Preparation and application of silicone rubber composite membrane with high interface stability

Abstract

The invention relates to the technical field of membrane separation, and discloses preparation and application of a silicone rubber composite membrane with high interface stability. The preparation method of the silicone rubber composite membrane with high interface stability comprises the following steps: placing a polyacrylonitrile ultrafiltration membrane in a modifier aqueous solution, and reacting to obtain a pretreated polyacrylonitrile support layer; dissolving polydimethylsiloxane and polyhydromethylsiloxane in an organic solvent, and adding a catalyst to obtain a separation layer membrane casting solution; the surface of the pretreated polyacrylonitrile supporting layer is coated with the separation layer membrane casting solution, curing and crosslinking are carried out, and the silicone rubber composite membrane with high interface stability is obtained; according to the invention, a stable interface connected by covalent bonds is constructed between the polyacrylonitrile support layer and the silicone rubber separation layer, so that the key technical problem that the composite membrane is easy to layer and peel in an organic solvent environment is fundamentally solved, and excellent separation performance, excellent long-term stability and a simple and economical preparation process are taken into account.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to the preparation and application of a silicone rubber composite membrane with high interfacial stability. Background Technology

[0002] Membrane separation technology is one of the most important methods in separation science today, with wide applications in the pharmaceutical, chemical, environmental protection, and energy fields. Composite membranes consist of a dense separation layer and a porous support layer. Due to their thinner separation layer and relatively lower mass transfer resistance, they have become the main type of membrane in industrial membrane separation processes, especially in processes such as pervaporation, nanofiltration, and gas separation. Among them, silicone rubber composite membranes have high hydrophobicity, good thermochemical stability, and film-forming properties, and are widely used in processes such as preferential permeation of organic matter through pervaporation and nanofiltration of organic solvents. However, because silicone rubber is a flexible material with low surface energy, the adhesion between the silicone rubber separation layer prepared by coating method and most support layers is poor. In practical applications, the two materials swell to different degrees by the solvent, leading to easy separation of the separation layer from the support layer and the phenomenon of silicone rubber layer peeling. Therefore, it is necessary to develop a new method to enhance the interfacial stability between the separation layer and the support layer of silicone rubber composite membranes to obtain composite membranes with high interfacial stability.

[0003] Chinese patent CN 107537329 B discloses a method for improving the interfacial adhesion between the polyacrylonitrile support layer and the silicone rubber release layer by plasma grafting a crosslinking agent onto the surface of the polyacrylonitrile support layer and utilizing a hydrosilylation crosslinking reaction. Qin Peiyong et al. from Beijing University of Chemical Technology, on the other hand, modified the polyacrylonitrile support layer through a two-step chemical modification with NaOH and GMA (Chinese patent application CN 116726728 A), or through a three-step chemical modification with NaOH, Na2SO4, and methacrylic acid (Chinese patent application CN 117717911). A) Introducing acrylate double bonds onto the surface of the PAN membrane, followed by photopolymerization grafting of a PDMS separation layer, effectively alleviates cracking and delamination of the PDMS / PAN composite membrane in application. Both of the above methods improve the interfacial adhesion of the silicone rubber composite membrane by modifying the support layer. However, plasma modification of the support layer requires specific instruments and equipment, and grafting a crosslinked layer onto the support layer surface increases the mass transfer resistance of the membrane, which may affect the separation performance of the membrane. On the other hand, the two-step or three-step chemical modification of the support layer involves a complicated operation process, a large number of chemical reagents, and is only applicable to photo-initiated crosslinking of silicone rubber to form a film.

[0004] Therefore, it is an urgent problem to solve to develop a method that is easy to operate, does not require a large investment in special equipment, and is easy to industrialize, in order to improve the phase interface stability of the separation layer and the support layer of silicone rubber composite membrane. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a silicone rubber composite film with high interfacial stability, comprising the following steps: Step (1): Place the polyacrylonitrile ultrafiltration membrane in an aqueous solution of a modifier, heat it, stir and react it, take it out, clean it with ultrasound, and then soak it in water for later use to obtain a pretreated polyacrylonitrile support layer. Step (2): Dissolve polydimethylsiloxane and polyhydromethylsiloxane in an organic solvent, add a catalyst, stir, and obtain a separation layer casting solution; Step (3): The separation layer casting solution is coated onto the surface of the pretreated polyacrylonitrile support layer, cured and crosslinked to form a separation layer, thereby obtaining a silicone rubber composite film with high interfacial stability.

