Cellulose acetate fiber and method for producing cellulose acetate fiber

Abstract

A cellulose acetate fiber and a method for producing the same are provided. The cellulose acetate fiber contains 10-35 wt% of an adipate ester compound, and has a crystal orientation degree of 0.010-0.260. The method for producing the cellulose acetate fiber includes a step for melt-spinning a cellulose acetate resin composition containing 10-35 wt% of an adipate ester compound at a draft ratio of 10-250, and, optionally, a step for stretching the fiber at a total draw ratio of 2.0 times or less.

Description

Cellulose acetate fiber and method for producing cellulose acetate fiber Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2022-187167, filed on November 24, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a cellulose acetate fiber that exhibits biodegradability in accordance with ISO 14851, and a method for producing the same.

[0003] Cellulose acetate is a semi-synthetic polymer obtained by acetylating the alcoholic hydroxyl groups in cellulose, the main component of plants such as wood fiber and cotton. Because cellulose acetate can be made from inedible plant materials, it is a polymer material that plays a very important role in the Sustainable Development Goals (SDGs).

[0004] Furthermore, in recent years, there has been a global demand for environmentally friendly plastic products, leading to an increasing demand for biodegradable materials. 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. This document reports that, in a biodegradability evaluation by a biodegradability test (MITI method) using activated sludge, the biodegradability of cellulose acetate fibers with a low average degree of substitution was improved.

[0005] Furthermore, Patent Document 2 (JP-A-9-291414) discloses biodegradable cellulose acetate fibers obtained by melt-spinning a biodegradable resin composition mainly composed of cellulose acetate, a biodegradable polymer, and a plasticizer. In this document, melt-spun long fibers are partially thermocompressed by self-fusion, then buried in outdoor soil to a depth of 25 cm, and removed after 6 months to evaluate biodegradability based on changes in shape and weight.

[0006] Furthermore, Patent Document 3 (JP 2003-82160 A) discloses a fiber obtained by melt spinning a thermoplasticized cellulose ester composition mainly composed of cellulose ester and polylactic acid. This document focuses on melt spinning of the thermoplasticized cellulose ester composition, and does not specifically evaluate the biodegradability.

[0007] On the other hand, Patent Document 4 (WO 2022 / 085119) discloses that cellulose acetate having a total degree of acetyl substitution of 1.75 or more and 2.55 or less, and at least one of the degrees of acetyl substitution at the 2-position and the 3-position being 0.7 or less, has good marine biodegradability, and describes that it has excellent melt moldability and can be used as a fiber for clothing.

[0008] Japanese Patent No. 6580348 Japanese Patent Application Laid-Open No. 9-291414 Japanese Patent Application Laid-Open No. 2003-82160 International Publication No. 2022 / 085119

[0009] Generally, the biodegradability of plastic materials is often evaluated based on their biodegradability in soil environments. However, because soil environments have a greater amount of enzymes produced by decomposing microorganisms than marine environments, even if biodegradability is demonstrated in soil environments or using the MITI method (OECD TG 301C) which simulates a soil environment, the results cannot be used directly to indicate biodegradability in low-enzyme environments.

[0010] Although Patent Document 1 evaluates biodegradability using the MITI method (OECD TG 301C), the effect is only demonstrated for cellulose acetate fibers with a low average degree of substitution of 1.4 to 1.85. Patent Document 2 evaluates biodegradability in soil, but it is thought that the biodegradability of these cellulose acetate fibers decreases in environments with low enzyme activity.

[0011] Furthermore, it is known that the polylactic acid used in Patent Document 3 decomposes in the high-temperature and humid environment of compost, but is difficult to decompose in normal soil or water environments. Therefore, it is considered that the thermoplastic cellulose ester fiber obtained in Patent Document 3, which is mainly composed of cellulose ester and polylactic acid, is not sufficiently biodegradable even in soil as in Patent Documents 1 and 2.

