Flame-retardant polyolefin hollow fiber membranes and methods for making the same

Abstract

The application discloses a kind of flame-retardant polyolefin hollow fiber membrane and its preparation method, and the raw material of flame-retardant polyolefin hollow fiber membrane includes the following mass percentage components: 20%~50% polyolefin, 20%~50% flame retardant and 20%~70% diluent;Wherein, the flame retardant is powdery.The application can solve the problem of low ignition point of polyolefin hollow fiber membrane material matrix, non-essential flame-retardant problem, thereby widening the use range of polyolefin hollow fiber membrane.

Description

Technical Field

[0001] This invention relates to the field of separation and filtration membrane technology, and more specifically, to a flame-retardant polyolefin hollow fiber membrane and its preparation method. Background Technology

[0002] Hollow fiber membranes are irregularly shaped fibers with axial cavities, a porous cross-section, and a fiber-like appearance. The hollow structure endows the fibers with excellent heat retention, fluffiness, and other specific properties and characteristics, while the porous structure allows for selective permeation / adsorption of fluids, thus enabling the separation and enrichment of mixed fluids. The selective adsorption capacity of hollow fiber membranes for fluids such as water, air, and blood has important applications in the field of filtration and separation.

[0003] Hollow fiber membranes mainly include polyacrylonitrile, cellulose and its derivatives, polyolefins, polyesters, poly(ether)sulfones, and fluoropolymers. Among them, polyolefin hollow fiber membranes, represented by polypropylene, have relatively low raw material prices and mature production processes, making them the most produced, widely used, and largest-scale hollow fiber membranes. However, polyolefin materials, represented by polypropylene, are flammable materials, posing a significant fire hazard and limiting their use in areas with high fire protection requirements. For example, when the gases being separated are combustion-supporting gases (oxygen, nitrogen dioxide, chlorine, fluorine, etc.) and combustible gases (carbon monoxide, hydrogen, methane, ethylene, propyne, etc.), a certain flame retardant rating must be achieved. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a flame-retardant polyolefin hollow fiber membrane and its preparation method, thereby solving the problems of low ignition point of the material matrix and non-inherent flame retardancy in polyolefin hollow fiber membranes, and thus broadening the application range of polyolefin hollow fiber membranes.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A flame-retardant polyolefin hollow fiber membrane, the raw material of which comprises the following components by mass percentage:

[0007] 20%–50% polyolefin, 20%–50% flame retardant and 20%–58% diluent;

[0008] The flame retardant is in powder form.

[0009] This invention also discloses a method for preparing the above-mentioned flame-retardant polyolefin hollow fiber membrane, comprising the following steps:

[0010] The components of the raw material are melted to obtain a casting solution;

[0011] The casting solution is extruded from an annular spinneret and solidified in a cooling bath through an air gap to obtain a hollow fiber primary membrane.

[0012] The primary membrane is extracted to remove the diluent, forming a microporous structure to obtain a secondary membrane;

[0013] The secondary membrane is dried to obtain the flame-retardant polyolefin hollow fiber membrane.

[0014] Implementing the embodiments of the present invention will have the following beneficial effects:

[0015] This invention, through the addition of flame retardants, endows polyolefin hollow fiber membranes with inherent flame-retardant properties, thus broadening their application range. Since the preparation process of hollow fiber membranes includes an extraction step to remove diluent and form a microporous structure in the cross-sectional direction, this invention uses powdered flame retardants. Powdered flame retardants are not dissolved by the extractant, thus avoiding flame retardant loss during the extraction step. Furthermore, if liquid flame retardants are used, the amount extracted by the extractant is uncontrollable and unpredictable, hindering stable control of the porosity, pore size, and pore distribution of the microporous structure in the cross-section, leading to unstable performance of the hollow fiber membrane. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] in:

[0018] Figure 1 This is a macroscopic structural diagram of flame-retardant polyolefin hollow fiber membrane filaments collected on a winding wheel according to a specific embodiment of the present invention.

[0019] Figure 2 This is a microstructure diagram of a single filament cross-section of a flame-retardant polyolefin hollow fiber membrane filament prepared according to a specific embodiment of the present invention.

[0020] Figure 3 This is a microstructure diagram of the dense structure of the outer surface layer of a single membrane filament of a flame-retardant polyolefin hollow fiber membrane filament prepared according to a specific embodiment of the present invention.

