Polyvinyl alcohol-based fibers

Abstract

Polyvinyl alcohol fibers are composed of polyvinyl alcohol polymers and layered silicates. The proportion of layered silicates is 30–400 parts by mass relative to 100 parts by mass of polyvinyl alcohol polymer, and the fiber swelling degree is 200–600%.

Description

Technical Field

[0001] This invention relates to polyvinyl alcohol fibers containing layered silicates. Background Technology

[0002] Layered silicates are the main components of clay minerals that are abundant in the Earth's surface. They are widely used as fillers in cosmetics, paper, etc. In particular, due to their excellent adsorption properties, they are used, for example, as adsorbents to adsorb and remove adsorbed substances contained in treatment liquids.

[0003] For example, a method for purifying water using layered silicates as adsorbents for adsorbing and removing contaminants (such as cesium) from water has been proposed (see Patent Document 1). For example, a method for purifying oil using clay minerals, primarily composed of hydrated aluminosilicates, or their purified forms as adsorbents (inorganic powders) for adsorbing and removing food residues and dissolved components present in waste oil (edible oil) has been proposed (see Patent Document 2).

[0004] However, in the methods described in the aforementioned patent documents 1 and 2, in order to obtain sufficient adsorption, it is necessary to use particulate (powder) layered silicates. Therefore, when used as adsorbents, the operability is poor and the adsorbent recovery process becomes complicated.

[0005] Furthermore, an adsorbent (deodorant) has been proposed, which is made by spinning a fiber raw material containing a thermoplastic polymer compound and an adsorbent for adsorbing odors into a fibrous form. It is also described that by using such an adsorbent, a high deodorization efficiency can be maintained for a long period of time (see, for example, Patent Document 3).

[0006] Prior art literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2013-696

[0008] Patent Document 2: Japanese Patent No. 2959975

[0009] Patent Document 3: Japanese Patent Application Publication No. 2-157040 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] However, in the fiber described in the aforementioned Patent Document 3, since the adsorbent is covered by a hydrophobic polymer, there is a problem that the adsorption capacity cannot be fully utilized when the adsorbent is used in an aqueous solution, for example.

[0012] Methods for solving technical problems

[0013] In order to achieve the above object, the polyvinyl alcohol fiber of the present invention is a polyvinyl alcohol fiber containing a polyvinyl alcohol polymer and a layered silicate, characterized in that: relative to 100 parts by mass of the polyvinyl alcohol polymer, the proportion of the layered silicate is 30 to 400 parts by mass, and the fiber swelling degree is 200 to 600%.

[0014] Effect of the invention

[0015] According to the present invention, polyvinyl alcohol fibers with excellent adsorption performance can be provided. Brief description of the drawings

[0016] Figure 1 It is a photograph of the PVA-based fiber prepared in Example 1 observed with a scanning electron microscope (SEM).

[0017] Figure 2 It is a photograph of the PVA-based fiber prepared in Example 2 observed with a scanning electron microscope (SEM). Detailed description of the specific implementation

[0018] The present invention will be described in detail below. The polyvinyl alcohol fiber of the present invention (hereinafter referred to as "PVA-based fiber") is composed of a polyvinyl alcohol polymer (hereinafter referred to as "PVA-based polymer") and a layered silicate.

[0019] <PVA-based polymer>

[0020] The PVA-based polymer constituting the PVA-based fiber of the present invention may be a polymer mainly composed of vinyl alcohol units, and is not particularly limited, and may also have other structural units. Such structural units that can be cited are, for example: olefins such as ethylene, propylene, and butene; acrylic acid and its salts, acrylic esters such as methyl acrylate; methacrylic acid and its salts, methacrylate esters such as methyl methacrylate; acrylamide derivatives such as acrylamide and N-methylacrylamide; methacrylamide derivatives such as methacrylamide and N-hydroxymethylmethacrylamide; N-vinylamide classes such as N-vinylpyrrolidone, N-vinylformamide, and N-vinylacetamide; allyl ethers having polyalkyleneoxide on the side chain; vinyl ethers such as methyl vinyl ether; nitriles such as acrylonitrile; vinyl halides such as vinyl chloride; unsaturated dicarboxylic acids such as maleic acid and its salts, its anhydride, and its esters. The introduction method of the above-mentioned modified units may be by copolymerization or by post-reaction.

[0021] The degree of saponification of the PVA-based polymers of the present invention is not particularly limited, but from the viewpoint of the crystallinity and orientation of the obtained fibers, it is preferably 98 mol% or more, more preferably 99 mol% or more. A degree of saponification of 99.7 mol% or more provides excellent hot water resistance and is therefore particularly preferred.