[0012] In Patent Document 4, biodegradability is determined by immersing a crushed sample of cellulose acetate film in seawater and measuring the amount of carbon dioxide generated after immersion, but the biodegradability of fibers is not specifically examined.

[0013] Therefore, there is a demand for cellulose acetate fibers that exhibit biodegradability according to the evaluation method of ISO 14851, which has stricter conditions than the MITI method (OECD TG 301C) for evaluating biodegradability in soil environments.

[0014] An object of the present disclosure is to solve the above-mentioned problems and to provide a cellulose acetate fiber that has good biodegradability based on ISO 14851.

[0015] As a result of investigations aimed at solving such problems, the present inventors have found that by combining cellulose acetate with a specific amount of an adipic acid ester compound and further controlling the degree of crystal orientation of the cellulose acetate fiber containing the adipic acid ester compound, the resulting fiber can have improved biodegradability based on ISO 14851, and have completed the present disclosure.

[0016] That is, the present disclosure can be configured in the following aspects. [Aspect 1] A cellulose acetate fiber containing 10 to 35 wt % (preferably 12 to 25 wt %, more preferably 13 to 20 wt %) of an adipic acid ester compound and having a degree of crystalline orientation of the fiber of 0.01 to 0.26 (preferably 0.02 to 0.25, more preferably 0.04 to 0.23, even more preferably 0.050 to 0.220, particularly preferably 0.06 to 0.20). [Aspect 2] The cellulose acetate fiber according to Aspect 1, wherein the average degree of substitution of the cellulose acetate is 2.0 to 2.6 (preferably 2.1 to 2.5, more preferably 2.3 to 2.5). [Aspect 3] The cellulose acetate fiber according to Aspect 1 or 2, wherein the weight-average molecular weight (Mw) of the cellulose acetate is 100,000 to 1,000,000 (preferably 100,000 to 500,000, particularly preferably 100,000 to 300,000). [Aspect 4] The cellulose acetate fiber according to any one of Aspects 1 to 3, wherein the cellulose acetate fiber has a tenacity of 0.3 cN / dtex or more (preferably 0.4 cN / dtex or more, more preferably 0.5 cN / dtex or more). [Aspect 5] A method for producing a cellulose acetate fiber, comprising the steps 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 adipate ester compound at a draft ratio of 10 to 250 (preferably 10 to 200, more preferably 15 to 150, and even more preferably 20 to 120), and optionally drawing the resulting cellulose acetate composition at a total draw ratio of 2 or less. [Aspect 6] A method for producing a cellulose acetate fiber according to Aspect 5, wherein the cellulose acetate fiber is melt-spun at a spinning temperature of 250 to 290°C (preferably 255 to 280°C, more preferably 260 to 270°C). In the present specification, the term "X to Y" indicates a range meaning "X or more and Y or less." Polyethylene adipate may be excluded from the adipic acid ester compounds.

[0017] As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, including "at least one," unless the content clearly dictates otherwise. As used herein, the terms "and / or," "at least one," and "one or more" include any and all combinations of the associated listed items.

[0018] It should be noted that any combination of at least two elements disclosed in the claims and / or the specification and / or the drawings is included in the present invention, and in particular any combination of two or more of the claims set forth in the claims is included in the present invention.

[0019] The cellulose acetate fiber of the present disclosure can have improved biodegradability based on ISO 14851 by containing a specific plasticizer and controlling the degree of crystal orientation.

[0020] (Cellulose acetate) Cellulose acetate, a component of cellulose acetate fiber, is a natural 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 is an acetate ester (—OCOCH ３ Cellulose acetate is a semi-synthetic polymer in which cellulose acetate is substituted with cellulose acetate. Cellulose acetate is a plant-derived polymeric material, and can be made from the inedible parts of plants.

[0021] The degree of substitution, which indicates the degree to which hydroxy groups in one glucose ring are substituted with acetate ester, is 1 to 3. The average degree of substitution is not particularly limited as long as it is within a range that allows fiber formation, but from the viewpoint of improving melt spinnability, it may be, for example, 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.

