Cellulose acetate fiber and method for producing cellulose acetate fiber

Abstract

The invention provides a cellulose acetate fiber and a manufacturing method thereof. The cellulose acetate fiber contains 10-35 wt% of an adipate compound, and the crystal orientation degree of the fiber is 0.010-0.260. This method for producing cellulose acetate fibers comprises: a step for melt-spinning a cellulose acetate resin composition containing 10-35 wt% of an adipate compound at a draw ratio of 10-250; and an arbitrary stretching step in which the total draw ratio is 2.0 times or less.

Description

[0001] Related Application

[0002] This application claims the priority of Japanese Patent Application No. 2022-187167 filed in Japan on November 24, 2022, and the entire content thereof is incorporated herein by reference and made a part of this application. Technical Field

[0003] The present invention relates to cellulose acetate fibers showing biodegradability based on ISO14851 and a method for manufacturing the same. Background Art

[0004] Cellulose acetate is a semi-synthetic polymer obtained by acetylating the alcoholic hydroxyl groups in cellulose, which is the main component of plants such as wood fibers and cotton. Since cellulose acetate can be made from non-edible parts of plant materials, it is a polymer material that plays a very important role in SDGs (Sustainable Development Goals of the United Nations).

[0005] In addition, in recent years, environmental protection measures for plastic products have been required worldwide, and the demand for the biodegradability of materials has been increasing. For example, Patent Document 1 (Japanese Patent No. 6580348) discloses a cigarette filter tow containing cellulose acetate fibers having an average degree of substitution of 1.4 to 1.85, an average degree of polymerization of 50 to 180, and a single fiber denier of 2 to 15 deniers. This document reports that in the biodegradability evaluation based on a biodegradability test (MITI method) using activated sludge, the biodegradability of cellulose acetate fibers with a low average degree of substitution increases.

[0006] In addition, Patent Document 2 (Japanese Patent Laid-Open No. 9-291414) discloses biodegradable cellulose acetate-based fibers obtained by melt-spinning a biodegradable resin composition mainly composed of cellulose acetate, a biodegradable polymer, and a plasticizer. In this document, the melt-spun long fibers are thermally bonded by partial self-fusion, buried in the soil at a depth of 25 cm in the field, taken out after 6 months, and the biodegradability is evaluated by morphological changes and weight changes.

[0007] Furthermore, Patent Document 3 (Japanese Patent Laid-Open No. 2003-82160) discloses a fiber obtained by melt-spinning a thermoplastic cellulose ester composition mainly composed of a cellulose ester and polylactic acid. In this document, the focus is mainly on the melt-spinning of the thermoplastic cellulose ester composition, and the biodegradability is not specifically evaluated.

[0008] On the other hand, Patent Document 4 (International Publication No. 2022 / 085119) discloses that cellulose acetate with a total degree of acetylation of 1.75 or more and 2.55 or less, and at least one of the degree of acetylation at the 2-position or the degree of acetylation at the 3-position being 0.7 or less, has good marine biodegradability, and it is described that its melt moldability is excellent and it can be used as a fiber for clothing.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent No. 6580348 Gazette

[0012] Patent Document 2: Japanese Unexamined Patent Application Publication No. 9-291414 Gazette

[0013] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2003-82160 Gazette

[0014] Patent Document 4: International Publication No. 2022 / 085119 Summary of the Invention

[0015] Problems to be Solved by the Invention

[0016] Generally, in many cases, the biodegradability of plastic materials can be evaluated by their biodegradability in a soil environment. However, compared with the marine environment, the amount of enzymes produced by the decomposing microorganisms in the soil environment is large. Therefore, even if biodegradability is shown in the soil environment or the MITI method (OECD TG 301C) that simulates the soil environment, the results cannot be directly used as biodegradability under low-enzyme conditions.

[0017] In Patent Document 1, although the biodegradability of the MITI method (OECD TG 301C) was evaluated, it showed an effect only in cellulose acetate fibers in a low range with an average degree of substitution of 1.4 to 1.85.

[0018] In Patent Document 2, although the biodegradability in soil was evaluated, it can be considered that the biodegradability of these cellulose acetate fibers will decrease in an environment with low enzyme activity.

[0019] In addition, although polylactic acid used in Patent Document 3 can be decomposed in the high-temperature and high-humidity environment of compost, it is difficult to decompose in a normal soil environment or water environment. Therefore, it can be considered that the thermoplastic cellulose ester fiber mainly composed of cellulose ester and polylactic acid obtained in Patent Document 3 is also fundamentally insufficient in biodegradability in soil like Patent Documents 1 and 2.

