa and maintained for 5-15 minutes.

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