A degradable and re-plasticable whole-lignin-based heat-conducting gel and a preparation method thereof

Abstract

The present application relates to a kind of degradable and reworkable full lignin-based heat-conducting gel and its preparation method and application.The present application uses different solvents to extract industrial alkali lignin in echelon, prepares alkali lignin with different molecular weight, phenol / alcohol hydroxyl content, respectively by adjusting the proportion of different grafting reagent and extracted lignin hydroxyl, double-component full lignin-based resin is prepared, based on the functional group characteristics of grafting reagent, realize the dynamic crosslinking between double-component alkali lignin unit, while the residual hydroxyl in alkali lignin provides bonding performance, so as to give it still has excellent reworkable characteristics and degradable characteristics after curing.In addition, the strong interface interaction is constructed between the benzene ring structure of lignin and graphene or carbon nanotube, the dispersion and interface combination of heat-conducting filler in double-component full lignin-based resin matrix are improved, the optimization of internal interface thermal resistance of full lignin-based heat-conducting gel is realized, and it is given excellent thermal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of lignin functional materials technology, and relates to a biodegradable and replastic all-lignin-based thermal conductive gel, its preparation method and application. Background Technology

[0002] As electronic devices evolve towards miniaturization, higher frequencies, and higher power densities, efficient heat dissipation has become crucial for ensuring their reliability and lifespan. Thermal interface materials, such as thermally conductive gels and pads, are widely used between chips and heat sinks to fill microscopic gaps and dissipate accumulated heat. Currently, most commercially available thermal interface materials are based on synthetic polymers (such as silicone rubber and epoxy resin) and filled with high thermal conductivity fillers (such as alumina and boron nitride). While these materials possess excellent thermal and mechanical properties, they lack replasticity after curing and cross-linking. Furthermore, the synthetic polymer matrix is ​​derived from non-renewable petrochemical resources and is difficult to degrade in the natural environment, easily leading to "white pollution" after disposal, which contradicts the strategic goals of global sustainable development.

[0003] To achieve green development in the electronics industry, the development of biodegradable or biomass-derived environmentally friendly thermal interface materials has become a research hotspot. Among these, utilizing natural polymer materials to construct the matrix is ​​one ideal solution. Lignin, the second most abundant natural aromatic polymer in the world, is a major byproduct of the pulp and paper industry. While its annual production is enormous, its utilization rate is low, with most being directly incinerated as "black liquor," resulting in significant resource waste. Utilizing lignin—a cheap, renewable, and biodegradable "waste"—in the field of thermal conductive materials can not only reduce dependence on fossil resources but also turn waste into treasure, yielding significant economic and environmental benefits.

[0004] However, the direct application of lignin to high-performance thermal conductive materials still faces two major technical bottlenecks: First, industrial lignin (such as alkali lignin) has a complex structure, limited reactive sites, and poor compatibility, resulting in weak interfacial interaction between it and thermally conductive fillers, making it difficult to construct an efficient heat conduction network; Second, lignin itself does not have the ability to be reversibly processed or controlled to degrade, and materials prepared with it as a matrix are often difficult to achieve controlled recycling or environmentally friendly degradation at the end of their life cycle.

[0005] Therefore, the purpose of this invention is to overcome the above limitations and provide a fully lignin-based thermally conductive gel that uses industrial alkali lignin as the core raw material. Based on the molecular structure characteristics of lignin, it is designed to impart reversible cross-linking properties, thereby preparing a gel with excellent thermal conductivity, mechanical properties, biodegradability, and replasticity. This material is expected to decompose under specific environmental conditions after disposal, ultimately degrading into environmentally harmless substances, providing an innovative solution for next-generation green electronic packaging and thermal management. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a biodegradable and replastic all-lignin-based thermally conductive gel. Using industrial waste alkali lignin as the starting material, and leveraging the unsaturated conjugated system and abundant hydroxyl groups within its molecular framework (composed of benzene rings and their substituents), the invention first extracts lignin with different molecular weights and phenol / alcohol hydroxyl contents through a stepwise extraction process using different solvents. Then, by adjusting the ratio of different grafting reagents to the extracted lignin hydroxyl groups, a two-component all-lignin-based resin acting as both resin and curing agent is prepared. This imparts weak dynamic cross-linking properties between lignin units, while the residual hydroxyl groups in the alkali lignin provide adhesive properties, resulting in excellent replasticity and biodegradability after curing. Secondly, graphene and carbon nanotubes are used as thermally conductive fillers. The strong π-π stacking interaction between the benzene rings of lignin and graphene or carbon nanotubes improves the dispersion and interfacial bonding of the thermally conductive fillers within the two-component all-lignin-based resin matrix, optimizing the interfacial thermal resistance of the all-lignin-based thermally conductive gel and giving it excellent thermal conductivity.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution.

