Preparation method of high-hardness mineralized agricultural solid waste straw board

Abstract

The invention discloses a preparation method of a high-hardness mineralized agricultural solid waste straw board, and belongs to the technical field of preparation methods of solid waste straw boards, wheat straw is cleaned and crushed, surface impurities are removed, the crushed straw is placed in a 2.5 M NaOH and 0.5 M AlCl3 and Na2SO3 mixed solution, a reaction is performed for 4 h at the temperature of 95 DEG C, then reduced-pressure suction filtration is performed, washing is performed with water until filtrate is neutral, and a solid waste straw board is obtained; the method comprises the following steps of: removing lignin in the straws, exposing components such as cellulose and the like, fully exposing hydroxyl on the surface of the cellulose, and promoting swelling and dispersion of fiber bundles by using AlCl3 as a swelling agent.

Description

Technical Field

[0001] The present invention relates to a method for preparing solid waste straw board, especially a method for preparing highly hard mineralized agricultural solid waste straw board, belonging to the technical field of solid waste straw board preparation methods. Background Art

[0002] In the modern material field, as an important basic material, boards are widely used in multiple industries such as furniture manufacturing, construction, and interior decoration. Traditional wood-based boards, with wood fibers as raw materials, occupy an important position in the market due to their good physical and mechanical properties and processing performance. According to relevant data, in 2023 alone, the global market value of wood-based boards reached as high as $175.1 billion.

[0003] However, the production of traditional wood-based boards faces many severe problems.

[0004] Its production process consumes a huge amount of wood. Long-term excessive logging of trees for board manufacturing has led to a series of serious consequences such as a sharp reduction in forest area and deterioration of the ecological environment. This not only gradually restricts the wood supply but also causes great damage to the global ecological balance, which prompts researchers to actively seek alternative raw materials to achieve the sustainable development of the board industry.

[0005] As a potential raw material for boards, crop straw has gradually come into people's view. Wheat, as a widely distributed, large-growing area, and high-yielding food crop in the world, its by-product wheat straw has a very considerable output, accounting for 66.7% of the total weight of wheat. Wheat straw is rich in cellulose, hemicellulose, and lignin and has the potential to become a raw material for boards. However, there are also significant problems in using wheat straw for board manufacturing. Its physical structure composed of secondary components such as wax and pectin on the surface will reduce the compatibility and adhesion between straw particles. At the same time, the rigid epidermal tissue rich in silicon makes the self-adhesion of wheat straw hot-pressed boards poor, and it is difficult to directly be used to produce boards with excellent performance.

[0006] In the exploration of solving the problems of straw boards, rosin, a natural polymer extracted from pine trees, has received extensive attention. Rosin has the advantages of being rich, renewable, and low-cost. Its hydrophobicity gives it unique value in the application of straw boards. It can not only be used as an adhesive to improve the bonding force between straw particles but also enhance the hydrophobic performance of the boards.

[0007] In addition, mineralization technology, as a common wood modification method, is widely used in the preparation of wood-derived materials. By impregnating metal salt solutions into wood and combining with the internal components of wood, the durability, anti-corrosion properties, etc. of the materials can be significantly improved. However, in the preparation of straw-derived functional materials, the application of mineralization technology has been less studied.

[0008] At present, although there are some technical solutions related to wood modification, they all have certain limitations. Some technologies use wood as raw material and still face the problem of wood resource consumption; some preparation processes are cumbersome and complex, with high requirements for equipment, which is not conducive to large-scale industrial production; there are also some that only modify at the physical level, with poor durability of the modification effect and insufficient attention to the comprehensive improvement of the mechanical properties of the material. Therefore, a preparation method for high-hardness mineralized agricultural waste straw board is designed to solve the above problems. Summary of the Invention

[0009] The main purpose of the present invention is to provide a preparation method for high-hardness mineralized agricultural waste straw board.

[0010] The object of the present invention can be achieved by adopting the following technical solutions:

[0011] A preparation method for high-hardness mineralized agricultural waste straw board, comprising the following steps:

[0012] Step 1: Wash and crush wheat straw to remove surface impurities;

[0013] Step 2: Place the crushed straw in a mixed solution of 2.5M NaOH, 0.5M AlCl3, and Na2SO3, react at 95 °C for 4 h, then perform vacuum filtration, and rinse with water until the filtrate is neutral to partially remove lignin in the straw, expose components such as cellulose, fully expose the hydroxyl groups on the surface of cellulose, and use AlCl3 as a swelling agent to promote the swelling and dispersion of fiber bundles;

[0014] Step 3: Dissolve chitosan in an acetic acid aqueous solution with a mass fraction of 5%, stir at 80 °C for 3 h, then slowly dropwise add a NaHCO3 aqueous solution with a mass fraction of 5% to precipitate chitosan, and then perform vacuum filtration to fully expose the amino groups on the surface of chitosan molecules;

[0015] Step 4: Dissolve slash pine rosin in DMSO, where the mass fraction of slash pine rosin is 70%, and stir at 80 °C for 1 h;

[0016] Step 5: Physically mix the above-treated straw, chitosan, and dissolved rosin, and stir for 1 h to uniformly disperse the straw powder;

[0017] Step 6: Transfer the mixed material to a mold, and perform wet hot pressing at 80 °C and 15 Mpa for 4 h to obtain a mineralized straw board modified with a two-component of chitosan and rosin.

