Method for preparing high-strength flame-retardant environment-friendly composite material from silicon-rich biomass waste

Abstract

The invention belongs to the technical field of biomass composite materials, and particularly relates to a method for preparing a high-strength flame-retardant environment-friendly composite material from silicon-rich biomass waste. Silicon-rich biomass waste is used as a raw material, the content of lignin and silicon dioxide in residues is regulated and controlled through hydrothermal pretreatment modification, polyvinyl alcohol, starch and glycerin are mixed to prepare a binder solution, modified biomass powder and the binder solution are mixed in proportion, and the high-strength flame-retardant biomass composite material is obtained through hot press molding. Wherein hot pressing enables a binder in the composite material and biomass components to form hydrogen bonds to promote a cross-linking effect, and residual silicon dioxide is combined to enhance the mechanical strength and flame retardance of the composite material. The preparation process is green, environment-friendly and low in cost, overcomes the defect that a traditional process relates to harmful substances or corrosivity, and has economic and environmental feasibility. The prepared biomass composite material does not release harmful substances and has good strength, and the high-value utilization of the silicon-rich biomass waste is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass composites, and particularly relates to a method for preparing a high-strength flame-retardant and environmentally friendly composite material from silicon-rich biomass waste. Background Art

[0002] China is a large agricultural country with abundant agricultural waste and various types. According to relevant data statistics, the annual output of rice husks in the national crops is nearly 40 million tons, and the annual output of rice straw is about 300 million tons. However, these silicon-rich biomasses with a relatively high content of silicon dioxide are difficult to serve as fuels or feeds. Therefore, most of them are directly discarded or burned in the fields, not only wasting a large amount of biomass resources but also bringing serious environmental problems.

[0003] Biomass composites have been widely used in the fields of building decoration, packaging materials, tableware materials, etc. due to their advantages such as low cost, good environmental friendliness, and easy processing. Currently, aldehyde-based adhesives are usually applied to biomass composites to enhance mechanical strength, which easily releases harmful volatile substances such as formaldehyde, causing serious environmental pollution and health problems. Therefore, developing environmentally friendly biomass composites has important value and commercial prospects. Starch, as a natural renewable resource, acts as a binder in biomass composites and has good compatibility with biomass components.

[0004] Patent CN119552426A prepares a flame-retardant composite material by mixing biomass fibers (wood powder) with starch, N-methylmorpholine-N-oxide, ammonium polyphosphate, pentaerythritol, etc., but involves a relatively high content of irritating organic substances, reducing the environmental friendliness. Patent CN115368748B uses a fully biomass gelatin-starch-based binder to brush the surface of poplar veneer and then performs lamination and hot pressing, but this simple surface brushing is not conducive to sufficient bonding inside the material. Patent CN119570120A uses high-pressure steam at 240-250°C to treat straw, and then mixes various straw powders with coupling agents, cotton and linen fibers, starch-based plastics, etc. to form a biodegradable composite material with relatively high strength, but the excessively high temperature in the pretreatment process significantly increases the energy consumption, and the mixing of multiple components and the use of multiple organic coupling agents increase the process complexity and cost. Sun Qingfeng et al. (Nano Letters, 2021, 21, 397-404) mixed silica extracted by hydrofluoric acid leaching of quartzite with wood powder pretreated with alkali solution, and then carried out hot pressing to obtain a high-strength structural material. Among them, the introduction of silica can significantly improve the mechanical strength and flame retardancy (limiting oxygen index) of the material, but strong corrosive acids are involved in the process, and the introduction of foreign inorganic substances also increases the cost. Hashim et al. (Construction and Building Materials, 2020, 263, 120906) mixed oil palm tree particles soaked in sodium chloride solution with PVA solution and then hot pressed to form a fiberboard, the flexural strength of which is 40% higher than that of the raw material fiberboard, and the limiting oxygen index reaches 29.3%, but the strength of the board is still relatively low.

[0005] In summary, aiming at the disadvantage of weak mechanical strength of environmentally friendly biomass composites, developing a green and environmentally friendly process to prepare high-strength composites from silicon-rich agricultural waste and taking into account the flame retardancy performance is of great significance for improving the high-value utilization of agricultural waste and expanding the application prospects of biomass composites. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems of weak mechanical strength, poor environmental friendliness in the processing process and high process cost of current biomass composites, and provide a low-cost and green method for preparing high-strength and environmentally friendly composites from silicon-rich biomass waste.

