Low-molecular-weight sulfate lignin epoxy compound, low-molecular-weight lignin-based adhesive as well as preparation method and application of low-molecular-weight sulfate lignin epoxy compound

Abstract

The invention relates to the field of lignin recycling, in particular to a low-molecular-weight sulfate lignin epoxy compound, a low-molecular-weight lignin-based adhesive and a preparation method and application of the low-molecular-weight sulfate lignin epoxy compound. The preparation method of the low-molecular-weight sulfate lignin epoxy compound comprises the following steps: mixing low-molecular-weight sulfate lignin, epoxy chloropropane and a catalyst, adding an alkali metal hydroxide aqueous solution, and carrying out reaction and extraction to prepare the low-molecular-weight sulfate lignin epoxy compound, the low-molecular-weight sulfate lignin is prepared by extracting sulfate lignin through ethyl acetate. According to the method, low-molecular-weight sulfate lignin with small polydispersity is obtained through ethyl acetate extraction and grading, and the reaction activity of the sulfate lignin is remarkably improved. Then the sulfate lignin and epichlorohydrin are subjected to epoxidation reaction to obtain a low-molecular-weight sulfate lignin epoxy compound, and the low-molecular-weight lignin-based adhesive formed by mixing the low-molecular-weight sulfate lignin epoxy compound with a polyamine compound is high in curing speed and high in adhesive strength.

Description

Technical Field

[0001] This invention relates to the field of lignin recycling and reuse, and more specifically, to a low molecular weight sulfate lignin epoxy compound, a low molecular weight lignin-based adhesive, and their preparation methods and applications. Background Technology

[0002] Epoxy resins are widely used in coatings, adhesives, and electronic potting materials due to their excellent mechanical properties, thermal stability, and good bonding and insulation properties. Resins are polymeric matrix materials that can cure to form cross-linked networks, and epoxy resins are an important class of them. The application of epoxy resin systems in the bonding field is in the form of epoxy adhesives, whose performance is mainly determined by the structure of the epoxy components and their reaction process with the curing agent. However, most existing commercial epoxy resin systems use bisphenol A (BPA) as the core structural unit. Their molecular structure and reactivity are highly dependent on specific petrochemical raw materials, which are not only non-renewable sources but also pose potential risks to environmental and health safety, thus hindering the sustainable development of epoxy resin systems.

[0003] Lignin, as the most abundant natural aromatic biomass resource on Earth, possesses a natural aromatic ring framework and polyphenol structural characteristics, theoretically providing rigid structural units and reaction sites for epoxy materials. However, industrial lignin generally suffers from problems such as wide molecular weight distribution and strong structural heterogeneity, leading to its current use in epoxy or thermosetting resin systems primarily as a filler or modifying component.

[0004] Existing technology 202111072332.7 discloses a method for separating industrially pre-hydrolyzed lignin using an acid gradient precipitation method to obtain lignin components with different molecular weight ranges, and further preparing lignin-based thermosetting resin materials based on these components. The lignin components obtained by this type of technology still need to be used in conjunction with existing bisphenol A type thermosetting resin systems, and are difficult to use as independent reactive raw materials to directly participate in the construction of resin or adhesive systems. Summary of the Invention

[0005] To overcome the deficiencies described in the prior art, the present invention provides a low molecular weight sulfate lignin epoxy compound.

[0006] The present invention also provides a method for preparing a low molecular weight sulfate lignin epoxy compound.

[0007] The present invention also provides a low molecular weight lignin-based adhesive.

[0008] The present invention also provides a method for preparing a low molecular weight lignin-based adhesive.

[0009] This invention also provides an application of a low molecular weight lignin-based adhesive.

[0010] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A low molecular weight sulfate lignin is prepared by extraction of sulfate lignin with ethyl acetate. The low molecular weight sulfate lignin has a weight-average molecular weight of 790-850 g / mol and a PDI of 1.75-1.85.

[0011] A method for preparing low molecular weight sulfate lignin includes the following steps: placing sulfate lignin (KL) in an extraction device, adding ethyl acetate for extraction, filtering after extraction, collecting the organic phase, distilling under reduced pressure to remove the solvent, and obtaining low molecular weight sulfate lignin (LKL).

[0012] Preferably, the mass-to-volume ratio of the sulfate lignin to ethyl acetate is 1 g: 10~800 mL. The extraction can be performed once or multiple times, preferably 2–4 times.

[0013] Preferably, the extraction time is not less than 30 minutes.

[0014] Preferably, the sulfate lignin is mainly obtained from wood fiber raw materials through sulfate pulping.

[0015] Preferably, the wood fiber raw material includes coniferous wood, broadleaf wood, and grasses.

[0016] Preferably, the wood fiber raw material includes hardwood.

[0017] Preferably, the wood fiber raw material is eucalyptus.

[0018] Preferably, the sulfate lignin includes eucalyptus sulfate lignin.

[0019] Preferably, the low molecular weight sulfate lignin has a weight-average molecular weight of 790-820 g / mol (Mw).

[0020] A method for preparing a low molecular weight sulfate lignin epoxy compound includes the following steps: Low molecular weight sulfate lignin, epichlorohydrin and catalyst are mixed, and then reacted with an aqueous solution of alkali metal hydroxide. Extraction is performed to obtain low molecular weight sulfate lignin epoxy compound. The ratio of low molecular weight sulfate lignin: epichlorohydrin: catalyst: alkali metal hydroxide aqueous solution is 10 g: 75~85 g: 3.8~4.2 g: 130~150 mL.

[0021] Preferably, the aqueous solution of the alkali metal hydroxide comprises the alkali metal hydroxide and water.

[0022] Preferably, the alkali metal hydroxide includes at least one of sodium hydroxide, magnesium hydroxide, and potassium hydroxide.

[0023] Preferably, the concentration of the alkali metal hydroxide aqueous solution is 4~6 mol / L.

[0024] Preferably, the catalyst comprises benzyltriethylammonium chloride.

[0025] Preferably, the extraction includes extraction with an ethyl acetate / acetone solution, wherein the volume ratio of ethyl acetate to acetone in the ethyl acetate / acetone solution is 1:0.9~1.1.

[0026] A method for preparing a low molecular weight lignin-based adhesive includes the following steps: A low molecular weight sulfate lignin epoxy compound is mixed evenly with a polyamine compound to obtain a low molecular weight lignin-based adhesive.

