EP4624641A1

EP4624641A1 - Cellulose acetate fiber and method for producing cellulose acetate fiber

Info

Publication number: EP4624641A1
Application number: EP23894574.5A
Authority: EP
Inventors: Kaname TACHIBANA; Ran NOBORU; Satoshi Koizumi; Ryokei Endo; Kohei Yamasaki; Takayuki Ogihara; Masaaki KUSUMOTO; Akihiro Higuchi
Original assignee: Daicel Corp; Kuraray Co Ltd
Current assignee: Daicel Corp; Kuraray Co Ltd
Priority date: 2022-11-24
Filing date: 2023-11-21
Publication date: 2025-10-01
Also published as: WO2024111569A1; JPWO2024111569A1; CN120239774A; TW202432610A

Abstract

Provided are a cellulose acetate fiber and a method for producing the cellulose acetate fiber. The cellulose acetate fiber contains 10 to 35 wt% of an adipic acid ester-based compound, and the cellulose acetate fiber has a degree of crystalline orientation of 0.010 to 0.260. The method for producing the cellulose acetate fiber includes: melt-spinning a cellulose acetate resin composition containing 10 to 35 wt% of an adipic acid ester-based compound, at a draft ratio of 10 to 250; and optionally drawing a melt-spun fiber at a total draw ratio of 2.0 or less.

Description

CROSS REFERENCE TO THE RELATED APPLICATION

This application is based on and claims Convention priority to Japanese patent application No. 2022-187167, filed November 24, 2022 , the entire disclosure of which is herein incorporated by reference as a part of this application.

FIELD OF THE INVENTION

The present invention relates to a cellulose acetate fiber having biodegradability based on ISO14851 and a method for producing the same.

BACKGROUND OF THE INVENTION

Cellulose acetate is a semi-synthetic polymer obtained by using, as a raw material, cellulose which is a main component of plants such as wood fibers and cottons, and acetylating alcoholic hydroxy groups in the cellulose. Since a non-edible portion of a plant material can be used as a raw material for cellulose acetate, cellulose acetate is a polymer material which plays a very important role in the SDGs (Sustainable Development Goals).
In recent years, there has been a worldwide demand for plastic products to be environmentally friendly, and materials are highly required to have biodegradability. For example, Patent Document 1 ( Japanese Patent No. 6580348 ) discloses a cigarette filter tow including a cellulose acetate fiber in which cellulose acetate constituting the cellulose acetate fiber has an average degree of substitution of 1.4 to 1.85 and an average degree of polymerization of 50 to 180, and the cellulose acetate fiber has a single fiber denier of 2 to 15 denier. Patent Document 1 reports that, in an evaluation by a biodegradability test (MITI method) using an activated sludge, the cellulose acetate fiber having a low average degree of substitution has an enhanced biodegradability.
Patent Document 2 (JP Laid-open Patent Publication No. H09-291414) discloses a biodegradable cellulose acetate-based fiber produced by melt-spinning a biodegradable resin composition containing cellulose acetate, a biodegradable polymer, and a plasticizer as main components. According to Patent Document 2, melt-spun filaments are partially subjected to a thermocompression bonding by self-fusing, and then, buried under the ground at the depth of 25 cm in the outdoors, and taken out after the elapse of six months, and biodegradability is evaluated on the basis of shape change and weight change.
Patent Document 3 ( JP Laid-open Patent Publication No. 2003-82160 ) discloses a fiber produced by melt spinning a thermoplastic cellulose ester composition containing cellulose ester and polylactic acid as main components. According to Patent Document 3, the main focus is on melt-spinning of the thermoplastic cellulose ester composition, and biodegradability is not specifically evaluated.
Meanwhile, Patent Document 4 (International Publication No. 2022/085119) discloses cellulose acetate in which a total degree of acetyl substitution is 1.75 or more and 2.55 or less, and at least one of a degree of acetyl substitution at 2-position and a degree of acetyl substitution at 3-position is 0.7 or less. Patent Document 4 indicates that the cellulose acetate has preferable marine biodegradability, and that the cellulose acetate has excellent melt-formability and is used as fibers for clothing.

