JP2013256635A - Method of producing powdered cellulose - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce powdered cellulose having a high-molecular weight.SOLUTION: A method of producing powdered cellulose having a high-molecular weight includes: cooling a cellulose-containing raw material that contains 30 to 200 mass% of water based on a dry mass, at ambient temperature of ≤-50°C; and pulverizing the cooled raw material.

Description

  The present invention relates to a method for producing powdered cellulose and a method for pulverizing cellulose.

  Cellulose, which is a natural polymer, is used not only as a raw material for fibers and papers but also in the food field, cosmetic field, and pharmaceutical field. Cellulose is not only used as it is, but also used as a cellulose derivative in which the hydroxyl group of cellulose is replaced with another functional group. For example, so-called cellulose ethers in which a hydrogen atom of a hydroxyl group is substituted with a methyl group, a hydroxyethyl group, a hydroxypropyl group, carboxymethyl, or the like are widely used as a thickener, a dispersant, a water absorbing agent, a water retention agent, and the like. Cellulose esters such as cellulose acetate are used as raw materials for films, filters and coatings.

  Cellulose derivatives having various degrees of polymerization suitable for the application are required. For example, in order to obtain a high thickening effect or a moisturizing effect, a higher degree of polymerization is preferable. On the other hand, in order to efficiently obtain a cellulose derivative from cellulose, it is preferable to derivatize after making cellulose-containing raw materials such as cotton linter and wood pulp into powder cellulose of an appropriate size. As a method for producing powdered cellulose from a cellulose-containing raw material, a method of mechanically pulverizing the cellulose-containing raw material (see, for example, Patent Document 1) is known.

JP 59-75901 A

  However, when powdered cellulose is produced by a conventional method, the degree of polymerization is greatly reduced, and it is difficult to obtain cellulose powder having a high degree of polymerization.

  The subject of this invention is enabling it to manufacture the cellulose powder of high polymerization degree.

  In the method for producing powdered cellulose of the present invention, a cellulose-containing raw material having a water content of 30% by mass to 200% by mass with respect to the dry mass is cooled and pulverized at an atmospheric temperature of −50 ° C. or less.

  According to the method for producing powdered cellulose of the present invention, a cellulose powder having a high degree of polymerization can be produced.

  In the method for producing powdered cellulose according to this embodiment, a cellulose-containing raw material having a water content with respect to a dry mass of 30% by mass to 200% by mass is cooled and pulverized at an atmospheric temperature of −50 ° C. or less.

  By pulverizing the cellulose-containing raw material containing a specific amount of water at a temperature at which the water is sufficiently frozen, the cellulose-containing raw material can be pulverized and powdered cellulose can be obtained while suppressing a decrease in the degree of polymerization.

  In the present embodiment, the cellulose-containing raw material is a material containing cellulose, and includes not only a material composed only of cellulose but also a material containing components other than cellulose. In addition, powdered cellulose is a powder obtained by pulverizing a cellulose-containing raw material, and includes not only a powder composed of cellulose alone but also a powder containing components other than cellulose.

  Any material containing cellulose can be used as the cellulose-containing raw material. Specific examples include wood chips, wood pulp made from wood, so-called non-wood pulp made from various plants except wood, paper, recycled pulp made from waste paper, cotton Cotton lint as a raw material, cotton linter that is a fiber attached to the periphery of cotton seeds, and the like can be used. Non-wood pulp includes pulp made from plant stems such as rice straw and corn, plant leaves, or plant shells such as rice husk, palm shell or coconut shell. The paper includes newspapers, cardboard, magazines and fine paper. Among these, wood pulp and cotton linter are preferable as the cellulose-containing raw material, and cotton linter is more preferable. These cellulose-containing raw materials can be used alone or in combination of two or more.

  The degree of polymerization of cellulose contained in the cellulose-containing raw material is not particularly limited, and those having an appropriate degree of polymerization may be used according to the purpose. However, the higher the degree of polymerization of the cellulose contained in the cellulose-containing raw material, the higher the molecular weight powdered cellulose can be obtained. For this reason, when high molecular weight powdered cellulose is required, the viscosity average degree of polymerization (hereinafter also simply referred to as the degree of polymerization) of the cellulose contained in the cellulose-containing raw material is preferably 500 or more, more preferably 1000 or more. More preferably, it is 1500 or more. There is no particular upper limit on the degree of polymerization, and even if it exceeds 3000, it can be used without any problem. Those having a polymerization degree of 3000 or less can be used, and those having a polymerization degree of 2000 or less can also be used. The degree of polymerization of cellulose contained in the cellulose-containing raw material can be determined by the copper ammonia method described in detail in Examples.