[0006] Preferably, in step (1), the concentration of the modifier aqueous solution is 8-12 wt%.

[0007] Preferably, in step (1), the modifier includes any one of ethanolamine, diethanolamine, and hydroxylamine.

[0008] Preferably, in step (1), the heating temperature is 60-80℃ and the stirring reaction time is 4-8h.

[0009] Preferably, in step (2), the mass ratio of polydimethylsiloxane to polyhydromethylsiloxane is (10-30):1.

[0010] Preferably, in step (2), the organic solvent includes at least one of n-heptane, benzene, and toluene; and the catalyst includes any one of platinum, ruthenium, and rhodium.

[0011] Preferably, in step (2), the solid content in the separation layer casting solution is 10-30 wt%.

[0012] Preferably, in step (3), the curing and crosslinking conditions are: temperature of 80-120°C and time of 6-20h.

[0013] The silicone rubber composite film with high interface stability is prepared by the aforementioned method.

[0014] The application of the silicone rubber composite membrane with high interfacial stability in membrane separation in the chemical, pharmaceutical and environmental protection fields.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The silicone rubber composite film with high interfacial stability and its preparation method of the present invention have the following advantages: (1) The interfacial bonding strength of the composite membrane is significantly enhanced, forming a stable covalent anchor: A polyacrylonitrile support layer with surface-grafted hydroxyl groups was prepared by a one-step chemical modification method. The interfacial bonding between the polyacrylonitrile support layer and the silicone rubber separation layer was enhanced by the silanium-hydrogen bond reaction between the surface hydroxyl groups and the polyhydrogen methylsiloxane crosslinking agent in the separation layer, forming a covalently bonded silicone rubber composite film. (2) The composite membrane exhibits excellent long-term solvent resistance and operational stability: The polysiloxane separation layer is anchored to the support layer, which effectively inhibits the excessive swelling and structural damage of silicone rubber in the solvent, ensuring the reliability of long-term operation. (3) Excellent separation performance without introducing additional mass transfer resistance: The composite membrane of the present invention enhances interfacial adhesion while perfectly inheriting the high permeability and selectivity of silicone rubber material itself; the pretreated polyacrylonitrile support layer only has an increased surface pore size and does not form a dense additional layer. Therefore, no additional mass transfer resistance layer is formed, and the surface pore structure of the support layer is preserved, thereby not increasing the mass transfer resistance and maintaining or even improving the separation performance of the composite membrane. (4) The preparation process is simple, the cost is low, and it is easy to scale up: The core technology of this invention lies in one-step liquid-phase chemical modification, which only requires heating the support layer in an aqueous solution of ethanolamine or hydroxylamine. It does not require special equipment such as plasma or ultraviolet light initiation, and avoids the complex process and reagent consumption of multi-step chemical modification. The entire process is mild (reaction temperature 40-80℃), simple, safe to operate, and all reagents used are common chemicals, which significantly reduces production costs and process control difficulty, and has good prospects for industrial application. In summary, this invention, through a one-step chemical modification strategy, successfully constructs a stable interface with covalent bonds between the polyacrylonitrile support layer and the silicone rubber separation layer. This not only fundamentally solves the key technical problem of easy delamination and peeling of composite membranes in organic solvent environments, but also takes into account excellent separation performance, outstanding long-term stability, and a simple and economical preparation process. It provides an efficient and feasible solution for the preparation of high-performance, long-life silicone rubber composite membranes, and also provides a strategy for achieving universal interface strengthening applicable to various silicone rubber systems and support materials, promoting their long-term stable application in actual pervaporation and organic solvent nanofiltration processes.

