A method for preparing high-strength, foldable, multi-functional wood paper

Abstract

The application relates to a preparation method of high-strength, foldable and multifunctional wood paper, and relates to a wood paper preparation method. The application aims at solving the problem that the prior art cannot prepare low-environmental-impact high-strength and high-toughness wood paper. The method comprises the following steps: one, swelling treatment; two, densification treatment. The application is used for the preparation of high-strength, foldable and multifunctional wood paper.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing wood paper. BACKGROUND

[0002] Cellulose paper is one of the most important basic materials in human life, which can be used for reading, writing, painting, cleaning, handicrafts, decoration, packaging, etc. Traditionally, cellulose paper made of cellulose fibers is assembled by a complex multi-step bottom-up method. Due to the random distribution of cellulose fibers, the mechanical properties of cellulose paper are poor, which hinders its further commercial application. With the help of various physical, chemical and in-situ assisted methods, the mechanical properties of cellulose paper can be effectively improved. However, all these processes, including physical hot-pressing method to increase the hydrogen bond packing density between cellulose fibers, chemical modification method to increase the specific surface area and functional groups of cellulose fibers, high-pressure homogenization method and ultrasonic method, and the method of using external pressure, magnetic field and electric field to make cellulose arrange directional, are very energy-consuming, expensive and ineffective.

[0003] Wood is a rich and sustainable renewable natural resource on earth, with the advantages of wide source, low thermal conductivity, good mechanical properties, good biocompatibility, low density, etc. In recent years, by using the method of chemical delignification combined with densification, natural wood can be converted into super strong cellulose film material, which shows great potential in seawater desalination, ion transmission and loudspeaker. In addition, adjusting the surface functional groups and degree of polymerization of cellulose nanofiber while maintaining the wood structure is also an effective method to improve the strength of wood-based film material. However, these modifications usually involve toxic chemicals such as TEMPO and anthraquinone, which greatly increase the environmental problems of high-performance wood film manufacturing. In addition, the prepared wood film cannot simultaneously consider both strength and toughness.

[0004] In summary, the prior art cannot prepare low environmental impact high-strength high-toughness wood paper. SUMMARY

[0005] The present application solves the problem that the prior art cannot prepare low environmental impact high-strength high-toughness wood paper, and further provides a method for preparing high-strength, foldable, multifunctional wood paper.

[0006] A method for preparing high-strength, foldable, multifunctional wood paper, which is carried out according to the following steps:

[0007] I. Swelling treatment:

[0008] Under room temperature conditions, delignified wood is immersed in a swelling solution for 1 min to 3 h to obtain delignified wood treated by swelling;

[0009] The swelling solution is one or a mixture of several of dimethyl sulfoxide solution, water, anhydrous ethanol, phosphoric acid and sodium hydroxide aqueous solution;

[0010] II. Densification treatment:

[0011] The swelling treated delignified wood is air-dried at room temperature to obtain the high-strength, foldable and multifunctional wood paper.

[0012] The present application has the following advantages:

[0013] The present application adopts chemical treatment on wood to remove most of the amorphous lignin and hemicellulose in wood, and retains the crystalline-amorphous cellulose in wood components, so that the content of amorphous component in wood components is reduced, and the content of crystalline component is increased. By using this precise regulation method of crystalline and amorphous regions, the two-phase structure of wood cell wall is reasonably adjusted, and the wood can be converted into wood paper without the help of additional hot-pressing equipment under atmospheric conditions. This process avoids the high-energy-intensive preparation process of nanocellulose and the hot-pressing process, and also solves the problem of incompatible strength and toughness of traditional paper materials. Taking sodium hydroxide aqueous solution as an example, during the swelling treatment process, hydrated sodium ions rapidly penetrate the surface of cellulose microfibers and combine with hydroxyl groups, significantly promoting the swelling of cellulose microfibers and causing partial dissociation of cellulose nanofibers. During the subsequent air-drying process, water molecules act as both hydrogen bond donors and acceptors. As the water molecules evaporate, the cellulose nanofibers re-aggregate to form a more dense cellulose interwoven network structure. This method realizes the rational design of the crystalline-amorphous two-phase structure, the increase of cellulose crystallinity, and the enhancement of the lateral bonding between cellulose, which provides the wood paper with super-strong mechanical properties. At the same time, the preparation process is simple and can be scaled up. From the aspect of environmental sustainability, the wood paper is compared with commercial printing paper and plastic, showing the lowest environmental impact. At the same time, the wood paper also takes into account the light transmission, writeability, and dyeability, showing its potential applications in flexible electronics, special decoration, and other fields. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Figure 1 is a macroscopic photo of the high-strength, foldable and multifunctional wood paper prepared in Example 1;

