CN106811815B

CN106811815B - porous polyolefin fibers containing micro-nano holes and preparation method and application thereof

Info

Publication number: CN106811815B
Application number: CN201510869817.7A
Authority: CN
Inventors: 李化毅; 黄骏; 李倩; 郑水蓉; 胡友良
Original assignee: Institute of Chemistry CAS
Current assignee: Institute of Chemistry CAS
Priority date: 2015-12-02
Filing date: 2015-12-02
Publication date: 2020-01-31
Anticipated expiration: 2035-12-02
Also published as: CN106811815A

Abstract

The invention provides porous polyolefin fibers containing micro-nano holes, a preparation method and an application thereof, wherein the micro-nano holes contained in the fibers are cylindrical, the average pore diameter of the micro-nano holes is 10-5000 nanometers, preferably 50-3000 nanometers, and the holes in the fibers are communicated or not.

Description

porous polyolefin fibers containing micro-nano holes and preparation method and application thereof

Technical Field

The invention relates to porous fibers, in particular to porous polyolefin fibers containing micro-nano pores and a preparation method and application thereof.

Background

In recent years, the preparation technology of porous polyolefin fibers containing micro-nano pores is rapidly developed, and various forming processes and methods capable of generating micro pores in a polymer matrix are developed, such as a phase separation method, a stretching method, a nuclear track method, a sintering method, a thermal decomposition method, a suspension polymerization method, a macromolecular structure template method, a colloidal crystal template method, a micro-foaming technology and the like.

With the development of science and technology, higher technical requirements are provided for the porous polyolefin fiber containing micro-nano pores, such as functionalization of the micro-nano pore fiber, environmental friendliness, controllability of a micro-pore structure and the like, and in order to meet the requirements, a preparation method with higher universality and variability needs to be researched, and more kinds of novel porous polyolefin fibers are developed.

At present, the methods for preparing porous polyolefin materials containing micro-nano pores include a radical polymerization method, a phase separation method, a stretching method, a micro-foaming method and the like, wherein the radical polymerization method is a suspension polymerization method, is just used for obtaining granular products, namely porous microspheres, and the whole continuous block-shaped or long-fiber porous polymer materials are difficult to obtain, the phase separation method, the stretching method and the like are used for preparing the existing polymers into porous films or porous fibers and the like through physical means, the requirements on equipment are high, the porous materials can be obtained by utilizing the micro-foaming technology, but the porous materials need to depend on a special physical process (such as a supercritical carbon dioxide gasification process), meanwhile, the porous fibers containing the micro-nano pores are difficult to obtain, the technical application range is narrow, and generally, simple and flexible methods are lacked in the field for preparing the porous polyolefin fibers containing the micro-nano pores, and the structure of the porous polyolefin fibers containing the micro-nano pores obtained by the existing methods is also required to be improved.

Disclosure of Invention

The invention aims to overcome the technical problems in the prior art, innovatively designs a porous polyolefin fiber structure containing micro-nano holes, and provides high-quality porous polyolefin fibers containing micro-nano holes, which have the characteristics of uniform pore size distribution, uniform pore size, high porosity and the like.

In order to achieve the purpose, the invention provides the following technical scheme:

porous polyolefin fibers containing micro-nano holes, wherein the micro-nano holes are cylindrical, and the average pore diameter of the micro-nano holes is 10-5000 nanometers.

According to the invention, the average pore diameter of the micro-nano pores is preferably 50-3000 nanometers, and can also be 100-2000 nanometers.

According to the present invention, the pores in the porous polyolefin fibers are connected or not connected.

According to the invention, the porosity of the porous polyolefin fibres is between 0.1 and 50%, preferably between 5 and 45%, more preferably between 20 and 45%.

According to the invention, the length of the micro-nano pores is 1-5000 times, more preferably 10-1000 times of the average pore diameter of the pores.

