Hydrophobized modified-cellulose-containing material and method for producing same

Abstract

[Problem] To provide a method for hydrophobizing cellulose that can be used as a substitute for plastic, and hydrophobized modified cellulose. [Solution] The aforementioned problem is solved by a method in which a cellulose-containing material is immersed in or brought into contact with a lignin / PVA solution or a lignin / hemicellulose solution, a complex of the lignin and the PVA or the hemicellulose is adsorbed onto a hydrophilic surface of the cellulose-containing material, and the lignin is adsorbed onto a hydrophobic surface of the cellulose-containing material. Examples of the modified-cellulose-containing material include: natural cellulose, such as paper materials; and regenerated cellulose fibers, such as viscose rayon, cupra, and Tencel (Lyocell).

Description

Hydrophobized modified cellulose-containing material and method for producing the same

[0001] The present invention relates to a hydrophobized modified cellulose-containing material and a method for producing the same, and more specifically, to a method for hydrophobizing a cellulose-containing material that can be used as a substitute for plastics, and to a hydrophobized modified cellulose-containing material.

[0002] Cellulose is the most abundant natural polymer on Earth and is attracting attention as a substitute for plastics due to its ecocompatibility, biodegradability, and low cost. On the other hand, cellulose is highly hydrophilic, and its mechanical strength decreases when wet, limiting its applications. Numerous studies have been conducted to improve the hydrophilicity of cellulose. However, many of these methods are complex or involve the use of environmentally harmful reagents, which weakens the characteristics of cellulose.

[0003] In contrast, Non-Patent Document 1 reports that, since lignin, the main component of wood, has many aromatic rings in its chemical structure, it is thought that hydrophobicity can be imparted to it, and that by adding it to paper and hot-pressing it, an improvement in wettability was confirmed. However, this report had the drawback that the adhesion between hydrophobic lignin and hydrophilic cellulose was poor, and the resulting material had low hydrophobicity, forcing the adoption of a complex experimental procedure. Non-Patent Document 2 also investigates how to improve such adhesion. In Non-Patent Document 2, it is thought that since cellulose and lignin exist in wood via hemicellulose, adhesion can be improved by using a material with many hydroxyl groups like hemicellulose, and it is reported that the adhesion between lignin and cellulose can be improved by adding PVA (polyvinyl alcohol) to cellulose and lignin.

[0004] Bo Jiang et al., “Lignin as a Wood-Inspired Binder Enabled Strong, Water Stable, and Biodegradable Paper for Plastic Replacement” Advanced Functional Materials Volume30, Issue4 January 23, 2020, 1906307Hyun-U Ko et al,, Journal of Applied Polymer Science, 2018, 135, 46655

[0005] In the above conventional method, there was a problem that the hydrophobicity of cellulose was not sufficient and its application as a substitute for plastic was not yet sufficient. In addition, there was no theoretical clarification, few experiments were conducted, and it was unclear whether cellulose was hydrophobized when PVA was used.

[0006] The present invention solves the above problems, and its object is to provide a method for hydrophobizing a cellulose-containing material that enables substitution of plastic, and a hydrophobized modified cellulose-containing material.

[0007] (1) The modified cellulose-containing material according to the present invention is a modified cellulose-containing material in which lignin and PVA or hemicellulose are adsorbed on the surface of the cellulose-containing material to be hydrophobized, and a complex of the lignin and the PVA or the hemicellulose is adsorbed on the hydrophilic surface of the cellulose-containing material, and the lignin is adsorbed on the hydrophobic surface of the cellulose-containing material.

[0008] Natural cellulose and regenerated cellulose fibers, which are cellulose-containing materials, have hydrophilic and hydrophobic surfaces. According to this invention, a composite of lignin and PVA is adsorbed on the hydrophilic surface of the cellulose-containing material, and lignin is adsorbed on the hydrophobic surface of the cellulose-containing material. Lignin is a hydrophobic molecule, and by adsorbing such lignin on the hydrophobic surface of the cellulose-containing material, and further adsorbing lignin compounded with PVA on the hydrophilic surface of the cellulose-containing material, it is possible to adsorb lignin, a hydrophobic molecule, on the hydrophilic surface of the cellulose-containing material, which was not possible with lignin alone in the past. As a result, hydrophobicization of the cellulose-containing material, which was previously insufficient, can be achieved. Furthermore, according to this invention, it has been found that even with a composite of lignin and hemicellulose in which hemicellulose is used instead of PVA, the composite of lignin and hemicellulose is adsorbed on the hydrophilic surface of the cellulose-containing material, and lignin is adsorbed on the hydrophobic surface of the cellulose-containing material. By adsorbing lignin, a hydrophobic molecule, onto the hydrophobic surface of a cellulose-containing material, and further adsorbing lignin compounded with hemicellulose onto the hydrophilic surface of the cellulose-containing material, it is possible to achieve hydrophobicity of the cellulose-containing material, which was previously insufficient, similar to the case of PVA described above.

