CN108816055A - A kind of preparation method of biodegradable water-oil separating perforated membrane - Google Patents

Abstract

The invention provides a method for preparing a biodegradable oil-water separation porous membrane. Using tetraethyl orthosilicate and methanol solution as raw materials, silica gel is prepared by a sol-gel method, and then hydrophobically modified. Critical drying yields silica aerogels. Add the airgel to the ethanol solution to prepare the silica airgel/ethanol dispersion, and then use the non-solvent-induced phase separation method to prepare the polylactic acid film, and dissolve the pretreated polylactic acid in the solvent, Stir at constant temperature to obtain the casting film, pour the casting film on the surface of a clean glass plate, scrape the film with a scraper of a certain thickness, immerse the preformed polylactic acid film in the ethanol dispersion containing silica airgel, solidify and dry Finally, silica airgel@polylactic acid film was obtained. The film has a simple preparation process, excellent oil-water separation performance, and is biodegradable after use, so it has broad application prospects.

Description

A kind of preparation method of biodegradable oil-water separation porous membrane

technical field

The invention belongs to the field of polymer materials, and in particular relates to a low-cost, large-scale preparation method for superhydrophobic-superoleophilic polymer porous membranes. The porous membrane can be used to separate the oil-water emulsion with added surfactant.

Background technique

At present, most superhydrophobic films on the market (such as polyvinylidene fluoride films, polypropylene films, etc.) have the characteristics of high oil-water selectivity and excellent separation effect, but most of the superhydrophobic polymer films for It is a polymer material, which is difficult to degrade or takes a long time to degrade in the natural environment, and the reusability of the film is poor, and it is easy to cause secondary pollution after use, etc., and the disposal of waste polymer films is difficult, further increasing The cost of handling oil-water mixtures. Therefore, more and more researchers have begun to pay attention to the research and development of naturally degradable materials, and the development of a biodegradable polymer film material has become an important way to solve the secondary pollution of materials.

In recent decades, due to the excellent properties of polylactic acid materials, such as excellent physical and mechanical properties, good ductility and tensile strength, easy processing and molding, etc., it has been considered as the most promising environmental protection material, and The material itself has a certain degree of hydrophobicity (at room temperature, the contact angle to water in air is 79°), and it is also expected to develop into a biodegradable separation material with special wettability. However, there is still a lack of general and facile methods for the large-scale preparation of efficient PLA separation materials with stable surface wettability, high mechanical stability, and practical application. Silica airgel exhibits unique properties due to its highly porous three-dimensional structure and numerous micro-nano-scale voids, and its micro-nano structure can capture air to exhibit super-hydrophobic characteristics. However, due to the low strength of the silica network, its application is greatly limited. Therefore, a biodegradable and recyclable oil-water separation membrane has broad application prospects.

Contents of the invention

The invention proposes a low-cost, large-scale preparation method for a biodegradable superhydrophobic-superoleophilic polymer porous membrane. The main preparation steps are as follows:

(1) Preparation of silica airgel/ethanol dispersion: Silica airgel was prepared by sol-gel method. Firstly, ethyl orthosilicate was dissolved in methanol, and oxalic acid solution was added and stirred for a period of time. Then, a methanol solution containing a certain amount of ammonia water is added, and the solution is further stirred, and finally, the solution is gelled at a constant temperature. After the SiO ₂ is gelled, take a certain amount of absolute ethanol and add it to the gel, and replace it at a constant temperature to remove oxalic acid and unreacted chemical substances, etc., and then add an appropriate amount of ethanol/n-hexane containing trimethylchlorosilane Hydrophobic modification of SiO ₂ was carried out with a mixed solution of alkane, and the ethanol washing treatment was repeated four times to ensure complete removal of oxalic acid and other chemical residues. After washing, the gel is subjected to supercritical drying, crushed and an appropriate amount of absolute ethanol is added, and dispersed uniformly by stirring and ultrasonic to prepare a _SiO2 airgel/ethanol dispersion.