[0007] The present invention provides a method for preparing a high-strength flame-retardant and environmentally friendly composite material from silicon-rich biomass waste, comprising the following steps:

[0008] (a) Hydrothermal treatment of biomass: Take silicon-rich biomass waste, wash, dry, and crush it to a particle size of 10-20 mesh. Load the crushed biomass into a high-pressure reactor and add distilled water according to a solid-liquid mass ratio of 1:15. After sealing the reactor, heat it to 160-200 °C under low-speed stirring for 1-2 h for hydrothermal reaction. After completion, quickly cool it to room temperature, filter out the solid residue, wash it with distilled water until neutral, vacuum dry it at 60 °C for 18-24 h, grind it, and sieve it to obtain a powder with a particle size of 100-150 mesh, and place it in a desiccator for standby.

[0009] Furthermore, the silicon dioxide content in the powder obtained by hydrothermal treatment of biomass is 5-12%, and the lignin content is 22-28%; the lignin / silicon dioxide content ratio is 2-5.

[0010] (b) Preparation of binder: Take a certain amount of polyvinyl alcohol (PVA) and add it to distilled water with a concentration of 5-10 wt%. Stir and heat it to 93 °C, and react for 2 h to form a transparent polyvinyl alcohol solution, then cool it to room temperature. Then sequentially add glycerol and starch to the polyvinyl alcohol solution. Glycerol acts as a plasticizer, heat it to 80-90 °C and continuously stir for 1 h to form a uniform binder solution, and then cool it to room temperature.

[0011] (c) Mixing: Add the biomass powder treated in step (a) to the binder solution obtained in step (b), where the mass ratio of biomass powder: (polyvinyl alcohol + starch + glycerol) is 1:0.1-0.2. Stir at room temperature for 1-2 h to mix evenly, and then dry the mixture at 40 °C until the moisture content is 10-15%.

[0012] (d) Hot pressing and forming: Add the mixture obtained in step (c) to the mold to form a billet, place it in a flat hot press, preheat it at 140-190 °C for 30 min, and then apply pressure and hot press at the same temperature for 8-20 min for forming. After cooling, demold to obtain the waste biomass composite material. Hot pressing promotes the formation of hydrogen bond interactions between the binder in the biomass and the biomass cellulose and lignin components, and combines with the residual silicon dioxide in the biomass to enhance the strength of the composite material.

[0013] In the specific implementation manner, in step (a), the silicon-rich biomass waste used is one of rice straw and rice husk.

[0014] In the specific implementation manner, in step (a), the temperature of the hydrothermal pretreatment is 160-200 °C, preferably 180 °C.

[0015] In the specific implementation manner, in step (b), the mass ratio of polyvinyl alcohol: starch is 1:0.5-1:2, preferably 1:0.5, and the mass ratio of (polyvinyl alcohol + starch): glycerol is 1:0.1-0.2.

[0016] In a specific embodiment, in step (c), the mass ratio of biomass powder: (polyvinyl alcohol + starch + glycerol) is 1:0.1 - 0.2

[0017] In a specific embodiment, in step (d), the hot pressing temperature of the composite material is preferably 170 - 180 °C.

[0018] The remarkable effects of the present invention compared with the prior art are as follows:

[0019] (1) In the method disclosed in the present invention, hydrothermal pretreatment is used for biomass, and the contents of lignin and silica in the product are regulated within a suitable range, so that lignin with a content of 22 - 28% acts as a binder. If the lignin content is too high, it indicates that the pretreatment degree is low and the surface roughness of the biomass is weak, which is not conducive to gluing and bonding. If the lignin content is too low, it is also not conducive to the bonding property. Silica with a content of 5 - 12% plays a role in enhancing as a filler. A small amount added can enhance the mechanical properties, and as an inorganic substance, it is beneficial for flame retardancy. However, too much amount will interfere with the bonding effect between lignin and cellulose. Then, an environmentally friendly binder composed of starch - polyvinyl alcohol - glycerol is applied, and finally, a high - strength environmental protection composite material is obtained by hot pressing. The hydrothermal pretreatment only uses water as the medium, and both starch and polyvinyl alcohol are biodegradable materials. The whole preparation process is environmentally friendly and pollution - free, with simple operation and low cost. Moreover, the obtained composite material has good mechanical strength and flame retardancy.

