A method of producing a hemp fiber building material

Abstract

A method for preparing hemp fiber building materials is disclosed. This invention aims to address the problem of poor mechanical properties in existing hemp fiber-reinforced composite materials. The method includes: 1. Preparation of modified hemp fibers; 2. Preparation of modified hemp fiber-reinforced gypsum composite materials. This invention is used for the preparation of hemp fiber building materials.

Description

Technical Field

[0001] This invention relates to a method for preparing building materials. Background Technology

[0002] Gypsum is a building material that has been used for centuries due to its excellent sound insulation, thermal insulation, flame retardant properties, and low cost. However, its mechanical properties limit its application in modern construction. To improve the mechanical properties of gypsum board, reinforcing fibers are usually added.

[0003] In current markets and research, synthetic fibers, such as glass fiber and polypropylene fiber, are commonly used to enhance the mechanical properties of gypsum. However, with changes in global resource structure and increased environmental awareness, biomass-based materials have received increasing attention in recent years. Biomass fibers are diverse, including palm fiber, cotton stalk fiber, wood fiber, and hemp fiber, all of which play a positive role in reinforcing gypsum matrices.

[0004] Compared to other biomass fibers, hemp fiber exhibits higher average toughness and stiffness. Hemp is an ancient crop that has been used since 1941 to reinforce resin matrices in car bodies, capable of withstanding impacts up to 10 times stronger than metal sheets. Furthermore, hemp fiber is effective in reinforcing various materials such as concrete, natural rubber, particleboard, epoxy resin, polyethylene, and polypropylene. Therefore, hemp fiber is also well-suited for reinforcing gypsum composites.

[0005] Recent research by some scholars has shown that adding a small amount of hemp fiber to gypsum can change its properties from brittle to non-linear. Furthermore, they observed that hemp fiber improves the thermodynamic properties of gypsum board through a "bridging effect" (the formation of cracks during high-temperature dehydration). Simultaneously, by comparing composite gypsum boards made with hemp fiber and glass fiber, they found that hemp fiber and glass fiber have similar reinforcing effects at the same addition level. Scanning electron microscopy (SEM) revealed that hemp fiber has better adhesion to the matrix material.

[0006] To further improve the performance of fiber-reinforced gypsum-based composites, modified fibers can be used. Modified fibers exhibit superior properties due to the presence of non-contributing substances and their inherent tendency to aggregate between fibers. There are three main methods for modifying fibers: chemical, physical, and biological. Among these, chemical methods, which modify fibers at the molecular level, are the most economical and effective.

[0007] Untreated hemp fibers typically consist of cellulose, hemicellulose, lignin, pectin, wax, protein, and a small amount of dust. Treatment with sodium hydroxide effectively removes impurities such as dust, pectin, wax, and protein from the fiber surface, and also removes small amounts of hemicellulose and lignin within the fiber, exposing the fiber strands. The mechanical properties of fiber-reinforced composites are primarily related to interfacial compatibility and fiber orientation; however, hemp fiber-reinforced composites treated only with sodium hydroxide do not achieve the desired mechanical properties. Summary of the Invention

[0008] The present invention aims to address the problem of poor mechanical properties of existing hemp fiber reinforced composite materials, and thereby provides a method for preparing hemp fiber building materials.

[0009] A method for preparing hemp fiber building materials, comprising the following steps:

[0010] I. Preparation of modified hemp fiber:

[0011] Hemp fibers are mixed with sodium hydroxide solution and heated, then washed and dried to obtain alkali-treated hemp fibers. Polyethylene is mixed with water to obtain an aqueous solution of polyethylene. The alkali-treated hemp fibers are then immersed in the aqueous solution of polyethylene to obtain a solution containing modified hemp fibers.

[0012] II. Preparation of modified hemp fiber reinforced gypsum composite materials:

[0013] Hemihydrate gypsum is added to a solution containing modified hemp fiber to obtain a gypsum slurry. The gypsum slurry is then equilibrated at room temperature and finally dried, thus completing the preparation method of hemp fiber building materials.