[0022] Furthermore, in cellulose acetate, the degrees of substitution at the 2-, 3-, and 6-positions may or may not be uniform. For example, when the degrees of substitution are uniform, the degrees of substitution at the 2-, 3-, and 6-positions may all exceed 0.70. On the other hand, when the degrees of substitution are nonuniform, either one of the degrees of substitution at the 2- and 3-positions may be 0.70 or less. Cellulose acetate in which either one of the degrees of substitution at the 2- and 3-positions is 0.70 or less can also be produced with reference to Mokuzai Gakkaishi, Vol. 60, pp. 144-168 (2014) and Biomacromolecules, 13, 2195-2201 (2012).

[0023] The weight average molecular weight (Mw) of the cellulose acetate may be, 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.

[0024] Cellulose acetate can be produced by acetylation by reacting dissolving pulp with an acylating agent such as acetic anhydride or glacial acetic acid in the presence of an acylation catalyst such as sulfuric acid.

[0025] Common cellulose acetates are commercially available from Daicel Corporation under the trade names "L-20," "L-30," "L-50," and "L-70" as part of the L series.

[0026] (Adipic acid ester compound) The cellulose acetate fiber contains an adipic acid ester compound as a constituent component. Examples of the adipic acid ester include esters of adipic acid and at least one alcohol selected from the group consisting of aromatic alcohols and aliphatic alcohols. The adipic acid esters may be used alone or in combination.

[0027] Examples of the esters of adipic acid and aliphatic alcohols include dibutyl adipate, dioctyl adipate, dimethoxyethoxyethyl adipate, and dibutoxyethoxyethyl adipate.

[0028] Examples of the esters of adipic acid and aromatic alcohols include diphenyl adipate, dibenzyl adipate, dicresyl adipate, and dixylyl adipate.

[0029] As the mixed ester of adipic acid with an aromatic alcohol and an aliphatic alcohol, benzyl alkyl diglycol adipate is preferred. Benzyl alkyl diglycol adipate may be used alone, or a mixture of an ester of adipic acid with an aromatic alcohol and / or an ester of adipic acid with an aliphatic alcohol containing benzyl alkyl diglycol adipate may be used.

[0030] When a mixture containing benzyl alkyl diglycol adipate is used, it is preferred to use one containing 35% by weight or more of benzyl alkyl diglycol adipate.

[0031] The alkyl group of the benzyl alkyl diglycol adipate may be either linear or branched, but it is preferable to use a linear one.

[0032] 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. Particularly preferred benzyl alkyl diglycol adipates have a linear alkyl group having 1 to 4 carbon atoms, such as benzyl methyl diglycol adipate, benzyl ethyl diglycol adipate, benzyl n-propyl diglycol adipate, and benzyl n-butyl diglycol adipate.

[0033] From the viewpoint of fiber formability and biodegradability, the adipic acid ester compound may be contained in the fiber in an amount of 10 to 35% by weight, preferably 12 to 25% by weight, and more preferably 13 to 20% by weight.

[0034] Adipate ester compounds are commercially available from Daihachi Chemical Industry Co., Ltd. under the trade name "DAIFATTY-101," for example.

[0035] (Method for Producing Cellulose Acetate Fiber) Cellulose acetate fiber can be produced by spinning a cellulose acetate resin composition containing 10 to 35% by weight of an adipic acid ester compound at a predetermined draft ratio or draw ratio.

[0036] From the viewpoint of suppressing the use of organic solvents during fiber formation and reducing the environmental impact, melt spinning is preferred. In melt spinning, cellulose acetate fibers can be produced by spinning a cellulose acetate resin composition containing 10 to 35 wt %, preferably 12 to 25 wt %, and more preferably 13 to 20 wt % of an adipic acid ester compound at a draft ratio (ratio of take-up speed to extrusion speed) of 10 to 250. Furthermore, the fibers obtained by melt spinning are advantageous in that they can be used to produce fibers with modified cross sections and composite fibers.