[0022] The degree of polymerization of the PVA-based polymers of the present invention is not particularly limited. Considering the mechanical properties and dimensional stability of the obtained fibers, PVA-based polymers with an average degree of polymerization of 1200 to 20000, determined by the viscosity of the aqueous solution at 30°C, are preferred. High-degree-of-polymer PVA-based polymers exhibit superior strength and resistance to damp heat, and are therefore preferred. However, from the viewpoint of cost in manufacturing the polymer and cost in fiberization, PVA-based polymers with an average degree of polymerization of 1500 to 5000 are particularly preferred.

[0023] The content of PVA polymers in the entire PVA fiber is preferably in the range of 20% to 77% by mass. This is because: when the content of PVA polymers is less than 20% by mass, it is sometimes difficult to form PVA fibers; when the content of PVA polymers is greater than 77% by mass, the adsorption performance cannot be fully utilized when used as an adsorbent material.

[0024] <Layered Silicates>

[0025] Preferably, the layered silicate of the present invention has a layer charge of 0.2 to 2.0 and a cation exchange capacity of 50 to 200 meq / 100g.

[0026] Specifically, examples include: montmorillonite, saponite, bedesite, chloropyrite, hydropyrite, and montmorillonite-type clay compounds such as styraxite (e.g., bentonite with montmorillonite as the main component), and clay minerals such as mica. These substances can be natural or synthetic. In this invention, these layered silicates can be used alone, or two or more of the above-mentioned layered silicates can be combined for use.

[0027] In the PVA-based fibers of the present invention, the content of the layered silicate is 30 to 400 parts by mass, preferably 60 to 300 parts by mass, relative to 100 parts by mass of the PVA-based polymer. This is because: when the content of the layered silicate is less than 30 parts by mass, since the coverage rate of the PVA-based polymer on the layered silicate becomes high, the permeability of the treatment liquid decreases, and as a result, the adsorptivity for adsorbates contained in the treatment liquid may not be fully exerted; when the content of the layered silicate is greater than 400 parts by mass, it is sometimes difficult to form a fiber shape (i.e., fibrillation) in the PVA-based fibers, and a large amount of the layered silicate detaches from the PVA-based fibers and mixes into the treatment liquid.

[0028] That is, when the content of the layered silicate is set to 30 to 400 parts by mass relative to 100 parts by mass of the PVA-based polymer, the problem of the layered silicate detaching from the fibers and mixing into the treatment liquid will not occur, and fine pores for adsorbing adsorbates can be formed, thereby obtaining PVA-based fibers with excellent adsorptivity (refer to Figure 1 , Figure 2 in the examples described later).

[0029] The average particle size of the layered silicate is not particularly limited, and is preferably 0.1 to 100 μm. This is because: when the average particle size of the layered silicate is less than 0.1 μm, since it is difficult to form fine pores in the fibers, the permeability of the treatment liquid penetrating into the fibers decreases, and thus the adsorptivity of the layered silicate decreases; when the average particle size of the layered silicate is greater than 100 μm, it is sometimes difficult to form a fiber shape in the PVA-based fibers, and a large amount of the layered silicate detaches from the PVA-based fibers and mixes into the treatment liquid.

[0030] The "average particle size" mentioned here refers to the 50% particle size (D50), and can be measured by a particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Nanotrac (registered trademark) particle size distribution measuring device UPA-EX150) using the laser Doppler method, etc.

[0031] <PVA-based fibers>

[0032] The PVA fibers of this invention have a fiber swelling degree of 200-600%. This is because: when the fiber swelling degree is less than 200%, the adsorption capacity decreases due to reduced permeability of the treatment solution. When the fiber swelling degree is greater than 600%, the fiber itself absorbs a large amount of treatment solution, causing its size to change with the swelling, making it difficult to recover and replace after adsorption treatment. Furthermore, the operability decreases because PVA resin dissolves and layered silicates easily detach from the PVA fibers. Moreover, the gaps for the treatment solution to pass through become smaller, reducing liquid permeability.

[0033] That is, by setting the fiber swelling degree of PVA fibers to 200-600%, PVA fibers with excellent adsorption properties can be obtained without causing a decrease in operability and liquid permeability.

[0034] It should be noted that the “fiber swelling degree” mentioned here refers to the fiber swelling degree calculated using the formula (1) described later.

[0035] The preferred single filament fineness of PVA fibers is in the range of 2 to 600 dtex. This is because: when the fiber is finer, the surface area increases, thus enabling more effective adsorption performance. However, when the single filament fineness is less than 2 dtex, insufficient strength leads to reduced operability. When the single filament fineness is greater than 600 dtex, the adsorption performance may not be fully utilized, and the fiber's softness decreases, resulting in reduced operability.