  Although content of the cellulose contained in a cellulose containing raw material is not specifically limited, From viewpoints of productivity etc., 20 mass% or more is preferable, 40 mass% or more is more preferable, 60 mass% or more is further more preferable, 90 mass% or more is 90 mass% or more. Particularly preferred. The cellulose content referred to here is the total amount of cellulose and hemicellulose contained in the remaining components after subtracting moisture. In a general commercial pulp, the content of cellulose contained in the remaining components after subtracting moisture is 75% by mass to 100% by mass. Lignin, fats and oils, etc. may be contained as components other than cellulose. Moreover, the material in which components other than cellulose were positively added can also be used as the cellulose-containing raw material. However, the higher the cellulose content, the higher the purity of the powdered cellulose. When the obtained powdered cellulose is used as a raw material for a cellulose derivative, it is advantageous that the content of cellulose is high and the content of components other than cellulose is low. The content of cellulose contained in cellulose-containing raw materials is determined by the holocellulose quantification method (edited by the Analytical Society of Japan, 4th edition of Analytical Chemistry Handbook, p. 1081-11082, published on Mar. 30, 1991) ).

  There are a plurality of crystal structures of cellulose, but in natural pulp and the like, the most common type is cellulose type I which is a parallel chain. The cellulose I crystallinity (hereinafter also simply referred to as crystallinity) in commercially available pulp is usually 60% or more. The crystallinity of cellulose in the cellulose-containing raw material of the present disclosure may be any value. However, normally, the low crystallization treatment of cellulose is accompanied by a decrease in the degree of polymerization due to breaking of the cellulose chain. From the viewpoint of obtaining alkali cellulose or cellulose ether having a high average degree of polymerization as described above, in the present disclosure, there is little decrease in the degree of polymerization, that is, low crystallization treatment is not performed or only a short time is performed, and more It is preferable to use a cellulose-containing raw material containing cellulose having a high degree of crystallinity. From this viewpoint, the crystallinity of cellulose in the cellulose-containing raw material is preferably 10% or more, more preferably 20% or more, further preferably 50% or more, and further preferably 60% or more. On the other hand, it is difficult to obtain a cellulose-containing raw material having a crystallinity exceeding 95% and a very high crystallinity. From the viewpoint of availability, the crystallinity of cellulose in the cellulose-containing raw material is preferably 95% or less, more preferably 90% or less, and still more preferably 80% or less.

  The crystallinity of cellulose is the ratio of the amount of crystal regions to the total cellulose including non-crystallized regions. The crystallinity of cellulose contained in the cellulose-containing raw material can be determined by the X-ray diffraction method described in detail in Examples.

  The cellulose-containing raw material of a sheet | seat, a roll, or another shape can be cut | judged and used for the magnitude | size according to the grinder to be used. For example, it can be used by cutting into chips having a size of 0.5 mm square or more, preferably 2 mm square or more, more preferably 3 mm square or more. The upper limit of the size of the chip is determined depending on the pulverizing apparatus to be used, and can be, for example, 70 mm square or less, preferably 50 mm square or less, more preferably 40 mm square or less, and further preferably 20 mm square or less. Depending on the pulverizer, the chip may be a larger chip or a smaller chip. From the viewpoint of efficiently performing pulverization, it is preferable that the sizes of the chips are uniform, but there is no problem even if the chips are in the range of several mm to several tens of mm.

  For the cutting, a shredder, a slitter cutter, a rotary cutter or the like can be used. When using a sheet-like cellulose-containing raw material, it is preferable to use a shredder or a slitter cutter. From the viewpoint of productivity, it is more preferable to use a slitter cutter. A sheet pelletizer which is a kind of slitter cutter is particularly preferable. When various wood chips or shapes are pulp or cellulose other than sheets or rolls, it is preferable to use a rotary cutter or the like.

