阅读说明：本技术 一种水蒸气辅助蛋白基复合膜材料二次交联的方法 (Method for secondary crosslinking of water vapor-assisted protein-based composite membrane material ) 是由 何明 尹国强 陈文杰 丁姣 高子姗 赖锐豪 于 2021-09-08 设计创作，主要内容包括：本发明涉及高分子材料交联技术领域,公开一种水蒸气辅助蛋白基复合膜材料二次交联的方法,包括以下步骤：(1)成膜液的制备；(2)将交联剂加入成膜液中,在40～60℃下搅拌20～60min,得到预交联成膜液；(3)通过浇铸法或静电纺丝法制得预交联蛋白基复合膜；(4)将预交联蛋白基复合膜置于水蒸气氛围中进行二次交联处理。本方法所得的二次交联改性蛋白基复合膜具有较高的交联度,能在不影响成膜性的情况下,有效提高蛋白基复合膜的耐水性和力学性能。(The invention relates to the technical field of high polymer material crosslinking, and discloses a secondary crosslinking method of a water vapor-assisted protein-based composite membrane material, which comprises the following steps: (1) preparing a film forming solution; (2) adding a cross-linking agent into the film-forming solution, and stirring for 20-60 min at 40-60 ℃ to obtain a pre-cross-linking film-forming solution; (3) preparing a pre-crosslinked protein-based composite membrane by a casting method or an electrostatic spinning method; (4) and (3) placing the pre-crosslinked protein-based composite membrane in a water vapor atmosphere for secondary crosslinking treatment. The secondary crosslinking modified protein-based composite membrane obtained by the method has higher crosslinking degree, and can effectively improve the water resistance and mechanical property of the protein-based composite membrane without influencing the membrane forming property.)

1. A method for secondary crosslinking of a water vapor-assisted protein-based composite membrane material is characterized by comprising the following steps:

(1) preparing a film forming solution: adding the protein powder and the water-soluble polymer into a sample dissolving bottle, adding a cosolvent, and uniformly stirring to obtain a film forming solution with the mass fraction of 6-15%;

(2) adding a cross-linking agent into the film-forming solution, and stirring for 20-60 min at 40-60 ℃ to obtain a pre-cross-linking film-forming solution;

(3) preparing a pre-crosslinked protein-based composite membrane by a casting method or an electrostatic spinning method;

(4) placing the pre-crosslinked protein-based composite membrane in a water vapor atmosphere for secondary crosslinking treatment;

wherein the total solid mass of the protein powder and the water-soluble polymer is 1.20-3.0 g, and the mixing mass ratio is 9: 1-5: 5; the addition amount of the cross-linking agent is 3-10% of the total solid mass of the protein powder and the water-soluble polymer.

2. The method for secondary crosslinking of a water vapor assisted protein based composite membrane material as claimed in claim 1, wherein the protein powder in step (1) comprises one or more of keratin, collagen, cottonseed protein, soybean protein and zein; the cosolvent comprises one of an alkaline aqueous solution with the pH value of 8-11, a formic acid solution or a hexafluoroisopropanol solution; the water-soluble polymer comprises one or more of polyvinyl alcohol, polyethylene oxide, polyethylene glycol, chitin, starch, carboxymethyl cellulose and gelatin.

3. The method for secondary crosslinking of a composite membrane material with water vapor-assisted protein according to claim 1, wherein the crosslinking agent in step (2) comprises genipin, glutaraldehyde, glyoxal, formaldehyde, transglutaminase, dialdehyde starch, or dialdehyde carboxymethyl cellulose.

4. The method for secondary crosslinking of a water vapor auxiliary protein-based composite membrane material according to claim 1, wherein in the step (3), if a casting method is adopted to prepare the crosslinked modified protein-based composite membrane, a polypropylene or polyvinylidene fluoride or polyethylene mold filled with the pre-crosslinked membrane-forming solution is placed in a constant temperature and humidity box with the temperature of 25-35 ℃ and the relative humidity of 40-50%, and is dried for 6-12 hours at constant temperature.

