Agricultural and forestry waste-based thermoplastic plastic and preparation method thereof

Abstract

The present invention relates to the technical field of wood fiber agricultural and forestry waste treatment, and in particular to an agricultural and forestry waste-based thermoplastic plastic and a preparation method thereof. The preparation method comprises: step S1, drying and crushing the wood fiber agricultural and forestry waste to obtain a powder; step S2, adding an esterifying agent, an acid binding agent, and the powder obtained in step S1 into a ball mill at once and grinding them to obtain a slurry; step S3, maturing the slurry obtained in step S2; step S4, pouring the matured slurry obtained in step S3 into a precipitant for sufficient precipitation, and then filtering and separating to obtain a crude agricultural and forestry waste-based thermoplastic plastic product; step S5, processing to obtain a pure agricultural and forestry waste-based thermoplastic plastic. The present invention provides a green and efficient preparation method for agricultural and forestry waste-based thermoplastic plastic using wood fiber agricultural and forestry waste, and the obtained agricultural and forestry waste-based thermoplastic plastic has a low melting temperature, a uniform structure, and stable mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of wood fiber agricultural and forestry waste treatment, and in particular to an agricultural and forestry waste-based thermoplastic plastic and a preparation method thereof. Background Art

[0002] Hundreds of millions of tons of agricultural and forestry waste are generated annually worldwide, primarily including straw, bagasse, and wood shavings. Currently, most of these wastes are directly landfilled or incinerated to generate electricity, with a small amount used as fertilizer, papermaking, or plastic fillers, failing to fully realize their value. Compositionally, most of these wastes are wood fibers, primarily composed of cellulose, hemicellulose, and lignin, and are promising for use in the preparation of various plastic products. However, strong hydrogen bonding between the components and within the molecular structure of wood fiber-based wastes makes these biomasses difficult to dissolve in common solvents and cannot be melted. This narrows the processing window for these waste materials and limits their application in polymer materials. Therefore, improving the processability of these waste materials is a prerequisite for converting them into environmentally friendly materials and is key to achieving their added value. In particular, melt processing of these waste materials is environmentally friendly and efficient, offering greater scale-up potential.

[0003] In order to achieve thermoplastic processing of lignocellulosic agricultural and forestry waste, it is necessary to destroy or reduce the hydrogen bonding between the components and within the molecules of lignocellulosic agricultural and forestry waste. It is also necessary to improve the flexibility of the molecular chains of the components in the lignocellulosic agricultural and forestry waste materials to give the macromolecular chains the ability to move. Up to now, the main means to achieve melt processing of lignocellulosic agricultural and forestry waste include physical modification and chemical modification. Physical modification mainly refers to the blending of lignocellulosic agricultural and forestry waste with thermoplastic polymers. However, due to the high polarity of lignocellulosic agricultural and forestry waste, its compatibility with common thermoplastic polymers is poor, resulting in generally unsatisfactory mechanical properties of the resulting composite materials. Chemical modification refers to the use of hydroxyl groups in the molecules of the components of lignocellulosic agricultural and forestry waste as reaction sites to introduce internal plasticizers into the molecules of lignocellulosic agricultural and forestry waste materials. On the one hand, it reduces the hydrogen bonding effect, and on the other hand, it also improves the flexibility of the molecular chain. It is one of the ideal means to obtain thermoplastic plastics based on agricultural and forestry waste.

[0004] Among the methods of obtaining thermoplastics based on agricultural and forestry wastes through chemical modification, esterification modification is relatively common. It has been reported that bagasse or wood powder is dissolved in ionic liquids (ILs) and phthalic anhydride (Chen, et al, ACS Sustainable Chemistry & Engineering, 2012, 3, 2510-2514; Chen, et al, Industrial Crops and Products, 2017, 108, 286-294), fatty acid vinyl esters (Suzuki, et al, ACS Sustainable Chemistry & Engineering, 2021, 9, 15249-15257) or fatty acid chlorides (Chinese patent: CN 201010542881; Thiebaud, et al, Bioresource Technology, 2017). Ogy, 1997, 59, 103-107) as an esterifying agent. After esterification, lignocellulosic agricultural and forestry waste can be converted into high-performance lignocellulosic biomass-based thermoplastics. Dissolving the agricultural and forestry waste facilitates control over the chemical modification process, and the resulting agricultural and forestry waste-based thermoplastics exhibit excellent melting behavior.