[0008] This invention provides a method for preparing a biodegradable and replastic all-lignin-based thermally conductive gel, comprising the following steps:

[0009] (1) Place lignin and organic solvent in a container and extract under ultrasonic conditions, then separate the solid and liquid and remove the solvent to obtain lignin extracted by organic solvent;

[0010] (2) Place the lignin extracted by organic solvent obtained in step (1) into a container, and slowly add a solution containing grafting reagent 1 under a protective gas atmosphere, and then carry out a reflux reaction; after the reaction is completed, remove the solvent to obtain the first component lignin-based resin.

[0011] (3) Place the lignin extracted by organic solvent obtained in step (1) in a container, and slowly add a solution containing grafting reagent 2 under a protective gas atmosphere, and then carry out a reflux reaction; after the reaction is completed, remove the solvent to obtain the second component lignin-based resin.

[0012] (4) Take the first component lignin-based resin obtained in step (2), the second component lignin-based resin obtained in step (3), the thermally conductive filler, and the solvent, stir and mix them, and then cure them to obtain the final product.

[0013] Preferably, the lignin in step (1) is selected from alkali lignin; more preferably, the lignin is selected from industrial waste alkali lignin, such as industrial alkali lignin from self-made pulp and paper waste.

[0014] Preferably, the organic solvent in step (1) is selected from one or more of ethyl acetate, acetone, ethanol, dichloromethane, tetrahydrofuran, and methanol.

[0015] Preferably, the mass-volume ratio (g:mL) of lignin to organic solvent in step (1) is 1:1-2.

[0016] Preferably, the ultrasonic power in step (1) is 500-800W and the time is 30-120min.

[0017] Preferably, the lignin extracted by the organic solvent in step (1) has a molecular weight of 553-4102 Da, a phenolic hydroxyl content of 1.577-2.342 mmol / g, and an alcoholic hydroxyl content of 0.4013-1.301 mmol / g.

[0018] Preferably, the grafting reagent 1 in step (2) is selected from one or more of 2-maleimide acetyl chloride, 3-maleimide propionyl chloride, 4-maleimide butyryl chloride, 6-maleimide hexanoyl chloride, 5-maleimide pentanoyl chloride, and 11-maleimide decanoyl chloride.

[0019] Preferably, the solvent used to dissolve the grafting reagent 1 in step (2) is selected from one or more of ethyl acetate, acetone, acetonitrile, dichloromethane, tetrahydrofuran, and butanone.

[0020] Preferably, the molar ratio of the total hydroxyl groups of the lignin extracted by the organic solvent in step (2) to the grafting reagent 1 is 1:0.8-1.8.

[0021] Preferably, the reflux reaction in step (2) is carried out at a temperature of 50-100°C for 12-48 hours.

[0022] Preferably, the protective gas in step (2) is selected from one or more of nitrogen, argon, helium, hydrogen, and carbon dioxide.

[0023] Preferably, the grafting reagent 2 in step (3) is selected from one or more of 3-(2-furan)propionyl chloride, 2-furan acetyl chloride, and 4-(furan-2-yl)-4-oxobutyric acid.

[0024] Preferably, the solvent used to dissolve the grafting reagent 2 in step (3) is selected from one or more of ethyl acetate, acetone, acetonitrile, dichloromethane, tetrahydrofuran, and butanone.

[0025] Preferably, the molar ratio of the total hydroxyl groups of the lignin extracted by the organic solvent in step (3) to the grafting reagent 2 is 1:0.8-1.8.

[0026] Preferably, the reflux reaction in step (3) is carried out at a temperature of 50-100°C for 12-48 hours.