[0021] Figure 4 This is a microstructure diagram of the internal structure of a single membrane filament of a flame-retardant polyolefin hollow fiber membrane filament prepared according to a specific embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention discloses a flame-retardant polyolefin hollow fiber membrane, the raw materials of which include the following components by mass percentage: 20%–50% polyolefin, 20%–50% flame retardant, and 20%–58% diluent; wherein the flame retardant is in powder form. By adding flame retardant, the polyolefin hollow fiber membrane acquires inherent flame-retardant function, broadening its application range. Since the preparation process of hollow fiber membranes includes an extraction step to remove the diluent and form a microporous structure in the cross-sectional direction, using a powdered flame retardant avoids dissolution by the extractant. This prevents flame retardant loss during the extraction step. Furthermore, if a liquid flame retardant is used, the amount extracted by the extractant is uncontrollable and unpredictable, hindering stable control of the porosity, pore size, and pore distribution of the microporous structure in the cross-section, leading to unstable performance of the hollow fiber membrane.

[0024] In the above scheme, the diluent is used on the one hand as a flux to enhance the fluidity of the casting liquid and facilitate the uniform mixing of the components, and on the other hand as a pore-forming agent to form a microporous structure on the cross-section of the hollow fiber membrane.

[0025] In one specific embodiment, the polyolefin may include one or more of polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylate copolymer, poly-1-butene, poly-1-pentene-poly-1-hexene, poly-1-octene, poly(4-methyl-1-pentene), and polycyclic olefins. Preferably, the polyolefin includes polypropylene and / or poly(4-methyl-1-pentene).

[0026] In one specific embodiment, the diluent may include one or more of the following: diethyl phthalate (DEP), dibutyl phthalate (DBP), di-n-octyl phthalate (DOP), di(2-ethylhexyl) phthalate (DEHP), dibutyl terephthalate (DOTP), and diphenyl phthalate (DPE).

[0027] In one specific embodiment, the flame retardant may include inorganic flame retardants (e.g., aluminum hypophosphite, aluminum hydroxide, magnesium hydroxide, microencapsulated red phosphorus, silicon micropowder (preferably)). (Dow Corning, US) and organic flame retardants (e.g., nitrogen-phosphorus intumescent flame retardants and / or triazine compound micropowders).

[0028] Preferably, the flame retardant is an organic flame retardant, with a mass percentage of 20%–30%. Organic flame retardants have strong compatibility with polyolefins and have minimal impact on the mechanical properties of polyolefin hollow fiber membranes. Surprisingly, experimental verification shows that to achieve the highest flame retardant rating of UL94-V0 for polyolefin hollow fiber membranes, the amount of organic flame retardant added is significantly less than that of inorganic flame retardants. The less flame retardant added, the less impact it has on the mechanical properties, pore morphology, fluid flux, and other indicators of the polyolefin hollow fiber membrane. Furthermore, since the additive is solid, it increases the viscosity of the molten casting solution. This makes the casting solution prone to breakage when extruded through a twin-screw extruder or spinneret, making it difficult to form a continuous fluid and hindering the use of spinning methods. By using powdered organic flame retardants, the amount of flame retardant can be significantly reduced to less than 30%, simplifying the preparation process.

[0029] Specifically, in one embodiment, the organic flame retardant includes a nitrogen-phosphorus intumescent flame retardant and / or triazine compound micropowder. More specifically, the nitrogen-phosphorus intumescent flame retardant may include the ADK STAB FP-2000 series, and the triazine compound micropowder includes poly(2-ethanolamino-4,6-ethylenediamino-1,3,5-triazine) (molecular formula: (C7H...). 12 ON6) n (n = 15 to 35).

[0030] Furthermore, the raw material also includes the following components by weight percentage: 0.1% to 5% flame retardant auxiliaries; the flame retardant auxiliaries include polytetrafluoroethylene micropowder (PTFE micropowder) and / or triazine compound micropowder (CFA micropowder). The triazine compound micropowder may include poly(2-ethanolamino-4,6-ethylenediamino-1,3,5-triazine) (molecular formula: (C7H...). 12 ON6) n (n = 15-35). The above-mentioned flame retardant synergists have a synergistic effect on nitrogen-phosphorus intumescent flame retardants, achieving the same flame retardant rating. The synergistic effect of the flame retardant synergists and flame retardants can further reduce the amount of flame retardant used. The total content of organic flame retardants and flame retardant synergists can be reduced to 20%-25%, which is very important for the performance of the membrane fibers and the ease of preparation. During combustion, nitrogen-phosphorus intumescent flame retardants expand to isolate air and heat, achieving a flame retardant effect. Polytetrafluoroethylene micropowder can enhance the anti-dripping properties of the expanded nitrogen-phosphorus intumescent flame retardants, prevent expansion and cracking, and enhance the flame retardant effect. Triazine compounds can serve as a char source for nitrogen-phosphorus intumescent flame retardants, thereby enhancing their flame retardant effect. The addition of flame retardant synergists can reduce the amount of nitrogen-phosphorus intumescent flame retardants used.