[0027] Preferably, the polyamine compound includes polyetheramine.

[0028] Preferably, the polyetheramine is polyetheramine D400.

[0029] Preferably, the mass ratio of the low molecular weight sulfate lignin epoxy compound to the polyamine compound is (0.95~0.7):(0.05~0.3).

[0030] Preferably, the mass ratio of the low molecular weight sulfate lignin epoxy compound to the polyamine compound is (0.95~0.8):(0.05~0.2).

[0031] More preferably, the mass ratio of the low molecular weight sulfate lignin epoxy compound to the polyamine compound is (0.85~0.8):(0.15~0.2).

[0032] A low molecular weight lignin-based adhesive is prepared by the method described in this invention.

[0033] An application of a low molecular weight lignin-based adhesive for bonding materials, and also for use in electronic packaging and insulating materials.

[0034] Preferably, the material includes wood or metal.

[0035] Furthermore, the wood materials include fiberboard, particleboard, plywood, wood flooring, wood wall panels, and wood doors and windows.

[0036] Preferably, in the application of the low molecular weight lignin-based adhesive, the single-sided application amount of the low molecular weight lignin-based adhesive is 30-200 g / m². 2 .

[0037] More preferably, in the application of the low molecular weight lignin-based adhesive, the single-sided application amount of the low molecular weight lignin-based adhesive is 30-100 g / m². 2 .

[0038] More preferably, in the application of the low molecular weight lignin-based adhesive, the single-sided application amount of the low molecular weight lignin-based adhesive is 60-100 g / m². 2 .

[0039] Preferably, the low molecular weight lignin-based adhesive is used at a bonding temperature of 80–160°C.

[0040] More preferably, the low molecular weight lignin-based adhesive is used at a bonding temperature of 120–160°C.

[0041] More preferably, the low molecular weight lignin-based adhesive is used at a bonding temperature of 120–130°C.

[0042] Preferably, the bonding time for the application of the low molecular weight lignin-based adhesive is 3 to 180 minutes.

[0043] More preferably, the bonding time for the application of the low molecular weight lignin-based adhesive is 3 to 20 minutes.

[0044] More preferably, the bonding time for the application of the low molecular weight lignin-based adhesive is 10-20 min.

[0045] More preferably, the bonding time for the low molecular weight lignin-based adhesive is 3 to 15 minutes.

[0046] Preferably, when low molecular weight lignin-based adhesives are used for electronic packaging, the curing temperature is 155~165℃ and the curing time is 5~7 h.

[0047] In this invention, low molecular weight sulfate lignin (LKL) with low polydispersity and high hydroxyl content is obtained by ethyl acetate extraction and fractionation, which significantly improves its reactivity. Subsequently, an epoxidation reaction with epichlorohydrin yields a low molecular weight sulfate lignin epoxy compound (LKLGE). The low molecular weight lignin-based adhesive formed by mixing this compound with polyamine compounds exhibits adhesive properties comparable to bisphenol A epoxy systems, with faster curing speed and higher adhesive strength.

[0048] In this invention, the plywood prepared using the technical solution of this invention still exhibits excellent durability and interface stability in extreme environments such as high temperature, humid heat, acid and alkali, and salt water.

[0049] In this invention, the single-sided application rate of the low molecular weight lignin-based adhesive is 30 g / m².2 Under these conditions, the plywood prepared can achieve good bonding effect in terms of mechanical properties.

[0050] This invention establishes an environmentally friendly route for the high-value utilization of lignin, providing a new technical approach for the preparation of high-performance, fast-curing lignin-based epoxy resins, and expanding the application prospects of lignin in high-reliability adhesives.

[0051] This invention utilizes ethyl acetate fractionation to obtain low-molecular-weight lignin sulfate, effectively controlling its molecular weight distribution, polydispersity, and reactive site utilization. Further epoxidation modification yields low-molecular-weight lignin sulfate epoxy compounds that can be directly mixed with polyamine compounds to form adhesive systems without the need for bisphenol A type epoxy resin as the system matrix. Thus, the lignin epoxy compounds can independently perform the reactive function of epoxy resins, serving as reactive raw materials in adhesive systems. Unlike existing techniques that require the introduction of lignin into bisphenol A type epoxy resin systems after fractionation and modification to construct adhesives or resin materials, this invention, starting from the molecular structure, composition, and molecular weight characteristics of low-molecular-weight lignin sulfate, avoids dependence on specific epoxy resin formulations and curing systems, significantly expanding the application of lignin sulfate in the adhesive field.

[0052] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: The low molecular weight sulfate lignin of this invention can be obtained by one-step ethyl acetate fractionation. The low molecular weight sulfate lignin has a narrow molecular weight distribution and high phenolic hydroxyl groups, significantly improving its reactivity and compatibility with epoxy systems. The low molecular weight lignin-based adhesive prepared using the low molecular weight sulfate lignin epoxy compound achieves a dry-state bond strength of up to 4.08 MPa when used to prepare plywood. The adhesive layer exhibits good strength retention after cycling through cold and heat, humidity and heat, liquid nitrogen, acids and alkalis, and salt spray. The dry-state bond strength of the low molecular weight lignin-based adhesive to steel and aluminum is >5 MPa. The cured product of the low molecular weight lignin-based adhesive has low dielectric loss, high volume resistivity, and stable thermal conductivity, demonstrating its potential application value in electronic packaging and insulation materials. This provides a new technical approach for preparing high-performance, fast-curing lignin-based epoxy resins and expands the application prospects of lignin in high-reliability adhesives. Attached Figure Description

[0053] Figure 1 This is a molecular weight test diagram of the lignin sample from Example 1.

[0054] Figure 2 This is a SEM image of the plywood bonding interface in Example 8.

[0055] Figure 3 This is a contact angle test diagram of sulfate lignin epoxy compound from Example 1. Figure 4 FT-IR spectra of sulfate lignin epoxy compounds from Examples 1, 1, and 2. Figure 5 This is a 2D HSQC NMR side chain diagram of low molecular weight sulfate lignin in Example 1. Figure 6 2D HSQC NMR side chain diagram of the low molecular weight sulfate lignin epoxy compound in Example 1. Figure 7 For example, lignin of 1 31 P NMR spectrum Figure 8 Dielectric loss diagram of low molecular weight lignin-based adhesives Figure 9 Dielectric constant diagram of low molecular weight lignin-based adhesives Figure 10 Volume resistivity diagram of low molecular weight lignin-based adhesives Figure 11 Thermal conductivity diagram of low molecular weight lignin-based adhesives Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0057] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0058] Ethyl acetate (99%), epichlorohydrin, triethylbenzylammonium chloride (TEBAC), sodium hydroxide (99%), sodium chloride, anhydrous magnesium sulfate, polyetheramine (D-400, average Mn molecular weight 400), and bisphenol A were purchased from Macklin Reagents Ltd. Artificial seawater was purchased from Guangzhou Yangkai Biotechnology Co., Ltd. Epoxy resins E-44 and E871955 were purchased from Macklin.

