A high-toughness wood-plastic composite material based on carboxyl-functionalized lignin modified by ionic liquid and a preparation method thereof

Abstract

The application relates to the field of high polymer composite materials, and particularly discloses a high-strength and high-toughness wood-plastic composite material based on carboxyl-functionalized ionic liquid modified lignin and a preparation method thereof. The carboxyl-functionalized ionic liquid is covalently grafted with the phenolic hydroxyl group of lignin to form a chemical bond, and the long-chain structure of the carboxyl-functionalized ionic liquid forms physical entanglement at the interface of the wood-plastic composite material, so that the interface bonding strength is improved through the double effects, the tensile property and the bending property are significantly improved, the impact strength can be effectively restored or even improved through improved microwave-assisted homogeneous reaction parameters, and the dilemma of "strengthening and being brittle" is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer composite materials, in particular to a method for modifying lignin by microwave-assisted carboxyl-functionalized ionic liquid and enhancing the interface performance of wood-plastic composite materials, and a high-toughness wood-plastic composite material prepared therefrom. BACKGROUND

[0002] Wood-plastic composites (WPCs) are widely used in the fields of construction and packaging due to their renewable nature of wood fibers and processability of plastics. However, natural biomass materials have strong hydrophilicity, which makes it difficult to fuse with hydrophobic thermoplastic, resulting in poor compatibility and mechanical properties between wood powder and plastic matrix. Adding coupling agents to modify each component in WPCs can improve the polarity between components to some extent and thus improve the compatibility and the performance of WPCs. Lignin is an amphiphilic polymer with two polarities, polar (hydrophilic) and non-polar (hydrophobic) parts in its structure. Studies have shown that lignin can be used as a coupling agent in wood-polymer composites. Compared with chemical coupling agents, lignin cannot fully meet the requirements of modern composite materials, so it is necessary to modify the structure of lignin to develop lignin as a bio-coupling agent. Traditional lignin modification methods (such as silane and maleic anhydride grafted polyethylene) rely on physical adsorption or simple esterification, and the interface bonding force is weak. In addition, there are problems such as long reaction time, high energy consumption, and the use of toxic solvents (Younesi-Kordkheili H, Pizzi A. Ionic liquid-modified lignin as a bio-coupling agent for natural fiber-recycled polypropylene composites[J]. Composites Part B: Engineering, 2020, 181:107587. DOI: [10.1016 / j.compositesb.2019.107587]). Therefore, it is necessary to find a green and efficient method with higher feasibility to improve the performance of lignin in this regard. SUMMARY

[0003] The present application aims to solve the technical problems of the prior art and provide a high-toughness wood-plastic composite material based on carboxyl-functionalized ionic liquid modified lignin and a preparation method thereof.

[0004] To solve the above technical problems, the present application discloses the following technical solutions:

[0005] In a first aspect, the present application discloses a carboxyl-functionalized ionic liquid modified lignin.

[0006] The carboxyl groups of the carboxyl-functionalized ionic liquid form covalent ester bonds with the phenolic hydroxyl groups of the lignin by interaction, and are grafted onto the surface of the lignin.

[0007] The carboxyl-functionalized ionic liquid includes 1-carboxymethyl-3-methyl imidazole chloride, 1-carboxymethyl-3-methyl imidazole bromide, 1-carboxymethyl-3-methyl imidazole bis(trifluoromethanesulfonyl) imide, 1-carboxymethyl-3-methyl imidazole trifluoromethanesulfonate, 1-carboxymethyl-3-methyl imidazole hydrogen sulfate, 1-carboxyethyl-3-methyl imidazole chloride, 1-carboxyethyl-3-methyl imidazole bromide, 1-carboxyethyl-3-methyl imidazole bis(trifluoromethanesulfonyl) imide, 1-carboxyethyl-3-methyl imidazole trifluoromethanesulfonate, and other ionic liquids containing carboxyl groups, preferably any one or a combination of 1-carboxyethyl-3-methyl imidazole chloride, 1-carboxymethyl-3-methyl imidazole chloride, 1-carboxymethyl-3-methyl imidazole bromide, 1-carboxymethyl-3-methyl imidazole trifluoromethanesulfonate, 1-carboxymethyl-3-methyl imidazole hydrogen sulfate, 1-carboxyethyl-3-methyl imidazole bromide, 1-carboxyethyl-3-methyl imidazole bis(trifluoromethanesulfonyl) imide, and 1-carboxyethyl-3-methyl imidazole trifluoromethanesulfonate.

