Method for forming crosslinked polymer films

Abstract

A method for forming a crosslinked polymer membrane is provided, comprising contacting a polymer membrane with a crosslinking solution to form a crosslinked polymer membrane, the crosslinking solution comprising a crosslinker containing at least one acyl halide functional group dissolved in a polar protic solvent. A crosslinked polymer membrane is also provided. In a preferred embodiment, hollow fiber polybenzimidazole (PBI) is crosslinked with trimesoyl chloride (TMC) or isophthaloyl chloride (IPC) in a solvent of ethanol or isopropyl alcohol (IPA).

Description

[Technical Field]

[0001] The present invention relates to a method for forming a crosslinked polymer film and the crosslinked polymer film formed therefrom. [Background technology]

[0002] Organic solvent nanofiltration (OSN) is a new membrane-based separation technology that can be directly used in current manufacturing systems. OSN is a cost-effective separation technique compared to adsorption, flash chromatography, evaporation, and distillation, which are usually energy intensive and use high temperatures and / or large amounts of solvent, thereby leading to higher production costs and environmental issues, and resulting in lower quality products.

[0003] The chemical stability of OSN membranes in harsh organic solvents remains a concern. Polybenzimidazole (PBI) membranes have been considered because they are chemically stable and exhibit good rejection, but most of the methods for fabricating PBI membranes utilize harmful and toxic solvents and chemicals.

[0004] WO2019 / 209177 discloses a method for crosslinking polymer membranes, but the crosslinking yield is not considered to be adequate enough for the method to be used on a large scale.

[0005] Therefore, there is a need for improved methods that are low-cost, environmentally friendly, and easily scalable to form high-yield crosslinked membranes, especially for OSN applications. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention seeks to address these challenges and / or provide improved methods for forming crosslinked polymer membranes, particularly, but not exclusively, polymer membranes suitable for organic solvent nanofiltration. [Means for solving the problem]

[0007] According to a first aspect, the present invention provides a method of forming a crosslinked polymer membrane, comprising contacting a polymer membrane with a crosslinking solution to form a crosslinked polymer membrane, the crosslinking solution comprising a crosslinker comprising at least one acyl halide functional group dissolved in a polar protic solvent.

[0008] According to a particular embodiment, the polymeric film can be formed from at least one polymer. Specifically, the at least one polymer can include at least one pyrrole nitrogen group. For example, the at least one polymer can be, but is not limited to, polybenzimidazole (PBI).

[0009] The polymer membrane may be, but is not limited to, a flat membrane, a hollow fiber membrane, a tubular membrane, or a dense membrane.

[0010] The crosslinking agent included in the crosslinking solution may be any suitable crosslinking agent containing at least one acyl halide functional group. In particular, the crosslinking agent may contain at least two or three acyl halide groups. According to certain embodiments, the at least one acyl halide functional group may be an acyl chloride functional group. For example, the at least one crosslinking agent may be, but is not limited to, trimesoyl chloride (TMC), isophthaloyl chloride (IPC), terephthaloyl chloride, or a combination thereof.

[0011] The crosslinking solution may include any suitable polar protic solvent. According to certain embodiments, the polar protic solvent may include, but is not limited to, an alcohol, a carboxylic acid, or a mixture thereof, where the alcohol is not a tertiary alcohol. In particular, the polar protic solvent may include, but is not limited to, methanol, ethanol, isopropyl alcohol (IPA), or a mixture thereof.

[0012] The cross-linking solution may contain a suitable amount of a cross-linking agent, particularly, 0.01 to 20% (w / w) of the cross-linking agent.

[0013] According to certain embodiments, the contacting may be at a predetermined temperature for a predetermined period of time. For example, the predetermined temperature may be from 5 to 100° C. For example, the predetermined period of time may be from 1 minute to 120 hours.

[0014] The method may further include performing a solvent exchange on the polymer membrane prior to the contacting. For example, performing the solvent exchange may include performing a solvent exchange with a polar protic solvent included in the crosslinking solution.

[0015] According to a particular embodiment, the crosslinked polymer membrane may have a thickness of 1 to 1000 μm.

[0016] According to another particular aspect, the cross-linked polymer membrane may be hydrophilic.

[0017] According to a second aspect, there is provided a crosslinked polymer membrane prepared from the method of the first aspect.

[0018] The present invention also provides a crosslinked polymer membrane comprising a polymer membrane crosslinked with a crosslinking agent comprising at least one acyl halide functional group, the crosslinked polymer membrane having a polymer gel content of ≧95% after polymer dissolution.

[0019] The polymer film may be any suitable polymer film. According to a particular embodiment, the polymer film may be as described above with respect to the first embodiment. In particular, the polymer film may be formed from a polymer comprising at least one pyrrolic nitrogen group.

