JP2019094482A - Composition containing cellulose nanofibers and halloysite nanotubes, and film and composite containing the same - Google Patents

Abstract

To provide a novel material which gives a film having good mechanical properties and is suitable as a reinforcement for wood found in the unearthed ruins.SOLUTION: Provided is a composition containing cellulose nanofibers and halloysite nanotubes.SELECTED DRAWING: None

Description

  FIELD [0001] The present invention relates to compositions comprising cellulose nanofibers and halloysite nanotubes.

[0002] Halloysite nanotubes are abundant and inexpensive nanoscale natural materials. In the past, halloysite nanotubes have been used as fillers for synthetic polymer composites.
[0003] On the other hand, with regard to cultural properties, preservation of the excavated items of waterlogged archaeological wood is an important issue for both restoration engineers and scientists. Methods to preserve them generally avoid shrinkage and deformation of the wood by removing water into wood vacancies which may constitute as much as 70-90% of the volume Including filling with reinforcements such as polymers to be added.

  [0004] Because halloysite nanotubes are natural materials, they can provide so-called environmentally friendly materials that are effective in reducing environmental impact. However, since halloysite nanotubes are rigid solid particles, their utility is limited. Thus, it is an object of the present invention to provide novel materials comprising halloysite nanotubes that are suitable for various applications.

  [0005] We have found that the combination of cellulose nanofibers and halloysite nanotubes solves this problem.

Film tensile measurement results SEM image of CM-CNF / HNT Optical image on CM-CNF / HNT Photograph of wood sample before and after drying

The present invention makes it possible to provide novel materials comprising halloysite nanotubes that are suitable for various applications.
[0007] The present invention is described in detail below. In the present invention, “A to B” means a range including both A and B.

[0008] 1. Compositions The compositions of the present invention include halloysite nanotubes (also referred to as "HNTs") and cellulose nanofibers (also referred to as "CNFs").
[0009] (1) Halloysite nanotube (HNT)
HNT is an aluminosilicate having a hollow tubular structure and is represented by the formula: Al ₂ Si ₂ O ₅ (OH) ₄ .2H ₂ O. The internal diameter of HNT is usually about 10 to 150 nm, and the length of HNT is usually 0.1 to 15 μm, preferably 0.1 to 1 μm.

[0010] (2) Cellulose nanofibers (CNF)
Cellulose nanofibers refer to fine fibers having an average fiber width of about 4 to 500 nm and an average aspect ratio of 100 or more. In the present invention, these are preferably those obtained by disintegrating an anion-modified cellulose such as carboxylated cellulose (also called oxidized cellulose), carboxymethylated cellulose, cellulose ester group-containing cellulose and the like. . Thus, in the present invention, the cellulose nanofibers are preferably anion-modified cellulose nanofibers (anion-modified CNF). Furthermore, since the inner pore of HNT is positively charged, anion modified CNF can penetrate into the inner pore, thereby improving the affinity between HNT and anion modified CNF.

  [0011] Examples of cellulose raw materials for producing CNF include vegetable materials such as wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp, softwood bleached kraft pulp Hardwood unbleached kraft pulp, hardwood bleached kraft pulp, softwood unbleached sulfite pulp, softwood bleached subsulfite pulp, thermomechanical pulp (TMP), regenerated pulp, used paper, etc., animal material (such as Hoya net), algae And microorganisms (eg, acetic acid bacteria (Acetobacter)), products derived from microbial production products, etc., and any of these can be used. Cellulose fibers derived from plants or microorganisms, more preferably cellulose fibers derived from plants are preferably used.

