Porous polyolefin composite mechanically strengthened in biaxial direction using fillers

Abstract

The present disclosure provides porous polyolefin composites that include a polyolefin polymer as a matrix and an embedded filler having a high aspect ratio as a reinforcing element, and that are mainly characterized by enhanced mechanical properties in a biaxial direction. These compounds can be used as filtration semipermeable membranes in the filtration / purification of air, water or other liquids, or as membranes in the energy industry.

Description

Technical Field

[0001] The present invention relates to a mechanically reinforced porous polyolefin composite comprising a polymer matrix and one or more fillers having a high aspect ratio, a semi-permeable membrane formed from a film of these porous composites, a membrane for a separator of a rechargeable battery comprising these porous composites, and a method for providing these porous composites. Background Art

[0002] The listing or discussion of previously published documents in this specification should not necessarily be regarded as an admission that such documents are part of the prior art or common general knowledge.

[0003] Water scarcity is a long-standing challenge facing the world today. Given the rapid growth of the global population and the fast development of manufacturing in the past few decades, the demand for clean water has become increasingly urgent. At the same time, many communities are still struggling to properly treat and dispose of huge amounts of industrial wastewater and municipal sewage. Water scarcity and environmental pollution pose a significant threat to community livelihoods, as well as having a negative impact on the environment and ecosystems. According to a UN report released in 2021, 2.3 billion people currently live in countries with water-stressed situations, and approximately 1.42 billion people (including one-third of children) live in areas of high or extremely high water stress.

[0004] Membrane technology is becoming a promising solution for water filtration to obtain clean water. Generally, membranes can be classified as microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. Microfiltration is usually used as a pretreatment step for removing large macromolecules. Ultrafiltration allows the removal of bacteria as well as some viruses. Nanofiltration and osmosis are used for separating salts. Porous membranes made of various materials including polymers, ceramics, or metals have been used in various separation applications. Polymer membranes are widely used due to many advantages such as low cost, ease of manufacture, and ease of installation. Typical polymer materials used for water purification membrane manufacture include cellulose and its derivatives, PA (polyamide), PSF (polysulfone), PES (polyethersulfone), PC (polycarbonate), PEI (poly(etherimide)), PTFE (polytetrafluoroethylene), PVDF (polyvinylidene fluoride), and PAN (polyacrylonitrile).

[0005] PVDF, a semi-crystalline thermoplastic fluoropolymer, is one of the most popular materials used to make the membranes most commonly used in membrane manufacture to date due to its good thermal stability, resistance to most chemicals, and excellent mechanical properties. However, the high price of PVDF limits its further and wider use, especially in developing countries and rural areas. With the soaring demand for PVDF as a separator in fuel cell units and lithium batteries, the cost of PVDF is expected to increase in the long term. In addition, PVDF membranes are usually prepared by the phase separation method, which generally requires large amounts of organic liquids, generating a series of complex and toxic wastewater.

[0006] Polyolefin polymers can be an economical alternative to PVDF for manufacturing porous membranes for water treatment due to their excellent chemical resistance and thermal stability. Compared with the high price of PVDF (i.e., 40,000 - 70,000 USD per metric ton), the price of polyolefins is much lower. For example, according to the data retrieved in May 2022, high - density polyethylene (HDPE) is only 1,216 USD per metric ton. This price advantage makes porous polyolefins an attractive option for replacing PVDF in various membrane applications. In addition, from the aspect of environmental sustainability, polyolefin membranes can be made by melt - spinning and stretching techniques, which do not involve the use of any toxic solvents, making polyolefin membranes an excellent green alternative to PVDF membranes and other polymer membranes made by the phase - separation method.

[0007] It has been demonstrated that porous polyolefin membranes can be manufactured by wet or dry methods. For example, U.S. Patent 4,828,772 teaches how to make microporous polyethylene by co - extruding polyethylene and a pore - forming agent and then removing the pore - forming agent. U.S. Patent 4,530,809 describes manufacturing HDPE hollow - fiber membranes by stretching melt - extruded hollow fibers, which can achieve a porous structure with a porosity of 30 - 90% by volume. As shown in U.S. Patent 5,435,955, fibrous or film - like porous polypropylene can be obtained by drawing.

[0008] Despite the many desirable properties of polyolefins, for practical applications, it is necessary to enhance the mechanical properties of porous polyolefins. Making composites by adding fillers to the polymer can be an effective method for manufacturing mechanically enhanced porous polyolefins. Compared with particulate fillers with a low aspect ratio, high - aspect - ratio fillers are more effective in enhancing the strength of polymers. High - aspect - ratio fillers can enhance the mechanical properties of polymers via a bridging or stitching effect, and a low loading of such fillers can lead to a significant improvement in mechanical properties.

[0009] The enhanced porous polyolefin composites can be used as membranes for filtering / purifying air, water, or other liquids. In addition, the porous structure also makes the mechanically enhanced porous polyolefin composites promising as separators in rechargeable batteries. SUMMARY OF THE INVENTION

[0010] Surprisingly, it has been found that the porous polyolefin composite is mainly characterized by increased mechanical properties in the biaxial direction and, in some cases, also demonstrates enhanced pore-forming ability. The enhanced porous polyolefin composite can be used as a filtration membrane for filtration applications. The enhanced porous polyolefin composite can also be used as a separator in rechargeable batteries. Accordingly, the present invention relates to such mechanically enhanced porous polyolefin composites comprising a polymer matrix and one or more fillers having a high aspect ratio, semi-permeable filter membranes formed from thin films of these porous composites, membranes for batteries comprising these porous composites as separators, and methods for providing these porous composites.

[0011] In a first aspect, there is provided a porous polyolefin composite comprising a polyolefin matrix in which an effective amount of a filler having a high aspect ratio is incorporated, and the porous polyolefin composite having pores in the range of 0.01 to 2 μm. The filler may be present in the porous composite at a loading between 0.05% and 30% by weight. The filler may be present with or without surface modification. The filler may be present directly in powder form or dispersed in a masterbatch.

[0012] In a second aspect, there is provided a method for providing a porous polyolefin composite reinforced with a high aspect ratio filler, the composite comprising a polyolefin matrix and a filler dispersed in the polyolefin, the method comprising: (a) compounding a polyolefin polymer with a high aspect ratio filler; (b) melt extruding the polyolefin composite into a polyolefin composite precursor structure having a specific draw ratio; (c) thermally annealing the polyolefin composite precursor structure at a certain temperature for a certain duration; (d) cold stretching the polyolefin composite precursor structure at a certain temperature for a certain duration; (e) hot stretching the polyolefin composite precursor structure at a certain temperature for a certain duration; and (f) thermally setting the porous polyolefin composite at a certain temperature for a certain duration.

[0013] Aspects and embodiments of the present invention are described in the following numbered clauses.

[0014] 1. A porous composite, comprising:

[0015] A polymer matrix formed from one or more polyolefins; and

[0016] One or more high aspect ratio filler materials, wherein

[0017] The porous composite has pores with a diameter of 0.01 to 2 μm; and

[0018] The one or more high aspect ratio filler materials are present in an amount of 0.05 to 30 wt% of the total weight of the porous composite material.

[0019] 2. The porous composite material according to clause 1, wherein each of the one or more polyolefins has a general repeating group of formula I:

[0020] (CH2CHR)n I

[0021] wherein R is an alkyl group, optionally wherein each R is a non-branched or branched C1 to C 10 alkyl group.

[0022] 3. The porous composite material according to clause 1 or 2, wherein the one or more polyolefins are selected from one or more of the group consisting of: polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polybutene-1 (PB-1), ethylene-octene copolymer, stereoblock PP, olefin block copolymer, or propylene-butane copolymer.

[0023] 4. The porous composite material according to any one of the preceding clauses, wherein each of the one or more polyolefins has a density of 0.80 to 0.99 g / cm 3 , such as 0.90 to 0.99 g / cm 3 , such as 0.94 to 0.97 g / cm 3 , such as 0.89 to 0.95 g / cm 3 , such as 0.92 to 0.98 g / cm 3 .

[0024] 5. The porous composite material according to any one of the preceding clauses, wherein each of the one or more polyolefins has a melt flow index measured according to ASTM D1238 at 230 °C / 2.16 kg of 0.1 to 30 g / 10 min, such as 0.1 to 15 g / 10 min, such as 0.3 to 0.5 g / 10 min.