[0036] The PVA-type fibers of the present invention are obtained by solution spinning of a spinning solution containing a PVA-type polymer and layered silicates, specifically by any one of the following spinning methods: wet spinning, dry-wet spinning, and dry spinning. The solvent used as the spinning solution can be one or a combination of two or more solvents used in the prior art for manufacturing PVA-type fibers. Examples of solvents used in the prior art include: dimethyl sulfoxide (DMSO); dimethylformamide; dimethylacetamide; methanol; water; or polyols such as glycerol, ethylene glycol, and triethylene glycol; diethylenetriamine; and thiocyanate. From the viewpoint of supply and environmental impact, DMSO and water are particularly preferred. The polymer concentration in the spinning solution varies depending on the composition, degree of polymerization of the PVA-type polymer, and the solvent, but is typically in the range of 6 to 60% by mass.

[0037] Without impairing the effects of the present invention, the spinning solution may contain, in addition to PVA polymers and layered silicates, additives such as antioxidants, antifreeze agents, pH adjusters, masking agents, colorants, and oils, depending on the purpose.

[0038] The PVA-based fibers of the present invention can be used in various fiber forms such as staple fibers, chopped fibers, filament yarns, and staple fiber yarns. The cross-sectional shape of the fibers is not particularly limited and can be a circular cross-section, a hollow cross-section, or a special cross-section such as a star shape.

[0039] The fibers of the present invention can also be mixed and combined with other fibers for use. At this time, the fibers that can be combined are not particularly limited, and examples include PVA-based fibers that do not contain layered clay compounds, polyester fibers, polyamide fibers, cellulose fibers, etc. In addition, it can also be used as fiber structures such as crimped cotton, fabrics, non-woven fabrics, and paper.

[0040] The fiber structures of the present invention can be applied to various uses such as beverages, clothing, and medical applications. For example, they can be used for: adsorbents that adsorb the adsorbed substances contained in the treatment liquid (for example, adsorption filters for removing caffeine contained in coffee extracts or green tea, adsorption filters for removing proteins from alcohol or edible oil), and various adsorption filters formed by fiber structures such as filaments, chopped fibers, crimped cotton, fabrics, and paper.

[0041] The PVA-based fibers of the present invention can be used in the following situations: when the cut short fibers are put into a treatment liquid container to treat the treatment liquid; when the crimped cotton is formed into a fiber rod shape and the treatment liquid is passed through the fiber rod for treatment; when it is formed into a long filament shape and then made into a wound filter element and the treatment liquid is passed through the wound filter element for treatment; and when, for example, the treatment liquid is passed through a tubular or sheet-like fabric or non-woven fabric for treatment, etc.

[0042] Examples

[0043] The present invention will be described below based on examples. It should be noted that the present invention is not limited to these examples, and these examples can be deformed and changed according to the gist of the present invention, and such deformations and changes should not be excluded from the scope of the present invention.

[0044] (Example 1)

[0045] (Manufacture of PVA-based fibers)

[0046] 100 parts by mass of PVA (manufactured by Kuraray, trade name: PVA-117) with an average degree of polymerization of 1700 and a saponification degree of 99 mol% and 100 parts by mass of bentonite (manufactured by Kunimine Industries, trade name: Kunipia F, average particle size: 1 μm) were dispersed in 800 parts by mass of DMSO. The PVA was then heated and dissolved under a nitrogen atmosphere at 105 °C to obtain the spinning solution.

[0047] Then, the obtained spinning solution was passed through a spinneret with an aperture of 0.15 mm and 40 holes, and dry-wet spinning was carried out in a coagulation bath of methanol / DMSO (mass ratio: methanol / DMSO = 70 / 30) at 5°C.

[0048] The obtained solidified filament was then subjected to a four-fold wet stretch in a methanol bath at 20°C and dried with hot air at 120°C to obtain fibers with a single filament fineness of 12 dtex. The obtained fibers were cut into 5 mm pieces to obtain the fibers (samples) of this embodiment.

[0049] <Evaluation of Spinning Properties>

[0050] Spinability was evaluated according to the following criteria. The results are shown in Table 1.

[0051] During wet and dry spinning, fibers can be continuously extracted for more than one hour: ○

[0052] When performing wet-dry spinning, it is impossible to continuously extract fibers for more than one hour: ×

[0053] The prepared samples were observed using scanning electron microscopy (SEM). An image of the prepared samples observed using SEM is shown below. Figure 1 .like Figure 1 As shown, numerous micropores are formed on the surface of the prepared sample.

