JPH0921018A - Biodegradable fiber and nonwoven fabric using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a biodegradable fiber consisting of polylactic acid reduced in the respective contents of lactic acid, lactide and lactyl lactate, thus good in stability with the lapse of time at room temperature and useful in such areas as civil engineering/construction materials, fishery materials, agricultural materials, clothing use, etc. SOLUTION: The objective biodegradable fiber consists of polylactic acid and/or a copolymer predominant therein with the content of low-molecular compounds (lactic acid, lactide and lactyl lactate) brought to <=1wt.% (pref. <=0.3wt.%) prepared by ring opening polymerization of L-lactide singly or its combination with a comonomer in the presence of a catalyst. It is preferable that the tensile tenacity, tensile elongation at break and knot tenacity of the fiber be >=2.5g/d, >=10% and >=1.5g/d, respectively.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a biodegradable fiber,
In particular, the present invention relates to a biodegradable fiber having good stability over time at room temperature.

[0002]

2. Description of the Related Art Fibers that have hitherto been used for living materials, agricultural materials, fishery materials, and civil engineering materials include synthetic fibers such as polyester, polyolefin, and polyamide. When these fibers are left in the natural environment after use, they are not easily decomposed, which causes various problems. For example, since these living materials, agricultural materials, civil engineering materials, etc. are difficult to decompose,
After use, it was necessary to bury it in the soil, incinerate it, and so on, and if it was buried in the soil, its biodegradability was low, so there was a limit to how it could be used. In the case of fishery materials,
Often left in the water, there were problems such as polluting the ocean. In order to solve such a problem, it has been considered to use a material that is decomposed in soil or water, but a material that has been sufficiently decomposed has not been obtained.

Examples of conventional biodegradable polymers include cellulose, cellulose derivatives, polysaccharides such as chitin and chitosan, proteins, poly-3-hydroxybutyrate and 3-.
Polymers produced by microorganisms such as copolymers of hydroxybutyrate and 3-hydroxyvalerate, and aliphatic polyesters such as polyglycolide, polylactide and polycaprolactone are known. Cellulose-based cotton and regenerated cellulose, which are mainly used, are inexpensive, but require binders because they are not thermoplastic and use polyolefins, polyester fibers, etc. as the binder fibers, and thus have a problem of being difficult to biodegrade. . Since poly-3-hydroxybutyrate, a copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate, etc. produced by a microorganism are expensive, their applications are limited, and their strength is low. Polycaprolactone is a relatively inexpensive biodegradable polymer, but its melting point is as low as about 60 ° C., which is a temperature that can occur in the distribution stage in summer in nature, and there was a problem in heat resistance. .

Further, a material obtained by mixing polyethylene with starch has been studied as an inexpensive material, but it is not satisfactory in terms of biodegradability and fibers having uniform mechanical properties cannot be obtained. JP-A-4-108331 discloses a fishing line in which a hydrolyzable polyester fiber having glycolic acid and / or lactic acid as a structural unit is coated with a degradable polymer having a lower hydrolyzability than the fiber. There was a problem that requires post-processing. Although polylactic acid is a relatively stable polymer, it has a problem in stability over time (strength retention rate) at room temperature, and particularly has a problem that strength is lowered.

As described above, the prior art has strength and practical heat resistance and stability at room temperature with time (strength retention rate).
It was not possible to obtain a biodegradable fiber that is practical, and is relatively inexpensive, since it does not have a thermoplastic biodegradable fiber that has good biodegradability, is quick by microorganisms, and has excellent biodegradability.

[0006] In view of such circumstances, the object of the present invention is to
It is an object of the present invention to provide a biodegradable fiber which has improved stability over time (strength retention rate) and has strength in a polylactic acid-based biodegradable fiber.

[0007]

Means for Solving the Problems As a result of intensive research to solve the above problems, the present inventors have found that biodegradable fibers are
The above problem has been solved by controlling the content of low molecular weight compounds using a thermoplastic resin composed of polylactic acid and / or a copolymer mainly composed of polylactic acid.