[0015] Figure 2 Figure 2 is a cross-sectional scanning electron microscope image of the high-strength, foldable and multifunctional wood paper prepared in Example 1;

[0016] Figure 3 Figure 3 is a component analysis chart, 1-1 is natural light wood, 1-2 is air-dried delignified wood prepared in Comparative Experiment 1, and 1-3 is the high-strength, foldable and multifunctional wood paper prepared in Example 1;

[0017] Figure 4Figure 1-1 is a tensile stress-strain curve of the high-strength, foldable, multi-functional wood paper prepared in Example 1, and Figure 1-2 is a tensile stress-strain curve of the air-dried delignified wood prepared in Comparative Experiment 1.

[0018] Figure 5 Figure 1-1 is a folding number column chart of the high-strength, foldable, multi-functional wood paper prepared in Example 1, and Figure 1-2 is a folding number column chart of the commercial printing paper.

[0019] Figure 6 Figure 1-1 is a folding number column chart of the high-strength, foldable, multi-functional wood paper prepared in Example 1, and Figure 1-2 is a folding number column chart of the commercial printing paper.

[0020] Figure 7 Figure 1-1 is a folding number column chart of the high-strength, foldable, multi-functional wood paper prepared in Example 1, and Figure 1-2 is a folding number column chart of the commercial printing paper. DETAILED DESCRIPTION

[0021] Specific embodiment 1: The present embodiment is a method for preparing a high-strength, foldable, multi-functional wood paper, which is performed according to the following steps:

[0022] I. Swelling treatment:

[0023] The delignified wood is immersed in a swelling solution for 1 min to 3 h at room temperature to obtain the swelling-treated delignified wood.

[0024] The swelling solution is one or a mixture of several of dimethyl sulfoxide solution, water, anhydrous ethanol, phosphoric acid, and sodium hydroxide aqueous solution.

[0025] II. Densification treatment:

[0026] The swelling-treated delignified wood is air-dried at room temperature to obtain the high-strength, foldable, multi-functional wood paper.

[0027] The wood paper of the present embodiment can be post-treated, such as one or a combination of both of dyeing and brushing treatment; various dyes are used for impregnation dyeing to prepare wood papers of various colors; various conductive materials or anti-fake materials can be brushed to prepare various multi-functional wood papers.

[0028] The present embodiment has the following beneficial effects:

[0029] The present embodiment adopts chemical treatment of wood, removes most of the amorphous lignin and hemicellulose in the wood, retains the crystalline-amorphous cellulose in the wood components, thereby reducing the content of amorphous components and increasing the content of crystalline components in the wood components. By using this precise regulation of crystalline and amorphous regions, the two-phase structure of the wood cell wall is reasonably adjusted, and the wood can be converted into wood paper without the aid of additional hot-pressing equipment under atmospheric conditions. This process avoids the high energy-intensive preparation process of nanocellulose and the hot-pressing process, and also solves the problem of incompatible strength and toughness of traditional paper materials. Taking sodium hydroxide aqueous solution as an example, during the swelling treatment process, hydrated sodium ions rapidly penetrate the surface of cellulose microfibers and combine with hydroxyl groups, significantly promoting the swelling of cellulose microfibers and causing partial dissociation of cellulose nanofibers. During the subsequent air-drying process, water molecules act as both hydrogen bond donors and acceptors. As the water molecules evaporate, the cellulose nanofibers re-aggregate to form a more dense cellulose interwoven network structure. This method achieves a reasonable design of the crystalline-amorphous two-phase structure, increases the crystallinity of cellulose, and enhances the lateral bonding between cellulose, providing wood paper with super-strong mechanical properties. At the same time, the preparation process is simple and can be scaled up. From the perspective of environmental sustainability, wood paper is compared with commercial printing paper and plastic, showing the lowest environmental impact. At the same time, wood paper also has the advantages of light transmission, writability, and dyeability, showing its potential applications in flexible electronics and special decoration fields.

[0030] Specific embodiment two: The difference between this embodiment and specific embodiment one is that the delignified wood in step one is prepared according to the following steps:

[0031] ① Soak the wood in distilled water or anhydrous ethanol, and ultrasonically clean it for 10 min to 1 h under the condition of a power of 40 w to 100 w to obtain cleaned wood.

[0032] ② Soak the cleaned wood in a delignification solution, heat it in a water bath at a temperature of 60°C to 90°C for 3 h to 6 h, then soak it in deionized water at a temperature of 20°C to 40°C for 1 h to 3 h, and repeat the deionized water soaking 1 to 5 times to obtain delignified wood. The rest is the same as specific embodiment one.