5. The method for secondary crosslinking of a steam-assisted protein-based composite membrane material according to claim 1, wherein in the step (3), if an electrostatic spinning method is adopted to prepare the crosslinked modified protein-based composite membrane, the pre-crosslinked membrane-forming solution is placed in a high-voltage electrostatic field for spinning, and the crosslinked modified protein-based composite nanofiber membrane is obtained after continuous spinning for 6-10 hours; wherein the electrostatic spinning process parameters are as follows: the voltage is 18-30 kV, the receiving distance is 8-15 cm, the spinning speed is 0.5-1.0 mL/h, the inner diameter of a spinneret orifice is 0.3-1.0 mm, the spinning temperature is 25-35 ℃, and the spinning humidity is 40-50%.

6. The method for secondary crosslinking of a water vapor auxiliary protein-based composite membrane material according to claim 1, wherein the water vapor atmosphere in the step (4) is a constant temperature and humidity environment with a relative humidity of 75-90% and a temperature of 25-50 ℃, and the secondary crosslinking treatment time is 0.5-24 h.

Technical Field

The invention relates to the technical field of high polymer material crosslinking, in particular to a method for secondary crosslinking of a protein-based membrane material assisted by water vapor.

Background

Some membrane materials prepared by using protein (such as keratin, cottonseed protein, soybean protein and the like) or water-soluble high polymer as a main raw material have poor water resistance or mechanical properties. Therefore, the film material needs to be modified by crosslinking, so that covalent bonds are constructed in or among the molecules of the film material to form a crosslinked network, thereby improving the water resistance and mechanical properties of the film material. Crosslinking methods for protein-based membrane materials include physical crosslinking methods, microbial crosslinking methods, and chemical crosslinking methods. Compared with physical crosslinking and microbial crosslinking, the chemical crosslinking method has more obvious crosslinking effect and more controllable crosslinking sites.

Common methods for chemical crosslinking of keratin materials are dip crosslinking, steam crosslinking, and in situ crosslinking. Wherein, the in-situ crosslinking is to directly add a crosslinking agent into the raw material solution to enable the crosslinking agent and the raw material solution to generate crosslinking reaction so as to achieve the effect of crosslinking modification. Compared with dipping crosslinking and steam crosslinking, the in-situ crosslinking can effectively reduce the usage amount of a chemical crosslinking agent, and the molecules of the crosslinking agent can be fully and directly contacted with a protein-based material, so that the crosslinking efficiency is effectively improved.

However, when a crosslinking agent is added to the raw film-forming solution, the degree of gelation increases as the degree of crosslinking of the film-forming solution increases. This affects the fluidity of the solution, thereby reducing the film-forming and spinnability of the solution, making it impossible to uniformly form a film or to successfully spin. At present, the method for solving the problem is mainly to control the crosslinking degree of the film forming solution after adding the crosslinking agent, namely to use the film forming solution with lower crosslinking degree to carry out casting film forming or electrostatic spinning film forming. Although this solution enables smooth film formation by the deposition solution, it is not effective in improving the water resistance and mechanical properties of the film material because of its low degree of crosslinking.

Therefore, a technology capable of assisting the secondary crosslinking of the protein-based membrane material is developed, the protein-based membrane material with high crosslinking degree, good water resistance and mechanical property is prepared, and the practicability of the protein-based composite membrane can be improved and the application field can be further widened.

Disclosure of Invention

The invention provides a method for assisting secondary crosslinking of a protein-based membrane material by using water vapor, which comprises the following steps of:

(1) preparing a film forming solution: adding the protein powder and the water-soluble polymer into a sample dissolving bottle, adding a cosolvent, and uniformly stirring to obtain a film forming solution with the mass fraction of 6-15%;

(2) adding a cross-linking agent into the film-forming solution, and stirring for 20-60 min at 40-60 ℃ to obtain a pre-cross-linking film-forming solution;

(3) preparing a pre-crosslinked protein-based composite membrane by a casting method or an electrostatic spinning method;

(4) and (3) placing the pre-crosslinked protein-based composite membrane in a water vapor atmosphere for secondary crosslinking treatment.