[0014] The beneficial effects of this invention are:

[0015] The main objective of this invention is to modify hemp fibers with sodium hydroxide and polyethylene oxide (PEO) to construct a gypsum-based composite material reinforced with double-modified hemp fibers and achieve good mechanical properties, thereby fundamentally solving the problem of low mechanical properties of traditional gypsum materials.

[0016] 1. This invention modifies hemp fibers with sodium hydroxide and PEO, and then mixes them with gypsum to successfully prepare a gypsum-based composite material with excellent mechanical properties. The preparation process of this material is simple, retaining the advantages of traditional gypsum materials such as good sound insulation, heat insulation, and flame retardancy, while also greatly improving the poor mechanical properties of pure gypsum, endowing it with excellent elastic modulus and static bending strength.

[0017] 2. This invention modifies hemp fibers using sodium hydroxide and PEO, which can shorten the initial and final setting times, thereby reducing internal defects and resulting in better mechanical properties.

[0018] 3. The hemp fiber used in this invention is a widely available biomass material that meets the requirements of being green and environmentally friendly in both its preparation process and practical application.

[0019] 4. The composite material prepared by this invention is non-toxic and harmless, and can be applied to many fields such as housing construction, interior decoration, municipal planning, and medical devices, and has a wide range of uses.

[0020] Instruction manual illustrations

[0021] Figure 1 The images are SEM images. a is unmodified hemp fiber, b is sodium hydroxide modified fiber prepared in Example 1, and c is sodium hydroxide / PEO double-modified fiber prepared in step one of Example 1.

[0022] Figure 2 The images are infrared spectra. 1 is unmodified hemp fiber, 2 is sodium hydroxide modified fiber prepared in Example 1, and 3 is sodium hydroxide / PEO double-modified fiber prepared in step 1 of Example 1.

[0023] Figure 3 The images are XRD patterns. 1 is hemihydrate gypsum, 2 is the unmodified fiber-reinforced composite material prepared in Comparative Experiment 1, 3 is the sodium hydroxide-modified fiber-reinforced composite material prepared in Comparative Experiment 2, and 4 is the sodium hydroxide / PEO dual-modified fiber-reinforced composite material prepared in Example 1.

[0024] Figure 4 The images show SEM images of the fractured composite materials. a) is the sodium hydroxide-modified fiber-reinforced composite material prepared in Comparative Experiment 2, and b) is the sodium hydroxide / PEO dual-modified fiber-reinforced composite material prepared in Example 1.

[0025] Figure 5 For the analysis of the mechanical properties of materials, 1 is hemihydrate gypsum, 2 is the sodium hydroxide modified fiber reinforced composite material prepared in comparative experiment 2, and 3 is the sodium hydroxide / PEO double modified fiber reinforced composite material prepared in example 1. a is the elastic modulus and b is the static bending strength.

[0026] Figure 6 The diagram shows the hydration process of the gypsum slurry prepared in step two of Example 1, where a represents 1 min, b represents 4 min, and c represents 9 min. Detailed Implementation

[0027] Specific Implementation Method 1: This implementation method is a preparation method for hemp fiber building materials, which is carried out according to the following steps:

[0028] I. Preparation of modified hemp fiber:

[0029] Hemp fibers are mixed with sodium hydroxide solution and heated, then washed and dried to obtain alkali-treated hemp fibers. Polyethylene is mixed with water to obtain an aqueous solution of polyethylene. The alkali-treated hemp fibers are then immersed in the aqueous solution of polyethylene to obtain a solution containing modified hemp fibers.

[0030] II. Preparation of modified hemp fiber reinforced gypsum composite materials:

[0031] Hemihydrate gypsum is added to a solution containing modified hemp fiber to obtain a gypsum slurry. The gypsum slurry is then equilibrated at room temperature and finally dried, thus completing the preparation method of hemp fiber building materials.

[0032] The beneficial effects of this embodiment are:

[0033] The main objective of this invention is to modify hemp fibers with sodium hydroxide and polyethylene oxide (PEO) to construct a gypsum-based composite material reinforced with double-modified hemp fibers and achieve good mechanical properties, thereby fundamentally solving the problem of low mechanical properties of traditional gypsum materials.

