JP2011208293A - Polyvinyl alcohol-based composite fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength PVA-based composite fiber capable of being easily produced.SOLUTION: The PVA-based composite fiber is produced by preparing an aqueous solution produced by adding cellulose nanofibers to PVA, as a spinning solution (spinning solution-preparing step), excluding the spinning solution into cooled methanol through a nozzle to obtain a spun fiber gel like raw fiber (gel spinning step), and drawing the spun fiber gel-like raw fiber at a draw ratio of 16 to 38 (drawing step). Even when general-purpose, inexpensive PVA having a polymerization degree of 1,500 is used as a raw material, the high strength PVA-based composite fiber having a tensile strength of not less than 1.7 GPa can be obtained.

Description

  The present invention relates to a PVA composite fiber in which a polyvinyl alcohol (hereinafter referred to as PVA) polymer is reinforced with cellulose nanofibers.

  Even when a general-purpose inexpensive PVA having a polymerization degree of 1500 to 2000 is used as a raw material, a PVA composite fiber that can obtain a strength comparable to that of a PVA fiber manufactured using an expensive PVA having a polymerization degree of 3000 or more as a raw material. A manufacturing method is proposed in Patent Document 1, for example. In this document, a PVA aqueous solution containing iodine and iodide salt is used as a spinning stock solution, and a spinning gel-like raw yarn is obtained by extruding this spinning stock solution into a cooling bath through a nozzle, and further, the spinning gel-like raw yarn is drawn, The strength of the PVA composite fiber is improved.

JP 2008-13855 A

  However, in the production method of Patent Document 1, since iodine is contained in the PVA composite fiber, there is a problem that a process for removing this is required in the final stage of making the product.

  In view of the above problems, an object of the present invention is to propose a high-strength PVA composite fiber that is easy to manufacture and a method for manufacturing the same.

In order to solve the above problems, the PVA composite fiber of the present invention is
Cellulose nanofibers are dispersed and blended with the PVA polymer,
The PVA polymer and the cellulose nanofiber are oriented in the fiber axis direction.

  According to the present invention, the PVA composite fiber has a structure in which the stress applied to the fiber matrix is quickly transmitted to the strong cellulose nanofiber. Therefore, high strength of the PVA composite fiber is achieved. Moreover, since the cellulose nanofiber can use the safe thing created from the component derived from nature, it is not necessary to include the process of removing the remaining component in the final stage used as a product. Therefore, a PVA composite fiber can be provided by a simple manufacturing method.

  In the present invention, the PVA composite fiber desirably has a cellulose nanofiber content of 0.1 wt% to 50 wt% with respect to the polyvinyl alcohol polymer. That is, if the blending amount of the cellulose nanofiber is 50 wt% or less, the strength of the fiber can be improved while taking advantage of the breaking elongation and alkali resistance of the PVA fiber. Moreover, if the compounding quantity of a cellulose nanofiber is 0.1 wt% or more, the reinforcement effect by a cellulose nanofiber will be confirmed.

  In the present invention, the PVA polymer preferably has a polymerization degree of 1500 to 2000 and a tensile strength exceeding 1.7 GPa. That is, the PVA composite fiber has a tensile strength comparable to that of a PVA fiber produced using a PVA polymer having a high degree of polymerization even when a general-purpose inexpensive PVA polymer is used as a raw material. it can.

  In the present invention, the PVA polymer preferably has a degree of polymerization of 1500 to 2000 and a tensile elastic modulus of more than 50 GPa. That is, even when a general-purpose inexpensive PVA polymer is used as a raw material, the PVA composite fiber has a tensile elastic modulus comparable to that of a PVA fiber manufactured using a PVA polymer having a high degree of polymerization. Can do.

  In the present invention, in order to disperse and blend cellulose nanofibers in a PVA polymer, the cellulose nanofibers preferably have a fiber diameter of less than 100 nm and a fiber length of 100 nm or more.