[0020] (2) The raw materials used in the method disclosed in the present invention are silicon - rich agricultural waste biomass, which has the advantages of wide sources and low cost, and can improve the value - added utilization of waste.

[0021] (3) In the method disclosed in the present invention, the silica in the composite material comes from the biomass itself. Hot pressing enables the formation of hydrogen bonds between the binder and the biomass components in the composite material to promote cross - linking, and the combined residual silica enhances the mechanical strength and flame retardancy of the composite material, avoiding the external introduction of inorganic reinforcing materials, reducing the cost, and also improving the biomass utilization rate. The density of the biomass composite material obtained by the present invention is 1.2 - 1.3 g / cm 3 , and the tensile strength is 47.2 - 58.5 MPa. The biomass composite material obtained by the present invention has the advantages of good environmental protection, high strength, and flame retardancy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the process flow chart of preparing a high - strength environmental protection composite material from silicon - rich biomass waste in the present invention.

[0023] Figure 2 is the physical picture of the composite material prepared in Example 1.

[0024] Figure 3It is the scanning electron microscope (SEM) image of the fracture surface of the composite material prepared in Example 1. Detailed implementation manners

[0025] The present invention will be described in detail below in conjunction with embodiments, so that those skilled in the art can better understand the present invention. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental materials and reagents in this article are all conventional commercially available products in this technical field.

[0026] As Figure 1 shown, it is the process flow chart for preparing the silicon-rich biomass waste composite material of the present invention. The present invention first uses silicon-rich biomass waste as raw material, crushes it and then conducts hydrothermal pretreatment to disassemble the dense structure of the biomass, regulates the lignin and silica contents therein, filters out the solid residue and then washes and dries it, and then grinds it to promote defibrillation. Then, a binder solution composed of starch, polyvinyl alcohol, and glycerol is prepared, and after being mixed evenly with the ground biomass powder, it is loaded into a mold and hot-pressed to obtain the biomass waste composite material.

[0027] In the high-strength environmental protection composite material of the present invention, the starch is cassava starch.

[0028] In the following examples, the purchased silicon-rich biomass is subjected to impurity removal, washing, and drying, then crushed and screened to 10-20 meshes, and placed in a dryer for standby.

[0029] In the following examples, the hot-pressing mold is a rectangular stainless steel mold; the hot-pressing treatment equipment is a flat hot press, both the upper and lower sides are equipped with heating plates, and are equipped with temperature and pressure sensors.

[0030] In the following examples, the method for measuring the silica content in the biomass after hydrothermal treatment: Take the biomass after hydrothermal treatment and dry it to constant weight at 105 °C, then weigh a certain mass of the sample and place it in a crucible, put it into a muffle furnace and calcine it in an air atmosphere at 600 °C for 4 h, the residue is the ash, and then use an X-ray fluorescence spectrometer (XRF) to analyze and determine the silica content therein, so as to determine the remaining silica content in the biomass after hydrothermal treatment. The lignin content is measured by using ultraviolet-visible spectrophotometer (UV-vis) after "two-step acid" hydrolysis. The flame retardancy test is expressed by the limiting oxygen index, that is, a limiting oxygen index tester is used to measure the lowest oxygen concentration required for the biomass composite to maintain combustion in a mixture of nitrogen and oxygen.

[0031] Example 1

[0032] A method for preparing a high-strength flame-retardant environmental protection composite material from silicon-rich biomass waste, comprising the following steps:

[0033] (a) Take 20 g of crushed and sieved rice husk biomass with a particle size of 10 - 20 mesh and put it into a high-pressure reactor. Add 300 g of distilled water, seal it, and heat it to 180 °C under low-speed stirring for 2 h of hydrothermal reaction. After completion, quickly cool it to room temperature, filter out the solid residue, wash it with distilled water until neutral, and vacuum dry it at 60 °C for 24 h. Then grind and sieve it to obtain a powder with a particle size of 100 - 150 mesh. The measured lignin mass content is 27.1%, the silica content is 9.6%, and the lignin / silica content ratio is 2.8. The obtained powder is placed in a desiccator for standby.

[0034] (b) According to a mass concentration of 5%, take polyvinyl alcohol (PVA) and add it to distilled water. Heat it to 93 °C while stirring for 2 h to form a transparent polyvinyl alcohol solution, and then cool it to room temperature. Then sequentially add glycerol and starch to the solution, where the mass ratio of polyvinyl alcohol to starch is 1:0.5, and the mass ratio of (polyvinyl alcohol + starch) to glycerol is 1:0.1. Heat it to 80 °C and continuously stir for 1.5 h to form a uniform binder solution, and then cool it to room temperature.

