Lightweight high-strength bio-strengthened wood and method for preparing the same

Abstract

The present application relates to a kind of lightweight high-strength biological reinforced wood and its preparation method, above-mentioned method includes the following steps: 1) after washing and drying, wood is immersed in lignin decomposition bacteria bacterial solution, constant temperature is handled for a period of time, is taken out, and biological treatment wood is obtained;2) after washing, the biological treatment wood in step 1) is placed in mould, and then is treated by hot pressing at the hot pressing temperature higher than the glass transition temperature of wood, that is, biological reinforced wood can be obtained.The present application is by first depolymerization lignin softening wood, then the hot pressing temperature higher than the glass transition temperature of wood is used to hot pressing treatment, the way that lignin is precipitated on the surface of cellulose, enhances the mechanical properties and thermal stability of material, so that the wood after treatment shows excellent lightweight high-strength characteristics.

Description

Technical Field

[0001] This invention relates to the field of lightweight and high-strength structural material preparation, and in particular to a lightweight and high-strength bio-reinforced wood and its preparation method. Background Technology

[0002] Compared to traditional materials such as steel, aluminum, alloys, or engineering plastics, lightweight high-strength materials possess advantages such as low density, high strength, and good impact resistance, making them safer and more energy-efficient when applied in fields such as construction, furniture, automobiles, and aerospace. Currently, widely used lightweight high-strength materials (such as carbon fiber and metal alloys) are often complex to process, non-renewable, and expensive. For example, the synthesis of carbon fiber requires extreme high-temperature processing, resulting in high energy consumption and the emission of large amounts of waste gas, negatively impacting the environment. With increasing environmental awareness, the development of green, sustainable, simple-to-process, and low-cost biomass-based lightweight high-strength materials has become a research hotspot in recent years.

[0003] Wood is an abundant renewable biomass resource on Earth, characterized by its low density and high strength. It has been used as a structural material for construction, furniture, and tools for thousands of years. The main component of wood is cellulose, which has a multi-layered structural feature. The stiffness of the elementary fiber crystalline region is 150 GPa, and its theoretical tensile strength is 1.6-7.7 GPa, higher than most engineering materials (including titanium alloys), while its density is only 1.5-1.6 g / cm³. 3 Therefore, there is great potential in transforming wood into lightweight and high-strength structural materials.

[0004] In recent years, the development of lightweight, high-strength wood-based materials has attracted widespread attention. Hu et al. (Nature, 554, 224–228 (2018)) used a chemical method to remove some lignin from wood, and then obtained a high-strength, impact-resistant "super wood" through a hot-pressing process. Its strength is more than 10 times that of ordinary wood, exceeding that of steel, while its weight is only one-sixth that of steel. CN112171830B discloses a method of first chemically treating wood to remove some lignin, then further chemically treating it with a solution of lithium chloride / N,N-dimethylacetamide, and finally drying it to obtain a high-strength wood-based material.

[0005] Although there are numerous research reports in the literature and patents regarding the preparation of lightweight, high-strength materials from wood, existing processes typically involve complex chemical treatments. Most of these chemicals are toxic and significantly reduce the degree of polymerization in wood, hindering large-scale material preparation and the design of irregular structures. Furthermore, these processes suffer from high energy consumption and large emissions of wastewater and exhaust gases, which to some extent limits the industrial application of wood-based lightweight, high-strength materials. Therefore, developing a simple, environmentally friendly, low-cost, and energy-efficient preparation method to obtain wood-based lightweight, high-strength materials with excellent mechanical properties and the ability to be designed in irregular shapes is a key research focus in this field. Summary of the Invention

[0006] To address the problems of high energy consumption and severe pollution in the traditional preparation process of lightweight high-strength materials, a lightweight high-strength bio-reinforced wood and its preparation method are provided to effectively solve the above-mentioned technical problems.

[0007] The specific technical solution is as follows:

[0008] A method for preparing lightweight, high-strength bio-reinforced wood includes the following steps:

[0009] 1) Immerse the cleaned and dried wood in a lignin-decomposing bacteria solution, maintain a constant temperature for a period of time, and then remove it to obtain biologically treated wood.

[0010] 2) After cleaning, the bio-treated wood from step 1) is placed into a mold and then hot-pressed at a temperature higher than the glass transition temperature of wood to obtain bio-reinforced wood.