(I) Carboxymethylation When carboxymethylated cellulose is used as anion-modified cellulose in the present invention, carboxymethylated cellulose is obtained by carboxymethylating any of the above-mentioned cellulose raw materials by a known method. It can be obtained or commercially available. In any case, the degree of carboxymethyl substitution on the cellulose is preferably 0.01 to 0.50 per anhydroglucose unit. An example of the method for producing such carboxymethylated cellulose is as follows. As a starting material, cellulose is used in a solvent composed of water or a lower alcohol in an amount of 3 to 20 times the weight of the starting material. Specifically, examples of the solvent include water, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutanol, tert-butanol and the like alone or a mixture of two or more of them. When a solvent mixture containing lower alcohol is used, the proportion of lower alcohol is 60 to 95% by weight. A mercerizing agent composed of an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide and the like, is used in an amount of 0.5 to 20 molar equivalents per anhydrous glucose unit of the base stock. The bottoming raw material, the solvent, and the mercerizing agent are mixed, and treated with a reaction temperature of 0 to 70 ° C., preferably 10 to 60 ° C., for a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Process. The carboxymethylating agent is then added in an amount of 0.05 to 10.0 molar equivalents per glucose unit, preferably for 30 minutes to 10 hours, at a reaction temperature of 30 to 90 ° C., preferably 40 to 80 ° C. Performs the etherification reaction for a reaction time of 1 to 4 hours.

  [0013] "Carboxymethylated cellulose" used to produce anionally modified CNF refers to those that at least partially retain their fibrous form, even when dispersed in water. Thus, it is distinguished from conventional carboxymethylcellulose, which is a type of water soluble polymer. The aqueous dispersion of "carboxymethylated cellulose" can be analyzed by electron microscopy to observe fibrous material. However, no fibrous material is observed in the aqueous dispersion of carboxymethylcellulose, which is a kind of water-soluble polymer. Furthermore, in "carboxymethylated cellulose", the crystal structure of cellulose type I can be observed by X-ray diffraction, but in carboxymethylcellulose used as a water-soluble polymer, the crystal structure of cellulose type I can not be seen.

(Ii) Carboxylation When carboxylated (oxidized) cellulose is used as the anion-modified cellulose in the present invention, the carboxylated cellulose (also referred to as oxidized cellulose) can be carboxylated by any known cellulose raw material (known as oxidized cellulose) It can be obtained by oxidation). During carboxylation, the content of carboxyl groups is preferably 0.6 to 2.0 mmol / g, more preferably 1.0 mmol / g to 2.0 mmol / g based on the dry weight of the anion-modified cellulose nanofibers. Adjust to g (but not particularly limited thereto).

[0015] An example of the carboxylation (oxidation) method is the presence of a compound selected from the group consisting of N-oxyl compounds, bromides, iodides, or mixtures thereof in water using an oxidizing agent as the cellulose raw material Including oxidizing below. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of cellulose is selectively oxidized to form an aldehyde group and a carboxyl group (-COOH) or a carboxylate group (-COO) on the surface. ^-) can provide cellulosic fibers having. During the reaction, the concentration of cellulose is not particularly limited, but is preferably 5% by weight or less.

  [0016] "N-oxyl compound" refers to a compound capable of generating a nitroxyl radical. Any N-oxyl compound can be used as long as they promote the desired oxidation reaction. For example, these include 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivatives (eg 4-hydroxy-TEMPO).

  [0017] The amount of N-oxyl compound used is not particularly limited as long as it is a catalytic amount sufficient to oxidize the cellulose used as a raw material. For example, it is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and still more preferably 0.05 to 0.5 mmol per gram of dead-dry cellulose. Also, it is preferably about 0.1 to 4 mmol / L to the reaction system.

  [0018] "Bromide" refers to a compound containing bromine, examples of which include alkali metal bromides that can be ionized by dissociation in water. Similarly, "iodide" refers to a compound that contains iodine, examples of which include alkali metal iodides. The amount of bromide or iodide used can be selected within the range capable of promoting the oxidation reaction. The total amount of bromide and iodide is preferably, for example, 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, still more preferably 0.5 to 5 mmol, per 1 g of dry-dried cellulose.