Wherein the total solid mass of the protein powder and the water-soluble polymer is 1.20-3.0 g, and the mixing mass ratio is 9: 1-5: 5; the addition amount of the cross-linking agent is 3-10% of the total solid mass of the protein powder and the water-soluble polymer.

Preferably, the protein powder in step (1) comprises one or more of keratin, collagen, cottonseed protein, soybean protein and zein.

Preferably, the cosolvent in the step (1) comprises one of an alkaline aqueous solution with a pH value of 8-11, a formic acid solution or a hexafluoroisopropanol solution.

Preferably, the water-soluble polymer in step (1) comprises one or more of polyvinyl alcohol, polyethylene oxide, polyethylene glycol, chitin, starch, carboxymethyl cellulose and gelatin.

Preferably, the cross-linking agent in step (2) comprises genipin or glutaraldehyde or glyoxal or formaldehyde or transglutaminase or dialdehyde starch or dialdehyde carboxymethyl cellulose.

Preferably, if the casting method is adopted to prepare the cross-linked modified protein-based composite membrane in the step (3), the polypropylene or polyvinylidene fluoride or polyethylene mold filled with the pre-cross-linking membrane forming solution is placed in a constant temperature and humidity box with the temperature of 25-35 ℃ and the relative humidity of 40-50%, and is dried for 6-12 hours at constant temperature.

Preferably, if the cross-linked modified protein-based composite membrane is prepared by adopting an electrostatic spinning method in the step (3), the pre-cross-linking membrane-forming solution is placed in a high-voltage electrostatic field for spinning, and the cross-linked modified protein-based composite nanofiber membrane is obtained after 6-10 h of continuous spinning. Wherein the electrostatic spinning process parameters are as follows: the voltage is 18-30 kV, the receiving distance is 8-15 cm, the spinning speed is 0.5-1.0 mL/h, the inner diameter of a spinneret orifice is 0.3-1.0 mm, the spinning temperature is 25-35 ℃, and the spinning humidity is 40-50%.

Preferably, the water vapor atmosphere in the step (4) refers to a constant-temperature and constant-humidity environment with a relative humidity of 75-90% and a temperature of 25-50 ℃, and the secondary crosslinking treatment time is 0.5-24 hours.

Compared with the prior art, the invention has the following beneficial effects:_。

the invention utilizes the water vapor to assist the protein-based membrane material to carry out secondary crosslinking reaction, and can effectively improve the crosslinking degree of the protein-based membrane material, thereby improving the water resistance and the mechanical property of the protein-based membrane material. In addition, the invention uses water vapor as a medium for assisting the secondary crosslinking reaction of the protein-based membrane material, and has the characteristics of simple process, low cost, no toxicity, no harm, strong applicability and the like.

Drawings

FIG. 1 is a microscopic topography before and after water absorption of samples of example 3, comparative example 1 and comparative example 2 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

(1) Preparing a film forming solution: respectively adding 0.60g of keratin powder and 0.60g of polyvinyl alcohol into a sample dissolving bottle, adding a sodium hydroxide solution with the pH value of 9 as a cosolvent, and uniformly stirring to obtain a film forming solution with the mass fraction of 12%;

(2) adding 0.072g of 50% glutaraldehyde into the film forming solution, and stirring at 40 ℃ for 20min to obtain a pre-crosslinked film forming solution;

(3) preparing a pre-crosslinked keratin/polyvinyl alcohol composite nanofiber membrane by an electrostatic spinning method, placing the pre-crosslinked membrane-forming solution in a high-voltage electrostatic field for spinning, and continuously spinning for 8 hours to obtain the crosslinked modified protein-based composite nanofiber membrane. Wherein the electrostatic spinning process parameters are as follows: the voltage is 18kV, the receiving distance is 15cm, the spinning speed is 0.5mL/h, the inner diameter of a spinneret orifice is 0.4mm, the spinning temperature is 25 ℃, and the spinning humidity is 40%;

(4) and (2) placing the pre-crosslinked keratin/polyvinyl alcohol composite nanofiber membrane in a constant-temperature and constant-humidity environment with the relative humidity of 80% and the temperature of 40 ℃ for secondary crosslinking treatment for 6 hours to obtain the secondarily crosslinked keratin/polyvinyl alcohol composite nanofiber membrane.

