WO2019138588A1 - Cellulose nanofiber, sheet-like material obtained therefrom, and method for producing cellulose nanofiber and sheet-like material - Google Patents

Abstract

The present invention provides: a cellulose nanofiber enabling the provision of a high-performance sheet-like material; a method for producing the cellulose nanofiber; and a sheet-like material obtained from the cellulose nanofiber. A bamboo-derived cellulose nanofiber having a cellulose purity of at least 90%, a fiber diameter of 10-20 nm, and a crystallinity of at least 70% can be obtained by a method comprising: (1) a step for subjecting a bamboo material to an alkali treatment and a mechanical treatment to prepare bamboo fibers; (2) a step for delignificating the obtained bamboo fibers; (3) a step for mechanically spreading the delignificated bamboo fibers; (4) a step for removing hemicellulose from the spread bamboo fibers; and (5) a step for removing metal components from the bamboo fibers from which hemicellulose has been removed. A high strength sheet material having a tensile strength of 7-200 N for a basis weight of 10-210 g/m² or a high strength sheet material having a tensile strength of 7-200 N for a density of 0.3-1.1 g/cm³ can be obtained by making this cellulose nanofiber into a sheet.

Description

Cellulose nanofibers, sheet-like material comprising the same, and method for producing them

The present invention relates to cellulose nanofibers, more specifically to cellulose nanofibers obtained from bamboo as a raw material, sheet-like materials comprising the same, and methods for producing them. The invention also relates to the nanofibers obtained by said process, which also contain some amount of lignin, also known as "lignocellulose nanofibers".

In recent years, plant-based cellulose nanofibers have attracted attention in a wide range of fields such as plastic reinforcements, solar cells, and medicine, and in particular to sheet-like materials produced from them. It has increased.

Conventionally, softwood pulp has been mainly used as a raw material of cellulose nanofibers. In recent years, in addition to softwood, manufacture of cellulose nanofibers using bamboo as a raw material is also performed.

For example, Patent Document 1 discloses a composite material obtained from bamboo-derived cellulose nanofibers and having high tensile strength and tensile modulus and excellent conductivity, and a method for producing the same.

Patent Document 2 describes a cellulose nanofiber having a diameter of about 50 nm and a method for producing the same, and bamboo is mentioned as a cellulose material together with various plant materials.

Patent Document 3 describes a method of producing fine fibrous cellulose, and as a cellulose raw material, bamboo is also mentioned together with various plant raw materials.

Methods of producing cellulose nanofibers include mechanical and chemical methods. When cellulose nanofibers are produced by mechanical loosening using softwood or bamboo as a raw material, the degree of crystallinity tends to be low. Industrial products made of bamboo are provided, for example, by Chuetsu Pulp Industry Co., Ltd., and their manufacture is carried out by a mechanical solution method.

The known cellulose nanofibers have a purity of at most about 87%, a cellulose crystallinity of at most about 66%, and an aspect ratio of at most about 100. In order to obtain a higher performance sheet-like material, improvement of the properties of cellulose nanofibers is required.

JP, 2017-115069, A Patent No. 5910504 JP 2012-012713 A

An object of the present invention is to provide a cellulose nanofiber capable of providing a sheet material having higher performance, a method of producing the same, and a sheet material obtained from the cellulose nanofiber, in view of the above-mentioned current situation. . Another object of the present invention is to provide nanofibers which are obtained by the above-mentioned production method and which contain some amount of lignin and which are also known as "lignocellulose nanofibers".

In the process of studying cellulose nanofibers that use bamboo as a raw material instead of softwood pulp, the inventors have used both a relatively mild mechanical loosening method (using a mixer) and a multi-step chemical unraveling method. As a result, the present inventors have found that cellulose nanofibers having a cellulose purity of 90% or more, a fiber diameter of about 10 to 20 nm, and a crystallinity of 70% or more can be obtained, thereby completing the present invention.

Specifically, the bamboo-derived cellulose nanofiber according to the present invention is characterized by having a cellulose purity of 90% or more, a fiber diameter of 10 to 20 nm, and a crystallinity of 70% or more.

The bamboo-derived cellulose nanofiber according to the present invention can be obtained by a production method characterized by including the following steps (1) to (5).
(1) A step of producing bamboo fiber by subjecting bamboo to alkali treatment and mechanical treatment (2) Step of delignifying the obtained bamboo fiber (3) mechanically unraveling bamboo fiber subjected to delignification treatment Process (4) Process of removing hemicellulose from unfolded bamboo fiber (5) Process of removing metal component from bamboo fiber after hemicellulose removal

The sheet-like material comprising bamboo-derived cellulose nanofibers according to the present invention is characterized by exhibiting a tensile strength of 7 to 200 N at a basis weight of 10 to 210 g / cm ² . It is also characterized in that it exhibits a tensile strength of 7 to 200 N for a density of 0.3 to 1.1 g / cm ³ .

The sheet-like material comprising bamboo-derived cellulose nanofibers according to the present invention can be obtained by the production method of sheet-forming bamboo-derived cellulose nanofibers according to the present invention.

Sheeting can be performed by a method of removing the dispersion medium from the suspension of cellulose nanofibers. Natural drying, hot pressing, or lyophilization can be mentioned as an example of the method of removing the dispersion medium. As the dispersion medium, water and an organic solvent can be used, and an alcohol can be mentioned as an example of the organic solvent.

In the case of hot pressing, preferably
(A) preparing a suspension of bamboo-derived cellulose nanofibers dispersed in water;
(B) removing water from the suspension to recover the residue;
(C) subjecting the recovered residue to hot pressing to obtain a sheet-like material,
The cellulose nanofibers can be sheeted by

The cellulose nanofibers may be recovered from the suspension (a), and another suspension obtained by dispersing the recovered cellulose nanofibers in alcohol may be hot-pressed to obtain a sheet-like material.