That is, the present invention comprises (1) a thermoplastic resin comprising polylactic acid and / or a copolymer mainly composed of polylactic acid, wherein the content of the low molecular weight compound is 1% by weight or less. Characteristic biodegradable fiber, (2) Melting point 120 ~
In the range of 200 ° C or the flow starting temperature is 100 to 1
(1) the biodegradable fiber in the range of 80 ° C., (3) the thermoplastic resin in which the carboxyl group in the thermoplastic resin is esterified with a compound having a hydroxyl group (1) Or (2) biodegradable fiber, (4) tensile strength of 2.5 g / d or more, tensile elongation at break of 10% or more
The biodegradable fiber according to any one of (1) to (3), (5) tensile strength 2.5 g / d or more, tensile elongation at break 10% or more, knot strength 1.5 g / d or more (1 ) ~ (3) biodegradable fiber, (6) in the form of multifilament (1) ~ (5) biodegradable fiber, (7) in the form of monofilament There is a biodegradable fiber according to any one of (1) to (5), (8) in the form of short fibers (1) to (7)
Biodegradable fiber according to any one of (1) to (3), (10) (1) to (3) biodegradable non-woven fabric using the biodegradable fiber according to (9) (8) The present invention relates to a long-fiber non-woven fabric using fibers.

Hereinafter, the present invention will be described in detail. The thermoplastic resin used in the present invention comprises polylactic acid and / or a copolymer mainly composed of polylactic acid. The lactic acid for producing polylactic acid may be only the D-form, the L-form, or a mixture of the D-form and the L-form. Examples of the copolymer containing polylactic acid as a main component include lactic acid (either D-form, L-form, or a mixture of D- and L-forms), cyclic lactones such as ε-caprolactone, and α-hydroxy. Butyric acid, α-hydroxyisobutyric acid, α-hydroxy acids such as α-hydroxyvaleric acid, ethylene glycol, glycols such as 1,4-butanediol, succinic acid, one of monomers selected from dicarboxylic acids such as sebacic acid, or The thing which copolymerized two or more types is mentioned. Among them, cyclic lactones and glycols are preferable from the viewpoint of polymer polymerizability. The proportion of copolymerization is not particularly limited, but 100 parts by weight or less of the monomer to be copolymerized is preferable, and 1 to 50 parts by weight is more preferable, relative to 100 parts by weight of lactic acid.

Further, the thermoplastic resin may be one in which the carboxyl group in the thermoplastic resin is esterified with a compound having a hydroxyl group. Examples of the compound having a hydroxyl group include higher alcohols having 6 or more carbon atoms such as octyl alcohol, lauryl alcohol and stearyl alcohol, and glycols such as ethylene glycol, diethylene glycol and 1,4-butanediol. By esterifying the carboxyl group at the molecular end of the thermoplastic resin with a compound having a hydroxyl group, the thermal stability during melt spinning and the temporal stability of the fiber after melt spinning can be improved. Among them, higher alcohols having 6 to 18 carbon atoms are preferable from the viewpoint of spinnability.

The thermoplastic resin may be synthesized by a method known per se. For example, ring-opening polymerization of L-lactide in the presence of a catalyst and reprecipitation purification if necessary to obtain a thermoplastic resin. Further, a monomer or oligomer to be copolymerized and L-lactide are subjected to ring-opening polymerization in the presence of a catalyst and, if necessary, reprecipitation purification is carried out to obtain a copolymerized thermoplastic resin.

The thermoplastic resin used in the present invention preferably has a viscosity average molecular weight of 5 × 10 ³ or more, more preferably 1 × 10 ⁴ to 1 × 10 ⁶ . 5 x 10
^If it is less than ³ , sufficient fiber strength tends not to be obtained, and if it exceeds 1 × 10 ⁶ , the viscosity tends to be high during spinning and the spinnability tends to be poor.

The viscosity average molecular weight [MV] is η _sp /
C = 7.79 × 10 ⁻⁴ MV ^0.73 [wherein, η _sp / C is the reduced specific viscosity (dl / g) and MV is the viscosity average molecular weight].

The thermoplastic resin used in the present invention preferably has a reduced specific viscosity of 0.5 to 19 (dl / g), more preferably 1.0 to 6.0 (dl / g).
It is. The reduced specific viscosity of the thermoplastic resin is 0.4 (dl /
If it is less than g), the tensile strength tends to be insufficient,
If it exceeds 20 (dl / g), the viscosity during spinning tends to be high and the processability tends to be poor.

Here, the reduced specific viscosity means that a sample is precisely weighed,
The solution was dissolved in chloroform at 0.5 g / dl, and the solution was measured at 25 ° C. using an Ubbelohde viscometer.

The average molecular weight of the thermoplastic resin can be adjusted by the polymerization initiator and the polymerization conditions.

The biodegradable fiber of the present invention can be obtained by subjecting the above-mentioned thermoplastic resin to a usual melt spinning method such as a spin draw method or a high speed spinning method.

