WO2024111569A1 - Cellulose acetate fiber and method for producing cellulose acetate fiber - Google Patents

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

This application claims priority to Patent Application No. 2022-187167, filed in Japan on November 24, 2022, the entire contents of which are incorporated by reference as part of this application.

The present invention relates to cellulose acetate fibers that exhibit biodegradability based on ISO 14851, and a method for producing the same.

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

Furthermore, in recent years, there has been a global demand for environmentally friendly plastic products, and the demand for biodegradable materials is on the rise. For example, Patent Document 1 (Patent Publication No. 6580348) discloses a cigarette filter tow containing cellulose acetate fibers with 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 using a biodegradability test (MITI method) using activated sludge, the biodegradability of cellulose acetate fibers with a low average degree of substitution was improved.

Patent Document 2 (JP Patent Publication 9-291414A) discloses biodegradable cellulose acetate fibers obtained by melt spinning a biodegradable resin composition whose main components are 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 six months to evaluate biodegradability based on changes in shape and weight.

Furthermore, Patent Document 3 (JP Patent Publication 2003-82160 A) discloses fibers obtained by melt spinning a thermoplasticized cellulose ester composition whose main components are cellulose ester and polylactic acid. This document focuses on melt spinning of a thermoplasticized cellulose ester composition, and does not specifically evaluate biodegradability.

On the other hand, Patent Document 4 (WO 2022/085119) discloses that cellulose acetate having a total degree of acetyl substitution of 1.75 to 2.55 and at least one of the degrees of acetyl substitution at the 2nd position and the 3rd position being 0.7 or less has good marine biodegradability, is excellent in melt moldability, and is used as a clothing fiber.

Patent No. 6580348 Japanese Patent Application Laid-Open No. 9-291414 JP 2003-82160 A International Publication No. 2022/085119

Generally, the biodegradability of plastic materials is often evaluated based on their biodegradability in soil environments, but because soil environments produce greater amounts of enzymes from 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 conditions.

Although Patent Document 1 evaluates biodegradability by the MITI method (OECD TG 301C), the effect is only shown for cellulose acetate fibers having a low average degree of substitution in the range of 1.4 to 1.85.
Although Patent Document 2 evaluates the biodegradability in soil, it is believed that the biodegradability of these cellulose acetate fibers decreases in environments with low enzyme activity.

In addition, the polylactic acid used in Patent Document 3 is known to decompose in the hot and humid environment of compost, but is not easily decomposed in normal soil or water environments. Therefore, it is believed that the thermoplasticized 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.

In Patent Document 4, biodegradability is determined by immersing crushed samples 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.

Therefore, there is a demand for cellulose acetate fibers that demonstrate biodegradability in soil environments using the ISO 14851 evaluation method, which has stricter conditions than the MITI method (OECD TG 301C).

The purpose of this disclosure is to solve the above problems and to provide a cellulose acetate fiber that has good biodegradability based on ISO14851.

As a result of research aimed at solving this problem, the inventors discovered 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 ISO14851, and thus completed the present disclosure.

That is, the present disclosure can be configured in the following manner.
[Aspect 1]
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 having a degree of crystal 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]
A cellulose acetate fiber according to claim 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]
A 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, and particularly preferably 100,000 to 300,000).
[Aspect 4]
A cellulose acetate fiber according to any one of Aspects 1 to 3, having a strength of 0.3 cN/dtex or more (preferably 0.4 cN/dtex or more, more preferably 0.5 cN/dtex or more).
[Aspect 5]
The method for producing a cellulose acetate fiber comprises 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 draft ratio of 10 to 250 (preferably 10 to 200, more preferably 15 to 150, even more preferably 20 to 120), and optionally a step of stretching the composition at a total draw ratio of 2 or less.
[Aspect 6]
A method for producing the cellulose acetate fiber according to claim 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 range "X to Y" means "X or more and Y or less." Also, polyethylene adipate may be excluded from the adipic acid ester compounds.