According to the present invention, the polyolefin includes α -olefin such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, etc., and -type thermoplastic polymers obtained by polymerizing or copolymerizing some cyclic olefins such as cyclohexene, etc., preferably polyethylene (e.g., Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Linear Low Density Polyethylene (LLDPE), etc.), polypropylene (PP), Polybutene (PB), and copolymers thereof such as ethylene-propylene copolymer (i.e., ethylene-propylene copolymer), ethylene-propylene-butylene copolymer (i.e., ethylene-propylene-butylene copolymer), ethylene-butylene copolymer (i.e., ethylene-butylene copolymer), propylene copolymer (i.e., propylene-butylene copolymer), etc., more Preferably Polypropylene (PP), ethylene-propylene copolymer (i.e., ethylene-propylene copolymer), ethylene-propylene-butylene copolymer (i.e., ethylene-propylene-butylene copolymer) or propylene copolymer (i.e., propylene-butylene copolymer).

The invention further provides the following technical proposal:

A preparation method of the porous polyolefin fiber containing the micro-nano holes comprises the following steps:

(1) preparing raw materials including polyolefin and polyvinyl acetal, blending the raw materials in proportion, performing melt extrusion for spinning, stretching the prepared fiber at constant temperature, and then shaping and rolling to obtain blend fiber;

(2) treating the blend fiber obtained in the step (1) in a proper solvent at a proper temperature, and dissolving out polyvinyl acetal in the fiber to form the porous polyolefin fiber containing micro-nano pores.

The invention also provides the following technical scheme:

(1) preparing raw materials including polyolefin and polyvinyl acetal; blending the raw materials in proportion, performing melt-blown spinning, and collecting to obtain blend fibers;

According to the invention, in the step (1), the raw materials are blended according to the proportion: the raw materials are melted and blended in a screw extruder according to the proportion.

According to the invention, the blending ratio of polyolefin to polyvinyl acetal is from 50:50 to 99.9:0.1, preferably from 50:50 to 90:10, most preferably from 60:40 to 80: 20. The proportions are mass ratios.

According to the present invention, the polyolefin includes α -olefin such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, etc., and -type thermoplastic polymers obtained by polymerizing or copolymerizing some cyclic olefins such as cyclohexene, etc., mainly polyethylene (e.g., Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Linear Low Density Polyethylene (LLDPE), etc.), polypropylene (PP), Polybutene (PB), and copolymers thereof such as ethylene-propylene copolymer (i.e., ethylene-propylene copolymer), ethylene-propylene-butylene copolymer (i.e., ethylene-propylene-butylene copolymer), ethylene-butylene copolymer (i.e., ethylene-butylene copolymer), propylene copolymer (i.e., propylene-butylene copolymer), etc., more Preferably Polypropylene (PP), ethylene-propylene copolymer (i.e., ethylene-propylene copolymer), ethylene-propylene-butylene copolymer (i.e., ethylene-propylene-butylene copolymer) or propylene copolymer (i.e., propylene-butylene copolymer).

Preferably, the polyvinyl acetal is selected from or more of polyvinyl formal (PVFO), polyvinyl acetal, polyvinyl propionaldehyde, polyvinyl butyral (PVB) and copolymers thereof such as polyvinyl formal, polyvinyl propionaldehyde, polyvinyl butyral, and the like, preferably, the polyvinyl acetal can be in the form of powder or solid pellets, preferably, the acetal group content in the polyvinyl acetal ranges from 10% to 80%, preferably from 40% to 80%, preferably, the polyvinyl acetal has a number average molecular weight of 5,000-500,000, preferably 10,000-200,000.

The invention further provides the following technical proposal:

the porous polyolefin fiber containing the micro-nano holes is used as a raw material for warming, sound absorption and filtering devices or a carrier material for preparing functional and intelligent materials.

Compared with the prior art, the invention has the following beneficial effects:

1. the porous polyolefin fiber containing the micro-nano holes has high porosity, smaller hole diameter, uniform hole diameter distribution and size, low thermal shrinkage, high solvent resistance and stable quality.

2. The preparation method of the porous polyolefin fiber containing the micro-nano holes is simple in process, and the prepared product is uniform in pore size and stable in quality.