[0009] In the modified cellulose-containing material according to the present invention, the cellulose-containing material is natural cellulose or regenerated cellulose fiber. According to this invention, it is preferable to apply not only to natural cellulose but also to regenerated cellulose fiber. Natural cellulose is a plant-derived fiber such as wood pulp or non-wood pulp (bamboo, bagasse, etc.), and in this application it may be simply abbreviated as "cellulose." Regenerated cellulose fiber is a fiber made by dissolving, reprecipitating, and reforming natural cellulose, and typical examples include rayon.

[0010] In the modified cellulose-containing material according to the present invention, the cellulose-containing material is a paper material. According to this invention, a paper material can be made hydrophobic with sufficient hydrophobic properties, and therefore it can be expected to be a substitute material for plastics.

[0011] In the modified cellulose-containing material according to the present invention, the cellulose-containing material is a regenerated cellulose fiber such as viscose rayon, cupro, or Tencel (lyocell). According to this invention, the regenerated cellulose fiber can be made hydrophobic with sufficient hydrophobic properties, and therefore it can be expected to be used as a substitute material for plastics.

[0012] In the modified cellulose-containing material according to the present invention, the hemicellulose can be xylan, glucomannan, galactomannan, arabinoxylan, or mannan. Among these, relatively low molecular weight is preferred, and examples include xylooligosaccharides, mannooligosaccharides, arabinooligosaccharides, short-chain glucomannan (partially decomposed glucomannan), etc.

[0013] In the modified cellulose-containing material according to the present invention, the OH groups of the lignin and the PVA or hemicellulose are hydrogen-bonded to the OH groups of the hydrophilic surface of the cellulose-containing material, thereby making the cellulose-containing material hydrophobic. According to this invention, the hydrophilic surface of the cellulose-containing material can be made hydrophobic by the hydrogen bonding described above.

[0014] (2) The method for producing a modified cellulose-containing material according to the present invention is characterized by immersing or contacting the cellulose-containing material with a lignin-PVA solution or a lignin-hemicellulose solution, thereby adsorbing a composite of lignin and PVA or hemicellulose onto the hydrophilic surface of the cellulose-containing material, and adsorbing lignin onto the hydrophobic surface of the cellulose-containing material.

[0015] In the method for producing a modified cellulose-containing material according to the present invention, the cellulose-containing material is natural cellulose or regenerated cellulose fiber. According to this invention, a modified cellulose-containing material with a hydrophobic hydrophilic surface can be produced not only from natural cellulose but also from regenerated cellulose fiber.

[0016] In the method for producing a modified cellulose-containing material according to the present invention, the cellulose-containing material is a paper material.

[0017] In the method for producing a modified cellulose-containing material according to the present invention, the cellulose-containing material is a regenerated cellulose fiber such as viscose rayon, cupro, or Tencel (lyocell).

[0018] In the method for producing a modified cellulose-containing material according to the present invention, the hemicellulose can be xylan, glucomannan, galactomannan, arabinoxylan, or mannan. Among these, relatively low molecular weight materials are preferred, and examples include xylooligosaccharides, mannooligosaccharides, arabinooligosaccharides, short-chain glucomannan (partially decomposed glucomannan), etc.

[0019] In the method for producing a modified cellulose-containing material according to the present invention, the OH groups of the lignin and the PVA or hemicellulose are hydrogen-bonded to the OH groups on the hydrophilic surface of the cellulose-containing material, thereby making the cellulose-containing material hydrophobic.

[0020] According to the present invention, a method for hydrophobizing modified cellulose-containing materials that can be used as a substitute for plastics (which can also be called a "method for producing modified cellulose-containing materials") and a hydrophobized modified cellulose-containing material can be provided. In particular, according to this invention, a composite of lignin and PVA or hemicellulose is adsorbed on the hydrophilic surface of the cellulose-containing material, and lignin is adsorbed on the hydrophobic surface of the cellulose-containing material. Therefore, lignin, which is a hydrophobic molecule, can be adsorbed on the hydrophilic surface of the cellulose-containing material by compounding it with PVA or hemicellulose, which was not possible with lignin alone in the past. As a result, hydrophobization of cellulose-containing materials, which was insufficient in the past, can be achieved.

[0021] These are photographs showing the results of contact angle measurements. (a) is water only, (b) is lignin only, (c) is PVA only, and (d) is lignin + PVA. These are the contact angle measurement results when the amount of PVA (x) is changed. These are the viscosity measurement results when the amount of PVA (x) is changed. This is a model diagram (a) and chemical formula (b) of a lignin dimer. This is a model diagram of PVA. This is a snapshot of the lignin concentration model system. (a) is the case of 0 ns, and (b) is the case of 10 ns. This is a graph showing the concentration dependence of the number of hydrogen bonds in a lignin-PVA aqueous solution. This is a PyMOL visualization diagram (a) and a partially enlarged view (b) of the hydrogen bonds between lignin and PVA. This is a model diagram in which PVA30 is placed on the hydrophobic and hydrophilic surfaces of cellulose, and lignin is placed randomly. This is an 18-chain model of cellulose. This is a simulation cell for cellulose-lignin-PVA molecules in water, with snapshots of the cellulose cross-section (left image) and side view (right image) at 0, 5, and 10 ns. This shows the relationship between the simulation time and the number of hydrogen bonds. This shows the adsorption behavior to the cellulose surface. This is hydrophobized modified cellulose. These are photographs showing the results of contact angle measurements. (a) is the result of test example 1-5, (b) is the result of test example 1-6, (c) is the result of test example 1-9, and (d) is the result of test example 1-10. These are photographs showing the results of contact angle measurements. (a) is the result of test example 2-1, (b) is the result of test example 2-2, and (c) is the result of test example 2-3.