[0027] Preferably, the protective gas in step (3) is selected from one or more of nitrogen, argon, helium, hydrogen, and carbon dioxide.

[0028] Preferably, the thermally conductive filler in step (4) is selected from one or more of graphene, graphite, and carbon nanotubes.

[0029] Preferably, the amount of thermally conductive filler used in step (4) is 20-40 wt% of the total mass of the first component lignin-based resin, the second component lignin-based resin and the thermally conductive filler; it should be understood that the total mass here is the sum of the masses of all solid components, that is, the total mass of the first component lignin-based resin, the second component lignin-based resin and the thermally conductive filler.

[0030] Preferably, the solvent in step (4) is selected from one or more of ethyl acetate, acetone, ethanol, dichloromethane, tetrahydrofuran, and butanone.

[0031] Preferably, the stirring temperature in step (4) is 25-60℃, the stirring speed is 10000-16000rpm, and the stirring time is 10-35min.

[0032] Preferably, the curing temperature in step (4) is 100-140℃ and the time is 2-6h.

[0033] A second aspect of the present invention provides a biodegradable and replastic all-lignin-based thermally conductive gel prepared according to the above preparation method.

[0034] The third aspect of the present invention provides the application of the biodegradable and replastic all-lignin-based thermal conductive gel prepared according to the above preparation method in heat dissipation of electronic devices.

[0035] Compared with existing technologies, the present invention has the following advantages:

[0036] (1) This invention uses industrial alkali lignin, a waste product of pulping and papermaking, as the starting material. It uses different solvents to extract alkali lignin with different molecular weights and phenol / alcohol hydroxyl contents in stages. By adjusting the ratio of different grafting reagents to the extracted lignin hydroxyl groups, a two-component all-lignin-based resin that acts as both resin and curing agent is prepared. Based on the functional group characteristics of the grafting reagent, dynamic cross-linking between alkali lignin units is achieved. At the same time, the residual hydroxyl groups in alkali lignin provide adhesive properties, thus endowing it with excellent replasticity and degradability after curing, and expanding the high-value utilization of biomass resources.

[0037] (2) This invention uses graphene, graphite, carbon nanotubes, etc., as thermally conductive fillers. It utilizes the strong π-π stacking effect between the benzene ring structure of lignin and graphene or carbon nanotubes to improve the dispersion and interfacial bonding of the thermally conductive filler in the two-component all-lignin-based resin matrix, thereby optimizing the interfacial thermal resistance of the all-lignin-based thermally conductive gel and endowing it with excellent thermal conductivity. The thermal conductivity of the prepared all-lignin-based thermally conductive gel can reach 3.89-9.887 W·m. -1 ·K -1 The thermal resistance is 0.0345-0.274. Detailed Implementation

[0038] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0039] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention. Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention are commercially available or can be prepared by existing methods.

[0040] Example 1

[0041] A biodegradable and replastic all-lignin-based thermal conductive gel, the preparation method of which specifically includes the following steps:

[0042] (1) 500g of industrial alkali lignin from pulp and paper waste and 500mL of ethyl acetate were placed in a 1000mL beaker and extracted by stirring at room temperature (25℃) and 700W ultrasonic conditions for 30min. The supernatant was then separated and the solvent was removed by rotary evaporation to obtain alkali lignin extracted by ethyl acetate. The molecular weight of the lignin was 1571Da, the phenolic hydroxyl content was 2.287mmol / g, and the alcoholic hydroxyl content was 0.4013mmol / g.

[0043] (2) Place 10g of alkali lignin (total hydroxyl content of 26.883mmol) extracted by ethyl acetate obtained in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 2-maleimide acetyl chloride solution (40.3245mmol 2-maleimide acetyl chloride dissolved in 20mL ethyl acetate) dropwise at 0℃ under nitrogen atmosphere, and then reflux at 95℃ for 12h; after the reaction is completed, remove ethyl acetate by rotary evaporation to obtain the first component lignin-based resin.

[0044] (3) Place 10g of alkali lignin (total hydroxyl content of 26.883mmol) obtained by ethyl acetate extraction in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 3-(2-furan)propionyl chloride solution (40.3245mmol 3-(2-furan)propionyl chloride dissolved in 20mL ethyl acetate) at 0℃ and under nitrogen atmosphere, and then reflux at 95℃ for 12h; after the reaction is completed, remove ethyl acetate by rotary evaporation to obtain the second component lignin-based resin.