  Furthermore, if the fiber diameter of the cellulose nanofiber is less than 50 nm, it is suitable for orienting the cellulose nanofiber together with the PVA polymer in the fiber axis direction.

Next, the method for producing the PVA composite fiber of the present invention is as follows.
A spinning solution preparation step of preparing a spinning solution in which cellulose nanofibers are blended with a polyvinyl alcohol-based polymer;
A spinning process in which the spinning solution is gelled by cooling to obtain a spinning gel-like raw yarn;
A stretching step of stretching the spun gel raw yarn;
It is characterized by including.

  As a result of intensive studies, the inventors of the present invention have a PVA-based composite fiber obtained by such a manufacturing method having higher strength than a PVA-based fiber manufactured without adding cellulose nanofibers. I found out. That is, the PVA composite fiber obtained by such a manufacturing method has a structure in which the stress applied to the fiber matrix is quickly transmitted to the strong cellulose nanofiber, so that the strength of the PVA composite fiber is increased. Achieved. Moreover, since the cellulose nanofiber can use the safe thing created from the component derived from nature, it is not necessary to include the process of removing the remaining component in the final stage used as a product. Therefore, the PVA composite fiber can be provided by a simple manufacturing method.

  In this invention, it is desirable to mix | blend a cellulose nanofiber so that it may become a compounding quantity of 0.1 wt%-50 wt% with respect to a polyvinyl alcohol-type polymer at a spinning solution preparation process. If the blending amount of the cellulose nanofibers in the spinning solution is 50 wt% or less, the strength of the fibers can be improved while taking advantage of the degree of elongation at break and the alkali resistance of the PVA fibers. Moreover, if the blending amount of the cellulose nanofibers in the spinning solution is 0.1 wt% or more, the reinforcing effect by the cellulose nanofibers is confirmed.

  In the present invention, the PVA polymer has a degree of polymerization of 1500 to 2000, and in the stretching step, it is desirable to stretch the spun gel-like yarn so that the tensile strength exceeds 1.7 GPa. In this way, even when a general-purpose inexpensive PVA polymer is used as a raw material, a PVA composite fiber having a tensile strength comparable to that of a PVA fiber produced using a PVA polymer having a high degree of polymerization can be produced. .

  In the present invention, the PVA polymer has a degree of polymerization of 1500 to 2000, and in the stretching step, it is desirable to stretch the spun gel raw yarn so that the tensile elastic modulus exceeds 50 GPa. In this way, even when a general-purpose inexpensive PVA polymer is used as a raw material, a PVA composite fiber having a tensile elastic modulus comparable to that of a PVA fiber produced using a PVA polymer having a high degree of polymerization is produced. it can.

  In the present invention, in order to disperse and blend cellulose nanofibers in a PVA polymer, the cellulose nanofibers preferably have a fiber diameter of less than 100 nm and a fiber length of 100 nm or more.

  Furthermore, if the fiber diameter of the cellulose nanofiber is less than 50 nm, it is suitable for orienting the cellulose nanofiber together with the PVA polymer in the fiber axis direction.

  In the present invention, in the spinning solution preparation step, it is desirable to use water or dimethyl sulfoxide or a mixed solution of water and dimethyl sulfoxide as a solvent for the spinning solution. Here, if water is used as the solvent, the production cost of the PVA composite fiber can be suppressed. When dimethyl sulfoxide is used as the solvent, the strength of the PVA composite fiber produced is improved as compared with the case where the solvent is water alone, and the solvent can be easily recovered and reused. If a mixed solution of water and dimethyl sulfoxide is used as a solvent, it is suitable for dispersing PVA and cellulose nanofibers, and a high-strength PVA composite fiber can be obtained as compared with the case where the solvent is water alone.