In the case of lyophilization, preferably
(A) preparing a suspension of cellulose nanofibers dispersed in alcohol,
(B) spreading the suspension on a substrate to form a film;
(C) subjecting the film-like suspension to a freeze-drying treatment to obtain a sheet-like material,
The cellulose nanofibers can be sheeted by

The lignocellulosic nanofibers derived from bamboo according to the present invention have a lignin content of about 1 to 2 wt%, and the delignification treatment in the step (2) of the method for producing cellulose nanofibers derived from bamboo described above is It is obtained by stopping when lignin content is obtained.

According to the present invention, it becomes possible to improve the performance of bamboo-derived cellulose nanofibers, and it is also possible to use a high-strength sheet material made from it. Thereby, application to those new applications can be expected. Furthermore, bamboo-derived lignocellulose nanofibers according to the present invention are more useful composite materials than composite materials using high purity cellulose nanofibers whose lignin content is further reduced by mixing with a resin (for example, automobile It can be expected that it can be used as a composite material for applications and home appliances.

It is a graph which shows content and extraction rate of lignin of bamboo fiber with respect to the processing time with peracetic acid. It is a graph which shows the content and extraction rate of the hemicellulose of bamboo fiber after peracetic acid treatment to processing time. It is a graph which shows the relationship between KOH aqueous solution concentration and the content and extraction rate of hemicellulose of bamboo fiber. It is a graph which shows the relationship between the amount of KOH aqueous solution, the content of hemicellulose of bamboo fiber, and the extraction rate. It is a graph which shows the relationship between the processing temperature of hemicellulose removal, hemicellulose content, and an extraction rate. It is a figure which shows the FE-SEM observation result of the bamboo fiber before a delignification process, Comprising: (a) is a FE-SEM image, (b) is a graph which shows fiber distribution. It is a figure which shows the FE-SEM observation result of the bamboo fiber 1 hour after delignification process, Comprising: (a) is a FE-SEM image, (b) is a graph which shows fiber distribution. It is a figure which shows the FE-SEM observation result of the bamboo fiber 3 hours after a delignification process, Comprising: (a) is a FE-SEM image, (b) is a graph which shows fiber distribution. It is a figure which shows the FE-SEM observation result of the bamboo fiber 6 hours after delignification process, Comprising: (a) is a FE-SEM image, (b) is a graph which shows fiber distribution. It is a figure which shows the FE-SEM observation result of the bamboo fiber 8 hours after delignification process, Comprising: (a) is a FE-SEM image, (b) is a graph which shows fiber distribution. It is a figure which shows the FE-SEM observation result of the bamboo fiber after hemicellulose removal, Comprising: (a) is a FE-SEM image, (b) is a graph which shows fiber distribution. 1 is an FT-IR spectrum of a cellulose nanofiber sheet according to the present invention. It is a figure which shows the electron microscope observation result of the cellulose nanofiber sheet which made dispersion medium water by hot press, and (a) is a TEM image, (b) shows a FE-SEM image with the external appearance photograph of a sheet. ing. It is a figure which shows the electron microscope observation result of the cellulose nanofiber sheet which made the dispersion medium ethanol by hot press, and (a) is a TEM image, (b) shows a FE-SEM image with the external appearance photograph of a sheet. ing. It is a figure which shows the electron microscope observation result of the cellulose nanofiber sheet | seat produced by freeze-drying, Comprising: (a) is a TEM image, (b) shows the FE-SEM image with the external appearance photograph of a sheet. It is a XRD pattern of one sample of a cellulose nanofiber sheet according to the present invention. It is a XRD pattern of another sample of the cellulose nanofiber sheet according to the present invention. It is a XRD pattern of another sample of the cellulose nanofiber sheet according to the present invention. It is a gas adsorption-desorption isotherm of the cellulose nanofiber sheet by this invention. It is a graph which shows pore diameter distribution of the cellulose nanofiber sheet by this invention which used dispersion medium as water and was hot-pressed. It is a graph which shows pore diameter distribution of the cellulose nanofiber sheet by this invention which made dispersion medium ethanol by hot press. It is a graph which shows the pore size distribution of the cellulose nanofiber sheet by this invention produced by freeze-drying. It is a graph which shows the tensile strength with respect to the mass of the cellulose nanofiber sheet by this invention which made dispersion medium water by hot press, and shows them with those of a comparison sheet. It is a graph which shows the tensile strength with respect to the thickness of the cellulose nanofiber sheet by this invention which used dispersion medium as water and was hot-pressed and with those of a comparison sheet. It is a graph which shows the tensile strength with respect to the density of the cellulose nanofiber sheet by this invention which used dispersion medium as water and was hot-pressed and with those of a comparison sheet. It is a graph which shows the tensile strength with respect to the basis weight of the cellulose nanofiber sheet by this invention which made dispersion medium water by hot press, and shows them with those of a comparison sheet. It is a figure explaining the fiber in the cellulose nanofiber sheet by this invention, Comprising: (a) is a FE-SEM image, (b) is a graph which shows fiber distribution. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the fiber in the sheet | seat produced by Celish (trademark), Comprising: (a) is a FE-SEM image, (b) is a graph which shows fiber distribution.

In order to obtain a sheet-like material composed of bamboo-derived cellulose nanofibers, it is necessary to produce bamboo-derived cellulose nanofibers as the raw material. According to the present invention, by using a combination of a relatively mild mechanical unwinding method (using a mixer) and a multi-step chemical unwinding method, cellulose nanofiber production exhibiting improved properties over the prior art can do.

Specifically, the method for producing bamboo-derived cellulose nanofibers according to the present invention includes the following steps (1) to (5).
(1) A step of producing bamboo fiber by subjecting bamboo to alkali treatment and mechanical treatment (2) Step of delignifying the obtained bamboo fiber (3) mechanically unraveling bamboo fiber subjected to delignification treatment Process (4) Process of removing hemicellulose from unfolded bamboo fiber (5) Process of removing metal component from bamboo fiber after hemicellulose removal

In the bamboo fiber production step (1), bamboo fibers are produced from bamboo using alkali treatment and mechanical treatment.

The bamboo material used in the present invention is not particularly limited, and for example, a plant containing so-called bamboo fibers such as jinso bamboo, bamboo bamboo, black bamboo, bamboo bamboo and the like can be used.

