POLYLACTIC ACID FIBER

Abstract

A polylactic acid fiber is provided. The polylactic acid fiber includes a first polylactic acid material and a second polylactic acid material. The first polylactic acid material is encapsulated by the second polylactic acid material. Based on a total volume of the polylactic acid fiber being 100%, a volume of the second polylactic acid material is at least 20%. The second polylactic acid material includes 15 wt % to 85 wt % of poly(D-lactic acid) and 15 wt % to 85 wt % of poly(L-lactic acid).

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of priority to Taiwan Patent Application No. 110119763, filed on Jun. 1, 2021. The entire content of the above identified application is incorporated herein by reference.

Some references, which may include patents, patent applications and various publications, may be cited and discussed in the description of this disclosure. The citation and/or discussion of such references is provided merely to clarify the description of the present disclosure and is not an admission that any such reference is “prior art” to the disclosure described herein. All references cited and discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a polylactic acid fiber, and more particularly to a core-sheath polylactic acid fiber.

BACKGROUND OF THE DISCLOSURE

Polylactic acid (PLA) is a biodegradable crystalline polymer. In recent years, with the rise of environmental awareness around the world, the polylactic acid is widely used in various applications.

The polylactic acid is a thermoplastic aliphatic polyester that does not have any benzene ring in its chemical structure. Therefore, a melting point and a thermal resistance of the polylactic acid are relatively low. Generally, a polylactic acid fiber can endure a processing temperature ranging from 110° C. to 115° C. However, as the processing temperature increases, the polylactic acid fiber will melt and lose its original mechanical strength. Therefore, the processing temperature of the polylactic acid fiber has an upper limit, and a processing speed for the polylactic acid fiber is also limited. For example, when the processing speed for the polylactic acid fiber is too high, the polylactic acid fiber cannot endure a corresponding stress, which results in filament breakage. In short, the polylactic acid fiber cannot endure the high processing temperature that other aromatic polymer fibers can endure (180° C. to 200° C.). As such, the polylactic acid fiber has a disadvantage of having poor processability.

For a better dyeing effect, the polylactic acid fiber is usually false twisted to increase its crystallinity. However, after a dyeing process, stripes are easily formed on the polylactic acid fiber due to the poor processability thereof, and a uniformly dyed polylactic acid fiber cannot be produced. Hence, the polylactic acid fiber tends to have an unpleasant appearance.

In the conventional technology, a chain extender or a nucleating agent is added into a polylactic acid material, so as to improve the processability of the polylactic acid. Through an addition of the chain extender, a molecular chain length of the polylactic acid can be extended, thereby increasing a molecular weight of the polylactic acid. In this way, the melting point of the polylactic acid can be increased. On the other hand, through an addition of the nucleating agent, the crystallinity of the polylactic acid can be increased, thereby increasing the thermal resistance of the polylactic acid. However, the improvements provided by adding the chain extender or the nucleating agent are limited, and problems such as the low thermal resistance and the poor processability of the polylactic acid still exist. Therefore, the conventional polylactic acid fiber still has room for improvement.

SUMMARY OF THE DISCLOSURE

In response to the above-referenced technical inadequacy, the present disclosure provides a polylactic acid fiber.

In one aspect, the present disclosure provides a polylactic acid fiber. The polylactic acid fiber includes a first polylactic acid material and a second polylactic acid material. The first polylactic acid material is encapsulated by the second polylactic acid material. Based on a total volume of the polylactic acid fiber being 100%, a volume of the second polylactic acid material is at least 20%. The second polylactic acid material includes 15 wt % to 85 wt % of poly(D-lactic acid) and 15 wt % to 85 wt % of poly(L-lactic acid).

In certain embodiments, the second polylactic acid material includes a stereocomplex of the poly(D-lactic acid) and the poly(L-lactic acid).

In certain embodiments, the second polylactic acid material includes 15 wt % to 50 wt % of the poly(D-lactic acid) and 50 wt % to 85 wt % of the poly(L-lactic acid).

In certain embodiments, a first melting point of the second polylactic acid material ranges from 160° C. to 180° C., and a second melting point of the second polylactic acid material ranges from 210° C. to 230° C.

In certain embodiments, a glass transition temperature of the second polylactic acid material ranges from 55° C. to 70° C.

