CN108816055B

CN108816055B - Preparation method of biodegradable oil-water separation porous membrane

Info

Publication number: CN108816055B
Application number: CN201810724501.2A
Authority: CN
Inventors: 张振秀; 王聪; 戴欣茹
Original assignee: Qingdao University of Science and Technology
Current assignee: Jiangsu Da Mao Niu New Material Co.,Ltd.
Priority date: 2018-07-04
Filing date: 2018-07-04
Publication date: 2021-05-14
Anticipated expiration: 2038-07-04
Also published as: CN108816055A

Abstract

The invention provides a preparation method of a biodegradable oil-water separation porous membrane, which takes ethyl orthosilicate and methanol solution as raw materials, adopts a sol-gel method to prepare silicon dioxide gel, and then carries out hydrophobic modification on the silicon dioxide gel, and then carries out supercritical drying to obtain silicon dioxide aerogel. Adding the aerogel into an ethanol solution to prepare a silicon dioxide aerogel/ethanol dispersion solution for later use; and then preparing a polylactic acid film by adopting a non-solvent induced phase separation method, dissolving the pretreated polylactic acid in a solvent, stirring at a constant temperature to obtain a casting solution, pouring the casting solution on the surface of a clean glass plate, scraping the film by using a scraper with a certain thickness, immersing the preformed polylactic acid film into ethanol dispersion containing silicon dioxide aerogel, and curing and drying to obtain the silicon dioxide aerogel @ polylactic acid film. The film is simple in preparation process, has excellent oil-water separation performance, is biodegradable after being used, and has wide application prospect.

Description

Preparation method of biodegradable oil-water separation porous membrane

Technical Field

The invention belongs to the field of high molecular materials, and particularly relates to a preparation method of a super-hydrophobic-super-oleophylic polymer porous membrane with low cost and capable of being prepared in a large scale. The porous membrane can be used for separating oil-water emulsion added with surfactant.

Background

At present, most of super-hydrophobic films (such as polyvinylidene fluoride films and polypropylene films) on the market have the characteristics of high oil-water selectivity, excellent separation effect and the like, but most of the super-hydrophobic polymer films for oil-water separation are high polymer materials, are difficult to degrade or have long degradation time in the natural environment and the like, and the film has poor reusability, is easy to generate secondary pollution and the like after being used, is difficult to treat the waste polymer films, and further increases the cost for treating oil-water mixtures. Therefore, more and more researchers are focusing on the development of naturally degradable materials, and the development of a biodegradable polymer film material has become an important way to solve the problem of secondary pollution of materials.

In recent decades, polylactic acid materials are considered as the most promising environment-friendly materials due to the advantages of excellent properties, such as excellent physical and mechanical properties, better ductility and tensile strength, easy processing and forming, and the like, and the materials themselves have certain hydrophobicity (the contact angle to water in air is 79 degrees at normal temperature), and are expected to be developed into biodegradable separation materials with special wettability. However, there is still a lack of a general and simple method for mass-producing a high-efficiency polylactic acid separation material having stable surface wettability, high mechanical stability, and practical applicability. Silica aerogel presents unique properties due to a highly porous three-dimensional structure and numerous micro-nano-scale gaps, and the micro-nano structure can capture air to present a super-hydrophobic characteristic. However, the silica network has been greatly limited in its application due to its low strength. Therefore, the oil-water separation film which is biodegradable and can be recycled has wide application prospect.

Disclosure of Invention

The invention provides a method for preparing a biodegradable super-hydrophobic-super-oleophylic polymer porous membrane with low cost and large scale. The preparation method mainly comprises the following steps:

(1) preparation of silica aerogel/ethanol dispersion: the silica aerogel is prepared by adopting a sol-gel method, firstly, ethyl orthosilicate is dissolved in methanol, and then, oxalic acid solution is added to the mixture to be stirred for a period of time. Then, a methanol solution containing a certain amount of ammonia water was added and the solution was further stirred, and finally, the solution was gelled at a constant temperature. SiO2₂After gelation, adding a certain amount of anhydrous ethanol into the gel, replacing at constant temperature to remove oxalic acid and unreacted chemical substances, and adding a proper amount of ethanol/n-hexane mixed solution containing trimethylchlorosilane to SiO₂The hydrophobic modification was performed and the ethanol washing treatment was repeated four times to ensure complete removal of oxalic acid and other chemical residues, etc. After washing, the gel is subjected to supercritical drying, crushed and added with a proper amount of absolute ethyl alcohol, and the mixture is uniformly dispersed by stirring and ultrasonic to prepare SiO₂Aerogel/ethanol dispersion.

