JP6402442B2 - Method for producing cellulose nanofiber dispersion and membrane using the method - Google Patents

Description

  The present invention relates to a production method in functionalizing a material using cellulose as a starting material.

  In recent years, against the background of global warming, environmental pollution, and waste problems due to depletion of resources and an increase in the concentration of carbon dioxide in the atmosphere, the amount of fossil resources used during production is low, and carbon dioxide can be processed with low energy during disposal. The use of environmentally friendly materials with low emissions is drawing attention. Under these circumstances, biodegradation typified by biomass resources that do not use fossil resources as raw materials, but partly or entirely use natural plants as raw materials, and polylactic acid that decomposes in the environment into water and carbon dioxide. Active use of functional materials is expected.

  Among biomass materials, cellulose, which accounts for about half of its production, is expected to be used effectively due to its large production. Furthermore, it has a high strength, a high elastic modulus, and an extremely low coefficient of thermal expansion, and in terms of heat resistance, it has no glass transition point and exhibits a high thermal decomposition temperature of 230 degrees.

  However, it cannot be said that cellulose is often used as a material for its large amount of production. One of the reasons is low solubility and dispersibility in aqueous and non-aqueous solvents. Cellulose is a homopolysaccharide in which D-glucopyranose, which is a 6-membered ring of glucose, is linked by β- (1 → 4) glucoside, and has hydroxyl groups at the C2, C3 and C6 positions. Therefore, a strong hydrogen bond is formed in and between the molecules and does not dissolve in water or a general solvent.

  One of the most common uses of cellulose is carboxymethylation. Carboxymethylated cellulose fibers in which carboxyl groups are randomly introduced into hydroxyl groups at the C2, C3, and C6 positions, are water-soluble and can be used as thickeners depending on the degree of substitution, and are insoluble at low degrees of substitution. And various materials can be obtained. However, in the carboxymethylation reaction of cellulose, a large amount of organic solvent is used, and toxic monochloroacetic acid is used, which causes problems such as environmental pollution and waste liquid treatment. In addition, since the introduced carboxyl group has no distinction in the position of the hydroxyl group, the product has a non-uniform chemical structure.

  On the other hand, when cellulose is treated using an oxidation reaction catalyzed by an N-oxyl compound such as 2,2,6,6-tetramethyl-1-piperidinyloxy radical (TEMPO), the degree of treatment is adjusted. A homogeneous dispersion can be obtained by mild dispersion treatment in water. In this case, cellulose is fibrillated to the microfibril level and exists as a cellulose nanofiber dispersion dispersed in a width of several nm to several hundred nm. Furthermore, in this TEMPO oxidation reaction, an organic solvent is not used and only water is used as a reaction medium, and the environmental adaptability of the reaction process is extremely high, for example, the reaction can be completed in a short time under mild conditions at normal temperature and normal pressure.

  The mechanism for dispersing the oxidized cellulose obtained by the TEMPO oxidation reaction to the nano level by a light mechanical treatment is known as follows. The hydroxyl group at the C6 position on the surface of cellulose microfibrils is selectively oxidized by an oxidation reaction, and a carboxyl group is introduced via an aldehyde group. This carboxyl group is repelled as an anion and exhibits an osmotic pressure effect in the dispersion medium, so that nano-order microfibrils are easily isolated and obtained as a homogeneous cellulose nanofiber dispersion. Furthermore, cellulose modified products having different characteristics can be obtained by forming various salts having a cationic property as a counter ion by utilizing the electrostatic action of a carboxyl group introduced into cellulose. In this treatment, since the crystallinity of the raw material cellulose can be maintained without breaking, it has high physical properties.

  In this way, cellulose can be used as a nano-dispersion, liquid state, or modified substance, and has a low environmental burden and higher physical properties. Therefore, the treatment and oxide by the TEMPO oxidation reaction are new to cellulose. It is expected as a usage form.

  One example that is being actively developed for industrial use is compounding with resin. By mixing a cellulose dispersion in the resin, it is intended to enhance the functionality of the resin utilizing the light weight, high strength, high elastic modulus, low linear thermal expansion coefficient, and high heat resistance of cellulose. In this case, the dispersibility of cellulose nanofibers in the resin is cited as an important factor for improving the functionality. It is known that when the cellulose nanofibers are unevenly distributed or aggregated, the effect of mixing the cellulose nanofibers is significantly reduced.

  Thus, in order to increase the affinity with a hydrophobic resin and improve the dispersibility, a method of hydrophobizing cellulose nanofibers that are hydrophilic has been developed.

  For example, in Patent Document 1, after the oxidized cellulose obtained by the TEMPO oxidation reaction is dispersed to form nanofibers, an acid is added and aggregated to be taken out as a gel. Hydrophobic cellulose containing an organic solvent by adding this to an organic solvent and replacing the water in the gel with a solvent, then allowing the alkali dissolved in the organic solvent to act, and further repeating the solvent substitution, followed by dispersion treatment A method for obtaining a nanofiber dispersion is shown. However, in order to use this method, it is necessary to go through a multi-step solvent replacement step, and it is industrially unsuitable because handling for recovering the gel is complicated.