[0031] In one specific embodiment, the total mass percentage of the flame retardant facilitator and the organic flame retardant is 20% to 25%.

[0032] In one specific embodiment, the raw material further includes the following components by weight percentage: 1% to 5% antioxidant, which is used to prevent polymer degradation during high-temperature melting.

[0033] Specifically, in one embodiment, the antioxidant includes one or more of the following: tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168), 2,6-di-tert-butyl-p-cresol (antioxidant BHT), pentaerythritol tetra(3-lauryl thiopropionate) (antioxidant 412s), β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol (antioxidant 1076), and N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine (antioxidant 1098).

[0034] This invention also discloses a method for preparing the above-mentioned flame-retardant polyolefin hollow fiber membrane, comprising the following steps:

[0035] 1) Melt the components of the raw material to obtain the casting solution;

[0036] 2) The casting solution is extruded from the annular spinneret and solidified in the cooling bath through the air gap to obtain a hollow fiber primary membrane;

[0037] 3) Extract the primary membrane to remove the diluent and form a microporous structure to obtain the secondary membrane;

[0038] 4) The secondary membrane is dried to obtain a flame-retardant polyolefin hollow fiber membrane.

[0039] In process 1) above, the melting temperature is 180℃~280℃.

[0040] In process 2) above, the inner diameter of the annular spinneret is 5μm-500μm, the outer diameter is 10μm-1000μm, the air gap is 0.5mm-500mm, the spinning speed is 5m / min-500m / min, and the cooling bath temperature is -30℃-80℃. The addition of a powdered flame retardant increases the viscosity of the casting solution, thus resulting in a slower spinning speed.

[0041] In process 3) above, the extractant can be one or more of the following: diethyl ether, propyl ether, butyl ether, methanol, ethanol, isopropanol, ethyl acetate, propyl acetate, butyl acetate, pentyl acetate, acetone, butanone, cyclohexanone, ethylene glycol dimethyl ether, ethylene glycol butyl ether, tetrahydrofuran, dichloromethane, chloroform, DMF, and DMAc; the extraction time is 10 h to 100 h.

[0042] In process 3) above, the drying temperature is 30℃-300℃ and the drying time is 0.2h-120h.

[0043] The following are specific examples.

[0044] As shown in Table 1, the raw material composition ratios of Examples 1 to 10 are provided. Examples 1 to 10 are specific examples where the amount of flame retardant added is the minimum when the flame retardant rating reaches the highest flame retardant rating UL94-V0.

[0045] Table 1: Proportion of each component of raw materials in each embodiment

[0046]

[0047] The preparation method includes the following steps:

[0048] The raw materials were stirred and mixed at 160℃ to obtain a uniform casting solution. After micro-vacuum degassing, the casting solution entered a twin-screw extruder and was extruded through a 160℃ spinneret (inner diameter: 100μm, outer diameter: 200μm) to form hollow fibers. These fibers were then passed through an air gap and placed in a cooling bath for curing. Finally, the fibers were extracted and dried with ethanol to obtain an intrinsically flame-retardant hollow fiber membrane. The air gap was 80mm, the cooling bath consisted of a -8℃ deionized water / ethylene glycol solution, the spinning speed was 80m / min, the residence time in the cooling bath was 2s, the drying temperature was 120℃, and the drying time was 1h.

[0049] Test case

[0050] The structure of the flame-retardant polyolefin hollow fiber membrane prepared by this invention was characterized, such as... Figures 1-4 As shown.

[0051] from Figure 1 As can be seen, the hollow fiber membrane filaments spun by this invention are flat and smooth, with no large pore defects on the surface and no yellowing caused by oxidation.

[0052] from Figures 2-4 As can be seen, the flame-retardant polyolefin hollow fiber membrane prepared by this invention has a stable microstructure and a dense surface layer and a sponge-like inner core layer.

[0053] Gas permeability was tested according to the GB / T 40260-2021 standard, and the results are shown in Table 2.