[0059] The present invention will be further described below: A low molecular weight sulfate lignin is prepared by extraction of sulfate lignin with ethyl acetate. The low molecular weight sulfate lignin has a weight-average molecular weight of 790-850 g / mol and a PDI of 1.75-1.85.

[0060] A method for preparing low molecular weight sulfate lignin includes the following steps: placing sulfate lignin (KL) in an extraction device, adding ethyl acetate for extraction, filtering after extraction, collecting the organic phase, distilling under reduced pressure to remove the solvent, and obtaining low molecular weight sulfate lignin (LKL).

[0061] In one preferred embodiment, the mass-to-volume ratio of the sulfate lignin to ethyl acetate is 1 g: 10~800 mL.

[0062] In a preferred embodiment, the extraction time is not less than 30 minutes.

[0063] In one preferred embodiment, the sulfate lignin is mainly obtained from wood fiber raw materials through sulfate pulping.

[0064] In one preferred embodiment, the wood fiber raw material includes coniferous wood, broadleaf wood, and grasses.

[0065] In one preferred embodiment, the wood fiber raw material includes hardwood.

[0066] In one preferred embodiment, the wood fiber raw material is eucalyptus.

[0067] In one preferred embodiment, the sulfate lignin includes eucalyptus sulfate lignin.

[0068] In one preferred embodiment, the weight-average molecular weight of the low molecular weight sulfate lignin is 790-820 g / mol (Mw).

[0069] In a preferred embodiment, the total amount of monomers and dimers of the low molecular weight sulfate lignin is 95~100 mg / g.

[0070] A method for preparing a low molecular weight sulfate lignin epoxy compound includes the following steps: Low molecular weight sulfate lignin, epichlorohydrin and catalyst are mixed, and then reacted with an aqueous solution of alkali metal hydroxide. Extraction is performed to obtain low molecular weight sulfate lignin epoxy compound.

[0071] In a preferred embodiment, the low molecular weight sulfate lignin: epichlorohydrin: catalyst: alkali metal hydroxide aqueous solution = 10 g: 75~85 g: 3.8~4.2 g: 130~150 mL.

[0072] In a preferred embodiment, the low molecular weight sulfate lignin: epichlorohydrin: catalyst: alkali metal hydroxide aqueous solution = 10 g: 79~83 g: 3.8~4.2 g: 135~145 mL.

[0073] A method for preparing a low molecular weight lignin-based adhesive includes the following steps: A low molecular weight sulfate lignin epoxy compound is mixed evenly with a polyamine compound to obtain a low molecular weight lignin-based adhesive.

[0074] In one preferred embodiment, the polyamine compound includes polyetheramine.

[0075] In a preferred embodiment, the polyetheramine is polyetheramine D400.

[0076] A low molecular weight lignin-based adhesive is prepared by the method described in this invention.

[0077] An application of a low molecular weight lignin-based adhesive for bonding materials, and also for use in electronic packaging and insulating materials.

[0078] In one preferred embodiment, the material includes wood or metal.

[0079] In one preferred embodiment, the wood materials include fiberboard, particleboard, plywood, wood flooring, wood wall panels, and wood doors and windows.

[0080] In a preferred embodiment, the application of the low molecular weight lignin-based adhesive involves a single-sided application rate of 30–200 g / m². 2 .

[0081] In a preferred embodiment, the application of the low molecular weight lignin-based adhesive involves a single-sided application rate of 30–100 g / m². 2 .

[0082] In a preferred embodiment, the application of the low molecular weight lignin-based adhesive involves a single-sided application rate of 60–100 g / m². 2 .

[0083] In a preferred embodiment, the low molecular weight lignin-based adhesive is applied at a bonding temperature of 80–160°C.

[0084] In one preferred embodiment, the low molecular weight lignin-based adhesive is applied at a bonding temperature of 120–160°C.

[0085] In one preferred embodiment, the low molecular weight lignin-based adhesive is applied at a bonding temperature of 120–130°C.

[0086] In one preferred embodiment, the bonding time of the low molecular weight lignin-based adhesive is 3 to 180 minutes.

[0087] In a preferred embodiment, the bonding time for the low molecular weight lignin-based adhesive is 3 to 20 minutes.

[0088] In a preferred embodiment, the bonding time of the low molecular weight lignin-based adhesive is 10-20 min.

[0089] As a preferred embodiment, when low molecular weight lignin-based adhesives are used for electronic packaging, the curing temperature is 155~165℃ and the curing time is 5~7 h.

[0090] Eucalyptus sulfate lignin can be provided by Jining Mingsheng New Materials Co., Ltd. The following is one of the sulfate pulping methods for preparing eucalyptus sulfate lignin: Sulfate pulping of eucalyptus wood chips is carried out in a rotary digester under the following conditions: active alkali content 25% (based on NaOH), liquor ratio (L / kg) 5, sulfurization degree 30%. The temperature is increased to 165℃ at a rate of 5℃ / min and held for 60 min. Then, the temperature is increased to 170℃ at a rate of 0.4℃ / min and held at this temperature for another 50 min. 100 mL of black liquor is taken, solid impurities are removed, and 2 mol / L hydrochloric acid solution is slowly added under magnetic stirring until the pH reaches 2. The mixture is left to stand in a 4℃ refrigerator for 24 h, centrifuged at 6000 rpm to obtain the precipitate, washed with deionized water until neutral, and finally freeze-dried to obtain eucalyptus sulfate lignin.