CONVENTIONAL ART DOCUMENT

PATENT DOCUMENT

[Patent Document 1] Japanese Patent No. 6580348
[Patent Document 2] JP Laid-open Patent Publication No. H09-291414
[Patent Document 3] JP Laid-open Patent Publication No. 2003-82160
[Patent Document 4] International Publication No. 2022/085119

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

In general, biodegradability of a plastic material is evaluated as biodegradability in a soil environment in many cases. An amount of enzyme produced in the soil environment by microorganisms which cause degradation is greater than that in a marine environment. Therefore, even in a case where biodegradability is demonstrated in the soil environment or by the MITI method (OECD TG 301C) in which the soil environment is simulated, the result thereof cannot be applied to biodegradability in a low enzyme state as it is.
In Patent Document 1, although biodegradability is evaluated by the MITI method (OECD TG 301C), the effect is shown merely by the cellulose acetate fibers having a lower average degree of substitution is in a range of 1.4 to 1.85.
In Patent Document 2, although biodegradability is evaluated in soil, the biodegradability of the cellulose acetate fibers is considered to be reduced in an environment with a lower enzyme activity.
The polylactic acid used in Patent Document 3 is degraded in a high temperature and high humidity environment in compost. However, it is known that polylactic acid is unlikely to be degraded in a normal soil environment or a normal water environment. Therefore, the thermoplastic cellulose ester fibers containing cellulose ester and polylactic acid as main components as obtained in Patent Document 3 are considered to have substantially insufficient biodegradability even in soil as in Patent Documents 1 and 2.
In Patent Document 4, a sample obtained by grinding a cellulose acetate film is put into sea water, and an amount of carbon dioxide generated after putting the sample into sea water is measured to determine biodegradability. However, biodegradability of fiber is not specifically examined.
Accordingly, there is a demand for a cellulose acetate fiber having biodegradability in an evaluation method in accordance with ISO14851 in which a condition is stricter than that in a MITI method (OECD TG 301C) for evaluating biodegradability in a soil environment.
An object of the present disclosure is to solve the above-mentioned problems and to provide a cellulose acetate fiber having good biodegradability based on ISO14851.

MEANS FOR SOLVING THE PROBLEMS

As a result of studies conducted by the inventors of the present invention to solve the above-mentioned problems, the inventors have found that, where cellulose acetate is used in combination with a specific amount of an adipic acid ester-based compound, and furthermore, a degree of crystalline orientation of a cellulose acetate fiber containing the adipic acid ester-based compound is adjusted to a specific range, the obtained fiber can enhance biodegradability based on ISO14851, and have thus completed the present disclosure.
That is, the present disclosure may include the following aspects.

[Aspect 1]

A cellulose acetate fiber containing 10 to 35 wt% (preferably 12 to 25 wt%, and more preferably 13 to 20 wt%) of an adipic acid ester-based compound, in which the cellulose acetate fiber has a degree of crystalline orientation 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, and particularly preferably 0.06 to 0.20).

[Aspect 2]

The cellulose acetate fiber according to aspect 1 in which a cellulose acetate constituting the cellulose acetate fiber has an average degree of substitution of 2.0 to 2.6 (preferably 2.1 to 2.5, and more preferably 2.3 to 2.5).

[Aspect 3]

The cellulose acetate fiber according to aspect 1 or 2 in which a cellulose acetate constituting the cellulose acetate fiber has a weight-average molecular weight (Mw) of 100000 to 1000000 (preferably 100000 to 500000, and particularly preferably 100000 to 300000).

[Aspect 4]

The cellulose acetate fiber according to any one of aspects 1 to 3 in which the cellulose acetate fiber has a tenacity of 0.3 cN/dtex or more (preferably 0.4 cN/dtex or more, and more preferably 0.5 cN/dtex or more).

[Aspect 5]

A method for producing a cellulose acetate fiber, the method including:

melt-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-based 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 a melt-spun fiber at a total draw ratio of 2 or less.

[Aspect 6]

The method for producing the cellulose acetate fiber according to aspect 5 in which the melt-spinning is performed at a spinning temperature of 250 to 290°C (preferably 255 to 280°C, and more preferably 260 to 270°C).
In the present specification, "X to Y" as a range means "X or more and Y or less". The adipic acid ester-based compound may exclude polyethylene adipate.
As used herein, the singular forms, "a," "an", and "the" are intended to include plural forms including "at least one", unless the content clearly indicates otherwise. As used herein, the terms "and/or", "at least one", and "one or more" include any and all combinations of the relevant listed items.
Any combination of at least two constructions, disclosed in the appended claims and/or the specification and/or the accompanying drawings should be construed as included within the scope of the present invention. In particular, any combination of two or more of the appended claims should be equally construed as included within the scope of the present invention.

EFFECT OF THE INVENTION

The cellulose acetate fiber of the present disclosure contains a specific plasticizer and is controlled to have a degree of crystalline orientation in a specific range, so that it can enhance biodegradability based on ISO14851.