Example 2

(1) Preparing a film forming solution: respectively adding 0.60g of keratin powder and 0.60g of polyvinyl alcohol into a sample dissolving bottle, adding a sodium hydroxide solution with the pH value of 9 as a cosolvent, and uniformly stirring to obtain a film forming solution with the mass fraction of 6%;

(2) adding 0.072g of 50% glutaraldehyde into the film forming solution, and stirring at 40 ℃ for 20min to obtain a pre-crosslinked film forming solution;

(3) preparing a crosslinked keratin/polyvinyl alcohol composite membrane by a casting method, placing a polypropylene mould filled with a pre-crosslinked film-forming solution in a constant-temperature and constant-humidity box with the temperature of 25 ℃ and the relative humidity of 50%, and drying at constant temperature for 10 hours;

(4) and (2) placing the pre-crosslinked keratin/polyvinyl alcohol composite membrane in a constant-temperature and constant-humidity environment with the relative humidity of 80% and the temperature of 40 ℃ for secondary crosslinking treatment for 6 hours to obtain the secondarily crosslinked keratin/polyvinyl alcohol composite membrane.

Example 3

(1) Preparing a film forming solution: adding 0.36g of keratin powder and 0.84g of gelatin into a sample dissolving bottle, adding hexafluoroisopropanol solution serving as a cosolvent, and uniformly stirring to obtain a film forming solution with the mass fraction of 6%;

(2) adding 0.06g of genipin into the film forming solution, and stirring at 40 ℃ for 60min to obtain a pre-crosslinking film forming solution;

(3) preparing a pre-crosslinked keratin/gelatin composite nanofiber membrane by an electrostatic spinning method, placing the pre-crosslinked membrane-forming solution in a high-voltage electrostatic field for spinning, and continuously spinning for 8 hours to obtain the crosslinked modified protein-based composite nanofiber membrane. Wherein the electrostatic spinning process parameters are as follows: the voltage is 21kV, the receiving distance is 15cm, the spinning speed is 0.5mL/h, the inner diameter of a spinneret orifice is 0.4mm, the spinning temperature is 25 ℃, and the spinning humidity is 50%;

(4) and (2) placing the pre-crosslinked keratin/gelatin composite nanofiber membrane in a constant-temperature and constant-humidity environment with the relative humidity of 80% and the temperature of 35 ℃ for 24h of secondary crosslinking treatment to obtain the secondarily crosslinked keratin/gelatin composite nanofiber membrane.

Comparative example 1

(1) Preparing a film forming solution: adding 0.36g of keratin powder and 0.84g of gelatin into a sample dissolving bottle, adding hexafluoroisopropanol solution serving as a cosolvent, and uniformly stirring to obtain a film forming solution with the mass fraction of 6%;

(2) adding 0.06g of genipin into the film forming solution, and stirring at 40 ℃ for 60min to obtain a pre-crosslinking film forming solution;

(3) preparing a pre-crosslinked keratin/gelatin composite nanofiber membrane by an electrostatic spinning method, placing the pre-crosslinked membrane-forming solution in a high-voltage electrostatic field for spinning, and continuously spinning for 8 hours to obtain the crosslinked modified protein-based composite nanofiber membrane. Wherein the electrostatic spinning process parameters are as follows: the voltage is 21kV, the receiving distance is 15cm, the spinning speed is 0.5mL/h, the inner diameter of a spinneret orifice is 0.4mm, the spinning temperature is 25 ℃, and the spinning humidity is 50%.