[0037] For melt spinning, a resin composition containing cellulose acetate and an adipic acid ester compound may be pelletized and supplied to a melt spinning device. A known melt spinning device may be used for melt spinning. For example, pellets are melt-kneaded in a melt extruder, and the molten material is introduced into a spinning tube. The molten material is then metered with a gear pump, and a predetermined amount is discharged from a spinning nozzle at a predetermined spinning temperature. The resulting yarn is then taken up (or wound up) at a predetermined draft ratio to produce cellulose acetate fiber.

[0038] The spinning temperature may be, for example, 250 to 290° C., preferably 255 to 280° C., and more preferably 260 to 270° C. The discharge speed from the spinning nozzle can be appropriately set depending on the spinning temperature, and may be, for example, 10 to 40 m / min, preferably 12 to 30 m / min, and more preferably 15 to 25 m / min.

[0039] The take-up speed of the extruded filaments is adjusted in accordance with the extrusion speed, and the draft ratio is preferably adjusted within an appropriate range from the viewpoints of biodegradability and fiber strength. By taking up the filaments at a draft ratio of 10 to 250, preferably 10 to 200, more preferably 15 to 1500, and even more preferably 20 to 120, the degree of crystal orientation of the spun cellulose acetate fibers can be controlled.

[0040] The obtained cellulose acetate fiber may be optionally stretched (preferably hot stretched) so long as the degree of crystal orientation is within the range specified in the present disclosure. From the viewpoint of biodegradability, a low stretching ratio is preferable, and when stretched, the total stretching ratio may be 2.0 times or less, preferably 1.5 times or less, more preferably 1.3 times or less, and even more preferably 1.1 times or less. However, it is particularly preferable that the fiber is unstretched. Note that the total stretching ratio refers to the stretching ratio when stretching is performed in a single stage, and when stretching is performed in multiple stages, refers to the ratio expressed as the product of the stretching ratios in each stage.

[0041] (Cellulose acetate fiber) The cellulose acetate fiber may have a crystalline orientation degree of 0.010 to 0.260, preferably 0.020 to 0.250, more preferably 0.040 to 0.230, even more preferably 0.050 to 0.220, and particularly preferably 0.060 to 0.200. By having such a crystalline orientation degree, the fiber can have excellent biodegradability even under low enzyme conditions as specified in ISO 14851. The crystalline orientation degree is a value measured by the method described in the examples below.

[0042] The cellulose acetate fiber may have a biodegradability after 3 days of 4.0% or more, preferably 5.0% or more, more preferably 7.0% or more, and even more preferably 9.0% or more, as measured for a 2 mm cut yarn according to ISO 14851. Here, the biodegradability according to ISO 14851 is a value measured by the method described in the Examples below.

[0043] From the viewpoint of biodegradability, the crystallinity of the cellulose acetate fiber may be, for example, 30% or less, preferably 28% or less, and more preferably 25% or less. There is no particular restriction on the lower limit of the crystallinity, but from the viewpoint of fiber strength, it may be 1% or more, preferably 2% or more, and more preferably 3% or more. The crystallinity can be calculated from the ratio of the area of ​​the crystalline peak to the area of ​​the amorphous peak using a wide-angle X-ray scattering profile obtained by irradiating X-rays.

[0044] The breaking strength of the cellulose acetate fiber (hereinafter also referred to as fiber strength) may 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. The upper limit of the fiber strength is not particularly limited, but may be 2.0 cN / dtex or less. The fiber strength is a value measured by the method described in the examples below.

[0045] The number of filaments in the cellulose acetate fiber can be appropriately adjusted depending on the application, etc., and the fiber may be a monofilament or a multifilament. In the case of a multifilament, the number of filaments may be, for example, 5 to 3,000, preferably 10 to 2,000, more preferably 30 to 1,500, and even more preferably 50 to 500.