DESCRIPTION OF EMBODIMENTS

(Cellulose acetate)

Cellulose acetate, which is a constituent component of a cellulose acetate fiber, is a semi-synthetic polymer in which at least one of three hydroxy groups (-OH) at 2-, 3-, and 6-positions in a glucose ring of cellulose, which is a natural polymer, is substituted with acetic ester (-OCOCH₃). For the cellulose acetate which is a polymer material derived from plants, a non-edible portion of a plant material can be used as a raw material.
A degree of substitution indicates a degree to which hydroxy groups in one glucose ring are substituted with acetic ester, and is within a range of 1 to 3. An average degree of substitution is not particularly limited to a specific one as long as a fiber can be formed, and may be, for example, 2.0 to 2.6, preferably 2.1 to 2.5, and more preferably 2.3 to 2.5 from the viewpoint of improvement in melt spinnability. The average degree of substitution is a value measured by the method described in the Examples below.
In the cellulose acetate, degrees of substitution at 2-, 3-, and 6-positions may be uniform or non-uniform. For example, in a case where the degrees of substitution are uniform, each of the degrees of substitution at 2-, 3-, and the 6-position may be greater than 0.70. On the other hand, in a case where the degrees of substitution are non-uniform, one of the degrees of substitution at 2- and 3-positions may be 0.70 or less.
The cellulose acetate in which one of the degrees of substitution at 2- and 3-positions is 0.70 or less can be produced also by referring to the Journal of the Japan Wood Research Society, vol. 60, p. 144-168 (2014), and Biomacromolecules, 13, 2195-2201 (2012).
A weight-average molecular weight (Mw) of the cellulose acetate may be, for example, 100000 to 1000000, preferably 100000 to 500000, and particularly preferably 100000 to 300000. The weight-average molecular weight is a value measured by the method described in the Examples below.
The cellulose acetate can be produced by an acetylation reaction of dissolving pulp with an acylating agent such as acetic anhydride and glacial acetic acid in the presence of an acylation catalyst such as sulfuric acid.
General cellulose acetate is marketed as, for example, the L series such as product names "L-20", "L-30", "L-50", and "L-70" from Daicel Corporation.

(Adipic acid ester-based compound)

The cellulose acetate fiber contains an adipic acid ester-based compound as a constituent component. Examples of the adipic acid ester include an ester of adipic acid and at least one alcohol selected from the group consisting of an aromatic alcohol and an aliphatic alcohol. These types of the adipic acid ester may be used singly or in combination of two or more.
Examples of the ester of adipic acid and an aliphatic alcohol include dibutyl adipate, dioctyl adipate, dimethoxyethoxyethyl adipate, and dibutoxyethoxyethyl adipate.
Examples of the ester of adipic acid and an aromatic alcohol include diphenyl adipate, dibenzyl adipate, dicresyl adipate, and dixylyl adipate.
A preferable mixed alcohol ester of adipic acid, and an aromatic alcohol and an aliphatic alcohol may be benzyl alkyl diglycol adipate. Benzyl alkyl diglycol adipate may be used singly, or a mixture containing benzyl alkyl diglycol adipate, and an ester of adipic acid and an aromatic alcohol, and/or an ester of adipic acid and an aliphatic alcohol may be used.
In a case where a mixture containing benzyl alkyl diglycol adipate is used, a content of the benzyl alkyl diglycol adipate is preferably 35 wt% or more.
An alkyl group of benzyl alkyl diglycol adipate may be linear or branched, and a linear alkyl group is preferably used.
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 preferable examples of benzyl alkyl diglycol adipate include benzyl methyl diglycol adipate, benzyl ethyl diglycol adipate, benzyl n-propyl diglycol adipate, and benzyl n-butyl diglycol adipate, which have linear C1 to C4 alkyl groups.
A content of the adipic acid ester-based compound is 10 to 35 wt%, and may be preferably 12 to 25 wt%, and more preferably 13 to 20 wt% in the fiber from the viewpoint of fiber formability and biodegradability.
The adipic acid ester-based compound is marketed as, for example, product name "DAIFATTY-101" from DAIHACHI CHEMICAL INDUSTRY CO., LTD.

(Method for producing cellulose acetate fiber)