In certain embodiments, a core of the polylactic acid fiber is formed from the first polylactic acid material, and a sheath of the polylactic acid fiber is formed from the second polylactic acid material.

In certain embodiments, a cross-section of the polylactic acid fiber has a circular shape, and a thickness ratio of the sheath to the core in a radial direction of the polylactic acid fiber ranges from 0.1 to 0.5.

In certain embodiments, based on the total volume of the polylactic acid fiber being 100%, the volume of the second polylactic acid material ranges from 25% to 50%.

In certain embodiments, a crystallinity of the polylactic acid fiber ranges from 35% to 45%.

In certain embodiments, a first melting point of the polylactic acid fiber ranges from 170° C. to 185° C., and a second melting point of the polylactic acid fiber ranges from 215° C. to 230° C.

In certain embodiments, a melting point of the first polylactic acid material is lower than a melting point of the second polylactic acid material.

In certain embodiments, the melting point of the first polylactic acid material is lower than the melting point of the second polylactic acid material by 40° C. to 60° C.

Therefore, in the polylactic acid fiber provided by the present disclosure, by virtue of “based on a total volume of the polylactic acid fiber being 100%, a volume of the second polylactic acid material being at least 20%” and “the second polylactic acid material including 15 wt % to 85 wt % of poly(D-lactic acid) and 15 wt % to 85 wt % of poly(L-lactic acid),” a thermal resistance of the polylactic acid fiber can be increased, thereby solving a problem of the polylactic acid fiber conventionally having a poor processability.

These and other aspects of the present disclosure will become apparent from the following description of the embodiment taken in conjunction with the following drawings and their captions, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments may be better understood by reference to the following description and the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of a polylactic acid fiber of the present disclosure; and

FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present disclosure is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. Like numbers in the drawings indicate like components throughout the views. As used in the description herein and throughout the claims that follow, unless the context clearly dictates otherwise, the meaning of “a”, “an”, and “the” includes plural reference, and the meaning of “in” includes “in” and “on”. Titles or subtitles can be used herein for the convenience of a reader, which shall have no influence on the scope of the present disclosure.

The terms used herein generally have their ordinary meanings in the art. In the case of conflict, the present document, including any definitions given herein, will prevail. The same thing can be expressed in more than one way. Alternative language and synonyms can be used for any term(s) discussed herein, and no special significance is to be placed upon whether a term is elaborated or discussed herein. A recital of one or more synonyms does not exclude the use of other synonyms. The use of examples anywhere in this specification including examples of any terms is illustrative only, and in no way limits the scope and meaning of the present disclosure or of any exemplified term. Likewise, the present disclosure is not limited to various embodiments given herein. Numbering terms such as “first”, “second” or “third” can be used to describe various components, signals or the like, which are for distinguishing one component/signal from another one only, and are not intended to, nor should be construed to impose any substantive limitations on the components, signals or the like.

Referring to FIG. 1, FIG. 1 is a schematic perspective view of a polylactic acid fiber of the present disclosure. A polylactic acid fiber 1 of the present disclosure is a sheath-core composite fiber. The polylactic acid fiber 1 includes a core 10 and a sheath 20.

The core 10 of the polylactic acid fiber 1 is formed from a first polylactic acid material. The first polylactic acid material includes poly(L-lactic acid) (PLLA). Specifically, the poly(L-lactic acid) used in the present embodiment is of a spinning-grade, and has a melting point of approximately 170° C.

In other embodiments, in addition to the poly(L-lactic acid), the first polylactic acid material can include other polymer materials, such as polycaprolactone (PCL), poly-lactic-glycolic acid (PLGA), polyhydroxyalkanoates (PHA), polyglycolic acid (PGA), hyaluronic acid, gelatin, or any combination thereof Preferably, the first polylactic acid material includes the poly(L-lactic acid) and at least one of the polycaprolactone, the polyhydroxyalkanoates, and any combination thereof. In this way, the first polylactic acid material is completely formed from biodegradable polymers.

The sheath 20 of the polylactic acid fiber is formed from a second polylactic acid material. The second polylactic acid material includes poly(L-lactic acid) and poly(D-lactic acid) (PDLA). Based on a total weight of the second polylactic acid material being 100 wt %, the second polylactic acid material includes 15 wt % to 85 wt % of the poly(D-lactic acid) and 15 wt % to 85 wt % of the poly(L-lactic acid).