[0034] 1. In this embodiment, hemp fibers are modified with sodium hydroxide and PEO, and then mixed with gypsum to successfully prepare a gypsum-based composite material with good mechanical properties. The preparation process of this material is simple, retaining the advantages of traditional gypsum materials such as good sound insulation, heat insulation, and flame retardancy, while also greatly improving the poor mechanical properties of pure gypsum, giving it excellent elastic modulus and static bending strength.

[0035] 2. In this embodiment, the hemp fiber is modified by sodium hydroxide and PEO, which can shorten the initial setting time and the final setting time, thereby reducing internal defects and resulting in better mechanical properties.

[0036] 3. The hemp fiber used in this embodiment is a widely available biomass material that meets the requirements of being green and environmentally friendly in both the preparation process and practical application.

[0037] 4. The composite material prepared in this embodiment is non-toxic and harmless, and can be applied to many fields such as housing construction, interior decoration, municipal planning, and medical devices, and has a wide range of uses.

[0038] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the length of the hemp fibers mentioned in step one is 10mm to 20mm, and the diameter is 10μm to 51μm. Everything else is the same as in Specific Implementation Method One.

[0039] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the mass percentage of the sodium hydroxide solution mentioned in step one is 15% to 25%; the mass ratio of the hemp fiber to the volume of the sodium hydroxide solution mentioned in step one is 1g:(8-15)mL. Everything else is the same as in Specific Implementation Method One or Two.

[0040] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the heating treatment described in step one is specifically carried out at a heating temperature of 70℃~80℃ for 2.5h~3.5h. Everything else is the same as in Specific Implementation Methods One to Three.

[0041] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the washing and drying in step one specifically involves washing with HCl at a concentration of 1 mol / L to 5 mol / L until the pH of the hemp fiber reaches neutral, and then drying at a temperature of 60℃ to 65℃ for 23 to 25 hours. Everything else is the same as in Specific Implementation Methods One to Four.

[0042] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the mass of polyethylene oxide in step one is 0.1% to 0.15% of the mass of water; and the mass of hemp fiber after alkali treatment in step one is 0.6% to 0.8% of the mass of water in the polyethylene oxide aqueous solution. Everything else is the same as in Specific Implementation Methods One to Five.

[0043] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: in step one, the alkali-treated hemp fibers are immersed in an aqueous solution of polyethylene oxide for 3 to 3.5 hours at room temperature. Everything else is the same as in Specific Implementation Methods One to Six.

[0044] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the water-to-plaster ratio of the gypsum slurry described in step two is 65wt% to 70wt%. Everything else is the same as in Specific Implementation Methods One to Seven.

[0045] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the equilibration at room temperature for 20 to 24 hours described in step two is carried out. Everything else is the same as in Specific Implementation Methods One to Eight.

[0046] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the drying process in step two is specifically carried out at a temperature of 60℃~65℃ for 23h~25h. Everything else is the same as in Specific Implementation Methods One to Nine.

[0047] The beneficial effects of the present invention are verified using the following embodiments:

[0048] Example 1:

[0049] A method for preparing hemp fiber building materials, comprising the following steps:

[0050] I. Preparation of modified hemp fiber:

[0051] Hemp fibers were mixed with sodium hydroxide solution and treated at 75°C for 3 hours. After washing and drying, the hemp fibers were obtained after alkali treatment. Polyethylene was mixed with water to obtain an aqueous solution of polyethylene. The alkali-treated hemp fibers were then immersed in the aqueous solution of polyethylene and treated at room temperature for 3 hours to obtain a solution containing modified hemp fibers.

[0052] II. Preparation of modified hemp fiber reinforced gypsum composite materials:

[0053] Hemihydrate gypsum was added to a solution containing modified hemp fiber and mixed at room temperature and relative humidity of 65% ± 5% to obtain a gypsum slurry. The gypsum slurry was poured into a mold with dimensions of 200mm × 50mm × 10mm (length × width × height) and then equilibrated at room temperature for 24 hours. Finally, it was dried at 60℃ for 24 hours to obtain a composite material reinforced with sodium hydroxide / PEO dual modified fibers.

