CN112981597A

CN112981597A - Composite fiber

Info

Publication number: CN112981597A
Application number: CN201911291533.9A
Authority: CN
Inventors: 徐青; 罗周荣; 吉宫隆之
Original assignee: Toray Fibers and Textiles Research Laboratories China Co Ltd
Current assignee: Toray Fibers and Textiles Research Laboratories China Co Ltd
Priority date: 2019-12-16
Filing date: 2019-12-16
Publication date: 2021-06-18

Abstract

The invention discloses a composite fiber, which is obtained by carrying out composite spinning on polyamide as a component A and polyester as a component B, and the elongation at expansion and contraction after the treatment for 20min by adding 2mg/D load in boiling water at 90 ℃ is 30-150%. The polyamide/polyester composite fiber has good elasticity, and the fabric made of the fiber has good hand feeling and softness, is lower in price than the existing polyamide composite fiber, and can be applied to sports fabrics.

Description

Composite fiber

Technical Field

The present invention relates to a conjugate fiber, and more particularly, to a conjugate fiber formed of polyamide and polyester or derivatives thereof.

Background

Polyamide fiber is a versatile fiber with a wide range of applications, ranging from clothing to industrial products such as fishing nets, filter cloths, cables, tires and parachute cloths. The polyamide fiber can be used independently, and can also be mixed with other natural fibers or chemical synthetic fibers to be made into fabrics, and the obtained fabrics have the characteristics of smooth hand feeling, fastness and durability. With the increasing demand for comfort, more new polyamide fibers are gradually replacing the traditional polyamide fibers. Among them, the fabric made of the polyamide composite fiber having good elasticity has great demand in the aspects of female professional wear, sportswear and casual wear because of good wearing comfort, elasticity and drapability. However, the polyamide composite fiber has a higher cost than the conventional polyester composite fiber, and in order to achieve the purpose of reducing the cost while pursuing comfort, it is considered to develop a polyamide/polyester composite fiber having good elasticity.

In the past patents, research on such products was also involved. For example, chinese patent CN109208119A discloses a polyamide composite fiber, which is made by composite spinning of a hexamethylene adipamide/caprolactam copolymer and common polyamide. The section is parallel or eccentric. Because the boiling water shrinkage of the two components has a relatively large difference, the polyamide composite fiber can be spontaneously crimped, and the fabric has excellent elasticity, and the stretching elongation of the fabric without false twisting is 30-150%. However, both components of the composite are polyamide, which is relatively expensive.

In addition, chinese patent CN103304985A discloses a polyamide/polyester alloy, which is added with a compatibilizer to improve the compatibility between polyester and polyamide, so that peeling does not occur. However, since the fiber is an alloy fiber, it does not have a composite fiber of a side-by-side type or an eccentric type, and therefore does not have good elasticity.

Disclosure of Invention

The invention aims to provide a polyamide/polyester composite fiber which has good elasticity and low cost and does not peel polyester and polyamide.

The technical solution of the invention is as follows:

a composite fiber is obtained by composite spinning of component A polyamide and component B polyester or derivatives thereof; after the composite fiber is treated by boiling water at 90 ℃ and a load of 2mg/D for 20min, the stretching elongation of the composite fiber is 30-150%.

The composite fiber preferably contains a compatibilizer.

The component A polyamide is preferably a copolyamide with the relative viscosity of 2.6-4.0.

The compatibilizer is preferably a maleic anhydride graft copolymer of an epoxy resin or a polyolefin.

The content of the compatibilizer in the composite fiber is preferably 0.1 to 10.0 wt%.

The weight ratio of the component A to the component B in the composite fiber is preferably 20/80-80/20.

The composite fiber is preferably a side-by-side composite fiber or an eccentric composite fiber.

The composite fiber prepared from the polyester and the polyamide with different boiling water shrinkage rates has good elasticity, and the fabric prepared from the fiber has good hand feeling and softness, and has more advantages than common fibers on sports fabrics.