In order to improve the effect of the alkali treatment and the purity of the obtained fiber, it is preferable to remove the inner and outer shells of bamboo in advance. More preferably, in order to make the diameter of the produced fiber uniform, inner and outer skin removal is performed such that only the portion where the fiber bundle of bamboo material used is uniform remains.

Also, it is preferable that the bamboo material be loosened by pressure rolling (squeezing treatment) with, for example, a pinch roll having a peripheral speed difference in advance, prior to the subsequent treatment with an aqueous alkaline solution. This makes it possible to increase the penetration rate of the alkaline aqueous solution and to make the penetration uniform, thereby enhancing the separation and removal efficiency of lignin and hemicellulose in the subsequent alkali treatment. For this purpose, it is also possible, for example, to use a treatment using a hydraulic press or a treatment using rollers.

In addition, when the bamboo material is dried during the treatment using an alkaline aqueous solution, the treatment effect is reduced, so the bamboo material may be stored in a liquid without being dried until the start of the treatment, or it may be stored frozen or refrigerated Is preferred. More preferably, in order to suppress the growth of various bacteria, it is immersed in an effective liquid such as an aqueous solution of hydrogen peroxide, perchloric acid, sulfuric acid and the like, and kept refrigerated. It is most preferable to use hydrogen peroxide in terms of safety and waste.

The bamboo material to which the alkali treatment is applied is appropriately cut and used according to the volume of the treatment container. In order to increase the treatment efficiency, in the present invention, it is preferable to use, for example, a bamboo material cut into chips of about 1 to 10 cm in length.

The alkali treatment can be performed, for example, by immersing bamboo in an aqueous alkaline solution such as sodium hydroxide, sodium hydrogencarbonate or potassium hydroxide. When an aqueous solution of sodium hydroxide is used, the concentration of the aqueous solution is preferably 0.01 to 1.00 M, more preferably 0.10 to 1.00 M, and still more preferably 0.10 to 0.50 M, from the viewpoint of efficiency. . The treatment temperature is preferably 30 to 200 ° C., more preferably 50 to 150 ° C., and still more preferably 100 to 150 ° C. The processing pressure is preferably 101 to 500 kPa, and preferably 101 to 200 kPa. The treatment time is preferably 1 to 3 hours, more preferably 3 hours. The alkali-treated bamboo pieces are removed from the aqueous alkali solution and washed with water. Washing with water continues until the water after washing becomes neutral.

The pieces of bamboo are then processed mechanically in order to obtain bamboo fibres. This process can be performed using a common mixer and stirring bamboo pieces with water at room temperature. The type of mixer used is not particularly limited as long as bamboo pieces can be disassembled into fibers. Further, the processing conditions may be appropriately set so as to obtain a predetermined processing effect. After treatment, it is dried to obtain bamboo fiber.

The delignification treatment step (2) can be carried out by bringing the bamboo fiber obtained in the step (1) into contact with the delignification treatment solution. As the delignification treatment solution, a solution of peracetic acid, chlorous acid, sodium sulfite, sulfuric acid, ozone, enzymes, microorganisms (bacteria) and the like can be used. Bamboo fibers are dispersed in a delignification treatment solution and allowed to stand, and then separated from the treatment solution, followed by washing and drying to obtain a bamboo fiber subjected to delignification treatment. The delignification treatment solution can be carried out, for example, at a temperature of about room temperature to about 220 ° C., preferably about 60 to 100 ° C. The standing time is preferably 1 to 8 hours, more preferably 1 to 6 hours, and still more preferably 3 to 6 hours.

The lignin extraction rate increases as the treatment time increases. For example, when peracetic acid (acetic acid: hydrogen peroxide volume ratio = 1: 1) is used and the standing temperature is 80 ° C., the extraction rate reaches 100% after 6 hours of treatment, and a white fiber is obtained. . In this case, little hemicellulose was extracted. The diameter of bamboo fiber became thinner as the treatment time became longer, and the treatment with 6 hours gave fibers with an average diameter of about 16 nm.

The bamboo-derived lignocellulose nanofibers according to the present invention having a lignin content of about 1 to 2 wt% have the lignin content of the bamboo fibers in the delignification treatment solution in this delignification treatment step (2) It is obtained by stopping when the amount is obtained. The standing here may be, for example, about 0.5 to 2 hours, or about 0.5 to 1.5 hours when left at 80 ° C. using peracetic acid as described above. Except for the standing time in step (2), the bamboo-derived lignocellulose nanofibers of the present invention can be produced by the same method as the production of bamboo-derived cellulose nanofibers of the present invention.

For example, when peracetic acid is used as a processing solution, cleavage of the aromatic ring of lignin occurs as shown below, and it is thought that lignin is removed from bamboo fiber (Keiyama, Heisei, Paper-Papers Technical Journal, Volume 20) , No. 11, p. 15 (1966)).

The mechanical loosening step (3) of the delignified bamboo fiber can be performed by stirring the bamboo fiber with water with a mixer. The type of mixer is not particularly limited as long as unwinding by stirring is performed without any problem. From the viewpoint of treatment efficiency, the amount of water is preferably about 10 to 1000 times, more preferably about 100 to 500 times, and still more preferably about 100 to 150 times the mass of bamboo fiber. The stirring treatment is preferably performed at a temperature of about 5 to 60 ° C., and more preferably about 5 to 40 ° C. The operating conditions of the mixer may be set appropriately so as to obtain a predetermined unwinding effect.

The step (4) of removing hemicellulose from the unfolded bamboo fiber can be carried out by alkali treatment of the unfolded bamboo fiber. The alkali treatment can be carried out by immersing the unfolded bamboo fiber in an aqueous alkali solution. As the aqueous alkali solution, an aqueous solution of potassium hydroxide can be used, and in addition, an aqueous sodium hydroxide solution or the like can also be used. In the case of using an aqueous potassium hydroxide solution, an aqueous solution of about 0.5 to 5.0 M, preferably about 1.0 to 2.0 M of KOH aqueous solution is used in an amount of about 50 to 500 ml, preferably 200 It can be used up to about 500 ml. The immersion can be performed at about 20 to 100 ° C. The immersion time is preferably 1 to 24 hours, more preferably 1 to 12 hours, and still more preferably 1 to 8 hours.