[0045] (4) Take the first component lignin-based resin obtained in step (2), the second component lignin-based resin obtained in step (3), and graphite accounting for 30% of the total mass fraction of the first and second components lignin and thermally conductive filler, respectively, mix them, add 15 mL of ethyl acetate, stir for 35 min at 50 °C and 12000 rpm, evaporate the solvent, place the mixture in a silicone mold and cure at 120 °C for 3 h, and cool to room temperature to obtain the final product.

[0046] Example 2

[0047] A biodegradable and replastic all-lignin-based thermal conductive gel, the preparation method of which specifically includes the following steps:

[0048] (1) Place 500g of industrial alkali lignin solid residue extracted with ethyl acetate in step (1) of Example 1 and 600mL of acetone in a 1000mL beaker and stir and extract for 50min at room temperature (25℃) and 700W ultrasonic conditions. Then take the supernatant for separation and remove the solvent by rotary evaporation to obtain alkali lignin extracted with acetone. The molecular weight of the lignin is 3055Da, the phenolic hydroxyl content is 1.68mmol / g, and the alcoholic hydroxyl content is 0.7588mmol / g.

[0049] (2) Place 10g of alkali lignin (total hydroxyl content of 24.388mmol) obtained by acetone extraction in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 3-maleimide propionyl chloride solution (26.8268mmol 3-maleimide propionyl chloride dissolved in 30mL acetone) at 0℃ under nitrogen atmosphere, and then reflux at 70℃ for 24h; after the reaction is completed, remove acetone by rotary evaporation to obtain the first component lignin-based resin.

[0050] (3) Place 10g of alkali lignin (total hydroxyl content of 24.388mmol) obtained by acetone extraction in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 2-furanacetyl chloride solution (26.8268mmol 2-furanacetyl chloride dissolved in 30mL acetone) at 0℃ under nitrogen atmosphere, and then reflux at 75℃ for 24h; after the reaction is completed, remove acetone by rotary evaporation to obtain the second component lignin-based resin.

[0051] (4) Take the first component lignin-based resin obtained in step (2), the second component lignin-based resin obtained in step (3), and graphene accounting for 20% of the total mass fraction of the first and second components lignin and thermally conductive filler, respectively, mix them, add 50 mL of acetone and stir for 10 min at 40 °C and 13000 rpm, evaporate the solvent, place the mixture in a silicone mold and cure at 130 °C for 2 h, and cool to room temperature to obtain the final product.

[0052] Example 3

[0053] A biodegradable and replastic all-lignin-based thermal conductive gel, the preparation method of which specifically includes the following steps:

[0054] (1) Place 500g of industrial alkali lignin solid residue extracted with acetone in step (1) of Example 2 and 800mL of anhydrous ethanol in a 2000mL beaker and stir and extract for 40min at room temperature (25℃) and 700W ultrasonic conditions. Then take the supernatant for separation and remove the solvent by rotary evaporation to obtain alkali lignin extracted with ethanol. The molecular weight of lignin is 2062Da, the phenolic hydroxyl content is 1.7874mmol / g, and the alcoholic hydroxyl content is 0.6812mmol / g.

[0055] (2) Place 10g of alkali lignin (total hydroxyl content of 24.686mmol) obtained by ethanol extraction in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 4-maleimide butyryl chloride solution (24.686mmol 4-maleimide butyryl chloride dissolved in 50mL acetonitrile) at 0℃ under nitrogen atmosphere, and then reflux at 85℃ for 48h; after the reaction is completed, remove acetonitrile by rotary evaporation to obtain the first component lignin-based resin.

[0056] (3) Place 10g of alkali lignin (total hydroxyl content of 24.388mmol) obtained by acetone extraction in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 3-(2-furan)propionyl chloride solution (24.686mmol 3-(2-furan)propionyl chloride dissolved in 50mL acetonitrile) at 0℃ and under nitrogen atmosphere, and then reflux at 90℃ for 48h; after the reaction is completed, remove acetonitrile by rotary evaporation to obtain the second component lignin-based resin.