[0016] 2. The preparation method of the present invention can be further extended: (1) The modifier of the present invention can be extended to other alkanolamine modifiers to achieve surface hydroxyl functionalization of the polyacrylonitrile support layer and enhance its interfacial bonding with the silicone rubber separation layer. (2) The separation layer material of the present invention can be extended to other silicone rubbers containing silane bonds or particle-filled silicone rubbers to further optimize the separation performance and solvent resistance of the membrane; in addition to being used for pervaporation and organic solvent nanofiltration, the composite membrane can also be extended to gas separation, membrane distillation and other fields, and is suitable for the separation of various organic / water systems or organic mixtures; (3) The method of the present invention can also be combined with processes such as layer-by-layer self-assembly and ultraviolet curing to construct multilayer or gradient structure composite membranes, further improving separation performance and mechanical stability; Therefore, the method of the present invention has the advantages of simple process, no need for complex equipment, and easy large-scale production, and has broad application prospects in membrane separation processes in chemical, pharmaceutical, and environmental protection fields. Attached Figure Description

[0017] Figure 1 The images show the FTIR-ATR diagrams of the pretreated polyacrylonitrile support layer of the silicone rubber composite film with high interfacial stability prepared in Examples 1-3 and the original polyacrylonitrile support layer of the ordinary silicone rubber composite film prepared in Comparative Example 1. Figure 2 SEM images of the pretreated polyacrylonitrile support layer (left) of the silicone rubber composite film with high interfacial stability prepared in Example 1 and the original polyacrylonitrile support layer (right) of the ordinary silicone rubber composite film prepared in Comparative Example 1. Figure 3 These are optical micrographs of the silicone rubber composite film (A) with high interfacial stability prepared in Example 1 and the ordinary silicone rubber composite film (B) prepared in Comparative Example 1 after X-ray tape scratching experiment. Figure 4 These are SEM images of the silicone rubber composite film (A) with high interfacial stability prepared in Example 1 and the ordinary silicone rubber composite film (B) prepared in Comparative Example 1 after X-ray tape slicing experiment. Figure 5 The results are the separation performance test results of the silicone rubber composite membrane with high interfacial stability prepared in Example 1 for removing rose red from n-heptane solvent. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] Example 1 This embodiment discloses a method for preparing a silicone rubber composite film with high interfacial stability, including the following steps: Step (1): Place the polyacrylonitrile ultrafiltration membrane in an aqueous solution of 10wt% ethanolamine, heat it to 80℃, react it for 6 hours under mechanical stirring, take out the membrane and ultrasonically clean it with water to remove unreacted reagents that are physically adsorbed, and then soak it in water for later use to obtain a pretreated polyacrylonitrile support layer. Step (2): Dissolve 1.89g of polydimethylsiloxane and 0.095g of polyhydromethylsiloxane in 50g of n-heptane, add platinum catalyst, stir, and obtain a separation layer casting solution with a solid content of 20wt%. Step (3): Remove the pretreated polyacrylonitrile support layer from the water and wipe off the surface moisture. Apply the separation layer casting solution to the surface of the pretreated polyacrylonitrile support layer and then transfer it to an oven at 80°C for curing and crosslinking for 12 hours to form a separation layer, thereby obtaining a silicone rubber composite film with high interfacial stability.

[0020] Example 2 This embodiment discloses a method for preparing a silicone rubber composite film with high interfacial stability, including the following steps: Step (1): Place the polyacrylonitrile ultrafiltration membrane in an aqueous solution of 10wt% ethanolamine, heat it to 60℃, react it for 6 hours under mechanical stirring, take out the membrane and ultrasonically clean it with water to remove unreacted reagents that are physically adsorbed, and then soak it in water for later use to obtain a pretreated polyacrylonitrile support layer. Step (2): Dissolve 1.89g of polydimethylsiloxane and 0.095g of polyhydromethylsiloxane in 50g of n-heptane, add platinum catalyst, stir, and obtain a separation layer casting solution with a solid content of 20wt%. Step (3): Remove the pretreated polyacrylonitrile support layer from the water and wipe off the surface moisture. Apply the separation layer casting solution to the surface of the pretreated polyacrylonitrile support layer and then transfer it to an oven at 80°C for curing and crosslinking for 12 hours to form a separation layer, thereby obtaining a silicone rubber composite film with high interfacial stability.