[0020] In Patent Document 4, a sample obtained by pulverizing a cellulose acetate film was immersed in seawater, and the biodegradability was determined by measuring the amount of carbon dioxide generated after immersion. However, the biodegradability of the fiber was not specifically studied.

[0021] Therefore, there is a need for a cellulose acetate fiber that exhibits biodegradability in the evaluation method of ISO 14851 under conditions more severe than the MITI method (OECD TG 301C) for evaluating biodegradability in a soil environment.

[0022] An object of the present disclosure is to solve the above problems and provide a cellulose acetate fiber having good biodegradability based on ISO 14851.

[0023] Means for Solving the Problems

[0024] The inventors of the present invention conducted research from the viewpoint of solving the above problems and found that for cellulose acetate, when a specific amount of adipate compound is combined and the crystal orientation degree of the cellulose acetate fiber containing the adipate compound is further controlled, the resulting fiber can improve biodegradability based on ISO 14851, thereby completing the present disclosure.

[0025] That is, the present disclosure can be configured as follows.

[0026] 〔Aspect 1〕

[0027] A cellulose acetate fiber containing 10 to 35% by weight (preferably 12 to 25% by weight, more preferably 13 to 20% by weight) of an adipate compound, and the crystal orientation degree of the fiber is 0.01 to 0.26 (preferably 0.02 to 0.25, more preferably 0.04 to 0.23, further preferably 0.050 to 0.220, particularly preferably 0.06 to 0.20).

[0028] 〔Aspect 2〕

[0029] The cellulose acetate fiber according to Aspect 1, wherein

[0030] the average degree of substitution of cellulose acetate is 2.0 to 2.6 (preferably 2.1 to 2.5, more preferably 2.3 to 2.5).

[0031] 〔Aspect 3〕

[0032] The cellulose acetate fiber according to Aspect 1 or 2, wherein

[0033] the weight average molecular weight (Mw) of cellulose acetate is 100,000 to 1,000,000 (preferably 100,000 to 500,000, particularly preferably 100,000 to 300,000).

[0034] 〔Method 4〕

[0035] The cellulose acetate fiber according to any one of Methods 1 to 3 has a strength of 0.3 cN / dtex or more (preferably 0.4 cN / dtex or more, more preferably 0.5 cN / dtex or more).

[0036] 〔Method 5〕

[0037] A method for manufacturing a cellulose acetate fiber, the method comprising:

[0038] A step of melt-spinning a cellulose acetate resin composition containing 10 to 35% by weight (preferably 12 to 25% by weight, more preferably 13 to 20% by weight) of an adipic acid ester compound at a draw ratio of 10 to 250 (preferably 10 to 200, more preferably 15 to 150, further preferably 20 to 120); and

[0039] An optional drawing step with a total draw ratio of 2 times or less.

[0040] 〔Method 6〕

[0041] According to the method for manufacturing a cellulose acetate fiber described in Method 5, wherein

[0042] Melt-spinning is performed at a spinning temperature of 250 to 290 °C (preferably 255 to 280 °C, more preferably 260 to 270 °C).

[0043] It should be noted that in the specification of this application, "X to Y" representing a range means "X or more and Y or less". In addition, polyethylene adipate can be removed from the adipic acid ester compound.

[0044] When used in this specification, unless the content clearly states otherwise, the singular forms "a", "an", and "the" all mean including the plural form containing "at least one". When used in this specification, the terms "and / or", "at least 1", and "1 or more" include any and all combinations of the relevant listed items.

[0045] It should be noted that any combination of at least two constituent elements disclosed in the claims and / or the specification and / or the drawings is included in the present invention. In particular, the combination of two or more claims recited in the claims is also included in the present invention.

[0046] Effects of the Invention

[0047] The cellulose acetate fiber of the present disclosure can improve biodegradability based on ISO14851 by containing a specific plasticizer and controlling the degree of crystal orientation. Detailed implementation mode

[0048] (Cellulose acetate)

[0049] Cellulose acetate, which is a constituent of cellulose acetate fibers, is a semi-synthetic polymer in which at least one of the three hydroxyl groups (-OH) at the 2nd, 3rd, and 6th positions of the glucose ring of cellulose, a natural polymer, is substituted with an acetate group (-OCOCH3). As a plant-derived polymer material, cellulose acetate can use plant materials that are not edible parts as raw materials.