[0020] The cross-linking agent may be any suitable cross-linking agent. According to a particular embodiment, the cross-linking agent may be as described above in relation to the first embodiment.

[0021] According to a particular embodiment, the cross-linked polymer membrane may be hydrophilic.

[0022] In order that the invention may be more fully understood and readily carried out in practice, exemplary embodiments will now be described, by way of non-limiting example only, with reference to the accompanying exemplary drawings, in which: [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 shows polymer gel % and absorbance values ​​for membranes crosslinked in ethanol, isopropyl alcohol (IPA), and tert-butanol. [Figure 2] FIG. 1 shows UV-Vis analysis of XPBI in neat DMAc (except tert-butanol at 10× dilution) and NXPBI (200× dilution). [Figure 3] FIG. 1 shows the assignment of chromophores of dissolved compounds. [Figure 4] FIG. 1 shows an ATR-FTIR comparison of NXPBI and XPBI(NH) stretching. [Figure 5] FIG. 1 shows an ATR-FTIR comparison of NXPBI and XPBI (C═N and imidazole ring stretching). [Figure 6] FIG. 1 illustrates a possible mechanism for polar protic solvents. [Figure 7] FIG. 1 illustrates a possible mechanism for solvent forming undesired reactions. [Figure 8] FIG. 1 shows the gel content (percentage mass loss) of crosslinked PBI membranes. [Figure 9] FIG. 1 shows the absorbance of non-crosslinked polymer in DMAc. [Figure 10] FIG. 1 shows crosslinked membrane performance (permeability and rejection). [Figure 11] FIG. 1 shows possible reaction pathways for PBI and IPC. [Figure 12] FIG. 1 shows the proposed cross-linking reaction between PBI and IPC. DETAILED DESCRIPTION OF THE INVENTION

[0024] As explained above, there is a need for improved methods for forming high yield crosslinked membranes that are particularly suitable for organic solvent nanofiltration (OSN), among other applications.

[0025] Membrane separation processes, namely organic solvent nanofiltration, gas separation, fuel cells, aqueous solution separation, and pervaporation, are considered to be energy-efficient and valuable processes in the fine chemical, food, pharmaceutical, petrochemical, and petroleum industries. These processes require stable and high-performance membranes.

[0026] Generally speaking, the present invention relates to improved crosslinked polymer membranes and methods for forming the same. In particular, the crosslinked polymer membranes may be, but are not limited to, those for organic solvent nanofiltration and may be resistant to dissolution in harsh organic solvents. Furthermore, the methods of the present invention may be environmentally friendly. In particular, the methods do not utilize any harmful or toxic solvents or chemicals. Furthermore, the methods of the present invention may be simple and therefore easily scalable on an industrial scale.

[0027] According to a first aspect, the present invention provides a method of forming a crosslinked polymer membrane, comprising contacting a polymer membrane with a crosslinking solution to form a crosslinked polymer membrane, the crosslinking solution comprising a crosslinker comprising at least one acyl halide functional group dissolved in a polar protic solvent.

[0028] The polymer film may be formed from at least one polymer. The polymer may be any suitable polymer. In particular, the polymer may include at least one nitrogen (N) atom nucleophile. The at least one N atom nucleophile may be at least one pyrrolic nitrogen (-NH-) group. Even more particularly, the at least one N atom nucleophile may be a pyridine N of an imidazole group. For example, the at least one polymer may be, but is not limited to, polybenzimidazole (PBI).

[0029] The method may further include forming a polymer membrane from a polymer solution containing at least one polymer before providing. For example, the at least one polymer may be dissolved in a suitable solvent to form a polymer solution. According to certain aspects, the method may further include preparing a polymer solution before forming the polymer membrane, the preparation comprising mixing at least one polymer in a first solvent. The first solvent may be any suitable solvent. For example, the first solvent may be any solvent in which the at least one polymer can be dissolved and which is compatible with the membrane application. For example, the solvent may be dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), 1-ethyl-3-methylimidazolium acetate ([EMIM]-OAc), tetrahydrofuran (THF), dichloromethane (DCM), or a mixture thereof. According to certain embodiments, the polymer solution may include PBI dissolved in DMAc.

[0030] The polymer solution may contain a suitable amount of at least one polymer. For example, the polymer solution may contain 2-40% (weight / weight (w / w)) of at least one polymer. In particular, the polymer solution may contain 5-30 w / w%, 7-25 w / w%, 10-22 w / w%, 12-20 w / w%, or 15-17 w / w% of at least one polymer. Even more particularly, the polymer solution may contain about 15-17 w / w% of at least one polymer.

