JP7452081B2 - Method for producing cellulose nanofiber-containing carbonate ester dispersion and cellulose nanofiber-containing polyurethane - Google Patents

Description

The present invention relates to a method for producing a carbonate ester dispersion containing cellulose nanofibers. The present invention also relates to a method for producing cellulose nanofiber-containing polycarbonate diol and cellulose nanofiber-containing polyurethane using a cellulose nanofiber-containing carbonate dispersion.

Polyurethane is widely used in fields such as highly durable artificial leather and synthetic leather, adhesives, paints, coatings, films, and optical materials.
In particular, when polycarbonate diol (hereinafter referred to as PCD) is used as a raw material for polyurethane, a highly durable polyurethane with excellent hydrolysis resistance and chemical resistance can be obtained compared to polyester diol and polyether diol. It has been known.

In addition, when PCD is used for leather, paint, and coating applications, in addition to the above properties, it has excellent heat and humidity resistance, abrasion resistance, and weather resistance, so it can be used as an interior material for automobiles, such as artificial leather for seats, synthetic leather, etc. It is used as a raw material for leather and exterior paints. Furthermore, in adhesive applications, it is used in automobiles, electronic equipment, electrical equipment, etc. as an adhesive with excellent durability and flexibility.

However, since carbonate bonds are less flexible than ester bonds, polyurethanes made from PCD that only have carbonate bonds are less flexible than polyurethanes made from polyester polyols, especially in terms of flexibility and elongation at low temperatures. Due to poor bending and elastic recovery properties, there is a problem of lack of flexibility and brittleness.

On the other hand, cellulose nanofiber (hereinafter referred to as CNF) is a cellulose fiber with a thickness on the order of nanometers and a high aspect ratio, which is obtained by mechanical or chemical defibration treatment in an aqueous medium using pulp as a raw material. It is.
In addition, although CNF is lightweight, it has five times the strength of iron, has a low coefficient of thermal expansion, and has the property that its elastic modulus does not change from low to high temperatures, so composite materials using CNF are lightweight, high strength, It is expected to have a low expansion coefficient and be resistant to temperature changes.

However, since the concentration of CNF dispersed in water is as low as 1 to 20% by mass, there is a problem in that a large amount of water must be removed when composited with a resin.
In addition, when defibrating pulp in resin, the resin generally has a high viscosity, so strong mechanical force is required. In addition, CNF that has been chemically defibrated through oxidation treatment has high hydrophilicity, so it is difficult to refine and surface it. CNF is a material that is difficult to handle industrially, as it requires processing.

In recent years, consideration has been given to blending CNF into polyurethane to improve its physical properties. A polyurethane resin composition containing a polyurethane resin is disclosed (Patent Document 1).
However, in order to obtain the polyurethane resin composition described in Patent Document 1, a raw material obtained by defibrating cellulose in a polyol is used, and in order to ensure the physical properties required for a polyurethane resin, a polyol with a high molecular weight is required. It becomes necessary.
For example, compared to polyester polyols and polyether polyols, highly functional PCDs with molecular weights of 1,000 to 2,000 are often used, and some of the polycarbonate polyols are solid at room temperature, but when heated to 50°C, the viscosity decreases. It is 1000 to 15000 mPa·s. When defibrating in such a highly viscous polyol, it is difficult to obtain the necessary shearing force, and defibration tends to be insufficient.
On the other hand, when strong mechanical force is applied while heating, defibration is promoted, but deterioration such as coloring of CNF and polyol is likely to occur.

On the other hand, CNF-containing polyurethane obtained by reacting an isocyanate compound with a CNF-containing PCD dispersion obtained by reacting a carbonate ester in which CNF is dispersed with a diol compound has been found to have excellent mechanical strength and chemical resistance. It has been disclosed (Patent Document 2).
Furthermore, as a method for obtaining a carbonate ester in which CNF is dispersed, a method is disclosed in which biomass, which is a type of cellulosic raw material, is mechanically pulverized in the coexistence of a carbonate ester solvent (Patent Document 3).