[0057] (4) Take the first component lignin-based resin obtained in step (2), the second component lignin-based resin obtained in step (3), and a mixture of graphene and carbon nanotubes accounting for 30% of the total mass fraction of the first and second components lignin and thermally conductive filler (where the mass ratio of graphene to carbon nanotubes is 3:1) and mix them. Add 60 mL of ethanol and stir for 15 min at 50 °C and 16000 rpm. After evaporating the solvent, place the mixture in a silicone mold and cure it at 140 °C for 3 h. Cool it to room temperature to obtain the final product.

[0058] Example 4

[0059] A biodegradable and replastic all-lignin-based thermal conductive gel, the preparation method of which specifically includes the following steps:

[0060] (1) 500g of industrial alkali lignin from pulp and paper waste and 700mL of dichloromethane were placed in a 1000mL beaker and extracted for 120min under ultrasonic conditions of 700W at room temperature (25℃). The supernatant was then separated and the solvent was removed by rotary evaporation to obtain alkali lignin extracted by dichloromethane. The molecular weight of the lignin was 553Da, the phenolic hydroxyl content was 2.342mmol / g, and the alcoholic hydroxyl content was 0.453mmol / g.

[0061] (2) Place 10g of alkali lignin (total hydroxyl content of 27.95mmol) obtained by dichloromethane extraction in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 6-maleimide hexanoyl chloride solution (22.36mmol 6-maleimide hexanoyl chloride dissolved in 40mL dichloromethane) dropwise at 0℃ and under nitrogen atmosphere, and then reflux at 50℃ for 24h; after the reaction is completed, remove dichloromethane by rotary evaporation to obtain the first component lignin-based resin.

[0062] (3) Place 10g of alkali lignin (total hydroxyl content of 27.95mmol) obtained in step (1) with dichloromethane extraction into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 4-(furan-2-yl)-4-oxobutyric acid solution (22.36mmol 4-(furan-2-yl)-4-oxobutyric acid dissolved in 40mL dichloromethane) dropwise at 0℃ and under nitrogen atmosphere, and then reflux at 50℃ for 12h; after the reaction is completed, remove dichloromethane by rotary evaporation to obtain the second component lignin-based resin.

[0063] (4) Take the first component lignin-based resin obtained in step (2), the second component lignin-based resin obtained in step (3), and graphene accounting for 40% of the total mass fraction of the first and second components lignin and thermally conductive filler, respectively, mix them, add 40 mL of dichloromethane and stir for 10 min at 50 °C and 12000 rpm, evaporate the solvent, place the mixture in a silicone mold and cure at 100 °C for 6 h, and cool to room temperature to obtain the final product.

[0064] Example 5

[0065] A biodegradable and replastic all-lignin-based thermal conductive gel, the preparation method of which specifically includes the following steps:

[0066] (1) 500g of industrial alkali lignin solid residue extracted with dichloromethane in step (1) of Example 4 and 900mL of tetrahydrofuran were placed in a 2000mL beaker and extracted with stirring at room temperature (25℃) and 700W ultrasonic for 90min. Then the supernatant was taken for separation and the solvent was removed by rotary evaporation to obtain alkali lignin extracted with tetrahydrofuran. The molecular weight of the lignin was 4102Da, the phenolic hydroxyl content was 1.931mmol / g, and the alcoholic hydroxyl content was 0.6581mmol / g.

[0067] (2) Place 10g of alkali lignin (total hydroxyl content of 25.891mmol) extracted from tetrahydrofuran obtained in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 5-maleimide pentanoyl chloride solution (33.6583mmol 5-maleimide pentanoyl chloride dissolved in 70mL tetrahydrofuran) dropwise at 0℃ under nitrogen atmosphere, and then reflux at 75℃ for 48h; after the reaction is completed, remove tetrahydrofuran by rotary evaporation to obtain the first component lignin-based resin.

[0068] (3) Place 10g of alkali lignin (total hydroxyl content of 25.891mmol) extracted from tetrahydrofuran obtained in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 4-(furan-2-yl)-4-oxobutyric acid solution (33.6583mmol 4-(furan-2-yl)-4-oxobutyric acid dissolved in 70mL tetrahydrofuran) dropwise at 0℃ and under nitrogen atmosphere, and then reflux at 75℃ for 48h; after the reaction is completed, remove tetrahydrofuran by rotary evaporation to obtain the second component lignin-based resin.