[0046] Depending on the intended use, the cellulose acetate fiber may have various single filament finenesses (single fiber finenesses). The cellulose acetate fiber may be a monofilament or a multifilament. The single filament fineness of the cellulose acetate fiber may be, for example, 0.05 to 100 dtex, preferably 0.1 to 50 dtex, more preferably 0.5 to 30 dtex, and even more preferably 1 to 30 dtex. The fineness here is a value measured with reference to JIS L 1013:2010.

[0047] The total fineness of the cellulose acetate fiber can be adjusted appropriately depending on the application, etc., and may be, for example, 1 to 10,000 dtex, preferably 10 to 5,000 dtex, more preferably 50 to 3,000 dtex, and even more preferably 100 to 1,500 dtex.

[0048] The cellulose acetate fiber may be continuous or discontinuous depending on the shape of the cellulose acetate fiber. The cellulose acetate fiber may be crimped or non-crimped. When the cellulose acetate fiber is used for a nonwoven fabric, it is cut to an appropriate length depending on the type of nonwoven fabric. Note that discontinuous fiber means a fiber having a fiber length of 100 mm or less, and continuous fiber means a fiber other than discontinuous fiber.

[0049] The fiber cross section may have various irregular cross sections, such as a circular, elliptical, cocoon-shaped, polygonal, such as a triangular, rectangular, star-shaped, or X-shaped cross section, or a curved, S-shaped cross section, etc. Furthermore, the cellulose acetate fiber may be used as a part of a composite fiber such as a core-sheath type fiber, an islands-in-the-sea type fiber, or a side-by-side type fiber.

[0050] As long as biodegradability is not impaired, cellulose acetate fibers may be combined with other polymers (e.g., various biodegradable polymers) to form composite fibers (e.g., core-sheath fibers, sea-island fibers, side-by-side fibers, splittable fibers), etc. However, from the viewpoint of controlling the degree of crystalline orientation of the fibers, non-composite fibers are preferred.

[0051] Cellulose acetate fibers may contain antioxidants, heat stabilizers, plasticizers, antistatic agents, radical inhibitors, delustering agents, UV absorbers, flame retardants, dyes, pigments, other polymers, and the like, as long as the effects of the present disclosure are not impaired. In the present disclosure, lubricants can be added as needed. Lubricants enhance the fluidity of resins. Lubricants are classified into two types: internal lubricants, which dissolve well in resins, reduce friction between polymers, and improve fluidity. External lubricants, which dissolve poorly in polymers, form a lubricating layer between the metal surface and the resin, improving fluidity. In the present disclosure, both internal and external lubricants can be added. Note that some lubricants have both effects. Even though cellulose acetate has a high melt viscosity, adding a lubricant can improve its slipperiness with molds and dies, thereby adjusting its fluidity. Lubricants include low-molecular-weight compounds with two moieties that have affinity for cellulose acetate molecules and metals, respectively. Such low molecular weight compounds tend to migrate to the interface between polymer and metal, and because of their low molecular weight, they have low viscosity and can provide lubricity with a small amount added. Some hydrocarbon-based, silicone-based, higher alcohol-based, higher fatty acid-based, and their compounds have this effect. In the present disclosure, known lubricants can be used as needed.

[0052] The cellulose acetate fiber may be further combined with other fibers as long as the effects of the present disclosure are not impaired. For example, the cellulose acetate fiber may be combined with other fibers to form a blended yarn or fabric.

[0053] The cellulose acetate fibers of the present disclosure can be used in various fields where biodegradability can be utilized, and can be effectively used in many applications including agricultural materials, forestry materials, fisheries materials, civil engineering materials, clothing fibers, daily necessities, sanitary materials, medical materials, etc.

[0054] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. In the following examples, various physical properties were measured by the following methods.