[0005] However, the composition of lignocellulosic agricultural and forestry waste is complex, and the solvent systems that can dissolve lignocellulosic agricultural and forestry waste are mostly high-cost ILs, etc., which have low solubility in lignocellulosic agricultural and forestry waste. Therefore, the overall cost of the modification method is high, which makes this method mostly limited to laboratory research on the feasibility of thermoplastic processing of lignocellulosic agricultural and forestry waste, and has not yet been promoted in industry.

[0006] A Chinese patent document (CN102964605B, "A Method for Esterification Modification of Lignocellulosic Biomass") discloses the use of ball milling to esterify lignocellulosic biomass. However, this technical solution requires pre-ball milling, which is a cumbersome process. Furthermore, the esterification reagent used is a solution of an acid anhydride in benzene, dimethyl sulfoxide, chloroform, and carbon tetrachloride, requiring the esterification agent to be prepared as a solution, resulting in high operating costs.

[0007] In summary, among the currently reported methods for preparing thermoplastics based on agricultural and forestry waste, physical modification is difficult to obtain products with excellent properties, while chemical modification requires the use of large amounts of expensive solvents, resulting in high preparation costs and low modification efficiency. Therefore, the production of lignocellulosic biomass-based thermoplastics from agricultural and forestry waste remains a significant challenge. Summary of the Invention

[0008] The purpose of the present invention is to overcome the problems of high cost, low preparation efficiency and poor performance of agricultural and forestry waste-based plastics in the existing preparation methods of agricultural and forestry waste-based thermoplastic plastics using wood fiber agricultural and forestry waste, and to provide a green and efficient preparation method for agricultural and forestry waste-based thermoplastic plastics using wood fiber agricultural and forestry waste. The obtained wood fiber biomass-based thermoplastic plastic (agricultural and forestry waste-based thermoplastic plastic) has a low melting temperature, uniform structure and stable mechanical properties.

[0009] To achieve the above objectives, the present invention provides a method for preparing agricultural and forestry waste-based thermoplastic plastics, which comprises:

[0010] Step S1, drying and crushing the wood fiber agricultural and forestry waste to obtain powder;

[0011] Step S2, adding the esterifying agent, the acid binding agent and the powder obtained in step S1 into a ball milling container at once, and continuously grinding under ball milling for 0.5 to 6 hours to obtain a slurry; the ball milling container is a stainless steel ball milling jar or a zirconium dioxide ball milling jar;

[0012] Wherein, the esterifying agent is one or more of hexanoyl chloride, octanoyl chloride, decanoyl chloride, lauroyl chloride, myristoyl chloride, palmitoyl chloride, stearoyl chloride, oleoyl chloride, benzoyl chloride, 3-phenylpropionyl chloride, 4-butylbenzoyl chloride, 4-tert-butylbenzoyl chloride, 2-ethylhexanoyl chloride or 2-butyloctanoyl chloride;

[0013] The acid binding agent is one or more of ethylenediamine, triethylamine, pyridine, 4-dimethylaminopyridine (DMAP), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) or tetramethylguanidine (TMG);

[0014] Step S3, placing the slurry obtained in step S2 in a constant temperature box at 60-120° C. and aging for 1-3 hours;

[0015] Step S4: pouring the matured slurry obtained in step S3 into a precipitant for sufficient precipitation, and then filtering and separating to obtain a crude agricultural and forestry waste-based thermoplastic plastic product;

[0016] Step S5: processing the crude agricultural and forestry waste-based thermoplastic plastic product to obtain pure agricultural and forestry waste-based thermoplastic plastic.

[0017] Preferably, the lignocellulosic agricultural and forestry waste is one or more of sawdust, wood powder, bamboo powder, bagasse, rape straw, wheat straw, rice straw or corn straw.

[0018] Preferably, the lignocellulosic biomass in step S1 is dried at 50-100° C. and crushed to 100-200 mesh.

[0019] Preferably, in step S2, the weight of the esterification agent is 1 to 15 times the weight of the wood fiber agricultural and forestry waste; the weight of the acid binding agent is 1 to 3 times the weight of the wood fiber agricultural and forestry waste;

[0020] Preferably, the weight of the esterification agent is 3 to 10 times the weight of the wood fiber agricultural and forestry waste.

[0021] Preferably, the weight of the acid binding agent is 1.2 to 2 times the weight of the wood fiber agricultural and forestry waste.

[0022] Preferably, the precipitant in step S4 is one of methanol, ethanol, n-propanol, isopropanol or acetone.