[0069] (4) Take the first component lignin-based resin obtained in step (2), the second component lignin-based resin obtained in step (3), and graphene accounting for 20% of the total mass fraction of the first and second components lignin and thermally conductive filler, respectively, mix them, add 70 mL of tetrahydrofuran, stir for 20 min at 45 °C and 15000 rpm, evaporate the solvent, place the mixture in a silicone mold and cure at 125 °C for 4 h, and cool to room temperature to obtain the final product.

[0070] Example 6

[0071] A biodegradable and replastic all-lignin-based thermal conductive gel, the preparation method of which specifically includes the following steps:

[0072] (1) 500g of industrial alkali lignin solid residue extracted with tetrahydrofuran in step (1) of Example 5 and 1000mL of methanol were placed in a 2000mL beaker and extracted with stirring at room temperature (25℃) and 700W ultrasonic for 60min. Then the supernatant was taken for separation and the solvent was removed by rotary evaporation to obtain methanol-extracted alkali lignin, wherein the molecular weight of lignin was 1815Da, the phenolic hydroxyl content was 1.577mmol / g, and the alcoholic hydroxyl content was 1.301mmol / g.

[0073] (2) Place 10g of methanol-extracted alkali lignin (total hydroxyl content of 28.78mmol) obtained in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 11-maleimide decanoyl chloride solution (51.804mmol 11-maleimide decanoyl chloride dissolved in 80mL butanone) at 0℃ and nitrogen atmosphere, and then reflux at 100℃ for 12h; after the reaction is completed, rotary evaporate to remove butanone to obtain the first component lignin-based resin.

[0074] (3) Place 10g of methanol-extracted alkali lignin (total hydroxyl content of 28.78mmol) obtained in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, and slowly add 4-(furan-2-yl)-4-oxobutyric acid solution (51.804mmol 4-(furan-2-yl)-4-oxobutyric acid dissolved in 80mL butanone) at 0℃ and under nitrogen atmosphere, and then reflux at 100℃ for 12h; after the reaction is completed, rotary evaporate to remove butanone to obtain the second component lignin-based resin.

[0075] (4) Take the first component lignin-based resin obtained in step (2), the second component lignin-based resin obtained in step (3), and carbon nanotubes accounting for 20% of the total mass fraction of the first and second components lignin and thermally conductive filler, respectively, mix them, add 80 mL of butanone, stir for 15 min at 60 °C and 10000 rpm, evaporate the solvent, place the mixture in a silicone mold and cure at 120 °C for 4 h, and cool to room temperature to obtain the final product.

[0076] Comparative Example 1

[0077] A thermally conductive gel, the preparation method of which specifically includes the following steps:

[0078] Commercially available polypropylene glycol diglycidyl ether and polyetheramine D-230 with a molecular weight of 500 were used as resin and curing agent, respectively. They were mixed evenly at a ratio of 1:1 between epoxy groups and amine active hydrogen. Then, graphene accounting for 20% of the total mass fraction of polypropylene glycol diglycidyl ether, polyetheramine D-230 and thermally conductive filler was added and mixed. The mixture was stirred at 40℃ and 10000rpm for 15min. Then, the mixture was placed in a silicone mold and cured at 130℃ for 2h and 180℃ for 2h respectively. After cooling to room temperature, the product was obtained.

[0079] Comparative Example 2

[0080] A thermally conductive gel, the preparation method of which specifically includes the following steps:

[0081] Using Dow Corning Sylgard 184 two-component PDMS as the resin matrix for the thermally conductive gel, PDMS and curing agent were mixed at a mass ratio of 10:1. Then, a mixture of graphene and carbon nanotubes (with a mass ratio of 3:1) at 20% of the total mass fraction of the two-component PDMS and thermally conductive filler was added, along with 10 mL of n-pentane. The mixture was stirred at 40°C and 8000 rpm for 10 min. Subsequently, the mixture was placed in a silicone mold and cured at 120°C for 2 h. After cooling to room temperature, the gel was obtained.