[0050] The degree of substitution indicating the degree of substitution of the hydroxyl group in one glucose ring by an acetate group is 1 to 3, and its average degree of substitution only needs to be in the range where fibers can be formed, and there is no particular limitation. From the viewpoint of improving melt spinning properties, for example, it can be 2.0 to 2.6, preferably 2.1 to 2.5, and more preferably 2.3 to 2.5. The average degree of substitution is a value measured by the method described in the examples below.

[0051] In addition, in cellulose acetate, the degrees of substitution at the 2nd, 3rd, and 6th positions can be uniform or non-uniform. For example, in the case of uniform degree of substitution, the degrees of substitution at the 2nd, 3rd, and 6th positions can all exceed 0.70. On the other hand, in the case of non-uniform degree of substitution, either the degree of substitution at the 2nd or 3rd position can be 0.70 or less.

[0052] It should be noted that cellulose acetate in which either the degree of substitution at the 2nd or 3rd position is 0.70 or less can be manufactured with reference to the Journal of the Wood Research Society, vol.60, p144 - 168 (2014) and Biomacromolecules, 13, 2195 - 2201 (2012).

[0053] The weight average molecular weight (Mw) of cellulose acetate is, for example, 100,000 to 1,000,000, preferably 100,000 to 500,000, and particularly preferably 100,000 to 300,000. The weight average molecular weight is a value measured by the method described in the examples below.

[0054] Cellulose acetate can be manufactured by acetylating dissolving pulp in the presence of an acylation catalyst such as sulfuric acid with an acylating agent such as acetic anhydride and glacial acetic acid.

[0055] General cellulose acetate is sold, for example, by Kuraray Co., Ltd. under the trade names "L-20", "L-30", "L-50", and "L-70" of the L series.

[0056] (Adipic acid ester compounds)

[0057] Cellulose acetate fiber contains an adipate compound as a constituent component. Examples of the adipate include esters of adipic acid and at least one alcohol selected from aromatic alcohols and aliphatic alcohols. The adipate may be used alone or in combination of two or more.

[0058] Examples of the esters of adipic acid and aliphatic alcohols include dibutyl adipate, dioctyl adipate, dimethoxyethoxyethyl adipate, and dibutoxyethoxyethyl adipate.

[0059] Examples of the ester of adipic acid and an aromatic alcohol include diphenyl adipate, dibenzyl adipate, ditolyl adipate, and di(xylyl) adipate.

[0060] The mixed ester of adipic acid, an aromatic alcohol and an aliphatic alcohol is preferably benzyl alkyl diethylene glycol adipate. Benzyl alkyl diethylene glycol adipate may be used alone, or a mixture of an ester of adipic acid, an aromatic alcohol and / or an ester of adipic acid, an aliphatic alcohol containing benzyl alkyl diethylene glycol adipate may be used.

[0061] When a mixture containing benzyl alkyl diethylene glycol adipate is used, it is preferred to use a mixture containing benzyl alkyl diethylene glycol adipate in an amount of 35% by weight or more.

[0062] The alkyl group of benzylalkyl diethylene glycol adipate may be either linear or branched, but a linear alkyl group is preferably used.

[0063] The number of carbon atoms in the alkyl group may be, for example, 1 to 20, preferably 1 to 8, and more preferably 1 to 4.

[0064] Particularly preferred benzyl alkyl diethylene glycol adipates are the following compounds having a linear alkyl group having 1 to 4 carbon atoms: benzyl methyl diethylene glycol adipate, benzyl ethyl diethylene glycol adipate, benzyl n-propyl diethylene glycol adipate, and benzyl n-butyl diethylene glycol adipate.

[0065] From the viewpoint of fiber formation and biodegradability, the adipate compound is contained in the fiber in an amount of 10 to 35 wt %, preferably 12 to 25 wt %, more preferably 13 to 20 wt %.

[0066] The adipate-based compound is sold, for example, by Daihachi Chemical Industry Co., Ltd. under the trade name "DAIFATTY-101" or the like.

[0067] (Method for producing cellulose acetate fiber)

[0068] The cellulose acetate fiber can be produced by spinning a cellulose acetate resin composition containing 10 to 35% by weight of an adipate-based compound at a given draft ratio or stretch ratio.