[0031] The polymer membrane may be, but is not limited to, a flat membrane, a hollow fiber membrane, a tubular membrane, or a dense membrane. The polymer membrane may be an integral-skin asymmetric membrane. Forming the polymer membrane may include any suitable method for preparing a polymer membrane. For example, if the polymer membrane is a hollow fiber membrane, forming it may include spinning a polymer solution under appropriate conditions. For example, if the polymer membrane is dense, forming it may include a solvent evaporation method under appropriate conditions. According to certain embodiments, forming may include a non-solvent-induced phase separation (NIPS) technique.

[0032] The crosslinking agent included in the crosslinking solution may be any suitable crosslinking agent. The crosslinking agent may include at least one acyl halide functional group. For example, the crosslinking agent may include at least two or three acyl halide functional groups. The acyl halide functional group may be a chlorine- or bromine-containing acyl functional group or an acyl group containing a mixture of halides. According to certain embodiments, the at least one acyl halide functional group may be an acyl chloride functional group. The crosslinking agent may be environmentally friendly and non-toxic. For example, the crosslinking agent may be, but is not limited to, trimesoyl chloride (TMC), isophthaloyl chloride (IPC), terephthaloyl chloride, or a combination thereof. In particular, the crosslinking agent may be TMC.

[0033] At least one crosslinking agent may be dissolved in a suitable solvent to form a crosslinking solution. The solvent may be a polar solvent. In particular, the solvent may be a polar protic solvent. According to certain aspects, the method may further include preparing the crosslinking solution prior to the contacting, where the preparation includes mixing the crosslinking agent in a polar protic solvent. The polar protic solvent may be any suitable polar protic solvent. In particular, the polar protic solvent may be any polar protic solvent in which the crosslinking agent can be dissolved and which is compatible with membrane applications. The polar protic solvent may be environmentally friendly and non-toxic. The polar protic solvent may include, but is not limited to, an alcohol, a carboxylic acid, or a mixture thereof, where the alcohol is not a tertiary alcohol. In particular, the polar protic solvent may be, but is not limited to, methanol, ethanol, isopropyl alcohol (IPA), or a mixture thereof. Even more particularly, the polar protic solvent may be IPA. According to certain embodiments, the crosslinking solution may include TMC dissolved in IPA.

[0034] The use of a polar protic solvent allows for favorable interactions, particularly hydrogen bonding interactions, with both the crosslinker and the polymer membrane, thereby improving mass transfer from the crosslinker into the polymer membrane. Furthermore, the polar protic solvent does not react with either the crosslinker or the polymer membrane in a way that would result in the formation of undesired products, thus enabling 100% product yield. In this way, consistent product quality can be achieved with reproducible results. Another advantage of using a polar protic solvent is that the crosslinking solution can be recycled, since the formation of undesired by-products does not occur, thereby reducing chemical usage and waste generation. The lack of any side reactions also allows the crosslinking solution to be prepared at any time prior to the contacting step. For example, the crosslinking solution may be prepared immediately before contacting or at least one day before contacting. This is important on an industrial scale, as it is not always necessary to prepare the crosslinking solution fresh, and therefore any delay in the further production step does not result in waste of the already prepared crosslinking solution.

[0035] The crosslinking solution may contain an appropriate amount of crosslinker. For example, the crosslinking solution may contain 0.01 to 20% (weight / weight (w / w)) of the crosslinking agent. In particular, the crosslinking solution may contain 0.05 to 18 w / w%, 0.1 to 15 w / w%, 0.5 to 12 w / w%, 1 to 10 w / w%, 2 to 9 w / w%, 3 to 8 w / w%, 4 to 7 w / w%, or 5 to 6 wt / wt% of the crosslinking agent. Even more particularly, the crosslinking solution may contain about 0.1 to 2 w / w% of the crosslinking agent.

[0036] The contacting step may include any suitable method for cross-linking the polymer film with the cross-linking solution. The contacting step may include cross-linking the polymer film such that the entire polymer film is cross-linked. For example, the contacting step may include immersing the polymer film in the cross-linking solution.

[0037] The contacting step may be performed at a predetermined temperature. For example, the predetermined temperature may be 5 to 100°C. In particular, the predetermined temperature may be 10 to 90°C, 15 to 85°C, 20 to 80°C, 25 to 75°C, 30 to 70°C, 35 to 65°C, 40 to 60°C, 45 to 55°C, or 50 to 52°C. Even more particularly, the predetermined temperature may be 20 to 50°C. According to a particular embodiment, the contacting step may be performed at room temperature. In particular, the contacting step may be performed without the application of any heat.