[0055] [Weight-average molecular weight] The weight-average molecular weight Mw can be determined by GPC analysis under the following conditions: Solvent: NMP Measurement column: Two PolyPore (7.8 mmφ×30 cm) manufactured by Agilent Technologies, Inc., with guard column Flow rate: 0.5 ml / min Column temperature: 55° C. Sample concentration: 0.5 wt % Injection volume: 50 μl Detection: RI Standard substance: polymethyl methacrylate (PMMA) (molecular weight 675,500, molecular weight 504,500, molecular weight 223,900, molecular weight 66,650, molecular weight 26,550, molecular weight 6,140, ​​molecular weight 1,780)

[0056] [Average Degree of Substitution of Cellulose Acetate] The degrees of acetyl substitution at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate can be measured by NMR according to the method of Tezuka (Tezuka, Carbonydr. Res. 273, 83 (1995)). Specifically, the free hydroxyl groups of a cellulose acetate sample are propionylated with propionic anhydride in pyridine. The resulting sample is dissolved in deuterated chloroform, and the C-NMR spectrum is measured. The carbon signals of the acetyl group appear in the region of 169 to 171 ppm in the order of 2-, 3-, and 6-positions from the high magnetic field, and the signals of the carbonyl carbon of the propionyl group appear in the same order in the region of 172 to 174 ppm. The degree of acetyl substitution at each of the 2-, 3-, and 6-positions of the glucose ring in the original cellulose acetate can be determined from the abundance ratio of the acetyl group and the propionyl group at the corresponding positions (in other words, the area ratio of each signal). １３ In addition to C-NMR, １ The total degree of acetyl substitution in the present disclosure is the sum of the degrees of acetyl substitution at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate, determined by the above-mentioned measurement method.

[0057] [Crystalline Orientation Degree] The crystalline orientation degree is calculated from the following formulas (1) and (2) using a wide-angle X-ray scattering profile obtained by irradiating X-rays under the following measurement conditions. <Measurement Conditions> Model: Bruker D8 Discover IμS X-ray source: Cu Collimator diameter: 0.5 mm Voltage: 50 kV Current: 1 mA Detector: 2D PSPC VANTEC-500 Exposure time: 10 minutes / frame

[0058]

[0059] In the formulas (1) and (2), f is the degree of crystal orientation, and Ii is the peak intensity at the azimuth angle θi. ２ θ> is the average value of the orientation state of all molecules, and f=0 in the case of no orientation and f=1 in the case of complete orientation. The integral range i is the azimuth angle from 0 to 90 degrees.

[0060] [Breaking Strength (cN / dtex)] Breaking strength was measured using a precision universal testing machine ("Autograph AGS-D" manufactured by Shimadzu Corporation). Test pieces 50 mm wide and 200 mm long were taken, and the distance between the gripping parts was set to 100 mm. Then, the ends of each test piece were fixed by the gripping parts and pulled at a rate of 100 mm / min until breakage. The average value of the test force at breakage was taken as the breaking strength, and the value obtained by dividing the breaking strength by the fineness was taken as the breaking strength.

[0061] [Biodegradability according to ISO 14851] In accordance with the biodegradability evaluation method described in ISO 14851:2019, fibers cut to 2 mm lengths 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, so that the concentration was 100 mg / L. This was cultured at 25±1°C, and the amount of oxygen consumed for biodegradation was measured using a BOD meter (WTW's "Oxitop"). The biodegradability was calculated from the ratio of this value to the theoretical oxygen demand (ThOD), and the biodegradability was evaluated according to the following criteria: ◎: Biodegradability after 3 days is 5.0% or more; ○: Biodegradability after 3 days is 4.0% or more but less than 5.0%; ×: Biodegradability after 3 days is less than 4.0%.