Drawings

FIG. 1 scanning electron microscope image (20000 times morphology) of cross-sectional structure of porous polyolefin fiber containing micro-nano pores formed in example 1

FIG. 2 is a scanning electron microscope image (250 times of morphology) of a cross-sectional structure of the porous polyolefin fiber containing micro-nano holes formed in example 1

FIG. 3 SEM image of cross-sectional structure of porous polyolefin fiber containing micro-nano pores formed in example 1 (fiber diameter 60 μm, magnification 10000)

FIG. 4 SEM image of cross-sectional structure of porous polyolefin fiber containing micro-nano pores formed in example 1 (fiber diameter 500 μm, magnification 1000)

FIG. 5 SEM image of cross-sectional structure of porous polyolefin fiber containing micro-nano holes formed in example 1 (fiber diameter 800 μm, magnification 500)

Detailed Description

The technical problem to be solved by the invention is to provide a preparation method of porous polyolefin fibers containing micro-nano holes aiming at the defects in the prior art, the porous polyolefin fibers obtained by the method have high porosity, smaller pore diameter (micro-nano pore diameter), uniform pore diameter distribution and size, definite mechanical strength, low density and high specific surface area, thus having low thermal shrinkage and high solvent resistance and stable quality.

In preferred embodiments of the present invention, the porous polyolefin fiber containing micro-nano pores is prepared by the following steps:

Specifically, in the step (1), the raw materials are added into a screw extruder in proportion, after full melt blending is carried out in the screw extruder, the raw materials are sprayed out from a spinneret plate with the aperture of 0.1-2 mm through a spinning assembly, and the sprayed melt trickle is cooled by blowing air to obtain the nascent fiber. Wherein, the temperature of each zone of the screw is as follows: the feeding section is 70-210 ℃, the compression section is 90-230 ℃ and the metering section is 90-230 ℃; the temperature of the spinning assembly is 90-230 ℃, the temperature of a spinneret plate is 90-250 ℃, and the spinning speed of the primary yarn is 10-200 m/min. And (3) subjecting the nascent fiber to hot air oven at 80-180 ℃ for 1-3-stage stretching, and performing heat setting and rolling at 60-120 ℃ to obtain the blend fiber. The diameter of the blend fiber is in the range of 1 to 1000. mu.m, preferably 200-900. mu.m, more preferably 60 to 800. mu.m. Specifically, in the method of the present invention, the pore size, the porosity distribution, and the like can be controlled by changing the spinning rate and controlling the diameter of the spun yarn.

Specifically, in the step (1), the raw materials are added into a screw extruder in proportion, fully melted and blended in the screw extruder, sprayed out from a spinneret plate with the aperture of 0.1-2 mm through a spinneret assembly, and cooled on a receiving net to form the blend fiber. Wherein, the temperature of each zone of the screw is as follows: the temperature of the feeding section is 70-210 ℃, the temperature of the compression section is 90-230 ℃, the temperature of the spinning pack is 200-250 ℃ (preferably 230 ℃) and the temperature of the spinning pack is 90-250 ℃ (preferably 190 ℃). The blend fibers have a diameter in the range of 0.1 to 100 μm, preferably 1 to 50 μm. Specifically, in the method of the present invention, the pore size, the porosity distribution, and the like can be controlled by changing the spinning rate and controlling the diameter of the spun yarn.

In preferred embodiments of the present invention, the polyvinyl acetal in the blend fiber obtained in the dissolution step (1) in the above step (2) is obtained by treating the blend fiber in a solvent to dissolve the polyvinyl acetal.

The solvent selected is a solvent which can dissolve the polyvinyl acetal polymer at ℃ but does not dissolve the polyolefin used, and may be pure solvents or a mixture of several solvents, preferably, the solvent includes alcohol solvents such as methanol, ethanol, N-propanol, isopropanol, butanol, N-pentanol, hexanol, heptanol, N-octanol, isooctanol, benzyl alcohol, diacetone alcohol, etc., ether solvents such as ethylene glycol ethyl ether, propylene glycol ethyl ether, methyl ether, propyl ether, etc., ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, diisobutyl ketone, isophorone, methyl pyrrolidone, etc., acid solvents such as acetic acid, etc., ester solvents such as methyl acetate, ethyl acetate, butyl acetate, isopropyl acetate, etc., amide solvents such as N, N-Dimethylacetamide (DMF), N, N-dimethylformamide, etc., hydrocarbon solvents such as dichloromethane, dichloroethane, chloroform, dichloropropane, toluene, etc., soluble vinyl acetal, and solvent which does not dissolve the polyolefin used, and the mixed solvent of the above solvents may be selected to obtain a more preferable effect, such as a mixed solution of toluene and water, a mixed solution of toluene, ethanol, acetone, and ethanol at a temperature of 100 ℃ for 12h, preferably, a mixed solution of ethanol and acetone, and a mixed solution of 100 h, and acetone, and a mixed solution of the above may be selected.