The temperature of the thermoplastic resin during melt spinning is preferably above its melting point and below 230 ° C. More preferably, it is not less than the melting point of the biodegradable fiber and not more than 210 ° C. If it exceeds 230 ° C, lactide tends to be regenerated in the biodegradable fiber, and heat deterioration tends to occur.

The melt-spun unstretched yarn is air-cooled or cooled in a water bath at 20 to 60 ° C. or an oil bath, and usually wound once, and then stretched in one or more stretching steps. It The total stretching ratio varies depending on the purpose of use and the required performance, but is usually 2 to 8 times, preferably 3 to 7 times.

The biodegradable fiber of the present invention is preferably 12
It has a melting point of 0 ° C. or higher, more preferably 130 ° C. or higher. Thus, it is possible to endure the temperature stability of the product in distribution, for example, storage at about 80 ° C. in summer. Also, from the viewpoint of the thermal stability of the thermoplastic resin during spinning,
The temperature is preferably 200 ° C or lower, more preferably 180 ° C or lower.

In the present invention, the melting point of the biodegradable fiber means
It is measured by using a DSC-50 manufactured by Shimadzu Corporation and heating at a rate of 10 ° C./min.

The melting point of the biodegradable fiber is as follows:
It can be adjusted by copolymerizing glycols, dicarboxylic acid and the like. It can also be adjusted by changing the D / L ratio of lactic acid.

When the biodegradable fiber does not show a crystal melting peak in DSC, its flow starting temperature is preferably 10.
The temperature is 0 to 180 ° C, more preferably 120 to 180 ° C. If the softening point is less than 100 ° C, the heat resistance tends to be low and the application tends not to be satisfied.

Here, the flow starting temperature is defined as the flow starting temperature by using a precision melting point measuring instrument manufactured by Yanaco Co., Ltd. to which shear stress is applied to indicate flow. The temperature rising temperature is 5 ° C./minute.

The flow initiation temperature of the biodegradable fiber can be adjusted by the copolymer and the copolymerization ratio.

In the biodegradable fiber of the present invention, the amount of the low molecular weight compound contained therein is 1% by weight or less. It is preferably 0.5% by weight or less, and more preferably 0.3% by weight. When the content of the low molecular weight compound in the biodegradable fiber exceeds 1% by weight, the stability with time at room temperature deteriorates.

In the present invention, the low molecular weight compound means lactic acid, lactide and lactyl lactic acid, and the content of the low molecular weight compound means the total amount of lactic acid, lactide and lactyl lactic acid.

Here, the content of low molecular weight compound means octadecylsilane (O) based on the liquid chromatography method.
It is measured by reverse phase high performance liquid chromatography using a DS column.

The content of the low molecular weight compound in the biodegradable fiber can be adjusted by lowering the content of the low molecular weight compound in the thermoplastic resin or suppressing the production of the low molecular weight compound during spinning. That is, a low molecular weight compound in the thermoplastic resin is removed under reduced pressure, or dissolved in a solvent for purification by reprecipitation, or a catalyst for suppressing depolymerization during spinning (preferably removed or deactivated after polymerization). It is used and so on.

The biodegradable fiber of the present invention preferably has a tensile strength of 2.5 g / d or more and a tensile elongation at break of 10% or more.

As described above, the tensile strength of the biodegradable fiber of the present invention is preferably 2.5 g / d or more, more preferably 4 g / d or more. Tensile strength is 2.5g /
If it is less than d, the tensile strength is insufficient for use in civil engineering / construction material applications, fishery material applications, agricultural material applications, other industrial material applications, and clothing applications.

In the present invention, tensile strength means JIS L
It is measured according to 1013.

The tensile strength of the biodegradable fiber can be adjusted by spinning and drawing conditions.

The biodegradable fiber of the present invention has a tensile elongation at break of preferably 10% or more, more preferably 20 to 100%, from the viewpoint of yarn physical properties.

In the present invention, the tensile elongation at break means JIS.
It is measured according to L1013.

The tensile elongation at break of the biodegradable fiber can be adjusted by spinning and drawing conditions.

The biodegradable fiber of the present invention preferably has a knot strength of 1.5 g / d or more, in addition to the tensile strength and the tensile elongation at break in the above-mentioned ranges.
/ D or more is more preferable. If the knot strength is less than 1.5 g / d, there is a tendency that the yarn physical properties required when used for civil engineering / construction material applications, fishery material applications, agricultural material applications, other industrial material applications, and clothing applications cannot be satisfied.