Detailed Description

The composite fiber is obtained by composite spinning of component A polyamide and component B polyester or derivatives thereof.

The polyamide of the component A can be single-component polyamide, such as nylon 6, nylon 66, nylon 10 and the like, and can also be copolyamide, such as copolyamide of nylon 6 and nylon 66 and the like. Copolyamides are preferred in the present invention because they have better shrinkage characteristics.

The component B polyester or the derivative thereof can be polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate and the like, or cationic dyeable modified polyester, antistatic modified polyester, flame-retardant modified polyester and the like thereof.

In order to obtain better elasticity of the composite fiber, the relative viscosity of the copolyamide is preferably 2.6-4.0, and the boiling water shrinkage is preferably 13-70%. When the relative viscosity is too large, the composition of the component A and the component B is abnormal, and spinning cannot be carried out; when the relative viscosity is too small, the resulting conjugate fiber has poor crimpability and insignificant elasticity. The relative viscosity of the copolyamide is more preferably 3.0-4.0.

Among all copolyamides, the copolyamide of the invention having the following structural unit A represented by the formula 1 and the following structural unit B represented by the formula 2 is more preferred,

—HN(CH₂)₆NHCO(CH₂)₄CO-is a compound represented by the formula 1,

—NH(CH₂)₅CO-formula 2.

The content of the structural unit A is 10-80 mol% and the content of the structural unit B is 90-20 mol% relative to the total amount of the structural unit A and the structural unit B.

The combination of the component A polyamide and the component B polyester or the derivative thereof has the problem of peeling because of poor compatibility of the component A polyamide and the component B polyester or the derivative thereof. To improve this problem, the composite fiber of the present invention preferably contains a compatibilizer to reduce the interfacial tension of the A, B component and suppress the occurrence of separation.

The compatibilizer may be an ionomer or copolymer that is more compatible with the polyamide and polyester, with maleic anhydride graft copolymers of epoxy or polyolefin being preferred for reasons of practicality and cost.

The content of the compatibilizer in the composite fiber is preferably 0.1-10.0 wt%. When the content of the compatibilizer is too large, compounding abnormality occurs, and spinning cannot be performed; when the content of the compatibilizing agent is too small, the problem of peeling is not well improved. The content of the compatibilizer is more preferably 2.0 to 10.0 wt%.

In the composite fiber, the weight ratio of the component A to the component B is preferably 20/80-80/20. When the amount of the A component is too large, the crimping property of the composite fiber is not conspicuous, and when the amount of the A component is too small, the polymer discharge at the time of spinning is abnormal, and the spinnability is poor.

The composite fiber of the present invention may be any type of composite fiber known in the art, such as core-sheath type, side-by-side type, etc., wherein the crimpability of the side-by-side type composite fiber and the eccentric type composite fiber is most significant, so that the side-by-side type composite fiber and the eccentric type composite fiber are preferred.

The composite fiber can be prepared by the following method:

respectively mixing the polyamide chip of the component A and the polyester chip of the component B with a compatibilizer by using parallel or eccentric composite open-end gold, feeding the mixture into a A, B feeding port, melting the mixture by a melt spinning machine, and compositely discharging the mixture into filaments by a spinneret plate. And cooling and oiling, and obtaining the polyamide composite fiber by using a spinning and stretching one-step coiling process.

The spinning speed is 1000-3000 m/min, preferably 1000-2000 m/min by adopting a spinning and stretching one-step process; the extension temperature is 20-90 ℃, and preferably 20-50 ℃; the elongation ratio is 1.0 to 3.0 times.