[0025] 6. The porous composite material according to any one of the preceding clauses, wherein the porous composite material further comprises one or more additives selected from the group consisting of: stabilizers, plasticizers, lubricants, flame retardants, anti-aging materials, colorants, nucleating agents, flavoring agents, anti-microbial materials, antistatic additives, or compatibilizers, optionally wherein the porous composite material further comprises a compatibilizer.

[0026] 7. The porous composite material according to any one of the preceding clauses, wherein the one or more high aspect ratio filler materials are materials having a high ratio of length or width to cross-sectional diameter and / or thickness, and the ratio is 5 to 100,000.

[0027] 8. The porous composite material according to any one of the preceding clauses, wherein the one or more high aspect ratio filler materials are present in an amount of 0.05 to 30 wt%, such as 0.1 to less than or equal to 10 wt%, such as 0.5 to 2 wt%, such as 0.7 to 1.5 wt% of the total weight of the porous composite material.

[0028] 9. The porous composite material according to any one of the preceding clauses, wherein at least one of the one or more high aspect ratio filler materials is surface-treated, and optionally, at least one of the one or more surface-treated high aspect ratio fillers is treated by one or more of chemical treatment and physical treatment.

[0029] 10. The porous composite material according to any one of the preceding clauses, wherein the one or more high aspect ratio filler materials are selected from one or more of the following: tubular fillers, rod-shaped fillers, fibers, filaments, plate-shaped fillers, disc-shaped fillers, sheet-shaped fillers, prismatic fillers, wall-shaped fillers, branched structure fillers, and hybrid structures including two or more structures mentioned herein.

[0030] 11. The porous composite material according to any one of the preceding clauses, wherein the one or more high aspect ratio filler materials have dimensions of 1 nm to 1,000 μm.

[0031] 12. The porous composite material according to any one of the preceding clauses, wherein the high aspect ratio filler material is selected from one or more of the group consisting of nanotubes, nanorods, nanowires, and sheet-shaped fillers, such as silver nanowires, metal nanorods, carbon nanotubes, clay, and graphene.

[0032] 13. The porous composite material according to any one of the preceding clauses, wherein the polyolefin porous composite is provided in the form of a flat sheet, in the form of a hollow fiber having a diameter between 0.05 and 2 mm, or in the form of a tubular structure having a diameter greater than 2 mm.

[0033] 14. The porous composite material according to any one of the preceding clauses, wherein the high aspect ratio filler material has an aspect ratio of 5 to 100,000, such as 500 to 36,000, such as 5,000 to 10,000.

[0034] 15. The porous composite material according to any one of the preceding clauses, wherein the porous composite material has one or both of the following:

[0035] In the transverse direction for a film formed only of the polyolefin, or in the circumferential direction for a fiber / tube formed only of the polyolefin, the mechanical strength is 5% to 1,000% higher, such as 20% to 100% higher, such as 30% to 50% higher; and

[0036] In the transverse direction for a film formed only of the polyolefin, or in the circumferential direction for a fiber / tube formed only of the polyolefin, the maximum strain is 10% to 50,000% higher, such as 1,000% to 40,000% higher, such as 10,000% to 27,000% higher.

[0037] 16. The porous composite material according to any one of the preceding clauses, wherein the porous composite material has one or both of the following:

[0038] In the machine direction for a film formed only of the polyolefin, or in the longitudinal direction for a fiber / tube formed only of the polyolefin, the mechanical strength is 5% to 100% higher, such as 11% to 50% higher, such as 14% to 33% higher; and

[0039] In the machine direction for a film formed only of the polyolefin, or in the longitudinal direction for a fiber / tube formed only of the polyolefin, the Young's modulus is 7% to 100% higher, such as 8% to 40% higher, such as 9% to 33% higher.

[0040] 17. A semi-permeable filter membrane formed from a film of the porous composite material according to any one of clauses 1 to 16.

[0041] 18. The semi-permeable filter membrane according to clause 17, wherein:

[0042] When measured at a pressure of 1 bar, the filter membrane has an average air flux of 1,000 LMH to 10,000 LMH, such as approximately 5,435 LMH; and / or

[0043] The filter membrane has a water permeability of 50 LMH / bar to 1,000 LMH / bar, such as approximately 196.5 LMH / bar.

[0044] 19. A membrane for a separator of a battery, comprising the porous composite material according to any one of clauses 1 to 12.

[0045] 20. A method for providing the porous composite material according to any one of clauses 1 to 18, the method comprising the following steps:

[0046] (a) Providing a polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold drawing, and hot drawing; and

[0047] (b) Subjecting the polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold drawing, and hot drawing to a heat setting step at a specific temperature for a specific period of time.

[0048] 21. The method according to clause 20, wherein one or both of the following are applied:

[0049] The temperature of the heat setting step is 100 to 150 °C, such as 120 to 140 °C; and

[0050] The period of time of the heat setting step is 1 to 120 minutes, such as 30 to 60 minutes.

[0051] 22. The method according to clause 20 or clause 21, wherein the polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold drawing, and hot drawing is provided by:

[0052] (ai) Providing a polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, and cold drawing; and

[0053] (aii) Subjecting the polyolefin composite precursor material to hot drawing at a specific temperature, a specific length per minute, and a specific elongation rate.

[0054] 23. The method according to clause 22, wherein one or both of the following are applied:

[0055] The temperature of the hot drawing is 100 to 150 °C;

[0056] The length per minute of the hot drawing is 1 mm / min to 200 mm / min, such as 8 mm / min to 40 mm / min.

[0057] 24. The method according to any one of clauses 20 to 23, wherein the polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, and cold drawing is provided by:

[0058] (bi) Providing a polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, and cold drawing; and

[0059] (bii) Subjecting the polyolefin composite precursor material to cold drawing at a specific temperature, a specific length per minute, and a specific elongation rate.

[0060] 25. The method according to clause 24, wherein one or both of the following are applied:

[0061] The temperature of the cold drawing is from -196 to 100 °C, such as 20 to 30 °C, such as about 25 °C;

[0062] The length per minute of the cold drawing is from 1 mm / min to 600 mm / min, such as 10 mm / min to 200 mm / min, such as 50 to 100 mm / min.

[0063] 26. The method according to any one of clauses 21 to 25, wherein the polyolefin composite precursor material that has undergone melt extrusion and thermal annealing is provided by:

[0064] (ci) providing a polyolefin composite precursor material that has undergone melt extrusion and thermal annealing; and

[0065] (cii) subjecting the polyolefin composite precursor material to thermal annealing for a specific period of time at a specific temperature.

[0066] 27. The method according to clause 26, wherein one or both of the following are applied:

[0067] The temperature of the thermal annealing is from 100 to 150 °C, such as 110 to 140 °C; and

[0068] The period of time of the thermal annealing is from 1 minute to 10 hours, such as 30 minutes to 8 hours.

[0069] 28. The method according to any one of clauses 20 to 25, wherein the polyolefin composite precursor material that has undergone melt extrusion is provided by:

[0070] (di) providing a polyolefin composite precursor material comprising the components described in any one of clauses 1 to 16; and

[0071] (dii) subjecting the polyolefin composite precursor material to melt extrusion at a specific temperature and a specific draw ratio.

[0072] 29. The method according to clause 28, wherein one or both of the following are applied:

[0073] The temperature of the melt extrusion is from 150 to 250 °C, such as 160 to 220 °C; and

[0074] The draw ratio of the melt extrusion is from 20 to 10,000. Description of the Drawings

[0075] Figure 1 SEM images of a porous pure HDPE film are depicted, with magnifications of (a) 5000 times and (b) 10000 times.

[0076] Figure 2Depicts SEM images of a porous HDPE / CNT (0.7 wt%) composite film at magnifications of (a) 5000x and (b) 10000x.

[0077] Figure 3 Depicts (a) SEM image and (b) TEM image of the carbon nanotubes (CNT) used.

[0078] Figure 4 Depicts SEM images of a porous HDPE / clay (3 wt%) composite film at magnifications of (a) 5000x and (b) 10000x.

[0079] Figure 5 Depicts SEM image of the clay used.

[0080] Figure 6 Depicts a representative AFM image of the clay (clay 1) used and its thickness.

[0081] Figure 7 Depicts another representative AFM image of the clay (clay 2) used and its thickness.

[0082] Figure 8 Depicts SEM image of pure PP porous hollow fibers.