In the present invention, knot strength means JIS L
1013 based on measurement.

The biodegradable fiber of the present invention can be used in the form of multifilament or monofilament, or short fiber or long fiber non-woven fabric.

The above-mentioned monofilament is a fiber composed of one fiber, and can be obtained by the spinning method.

The multifilament is a fiber in which 2 to 100 monofilaments are bundled,
These can be obtained by the same method as the monofilament.

The short fiber is a fiber having a fiber length of about 2 to 80 mm and is used for spun yarn, wet non-woven fabric, dry non-woven fabric and the like. Normally, when used for spun yarn,
The fiber length is 20 to 80 mm, preferably 30 to 70 mm,
When used in a wet non-woven fabric, it is 2 to 10 mm, preferably 2
~ 8 mm, 20-80 mm when used for dry non-woven fabric,
It is preferably about 20 to 70 mm. The staple fiber of the present invention can be obtained, for example, after melt spinning, drawing, or high speed spinning.

The above-mentioned wet non-woven fabric is a non-woven fabric obtained by dispersing short fibers in a liquid, paper-making and drying, and the dry-type non-woven fabric is opened with a card, a roller or the like, and then made into a web with a webber, which is required. It is a non-woven fabric which is partially or wholly fused or entangled three-dimensionally.

The biodegradable short fibers may be crimped in order to improve the card opening property. The crimping method is not particularly limited, and a known method can be used, for example, a pushing gear method or a stuffing box method can be used.

The number of crimps is 5 to 50/25 mm, preferably 10 to 30/25 mm. If the number of crimps is less than 5/25 mm, unopened portions are likely to occur during opening, and if it exceeds 50/25 mm, uniform opening tends not to be obtained. Here, the number of crimps means JIS L
It is measured according to 1015.

The crimping rate is 5% or more, preferably 8% or more. When the crimping rate is less than 5%, it is difficult to obtain a uniform web when applied to a card, and a sparse and dense portion tends to occur. Here, the crimp ratio means JIS L101.
It was measured according to 5.

The short fiber nonwoven fabric using the biodegradable fiber of the present invention may be produced by a method known per se using the above short fibers. For example, short fibers are carded with a roller card to form a web, If necessary, it can be produced by entanglement or adhesion by needle punching, calendaring, embossing or the like. If necessary, the fiber orientation can be changed by a random webber.

The long-fiber non-woven fabric using the biodegradable fiber of the present invention may be manufactured by a method known per se.
For example, it can be manufactured by a spun bond method or a melt blow method. The spunbond method is a method in which a thermoplastic resin is heated and melted to a temperature equal to or higher than the melting point, spun from a spinneret, and the spun long fibers are cooled and solidified while being cooled and solidified by an air sucker or the like to be installed at 2000 m / min Tow at the above take-up speed, then open the fiber and collect it on the endless collection surface moving at a constant speed to form a web, which is thermo-compressed wholly or partially by embossing or calendering, or It is a method of entanglement by needle punching and hydroentanglement. In the melt blow method, a thermoplastic resin is heated and melted to a temperature equal to or higher than the melting point, discharged from a spinneret having spinning holes arranged in a straight line, and made into microfibers by high-temperature and high-pressure air jetted at high speed from both sides of a spinning nozzle. After that, it collects on the endless collecting surface moving at a constant speed to form a web, which is thermocompressed wholly or partially by embossing or calendering, or entangled by needle punching or hydroentanglement. is there.

The biodegradable fiber of the present invention has an antistatic property,
Considering the focusing property, anionic surfactants such as lauryl phosphate potassium salt, cationic surfactants such as quaternary ammonium salt, nonionic surfactants such as ethylene oxide adducts of higher aliphatic alcohols and higher fatty acids. One or more kinds of silicone oils such as polyalkylene glycols such as polyethylene glycol and polyethylene glycol / polypropylene glycol block copolymers, dimethylpolysiloxane, polyether modified silicone oil, higher alkoxy modified silicone oil, etc. it can.

The biodegradable fibers used in the present invention include thermoplastic resins, other aliphatic polyesters such as polycaprolactone, polymers such as polyvinyl alcohol, polyalkylene glycol and polyamino acid, talc, calcium carbonate, calcium sulfate and chloride. One or more inorganic substances such as calcium, starch, protein, food additives, etc.,
An appropriate amount can be mixed, and various mechanical properties, biodegradation properties, etc. can be changed.