[0054] <Measurement of Swelling Degree>

[0055] The prepared sample (approximately 1 g) was dried in a vacuum dryer at 80 °C for 24 hours, and the weight of the absolutely dried sample was measured. Next, the sample was immersed in ion-exchange water at 20 °C for 60 minutes. Then, the sample was filtered, and water droplets adhering to the surface were gently removed with filter paper. The weight of the immersed sample was then measured. The degree of swelling of the prepared sample was then calculated using the following formula (1). The results are shown in Table 1.

[0056] (Mathematical Formula 1)

[0057] The swelling degree (%) of the sample = (weight of the sample after impregnation ÷ weight of the absolutely dry sample) × 100···(1)

[0058] <Adsorption Evaluation>

[0059] As an indicator of adsorption, the removal performance (adsorption rate) of methylene blue, a water-soluble compound, was evaluated. More specifically, the sample was added to a concentration of 1% by mass in 500 mL of an aqueous solution containing 100 ppm methylene blue, and stirred at 20°C for 60 minutes. The treated liquid was extracted, and the maximum absorption wavelength at 664 nm was measured using a spectrophotometer (HITACHI, trade name: U-2001 Spectrophotometer) to calculate the concentration of methylene blue in the treated liquid. The adsorption rate of the prepared sample was calculated using the following formula (2). The results are shown in Table 1.

[0060] (Mathematical Formula 2)

[0061] Adsorption rate of methylene blue (%) = ((methylene blue concentration in untreated liquid - methylene blue concentration in treated liquid) ÷ methylene blue concentration in untreated liquid) × 100···(2)

[0062] <Operational Evaluation>

[0063] Immediately after the above adsorption evaluation, the supernatant of the treated solution was extracted, and the turbidity (mg / L) was measured using a turbidimeter (HACH 2100P portable turbidimeter). The results are shown in Table 1. It should be noted that the higher the turbidity value, the more difficult it is to recover the treated solution, thus indicating poor operability.

[0064] (Example 2)

[0065] 100 parts by mass of PVA (manufactured by Kuraray, trade name: PVA-117) with an average degree of polymerization of 1700 and a degree of saponification of 99 mol% and 300 parts by mass of bentonite (manufactured by Kunimine Industries, trade name: Kunipia F, average particle size: 1 μm) were dispersed in 1600 parts by mass of DMSO. The PVA was then heated and dissolved under a nitrogen atmosphere at 105 °C to obtain the spinning solution.

[0066] Then, the obtained spinning solution was passed through a spinneret with an aperture of 1.00 mm and 5 holes, and dry-wet spinning was carried out in a coagulation bath of methanol / DMSO (mass ratio: methanol / DMSO = 70 / 30) at 5°C.

[0067] The obtained solidified filament was then subjected to a four-fold wet stretch in a methanol bath at 20°C and dried with hot air at 120°C to obtain fibers with a single filament fineness of 150 dtex. The obtained fibers were cut into 5 mm pieces to obtain the fibers (samples) of this embodiment.

[0068] The prepared samples were observed using scanning electron microscopy (SEM). An image of the prepared samples observed using SEM is shown below. Figure 2 .like Figure 2 As shown, similar to Example 1, many micropores are formed on the surface of the prepared sample.

[0069] Then, following the same procedure as in Example 1 above, spinnability evaluation, swelling degree measurement, adsorption evaluation, and operability evaluation were performed. The results are shown in Table 1.

[0070] (Example 3)

[0071] Except that 300 parts by weight of synthetic mica (manufactured by Co-op Chemical, trade name: ME100, average particle size: 5 μm) was used instead of the bentonite, fibers (samples) were prepared in the same manner as in Example 2 above.

[0072] Then, following the same procedure as in Example 1 above, spinnability evaluation, swelling degree measurement, adsorption evaluation, and operability evaluation were performed. The results are shown in Table 1.

[0073] (Example 4)

[0074] Except that the amount of bentonite was changed to 60 parts by mass, fibers (samples) were prepared in the same manner as in Example 1 above.

[0075] Then, following the same procedure as in Example 1 above, spinnability evaluation, swelling degree measurement, adsorption evaluation, and operability evaluation were performed. The results are shown in Table 1.

[0076] (Comparative Example 1)

[0077] Except that the amount of bentonite was changed to 20 parts by mass, fibers (samples) were prepared in the same manner as in Example 1 above.

[0078] Then, following the same procedure as in Example 1 above, spinnability evaluation, swelling degree measurement, adsorption evaluation, and operability evaluation were performed. The results are shown in Table 1.