[0008] In a second aspect, the present application discloses a preparation method of the modified lignin of the first aspect.

[0009] The method is a covalent grafting reaction of the carboxyl-functionalized ionic liquid and the lignin in a microwave reactor. In some embodiments, water is added to dilute the carboxyl-functionalized ionic liquid, and to ensure that the ionic liquid and the lignin are uniformly dispersed. In some embodiments, the method specifically includes: (1) mixing the lignin with water to obtain a first mixture, and adding the carboxyl-functionalized ionic liquid to the first mixture to obtain a second mixture; (2) dispersing the obtained second mixture in an ultrasonic disperser for pre-mixing; (3) performing a covalent grafting reaction of the pre-mixed mixture in a microwave reactor; and (4) after the reaction is completed, centrifuging, drying, and obtaining the modified lignin.

[0010] The mass ratio of the lignin to water is 1: (4-10), and preferably 1: (6-8).

[0011] The mass of the carboxyl-functionalized ionic liquid is 0.03%-1% of the mass of the lignin, preferably 0.45%-0.55%, or 0.5%-0.6%.

[0012] The ultrasonic power of the ultrasonic disperser is 300-500 W, and the ultrasonic frequency is 23-33 KHz.

[0013] wherein the premixing time is 3-5 min.

[0014] wherein the microwave reactor has a power of 200-800 W, preferably 240-400 W.

[0015] wherein the covalent grafting reaction has a temperature of 60-140 °C, preferably 90-135 °C.

[0016] wherein the covalent grafting reaction has a time of 3-15 min, preferably 6-12 min.

[0017] In a third aspect, the present application discloses a high-strength and high-toughness wood-plastic composite material.

[0018] wherein the wood-plastic composite material is made of the modified lignin of the first aspect and the modified lignin made by the method of the second aspect, and a plastic matrix, biomass powder and auxiliary materials.

[0019] wherein the plastic matrix includes polypropylene (PP), polyethylene (PE) and the like.

[0020] wherein the biomass powder includes bamboo powder, wood powder and the like.

[0021] wherein the modified lignin is 0.5%-20% of the total mass of the modified lignin, the plastic matrix, the biomass powder and the auxiliary materials, such as 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15% and the like.

[0022] wherein the auxiliary materials include an antioxidant; and the mass ratio of the modified lignin to the antioxidant is (1-5):(0.5-1), preferably 3:(0.5-0.8).

[0023] wherein the mass ratio of the plastic matrix to the biomass powder is 4:(5-6).

[0024] wherein the wood-plastic composite material is made by the following method: melting, blending, plasticizing, granulating the mixture containing the modified lignin, the plastic matrix, the biomass powder and the auxiliary materials in a twin-screw extruder, and hot-pressing the obtained particles to form the wood-plastic composite material.

[0025] wherein the temperature of the heating section of the twin-screw extruder is 165-180 °C, the temperature of the die head is 165-175 °C, and the rotation speed of the twin-screw extruder is 50-70 rpm. In some embodiments, the heating section of the twin-screw extruder is set to 165, 170, 175, 180, 180, 175 °C, the die head temperature is 170 °C, the screw rotation speed is 60 rpm, and the feeding speed is 3 rpm for extrusion and granulation.

[0026] The temperature of the hot-pressing forming is 170-210 DEG C, such as 180 DEG C, 190 DEG C, 200 DEG C.

[0027] The time of the hot-pressing forming is 5-50 min.

[0028] The biomass powder in the application is the biomass powder passing through a 60, 80, 100 or 120 mesh screen.

[0029] The high-toughness wood-plastic composite material provided by the application breaks the dilemma of "strengthening and brittleness", and compared with the wood-plastic composite material made of unmodified lignin, the carboxylic acid functionalized ionic liquid modified lignin can further improve the mechanical properties of the wood-plastic composite material, and especially can greatly restore or even improve the impact strength.