[0069]

[0069] From the viewpoint of suppressing the use of organic solvents during fibrosis suppression and reducing the environmental burden, melt spinning is preferably used for spinning. In melt spinning, a cellulose acetate resin composition containing 10 to 35% by weight, preferably 12 to 25% by weight, more preferably 13 to 20% by weight of an adipate compound can be spun at a draw ratio (the ratio of the draw speed to the ejection speed) of 10 to 250 to produce cellulose acetate fibers. In addition, the fibers obtained by melt spinning are advantageous in terms of being able to produce fibers with a profiled cross-section and composite fibers.

[0070] During melt spinning, the resin composition containing cellulose acetate and an adipate compound can be granulated and supplied to the melt spinning apparatus. During melt spinning, a known melt spinning apparatus can be used. For example, the granules are melt-kneaded with a melt extruder, and the melt is guided to a spinning cylinder. Then, the melt can be metered with a gear pump, ejected in a given amount from a spinning nozzle at a given spinning temperature, and the resulting filament can be drawn (or wound up) at a given draw ratio to produce cellulose acetate fibers.

[0071]

[0070] The spinning temperature can be, for example, 250 to 290°C, preferably 255 to 280°C, more preferably 260 to 270°C.

[0072] The ejection speed from the spinning nozzle can be appropriately set according to the spinning temperature. The ejection speed can be, for example, 10 to 40 m / minute, preferably 12 to 30 m / minute, more preferably 15 to 25 m / minute.

[0073]

[0071] For the ejected filament, the draw speed is adjusted according to the ejection speed. From the viewpoints of biodegradability and fiber strength, it is preferable to adjust the draw ratio to an appropriate range. By stretching at a draw ratio of 10 to 250, preferably 10 to 200, more preferably 15 to 150, and further preferably 20 to 120, the degree of crystal orientation of the cellulose acetate fiber after spinning can be controlled.

[0074] It should be noted that as long as the degree of crystal orientation is within the range defined in the present disclosure, the obtained cellulose acetate fiber can be stretched arbitrarily (preferably dry heat stretching). From the viewpoint of biodegradability, a low draw ratio is preferred. The total draw ratio during stretching can be 2.0 times or less, preferably 1.5 times or less, more preferably 1.3 times or less, further preferably 1.1 times or less, and particularly preferably not stretched. It should be noted that for the total draw ratio, it refers to this draw ratio when stretching is performed in one step, and refers to the ratio represented by the value obtained by multiplying the draw ratios of each step when stretching is performed in multiple steps.

[0075] (Cellulose Acetate Fiber)

[0076] The degree of crystalline orientation of the cellulose acetate fiber is 0.010 to 0.260, preferably 0.020 to 0.250, more preferably 0.040 to 0.230, further preferably 0.050 to 0.220, and particularly preferably 0.060 to 0.200. By having such a degree of crystalline orientation, excellent biodegradability can be achieved even under the low enzyme conditions of ISO 14851. Here, the degree of crystalline orientation is a value measured by the method described in the examples below.

[0077] Regarding the biodegradability of ISO 14851 for a 2-mm cut-off line, the degree of biodegradation of the cellulose acetate fiber after, for example, 3 days can be 4.0% or more, preferably 5.0% or more, more preferably 7.0% or more, and further preferably 9.0% or more. Here, the degree of biodegradation of ISO 14851 is a value measured by the method described in the examples below.

[0078] From the viewpoint of biodegradability, the crystallinity of the cellulose acetate fiber can be, for example, 30% or less, preferably 28% or less, and more preferably 25% or less. There is no particular limitation on the lower limit value of the crystallinity. From the viewpoint of fiber strength, it can be 1% or more, preferably 2% or more, and more preferably 3% or more. It should be noted that the crystallinity can be calculated based on the ratio of the area of the crystalline peak to the area of the amorphous peak using the wide-angle X-ray scattering curve obtained by irradiating X-rays.

[0079] The breaking strength of the cellulose acetate fiber (hereinafter, also referred to as fiber strength) can be, for example, 0.3 cN / dtex or more, preferably 0.4 cN / dtex or more, and more preferably 0.5 cN / dtex or more. There is no particular limitation on the upper limit of the fiber strength, and it can be 2.0 cN / dtex or less. It should be noted that the fiber strength is a value measured by the method described in the examples below.

[0080] The number of filaments of the cellulose acetate fiber can be appropriately adjusted according to the use, etc. It can be a monofilament or a multifilament. In the case of a multifilament, for example, the number of filaments can be 5 to 3000, preferably 10 to 2000, more preferably 30 to 1500, and further preferably 50 to 500.