[0091] The present invention will be further illustrated below with reference to specific embodiments: Example 1

[0092] (1) Preparation of low molecular weight sulfate lignin. The method for preparing low molecular weight sulfate lignin includes the following steps: 10 g of eucalyptus sulfate lignin (KL) is placed in an extraction device, and 200 mL of ethyl acetate is added for extraction once for 1 hour. After extraction, the mixture is filtered, and the dissolved organic phase is collected. The above extraction process is repeated 3 times. The collected organic phases are combined and subjected to vacuum distillation at 40°C to remove the solvent, thereby obtaining low molecular weight sulfate lignin (LKL). The solid portion of the filter cake after filtration is dried at 40°C to obtain high molecular weight sulfate lignin (HKL).

[0093] (2) Preparation of low molecular weight sulfate lignin epoxy compound. 10 g of low molecular weight sulfate lignin (LKL, Mw weight average molecular weight of 800 g / mol), 81.7 g of epichlorohydrin and 4.01 g of benzyltriethylammonium chloride were added to a three-necked flask and reacted at 80 °C for 2 hours. Then 70.65 mL of sodium hydroxide solution (5 mol / L) was added and reacted at 60 °C for 1 hour. Then 70.65 mL of sodium hydroxide solution (5 mol / L) was added and reacted at 60 °C for 3 hours. After the reaction was completed, the organic phase was extracted with ethyl acetate / acetone solution (ethyl acetate:acetone volume ratio of 1:1), and the organic phase was collected. The organic phase was washed with saturated sodium chloride aqueous solution, dried with anhydrous magnesium sulfate, and then filtered to collect the filtrate. The collected filtrate was distilled under reduced pressure at 40 °C to remove excess ethyl acetate, acetone and epichlorohydrin, to obtain a brown viscous substance, namely low molecular weight sulfate lignin epoxy compound (LKLGE).

[0094] (3) Preparation of low molecular weight lignin-based adhesive. 0.95 g of low molecular weight sulfate lignin epoxy compound (LKLGE) and 0.05 g of polyetheramine D400 were stirred and mixed evenly at 250 rpm to obtain low molecular weight lignin-based adhesive.

[0095] (4) Preparation of plywood: Poplar veneer (moisture content 10 wt%) was selected for plywood preparation. The length, width and thickness of the veneer were 100 mm, 25 mm and 3 mm, respectively. The low molecular weight lignin-based adhesive prepared in step (3) was used to apply glue to the poplar veneer. The glue application method was single-sided glue application, and the glue was applied manually. The glue application amount on one side was 100 g / m. 2 The unveneeded veneer and the veneer are glued together along the fiber direction and secured with dovetail clips. The mixture is then placed in an oven at 120℃ for 3 hours to obtain plywood.

[0096] Example 2 This embodiment is similar to Embodiment 1, except that step (3) involves the preparation of the low molecular weight lignin-based adhesive. 0.85 g of low molecular weight sulfate lignin epoxy compound and 0.15 g of polyetheramine D400 are mixed evenly at 250 rpm to obtain the low molecular weight lignin-based adhesive.

[0097] Step (4) Preparation of plywood: Poplar veneer (moisture content 10 wt%) was selected for plywood preparation. The length, width, and thickness of the veneer were 100 mm, 25 mm, and 3 mm, respectively. The low molecular weight lignin-based adhesive prepared in step (3) was used to apply the adhesive to the poplar veneer. The adhesive application method was single-sided application, and the adhesive was applied manually. The amount of adhesive applied to one side was 100 g / m². 2The unveneeded veneer and the glued veneer are glued together along the fiber direction and secured with dovetail clips. The mixture is then placed in an oven at 80°C for 3 hours to obtain plywood.

[0098] Example 3 This embodiment is similar to Embodiment 1, except that in step (3), 0.80g of low molecular weight sulfate lignin epoxy compound and 0.20g of polyetheramine D400 are stirred and mixed evenly at 250rpm.

[0099] Example 4 This embodiment is similar to Embodiment 1, except that in step (3), 0.70g of low molecular weight sulfate lignin epoxy compound and 0.30g of polyetheramine D400 are stirred and mixed evenly at 250rpm. In step (4), the mixture is placed in an oven at 160℃ and kept warm for 15 minutes to obtain plywood.

[0100] Example 5 This embodiment 5 is similar to embodiment 2, except that in step (4), the plywood is placed in an oven at 120°C for 15 minutes to obtain the plywood.

[0101] Example 6 This embodiment 6 is similar to embodiment 2, except that in step (4), the plywood is placed in an oven at 120°C for 3 hours to obtain the plywood.

[0102] Example 7 This embodiment 7 is similar to embodiment 2, except that in step (4), the plywood is placed in an oven at 140°C for 3 hours to obtain the plywood.

[0103] Example 8 This embodiment 8 is similar to embodiment 2, except that in step (4), the plywood is placed in an oven at 160°C for 3 hours to obtain the plywood.

[0104] Example 9 This embodiment 9 is similar to embodiment 2, except that in step (4), the wood is placed in an oven at 160°C for 15 minutes to obtain plywood. Figure 2 The SEM image of the glued interface is shown.

[0105] The plywood prepared in this embodiment was tested after being immersed in boiling water, acid (pH 3.5), alkali (pH 12.5), and artificial seawater for 3 hours. The wet strength was as follows: 3.46 MPa after boiling water treatment, 2.60 MPa after acid treatment, 2.14 MPa after alkali treatment, and 2.60 MPa after seawater treatment. All of these values ​​are higher than the requirement of GB / T 9846-2015 Class II board wet strength ≥ 0.7 MPa, showing excellent water resistance, acid and alkali resistance, and salt spray resistance.

[0106] Further aging was performed using a hot-cold cycle of 100℃ for 2 h, then room temperature for 0.5 h, then -20℃ for 20 h, and then room temperature for 0.5 h. The strength was 3.00 MPa after 1 day of aging, 3.08 MPa after 3 days, 3.03 MPa after 5 days, 3.12 MPa after 7 days, and 2.91 MPa after 10 days, all of which met the requirement of ≥ 0.7 MPa. This demonstrates that the plywood prepared in this embodiment has good mechanical properties in a long-term freeze-thaw-dry heat alternating environment and still maintains the integrity of the interface.

[0107] Example 10 This embodiment 10 is similar to embodiment 2, except that in step (4), the plywood is placed in an oven at 160°C for 3 minutes to obtain the plywood.

[0108] Example 11 This embodiment 11 is similar to embodiment 2, except that the amount of adhesive applied to one side in step (4) is 30 g / m. 2 .