[0038] The contacting step may be for a predetermined period of time. The predetermined period of time may be any suitable length of time to allow a crosslinking reaction between the polymer membrane and the crosslinking agent to occur, whereby the polar protic solvent facilitates mass transfer of the crosslinking agent through favorable interactions, such as hydrogen bonding interactions, with both the polymer membrane and the crosslinking agent. For example, the contacting step may be for a suitable period of time to allow complete crosslinking of the polymer membrane. For example, the predetermined period of time may be from 1 minute to 120 hours. Specifically, the predetermined period of time may be from 5 minutes to 100 hours, 0.5 to 96 hours, 1 to 72 hours, 5 to 60 hours, 6 to 48 hours, 12 to 36 hours, or 18 to 24 hours. Even more specifically, the predetermined period of time may be from 1 minute to 48 hours, particularly from 5 minutes to 6 hours. According to one particular embodiment, the contacting step may be for 5 minutes to 6 hours at a temperature of 20 to 50°C.

[0039] The contacting step may further include agitating the crosslinking solution and the polymer film during the contacting step to ensure uniformity of crosslinking throughout the polymer film. Agitation may occur throughout the entire contacting step or for only a period during the contacting step. According to certain embodiments, agitation may include continuous or intermittent recirculation of the crosslinking solution during the contacting step. According to another particular embodiment, agitation may include moving the polymer film through the crosslinking solution during the contacting step.

[0040] The method may further include performing a solvent exchange on the polymer membrane before and / or after the contacting step. According to certain embodiments, the method may include performing a solvent exchange on the polymer membrane either before or after the contacting step. According to another particular embodiment, the method may include performing a solvent exchange on the polymer membrane before and after the contacting step. For example, performing a solvent exchange may include performing a solvent exchange with the polar protic solvent contained in the crosslinking solution. However, if the polymer membrane is stored after formation using the same polar protic solvent as in the crosslinking solution, solvent exchange does not need to be performed on the polymer membrane before the contacting step.

[0041] The solvent exchange may be carried out for a suitable period of time. For example, the solvent exchange may be carried out for 1 minute to 48 hours. Specifically, the solvent exchange may be carried out for 5 minutes to 42 hours, 0.25 to 36 hours, 0.5 to 30 hours, 1 to 24 hours, 2 to 20 hours, 3 to 18 hours, 5 to 15 hours, 6 to 12 hours, 7 to 10 hours, or 8 to 9 hours. Even more specifically, the solvent exchange may be carried out for 1 to 6 hours.

[0042] The solvent may be exchanged a sufficient number of times. For example, the solvent may be exchanged 1 to 20 times. In particular, the solvent may be exchanged 1 to 20 times, 2 to 18 times, 5 to 15 times, 7 to 12 times, or 8 to 10 times. Even more particularly, the solvent may be exchanged 1 to 5 times.

[0043] The solvent exchange may be carried out at any suitable temperature. For example, the solvent exchange may be carried out at a temperature of 5 to 100°C. In particular, the solvent exchange may be carried out at a temperature of 5 to 100°C, 10 to 90°C, 15 to 75°C, 20 to 70°C, 25 to 65°C, 30 to 60°C, or 35 to 45°C. Even more particularly, the solvent exchange may be carried out at room temperature, about 25°C.

[0044] According to a particular embodiment, the solvent exchange may be performed 1 to 5 times, each solvent exchange lasting 1 to 6 hours at a temperature of about 25°C.

[0045] According to a particular embodiment, the formed crosslinked polymer film may have a thickness of 1 to 1000 μm, for example, 5 to 900 μm, 10 to 750 μm, 25 to 500 μm, 50 to 250 μm, or 100 to 200 μm.

[0046] The crosslinked polymer film formed may be hydrophilic. In particular, the static water contact angle of the crosslinked polymer film formed may be 50 to 90°. Even more particularly, the static water contact angle of the crosslinked polymer film formed may be 60 to 85°.

[0047] The crosslinked polymer film formed may have a suitable gel polymer content. According to certain embodiments, the polymer gel content of the crosslinked polymer film formed may be ≥95% after polymer dissolution. For purposes of the present invention, the polymer gel content may be considered to be the crosslinking yield and may indicate the chemical stability of the polymer film after dissolution in a harsh organic solvent. The polymer dissolution may be over a suitable period of time. For example, the polymer dissolution may be over a period of 48 to 100 hours. The organic solvent may be any suitable solvent, such as, but not limited to, dimethylacetamide (DMAc). In particular, the crosslinked polymer film formed from the method of the present invention may have a polymer gel content of 95 to 100%, 96 to 99%, or 97 to 98%. Even more particularly, the crosslinked polymer film formed may have a polymer gel content of ≥98%, particularly about 100%, after polymer dissolution.

[0048] Most of the prior art methods, such as PBI crosslinking methods, require multiple steps, high temperatures, or the use of hazardous chemicals. In contrast, the method of the present invention can be carried out at room temperature, involves a single crosslinking step, utilizes an environmentally friendly crosslinking technique that is easily scalable, and does not require long periods of time to complete crosslinking. Therefore, the method of the present invention is believed to be suitable for preparing PBI-based OSN films.