Comparative example 2

(1) Preparing a film forming solution: adding 0.36g of keratin powder and 0.84g of gelatin into a sample dissolving bottle, adding hexafluoroisopropanol solution serving as a cosolvent, and uniformly stirring to obtain a film forming solution with the mass fraction of 6%;

(2) preparing the keratin/gelatin composite nanofiber membrane by an electrostatic spinning method, putting the pre-crosslinking membrane-forming solution in a high-voltage electrostatic field for spinning, and continuously spinning for 8 hours to obtain the crosslinked modified protein-based composite nanofiber membrane. Wherein the electrostatic spinning process parameters are as follows: the voltage is 21kV, the receiving distance is 15cm, the spinning speed is 0.5mL/h, the inner diameter of a spinneret orifice is 0.4mm, the spinning temperature is 25 ℃, and the spinning humidity is 50%;

(4) and (2) placing the pre-crosslinked keratin/gelatin composite nanofiber membrane in a constant-temperature and constant-humidity environment with the relative humidity of 80% and the temperature of 35 ℃ for 24h of water vapor atmosphere treatment to obtain the non-crosslinked keratin/gelatin composite nanofiber membrane.

Keratin and gelatin of the same type extracted from the same batch are used as raw materials, genipin of the same type is used as a cross-linking agent, a keratin/gelatin composite nanofiber membrane subjected to water vapor auxiliary secondary cross-linking, a pre-cross-linked keratin/gelatin composite nanofiber membrane and an uncrosslinked keratin/gelatin composite nanofiber membrane (prepared samples are respectively marked as A, B, C) are prepared according to the methods of example 3, comparative example 1 and comparative example 2, and the micro-morphologies before and after water absorption are observed to evaluate the water resistance of the membranes and the mechanical properties of the membranes.

And (3) micro-morphology testing: and shearing a small sample, attaching the sample to a sample table adhered with conductive adhesive, spraying gold on the sample, and observing the microscopic morphology of the sample under a scanning electron microscope with the acceleration voltage of 10 kV.

And (3) testing mechanical properties: the samples were cut to 75mm by 10mm dimensions with a clamp spacing of 40mm and a draw rate of 5mm/min, and 3 measurements per sample were averaged.

Sample A is the keratin/gelatin composite nanofiber prepared according to example 3, added with genipin cross-linking agent and subjected to water vapor-assisted secondary cross-linking; sample B is the keratin/gelatin composite nanofiber prepared according to comparative example 1 with the genipin crosslinker added but without steam assisted secondary crosslinking; sample C was the keratin/gelatin composite nanofiber prepared according to comparative example 2 without the addition of a cross-linking agent but subjected to water vapor treatment.

Table 1 shows the results of mechanical property measurements of the respective samples.

Sample (I)	Elongation at Break (%)	Tensile strength (MPa)
			A	8.61	7.28
B	1.07	0.57
			C	2.00	5.56

Comparing A, B, C samples, in terms of micro-topography before and after water absorption, sample A still maintained good fiber topography after water absorption, the fibers swelled but not completely dissolved, while samples B and C dissolved after water absorption, and had lost fiber topography. The elongation at break and tensile strength of the a sample are higher than those of the B and C samples in terms of mechanical properties.

The reason is that in the atmosphere of water vapor, free hydrophilic groups such as amino, hydroxyl and the like in the keratin/gelatin molecular chain of the sample A can react with genipin molecules again, so that the number of the hydrophilic groups in the molecular chain is reduced, and the water resistance of the sample is effectively improved; forming a cross-linked network, and improving the mechanical property of the sample. And because of lack of a cross-linking agent or no water vapor treatment, more hydrophilic groups still exist in the molecular chains of the sample C and the sample B, no cross-linked network is formed, and the water resistance is poor. The method proves that the water vapor assisted secondary crosslinking of the membrane material can effectively improve the crosslinking degree of the membrane material, thereby improving the water resistance and the mechanical property.

The technical solutions provided by the embodiments of the present invention are described in detail above, and the principles and embodiments of the present invention are explained herein by using specific examples, and the descriptions of the embodiments are only used to help understanding the principles of the embodiments of the present invention; meanwhile, for a person skilled in the art, the specific implementation and the application range can be changed according to the embodiment of the present invention. In view of the above, the present disclosure should not be construed as limiting the invention.