[0109] Example 12 This embodiment 12 is similar to embodiment 2, except that the amount of adhesive applied to one side in step (4) is 60 g / m. 2 .

[0110] Example 13 Steps (1) to (3) of this embodiment are the same as those of embodiment 2. The prepared low molecular weight lignin-based adhesive is used to bond steel sheets. The size of the steel sheets, the amount of adhesive applied, and the curing conditions are the same as those of embodiment 2.

[0111] Example 14 Steps (1) to (3) of this embodiment are the same as those of embodiment 2. The prepared low molecular weight lignin-based adhesive is used to bond aluminum sheets. The size of the aluminum sheets, the amount of adhesive applied, and the curing conditions are the same as those of embodiment 2.

[0112] Example 15 (1) Preparation of low molecular weight sulfate lignin. The method for preparing low molecular weight sulfate lignin includes the following steps: 10 g of eucalyptus sulfate lignin (KL) is placed in an extraction device, and 200 mL of ethyl acetate is added for extraction once for 1 hour. After extraction, the mixture is filtered, and the dissolved organic phase is collected. The above extraction process is repeated 3 times. The collected organic phases are combined and subjected to vacuum distillation at 40°C to remove the solvent, thereby obtaining low molecular weight sulfate lignin (LKL). The solid portion of the filter cake after filtration is dried at 40°C to obtain high molecular weight sulfate lignin (HKL).

[0113] (2) Preparation of low molecular weight sulfate lignin epoxy compound. 10 g of low molecular weight sulfate lignin (LKL, Mw molecular weight 800 g / mol), 81.7 g of epichlorohydrin and 4.01 g of benzyltriethylammonium chloride were added to a three-necked flask and reacted at 80 °C for 2 hours. Then 70.65 mL of sodium hydroxide solution (5 mol / L) was added and reacted at 60 °C for 1 hour. Then 70.65 mL of sodium hydroxide solution (5 mol / L) was added and reacted at 60 °C for 3 hours. After the reaction was completed, the organic phase was extracted with ethyl acetate / acetone solution (ethyl acetate:acetone volume ratio of 1:1), and the organic phase was collected. The organic phase was washed with saturated sodium chloride aqueous solution, dried with anhydrous magnesium sulfate, and then filtered to collect the filtrate. The collected filtrate was subjected to vacuum distillation at 40 °C to remove excess ethyl acetate, acetone and epichlorohydrin, to obtain a brown viscous substance, namely low molecular weight sulfate lignin epoxy compound (LKLGE).

[0114] (3) Preparation of low molecular weight lignin-based adhesive. 0.85g of low molecular weight sulfate lignin epoxy compound (LKLGE) and 0.15g of polyetheramine D400 were stirred and mixed evenly at 250rpm to obtain low molecular weight lignin-based adhesive.

[0115] The prepared low molecular weight lignin-based adhesive was poured into a silicone mold and placed in an oven at 80°C for 6 hours to cure. The volume resistivity, thermal conductivity, and dielectric properties of the cured product were tested.

[0116] Example 16 This embodiment is similar to Embodiment 15, except that the prepared low molecular weight lignin-based adhesive is poured into a silicone mold and placed in an oven at 120°C for 6 hours for curing. The volume resistivity, thermal conductivity, and dielectric properties of the cured product are tested.

[0117] Example 17 This embodiment is similar to Embodiment 15, except that in step (3), 0.70g of low molecular weight sulfate lignin epoxy compound and 0.30g of polyetheramine D400 are stirred and mixed evenly at 250rpm to obtain a low molecular weight lignin-based adhesive.

[0118] The prepared low molecular weight lignin-based adhesive was poured into a silicone mold and cured in an oven at 120°C for 6 hours. The volume resistivity, thermal conductivity, and dielectric properties of the cured product were tested.

[0119] Example 18 This embodiment is similar to Embodiment 15, except that the prepared low molecular weight lignin-based adhesive is poured into a silicone mold and placed in an oven at 160°C for 6 hours for curing. The volume resistivity, thermal conductivity, and dielectric properties of the cured product are tested.

[0120] Comparative Example 1 Comparative Example 1 is similar to Example 1, except that in step (2), high molecular weight lignin (HKL) is used instead of low molecular weight sulfate lignin for lignin epoxidation. The specific step (2) is as follows: 10 g of high molecular weight sulfate lignin (HKL) (Mw molecular weight is 4206 g / mol), 33.8 g of epichlorohydrin and 1.66 g of benzyltriethylammonium chloride are added to a three-necked flask and reacted at 80°C for 2 hours. Then 29.2 mL of sodium hydroxide solution (5 mol / L) is added and reacted at 60°C for 1 hour. Then 29.2 mL of sodium hydroxide solution (5 mol / L) is added and reacted at 60°C for 3 hours. After the reaction was completed, the organic phase was extracted with an ethyl acetate / acetone solution (ethyl acetate:acetone volume ratio of 1:1), and the organic phase was collected. The organic phase was washed with a saturated sodium chloride aqueous solution, dried with anhydrous magnesium sulfate, and then filtered to collect the filtrate. The collected filtrate was subjected to vacuum distillation at 40°C to remove excess ethyl acetate, acetone and epichlorohydrin, to obtain a brown viscous substance, namely high molecular weight sulfate lignin epoxy compound (HKLGE).

[0121] (3) Preparation of high molecular weight lignin-based adhesive. 0.95 g of high molecular weight sulfate lignin epoxy compound (HKLGE) and 0.05 g of polyetheramine D400 were stirred and mixed evenly at 250 rpm to obtain high molecular weight lignin-based adhesive.

[0122] (4) Preparation of plywood: Poplar veneer (moisture content 10 wt%) was selected for plywood preparation. The length, width, and thickness of the veneer were 100 mm, 25 mm, and 3 mm, respectively. The high molecular weight lignin-based adhesive prepared in step (3) was used to apply the adhesive to the poplar veneer. The adhesive application method was single-sided application, and the adhesive was applied manually. The amount of adhesive applied to one side was 100 g / m². 2 The un-veneered veneer and the veneered veneer are glued together along the fiber direction and secured with dovetail clips. The mixture is then placed in an oven at 120℃ for 15 minutes to obtain plywood.