From the viewpoint of suppressing a decrease in the degree of polymerization, the cellulose-containing raw material only needs to have an amount of water (water content) of 30% by mass or more with respect to its dry mass during pulverization. The water content is preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 100% by mass or more. From the viewpoint of grinding efficiency, the water content may be 200% by mass or less, preferably 180% by mass or less, and more preferably 150% by mass or less. In this embodiment, the content of water is the ratio of the mass (m ₂ ) of water contained in the cellulose-containing raw material to the mass (dry mass, m ₁ ) of the component obtained by subtracting the water contained in the cellulose-containing raw material ( m ₂ / m ₁ ).

  The water content in the cellulose-containing raw material may be adjusted to a predetermined value by adding water as necessary or drying in accordance with a conventional method. When adding water, measure the amount of water (initial moisture content) and dry mass contained in the cellulose-containing raw material before adding water in advance, and determine the initial moisture content from the required amount of water. A subtracted amount of water may be added. The initial moisture content can be measured by a method using an infrared moisture meter described in detail in the examples.

  In the case of preparing water content in a cellulose-containing raw material by adding water, since cellulose has high water absorption, a predetermined amount of water and a cellulose-containing raw material are mixed and allowed to stand in the cellulose-containing raw material. The water content can be easily adjusted. Moreover, after mixing water and a cellulose containing raw material, water absorption can also be performed more rapidly by performing heating or pressurization.

  Even when water is added to prepare the water content in the cellulose-containing raw material, the cellulose-containing raw material is once dried before adding water in order to accurately control the water content in the cellulose-containing raw material. May be. However, it is sufficient that the amount of water contained in the pulverization can be controlled to a predetermined value, and it is not necessary to dry if the initial moisture content of the cellulose-containing raw material is clear.

  Moreover, when the initial moisture content in a cellulose containing raw material exists in the range of the content of water specified in this indication, it is not necessary to add and dry water.

  In order to obtain high-purity powdered cellulose, it is preferable that the purity of the added water is high. For this reason, it is preferable to use ion-exchanged water or the like. However, tap water or industrial water can be used depending on the purpose.

  It is important for efficient pulverization that water contained in the cellulose-containing raw material is sufficiently frozen during pulverization. For this reason, the pulverization may be performed in a state where the cellulose-containing raw material is cooled at an atmospheric temperature of −50 ° C. or lower, and is preferably performed in a state of being cooled at an atmospheric temperature of −150 ° C. or lower. For example, in the case of a container-driven pulverizer, the cellulose-containing raw material can be cooled from the outside of the container in which the cellulose-containing raw material is charged using a low-temperature liquid coolant. As the liquid coolant, for example, dry ice methanol having a temperature of −78 ° C. or liquid nitrogen having a temperature of −196 ° C. can be used. By using a low-temperature liquid coolant, it can be rapidly cooled, and the working efficiency is improved. Dry ice methanol is preferred because it is easy to handle. Further, liquid nitrogen is preferable because a sufficiently low temperature state can be realized quickly. For example, if the container is cooled from the outside using liquid nitrogen, the atmospheric temperature inside the container can be quickly reduced to -50 ° C or lower. It is also easy to set it to −100 ° C. or lower or −150 ° C. or lower. By cooling from the outside of the container using such a low-temperature liquid coolant, the water in the container can be sufficiently frozen in a very short time. However, liquid coolants other than these liquid coolants may be used.

  Moreover, you may cool by methods other than the method of using a liquid coolant. For example, the container containing the cellulose-containing raw material may be cooled using a low-temperature freezer or a cryogenic freezer. You may make it cool not only a container but the required part or the whole of a grinding | pulverization apparatus. A gas having a temperature of −50 ° C. or lower, preferably −150 ° C. or lower, or a liquid that becomes a gas at room temperature may be introduced into the container and cooled. Furthermore, it is also possible to take a method such as freezing the cellulose-containing raw material in advance and then putting it into the pulverizing apparatus. It does not have to be a constant temperature from the start to the end of pulverization. If the temperature is below a predetermined temperature from the start to the end of pulverization, there is a problem even if the temperature rises or falls during the pulverization. Absent. Further, the cooling rate does not matter and may be rapidly or gradually cooled.