  [0019] Any of the known oxidizing agents can be used including, for example, halogen, hypohalous acid, halogenous acid, perhalic acids, or salts thereof, halogen oxides, peracids, and the like. Among them, sodium hypochlorite is preferable because it is inexpensive and has less influence on the environment. The suitable amount of the oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, most preferably 3 to 10 mmol, per 1 g of dead-dried cellulose. This is also preferably, for example, 1 to 40 mol per mol of the N-oxyl compound.

  [0020] During the process of cellulose oxidation, the reaction proceeds efficiently even under relatively mild conditions. Thus, the reaction temperature is preferably 4 to 40 ° C, or may be room temperature of about 15 to 30 ° C. As the reaction proceeds, the pH of the reaction solution decreases because carboxyl groups are formed in the cellulose. In order to ensure that the oxidation reaction proceeds efficiently, an alkaline solution such as aqueous sodium hydroxide is preferably added to maintain the pH of the reaction solution at 8-12, preferably 10-11. The reaction medium is preferably water, for reasons such as easy handling, low possibility of side reactions and the like.

  [0021] The reaction time in the oxidation reaction can be appropriately selected usually in 0.5 to 6 hours, for example, 0.5 to 4 hours, depending on the extent to which the oxidation proceeds.

  [0022] Furthermore, the oxidation reaction can be performed in two stages. For example, the oxidized cellulose obtained by filtration after the end of the first stage reaction can be reoxidized under the same or different reaction conditions, whereby the reaction is carried out with sodium chloride formed as a by-product during the first stage reaction. Efficient oxidation can be achieved while preventing

[0023] Another example of a carboxylation (oxidation) process involves contacting a cellulose source with an ozone containing gas. By this oxidation reaction, at least the 2- and 6-position hydroxyl groups of the glucopyranose ring can be oxidized to cleave the cellulose chain. The ozone concentration in the ozone-containing gas is preferably 50 to 250 g / m ³ , more preferably 50 to 220 g / m ³ . The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by weight, more preferably 5 to 30 parts by weight, per 100 parts by weight of the solid content of the cellulose raw material. The ozone treatment temperature is preferably 0 to 50 ° C, more preferably 20 to 50 ° C. The ozone treatment time is not particularly limited, but is 1 to 360 minutes, preferably 30 to 360 minutes. When the ozone treatment conditions are within these ranges, it is possible to prevent excessive oxidation and cleavage of cellulose, and oxidized cellulose can be obtained in a good yield. After the ozone treatment, post-oxidation using an oxidant can be performed. The oxidizing agent used for the post-oxidation is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite; oxygen, hydrogen peroxide, persulfuric acid, peracetic acid and the like. For example, post-oxidation may be performed by dissolving one of these oxidizing agents in a polar organic solvent such as water or alcohol to form a solution of the oxidizing agent and immersing the cellulose raw material in this solution it can.
[0024] The carboxyl group content of oxidized cellulose can be adjusted by controlling reaction conditions such as the amount of oxidizing agent added, the reaction time, etc. described above.

(Iii) Pulverization [0025] Examples of devices that can be used to fibrillate anion-modified cellulose include high-speed rotation type, colloid mill type, high pressure type, roll mill type, and ultrasonic type. It is not particularly limited to these. During defibration, high shear is preferably applied to the aqueous dispersion of anionically modified cellulose. For particularly efficient disintegration, a wet high pressure or ultra high pressure homogenizer is preferably used which can apply a pressure of 50 MPa or more and high shear to the aqueous dispersion. The pressure is more preferably 100 MPa or more, still more preferably 140 MPa or more. If desired, pretreat the aqueous dispersion by using known mixing, stirring, emulsifying, or dispersing equipment, such as a high speed shear mixer, prior to the disintegration and dispersion process in the high pressure homogenizer. Can.