In other embodiments, in addition to the poly(D-lactic acid) and the poly(L-lactic acid), the second polylactic acid material can include other polymer materials, such as polycaprolactone, poly-lactic-glycolic acid, polyhydroxyalkanoates, polyglycolic acid, hyaluronic acid, gelatin, or any combination thereof Preferably, the second polylactic acid material includes the poly(L-lactic acid), the poly(D-lactic acid), and at least one of the polycaprolactone, the polyhydroxyalkanoates, and any combination thereof In this way, the second polylactic acid material is completely formed from biodegradable polymers. Moreover, the second polylactic acid material can further include dyes.

The poly(D-lactic acid) and the poly(L-lactic acid) in the second polylactic acid material are mixed in a melted state or a solution state, so as to form a stereocomplex (abbreviated as a PDLA/PLLA stereocomplex in the specification). Compared to the poly(D-lactic acid) or the poly(L-lactic acid) by itself, the PDLA/PLLA stereocomplex has a higher melting point and a higher crystallinity. In the present disclosure, the second polylactic acid material includes the PDLA/PLLA stereocomplex. In some embodiments, in addition to the PDLA/PLLA stereocomplex, the second polylactic acid material can further include the poly(D-lactic acid) or the poly(L-lactic acid) by itself.

In order to observe a relationship between composition of the PDLA/PLLA stereocomplex and properties of the second polylactic acid material, different weight ratios of the poly(D-lactic acid) to the poly(L-lactic acid) are mixed in a melted state, so as to obtain the second polylactic acid material of samples 1 to 4 as listed in Table 1.

Subsequently, a glass transition temperature, melting points (Tm1 and Tm2), and variation amounts of heat of fusion (ΔH1 and ΔH2) of each sample are measured by a differential scanning calorimeter (DSC) (brand: TA Instrument, Inc.; model: DSC Q10), and results are listed in Table 1. Parameters set on the differential scanning calorimeter include: a measuring temperature range that is from a room temperature to 250° C., a temperature rising rate being 20° C. per minute, and a temperature cooling rate being 20° C. per minute.

TABLE 1
Second polylactic
acid material
	PDLA/	Properties
	PLLA			Δ		Δ
Sample	(wt %)	Tg(° C.)	Tm1(° C.)	H1(J/g)	Tm2(° C.)	H2(J/g)
1	20/80	61.8	171.6	40.6	220.0	17.5
2	40/60	62.3	173.0	28.5	221.3	22.3
3	60/40	62.1	174.2	33.5	221.7	18.1
4	80/20	62.4	175.9	44.4	221.6	6.9

The second polylactic acid material includes the PDLA/PLLA stereocomplex and the poly(D-lactic acid) and the poly(L-lactic acid) that do not form the PDLA/PLLA stereocomplex. Therefore, two melting points (Tm1 and Tm2) and two variation amounts of heat of fusion (ΔH1 and ΔH2) can be observed after the second polylactic acid material is analyzed by way of differential scanning calorimetry.

According to Table 1, the glass transition temperature of the second polylactic acid material ranges from 55° C. to 70° C. Preferably, the glass transition temperature of the second polylactic acid material ranges from 60° C. to 65° C. A lower melting point of the second polylactic acid material ranges from 160° C. to 180° C., and is hereinafter referred to as a first melting point (Tm1). Preferably, the first melting point of the second polylactic acid material ranges from 170° C. to 176° C. A higher melting point of the second polylactic acid material ranges from 210° C. to 230° C., and is hereinafter referred to as a second melting point (Tm2) Preferably, the second melting point of the second polylactic acid material ranges from 219° C. to 222° C. A difference between the first melting point and the second melting point ranges from 40° C. to 60° C. Preferably, the difference between the first melting point and the second melting point ranges from 40° C. to 50° C.

In other words, in an exemplary embodiment, the melting point of the second polylactic acid material is higher than the melting point of the first polylactic acid material. Specifically, the melting point of the second polylactic acid material is higher than the melting point of the first polylactic acid material by 40° C. to 60° C. Preferably, the melting point of the second polylactic acid material is higher than the melting point of the first polylactic acid material by 45° C. to 55° C.