Specifically, the pore size of the micro-nano pores is affected by the polyvinyl acetal content, the processing temperature and/or the spinning rate. By controlling the parameters, proper process parameters are preferably selected, and the prepared porous polyolefin fiber containing micro-nano pores has the characteristics of adjustable pore size, uniform pore size distribution, high porosity, stable quality and the like.

Compared with the existing porous polyolefin fiber and the preparation technology thereof, the invention has the advantages that:

(1) the preparation method provided by the invention has the advantages of simple preparation process and strong universality, and is applicable to polymer materials.

(2) The porous polyolefin fiber containing the micro-nano pores has uniform pore size distribution, adjustable pore size and good repeatability. The preparation of the porous polyolefin fiber containing the micro-nano holes does not need polymerization reaction, adopts an industrially known melt blending mode, and can control the phase separation generated in the processing process, so that the prepared porous polyolefin fiber containing the micro-nano holes has a continuous structure, and the pore diameter is easy to control.

(3) The polyolefin fiber containing the micro-nano pores can be used as a carrier material for preparing functional and intelligent materials is widely applied to separation, filtration, adsorption and integration in the industries of instrument analysis, water treatment, heat preservation and insulation materials, battery diaphragms, biomedicine and the like, such as microfiltration and intelligent heat preservation materials, heavy metal removal, integral chromatographic column stationary phases, enzyme fixation, cell culture, drug slow release, chemical sensors and the like.

The present invention is further described in with reference to specific embodiments for clarity of the invention to protect the technical solutions, it should be noted that these embodiments are the best examples for the skilled in the art to understand the present invention, but the present invention is not limited to these embodiments.

The materials used in the following examples are, unless otherwise specified, commercially available or known in the art.

Example 1

Adding 30 parts of polyvinyl butyral (PVB) powder and 70 parts of PP granules into a screw extruder, fully melting and blending in the screw extruder, passing through a spinning assembly, spraying out from a spinneret plate with the aperture of 0.1-2 mm, and blowing and cooling sprayed melt fine flow to obtain nascent fibers, wherein the temperature of each zone of the screw is 70-210 ℃ in a feeding section, 90-230 ℃ in a compression section and 90-230 ℃ in a metering section, the temperature of the spinning assembly is 90-230 ℃, the temperature of the spinneret plate is 90-250 ℃, the spinning speed of the nascent fibers is 10-200 m/min, the nascent fibers are subjected to 1-3-stage drawing in a hot air oven with the temperature of 80-180 ℃, and are subjected to heat setting at the temperature of 60-120 ℃ to obtain the blend fibers, wherein the drawing speed (i.e. the spinning speed of the nascent fibers) during spinning is changed to obtain series of blend fibers with different diameters (the fiber diameter is between 60 and 800 mu m).

The obtained blend fibers with different diameters are placed in a container filled with absolute ethyl alcohol solvent, and the fibers are boiled for 12 hours at the temperature of 80 ℃. And fully drying the PVB-removed fibers to obtain the porous polyolefin fibers containing the micro-nano holes. For porous polyolefin fibers with different fiber diameters, a small amount of the porous polyolefin fibers are taken respectively, are brittle-broken by liquid nitrogen, are subjected to surface metal spraying, and are observed in a scanning electron microscope in section morphology. FIGS. 1-5 are scanning electron micrographs at different magnifications for different fiber diameters.