  Patent Document 2 discloses a method in which oxidized cellulose obtained by the TEMPO oxidation reaction is adjusted in pH with an organic alkali and dispersed in water or an organic solvent. However, in this method, the dispersion medium is basically captured as water, and an organic solvent containing water can be used. In the cellulose fiber dispersion containing water, the drying efficiency is low and it is difficult to improve the productivity. Furthermore, in the drying process, the organic solvent component is first evaporated and removed, and as a result, the cellulose fiber maintains its original hydrophilic property as the characteristics of the aqueous dispersion, and is modified using an organic alkali as an alkali. It is difficult to fully demonstrate the effect of quality.

International Publication No. 2013/077354 International Publication No. 2011-111612

  The present invention has been made in consideration of the background art as described above, and it is an object of the present invention to provide a method for promoting industrial use of natural resources and expanding use applications. In particular, versatility can be remarkably improved by processing cellulose having high hydrophilicity to improve the affinity with an organic solvent and disperse it.

The invention according to claim 1 is an oxidation step of introducing a carboxyl group by oxidizing cellulose, and the cellulose having a carboxyl group obtained in the oxidation step is replaced with an organic onium ion using an organic onium compound. A counter ion substitution step, a solvent substitution step of solvent substitution of the cellulose obtained in the counter ion substitution step with an organic solvent, a dispersion step of dispersing the cellulose obtained in the solvent substitution step in a dispersion medium, wherein the said Ri der permittivity 15ε more 80ε less at 25 ° C. the dispersion medium in the dispersion step, the cellulose and cellulose modifications introduced with carboxyl groups, characterized by Rukoto be prepared cellulose nanofibers It is a manufacturing method of a cellulose nanofiber dispersion.

The invention according to claim 2 is characterized in that in the oxidation step, cellulose is recovered by using the carboxyl group introduced in the oxidation treatment as a carboxylic acid using an acid, and recovering cellulose. It is a manufacturing method .

The invention according to claim 3 is the method for producing a cellulose nanofiber dispersion according to claim 1 or 2, wherein the solvent used in the solvent replacement step includes a solvent used as the dispersion medium.
The invention according to claim 4 is an oxidation process for introducing a carboxyl group by oxidizing cellulose, and the cellulose having a carboxyl group obtained in the oxidation process is replaced with an organic onium ion by using an organic onium compound. A counterion substitution step, a solvent substitution step of solvent substitution of the cellulose obtained in the counterion substitution step with an organic solvent, and a cellulose obtained in the solvent substitution step having a dielectric constant at 25 ° C. of not less than 15ε and not more than 80ε. cellulose and cellulose modifications introduced with carboxyl groups in a dispersion medium is is a film using the cellulose nanofibers dispersion treated with the dispersion step that will be prepared on cellulose nanofibers,
The content of the carboxyl group is not more than the dry weight per 0.1mmol more 3.0mmol of cellulose nanofibers, cellulose nanofiber dispersion contact angle containing organic onium ion is at 85 ° to the carboxyl group as a counterion This is the film used .
The invention according to claim 5 is a film using the cellulose nanofiber dispersion according to claim 4 whose tensile strength at 40 ° C. and 90 RH is 110 MPa or more.

  ADVANTAGE OF THE INVENTION According to this invention, the method for promoting the industrial use of natural resources and expanding a utilization use can be provided. According to this method, the versatility can be remarkably improved by processing cellulose having high hydrophilicity to improve the affinity with an organic solvent and disperse it.

It is the schematic of the manufacturing method of the dispersion in this invention.

  Hereinafter, an embodiment of the present invention will be described.

(Method for producing cellulose nanofiber dispersion)
The method for producing a cellulose nanofiber dispersion and a modified cellulose according to the present invention includes at least an oxidation step and a counter ion substitution step. Furthermore, a solvent replacement step and a dispersion step may be included.

  As a material starting from cellulose used in the present invention, natural cellulose or chemically modified cellulose can be used. Specifically, pulp made from wood such as bleached and unbleached kraft wood pulp, prehydrolyzed kraft wood pulp, sulfite wood pulp, non-wood pulp such as cotton and bacterial cellulose, and mixtures thereof are used. Any of materials obtained by physically or chemically treating these materials may be used. Preferably, natural cellulose having crystalline form I is desirable.

<Oxidation process>
The method for oxidizing cellulose is not particularly limited as long as it is a method for introducing a carboxyl group into cellulose as a raw material, and is appropriately selected according to the purpose. For example, it can be appropriately selected from the generally known methods of oxidizing from a hydroxyl group to a carboxylic acid via an aldehyde. Among them, a method using an N-oxyl compound as a catalyst and using a hypohalite or a halite as a co-oxidant is preferable. In particular, 2,2,6,6-tetramethyl-1-pipedinyloxy radical (TEMPO) is used as a catalyst, and an oxidizing agent such as sodium hypochlorite and bromide such as sodium bromide while adjusting pH. The TEMPO oxidation method in which the reaction is carried out using a chemical compound is preferable from the standpoint of complete reaction in water without using an organic solvent as a reaction medium, availability of reagents, cost, and reaction stability.

  In the TEMPO oxidation method, only the surface of crystalline cellulose microfibrils is oxidized, and no oxidation occurs inside the crystal, so that the crystal structure can be maintained. For this reason, the product has the inherent high strength, high elastic modulus, low linear thermal expansion coefficient, and high heat resistance characteristics of cellulose.