[0054] The hemp fibers mentioned in step one are 10 mm in length and 10 μm to 51 μm in diameter.

[0055] The sodium hydroxide solution mentioned in step one has a mass percentage of 20%; the mass ratio of hemp fiber to sodium hydroxide solution mentioned in step one is 1g:10mL.

[0056] The washing and drying process described in step one involves washing with 1 mol / L HCl until the pH of the hemp fiber reaches neutral, and then drying at 65°C for 24 hours.

[0057] The mass of polyethylene oxide mentioned in step one is 0.15% of the mass of water; the mass of hemp fiber after alkali treatment in step one is 0.6% of the mass of water in the aqueous solution of polyethylene oxide.

[0058] The water-to-gypsum ratio of the gypsum slurry mentioned in step two is 65 wt%, that is, the mass ratio of water to hemihydrate gypsum in the gypsum slurry is 65:100.

[0059] The alkali-treated hemp fiber prepared in step one of Example 1 is sodium hydroxide modified fiber; the solution containing modified hemp fiber prepared in step one of Example 1 is dried to obtain sodium hydroxide / PEO double modified fiber.

[0060] Comparative Experiment 1: This comparative experiment differs from Example 1 in that the modification in step one is omitted; in step two, hemihydrate gypsum, unmodified hemp fiber, and water are mixed to obtain a gypsum slurry. Everything else is the same as in Example 1. Comparative Experiment 1 yields an unmodified fiber-reinforced composite material.

[0061] Comparative Experiment 2: This comparative experiment differs from Example 1 in that the modification treatment of polyethylene oxide in step one is omitted; in step two, hemihydrate gypsum, alkali-treated hemp fibers, and water are mixed to obtain a gypsum slurry. Everything else is the same as in Example 1. Comparative Experiment 2 yields a composite material reinforced with sodium hydroxide-modified fibers.

[0062] Figure 1 The images are SEM images. a) Unmodified hemp fiber; b) Sodium hydroxide-modified fiber prepared in Example 1; c) Sodium hydroxide / PEO dual-modified fiber prepared in step one of Example 1. As shown, the unmodified fiber has a relatively smooth surface and forms a bundled structure. Hemp fibers treated with NaOH exhibit grooves on the fiber surface, exposing more individual fibers from the fiber bundles, becoming finer, and even showing broken sections, indicating improved dispersion. Fibers treated with sodium hydroxide and PEO maintain good orientation, exposing more individual fibers from the fiber bundles, indicating improved dispersion.

[0063] Figure 2 The figures show infrared spectra. 1 represents unmodified hemp fiber, 2 represents sodium hydroxide-modified fiber prepared in Example 1, and 3 represents sodium hydroxide / PEO dual-modified fiber prepared in step one of Example 1. As can be seen from the figures, the unmodified fiber has a wavelength of 2921 cm⁻¹. -1 and 2854cm -1 Two characteristic absorption peaks were observed at 1727 cm⁻¹, which is due to the stretching vibrations of the methyl and methylene groups in the lipid. However, the corresponding absorption peaks decreased in the double-modified fiber, indicating the removal of wax from the fiber. Secondly, the characteristic absorption peaks of hemicellulose were located at 1727 cm⁻¹. -1 and 1028cm -1 The characteristic absorption peaks of lignin are located at 1632 cm⁻¹. -1 and 1245cm -1 Compared to unmodified fibers, the weakening of these absorption peaks in the spectra of double-modified fibers indicates a decrease in hemicellulose and lignin content. Furthermore, cellulose, hemicellulose, lignin, and pectin all contain hydroxyl functional groups, which is reflected in the 3300 cm⁻¹ spectrum. -1 In the infrared spectrum around 3300 nm, the absorption peak of the double-modified fiber is weakened, indicating a decrease in the hydroxyl content of the double-modified hemp fiber. Furthermore, compared to the infrared spectrum of fiber treated only with sodium hydroxide, the double-modified fiber shows a higher absorption peak at 3300 cm⁻¹. -1 The enhanced absorption peaks around the left and right indicate increased fiber dispersion and more exposed hydroxyl groups.