(2) Preparation of silica aerogel @ polylactic acid film: preparing a polylactic acid film by adopting a non-solvent induced phase separation method, dissolving the pretreated polylactic acid in a solvent, stirring at constant temperature to obtain a casting solution, and standing at a certain temperature to remove bubbles. Pouring the casting solution on the surface of a clean glass plate, scraping the film by using a scraper with a certain thickness, immersing the preformed polylactic acid film into ethanol dispersion liquid containing silicon dioxide aerogel, curing to obtain the polylactic acid super-hydrophobic film, and finally drying in vacuum.

In the invention, the volume ratio of the preferred tetraethoxysilane, methanol and oxalic acid solution (10mmol/L) in the step (1) is 1: 2: 0.5; the volume ratio of ammonia (20%) to methanol was 1: 6; the gel temperature is 25-50 ℃, the gel time is 0.5-2h, and the replacement time is 6-10 h; then crushing the gel, adding a proper amount of absolute ethyl alcohol, and uniformly stirring and ultrasonically dispersing to prepare a silicon dioxide aerogel/ethyl alcohol dispersion liquid with the content of 0.1-5%.

In the invention, the preferable solvent for dissolving the polylactic acid in the step (2) is N-methyl pyrrolidone, the content of the N-methyl pyrrolidone is 0.5-4%, the constant-temperature stirring temperature is 80-100 ℃, the stirring time is 10-12h, then the mixture is kept stand at 80 ℃ for 6h to remove bubbles, and the mixture is subjected to vacuum drying at 40 ℃ for 24h after film scraping. Compared with the materials with unique wettability reported previously, the film prepared by the invention has the following beneficial effects:

(1) the super-hydrophobic-super-oleophylic biodegradable film has wider application range, such as separation of oil-water mixture and separation of oil-water emulsion which does not contain surfactant and is stable by the surfactant;

(2) has an economical and convenient preparation process;

(3) the invention selects the polylactic acid with the biodegradable characteristic as the raw material, is more biological and environment-friendly, and can be biodegraded without forming white garbage after being used up.

Drawings

FIG. 1 is a scanning electron microscope photograph of the silica aerogel @ polylactic acid film of example 1;

FIG. 2 is a scanning electron microscope photograph of the silica aerogel @ polylactic acid film of example 2;

FIG. 3 is a scanning electron microscope photograph of the silica aerogel @ polylactic acid film of example 3;

FIG. 4 is a graph showing the oil-water separation effect of the silica aerogel @ polylactic acid film in example 2;

FIG. 5 is a photomicrograph of the silica aerogel @ polylactic acid film of example 2 in water after oil and water separation.

Detailed Description

The technical solution of the present invention is described in detail by the following specific examples, but the scope of the present invention is not limited by these examples.

Examples 1 to 3

(1)SiO₂Preparation of aerogel/ethanol dispersions

1ml of ethyl orthosilicate was dissolved in 2ml of methanol, and 0.5ml of oxalic acid solution was slowly added to the mixture and stirred for 30 min. Then, 5ml of a methanol solution containing 0.6ml of ammonia (20%) was added, and the solution was further stirred for 15min, and the solution was left at 25 ℃ for 1h to form a gel. After gelation, 20ml of anhydrous ethanol was added to the gel and replaced at 25 ℃ for 6 hours to remove oxalic acid and unreacted chemicals, etc., after which 5ml of a 5% trimethylchlorosilane in ethanol/n-hexane mixed solution was added and the ethanol washing treatment was repeated four times to ensure complete removal of oxalic acid and other chemical residues, etc. Washing, performing supercritical drying to obtain SiO2 aerogel, adding appropriate amount of anhydrous ethanol into the obtained SiO2 aerogel, stirring, and ultrasonically dispersing to obtain 0.1%, 0.5%, and 1% SiO respectively₂Aerogel/ethanol dispersion.