[0049] The present invention provides a simple and reliable method that does not utilize harsh process conditions. In particular, the method of the present invention is relatively short while achieving high crosslinking yields. As such, the method of the present invention is believed to be suitable for industrial-scale production of crosslinked polymer membranes of consistent quality.

[0050] According to a second aspect, there is provided a crosslinked polymer membrane prepared from the method of the first aspect.

[0051] A third aspect of the present invention provides a crosslinked polymer membrane comprising a polymer membrane crosslinked with a crosslinker comprising at least one acyl halide functional group, the crosslinked polymer membrane having a polymer gel content of ≧95% after polymer dissolution.

[0052] In particular, the crosslinked polymer membrane may have a polymer gel content of 95-100%, 96-99%, or 97-98%. Even more particularly, the crosslinked polymer membrane may have a polymer gel content of ≥ 98%, especially about 100%, after polymer dissolution when immersed in an organic solvent for 2-100 hours, especially 48-100 hours.

[0053] The polymer film may be any suitable polymer film. According to a particular embodiment, the polymer film may be as described above in relation to the first embodiment. In particular, the polymer film may be formed from a polymer containing at least one pyrrole nitrogen group. For example, the at least one polymer may be, but is not limited to, polybenzimidazole (PBI).

[0054] The polymeric membrane may be, but is not limited to, a flat membrane, a hollow fiber membrane, a tubular membrane, or a dense membrane. The polymeric membrane may be an integral skin asymmetric membrane. In particular, the polymeric membrane may be a hollow fiber membrane.

[0055] The cross-linking agent may be any suitable cross-linking agent. According to a particular embodiment, the cross-linking agent may be as described above in relation to the first embodiment.

[0056] According to a specific embodiment, the crosslinked polymer membrane may be hydrophilic. Furthermore, the formed crosslinked polymer membrane may have a thickness of 1 to 1000 μm. For example, the thickness may be 5 to 900 μm, 10 to 750 μm, 25 to 500 μm, 50 to 250 μm, or 100 to 200 μm.

[0057] Crosslinked polymer membranes may be used in many different applications, including but not limited to organic solvent nanofiltration (OSN), gas separation, aqueous solution separation, pervaporation, and fuel cells.

[0058] Having now generally described the invention, the same will be more readily understood through reference to the following embodiments, which are provided by way of illustration and not limitation. [Example]

[0059] [Example 1] Ethanol / isopropyl alcohol (IPA) / tert-butanol as solvents (Membrane production) The solvents used were ethanol, isopropyl alcohol (IPA), or tert-butanol. All solvents used had a purity greater than 99.5%.

[0060] 150 mg of hollow fiber polybenzimidazole (PBI) fibers were placed in a reactor (35 mL glass bottle) for solvent exchange with IPA. All fibers were immersed in 35 mL of fresh IPA for 2 hours. The fibers were then left immersed in the fresh IPA for 24 hours. Subsequently, the fibers were immersed in 10 mL of the solvent (ethanol / IPA / tert-butanol) to be used for crosslinking for 2 hours, and then left immersed in the fresh solvent for 24 hours. The fibers were subsequently immersed in each of the fresh solvents (ethanol / IPA / tert-butanol) for 2 hours before the crosslinking step.

[0061] The solvent was drained from the reactor and the crosslinking solution was poured into the reactor. The crosslinking reaction was carried out at room temperature for 2 hours.

[0062] The crosslinking solution was then drained and the fibers were solvent exchanged with 35 mL of fresh solvent three times, with a duration of 30 min per soak. The fibers were then solvent exchanged with 35 mL of fresh IPA four times, with a duration of 30 min per solvent exchange.

[0063] (characterization) ·Weight measurement: Two 320 mm long fibers were randomly selected from each experimental run and cut into short strips measuring 20 mm each.

[0064] The fibers were lightly blotted with tissue paper, then rinsed four times with reverse osmosis (RO) water for 30 minutes each, and then dried in an oven at 105° C. The fibers were dried until a constant weight was achieved, which was referred to as the "initial fiber weight."

[0065] Another two fibers were randomly selected and gently wiped to remove excess IPA. The fibers were then cut into short strips measuring 20 mm each and immersed in 35 mL or 20 mL of dimethylacetamide (DMAc) (>99.5%) for 100 hours. The fibers were then removed and gently wiped with tissue paper to remove excess DMAc. The fibers were rinsed four times with 50 mL of RO water for 30 minutes each, then removed and gently wiped with tissue paper. The fibers were further dried in an oven at 105°C. The fibers were dried to a constant weight, which is referred to as the "final fiber weight."