[0081] It can have various deniers (the fineness of a single fiber) according to the use of the target. The cellulose acetate fiber can be a monofilament or a multifilament. The denier of the cellulose acetate fiber can be, for example, 0.05 to 100 dtex, preferably 0.1 to 50 dtex, more preferably 0.5 to 30 dtex, and further preferably 1 to 30 dtex. Here, the fineness is a value measured with reference to JIS L1013:2010.

[0082] The total fineness of the cellulose acetate fiber can be appropriately adjusted according to the use and the like, and can be, for example, 1 to 10,000 dtex, preferably 10 to 5,000 dtex, more preferably 50 to 3,000 dtex, and further preferably 100 to 1,500 dtex.

[0083] Depending on the shape of the cellulose acetate fiber, the cellulose acetate fiber can be a continuous fiber or a discontinuous fiber. The cellulose acetate fiber can be a crimped fiber or a non-crimped fiber. In the case of non-woven fabric, the cellulose acetate fiber can be cut to an appropriate length according to the type of non-woven fabric. It should be noted that the discontinuous fiber refers to a fiber with a fiber length of 100 mm or less, and the continuous fiber refers to a fiber other than the discontinuous fiber.

[0084] In addition to circular cross-sections such as circular, oval, and eyebrow-shaped, the fiber cross-section can also have various non-circular cross-sections such as polygonal shapes like triangular, square, star-shaped, X-shaped, the leaf shape of clover, and curved shapes like S-shaped. In addition, the cellulose acetate fiber can be used as part of composite fibers such as core-sheath type fibers, sea-island type fibers, and side-by-side type fibers.

[0085] Within the range that does not impair biodegradability, the cellulose acetate fiber can be a composite fiber (such as core-sheath fiber, sea-island fiber, side-by-side fiber, segmented fiber) combined with other polymers (for example, various biodegradable polymers), and from the viewpoint of controlling the crystal orientation degree of the fiber, a non-composite fiber is preferred.

[0086] Within the scope of not impairing the effects of the present disclosure, the cellulose acetate fiber may contain antioxidants, heat stabilizers, plasticizers, antistatic agents, free radical inhibitors, delustering agents, ultraviolet absorbers, flame retardants, dyes, pigments, other polymers, etc. Lubricants can be added as needed in the present disclosure. The lubricant can improve the fluidity of the resin. Lubricants are divided into two categories. One type is called an internal lubricant, which is fully dissolved in the resin, reducing the friction between macromolecules and improving fluidity. The other type is called an external lubricant, which has poor solubility in the macromolecule and forms a lubricating layer between the metal surface and the resin, thereby improving fluidity. In the present disclosure, any lubricant among the internal lubricant and the external lubricant may be contained. It should be noted that depending on the lubricant, there are also lubricants having the effects of both. Even if the melt viscosity of cellulose acetate is high, the slidability with the mold and die head can be improved by adding a lubricant, thereby adjusting the fluidity. There are the following low-molecular compounds in the lubricant, and this low-molecular compound has two parts having affinity with the cellulose acetate molecule and the metal respectively. Such a low-molecular compound easily migrates to the interface between the macromolecule and the metal, and due to its low molecular weight and low viscosity, lubricity can be obtained by adding a small amount. Hydrocarbons, silicones, higher alcohols, higher fatty acids, and there are substances having such effects among these compounds. In the present disclosure, it can be used in known lubricants as needed.

[0087] As long as the effects of the present disclosure are not impaired, the cellulose acetate fiber may further be combined with other fibers. For example, the cellulose acetate fiber may be a blended yarn or fabric formed by combining with other fibers.

[0088] The cellulose acetate fiber of the present disclosure can be used in various fields capable of utilizing biodegradability, and can be effectively used for various applications including agricultural materials, forestry materials, aquatic materials, civil engineering materials, clothing fibers, living materials, sanitary materials, medical materials, etc.

[0089] Examples

[0090] Hereinafter, the present disclosure will be described in more detail by way of examples, but the present disclosure is not limited by any of these examples. It should be noted that in the following examples, various physical properties were measured by the following methods.

[0091] [Weight average molecular weight]

[0092] The weight average molecular weight Mw can be determined by performing GPC analysis by GPC under the following conditions.