[0021] Example 3 This embodiment discloses a method for preparing a silicone rubber composite film with high interfacial stability, including the following steps: Step (1): Place the polyacrylonitrile ultrafiltration membrane in an aqueous solution of 10wt% ethanolamine and react it at 20°C with mechanical stirring for 6 hours. Remove the membrane and ultrasonically clean it with water to remove unreacted reagents that are physically adsorbed. Then soak it in water for later use to obtain a pretreated polyacrylonitrile support layer. Step (2): Dissolve 1.89g of polydimethylsiloxane and 0.095g of polyhydromethylsiloxane in 50g of n-heptane, add platinum catalyst, stir, and obtain a separation layer casting solution with a solid content of 20wt%. Step (3): Remove the pretreated polyacrylonitrile support layer from the water and wipe off the surface moisture. Apply the separation layer casting solution to the surface of the pretreated polyacrylonitrile support layer and then transfer it to an oven at 80°C for curing and crosslinking for 12 hours to form a separation layer, thereby obtaining a silicone rubber composite film with high interfacial stability.

[0022] Comparative Example 1 This comparative example discloses a method for preparing a common silicone rubber composite film, including the following steps: Step (1): Use the polyacrylonitrile ultrafiltration membrane as the original polyacrylonitrile support layer, immerse it in water, and set it aside. Step (2): Dissolve 1.89g of polydimethylsiloxane and 0.095g of polyhydromethylsiloxane in 50g of n-heptane, add platinum catalyst, stir, and obtain a separation layer casting solution with a solid content of 20wt%. Step (3): Remove the original polyacrylonitrile support layer from the water and wipe off the surface moisture. Apply the separation layer casting solution to the surface of the original polyacrylonitrile support layer and then transfer it to an oven at 80°C for curing and crosslinking for 12 hours to form a separation layer, thereby obtaining a common silicone rubber composite film.

[0023] Experimental Example The performance of the silicone rubber composite film with high interfacial stability prepared in Example 1 and the ordinary silicone rubber composite film prepared in Comparative Example 1 were tested: Test 1: Fourier transform infrared spectroscopy (FTIR) analysis was performed on the pretreated polyacrylonitrile support layer of the silicone rubber composite film with high interfacial stability prepared in Examples 1-3 and the original polyacrylonitrile support layer of the ordinary silicone rubber composite film prepared in Comparative Example 1. The results are as follows Figure 1 As shown, Figure 1 These are FTIR-ATR images of the pretreated polyacrylonitrile support layer of the silicone rubber composite membranes with high interfacial stability prepared in Examples 1-3 and the original polyacrylonitrile support layer of the ordinary silicone rubber composite membrane prepared in Comparative Example 1. In these images, PAN20 represents the original polyacrylonitrile support layer of the ordinary silicone rubber composite membrane prepared in Comparative Example 1; PAN20-ETA-80-6 (referring to the polyacrylonitrile ultrafiltration membrane treated with ethanolamine at 80°C for 6 hours) represents the pretreated polyacrylonitrile support layer of the silicone rubber composite membrane with high interfacial stability prepared in Example 1; PAN20-ETA-60-6 (referring to the polyacrylonitrile ultrafiltration membrane treated with ethanolamine at 60°C for 6 hours) represents the pretreated polyacrylonitrile support layer of the silicone rubber composite membrane with high interfacial stability prepared in Example 2; and PAN20-ETA-20-6 (referring to the polyacrylonitrile ultrafiltration membrane treated with ethanolamine at 60°C for 6 hours) represents the pretreated polyacrylonitrile support layer of the silicone rubber composite membrane with high interfacial stability prepared in Example 3. Depend on Figure 1 It can be seen that the infrared spectrum of the polyacrylonitrile membrane after immersion in ethanolamine solution at room temperature and then ultrasonic cleaning is exactly the same as that of the original membrane, indicating that no modification reaction can occur at room temperature. However, when the temperature is increased to 60℃ and 80℃, a 1555 cm⁻¹ appears in the FTIR spectrum of the pretreated polyacrylonitrile support layer in Example 1. -1 Peak (NH bending vibration peak), and 1653 cm. -1 and 3200-3600 cm -1 The enhanced peak indicates that the support layer underwent a modification reaction at high temperature, and the modified membrane surface contains C=N, CN and hydroxyl groups.