[0035] (c) According to the mass ratio of rice husk : (starch + polyvinyl alcohol + glycerol) of 1:0.2, take the rice husk powder treated in step (a) and add it to the binder solution obtained in step (b). Stir it at room temperature for 2 h to mix evenly, and then dry the mixture at 40 °C until the water content is 10%.

[0036] (d) Add the mixture obtained in step (c) to a mold to form a billet, place it in a flat hot press, preheat it at 180 °C for 30 min, and then apply pressure and hot press it at the same temperature for 10 min for molding. After cooling, demold it to obtain the rice husk biomass composite material. The tensile strength of the obtained product is 51.7 MPa, and the limiting oxygen index of the flame retardancy test result is 32.3%.

[0037] The density of the biomass composite material obtained in Example 1 is 1.28 g / cm 3 。

[0038] Figure 2 The physical picture of the prepared biomass composite material is shown as follows. Figure 3 This is the fracture surface of the composite material. It can be seen that the biomass particles on the fracture surface are fully glued together without obvious voids.

[0039] Example 2

[0040] Compared with Example 1, Example 2 is different in that: the hydrothermal reaction temperature in step (a) is 200 °C, and other operations are the same as those in Example 1.

[0041] A method for preparing a high-strength flame-retardant and environmentally friendly composite material from silicon-rich biomass waste, according to the following steps:

[0042] (a) Take 20 g of crushed and sieved rice husk biomass with a particle size of 10 - 20 mesh and put it into a high-pressure reactor. Add 300 g of distilled water. After sealing, heat it to 200 °C under low-speed stirring and carry out hydrothermal reaction for 2 h. After completion, quickly cool it to room temperature, filter out the solid residue, wash it with distilled water until neutral, and vacuum dry it at 60 °C for 24 h. Then grind and sieve it to obtain a powder with a particle size of 100 - 150 mesh. The measured lignin mass content is 25.5%, the silica content is 7.5%, and the lignin / silica content ratio is 3.4. Place the powder in a desiccator for standby.

[0043] (b) According to a mass concentration of 5%, take polyvinyl alcohol (PVA) and add it to distilled water. Stir while heating to 93 °C and react for 2 h to form a transparent polyvinyl alcohol solution, then cool it to room temperature. Then sequentially add glycerol and starch to the solution, where the mass ratio of polyvinyl alcohol to starch is 1:0.5, and the mass ratio of (polyvinyl alcohol + starch) to glycerol is 1:0.1. Heat it to 80 °C and continuously stir for 1.5 h to form a uniform binder solution, and then cool it to room temperature.

[0044] (c) According to the mass ratio of rice husk : (starch + polyvinyl alcohol + glycerol) of 1:0.2, take the rice husk powder treated in step (a) and add it to the binder solution obtained in step (b). Stir at room temperature for 2 h to mix evenly, and then dry the mixture at 40 °C until the moisture content is 10%.

[0045] (d) Add the mixture obtained in step (c) to a mold to form a billet, place it in a flat hot press, preheat it at 180 °C for 30 min, and then apply pressure and hot press at the same temperature for 10 min for solidification. After cooling, demold to obtain the rice husk biomass composite material.

[0046] The tensile strength of the obtained product is 50.5 MPa, and the limiting oxygen index of the flame retardancy test result is 31.2%.

[0047] Example 3

[0048] Compared with Example 1, the difference in Example 3 is that: the hydrothermal reaction temperature in step (a) is 160 °C, and other operations are the same as those in Example 1.

[0049] A method for preparing a high-strength flame-retardant and environmentally friendly composite material from silicon-rich biomass waste, according to the following steps:

[0050] (a) Take 20 g of crushed and sieved rice husk biomass with a particle size of 10 - 20 mesh and put it into a high-pressure reactor. Add 300 g of distilled water, seal it, and heat it to 160 °C under low-speed stirring for 2 h of hydrothermal reaction. After completion, quickly cool it to room temperature, filter out the solid residue, wash it with distilled water until neutral, and vacuum dry it at 60 °C for 24 h. Then grind and sieve it to obtain a powder with a particle size of 100 - 150 mesh. The lignin content is measured to be 28.0%, the silica content is 11.1%, and the lignin / silica content ratio is 2.5. The obtained powder is placed in a desiccator for standby.