The cellulose acetate fiber can be produced by spinning a cellulose acetate resin composition containing 10 to 35 wt% of the adipic acid ester-based compound, at a predetermined draft ratio or draw ratio.
The spinning is preferably melt-spinning from the viewpoint of reducing use of an organic solvent during fiber forming and reducing an environmental load. In the melt-spinning, the cellulose acetate resin composition containing the adipic acid ester-based compound at a content of 10 to 35 wt%, preferably 12 to 25 wt%, and more preferably 13 to 20 wt%, can be spun at a draft ratio (ratio of a take-up speed to a discharge speed) of 10 to 250 to produce the cellulose acetate fiber. Furthermore, the fiber obtained by the melt-spinning is advantageous in that the fiber can be produced as a fiber having a modified cross-section or a composite fiber.
For the melt-spinning, a resin composition containing the cellulose acetate and the adipic acid ester-based compound may be pelletized and fed to a melt-spinning machine. For the melt-spinning, a known melt-spinning machine can be used. For example, the pellets may be melt-kneaded using a melt-extruder to obtain a molten material, and the molten material is fed to a spinning chimney. The molten material may be metered using a gear pump to discharge a predetermined amount from a spinneret at a predetermined spinning temperature, and the discharged fiber may be taken up (or wound up) at a predetermined draft ratio to produce a 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 spinneret can be suitably 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.
For the discharged fiber, the take-up speed is adjusted depending on the discharge speed, and the draft ratio is preferably adjusted within a suitable range from the viewpoint of biodegradability and fiber tenacity. The discharged fiber is taken up such that the draft ratio is 10 to 250, preferably 10 to 200, more preferably 15 to 1500, and even more preferably 20 to 120, whereby the degree of crystalline orientation of the spun cellulose acetate fiber can be controlled.
The obtained cellulose acetate fiber may be optionally drawn (preferably dry heat drawing) as long as the degree of crystalline orientation is within a range defined in the present disclosure. From the viewpoint of biodegradability, the draw ratio is preferably low, and the total draw ratio may be 2.0 or less, preferably 1.5 or less, more preferably 1.3 or less, and even more preferably 1.1 or less in a case where the drawing is performed. It is particularly preferable that the obtained cellulose acetate fiber is undrawn. In a case where single-stage drawing is performed, the total draw ratio refers to a draw ratio for the single-stage drawing. In a case where multi-stage drawing is performed, the total draw ratio refers to a draw ratio represented as a value obtained by multiplying draw ratios at the respective stages.

(Cellulose acetate fiber)

The cellulose acetate fiber has the degree of crystalline orientation of 0.010 to 0.260, and may have the degree of crystalline orientation of 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. Such a degree of crystalline orientation allows the cellulose acetate fiber to have excellent biodegradability to be demonstrated even in a low enzyme state as defined in ISO14851. The degree of crystalline orientation is a value measured by the method described in the Examples below.
As biodegradability of 2 mm cut fiber of the cellulose acetate fiber in accordance with ISO14851, for example, a degree of biodegradation after three days may be 4.0% or more, preferably 5.0% or more, more preferably 7.0% or more, and even more preferably 9.0% or more. The degree of biodegradation in accordance with ISO 14851 is a value measured by the method described in the Examples below.
The cellulose acetate fiber may have a degree of crystallinity of, for example, 30% or less, preferably 28% or less, and more preferably 25% or less from the viewpoint of biodegradability. The lower limit value of the degree of crystallinity is not particularly limited to a specific one, and may be 1% or more, preferably 2% or more, and more preferably 3% or more from the viewpoint of fiber tenacity. The degree of crystallinity can be determined by a ratio between an area of a crystalline peak and an area of an amorphous peak using a wide-angle X-ray scattering profile obtained by an X-ray irradiation.
The cellulose acetate fiber may have a breaking tenacity (hereinafter, also referred to as fiber tenacity) of, 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 tenacity is not particularly limited to a specific one, and may be 2.0 cN/dtex or less. The fiber tenacity is a value measured by the method described in the Examples below.
The number of filaments can be suitably adjusted depending on the application and the like, and the cellulose acetate fiber may be a monofilament or a multifilament. In a case of a multifilament, for example, the number of filaments may be 5 to 3000, preferably 10 to 2000, more preferably 30 to 1500, and even more preferably 50 to 500.
A single fiber fineness (fineness of single fiber) can be varied depending on a target application. The cellulose acetate fiber may be a monofilament or a multifilament. The cellulose acetate fiber may have a single fiber fineness of, 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 is a value measured in accordance with JIS L 1013:2010.
The total fineness of the cellulose acetate fiber can be suitably adjusted depending on the application and the like, and may be, for example, 1 to 10000 dtex, preferably 10 to 5000 dtex, more preferably 50 to 3000 dtex, and even more preferably 100 to 1500 dtex.
The cellulose acetate fiber may be a continuous fiber or a discontinuous fiber depending on the shape of the cellulose acetate fiber. The cellulose acetate fiber may be a crimped fiber or a non-crimped fiber. In a case where the cellulose acetate fiber is used for a nonwoven fabric, the cellulose acetate fiber is cut so as to have a suitable length depending on a type of the nonwoven fabric. The discontinuous fiber refers to a fiber having a fiber length of 100 mm or less. The continuous fiber refers to a fiber other than the discontinuous fibers.
A cross-section of the fiber may have a round shape such as a circular shape, an elliptical shape, and a cocoon-like shape, and, in addition thereto, the cross-section of the fiber may have various modified cross-sectional shapes the examples of which include a polygonal shape such as a triangular shape, a quadrangular shape, a star shape, and an X shape, and a curved shape such as a clover-leave shape and an S shape. The cellulose acetate fiber may be a part of composite fiber such as core-sheath-type fiber, sea-island-type fiber, and side-by-side type fiber.
The cellulose acetate fiber may be, for example, a composite fiber (for example, a core-sheath fiber, a sea-island fiber, a side-by-side fiber, a split-type fiber) obtained in combination with another polymer (for example, various biodegradable polymers) as long as biodegradability is not impaired. However, the cellulose acetate fiber is preferably non-composite fiber from the viewpoint of controlling the degree of crystalline orientation of the fiber.
The cellulose acetate fiber may contain an antioxidant, a heat stabilizer, a plasticizer, an antistatic agent, a radical inhibitor, a delustering agent, an ultraviolet absorber, a flame retardant, a dye, a pigment, another polymer, etc., as long as the effect of the present disclosure is not impaired. In the present disclosure, the cellulose acetate fiber may contain a lubricant as necessary. The lubricant allows enhancement of fluidity of resin. The lubricant is classified into two types. One type of the lubricants is called an internal lubricant, and is dissolved well in the resin and reduces friction between polymers to enhance fluidity of resin. The other type of the lubricants is called an external lubricant, and is not dissolved well in the polymer and forms a lubricating layer between a metal surface and the resin to enhance fluidity of resin. In the present disclosure, each of the internal lubricant and the external lubricant can be contained in the cellulose acetate fiber. Some lubricants function as both. Even where the cellulose acetate has a high melt viscosity, fluidity can be adjusted by adding the lubricant so as to enhance lubricity with respect to a mold and a die. Examples of the lubricant include a low molecular weight compound which has two moieties having affinities to cellulose acetate molecules and a metal, respectively. Such a low molecular weight compound is likely to migrate to an interface between a polymer and a metal, and has a low viscosity due to a low molecule weight, so that some low molecular weight compounds can impart lubricity with a small amount added. Some of hydrocarbon-based, silicone-based, higher alcohol-based, and higher fatty acid-based lubricants and compounds thereof have such an effect. In the present disclosure, the lubricant can be selected from known lubricants and used as necessary.
The cellulose acetate fiber may be further combined with another fiber as long as the effect of the present disclosure is not impaired. For example, the cellulose acetate fiber may be a commingled yarn obtained in combination with another fiber, or a fabric.
The cellulose acetate fiber of the present disclosure can be used in various fields in which biodegradability can be utilized, and can be effectively used in many applications such as agricultural materials, forestry materials, fishery materials, civil engineering materials, clothing fibers, daily materials, sanitary materials, and medical materials.