[0024] Test 2: SEM analysis was performed on the pretreated polyacrylonitrile support layer of the silicone rubber composite film with high interfacial stability prepared in Example 1 and the original polyacrylonitrile support layer of the ordinary silicone rubber composite film prepared in Comparative Example 1. The results are as follows Figure 2 As shown, Figure 2 SEM images of the pretreated polyacrylonitrile support layer (left) of the silicone rubber composite film with high interfacial stability prepared in Example 1 and the original polyacrylonitrile support layer (right) of the ordinary silicone rubber composite film prepared in Comparative Example 1. Depend on Figure 2 It can be seen that the pretreated polyacrylonitrile support layer only has an increased surface pore size, without forming a dense additional layer or an additional mass transfer resistance layer. The surface pore structure of the support layer is preserved and will not have a significant impact on the separation performance of the composite membrane.

[0025] Test 3: According to the international standard ASTM D3359-B, the interfacial adhesion of the silicone rubber composite film with high interfacial stability prepared in Example 1 and the ordinary silicone rubber composite film prepared in Comparative Example 1 were tested: Test results are as follows Figure 3 and Figure 4 As shown, Figure 3 These are optical micrographs of the silicone rubber composite film (A) with high interfacial stability prepared in Example 1 and the ordinary silicone rubber composite film (B) prepared in Comparative Example 1 after X-ray tape scratching experiment. Figure 4 These are SEM images of the silicone rubber composite film (A) with high interfacial stability prepared in Example 1 and the ordinary silicone rubber composite film (B) prepared in Comparative Example 1 after X-ray tape slicing experiment. Depend on Figure 3 and Figure 4It is known that during the subsequent coating and curing process, the hydroxyl groups on the surface of the pretreated polyacrylonitrile support layer react chemically with the silicon-hydrogen bonds (Si-H) of the polyhydrogen methylsiloxane crosslinking agent in the casting solution of the release layer, forming covalent bonds in situ at the interface between the release layer and the support layer. Therefore, the release layer of the silicone rubber composite film with high interface stability in Example 1 can better adhere to the support layer, and its interface adhesion level is ASTM-5B. After the tape peel test, the release layer is intact and there is no peeling, proving that its interface stability has been fundamentally improved. In contrast, the interface adhesion level of the ordinary silicone rubber composite film in Comparative Example 1 is ASTM-0B.