The step (5) of removing metal components from bamboo fiber after hemicellulose removal can be carried out by acid treatment of bamboo fiber from which hemicellulose has been removed. The acid treatment can be carried out by bringing bamboo fiber into contact with an acid solution and shaking for a predetermined time. As the acid solution, an aqueous solution of hydrochloric acid, perchloric acid, sulfuric acid, nitric acid or the like can be used. For example, when using an aqueous solution of hydrochloric acid, the concentration of the solution is preferably about 0.001 to 1.0 M, more preferably 0.01 to 1.0 M, and still more preferably 0.01 to 0.1 M. The contact time is preferably 1 to 24 hours, more preferably 3 to 24 hours, still more preferably 1 to 12 hours. This treatment can be carried out at room temperature (about 20 to 30 ° C.).

The amount of lignin in bamboo fiber can be measured, for example, by the sulfuric acid method (Japanese Wood Research Society, Wood Science Experiment Manual, pp. 96-97, Bun-ei-do (2010)) (see Examples described later).

The hemicellulose content of bamboo fiber can be measured based on the mass of bamboo fiber before and after hemicellulose removal (see Examples described later).

The characteristics of bamboo-derived cellulose nanofibers produced by the method of the present invention are that the cellulose purity is 90% or more, the fiber diameter is 10 to 20 nm, and the crystallinity is 70% or more. The cellulose purity and crystallinity of the cellulose nanofibers of the present invention are much higher than those of conventional cellulose nanofibers (about 87% at the maximum) and crystallinity (about 66% at the maximum).

The sheet-like material according to the present invention can be obtained by forming the bamboo-derived cellulose nanofibers according to the present invention into a sheet. Sheeting can be performed, for example, using a hot press or using lyophilization. It is also possible to use natural drying.

Sheeting by hot pressing can be preferably performed using a suspension obtained by stirring a liquid to be treated to which cellulose nanofibers after removal of metal components are added to water. Water remaining in the dispersion medium is removed from the suspension, and the recovered residue is processed with a hot press into a sheet without drying, and a sheet-like material comprising cellulose nanofibers according to the present invention can be obtained.

The residue obtained by removing the water from the suspension may be re-dispersed in a dispersion medium of an alcohol such as ethanol. When the dispersion medium is water, aggregation of the fibers is observed in the obtained sheet-like material, while when the dispersion medium is alcohol, disintegration of the fibers occurs by alcohol solvation between the cellulose molecules. Is recognized.

Sheeting by lyophilization can be preferably performed using a suspension containing an organic solvent (for example, alcohol) as a dispersion medium. The suspension can be spread on a predetermined substrate to form a film, frozen, and subjected to a freeze-drying treatment to obtain a sheet-like material comprising cellulose nanofibers according to the present invention. When the dispersion medium is alcohol, ethanol, butanol or the like can be used. As the organic solvent other than alcohol, ketones (eg, acetone), aromatic compounds (eg, toluene), carboxylic acids (eg, acetic acid), amines (eg, N, N-dimethylformamide), acetonitrile and the like can be used. Coagulation of the fibers is suppressed by sublimation of the dispersion medium (such as alcohol) by lyophilization. As the dispersion medium, only one type (for example, ethanol) may be used, or a mixture of two or more types may be used, or two or more types may be sequentially used (for example, after temporarily recovering bamboo fiber from a suspension of ethanol) , Making a sheet-like material from a suspension in which it is redispersed in butanol). The latter case is advantageous in suppressing aggregation of the cellulose nanofibers.

Regardless of the means of sheeting, stirring to obtain the suspension can be carried out, for example, using a common mixer or by means of ultrasound. The content of cellulose nanofibers in the suspension may generally be 0.1 to 10 wt%, more preferably 0.1 to 2.0 wt%, and still more preferably 0.1 to 1.0 wt%. The stirring conditions are not particularly limited as long as a suspension in which the cellulose nanofibers are sufficiently dispersed can be obtained. Any treatment such as filtration can be used to remove the dispersion medium water or alcohol.

When natural drying is used, it can be carried out by dispersing bamboo-derived cellulose nanofibers and spreading it on a substrate to allow a film-like suspension to stand and remove the dispersion medium. The dispersion medium may be water or an organic solvent such as alcohol. In some cases, the removal of the dispersion medium can be promoted by ventilation or the like.

The sheet-like material produced from the bamboo-derived cellulose nanofiber according to the present invention exhibits improved strength when measured under the same conditions as compared to the sheet-like material produced from conventional cellulose nanofibers. Cellulose for example, when comparing the tensile strength for the basis weight of 200 g / m ² (mass per sheet material 1 m ^2), tensile strength of the sheet material according to the present invention whereas about 200 N, were obtained from Daicel Finechem Corporation The tensile strengths of the sheet material produced from the fiber FD100G and the commercial paper obtained from Mondi (ISO 9707-obtained paper) are about 100 N and 145 N, respectively.

The sheet-like material made of bamboo-derived cellulose nanofibers according to the present invention exhibiting such high tensile strength can be expected to be used in the fields of reinforcement, acoustics, medicine, food, packaging materials, transportation and the like.

The invention will now be further described by way of examples. Needless to say, the present invention is not limited to the following examples.

1. Preparation of Nanometer-Sized Bamboo Fiber The endothelium and the shell were removed and squeezed, and 120 g of bamboo chips which had been chipped to a length of about 10 cm were placed in an electric pressure cooker (Panasonic, SR-P37-N), and 2 L of 0. It was immersed in a 10 M aqueous solution of sodium hydroxide and treated at 120 ° C. and 200 kPa for 3 hours. The treated bamboo pieces were allowed to cool, transferred to a metal sieve, and washed with ultrapure water until the water after washing became neutral, to obtain bamboo fibers. 60 g of the obtained fibers were placed in a mixer (VitamixTM ABS-BU), 1 L of ultrapure water was added, and the mixture was stirred at 37,000 rpm for 1 minute. Thereafter, the ultrapure water was discarded and dried to obtain bamboo fiber.