  The oxidation treatment by the TEMPO oxidation method described above is performed according to the following procedure.

  The cellulose is oxidized by adding an N-oxyl compound and an oxidizing agent or a co-oxidizing agent to cellulose dispersed in water. Sodium hydroxide is added during the oxidation reaction to control the pH in the reaction system from 9 to 11. The reaction temperature is preferably 0 ° C. or higher and 40 ° C. or lower. At this time, the hydroxyl group at the C6 position on the surface of the cellulose fiber is oxidized to a carboxyl group. After completion of the reaction, it is sufficiently washed and collected, and can be used as a constituent material in the present invention.

  In addition, as an oxidizing agent, hypohalous acid or its salt, a halogenous acid or its salt can be used, and sodium hypochlorite is preferable. Examples of the bromide include lithium bromide, potassium bromide, sodium bromide and the like, and sodium bromide is preferable because of easy handling.

  Content of the carboxyl group introduce | transduced into a cellulose can be adjusted by setting reaction conditions suitably. Cellulose introduced with a carboxyl group is dispersed in the dispersion medium by the charge repulsion of the carboxyl group through a dispersion step described later. Therefore, if the content of carboxyl groups in the cellulose is too small, the cellulose is stably dispersed in the dispersion medium. I can't let you. Moreover, when there is too much content of the carboxyl group in a cellulose, the affinity to a dispersion medium will increase and water resistance will fall. From these viewpoints, the content of the carboxyl group introduced into the cellulose is preferably 0.1 mmol or more and 3 mmol or less, more preferably 0.6 mmol or more and 2.5 mmol or less per dry weight.

  In addition, the amount of carboxyl groups contained in cellulose is calculated by the following method. 0.2 g of dry weight conversion of oxidized cellulose is put in a beaker, and 80 ml of ion exchange water is added. Thereto was added 5 ml of a 0.01 M sodium chloride aqueous solution, and 0.1 M hydrochloric acid was added while stirring to adjust the whole to pH 2.0. Here, 0.1M sodium hydroxide aqueous solution was injected at 0.05 ml / 30 seconds using an automatic titrator (AUT-701, manufactured by Toa DKK Co.), and the conductivity and pH value were measured every 30 seconds. Measurement was continued until. The titration amount of sodium hydroxide can be obtained from the obtained conductivity curve, and the carboxyl group content can be calculated.

After finishing the oxidation step by stopping the oxidation reaction, the product is recovered from the reaction solution by filtration. After completion of the reaction, the carboxyl group introduced into the cellulose forms a salt having a metal ion derived from a cation present in the reaction medium as a counter ion.
As a method for recovering the cellulose after the oxidation treatment, (a) a method in which the carboxyl group is filtered while forming a salt, (b) an acid is added to the reaction solution to adjust the system under acidity, (C) The method of filtering after adding an organic solvent and making it aggregate is mentioned. Among these, from the viewpoint of handling properties, recovery efficiency, and waste liquid treatment, (b) a method of recovering as carboxylic acid is preferable. Further, in the counter ion substitution step to be described later, the method of recovering as a carboxylic acid is preferable because it does not contain a metal ion as a counter ion, because generation of by-products can be suppressed and substitution efficiency is excellent.

In addition, the metal ion content in the cellulose after the oxidation reaction can be examined by various analysis methods, for example, simply by elemental analysis of EPMA method or X-ray fluorescence analysis method using an electron beam microanalyzer. be able to. When recovered using a method of filtering while forming a salt, the content of metal ions is 5 wt% or more, whereas when recovered by a method of filtering after carboxylic acid, it is 1 wt% or less.
Furthermore, the recovered cellulose can be purified by repeated washing, and the catalyst and by-products can be removed. At this time, the amount of remaining metal ions and salts can be reduced by repeating washing with pure water after washing with a cleaning solution prepared using hydrochloric acid or the like under acidic conditions of pH 3 or lower.

<Counterion replacement step>
Next, the counter ion substitution step is performed by adding an alkali to the cellulose suspension into which the carboxyl group is introduced. The amount of alkali added is preferably 0.8 equivalents or more and 2 equivalents or less with respect to the carboxyl group introduced into the cellulose. In particular, the amount of 1 equivalent or more and 1.8 equivalents or less is more preferable because the counter ion exchange can be performed without adding an excessive amount of alkali. Here, although it is possible to disperse cellulose to some extent even with less than 0.8 equivalent, it takes a long time and high energy by the dispersion treatment, and the fiber diameter of the obtained fiber is larger than that of the present invention, so that the dispersion is homogeneous. Sex is reduced. On the other hand, when the amount exceeds 2 equivalents, decomposition with an excessive amount of alkali and affinity for the dispersion medium may decrease, which is not preferable.