As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms "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.

It should be noted that any combination of at least two components disclosed in the claims and/or the specification and/or the drawings is also included in the present invention. In particular, any combination of two or more of the claims described in the claims is also included in the present invention.

The cellulose acetate fiber disclosed herein contains a specific plasticizer and has a controlled degree of crystal orientation, which allows for improved biodegradability based on ISO 14851.

(Cellulose Acetate)
Cellulose acetate, a component of cellulose acetate fiber, is a semi-synthetic polymer in which at least one of the three hydroxyl groups (-OH) at the 2-, 3-, and 6-positions of the glucose ring of cellulose, a natural polymer, is substituted with an acetate ester (-OCOCH ₃ ). Cellulose acetate is a polymer material derived from plants, and can be made from plant materials that are inedible parts.

The degree of substitution, which indicates the degree to which the hydroxyl group in one glucose ring is replaced with an acetate ester, is 1 to 3, and the average degree of substitution is not particularly limited as long as it is within a range in which fibers can be formed, 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.

In addition, in cellulose acetate, the degrees of substitution at the 2-, 3-, and 6-positions may be uniform or not. 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 non-uniform, either one of the degrees of substitution at the 2- and 3-positions may be 0.70 or less.
Cellulose acetate having a substitution degree at either the 2-position or the 3-position of 0.70 or less can also be produced by referring to Mokuzai Gakkaishi, vol. 60, pp. 144-168 (2014) and Biomacromolecules, 13, 2195-2201 (2012).

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.

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.

General cellulose acetate is, for example, sold by Daicel Corporation under the product names "L-20," "L-30," "L-50," and "L-70" in the L series.

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

Esters of adipic acid and aliphatic alcohols include dibutyl adipate, dioctyl adipate, dimethoxyethoxyethyl adipate, and dibutoxyethoxyethyl adipate.

Esters of adipic acid and aromatic alcohols include diphenyl adipate, dibenzyl adipate, dicresyl adipate, and dixylyl adipate.

As a mixed ester of adipic acid with an aromatic alcohol and an aliphatic alcohol, benzyl alkyl diglycol adipate is preferred, and benzyl alkyl diglycol adipate may be used alone, or a mixture of esters of adipic acid with an aromatic alcohol and/or esters of adipic acid with an aliphatic alcohol, including benzyl alkyl diglycol adipate, may be used.

When using a mixture containing benzyl alkyl diglycol adipate, it is preferable to use one that contains 35% or more by weight of benzyl alkyl diglycol adipate.

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

The alkyl group may have, for example, 1 to 20 carbon atoms, preferably 1 to 8 carbon atoms, and more preferably 1 to 4 carbon atoms.
Particularly preferred benzyl alkyl diglycol adipates have a linear alkyl group having 1 to 4 carbon atoms, and are, for example, benzyl methyl diglycol adipate, benzyl ethyl diglycol adipate, benzyl n-propyl diglycol adipate, and benzyl n-butyl diglycol adipate.

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

Adipate ester compounds are, for example, available from Daihachi Chemical Industry Co., Ltd. under the product name "DAIFATTY-101."

(Method of producing cellulose acetate fiber)
The 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 prescribed draft ratio or draw ratio.

From the viewpoint of reducing the use of organic solvents during fiberization 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% by weight, preferably 12 to 25% by weight, and more preferably 13 to 20% by weight 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 irregular cross sections and composite fibers.

When performing melt spinning, a resin composition containing cellulose acetate and an adipic acid ester compound may be pelletized and supplied to a melt spinning device. When performing melt spinning, a known melt spinning device may be used. For example, the 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 thread is then drawn up (or wound up) at a predetermined draft ratio to produce cellulose acetate fiber.

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 the discharge speed may be, for example, 10 to 40 m/min, preferably 12 to 30 m/min, and more preferably 15 to 25 m/min.