  The pulverizer used for pulverization is not particularly limited, but a medium pulverizer is preferable. The medium type pulverizer includes a container driven pulverizer and a medium stirring pulverizer. As the container-driven crusher, a rolling mill, a vibration mill, a planetary mill, a centrifugal fluid mill, or the like can be used. Among these, a vibration mill is preferable from the viewpoint of high grinding efficiency and productivity. As the medium agitating pulverizer, a tower-type pulverizer such as a tower mill, an agitator, an aquamizer or a sand grinder, a stirred tank-type pulverizer, a visco mill or a pearl mill, etc. An annular type pulverizer, a continuous dynamic pulverizer, and the like can be used. Among these, a stirring tank type pulverizer is preferable from the viewpoint of high pulverization efficiency and productivity. The type of pulverizer can be referred to “Chemical Engineering Advances 30th Particulate Control” (Chemical Engineering Society, Tokai Branch, issued October 10, 1996, Sakai Shoten). The processing method may be either a batch type or a continuous type.

  In the case of a conventional pulverization method, a cellulose having a higher degree of polymerization tends to lower the degree of polymerization during pulverization. For example, when the degree of polymerization is about 200, the degree of polymerization is not greatly reduced even when a dry cellulose-containing raw material having a water content of 10% by mass or less is pulverized. However, when a cellulose-containing raw material having a degree of polymerization of about 1800 is pulverized in a dry state, for example, until the particle size is 100 μm or less, the degree of polymerization is reduced to about 1000.

  On the other hand, according to the pulverization method of the present embodiment, for example, even when the degree of polymerization of cellulose contained in the cellulose-containing raw material is about 1800, the degree of polymerization of powdered cellulose after pulverization is the degree of polymerization of cellulose contained in the cellulose-containing raw material. Of 75% or more. Even in the case where the degree of polymerization is higher and about 3000, a decrease in the degree of polymerization can be similarly suppressed. By optimizing the pulverization conditions, the degree of polymerization of the powdered cellulose can be 90% or more of the degree of polymerization of the cellulose-containing raw material, and can be 95% or more.

  As a specific example, for example, if a cellulose-containing raw material containing cellulose having a degree of polymerization of about 1800 is used, powdered cellulose having a degree of polymerization of 1400 or more can be obtained, and powdered cellulose having a degree of polymerization of 1600 or more can be obtained. The above powdered cellulose can also be obtained. If a cellulose-containing raw material having a higher degree of polymerization is used, a cellulose powder having a higher degree of polymerization can be obtained. The degree of polymerization of powdered cellulose can also be measured by the same method as the degree of polymerization of the cellulose-containing raw material.

  The median diameter of powdered cellulose obtained by the method of the present disclosure is preferably 120 μm or less, and more preferably 100 μm or less, from the viewpoint of reactivity when producing a cellulose derivative. On the other hand, if the particle size is too small, scattering or the like tends to occur. For this reason, from the viewpoint of easy handling, the median diameter of the pulverized powdered cellulose is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more. However, it is possible to obtain powdered cellulose having a median diameter of greater than 120 μm or powdered cellulose of less than 10 μm. The median diameter of the powdered cellulose can be measured by a laser diffraction / scattering particle size distribution measuring method described in detail in Examples.

  The pulverization time is not particularly limited, and may be performed until the cellulose-containing raw material has a desired particle diameter. However, if the pulverization is performed in a short time, an increase in cost is less likely to occur. Accordingly, the grinding time is preferably 30 minutes or less, more preferably 20 minutes or less, and particularly preferably 10 minutes or less.

  In the cellulose pulverization method of the present embodiment, the reason why powdered cellulose having a small particle size can be produced without greatly reducing the degree of polymerization of the cellulose is due to the presence of frozen water around the cellulose molecules and the energy of pulverization. This may be because the cellulose molecules are less likely to be cut.

  The obtained powdered cellulose can be used for various applications. For example, it can be used as it is as an additive such as food, feed, cosmetics or pharmaceuticals, as a filler for resin products, or as a filter aid. Moreover, it can use as a raw material of cellulose derivatives, such as an ether type or ester type.

  Examples of the ether cellulose derivative include methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, glycerol-modified cellulose, carboxymethyl cellulose, cationized cellulose, cationized hydroxycellulose, and cationized hydroxypropylcellulose. Examples of the ester-based cellulose derivative include cellulose monoacetate, cellulose diacetate, and cellulose triacetate.