At this time, it is preferable to adjust the pH of the cellulose suspension to a range of pH 4 or more and pH 12 or less using an alkali. In particular, the pH is made alkaline between pH 7 and pH 12 and the added alkali and carboxylate are formed. Thereby, since charge repulsion between carboxyl groups is likely to occur, dispersibility is improved and a cellulose nanofiber dispersion is easily obtained.
Here, although it is possible to disperse cellulose by mechanical dispersion treatment even when the pH is less than 4, the homogeneity of the dispersion is lowered for the same reason as in the case where the amount of alkali added is too small. On the other hand, when the pH exceeds 12, the molecular weight is lowered by the peeling reaction of oxidized cellulose or alkali hydrolysis during the dispersion treatment, and the yellowing of the dispersion is promoted due to the formation of terminal aldehydes and double bonds. Decreases.

As the alkali for adjusting the pH of the suspension, an organic onium compound can be used.
The organic onium compound has a cation structure represented by the following structural formula (1).
Structural formula (1)

In the structural formula (1), M represents a nitrogen atom or a phosphorus atom, and R1, R2, R3, and R4 represent a hydrogen atom, a hydrocarbon group, or a hydrocarbon group containing a hetero atom.

  For example, ammonia can be used when M is a nitrogen element and R1, R2, R3, and R4 are all hydrogen atoms. Moreover, when R1, R2, R3, and R4 are hydrocarbon groups, an alkyl group, an aralkyl group, an aromatic group, etc. can be mentioned. As the alkyl group, an alkyl group having 1 to 18 carbon atoms is preferable, and methyl, ethyl, n-propyl, n-butyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n- Heptadecyl, n-octadecyl and the like can be used. The aralkyl group preferably has 7 to 20 carbon atoms, benzyl group, o-toluylmethyl group, m-toluylmethyl group, p-toluylmethyl group, 2-phenylethyl group, 1-naphthylmethyl group, 2-naphthylmethyl. Group and the like. Moreover, as an aromatic group, C6-C20 is preferable and a phenyl group, a biphenyl group, a naphthyl group, a tosyl group etc. are mentioned. R1, R2, R3 and R4 may be a hydrocarbon group containing a hetero atom, and R1, R2, R3 and R4 may form a ring. Further, the counter ion of the cation structure of the organic onium compound is not limited, but a hydroxide ion is preferable in view of adverse effects of mixing of metal ions or dispersibility in a dispersion medium.

  As described above, the modified cellulose obtained using an organic onium compound as an alkali can be dispersed at a lower energy and in a shorter time than when an inorganic alkali having a metal ion as a counter ion is used, and The homogeneity of the finally reached dispersion is also high. This is probably because the use of the organic onium compound has a larger effect of separating fine cellulose fibers in the dispersion medium because the counter ion has a larger ion diameter. Furthermore, when an organic onium compound is included as a dispersion medium, the viscosity and thixotropy of the dispersion can be reduced as compared with inorganic alkali, which is advantageous in the ease of dispersion treatment and subsequent handling. Usually, the cellulose nanofiber dispersion becomes a gel, and the viscosity increases as the concentration is increased. Therefore, a large amount of energy is required in the dispersion treatment, and the dispersion treatment becomes difficult. Dispersion treatment becomes easy because the viscosity of the resin decreases. By combining the organic onium compound and the solvent, it is possible to adjust the viscosity characteristics of the dispersion, and the industrial application range is remarkably increased.

<Solvent replacement step>
When the cellulose introduced with carboxyl groups by the oxidation treatment is used as a dispersion, the cellulose can be dispersed to a homogeneous dispersion by mixing the cellulose and the dispersion medium and performing a dispersion treatment using a method described later. It becomes possible. As pretreatment for mixing with the dispersion medium, the oxidized cellulose can be solvent-substituted. Here, since the reaction medium is water in the cellulose oxidation step and the cleaning agent used for washing after the reaction is mainly water, the cellulose after the oxidation treatment is recovered in a wet state including water. Therefore, in the case where an organic solvent other than water is included as the dispersion medium, the purpose of removing water that becomes an impurity in the dispersion medium, the purpose of improving the dispersibility by previously making the cellulose and the dispersion medium compatible, or the dispersion medium insoluble component It is preferable to perform solvent substitution depending on the purpose of removal.

  Although it is possible to replace the oxidized cellulose with an organic solvent before the counter ion substitution step, the charge repulsion of the carboxyl group is shielded by eliminating the included water, or the charge repulsion in the case of carboxylic acid. Since it does not occur, the cellulose aggregates, which may adversely affect the subsequent dispersion process. Accordingly, when solvent substitution is performed with an organic solvent, it is preferable to use a modified cellulose in which the counter ion of the carboxyl group of cellulose is substituted with the desired organic onium ion. Since charge repulsion due to carboxyl groups can be maintained even after solvent substitution, aggregation of cellulose fibers can be suppressed. Furthermore, by coordinating the organic onium ions, the affinity with the organic solvent is improved, so that water can be easily discharged and solvent replacement can be performed efficiently.

  The method for solvent replacement is appropriately selected according to the organic solvent to be solvent-substituted, the characteristics of the organic onium compound to be used, and other desired characteristics. Cellulose that has been oxidized and washed may be dehydrated or dried after counterion substitution with an organic onium compound, or an organic onium compound may be used after dehydrated or dried cellulose that has been oxidized and washed. Here, there is no limitation about the dehydration method, and a centrifuge, various filters, etc. can be selected suitably. There is no limitation on the drying method, and hot air drying, infrared drying, vacuum drying, freeze drying and the like can be selected as appropriate. Various solvents and additives are added for the purpose of suppressing aggregation due to drying and deterioration of cellulose due to heat. An agent can be added as appropriate. Furthermore, the modified cellulose having a counter ion substituted as an organic onium ion may be directly charged into an organic solvent to be solvent-substituted, or may be charged into an organic solvent containing water and sequentially solvent-substituted.