[0093] Solvent: NMP

[0094] Columns for measurement: Two PolyPore (7.8 mmφ × 30 cm) columns manufactured by Agilent technology, with a guard column

[0095] Flow rate: 0.5 ml / min

[0096] Column temperature: 55 °C

[0097] Sample concentration: 0.5 wt%

[0098] Injection volume: 50 μl

[0099] Detection: RI

[0100] Standard substances: Polymethyl methacrylate (PMMA) (molecular weights 675500, 504500, 223900, 66650, 26550, 6140, 1780)

[0101] [Average degree of substitution of cellulose acetate]

[0102] The degree of substitution of each acetyl group at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate can be determined by NMR according to the method of Tezuka (Tezuka, Carbonydr. Res. 273, 83 (1995)). That is, the free hydroxyl groups of the cellulose acetate sample are propionylated with propionic anhydride in pyridine. The obtained sample is dissolved in deuterated chloroform, and the 13C-NMR spectrum is measured. The carbon signals of the acetyl groups appear in the region of 169 - 171 ppm in the order of 2-, 3-, and 6-positions from high magnetic field, and the carbonyl carbon signals of the propionyl groups appear in the same order in the region of 172 - 174 ppm. The degree of substitution of each acetyl group at the 2-, 3-, and 6-positions of the glucose ring in the original cellulose acetate can be obtained based on the ratio of the presence of acetyl groups and propionyl groups at the respective corresponding positions (in other words, the area ratio of each signal). It should be noted that in addition to 13 C-NMR, it can also be analyzed by 1 H-NMR.

[0103] The total degree of substitution of acetyl groups in the present disclosure is the sum of the degrees of substitution of each acetyl group at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate obtained by the above measurement method.

[0104] [Degree of crystal orientation]

[0105] The degree of crystal orientation is calculated by the following formulas (1) and (2) using the wide-angle X-ray scattering curve obtained by irradiating X-rays under the following measurement conditions

[0106] [Measurement conditions]

[0107] Equipment type: Bruker·D8 Discоver IμS

[0108] X-ray source: Cu

[0109] Collimator diameter: 0.5 mm

[0110] Voltage: 50 kV

[0111] Current: 1 mA

[0112] Detector: 2D PSPC·VANTEC-500

[0113] Exposure time: 10 minutes / 1 frame

[0114] [Mathematical formula 1]

[0115]

[0116] In Formula (1) and Formula (2), f is the degree of crystal orientation, and Ii is the peak intensity at the azimuth angle θi. <cos 2 θ> is the average value of the orientation state of all molecules. In the case of no orientation, f = 0, and in the case of complete orientation, f = 1. The integration range i is the azimuth angle from 0 to 90 degrees.

[0117] [Breaking strength (cN / dtex)]

[0118] The breaking strength was measured using a precision universal testing machine ("Autograph AGS-D type" manufactured by Shimadzu Corporation). Test pieces with a width of 50 mm and a length of 200 mm were collected, the distance between the clamping parts was set to 100 mm, and then the ends of each test piece were fixed with the clamping parts and stretched at a speed of 100 mm / min until fracture. The average value of the test force at fracture was taken as the breaking strength, and the value obtained by dividing the breaking strength by the fineness was taken as the breaking strength.

[0119] [Biodegradability of ISO14851]

[0120] According to the biodegradability evaluation method described in ISO14851:2019, fibers cut to a length of 2 mm were added to 300 mL of a standard test culture solution containing activated sludge from a sewage treatment plant in Kurashiki City, Okayama Prefecture, at a concentration of 100 mg / L, and the concentration was made 100 mg / L. It was cultured at 25 ± 1 °C, and the amount of oxygen consumed by biodegradation was measured using a BOD meter ("Oxitop" manufactured by WTW). The biodegradation degree was calculated from the ratio of this value to the theoretical oxygen demand (ThOD), and the biodegradability was judged based on the following criteria.