The take-up speed of the extruded yarn is adjusted to match the extrusion speed, and from the standpoint of biodegradability and fiber strength, it is preferable to adjust the draft ratio to an appropriate range. By taking up the yarn 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 fiber can be controlled.

The obtained cellulose acetate fiber may be optionally stretched (preferably dry heat stretched) so long as the degree of crystal orientation is within the range specified in this disclosure. From the viewpoint of biodegradability, a low stretching ratio is preferable, and when stretching is performed, 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, but it is particularly preferable that the fiber is unstretched. Note that the total stretching ratio means the stretching ratio when stretching is performed in one stage, and means the ratio expressed as the multiplication of the stretching ratios in each stage when stretching is performed in multiple stages.

(Cellulose acetate fiber)
The cellulose acetate fiber may have a crystal 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 crystal orientation degree, the fiber can have excellent biodegradability even under low enzyme conditions as specified in ISO 14851. The crystal orientation degree is a value measured by the method described in the examples described later.

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 by ISO 14851 for a 2 mm cut thread. Here, the biodegradability according to ISO 14851 is a value measured by the method described in the examples below.

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.

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. There is no particular upper limit to the fiber strength, but it may be 2.0 cN/dtex or less. The fiber strength is a value measured by the method described in the examples below.

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

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 finenesses here are values measured with reference to JIS  L  1013:2010.

The total fineness of the cellulose acetate fiber can be adjusted as appropriate 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.

Cellulose acetate fibers may be continuous or discontinuous depending on the shape of the cellulose acetate fibers. Cellulose acetate fibers may be crimped or non-crimped. When the cellulose acetate fibers are nonwoven fabrics, they are cut to an appropriate length depending on the type of nonwoven fabric. Note that discontinuous fibers are fibers with a fiber length of 100 mm or less, and continuous fibers refer to fibers other than discontinuous fibers.

Furthermore, the fiber cross section may have various irregular cross sections, such as a circular, elliptical, cocoon-shaped, polygonal shapes such as a triangular, rectangular, star-shaped, or X-shaped cross section, or a cloverleaf-shaped, S-shaped, or other curved shape. Furthermore, cellulose acetate fibers may be used as a part of composite fibers such as core-sheath type fibers, sea-island type fibers, and side-by-side type fibers.

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), but from the viewpoint of controlling the degree of crystalline orientation of the fibers, non-composite fibers are preferred.

As long as the effect of the present disclosure is not impaired, the cellulose acetate fiber may contain antioxidants, heat stabilizers, plasticizers, antistatic agents, radical inhibitors, matting agents, ultraviolet absorbers, flame retardants, dyes, pigments, other polymers, etc. In the present disclosure, a lubricant can be added as necessary. A lubricant enhances the fluidity of the resin. Lubricants are classified into two types. One type is called an internal lubricant, which dissolves well in the resin, reduces friction between polymers, and improves fluidity. The other type is called an external lubricant, which dissolves poorly in the polymer, forms a lubricating layer between the metal surface and the resin, and improves fluidity. In the present disclosure, both internal and external lubricants can be contained. Note that some lubricants have both effects. Even if the melt viscosity of cellulose acetate is high, the fluidity can be adjusted by adding a lubricant to increase the slipperiness with the mold or die. Lubricants include low molecular weight compounds that have two sites 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, some have low viscosity and can provide lubricity with the addition of a small amount. Some compounds based on hydrocarbons, silicones, higher alcohols, higher fatty acids, and their compounds have this effect. In this disclosure, any known lubricant can be used as needed.

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

The cellulose acetate fibers disclosed herein can be used in a variety of fields where biodegradability can be utilized, and can be effectively used for many applications, including agricultural materials, forestry materials, fishery materials, civil engineering materials, clothing fibers, daily materials, sanitary materials, medical materials, etc.

The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is in no way limited to these examples. In the following examples, the various physical properties were measured using the following methods.