[0051] (b) According to a mass concentration of 5%, take polyvinyl alcohol (PVA) and add it to distilled water. Heat it to 93 °C while stirring for 2 h to form a transparent polyvinyl alcohol solution, and then cool it to room temperature. Then sequentially add glycerol and starch to the solution, where the mass ratio of polyvinyl alcohol to starch is 1:0.5, and the mass ratio of (polyvinyl alcohol + starch) to glycerol is 1:0.1. Heat it to 80 °C and continuously stir for 1.5 h to form a uniform binder solution, and then cool it to room temperature.

[0052] (c) According to the mass ratio of rice husk : (starch + polyvinyl alcohol + glycerol) of 1:0.2, take the rice husk powder treated in step (a) and add it to the binder solution obtained in step (b). Stir it at room temperature for 2 h to mix evenly, and then dry the mixture at 40 °C until the moisture content is 10%.

[0053] (d) Add the mixture obtained in step (c) to a mold to form a billet, place it in a flat hot press, preheat it at 180 °C for 30 min, and then apply pressure and hot press it at the same temperature for 15 min for solidification. After cooling, demold it to obtain the wheat straw biomass composite material. The tensile strength of the obtained product is 51.2 MPa, and the limiting oxygen index of the flame retardancy test result is 31.8%.

[0054] Example 4

[0055] The difference between Example 4 and Example 1 is that: the hot pressing temperature in step (d) is 160 °C, and other operations are the same as those in Example 1.

[0056] A method for preparing a high-strength flame-retardant and environmentally friendly composite material from silicon-rich biomass waste, which is carried out according to the following steps:

[0057] (a)-(c) are the same as those in Example 1.

[0058] (d) Add the mixture obtained in step (c) to a mold to form a billet, place it in a flat hot press, preheat it at 160 °C for 30 min, and then apply pressure and hot press it at the same temperature for 15 min for solidification. After cooling, demold it to obtain the rice husk straw biomass composite material. The tensile strength of the obtained product is 49.2 MPa, and the density is 1.25 g / cm3 , the limiting oxygen index of the flame retardancy test result is 31.7%.

[0059] Example 5

[0060] Compared with Example 1, Example 5 is different in that: the hot pressing temperature in step (d) is 140 °C, and other operations are the same as those in Example 1.

[0061] A method for preparing a high-strength flame-retardant and environmentally friendly composite material from silicon-rich biomass waste, comprising the following steps:

[0062] (a)-(c) are the same as those in Example 1.

[0063] (d) Add the mixture obtained in step (c) to a mold for blanking, place it in a flat hot press, preheat at 140 °C for 30 min, then apply pressure and hot press at the same temperature for 15 min for solidification, and demold after cooling to obtain a rice husk biomass composite material. The tensile strength of the obtained product is 47.2 MPa, and the density is 1.23 g / cm 3 , and the limiting oxygen index of the flame retardancy test result is 29.4%.

[0064] Example 6

[0065] Compared with Example 1, Example 6 is different in that: the hot pressing temperature in step (d) is 220 °C, and other operations are the same as those in Example 1.

[0066] A method for preparing a high-strength flame-retardant and environmentally friendly composite material from silicon-rich biomass waste, comprising the following steps:

[0067] (a)-(c) are the same as those in Example 1.

[0068] (d) Add the mixture obtained in step (c) to a mold for blanking, place it in a flat hot press, preheat at 220 °C for 30 min, then apply pressure and hot press at the same temperature for 15 min for solidification, and demold after cooling to obtain a rice husk biomass composite material. The tensile strength of the obtained product is 50.2 MPa.

[0069] Furthermore, too high a temperature will cause the components such as lignin to gradually degrade, which will instead affect the bonding performance and damage the strength.

[0070] Example 7

[0071] Compared with Example 1, Example 7 is different in that: the raw materials are replaced with rice straws, and other operations are the same as those in Example 1.

[0072] A method for preparing a high-strength flame-retardant and environmentally friendly composite material from silicon-rich biomass waste, comprising the following steps:

[0073] (a) Take 20 g of rice straw biomass that has been crushed and screened to 10 - 20 mesh and place it in a high-pressure reactor. Add 300 g of distilled water, seal it, and heat it to 180 °C under low-speed stirring for 2 h of hydrothermal reaction. After completion, quickly cool it to room temperature, filter out the solid residue, wash it with distilled water until neutral, and vacuum dry it at 60 °C for 24 h. Then grind and screen it to obtain a powder with a particle size of 100 - 150 mesh. The measured lignin mass content is 24.8%, the silica content is 6.5%, and the lignin / silica content ratio is 3.8. The obtained powder is placed in a desiccator for standby.