[0018] Preferably, the NaOH and Na2SO3 are replaced by other alkaline substances, and the alkaline substances include but are not limited to Ca(OH)2.

[0019] Preferably, the AlCl3 can be replaced by other acidic catalysts, and the acidic catalysts include but are not limited to HCl and sulfuric acid.

[0020] Preferably, the wheat straw can be replaced by other lignocellulosic biomass raw materials, and the lignocellulosic biomass raw materials include but are not limited to rice straw and sunflower straw.

[0021] Preferably, the slash pine rosin can be replaced by other rosins.

[0022] The beneficial technical effects of the present invention:

[0023] For the preparation method of the high-hardness mineralized agricultural waste straw board provided by the present invention, in terms of density, the density of the RC-A-WSB board reaches 1733 Kg / m 3 , which is significantly higher than 1158 Kg / m of the A-WSB board 3 , making the board more compact and heavy.

[0024] It has obvious advantages in mechanical strength indexes. The tensile strength is increased from 9.23 Mpa of the A-WSB to 13.41 Mpa, the internal bond strength is increased from 0.84 Mpa to 1.08 Mpa, the bending strength is increased from 21.14 Mpa to 28.25 Mpa, and the impact toughness even jumps from 24.31 KJ / m 2 to 45.64 KJ / m 2 , and the abrasion loss is reduced from 21.37 mg / 100r to 16.44 mg / 100r.

[0025] This makes the board perform better under external forces such as tension, bending and impact, has better wear resistance, and can better meet the actual use requirements.

[0026] From the results of the dynamic contact angle test, the hydrophobicity of the RC-A-WSB board is enhanced, and the contact angle is significantly larger than that of the A-WSB board; in the water resistance test, as the impregnation time prolongs, the water absorption rate of the RC-A-WSB board increases slowly and is always lower than that of the A-WSB board.

[0027] This indicates that the introduction of rosin greatly improves the waterproof and moisture-proof ability of the board, enables it to maintain good performance in a humid environment, and extends the service life.

[0028] The addition of chitin significantly increases the hardness of the board and successfully achieves the mineralization purpose. This enhances the wear resistance and compressive capacity of the board, broadens the application range of the board, and can be used in occasions with higher hardness requirements.

[0029] It can be characterized by infrared spectroscopy that rosin, chitin and the straw after exposing hydroxyl groups are compounded in the form of chemical bonds, generating new chemical bonds. SEM tests also prove that the filling of chitin and rosin makes the structure of the board more compact. This chemical compounding and structure optimization improve the performance of the board at the microscopic level, enhance the binding force between components, and make the overall performance of the board more stable and reliable. Description of the Drawings

[0030] Figure 1 It is a flowchart of a preferred embodiment of the preparation method of the high-hardness mineralized agricultural waste straw board according to the present invention;

[0031] Figure 2 It is an SEM characterization diagram of a preferred embodiment of the preparation method of the high-hardness mineralized agricultural waste straw board according to the present invention;

[0032] Figure 3 It is an infrared characterization diagram of a preferred embodiment of the preparation method of the high-hardness mineralized agricultural waste straw board according to the present invention;

[0033] Figure 4 It is a dynamic contact angle diagram of a preferred embodiment of the preparation method of the high-hardness mineralized agricultural waste straw board according to the present invention;

[0034] Figure 5 It is a water resistance result diagram of a preferred embodiment of the preparation method of the high-hardness mineralized agricultural waste straw board according to the present invention. Detailed Embodiments

[0035] To make the technical solutions of the present invention clearer and more definite to those skilled in the art, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0036] Experimental Raw Material Preparation

[0037] Select an appropriate amount of fresh wheat straw and remove obvious impurities such as soil, stones, etc. These wheat straws will be used as the main basic raw materials for preparing the board, and a series of treatments will be carried out on them subsequently to improve the performance.

[0038] Prepare 2.5M NaOH solution, 0.5M AlCl3 solution, Na2SO3, 5% acetic acid aqueous solution by mass fraction, 5% NaHCO3 aqueous solution by mass fraction, DMSO (dimethyl sulfoxide), slash pine rosin, and chitosan.