  In order to produce a cellulose derivative, cellulose is generally immersed in an alkaline aqueous solution and once activated as alkali cellulose. In order to produce a cellulose derivative efficiently, it is preferable to reduce the amount of alkali used when converting cellulose to alkali cellulose (hereinafter also referred to as “alkalization”) as much as possible. The method for producing powdered cellulose of the present embodiment can easily obtain powdered cellulose having a small particle size that can be easily alkalized and having a high degree of polymerization. For example, the powdered cellulose produced by the method for producing powdered cellulose of the present embodiment and having a median diameter of 46 μm and a degree of polymerization of 1750 is 1 mole of water per mole of anhydroglucose units constituting the obtained powdered cellulose. Can be easily alkalized with sodium oxide. There is no significant change in the degree of polymerization due to alkalinization.

  When methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, or the like is used as a thickener for foods, pharmaceuticals, cosmetics, or the like, a higher thickening effect can be obtained with a higher degree of polymerization. Moreover, when adding cationized cellulose, cationized hydroxyethyl cellulose, etc. to a shampoo or a conditioner etc., the one where a polymerization degree is higher can obtain a better conditioning effect. For this reason, the powdered cellulose which has been produced by the method for producing powdered cellulose according to this embodiment and which has a high degree of polymerization and is easily alkalized is particularly useful as a raw material for these cellulose derivatives.

  The powdered cellulose after pulverization contains a predetermined amount of water. For this reason, when derivatizing the obtained powdered cellulose, the water content of the powdered cellulose may need to be adjusted depending on the conditions used. In reducing the water content, a normal vacuum dryer, vacuum dryer, hot air dryer, or the like can be used.

  In relation to the above embodiments, the present invention further discloses the following production method and pulverization method.

<1>
The water content relative to the dry mass is 30% by mass or more, preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 100% by mass or more, 200% by mass or less, preferably 180% by mass or less, and more. A method for producing powdered cellulose or a method for pulverizing cellulose, wherein a cellulose-containing raw material that is preferably 150% by mass or less is cooled and pulverized at an atmospheric temperature of -50 ° C or less, preferably -150 ° C or less.

<2>
The method for producing powdered cellulose according to the above <1> or cellulose, wherein pulverization is performed so that the median diameter of the powdered cellulose is 10 μm or more, preferably 20 μm or more, more preferably 40 μm or more, 120 μm or less, preferably 100 μm or less. Grinding method.

<3>
The viscosity average polymerization degree of cellulose contained in the cellulose-containing raw material is 500 or more, preferably 1000 or more, more preferably 1500 or more, and 3000 or less, preferably 2000 or less, according to <1> or <2>. A method for producing powdered cellulose or a method for pulverizing cellulose.

<4>
<1> to <1>, wherein the cellulose-containing raw material is wood chip, wood pulp, non-wood pulp, recycled pulp, cotton lint or cotton linter, preferably wood pulp or cotton linter, more preferably cotton linter. The manufacturing method of the powdered cellulose as described in any one of <3>, or the pulverization method of a cellulose.

<5>
The method for producing powdered cellulose or the method for grinding cellulose according to any one of <1> to <4>, wherein the grinding is performed using a medium grinding device.

<6>
The method for producing powdered cellulose or the method for pulverizing cellulose according to <5>, wherein the medium-type pulverizer is a container-driven pulverizer or a medium stirring pulverizer.

<7>
The method for producing powdered cellulose or the method for pulverizing cellulose according to any one of <1> to <6>, wherein the method is cooled to the ambient temperature using a liquid coolant.

<8>
The method for producing powdered cellulose or the method for pulverizing cellulose according to <7>, wherein the liquid coolant is dry ice methanol or liquid nitrogen, preferably liquid nitrogen.

<9>
The water content relative to the dry mass is 30% by mass or more, preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 100% by mass or more, 200% by mass or less, preferably 180% by mass or less, and more. A method for pulverizing cellulose, wherein a cellulose-containing raw material that is preferably 150% by mass or less is cooled and pulverized at an atmospheric temperature of −50 ° C. or less, preferably −150 ° C. or less.

<10>
The bulk density of the cellulose-containing raw material is 100 kg / m ³ or more, preferably 120 kg / m ³ or more, more preferably 150 kg / m ³ or more, 500 kg / m ³ or less, preferably 400 kg / m ³ or less, more preferably The method for producing powdered cellulose or the method for pulverizing cellulose according to any one of <1> to <9>, which is 350 kg / m ³ or less.

<11>
The said cellulose containing raw material before a grinding | pulverization is a manufacturing method of the powdered cellulose or the grinding | pulverization method of a cellulose as described in any one of said <1>-<10> which is chip shape.