(3) Compositional Ratio In the composition, the quantitative ratio of CNF: HNT is preferably 1: 0.1 to 1:25, more preferably 1: 1 to 1:10. If the amount of HNT is less than this lower limit, the mechanical properties of the film produced by the composition may be degraded. If the amount of HNT is higher than this upper limit, the flexibility of the film produced by the composition may be reduced. The composition can include a liquid medium. In this case, the composition is in the form of a slurry or dispersion. Media include water and water soluble organic solvents such as alcohols. In consideration of the stability of the composition, the composition preferably comprises water. In compositions comprising a liquid medium, the amount of solid component is preferably 1 to 10% by weight, more preferably 1 to 5% by weight.

(4) Additives The composition may contain conventional additives. Additives include surface conditioners such as acetylene glycol and silicon compounds, and water soluble polymers such as carboxymethyl cellulose. The surface conditioner improves leveling and defoaming properties. Water soluble polymers improve the stability of the composition.

(5) Production of Composition The method of producing the composition is not limited. However, the composition is preferably prepared by mixing CNF and HNT in the liquid medium described above. The mixing is carried out using conventional equipment. Devices include, but are not limited to, mixers, agitators, and homogenizers. The temperature for mixing is not limited but is preferably in the range of 20 to 50 ° C.

(6) Applications The present composition is used as a material for a film or a coating. For such applications, compositions in the form of a slurry or dispersion are used. Furthermore, the composition is used for reinforcing porous materials such as wood or polymer foams, in particular for excavated timber. For this application, compositions in the form of a slurry or dispersion are used as reinforcements. The concentration of HNT in the slurry or dispersion is preferably 2% by weight or less.

[0030] 3. Film The film produced by the present composition usually has a thickness of 0.1 to 500 μm, preferably 0.5 to 100 μm. The film can be produced by known methods such as casting. The films of the invention have good mechanical properties.

[0031] 4. Composites In the present invention, the term "composite" means composite materials. The composite of the present invention comprises a porous material and the composition of the present invention, wherein the composition is contained within the pores of the material. Porous materials include, but are not limited to, wood and polymer foams such as plastic foams and thermosetting foams. The composition contained in the pores improves the mechanical properties of the composite and the dimensional stability of the composite during storage or drying. The composite is produced by immersing the porous material in a slurry or dispersion of the composition.

[0032] (1) Preparation of CNF Preparation of Carboxymethylated CNF (CM-CNF):
200 g of pulp manufactured by Nippon Paper Industries Co., Ltd. (softwood bleached kraft pulp) on a dry weight basis and 111 g of sodium hydroxide on a dry weight basis were added to a stirring apparatus capable of mixing pulp, and the pulp was 20% An amount of water was added to have a solids content of w / v). The mixture is then stirred for 30 minutes at 30 ° C. and then 216 g (based on active weight) of sodium monochloroacetate are added. The mixture was stirred for 30 minutes, then warmed to 70 ° C. and stirred for 1 hour. The reaction mixture was then removed, neutralized and washed to obtain carboxymethylated pulp. The degree of carboxymethyl substitution was 0.25 per glucose unit. Next, the carboxymethylated pulp was adjusted to a solid content of 1% with water, and disintegrated by 5 cycles of treatment with a high pressure homogenizer at 20 ° C. and 150 MPa to obtain carboxymethylated cellulose fibers. The resulting fibers had an average fiber diameter of 50 nm and an aspect ratio of 120.

[0033] Method of measuring degree of carboxymethyl substitution About 2.0 g of carboxymethylated cellulose (absolutely dry) was precisely weighed and placed in a 300 mL stoppered Erlenmeyer flask. 100 mL of a solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol nitrate was added, and shaken for 3 hours to convert carboxymethylcellulose salt (carboxymethylated cellulose) into H-type carboxymethylated cellulose. The H-type carboxymethylated cellulose (absolute drying) was precisely weighed in 1.5 to 2.0 g and placed in a 300 mL stoppered Erlenmeyer flask. The H-type carboxymethylated cellulose was wetted with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added, and shaken at room temperature for 3 hours. The excess NaOH was back titrated with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator. The degree of carboxymethyl substitution (DS) was calculated by the following equation.
A = [(100 × F ′ − (0.1 N H ₂ SO ₄ ) (mL) × F) × 0.1] / (absolute dry weight of hydrogen-substituted CM cellulose (g))
DS = 0.162 × A / (1−0.058 × A)
A: Amount (mL) of 1N-NaOH necessary to neutralize 1 g of hydrogen-substituted CM cellulose
F ': Factor of 0.1 N H ₂ SO ₄ F: Factor of 0.1 N NaOH