[Weight average molecular weight]
The weight average molecular weight Mw can be determined by GPC analysis under the following conditions.
Solvent: NMP
Measurement column: Agilent Technologies PolyPore (7.8 mmφ×30 cm), 2 columns, 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)

[Average Degree of Substitution of Cellulose Acetate]
The degree of acetyl substitution at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate can be measured by the NMR method according to the method of Tezuka (Tezuka, Carbonydr. Res. 273, 83 (1995)). That is, the free hydroxyl groups of a cellulose acetate sample are propionylated with propionic anhydride in pyridine. The obtained sample is dissolved in deuterated chloroform and a 13C-NMR spectrum is measured. The carbon signals of the acetyl groups 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 carbons of the propionyl groups appear in the same order in the region of 172 to 174 ppm. The degree of acetyl substitution at the 2-, 3-, and 6-positions of the glucose ring of 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). The degree of acetyl substitution can also be analyzed by ¹ H-NMR in addition to ¹³ C-NMR.
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, which is determined by the above-mentioned measurement method.

[Crystalline Orientation Degree]
The degree of crystal orientation 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: 1mA
Detector: 2D PSPC・VANTEC-500
Exposure time: 10 min/frame

In formulas (1) and (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, with f=0 for no orientation and f=1 for complete orientation. The integral range i is the azimuth angle from 0 to 90 degrees.

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

[Biodegradability according to ISO 14851]
In accordance with the biodegradability evaluation method described in ISO14851:2019, 300 mL of standard test culture solution containing activated sludge from a sewage treatment plant in Kurashiki City, Okayama Prefecture at a concentration of 100 mg/L was added with fibers cut to a length of 2 mm so as to give a concentration of 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"), and the biodegradability was determined from the ratio of this value to the theoretical oxygen demand (ThOD), and the biodegradability was judged according to the following criteria.
◎: Biodegradability after 3 days is 5.0% or more. ◯: Biodegradability after 3 days is 4.0% or more and less than 5.0%. ×: Biodegradability after 3 days is less than 4.0%.

[Example 1]
Hardwood prehydrolyzed kraft pulp with an α-cellulose content of 98.4 wt% was crushed into a cotton-like state using a disc refiner. 26.8 parts by weight of acetic acid was sprayed onto 100 parts by weight of the crushed pulp (water content 8%), and after thorough mixing, the mixture was left to stand for 60 hours as a pretreatment for activation. 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 mixture was adjusted to a maximum temperature of 5 to 40°C over 40 minutes, and acetylated for 90 minutes. A neutralizing agent (24% magnesium acetate aqueous solution) was added over 3 minutes so that the amount of sulfuric acid (amount of aged sulfuric acid) was adjusted to 2.5 parts by weight. Furthermore, the reaction bath was heated to 75°C, and water was added to adjust the reaction bath moisture (aging moisture) to a concentration of 52 mol%. Thereafter, aging was performed at 85°C, and the aging was stopped by neutralizing the sulfuric acid with magnesium acetate, and a reaction mixture containing cellulose acetate was obtained. A dilute aqueous solution of acetic acid was added to the reaction mixture obtained, and the cellulose acetate was separated. The mixture was then washed with water, dried, and stabilized 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 ester compound (manufactured by Daihachi Chemical Industry Co., Ltd., "DAIFATTY-101") were added to a Henschel mixer, and the mixture was stirred and mixed to a temperature of 70°C or higher due to frictional heat in the mixer. The mixture was then fed to a twin-screw extruder (cylinder temperature: 200°C, die temperature: 210°C), extruded, and pelletized.
The obtained pellet-like 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 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%.

[Example 2]
Cellulose acetate fibers were produced in the same manner as in Example 1, except that the amount of the adipic acid ester compound was 13% by weight 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%.

[Example 3]
Cellulose acetate fibers were produced in the same manner as in Example 1, except that the amount of the adipate 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 crystal orientation degree of Example 3 is between those of Examples 1 and 4, it is expected to have excellent biodegradability like Examples 1 and 4.