[0033] Specific embodiment three: The difference between this embodiment and one of specific embodiments one or two is that the wood in step ① is coniferous wood, broad-leaved wood, or straw material. The rest is the same as specific embodiments one or two.

[0034] Specific embodiment four: The difference between this embodiment and one of specific embodiments one to three is that the thickness of the wood in step ① is 0.1 mm to 1.5 mm. The rest is the same as specific embodiments one to three.

[0035] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the solute in the delignification solution in step 2 is one or a combination of several of sodium sulfite, sodium chlorite, hydrogen peroxide, glacial acetic acid, sodium hydroxide, sodium sulfide, sodium bisulfite and chlorine dioxide. The others are the same as specific embodiments one to four.

[0036] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that when the swelling solution in step one is dimethyl sulfoxide solution, phosphoric acid or aqueous sodium hydroxide solution, the mass percentage of the swelling solution is 0.05% to 15%. The others are the same as specific embodiments one to five.

[0037] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that when the swelling solution in step one is aqueous sodium hydroxide solution, the mass fraction of the swelling solution is 0.05% to 1%. The others are the same as specific embodiments one to six.

[0038] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that in step one, the delignified wood is immersed in the swelling solution at room temperature for 2h to 3h to obtain the swelling treatment of delignified wood. The others are the same as specific embodiments one to seven.

[0039] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that in step one, the delignified wood is immersed in the swelling solution at room temperature for 2h to obtain the swelling treatment of delignified wood. The others are the same as specific embodiments one to eight.

[0040] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that in step two, the swelling treatment of delignified wood is air dried at room temperature for 24h to 48h. The others are the same as specific embodiments one to nine.

[0041] The following examples are used to verify the beneficial effects of the present application:

[0042] Example one:

[0043] A method for preparing a high-strength, foldable, multifunctional wood paper, which is carried out according to the following steps:

[0044] I. Swelling treatment:

[0045] The delignified wood is immersed in the swelling solution at room temperature for 2h to obtain the swelling treatment of delignified wood;

[0046] The swelling solution is aqueous sodium hydroxide solution, and the mass percentage of the swelling solution is 1%;

[0047] II. Densification treatment:

[0048] The swelled delignified wood was air-dried at room temperature (25℃) for 24 h to obtain the high-strength, foldable, multifunctional wood paper with the length, width and thickness of 10 cm x 10 cm x 0.04 cm.

[0049] The delignified wood in step one was prepared according to the following steps:

[0050] ① The wood was immersed in distilled water and ultrasonically cleaned at a power of 50 w for 1 h to obtain the cleaned wood.

[0051] ② The cleaned wood was immersed in a delignification solution and heated in a water bath at a temperature of 90℃ for 4 h, then soaked in deionized water at a temperature of 25℃ for 1 h, and repeated the deionized water soaking for 3 times to obtain the delignified wood.

[0052] The wood in step ① was balsa wood with a size of 100 mm x 100 mm x 1 mm (thickness).

[0053] The delignification solution in step ② was a mixture of 500 mL of 5% sodium chlorite solution and 5 mL of pH 4.6 acetic acid buffer.

[0054] Comparative experiment one: The difference between this comparative experiment and example one is that the swelling treatment in step one is omitted, and the delignified wood is directly subjected to step two. The delignified wood is air-dried at room temperature (25℃) for 24 h to obtain the air-dried delignified wood. The other steps are the same as example one.

[0055] Comparative experiment one lacks the regulation of the ratio of crystalline and amorphous phases in the wood, the bonding between cellulose microfibers is weak, the cellulose network structure is not dense enough, and there are structural defects, so the tensile strength and toughness are poor.

[0056] Figure 1 Macro photograph of the high-strength, foldable, multifunctional wood paper prepared in example one. As can be seen from the figure, the wood paper has a relatively thin thickness and a certain optical transparency.

[0057] Figure 2 Cross-sectional scanning electron micrograph of the high-strength, foldable, multifunctional wood paper prepared in example one. As can be seen from the figure, the wood cell wall of the wood paper is highly collapsed and has a layered structure.

[0058] Figure 3This is a composition analysis chart. 1-1 shows natural balsa wood, 1-2 shows air-dried delignified wood prepared in Comparative Experiment 1, and 1-3 shows the high-strength, foldable, multifunctional wood paper prepared in Example 1. As can be seen from the chart, the swelling treatment in Example 1 modifies the ratio of crystalline and amorphous regions, increasing the cellulose content (65.1%) and reducing the amorphous hemicellulose (27.8%) and lignin (0.35%) contents.