<12>
The content of cellulose contained in the cellulose-containing raw material is 20% by mass or more, preferably 40% by mass or more, more preferably 60% by mass or more, and further preferably 90% or more. The manufacturing method of the powdered cellulose as described in any one, or the pulverization method of a cellulose.

<13>
The method for producing powdered cellulose according to any one of <1> to <12>, wherein the crystallinity of the cellulose-containing raw material is 50% or more, preferably 60% or more, and more preferably 70% or more. Cellulose grinding method.

<14>
The polymerization degree of the powdered cellulose obtained after pulverization is 75% or more, preferably 90% or more, more preferably 95% or more of the polymerization degree of cellulose contained in the cellulose-containing raw material. The manufacturing method of the powdered cellulose as described in any one, or the pulverization method of a cellulose.

<15>
The method for producing powdered cellulose according to any one of <1> to <14>, wherein the viscosity-average polymerization degree of the powdered cellulose obtained after pulverization is 1400 or more, preferably 1600 or more, more preferably 1700 or more or Cellulose grinding method.

<16>
The manufacturing method of a cellulose derivative using the powder cellulose manufactured by the method as described in any one of said <1>-<15>.

≪Measurement method≫
(1) Initial moisture content of cellulose-containing raw material The initial moisture content of the cellulose-containing raw material was measured with an infrared moisture meter (manufactured by Kett Scientific Laboratory: FD-610). The point at which the measurement temperature was 120 ° C. and the weight change rate for 30 seconds was 0.1% or less was taken as the end point of the measurement. The value of the measured moisture content was converted to mass% with respect to the dry mass of the cellulose-containing raw material, and this was used as the initial moisture content of the cellulose-containing raw material.

(2) Measurement of viscosity-average polymerization degree of cellulose-containing raw material and powdered cellulose (i) Preparation of measurement solution 0.5 g of cuprous chloride and 20-30 mL of aqueous ammonia (25% by mass) are charged into a 100 mL measuring flask. The cuprous chloride was completely dissolved. Thereafter, 1.0 g of cupric hydroxide was introduced into the volumetric flask, and ammonia water (25% by mass) was further added before the marked line of the volumetric flask. Thereafter, the mixture was stirred for 30 to 40 minutes to completely dissolve cupric hydroxide. Thereafter, a precisely weighed sample (cellulose-containing raw material or powdered cellulose) was put into a measuring flask, and ammonia water (25% by mass) was added up to the marked line of the measuring flask. The sample was dissolved by stirring for 12 hours using a magnetic stirrer in a sealed state so that air would not enter. A plurality of measurement solutions having different cellulose concentrations were prepared by changing the amount of the sample to be added in a range of 20 mg to 500 mg. The sample was used after drying under reduced pressure for 12 hours at 105 ° C. and 20 kPa.

(Ii) Measurement of viscosity average degree of polymerization After the measurement solution (copper ammonia aqueous solution) prepared in the above (i) was put in an Ubbelohde viscometer and allowed to stand in a thermostat (20 ± 0.1 ° C.) for 1 hour, The flow rate of the measurement solution was measured. Based on the flow time (t (second)) of a plurality of measurement solutions having different sample concentrations and the flow time (t ₀ (second)) of the copper ammonia aqueous solution to which no sample is added, the reduced viscosity (η _sp / c) was determined by the following equation (1).

η _sp / c = (t / t ₀ −1) / c (1)
However, c in a formula is a density | concentration (g / dL) of a sample.

Furthermore, the intrinsic viscosity [η] (dL / g) was obtained by extrapolating the reduced viscosity to c = 0, and the viscosity average degree of polymerization (DP _v ) was obtained by the following equation (2).

DP _v = 2000 × [η] (2)
However, the value of 2000 in the formula is a coefficient specific to cellulose.

(3) Measurement of particle diameter The particle diameter of powdered cellulose was determined as the median diameter in a state dispersed in ion-exchanged water. For the measurement, a laser diffraction / scattering particle size distribution measuring apparatus (Horiba, Ltd .: LA-950) was used. Specifically, before measuring the median diameter, powdered cellulose was added to ion-exchanged water, and the concentration was adjusted so that the transmittance was 70 to 95%. Thereafter, ultrasonic dispersion treatment was performed for 1 minute to disperse the powdered cellulose, and then the median diameter was measured.