In addition to the above, the biodegradable fiber of the present invention may be mixed with known additives such as an antioxidant, an ultraviolet absorber and a plasticizer, if necessary.

[0052]

The present invention will be further described with reference to the following examples. Moreover, each measuring method is demonstrated below.

The content of low molecular weight compounds was measured by reversed phase high performance liquid chromatography using an octadecylsilane (ODS) column based on the liquid chromatography method.

The reduced specific viscosity is 0.5 g /
It was dissolved in chloroform so as to have a dl, and the solution was measured at 25 ° C. using an Ubbelohde viscometer.

The tensile strength, tensile breaking elongation and knot strength were measured according to JIS L1013.

The melting point was measured by using DSC-50 manufactured by Shimadzu Corp., while raising the temperature at a rate of 10 ° C./min.

The strength retention is defined as the initial tensile strength of the fiber,
The tensile strength of the fiber after standing for 12 months in a room temperature of 25 ° C. and a relative humidity of 60% was measured and determined by (Equation 2). Strength retention rate (%) = (T / T ₀ ) × 100 (Equation 2) [In the equation, T is the tensile strength (g / d) of the fiber after standing for 12 months at room temperature of 25 ° C. and relative humidity of 60%, T ₀ is the initial tensile strength (g / d) of the fiber]

Regarding the biodegradability, the fiber was buried in the soil, and the state of degradation after 6 months was examined by a scanning electron microscope (SE).
M: Scanning Electron Microscope). When the shape was lost (irregularities on the surface, breakage, etc.), the biodegradability was considered good.

Example 1 A polylactic acid obtained by esterifying a carboxyl group at the molecular end with lauryl alcohol, having a reduced specific viscosity of 1.57, was prepared.
Melt spinning was performed at a spinning speed of 300 m / min from a spinning nozzle having a spinning temperature of 190 ° C. and 20 spinning holes having a diameter of 3 mm. After unwinding the undrawn yarn, it was drawn 4.5 times at 140 ° C. to obtain a single yarn fineness of 2.1 d and a low molecular weight compound content of 0.2.
A weight percent of fiber was obtained.

Example 2 Polylactic acid having a reduced specific viscosity of 1.54 was prepared at a spinning temperature of 20.
Melt spinning was performed at 0 ° C. from a spinning nozzle having 20 spinning holes with a diameter of 0.3 mm at a spinning speed of 300 m / min. The undrawn yarn was once wound and then drawn 4.5 times at 140 ° C. to obtain a fiber having a single yarn fineness of 2.2 d and a low molecular weight compound content of 0.4% by weight.

Example 3 Polylactic acid having a reduced specific viscosity of 1.55 was added at a spinning temperature of 19
Melt spinning was performed at 0 ° C. from a spinning nozzle having 20 spinning holes with a diameter of 0.3 mm at a spinning speed of 300 m / min. The unstretched yarn was once wound up and then stretched 4.5 times at 140 ° C. to obtain a fiber having a single yarn fineness of 2.2 d and a low molecular weight compound content of 0.9% by weight.

Example 4 Polylactic acid having a reduced specific viscosity of 1.73 was added at a spinning temperature of 19
Melt spinning from a spinning nozzle having one spinning hole with a diameter of 1.0 mm at 0 ° C., solidify in a water bath (30 ° C.), and spin speed 2
It was spun at 0 m / min. After winding the undrawn yarn once,
It was stretched 5 times at 140 ° C. to obtain a fiber having a fineness of 380 d and a low molecular weight compound content of 0.8% by weight.

Comparative Example 1 Polylactic acid having a reduced specific viscosity of 1.56 was spun at a spinning temperature of 19
Melt spinning was performed at 0 ° C. from a spinning nozzle having 20 spinning holes with a diameter of 0.3 mm at a spinning speed of 300 m / min. The undrawn yarn was once wound and then drawn 4.5 times at 140 ° C. to obtain a fiber having a single yarn fineness of 2.0 d and a low molecular weight compound content of 3.0 wt%.

Comparative Example 2 Polylactic acid having a reduced specific viscosity of 1.56 was used at a spinning temperature of 22.
Melt spinning was performed at 0 ° C. from a spinning nozzle having 20 spinning holes with a diameter of 0.3 mm at a spinning speed of 300 m / min. The unstretched yarn was once wound up and then stretched 4.5 times at 140 ° C. to obtain a fiber having a single yarn fineness of 2.1 d and a low molecular weight compound content of 2.2% by weight.