Porosity is defined as pore volume/bulk material volume, herein converted to blend mass:

porosity ═ porosity (polyvinyl acetal mass/polyvinyl acetal density)/(polyolefin mass/polyolefin density)

The obtained porous fiber has uniform pore size distribution and high porosity, and the related parameters are shown in the following table:

example 2

The difference from example 1 is that 20 parts of polyvinyl butyral (PVB) powder was melt blended with 80 parts of PP pellets, the PVB-removing solvent chosen was isopropanol, and the fibers were cooked at 90 ℃ for 24 hours, the rest being the same as in example 1.

The pore diameter, pore spacing, porosity and the like of the obtained porous polyolefin fiber were similar to those of example 1.

Example 3

The difference from example 2 is that 15 parts of polyvinyl butyral (PVB) powder was melt blended with 85 parts of HDPE pellets, which was otherwise the same as in example 2.

The pore diameter, pore spacing, porosity and the like of the obtained porous polyolefin fiber were similar to those of example 2.

Example 4

The difference from example 2 is that 20 parts of polyvinyl formal (PVFO) powder and 80 parts of PP pellets are melt blended, the solvent chosen to remove the PVFO being n-butanol, the rest being the same as in example 2.

Example 5

The difference from example 2 is that 5 parts of polyvinyl butyral (PVB) powder and 95 parts of PP pellets were melt blended, and the rest is the same as example 2.

Example 6

The difference from example 1 is that the solvent chosen to remove the PVB is isooctanol and the fibers are cooked for 24 hours at a temperature of 80 ℃ and the rest is the same as example 1.

Example 7

The difference from example 1 is that the solvent for removing PVB is a mixed solution of toluene and absolute ethyl alcohol, the weight ratio of toluene to absolute ethyl alcohol is 3:2, and the rest is the same as example 1.

Example 8

The difference from example 1 is that the solvent for removing PVB is a mixed solution of xylene and n-butanol, the weight ratio of xylene to n-butanol is 3:2, and the rest is the same as example 1.

Example 9

The difference from example 1 is that 30 parts of polyvinyl butyral (PVB) powder and 70 parts of ethylene propylene butadiene terpolymer pellets were melt blended, and the rest is the same as example 1.

Example 10

The difference from example 1 is that 30 parts of polyvinyl formal powder and 70 parts of PP pellets were melt-blended, and the rest was the same as example 1.

Example 11

The difference from example 1 is that the solvent used to remove PVB was 85% by weight ethyl acetate, and the rest was the same as example 1.

Example 12

The difference from example 1 is that the solvent selected to remove the PVB is ethylene glycol butyl ether, which is otherwise the same as in example 1.

Example 13

The difference from example 1 is that the solvent selected to remove PVB is cyclohexanone, which is otherwise the same as in example 1.

Example 14

The difference from example 1 is that the solvent selected to remove PVB is diacetone alcohol, which is otherwise the same as in example 1.

Example 15

The difference from example 1 is that the solvent selected to remove the PVB is anhydrous acetic acid, and the rest is the same as example 1.

Example 16

The difference from example 1 is that the solvent selected to remove PVB is N, N-dimethylformamide, and the rest is the same as example 1.

Example 17

The difference from example 1 is that the solvent selected to remove PVB is dimethyl sulfoxide, which is otherwise the same as in example 1.

Example 18

The difference from example 1 is that the solvent selected to remove PVB is methanol, which is otherwise the same as in example 1.

Example 19

The difference from example 1 is that the solvent selected to remove the PVB is methylene chloride, which is otherwise the same as example 1.

Example 20

The difference from example 1 is that the solvent selected to remove the PVB is methyl pyrrolidone, which is otherwise the same as in example 1.

Example 21

The difference from example 1 is that the solvent selected to remove PVB is Tetrahydrofuran (THF), and the rest is the same as example 1.

Example 22

The difference from example 1 is that 30 parts of polyvinyl butyral (PVB) powder and 70 parts of PB pellets were melt blended, and the rest is the same as example 1.

Example 23

The difference from example 1 is that the solvent selected to remove PVB is N, N-Dimethylacetamide (DMF), and the rest is the same as example 1.