[0121] ◎: Biodegradation degree after 3 days is 5.0% or more

[0122] ○: Biodegradation degree after 3 days is 4.0% or more and less than 5.0%

[0123] ×: Biodegradation after 3 days is less than 4.0%

[0124] [Example 1]

[0125] The kraft pulp of hardwood with 98.4 wt% α-cellulose content before hydrolysis was crushed into cotton with a disc refiner. 26.8 parts by weight of acetic acid was sprayed on 100 parts by weight of the crushed pulp (water content 8%), and after sufficient mixing, it was activated by standing for 60 hours as a pretreatment. The activated pulp was added to a mixture of 323 parts by weight of acetic acid, 245 parts by weight of acetic anhydride, and 13.1 parts by weight of sulfuric acid, and the maximum temperature was adjusted to 5-40°C in 40 minutes, and acetic acidization was performed for 90 minutes. A neutralizer (24% magnesium acetate aqueous solution) was added for 3 minutes, so that the amount of sulfuric acid (matured sulfuric acid amount) was adjusted to 2.5 parts by weight. Further, after the reaction bath was heated to 75°C, water was added, and the reaction bath water (matured water) was set to a concentration of 52 mol%. Then, it was matured at 85°C, and the ripening was stopped by neutralizing the sulfuric acid with magnesium acetate, and a reaction mixture containing cellulose acetate was obtained. A dilute aqueous acetic acid solution was added to the obtained reaction mixture, and the cellulose acetate was separated, followed by washing / drying / stabilization with calcium hydroxide to obtain cellulose acetate having an acetyl substitution degree of 2.4 and a weight average molecular weight of 180,000. 80% by weight of the obtained cellulose acetate and 20% by weight of an adipate compound (manufactured by Daihachi Chemical Industry Co., Ltd., "DAIFATTY-101") were added to a Henschel mixer, and stirred and mixed so that the temperature reached 70°C or higher due to friction heat in the mixer. Then, the mixture was supplied to a twin-screw extruder (barrel temperature: 200°C, die temperature: 210°C) for extrusion and pelletization.

[0126] The obtained pelletized cellulose acetate composition was discharged from a round hole nozzle at a discharge speed of 400 m / min using a melt spinning machine at a spinning temperature of 260°C, and then wound up at a draft ratio of 31 to obtain a multifilament of 500 dtex / 24 filaments. The biodegradability of the obtained fiber after 3 days was 11.3%.

[0127] [Example 2]

[0128] Cellulose acetate fibers were produced in the same manner as in Example 1 except that the amount of the adipate compound was 13 wt % and the spinning temperature was 250° C. The obtained cellulose acetate fibers were evaluated and the results are shown in Table 1. The biodegradability of the obtained fibers after 3 days was 7.2%.

[0129] [Example 3]

[0130] The amount of the adipate compound was set to 30% by weight, and the spinning temperature was set to 270 °C. Otherwise, the cellulose acetate fiber was produced in the same manner as in Example 1. The obtained cellulose acetate fiber was evaluated, and the results are shown in Table 1. Regarding Example 3, since the degree of crystal orientation was between that of Example 1 and Example 4, it was predicted that it would have equally excellent biodegradability as Example 1 and Example 4.

[0131] [Example 4]

[0132] The spinning temperature was set to 270 °C, and the draw ratio was set to 118 times. Otherwise, the cellulose acetate fiber was produced in the same manner as in Example 1. The obtained cellulose acetate fiber was evaluated, and the results are shown in Table 1. The biodegradation degree of the obtained fiber after 3 days was 9.0%.

[0133] [Example 5]

[0134] The fiber obtained in Example 1 was dry-heat stretched at 180 °C so that the total draw ratio was 1.2 times, and a cellulose acetate fiber was produced. The obtained cellulose acetate fiber was evaluated, and the results are shown in Table 1. The biodegradation degree of the obtained fiber after 3 days was 10.8%.

[0135] [Example 6]

[0136] The draw ratio was set to 247 times. Otherwise, the cellulose acetate fiber was produced in the same manner as in Example 2. The obtained cellulose acetate fiber was evaluated, and the results are shown in Table 1. The biodegradation degree of the obtained fiber after 3 days was 4.8%.

[0137] [Comparative Example 1]

[0138] The amount of the adipate compound was set to 3% by weight, and the spinning temperature was set to 270 °C. Otherwise, the same operation as in Example 1 was carried out to attempt to produce a cellulose acetate fiber, but the cellulose acetate resin composition did not show fluidity at the spinning temperature, so spinning was impossible.

[0139] [Comparative Example 2]

[0140] The amount of the adipate compound was set to 50% by weight, and the spinning temperature was set to 204 °C. Otherwise, the same operation as in Example 1 was carried out to attempt to produce a cellulose acetate fiber, but the strength of the extruded filament was low and winding was impossible.