[0083] Figure 9 Depicts SEM image of graphene composite porous hollow fibers with 0.1 wt% graphene.

[0084] Figure 10 Depicts SEM image of graphene composite porous hollow fibers with 0.2 wt% graphene. Detailed Description

[0085] The porous polyolefin composite is a promising alternative to PVDF in water treatment membranes. It has surprisingly been found that introducing fillers with a high aspect ratio is an easy and effective way to enhance the mechanical properties of porous polyolefins.

[0086] Accordingly, in a first aspect of the present invention, there is provided a porous composite material comprising:

[0087] a polymer matrix formed from one or more polyolefins; and

[0088] one or more high aspect ratio filler materials, wherein

[0089] the porous composite material has pores with a diameter of 0.01 to 2 μm; and

[0090] the one or more high aspect ratio filler materials are present in an amount of 0.05 to 30 wt% of the total weight of the porous composite material.

[0091] The term "comprising" as used herein can be interpreted as requiring the recited features, but not precluding the presence of other features. Alternatively, the term "comprising" can also relate to situations where only the recited components / features are intended to be present (e.g., the term "comprising" can be replaced by the phrase "consisting of" or "consisting essentially of"). It is expressly contemplated that both the broad and narrow interpretations can apply to all aspects and embodiments of the present invention. In other words, the term "comprising" and its synonyms can be replaced by the phrase "consisting of" or the phrase "consisting essentially of" or their synonyms, and vice versa.

[0092] The phrase "consisting essentially of" and its pseudonyms can be interpreted herein to mean a material in which a small amount of impurities may be present. For example, the material can be of a purity greater than or equal to 90%, such as greater than 95% purity, such as greater than 97% purity, such as greater than 99% purity, such as greater than 99.9% purity, such as greater than 99.99% purity, such as greater than 99.999% purity, such as 100% purity.

[0093] As used herein, unless the context otherwise clearly dictates, the singular forms "a", "an", and "the" include plural referents. Thus, for example, reference to "a composition" includes mixtures of two or more such compositions, etc.

[0094] In the present invention, the term "polyolefin" refers to a group of polymers having the general formula (CH2CHR)n, where "R" is an alkyl group. They are typically prepared by polymerizing simple olefins (alkenes).

[0095] Thus, in embodiments of the present invention, one or more polyolefins can each have a general repeating group of Formula I:

[0096] (CH2CHR)n I

[0097] wherein R is an alkyl group.

[0098] Unless otherwise specified, the term "alkyl" refers to a non-branched or branched, non-cyclic or cyclic, saturated hydrocarbon group, which can be substituted or unsubstituted (having, for example, one or more halogen atoms). Where the term "alkyl" refers to a non-cyclic group, it is preferably a C 1-10 alkyl, and more preferably, a C 1-6Alkyl groups (such as ethyl, propyl (e.g., n-propyl or isopropyl), butyl (e.g., branched or unbranched butyl), pentyl, or more preferably, methyl). Wherein the term "alkyl" is a cyclic group (which may be the case designated as the group "cycloalkyl"), which is preferably C 3-12 cycloalkyl, and more preferably C 5-10 (e.g., C 5-7 ) cycloalkyl.

[0099] In a specific embodiment of the present invention, each R may be a non-branched or branched C1 to C 10 alkyl group. In a specific embodiment of the present invention, the alkyl group may be acyclic.

[0100] In a specific embodiment of the present invention, one or more polyolefins are selected from one or more of the group consisting of: polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polybutene-1 (PB-1), ethylene-octene copolymer, stereoblock PP, olefin block copolymer or propylene-butane copolymer.

[0101] In certain embodiments, one or more polyolefins may be polypropylene and / or polyethylene. In some other cases, one or more polyolefins used to manufacture the porous composite may consist of one type of polyolefin, while in other cases, a combination of two or more types of polyolefins may be used as a blend. It should be understood that copolymers (whether random or block) can be formed by using one or more of the polyolefins discussed herein, and these can also be used in the embodiments of the present invention.

[0102] The density of the polyolefin can vary, for example, in the range of 0.94 to 0.97 g / cm 3 , or in the range of 0.89 - 0.95 g / cm 3 , or in the range of 0.92 - 0.98 g / cm 3 . The polyolefin may have a melt index generally in the range of 0.1 to 30 g / 10 min (at 230 °C / 2.16 kg, ASTM D1238).

[0103] In a more specific embodiment of the present invention, one or more polyolefins may have a density of 0.8 to 0.99 g / cm 3 , such as 0.9 to 0.99 g / cm 3 , such as 0.94 to 0.97 g / cm 3 , such as 0.89 to 0.95 g / cm 3 , such as 0.92 to 0.98 g / cm 3。For the avoidance of doubt, it is expressly contemplated that, where multiple numerical ranges relating to the same feature are recited herein, the endpoints of each range are intended to be combined in any order to provide further contemplated (and implicitly disclosed) ranges. For example, the ranges in this paragraph are expressly intended to provide the following sub-ranges:

[0104] 0.8 to 0.89 g / cm 3 、0.8 to 0.9 g / cm 3 、0.8 to 0.92 g / cm 3 、0.8 to 0.94 g / cm 3 、0.8 to 0.95 g / cm 3 、0.8 to 0.97 g / cm 3 、0.8 to 0.98 g / cm 3 、0.8 to 0.99 g / cm 3 ;

[0105] 0.89 to 0.9 g / cm 3 、0.89 to 0.92 g / cm 3 、0.89 to 0.94 g / cm 3 、0.89 to 0.95 g / cm 3 、0.89 to 0.97 g / cm 3 、0.89 to 0.98 g / cm 3 、0.89 to 0.99 g / cm 3 ;

[0106] 0.9 to 0.92 g / cm 3 、0.9 to 0.94 g / cm 3 、0.9 to 0.95 g / cm 3 、0.9 to 0.97 g / cm 3 、0.9 to 0.98 g / cm 3 、0.9 to 0.99 g / cm 3 ;

[0107] 0.92 to 0.94 g / cm 3 、0.92 to 0.95 g / cm 3 、0.92 to 0.97 g / cm 3 、0.92 to 0.98 g / cm 3 、0.92 to 0.99 g / cm 3 ;

[0108] 0.94 to 0.95 g / cm 3 、0.94 to 0.97 g / cm 3 、0.94 to 0.98 g / cm 3, 0.94 to 0.99 g / cm 3 ;

[0109] 0.95 to 0.97 g / cm 3 , 0.95 to 0.98 g / cm 3 , 0.95 to 0.99 g / cm 3 ;

[0110] 0.97 to 0.98 g / cm 3 , 0.97 to 0.99 g / cm 3 ; and

[0111] 0.98 g / cm 3 to 0.99 g / cm 3 .

[0112] In an embodiment of the present invention, each of one or more polyolefins may have a melt flow index measured according to ASTM D1238 at 230 °C / 2.16 kg of 0.1 to 30 g / 10 min, such as 0.1 to 15 g / 10 min, such as 0.3 to 0.5 g / 10 min.

[0113] In some cases, the polyolefin may also be a polyolefin polymer with or without other additives (such as processing aids). Processing aids may include, but are not limited to, stabilizers, plasticizers, lubricants, flame retardants, anti-aging materials, colorants, nucleating agents, odour-generating agents, anti-microbial materials, antistatic additives, compatibilizers, and combinations thereof. In a specific embodiment of the present invention that may be mentioned herein, the porous composite material may further include a compatibilizer.

[0114] Specifically, a compatibilizer refers to a type of material added to a mixture of incompatible materials to inhibit phase separation by enhancing the interaction between the components within the mixture. Even more specifically in the present invention, a compatibilizer can be used to increase the interfacial strength between the filler and the polyolefin polymer matrix.

[0115] In various embodiments, the high aspect ratio filler material may be present in a loading amount greater than or equal to 0.05 wt.% and less than 30 wt.%, preferably in a loading amount greater than or equal to 0.1 wt.% and less than 10 wt.%, preferably in a loading amount greater than or equal to 0.5 wt.% and less than 10 wt.%. The loading percentage is calculated based on the total weight of the porous composite material. In a more specific embodiment of the present invention, one or more high aspect ratio filler materials may be present in an amount of 0.05 to 30 wt.%, such as 0.1 to less than or equal to 10 wt.%, such as 0.5 to 2 wt.%, such as 0.7 to 1.5 wt.%, based on the total weight of the porous composite material.