[0074] (b) According to a mass concentration of 5%, take polyvinyl alcohol (PVA) and add it to distilled water. Heat it to 93 °C while stirring for 2 h to form a transparent polyvinyl alcohol solution, and then cool it to room temperature. Then sequentially add glycerol and starch to the solution, where the mass ratio of polyvinyl alcohol to starch is 1:0.5, and the mass ratio of (polyvinyl alcohol + starch) to glycerol is 1:0.1. Heat it to 80 °C and continuously stir for 1.5 h to form a uniform binder solution, and then cool it to room temperature.

[0075] (c) According to the mass ratio of rice straw : (starch + polyvinyl alcohol + glycerol) being 1:0.2, take the rice straw powder treated in step (a) and add it to the binder solution obtained in step (b). Stir it at room temperature for 2 h to mix evenly, and then dry the mixture at 40 °C until the water content is 10%.

[0076] (d) Add the mixture obtained in step (c) into a mold to form a blank, place it in a flat hot press, preheat it at 180 °C for 30 min, and then apply pressure and hot press it at the same temperature for 15 min for solidification. After cooling, demold it to obtain the rice straw biomass composite material.

[0077] The tensile strength of the obtained product is 49.7 MPa, and the limiting oxygen index of the flame retardancy test result is 28.4%.

[0078] Example 8

[0079] If the mass ratio of polyvinyl alcohol to starch in Example 1 is changed from 1:0.5 to 1:1, and the mass ratio of (polyvinyl alcohol + starch) to glycerol is 1:0.1 to prepare the binder. Other operations are the same as in Example 1. The tensile strength of the prepared composite material is 49.4 MPa.

[0080] If the mass ratio of polyvinyl alcohol to starch in Example 1 is changed from 1:0.5 to 0.5:1, and the mass ratio of (polyvinyl alcohol + starch) to glycerol is 1:0.1 to prepare the binder. Other operations are the same as in Example 1. The tensile strength of the prepared composite material is 46.9 MPa.

[0081] Example 9

[0082] For the polyvinyl alcohol:starch mass ratio in Example 9, it is 1:0.5, and for the (polyvinyl alcohol + starch):glycerol mass ratio, it is 1:0.2. Other operations are the same as in Example 1.

[0083] The tensile strength of the composite material prepared in Example 9 is 50.6 MPa. This is because glycerol acts as a plasticizer. If there is too much glycerol, the dimensional stability is poor and the strength becomes low.

[0084] Example 10

[0085] If the mass ratio of the rice husk powder after the treatment in step (c) of Example 1 to (starch + polyvinyl alcohol + glycerol) is 1:0.1. Other operations are the same as in Example 1. The tensile strength of the prepared composite material is 49.4 MPa, and the density is 1.29 g / cm 3 。

[0086] If the mass ratio of the rice husk powder after the treatment in step (c) of Example 1 to (starch + polyvinyl alcohol + glycerol) is 1:0.4. Other operations are the same as in Example 1. The tensile strength of the prepared composite material is 50.7 MPa, and the density is 1.26 g / cm 3 。

[0087] Comparative Example 1:

[0088] Compared with Example 1, the difference is that: the biomass is not pretreated, and a blank control group is set. The rice husk and the binder solution are directly used to prepare the biomass composite material. Other operations are the same as in Example 1.

[0089] The tensile strength of the unpretreated rice husk biomass composite material prepared is 26.3 MPa, and the limiting oxygen index of the flame retardancy test result is 24.6%

[0090] Comparative Example 2:

[0091] Compared with Example 1, the difference in Comparative Example 2 is that: the pretreatment method of the rice husk biomass is different, and the hydrothermal reaction is replaced by treating the rice husk with 1 M NaOH solution.

[0092] (a) Take 20 g of rice husk biomass that has been crushed and sieved to 10 - 20 mesh, add it to 1 M NaOH solution to treat the rice husk. The treatment time is 2 h. After treatment, filter out the solid residue, wash it with distilled water until neutral, and vacuum dry it at 60 °C for 24 h. Then grind and sieve it to obtain a powder with a particle size of 100 - 150 mesh. The lignin content is measured to be 23.7%, the silica content is 1.1%, and the lignin / silica content ratio is 47.4. The obtained powder is placed in a desiccator for standby.