[0026] Test 4 (1) The silicone rubber composite membrane with high interfacial stability prepared in Example 1 and the ordinary silicone rubber composite membrane prepared in Comparative Example 1 were immersed in 30wt% dimethyl carbonate / methanol azeotrope for several days, and then used for pervaporation separation of dimethyl carbonate / methanol azeotrope. The separation results are shown in Table 1: Table 1 ; (2) The silicone rubber composite membrane with high interfacial stability prepared in Example 1 was used to separate rose red in n-heptane solvent, and the separation results of rose red were tested. Test results are as follows Figure 5 As shown, Figure 5 The results are the separation performance test results of the silicone rubber composite membrane with high interfacial stability prepared in Example 1 for removing rose red from n-heptane solvent; From Table 1 and Figure 5 The results show that the silicone rubber composite film with high interfacial stability prepared in Example 1 only introduces active groups in situ on the surface of the support layer, without forming a dense additional layer. Figure 2 (As confirmed), the porous structure of the support layer surface is preserved, thus not significantly increasing the mass transfer resistance. The resulting composite membrane exhibits a balance between high permeation flux (4.2-4.7 kg / m²·h) and a good separation factor (3.4-3.5) when pervaporating the dimethyl carbonate / methanol system. Furthermore, the silicone rubber composite membrane with high interfacial stability of this invention exhibits excellent durability in harsh organic solvent environments. After immersing it in dimethyl carbonate / methanol azeotrope for up to 60 days, the membrane structure remains intact, and when used for pervaporation separation, the separation factor remains stable at around 3.4, the flux remains at approximately 4.7 kg / m²·h, and the performance shows no significant degradation. In contrast, the ordinary silicone rubber composite membrane prepared in Comparative Example 1 showed severe performance degradation after immersion for 30 days, and after 60 days, the separation layer separated from the original support layer, and the integrity of the membrane was destroyed. Furthermore, although the polysiloxane material alone swells significantly in n-heptane solvent, in the 80-hour continuous test of nanofiltration separation of rose red in n-heptane solvent, the polysiloxane separation layer on the silicone rubber composite membrane with high interfacial stability prepared in Example 1 was anchored on the support layer, and its swelling was suppressed, resulting in a rejection rate of over 95% for rose red in n-heptane. At the same time, it maintained a high solvent flux, and the solvent flux and rose red rejection rate remained stable throughout the test. This is because the membrane structure and separation properties remained stable, ensuring the reliability of long-term operation. In addition, the separation results of rose red further proved that the silicone rubber composite membrane with high interfacial stability prepared in Example 1, while strengthening interfacial adhesion, perfectly inherited the high permeability and selectivity of silicone rubber material itself.

[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a silicone rubber composite film with high interfacial stability, characterized in that, Includes the following steps: Step (1): Place the polyacrylonitrile ultrafiltration membrane in an aqueous solution of a modifier, heat it, stir and react it, take it out, clean it with ultrasound, and then soak it in water for later use to obtain a pretreated polyacrylonitrile support layer. Step (2): Dissolve polydimethylsiloxane and polyhydromethylsiloxane in an organic solvent, add a catalyst, stir, and obtain a separation layer casting solution; Step (3): The separation layer casting solution is coated onto the surface of the pretreated polyacrylonitrile support layer, cured and crosslinked to form a separation layer, thereby obtaining a silicone rubber composite film with high interfacial stability.

2. The method for preparing a silicone rubber composite film with high interfacial stability according to claim 1, characterized in that, In step (1), the concentration of the modified agent aqueous solution is 8-12 wt%.

3. The method for preparing a silicone rubber composite film with high interfacial stability according to claim 1, characterized in that, In step (1), the modifier includes any one of ethanolamine, diethanolamine and hydroxylamine.

4. The method for preparing a silicone rubber composite film with high interfacial stability according to claim 1, characterized in that, In step (1), the heating temperature is 60-80℃ and the stirring reaction time is 4-8h.

5. The method for preparing a silicone rubber composite film with high interfacial stability according to claim 1, characterized in that, In step (2), the mass ratio of polydimethylsiloxane to polyhydromethylsiloxane is (10-30):

1.

6. The method for preparing a silicone rubber composite film with high interfacial stability according to claim 1, characterized in that, In step (2), the organic solvent includes at least one of n-heptane, benzene, and toluene; the catalyst includes any one of platinum, ruthenium, and rhodium.

7. The method for preparing a silicone rubber composite film with high interfacial stability according to claim 1, characterized in that, In step (2), the solid content in the separation layer casting solution is 10-30 wt%.

8. The method for preparing a silicone rubber composite film with high interfacial stability according to claim 1, characterized in that, In step (3), the curing and crosslinking conditions are: temperature 80-120°C and time 6-20h.

9. A silicone rubber composite film with high interfacial stability prepared by the method for preparing a silicone rubber composite film with high interfacial stability as described in any one of claims 1-8.

10. The application of the silicone rubber composite membrane with high interfacial stability as described in claim 9 in membrane separation in the chemical, pharmaceutical, and environmental protection fields.

Images