(4) Measurement of crystallinity The crystallinity of cellulose type I was determined by measuring the X-ray diffraction intensity of a sample using the “RigakuRINT 2500VC X-RAY diffractometer” manufactured by Rigaku Corporation under the following conditions. It calculated based on Formula (3).

The measurement conditions were as follows: X-ray source: Cu / Kα-radiation, tube voltage: 40 kv, tube current: 120 mA, measurement range: diffraction angle 2θ = 5-45 °, and X-ray scan speed: 10 ° / min. The measurement sample was prepared by compressing a pellet having an area of 320 mm ² × thickness of 1 mm.

Crystallinity (%) = [(I _22.6 −I _18.5 ) / I _22.6 ] × 100 (3)
However, I _22.6 is the diffraction intensity of the grating plane (002 plane) (diffraction angle 2θ = 22.6 °) in X-ray diffraction, and I _18.5 is the diffraction intensity of the amorphous portion (diffraction angle 2θ = 18.5 °). Show.

≪Production of powdered cellulose≫
Example 1
<Chip forming process>
Sheet pulp made from cotton linter, which is a cellulose-containing raw material (Shandong High Density Fibers Co., Ltd .: PCS2400, moisture content 7.0% by mass) is used with a sheet pelletizer (HOLAI Co., Ltd .: SGG-220 type). Chip-like pulp was produced by cutting into -5 mm square chips.

  The obtained chip-like pulp was dried under reduced pressure for 2 hours using a vacuum dryer (manufactured by Advantech Toyo Co., Ltd .: VO-320) at a temperature of 105 ° C. and a pressure of 20 kPa under flowing nitrogen. As a result, a dry chip-like pulp having an average degree of polymerization of 1878, a degree of crystallinity of 72%, and a moisture content of 3.0% by mass (per dry mass) was obtained. In addition, the ratio of the cellulose contained in the component which deducted the water | moisture content of the dry chip-like pulp is 95% or more, and the whole degree was considered as the cellulose below and the polymerization degree etc. were measured. Cellulose content was measured by the holocellulose quantification method described in pages 1081 to 1082 of the Japan Analytical Chemistry Society, Analytical Chemistry Handbook (4th revised edition, published on November 30, 1991, Maruzen Co., Ltd.). .

<Wetting process>
A screw having a capacity of 20 mL of 0.515 g of the obtained dry chip-like pulp (0.50 g as the dry mass of the cellulose-containing raw material, average polymerization degree 1878, crystallinity 72%, initial water content 3.0 mass%) It put into the pipe | tube, 0.485g of water was added, and the wet process was performed by leaving still at room temperature for 1 hour. As a result, 1.0 g of wet pulp having a water content of 100% by mass relative to the dry mass of the cellulose-containing raw material was obtained.

<Crushing process>
1.0 g of the obtained wet pulp (0.50 g as the dry mass of the cellulose-containing raw material, viscosity average polymerization degree 1878, crystallinity 72%, water content 100 mass%) was transferred to a container-driven freeze pulverizer. (Product number 6700, manufactured by SPEX Co., Ltd.), and pulverized for 1 minute at a rotational frequency of 5 Hz under cooling with liquid nitrogen (refrigerant temperature -196 ° C). Thereby, powdered cellulose was obtained. The median diameter of the obtained powdered cellulose was 45.8 μm. The viscosity average degree of polymerization was 1753, which was 93% of the viscosity average degree of polymerization of the cellulose-containing raw material.

(Example 2)
Except for using 0.75 g of wet pulp having a water content of 50 mass% prepared by adding 0.235 g of water to 0.515 g of dry chip-like pulp (0.50 g as the dry mass of the cellulose-containing raw material) Grinding was performed in the same manner as in Example 1. The median diameter of the obtained powdered cellulose was 97.1 μm. The viscosity average degree of polymerization was 1789, which was 95% of the viscosity average degree of polymerization of the cellulose-containing raw material.

(Example 3)
Using 0.15 g of water prepared by adding 0.135 g of water to 0.515 g of dry chip-like pulp (the dry mass of the cellulose-containing raw material), using 0.65 g of wet pulp having a water content of 30% by mass, Was pulverized in the same manner as in Example 1 except that the time was changed to 8 minutes. The obtained powdered cellulose had a median diameter of 88.6 μm. The viscosity average degree of polymerization was 1433, which was 76% of the viscosity average degree of polymerization of the cellulose-containing raw material.