  The PVA composite fiber of the present invention has a structure in which the stress applied to the fiber matrix is quickly transmitted to the strong cellulose nanofiber. Therefore, high strength of the PVA composite fiber is achieved. Moreover, since the cellulose nanofiber can use the safe thing created from the component derived from nature, it is not necessary to include the process of removing the remaining component in the final stage used as a product. Therefore, the PVA composite fiber of the present invention can be provided by a simple manufacturing method.

It is a transmission electron microscope image of the cellulose nanofiber which uses cotton as a cellulose source. It is a transmission electron microscope image of the cellulose nanofiber derived from a sea squirt. It is a flowchart which shows the manufacturing method of a PVA type composite fiber. It is the stress-strain curve obtained by the tension test about the PVA type composite fiber of Examples 1-5. It is a graph which shows the tensile strength of the PVA type composite fiber of Examples 1-5. It is a graph which shows the tensile elasticity modulus of the PVA type composite fiber of Examples 1-5. It is a graph which shows the breaking elongation of the PVA type composite fiber of Examples 1-5. It is a graph which shows the knot | strong strength of the PVA type composite fiber of Examples 1-5. It is a graph which shows the temperature dependence of the dynamic storage elastic modulus of the undrawn fiber of Examples 1-5. It is a graph which shows the temperature dependence of the dynamic storage elastic modulus of the stretched fiber of Examples 1-5. It is a graph which shows the DSC curve of the undrawn fiber of Examples 1-5. It is a graph which shows the DSC curve of the drawn fiber of Examples 1-5. It is a X-ray-diffraction photograph of the undrawn fiber of Examples 1-5. It is an X-ray diffraction photograph of the drawn fiber of Examples 1-5. It is a scanning electron microscope image of Examples 1, 2, 4, and 5. It is a graph which shows the temperature dependence of the dynamic storage elastic modulus of the stretched fiber of Examples 6-8.

  Hereinafter, embodiments of the present invention will be described in detail.

(Cellulose nanofiber)
As the cellulose nanofiber used in the present invention, a general cellulose nanofiber, that is, a fiber diameter of 100 nm or less and a fiber length of 100 nm or more can be used. Cellulose sources of cellulose nanofibers include cotton, hemp, vegetation such as conifers and broadleaf trees, seaweed, seaweed, cellulose produced by sea squirts, and bacterial cellulose produced by certain acetic acid bacteria. FIG. 1 is a transmission electron microscope image of cellulose nanofibers using cotton as a cellulose source. FIG. 2 is a transmission electron microscope image of sea squirt-derived cellulose nanofibers.

  As the cellulose nanofiber, those created by a known method can be used. For example, cellulose nanofibers obtained by selectively hydrolyzing non-crystalline portions of cellulose fibers such as cotton and hemp with a mineral acid aqueous solution can be used. Cellulose nanofibers obtained by dispersing cellulose fibers in an aqueous medium and fibrillating cellulose microfibrils obtained by TEMPO (2, 2, 6, 6-tetramethylpiperidinooxy radical) catalytic oxidation Can be used. Furthermore, cellulose nanofibers obtained by defibrating cellulose microfibrils obtained by subjecting an aqueous dispersion of cellulose to a high-pressure homogenizer treatment can be used. Furthermore, ionic functional groups such as sulfate ester groups, phosphate ester groups, carboxyl groups, primary, secondary, tertiary, and quaternary amino groups are introduced into the surface of these cellulose nanofibers by chemical post-treatment. It is also possible to use nanofibers with improved dispersibility. In order to obtain a high-strength PVA composite fiber, it is preferable to use a cellulose nanofiber having a high degree of crystallinity. If cellulose nanofibers having a fiber diameter of 50 nm or less are used, it is easy to disperse and blend the cellulose nanofibers in the PVA polymer, and the cellulose nanofibers are aligned with the PVA polymer in the fiber axis direction. Suitable for

(PVA)
As PVA, those having a polymerization degree of 1500 to 5000 can be used. In order to obtain high-strength PVA-based composite fibers, those having a high degree of polymerization are preferred. However, by using inexpensive general-purpose PVA having a degree of polymerization of 1500 to 2000, the production cost of the PVA-based composite fibers can be suppressed.