Japanese Patent Application Publication No. 2013-194162 International publication WO2019/172058 JP2017-23921A

However, in the manufacturing method of CNF-containing carbonate ester dispersion described in Patent Document 2 and Patent Document 3, when a carbonate ester with a high solidification point is used, carbonate ester is generated in the apparatus when defibrating the pulp under high pressure conditions. It was found that stable production was not possible due to solidification.
An object of the present invention is to provide a method for stably producing a CNF-containing carbonate dispersion that is a raw material for a CNF-containing polyurethane that has excellent mechanical strength and chemical resistance.

In order to solve the above-mentioned problems, the present inventors conducted extensive studies and found that a diol compound was reacted with a CNF-containing carbonate ester dispersion obtained by defibrating a cellulose raw material in a carbonate ester having a freezing point of 35°C or lower. The present inventors have discovered that a CNF-containing polyurethane obtained by reacting a CNF-containing PCD dispersion obtained by this process with an isocyanate compound has excellent mechanical strength and chemical resistance, and has completed the present invention.

That is, the first aspect of the present invention is a method for producing a CNF-containing carbonate ester dispersion, which comprises defibrating a cellulose-based raw material in the presence of a carbonate ester having a freezing point of 35° C. or lower.

Moreover, the second invention of the present invention is a method for producing the CNF-containing carbonate ester dispersion according to the first invention, wherein the carbonate ester is a cyclic carbonate.

Further, a third invention of the present invention is a method for producing a CNF-containing carbonate ester dispersion according to the first invention or the second invention, wherein the carbonate ester is a mixture of ethylene carbonate and propylene carbonate.

A fourth invention of the present invention is a method for producing a CNF-containing polycarbonate diol, which comprises reacting a CNF-containing carbonate dispersion obtained by any of the methods of the first to third inventions with a diol.

A fifth invention of the present invention is a method for producing a CNF-containing polyurethane, characterized by reacting the CNF-containing polycarbonate diol obtained in the fourth invention with an isocyanate compound.

According to the production method of the present invention, a CNF-containing carbonate ester dispersion can be stably produced with less load on equipment for fibrillating cellulosic raw materials. Furthermore, CNF-containing polyurethane, which is made from a CNF-containing carbonate ester dispersion, can be used as a highly functional composite material with excellent properties such as mechanical strength and heat resistance in artificial leather, synthetic leather, adhesives, paints, and coatings. It is useful for etc.

1 is a schematic diagram of a cellulosic raw material defibration apparatus used in Example 1. FIG. 1 is a micrograph of the CNF-containing carbonate ester dispersion obtained in Example 1. 3 is a graph of a tensile test of the CNF-containing polyurethane obtained in Example 4.

The present invention is a method for producing a CNF-containing carbonate ester dispersion, which is characterized by defibrating a cellulosic raw material in the presence of a carbonate ester having a freezing point of 35° C. or lower.

The cellulosic raw material in the present invention is not particularly limited as long as it is a material mainly composed of cellulose, and includes, for example, pulp, natural cellulose, regenerated cellulose, and fine cellulose depolymerized by mechanical treatment of cellulose raw materials. It will be done. Note that as the cellulose-based raw material, commercially available products such as crystalline cellulose made from pulp can be used as they are.

When defibrating a cellulosic raw material, it is preferable to refine the cellulosic raw material in advance and then defibrate it in a carbonate ester. If it is not purified in advance, impurities contained in the cellulosic raw material may dissolve in the carbonate ester, thereby inhibiting the transesterification reaction with the diol compound.
The method for purifying the cellulosic raw material is not particularly limited, but the following purification methods are exemplified. After charging the cellulosic raw material and water into a pressure vessel, the pressure vessel is heated and pressurized, and while removing the supernatant liquid, water is added, heated and pressurized repeatedly, and then filtered and washed with water to form a cake. After obtaining the cellulose, it is dried under reduced pressure to obtain a purified cellulose-based raw material.