2. Delignification treatment A 17.5 M acetic acid solution was added to a 300 ml glass Erlenmeyer flask, to which a 11.6 M aqueous hydrogen peroxide solution was gradually dropped with a separatory funnel to prepare 100 ml of a peracetic acid solution. The volume ratio of acetic acid to hydrogen peroxide was 1: 1.

After adding about 1 g of bamboo fiber obtained from the above 1 to a container containing 100 mL of peracetic acid solution while stirring with a glass rod, the temperature of the water bath (EYELA, SB-350) is 80 ^The vessel was set in a low-temperature water bath (EYELA, NCB-1200) set at ^o C, and allowed to stand for 1, 3, 6 or 8 hours while refluxing. Thereafter, it was allowed to cool, and suction filtration was performed using a plastic filter (ADVANTEC, KP-47H and KP-47S). The residue was washed with ultrapure water until neutral and then dried for 12 hours with a drier maintained at 60 ^° C. to obtain a delignified bamboo fiber.

At 1 hour of treatment in peracetic acid, the fibers turned from brown to yellow and became pale yellow after 3 hours of treatment. The treatment was continued for 6 hours to obtain white bamboo fiber. This is considered to correspond to the removal of lignin which is a coloring component as the peracetic acid treatment time passes. No change was observed after 6 hours of treatment.

3. Clarification Add delignified bamboo fiber to ultra pure water so that its concentration becomes 0.7 wt%, and stir for 5 minutes at 37,000 rpm using a mixer (VitamixTM ABS-BU) did. The mixture was then allowed to cool and stirred intermittently for a total of 60 minutes to obtain a thawed bamboo fiber suspension.

4. Determination of lignin In a 100 mL glass beaker, add 15 mL of 13.4 M sulfuric acid and 1 g of the product obtained from the above 2 (delignified bamboo fiber) and stir until the fibers uniformly impregnate the fibers with a glass rod did. After standing for 4 hours, it was boiled for 4 hours under reflux and allowed to cool. Thereafter, the residue was collected by suction filtration using a glass filter (Shibata Scientific Co., Ltd., 1 GP 16), washed with 500 mL of hot water, and dried with a drier maintained at 105 ^° C. for 12 hours. After drying, the yield was weighed to the fourth decimal place, and the content of lignin was determined using the following equation (1) (see Japan Wood Research Society, Wood Science Experiment Manual, p. 97, Bun-eidou Publishing (2010)).
Lignin content (wt%) = (mass after experiment / mass before experiment) x 100 (1)

The content of lignin and the extraction ratio with respect to the treatment time with peracetic acid are shown in Table 1, and the graph is shown in FIG. The longer the peracetic acid treatment time, the higher the extraction rate, and the total amount of lignin was extracted in 6 hours.

When it is intended to obtain nanofibers with some residual lignin known as so-called "lignocellulose nanofibers", bamboo fibers (containing about 1 wt% residual lignin) obtained after about 1 hour of treatment However, the process can be continued according to the procedure described below.

5. Determination of hemicellulose According to the reference, β-cellulose and γ-cellulose and hemicellulose are classified as hemicellulose, and others are classified as α-cellulose (Japan Wood Research Society, Wood Science Experiment Manual, pp. 95, Bungeidou Press (2010) )reference). In the present invention, according to that, hemicellulose was measured using a method for quantifying α-cellulose (see Japan Wood Research Society, Wood Science Experiment Manual, pp 96-97, Bun-ei-do (2010)). Thus, the hemicellulose here also includes beta and gamma cellulose.

In a 200 mL plastic beaker, 25 mL of a 5.80 M aqueous sodium hydroxide solution and 1 g of the product obtained from 2 above (delignified bamboo fiber) were added. The fiber was uniformly impregnated with the liquid, allowed to stand for 4 minutes, then stirred using a plastic stir bar for 5 minutes, and then allowed to stand for 30 minutes. Ultrapure water was further added to the beaker, stirred for 1 minute, and allowed to stand for 5 minutes. After that, suction filtration was performed using a glass filter (Shibata Scientific Co., Ltd., 1 GP 250), and the filtrate was recovered and refiltered, and then the residue was washed with ultrapure water until the filtrate became neutral. The residue and 40 mL of 1.75 M aqueous acetic acid solution were placed in a 100 mL glass beaker and allowed to stand for 5 minutes. The residue was collected by suction filtration and washed with 1 L of ultrapure water. Thereafter, the residue was dried in a dryer maintained at 105 ° C. for 12 hours, weighed to the fourth decimal place, and the hemicellulose content was determined using the following equation (2) (The Japan Wood Research Society, Wood Science Experiment Manual) , Pp. 96, Bungeidou Publishing (2010)).
Hemicellulose content (wt%) =
((Pre-experiment mass-(α-cellulose mass)) / pre-experiment mass) × 100 (2)

The hemicellulose content and extraction rate of bamboo fiber after peracetic acid treatment are shown in Table 2, and the graph is shown in FIG. The peracetic acid treatment did not significantly reduce the hemicellulose content. In addition, there was no significant difference depending on the processing time.

6. Removal and quantification of hemicellulose 5 g of bamboo fiber that has been subjected to delignification treatment and cracking treatment with peracetic acid for 6 hours is put in a 200 mL glass Erlenmeyer flask, and 200 mL of 0.71 or 1.18 M aqueous potassium hydroxide solution is added. The fibers were uniformly impregnated with the solution. After tightly sealing and leaving at room temperature for 12 hours, suction filtration is performed using a plastic filter (ADVANTEC, KP-47H and KP-47S), and the residue is washed with ultrapure water until the washing solution becomes neutral. Was washed. After that, the residue was dried for 12 hours with a dryer maintained at 60 ° C., and the content of hemicellulose was measured using the same procedure and formula as in 5 above. The results are shown in Table 3, and the relationship between the treatment solution concentration and the content of hemicellulose and the extraction rate is shown in FIG. In the case of 1.18 M, it turned out that about 7% of hemicellulose is contained. The α-cellulose content is about 93%.