  Although there is no big restriction | limiting about the saponification degree of PVA, 90 mol% or more is preferable in order to advance the gelatinization by cooling rapidly, Moreover, from a heat resistant and water-resistant viewpoint of the PVA type composite fiber manufactured, More preferably, it is about 99 mol% or more. PVA may contain some copolymer component such as other vinyl group-containing monomers such as vinyl acetate, ethylene, polyethylene glycol, etc., but this ratio is preferably small.

(Method for producing PVA composite fiber)
FIG. 3 is a flowchart showing a method for producing a PVA composite fiber. The method for producing a PVA composite fiber of the present invention comprises a spinning solution preparation step for preparing a spinning solution containing a PVA polymer and cellulose nanofiber, a deaeration step for degassing the spinning solution, and cooling the spinning solution. The method includes a spinning step of gelling to obtain a spun gel raw yarn, a solvent removal / drying step of removing and drying the spun gel raw yarn, and a stretching step of drawing the spun gel raw yarn.

  In the spinning solution preparation step, a method of adding solid cellulose nanofibers to a PVA polymer solution, a method of mixing a PVA polymer solution and a solvent dispersion of cellulose nanofibers, and a solid solution of a cellulose nanofiber solvent dispersion Any method of adding a PVA polymer and dissolving the PVA polymer, or a method of dispersing and dissolving a solid content obtained by drying a cellulose nanofiber dispersion and solid PVA in a solvent can be used. In this example, a PVA polymer aqueous solution in which a PVA polymer is dissolved is mixed with a dispersion in which cellulose nanofibers are dispersed in water.

  The solvent for the spinning solution is not particularly limited as long as it can easily dissolve the PVA-based polymer and highly disperse the cellulose nanofibers. For example, water or dimethyl sulfoxide, or water and dimethyl A mixed solution of sulfoxide can be used. Here, if water is used as the solvent, the production cost of the PVA composite fiber can be suppressed. When dimethyl sulfoxide is used as the solvent, the strength of the PVA composite fiber produced is improved as compared with the case where the solvent is water alone, and the solvent can be easily recovered and reused. If a mixed solution of water and dimethyl sulfoxide is used as a solvent, it is suitable for dispersing PVA and cellulose nanofibers, and a high-strength PVA composite fiber can be obtained as compared with the case where the solvent is water alone.

  Here, if the blending amount of the cellulose nanofibers with respect to the PVA polymer in the spinning solution is 50 wt% or less, the strength of the fiber is improved while taking advantage of the breaking elongation and alkali resistance, which are the characteristics of the PVA fibers. be able to. Moreover, if the compounding quantity of the cellulose nanofiber with respect to PVA-type polymer in a spinning solution shall be 0.1 wt% or more, the reinforcement effect by a cellulose nanofiber will be confirmed. Furthermore, if the blending amount of the cellulose nanofiber with respect to the PVA polymer in the spinning solution is 1 wt% or more, the reinforcing effect by the cellulose nanofiber becomes remarkable. In addition, the compounding quantity of the cellulose nanofiber with respect to PVA type polymer in the PVA type composite fiber manufactured by the manufacturing method of this example becomes a value substantially the same as the compounding quantity of the cellulose nanofiber with respect to the PVA type polymer in the spinning solution.

  Here, in order to improve the strength of the PVA composite fiber, it is preferable that the cellulose nanofibers are uniformly dispersed in the spinning solution. For this reason, the PVA polymer aqueous solution and the dispersion of cellulose nanofibers are sufficiently mixed while stirring. In this example, mixing is performed using a rotary evaporator, a homogenizer, or the like.