[0064] Figure 3 The XRD patterns are as follows: 1 represents the sodium hydroxide / PEO dual-modified fiber-reinforced composite material prepared in Example 1; 2 represents the sodium hydroxide modified fiber-reinforced composite material prepared in Comparative Experiment 2; 3 represents the unmodified fiber-reinforced composite material prepared in Comparative Experiment 1; and 4 represents hemihydrate gypsum. Analysis of the diffraction patterns shows that the crystal diffraction peaks of hemihydrate gypsum (line 4) are mainly located at 11.5°, 21°, 29°, 31°, and 33°. Compared to line 4, the composite material with untreated fibers (line 3) shows sharper diffraction peaks at 29° and 31°, and weaker diffraction peaks at 11.5° and 21°, indicating that the diffraction peaks of gypsum crystals on different crystal planes changed after the addition of untreated fibers. The diffraction peaks of the composite material with sodium hydroxide treated fibers (line 2) are enhanced in all directions, indicating that the addition of sodium hydroxide treated fibers significantly improves the crystallization process of the composite material and correspondingly improves its mechanical properties. However, the diffraction peaks in all ranges of the composite material treated with sodium hydroxide / PEO fibers (1) weakened, which may be due to the disordered distribution of fibers in the composite material affecting the crystal growth process and leading to a decrease in crystallinity. However, although crystal growth was hindered, the strength of the PEO groups was still improved, indicating that the addition of uniform and loose fibers can compensate for the effect of reduced crystallinity.

[0065] Figure 4 The images show SEM images of the fractured composite materials. Image a shows the sodium hydroxide-modified fiber-reinforced composite material prepared in Comparative Experiment 2, and image b shows the sodium hydroxide / PEO dual-modified fiber-reinforced composite material prepared in Example 1. As can be seen from the images, compared to the sodium hydroxide-modified fiber-reinforced composite material, the composite material prepared using the sodium hydroxide / PEO dual-modified fiber exhibits better morphology, with abundant gypsum crystals strongly adhering to the fibers. The hemp fibers, after fracture, appear soft and uniform, without obvious branching.

[0066] According to the standards "LY / T 1598-2011 Gypsum Particleboard" and "GB / T 17669.3-1999 Determination of Mechanical Properties of Building Gypsum", mechanical properties were tested under laboratory conditions of 20°±2° and relative humidity of 65%±5%. Figure 5For the analysis of the mechanical properties of the materials, 1 represents hemihydrate gypsum, 2 represents the sodium hydroxide-modified fiber-reinforced composite material prepared in Comparative Experiment 2, and 3 represents the sodium hydroxide / PEO dual-modified fiber-reinforced composite material prepared in Example 1. a represents the elastic modulus, and b represents the static bending strength. It can be clearly seen that the elastic modulus of hemihydrate gypsum is 1647 (MPa), and the static bending strength is 1.23 (MPa); the elastic modulus of the sodium hydroxide-modified fiber-reinforced composite material is 3526 (MPa), and the static bending strength is 3.29 (MPa); the elastic modulus of the sodium hydroxide / PEO dual-modified fiber-reinforced composite material is 5077 (MPa), and the static bending strength is 4.5 (MPa). The composite material made using PEO-modified fibers has the best mechanical properties, and its elastic modulus and static bending strength are significantly improved compared with pure gypsum.