[0082] Comparative Example 3

[0083] A thermally conductive gel, the preparation method of which specifically includes the following steps:

[0084] (1) 500g of industrial alkali lignin from pulp and paper waste and 700mL of dichloromethane were placed in a 1000mL beaker and extracted for 120min under ultrasonic conditions of 700W at room temperature (25℃). The supernatant was then separated and the solvent was removed by rotary evaporation to obtain alkali lignin extracted by dichloromethane. The molecular weight of the lignin was 553Da, the phenolic hydroxyl content was 2.342mmol / g, and the alcoholic hydroxyl content was 0.453mmol / g.

[0085] (2) Place 10g of alkali lignin (total hydroxyl content of 27.95mmol) obtained by dichloromethane extraction in step (1) into a 1000mL three-necked flask equipped with a magnetic stirrer, add 5% tetrabutylammonium chloride of the alkali lignin extracted by dichloromethane, and continue to add 117.1 mmol of epichlorohydrin. Stir at 95℃ for 3 h, remove excess epichlorohydrin by rotary evaporation, slowly add 4.684 g of 20% sodium hydroxide aqueous solution at room temperature, stir at room temperature for 1 h, finally extract with dichloromethane, wash with water 6 times, dry with anhydrous magnesium sulfate, remove dichloromethane by rotary evaporation to obtain lignin-based epoxy resin.

[0086] (3) Take the lignin-based epoxy resin obtained in step (2) and use 4,4'-diaminodiphenylmethane as a curing agent. Mix them evenly with epoxy groups and amino active hydrogen in a ratio of 1:1. Then, add lignin-based epoxy resin, 4,4'-diaminodiphenylmethane and a mixture of graphene and carbon nanotubes with a total mass fraction of 30% of thermally conductive filler (where the mass ratio of graphene to carbon nanotubes is 3:1) and mix. Add 40 mL of dichloromethane and stir for 10 min at 50 °C and 12000 rpm. After evaporating the solvent, place the mixture in a silicone mold and cure at 130 °C for 2 h and 150 °C for 2 h. Cool to room temperature to obtain the final product.

[0087] Verification Example

[0088] The thermally conductive interface materials prepared in Examples 1-6 and Comparative Examples 1-3 were tested for their thermal conductivity and thermal resistance according to ASTM D5470-2017 standard, and the replasticity of the cured materials was characterized. The test results are shown in Table 1 below.

[0089] Table 1. Thermal conductivity, thermal resistance, and replasticity of the thermally conductive materials in the examples and comparative examples.

[0090] Comparative Example 1 2.58 0.372 no Comparative Example 2 4.732 0.133 no Comparative Example 3 6.221 0.081 no Example 1 3.89 0.274 yes Example 2 5.459 0.0972 yes Example 3 9.887 0.0345 yes Example 4 8.538 0.053 yes Example 5 5.17 0.105 yes Example 6 4.816 0.127 yes

[0091] The results show that, although the thermally conductive materials prepared in Comparative Example 1 and Comparative Example 2 can still achieve high thermal conductivity (2.58 W·m), the thermal conductivity of the materials prepared in Comparative Example 1 and Comparative Example 2 is still relatively high. -1 ·K -1 and 4.732 W·m -1 ·K -1 ) and low thermal resistance (0.372 cm) 2 ·K·W -1 and 0.133cm 2 ·K·W -1Compared to materials with the same filler content, its thermal conductivity remains poor. This is because the interfacial interaction between the resin and thermally conductive fillers such as graphene, graphite, and carbon nanotubes in the comparative examples is weak. Furthermore, the two materials prepared in Comparative Examples 1 and 2 still lack post-curing plasticity. In addition, although Comparative Example 3 used lignin-based epoxy resin to prepare a thermally conductive material, the thermal conductivity was further improved with a high content of composite filler (thermal conductivity and thermal resistance were 6.221 W·m). -1 ·K -1 and 0.081 cm 2 ·K·W -1 However, the permanent cross-linked network formed after the epoxy groups react with the amino groups means that the final material does not have replastic properties after curing.