  After mixing the PVA polymer solution and the cellulose nanofiber solvent dispersion, a degassing step is performed. In this example, the spinning dope is degassed by leaving it at 80 ° C. for 4 hours or longer. For example, by using a stirring defoaming mixer manufactured by Shinky Co., Ltd. It can also foam.

  The spinning process is performed by a gel spinning method. As the gel spinning method for transferring the spinning solution from the sol to the gel, dry gelation by blowing a cooling gas can be used, but in this example, the spinning solution is solidified from a nozzle with a cooling solvent such as methanol. A spun gel raw yarn is obtained by using extruded gel spinning extruded into a bath. Extruded gel spinning can produce fibers with a uniform and stable structure. Further, according to extrusion gel spinning, the PVA polymer and cellulose nanofibers are sheared between the solution and the nozzle at the time of spinning, or by the extension flow acting on the spinning solution until it is discharged from the nozzle and solidified, It can be oriented in the fiber axis direction.

  Here, since the spinning solution has a high viscosity around room temperature, the spinning solution may gel in some cases, which hinders spinning. Therefore, it is desirable to perform gel spinning in a complete sol (solution) state by heating the spinning solution to 70 ° C. or more for the purpose of imparting spinnability to lower the solution viscosity. For rapid solidification, it is preferable to use a cooling solvent in the range of -40 ° C to 10 ° C. In this example, -10 [deg.] C. cooled methanol is used.

  Next, a solvent removal / drying step is performed. In this example, the spun gel raw yarn is dipped in an organic solvent such as methanol to proceed with desolvation, and then air-dried or dried under reduced pressure. The spun gel raw yarn can be air-dried or dried under reduced pressure without using an organic solvent.

  In the stretching step, the dried spun gel raw yarn is subjected to dry heat stretching, and the PVA polymer and cellulose nanofibers are oriented in the fiber axis direction by a shearing action caused by plastic deformation accompanying stretching. In this example, the draw ratio is 16 to 38 times. The stretching atmosphere in dry heat stretching is preferably an inert gas such as nitrogen in order to suppress oxidative degradation.

  Hereinafter, embodiments of the present invention will be described in detail.

(Examples 1-5)
Examples 1-5 add the cellulose nanofiber derived from cotton to PVA. As the raw material PVA polymer, a PVA polymer having a polymerization degree of 1500 and a saponification degree of 99.9 mol% is used. As the cellulose nanofibers, those having a fiber diameter of 5 nm to 10 nm and a fiber length of 100 to 150 nm are used.

  In the spinning dope preparation step, each aqueous solution prepared by adding 5 wt%, 10 wt%, 15 wt%, 20 wt%, and 30 wt% of cellulose nanofibers to the PVA polymer was used as the spinning dope for Examples 1 to 5, respectively. . A PVA polymer aqueous solution and a dispersion obtained by dispersing cellulose nanofibers in water are mixed at 100 ° C. over 1 hour using a rotary evaporator. In the comparative example, cellulose nanofibers were not added to the PVA polymer, and a PVA polymer aqueous solution was used as the spinning dope. In each example and comparative example, the final spinning solution has a PVA-based polymer concentration of 15 wt%.

  In the degassing step, each spinning dope is left at 80 ° C. for 4 hours.

  In the spinning step, the spinning solution is heated to 75 ° C., and extruded into cooled methanol at −10 ° C. using a 22 GPa (gauge) nozzle to obtain a spun gel raw yarn.

  In the solvent removal / drying step, each spinning gel raw yarn is immersed in cooled methanol for 24 hours and then dried in air.

  In the stretching step, the spun gel raw yarn is hand-drawn in an oven at 210 ° C. and stretched 24 to 25 times using a stretching machine.