Example 24

Adding 30 parts of polyvinyl butyral (PVB) powder and 70 parts of PP granules into a screw extruder, fully melting and blending in the screw extruder, passing through a spinneret pack, spraying from a spinneret plate with the aperture of 0.1-2 mm, and cooling on a receiving net to obtain series of fibers with different diameters (the fiber diameter is 1-50 mu m), wherein the temperature of each zone of the screw is 70-210 ℃ in a feeding section, 90-230 ℃ in a compression section and 90-230 ℃ in a metering section, the temperature of the spinneret pack is 230 ℃ and the temperature of the spinneret plate is 190 ℃.

The obtained fibers with different diameters are placed in a container filled with absolute ethyl alcohol solvent, and the fibers are boiled for 12 hours at the temperature of 80 ℃. And fully drying the PVB-removed fibers to obtain the porous polyolefin fibers containing the micro-nano holes. The scanning electron micrograph of the fiber was similar to that of example 1.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

The preparation method of porous polyolefin fibers containing micro-nano holes comprises the steps of preparing cylindrical porous polyolefin fibers containing micro-nano holes, wherein the average pore diameter of the micro-nano holes is 100-2000 nm, the porosity of the porous polyolefin fibers is 5-50%, and the length of the micro-nano holes is 10-1000 times of the average pore diameter of the micro-nano holes;

the method comprises the following steps:

(1) preparing raw materials comprising polyolefin and polyvinyl acetal, wherein the polyvinyl acetal is in the form of powder or solid small particles; wherein the blending ratio of the polyolefin to the polyvinyl acetal is more than 60:40 and less than or equal to 80:20, and the ratio is a mass ratio; the content of acetal group in the polyvinyl acetal is 10-80%, and the number average molecular weight of the polyvinyl acetal is selected to be 5,000-500,000; adding the raw materials into a screw extruder in proportion, fully melting and blending in the screw extruder, spraying out the raw materials from a spinneret plate with the aperture of 0.1-2 mm through a spinning assembly, and blowing and cooling sprayed melt trickle to obtain nascent fiber; subjecting the nascent fiber to a temperature of 80-180 DEG C^oC, performing 1-3-stage stretching in a hot air oven at the temperature of 60-120 DEG C^oC, performing heat setting and rolling to obtain the blend fiber; wherein, the temperature of each zone of the screw is as follows: 70-210 of a feeding section^oC. Compression section 90-230^oC and metering section 90-230^oC; the temperature of the spinning assembly is 90-230 DEG C^oC, the temperature of a spinneret plate is 90-250 DEG^oC, spinning the primary raw silk at a speed of 10-200 m/min;

(2) treating the blend fiber obtained in the step (1) in a proper solvent at a proper temperature, and dissolving out polyvinyl acetal in the fiber to form the porous polyolefin fiber containing micro-nano pores.
2, preparation methods of porous polyolefin fibers containing micro-nano holes, wherein the micro-nano holes in the porous polyolefin fibers containing micro-nano holes are cylindrical, the average pore diameter of the micro-nano holes is 100-2000 nm, the porosity of the porous polyolefin fibers is 5-50%, and the length of the micro-nano holes is 10-1000 times of the average pore diameter of the micro-nano holes;

the method comprises the following steps:

(1) preparing raw materials comprising polyolefin and polyvinyl acetal, wherein the polyvinyl acetal is in the form of powder or solid small particles; wherein the blending ratio of the polyolefin to the polyvinyl acetal is more than 60:40 and less than or equal to 80:20, and the ratio is a mass ratio; the content of acetal group in the polyvinyl acetal is 10-80%, and the number average molecular weight of the polyvinyl acetal is selected to be 5,000-500,000; adding the raw materials into a screw extruder in proportion, fully melting and blending in the screw extruder, spraying the mixture from a spinneret plate with the aperture of 0.1-2 mm through a spinneret assembly, and cooling on a receiving net to form the blend fiber; wherein, the temperature of each zone of the screw is as follows: 70-210 of a feeding section^oC. Compression section 90-230^oC and metering section 90-230^oC; the temperature of the spinning pack is 200-250 DEG C^oC, the temperature of a spinneret plate is 90-250 DEG^oC；