(2) Preparation of silica aerogel @ polylactic acid film

Dissolving 1g of pretreated polylactic acid in 100g of NMP solvent, continuously and mechanically stirring for 12h at 85 ℃ to obtain uniform membrane casting solution, standing for 8h at 80 ℃ to remove bubbles, pouring the membrane casting solution on the surface of a clean glass plate, scraping the membrane by using a scraper with the thickness of 200 mu m, immediately soaking the preformed polylactic acid film into ethanol dispersion liquid containing 0.1%, 0.5% and 1% of silica aerogel, curing to obtain the silica aerogel @ polylactic acid film, and performing vacuum drying for 24h at 40 ℃ to obtain a finished product. Then measuring the surface structure and the contact angle, and measuring the mechanical property, the specific data is shown in table 1.

To test the oil-water separation ability of the superhydrophobic membrane, water-in-oil emulsions with nano-and micro-droplet sizes containing surfactants were prepared. For common oil-water mixtures (such as oil slick), the common super-hydrophobic material can realize the separation of oil and water. For oil-water emulsions (especially those with surfactants), the separation of oil-water emulsions is difficult to achieve with common superhydrophobic materials due to the limitation of their own pore size. The invention uses the polylactic acid film of example 2 and 0.5% SiO₂The film obtained by compounding the aerogel ethanol dispersion liquid is taken as an example and subjected to an oil-water separation experiment, as shown in fig. 4, the oil-water mixture which is stabilized by adding the surfactant before separation is in a white emulsion state, the filtrate collected after separation is changed into a colorless transparent liquid, and the existence of micro-nano-sized liquid drops is not observed in a microscope, as shown in fig. 5, so that the separation of the oil-water emulsion containing the surfactant is realized.

TABLE 1

Item	Example 1	Example 2	Example 3
				SiO₂Mass fraction/% of aerogel	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

1. A preparation method of a biodegradable oil-water separation porous membrane is characterized by comprising the following steps:

(1) preparation of silica aerogel/ethanol dispersion: the silica aerogel is prepared by adopting a sol-gel method, firstly, ethyl orthosilicate is dissolved in methanol, oxalic acid solution with the concentration of 10mmol/L is added, and then the mixture is stirred for a period of time, wherein the volume ratio of the ethyl orthosilicate to the methanol to the oxalic acid solution is 1: 2: 0.5; then adding a methanol solution containing 20% ammonia water, wherein the volume ratio of the ammonia water to the methanol is 1: further stirring the solution, and gelling the solution at a constant temperature, wherein the gelling temperature is 25-50 ℃ and the gelling time is 0.5-2 h; SiO2₂After gelation, adding a certain amount of anhydrous ethanol into the gel, replacing at constant temperature for 6-10h, removing oxalic acid and unreacted chemical substances, and adding a proper amount of ethanol/n-hexane mixed solution containing trimethylchlorosilane for treating SiO₂Hydrophobic modification is carried out, the ethanol washing treatment is repeated for four times to ensure that oxalic acid and other chemical residues are completely removed, and after washing, supercritical drying is carried out to obtain SiO₂Crushing the aerogel, adding a proper amount of absolute ethyl alcohol, uniformly dispersing by stirring and ultrasonic,to form SiO₂Aerogel/ethanol dispersion;

(2) preparation of silica aerogel @ polylactic acid film: preparing a polylactic acid film by adopting a non-solvent induced phase separation method, dissolving pretreated polylactic acid in a solvent, wherein the content of N-methyl pyrrolidone is 0.5-4%, stirring at a constant temperature to obtain a casting solution, standing at the constant temperature of 80-100 ℃ for 10-12h, removing bubbles after standing at the temperature of 80 ℃ for 6h, pouring the casting solution on the surface of a clean glass flat plate, scraping the film by using a scraper with a certain thickness, immersing the preformed polylactic acid film into ethanol dispersion containing silicon dioxide aerogel, curing to obtain a polylactic acid super-hydrophobic film, and finally drying in vacuum at the temperature of 40 ℃ for 24 h.