Devices for defibrating cellulose raw materials in the present invention include ball mills, bead mills, hammer mills, rod mills, disk mills, cutter mills, jet mills, water jet devices, stone mill mills, extrusion molding machines, refiners, high-pressure homogenizers, Any of an ultrasonic homogenizer, a high-speed homogenizer, an underwater counter-collision device, etc. can be used, but it is particularly desirable to use a water jet device.

Examples of the carbonate esters used include cyclic carbonates and chain carbonates that can give PCD by reaction with a diol compound. A mixture of these or a mixture with water can also be used.
Examples of the cyclic carbonates include alkylene carbonates having an alkylene group having 2 to 4 carbon atoms, such as ethylene carbonate, propylene carbonate, and butylene carbonate.
Further, as the chain carbonates, dialkyl carbonates are preferred, and the number of carbon atoms in the constituent alkyl groups is preferably 1 to 5, particularly preferably 1 to 4. Specific examples include symmetrical chain alkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate, and asymmetric chain alkyl carbonates such as ethylmethyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. Examples include dialkyl carbonates such as the following.

In the present invention, since the cellulose-based raw material is defibrated while being dispersed in carbonate ester, for example, when defibrated under high temperature and high pressure conditions, the freezing point of the carbonate ester rises and it solidifies in the equipment. There is a fear. In this sense, the freezing point of the carbonate ester is important, and it is necessary that the freezing point is 35°C or lower. Furthermore, in order to defibrate under safer conditions, the freezing point is preferably 20°C or lower, more preferably 10°C or lower.

From the viewpoint of the freezing point, the carbonate ester is preferably a cyclic carbonate with a freezing point of 35° C. or lower, and among these, ethylene carbonate, propylene carbonate and butylene carbonate are preferable, and mixtures thereof can also be used. A mixture of ethylene carbonate and propylene carbonate is particularly preferred because the resulting CNF-containing polyurethane has excellent physical properties.
Although ethylene carbonate alone has a freezing point of 38°C, it can be used as a mixture with propylene carbonate or the like to have a freezing point of 35°C or lower.
In the mixture of ethylene carbonate and propylene carbonate, the mixing ratio of ethylene carbonate and propylene carbonate is preferably 1:9 to 9:1 in terms of mass ratio, and more preferably 2:8 to 8:2. The ratio is preferably 3:7 to 7:3, particularly preferably 3:7 to 7:3.

When the freezing point of the carbonate ester is 35° C. or lower, the load on the defibrating equipment used is reduced, so the defibrating equipment is less likely to malfunction, and the cellulose-based material can be stably defibrated. Furthermore, when a mixture of ethylene carbonate and propylene carbonate is used, a CNF-containing polyurethane with excellent physical properties can be obtained using a CNF-containing carbonate ester dispersion as a raw material.

For example, by using a 5:5 mixture of ethylene carbonate and propylene carbonate as the carbonate ester and defibrating the pulp, which is a cellulose material, in a pulp crusher, microscopic observation shows that 0.2 CNF-containing carbonate ester is produced with a fiber diameter centered around ~1 μm and a fiber length centered around 10-100 μm.

Furthermore, a CNF-containing PCD dispersion can be obtained by reacting the CNF carbonate dispersion obtained by the production method of the present invention with a diol compound. In this case, the CNF may contain a cellulosic raw material before pulverization.
As a method for obtaining a PCD dispersion in which CNF is dispersed by reaction with a diol compound using a CNF-containing carbonate ester dispersion, a known method for producing PCD is applied, for example, as disclosed in JP-A No. 2015-044986. and the method described in JP-A No. 2017-025155.
In these cases, since CNF itself does not contribute to the reaction, a similar reaction occurs even if CNF is contained.