[0062] Example 1: Hardwood prehydrolyzed kraft pulp with an α-cellulose content of 98.4 wt% was disintegrated into a flocculent state using a disc refiner. 26.8 wt. parts of acetic acid were sprayed onto 100 wt. parts of the disintegrated pulp (moisture content: 8%), mixed thoroughly, and then allowed to stand for 60 hours for activation as a pretreatment. The activated pulp was added to a mixture of 323 wt. parts of acetic acid, 245 wt. parts of acetic anhydride, and 13.1 wt. parts of sulfuric acid, and the mixture was heated to a maximum temperature of 5-40°C over 40 minutes and then acetylated for 90 minutes. A neutralizer (24% aqueous magnesium acetate solution) was added over 3 minutes to adjust the amount of sulfuric acid (amount of aging sulfuric acid) to 2.5 wt. parts. The reaction bath was then heated to 75°C, and water was added to adjust the reaction bath moisture (aging moisture) to a concentration of 52 mol%. The mixture was then aged at 85°C, and the aging was stopped by neutralizing the sulfuric acid with magnesium acetate, yielding a reaction mixture containing cellulose acetate. A dilute aqueous acetic acid solution was added to the resulting reaction mixture, and the cellulose acetate was separated. The mixture was then washed with water, dried, and stabilized with calcium hydroxide to obtain cellulose acetate with an acetyl substitution degree of 2.4 and a weight-average molecular weight of 180,000. 80% by weight of the resulting cellulose acetate and 20% by weight of an adipate ester compound (manufactured by Daihachi Chemical Industry Co., Ltd., "DAIFATTY-101") were added to a Henschel mixer and stirred to a temperature of 70°C or higher due to frictional heat within the mixer. The mixture was then fed into a twin-screw extruder (cylinder temperature: 200°C, die temperature: 210°C), extruded, and pelletized. The resulting pelletized cellulose acetate composition was extruded from a round-hole nozzle at a spinning temperature of 260°C using a melt spinning machine at a discharge speed of 400 m / min, and then wound at a draft ratio of 31 to obtain a 500 dtex / 24 filament multifilament. The biodegradability of the resulting fiber after 3 days was 11.3%.

[0063] Example 2 Cellulose acetate fibers were produced in the same manner as in Example 1, except that the amount of the adipate ester compound was 13% by weight and the spinning temperature was 250° C. The resulting cellulose acetate fibers were evaluated, and the results are shown in Table 1. The biodegradability of the resulting fibers after 3 days was 7.2%.

[0064] Example 3 Cellulose acetate fibers were produced in the same manner as in Example 1, except that the amount of the adipate ester compound was 30% by weight and the spinning temperature was 270°C. The obtained cellulose acetate fibers were evaluated, and the results are shown in Table 1. Since the degree of crystal orientation of Example 3 is between that of Examples 1 and 4, it is expected to have excellent biodegradability, similar to that of Examples 1 and 4.

[0065] Example 4 Cellulose acetate fibers were produced in the same manner as in Example 1, except that the spinning temperature was 270°C and the draft ratio was 118. 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 9.0%.

[0066] [Example 5] The fiber obtained in Example 1 was hot drawn at 180°C to a total draw ratio of 1.2 to produce a cellulose acetate fiber. The obtained cellulose acetate fiber was evaluated, and the results are shown in Table 1. The biodegradability of the obtained fiber after 3 days was 10.8%.

[0067] Example 6 Cellulose acetate fibers were produced in the same manner as in Example 2, except that the draft ratio was set to 247. 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 4.8%.

[0068] Comparative Example 1 An attempt was made to produce cellulose acetate fibers in the same manner as in Example 1, except that the amount of the adipic acid ester compound was 3% by weight and the spinning temperature was 270°C. However, spinning was not possible because the cellulose acetate resin composition did not exhibit fluidity at the spinning temperature.

[0069] Comparative Example 2 An attempt was made to produce cellulose acetate fibers in the same manner as in Example 1, except that the amount of the adipic acid ester compound was 50% by weight and the spinning temperature was 204°C. However, the strength of the extruded filaments was low and they could not be wound up.