[0034] Method of measuring average fiber diameter and aspect ratio: 200 fibers of anion-modified CNF randomly selected using a field emission scanning electron microscope (FE-SEM), their average fiber diameter and average fiber length It analyzed about. It should be noted that the aspect ratio was calculated by the following equation.
Aspect ratio = average fiber length / average fiber diameter
[0035] Production of Carboxylated CNF (TM-CNF)

  To 500 mL of an aqueous solution of 780 mg TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide dissolved therein, 500 g (absolutely dry) of unbeaten softwood bleached kraft pulp (whiteness = 85%) is added and the pulp is The mixture was stirred until it was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system in an amount of 6.0 mmol / g to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, and 3 M aqueous sodium hydroxide solution was sequentially added to adjust the reaction system to pH 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system showed no change. After reaction, the mixture was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to give oxidized pulp (carboxylated cellulose). The yield of pulp was 90%, the time required for the oxidation reaction was 90 minutes, and the carboxyl group content was 1.6 mmol / g.

  [0036] The oxidized pulp obtained by the process described above is adjusted to 1.0% (w / v) with water, treated with an ultrahigh pressure homogenizer (20 ° C, 150MPa) for 3 cycles to obtain anion-modified cellulose nano A fiber dispersion was obtained. The resulting fibers had an average fiber diameter of 40 nm and an aspect ratio of 150.

[0037] Measurement Method of Carboxyl Group Content 60 mL of a 0.5 wt% slurry (aqueous dispersion) of carboxylated cellulose is prepared, adjusted to pH 2.5 by adding 0.1 M aqueous hydrochloric acid, and then pH 0.05N aqueous sodium hydroxide solution is added dropwise while measuring the conductivity until the reaches 11 and during the neutralization phase of the weak acid characterized by a slow change in the conductivity according to the following equation The carboxyl group content was calculated from the amount (a) of sodium hydroxide consumed.
Carboxyl group content [mmol / g-carboxylated cellulose] = a [mL] x 0.05 / weight of carboxylated cellulose [g]

(2) Measurement Scanning Electron Microscope The morphology of the composite material was observed using a microscope ESEM-FEI-QUANTA 200F. Prior to each experiment, the surface of the sample was evaporated in gold using an Edwards sputter coater S150A in argon to prevent charging under the electron beam. A minimum electron dose condition was set (10 kV) to prevent sample damage.

Dynamic Viscoelasticity Measurement Dynamic Viscoelasticity Measurement to Control Relative Humidity (RH) During Experiment Using DMA-Q800 Device (manufactured by TA Instruments) equipped with a Relative Humidity (DMA-RH) Accessory The mechanical properties were determined. For all mechanical measurements, the sample was a rectangular (6.00 × 4.00 × 0.06 mm ³ ) film, while the temperature was set to 25.0 ± 0.5 ° C. Tensile tests were conducted using the ideal "tensile clamp" for films, fibers, and low modulus materials. The stress increase at ¹ MPa · m ⁻¹ and RH = 40%. The values of modulus of elasticity, tensile strength (specified as tensile stress at the time of material rupture), and elongation at break were determined. Each film is measured 5 times and the average value is reported.
For wood samples, a "three-point bend clamp" was used. The sample was supported at both ends and a force was applied in the middle, taking into account the most basic deformation mode.