[0022] The modified cellulose-containing material and its manufacturing method according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, as long as it is within the scope of its gist.

[0023] Cellulose consists of both hydrophilic and hydrophobic parts, and conventionally, hydrophobization has been difficult. When hydrophobic substances are brought close to cellulose in an attempt to hydrophobize it, these hydrophobic substances adsorb to the hydrophobic parts, leaving the hydrophilic parts intact and preventing hydrophobization. The inventors have been conducting research to solve these problems and have found that cellulose-containing materials, such as natural cellulose (paper, etc.) and regenerated cellulose fibers (rayon, etc.), can be hydrophobized by treating them in a solution of PVA or hemicellulose and lignin, followed by heat treatment, as shown in the experimental results below. Molecular dynamics analysis of these hydrophobized modified cellulose-containing materials revealed that PVA or hemicellulose and lignin can be compounded even in water, and that the composite of PVA or hemicellulose and lignin approaches the hydrophilic parts of the cellulose-containing material, causing hydrogen bonds to form between the OH groups of lignin and cellulose.

[0024] [Modified Cellulose-Containing Material and Method for Producing the Same (Hydrophobicization Method)] In other words, the modified cellulose-containing material according to the present invention is a modified cellulose-containing material that has been hydrophobized by adsorption of lignin and PVA or hemicellulose onto its surface, characterized in that a composite of lignin and PVA or hemicellulose is adsorbed on the hydrophilic surface of the cellulose-containing material, and lignin is adsorbed on the hydrophobic surface of the cellulose-containing material. Furthermore, the method for producing the modified cellulose-containing material according to the present invention (which can also be called a hydrophobicization method) is characterized in that the cellulose-containing material is immersed in or brought into contact with a lignin-PVA solution or a lignin-hemicellulose solution, thereby adsorbing a composite of lignin and PVA or hemicellulose onto the hydrophilic surface of the cellulose-containing material, and adsorbing lignin onto the hydrophobic surface of the cellulose-containing material.

[0025] Natural cellulose and regenerated cellulose fibers, which are cellulose-containing materials, have hydrophilic and hydrophobic surfaces. According to this invention, a composite of lignin and PVA is adsorbed on the hydrophilic surface of the cellulose-containing material, and lignin is adsorbed on the hydrophobic surface of the cellulose-containing material. Lignin is a hydrophobic molecule, and by adsorbing such lignin on the hydrophobic surface of the cellulose-containing material, and further adsorbing lignin compounded with PVA on the hydrophilic surface of the cellulose-containing material, it is possible to adsorb lignin, a hydrophobic molecule, on the hydrophilic surface of the cellulose-containing material, which was not possible with lignin alone in the past. As a result, hydrophobicization of the cellulose-containing material, which was previously insufficient, can be achieved. Furthermore, according to this invention, it has been found that even with a composite of lignin and hemicellulose in which hemicellulose is used instead of PVA, the composite of lignin and hemicellulose is adsorbed on the hydrophilic surface of the cellulose-containing material, and lignin is adsorbed on the hydrophobic surface of the cellulose-containing material. By adsorbing lignin, a hydrophobic molecule, onto the hydrophobic surface of a cellulose-containing material, and further adsorbing lignin compounded with hemicellulose onto the hydrophilic surface of the cellulose-containing material, it is possible to achieve hydrophobicity of the cellulose-containing material, which was previously insufficient, similar to the case of PVA described above. Adsorption can be confirmed, for example, by analyzing the peak change of FTIR. In this application, "hydrophobicity" refers to a state in which the contact angle measurement shows 90° or more. In cellulose, the hydrophilic surface F1 corresponds to the (1-10) plane of the cellulose Iβ crystal, and the hydrophobic surface F2 corresponds to the (110) plane.

[0026] (Cellulose-containing material) The cellulose-containing material may be either natural cellulose or regenerated cellulose fiber, and is not limited to natural cellulose; it is also preferably applicable to regenerated cellulose fiber. Natural cellulose is a plant-derived fiber from wood pulp or non-wood pulp (bamboo, bagasse, etc.) (in this application, it may be simply abbreviated as "cellulose"), and paper materials are also included in this natural cellulose. Regenerated cellulose fiber is a fiber made by dissolving, reprecipitating, and reforming natural cellulose, and typical examples include rayon, for example, viscose rayon, cupro, Tencel (lyocell) and other regenerated cellulose fibers.

[0027] (PVA or Hemicellulose) PVA (polyvinyl alcohol) is preferred because it can readily form a complexed solution with lignin. Alternatively, hemicellulose can also readily form a complexed solution with lignin. Examples of hemicellulose include xylan, glucomannan, galactomannan, arabinoxylan, or mannan. Among these, relatively low molecular weight varieties are preferred, such as xylooligosaccharides, mannooligosaccharides, arabinooligosaccharides, and short-chain glucomannan (partially decomposed glucomannan). Low molecular weight hemicellulose has high solubility and readily undergoes uniform complexation with lignin.