EXAMPLES

The present disclosure will be described below in more detail with reference to Examples. The Examples, however, are not intended to limit the present disclosure. In the Examples below, various physical properties were determined in accordance with the following methods.

[Weight-average molecular weight]

A weight-average molecular weight Mw can be determined by GPC analysis under the following GPC conditions.

Solvent: NMP
Column for measurement: Two PolyPore columns (7.8 mmϕ×30 cm) equipped with guard columns, manufactured by Agilent Technologies, Inc.
Flow rate: 0.5 ml/min
Column temperature: 55°C
Sample concentration: 0.5 wt%
Injection amount: 50 µl
Detector: RI
Standard substance: polymethyl methacrylate (PMMA) (molecular weight of 675,500, molecular weight of 504,500, molecular weight of 223,900, molecular weight of 66,650, molecular weight of 26,550, molecular weight of 6,140, and molecular weight of 1,780)

[Average degree of substitution of cellulose acetate]

Each of degrees of acetyl substitution at 2-, 3-, and 6-positions in a glucose ring of cellulose acetate can be measured by an NMR method according to method described in Tezuka (Tezuka, Carbonydr. Res. 273, 83 (1995)). Specifically, free hydroxy groups in a cellulose acetate sample are propionylated with propionic anhydride in pyridine. The obtained sample is dissolved in deuterated chloroform, and ¹³C-NMR spectrum is measured. Carbon signals of acetyl groups appear in a region of 169 to 171 ppm in the order of the 2-position, the 3-position, and the 6-position from a higher magnetic field, and carbonyl carbon signals of propionyl groups appear in a region of 172 to 174 ppm in the same order. The degree of acetyl substitution at each of the 2-, 3-, and 6-positions in the glucose ring of the original cellulose acetate can be determined from an abundance ratio (in other words, area ratio between the signals) between the acetyl group and the propionyl group at each of the corresponding positions. The degree of acetyl substitution can be analyzed by ¹H-NMR as well as ¹³C-NMR.
In the present disclosure, a total degree of acetyl substitution is a sum of the degrees of acetyl substitution at the 2-, 3-, and 6-positions in the glucose ring of the cellulose acetate as obtained by the above-described measurement method.