According to Table 1, the variation amount of heat of fusion (ΔH1) of the second polylactic acid material at the first melting point ranges from 20 J/g to 50 J/g. Preferably, the variation amount of heat of fusion of the second polylactic acid material at the first melting point ranges from 25 J/g to 45 J/g. The variation amount of heat of fusion (ΔH2) of the second polylactic acid material at the second melting point ranges from 3 J/g to 30 J/g. Preferably, the variation amount of heat of fusion of the second polylactic acid material at the second melting point ranges from 5 J/g to 25 J/g.

Therefore, the second polylactic acid material of the present disclosure can have a higher glass transition temperature and a higher melting point, and can thus be used at a higher processing temperature, thereby solving a problem of the polylactic acid fiber conventionally having a poor processability due to its original properties.

Due to a raw material cost of the poly(D-lactic acid) is higher than a raw material cost of the poly(L-lactic acid), the second polylactic acid material includes 15 wt % to 50 wt % of the poly(D-lactic acid) and 50 wt % to 85 wt % of the poly(L-lactic acid).

In some embodiments, an amount of the poly(D-lactic acid) and an amount of the poly(L-lactic acid) are the same. In other words, a weight ratio of the poly(D-lactic acid) to the poly(L-lactic acid) is 50/50. In other embodiments, the amount of the poly(D-lactic acid) is lower than the amount of the poly(L-lactic acid). In other words, in the second polylactic acid material, the amount of the poly(D-lactic acid) ranges from 15 wt % to less than 50 wt %, and the amount of the poly(L-lactic acid) ranges from greater than 50 wt % to 85 wt %.

In addition, based on a total volume of the polylactic acid fiber 1 being 100%, a volume of the sheath 20 is at least 20% so that the core 10 can be completely encapsulated by the sheath 20. In order to observe a relationship between a volume ratio of the sheath 20 to the core 10 and properties of the polylactic acid fiber 1, various polylactic acid fibers 1 of Examples 1 to 4 that contain different amounts of the first polylactic acid material and the second polylactic acid material are prepared, and the specific properties are listed in Table 2. In Examples 1 to 4, the second polylactic acid material used in the polylactic acid fiber 1 is the sample 3 listed in Table 1.

Subsequently, melting points (Tm1 and Tm2), variation amounts of heat of fusion (ΔH1 and ΔH2), and a crystallinity (Xc1) of the polylactic acid fiber 1 in Examples 1 to 4 are measured by a differential scanning calorimeter (DSC), and results are listed in Table 2. Parameters set on the differential scanning calorimeter include: a measuring temperature range that is from a room temperature to 250° C., a temperature rising rate being 20° C. per minute, and a temperature cooling rate being 20° C. per minute.

TABLE 2
Polylactic acid fiber
	Sheath/	Property
	core		Δ			Δ
Example	(vol %)	Tm1(° C.)	H1(J/g)	Xc1(%)	Tm2(° C.)	H2(J/g)
1	25/75	175.52	39.31	42.27	222.40	14.65
2	30/70	176.88	38.47	41.37	223.42	19.05
3	40/60	178.79	35.75	38.44	223.73	24.06
4	50/50	177.22	34.76	37.38	223.01	23.60

A material forming the polylactic acid fiber 1 contains the PDLA/PLLA stereocomplex and the poly(D-lactic acid) and the poly(L-lactic acid) that do not form the PDLA/PLLA stereocomplex. Therefore, two melting points (Tm1 and Tm2) and two variation amounts of heat of fusion (ΔH1 and ΔH2) can be observed after said material is analyzed by way of the differential scanning calorimetry.

According to Table 2, a lower melting point of the polylactic acid fiber 1 ranges from 160° C. to 180° C., and is hereinafter referred to as a first melting point (Tm1). Preferably, the first melting point of the polylactic acid fiber 1 ranges from 175° C. to 180° C. A higher melting point of the polylactic acid fiber 1 ranges from 210° C. to 230° C., and is hereinafter referred to as a second melting point (Tm2) Preferably, the second melting point of the polylactic acid fiber 1 ranges from 220° C. to 225° C. The crystallinity (Xc1) of the polylactic acid fiber 1 ranges from 30% to 50%. Preferably, the crystallinity (Xc1) of the polylactic acid fiber 1 ranges from 35% to 45%.