[0028] In a composite solution of PVA or hemicellulose and lignin, hydrogen bonds are formed between the OH groups of lignin and PVA or hemicellulose and the OH groups of the hydrophilic surface of the cellulose-containing material, making the cellulose-containing material hydrophobic. Such hydrogen bonding can make the hydrophilic surface of the cellulose-containing material hydrophobic. The composite of PVA or hemicellulose and lignin is formed by hydrogen bonds and hydrophobic interactions between lignin and PVA or between lignin and hemicellulose. Hemicellulose also contains many OH groups (hydroxyl groups), similar to PVA. In fact, it often contains OH groups at a higher density than PVA, so it has a higher ability to form hydrogen bonds with lignin and cellulose. The reason why hemicellulose works similarly to PVA is that hemicellulose has many OH groups and can form hydrogen bond composites with lignin with the same or even greater bonding strength as PVA, and as a result it is easily adsorbed onto the surface of cellulose. Furthermore, hemicellulose, particularly xylan, has a linear structure that easily aligns parallel to the cellulose chains (parallel arrangement), resulting in high adsorption capacity. Although hydrophilic, it can form hydrophobic blocks on its surface by intertwining with lignin. This can be attributed to the exact same mechanism as that of the PVA-lignin complex.

[0029] [Example 1 of Manufacturing Modified Cellulose-Containing Material] First, an example of manufacturing a hydrophobized modified cellulose-containing material will be described. The hydrophobized modified cellulose-containing material was prepared as follows. In this manufacturing example 1, "filter paper," which is natural cellulose, is used as the cellulose-containing material, so it will simply be called "filter paper" or "cellulose."

[0030] (Preparation of each sample) Lignin and PVA were used as solutes, and deionized water or distilled water (hereinafter abbreviated as "water") was used as the solvent. Lignin-PVA aqueous solution was prepared by stirring at room temperature (at room temperature of about 25°C for 15 minutes) and stirring with heating (at 95°C for 1 hour until the PVA is sufficiently dissolved) as appropriate. The weight ratio at this time was water:PVA:lignin = 100:0 to 7:0 to 1. Filter paper was immersed in the prepared lignin-PVA aqueous solution as a cellulose material (at 25°C for 1 minute), then the removed filter paper was dehydrated, dried (at 180°C for 2 hours), washed (at 95°C for 1 hour), and dried (at 105°C for 1 hour) to obtain the sample of the present invention. For comparison, we prepared filter paper soaked in water, filter paper soaked in a lignin aqueous solution containing only lignin, and filter paper soaked in a PVA aqueous solution containing only PVA.

[0031] The temperatures and times for room temperature stirring, heated stirring, immersion, heating, washing, and drying described above are merely examples, and appropriate temperatures and times should be adjusted as needed. Washing was performed to remove excess PVA, as excessive PVA adhesion inhibited hydrophobicity. In this production example 1, ADVANTEC filter paper was used, fully saponified polyvinyl alcohol with a degree of polymerization of 1700 (manufactured by Kuraray Co., Ltd.) was used as PVA, and high-purity partially desulfonated sodium lignin sulfonate (amphiphilic lignin, manufactured by Nippon Paper Industries Co., Ltd.) was used as lignin. Drying was performed using a dry oven.

[0032] (Contact Angle Measurement) Contact angle measurements were performed on each of the obtained samples (inventive sample, comparative sample), and the results are shown in Figure 1. The contact angle was measured using a contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd., device name: DropMaster FAMAS) by dropping a 5 μL droplet onto the sample and measuring the contact angle after 1 minute (the same procedure was followed for the measurements in the manufacturing example below). The contact angle value was measured 1 minute after dropping the water droplet onto the sample. For the inventive sample used in the contact angle measurement in Figure 1, a water:PVA:lignin = 100:7:1 mixture was used. For the lignin aqueous solution containing only lignin, a water:lignin = 100:1 mixture was used. For the PVA aqueous solution containing only PVA, a water:PVA = 100:7 mixture was used. As shown in Figure 1, when water was dropped onto each of the obtained samples, the comparative samples in Figures 1(a), 1(b), and 1(c) absorbed the water droplets instantly upon contact, making it impossible to measure the contact angle. On the other hand, the sample of the present invention shown in Figure 1(d) retained the water droplets, and the contact angle was 90° or more (92.8°), indicating sufficient hydrophobicity. From these results, it was found that the filter paper can be made hydrophobic only when both lignin and PVA are used.

[0033] (PVA composition and contact angle) Next, the relationship between PVA composition and contact angle was measured, and the results are shown in Figure 2. As shown in Figure 2, when the weight ratio (x) of PVA in the lignin-PVA aqueous solution was 1 to 3, water droplets were immediately absorbed and hydrophobicity did not occur. On the other hand, when the weight ratio (x) of PVA in the lignin-PVA aqueous solution was 4 to 7, the contact angle was 90° or higher (99.9°, 112.2°, 110.9°, and 92.8°, respectively). Based on the molecular dynamics simulation described later, these results indicate that hydrophobicity occurs when the concentration of PVA is higher because hydrogen bonds with lignin are more easily formed.