Compared with the polyamide composite fiber, the polyamide/polyester composite fiber prepared by the invention has good crimpling performance and elasticity, and simultaneously, the cost is greatly reduced. After the fibers are treated by boiling water at 90 ℃ and a load of 2mg/D for 20min, the stretching elongation is 30-150%, and the elastic recovery rate is more than 60%; after the fiber is subjected to load-free treatment with hot water at 60 ℃ for 20min, the stretch recovery rate is 20-50%. In the preferred technical scheme, the compatilizer relieves the difference of interfacial tension between the two components and inhibits the stripping of the two components in the composite fiber. The fabric made of the polyamide composite fiber has good hand feeling and softness, and is suitable for sports fabrics.

The evaluation methods of the physical properties and the like mentioned in the present invention are as follows.

1. Relative viscosity (. eta.r)

Sampling, with a ratio of 1: when the bath of 30% by weight was smaller than the amount of 2% by weight of the fiber sample obtained by immersing the fiber sample in a 30wt% caustic soda solution, the residual fiber sample was collected. After washing and drying, an automatic viscosity measuring apparatus (model SS-600-L1) manufactured by Chaishan scientific machinist was used. The residual fiber sample was dissolved in a solvent of 95.8% concentrated sulfuric acid at a concentration of 1g/dl, and the measurement was carried out in a thermostatic bath at 25 ℃.5 samples were tested and averaged.

2. Elongation at extension and contraction:

sampling, and coiling ten turns of the sample by using a fiber number tester;

② processing the sample (load 2 mg/D) with hot water at 90 ℃ for 20min, taking out the sample after the processing, and drying;

③ after drying, hanging the load 2mg/D, reading the length L of the yarn in 30 seconds₀；

Fourthly, the load of 2mg/D is taken down, the load of 100mg/D is changed, and the yarn length L is read after 30 seconds₁；

Fifthly, the load of 100mg/D is taken down and the length L of the yarn is read for 30 seconds₂；

Sixthly, the calculation formula of the stretching elongation and the elastic recovery rate is as follows:

tensile elongation (%) = (L)₁-L₀)/L₀×100%，

Elastic recovery (%) = (L)₁-L₂)/(L₁-L₀)×100%。

3. Degree of peeling

A bundle of yarns is taken, black cotton is used for wrapping the yarns which penetrate through the holes of the copper plate and then the yarns are cut by a blade, and then the section shape of the fibers is observed by using an optical electron microscope, and the number of the separated yarns N1 and the total number of the yarns N2 are counted. The criterion for the degree of peeling was as follows:

N1/N2= 0: not peeled off (good),

N1/N2 < 50%: a partial peeling off (a),

N1/N2 > 50%: peeling off (x).

The present invention will be described in detail with reference to specific examples.

Example 1

Raw materials: the component A is a polyamide copolymer (eta r = 3.6), and the component B is a polyester (eta r = 0.53).

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 110% and two components are not separated by a cross-sectional observation A, B.

Example 2

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 60/40. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber had a tensile elongation of 115% and two components were not separated by a cross-sectional observation of A, B.

Example 3

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 70/30. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber had a tensile elongation of 130% and two components were not separated by a cross-sectional observation of A, B.

Example 4

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 80/20. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 125% and two components are not separated by a cross-sectional observation A, B.

Example 5

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 40/60. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 95% and two components are not separated by a cross-sectional observation A, B.

Example 6

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 30/70. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 80% and two components are not separated by a cross-sectional observation A, B. .

Example 7

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 20/80. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 60% and two components are not separated by a cross-sectional observation A, B.

Example 8

Raw materials: the component A is a polyamide copolymer (eta r = 3.60), and the component B is a polyester (eta r = 0.53).

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, and spinning is carried out by using eccentric composite metal, wherein the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 80% and two components are not separated by a cross-sectional observation A, B.

Example 9

Raw materials: the a component is polyamide 6 (η r = 2.6) and the B component is polyester (η r = 0.53).

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 30% and two components are not separated by a cross-sectional observation A, B.

Example 10

Raw materials: the component A is a polyamide copolymer (eta r = 3.2), and the component B is a polyester (eta r = 0.53).

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has 75% stretch elongation and A, B cross-section observation, and the two components are not separated.