(2) Preparation of silica airgel@polylactic acid film: the polylactic acid film was prepared by the non-solvent induced phase separation method, the pretreated polylactic acid was dissolved in the solvent, and the casting solution was obtained by stirring at a constant temperature. Let stand to remove air bubbles. Pour the casting solution on the surface of a clean glass plate, scrape the film with a scraper of a certain thickness, then immerse the preformed polylactic acid film in the ethanol dispersion containing silica airgel, and solidify to obtain a polylactic acid superhydrophobic film. Vacuum dry.

The preferred volume ratio of tetraethyl orthosilicate, methanol, and oxalic acid solution (10mmol/L) in step (1) of the present invention is 1:2:0.5; the volume ratio of ammonia water (20%) to methanol is 1:6; The gel temperature is 25-50°C, the gel time is 0.5-2h, and the replacement time is 6-10h; after that, the gel is broken and an appropriate amount of absolute ethanol is added, and the content can be made into 0.1%-5% by stirring and ultrasonic dispersion. silica airgel/ethanol dispersion.

In the present invention, the preferred solvent for dissolving polylactic acid in step (2) is N-methylpyrrolidone, the content is 0.5%-4%, the temperature of constant temperature stirring is 80-100°C, the stirring time is 10-12h, and then at 80°C Stand still for 6 hours to remove air bubbles, and then vacuum dry at 40°C for 24 hours after scraping the film. Compared with previously reported materials with unique wettability, the film prepared by the present invention has the following beneficial effects:

(1) The superhydrophobic-superoleophilic biodegradable film of the present invention has a wider range of applications, such as the separation of oil-water mixtures, the separation of surfactant-free and surfactant-stabilized oil-water emulsions;

(2) It has an economical and convenient preparation process;

(3) The present invention selects polylactic acid with biodegradable properties as the raw material, which is more biologically environmentally friendly, and can be biodegraded after use without forming white garbage.

Description of drawings

Fig. 1 is the scanning electron microscope picture of silica airgel@polylactic acid film in embodiment 1;

Fig. 2 is the scanning electron microscope picture of silica airgel@polylactic acid film in embodiment 2;

Fig. 3 is the scanning electron microscope picture of silica airgel@polylactic acid film in embodiment 3;

Fig. 4 is the oil-water separation effect figure of silica airgel@polylactic acid film in embodiment 2;

Fig. 5 is a micrograph in water after the oil-water separation of the silica airgel@polylactic acid film in Example 2.

Detailed ways

The technical solutions of the present invention will be described in detail below through specific examples, but the scope of the present invention is not limited by these examples.

Example 1-3

(1) Preparation of _SiO2 airgel/ethanol dispersion

1ml tetraethyl orthosilicate was dissolved in 2ml methanol, and 0.5ml oxalic acid solution was slowly added to the mixture, and stirred for 30min. Then, 5 ml of methanol solution containing 0.6 ml of ammonia water (20%) was added, and the solution was further stirred for 15 min, and the solution was left at 25° C. for 1 h to form a gel. After gelation, add 20ml of absolute ethanol to the gel, and replace it at 25°C for 6h to remove oxalic acid and unreacted chemical substances, etc., then add 5ml of ethanol/n-hexane containing 5% trimethylchlorosilane Mix the solutions and repeat the ethanol wash treatment four times to ensure complete removal of oxalic acid and other chemical residues. After washing, obtain SiO2 aerogel by supercritical drying, add appropriate amount of absolute ethanol to the gained SiO2 aerogel, disperse evenly by stirring and ultrasonic, respectively make 0.1%, 0.5%, 1% _SiO2 aerogel/ ethanol dispersion.

(2) Preparation of silica airgel@polylactic acid film

Dissolve 1g of pretreated polylactic acid in 100g of NMP solvent, and continue to stir mechanically at 85°C for 12 hours to obtain a uniform casting solution. Stand at 80°C for 8 hours to remove air bubbles, and pour the casting solution on the surface of a clean glass plate. After scraping the film with a 200μm thick scraper, immediately immerse the preformed polylactic acid film into the ethanol dispersion containing 0.1%, 0.5%, and 1% silica airgel respectively, and cure to obtain silica airgel@polylactic acid The film was vacuum-dried at 40°C for 24 hours to obtain the finished product. Then measure its surface structure and contact angle, and test its mechanical properties. The specific data are shown in Table 1.