[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%.

[Example 5]
The fiber obtained in Example 1 was subjected to hot drawing at 180° C. so that the total draw ratio was 1.2 times 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%.

[Example 6]
A cellulose acetate fiber was produced in the same manner as in Example 2, except that the draft ratio was set to 247. 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 4.8%.

[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.

[Comparative Example 2]
An attempt was made to produce cellulose acetate fiber 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., but the filaments after extrusion had low strength and could not be wound up.

[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 dope with a polymer concentration of 24 wt%. This spinning dope was passed through a nozzle with 80 holes and a hole diameter of 0.12 mmφ, and was subjected to dry-wet spinning in a solidification bath at 10 ° C using water as a solidification liquid, and wet stretching was performed at 1.5 times in a water bath at 20 ° C. Next, the DMSO in the thread was extracted with water, and the thread was given a spinning oil and dried at 120 ° C. Thereafter, the obtained cellulose acetate fiber was subjected to dry heat stretching at 220 ° C to a total stretch ratio of 3.0 times. The biodegradability of the obtained fiber after 3 days was 3.1%.

[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 yarn after extrusion, and fiber could not be obtained.

[Comparative Example 5]
The fiber obtained in Example 1 was subjected to hot drawing at 220° C. so that the total draw ratio became 2.5 times to prepare a cellulose acetate fiber. The obtained cellulose acetate fiber was evaluated, and the results are shown in Table 1.

As shown in Table 1, the crystal orientation of Examples 1 to 6 is in the range of 0.010 to 0.260, and these Examples have good biodegradability based on ISO 14851, and biodegradation proceeds rapidly in a short period of time despite being in a low enzyme environment of around 25°C. Furthermore, according to ISO 14851, biodegradability can be confirmed at low temperatures (around 25°C) that are used for biodegradability in the ocean, so these Examples, which show rapid biodegradability in low temperature and low enzyme environments, are predicted to have excellent biodegradability even in the ocean. Furthermore, when comparing Examples 2 and 6, which have the same ratio of cellulose acetate and adipic acid ester compound, it is possible to improve fiber strength by increasing the draft ratio during spinning.

On the other hand, in Comparative Examples 3 and 5, where the crystal orientation degree is 0.604 and 0.270, the biodegradability based on ISO14851 is not good.

In addition, when melt spinning is performed, the melt spinnability differs depending on the amount of plasticizer. In Comparative Example 1, where the amount of plasticizer is 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.

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

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

The cellulose acetate fibers disclosed herein have excellent biodegradability and can therefore be suitably used in many applications, including agricultural materials, forestry materials, fishery materials, civil engineering materials, clothing fibers, daily necessities, sanitary materials, medical materials, etc.

As described above, a preferred embodiment of the present disclosure has been described. However, a person skilled in the art will be able to easily imagine various changes and modifications within the obvious scope upon reading this specification. Therefore, such changes and modifications are to be interpreted as being within the scope of the invention as determined by the scope of the claims.

Claims (7)

Cellulose acetate fiber containing 10-35% by weight of an adipate ester compound and having a degree of crystal orientation of the fiber of 0.010-0.260. Cellulose acetate fiber according to claim 1, in which the average degree of substitution of cellulose acetate is 2.0 to 2.6. Cellulose acetate fiber according to claim 1 or 2, in which the weight average molecular weight (Mw) of the cellulose acetate is 100,000 to 1,000,000. Cellulose acetate fiber according to claim 1 or 2, having a strength of 0.3 cN/dtex or more. Cellulose acetate fiber according to claim 3, having a strength of 0.3 cN/dtex or more. A method for producing cellulose acetate fiber, comprising a step 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 an optional step of stretching the composition to a total stretch ratio of 2.0 or less. A method for producing the cellulose acetate fiber according to claim 5, in which the cellulose acetate fiber is melt spun at a spinning temperature of 250 to 290°C.