  The organic solvent used for solvent replacement can be appropriately selected according to the purpose within a range in which the cellulose fibers are not aggregated or modified. Moreover, it may be the same as the dispersion medium used when preparing the cellulose nanofiber dispersion.

<Dispersing process>
By the dispersion step, cellulose introduced with a carboxyl group and a modified cellulose are prepared into cellulose nanofibers. In other words, in the present invention, the cellulose introduced with carboxyl groups and the modified cellulose are described as one form of cellulose prior to the stage of preparation into cellulose nanofibers.

  As the dispersion processing method in the dispersion step, various known dispersion processes can be used. For example, homomixer processing, mixer processing with rotary blade, high pressure homogenizer processing, ultra high pressure homogenizer processing, ultrasonic homogenizer processing, nanogenizer processing, disc type refiner processing, conical type refiner processing, double disc type refiner processing, grinder processing, ball mill processing , Kneading treatment with a biaxial kneader, underwater facing treatment, etc. Among these, the mixer treatment with a rotary blade, the high-pressure homogenizer treatment, the ultra-high pressure homogenizer treatment, and the ultrasonic homogenizer treatment are preferable from the viewpoint of miniaturization efficiency. Of these processes, two or more processing methods can be combined and distributed.

  When using a modified cellulose with a counter ion substituted as an organic onium ion of a carboxyl group introduced into cellulose in the dispersion treatment, since the affinity for the organic solvent is high, even when using an organic solvent such as alcohol as a dispersion medium, Cellulose nanofiber dispersions can be prepared. Furthermore, if necessary, water can be added after the dispersion treatment to the cellulose nanofiber dispersion obtained by dispersing the cellulose modification in an organic solvent. In addition, since the affinity between the cellulose modified product and the dispersion medium can be improved by solvent replacement in advance, a homogeneous cellulose nanofiber dispersion can be obtained without aggregation even in a single organic solvent that does not contain water. .

  Examples of the organic solvent used as the dispersion medium include methanol, ethanol, isopropyl alcohol, acetone, ethyl acetate, N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N- Examples thereof include methyl-2-pyrrolidone (NMP) and the like, and any one of them, or a mixture of any two or more of these. Here, when an inorganic alkali such as sodium hydroxide is used, it is difficult to perform dispersion treatment in a solvent or mixing with a solvent after dispersion treatment. In a cellulose nanofiber dispersion containing metal ions due to an inorganic alkali, the addition of an organic solvent causes the cellulose fibers to agglomerate, causing agglomerated cloudiness and non-uniformity of the dispersion. Furthermore, when an organic solvent alone that does not contain water without using a solvent replacement step is used as a dispersion medium, the aggregation of cellulose fibers works more strongly, making it difficult to obtain a homogeneous dispersion.

  The dielectric constant of the organic solvent used as the dispersion medium is preferably 15ε or more and 80ε or less at 25 ° C. A substance having a dielectric constant higher than that of water having a dielectric constant of 80ε (20 ° C.) is not practical for general use. On the other hand, when the dielectric constant is lower than 15ε, the cellulose cannot be maintained in a dispersed state as a dispersion and aggregates. One reason for this is that the coulomb force between the organic onium ion and the carboxylic acid present as a counter ion of the carboxyl group of cellulose becomes too strong, and the charge repulsion in the dispersion medium of cellulose fibers does not work.

  The principle of maintaining the dispersibility by dispersing the inherently highly hydrophilic cellulose in the form of nanofibers in an organic solvent not containing water by this method is considered as follows. First, it is mentioned that the dissociation property of the organic onium ion used in the counter ion exchange step is extremely high. Further, the hydrocarbon group of the organic onium compound has a hydrophobic interaction. Due to these effects, ions are dissociated even in an organic solvent, and the ionization of the carboxyl group of oxidized cellulose and the osmotic pressure effect of the hydrocarbon group work, and it is considered that dispersion in the organic solvent is possible.

  The light transmittance at 660 nm in the optical path length of 10 mm of the cellulose nanofiber dispersion obtained by the dispersion process is as follows. The solid content concentration of the cellulose nanofiber contained in the cellulose nanofiber dispersion is 0.2%. It is preferably 85% or more. If it is in said range, it will be shown that a dispersion is excellent in homogeneity. That is, when the light transmittance is low in the visible light region of 660 nm, it indicates that there are a large number of cellulose fiber aggregates that hinder the transmission of the test light. By measuring the light transmittance, it can be easily used as an index representing the dispersibility of cellulose.