[0116] The high aspect ratio filler materials used herein are materials that can be incorporated into a specific matrix to achieve (i.e., improve) one or more of certain properties, such as mechanical properties, thermal properties, electrical properties, etc. In particular, the high aspect ratio filler materials used herein can be used to enhance the mechanical properties of porous polyolefins.

[0117] The high aspect ratio filler materials can be classified into different types according to their size, morphology, physical and chemical properties. Based on composition, some high aspect ratio filler materials can be carbon-based materials, metal nanomaterials, ceramic nanomaterials, polymers, and lipids.

[0118] One or more high aspect ratio filler materials are materials having a high ratio of length or width to cross-sectional diameter and / or thickness. For example, these ratios can be from 5 to 100,000. More particularly, the high aspect ratio filler materials can have an aspect ratio of from 5 to 100,000, such as from 500 to 36,000, such as from 5,000 to 10,000.

[0119] One or more high aspect ratio filler materials can be any suitable material. For example, one or more high aspect ratio filler materials can be selected from one or more of the following: tubular fillers, rod-shaped fillers, fibers, wires, plate-shaped fillers, disc-shaped fillers, sheet-shaped fillers, prismatic fillers, wall-shaped fillers, branched structure fillers, and hybrid structures including two or more of the structures mentioned herein.

[0120] For example, one or more high aspect ratio filler materials can be fibrous fillers having a high ratio of filler length to filler diameter. This type of filler can include various tubular fillers, rod-shaped fillers, fibers, and wires. For example, carbon nanotubes, silver wires, and metal rods. In some embodiments, the fibrous filler particularly refers to carbon nanotubes.

[0121] The high aspect ratio filler materials having a plate-like or disc-like form have a high ratio of planar length to filler thickness. Various sheet-like, disc-like, plate-like, prismatic, wall-like, and other branched structures fall into this group. Some typical examples include, but are not limited to, graphene, clay, and MXene. In some embodiments, the plate-like or disc-like filler can particularly refer to graphene.

[0122] In the present invention, one or more high aspect ratio filler materials may be present with or without surface treatment. Surface treatment refers to a process of changing the surface properties of high aspect ratio filler materials by chemical or physical methods to improve the processing ability of the fillers. In particular, the purpose of surface treatment is to promote the dispersion of high aspect ratio filler materials or enhance the interfacial strength between high aspect ratio filler materials and polyolefin polymer matrices. By chemical treatment methods, the surface of high aspect ratio filler materials is chemically linked to other substances (such as silane coupling agents). By physical treatment methods, the surface of high aspect ratio filler materials is physically attached or linked to other substances. One or more chemical treatments and physical treatments, along with their combinations, may be applied.

[0123] In a specific embodiment of the present invention, the high aspect ratio filler materials may be selected from one or more of the group consisting of nanotubes, nanorods, and nanowires, such as silver nanowires, metal nanorods, and carbon nanotubes.

[0124] One or more high aspect ratio filler materials may have any suitable size, for example, from the nanoscale to the microscale. In a specific embodiment of the present invention, the size that one or more high aspect ratio filler materials may have is from 1 nm to 1,000 μm.

[0125] The porous composites described herein may have particularly good properties. These may include one or both of the following:

[0126] In the transverse direction for a film formed only of the polyolefin, or in the circumferential direction for a fiber / tube formed only of the polyolefin, the mechanical strength is 5% to 1,000% higher, such as 20% to 100% higher, such as 30% to 50% higher; and

[0127] In the transverse direction for a film formed only of the polyolefin, or in the circumferential direction for a fiber / tube formed only of the polyolefin, the maximum strain is 10% to 50,000% higher, such as 1,000% to 40,000% higher, such as 10,000% to 27,000% higher. In a specific embodiment of the present invention that may be mentioned herein, the porous composites may have one or both of the following properties:

[0128] In the machine direction for a film formed only of the polyolefin, or in the longitudinal direction for a fiber / tube formed only of the polyolefin, the mechanical strength is 5% to 100% higher, such as 11% to 50% higher, such as 14% to 33% higher; and

[0129] In the machine direction for a film formed only of the polyolefin, or in the longitudinal direction for a fiber / tube formed only of the polyolefin, the Young's modulus is 7% to 100% higher, such as 8% to 40% higher, such as 9% to 33% higher.

[0130] The porous composite material described herein can be used in any suitable application. One such application can be as a semi-permeable filtration membrane. Thus, in another aspect of the present invention, there is provided a semi-permeable filtration membrane formed from a thin film of the porous composite material described herein. In certain embodiments that may be mentioned herein, when measured at a pressure of 1 bar, the filtration membrane can have an average air flux of 1,000 LMH to 10,000 LMH, such as approximately 5,435 LMH. In other embodiments, the filtration membrane can have a water permeability of 50 to 1,000 LMH / bar, such as 196.5 LMH / bar.

[0131] Another application of the porous composite material described herein can be as a membrane for a separator. Thus, in another aspect of the present invention, there is provided a membrane for a separator of a battery, the membrane of the separator comprising the porous composite material described herein.

[0132] The porous composite material described herein can be formed by any suitable method. Thus, in another aspect of the present invention, there is provided a method of providing the porous composite material described herein, the method comprising the following steps:

[0133] (a) providing a polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold drawing, and hot drawing; and

[0134] (b) subjecting the polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold drawing, and hot drawing to a heat setting step at a specific temperature for a specific period of time. In the method described herein, one or both of the following can be applied:

[0135] The temperature of the heat setting step can be 100 to 150 °C, such as 120 to 140 °C; and

[0136] The period of time of the heat setting step can be 1 to 120 minutes, such as 30 to 60 minutes.

[0137] The polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold drawing, and hot drawing can be provided by:

[0138] (ai) providing a polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, and cold drawing; and

[0139] (aii) subjecting the polyolefin composite precursor material to hot drawing at a specific temperature, a specific length per minute, and a specific elongation rate. In such embodiments, one or both of the following can be applied:

[0140] The temperature of the hot drawing can be 100 to 150 °C;

[0141] The length per minute of the hot drawing can be from 1 mm / min to 200 mm / min, such as from 8 mm / min to 40 mm / min.

[0142] A polyolefin composite precursor material that has undergone melt extrusion, thermal annealing, and cold drawing can be provided by:

[0143] (bi) providing a polyolefin composite precursor material that has undergone melt extrusion, thermal annealing, and cold drawing; and

[0144] (bii) subjecting the polyolefin composite precursor material to cold drawing at a specific temperature, a specific length per minute, and a specific elongation ratio. In such an embodiment, one or both of the following can be applied:

[0145] The temperature of the cold drawing can be from -196 to 100 °C, such as from 20 to 30 °C, such as about 25 °C;

[0146] The length per minute of the cold drawing can be from 1 mm / min to 600 mm / min, such as from 10 mm / min to 200 mm / min, such as from 50 to 100 mm / min.

[0147] A polyolefin composite precursor material that has undergone melt extrusion and thermal annealing can be provided by:

[0148] (ci) providing a polyolefin composite precursor material that has undergone melt extrusion and thermal annealing; and

[0149] (cii) subjecting the polyolefin composite precursor material to thermal annealing at a specific temperature for a specific period of time. In such an embodiment, one or both of the following can be applied:

[0150] The temperature of the thermal annealing can be from 100 to 150 °C, such as from 110 to 140 °C; and

[0151] The period of time of the thermal annealing can be from 1 minute to 10 hours, such as from 30 minutes to 8 hours.

[0152] A polyolefin composite precursor material that has undergone melt extrusion can be provided by:

[0153] (di) providing a polyolefin composite precursor material comprising the components described herein; and

[0154] (dii) subjecting the polyolefin composite precursor material to melt extrusion at a specific temperature and a specific draw ratio. In such an embodiment, one or both of the following can be applied:

[0155] The temperature of the melt extrusion can be from 150 to 250 °C, such as from 160 to 220 °C; and

[0156] The draw ratio for melt extrusion can be from 20 to 10,000.

[0157] The exact ratio used will depend on the shape of the desired porous polyolefin composite. That is, there will be a very large difference in the draw ratio between a film in the form of a flat sheet and a film in the form of a fiber. Thus, for a flat sheet, the draw ratio can be from 20 to 200, and for a hollow fiber, the draw ratio can be from 500 to 10,000.