[0054] Table 2: Gas Permeability Test Results

[0055]

[0056] Mechanical properties were tested using the ASTM D638 standard, and the results are shown in Table 3.

[0057] Table 3: Mechanical Performance Test Results

[0058]

[0059] As can be seen from Table 1 above, when the flame retardant rating UL94-V0 is achieved, the amount of inorganic flame retardant added in Examples 1 to 5 alone is 29% to 50%, which is significantly greater than that of organic flame retardants (20% to 27%, Examples 7 to 13). When flame retardant synergists are used to synergistically retard organic flame retardants (Examples 8, 9, 11 to 13), the total content of flame retardants and synergists can be further reduced.

[0060] As can be seen from Table 2, the more flame retardant added, the worse the gas flux and gas selectivity of the membrane fibers become. It is preferable to add organic flame retardants and flame retardant auxiliaries, as they have little impact on the gas flux and gas selectivity of the membrane fibers. In particular, when the total content of flame retardants and auxiliaries is 20% to 25%, it has virtually no impact on the gas flux and gas selectivity of the membrane fibers. This can impart excellent flame retardant properties to the membrane fibers while ensuring their gas flux and selectivity.

[0061] As shown in Table 3, when inorganic flame retardants were used in Examples 1-5, the elongation at break dropped sharply. In Examples 7-13, the use of organic flame retardants ensured sufficient toughness of the membrane fibers, guaranteeing that the fibers could be woven into a block. Examples 1-13 also show that adding flame retardants significantly improved the tensile strength and elastic modulus of the membrane fibers, meaning the stiffness of the fibers was improved. This ensured that the hollow cavity of the membrane fibers would not collapse or become blocked during subsequent weaving or use, maintaining the stability of the membrane fiber's internal cavity.

[0062] In summary, while maintaining the membrane fiber gas flux and gas selectivity essentially unchanged, organic flame retardants are preferred, and more preferably, flame retardant auxiliaries are further combined.

[0063] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A flame-retardant polyolefin hollow fiber membrane, characterized in that, Its raw materials include the following components by mass percentage: 20%~50% polyolefin, 20%~30% organic flame retardant, 0.1%~5% flame retardant auxiliaries, 1%~5% antioxidant, and 20%~58% diluent; The organic flame retardant is in powder form and is a nitrogen-phosphorus intumescent flame retardant; the flame retardant auxiliaries include polytetrafluoroethylene micropowder and / or triazine compound micropowder.

2. The flame-retardant polyolefin hollow fiber membrane according to claim 1, characterized in that, The total mass percentage of the flame retardant facilitator and the organic flame retardant is 20% to 25%.

3. The flame-retardant polyolefin hollow fiber membrane according to claim 1, characterized in that, The nitrogen-phosphorus intumescent flame retardant includes the ADK STAB FP-2000 series; the triazine compound micron powder includes poly(2-ethanolamino-4,6-ethylenediamino-1,3,5-triazine) with the molecular formula (C7H). 12 ON6) n , where n = 15~35.

4. The flame-retardant polyolefin hollow fiber membrane according to claim 1, characterized in that, The polyolefins include one or more of polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene acrylate copolymer, poly-1-butene, poly-1-pentene, poly-1-hexene, poly-1-octene, poly(4-methyl-1-pentene), and polycyclic olefins. The diluent includes one or more of diethyl phthalate, dibutyl phthalate, di-n-octyl phthalate, di(2-ethylhexyl) phthalate, dibutyl terephthalate and di-n-octyl terephthalate, di(2-ethylhexyl) terephthalate and diphenyl ether.

5. The flame-retardant polyolefin hollow fiber membrane according to claim 1, characterized in that, The antioxidants include one or more of the following: tris(2,4-di-tert-butylphenyl) phosphite, 2,6-di-tert-butyl-p-cresol, pentaerythritol tetra(3-lauryl thiopropionate), β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester, and N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine.

6. A method for preparing a flame-retardant polyolefin hollow fiber membrane as described in any one of claims 1 to 5, characterized in that, Includes the following processes: The components of the raw material are melted to obtain a casting solution; The casting solution is extruded from an annular spinneret and solidified in a cooling bath through an air gap to obtain a hollow fiber primary membrane. The primary membrane is extracted to remove the diluent, forming a microporous structure to obtain a secondary membrane; The secondary membrane is dried to obtain the flame-retardant polyolefin hollow fiber membrane.

Images