[0092] In contrast, this invention uses industrial alkali lignin, a waste product from pulping and papermaking, as the starting material. It utilizes the differences in solubility of different molecular weight components of lignin in different solvents to extract alkali lignin with different molecular weights and phenol / alcohol hydroxyl contents. By adjusting the ratio of different grafting reagents to the extracted lignin hydroxyl groups, a two-component all-lignin-based resin acting as both resin and curing agent is prepared. Based on the functional group characteristics of the grafting reagent, dynamic cross-linking between alkali lignin units is achieved. Simultaneously, the residual hydroxyl groups in the alkali lignin provide adhesive properties, thus endowing it with excellent replasticity and biodegradability after curing. Since the thermal conductivity of graphite is much lower than that of graphene, except for the material prepared in Example 1 which exhibits a slightly lower thermal conductivity, the other examples utilize the benzene ring structure of lignin to construct a strong π-π stacking interaction with graphene or carbon nanotubes. This improves the dispersion and interfacial bonding of the thermally conductive filler in the two-component all-lignin-based resin matrix, optimizing the internal interfacial thermal resistance of the all-lignin-based thermally conductive gel and endowing it with excellent thermal conductivity. The thermal conductivity of the prepared all-lignin-based thermally conductive gel can reach 3.89-9.887 W·m. -1 ·K -1 The thermal resistance is 0.0345-0.274m. 2 ·K·W -1 .

[0093] The above detailed embodiments provide a specific description of the technical solutions involved in this invention. It should be noted that the above description is only intended to help those skilled in the art better understand the methods and ideas of this invention, and is not intended to limit the scope of the invention. Without departing from the principles of this invention, those skilled in the art can make appropriate adjustments or modifications to this invention, and such adjustments and modifications should also fall within the protection scope of this invention.

Claims

1. A method for preparing a biodegradable and replastic all-lignin-based thermally conductive gel, characterized in that, Includes the following steps: (1) Place lignin and organic solvent in a container and extract under ultrasonic conditions, then separate the solid and liquid and remove the solvent to obtain lignin extracted by organic solvent; (2) Place the lignin extracted by organic solvent obtained in step (1) into a container, and slowly add a solution containing grafting reagent 1 under a protective gas atmosphere, and then carry out a reflux reaction; after the reaction is completed, remove the solvent to obtain the first component lignin-based resin. (3) Place the lignin extracted by organic solvent obtained in step (1) in a container, and slowly add a solution containing grafting reagent 2 under a protective gas atmosphere, and then carry out a reflux reaction; after the reaction is completed, remove the solvent to obtain the second component lignin-based resin. (4) Take the first component lignin-based resin obtained in step (2), the second component lignin-based resin obtained in step (3), the thermally conductive filler, and the solvent, stir and mix them, and then cure them to obtain the final product.

2. The preparation method according to claim 1, characterized in that, The organic solvent mentioned in step (1) is selected from one or more of ethyl acetate, acetone, ethanol, dichloromethane, tetrahydrofuran and methanol.

3. The preparation method according to claim 1, characterized in that, The lignin extracted by the organic solvent in step (1) has a molecular weight of 553-4102 Da, a phenolic hydroxyl content of 1.577-2.342 mmol / g, and an alcoholic hydroxyl content of 0.4013-1.301 mmol / g.

4. The preparation method according to claim 1, characterized in that, The grafting reagent 1 mentioned in step (2) is selected from one or more of 2-maleimide acetyl chloride, 3-maleimide propionyl chloride, 4-maleimide butyryl chloride, 6-maleimide hexanoyl chloride, 5-maleimide pentanoyl chloride, and 11-maleimide decanoyl chloride.

5. The preparation method according to claim 1, characterized in that, The reflux reaction in step (2) is carried out at a temperature of 50-100℃ for 12-48 hours.

6. The preparation method according to claim 1, characterized in that, The grafting reagent 2 mentioned in step (3) is selected from one or more of 3-(2-furan)propionyl chloride, 2-furan acetyl chloride, and 4-(furan-2-yl)-4-oxobutyric acid.

7. The preparation method according to claim 1, characterized in that, The reflux reaction in step (3) is carried out at a temperature of 50-100℃ for 12-48 hours.

8. The preparation method according to claim 1, characterized in that, The curing temperature in step (4) is 100-140℃ and the time is 2-6h.

9. A biodegradable and replastic all-lignin-based thermally conductive gel prepared by the preparation method according to any one of claims 1-8.

10. The application of the biodegradable and replastic all-lignin-based thermal conductive gel prepared by the preparation method according to any one of claims 1-8 in heat dissipation of electronic devices.