[0158] For example, the porous composite described herein can be obtained by mixing a polyolefin resin with a masterbatch containing a high loading of a high aspect ratio filler material, or by directly adding the high aspect ratio filler material in powder form to an extruder containing the polyolefin, where the extruder is at a temperature above the melting point of the polyolefin. As used herein, a masterbatch refers to a composite containing a higher loading of filler than the final porous composite. The compounding process for forming the masterbatch involves mixing the high aspect ratio filler material with the polyolefin in a single or twin extruder at different temperatures (such as 130 to 250 °C, preferably at a temperature greater than or equal to 160 °C and less than or equal to 250 °C, depending on the type of polyolefin used). Compounding can be carried out using a screw speed in the range of 5 to 200 rad / min and a duration of 1 to 30 minutes, preferably using a screw speed in the range of 50 to 150 rad / min and a duration of 3 to 15 minutes. Compounding can be carried out with or without gas protection (such as nitrogen).

[0159] The porous composite can be melt extruded into any suitable precursor structure, such as a flat sheet, which can be manufactured by a film casting device. The composite polyolefin precursor film can also be made into other shape factors, such as a fibrous shape, which can be manufactured by a fiber spinning device. The drawing process during the manufacture of the composite polyolefin precursor film is necessary to increase the crystallization of the polyolefin and the alignment of the crystals. In particular, composite polyolefin precursor flat sheets or films can be manufactured at a draw ratio of 30 to 300, achieving a thickness typically in the range of 10 to 100 μm, preferably in the range of 10 to 50 μm. Composite polyolefin precursor fibers can be manufactured at a draw ratio of 500 to 10,000, achieving a diameter of 200 to 1000 μm, preferably in the range of 400 to 700 μm.

[0160] Heat treatment processes, or thermal annealing, are typically required to further enhance the crystallization and crystal alignment of polyolefins. The heat treatment process can be carried out at a temperature 1 to 30 °C below the melting point of the polyolefin polymer. For example, for HDPE, depending on the actual melting point of the HDPE, the annealing process can be carried out at 100 to 130 °C, preferably in the range of 115 to 130 °C. Again, for PP, depending on the actual melting point of the PP, the annealing process can be carried out at 120 to 170 °C, preferably in the range of 120 to 150 °C. Depending on the type of polyolefin and the annealing temperature, the annealing process can last from 1 minute to several hours. Generally, a higher annealing temperature requires a shorter annealing duration.

[0161] Subject the annealed polyolefin composite precursor to a stretching process to produce a porous structure. The stretching process comprises two stages, where the first stretching is carried out at a lower temperature and the other stage is carried out at a relatively higher temperature.

[0162] Depending on the type of polyolefin polymer, the first stretching can be carried out at a temperature between -196 and 100 °C, preferably at a temperature between 20 and 40 °C. In particular, the first stretching can be carried out at room temperature. In particular, depending on the type of polyolefin polymer and depending on the form of the sample, the stretching speed can be in the range of 1 to 1000 mm / min, preferably at a speed in the range of 10 to 100 mm / min.

[0163] The second stretching can be carried out at a temperature 1 to 30 °C below the melting point of the polyolefin or polyolefin composite. For example, for HDPE, depending on the actual melting point of the HDPE, the second stretching can be carried out at 100 to 130 °C, preferably in the range of 115 to 130 °C. Again, for PP, depending on the actual melting point of the PP, the second stretching can be carried out at 120 to 170 °C, preferably in the range of 120 to 150 °C. Depending on the type of polyolefin polymer, the stretching speed can be in the range of 1 to 200 mm / min, preferably at a speed in the range of 5 to 50 mm / min. In the present invention, based on the original length of the precursor before the stretching process, the total stretch ratio including the first and second stretching processes can be in the range of 50% to 1000%.

[0164] A second heat treatment process is typically required to stabilize the porous structure of the porous polyolefin composite after the stretching process. The second heat treatment process can be carried out at a temperature 1 to 30 °C below the melting point of the polyolefin polymer or polyolefin composite. For example, for HDPE, depending on the actual melting point of HDPE, the second heat treatment process can be carried out at 100 to 130 °C, preferably in the range of 115 to 130 °C. Again, for PP, depending on the actual melting point of PP, the second heat treatment process can be carried out at 120 to 170 °C, preferably in the range of 120 to 150 °C. Depending on the type of polyolefin and the heat treatment temperature, the second heat treatment process can last from 1 minute to several hours. Generally, a higher heat treatment temperature requires a shorter heat treatment duration.

[0165] Additional aspects and embodiments of the present invention will now be described by reference to the following non-limiting embodiments.

[0166] Examples

[0167] Materials

[0168] HDPE and PP were purchased from LyondellBasell and Sabic respectively. The CNT-PE masterbatch was purchased from CNano Technology Limited. The clay masterbatch was supplied by the Chinese Academy of Sciences. The graphene-PP masterbatch was provided by Jixi Hanyu graphene technology Co., Ltd. Isopropyl alcohol was purchased from Aik Moh.

[0169] Example 1. General protocol for the manufacture and characterization of porous polyolefin composites

[0170] Manufacture of porous polyolefin composite structures

[0171] The porous polyolefin composite is manufactured by subjecting a polyolefin composite precursor material that has undergone melt extrusion, thermal annealing, first stretching, and second stretching to a heat setting step at a specific temperature for a specific period of time. The polyolefin composite is obtained through a compounding process that involves mixing a masterbatch or filler with the polyolefin in a single extruder or a twin extruder at different temperatures.

[0172] Characterization of porous polyolefin composite structures

[0173] Then, the porous polyolefin composite structure is characterized by electron microscopy, mechanical properties, pore size analyzer, and filtration tests.

[0174] Field emission scanning electron microscopy (FESEM)

[0175] The morphology of the samples was studied by a field emission scanning electron microscope (FESEM) JEOL JSM-7600F.

[0176] Mechanical property testing

[0177] The mechanical properties of the composites in the form of flat sheets were tested in the machine direction (MD) and the transverse direction (TD), and the values of strength, Young's modulus, and fracture strain were calculated. The mechanical tests were carried out using an MTS Criterion electromechanical test system model C43 according to ASTM D638 method. To determine the mechanical properties of the porous composites in the fibrous shape form, 20-mm fibre segments were stretched at a crosshead speed of 50 mm / min by a mechanical tester until fracture.

[0178] Filtration testing

[0179] Filtration tests were carried out to evaluate the flux and permeability of the porous polyolefin composite structures. Filtration was carried out using a gas or liquid filtration setup including a sample holder, a pressure vessel, and an air or liquid measurement system to determine the filtration performance of the porous composite structures.

[0180] The membrane flux is defined as the amount of permeate produced per unit area of the membrane surface per unit time (Equation 1).

[0181]

[0182] where J is the filtrate flux rate V is the volume (liters) of the filtrate produced, A is the membrane area (m 2 ) and T is the filtration time (hours).

[0183] The permeability of the porous polyolefin film is defined as the diffusion rate of molecules or ions through the membrane. In the application of filtration membranes, the permeability of the membrane can be determined using Equation 2:

[0184]

[0185] where L p is the permeability of the membrane J is the filtrate flux rate and ΔP is the pressure (bar) applied across the membrane. Filtration can be carried out at transmembrane pressures ranging from 0.05 to 2 bar, and the permeate is collected and weighed to determine the average flux of the porous structure.

[0186] Example 2. Comparison of a porous pure HDPE film with a porous HDPE / CNT composite film having 0.7 wt% CNT

[0187] According to the general scheme disclosed in Example 1, porous pure HDPE films and porous HDPE / CNT composite films with 0.7 wt% CNT were fabricated and characterized.

[0188] Fabrication of porous HDPE / CNT composite films with 0.7 wt% CNT

[0189] High-density polyethylene (HDPE) with a density of 0.95 g / cm 3 and a melt flow index (MFI) of 0.45 g / 10 min (at 190 °C / 2.16 kg) was compounded with a carbon nanotube masterbatch with a 15 wt% loading using a twin extruder at a temperature of 160 °C. The carbon nanotubes used had an average diameter of 7 - 12 nm and a length of approximately 50 - 250 μm. The polyolefin composite consisting of 0.7 wt% CNT was melt extruded into thin films at a draw ratio of 75 at a temperature of 195 °C. Subsequently, the obtained films were annealed at a temperature of 120 °C for 4 hours, then stretched at room temperature at 400 mm / min to an elongation of 60% in length, and further stretched at 120 °C at 10 mm / min to an elongation of 100% in length. After that, the stretched samples were heat-treated at 120 °C for 15 minutes.