Contact Angle Measurement Contact angles were studied using an optical contact angle device (OCA 20, Data Physics Instruments) equipped with a video measurement system with a high resolution CCD camera and a high performance digitizing adapter. SCA 20 software (Data Physics Instruments) was used for data acquisition. The film was fixed on a flat solid support and held flat during analysis. The contact angle of water in air was measured by the drop method, by gently placing 6 ± 0.5 μL drops on the surface of the film. The temperature was set to 25.0 ± 0.1 ° C. for the support and was similar for the injection syringe. Images were collected 25 times per second for up to 60 seconds starting from droplet placement. A minimum of 5 droplets were examined for each film sample.

[0041] (3) Composition and Film Example 1
Water, CNF, and HNT (from Applied Minerals, Inc. or Imerys Ceramics) were mixed by a mixer at 25 ° C. to obtain the composition of the aqueous dispersion shown in Table 1. Then, the Z potential of the composition was measured using a zeta potential measurement device (ZETASIZER NAMO ZS, manufactured by Malvern Instruments). As shown in Table 1, the absolute value of the Z potential of the composition is higher than that of TM-CNF, CM-CNF, and HNT. An aqueous dispersion of the composition of the invention was found to be stable.

[0042]

Example 2
Composition No. 1 in the form of an aqueous dispersion described in Table 1 A film was produced using 2. The composition was cast onto a substrate to form a wet film, and then the wet film was dried in an oven at a temperature of 80 ° C. or less.
[0044] The dried film was separated and subjected to water contact angle measurement. The curve of contact angle (θ) vs time (t) was successfully fitted by using the following equation:

Where θ _i is the contact angle at t = 0,

Is a measure of the process rate, n is a fractional value due to absorption and broadening contributions, n = 0 and 1 for pure absorption and pure broadening, respectively. The film was uniform and, as shown in Table 2, both sides showed comparable values for the water contact angle and dynamic parameters for water spread / absorption.

[0045]

Example 3
In the same manner as Example 2, films containing CM-CNF and HNT in different weight ratios shown in Table 3 were produced. Film tensile measurements were made and the results reported in Table 3. The results clearly show that it is possible to obtain materials with interesting mechanical performance. Furthermore, as shown in Table 4 and FIG. 1, the humidity played a strong plasticizing effect. That is, under high humidity conditions, the film becomes very plastic and deformable.

[0047]

[0048]

  [0049] Film No. Scanning electron microscope observation was performed on B. The film was very uniform, as shown in FIG. The optical image for this film is reported in FIG.

Example 4
Excavated timber was prepared from the Chretienne C vessel (2nd century BC) found on the coast of Provence. The wood sample in this experiment was severely degraded and had a porosity of about 80%. Furthermore, 100 parts by weight of water, 0.2 parts by weight of CM-CNF, and 2 parts by weight of HNT were mixed by a mixer to prepare a composition in the form of an aqueous dispersion. This dispersion was used as a reinforcing material.
[0051] Wood impregnation was performed in a single step (multiple treatments were not required) by immersing the wet wood in the reinforcement and holding it for 48 hours. After impregnation, the samples were dried at 25 ° C.

Comparative Example 1
The unearthed excavated site wood was dried at 25 ° C.
Comparative Examples 2 and 3
Samples were prepared in the same manner as Example 4 except that different reinforcements described in Table 4 were used instead of those in Example 4.

  [0054] As shown in FIG. 4, it is apparent that the untreated excavated timber samples caused large bending due to drying, while the samples treated with the CNF / HNT composition significantly reduced the deformation of the wood. Met. Furthermore, as shown in FIG. 4, the mechanical properties of the sample were improved by treatment with the CNF / HNT composition. Furthermore, rapid impregnation (1-2 hours or less) was not sufficient for this treatment.

Claims (4)

  Composition comprising cellulose nanofibers and halloysite nanotubes.   The composition according to claim 1, wherein the cellulose nanofibers are anion-modified cellulose nanofibers.   A film formed by the composition of claim 1.   A composite comprising a porous material and the composition according to claim 1, wherein the composition is contained within the pores of the material.