[Degree of crystalline orientation]

A degree of crystalline orientation is determined according to the following formulae (1) and (2) using a wide-angle X-ray scattering profile obtained by an X-ray irradiation under the following measurement conditions.

Measurement device: Bruker D8 Discover IµS
X-ray source: Cu
Collimator diameter: 0.5 mm
Voltage: 50 kV
Current: 1 mA
Detector: two-dimensional PSPC·VANTEC-500
Time of exposure to light: 10 minutes/1 frame

\begin{array}{l} f = (3 〈\cos^{2} θ〉 - 1) / 2 (1) \\ \underset{\begin{matrix} STATISTICAL \\ AVERAGE VALUE \end{matrix}}{〈\cos^{2} θ〉} = \frac{\sum_{i = 0}^{i = 90} I_{1} \cdot \cos^{2} θ_{1} \sin θ_{1}}{\sum_{i = 0}^{i = 90} I_{1} \cdot \sin θ_{1}} (2) \end{array}

In the formulae (1) and (2), f represents a degree of crystalline orientation, and Ii represents a peak intensity at an azimuth angle of θi. <cos²θ> represents an average of orientations of all molecules. In a case of non-orientation, f = 0 is satisfied. In a case of full orientation, f = 1 is satisfied. An integration range i is azimuth angles of 0 to 90 degrees.

[Breaking tenacity (cN/dtex)]

Breaking tenacity was measured using a universal testing machine ("Autograph type AGS-D" manufactured by SHIMADZU CORPORATION). Test pieces each having a width of 50 mm and a length of 200 mm were prepared, and a distance between gripping portions was set to 100 mm, and then, end portions of each test piece were fixed by the gripping portions, and the test piece was pulled at a speed of 100 mm/min until the test piece was broken. An average value of testing forces at break was defined as breaking strength, and a value calculated by dividing the breaking strength by fineness was defined as breaking tenacity.

[Biodegradability based on ISO14851]

According to the evaluation method of biodegradability defined in ISO14851:2019, fibers cut so as to have a length of 2 mm were added into 300 mL of a standard test culture solution containing, at a concentration of 100 mg/L, activated sludge in a sewage treatment plant in Kurashiki City, Okayama Prefecture such that a content of the fibers was 100 mg/L. The obtained product was cultured at 25 ± 1°C, and an amount of oxygen consumed by biodegradation was measured using a BOD meter ("Oxitop" manufactured by WTW). A degree of biodegradation was obtained from a ratio between the measured value and a theoretical oxygen demand (ThOD), and the biodegradability was determined according to the following criteria.

A: Degree of biodegradation after three days was 5.0% or more.
B: Degree of biodegradation after three days was 4.0% or more and less than 5.0%.
C: Degree of biodegradation after three days was less than 4.0%.

[Example 1]

Hardwood prehydrolyzed kraft pulp containing 98.4 wt% of α-cellulose was ground into a cotton-like form using a disc refiner. Onto 100 parts by weight of the ground pulp (water content of 8%), 26.8 parts by weight of acetic acid was sprayed, and the resulting mixture was stirred well, and was then allowed to stand for 60 hours for activation 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 resulting mixture was adjusted to have a maximum temperature of 5 to 40°C over 40 minutes, and acetylated for 90 minutes. A neutralizer (24% aqueous solution of magnesium acetate) was added over three minutes so as to adjust an amount of sulfuric acid (amount of ripening sulfuric acid) to 2.5 parts by weight. The temperature of the reaction bath was further increased to 75°C, and then water was added thereto such that the concentration of water (ripening water) in the reaction bath was adjusted to 52 mol%. Thereafter, ripening was performed at 85°C, and then the ripening was stopped by neutralizing sulfuric acid with magnesium acetate, to obtain a reaction mixture containing cellulose acetate. A diluted acetic acid aqueous solution was added to the obtained reaction mixture, and the cellulose acetate was separated, and then washed with water, dried, and stabilized by calcium hydroxide, to obtain cellulose acetate having a degree of acetyl substitution of 2.4 and a weight-average molecular weight of 180000. Into a Henschel mixer, 80 wt% of the obtained cellulose acetate and 20 wt% of an adipic acid ester-based compound ("DAIFATTY-101" manufactured by DAIHACHI CHEMICAL INDUSTRY CO., LTD.) were added, and stirred and mixed so as to reach a temperature of 70°C or higher by frictional heat in the mixer. Thereafter, the resultant product was fed to a twin-screw extruder (cylinder temperature: 200°C, die temperature: 210°C), extruded, and pelletized.
The obtained cellulose acetate composition in the form of pellets was discharged from a spinneret having round holes at a discharge speed of 400 m/min at a spinning temperature of 260°C using a melt-spinning machine, and then wound at a draft ratio of 31, to obtain multifilaments each having 500 dtex/24 filaments. The degree of biodegradation after three days of the obtained fibers was 11.3%.