[0190] Fabrication of porous pure HDPE films

[0191] The manufacturing steps of the porous films of pure HDPE were the same as those above and in Example 1, but the compounding stage was excluded.

[0192] FESEM of the CNTs used, porous pure HDPE films, and porous HDPE / CNT composite films with 0.7 wt% CNT

[0193] By following the scheme in Example 1, SEM images of the CNTs used, porous pure HDPE films, and porous HDPE / CNT composite films (0.7 wt%) were measured.

[0194] TEM images of carbon nanotubes

[0195] TEM images were obtained using a FEI Tecnai G2 F30 TEM.

[0196] Mechanical property tests of porous pure HDPE films and porous HDPE / CNT composite films with 0.7 wt% CNT

[0197] According to the general scheme described in Example 1, mechanical tests were carried out on both the machine direction and the transverse direction of pure porous HDPE and porous HDPE / CNT composite films (0.7 wt%).

[0198] Filtration Tests of Porous Pure HDPE Film and Porous HDPE / CNT Composite Film with 0.7 wt% CNT

[0199] The filtration performance test was conducted as described in Example 1.

[0200] Results and Discussion

[0201] Figure 1 and Figure 2 SEM images of both pure HDPE and HDPE / CNT composite films are shown. It is clearly seen that both HDPE and HDPE / CNT composite film (0.7 wt%) produce abundant pores.

[0202] The carbon nanotubes used have an average diameter of 7 - 12 nm and a length of about 50 - 250 μm, which gives an aspect ratio (length / diameter) in the range of about 4200 to 36000 ( Figure 3 ). The introduction of CNT fillers with such a high aspect ratio has been shown to enhance the mechanical properties of porous polyolefins. Mechanical tests were performed on both pure porous HDPE and porous HDPE / CNT composite film (0.7 wt%) in both the machine direction and the transverse direction. In the machine direction, it was found that the strength of the pure HDPE film had an average value of 113 MPa, while the value of the porous HDPE / CNT composite film (0.7 wt%) increased by 7.1% to reach 121 MPa, while the modulus and maximum strain did not change significantly. In the transverse direction, the strength increased from 6.81 MPa of the HDPE film to 9.6 MPa of the HDPE / CNT composite film (0.7 wt%), achieving an increment of 41%. It was found that the average fracture strain of the HDPE / CNT composite film (0.7 wt%) had a value of 2807%, representing an improvement of 26890.4% compared to 10.4% of pure HDPE. No significant change in modulus was observed, probably due to the change in porosity. These mechanical data in the transverse direction are summarized in Table 1.

[0203] Table 1. Mechanical Properties (Transverse) of Porous Pure HDPE and Porous HDPE / CNT Composite Film (0.7 wt%).

[0204]

[0205] Note: Values in parentheses are standard deviations.

[0206] The filtration performance test was conducted as described. When measured at a pressure of 1 bar, the average air flux of the pure HDPE film was calculated to be 270 LMH, while that of the HDPE / CNT composite film (0.7 wt%) was 5435 LMH. With 0.7 wt% CNT added to the HDPE film, the air flux increased by 2000%. The liquid permeability of the HDPE / CNT composite film (0.7 wt%) was measured using isopropanol, and the flux was determined to be 45 LMH at a pressure of 1 bar. The higher flux performance and the observation of the SEM images indicate that the addition of CNT can enhance the pore-forming ability without compromising the mechanical properties.

[0207] Example 3. Comparison between a porous pure HDPE film and a porous HDPE / CNT composite film with 1.5 wt% CNT

[0208] According to the general procedure disclosed in Example 1, a porous pure HDPE film and a porous HDPE / CNT composite film with 1.5 wt% CNT were fabricated and characterized.

[0209] Fabrication of a porous HDPE / CNT composite film with 1.5 wt% CNT

[0210] Using a twin extruder, at a temperature of 160 °C, HDPE with a density of 0.95 g / cm 3 and an MFI of 0.4 was compounded with 1.5 wt% CNT. The carbon nanotubes used had an average diameter of 7 - 12 nm and a length of about 50 - 250 μm. Then the composite was melt-extruded into a thin film at a draw ratio of 75 at a temperature of 195 °C. Subsequently, the HDPE / CNT composite film (1.5 wt%) was annealed at a temperature of 110 °C for 2 hours, then stretched at room temperature at 480 mm / min to an elongation of 45% in length, and further stretched at 120 °C at 8 mm / min to an elongation of 80% in length. After that, the stretched film was further heat-treated at 120 °C for 10 minutes.

[0211] Fabrication of the porous pure HDPE film

[0212] The film fabrication steps of the pure HDPE film were the same as those above and in Example 1, but without the compounding stage.

[0213] Mechanical property tests of the porous pure HDPE film and the porous HDPE / CNT composite film with 1.5 wt% CNT

[0214] According to the general procedure described in Example 1, mechanical tests were conducted on both the porous pure HDPE and the porous HDPE / CNT composite film (1.5 wt%) in the machine direction.

[0215] Results and Discussion

[0216] The strength of the porous pure HDPE film was tested to have an average value of 87.5 MPa, while the porous HDPE / CNT composite film (1.5 wt%) obtained an average strength of 112.5 MPa, achieving a 28.6% increase. The Young's modulus increased by 21.5% from 327.8 MPa of the pure HDPE film to 398.4 MPa of the HDPE / CNT composite film (1.5 wt%). Although there were significant increases in strength and modulus, the fracture strain did not change significantly. These results are summarized in Table 2.

[0217] Table 2. Mechanical properties (machine direction) of porous pure HDPE and porous HDPE / CNT composite film (1.5 wt%).

[0218]

[0219] Note: The values in parentheses are standard deviations.

[0220] The carbon nanotubes used had an average diameter of 7 - 12 nm and a length of about 50 - 250 μm, which gave an aspect ratio (length / diameter) in the range of about 4200 to 36000 ( Figure 3 ). Introducing CNT fillers with such a high aspect ratio was also shown to enhance the mechanical properties of the porous polyolefin in this example.

[0221] Example 4. Comparison between porous pure HDPE film and porous HDPE / clay composite film

[0222] According to the general procedure disclosed in Example 1, porous pure HDPE films and porous HDPE / clay composite films were fabricated and characterized.

[0223] Fabrication of porous HDPE / clay composite film

[0224] Using a twin-screw extruder, at a temperature of 160 °C, HDPE with a density of 0.95 g / cm 3 and a melt index of 0.4 was compounded with clay. The clay used had an average thickness of 1 nm and a planar length of about 0.5 - 5 μm. The composite consisting of 3 wt% clay and a compatibilizer was melt-extruded into a thin film at a draw ratio of 75 at a temperature of 195 °C. Subsequently, the HDPE / clay (3 wt%) film was annealed at a temperature of 117 °C for 8 hours, then stretched at room temperature at 500 mm / min to an elongation of 50% in length, and further stretched at 120 °C at 12 mm / min to an elongation of 110% in length. The stretched HDPE / clay (3 wt%) film was further heat-set at 120 °C for 15 minutes.

[0225] Manufacture of Porous Pure HDPE Film

[0226] The film manufacturing steps of the pure HDPE film are the same as those in the above and Example 1, but do not include the lamination stage.

[0227] SEM Images of Clay, Porous Pure HDPE Film, and Porous HDPE / Clay Composite Film

[0228] By following the protocol in Example 1, SEM images of the clay, porous pure HDPE film, and porous HDPE / Clay composite film used were measured.

[0229] AFM Image of Clay

[0230] The thickness of the clay was measured by Bruker Dimension Edge TM Atomic Force Microscope (AFM).

[0231] Mechanical Property Tests of Porous Pure HDPE Film and Porous HDPE / Clay Composite Film

[0232] According to the general protocol described in Example 1, mechanical tests were performed on both porous pure HDPE and porous HDPE / Clay composite film (3 wt%) in the machine direction.

[0233] Results and Discussion

[0234] Figure 4 SEM image of the porous HDPE / Clay (3 wt%) composite is shown.