[0030] As in some embodiments, when PE is used as the plastic matrix, the tensile strength of the high-toughness wood-plastic composite material is 25-32.66 MPa, such as 26.5 MPa, 27.66 MPa; compared with the wood-plastic composite material without adding lignin, the tensile properties of the high-toughness wood-plastic composite material prepared by the application are improved by 21%-58%, such as 28%, 29%, 30%, 31%, 32%, 33%, 35%, 38%, 40%, 45%, 50%; compared with the wood-plastic composite material without adding lignin, the tensile strength of the wood-plastic composite material using unmodified lignin can only be improved by 12%. It can be seen that compared with the wood-plastic composite material without adding lignin, the tensile strength of the high-toughness wood-plastic composite material of the application is improved by a much larger margin than the wood-plastic composite material using unmodified lignin.

[0031] As in some embodiments, when PE is used as the plastic matrix, the tensile modulus of the high-toughness wood-plastic composite material is 445-500 MPa, such as 451.3 MPa, 492.5 MPa; compared with the wood-plastic composite material without adding lignin, the tensile modulus of the high-toughness wood-plastic composite material prepared by the application is improved by 8%-21%, such as 9%, 10%, 13%, 15%, 17%, 19%. Compared with the wood-plastic composite material without adding lignin, the tensile modulus of the wood-plastic composite material using unmodified lignin can only be improved by 2%. It can be seen that compared with the wood-plastic composite material without adding lignin, the tensile modulus of the high-toughness wood-plastic composite material of the application is improved by a much larger margin than the wood-plastic composite material using unmodified lignin.

[0032] As in some embodiments, in the PE as the plastic matrix, the bending strength of the high-toughness wood-plastic composite material is 37-43.48 MPa, such as 37.41 MPa, 40.48 MPa; compared with the wood-plastic composite material without adding lignin, the bending strength of the high-toughness wood-plastic composite material prepared by the application is increased by 6%-24%, such as 7%, 9%, 11%, 13%, 15%, 17%, 19%. Compared with the wood-plastic composite material without adding lignin, the bending strength of the wood-plastic composite material prepared by using unmodified lignin can only be increased by 2%. It can be seen that compared with the wood-plastic composite material without adding lignin, the bending strength of the high-toughness wood-plastic composite material of the application is increased by far more than the wood-plastic composite material prepared by using unmodified lignin.

[0033] As in some embodiments, in the PE as the plastic matrix, the bending modulus of the high-toughness wood-plastic composite material is 2400-2700 MPa, such as 2435.2 MPa, 2685.4 MPa; compared with the wood-plastic composite material without adding lignin, the bending modulus of the high-toughness wood-plastic composite material prepared by the application is increased by 30%-46%, such as 32%, 34%, 36%, 38%, 40%; compared with the wood-plastic composite material without adding lignin, the bending modulus of the wood-plastic composite material prepared by using unmodified lignin can only be increased by 13%. It can be seen that compared with the wood-plastic composite material without adding lignin, the bending modulus of the high-toughness wood-plastic composite material of the application is increased by far more than the wood-plastic composite material prepared by using unmodified lignin.

[0034] As in some embodiments, in the PE as the plastic matrix, the impact strength of the wood-plastic composite material prepared by using unmodified lignin decreases, while the high-toughness wood-plastic composite material of the application can improve the impact strength by using the modified lignin of the application, and the impact strength is 13-15 KJ·m 2 , such as 13.5 KJ·m 2 , 14 KJ·m 2 , 14.5 KJ·m 2 , 15 KJ·m 2 .

[0035] Beneficial effects:

[0036] 1. The application forms a chemical bond by covalent grafting of functional ionic liquid and lignin phenolic hydroxyl group, and at the same time, the long chain structure forms physical entanglement at the interface of the wood-plastic composite material, which improves the interface bonding strength through double action, and the tensile property and bending property are significantly improved. The impact strength can be restored or even improved through improved microwave-assisted homogeneous reaction parameters, and the "strengthening and brittleness" dilemma is solved.