[0066] Determination of polymer gel content %: The % polymer gel content was calculated using the formula:

[0067]

number

[0068] ·UV-Vis analysis: Crosslinked PBI polymer membranes are referred to as XPBI, while non-crosslinked PBI polymer membranes are referred to as NXPBI.

[0069] UV-VIS analysis was performed undiluted and for NXPBI, except for XPBI, which used tert-butanol as the solvent, in which case the tert-butanol was diluted 10× before UV-Vis analysis was performed.

[0070] (result) Results from crosslinked PBI polymer membranes using various solvents to dissolve the crosslinker are described below.

[0071] ·Weight measurement: Table 1 shows the initial and final fiber weights.

[0072] [Table 1]

[0073] Determination of polymer gel content %: Table 2 shows the % polymer gel (i.e., degree of crosslinking) using various solvents for 0.5 mmol TMC:10 mL solvent:150 mg PBI fiber over a 2 hour crosslinking time. The crosslinked fiber was dissolved in DMAc for 100 hours.

[0074] [Table 2]

[0075] Due to experimental error, the polymer gel percentage may be greater than 100%. The results suggest that for polar solvents, except for tert-butanol, the solvent facilitates mass transfer of the crosslinker, allowing the reaction between the crosslinker and the membrane to occur easily. The solvent also minimizes or eliminates the formation of undesired by-products, thereby achieving a high yield (crosslinked membrane). Furthermore, although the solvent may participate in the reaction as an autocatalyst, the yield (crosslinked membrane) was not reduced, as seen in the low absorbance values ​​and polymer gel percentage (Figure 1), due to the lack of formation of other stable products.

[0076] ·UV-Vis analysis: UV-Vis analysis of the dissolved products provided an indication of the type of cross-linking modification occurring in the membrane (Figure 2).

[0077] The formation of a new peak at 284 nm indicates the addition of TMC molecules to the PBI membrane. As can be seen in Figure 2, NXPBI exhibited two distinct peaks at 268 nm and 346 nm, while XPBI exhibited at least three distinct peaks at 268 nm, 284 nm, and 340 nm.

[0078] FIG. 3 shows the UV-Vis chromophore dissolved in DMAc.

[0079] Fourier transform infrared spectroscopy (FTIR) analysis: Fourier transform infrared spectroscopy (FTIR) was used to analyze changes in molecular functional groups before and after crosslinking modification. The loss of the imidazole NH stretch, imidazole ring stretch, and C=N stretch is characteristic of crosslinking reactions when tertiary amides are formed. However, the tertiary amide (C=O) stretch and (C=N) stretch are difficult to identify and differentiate using FTIR spectra due to the numerous overlapping peaks from benzene structures present in that region. Nevertheless, differences in XPBI chemical functional groups based on ATR-FTIR spectra were observed, as can be seen in Figures 4 and 5.

[0080] Figures 6 and 7 show possible mechanisms for solvents: Figure 6 shows a possible mechanism for polar protic solvents such as ethanol or IPA, while Figure 7 shows a possible mechanism for solvents that form undesired reactions, such as tert-butanol.

[0081] Contact angle measurement: Contact angle measurements were performed to determine the hydrophobicity of NXPBI and XPBI(IPA) films (Table 3).

[0082] [Table 3]

[0083] Due to the formation of new amide bonds, the crosslinked membranes were expected to become more hydrophilic. As seen in Table 3, the crosslinked polymer membranes had greater hydrophilic properties than the non-crosslinked polymer membranes.

[0084] [Example 2] Isophthaloyl chloride (IPC) as a crosslinking agent (Membrane production) Pristine PBI hollow fiber membranes were spun using a dry-jet wet-spinning technique. The as-spun fibers were rinsed with water treated with a reverse osmosis system (RO water) to remove residual solvent present in the membrane matrix. The fibers were rinsed four times for 1 hour each. The fibers were solvent exchanged with 800 mL of IPA (>99.5%) for 24 hours to prepare the crosslinks.

[0085] 0.6 g of IPC was dissolved in 2 L of IPA to form a 0.1 mol / L IPC crosslinking solution. The crosslinking solution was stirred until completely dissolved. Five hundred fibers, each 600 mm long, were immersed in the crosslinking solution. A minimum crosslinking solution of 0.2 L / g of fiber was maintained to ensure sufficient crosslinking in the solution. The fibers were then removed from the crosslinking solution and quenched with RO water to stop the crosslinking reaction. The crosslinking times are shown in Table 4.