[0235] The clay used had an average thickness of 1 nm and a planar length of about 0.5 - 5 μm, which gave an aspect ratio (planar length / thickness) in the range of about 500 - 5000( Figure 5 , Figure 6 , Figure 7 ). The introduction of clay with such a high aspect ratio was shown to improve the mechanical properties of the porous polyolefin in this example. Mechanical tests were performed on the porous pure HDPE and porous HDPE / Clay (3 wt%) composite films in the machine direction. The strength of the pure porous HDPE film was tested to have an average value of 80.2 MPa, while the porous HDPE / Clay (3 wt%) film obtained a strength value of 91.8 MPa, achieving a 14.4% increase. The modulus increased from 249.6 MPa for pure HDPE to 272.0 MPa for the HDPE / Clay (3 wt%) composite, with an increment of 9.0%. The fracture strain of both samples was maintained, with both exceeding 160%, indicating that the ductility of the composite was not impaired. The results are summarized in Table 3.

[0236] Table 3. Mechanical properties of porous pure HDPE and porous HDPE / clay (3 wt%) composite films.

[0237]

[0238] Note: Values in parentheses are standard deviations.

[0239] Example 5. Comparison of pure PP porous hollow fibers and PP / graphene composite (0.1 wt%) porous hollow fibers

[0240] Manufacture of hollow fiber precursors

[0241] Polypropylene (PP, Sabic 500P) with a density of 9.05 g / cm 3 and a melt flow index of 3.0 was spun into hollow fibers using a fiber spinning device that mainly included an extruder, a gear pump, and a diehead. To produce the unstretched precursor hollow fibers, zones 1, 2, 3, and 4 of the extruder were maintained at 170 °C, 220 °C, 230 °C, and 220 °C, respectively. The temperatures of the extruder end, the gear pump, and the diehead were all maintained at 190 °C. The diehead had an OD of 15 mm and an ID of 10 mm, and the extruder port area was 0.98 cm 2 . Nitrogen was used for the bore gas, which had a flow rate of 10 ml / min. The PP melt was extruded from the diehead at a speed of 4.4 cm / min and collected using a winder at a takeup speed of 81 m / min, which gave a draw ratio of 1825. The PP / graphene composite precursor fibers with a graphene loading of 0.1 wt.% were produced by premixing pure PP and a PP masterbatch with 5.0 wt% and then introducing them into the extruder hopper. The graphene used in this example, which can also be referred to as few-layer graphene or few-layer graphite, had a planar width between 100 - 2000 nm and a thickness of approximately 1 nm, giving an aspect ratio in the range of about 100 - 2000. During the manufacture of the hollow fiber precursors, all other parameters were kept the same as for pure PP. Both the pure PP and the graphene-filled PP precursor fibers were heat annealed in an oven at 140 °C for 30 minutes before stretching.

[0242] Manufacture of porous hollow fibers

[0243] To produce the porous structure, 300 loops with a diameter of 34 cm were made from pure PP and graphene composite fibers and then loaded into a stretching device, where the two ends of the loops were fixed by hooks in a stretching machine. The fibers were cold-stretched to 60 cm in length at room temperature with a stretching speed of 10 mm / min; and further hot-stretched to a final length of 140 cm at 140 °C with a stretching speed of 10 mm / min, resulting in a total elongation rate of 260% (final length / original length). After the stretching process was completed, the pure porous PP hollow fibers and the porous graphene composite hollow fibers were immediately heat-stabilized at 140 °C for 30 minutes.

[0244] SEM images of pure PP porous hollow fibers and graphene composite porous hollow fibers

[0245] By following the protocol in Example 1, SEM images of pure PP porous hollow fibers and graphene composite porous hollow fibers were measured.

[0246] Mechanical property tests of pure PP porous hollow fibers and graphene composite porous hollow fibers

[0247] According to the general protocol described in Example 1, mechanical tests were performed on both pure PP porous hollow fibers and PP / graphene composite (0.1 wt%) porous hollow fibers in the fiber direction.

[0248] Permeability test

[0249] To determine the permeability of the porous hollow fibers, a module was fabricated using 20 fibers with a length of 30 cm. The fiber bundle was fixed in a tube with a diameter of 8 mm using epoxy resin, and one end was sealed while the other end was connected to a sucking pump. Before the permeability test, the module was soaked in IPA for 15 minutes and washed with water to make the fibers more hydrophilic. The amount of water inhaled into the inner cavity of the hollow fibers was used to calculate the permeability, taking into account the surface area of the fibers.

[0250] Rejection rate test

[0251] To test the rejection rate of the porous hollow fibers, a yeast solution with a concentration of 1 g / L was prepared. The rejection rate was defined as the ratio between the turbidity of the produced water and the turbidity of the influent water. The turbidity was determined by a Lovibond TB 211IR infrared turbidimeter.

[0252] Pore size analysis

[0253] The pore size analysis of the porous hollow fibers was carried out using an ultrafiltration membrane porosity meter GAOQ PSMA-20 (GaoQ Functional Materials Co., Ltd).

[0254] Porosity determination

[0255] The porosity of the porous hollow fiber is calculated by the following equation (Equation 3):

[0256]

[0257] where ρ1 and ρ2 are the density of the porous structure after stretching and the density of the precursor before stretching, respectively.

[0258] Results and Discussion

[0259] The pure PP porous hollow fiber and the graphene composite porous hollow fiber have average diameters of 439 and 435 μm, respectively, and thicknesses of 37 and 33 μm, respectively. The morphologies of the pure PP porous hollow fiber and the graphene composite porous hollow fiber are shown in Figure 8 and Figure 9 . It can be seen that a large number of slit pores are generated from both types of hollow fibers. The porosities of the pure PP porous hollow fiber and the graphene composite porous hollow fiber are calculated to be 55% and 50.5%, respectively. According to the pore size analysis, the average pore sizes of the pure PP porous hollow fiber and the graphene composite porous hollow fiber are 48.2 and 47.6 nm, respectively. The pure water permeabilities of the pure PP porous hollow fiber and the graphene composite porous hollow fiber are 192.2 and 196.5 LMH / bar, respectively. The rejection rates of yeast for the pure PP porous hollow fiber and the graphene composite porous hollow fiber are 99.07% and 99.96%, respectively. According to the mechanical tests, the strength and fracture strain of the pure PP porous hollow fiber are 125 MPa and 136%, respectively, while the strength and fracture strain of the graphene composite porous hollow fiber are 148 MPa and 170%, respectively. Compared with the pure PP porous hollow fiber, for the porous hollow fiber filled with 0.1 wt% graphene, the increments in terms of strength and fracture strain are 18.4% and 25%, respectively.

[0260] Comparison of pure PP porous hollow fiber and PP / graphene composite (0.2 wt%) porous hollow fiber in Example 6

[0261] Manufacture of pure PP porous hollow fiber and PP / graphene composite (0.2 wt%) porous hollow fiber

[0262] Another PP / graphene composite precursor hollow fiber with a graphene loading of 0.2 wt% was produced using PP / graphene composite pellets containing 0.2 wt.% graphene, and these pellets were manufactured by compounding pure PP and a PP / graphene masterbatch with 5.0 wt.% graphene. The PP / graphene composite precursor hollow fiber was manufactured according to the procedure described in Example 5. To produce the porous structure, the PP / graphene composite precursor hollow fiber was stretched according to the procedure described in Example 5.

[0263] Results and Discussion

[0264] The graphene composite porous hollow fiber with 0.2 wt.% loading of graphene has an average diameter and wall thickness of 443 and 33 μm, respectively. The morphology of the graphene composite porous hollow fiber is shown in Figure 10 . The porosity of the graphene composite porous hollow fiber was calculated to be 48.4%. According to the pore size analysis, the average pore size was 52.0 nm. The permeability of the graphene composite porous hollow fiber was 204.8 LMH / bar. The rejection rate of yeast was 99.87%. According to the mechanical tests, the strength and fracture strain were 138 MPa and 177%, respectively. Compared with the pure PP porous hollow fiber in Example 5, the strength and fracture strain increased by 10.4% and 30.1%, respectively.

[0265] In summary, introducing high aspect ratio fillers into porous polyolefins can effectively enhance the mechanical properties in the biaxial direction while having a limited negative impact on the pore-forming ability and filtration performance.

Claims

1. A porous composite material, comprising: a polymer matrix formed from one or more polyolefins; and one or more high aspect ratio filler materials, wherein the porous composite material has pores with a diameter of 0.01 to 2 μm; and the one or more high aspect ratio filler materials are present in an amount of 0.05 to 30 wt% of the total weight of the porous composite material.