[0059] Tensile tests were performed on the air-dried delignified wood prepared in Comparative Experiment 1 and the high-strength, foldable, multifunctional wood paper prepared in Example 1 according to the national standard for tensile tests on metal materials GB / T 22.1-2010. Figure 4 Figure 1-1 shows the tensile stress-strain curve for the high-strength, foldable, multifunctional wood paper prepared in Example 1, and Figure 1-2 shows the air-dried delignified wood prepared in Comparative Experiment 1. As can be seen from the figure, the high-strength, foldable, multifunctional wood paper prepared in Example 1 exhibits excellent mechanical strength, with a tensile strength of up to 530 MPa, demonstrating a good reinforcement effect.

[0060] According to the national standard GB / T457-2008, the high-strength, foldable, multifunctional wood paper and commercial printing paper (Deli No. 7362) prepared in Example 1 were subjected to a folding endurance test; Figure 5 This is a bar graph showing the number of folds. 1-1 is the high-strength, foldable, multifunctional wood-based paper prepared in Example 1, and 1-2 is commercial printing paper. As shown in the figure, under different loads, the wood-based paper exhibits superior toughness compared to printing paper, leveraging the dense and strong hydrogen-bonded network of its crystalline-amorphous two-phase structure. Under a load of 2.94 N, the paper can be folded nearly 4,000 times. Under loads of 4.9 N, 9.8 N, and 14.7 N, the paper can be folded 8, 12, and 44 times more frequently than commercial printing paper, respectively.

[0061] The high-strength, foldable, multifunctional wood paper prepared in Example 1 was soaked in dyes such as malachite green, crystal violet, methyl orange, methylene blue and safranin to prepare colorful wood paper. Figure 6 As shown; Figure 6 The following are photos of the dyed and undyed high-strength, foldable, multifunctional wood paper prepared in Example 1. As can be seen from the figure, by soaking wood paper in dyes, colorful wood paper can be prepared, enriching its application areas.

[0062] Conductive silver paste circuits were brushed on the high-strength, foldable, multifunctional wood paper prepared in Example 1, and the conductive performance test was carried out. Figure 7 As shown; Figure 7The photo of the conductive performance of the high-strength, foldable, multifunctional wood paper prepared in Example 1. As can be seen from the photo, under a voltage of 1.5 V, the small bulb can be lighted up when the wood paper is connected into the circuit, and the wood paper can be applied as a flexible substrate in the field of flexible electronics, etc.

Claims

1. A method for preparing high-strength, foldable, multifunctional wood paper, characterized in that It is carried out in the following steps:

1. Swelling treatment: Under room temperature, the delignified wood is immersed in a swelling solution for 1 minute to 3 hours to obtain a swelling-treated delignified wood; The swelling solution is a sodium hydroxide aqueous solution, and the mass fraction of the swelling solution is 1%; The delignified wood is specifically prepared according to the following steps: ① Soak the wood in distilled water or anhydrous ethanol, and ultrasonically clean it for 10 minutes to 1 hour at a power of 40w to 100w to obtain the cleaned wood; ② Immersing the cleaned wood in a delignification solution, heating it in a water bath at a temperature of 60°C to 90°C for 3 to 6 hours, then soaking it in deionized water at a temperature of 20°C to 40°C for 1 to 3 hours, and repeating the deionized water soaking 1 to 5 times to obtain delignified wood; the delignification solution is a mixture of a 5% by mass sodium chlorite solution and an acetic acid buffer solution with a pH of 4.6 in a volume ratio of 100:1; 2. Densification treatment: The delignified wood treated with swelling is air-dried at room temperature to obtain high-strength, foldable, and multifunctional wood paper. The high-strength, foldable and multifunctional wood paper has a cellulose content of 65.1%, an amorphous hemicellulose content of 27.8% and a lignin content of 0.35%.

2. The method for preparing a high-strength, foldable, multifunctional wood paper according to claim 1, characterized in that The wood described in step ① is coniferous wood, broad-leaved wood or straw material.

3. The method for preparing a high-strength, foldable, multifunctional wood paper according to claim 1, characterized in that The thickness of the wood described in step ① is 0.1mm to 1.5mm.

4. The method for preparing a high-strength, foldable, multifunctional wood paper according to claim 1, characterized in that In step 1, the delignified wood is immersed in a swelling solution for 2 hours to 3 hours at room temperature to obtain swollen delignified wood.

5. The method for preparing high-strength, foldable, multifunctional wood paper according to claim 1, characterized in that In step 1, the delignified wood is immersed in the swelling solution for 2 hours at room temperature to obtain the swollen delignified wood.

6. The method for preparing high-strength, foldable, multifunctional wood paper according to claim 1, characterized in that In step 2, the delignified wood subjected to swelling treatment is air-dried at room temperature for 24 hours to 48 hours.

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