[0093] (b)-(d) are the same as in Example 1.

[0094] The strength of the final rice husk biomass composite material obtained in Comparative Example 2 was 20.5 MPa, and the limiting oxygen index of the flame retardancy test result was 20.7%.

[0095] Comparative Example 3:

[0096] The difference between Comparative Example 3 and Example 1 is that the rice husk biomass was replaced with wood chips (using non-silica-rich biomass), and an additional silica inorganic filler was added to make the silica content the same as that in Example 1, and other operations were the same as those in Example 1.

[0097] The tensile strength of the obtained composite material was 40.2 MPa, and the limiting oxygen index of the flame retardancy test result was 24.3%.

[0098] Adding an additional silica filler not only increases the cost, but also the strength and flame retardancy are not equivalent. The silica in the silica-rich biomass is naturally occurring, evenly distributed, and has a good connection with lignin, and can be well and evenly distributed during hot pressing, improving the strength and flame retardancy. For non-silica-rich biomass with externally added silica, the performance can be partially improved, but it still cannot fully achieve the effect of silica-rich biomass.

[0099] Comparative Example 4

[0100] The difference between Comparative Example 4 and Example 1 is that the binder solution in step (b) does not contain polyvinyl alcohol and is only prepared by mixing starch and glycerol, and other operations are the same as those in Example 1.

[0101] The tensile strength of the product obtained from the rice husk biomass hydrothermally treated at 180 °C and the binder solution prepared from starch and glycerol was 43.8 MPa, and the limiting oxygen index of the flame retardancy test result was 27.3%.

[0102] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-strength flame-retardant environmental protection composite material from silicon-rich biomass waste, characterized in that, It includes the following steps: (a) Hydrothermally treating biomass: Take silicon-rich biomass, wash, dry, and crush it. Load the crushed biomass into a high-pressure reactor, add distilled water, seal the reactor, and heat it to 160 - 200 °C under low-speed stirring for hydrothermal reaction. After the reaction, filter out the solid residue, wash, dry, crush, and screen it to obtain the treated biomass powder; the silicon dioxide content in the treated biomass powder is 5 - 12%, and the lignin content is 22 - 28%; (b) Preparation of binder: Add glycerol and starch to the polyvinyl alcohol solution, heat it to 80 - 90 °C and stir continuously to form a uniform binder solution, and then cool it to room temperature; (c) Mixing: Add the treated biomass powder in step (a) to the binder solution obtained in step (b), stir and mix evenly at room temperature, and then dry the mixture to a water content of 10 - 15%; (d) Hot pressing and forming: Add the mixture obtained by drying in step (c) into a mold to form a billet, place it in a flat hot press, preheat it at 140 - 190 °C, and then apply pressure and hot press at the same temperature for forming. After cooling, demold to obtain a high-strength flame-retardant and environmentally friendly composite material.

2. The method for preparing a high-strength flame-retardant environmental protection composite material from silicon-rich biomass waste according to claim 1, characterized in that, The silicon-rich biomass waste described in step (a) is one of rice straw and rice husk.

3. The method for preparing a high-strength flame-retardant environmental protection composite material from silicon-rich biomass waste according to claim 1, characterized in that, The hydrothermal reaction temperature in step (a) is 170 - 190 °C, and the hydrothermal time is 1 - 2 h.

4. The method for preparing a high-strength flame-retardant environmental protection composite material from silicon-rich biomass waste according to claim 1, characterized in that, In step (b), the mass ratio of polyvinyl alcohol to starch is 1:0.5 - 1:2, and the mass ratio of (polyvinyl alcohol + starch) to glycerol is 1:0.1 - 1:0.

2.

5. The method for preparing a high-strength flame-retardant environmental protection composite material from silicon-rich biomass waste according to claim 1, characterized in that, In step (c), the mass ratio of biomass powder to (polyvinyl alcohol + starch + glycerol) is 1:0.1 - 0.

2.

6. The method for preparing a high-strength flame-retardant environmental protection composite material from silicon-rich biomass waste according to claim 1, wherein In step (d), the hot pressing temperature is 170 - 180 °C.

7. A high-strength flame-retardant and environmentally friendly composite material prepared from silicon-rich biomass waste by the method according to any one of claims 1 - 6.

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