[0023] Preferably, step S5 specifically includes:

[0024] Washing the crude agricultural and forestry waste-based thermoplastic plastic product with the precipitant in step S4 for 3 to 5 times to obtain a pure agricultural and forestry waste-based thermoplastic plastic; or:

[0025] The crude agricultural and forestry waste-based thermoplastic plastic product is treated by Soxhlet extraction with the precipitant in step S4 as a solvent for 24 to 48 hours to obtain a pure agricultural and forestry waste-based thermoplastic plastic.

[0026] The present invention also provides an agricultural and forestry waste-based thermoplastic plastic, which is prepared using the method for preparing an agricultural and forestry waste-based thermoplastic plastic.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention uses a ball mill mechanochemical method to prepare agricultural and forestry waste-based thermoplastics from lignocellulosic agricultural and forestry waste. Without using a solvent, the hydroxyl groups in the agricultural and forestry waste molecules are replaced with acyl groups through an esterification reaction. This, on the one hand, reduces the hydrogen bonding in the lignocellulosic agricultural and forestry waste; on the other hand, the introduced substituents can act as internal plasticizers, improving the mobility of the molecular chains of the components in the lignocellulosic agricultural and forestry waste. The present invention can prepare a series of agricultural and forestry waste-based thermoplastics without the need for solvents, avoiding the solvent post-treatment step, reducing reaction costs, and improving environmental protection and production efficiency.

[0029] (2) The agricultural and forestry waste-based thermoplastic plastic prepared by the present invention using wood fiber agricultural and forestry waste has a low melting temperature, uniform structure, and stable mechanical properties. In addition, the wood fiber biomass-based thermoplastic plastic with specified properties can be obtained by regulating the structure of the esterification agent.

[0030] (3) To achieve thermoplastic properties in lignocellulosic agricultural and forestry waste, the present invention uses a fatty acid chloride or aromatic acid chloride containing more than 6 carbon atoms as an esterifying agent. Esterifying agents with larger molecular weights can effectively disrupt hydrogen bonding, so the esterification modification of the present invention can achieve the melting properties of lignocellulosic agricultural and forestry waste.

[0031] (4) The present invention uses an organic base that has a catalytic effect on the esterification reaction as an acid binding agent. The acid binding agent in the present invention actually has catalytic efficiency and can greatly improve the degree of esterification. At the same time, thanks to the catalytic effect of the acid binding agent, the present invention does not require pre-ball milling of wood fiber agricultural and forestry waste.

[0032] (5) In order to improve the reaction efficiency, the present invention combines mechanochemistry and thermochemistry. After 1.5 hours of ball milling forced mixing and initial reaction, an additional aging at 80-110°C is added, which can greatly increase the esterification degree. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the infrared spectrum of bagasse powder and Example 1. Figure 1 It can be seen that compared with the infrared spectrum of bagasse, the sample prepared in Example 1 has a -1 and 1155cm -1 The characteristic diffraction peak of the ester group appeared, indicating that the esterification modification of bagasse was successfully achieved through the present invention;

[0034] Figure 2 The figure is a comparison chart of the degree of substitution of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1. Figure 2 As can be seen, Example 1 has a higher degree of substitution than Comparative Example 1 and Comparative Example 2, indicating that the ball milling mechanization method of the present invention has a significant benefit in the esterification modification of bagasse. Example 1 and Comparative Example 3 have similar degrees of substitution, but the amount of pyridine used in the present invention is only 1 / 10 of that in Comparative Example 3, indicating that the present invention has higher environmental friendliness and economic efficiency.

[0035] Figure 3 The melt flow pictures of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1 are shown. Figure 3It can be seen that Comparative Examples 1 and 2 do not have thermoplastic properties. Comparative Example 3 has a similar melt flow temperature to Example 1. This demonstrates that the present invention can produce agricultural and forestry waste-based thermoplastics with the same benefits as traditional methods while significantly improving economic efficiency, environmental friendliness, and production efficiency.

[0036] Figure 4 The present invention provides a flow chart of the preparation method. DETAILED DESCRIPTION

[0037] The present invention is further described below by way of examples. However, the following examples are only used to help understand the technology of the present invention and are not intended to further limit the scope of protection of the present invention.

[0038] To illustrate the effect of the embodiment, the structure of the obtained wood fiber agricultural and forestry waste was analyzed by infrared spectroscopy; the degree of substitution of the wood fiber agricultural and forestry waste was calculated by weighing method (unit: mmol / g); the melting temperature (T f , unit: ℃), the temperature at which the sample is heated to the point where it just begins to flow is recorded as T f ; In addition, after the agricultural and forestry waste-based thermoplastic plastic was hot-pressed (160°C, 10 MPa, 5 min) to form a film, the tensile strength (σ, unit: MPa) and elongation at break (ε, unit: %) of the agricultural and forestry waste-based thermoplastic plastic hot-pressed film were tested using an electronic universal testing machine, and the tensile rate was 5 mm / min.