Therefore, in order to clarify the relationship between the volume and the extraction rate at the time of potassium hydroxide treatment, the concentration of KOH aqueous solution is fixed at 1.18 M, and the amount of solution is changed to 100 or 200 mL. 4 and the relationship between the solution amount and the hemicellulose content and extraction rate is shown in FIG. From these results, it was found that in this example, the largest amount of hemicellulose was extracted when 200 mL of 1.18 M KOH aqueous solution was used for 5 g of bamboo fiber.

Next, the relationship between the treatment temperature and the hemicellulose content and the extraction rate is examined, and the quantitative results are shown in Table 5 and FIG. When the KOH aqueous solution concentration was 1.18 M and the amount of solution for 5 g of bamboo fiber was 200 mL, more hemicellulose was extracted when treated at room temperature than 100 ^° C. In the case of a processing temperature of 100 ° C., bamboo fiber and a KOH aqueous solution were added to a Teflon (registered trademark) container, and the container was further put in a heat-resistant stainless steel container and sealed. The temperature of the dryer was set to 100 ^° C. and allowed to stand for 12 hours. After leaving to cool, suction filtration, washing with water and drying were performed as described above.

7. Determination of β-cellulose The α-cellulose content in the product treated under the most appropriate conditions is around 93%. In order to determine the correct amount of β-cellulose in the product, 200 mL of the washing solution obtained in the above 5 is added to 10 mL of a 30% aqueous acetic acid solution, heated to 80 ° C., and kept warm for 9 hours I left it. The obtained precipitate was collected by a filter paper which was weighed in advance, and the mass increase after drying was taken as the β-cellulose content (The Japan Wood Research Society, Wood Science Experiment Manual, pp 96, Bun Eido Press (2010) reference).

From the results described in the third and fourth rows from the top of Table 6, it was found that 97% of hemicelluloses measured by the method described in the above 5 is β-cellulose. It was confirmed that the cellulose content is 99.8% when added to the α-cellulose content.

8. Morphological observation with a field emission scanning electron microscope 1 mL of ethanol was added to 1 drop of the suspension of bamboo fiber (before delignification) obtained in the above 1 and ultrasonically dispersed. 10 μL of the suspension after ultrasonic dispersion was dropped on glassy carbon and dried in a dryer maintained at 60 ° C. Thereafter, platinum is deposited on dried bamboo fiber using a vapor deposition apparatus (JEOL, JFC-1600), and the form of bamboo fiber is measured with a field emission scanning electron microscope (FE-SEM (JEOL, JSM-6701F)) I observed it. The deposition conditions are shown in Table 7 and the measurement conditions are shown in Table 8. Moreover, the same observation was performed about the bamboo fiber which gave the delignification process demonstrated by said 2 for 1, 3, 6, 8 hours. Each observation result is shown in FIGS. 6 (a) to 10 (a) (FE-SEM image) and FIGS. 6 (b) to 10 (b) (fiber distribution map), respectively.

When observed at high magnification using FE-SEM, short fibers (not shown) having a diameter of about 16 μm confirmed by light microscopy of bamboo fibers before delignification are intertwined with fibers having a wide diameter, into bundles. It became clear that it became (Fig. 6 (a) and (b)). The longer the delignification time, the smaller the fiber diameter tended to be. The particulate matter seen in the FE-SEM image is vapor-deposited platinum.

The fiber diameter was 15.9 nm on average after 8 hours. Generally, since the diameter of cellulose nanofibers contained in wood and the like is several nm, the diameter is slightly larger than that. The reason for this is that it is essential for the observation material to be completely dried in the observation by FE-SEM, which may be due to the association by the hydrogen bond between the cellulose molecules at the time of the drying.

Next, the same observation by FE-SEM was performed on bamboo fiber from which hemicellulose was also removed in addition to removal of lignin (bamboo fiber treated with 1.18 M potassium hydroxide aqueous solution in 6 above). The results are shown in FIG. 11 (a) (FE-SEM image) and FIG. 11 (b) (fiber distribution map). Even in the fibers in which removal of hemicellulose was attempted, a part of the bundle remained, but the average fiber diameter is smaller, and it is thought that there is a relationship between the hemicellulose extraction and the diameter of the produced cellulose nanofibers.

9. Qualitative analysis by Fourier transform infrared spectroscopy Bamboo fiber after peracetic acid treatment (delignification treatment) for 1, 3, 6 and 8 hours, and bamboo fiber which has been subjected to further hemicellulose removal after peracetic acid treatment for 8 hours The mixture was placed in Vitamix (trademark) ABS-BU, added with ultrapure water, and stirred for 60 minutes. Thereafter, a bamboo fiber sheet obtained by suction filtration using a plastic filter (ADVANTEC, KP-47H and KP-47S) and dried by a dryer maintained at 60 ^° C. is provided with a diffuse reflection unit The FT-IR spectrum was measured in the range of 4000 to 550 cm ^-1 with a Fourier transform infrared spectrometer (FT-IR (Thermo Fisher SCIENTIFIC, ART iD5)). The results are shown in FIG.

Peracetic acid treatment (delignification) before the raw material bamboo (not shown) FT-IR spectra of the fiber CO expansion and contraction of 1760 cm ^-1 attributable to the confirmed lignins, C = C stretching of the aromatic ring of 1500 cm ^-1 , CO antisymmetric stretching methoxy groups of 1250 cm ^-1, the peak of the CH stretching of the aromatic ring of 840 cm ^-1 is not observed, OH stretching of 3600 ~ 3000 cm ^-1 attributed to the cellulose and hemicellulose, CH of 2920 cm ^-1 The peak of expansion and contraction was confirmed.