[0067] According to the standards GB / T 9776-2008 Building Gypsum and GB / T 17669.4-1999 Determination of Physical Properties of Building Gypsum Paste, the initial and final setting times of gypsum paste were determined under laboratory conditions of 20°±2°C and 65%±5% relative humidity. The preparation results of gypsum paste under different conditions are shown in Table 1. The initial and final setting times reflect the rate of hydration to some extent. Prolonging the hydration process leads to more internal defects; therefore, its mechanical properties can be analyzed from this perspective. The untreated fiber and gypsum mixture prolonged the setting time because the pectin in hemp fiber is a chelating agent that can capture Ca... 2+ The ions prevent the precipitation of some CaSO4·2H2O. Treatment of hemp fibers with sodium hydroxide shortens the setting time. The composite material made from the double-modified fibers has an initial setting time of only 9 minutes and a final setting time of only 12.3 minutes, with fewer internal defects and better mechanical properties.

[0068] Table 1 Initial and final setting times of gypsum slurry under different conditions

[0069]

[0070] Figure 6The diagram shows the hydration process of the gypsum slurry prepared in step two of Example 1, with a representing 1 min, b representing 4 min, and c representing 9 min. Hydration and curing processes, and interfacial compatibility, are two crucial factors determining the performance of composite materials. Observing the hydration process of the gypsum-based composite material prepared with sodium hydroxide / PEO dual-modified fibers using SEM can explain the enhanced properties of the gypsum material. The composite material was photographed at 1 min, 4 min, and 9 min. With increasing time, the gypsum crystals gradually changed from needle-like to disordered, loosely plate-like, and from planar to three-dimensional growth—a one-dimensional to two-dimensional growth process—which is also the process of hardening and improving the mechanical properties of the gypsum composite material. Simultaneously, as time progresses, the crystals continue to grow in the planar direction and become more dense; dense two-dimensional materials generally imply better mechanical properties. In summary, these observations indicate that adding sodium hydroxide treatment and PEO dual-modified fibers to gypsum materials can lead to faster and denser crystal growth during hydration, thereby improving the mechanical properties of the composite material.

Claims

1. A method of producing a hemp fiber building material, characterized by It is carried out according to the following steps: I. Preparation of modified hemp fiber: Mix hemp fiber with sodium hydroxide solution and heat treatment, then wash and dry to obtain alkali-treated hemp fiber, mix polyethylene oxide with water to obtain polyethylene oxide aqueous solution, and immerse alkali-treated hemp fiber in polyethylene oxide aqueous solution to obtain a solution containing modified hemp fiber; The mass percentage of the sodium hydroxide solution is 15% to 25%; the mass of hemp fiber to the volume of sodium hydroxide solution is 1g to (8 to 15)mL; The heating treatment is specifically 2.5h to 3.5h at a heating temperature of 70℃ to 80℃; The mass of polyethylene oxide is 0.1% to 0.15% of the mass of water; the mass of alkali-treated hemp fiber is 0.6% to 0.8% of the mass of water in the polyethylene oxide aqueous solution. II. Preparation of modified hemp fiber reinforced gypsum composite material: Add hemihydrate gypsum to the solution containing modified hemp fiber to obtain a gypsum slurry, balance the gypsum slurry at room temperature, and finally dry to complete the preparation method of hemp fiber building material.

2. A process for the preparation of a hemp fiber building material according to claim 1, characterized in that The length of the hemp fiber in step one is 10mm to 20mm, and the diameter is 10μm to 51μm.

3. A process for the preparation of a hemp fiber building material according to claim 1, characterized in that The washing and drying in step one is specifically washing with HCl with a concentration of 1mol / L to 5mol / L until the pH of the hemp fiber reaches neutral, and then drying at a temperature of 60℃ to 65℃ for 23h to 25h.

4. A process for the preparation of a hemp fiber building material according to claim 1, characterized by In step one, the alkali-treated hemp fiber is immersed in the polyethylene oxide aqueous solution at room temperature for 3h to 3.5h.

5. A process for the preparation of a hemp fiber building material according to claim 1, characterized by The water-gypsum ratio of the gypsum slurry in step two is 65wt% to 70wt%.

6. A process for the preparation of a hemp fiber building material according to claim 1, characterized by The balance at room temperature in step two is 20h to 24h.

7. A process for the preparation of a hemp fiber building material according to claim 1, characterized by The drying in step two is specifically drying at a temperature of 60℃ to 65℃ for 23h to 25h.

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