[0039] The technical principle behind the embodiments of the present invention is to achieve esterification modification of agricultural and forestry waste, which is a type of lignocellulosic biomass, by combining ball milling mechanochemistry with heat aging, thereby imparting thermoplastic properties to the waste. Ball milling mechanochemistry, with its ability to force mixing and rapid molecular transformation, enables uniform mixing of agricultural and forestry waste and an esterifying agent in a solvent-free environment. This esterification modification can disrupt or even completely eliminate hydrogen bonds between the molecular chains of the lignocellulosic agricultural and forestry waste, increasing the distance between the molecular chains and thereby producing an agricultural and forestry waste-based thermoplastic.

[0040] Example 1

[0041] Bagasse powder and lauroyl chloride were added to a zirconia ball mill at a weight ratio of 1:5, and then anhydrous pyridine twice the weight ratio of the bagasse powder was added. Subsequently, the ball mill was transferred to a planetary ball mill and ball-milled at a speed of 500 rpm for 1 hour, and then the ball mill was transferred to an oven at 80°C for aging for 1.5 hours. Finally, the product in the ball mill was washed out with an appropriate amount of ethanol, and the solid matter was separated by filtration to obtain a crude product of bagasse laurate. After further Soxhlet extraction with ethanol as a solvent for 24 hours, the solid product was placed at 60°C and fully dried to obtain the final bagasse laurate. The bagasse-based thermoplastic was a light yellow powder with a degree of substitution of 6.8 mmol / g. Its infrared spectrum is shown in the figure below. Figure 1 Some of the performance is shown in Table 1.

[0042] Example 2

[0043] Bagasse powder and 3-phenylpropionyl chloride were added to a zirconia ball mill at a weight ratio of 1:5. Anhydrous pyridine was then added at a weight ratio twice the amount of bagasse powder. The mill was then transferred to a planetary ball mill and milled at 500 rpm for 1 hour. The mill was then transferred to an 80°C oven and aged for 1.5 hours. Finally, the product was washed out of the mill with an appropriate amount of ethanol, and the solids were separated by filtration to obtain a crude bagasse 3-phenylpropionate. After Soxhlet extraction with ethanol for 24 hours, the solid product was thoroughly dried at 60°C to obtain the final crude bagasse 3-phenylpropionate. This bagasse-based thermoplastic was a pale yellow powder with a degree of substitution of 6.3 mmol / g. Some of its properties are shown in Table 1.

[0044] Example 3

[0045] Bagasse powder and lauroyl chloride were added to a zirconia ball mill at a weight ratio of 1:5. Anhydrous pyridine was then added at a weight ratio twice that of the bagasse powder. The mill was then transferred to a planetary ball mill and milled at 500 rpm for 1 hour. The mill was then transferred to a 110°C oven and aged for 1 hour. Finally, the product was washed out of the mill with an appropriate amount of ethanol, and the solids were separated by filtration to obtain the crude bagasse laurate. After Soxhlet extraction with ethanol for 24 hours, the solid product was fully dried at 60°C to obtain the final bagasse laurate. This bagasse-based thermoplastic was a yellow powder with a degree of substitution of 7.3 mmol / g. Some of its properties are shown in Table 1.

[0046] Example 4

[0047] Wood powder and lauroyl chloride were added to a zirconia ball mill at a weight ratio of 1:5. Anhydrous pyridine was then added at a weight ratio twice that of the wood powder. The mill was then transferred to a planetary ball mill and milled at 500 rpm for 1 hour. The mill was then transferred to an 80°C oven and aged for 1.5 hours. Finally, the product was washed out with an appropriate amount of ethanol, and the solids were separated by filtration to obtain the crude wood laurate. After Soxhlet extraction with ethanol for 24 hours, the solid product was dried at 60°C to obtain the final wood laurate. This wood powder-based thermoplastic was a light gray powder with a degree of substitution of 6.9 mmol / g. Some of its properties are shown in Table 1.