[0011] This invention utilizes lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase (Lac) secreted by lignin-decomposing bacteria to break β-O-4 bonds, α-O-4 bonds, and biphenyl bonds (5-5′ bonds) in lignin macromolecules, thereby partially depolymerizing lignin and decomposing it into CO2 and H2O. Lignin acts as a binder for microfibers in wood, binding fiber cells together to form a tough and robust wood matrix. After partially converting lignin into oligomers, the interaction between lignin and cellulose weakens, resulting in a moderate softening of the wood structure. Subsequently, hot pressing is performed at conditions slightly above the glass transition temperature of wood to force lignin to precipitate on the hydrophobic surface of cellulose and undergo self-aggregation, thereby closing the existing pores and tightly binding the fibers, significantly improving the mechanical properties and water resistance of the material.

[0012] Although different wood species have different structures, they all contain the three major components: lignin, cellulose, and hemicellulose. Therefore, this invention can be widely used in the preparation of various types of bio-reinforced wood. Bamboo also contains abundant cellulose and lignin components (accounting for approximately 60% and 30% of the total components, respectively), so the method of this invention can also be used to produce bio-reinforced bamboo.

[0013] The beneficial effects of the above scheme are:

[0014] 1) The biological treatment method provided by this invention has minimal damage to cellulose and, compared with traditional chemical treatment methods, can protect the original oriented cellulose structure in natural wood.

[0015] 2) The biological treatment process provided by this invention is a closed-loop environmentally friendly strategy that uses a variety of enzymes secreted by fungi for treatment. It does not require the addition of chemical reagents or high-temperature conditions. The preparation process is simple, the operating cost is low, and the environmental pollution is minimal.

[0016] 3) In this invention, the mechanical properties and thermal stability of the material are enhanced by first depolymerizing lignin to soften the wood and then hot-pressing it at a temperature higher than the glass transition temperature of the wood to allow lignin to precipitate on the surface of cellulose. This results in the treated wood exhibiting excellent lightweight and high strength characteristics.

[0017] 4) As a typical bio-reinforced wood, bio-reinforced linden wood has a tensile strength as high as 539.7±21.7 MPa, which is more than 12 times higher than that of raw wood; the tensile strength of 304 stainless steel 06Cr19Ni10 (>520 MPa, GB / T 1220-2007) is similar to that of bio-reinforced linden wood, but its density is 7.93 g / cm³. 3 Much higher than the 1.35±0.5 g / cm³ of bio-reinforced linden wood. 3 Compared with commercial petrochemical-based engineering plastics such as polyoxymethylene (POM), polyvinyl chloride (PVC), polypropylene (PP), and polyurethane (PU), the bio-reinforced wood provided by this invention exhibits superior thermal stability. Attached Figure Description

[0018] Figure 1 Scanning electron microscope image of natural linden wood;

[0019] Figure 2 This is a scanning electron microscope image of bio-enhanced linden wood provided in an embodiment of the present invention;

[0020] Figure 3 This is a diagram showing the heat resistance test of the bio-reinforced wood in this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0024] This invention provides a lightweight, high-strength bio-reinforced wood, the preparation method of which includes the following steps:

[0025] 1) Immerse the cleaned and dried wood in a lignin-decomposing bacteria solution, maintain a constant temperature for a period of time, and then remove it to obtain biologically treated wood.

[0026] 2) After cleaning, the bio-treated wood from step 1) is placed into a mold and hot-pressed under conditions higher than the glass transition temperature of wood to obtain bio-reinforced wood.

[0027] In step 1) of the above preparation method, the lignin-decomposing bacteria are one of the following: brown rot fungi, white rot fungi (including but not limited to one of the genera Coriolus, Sjekandera, Phanerochaete, Pleurotus, and Poria), soft rot fungi, anaerobic Clostridium sp., Acinetobacter, Flavobacterium, Micrococcus, Pseudomonas, Amphibacillus, Xanthomonas, Mycoplana, Branhamella catarrhalis, Brochothrix, and Bacillus firmus.

[0028] The wood used in step 1) of the above preparation method is one of the following: linden, pine, oak, paulownia, maple, birch, alder, poplar, beech, mahogany, cedar, ebony, fir, poplar, walnut, willow, sandalwood, nanmu, elm, and bamboo.

[0029] In step 1) of the above preparation method, the dry weight of the lignin-decomposing bacteria solution is 0.2-0.4 g / L.

[0030] In step 1) of the above preparation method, the wood cultivation time is 1-28 days and the cultivation temperature is 28-35℃.

[0031] In step 1) of the above preparation method, the volume ratio of lignin-decomposing bacteria solution to wood is (100-130 mL): (8-15 cm⁻¹). 3 ).

[0032] The specific preparation parameters for each embodiment of this invention are shown in the table below:

[0033]

[0034]

[0035] Although different types of wood have different proportions of the three phenylpropane units that make up lignin, they do not significantly affect the glass transition temperature of lignin. In addition, all wood was hot-pressed under moist conditions after cleaning during the experiment. The glass transition temperature of lignin will be significantly reduced under moist conditions. Therefore, in this application, hot pressing was carried out under conditions that are higher than the glass transition temperature of lignin.