For example, PCD can be obtained through a two-step reaction consisting of a transesterification reaction and a polycondensation reaction. A carbonic acid ester containing CNF and a diol compound are mixed at a molar ratio of 20:1 to 1:10 and reacted at a temperature of 100 to 300°C under normal pressure or reduced pressure to produce by-produced ethylene glycol and unreacted ethylene carbonate. is distilled off to obtain low molecular weight PCD of 2 to 10 units, and then unreacted raw material diol compound and ethylene carbonate are distilled off at 100 to 300° C. under reduced pressure, and the low molecular weight PCD is polycondensed. PCD with a predetermined molecular weight can be obtained by adjusting the distillation amount of the raw material diol compound.
In addition, when manufacturing PCD using two or more types of raw material diol compounds, the composition ratio of PCD can be determined by analyzing the composition of the raw material diol compounds to be distilled using a gas chromatograph, etc. The ratio can be adjusted to any desired composition ratio by adding a raw material diol compound during the reaction.

For example, PCD having a 1,6-hexanediol (hereinafter referred to as HDO) skeleton and a molecular weight of 1000 can be obtained by the method shown below.
A reaction apparatus equipped with a rectification column was charged with 400 g of an ethylene carbonate/propylene carbonate mixture containing 1% by mass of CNF, 450 g of HDO, and 0.8 g of tetrabutyl titanate as a catalyst, and the temperature was gradually raised at 50 torr. The internal temperature is raised to 160°C to 170°C so that distillation continues, and the process ends when distillation stops. In this first stage reaction, addition of EC to HDO and transesterification reaction occur between EC and HDO to produce oligomers, and the distillate is mainly ethylene glycol.
Next, the rectifying column is removed, the degree of vacuum is increased to 5 torr to 0 torr, and the internal temperature is raised to 150 to 185° C. so that distillation occurs continuously. The process ends when distillation stops and a predetermined hydroxyl value is reached. In the second stage reaction, unreacted EC and ethylene glycol are distilled off and HDO is distilled out by polycondensation of low molecular weight carbonate diols, thereby increasing the molecular weight. The distillate is mainly HDO.

In addition, a tertiary amine catalyst, an organometallic catalyst, etc. may be used in the above reaction if necessary, but there is an advantage that the step of deactivating the catalyst is unnecessary and the coloring of the reaction liquid is reduced. , it is preferable to react without a catalyst.

Furthermore, a CNF-containing polyurethane can be obtained by reacting the CNF-containing PCD dispersion with an isocyanate compound.
The isocyanate compound has two or more isocyanate groups in the molecule, such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, Hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, and the like can be used.

As the hydroxyl group of PCD that reacts with the isocyanate compound, the hydroxyl value determined according to JIS K 1557-1 (Plastics? Polyurethane raw material polyol test method? Part 1: How to determine hydroxyl value) may be used. The molar ratio ([NCO/OH]) between the hydroxyl group of PCD and the isocyanate group of the isocyanate compound is generally 1.0 or less, but when producing a urethane prepolymer, it is recommended to set the molar ratio to more than 1.0. preferable.
For example, when producing a polyurethane sheet, PCD and an isocyanate compound are mixed at room temperature to 70°C, and after vacuum defoaming, a catalyst is added as needed and mixed, and then vacuum defoamed again and molded. It is cast and cured by heating at 40°C to 110°C for 3 to 12 hours to produce a polyurethane sheet.