[0037] 2、The present application realizes rapid grafting (the traditional method needs several hours) in 5-12 minutes by microwave-assisted homogeneous reaction, accelerates the reaction of ionic liquid and functional groups of lignin by using the high-efficiency heating characteristics of microwave, obtains a lignin biological coupling agent, aims to improve the interfacial bonding strength between wood powder and polyolefin, avoids a large number of agglomeration phenomena in the blending process of wood powder and polyolefin, and obtains a preparation method of modified lignin reinforced wood-plastic composite material which is simple in process and excellent in performance.

[0038] 3、The present application selects water as a diluent of ionic liquid, adopts a low-toxicity solvent system, the microwave reaction has low energy consumption, after modification of lignin, only the solvent needs to be recovered by centrifugation, and drying is performed, problems such as a large amount of wastewater discharge caused by repeated washing are avoided, the process is simple and convenient to operate, production time is saved, modification efficiency is improved, and environmental protection requirements are met. BRIEF DESCRIPTION OF DRAWINGS

[0039] The above and / or other aspects of the present application will become apparent from the following detailed description of the application taken in conjunction with the accompanying drawings.

[0040] Figure 1 The infrared spectra of unmodified lignin and modified lignin.

[0041] Figure 2 The electron microscope graph of the wood-plastic composite material. DETAILED DESCRIPTION

[0042] The present application can be better understood from the following examples. However, it will be readily apparent to those skilled in the art that the examples described are merely illustrative of the present application and should not be considered as limiting the scope of the application as described in the claims.

[0043] In the following examples, the experimental methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0044] In the following examples, the bamboo powder and wood powder are both powders passing through a 100-mesh screen.

[0045] In the present application, the method for detecting various mechanical properties is as follows: granulation by melt extrusion through a twin-screw extruder with a temperature range of 160-180 DEG C, and finally injection molding into dumbbell-shaped standard test samples under the conditions of 210 DEG C and 40 MPa by an injection molding machine. The tensile strength, tensile modulus, bending strength and bending modulus are tested by an electronic universal testing machine, and the impact strength is tested by a cantilever beam impact tester. The test conditions are as follows: the tensile strength and tensile modulus are tested in accordance with the standard GB / T 1040.1, the bending strength and bending modulus are tested in accordance with the standard GB / T 9341-2008, and the impact strength is tested in accordance with the standard GB / T 1843-2008.

[0046] The proportions described in the present application are all weight proportions unless otherwise specified.

[0047] Example 1: Preparation of modified lignin

[0048] (1) A first mixed solution was obtained by mixing lignin and deionized water in a mass ratio of 1:7, and a second mixed solution was obtained by diluting 0.5% of a functional ionic liquid of the mass of the lignin in the first mixed solution. The second mixed solution was placed in an ultrasonic disperser and pre-mixed for 3-5 min at a certain ultrasonic power (400 W) and ultrasonic frequency (28 KHz).

[0049] (2) In a microwave reactor, the microwave power was controlled at 240-400 W, and the reaction was carried out at 90-132.5°C for 6-12 min to allow the covalent grafting reaction between the carboxyl active functional groups in the ionic liquid and the phenolic hydroxyl groups of the lignin.

[0050] (3) After the reaction, centrifugation and drying were performed to obtain modified lignin 1-7.

[0051] Table 1: Ionic liquids used in Example 1 and reaction conditions of step (2)

[0052]

[0053] Comparing the infrared spectra of unmodified lignin and carboxyl-functionalized ionic liquid modified lignin Figure 1 , it can be seen that a new significant absorption peak appears at 1735 cm -1 after modification, which is attributed to the stretching vibration of ester carbonyl (C=O), proving that esterification reaction occurs between the carboxyl groups in the ionic liquid and the phenolic hydroxyl groups of the lignin, forming a covalent ester bond, and successfully achieving grafting. In addition, the aromatic ring characteristic peaks (1600 cm -1 and 1510 cm -1 ) are retained after modification, indicating that the lignin skeleton is not damaged. The FTIR results fully confirm that the carboxyl-functionalized ionic liquid is efficiently grafted to the surface of the lignin by the microwave-assisted method.

[0054] Example 2: Preparation of wood-plastic composite materials

[0055] (1) Unmodified lignin or modified lignin, wood powder, plastic matrix PE, and antioxidant (BASF antioxidant 1010 in Germany) were placed in a high-speed mixer and pre-mixed at a certain rotation speed (800 rpm / min) for 8 min to obtain a uniformly dispersed blend.