Example 4
Grinding was carried out in the same manner as in Example 1 except that the amount of wet pulp was 2.0 g (1.0 g as the dry mass of the cellulose-containing raw material) and the grinding time was 3 minutes. The median diameter of the obtained powdered cellulose was 46.3 μm. The viscosity average degree of polymerization was 1763, which was 94% of the viscosity average degree of polymerization of the cellulose-containing raw material.

(Comparative Example 1)
The pulverization was performed in the same manner as in Example 1 except that 0.515 g of dry chip-like pulp having a water content of 3 mass% was used instead of the wet pulp. The median diameter of the obtained powdered cellulose was 745.7 μm. The viscosity average degree of polymerization was 1339, which was 71% of the viscosity average degree of polymerization of the cellulose-containing raw material.

(Comparative Example 2)
Grinding was performed in the same manner as in Comparative Example 1 except that the grinding time was 3 minutes. The obtained powdered cellulose had a median diameter of 45.2 μm. The viscosity average degree of polymerization was 1012 and was 54% of the viscosity average degree of polymerization of the cellulose-containing raw material.

(Comparative Example 3)
103 g of dried chip-like pulp obtained in the same step as the chip-forming step of Example 1 (100 g as the dry mass of the cellulose-containing raw material, average polymerization degree 1878, crystallinity 72%, water content 3.0 mass%) The product was put into a polyethylene bag with a chuck (manufactured by Nippon Co., Ltd .: Unipack J-4). Thereby, the wet pulp whose water content is 100 mass% was obtained.

  The obtained wet pulp was oscillated rod mill (Chuo Kako Co., Ltd .: MB-1, container total volume 3.5L, as a rod, φ30 mm, length 218 mm, 13 SUS304 rods with a circular cross section, filling rate 57 %), And pulverization was performed at 10 ° C. for 10 minutes at an amplitude of 8 mm and a rotation speed of 20 Hz. Thereby, cotton-like cellulose was obtained. The obtained cellulose had a median diameter of 569 μm. The viscosity average degree of polymerization was 1571, which was 84% of the viscosity average degree of polymerization of the cellulose-containing raw material. During pulverization, the jacket temperature of the pulverization vessel was set to 10 ° C. by an external closed system cooling water circulation device (manufactured by Yamato Kagaku Co., Ltd .: Neocool Circulator CF701G).

(Comparative Example 4)
Grinding was performed in the same manner as in Comparative Example 3 except that the grinding time was 60 minutes. The median diameter of the powdered cellulose thus obtained was 140 μm. The viscosity average degree of polymerization was 1068, which was 57% of the viscosity average degree of polymerization of the cellulose-containing raw material.

  Table 1 summarizes the results of each example and comparative example. As shown in Table 1, according to the methods of Examples 1 to 4, it is possible to obtain powdered cellulose having a small median diameter and a high degree of polymerization as compared with the methods of Comparative Examples 1 to 4.

  The present invention is useful as a method for producing powdered cellulose and a method for pulverizing cellulose.

Claims (9)

  A method for producing powdered cellulose, wherein a cellulose-containing raw material having a water content with respect to a dry mass of 30% by mass or more and 200% by mass or less is cooled and pulverized at an atmospheric temperature of −50 ° C. or less.   The manufacturing method of the powder cellulose of Claim 1 which grind | pulverizes so that the median diameter of powdered cellulose may be 10 micrometers or more and 120 micrometers or less.   The manufacturing method of the powdered cellulose of Claim 1 or 2 whose viscosity average polymerization degree of the cellulose contained in the said cellulose containing raw material is 500 or more and 3000 or less.   The manufacturing method of the powdered cellulose of any one of Claims 1-3 whose said cellulose containing raw material is a cotton linter.   The manufacturing method of the powder cellulose of any one of Claims 1-4 which grind | pulverize using a medium type grinder.   The method for producing powdered cellulose according to claim 5, wherein the medium type pulverizer is a container-driven pulverizer or a medium agitating pulverizer.   The manufacturing method of the powdered cellulose of any one of Claims 1-6 cooled to the said atmospheric temperature using a liquid coolant.   The method for producing powdered cellulose according to claim 7, wherein the liquid coolant is liquid nitrogen.   A cellulose pulverization method in which a cellulose-containing raw material containing 30% by mass or more and 200% by mass or less of water with respect to a dry mass is cooled and pulverized at an atmospheric temperature of −50 ° C. or less.