[0036] The properties of the wood obtained in each embodiment and comparative example of this invention are shown in the table below:

[0037] Tensile stress / MPa Bending stress / MPa Compressive stress / MPa Example 1 539.7 285.9 155.8 Example 2 345.3 310.8 — Example 3 456.7 206.6 — Example 4 478.8 283.7 — Example 5 507.7 324.0 — Example 6 483.1 327.1 — Comparative Example 1 105.2 115.6 79.7 Comparative Example 2 41.0 68.8 4.2 Comparative Example 3 62.2 78.7 — Comparative Example 4 45.4 51.6 — Comparative Example 5 73.8 90.6 — Comparative Example 6 126.8 101.9 — Comparative Example 7 88.4 87.2 —

[0038] In this invention, comparative examples 2-7 are natural linden wood, natural pine wood, natural paulownia wood, natural oak wood, natural birch wood, and natural maple wood, respectively.

[0039] like Figure 1 , Figure 2 As shown, the pores in the bio-reinforced wood provided in Example 1 of this application are closed, which is quite different from the porous structure of the original wood. This is because after the original wood is softened by biological treatment and hot-pressed, it achieves structural reconstruction. The original pore structure of the wood collapses, the cell walls are in close contact, and are wrapped and tightly connected by redistributed lignin.

[0040] like Figure 3 As shown, in this invention, the prepared bio-reinforced wood (Example 1), POM, PVC, PP, and PU were simultaneously heated to 250°C. Observations showed that, except for the bio-reinforced wood provided in this application, POM, PVC, PP, and PU all exhibited a certain degree of melting, which indicates that the bio-reinforced wood provided in this application has good heat resistance.

[0041] As shown in Table 1, in this invention, the samples of Examples 1, 2 and Comparative Example 1 were simultaneously placed in an environment with 97% relative humidity, and their volume and weight changes were measured. The results are shown in the table below:

[0042] Testing items Example 1 Comparative Example 1 Example 2 24h water absorption thickness expansion rate 1.69％ 13.59％ 1.68％ 24h water absorption rate 2.60％ 3.10％ 2.01％

[0043] As can be seen from the table above, the bio-reinforced wood provided in this application has very little variation in terms of water absorption thickness swelling rate and water absorption rate. This is because when hot-pressed above the glass transition temperature of lignin, the lignin will rearrange. The hydrophobic lignin will seal the original wood pores, making it less susceptible to water intrusion, thereby greatly improving the waterproof performance of the bio-reinforced wood.

[0044] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing a lightweight high-strength bio-strengthened wood, characterized by, The method comprises the following steps: 1) soaking the air-dried wood in a lignin-decomposing bacteria solution, treating at a constant temperature for a period of time to convert part of the lignin into oligomers, thereby softening the wood structure, and taking out the wood to obtain a biologically treated wood; 2) placing the biologically treated wood after cleaning in a mold, and hot-pressing at a temperature higher than the glass transition temperature of the wood to make the lignin in the wood precipitate on the hydrophobic surface of the cellulose and self-aggregate, thereby closing the original pores and tightly bonding the fibers, to obtain a biologically strengthened wood.

2. The production method according to claim 1, characterized by, The lignin-decomposing bacteria in step 1) are one of brown rot fungi, white rot fungi, soft rot fungi, Clostridium, Acinetobacter, Flavobacterium, Micrococcus, Pseudomonas, Bifidobacterium, Xanthomonas, Ochrobactrum, Branhamella catarrhalis, Streptomyces, and Bacillus firmus.

3. The production method according to claim 2, characterized by, The white rot fungi are one of genus Coriolus, genus Bjerkandera, genus Phanerochaete, genus Pleurotus, and genus Fomitiporia.

4. The method of claim 1, wherein, The wood in step 1) is one or more of linden wood, pine wood, oak wood, Paulownia wood, maple wood, birch wood, alder wood, beech wood, cedar wood, fir wood, poplar wood, walnut wood, willow wood, and elm wood.

5. The preparation method according to claim 1, characterized in that, The treatment time in step 1) is 1-28 days, and the treatment temperature is 28-35℃.

6. The method of claim 1, wherein, The dry weight of the lignin-decomposing bacteria solution in step 1) is 0.2-0.4g / L.

7. The preparation method according to claim 1, characterized in that, The volume ratio of the lignin-decomposing bacteria solution and the wood in Step 1) is (100-130 mL) : (8-15 cm 3 ).

8. The method of claim 1, wherein, The hot-pressing temperature in step 2) is 130-170℃.

9. A lightweight, high-strength, bio-strengthened wood, characterized by, The method is prepared according to any one of claims 1-8.

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