[0034] (PVA Composition and Viscosity) Next, the relationship between PVA composition and viscosity was measured, and the results are shown in Figure 3. Viscosity was measured using a viscometer, and the viscosity of the coating solutions prepared with each composition at 25°C was measured. As shown in Figure 3, when the weight ratio (x) of PVA in the lignin-PVA aqueous solution was 1 to 3, the viscosity increased steadily regardless of the presence or absence of lignin. On the other hand, when the weight ratio (x) of PVA in the lignin-PVA aqueous solution was 4 to 7, the viscosity of the solution with lignin increased as the PVA concentration increased. From these results, it can be said that the viscosity increases as the concentration of PVA increases because it forms a complex with lignin.

[0035] [Molecular Dynamics Simulation] Next, in order to elucidate the hydrophobicity mechanism of the modified cellulose described above, we investigated the behavior of PVA, lignin, and cellulose in aqueous solution using molecular dynamics simulations, and revealed the mechanism by which cellulose becomes hydrophobic.

[0036] (Simulation of Lignin and PVA in Water) Figure 4 shows a model diagram (a) and chemical formula (b) of a lignin dimer, and Figure 5 shows a model diagram of PVA. Here, aqueous solutions with lignin concentrations of 1 to 10 wt% and PVA concentrations of 5.5 wt% were modeled and simulated under constant temperature and pressure conditions (300 K, 1 atm) for 10 ns. In this application, wt% is synonymous with mass%.

[0037] Figure 6 is a snapshot of a model system with a lignin concentration of 3.23 wt% (0.08 mol / L). Figure (a) on the left shows the start of a 10 ns constant temperature and pressure (300 K, 1 atm) simulation (0 nanoseconds), and Figure (b) on the right shows the end of the simulation (10 nanoseconds). Water molecules are omitted. Figure 6 shows that although both lignin and PVA are dispersed in water, they form a complex in water. In the snapshot after 10 ns of simulation time, a complex was observed in which lignin had interwoven between PVA chains, forming a complex.

[0038] Figure 7 is a graph showing the concentration dependence of the number of hydrogen bonds in a lignin-PVA aqueous solution. This graph shows the results when the PVA molar concentration was kept constant (0.04 mol / L) and the lignin molar concentration was varied in the range of 0.04 to 0.19 mol / L. This figure shows the average number of intermolecular hydrogen bonds at each lignin concentration during the simulation time (5-10 ns). From the results in Figure 7, it can be seen that hydrogen bonds are formed between lignin and PVA at all concentrations. Furthermore, the number of hydrogen bonds between lignin and PVA remained almost constant from a certain concentration (0.12 mol / L). This is likely because the lignin molecules aggregate and adsorb to the PVA.

[0039] Figure 8 shows a PyMOL visualization of hydrogen bonding between lignin and PVA (a) and a magnified view of a portion of it (b), illustrating the hydrogen bond (L5P5) between the lignin molecule coordinated along the PVA main chain and PVA. The PyMOL visualization reveals that hydrogen bonding occurs between the OH group of lignin, which has less steric hindrance, and the OH group of PVA. This result indicates that PVA and lignin form a complex by forming hydrogen bonds in water.

[0040] Figure 9 is a model diagram in which PVA30 is placed on the hydrophobic surface (represented as "F2"; the same applies hereafter) and hydrophilic surface (represented as "F1"; the same applies hereafter) of cellulose, and lignin is randomly placed. Figure 10 is an 18-chain model of cellulose 234432. Figure 11 is a simulation cell of cellulose-lignin-PVA molecules in water, and is a snapshot from the cross section (left image) and side view (right image) of cellulose at 0ns, 5ns, and 10ns. Figure 12 shows the relationship between the number of hydrogen bonds between cellulose-lignin-PVA and the progression of simulation time. Figure 12 is an output of the time evolution of hydrogen bonds formed on cellulose, lignin, and PVA in a C(cellulose)-L(lignin)-P(PVA) simulation cell using the GROMACS hbond command to elucidate the cellulose-lignin-PVA interaction from the perspective of hydrogen bonding. In Figure 12, (a) shows the number of hydrogen bonds between cellulose and PVA, (b) shows the number of hydrogen bonds between cellulose and lignin, and (c) shows the number of hydrogen bonds between lignin and PVA. Comparing the average values ​​of the number of hydrogen bonds between each molecule during simulation times of 5 ns to 10 ns, where the potential energy of the system is relatively stable, the number of hydrogen bonds between cellulose and PVA was lower in the presence of lignin. This is thought to be because the hydrogen bonds formed between lignin and PVA correspond to the decrease in hydrogen bonds between cellulose and PVA. The simulation conditions and molecular model selection are generally used methods and qualitatively agree with the experimental results.