[0123] Comparative Example 2 Comparative Example 2 is similar to Example 1, except that in step (2), lignin epoxidation uses ungraded eucalyptus sulfate lignin (KL) instead of low molecular weight sulfate lignin. The specific step (2) is as follows: 10 g of eucalyptus sulfate lignin (KL) (Mw molecular weight is 1786 g / mol), 64.9 g of epichlorohydrin and 3.18 g of benzyltriethylammonium chloride are added to a three-necked flask and reacted at 80°C for 2 hours. Then, 56.1 mL of sodium hydroxide solution (5 mol / L) is added and reacted at 60°C for 1 hour. Then, 56.1 mL of sodium hydroxide solution (5 mol / L) is added and reacted at 60°C for 3 hours. After the reaction was completed, the organic phase was extracted with an ethyl acetate / acetone solution (ethyl acetate:acetone volume ratio of 1:1), and the organic phase was collected. The organic phase was washed with a saturated sodium chloride aqueous solution, dried with anhydrous magnesium sulfate, and then filtered to collect the filtrate. The collected filtrate was subjected to vacuum distillation at 40°C to remove excess ethyl acetate, acetone and epichlorohydrin, to obtain a brown viscous substance, namely eucalyptus sulfate lignin epoxy compound (KLGE).

[0124] (3) Preparation of eucalyptus sulfate lignin-based adhesive. 0.70 g of eucalyptus sulfate lignin epoxy compound (KLGE) and 0.30 g of polyetheramine D400 were stirred and mixed evenly at 250 rpm to obtain eucalyptus sulfate lignin-based adhesive.

[0125] (4) Preparation of plywood: Poplar veneer (moisture content 10 wt%) was selected for plywood preparation. The length, width and thickness of the veneer were 100 mm, 25 mm and 3 mm, respectively. The eucalyptus sulfate lignin-based adhesive prepared in step (3) was used to apply glue to the poplar veneer. The glue application method was single-sided glue application, and the glue was applied manually. The glue application amount on one side was 100 g / m. 2 The unveneeded veneer and the veneer are glued together along the fiber direction and secured with dovetail clips. The mixture is then placed in an oven at 120℃ for 3 hours to obtain plywood.

[0126] Comparative Example 3 This comparative example is similar to Example 1, except that polyetheramine D400 is not added in step (3).

[0127] Comparative Example 4 This comparative example is similar to Example 1, except that in step (3), 0.40 g of low molecular weight sulfate lignin epoxy compound and 0.60 g of polyetheramine D400 are stirred and mixed evenly at 250 rpm.

[0128] Comparative Example 5 This comparative example of low molecular weight sulfate lignin was prepared by extraction of sulfate lignin with dichloromethane, including the following steps: 10 g of eucalyptus sulfate lignin (KL) was placed in an extraction apparatus, and 200 mL of dichloromethane was added for extraction once, with an extraction time of 1 hour. After extraction, the mixture was filtered, and the dissolved organic phase was collected. This extraction process was repeated three times. The collected organic phases were combined and subjected to vacuum distillation at 40°C to remove the solvent, yielding dichloromethane-based low molecular weight sulfate lignin.

[0129] Comparative Example 6 Comparative Example 6 is similar to Example 8, except that in step (2), lignin epoxidation uses bisphenol A (BPA) instead of low molecular weight sulfate lignin. The specific step (2) is as follows: 10 g of bisphenol A (BPA), 68.6 g of epichlorohydrin and 4.00 g of benzyltriethylammonium chloride are added to a three-necked flask and reacted at 80°C for 2 hours. Then, 70.1 mL of sodium hydroxide solution (5 mol / L) is added and reacted at 60°C for 1 hour. Then, 70.1 mL of sodium hydroxide solution (5 mol / L) is added and reacted at 60°C for 3 hours. After the reaction is completed, the organic phase is extracted with ethyl acetate / acetone solution (the volume ratio of ethyl acetate to acetone is 1:1). The organic phase is collected, washed with saturated sodium chloride aqueous solution, dried with anhydrous magnesium sulfate, and then filtered to collect the filtrate. The collected filtrate is distilled under reduced pressure at 40°C to remove excess ethyl acetate, acetone and epichlorohydrin, to obtain a brown viscous substance, namely bisphenol A epoxy compound (DGEBA).

[0130] Step (3) Preparation of low molecular weight lignin-based adhesive. 0.85 g of bisphenol A epoxy compound (DGEBA) and 0.15 g of polyetheramine D400 were mixed evenly at 250 rpm to obtain the adhesive.

[0131] Step (4) Preparation of plywood: Poplar veneer (moisture content 10 wt%) was selected for plywood preparation. The length, width, and thickness of the veneer were 100 mm, 25 mm, and 3 mm, respectively. The adhesive prepared in step (3) was used to apply glue to the poplar veneer. The glue application method was single-sided glue application, which was done manually. The glue application amount on one side was 100 g / m². 2 The un-veneered veneer and the veneered veneer are glued together along the fiber direction and secured with dovetail clips. The mixture is then placed in an oven at 160℃ for 15 minutes to obtain plywood.

[0132] Comparative Example 7 This comparative example is similar to Comparative Example 6, except that in step (3), 0.60 g of bisphenol A epoxy compound (DGEBA) and 0.40 g of polyetheramine D400 are stirred and mixed evenly at 250 rpm to obtain an adhesive. In step (4), the adhesive is placed in an oven at 120°C for 3 hours to obtain plywood.

[0133] Comparative Example 8 This comparative example is similar to Comparative Example 6, except that in step (3), 0.70 g of bisphenol A epoxy compound (E-44) and 0.30 g of polyetheramine D400 are stirred and mixed evenly at 250 rpm to obtain an adhesive.

[0134] Comparative Example 9 This comparative example uses a commercially available epoxy adhesive; 0.60 g of commercially available epoxy compound (E-44) and 0.40 g of polyetheramine D400 were mixed evenly at 250 rpm to obtain the adhesive. The mixture was then placed in an oven at 120°C for 3 hours to obtain plywood.

[0135] Preparation of plywood: Poplar veneer (moisture content 10 wt%) was selected for plywood preparation. The length, width, and thickness of the veneer were 100 mm, 25 mm, and 3 mm, respectively. Commercially available epoxy adhesive was used to apply the poplar veneer to one side by hand, with a single-sided application rate of 100 g / m². 2 The unveneeded veneer and the veneer are glued together along the fiber direction and secured with dovetail clips. The mixture is then placed in an oven at 120℃ for 3 hours to obtain plywood.