[0039] Among them, NaOH and Na2SO3 are used to remove lignin from the straw, AlCl3 is used as a swelling agent, the acetic acid aqueous solution is used to dissolve chitosan, NaHCO3 is used to precipitate chitosan, DMSO is used to dissolve slash pine rosin and chitosan, and slash pine rosin and chitosan are the key components for modifying the straw board.

[0040] Experimental step 1. Straw cleaning and pulverization: The selected wheat straw is rinsed with clean water to remove surface dust, debris and impurities.

[0041] After cleaning, the straw is pulverized to a suitable particle size to ensure that subsequent processing can be carried out fully. This step is to increase the specific surface area of the straw and make it more likely to react with chemical reagents.

[0042] The pulverized straw is put into a mixed solution of 2.5M NaOH, 0.5M AlCl3 and Na2SO3 and reacted at 95 °C for 4 h.

[0043] During this process, NaOH and Na2SO3 partially remove lignin in the straw, thus exposing components such as cellulose and fully exposing the hydroxyl groups (-OH) on the surface of cellulose; while AlCl3 acts as a swelling agent to further promote the swelling and dispersion of the exposed fiber bundles and enhance the exposure degree of -OH. After the reaction, the mixed solution is filtered under reduced pressure and then rinsed with water until the filtrate is neutral to remove residual chemical reagents.

[0044] Chitosan is dissolved in an acetic acid aqueous solution with a mass fraction of 5% and stirred at 80 °C for 3 h to fully dissolve chitosan. Then, an aqueous solution of NaHCO3 with a mass fraction of 5% is slowly added dropwise to the solution to precipitate chitosan. This process can fully expose the amino groups (-NH2) on the surface of chitosan molecules. Then it is filtered under reduced pressure to obtain the treated chitosan.

[0045] Wetland pine rosin is dissolved in DMSO, where the mass fraction of wetland pine rosin is 70%, and stirred at 80 °C for 1 h to fully dissolve it for standby.

[0046] The straw that has been alkali-treated and swollen is physically mixed with the treated chitosan and the dissolved wetland pine rosin and stirred for 1 h to ensure that the straw powder is evenly dispersed in the system.

[0047] Subsequently, the uniformly mixed material is transferred to a mold and subjected to wet hot pressing at 80 °C and 15 Mpa for 4 h to make each component fully react and form, and finally a high-hardness mineralized agricultural waste straw board (RC-A-WSB) modified with chitosan and rosin is obtained.

[0048] Density test: The density of the board is measured by the drainage method. Prepare a graduated cylinder filled with water and record the volume of water V1 at this time. Carefully put the prepared board into the graduated cylinder, and after the water no longer overflows, record the total volume of water and the board V2 at this time.

[0049] According to the formula ρ = m / (V2 - V1) (where m is the mass of the plate), the density of the RC-A-WSB plate is calculated to be 1733 Kg / m 3 , which is significantly higher than that of the unmodified A-WSB plate (with a density of 1158 Kg / m 3 ).

[0050] Tensile strength: Using an electronic universal testing machine, in accordance with relevant standards, a tensile test was conducted on the prepared plates.

[0051] The plates were made into standard specimens, installed on the testing machine, and stretched at a certain tensile speed until the specimens broke.

[0052] The tensile force value at break was recorded, and the tensile strength was calculated according to the formula. After testing, the tensile strength of the RC-A-WSB plate reached 13.4 Mpa, which was significantly higher than 9.23 Mpa of the A-WSB plate.

[0053] The internal bond strength of the plates was tested by the direct tension method.

[0054] Special tensile heads were pasted on the surface of the plates, and tensile force was applied through the testing machine to measure the tensile force value when internal damage occurred in the plates, and then the internal bond strength was calculated.

[0055] The results showed that the internal bond strength of the RC-A-WSB plate was 1.08 Mpa, while that of the A-WSB plate was only 0.84 Mpa.

[0056] The flexural strength of the plates was determined by the three-point bending test.

[0057] The plates were placed on the support device of the testing machine, and a concentrated load was applied in the middle of the plates, and the load was gradually increased until the plates broke.

[0058] According to the test data and relevant formulas, the flexural strength of the RC-A-WSB plate was 28.25 Mpa, which was higher than 21.14 Mpa of the A-WSB plate.

[0059] An impact test was conducted on the plates using an impact testing machine.

[0060] The plates were made into standard specimens, placed on the impact table of the impact testing machine, and the pendulum was used to impact the specimens to measure the energy absorbed by the specimens, thereby calculating the impact toughness. The impact toughness of the RC-A-WSB plate was 45.64 KJ / m 2 , which was much higher than 24.31 KJ / m of the A-WSB plate 2 .

[0061] A wear test was conducted on the plates using a wear tester.