(Characteristics of Examples 1 to 5)
4 to 9 show the characteristics of the PVA composite fibers of each example and the PVA fibers of the comparative example. FIG. 4 is a stress-strain curve obtained by a tensile test for each of the PVA composite fibers of Examples 1 to 5 and the PVA fiber of the comparative example. 5 to 8 are graphs showing the tensile strength, tensile elastic modulus (Young's modulus), elongation at break, and knot strength of each PVA composite fiber of Examples 1 to 5 and PVA fiber of Comparative Example, respectively. is there. The knot strength was determined by forming a single knot in the middle of the fiber and conducting a tensile test. The tensile test was performed using a Tensilon RTC1250A tensile tester manufactured by A & D Co., Ltd. at room temperature, an original length of 40 mm, and a tensile speed of 100% / min. Table 1 summarizes the characteristics of each example and comparative example.

  As shown in Table 1, all of the PVA composite fibers of Examples 1 to 5 have a tensile strength of 1.7 GPa or more and a tensile modulus of 50 GPa or more and a high strength and a high modulus of elasticity. Better than. In addition, the PVA composite fibers of Examples 1 to 5 have a knot strength of 150 MPa or more, which is superior to the PVA fibers of the comparative example. Regarding the breaking elongation, the value is not significantly lower than the value of the PVA fiber of the comparative example, and the value of 4% or more is maintained.

  In particular, Examples 1 and 2 in which 5 wt% and 10 w% of cellulose nanofibers are added to the PVA polymer are higher in tensile strength than 2 GPa, and expensive PVA having a polymerization degree of 3000 or more is used as a raw material. It is comparable to or better than PVA fiber. In Examples 1 and 2, the tensile modulus is 60 GPa or more, the knot strength is 160 MPa or more, the elongation at break is 5% or more, and excellent mechanical properties are provided.

  Here, if there is little addition amount of a cellulose nanofiber, a cellulose nanofiber can be easily disperse | distributed in a spinning solution preparation process. Moreover, since the cost of the raw material can be suppressed, the manufacturing cost of the PVA composite fiber can be suppressed.

  Next, FIG. 9 is a graph showing the temperature dependence of the dynamic storage elastic modulus of the undrawn fiber (spun gel raw yarn) of each example, and FIG. 10 shows the drawn fiber (after the drawing step) of each example. It is a graph which shows the temperature dependence of the dynamic storage elastic modulus of the manufactured PVA-type composite fiber). The dynamic viscoelasticity measurement is performed using ITK DVA-225 manufactured by IT Measurement Control Co., Ltd., with an original length of 20 mm, a tensile mode, a frequency of 10 Hz, and a temperature rising rate of 10 ° C./min.

  According to FIG. 9, the elastic modulus increases as the amount of cellulose nanofiber added increases. In particular, the degree of decrease in the elastic modulus at a high temperature range is small, and it can be seen that the heat resistance is improved by the addition of cellulose nanofibers. According to FIG. 10, the drawn fibers of Examples 1 to 5 (PVA composite fibers produced through the drawing process) have a lower dynamic storage elastic modulus at high temperatures than the PVA fibers of the comparative example. The degree of is small. That is, the PVA composite fiber has a small degree of decrease in elastic modulus even at high temperatures and is suitable for applications such as tire cords.

  FIG. 11 is a graph showing a DSC (Differential Scanning Calorimetry) curve of undrawn fiber (spun gel raw yarn) of each example, and FIG. 12 is a drawn fiber (PVA produced through a drawing process) of each example. It is a graph which shows the DSC curve of a system composite fiber). Differential scanning calorimetry is performed using Thermo Plus II manufactured by Rigaku Corporation at a sample weight of about 3 mg and a heating rate of 10 ° C./min.