The CNF-containing PCD dispersion is made of a dispersion obtained by crushing a cellulose raw material in a carbonate ester or a dispersion in which powdered CNF is dispersed in a carbonate ester.
It is known that when cellulose raw materials are crushed in a medium that is more hydrophobic than water, the CNF produced has a more hydrophobic surface than CNF crushed in water and has better dispersibility in organic media. There is.
Therefore, CNF obtained by crushing in carbonate ester, which is more hydrophobic than water, is also more hydrophobic than CNF crushed in water, and therefore has better dispersibility in carbonate ester, and can be manufactured using this as a raw material. The dispersibility of CNF in the PCD is also good, and the dispersibility of CNF in the CNF-containing polyurethane made from the CNF-containing PCD dispersion is also good.
Hydrophilic CNF generally tends to cause problems such as aggregation and thickening in hydrophobic resins, and the expected properties may not be exhibited, but the manufacturing method of the present invention solves these problems. or can be reduced, making it possible to obtain polyurethane with higher functionality.

For example, CNF-containing polyurethane can be produced by the following method.
Cellulose containing CNF obtained by dispersing powdered CNF in a carbonate ester at a concentration of 1 to 5% by mass using a rotation-revolution stirrer and reacting the carbonate ester with 1,6-hexanediol (HDO). CNF-containing polyurethane can be produced by reacting PCD dispersed with dicyclohexylmethane diisocyanate (HMDI).
Using dibutyltin dilaurate or the like as a catalyst for promoting urethanization, curing is carried out in an amount of 0.04 parts by mass relative to 100 parts by mass of a composition consisting of PCD and isocyanate. The pot life is about 20 minutes at room temperature, and the obtained polyurethane is thermoplastic. Although cellulose containing CNF contains many hydroxyl groups in its molecules, it does not extremely accelerate or retard curing, and the curing time can be adjusted by adjusting the amount of catalyst added. Furthermore, gelled polyurethane does not occur due to the presence of cellulose containing CNF.

The present invention will be explained in detail below using Examples and Comparative Examples.
The freezing point of the carbonate ester mixture was determined by DSC (device: DCS Q100TA, manufactured by Instrument). That is, when a mixture of carbonate esters is solidified by cooling it from 60°C to -80°C at a rate of 10°C/min, and melted by heating it from -80°C to 80°C at a rate of 10°C/min. The top of the heat of fusion peak was taken as the freezing point.
<Example 1>
Ethylene carbonate (manufactured by Toagosei Co., Ltd.)/propylene carbonate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) = 8/2 (mass ratio) mixture (solidification point 26°C) was pre-pulverized using a stone mill type mill (Super Mascolloider MKCA6-5Jα, manufactured by Masuko Sangyo Co., Ltd.) to obtain 1250 g (approximately 1 L) of a dispersion.
This was charged into a water jet device (Starburst Lab HJP-25008, manufactured by Sugino Machine Co., Ltd.) shown in Figure 1, and subjected to continuous treatment 50 times at 200 MPa using a ball collision type atomization chamber to produce CNF-containing ethylene. 720 g of carbonate/propylene carbonate (mass ratio 8/2) dispersion was obtained.
During the defibration process, there was no damage to the seal packing around the plunger of the pulp defibration device, and stable operation was possible. The CNF in the obtained dispersion had good dispersibility, with individual fibers having a fiber diameter of 0.2 to 1.0 μm existing separately. Fibers with a length of 10 to 100 μm were mainly present. FIG. 2 shows a micrograph (400 times magnification) of the dispersion obtained in Example 1.

<Example 2>
CNF-containing ethylene carbonate/propylene carbonate (mass ratio 5/5) was obtained by carrying out the same method as in Example 1, except that the carbonate ester was a mixture of ethylene carbonate/propylene carbonate (mass ratio 5/5) (freezing point 9°C). 5) 720 g of dispersion was obtained.
During the defibration process, there was no damage to the seal packing around the plunger, and stable operation was possible. The CNF in the obtained dispersion had good dispersibility, with individual fibers having a fiber diameter of 0.2 to 1.0 μm existing separately. Fibers with a length of 10 to 100 μm were mainly present.

<Comparative example 1>
The same method as in Example 1 was carried out except that the dispersion medium was ethylene carbonate alone (the temperature was set at 60° C. when charging the apparatus to prevent ethylene carbonate from coagulating). As a result, the seal packing around the plunger broke after the 10th pass, and liquid leaked from there, making it necessary to abandon the test.