[0056] (2) The obtained blend is melt blended, plasticized and granulated by entering a twin-screw extruder; the twin-screw extruder is provided with heating intervals of 165, 170, 175, 180, 180, 175°C, the die head temperature is 170°C, the screw rotation speed is 60 rpm, and the feeding speed is 3 rpm for extrusion and granulation.

[0057] (3) The prepared sample is dried in a 102°C oven for 2h for standby; finally, the composite material is prepared by hot pressing at 190°C (pre-pressing for 10 min, and hot pressing for 30 min).

[0058] Table 2 Preparation conditions of wood-plastic composites with no lignin, unmodified lignin and lignin modified by different ionic liquids

[0059]

[0060] The electron microscope images of the prepared composite materials are shown in Figure 2 .

[0061] PE0 (no lignin): Obvious gaps or cavities between wood powder and plastic matrix should be visible, and the interface bonding is poor. The surface of the wood powder is smooth, and it is not fully wrapped by plastic, indicating poor compatibility.

[0062] PE 未改性 : Adding unmodified lignin, the interface of the composite material is improved, but there are still local peeling or gaps, indicating that physical mixing has some effect but is limited. Lignin may exist in the form of particles and is not uniformly distributed.

[0063] PE1: Adding modified lignin 1, the interface of the composite material is significantly improved, and the wood powder is more closely combined with the plastic, and the gap is reduced. Lignin may be more uniformly dispersed, forming a transition layer.

[0064] PE4: Adding modified lignin 4, the interface of the composite material is the most continuous and dense, and almost no gap is visible. Lignin and plastic form good combination, and may present a "bridging" structure.

[0065] PE5: Adding modified lignin 5, the interface of the composite material is improved to a limited extent, and there are still obvious gaps or interface peeling, indicating that the non-functional ionic liquid has poor effect.

[0066] PE7: Adding modified lignin 7, the interface of the composite material is improved, but not as uniform as the microwave method (such as PE4), and there may be local agglomeration or uneven reaction.

[0067] The properties of the prepared composite materials are shown in Table 3. Compared with no lignin (PE0), the wood-plastic composite material (PE 未改性) can improve the mechanical properties such as tensile strength to some extent, but the impact strength decreases obviously. Compared with the wood-plastic composite material (PE 未改性 ) made of unmodified lignin, the wood-plastic composite material (PE1, PE4) made of the carboxyl-functionalized ionic liquid modified lignin provided by the present application can further improve the mechanical properties of the wood-plastic composite material, especially the PE4 can restore the impact strength, and can improve 14% (13.80 vs 12.14 KJ / m²) compared with the blank group, and break the dilemma of "strengthening and brittleness"; and the part of the mechanical properties of the wood-plastic composite material (PE2, PE3, PE5, PE6) made of other ionic liquid modified lignin decreases instead. Compared with PE7, the mechanical properties of PE1 are higher, indicating that the microwave-assisted carboxyl-functionalized ionic liquid realizes the rapid homogeneous modification of lignin, and the carboxyl functional groups are covalently grafted to the surface of lignin by the interaction with the phenolic hydroxyl groups of the lignin matrix, realizing the chemical bonding and physical synergistic reinforcement of the wood-plastic composite material interface.

[0068] Table 3 Properties of the wood-plastic composite materials made of unmodified lignin and different ionic liquid modified lignin

[0069]

[0070] Example 3: Preparation of wood-plastic composite material

[0071] Referring to the preparation method of modified lignin 4 in Table 1, the carboxyl-functionalized ionic liquid used for modifying the lignin is replaced by other carboxymethyl series and carboxyethyl series functional ionic liquids, and the properties of the obtained wood-plastic composite materials are shown in Table 4.

[0072] Table 4 Properties of the wood-plastic composite materials made of carboxymethyl series and carboxyethyl series functional ionic liquid modified lignin

[0073]

[0074] Example 4: Preparation of wood-plastic composite material

[0075] Referring to the preparation method of modified lignin 4 in Table 1, 1-carboxyethyl-3-methyl imidazole chloride is used as a functional ionic liquid for modification, and the amount of 1-carboxyethyl-3-methyl imidazole chloride is 0%, 0.3% and 0.5% of the mass of lignin, respectively, and the obtained lignins are named as IL-0, IL-0.3 and IL-0.5.