(2) Treating the blend fiber obtained in the step (1) in a proper solvent at a proper temperature, and dissolving out polyvinyl acetal in the fiber to form the porous polyolefin fiber containing micro-nano pores.
3. The process according to claim 1 or 2, wherein the pores in the porous polyolefin fibers are connected or not connected.
4. The process according to claim 1 or 2, wherein the porous polyolefin fibers have a porosity of 5-45%.
5. The method of claim 4, wherein the porous polyolefin fibers have a porosity of 20-45%.
6. The method of claim 1, wherein the blend fibers have a diameter in the range of 1-1000 μ ι η.
7. The method as claimed in claim 6, wherein the diameter of the blend fiber is in the range of 200-900 μm.
8. The method of claim 7, wherein the blend fibers have a diameter in the range of 60-800 μ ι η.
9. The method of claim 1, wherein the polyolefin is polypropylene (PP), ethylene-propylene copolymer, ethylene-propylene-butene copolymer, or propylene-butene copolymer.
10. The method of claim 2, wherein the blend fibers have a diameter in the range of 0.1-100 μ ι η.
11. The method of claim 10, wherein the blend fibers have a diameter in the range of 1-50 μ ι η.
12. The method of claim 2, wherein the polyolefin is polyethylene or polypropylene (PP).
13. The method of claim 12, wherein the polyethylene is Low Density Polyethylene (LDPE) or High Density Polyethylene (HDPE).
14. The process according to claim 1 or 2, wherein the polyvinyl acetal is a condensation product of polyvinyl alcohol and an aldehyde.
15. The method of claim 14, wherein the polyvinyl acetal is selected from or more of polyvinyl formal (PVFO), polyvinyl acetal, polyvinyl propionaldehyde, polyvinyl butyral (PVB), polyvinyl formal, polyvinyl propionaldehyde, polyvinyl butyral.
16. The process according to claim 1 or 2, wherein the acetal group content in the polyvinyl acetal ranges from 40% to 80%.
17. The process according to claim 1 or 2, wherein the number average molecular weight of the polyvinyl acetal is 10,000-200,000.
18. The process according to claim 1 or 2, wherein the suitable solvent in step (2) is a solvent which is soluble in the polyvinyl acetal polymer but not in the polyolefin used at , pure solvents or a mixture of several solvents.
19. The process according to claim 18, wherein the solvent is selected from kinds of solvents which can dissolve the polyvinyl acetal without dissolving the polyolefin used or a mixed solvent of an alcohol solvent, an ether solvent, an acid solvent, an ester solvent, an amide solvent, and a hydrocarbon solvent.
20. The method of claim 19, wherein the alcoholic solvent is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, butanol, n-pentanol, hexanol, heptanol, n-octanol, isooctanol, benzyl alcohol, diacetone alcohol; the ether solvent is selected from ethylene glycol ethyl ether, propylene glycol ethyl ether, methyl ether and propyl ether; the ketone solvent is selected from acetone, methyl ethyl ketone, cyclohexanone, diisobutyl ketone, isophorone and methyl pyrrolidone; the acid solvent is selected from acetic acid; the ester solvent is selected from methyl acetate, ethyl acetate, butyl acetate and isopropyl acetate; the amide solvent is selected from N, N-Dimethylacetamide (DMF), N, N-Dimethylformamide (DMF); the hydrocarbon solvent is selected from dichloromethane, dichloroethane, chloroform, dichloropropane and toluene; the mixed solvent is selected from a mixed solution of toluene and absolute ethyl alcohol, a mixed solution of xylene and n-butyl alcohol, a mixed solution of ethanol and propanol, a mixed solution of propanol and acetone, and a mixed solution of butanol, toluene and ethyl acetate.
21. The method according to claim 1 or 2, wherein the treatment temperature in the step (2) is in the range of 0-130 ℃^oC; the treatment time is 12-48 h.
22. The method as claimed in claim 21, wherein the treatment temperature in the step (2) is in the range of 25-100 deg.f^oC; the treatment time is 12-24 h.
23. The method of claim 12, wherein the polyethylene is a Linear Low Density Polyethylene (LLDPE).