According to Table 2, the variation amount of heat of fusion (ΔH1) of the polylactic acid fiber 1 at the first melting point ranges from 20 J/g to 50 J/g. Preferably, the variation amount of heat of fusion of the polylactic acid fiber 1 at the first melting point ranges from 30 J/g to 40 J/g. The variation amount of heat of fusion (ΔH2) of the polylactic acid fiber 1 at the second melting point ranges from 5 J/g to 30 J/g. Preferably, the variation amount of heat of fusion of the polylactic acid fiber 1 at the second melting point ranges from 10 J/g to 25 J/g.

In the present disclosure, a material of the sheath 20 of the polylactic acid fiber 1 is the second polylactic acid material. Even when the core 10 is formed from a common polylactic acid material, the polylactic acid fiber 1 can still have a good thermal resistance and a high crystallinity, and can thus be used at a higher processing temperature, thereby solving the problem of the polylactic acid fiber conventionally having a poor processability due to its original properties.

A raw material cost of the second polylactic acid material is higher than a raw material cost of the first polylactic acid material. As such, based on a total volume of the polylactic acid fiber being 100%, a volume of the sheath ranges from 25% to 50% in an exemplary embodiment.

Referring to FIG. 2, in an exemplary embodiment, a cross-section of the polylactic acid fiber 1 has a circular shape. In order to observe a relationship between a volume ratio of the core 10 to the sheath 20 and a thickness ratio of the core 10 to the sheath 20, the polylactic acid fibers 1 of Examples 1 to 4 with different volume ratios of the core 10 to the sheath 20 in a radial direction are listed in Table 3.

	TABLE 3
		Volume ratio of	Thickness of sheath:thickness
	Example	core to sheath	of core = D2/D1
	1	25/75	(√{square root over (4/3)} − 1):1 = 0.155
	2	30/70	(√{square root over (10/7)} − 1):1 = 0.195
	3	40/60	(√{square root over (5/3)} − 1):1 = 0.291
	4	50/50	(√{square root over (2)} − 1):1 = 0.414

In the radial direction, a ratio (D2/D1) of the thickness D2 of the sheath 20 to the thickness D1 of the core 10 ranges from 0.1 to 0.5. Preferably, the ratio of the thickness D2 of the sheath 20 to the thickness D1 of the core 10 ranges from 0.15 to 0.45.

The polylactic acid fiber 1 of the present disclosure can be used to manufacture a polylactic acid fabric. The polylactic acid fiber 1 can be formed through various weaving methods. For example, the polylactic acid fiber 1 can be formed through a melt spinning method or an electrospinning method.

To manufacture the polylactic acid fiber 1, the first polylactic acid material and the second polylactic acid material are prepared. The first polylactic acid material includes the poly(L-lactic acid) as a main component, and can further include other aforesaid polymer materials. The second polylactic acid material includes the poly(L-lactic acid) and the poly(D-lactic acid) as main components, and can further include other aforesaid polymer materials.

In an exemplary embodiment, the polylactic acid fiber 1 is formed through the melt spinning method. The first polylactic acid material and the second polylactic acid material are separately put into a melt spinning machine. A partial oriented yarn (POY) is formed by the melt spinning machine, and then a draw textured yarn (DTY) can be formed from the partial oriented yarn by a false twisting machine. Subsequently, the polylactic acid fiber 1 can be used to manufacture various polylactic acid fabrics. In this embodiment, the poly(L-lactic acid) and the poly(D-lactic acid) in the second polylactic acid material are mixed at a melted state, so that a part of the poly(L-lactic acid) and a part of the poly(D-lactic acid) are mixed to form the PDLA/PLLA stereocomplex.