[0062] Fix the board on the tester and let the grinding head rub on the board surface with a certain pressure and speed. After a certain number of rubbing times, measure the mass loss of the board and calculate the abrasion amount.

[0063] The abrasion amount of the RC-A-WSB board is 16.44 mg / 100 r, which is significantly lower than 21.37 mg / 100 r of the A-WSB board.

[0064] Dynamic contact angle test: Use a contact angle measuring instrument to drop a certain amount of deionized water on the board surface and measure the contact angle between the water and the board surface.

[0065] The results show that the contact angle of the RC-A-WSB board is significantly larger than that of the A-WSB board, indicating that the RC-A-WSB board has stronger hydrophobicity, which is mainly due to the addition of rosin.

[0066] Immerse the two types of boards in water respectively and take them out at different immersion times (2 days, 4 days, 6 days, 8 days, 10 days, 12 days) to measure the water absorption rate of the boards. As the immersion time prolongs, the water absorption rate of the RC-A-WSB board increases slowly and is always lower than that of the A-WSB board, indicating that its water resistance is better. This is also due to the important role played by rosin.

[0067] SEM characterization: Use a scanning electron microscope (SEM) to observe the microstructure of the A-WSB and RC-A-WSB boards.

[0068] It can be clearly seen from the SEM images that the structure of the RC-A-WSB board is more compact, and chitin and rosin are evenly filled in the pores of the straw, enhancing the internal structural stability of the board.

[0069] Through infrared spectrum analysis, detect the changes in chemical bonds in the board.

[0070] The results show that the rosin component and the chitin component have fully undergone chemical form compounding with the straw component, generating new chemical bonds, which provides a chemical basis for the improvement of the board performance.

[0071] Through this example, a high-hardness mineralized agricultural solid waste straw board modified with chitosan and rosin in a two-component manner was successfully prepared, and its performance was comprehensively tested and analyzed, verifying that this preparation method can effectively improve the comprehensive performance of the board.

[0072] Compare the performance of the reference boards A-WSB and RC-A-WSB as shown in the following table:

[0073] Sequence A-WSB RC-A-WSB <![CDATA[Density (Kg / m 3 )]]> 1158 1733 Tensile strength (Mpa) 9.23 13.41 Internal bond strength (Mpa) 0.84 1.08 Flexural strength (Mpa) 21.14 28.25 <![CDATA[Impact toughness (KJ / m 2 )]]> 24.31 45.64 Wear loss (mg / 100r) 21.37 16.44

[0074] The performance of RC-A-WSB is improved in all aspects compared to A-WSB. The wear amount of RC-A-WSB is significantly reduced.

[0075] As described above, it is only a further embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, all belong to the protection scope of the present invention.

Claims

1. A method for preparing high-hardness mineralized agricultural solid waste straw board, characterized in that: The steps include: Step 1: Wash and crush the wheat straw to remove surface impurities; Step 2: Place the crushed straw in a mixed solution of 2.5M NaOH and 0.5M AlCl3 and Na2SO3, react at 95°C for 4h, then perform vacuum filtration, and then rinse with water until the filtrate is neutral, so that the lignin in the straw is partially removed, exposing components such as cellulose, and at the same time fully exposing the hydroxyl groups on the surface of cellulose, and using AlCl3 as a swelling agent to promote the swelling and dispersion of fiber bundles; Step 3: Dissolve chitosan in a 5% acetic acid aqueous solution, stir at 80°C for 3h, then slowly drop a 5% NaHCO3 aqueous solution to precipitate chitosan, and then perform vacuum filtration to fully expose the amino groups on the surface of the chitosan molecules; Step 4: dissolving the slash pine rosin in DMSO, wherein the mass fraction of the slash pine rosin is 70%, and stirring at 80° C. for 1 h; Step 5: Physically mix the above-treated straw, chitosan and dissolved rosin, and stir for 1 hour to evenly disperse the straw powder; Step six: transfer the mixed material into a mold, and perform wet hot pressing for 4 hours at 80° C. and 15 MPa to obtain a two-component modified mineralized straw board of chitosan and rosin.

2. The method for preparing high-hardness mineralized agricultural solid waste straw board according to claim 1, characterized in that: The NaOH and Na2SO3 are replaced by other alkaline substances, including but not limited to Ca(OH)2.

3. The method for preparing high-hardness mineralized agricultural solid waste straw board according to claim 2, characterized in that: The AlCl3 can be replaced by other acidic catalysts, including but not limited to HCl and sulfuric acid.

4. The method for preparing high-hardness mineralized agricultural solid waste straw board according to claim 3, characterized in that: The wheat straw may be replaced by other lignocellulosic biomass raw materials, including but not limited to rice straw and sunflower straw.

5. The method for preparing high-hardness mineralized agricultural solid waste straw board according to claim 4, characterized in that: The elliott pine rosin may be replaced by other rosins.

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