[Example 2]

Cellulose acetate fibers were produced in the same manner as in Example 1 except that an amount of the adipic acid ester-based compound was 13 wt% and a spinning temperature was 250°C. The obtained cellulose acetate fibers were evaluated, and the evaluation results are shown in Table 1. The degree of biodegradation after three days of the obtained fibers was 7.2%.

[Example 3]

Cellulose acetate fibers were produced in the same manner as in Example 1 except that an amount of the adipic acid ester-based compound was 30 wt% and a spinning temperature was 270°C. The obtained cellulose acetate fibers were evaluated, and the evaluation results are shown in Table 1. Also in Example 3, the degree of crystalline orientation indicated a value between that of Example 1 and that of Example 4, and thus, biodegradability is expected to be excellent as in Examples 1 and 4.

[Example 4]

Cellulose acetate fibers were produced in the same manner as in Example 1 except that a spinning temperature was 270°C and a draft ratio was 118. The obtained cellulose acetate fibers were evaluated, and the evaluation results are shown in Table 1. The degree of biodegradation after three days of the obtained fibers was 9.0%.

[Example 5]

Cellulose acetate fibers were produced by subjecting the fibers obtained in Example 1 to dry heat drawing at 180°C such that a total draw ratio was 1.2. The obtained cellulose acetate fibers were evaluated, and the evaluation results are shown in Table 1. The degree of biodegradation after three days of the obtained fibers was 10.8%.

[Example 6]

Cellulose acetate fibers were produced in the same manner as in Example 2 except that a draft ratio was 247. The obtained cellulose acetate fibers were evaluated, and the evaluation results are shown in Table 1. The degree of biodegradation after three days of the obtained fibers was 4.8%.

[Comparative Example 1]

Cellulose acetate fibers were attempted to be produced in the same manner as in Example 1 except that an amount of the adipic acid ester-based compound was 3 wt% and a spinning temperature was 270°C. However, the cellulose acetate resin composition did not have fluidity at the spinning temperature, so that spinning was not able to be performed.

[Comparative Example 2]

Cellulose acetate fibers were attempted to be produced in the same manner as in Example 1 except that an amount of the adipic acid ester-based compound was 50 wt% and a spinning temperature was 204°C. However, the discharged fibers had a low tenacity, and thus, was not able to be wound.

[Comparative Example 3]

Cellulose acetate having a degree of acetyl substitution of 2.4 and a weight-average molecular weight of 180000 was added to DMSO, and stirred and dissolved at 90°C for 5 hours, to obtain a spinning dope in which a polymer concentration was 24 wt%. The spinning dope was subjected to dry-wet spinning in a coagulation bath using water as the coagulating liquid at 10°C through a spinneret having 80 holes each having a hole diameter of 0.12 mmϕ, and subjected to wet drawing at 1.5 times in a water bath at 20°C. Subsequently, DMSO in the fibers was extracted by water, a spinning oil was applied to the fibers, and the fibers was dried at 120°C. Thereafter, the obtained cellulose acetate fibers were subjected to dry heat drawing at 220°C such that a total draw ratio was 3.0. The degree of biodegradation after three days of the obtained fibers was 3.1%.

[Comparative Example 4]

Cellulose acetate fibers were attempted to be produced in the same manner as in Example 2 except that a draft ratio was 300. However, since the winding speed was excessively high, the discharged fibers were frequently broken while the fibers were wound, and fibers were not able to be obtained.

[Comparative Example 5]

Cellulose acetate fibers were produced by subjecting the fibers obtained in Example 1 to dry heat drawing at 220°C such that a total draw ratio was 2.5. The obtained cellulose acetate fibers were evaluated, and the evaluation results are shown in Table 1.