[0048] Table 1 Some properties of agricultural and forestry waste-based thermoplastics prepared by the present invention

[0049]

[0050] As can be seen from Table 1, the present invention can obtain T using bagasse powder as raw material. f Bagasse-based thermoplastics with a temperature of 112 to 135°C can also be obtained based on the upper and lower ranges of the present invention. f Wider bagasse-based thermoplastics. In addition, the performance of polymer materials is mainly determined by the structure. According to the present invention, the structure of the esterifying agent can be regulated to achieve the purpose of regulating the mechanical properties of bagasse-based thermoplastics. As shown in Table 1, the lauroyl chloride used in Example 1 is a linear structure, and the tensile strength of the obtained bagasse-based thermoplastic is moderate, and the elongation at break is high; the 3-phenylpropionyl chloride used in Example 2 is a rigid structure with a benzene ring, and the tensile strength of the obtained bagasse-based thermoplastic is high, and the elongation at break is low. In addition, the present invention also prepares thermoplastics with other wood fiber agricultural and forestry wastes. For example, in Example 3, wood powder was used as raw material to prepare T f Thermoplastic plastics with a temperature of 146° C. The following will illustrate the gain effect of the present invention through comparative examples.

[0051] Comparative Example 1

[0052] Bagasse powder and lauroyl chloride were added to a glass mortar at a weight ratio of 1:5, and then anhydrous pyridine was added in an amount twice the weight ratio of the bagasse powder. Subsequently, the bagasse powder, lauroyl chloride and anhydrous pyridine were evenly mixed by grinding, and the resulting slurry was placed in an oven at 80°C for aging for 1.5 hours. Finally, the product in the mortar was washed out with an appropriate amount of ethanol, and the solid matter was separated by filtration to obtain the crude product of Comparative Example 1. After further Soxhlet extraction with ethanol as a solvent for 24 hours, the solid product was placed at 60°C and fully dried to obtain the final product of Comparative Example 1. The modified bagasse was a white powder with a degree of substitution of 0.25 mmol / g. The OM photograph during the heating process is shown in FIG. Figure 3Some of its performances are shown in Table 2.

[0053] Comparative Example 2

[0054] Bagasse powder and lauroyl chloride were added to a round-bottom flask at a weight ratio of 1:5, and then anhydrous pyridine 10 times the weight of the bagasse powder was added. Subsequently, the round-bottom flask was immersed in an oil bath at 80°C and stirred for 1.5 hours. After the reaction, the product in the round-bottom flask was washed out with an appropriate amount of ethanol, and the solid matter was separated by filtration to obtain the crude product of Comparative Example 2. After further Soxhlet extraction with ethanol as the solvent for 24 hours, the solid product was placed at 60°C and fully dried to obtain the final product of Comparative Example 2. The modified bagasse was a light yellow powder with a degree of substitution of 3.12 mmol / g. The OM photograph during the heating process is shown in FIG. Figure 3 Some of its performances are shown in Table 2.

[0055] Comparative Example 3

[0056] Bagasse powder and lauroyl chloride were added to a round-bottom flask at a weight ratio of 1:5, and then anhydrous pyridine 20 times the weight of the bagasse powder was added. Subsequently, the round-bottom flask was immersed in an oil bath at 80°C and stirred for 1.5 hours. After the reaction, the product in the round-bottom flask was washed out with an appropriate amount of ethanol, and the solid matter was separated by filtration to obtain the crude product of Comparative Example 3. After further Soxhlet extraction with ethanol as the solvent for 24 hours, the solid product was placed at 60°C and fully dried to obtain the final product of Comparative Example 3. The modified bagasse was a yellow powder with a degree of substitution of 7.0 mmol / g. The OM photograph during the heating process is shown in FIG. Figure 3 Some of its performances are shown in Table 2.

[0057] Table 2 Performance comparison of modified bagasse prepared by the present invention and traditional means

[0058]

[0059] Note: The amount of pyridine is calculated based on the weight of bagasse powder.

[0060] As shown in Table 2, under the same other conditions, if the ball milling mechanochemical method of the embodiment of the present invention is not used (i.e., Comparative Example 1), the conventional heating method cannot obtain a modified bagasse with thermoplasticity due to the lack of forced mixing and efficient molecular conversion of ball milling; even if the amount of pyridine (serving as both an acid binding agent and a solvent) is increased to 5 times that of the embodiment of the present invention, the conventional heating method cannot obtain a modified bagasse with good thermoplasticity. The T of the modified bagasse obtained in Comparative Example 2 is fThe temperature is still as high as 223°C, which does not meet the requirements of traditional melt processing. When a large amount of pyridine is used, a bagasse-based thermoplastic can also be obtained by traditional heating methods (Comparative Example 3), and its performance is similar to that of the present invention. However, the large amount of solvent not only increases manufacturing costs but also may cause environmental pollution. Therefore, the present invention has significant benefits in reducing costs, improving environmental protection, and increasing efficiency.