  The light transmittance of the cellulose nanofiber dispersion can be obtained by adjusting the solid content concentration of the cellulose nanofiber, filling the quartz cell, and measuring the transmittance at a specified wavelength using a spectrophotometer. Moreover, it is preferable that the fiber width of the cellulose as a cellulose nanofiber dispersion is 2 nm or more and 200 nm or less. That is, in order to maintain a fiber shape, 2 nm or more is preferable, and if it is 200 nm or less, since it has optical transparency, the freedom degree in product design improves. In addition, the fiber shape of cellulose can be confirmed by SEM or AFM observation by spreading the cellulose nanofiber dispersion prepared to 0.0001 to 0.001 wt% on mica having a smooth surface and drying it.

  The solid content concentration of the cellulose fiber with respect to the dispersion medium in the dispersion step can be adjusted as appropriate within a range that does not hinder the dispersion treatment, and the concentration treatment may be performed after the dispersion treatment. The concentration method is not particularly limited, but a method such as centrifugation, reduced pressure, or vacuum evaporation can be appropriately selected as long as degradation of characteristics due to aggregation or decomposition reaction due to drying of cellulose fibers does not become a problem.

  Further, in the cellulose nanofiber dispersion after the dispersion step, water is added depending on the function to be added for the purpose of adjusting the viscosity, adjusting the drying speed, improving the affinity with different materials, etc. within a range where aggregation and precipitation do not occur. In addition, various organic solvents can be mixed. At this time, in order to relieve shock caused by mixing different solvents, the addition rate, pH adjustment, stirring method, temperature and the like can be appropriately selected.

  Moreover, the obtained modified cellulose or cellulose nanofiber dispersion may contain a metal or the like. Metals include gold, silver, platinum, palladium, ruthenium, iridium, rhodium, osmium, platinum group elements, and metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. Alternatively, alloys thereof, oxides, double oxides, carbides, or the like can be used. As a method for supporting the metal, in addition to mixing fine particles such as metal or metal oxide, a metal nanoparticle dispersion containing a carboxyl group forms a metal or metal oxide complex, and a reducing agent is added to form metal particles. Can be deposited as When this method is used, fine metal particles are uniformly immobilized on the surface of the cellulose fiber, so that the effect can be efficiently exhibited with a small amount of metal.

  In addition, as long as aggregation and precipitation do not occur, various additives including water-soluble polysaccharides and various resins may be included for the purpose of increasing the charge repulsion between fibers and controlling the viscosity of the dispersion. For example, chemically modified cellulose, carrageenan, xanthan gum, guar gum, gum arabic, sodium alginate, agar, solubilized starch, glycerin, sorbitol, antifoaming agent, water-soluble polymer, synthetic polymer and the like can be used. Alternatively, various solvents may be included for imparting functionality such as coatability and wettability. Alcohols, cell solves, glycols, and the like can be used. Furthermore, various dyes, pigments, organic fillers, and inorganic fillers may be included for the purpose of imparting design properties.

  Moreover, in order to improve water resistance and electrolyte solution resistance, various crosslinking agents may be included. For example, oxazoline, divinyl sulfone, carbodiimide, dihydrazine, dihydrazide, epichlorohydrin, glyoxal, organic titanium compound, organic zirconium compound, and the like can be used. Further, for the purpose of improving the reactivity, the pH can be adjusted by adding an acid or an alkali.

  Thus, the obtained cellulose modification body and cellulose nanofiber dispersion can maintain a dispersion state in the state which excluded water as mentioned above. Furthermore, it has excellent affinity with an organic solvent and can exist as cellulose nanofibers that are homogeneous in the organic solvent.

  In addition, cellulose nanofibers can be formed by forming a resin composite for the purpose of strength improvement and weight reduction by mixing with a resin using a cellulose modification or cellulose nanofiber dispersion, or by applying to a substrate or the like. For example, a functional layer containing can be used as a constituent material of the molded body.

This makes it possible to form a more homogeneous composite with a highly hydrophobic substance such as a resin, thereby greatly expanding the industrial application range of cellulose.

  Examples of the present invention will be described below. The following examples are examples of the present invention, and the present invention is not limited to these examples.

Example 1
The cellulose modified body and the cellulose nanofiber dispersion were prepared by the following procedure.

(1) Reagent / Material Cellulose: Bleached Kraft Pulp (Fletcher Challenge Canada “Machenzie”)
TEMPO: Commercial product (Tokyo Chemical Industry Co., Ltd., 98%)
Sodium hypochlorite: Commercial product (Wako Pure Chemical Industries, Cl: 5%)
Sodium bromide: Commercial product (Wako Pure Chemical Industries, Ltd.)

(2) Oxidation step A bleached kraft pulp having a dry weight of 10 g was allowed to stand overnight in 500 ml of ion-exchanged water in a 2 L glass beaker to swell the pulp. Here, 0.1 g of TEMPO and 1 g of sodium bromide were added and stirred to obtain a pulp suspension. Further, 5 mmol / g sodium hypochlorite per cellulose weight was added with stirring. At this time, about 1N sodium hydroxide aqueous solution was added to maintain the pH of the pulp suspension at about 10.5. Then, it was made to react for 2 hours, ethanol 10g was added, reaction was stopped, and the oxidized cellulose in which the carboxyl group was introduce | transduced into the cellulose was obtained. In addition, the carboxyl group introduced at this time forms a salt having a sodium ion derived from the reaction reagent remaining in the reaction medium as a counter ion. Subsequently, 0.5N hydrochloric acid was added dropwise to lower the pH to 2. Cellulose is filtered off using a glass filter, further washed three times with 0.05N hydrochloric acid to convert the carboxyl group to carboxylic acid, then washed five times with pure water, and wet cellulose oxide with a solid content of 20%. Got. The obtained oxidized cellulose was calculated to have a carboxyl group amount of 1.6 mmol per dry weight of cellulose from neutralization titration with sodium hydroxide.