[Table 1]

	Spinning method	Draft ratio	Total draw ratio	Adipic acid ester-based compound	Spinning temperature	Average degree of substitution	Weight-average molecular weight	Tenacity	Degree of crystalline orientation	Biodegradability
	Spinning method	(times)	(times)	(wt%)	(°C)	Average degree of substitution	Weight-average molecular weight	(cN/dtex)	Degree of crystalline orientation	Biodegradability
Example 1	Melt-spinning	31	-	20	260	2.4	18×10⁴	0.66	0.110	A
Example 2	Melt-spinning	31	-	13	250	2.4	18×10⁴	0.68	0.115	A
Example 3	Melt-spinning	31	-	30	270	2.4	18×10⁴	0.42	0.149	A
Example 4	Melt-spinning	118	-	20	270	2.4	18×10⁴	0.99	0.180	A
Example 5	Melt-spinning	31	1.2	20	260	2.4	18×10⁴	0.90	0.192	A
Example 6	Melt-spinning	247	-	13	250	2.4	18×10⁴	0.94	0.232	B
Comparative Example 1	Melt-spinning	31	-	3	270	2.4	18×10⁴	Spinning was not able to be performed due to no fluidity
Comparative Example 2	Melt-spinning	31	-	50	204	2.4	18×10⁴	Winding-up was not able to be performed due to tenacity being 0.1 cN/dtex or less
Comparative Example 3	Wet-spinning	-	3.0	-	-	2.4	18×10⁴	1.8	0.604	C
Comparative Example 4	Melt-spinning	300	-	13	250	2.4	18×10⁴	Spinning was not able to be performed due to high draft ratio
Comparative Example 5	Melt-spinning	31	2.5	20	260	2.4	18×10⁴	1.07	0.270	C

As shown in Table 1, the degrees of crystalline orientation in Examples 1 to 6 were in a range of 0.010 to 0.260. In these Examples, biodegradability based on ISO14851 is good, and biodegradation quickly progresses in a short period of time in spite of a low-enzyme environment at or around 25°C. Furthermore, according to ISO14851, biodegradability at a low temperature (at or around 25°C) adopted for marine biodegradability can be evaluated. Therefore, in these Examples in which biodegradability is quickly demonstrated at a low temperature under a low-enzyme environment, biodegradability is expected to be excellent also in the marine environment. Further, in the comparison between Example 2 and Example 6, in which the proportion between the cellulose acetate and the adipic acid ester-based compound is the same, it is found that fiber tenacity can be enhanced by increasing the draft ratio for spinning.
On the other hand, in Comparative Examples 3 and 5 having the degree of crystalline orientation of 0.604 and 0.270, respectively, biodegradability based on ISO14851 is not good.
In a case where melt-spinning is performed, melt spinnability differs depending on an amount of a plasticizer. In Comparative Example 1, in which an amount of the plasticizer was 3 wt%, the resin composition did not have fluidity even at a higher spinning temperature, so that the resin composition was not able to be melt-spun.
In Comparative Example 2, in which an amount of the plasticizer was 50 wt%, spinning was attempted, but discharged fibers were frequently broken due to low tenacity, and traveling fibers were not able to be wound.
In Comparative Example 4, in which an amount of the plasticizer was the same as that in Example 1, but discharged fibers were frequently broken and traveling fibers were not able to be wound due to the higher draft ratio.

INDUSTRIAL APPLICABILITY

The cellulose acetate fiber of the present disclosure has excellent biodegradability, and can thus be suitably used in many applications such as agricultural materials, forestry materials, fishery materials, civil engineering materials, clothing fibers, daily materials, sanitary materials, and medical materials.
Although the present disclosure has been fully described above in connection with the preferred embodiments thereof, those skilled in the art would readily arrive at various changes and modifications in view of the present specification without departing from the scope of the invention. Accordingly, such changes and modifications are included within the scope of the present invention defined by the appended claims.

Claims

A cellulose acetate fiber containing 10 to 35 wt% of an adipic acid ester-based compound, wherein the cellulose acetate fiber has a degree of crystalline orientation of 0.010 to 0.260.
The cellulose acetate fiber according to claim 1, wherein a cellulose acetate constituting the cellulose acetate fiber has an average degree of substitution of 2.0 to 2.6.
The cellulose acetate fiber according to claim 1 or 2, wherein a cellulose acetate constituting the cellulose acetate fiber has a weight-average molecular weight (Mw) of 100000 to 1000000.
The cellulose acetate fiber according to claim 1 or 2, wherein the cellulose acetate fiber has a tenacity of 0.3 cN/dtex or more.
The cellulose acetate fiber according to claim 3, wherein the cellulose acetate fiber has a tenacity of 0.3 cN/dtex or more.
A method for producing a cellulose acetate fiber, the method comprising:
melt-spinning a cellulose acetate resin composition containing 10 to 35 wt% of an adipic acid ester-based compound, at a draft ratio of 10 to 250; and

optionally drawing a melt-spun fiber at a total draw ratio of 2.0 or less.
The method for producing the cellulose acetate fiber according to claim 5, wherein the melt-spinning is performed at a spinning temperature of 250 to 290°C.