[0136] Comparative Example 10 This comparative example is similar to Comparative Example 9, except that: 0.95 g of commercially available epoxy compound (E-44) and 0.05 g of polyetheramine D400 were mixed evenly at 250 rpm to obtain an adhesive.

[0137] Comparative Example 11 This comparative example is similar to Comparative Example 9, except that: 0.85 g of commercially available epoxy compound (E-44) and 0.15 g of polyetheramine D400 were mixed evenly at 250 rpm to obtain an adhesive.

[0138] Comparative Example 12 This comparative example is similar to Comparative Example 9, except that: 0.80 g of commercially available epoxy compound (E-44) and 0.20 g of polyetheramine D400 were mixed evenly at 250 rpm to obtain an adhesive.

[0139] Comparative Example 13 This comparative example is similar to Comparative Example 11, except that: it is placed in an oven at 160℃ for 15 minutes to obtain plywood.

[0140] Comparative Example 14 This comparative example is similar to Comparative Example 9, except that: 0.70 g of commercially available epoxy compound (E-44) and 0.30 g of polyetheramine D400 were mixed evenly at 250 rpm to obtain an adhesive. Step (4) was placed in an oven at 160℃ for 15 minutes to obtain plywood.

[0141] Analysis and detection Mechanical property testing: After the prepared poplar plywood was placed at room temperature for 48 hours, dry and wet shear strength tests were conducted. Shear strength was measured under three conditions: dry, immersion in 63℃ water for 3 hours, and immersion in boiling water (100℃) for 3 hours. According to GB / T 9846-2015 standard, a universal testing machine (CMT5504, MTS) was used to test the samples, with each sample tested five times and the average value taken. The effective carbon number (ECN) method was used to detect monomers and dimers in lignin, referring to the master's thesis "Study on Hydrogenation Deoxygenation of Low Molecular Weight Components of Eucalyptus Sulfate Lignin," Zhang Shuo, South China University of Technology, 2024, pp. 19-22. Lignin molecular weight was determined using high-performance liquid chromatography (Agilent Infinity 1260, Agilent Technologies, USA). Infrared spectroscopy was performed using a Nicolet IS50-Nicolet Continuum (Thermo Fisher Scientific, USA). Reference for phosphorus spectroscopy: Application of quantitative 31P NMR in biomass lignin and biofuel precursors characterization. Energy & environmental science, 2011, 4(9), pp. 3154-3166. Specifically, the 31P NMR assay method was as follows: A deuterated pyridine-deuterated chloroform (1.6:1, v / v) mixed solution was prepared, and an internal standard-relaxant (cyclohexanol concentration 4.02 mg / mL, chromium acetylacetone concentration 3.57 mg / mL) was prepared using this mixed solution. 30 mg of lignin sample (vacuum dried for 24 h) was weighed into an NMR tube, and 400 mL of the mixed solution was added to dissolve the lignin. Then, 150 mL of the internal standard-relaxant was added, and the mixture was thoroughly mixed. Next, 100 mL of the phosphating reagent TMDP was added, allowing the phosphating reagent and lignin to react fully. The NMR tube was placed on a 500 M superconducting NMR spectrometer (AVANCENEO 500M, Bruker, Germany) to scan and obtain the 31P NMR spectrum of the lignin, using the default parameters. Volume resistivity was tested using an ST2643 ultra-high resistance microcurrent tester, thermal conductivity was tested using a German NETZSCH-LFA42, and dielectric properties were tested using an American Agilent-4294A.

[0142] The specific data is shown in the table below: Table 1. Molecular weight data of different lignins (KL, LKL, HKL) in Example 1

[0143] Table 2. Detection data of total monomers and dimers in low molecular weight sulfate lignin obtained in Example 1 and Comparative Example 5.

[0144] Table 3. Bond strength test data for the examples and comparative examples

[0145] Table 4. Volume resistivity and thermal conductivity of the cured products of Examples 15-18

[0146] Results analysis: Example 1, Molecular Weight Distribution Figure 1 As shown in Table 1, the weight-average molecular weight (Mw) of the low molecular weight sulfate lignin LKL extracted by ethyl acetate in this invention is 800 g / mol, significantly lower than that of KL and HKL; and the distribution coefficient decreased from 2.97 (KL) to 1.82 (LKL), with a significantly narrower peak shape, confirming that the ethyl acetate fractionation successfully enriched the low molecular weight oligomers with low polydispersity. This invention's ethyl acetate extraction and fractionation can precisely reduce the molecular weight and narrow the distribution in a single step, significantly enriching the active terminal groups, making LKL a high-quality lignin component with low molecular weight, narrow dispersion, and high reactivity, laying a key structural foundation for subsequent epoxidation and the preparation of high-performance lignin-based adhesives.

[0147] A comparison of Example 1 with Comparative Example 5 and Table 2 shows that the total amount of monomers and dimers in the low molecular weight sulfate lignin (LKL) extracted with ethyl acetate was 97.85 mg / g, less than 100 mg / g, while the total amount of monomers and dimers in the low molecular weight sulfate lignin (LKL) extracted with dichloromethane (Comparative Example 5) was 216.8 mg / g, a reduction of 54.9%. This result indicates that ethyl acetate has higher selectivity for oligomers, effectively enriching oligomers with low polydispersity and higher reactivity while removing large molecular fragments. The weight-average molecular weight (Mw) was 800 g / mol. Therefore, ethyl acetate fractionation not only simplifies the molecular weight distribution but also improves the efficiency of subsequent epoxidation and bonding performance.

[0148] As can be seen from Examples 1 to 14, the dry bonding strength of the plywood prepared by the technical solution of the present invention is >1.40 MPa, and can reach up to 4.08 MPa, showing good bonding performance.

[0149] Based on the results of Examples 15-18 and Table 4, Figure 8 , Figure 9 It is evident that the cured product exhibits good insulation properties, with an overall thermal conductivity ranging from 0.16 to 0.36 W·m. -1 ·K -1 Within this range, it meets the requirements for moderate thermal insulation performance in the electronic potting field. The cured product of Example 17 has a low dielectric constant and the lowest dielectric loss across the entire frequency range; the volume resistivity results show that the cured product of Example 17 reaches 3.42 × 10⁻⁶. 11 The Ω·cm value is significantly better than other samples, indicating that its network structure can effectively restrict carrier migration and has higher electrical insulation.