[0086] [Table 4]

[0087] The RO water was then changed every hour for 4 hours to remove any residual cross-linker and solvent. The cross-linked fibers were again solvent-exchanged with 800 mL of IPA for 24 hours to prepare them for post-processing. The cross-linked fibers were then immersed in 2 L of 60 / 40 weight percent (wt.%) glycerol / IPA for 24 hours to preserve the pores for storage. The fibers were then dried at 25°C in a dehumidifier (<40% relative humidity) before use.

[0088] (characterization) ·Weight measurement: For each data point, 30 fibers of 600 mm length were used. The fibers were cut to approximately 50 mm length for ease of handling. The fibers were immersed in 500 mL of IPA (>99.5%) to remove glycerol from their pores.

[0089] The fibers were then dried in an oven at 70°C for approximately 6 hours to remove residual IPA. The mass of the fibers was measured and recorded as the "initial fiber mass."

[0090] The fibers were then immersed in 100 mL of DMAc (>99.5%) for 36 hours to dissolve the non-crosslinked polymer into the membrane matrix. The fibers were removed from the DMAc solution and transferred to 100 mL of IPA (>99.5%) to remove any residual DMAc. The fibers were then dried in an oven at 70 °C for approximately 6 hours. The mass of the fibers was measured again and recorded as the "final fiber mass."

[0091] Determination of polymer gel content %: The % polymer gel content was calculated using the formula:

[0092]

number

[0093] UV-Vis analysis: The polymer dissolved in DMAc solution was also measured using a Thermo Fisher Scientific GENESYS 50 Vis spectrophotometer. A set of uncrosslinked fibers was dissolved in DMAc to obtain the maximum absorbance of the polymer under UV-Vis. The solution was diluted to the appropriate concentration to ensure accurate data from the instrument.

[0094] Peaks were obtained at 268 nm and 345 nm and used to calculate the gel content using the following formula, where i is the sample name with respect to the crosslinking time, and XL and NXL are the absorbance values ​​of the solution from crosslinked and non-crosslinked fibers, respectively.

[0095]

number

[0096] Membrane performance test: Twenty crosslinked fibers were placed in a module with an effective length of 220 mm and one end was sealed with epoxy. The epoxy was allowed to cure. The RO water permeability was then tested at 5 bar using a crossflow device. The permeate was collected after the system stabilized (approximately 1 hour).

[0097] A 50 ppm 4-chloro-1-naphthol (4C1N) solution was prepared by adding 50 g of 4C1N to 1 L of RO water. The solution was sonicated at room temperature for at least 1 hour to completely dissolve the solute. The same high differential flow apparatus was used to measure the membrane selectivity using the dye solution. Similarly, the permeate was collected after the system stabilized (approximately 1 hour). The rejection of 4C1N was measured using a GENESYS 50 Vis spectrophotometer from Thermo Fisher Scientific. Peaks were obtained at 236 nm and 302 nm, which were used to calculate the rejection of the solute using the following equation, where C i and C0 are the absorbances of the permeate and feed water, respectively.

[0098]

number

[0099] (result) Determination of polymer gel content %: The gel content of the crosslinked fibers was obtained by measuring the difference in the mass of the fibers before and after immersion in DMAc solution, and the results are shown in Figure 8.

[0100] As seen in Figure 8, fibers crosslinked with IPC in IPA for 1 hour had the lowest gel content after immersion in DMAc solution. This is due to incomplete crosslinking of IPC by the amine on the imidazole ring of PBI. PBI polymer that did not crosslink during the reaction was dissolved in DMAc solution. Subsequent increases in crosslinking time demonstrated higher gel content, from 85.3% at 1 hour to 98.3% at 24 hours. This indicates that a longer crosslinking time than 24 hours is required to achieve 100% gel content.

[0101] ·UV-Vis analysis: The DMAc solution used to dissolve the crosslinked fibers was measured by UV-Vis spectroscopy and the absorbance data is shown in FIG.

[0102] The DMAc solution from the crosslinked fibers showed very low UV absorbance, indicating a low level of polymer dissolution in DMAc. The gel content of the crosslinked fibers was obtained using the peak absorbance at wavelengths of 268 nm and 345 nm. The calculated gel content was very similar when either peak was used. From Table 5, a trend of increasing gel content with increasing crosslinking time can be observed.

[0103] [Table 5]

[0104] Membrane performance test: The permeability and selectivity of the crosslinked membranes were measured to evaluate the effect of crosslinking on membrane performance, and the data obtained are shown in Figure 10.

[0105] As shown in Figure 10, the water permeability remained relatively constant with increasing crosslinking time. This may be due to the looser crosslinking between IPC and PBI, which did not significantly affect pore size. Similarly, the rejection of 4C1N dye by the crosslinked membrane was relatively high, with a solute rejection of approximately 99%. This result indicates that crosslinking the PBI membrane with IPC did not have a significant impact on the membrane's performance. However, the solvent resistance of the crosslinked membrane was dramatically improved, as evidenced by the significant improvement in gel content.