10. Removal of metal component and qualitative and quantitative analysis of metal by ICP emission spectral analysis The bamboo fiber (bamboo fiber from which lignin was removed) obtained from the above 2 was brought into contact with a hydrochloric acid aqueous solution to remove the metal component. In a plastic sample tube, 1 g of bamboo fiber and 50 mL of a 0.01 M hydrochloric acid aqueous solution were placed. From the sample tube, the solution was immediately removed leaving bamboo fiber to obtain a "pre-treatment" solution. After adding 50 mL of a new hydrochloric acid aqueous solution to the sample tube and continuing shaking for 24 hours, the solution was taken out immediately, leaving bamboo fibers, to obtain a “post-treatment” solution. Each solution was placed in a glass 10 mL screw test tube and treated with a centrifuge (As One, C-12B) to precipitate solid components, and the supernatant solution was withdrawn. The supernatant solution was analyzed by inductively coupled plasma emission spectrometry (ICP-OES (Agilent Technologies, 710 ICP-OES)) to characterize and quantify the metals contained in bamboo fiber. The results are shown in Table 9.

It is known that bamboo is mainly rich in silica (silicon oxide), calcium, potassium, magnesium and sodium as an inorganic substance. The bamboo fiber according to the present invention analyzed here was confirmed to contain potassium and zinc, but other than these, it was a very small amount close to 0%. According to the present invention, it was revealed that metals can be removed by immersing them in hydrochloric acid for 24 hours, and the content can be reduced to about 0.06% with respect to the mass of the obtained cellulose nanofibers.

11. Preparation of Cellulose Nanofiber Sheet Using Hot Press 3.5 g of bamboo fiber reacted with a peracetic acid solution for 6 hours according to the procedure described in 2 above, 500 mL of ultrapure water so that the fiber content is 0.7 wt% And stirred for 5 minutes at 37,000 rpm using a mixer (VitamixTM ABS-BU), allowed to cool, and then intermittently stirred for a total of 60 minutes to obtain a suspension. The resulting suspension is suction filtered using a glass filter (ADVANTEC, KG-47) and then dried, using a small heat press (AS ONE, AH-2003) at 120 ^{° C.} It pressed by C and produced the sheet. In addition, after the suspension obtained as described above was filtered, the residue was added to 100 mL of ethanol, ultrasonically dispersed, and suction filtered. After repeating this twice, a sheet was produced in the same manner using a small heat press.

12. Preparation of Cellulose Nanofiber Sheet Using Lyophilization The suspension obtained in 11 above was filtered, added to 50 mL of ethanol, ultrasonically dispersed, and suction filtered. After repeating this twice, the residue was added to 50 mL of t-butyl alcohol and ultrasonically dispersed. This was also repeated twice, and after filtration, the residue was transferred to a petri dish, frozen in a freezer (Panasonic, NR-B175W), and dried using a freeze vacuum dryer (Hitachi, ES-2030) to produce a sheet . The drying conditions are shown in Table 10. Moreover, in order to compare the form, a suspension of water was frozen in a freezer as it was, and a freeze-dried sheet was also produced.

13. Morphology observation of sheet by field emission scanning electron microscope and transmission electron microscope The morphology of the obtained cellulose nanofiber sheet was observed by a field emission scanning electron microscope (FE-SEM). The measurement conditions are shown in Table 11. Before the observation, platinum was deposited on the sheet using a deposition apparatus (JFC-1600, JEOL Ltd.). The deposition conditions are shown in Table 12.

The prepared sheet is ultrasonically dispersed in 1-butanol, dropped onto a grid for TEM (Sek 150, STEM 150 Cu grid), dried in a dryer at 100 ° C., and then the sheet form is transmitted. Observation was performed with an electron microscope (TEM (JEOL, JEM-2100).

A TEM image of a cellulose nanofiber sheet prepared by hot pressing using water as a dispersion medium is shown in FIG. 13 (a), an appearance photograph and an FE-SEM image are shown in FIG. 13 (b). Those of the sheets are shown in FIGS. 14 (a) and 14 (b).

When the dispersion medium is water, it is confirmed that fibers are aggregated, which is considered to be due to strong hydrogen bonding between cellulose molecules. When the dispersion medium was changed to ethanol, it was confirmed that the fibers were slightly dispersed, which is considered to be because ethanol entered between cellulose molecules and was disintegrated by solvation.

The TEM image of the cellulose nanofiber sheet produced by lyophilization is shown in FIG. 15 (a), the appearance photograph and the FE-SEM image are shown in FIG. 15 (b). Compared with the sheet (Figs. 13 (a) and (b) and Figs. 14 (a) and 14 (b)) produced by hot pressing by freeze-drying, it is confirmed that the fibers are not aggregated but disintegrated. It was done. This is considered to be because aggregation of the fibers was suppressed by sublimating the dispersion medium t-butyl alcohol directly from the solid state into a gas without passing through the liquid by lyophilization.

14. Evaluation of the crystallinity of the sheet by XRD The crystallinity of the obtained cellulose nanofiber sheet was evaluated using an X-ray diffractometer (XRD (Rigaku-Denki, RINT-Ultima III)). The measurement conditions are shown in Table 13.

Further, the crystallinity of the cellulose, in 20 ° from the intensity _{(I A)} and 2 [Theta] = 10 ° from baseline drawn by 80 ° from the 2 [Theta] = 10 ° 10-1 diffraction lines cellulose 2 [Theta] = 15 ^o The intensity from the subtracted baseline (I _B ) was calculated using equation (3).
Crystallinity = (I _A / I _B ) x 100 (3)

The XRD patterns of three samples of cellulose nanofiber sheet obtained from three samples are shown in FIGS. In both samples, 10-1 and 002 diffraction lines of cellulose were confirmed at 2θ = 15 ° and 22.5 °. In addition, the crystallinity of cellulose calculated from these peak intensities is shown in Table 14. The degree of crystallinity was 71 to 77% regardless of the dispersion medium.