[0150] As can be seen from Comparative Example 1, the adhesive prepared by replacing low molecular weight sulfate lignin with high molecular weight lignin (HKL) does not have adhesive properties.

[0151] As can be seen from Comparative Example 2, the adhesive prepared by further processing sulfate lignin (KL) has a dry strength of 1.18 MPa and a wet strength of 0.39 MPa, which do not meet the standard requirements.

[0152] As can be seen from Comparative Example 3, the adhesive prepared without the addition of polyamine compounds has poor mechanical properties, with a strength of 0.61 MPa.

[0153] As can be seen from Comparative Example 4, the adhesive prepared by the mass ratio of low molecular weight sulfate lignin epoxy compound to polyamine compound of 0.6:0.4 has a dry strength of 0.46 MPa and a wet strength of 0.18 MPa, which does not meet the standard requirements.

[0154] As can be seen from Comparative Examples 6-8, bisphenol A (BPA) replaced low molecular weight sulfate lignin. The results show that when the mass ratio of the epoxy compound to the polyamine compound prepared by bisphenol A in Comparative Example 6 was 0.85:0.15, the resulting adhesive had a dry strength of 1.11 and a wet strength that was unadhesive, which was lower than that of the low molecular weight lignin-based adhesive with the same proportion.

[0155] As shown in Comparative Example 9, when the mass ratio of commercially available epoxy compound to polyamine compound is 0.6:0.4, the adhesive strength exhibited by the adhesive prepared from the commercially available epoxy compound is similar to that of the adhesive prepared from the low molecular weight sulfate lignin epoxy compound and polyamine compound. This result indicates that the system of the present invention can still achieve adhesive performance on the same order of magnitude as the commercially available epoxy system without relying on the bisphenol A structural unit.

[0156] The results of Comparative Examples 10-14 show that adhesives prepared using commercially available epoxy compounds and polyamine compounds, under the condition that the mass ratio of commercially available epoxy compounds to polyamine compounds is 0.95-0.70:0.05-0.30, have lower adhesive strength than adhesives prepared using low molecular weight sulfate lignin epoxy compounds and polyamine compounds under the same mass ratio of epoxy compounds to polyamine compounds.

[0157] Figure 3 The graph shows the contact angle test data of the low molecular weight lignin-based adhesive cured product (LKLEP) of Example 1 and the eucalyptus sulfate lignin epoxy compound cured product (KLEP) of Comparative Example 2. The results show that the water contact angle of the obtained LKLEP sample is 97°~101°, which is significantly higher than that of the comparative sample KLEP (38°~45°). This indicates that the LKLEP surface has stronger hydrophobicity, which can effectively reduce the risk of water wetting and diffusion at the interface and provide reliable support for LKLEP to maintain high bonding strength in a humid environment.

[0158] From infrared spectroscopy FT-IR ( Figure 4 ) and 2D HSQC ( Figure 5 , Figure 6 The test results confirm that ethyl acetate graded lignin successfully introduced an epoxy structure during the epoxidation reaction.

[0159] In the FT-IR spectrum, Example 8 LKLGE ( Figure 6 The sample was at 910 cm. -1The presence of characteristic absorption peaks associated with epoxy groups, coupled with a decrease in the intensity of absorption peaks related to hydroxyl groups, indicates that hydroxyl groups participated in the epoxidation reaction. Furthermore, the enhanced COC stretching vibrations suggest an increase in ether structures within the system. In the 2D HSQC spectrum, epoxy group-related signals appeared in the LKLGE sample of Example 8, a signal absent in LKL, indicating the formation of new epoxy ether structures on the lignin fragments. Simultaneously, structural signals related to the lignin backbone remained, indicating that the reaction was primarily confined to hydroxyl sites and did not disrupt the aromatic backbone. In summary, the LKLGE prepared in this application introduces epoxy functional groups and forms corresponding etherified structures.

[0160] Figure 7 The results are from the phosphorus spectrum analysis of Example 1. The results show that the phenolic hydroxyl content of LKL is 8.83 mmol·g. -1 The concentration of α was significantly higher than that of KL (7.01 mmol·g). -1 ) and HKL (3.65 mmol·g -1 This provides more potential epoxidation reaction sites.

[0161] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A low molecular weight sulfate lignin, characterized in that, It is prepared by extraction of sulfate lignin with ethyl acetate. The weight-average molecular weight of the low molecular weight sulfate lignin is 790~850 g / mol, and the PDI is 1.75~1.

85.

2. The low molecular weight sulfate lignin according to claim 1, characterized in that, The sulfate lignin is mainly obtained from wood fiber raw materials through sulfate pulping.

3. A method for preparing a low molecular weight sulfate lignin epoxy compound, characterized in that, Includes the following steps: The low molecular weight sulfate lignin, epichlorohydrin and catalyst described in any one of claims 1 to 2 are mixed, and an aqueous solution of alkali metal hydroxide is added to react and extract to obtain a low molecular weight sulfate lignin epoxy compound. The ratio of low molecular weight sulfate lignin: epichlorohydrin: catalyst: alkali metal hydroxide aqueous solution is 10 g: 75~85 g: 3.8~4.2 g: 130~150 mL.

4. A low molecular weight sulfate lignin epoxy compound, characterized in that, It is prepared by the preparation method described in claim 3.

5. A method for preparing a low molecular weight lignin-based adhesive, characterized in that, Includes the following steps: The low molecular weight sulfate lignin epoxy compound of claim 4 is mixed evenly with a polyamine compound to obtain a low molecular weight lignin-based adhesive. The mass ratio of the low molecular weight sulfate lignin epoxy compound to the polyamine compound is (0.95~0.7):(0.05~0.3).

6. A low molecular weight lignin-based adhesive, characterized in that, It is prepared by the preparation method described in claim 5.

7. An application of a low molecular weight lignin-based adhesive, characterized in that, It is used for bonding materials and can also be used in the fields of electronic packaging and insulating materials.

8. The application of the low molecular weight lignin-based adhesive according to claim 7, characterized in that, For bonding materials, the single-sided application rate of low molecular weight lignin-based adhesives is 30–200 g / m². 2 .

9. The application of the low molecular weight lignin-based adhesive according to claim 7, characterized in that, Used in the bonding of materials, the bonding temperature is 80-160℃.

10. The application of the low molecular weight lignin-based adhesive according to claim 7, characterized in that, When used in the bonding of materials, the bonding time is 3 to 180 minutes.

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