[0141] [Comparative Example 3]

[0142] Cellulose acetate with an acetyl substitution degree of 2.4 and a weight-average molecular weight of 180,000 was added to DMSO and stirred at 90 °C for 5 hours to dissolve, obtaining a spinning dope with a polymer concentration of 24% by weight. This spinning dope was passed through a nozzle with 80 holes and a pore diameter of 0.12 mmφ, and water was used as the coagulating liquid. Wet-dry spinning was carried out in a coagulation bath at 10 °C, and wet drawing 1.5 times was carried out in a water bath at 20 °C. Then, the DMSO in the filament was extracted with water, a spinning finish was applied to the filament, and it was dried at 120 °C. Then, the obtained cellulose acetate fiber was dry-heat drawn at 220 °C to make the total draw ratio 3.0 times. The biodegradation degree of the obtained fiber after 3 days was 3.1%.

[0143] [Comparative Example 4]

[0144] The draw ratio was set to 300 times, and otherwise, the same operations as in Example 2 were carried out to attempt to produce cellulose acetate fiber. However, due to the too-fast winding speed, continuous breakage occurred during the winding of the filament after ejection, and no fiber was obtained.

[0145] [Comparative Example 5]

[0146] The fiber obtained in Example 1 was dry-heat drawn at 220 °C to make the total draw ratio 2.5 times, and cellulose acetate fiber was produced. The obtained cellulose acetate fiber was evaluated, and the results are shown in Table 1.

[0147]

[0148] As shown in Table 1, the crystallinity orientation degrees of Examples 1 to 6 were all in the range of 0.010 to 0.260. In these examples, the biodegradability based on ISO14851 was good, and even in a low-enzyme environment around 25 °C, biodegradation could be carried out rapidly in a short time. In addition, according to ISO14851, biodegradability could be confirmed at a low temperature (around 25 °C) adopted for biodegradability in the ocean. Therefore, it could be predicted that these examples showing rapid biodegradability in a low-temperature and low-enzyme environment also had excellent biodegradability in the ocean. In addition, compared with Examples 2 and 6 with the same ratio of cellulose acetate and adipic ester compounds, by increasing the draw ratio during spinning, the fiber strength could be improved.

[0149] On the other hand, in Comparative Examples 3 and 5 with crystallinity orientation degrees of 0.604 and 0.270, the biodegradability based on ISO14851 was not good.

[0150] In addition, during melt spinning, the melt spinnability varies depending on the amount of the plasticizer. In Comparative Example 1 where the amount of the plasticizer is 3% by weight, even when the spinning temperature is increased, the resin composition does not exhibit fluidity, and thus the resin composition cannot be melt spun.

[0151] In Comparative Example 2 where the amount of the plasticizer is 50% by weight, although spinning was attempted, the strength was low, and thus continuous thread breakage occurred and the advancing filament could not be wound up.

[0152] In Comparative Example 4, even when the amount of the plasticizer is the same as that in Example 1, when the draw ratio is increased, continuous thread breakage still occurs and the advancing filament cannot be wound up.

[0153] Industrial Applicability

[0154] Due to the excellent biodegradability, the cellulose acetate fiber of the present disclosure can be suitably used for various applications including agricultural materials, forestry materials, aquatic materials, civil engineering materials, clothing fibers, living materials, sanitary materials, medical materials, and the like.

[0155] As described above, the preferred embodiments of the present disclosure have been described. For those skilled in the art, various changes and modifications can be easily conceived within the obvious scope after reading this specification. Therefore, such changes and modifications should be construed as being within the scope of the invention defined by the claims.

Claims

1. A cellulose acetate fiber containing 10 to 35% by weight of an adipate compound, and having a crystallinity orientation degree of 0.010 to 0.

260.

2. The cellulose acetate fiber according to claim 1, wherein the average degree of substitution of the cellulose acetate is 2.0 to 2.

6.

3. The cellulose acetate fiber according to claim 1 or 2, wherein the weight-average molecular weight (Mw) of the cellulose acetate is 100,000 to 1,000,000.

4. The cellulose acetate fiber according to claim 1 or 2, having a strength of 0.3 cN / dtex or more.

5. The cellulose acetate fiber according to claim 3, having a strength of 0.3 cN / dtex or more.

6. A method for manufacturing a cellulose acetate fiber, the method comprising: a step of melt-spinning a cellulose acetate resin composition containing 10 to 35% by weight of an adipate compound at a draw ratio of 10 to 250, and an optional drawing step with a total draw ratio of 2.0 times or less.

7. The method for manufacturing a cellulose acetate fiber according to claim 5, wherein melt-spinning is performed at a spinning temperature of 250 to 290 °C.

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