[0070] [Comparative Example 3] 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 and dissolved at 90 ° C for 5 hours to obtain a spinning solution with a polymer concentration of 24 wt%. This spinning solution was passed through a nozzle with 80 holes and a hole diameter of 0.12 mmφ, and using water as a solidification liquid, dry-wet spun in a solidification bath at 10 ° C., and then wet-stretched 1.5 times in a water bath at 20 ° C. Next, the DMSO in the thread was extracted with water, and the thread was applied with a spinning oil and dried at 120 ° C. The resulting cellulose acetate fiber was then dry-stretched at 220 ° C. to a total stretch ratio of 3.0 times. The biodegradability of the resulting fiber after 3 days was 3.1%.

[0071] Comparative Example 4 An attempt was made to produce cellulose acetate fiber in the same manner as in Example 2, except that the draft ratio was set to 300 times. However, because the winding speed was too fast, yarn breakage occurred frequently when winding the extruded yarn, and fiber could not be obtained.

[0072] Comparative Example 5 A cellulose acetate fiber was produced by hot drawing the fiber obtained in Example 1 at 220°C to a total draw ratio of 2.5 times. The obtained cellulose acetate fiber was evaluated, and the results are shown in Table 1.

[0073]

[0074] As shown in Table 1, the crystal orientation degrees of Examples 1 to 6 were all in the range of 0.010 to 0.260, and these Examples demonstrated good biodegradability based on ISO 14851, with rapid biodegradation occurring in a short period of time despite being in a low-enzyme environment of around 25°C. Furthermore, ISO 14851 confirms biodegradability at the low temperatures (around 25°C) used for marine biodegradation. Therefore, these Examples, which exhibit rapid biodegradability in low-temperature, low-enzyme environments, are expected to also exhibit excellent biodegradability in the marine environment. Furthermore, comparing Examples 2 and 6, which contain the same ratio of cellulose acetate and adipic acid ester compound, fiber strength can be improved by increasing the draft ratio during spinning.

[0075] On the other hand, in Comparative Examples 3 and 5, in which the degrees of crystal orientation were 0.604 and 0.270, the biodegradability based on ISO14851 was not good.

[0076] Furthermore, when melt spinning is performed, the melt spinnability differs depending on the amount of plasticizer. In Comparative Example 1, in which the amount of plasticizer was 3% by weight, the resin composition did not exhibit fluidity even when the spinning temperature was increased, and as a result, the resin composition could not be melt spun.

[0077] In Comparative Example 2, in which the amount of plasticizer was 50% by weight, spinning was attempted, but due to the low strength, yarn breakage occurred frequently and the running yarn could not be wound up.

[0078] In Comparative Example 4, even though the amount of plasticizer was the same as in Example 1, when the draft ratio increased, yarn breakage continued and the running yarn could not be wound up.

[0079] The cellulose acetate fibers of the present disclosure have excellent biodegradability and can therefore be suitably used in many applications, including agricultural materials, forestry materials, fisheries materials, civil engineering materials, clothing fibers, daily necessities, sanitary materials, medical materials, and the like.

[0080] Although the preferred embodiments of the present disclosure have been described above, those skilled in the art will readily envision various changes and modifications within the scope of the present disclosure upon reading the present specification. Accordingly, such changes and modifications are to be interpreted as falling within the scope of the invention as defined by the claims.

Claims

1. Cellulose acetate fiber containing 10 to 35% by weight of an adipic acid ester compound, and having a fiber crystal orientation degree of 0.010 to 0.

260.

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

6.

3. A 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. A cellulose acetate fiber according to claim 1 or 2, wherein the strength is 0.3 cN / dtex or more.

5. A cellulose acetate fiber according to claim 3, wherein the strength is 0.3 cN / dtex or more.

6. A method for producing cellulose acetate fibers, comprising the steps of melt-spinning a cellulose acetate resin composition containing 10 to 35% by weight of an adipic acid ester compound at a draft ratio of 10 to 250, and optionally a stretching step with a total stretch ratio of 2.0 or less.

7. A method for producing cellulose acetate fibers according to claim 6, wherein the fibers are melt-spun at a spinning temperature of 250 to 290°C.