(3) Counterion substitution step Tetramethylammonium hydroxide (TMAH), which is an organic onium compound as an alkali species, is prepared by adding water to the oxidized cellulose prepared above to a solid content concentration of 5%. Was added in an amount of 1.0 equivalent to the amount of carboxyl groups of oxidized cellulose. After stirring for 2 hours, the oxidized cellulose was filtered off using a glass filter to obtain counterion-substituted oxidized cellulose.

(4) Solvent replacement step The oxidized cellulose subjected to counter ion replacement as described above was subjected to solvent replacement using ethanol as an organic solvent serving as a replacement solvent. That is, the mixture was poured into an aqueous solution of an organic solvent mixed so that water and the organic solvent were in a volume ratio of 2 to 1, and stirred for 30 minutes, and then the oxidized cellulose was filtered and collected using a glass filter. In the same manner, the mixture was poured into an aqueous solution of an organic solvent in which water and an organic solvent were in a 1: 1 ratio, stirred for 30 minutes, collected by filtration, and then washed and collected three times with the organic solvent. Oxidized cellulose containing was obtained.

(5) Dispersion step In addition to ethanol, which is an organic solvent serving as a dispersion medium, the solvent-substituted oxidized cellulose is treated with a mixer (Osaka Chemical, Absolute Mill, 14,000 rpm) for 1 hour to obtain a solid concentration of 0.2. % Cellulose nanofiber dispersion was obtained. The obtained dispersion had a light transmittance of 94% at 660 nm. Moreover, the fiber width of the cellulose fiber at this time was 5 nm.

(Examples 2, 3, 4, 5, 6)
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that the alkali species used in the counter ion substitution step was changed. The types of organic onium compounds are shown in Table 1. (However, abbreviations indicate the following compounds: TEAH: tetraethylammonium hydroxide, TPAH: tetrapropylammonium hydroxide, TBAH: tetrabutylammonium hydroxide, TBPH: tetrabutylphosphonium hydroxide)

(Examples 7 and 8)
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that the organic solvent used in the solvent substitution step and the dispersion step was changed. The types of organic solvents are shown in Table 1.

Example 9
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that the solvent replacement step was not performed and the dispersion medium in the dispersion step was changed to water.

(Comparative Example 1)
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that raw material cellulose not subjected to an oxidation step was used.

(Comparative Example 2)
In the same manner as in Example 1, the carboxylic acid salt was washed only with water without being converted into carboxylic acid using an acid in the oxidation step, and the organic solvent used in the solvent replacement step and the dispersion step was changed to water. Prepared a cellulose nanofiber dispersion under the same conditions.

(Comparative Example 3)
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that the acid was used in the oxidation step and the carboxylic acid salt was washed only with water without being converted into carboxylic acid.

(Comparative Example 4)
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that the counter ion substitution step was not performed.

(Comparative Example 5)
In the same manner as in Example 8, a cellulose nanofiber dispersion was prepared under the same conditions except that the counter ion substitution step was not performed.

(Comparative Example 6)
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that the counter ion substitution step and the solvent substitution step were not performed.

(Comparative Example 7)
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that sodium hydroxide (NaOH) was used as an alkali species in the counter ion substitution step.

(Comparative Example 8)
In the same manner as in Example 1, a cellulose nanofiber dispersion was prepared under the same conditions except that the solvent replacement step was not performed.

[Evaluation]
The evaluation result was shown in Table 2 and Table 3 about Examples 1-9 and Comparative Examples 1-8.

[Amount of carboxyl group]
The amount of carboxyl groups contained in the oxidized cellulose obtained in the oxidation step was calculated by the following method. 0.2 g of dry weight conversion of cellulose that has undergone the oxidation step is placed in a beaker, and 80 ml of ion exchange water is added. Thereto was added 5 ml of a 0.01 M sodium chloride aqueous solution, and 0.1 M hydrochloric acid was added while stirring to adjust the whole to pH 2.5. Here, 0.1M sodium hydroxide aqueous solution was injected at 0.05 ml / 30 seconds using an automatic titrator (AUT-701, manufactured by Toa DKK Co.), and the conductivity and pH value were measured every 30 seconds. Measurement was continued until. From the obtained conductivity curve, the titration amount of sodium hydroxide was determined, and the carboxyl group content was calculated.

[Light transmittance]
About the cellulose nanofiber dispersion obtained through the dispersion process, the light transmittance was measured using a UV-vis spectrophotometer (manufactured by Shimadzu Corporation, UV3600). A cellulose nanofiber dispersion liquid prepared in advance to a solid content concentration of 0.2% was filled in a 10 mm square quartz cell so that no bubbles would enter, and the light transmittance at 660 nm was determined. The measurement results are shown in Table 2.