15. Measurement of Surface Area by Gas Adsorption / Desorption Measurement The BET surface area of the obtained cellulose nanofiber sheet was measured by using a nitrogen gas adsorption / desorption device (AUTOSARB-3, manufactured by Yuasa Ionics Co., Ltd.). An adsorption / desorption isotherm was obtained by adsorbing nitrogen (purity 99.9%) at 77 K to the sheet in the cell and measuring the adsorption amount and the pressure in the cell. The BET surface area was calculated by analyzing the obtained adsorption and desorption isotherm by the BET method. In addition, the sample was deaerated by applying a vacuum at 200 ^° C. for 24 hours before measurement. The measured gas adsorption / desorption isotherm is shown in FIG. 19, and its BET surface area is shown in Table 15.

In the case of a sheet produced by hot pressing using ethanol as the dispersion medium, the surface area became larger than when the dispersion medium was made into water because the disintegration of the fibers proceeded. In the sheet produced by lyophilization, fiber aggregation was prevented as compared to the sheet produced by hot pressing, and thus a larger surface area was obtained.

In addition, the pore size distribution of the sheet is shown in FIG. 20 (sheet produced by hot press using dispersion medium as water), FIG. 21 (sheet produced by hot press using dispersion medium as ethanol), and FIG. Sheet).

16. Measurement of Strength by Tensile Test The dispersion medium was water, and the tensile strength of a cellulose nanofiber sheet produced using a hot press was measured. Cut the prepared sheet into a strip 1.5 cm wide and 2.5 cm long, grasp the top and bottom about 5 mm, and use a bench-type precision universal testing machine (SHIMADZU, AGS-J) at a tension speed of 1 mm / min. Measurements were taken. In addition, as a comparison, a sheet formed by using a hot press from cellulose nanofibers for food (Celish (trademark)) manufactured by Daicel Finechem Co., Ltd. and a commercially available paper manufactured by Mondi (ISO 9707 acquired paper, residual amount of low lignin) are the same. It measured.

The maximum intensity for the mass of each sample in Figure 23, the maximum intensity on the thickness in FIG. 24, FIG. 25 the maximum intensity for the density shows the maximum intensity for basis weight (mass per 1 m ²⁾ in FIG. 26. It was confirmed that the strength was also improved as the mass, thickness, density and basis weight were increased in any of the samples.

In addition, among the three sheets tested, the bamboo-derived cellulose nanofiber sheet according to the present invention showed the largest strength. This is thought to be because the bamboo-derived cellulose nanofibers according to the present invention are thinner than other fibers, so the amount of fibers per mass is large and the points at which hydrogen bonds between fibers are increased, thereby increasing the strength. Be For example, an FE-SEM image and a fiber diameter distribution obtained from a sheet of bamboo-derived cellulose nanofiber according to the present invention and a sheet made of Celish (trademark), which is similarly a cellulose nanofiber (FIG. 28) (a) and (b)), it can be confirmed that the fiber of the former is thinner.

Claims (19)

1. A bamboo-derived cellulose nanofiber characterized in that the cellulose purity is 90% or more, the fiber diameter is 10 to 20 nm, and the crystallinity is 70% or more.
2. A suspension in which the bamboo-derived cellulose nanofibers according to claim 1 are dispersed in water.
3. A suspension in which the bamboo-derived cellulose nanofibers according to claim 1 are dispersed in an organic solvent.
4. A method for producing bamboo-derived cellulose nanofibers, comprising the following steps (1) to (5):
   (1) A step of producing bamboo fiber by subjecting bamboo to alkali treatment and mechanical treatment (2) Step of delignifying the obtained bamboo fiber (3) mechanically unraveling bamboo fiber subjected to delignification treatment Process (4) Process of removing hemicellulose from unfolded bamboo fiber (5) Process of removing metal component from bamboo fiber after hemicellulose removal
5. The method according to claim 4, wherein the inner and outer shells are removed to make a chipped bamboo material.
6. The method according to claim 5, wherein the length of the chimney bamboo is 1 to 10 cm.
7. The method according to any one of claims 4 to 6, wherein the alkali treatment of bamboo is carried out using sodium hydroxide.
8. The method according to any one of claims 4 to 7, wherein the mechanical treatment of bamboo is performed using a mixer.
9. 9. The bamboo fiber delignification process is carried out using a solution of at least one of peracetic acid, chlorous acid, sodium sulfite, sulfuric acid, ozone, an enzyme and a microorganism (bacteria). The method described in.
10. The method according to any one of claims 4 to 9, wherein the hemicellulose removal is carried out using an aqueous solution of potassium hydroxide.
11. The method according to any one of claims 4 to 10, wherein the removal of the metal component is performed using an acid solution.
12. The method according to claim 11, wherein a hydrochloric acid solution is used as the acid solution.
13. A sheet material comprising bamboo-derived cellulose nanofibers, which exhibits a tensile strength of 7 to 200 N at a basis weight of 10 to 210 g / m ² .
14. A sheet material comprising bamboo-derived cellulose nanofibers, which exhibits a tensile strength of 7 to 200 N at a density of 0.3 to 1.1 g / cm ³ .
15. A method for producing a sheet-like material comprising bamboo-derived cellulose nanofibers, characterized in that the bamboo-derived cellulose nanofibers obtained by the method according to any one of claims 4 to 12 are sheeted.
16. Sheeting,
    (A) preparing a suspension of bamboo-derived cellulose nanofibers dispersed in water;
    (B) removing water from the suspension to recover the residue;
    (C) subjecting the recovered residue to hot pressing to obtain a sheet-like material,
    The method according to claim 15, wherein the method is performed by
17. The sheet formation is performed by recovering cellulose nanofibers from the suspension of the above (a) and subjecting the recovered cellulose nanofibers to another suspension obtained by dispersing in alcohol a hot press treatment. the method of.
18. Sheeting,
    (A) preparing a suspension of cellulose nanofibers dispersed in alcohol,
    (B) spreading the suspension on a substrate to form a film;
    (C) subjecting the film-like suspension to a freeze-drying treatment to obtain a sheet-like material,
    The method according to claim 15, which is performed by
19. A bamboo-derived lignocellulose nanofiber produced by the method according to any one of claims 4 to 12, characterized in that the lignin content is 1 to 2 wt%.

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