Comparative Example 3 Polylactic acid having a reduced specific viscosity of 1.54 was added at a spinning temperature of 23.
Melt spinning was performed at 0 ° C. from a spinning nozzle having 20 spinning holes with a diameter of 0.3 mm at a spinning speed of 300 m / min. After unwinding the undrawn yarn, it was drawn 4.5 times at 140 ° C. to obtain a fiber having a single yarn fineness of 2.1 d and a low molecular weight compound content of 5.1% by weight.

Comparative Example 4 Polylactic acid having a reduced specific viscosity of 1.78 was added at a spinning temperature of 19
Melt spinning from a spinning nozzle having one spinning hole with a diameter of 1.0 mm at 0 ° C., solidify in a water bath (30 ° C.), and spin speed 2
It was spun at 0 m / min. After winding the undrawn yarn once,
The fiber was stretched 5 times at 140 ° C. to obtain a fiber having a fineness of 380 d and a low molecular weight compound content of 3.5 wt%.

Table 1 shows the fiber physical property values obtained in Examples 1 to 4 and Comparative Examples 1 to 4 and the evaluation results of biodegradability.

[0068]

[Table 1]

From Table 1, it was found that the biodegradable fiber of the present invention has excellent biodegradability and good physical properties, has a good strength retention rate at room temperature, and is also excellent in heat resistance.

Example 5 The biodegradable fiber obtained in Example 1 was crimped by a stuffing box method and then cut into 64 mm to obtain biodegradable short fibers. The obtained short fibers were made into a web having a basis weight of 100 g / m ² by a random webber and then needle punched to obtain a nonwoven fabric.

Example 6 A polylactic acid obtained by esterifying a terminal carboxyl group of a molecule having a reduced specific viscosity of 1.51 with lauryl alcohol was obtained by a spunbond method to obtain a nonwoven fabric having a basis weight of 100 g / cm ² . The spinning conditions are as follows: a spinning temperature of 200 ° C., and a discharge amount of 0.8 g / min. Hole, pulling speed = 3500 m / min. Met. The content of low molecular weight compounds in spunbonded non-woven fabric is 0.5% and the melting point is 1
73 ° C.

Example 7 Polylactic acid having a reduced specific viscosity of 1.21 was added at a spinning temperature of 210.
° C, air temperature 210 ° C, discharge rate = 0.8 g / min. Average fiber diameter of 3.5μm by melt blow method under pore condition,
A melt blown nonwoven fabric having a basis weight of 100 g / cm ² was obtained. The content of low molecular weight compounds in meltblown nonwoven fabric is 0.8%
And the melting point was 172 ° C.

When the biodegradability of the nonwoven fabrics of Examples 5, 6, and 7 was evaluated, the biodegradability was good.

[0074]

Industrial Applicability The biodegradable fiber of the present invention is a polylactic acid type biodegradable fiber, and has stability over time (strength retention rate).
It is a biodegradable fiber that has excellent properties, strength, and practical heat resistance, is practical, and is relatively inexpensive. Further, the biodegradable fiber of the present invention is suitable for living materials, agricultural materials, fishery materials, civil engineering and construction materials, other industrial materials, and clothing, and has complete biodegradability in the natural world.

Claims (10)

[Claims] 1. A biodegradable fiber comprising a thermoplastic resin composed of polylactic acid and / or a copolymer mainly composed of polylactic acid, and containing a low molecular weight compound in an amount of 1% by weight or less. . 2. The biodegradable fiber according to claim 1, which has a melting point in the range of 120 to 200 ° C. or a flow starting temperature in the range of 100 to 180 ° C. 3. The biodegradable fiber according to claim 1, wherein the thermoplastic resin is obtained by esterifying a carboxyl group in the thermoplastic resin with a compound having a hydroxyl group. 4. The biodegradable fiber according to claim 1, which has a tensile strength of 2.5 g / d or more and a tensile elongation at break of 10% or more. 5. The biodegradable fiber according to claim 1, which has a tensile strength of 2.5 g / d or more, a tensile elongation at break of 10% or more, and a knot strength of 1.5 g / d or more. 6. The biodegradable fiber according to claim 1, which is in the form of a multifilament. 7. A monofilament form.
6. The biodegradable fiber according to any one of to 5. 8. The biodegradable fiber according to claim 1, which is in the form of short fibers. 9. A short fiber non-woven fabric comprising the biodegradable fiber according to claim 8. 10. A long-fiber nonwoven fabric comprising the biodegradable fiber according to any one of claims 1 to 3.