[0076] (1) 39.5 parts of polypropylene, 55 parts of bamboo powder and 5 parts of the aforementioned different lignins and 0.5 parts of antioxidant are taken to prepare the wood-plastic composite material according to the method of Example 2, and the experimental results are shown in Table 5.

[0077] As can be seen from Table 5, when PP is used as a matrix, compared with the wood-plastic composite material made of unmodified lignin, the impact performance of the wood-plastic composite material made of modified lignin IL-0.3 and IL-0.5 is obviously improved, and the mechanical properties of the wood-plastic composite material made of modified lignin IL-0.5 are all superior to those of the wood-plastic composite material made of unmodified lignin.

[0078] (2) 39.5 parts of polypropylene, bamboo powder and lignin IL-0.5 (the specific parts of bamboo powder and lignin are shown in Table 6) and 0.5 parts of antioxidant were taken, and the wood-plastic composite material was prepared according to the method of Reference Example 2, and the experimental results are shown in Table 6.

[0079] As can be seen from Table 6, when PP is used as a matrix, compared with the wood-plastic composite material without adding lignin, the wood-plastic composite material made of modified lignin IL-0.5 in the amount of 1 part and 3 parts can effectively improve the mechanical properties of the wood-plastic composite material, and especially when the amount is 1 part, the impact strength is as high as 3.94 kJ / m 2 .

[0080] Table 5 Properties of polypropylene wood-plastic composite material

[0081]

[0082] Table 6 Properties of polypropylene wood-plastic composite material

[0083]

[0084] The lignin is rapidly and homogeneously modified by microwave-assisted carboxyl functional ionic liquid, the carboxyl functional group is covalently grafted to the surface of lignin by the interaction with the phenolic hydroxyl group of the lignin matrix, and the interface chemical bonding and physical synergistic reinforcement of the wood-plastic composite material are realized.

[0085] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent of the present application. It should be pointed out that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A lignin modified with a carboxyl-functionalized ionic liquid, characterized in that, A carboxyl-functionalized ionic liquid is covalently grafted onto lignin in a microwave reactor. The carboxyl groups of the carboxyl-functionalized ionic liquid interact with the phenolic hydroxyl groups of lignin to form covalent bonds, which are then grafted onto the surface of the lignin. The carboxyl-functionalized ionic liquid is any one or a combination of several of the following: 1-carboxymethyl-3-methylimidazolium chloride, 1-carboxymethyl-3-methylimidazolium bromide, 1-carboxymethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-carboxymethyl-3-methylimidazolium trifluoromethanesulfonate, 1-carboxymethyl-3-methylimidazolium hydrogen sulfate, 1-carboxyethyl-3-methylimidazolium chloride, 1-carboxyethyl-3-methylimidazolium bromide, 1-carboxyethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-carboxyethyl-3-methylimidazolium trifluoromethanesulfonate.

2. The modified lignin according to claim 1, characterized in that, The mass of the carboxyl-functionalized ionic liquid is 0.03%-1% of the lignin content.

3. The modified lignin according to claim 1, characterized in that, The power of the microwave reactor is 200-800W.

4. The modified lignin according to claim 1, characterized in that, The temperature for the covalent grafting reaction is 60-140℃.

5. A wood-plastic composite material, characterized in that, It is made from the modified lignin according to any one of claims 1-4, together with a plastic matrix, biomass powder and excipients; wherein the plastic matrix is ​​polyethylene.

6. The wood-plastic composite material according to claim 5, characterized in that, The modified lignin comprises 0.5%-20% of the total mass of modified lignin, plastic matrix, biomass powder, and auxiliary materials.

7. The wood-plastic composite material according to claim 5 or 6, characterized in that, The mass ratio of the plastic matrix to the biomass powder is 4:(5-6).

8. The wood-plastic composite material according to claim 5 or 6, characterized in that, The auxiliary materials include antioxidants; the mass ratio of the modified lignin to the antioxidant is (1-5):(0.5-1).

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