In an exemplary embodiment, the polylactic acid fiber 1 is formed through the electrospinning method. The first polylactic acid material and the second polylactic acid material are respectively dissolved by a same or different electrospinning solvents. Since the second polylactic acid material simultaneously contains the poly(L-lactic acid) and the poly(D-lactic acid), the electrospinning solvent for the second polylactic acid material is required to dissolve both of the poly(L-lactic acid) and the poly(D-lactic acid). For example, the electrospinning solvent for the second polylactic acid material can be dichloromethane or chloroform. Subsequently, the first polylactic acid material and the second polylactic acid material are sprayed onto a carrier through an electrospinning device. By moving a sprayer, the polylactic acid fiber 1 can be closely stacked, entangled, or interwoven along a specific direction, so as to form the polylactic acid fabric with uniform thickness. In this embodiment, the poly(L-lactic acid) and the poly(D-lactic acid) in the second polylactic acid material are mixed at a solution state, so that a part of the poly(L-lactic acid) and a part of the poly(D-lactic acid) are mixed to form the PDLA/PLLA stereocomplex.

The polylactic acid fabric formed from the polylactic acid fiber 1 of the present disclosure is biodegradable, and has a good thermal resistance and a good processability, which are beneficial for further processing of the polylactic acid fabric.

Beneficial Effects of the Embodiments

In conclusion, in the polylactic acid fiber provided by the present disclosure, by virtue of “based on a total volume of the polylactic acid fiber 1 being 100%, a volume of the second polylactic acid material being at least 20%” and “the second polylactic acid material including 15 wt % to 85 wt % of poly(D-lactic acid) and 15 wt % to 85 wt % of poly(L-lactic acid),” the thermal resistance of the polylactic acid fiber can be increased, thereby solving the problem of the polylactic acid fiber conventionally having a poor processability.

Further, by virtue of “the second polylactic acid material including a stereocomplex of the poly(D-lactic acid) and the poly(L-lactic acid)”, the melting point of the second polylactic acid material can be increased.

The foregoing description of the exemplary embodiments of the disclosure has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching.

The embodiments were chosen and described in order to explain the principles of the disclosure and their practical application so as to enable others skilled in the art to utilize the disclosure and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present disclosure pertains without departing from its spirit and scope.

Claims

1. A polylactic acid fiber, comprising: a first polylactic acid material and a second polylactic acid material, wherein the first polylactic acid material is encapsulated by the second polylactic acid material; wherein, based on a total volume of the polylactic acid fiber being 100%, a volume of the second polylactic acid material is at least 20%, and the second polylactic acid material includes 15 wt % to 85 wt % of poly(D-lactic acid) and 15 wt % to 85 wt % of poly(L-lactic acid).

2. The polylactic acid fiber according to claim 1, wherein the second polylactic acid material includes a stereocomplex of the poly(D-lactic acid) and the poly(L-lactic acid).

3. The polylactic acid fiber according to claim 1, wherein the second polylactic acid material includes 15 wt % to 50 wt % of the poly(D-lactic acid) and 50 wt % to 85 wt % of the poly(L-lactic acid).

4. The polylactic acid fiber according to claim 1, wherein a first melting point of the second polylactic acid material ranges from 160° C. to 180° C., and a second melting point of the second polylactic acid material ranges from 210° C. to 230° C.

5. The polylactic acid fiber according to claim 1, wherein a glass transition temperature of the second polylactic acid material ranges from 55° C. to 70° C.

6. The polylactic acid fiber according to claim 1, wherein a core of the polylactic acid fiber is formed from the first polylactic acid material, and a sheath of the polylactic acid fiber is formed from the second polylactic acid material.

7. The polylactic acid fiber according to claim 6, wherein a cross-section of the polylactic acid fiber has a circular shape, and a thickness ratio of the sheath to the core in a radial direction of the polylactic acid fiber ranges from 0.1 to 0.5.

8. The polylactic acid fiber according to claim 1, wherein, based on the total volume of the polylactic acid fiber being 100%, the volume of the second polylactic acid material ranges from 25% to 50%.

9. The polylactic acid fiber according to claim 1, wherein a crystallinity of the polylactic acid fiber ranges from 35% to 45%.

10. The polylactic acid fiber according to claim 1, wherein a first melting point of the polylactic acid fiber ranges from 170° C. to 185° C., and a second melting point of the polylactic acid fiber ranges from 215° C. to 230° C.

11. The polylactic acid fiber according to claim 1, wherein a melting point of the first polylactic acid material is lower than a melting point of the second polylactic acid material.

12. The polylactic acid fiber according to claim 11, wherein the melting point of the first polylactic acid material is lower than the melting point of the second polylactic acid material by 40° C. to 60° C.