<Example 3>
By pressurizing the CNF-containing dispersion obtained in Example 1, a dispersion with a CNF concentration concentrated to 2.2% by mass was obtained. 232 g of this dispersion, 104 g of 1,5-pentanediol (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.), and 118 g of 1,6-hexanediol (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) were mixed and heated while stirring. It started. When the liquid temperature reached 100°C, 0.225 g of tetrabutyl titanate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was added, and then the liquid temperature was raised to 160°C.
Next, the internal pressure was reduced to 40 Torr using a vacuum pump, and distillation was started. As the distillation progressed, heating and pressure reduction were progressed, and the distillation was stopped when the liquid temperature reached 186° C. and the pressure reached 0.3 Torr, thereby obtaining 141 g of CNF-containing PCD. The CNF concentration was found to be 3.2% by mass from the distillation fraction, and the molecular weight of PCD was determined to be 730 by titration.

<Example 4>
5.50 g of CNF-containing PCD obtained in Example 3, 2.32 g of dicyclohexylmethane 4,4'-diisocyanate (manufactured by Tokyo Kasei Co., Ltd.), and 5.5 mg of dibutyltin dilaurate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) were mixed into a resin. Place the mixture in a vacuum planetary stirrer (V-mini300, manufactured by EME) for 6 minutes at a revolution speed of 1000 rpm, including 5 minutes for vacuum (after 1 minute of rotation and revolution, 5 minutes of vacuuming). The mixture was stirred with constant rotation and revolution) and polymerized at 35° C. for 16 hours and at 60° C. for 6 hours to obtain a CNF-containing polyurethane (CNF concentration was 2.3% by mass).

The CNF-containing polyurethane obtained in Example 4 was cut into strips of 0.5 cm x 7 cm x 0.2 cm and tested using a Shimadzu Autograph AG50KNXDplus (manufactured by Shimadzu Corporation) tensile testing device with a distance between chucks of 3 cm. The tensile strength was measured by tightening the chuck with air pressure and pulling at a speed of 200 mm/min at 60°C.
The CNF-containing polyurethane was compared to a CNF-free polyurethane (a polyurethane synthesized by the same method as in Example 4 except that PCD synthesized from a CNF-free ethylene carbonate/propylene carbonate (mass ratio 8/2) mixture was used). It was confirmed that the tensile strength was improved (Figure 3). Further, the CNF-containing polyurethane did not break during stretching, but the CNF-free polyurethane did break during stretching. From the above, the reinforcing effect of CNF was confirmed for the polyurethane produced using the CNF-containing carbonate ester dispersion obtained in Example 1 as a raw material.

1: Hopper, 2: Liquid pump, 3: Pressure booster, 4: Plunger, 5: Seal packing, 6: Atomization chamber, 7: Heat exchanger, 8: Recovery section

Claims (4)

A method for producing a carbonate ester dispersion containing cellulose nanofibers, the method comprising defibrating a cellulose-based raw material in the presence of a carbonate ester having a freezing point of 35° C. or lower ,
The production method, wherein the carbonic acid ester is a mixture of ethylene carbonate and propylene carbonate, and the mixing ratio of the ethylene carbonate and the propylene carbonate is 2:8 to 8:2 in terms of mass ratio. The method for producing a carbonate ester dispersion containing cellulose nanofibers according to claim 1, wherein the carbonate ester is a cyclic carbonate. A method for producing a cellulose nanofiber-containing polycarbonate diol, which comprises reacting a cellulose nanofiber-containing carbonate ester dispersion obtained by the production method according to claim 1 or 2 with a diol compound. A method for producing a cellulose nanofiber-containing polyurethane, which comprises reacting the cellulose nanofiber-containing polycarbonate diol obtained by the production method according to claim 3 with an isocyanate compound.

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