  According to FIG. 11, although the melting | fusing point of a PVA polymer component falls in the PVA type composite fiber of Examples 1-5, this is because the hydroxyl groups of both are hydrogen bonding in the interface of a PVA type polymer and a cellulose nanofiber. This is considered to be because the crystal growth is less likely to occur compared to the PVA alone because the PVA is strongly bonded and partially inhibits the crystallization of PVA. This is considered that the hydrogen bond between PVA and cellulose is strong, and the adhesiveness between the matrix and the filler is high. Here, if the adhesiveness between the filler and the matrix is high, the stress applied to the fiber matrix is quickly transmitted to the strong nanofibers, and a reinforcing effect is exhibited. Therefore, it is considered that high strength of the PVA composite fiber is achieved.

  According to FIG. 12, since the melting point of the PVA polymer component is almost the same for all the stretched fibers, crystallization of PVA proceeds by orientation crystallization during stretching, and cellulose nanofibers are not added. It is thought that it became the same crystal as the sample. Therefore, it is thought that cellulose nanofiber exists in the amorphous part of the PVA component.

  Next, FIG. 13 is an X-ray diffraction photograph of the unstretched fiber (spun gel raw yarn) of each example, and FIG. 14 is a stretched fiber of each example (PVA composite fiber produced through a stretching process). Is an X-ray diffraction photograph of In particular, from the photograph in FIG. 14, it is confirmed that the PVA polymer and cellulose nanofibers are highly oriented in the fiber axis direction by stretching.

  FIG. 15 is a scanning electron microscope image of an example in which a fiber blender (Commercial Laboratory Blender 7012G manufactured by Waring) was used and the fiber was defibrated for 30 seconds at room temperature, in water, and at a blender blade speed of 14500 rpm. In FIG. 15, the scanning electron microscope image of Example 3 is omitted. According to FIG. 15, although clear fibrillation is seen in the PVA fiber of the comparative example, fibrillation that causes a decrease in fiber physical properties is greatly suppressed in the case of adding cellulose nanofibers.

(Examples 6 to 8)
Examples 6 to 8 below are obtained by adding sea squirt-derived cellulose nanofibers to PVA. As the raw material PVA polymer, a PVA polymer having a polymerization degree of 1500 and a saponification degree of 99.9 mol% is used. Moreover, as a cellulose nanofiber, the fiber diameter is 10 nm-25 nm, and the fiber length is 1 micrometer-3 micrometers.

  In the spinning dope preparation step, each aqueous solution prepared by adding 1 wt%, 3 wt%, and 5 wt% of cellulose nanofibers to the PVA polymer was used as the spinning dope of Examples 6-8. In Examples 6 to 8, a PVA polymer aqueous solution and a dispersion obtained by dispersing cellulose nanofibers in water were mixed using a homogenizer over 10 minutes under the conditions of 80 ° C. and 10,000 rpm. In the comparative example, cellulose nanofibers were not added to the PVA polymer, and a PVA polymer aqueous solution was used as the spinning dope. In each of Examples and Comparative Examples, the final spinning solution has a PVA polymer concentration of 13 wt%.

  In the degassing step, each spinning dope is left at 80 ° C. overnight.

  In the spinning step, the spinning solution is heated to 75 ° C., and extruded into cooled methanol at −10 ° C. using a 22 GPa (gauge) nozzle to obtain a spun gel raw yarn.

  In the solvent removal / drying step, each spun gel raw yarn is immersed in cooled methanol for 24 hours and then dried in air.

  In the stretching step, the spun gel raw yarn is hand-drawn in an oven at 210 ° C. and stretched to a stretching ratio close to the limit using a stretching machine. In Examples 6 to 8, the draw ratios are different from each other, 38 times in Example 6, 28 times in Example 7, and 16 times in Example 8. The draw ratio of the comparative example is 32 times.

(Characteristics of Examples 6 to 8)
Table 2 shows the characteristics of the PVA composite fibers of Examples 6 to 8 and the PVA fibers of the comparative examples. The tensile test is performed in the same manner as in Examples 1-5.