[0079] (Comparative Example 2)

[0080] First, following the same procedure as in Example 1 above, wet and dry spinning was performed. The resulting spun yarn was then stretched in a hot air stretching furnace with a first furnace at 180°C and a second furnace at 235°C, with a total stretching ratio (wet stretching ratio × hot air furnace stretching ratio) of 10, to obtain 5 dtex fibers. The obtained fibers were then cut into 5 mm pieces to obtain the fibers (samples) of this comparative example.

[0081] Then, following the same procedure as in Example 1 above, spinnability evaluation, swelling degree measurement, adsorption evaluation, and operability evaluation were performed. The results are shown in Table 1.

[0082] (Comparative Example 3)

[0083] Adsorption and operability evaluations were conducted on 100 parts by weight (powder) of bentonite in the same manner as in Example 1 above. The results are shown in Table 1.

[0084] (Comparative Example 4)

[0085] Except that the amount of bentonite was changed to 450 parts by mass, dry and wet spinning was carried out in the same manner as in Example 2 above.

[0086] It should be noted that in this comparative example, continuous fiber extraction was not achieved during the wet-dry spinning process. In this comparative example, because the bentonite (layered silicate) content was greater than 400 parts by mass (450 parts by mass), it was difficult to form a fiber shape (i.e., fiberization), and a large amount of bentonite detached from the fibers and mixed into the treatment solution. Therefore, as shown in Table 1, it was impossible to perform swelling degree determination, adsorption evaluation, and operability evaluation.

[0087] (Comparative Example 5)

[0088] Except that PVA (manufactured by Kuraray Corporation, trade name: PVA-CST) with an average degree of polymerization of 1700 and a saponification degree of 96 mol% was used instead of the PVA, fibers (samples) were prepared in the same manner as in Example 2 above.

[0089] Then, spinnability evaluation, swelling degree measurement, adsorption evaluation, and operability evaluation were performed in the same manner as in Example 1 above. The results are shown in Table 1.

[0090] [Table 1]

[0091]

[0092] As shown in Table 1, it can be seen that in the PVA fibers of Examples 1 to 4, the proportion of layered silicate (bentonite or synthetic mica) is 30 to 400 parts by mass relative to 100 parts by mass of PVA, and the fiber swelling degree is 200 to 600%, thus exhibiting excellent adsorption and workability.

[0093] On the other hand, it can be seen that in the PVA fibers of Comparative Example 1, since the proportion of bentonite is less than 30 parts by mass, the coverage of bentonite by PVA is high, the permeability of the treatment solution is reduced, and therefore the adsorption of methylene blue contained in the treatment solution is reduced.

[0094] It can be seen that in the PVA fibers of Comparative Example 2, since the fiber swelling degree is less than 200%, the permeability of the treatment solution is reduced, resulting in a decrease in the adsorption of methylene blue.

[0095] It can be seen that in Comparative Example 3, since only bentonite was used and PVA was not used, the presence of bentonite in the treatment solution resulted in increased turbidity and poor operability.

[0096] It can be seen that in the PVA fibers of Comparative Example 5, since the fiber swelling degree is greater than 600%, the dissolution of PVA or the shedding of silicates will cause a decrease in operability.

[0097] Industrial applicability

[0098] In summary, the present invention is applicable to polyvinyl alcohol fibers containing layered silicates. Furthermore, fiber structures incorporating the polyvinyl alcohol fibers of the present invention are suitable for various applications such as beverages, clothing, and medical use.

Claims

1. A polyvinyl alcohol fiber comprising a polyvinyl alcohol polymer and layered silicate, wherein, The proportion of layered silicate is 60 to 300 parts by weight relative to 100 parts by weight of the polyvinyl alcohol polymer. The polyvinyl alcohol fibers have a fiber swelling degree of 320-414% and a single filament fineness of 12-150 dtex.

2. The polyvinyl alcohol fiber according to claim 1, wherein, The layered silicate is a montmorillonite-type clay compound.

3. The polyvinyl alcohol fiber according to claim 2, wherein, The layered silicate is bentonite.

4. The polyvinyl alcohol fiber according to any one of claims 1 to 3, wherein, The average particle size of the layered silicate is 0.1–100 μm.

5. A fibrous structure comprising polyvinyl alcohol fibers as described in any one of claims 1 to 4.

6. The fiber structure according to claim 5 is an adsorbent for the adsorbed substance contained in the adsorption treatment liquid.

7. The fiber structure according to claim 6, wherein, The adsorbed substance is caffeine.

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