[0041] Figures 9 to 12 show that at the lignin adsorption sites (in the 10 ns constant temperature and pressure simulation), PVA is adsorbed onto both the hydrophobic and hydrophilic surfaces of cellulose. Furthermore, hydrogen bonds are observed between the cellulose surface, lignin, and PVA. These results indicate that the cellulose surface and lignin coordinate to the hydrophobic surface of cellulose. Since lignin alone cannot cover the hydrophilic surface of cellulose, hydrophobicization is not possible. PVA exhibited behavior toward the hydrophilic surface of cellulose. Lignin and PVA formed a complex, and this complex adsorbed to cover the hydrophilic surface of cellulose. It is thought that hydrogen bonds formed between the OH groups of lignin and PVA and the OH groups of the hydrophilic surface of cellulose, thereby hydrophobicizing the cellulose.

[0042] Figure 13 shows the adsorption behavior on the cellulose surface. The top panel (a) shows the cellulose surface, the middle panel (b) shows the case when PVA is adsorbed onto the cellulose surface, and the bottom panel (c) shows the case when a composite of PVA and lignin is adsorbed onto the cellulose surface. It can be seen that when lignin is adsorbed onto the cellulose surface and exposed to the surface, it becomes hydrophobic.

[0043] Figure 14 shows hydrophobized modified cellulose. From the above results, it is thought that hydrophobicity occurs when hydrophobic lignin covers the cellulose surface by the following mechanisms: (1) PVA is adsorbed onto the hydrophilic surface F1 of the cellulose, forming a hydrophobic surface F3; (2) Lignin is adsorbed onto the PVA adsorption surface (hydrophobic surface) F3 in the form of a complex with PVA; and (3) Lignin is adsorbed alone onto the hydrophobic surface F2 of the cellulose. The reason why lignin alone does not cause hydrophobicity is that lignin is adsorbed onto the hydrophobic surface F2 of the cellulose but not onto the hydrophilic surface F1, so it does not cause hydrophobicity. With PVA alone, it is adsorbed only onto the hydrophilic surface F1 of the cellulose surface, so hydrophobicity occurs only when the hydrophobic portion of the adsorbed PVA is exposed to the surface. Therefore, the hydrophobicity is not sufficient. As in the present invention, when both PVA and lignin are present, PVA is first adsorbed onto the hydrophilic surface F1 of the cellulose surface, and sufficient hydrophobicity can be achieved by the action of the hydrophobic portion of the lignin adsorbed onto the hydrophilic surface F1.

[0044] As described above, it has been found that filter paper (natural cellulose material) can be hydrophobized by using both lignin and PVA. Also, it has been found that a higher concentration of PVA is more advantageous for hydrophobization. Molecular dynamics simulations have shown that the OH groups of lignin and PVA hydrogen bond with the OH groups on the hydrophilic surface of cellulose, hydrophobizing the cellulose. The increase in the viscosity of the PVA-lignin solution with an increase in the concentration of PVA is considered to be due to the formation of a complex between lignin and PVA as the concentration of PVA increases. According to the present invention, since cellulose can be hydrophobized by lignin, which is a component of wood, it has been clarified that the weakness of cellulose to water can be improved and that there is a special effect that it can be applied as a plastic substitute.

[0045] Such modified cellulose materials can be applied as hydrophobized paper containers as an alternative to plastic containers by hydrophobizing the cellulose material, paper. Moreover, the contained components (PVA, lignin) are also unproblematic, and co-composting of the waste is possible. Also, it becomes possible to hydrophobize rayon fibers, which are cellulose materials, and the hydrophilicity of rayon fibers can be controlled and applied. Also, it becomes possible to hydrophobize pulp fibers, and they can be applied as an alternative to hydrophobic fibers.

[0046] In addition, as described above, molecular dynamics simulations modeling cellulose-PVA in water were performed, and it was shown that PVA adsorbs on the cellulose hydrophilic surface F1 and forms a new hydrophobic surface F3. Since such PVA has properties similar to hemicellulose, hemicellulose was used instead of PVA in the following production examples. Hemicellulose (especially xylan, etc.) shows complexation similar to that of PVA in terms of structure, from the viewpoints of multi-point hydrogen bonding and hydrophilic linear chains. That is, hemicellulose has a large number of OH groups like PVA, is a linear polymer, and can form a complex by hydrogen bonding with lignin, so it can adsorb on the hydrophilic surface like PVA.

[0047] [Production Example 2 of Modified Cellulose-Containing Material] Next, a production example of a hydrophobized modified cellulose-containing material when hemicellulose is used instead of PVA will be described. When hemicellulose is used, the hydrophobized modified cellulose-containing material was produced as follows.