  As shown in Table 1, all of the PVA composite fibers of Examples 6 to 8 have a tensile strength of 1.8 GPa or more and a tensile modulus of 50 GPa or more and a high strength and a high modulus of elasticity. Better than. Moreover, about the elongation at break, the value is not significantly lower than the value of the PVA fiber of the comparative example, and the value of 3.8% or more is maintained.

  Here, in Examples 6 to 8, since the blending amount of the cellulose nanofiber with respect to the PVA polymer is a small amount of 1 wt% to 5 w%, the cellulose nanofiber can be easily dispersed in the spinning solution preparation step. Moreover, since the cost of the raw material can be suppressed, the manufacturing cost of the PVA composite fiber can be suppressed.

  FIG. 16 is a graph showing the temperature dependence of the dynamic storage elastic modulus of the drawn fiber (PVA composite fiber produced through the drawing process) of each example. The dynamic viscoelasticity measurement is performed by the same method as in Examples 1-5. The PVA composite fibers of Examples 6 to 8 have a lower degree of decrease in dynamic storage elastic modulus at high temperatures than the PVA fibers of Comparative Examples. That is, the PVA composite fiber has a small degree of decrease in elastic modulus even at high temperatures and is suitable for applications such as tire cords.

  The scope of the present invention is not limited to these examples.

Claims (13)

Cellulose nanofibers are dispersed and blended in a polyvinyl alcohol polymer,
The polyvinyl alcohol-based composite fiber, wherein the polyvinyl alcohol-based polymer and the cellulose nanofiber are oriented in the fiber axis direction. In claim 1,
A polyvinyl alcohol composite fiber, wherein a blending amount of cellulose nanofibers is 0.1 wt% to 50 wt% with respect to the polyvinyl alcohol polymer. In claim 1 or 2,
The polyvinyl alcohol polymer has a polymerization degree of 1500 to 2000,
A polyvinyl alcohol composite fiber characterized by having a tensile strength exceeding 1.7 GPa. In claim 1 or 2,
The polyvinyl alcohol polymer has a polymerization degree of 1500 to 2000,
A polyvinyl alcohol-based composite fiber having a tensile elastic modulus exceeding 50 GPa. In any one of claims 1 to 4,
The cellulose nanofiber is a polyvinyl alcohol composite fiber having a fiber diameter of less than 100 nm and a fiber length of 100 nm or more. In claim 5,
The cellulose nanofiber is a polyvinyl alcohol composite fiber having a fiber diameter of less than 50 nm. A spinning solution preparation step of preparing a spinning solution in which cellulose nanofibers are blended with a polyvinyl alcohol-based polymer;
A spinning process in which the spinning solution is gelled by cooling to obtain a spinning gel-like raw yarn;
A stretching step of stretching the spun gel raw yarn;
A process for producing a polyvinyl alcohol-based composite fiber, comprising: In claim 7,
In the spinning solution preparation step, a cellulose nanofiber is blended so as to have a blending amount of 0.1 wt% to 50 wt% with respect to the polyvinyl alcohol polymer. In claim 7 or 8,
The polyvinyl alcohol polymer has a polymerization degree of 1500 to 2000,
In the drawing step, the spinning gel-like raw yarn is drawn so that the tensile strength exceeds 1.7 GPa. In claim 7 or 8,
The polyvinyl alcohol polymer has a polymerization degree of 1500 to 2000,
In the drawing step, the spinning gel-like raw yarn is drawn so that the tensile elastic modulus exceeds 50 GPa. In any one of claims 7 to 10,
The method for producing a polyvinyl alcohol-based composite fiber, wherein the cellulose nanofiber has a fiber diameter of less than 100 nm and a fiber length of 100 nm or more. In claim 11,
The method for producing a polyvinyl alcohol-based composite fiber, wherein the cellulose nanofiber has a fiber diameter of less than 50 nm. In any one of claims 7 to 12,
In the spinning solution preparation step, water or dimethyl sulfoxide or a mixed solution of water and dimethyl sulfoxide is used as a solvent for the spinning solution.