In order to test the oil-water separation ability of the super-hydrophobic membrane, the present invention prepares a water-in-oil emulsion containing a surfactant with nanoscale and micron droplet sizes. For ordinary oil-water mixtures (such as slick oil), ordinary super-hydrophobic materials can separate oil and water. However, for oil-water emulsions (especially oil-water emulsions added with surfactants), ordinary superhydrophobic materials are difficult to separate oil-water emulsions due to their own pore size limitations. The present invention carries out the oil-water separation experiment with the film obtained after the composite of embodiment ₂ -polylactic acid film and 0.5% SiO gas-condensed ethanol dispersion liquid, as shown in Figure 4, the oil-water mixture that adds surfactant stability before separation It was in the form of a white emulsion, and the filtrate collected after separation became a colorless and transparent liquid, and the existence of micro-nano droplets was not observed from the microscope, as shown in Figure 5, and the separation of the oil-water emulsion containing surfactant was realized.

Table 1

project Example 1 Example 2 Example 3 SiO ₂ airgel mass fraction/% 0.1% 0.5% 1% Contact angle/° 148 156 157 Tensile strength/MPa 12.0 11.5 10.8 Elongation at break/% 5.5 4.5 3.8

Claims (3)

1. A preparation method of biodegradable oil-water separation porous membrane, characterized in that, the preparation method is as follows: (1) preparation of silica airgel/ethanol dispersion: adopt sol-gel method to prepare silica airgel Glue, first dissolve ethyl orthosilicate in methanol, add oxalic acid solution and stir for a while; then add methanol solution containing a certain amount of ammonia water, and further stir the solution, and gel the solution at constant temperature; SiO ₂ condenses After gelation, add a certain amount of absolute ethanol to the gel, and replace it at a constant temperature to remove oxalic acid and unreacted chemical substances, etc., and then add an appropriate amount of ethanol/n-hexane mixture containing trimethylchlorosilane The solution is hydrophobically modified on SiO ₂ , and the ethanol washing treatment is repeated four times to ensure that oxalic acid and other chemical residues are completely removed. After washing, the gel is broken and an appropriate amount of absolute ethanol is added, and it is uniformly dispersed by stirring and ultrasonic to prepare SiO ₂ airgel/ethanol dispersion; (2) Preparation of silica airgel@polylactic acid film: the polylactic acid film was prepared by the non-solvent induced phase separation method, the pretreated polylactic acid was dissolved in the solvent, and the casting solution was obtained by stirring at a constant temperature. Stand still to remove air bubbles, pour the casting solution on the surface of a clean glass plate, scrape the film with a scraper of a certain thickness, immerse the preformed polylactic acid film in the ethanol dispersion containing silica airgel, and solidify to obtain a polylactic acid film. Lactic acid superhydrophobic film, finally vacuum dried. 2. according to the preparation method of a kind of biodegradable oil-water separation porous membrane described in claims 1, it is characterized in that, in the step (1), the volume ratio of ethyl orthosilicate, methyl alcohol, oxalic acid solution (10mmol/L) is 1:2:0.5; the volume ratio of ammonia water (20%) to methanol is 1:6; the gel temperature is 25-50°C, the gel time is 0.5-2h, and the replacement time is 6-10h. 3. according to the preparation method of a kind of biodegradable oil-water separation porous membrane described in claim 1, it is characterized in that, the solvent for dissolving polylactic acid in step (2) is N-methylpyrrolidone, and content is 0.5%-4 %, the temperature of constant temperature stirring is 80-100°C, the stirring time is 10-12h, and then stand at 80°C for 6h to remove air bubbles, and then vacuum dry at 40°C for 24h after scraping the film.