2. The porous composite material according to claim 1, wherein The one or more polyolefins each have a general repeating group of formula I: (CH2CHR)n I wherein R is an alkyl group, optionally wherein each R is an unbranched or branched C1 to C 10 alkyl group.

3. The porous composite material according to claim 1 or 2, wherein The one or more polyolefins are selected from one or more of the group consisting of polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polybutene-1 (PB-1), ethylene-octene copolymer, syndiotactic block PP, olefin block copolymer, or propylene-butane copolymer.

4. The porous composite material according to any one of the preceding claims, wherein, Each of said one or more polyolefins has a density of 0.8 to 0.99 g / cm 3 , such as 0.9 to 0.99 g / cm 3 , such as 0.94 to 0.97 g / cm 3 , such as 0.89 to 0.95 g / cm 3 , such as 0.92 to 0.98 g / cm 3 .

5. The porous composite material according to any one of the preceding claims, wherein, Each of the one or more polyolefins has a melt flow index measured according to ASTM D1238 at 230 °C / 2.16 kg of 0.1 to 30 g / 10 min, such as 0.1 to 15 g / 10 min, such as 0.3 to 0.5 g / 10 min.

6. The porous composite material according to any one of the preceding claims, wherein, The porous composite material further comprises one or more additives selected from the group consisting of stabilizers, plasticizers, lubricants, flame retardants, anti-aging materials, colorants, nucleating agents, flavoring agents, anti-microbial materials, antistatic additives, or compatibilizers, optionally wherein the porous composite material further comprises a compatibilizer.

7. The porous composite material according to any one of the preceding claims, wherein, The one or more high aspect ratio filler materials are materials having a high ratio of length or width to cross-sectional diameter and / or thickness, wherein the ratio is 5 to 100,000.

8. The porous composite material according to any one of the preceding claims, wherein the one or more high aspect ratio filler materials are present in an amount of 0.01 to 30 wt% of the total weight of the porous composite material, such as 0.1 to less than or equal to 10 wt%, such as 0.5 to 2 wt%, such as 0.7 to 1.5 wt%.

9. The porous composite material according to any one of the preceding claims, wherein, At least one of the one or more high aspect ratio fillers is surface-treated, optionally wherein at least one of the surface-treated one or more high aspect ratio fillers is treated by one or more of chemical treatment and physical treatment.

10. The porous composite material according to any one of the preceding claims, wherein, The one or more high aspect ratio filler materials are selected from one or more of the following: tubular fillers, rod-shaped fillers, fibers, filaments, plate-shaped fillers, disk-shaped fillers, sheet-shaped fillers, prismatic fillers, wall-shaped fillers, branched structure fillers, and hybrid structures comprising two or more of the structures mentioned herein.

11. The porous composite material according to any one of the preceding claims, wherein, The one or more high aspect ratio filler materials have dimensions of 1 nm to 1,000 μm.

12. The porous composite material according to any one of the preceding claims, wherein, The high aspect ratio filler materials are selected from one or more of the group consisting of nanotubes, nanorods, nanowires, and sheet-shaped fillers, such as silver nanowires, metal nanorods, carbon nanotubes, clay, and graphene.

13. The porous composite material according to any one of the preceding claims, wherein, The polyolefin porous composite is provided in the form of a flat sheet, in the form of a hollow fiber having a diameter between 0.05 and 2 mm, or in the form of a tubular structure having a diameter greater than 2 mm.

14. The porous composite material according to any one of the preceding claims, wherein, The high aspect ratio filler material has an aspect ratio of 5 to 100,000, such as 500 to 36,000, such as 5,000 to 10,000.

15. The porous composite material according to any one of the preceding claims, wherein, The porous composite material has one or both of the following: In the transverse direction for a film formed only of the polyolefin, or in the circumferential direction for a fiber / tube formed only of the polyolefin, the mechanical strength is 5% to 1,000% higher, such as 20% to 100% higher, such as 30% to 50% higher; And In the transverse direction for a film formed only of the polyolefin, or in the circumferential direction for a fiber / tube formed only of the polyolefin, the maximum strain is 10% to 50,000% higher, such as 1,000% to 40,000% higher, such as 10,000% to 27,000% higher.

16. The porous composite material according to any one of the preceding claims, wherein, The porous composite material has one or both of the following: In the machine direction for a film formed only of the polyolefin, or in the longitudinal direction for a fiber / tube formed only of the polyolefin, the mechanical strength is 5% to 100% higher, such as 11% to 50% higher, such as 14% to 33% higher; And In the machine direction for a film formed only of the polyolefin, or in the longitudinal direction for a fiber / tube formed only of the polyolefin, the Young's modulus is 7% to 100% higher, such as 8% to 40% higher, such as 9% to 33% higher.

17. A semipermeable filtration membrane, the semipermeable filtration membrane being formed of a film of the porous composite material according to any one of claims 1 to 16.

18. The semipermeable filtration membrane according to claim 17, wherein: When measured at a pressure of 1 bar, the filtration membrane has an average air flux of 1,000 LMH to 10,000 LMH, such as about 5,435 LMH; and / or The filtration membrane has a water permeability of 50 LMH / bar to 1,000 LMH / bar, such as about 196.5 LMH / bar.

19. A membrane for a separator of a battery, comprising the porous composite material according to any one of claims 1 to 12.

20. A method of providing the porous composite material according to any one of claims 1 to 18, the method comprising the following steps: (a) Providing a polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold stretching, and hot stretching; And (b) Subjecting the polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold stretching, and hot stretching to a heat setting step at a specific temperature for a specific period of time.

21. The method according to claim 20, wherein, Apply one or both of the following: The temperature of the heat setting step is 100 to 150 °C, such as 120 to 140 °C; and The period of time of the heat setting step is 1 to 120 minutes, such as 30 to 60 minutes.

22. The method according to claim 20 or claim 21, wherein The polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, cold stretching, and hot stretching is provided by: (ai) Providing a polyolefin composite precursor material that has been subjected to melt extrusion, thermal annealing, and cold stretching; and (aii) Subjecting the polyolefin composite precursor material to hot stretching at a specific temperature, a specific length per minute, and a specific elongation rate.

23. The method according to claim 22, wherein Apply one or both of the following: The temperature of the hot drawing is 100 to 150 °C; The length per minute of the hot drawing is 1 mm / min to 200 mm / min, such as 8 mm / min to 40 mm / min.

24. The method according to any one of claims 20 to 23, wherein The polyolefin composite precursor material that has undergone melt extrusion, thermal annealing, and cold drawing is provided by the following: (bi) Providing a polyolefin composite precursor material that has undergone melt extrusion, thermal annealing, and cold drawing; And (bii) Subjecting the polyolefin composite precursor material to cold drawing at a specific temperature, a specific length per minute, and a specific elongation ratio.

25. The method according to claim 24, wherein, Apply one or both of the following: The temperature of the cold drawing is -196 to 100 °C, such as 20 to 30 °C, such as about 25 °C; The length per minute of the cold drawing is 1 mm / min to 600 mm / min, such as 10 mm / min to 200 mm / min, such as 50 to 100 mm / min.

26. The method according to any one of claims 21 to 25, wherein The polyolefin composite precursor material that has undergone melt extrusion and thermal annealing is provided by the following: (ci) Providing a polyolefin composite precursor material that has undergone melt extrusion and thermal annealing; and (cii) Subjecting the polyolefin composite precursor material to thermal annealing for a specific period of time at a specific temperature.

27. The method according to claim 26, wherein, Apply one or both of the following: The temperature of the thermal annealing is 100 to 150 °C, such as 110 to 140 °C; and The period of time of the thermal annealing is 1 minute to 10 hours, such as 30 minutes to 8 hours.

28. The method according to any one of claims 20 to 25, wherein The polyolefin composite precursor material that has undergone melt extrusion is provided by the following: (di) Providing a polyolefin composite precursor material comprising the components described in any one of claims 1 to 16; and (dii) Subjecting the polyolefin composite precursor material to melt extrusion at a specific temperature and a specific draw ratio.

29. The method according to claim 28, wherein, Apply one or both of the following: The temperature of the melt extrusion is 150 to 250 °C, such as 160 to 220 °C; and The draw ratio of the melt extrusion is 20 to 10,000.

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