[0048] (Preparation of Each Sample) The solutes were lignin and hemicellulose, and the solvent was distilled water (hereinafter abbreviated as "water"). 100 g of water and 0 to 20 g of hemicellulose were stirred at room temperature (stirred at about 25 °C for 15 minutes) and heated and stirred (stirred at 95 °C for 1 hour until hemicellulose was sufficiently dissolved). Then, 0 to 10 g of lignin was added and heated and stirred (stirred at 95 °C for 1 hour) to prepare an aqueous lignin-hemicellulose solution. At this time, the weight ratio was water: hemicellulose: lignin = 100: 0 to 20: 0 to 10 as shown in Table 1. The prepared aqueous lignin-hemicellulose solution was immersed in filter paper as a cellulose material (immersed at 95 °C for 10 minutes), and then the taken-out filter paper was dehydrated, dried (dried at 180 °C for 2 hours), washed (washed at room temperature of about 25 °C to 95 °C for 1 hour), and dried (dried at 105 °C for 1 hour) to obtain Test Examples 1-1 to Test Examples 1-10. Note that Test Example 1-1 is a sample in which filter paper was immersed in an aqueous solution containing only hemicellulose, and Test Example 1-2 is a sample in which filter paper was immersed in an aqueous solution containing only lignin.

[0049] Note that, similar to Production Example 1, the temperatures and times of the above-mentioned room temperature stirring, heating and stirring, immersion, dehydration, drying, washing, and drying are each an example, and appropriate temperatures and times are adjusted and implemented as appropriate. High-temperature drying such as at 180 °C for 2 hours is for promoting the fixing of the composite, and the temperature can be appropriately changed according to the material. For example, a range of 120 to 200 °C can be used. Washing is preferably performed to remove excessively attached PVA and the like. Also, in this Production Example 2, filter paper made by ADVANTEC was used, lignin was high-purity partially desulfonated sodium lignin sulfonate (lignin having amphiphilicity, manufactured by Nippon Paper Industries Co., Ltd.), and hemicellulose was xylan. Drying was performed using a drying oven.

[0050]

[0051] Figure 15 shows the results of contact angle measurements performed in the same manner as in Manufacturing Example 1 for Test Examples 1-5(a), 1-6(b), 1-9(c), and 1-10(d). As can be seen from the contact angle results in Table 1, when the mixing ratio of hemicellulose and lignin in the hemicellulose and lignin composite was changed as shown in Table 1, the contact angle was in the range of 106° to 123° in both cases where the hemicellulose was in the range of 5 to 20 parts by weight and the lignin was in the range of 5 to 10 parts by weight, indicating an effect on hydrophobicizing the cellulose.

[0052] Thus, when xylan, a hemicellulose, is used on the cellulose surface, the adsorption pattern is thought to be as follows: first, the xylan is positioned so that its chain elongation direction is parallel to the cellulose chain elongation direction, and then it is adsorbed so that its chain elongation direction is parallel to the cellulose chain elongation direction. Cellulose and PVA in water are thought to exhibit behavior similar to that of molecular dynamics simulations of cellulose and xylan in water, but PVA has a higher proportion of -OH groups in its chains compared to xylan.

[0053] [Production Example 3 of Modified Cellulose-Containing Material] Next, a modified cellulose-containing material was produced using the hemicellulose from Production Example 2, but with different washing conditions. In this Production Example 3, the washing conditions were changed as shown in Table 2, based on the production conditions (materials, compounding conditions, immersion conditions, drying conditions 1, drying conditions 2, etc.) of Test Examples 1-5 of Production Example 2 described above.

[0054]

[0055] The washing conditions were as follows, as shown in Table 2: no washing (Test Example 2-1), room temperature (RT) for 1 hour (Test Example 2-2), 40°C for 1 hour (Test Example 2-3), 50°C for 1 hour (Test Example 2-4), 60°C for 1 hour (Test Example 2-5), 80°C for 1 hour (Test Example 2-6), and 95°C for 1 hour (Test Example 2-7). Figure 16 shows the results of contact angle measurements performed on Test Examples 2-1(a), 2-2(b), and 2-3(c) in the same manner as in Manufacturing Example 1. As can be seen from the contact angle results in Table 2, room temperature (RT) for 1 hour (Test Example 2-2) and 40°C for 1 hour (Test Example 2-3) were effective in hydrophobizing the cellulose.

[0056] [Example 4 of the production of modified cellulose-containing material] Next, as shown in Table 3, modified cellulose-containing material was produced by changing the amount of hemicellulose added and the immersion conditions in the composite solution.

[0057]

[0058] The amount of hemicellulose was varied from 5 to 20 parts by weight, as shown in Table 3, and each amount was immersed under two conditions (RT for 10 minutes and 95°C for 10 minutes). The contact angle was measured using the same method as in Production Example 1. As can be seen from the results in Table 3, the hydrophobic effect on cellulose was observed at room temperature (RT) for 1 hour (Test Example 2-2) and at 40°C for 1 hour (Test Example 2-3). While all hemicellulose additions in the range of 5 to 20 parts by weight were effective in hydrophobicating cellulose, the hydrophobic effect was more pronounced at room temperature.

[0059] [Production Example 5 of Modified Cellulose-Containing Material] In Production Examples 1 to 4, filter paper was used, but in Production Example 5, rayon (rayon fabric, Apitas TAE-50A, Daiwa Spinning Co., Ltd.), which is a regenerated cellulose fiber, was used as the cellulose-containing material. PVA used was PVA28-98 (Kuraray Co., Ltd., fully saponified type, degree of saponification: 98-99, viscosity: 25-31).