[Contact angle measurement]
Using the cellulose nanofiber dispersion obtained through the dispersion step, coating was performed on a PET substrate using a bar coater and heated at 40 ° C. for 1 hour to form a coating film having a thickness of about 0.1 μm. The contact angle of the coating film was measured using a contact angle meter (PCA-1 manufactured by Kyowa Interface Science Co., Ltd.). In addition, pure water was used as the evaluation liquid, and the wettability of the droplets adhering to the coating film surface was evaluated. The measurement results are shown in Table 3.

[Tensile strength measurement]
The cellulose nanofiber dispersion obtained through the dispersion process was spread on a glass substrate and dried at 60 ° C. for 4 days to form a 10 μm thick free-standing film. This self-supporting film was cut into a strip shape having a width of 5 mm and a length of 50 mm, and the temperature was 40 ° C., the relative humidity was 30%, and the temperature was 40 ° C. using a tensile tester with a constant temperature and humidity chamber (TE-7001, manufactured by Tester Sangyo Co., Ltd.). Tensile strength was measured in an environment with a relative humidity of 90%. The measurement results are shown in Table 4.

  As shown in Table 2, Examples 1 to 8 were able to prepare cellulose nanofiber dispersions having high light transmittance using an organic solvent as a dispersion medium. On the other hand, in the comparative example, when water was used as a dispersion medium, high transparency was obtained, but dispersibility in an organic solvent was low. This indicates that the dispersibility in organic solvents is improved by sufficiently substituting the carboxyl groups introduced into the cellulose in the oxidation step with organic onium ions and then substituting with organic solvents. It was done.

As shown in Table 3, in the examples, the coating film formed from the cellulose nanofiber dispersion in which the carboxyl group introduced into the cellulose in the oxidation step is counter-substituted with organic onium ions exhibits a high contact angle. It was shown that. This is due to the hydrophobicity of the hydrocarbon group contained in the organic onium ion, and by not containing water in the dispersion, it was possible to significantly reduce the water bound to the cellulose during the film formation process. It is thought to be derived from that. In addition, it was shown that the hydrophobicity and contact angle can be designed by selecting various types of alkali species and dispersion media of counter ions.
In addition, Example 9 in Table 3 is a reference example.

  As shown in Table 4, in Examples 1 and 9, the self-supporting membrane formed from the cellulose nanofiber dispersion in which the carboxyl group introduced into the cellulose was counterion-substituted with the organic onium ions, the humidity deterioration was suppressed in the tensile strength. Rukoto has been shown. This is considered to be due to the fact that the cellulose-bound water that forms the self-supporting membrane could be reduced, as described in Table 3.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  According to the present invention, the cellulose modified product and the cellulose nanofiber dispersion can maintain a dispersed state in a state where water is excluded as described above. Furthermore, it has excellent affinity with an organic solvent and can exist as cellulose nanofibers that are homogeneous in the organic solvent. This makes it possible to form a more homogeneous composite with a highly hydrophobic substance such as a resin, thereby greatly expanding the industrial application range of cellulose. In addition, by combining with organic onium ions, application to structures and the like utilizing the original antibacterial action and catalytic action of organic onium compounds using cellulose as a binder becomes possible.

Claims (5)

An oxidation step of introducing carboxyl groups by oxidizing cellulose;
A counter ion substitution step of substituting the organic ion with the organic ion for the cellulose having a carboxyl group obtained in the oxidation step using an organic onium compound;
A solvent substitution step of solvent substitution of the cellulose obtained in the counter ion substitution step with an organic solvent, a dispersion step of dispersing the cellulose obtained in the solvent substitution step in a dispersion medium,
Hints, Ri 80ε der below dielectric constant of more than 15ε at 25 ° C. of the dispersion medium,
In the dispersing step, cellulose and cellulose modifications introduced with carboxyl groups, method for producing a cellulose nanofiber dispersion, characterized in Rukoto be prepared cellulose nanofibers.   2. The method for producing a cellulose nanofiber dispersion according to claim 1, wherein in the oxidation step, the cellulose is recovered using the carboxyl group introduced in the oxidation treatment as a carboxylic acid using an acid.   3. The method for producing a cellulose nanofiber dispersion according to claim 1, wherein the solvent used in the solvent substitution step includes a solvent used as the dispersion medium. An oxidation step of introducing a carboxyl group by oxidizing cellulose, a counter ion substitution step of substituting a counter ion with an organic onium ion for the cellulose having a carboxyl group obtained in the oxidation step using an organic onium compound, a solvent substitution step of solvent replacement by cellulose organic solvent obtained in counterion exchange step, the cellulose obtained by the solvent substitution step, Ri 80ε der below dielectric constant of more than 15ε at 25 ° C., in the dispersing step , cellulose and cellulose modifications introduced with carboxyl groups, a film using the cellulose nanofibers dispersion treated with a dispersing step of dispersing treatment with a dispersion medium that will be prepared on cellulose nanofibers,
The content of the carboxyl group is not more than the dry weight per 0.1mmol more 3.0mmol of cellulose nanofibers, cellulose nanofiber dispersion contact angle containing organic onium ion is at 85 ° to the carboxyl group as a counterion The membrane used. The film | membrane using the cellulose nanofiber dispersion of Claim 4 whose tensile strength in 40 degreeC90RH is 110 Mpa or more .