Example 11

Raw materials: the component A is a polyamide copolymer (eta r = 4.0), and the component B is a polyester (eta r = 0.53).

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber had a stretch elongation of 140% and two components were not separated by cross-sectional observation A, B.

Example 12

Raw materials: the component A is polyamide copolymer (eta r = 3.6), and the component B is cation dyeable polyester (eta r = 0.51).

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 1 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 150% and two components are not separated by a cross-sectional observation A, B.

Example 13

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 0.05 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 150%, and the two components of the monofilament are separated by less than half of the two components of A, B through section observation.

Example 14

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 2.5 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber had a tensile elongation of 130% and two components were not separated by a cross-sectional observation of A, B.

Example 15

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 5 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber had a tensile elongation of 115% and two components were not separated by a cross-sectional observation of A, B.

Example 16

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. And simultaneously, respectively mixing maleic anhydride graft polymers of polyolefin accounting for 1 percent of the total mass of the fiber into the component A and the component B, putting the mixture into a spinning bin, and spinning by using parallel composite metal, wherein the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fiber has a stretch elongation of 90% and the two components are not separated by a cross-sectional observation A, B.

Example 17

Raw materials: the component A is polyamide copolymer (eta r = 3.60), and the component B is cation dyeable polyester (eta r = 0.51).

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Respectively putting the components into spinning bins, and spinning by using eccentric composite opening gold, wherein the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. Due to the eccentric section, the problem of peeling of the two components can be improved to a certain extent through section observation, but the fiber crimping property is poor, and the extension elongation of the fiber is 35%.

Comparative example 1

Raw materials: the component A is a polyamide copolymer (eta r = 4.6), and the component B is a polyester (eta r = 0.53).

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Meanwhile, epoxy resin accounting for 7.5 percent of the total mass of the fiber is respectively mixed into the component A and the component B, the mixture is put into a spinning bin, spinning is carried out by using parallel composite metal, and the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, and the viscosity of the component A is too high, so that the polymer can be adhered to the surface of the metal after being discharged, and the spinning cannot be carried out.

Comparative example 2

The component A slices are dried to the moisture content of below 400ppm, and the component B slices are dried to the moisture content of below 80 ppm. Respectively putting the components into spinning bins, and spinning by using eccentric composite opening gold, wherein the weight ratio of the component A to the component B is 50/50. The spinning temperature is 300 ℃, the spinning speed is 1000m/min, and the extension ratio is 2.8 times. After the spinneret plate produces the filaments, the filaments are cooled and oiled, and then the composite fiber is obtained through one-step spinning. The fibers obtained were not crimped and had a tensile elongation of 0% although A, B fractions were not separated from each other when observed from the cross section because of the core-sheath cross section.

Specific parameters of examples and comparative examples are shown in tables 1 and 2.

TABLE 1

TABLE 2

Claims

1. A composite fiber characterized by: the composite fiber is obtained by composite spinning of component A polyamide and component B polyester or derivatives thereof; after the composite fiber is treated by boiling water at 90 ℃ and a load of 2mg/D for 20min, the stretching elongation of the composite fiber is 30-150%.

2. The composite fiber according to claim 1, wherein: the composite fiber contains a compatibilizer.

3. The composite fiber according to claim 1 or 2, characterized in that: the component A polyamide is copolyamide with relative viscosity of 2.6-4.0.

4. The composite fiber according to claim 2, wherein: the compatibilizer is a maleic anhydride graft copolymer of an epoxy resin or a polyolefin.

5. The composite fiber according to claim 1 or 2, characterized in that: in the composite fiber, the weight ratio of the component A to the component B is 80/20-20/80.

6. The composite fiber according to claim 1 or 2, characterized in that: in the composite fiber, the content of the compatibilizer is 0.1-10.0 wt%.

7. The composite fiber according to claim 1 or 2, characterized in that: the composite fiber is a parallel composite fiber or an eccentric composite fiber.