[0106] Figure 11 shows a possible reaction pathway of IPC and PBI. IPC, which contains two acyl chloride functional groups, reacts with the secondary amine on the imidazole ring of PBI to form a tertiary amide group. Figure 12 shows the proposed crosslinked PBI membrane using IPC. The two acyl chloride groups from IPC will crosslink with two different PBI polymers, forming a larger polymer with a higher molecular weight. This likely increases the structural rigidity of the polymer, thereby improving its solvent resistance. A high degree of crosslinking is required to achieve excellent chemical stability in harsh organic solvents such as DMAc. This can be achieved by increasing the crosslinker concentration, temperature, and crosslinking time.

[0107] While the foregoing description has set forth exemplary embodiments, it will be appreciated by those skilled in the relevant art that many modifications may be made without departing from the invention.

Claims

1. 1. A method of forming a crosslinked polymer membrane, comprising contacting a polymer membrane with a crosslinking solution to form a crosslinked polymer membrane, the crosslinking solution comprising a crosslinker comprising at least one acyl halide functional group dissolved in a polar protic solvent; the polar protic solvent comprises an alcohol, and the alcohol is not a tertiary alcohol; the crosslinked polymer film has a polymer gel content of ≥ 95% after polymer dissolution; wherein the polymer gel content is calculated by the following formula: Formula: Polymer gel content = [(final fiber weight) / (initial fiber weight)] x 100%

2. The method of claim 1 , wherein the polymer film is formed from a polymer containing at least one imidazole group.

3. The method of claim 2 wherein the polymer is polybenzimidazole (PBI).

4. The method according to any one of claims 1 to 3, wherein the at least one acyl halide functional group contained in the crosslinking agent is an acyl chloride functional group.

5. The method of any one of claims 1 to 4, wherein the cross-linking agent comprises at least two or three acyl halide functional groups.

6. The method of any one of claims 1 to 5, wherein the cross-linking agent is trimesoyl chloride (TMC), isophthaloyl chloride (IPC), terephthaloyl chloride, or a combination thereof.

7. 7. The method of claim 1, wherein the polar protic solvent comprises at least one alcohol selected from methanol, ethanol, and isopropyl alcohol (IPA).

8. A method according to any one of claims 1 to 7, wherein the contact is carried out at a predetermined temperature of 5 to 100°C.

9. The method of claim 1, wherein the contact is carried out for a predetermined period of time ranging from 1 minute to 120 hours.

10. The method according to any one of claims 1 to 9, wherein the polymer membrane is a flat membrane, a hollow fiber membrane, a tubular membrane, or a dense membrane.

11. The method of any of claims 1 to 10, wherein the cross-linking solution comprises 0.01 to 20% (w / w) of the cross-linking agent.

12. The method of any of claims 1 to 11, wherein the method further comprises performing a solvent exchange on the polymer membrane prior to the contacting.

13. 13. The method of claim 12, wherein performing the solvent exchange comprises performing a solvent exchange with the polar protic solvent contained in the crosslinking solution.

14. The method of any one of claims 1 to 13, wherein the crosslinked polymer membrane has a thickness of 1 to 1000 µm.

15. The method of any one of claims 1 to 14, wherein the crosslinked polymer membrane is hydrophilic.

16. a polymer film crosslinked with a crosslinker containing at least one acyl halide functional group, having a polymer gel content of ≥ 95% after polymer dissolution; A crosslinked polymer film, wherein the polymer gel content is calculated by the following formula: Formula: Polymer gel content = [(final fiber weight) / (initial fiber weight)] x 100%

17. 17. The crosslinked polymer membrane of claim 16, wherein the polymer membrane is formed from a polymer containing at least one imidazole group.

18. 18. The crosslinked polymer membrane of claim 17, wherein the polymer is polybenzimidazole (PBI).

19. The crosslinked polymer membrane according to any one of claims 16 to 18, wherein the at least one acyl halide functional group contained in the crosslinking agent is an acyl chloride functional group.

20. 20. The crosslinked polymer membrane of any of claims 16 to 19, wherein the crosslinker comprises at least two or three acyl halide functional groups.

21. 21. The crosslinked polymer membrane of any of claims 16 to 20, wherein the crosslinking agent is trimesoyl chloride (TMC), isophthaloyl chloride (IPC), terephthaloyl chloride, or a combination thereof.

22. The crosslinked polymer membrane according to any one of claims 16 to 21, wherein the polymer membrane is a flat membrane, a hollow fiber membrane, a tubular membrane, or a dense membrane.

23. The crosslinked polymer membrane of any one of claims 16 to 22, wherein the crosslinked polymer membrane is hydrophilic.

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