[0061] The present invention achieves esterification modification of wood fiber agricultural and forestry wastes through a ball mill mechanochemical process, without the use of expensive ILs or other toxic or hazardous solvents. This reduces hydrogen bonding between and within the molecules of the waste components, improving the mobility of their molecular chains in thermal environments, and producing a series of agricultural and forestry waste-based thermoplastics with low melting temperatures, uniform structures, and stable mechanical properties. The present invention's preparation process is simple, requires minimal equipment, and offers low production costs and environmental friendliness.

[0062] The upper and lower limits, and interval values ​​of the raw materials in the embodiment of the present invention, as well as the upper and lower limits, and interval values ​​of the process parameters can all realize the embodiment of the present invention, and examples are not listed here one by one.

[0063] It is easy to understand that those skilled in the art can combine, split, reorganize, etc. the embodiments of the present application based on one or several embodiments provided in the present application to obtain other embodiments, and these embodiments do not exceed the scope of protection of the present application.

[0064] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The embodiments shown in the embodiments are only part of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by the above and, without departing from the purpose of the present invention, designs a structure and embodiment similar to the technical solution without creatively designing, they shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing thermoplastic plastics based on agricultural and forestry wastes, characterized in that: include: Step S1: drying and crushing lignocellulosic agricultural and forestry waste to obtain powder; the lignocellulosic agricultural and forestry waste is wood powder or bagasse; Step S2: adding the esterifying agent, the acid binding agent and the powder obtained in step S1 into a ball mill container at once, and continuously grinding them at a speed of 500 rpm for 1 hour under ball milling to obtain a slurry; Wherein, the esterifying agent is lauroyl chloride or 3-phenylpropionyl chloride; The acid binding agent is one or more of ethylenediamine, triethylamine, pyridine, 4-dimethylaminopyridine, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5,7-triazabicyclo[4.4.0]dec-5-ene or tetramethylguanidine; Step S3, placing the slurry obtained in step S2 in a thermostat at 80-110° C. for 1-1.5 hours; Step S4: pouring the matured slurry obtained in step S3 into a precipitant for sufficient precipitation, and then filtering and separating to obtain a crude agricultural and forestry waste-based thermoplastic plastic product; Step S5: processing the crude agricultural and forestry waste-based thermoplastic plastic product to obtain pure agricultural and forestry waste-based thermoplastic plastic.

2. The method for preparing agricultural and forestry waste-based thermoplastic plastic according to claim 1, characterized in that: In step S1, the lignocellulosic biomass is dried at 50-100° C. and crushed to 100-200 mesh.

3. The method for preparing agricultural and forestry waste-based thermoplastic plastic according to claim 1, characterized in that: In step S2, the weight of the esterifying agent is 1 to 15 times the weight of the lignocellulosic agricultural and forestry waste; the weight of the acid binding agent is 1 to 3 times the weight of the lignocellulosic agricultural and forestry waste.

4. The method for preparing agricultural and forestry waste-based thermoplastic plastic according to claim 3, characterized in that: The weight of the esterification agent is 3 to 10 times the weight of the wood fiber agricultural and forestry waste.

5. The method for preparing agricultural and forestry waste-based thermoplastic plastic according to claim 3, characterized in that: The weight of the acid binding agent is 1.2 to 2 times the weight of the wood fiber agricultural and forestry waste.

6. The method for preparing agricultural and forestry waste-based thermoplastic plastic according to claim 1, characterized in that: The precipitant in step S4 is one of methanol, ethanol, n-propanol, isopropanol or acetone.

7. The method for preparing thermoplastic plastics based on agricultural and forestry wastes according to claim 1, characterized in that: Step S5 specifically includes: Washing the crude agricultural and forestry waste-based thermoplastic plastic product with the precipitant in step S4 for 3 to 5 times to obtain a pure agricultural and forestry waste-based thermoplastic plastic; or: The crude agricultural and forestry waste-based thermoplastic plastic product is treated by Soxhlet extraction for 24 to 48 hours using the precipitant in step S4 as a solvent to obtain a pure agricultural and forestry waste-based thermoplastic plastic.

8. An agricultural and forestry waste-based thermoplastic plastic, characterized by: The thermoplastic plastic based on agricultural and forestry waste is prepared using the preparation method of any one of claims 1 to 7.

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