[0060] (Preparation of each sample) Lignin and PVA were used as solutes, and distilled water (hereinafter abbreviated as "water") was used as the solvent. First, distilled water (100 g) and PVA (0 or 8 g) were stirred at room temperature (at room temperature of about 25°C for 15 minutes) and heated and stirred (at 95°C for 2 hours until the PVA is sufficiently dissolved) as appropriate to dissolve the PVA. Then, lignin (0 to 8 g) was added to prepare a lignin-PVA aqueous solution. The weight ratio at this time was water:PVA:lignin = 100:0 or 8:0 to 8. In rayon fabric, if there is too much PVA the fabric becomes hard, and if there is too much lignin the fabric discolors, so initially a highly concentrated lignin-PVA aqueous solution was prepared, and then compounding (compounding conditions, immersion conditions, etc.) was performed using a lignin-PVA aqueous solution diluted with distilled water. The lignin-PVA aqueous solution was diluted to the ratios shown in Table 4 and heated and stirred (95°C for 1 hour). Rayon fabric, a cellulose-containing material (regenerated cellulose fiber), was immersed in the diluted lignin-PVA aqueous solution at 90°C for 10 minutes. The rayon fabric was then removed, dehydrated, dried (150°C for 3 hours), washed (95°C for 1 hour), and dried again (105°C for 1 hour) to obtain the test sample.

[0061] In this production example 5, as shown in Table 5, an initial high-concentration lignin-PVA aqueous solution and diluted lignin-PVA aqueous solutions as described in Test Examples 4-3 to 4-13 in Table 5 were used. Table 4 shows the evaluation results of the hydrophobicity of the rayon fabric surface in relation to the amounts of PVA and lignin blended. Contact angle measurements were performed on the obtained samples in the same manner as in production example 1. As shown in Table 4, it was found that the PVA-lignin composite is effective in hydrophobicizing the rayon fabric.

[0062]

[0063] [Production Example 6 of Modified Cellulose-Containing Material] In this production example 6, the same rayon fabric as in production example 5 was used. As shown in Table 5, modified cellulose-containing material was produced by changing the compounding conditions with lignin among the compounding conditions.

[0064]

[0065] For preparing the PVA-lignin composite, 95°C for 1 hour is sufficient, but a longer time is also acceptable, preferably 95°C for 3 hours. Both conditions were effective in hydrophobicization.

[0066] [Production Example 7 of Modified Cellulose-Containing Material] This production example 7 also uses the same rayon fabric as production examples 5 and 6. As shown in Table 6, modified cellulose-containing material was produced by changing the drying conditions after immersion.

[0067]

[0068] The drying conditions after immersion of the rayon fabric in the composite solution were all hydrophobic, as shown in Table 6, but 150°C for 3 hours or 160°C for 1 hour were preferred.

Claims

1. A modified cellulose-containing material characterized in that lignin and PVA or hemicellulose are adsorbed onto the surface of the cellulose-containing material to make it hydrophobic, wherein a composite of lignin and PVA or hemicellulose is adsorbed on the hydrophilic surface of the cellulose-containing material, and lignin is adsorbed on the hydrophobic surface of the cellulose-containing material.

2. The modified cellulose-containing material according to claim 1, wherein the cellulose-containing material is natural cellulose or regenerated cellulose fiber.

3. The modified cellulose-containing material according to claim 1, wherein the cellulose-containing material is a paper material.

4. The modified cellulose-containing material according to claim 1, wherein the cellulose-containing material is a regenerated cellulose fiber such as viscose rayon, cupro, or Tencel (lyocell).

5. The modified cellulose-containing material according to claim 1 or 2, wherein the hemicellulose is xylan, glucomannan, galactomannan, arabinoxylan, or mannan.

6. The modified cellulose-containing material according to claim 1 or 2, wherein the OH groups of the lignin and the PVA are hydrogen-bonded to the OH groups of the hydrophilic surface of the cellulose-containing material, and the cellulose-containing material is hydrophobic.

7. A method for producing a modified cellulose-containing material, characterized by immersing or contacting a cellulose-containing material with a lignin-PVA solution or a lignin-hemicellulose solution to adsorb a composite of lignin and PVA or hemicellulose onto the hydrophilic surface of the cellulose-containing material, and adsorbing lignin onto the hydrophobic surface of the cellulose-containing material.

8. The method for producing a modified cellulose-containing material according to claim 7, wherein the cellulose-containing material is natural cellulose or regenerated cellulose fiber.

9. The method for producing a modified cellulose-containing material according to claim 7, wherein the cellulose-containing material is a paper material.

10. The method for producing a modified cellulose-containing material according to claim 7, wherein the cellulose-containing material is a regenerated cellulose fiber such as viscose rayon, cupro, or Tencel (lyocell).

11. The method for producing a modified cellulose-containing material according to claim 7 or 8, wherein the hemicellulose is xylan, glucomannan, galactomannan, arabinoxylan, or mannan.

12. A method for producing a modified cellulose-containing material according to claim 7 or 8, wherein the OH groups of the lignin and the PVA are hydrogen-bonded to the OH groups of the hydrophilic surface of the cellulose-containing material, and the cellulose-containing material is hydrophobic.

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