A modified cellulose film, and a method for preparing and using the same

Abstract

The application discloses a modified cellulose membrane and a preparation method and application thereof, and belongs to the technical field of cellulose membrane preparation, and the method comprises the following steps: preparing cellulose carbamate and phosphorylating, contacting a solution containing phosphorylated cellulose carbamate with a coagulation bath to form, washing to obtain regenerated cellulose membrane, and chlorinating the cellulose membrane; the solution containing phosphorylated cellulose carbamate contains 8 wt% alkali and 12% urea; the coagulation bath is 8 wt% sulfuric acid aqueous solution; the contacting condition comprises that the temperature is 0-25 DEG C; and the chlorination condition is 8 wt% sodium hypochlorite solution with pH being 5.5. The regenerated cellulose membrane prepared by the method has the properties of antibiosis, flame retardation and hydrophobicity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural polymers, in particular to a modified cellulose membrane and a preparation method and application thereof. BACKGROUND

[0002] Cellulose is a kind of abundant renewable biological natural material, which has the advantages of biocompatibility, biodegradability and environmental friendliness, and has been widely used in membrane materials. Cellulose is mainly composed of carbon (C), hydrogen (H) and oxygen (O), which is flammable and easy to breed bacteria. In the process of combustion chemical reaction, the carbon and hydrogen inside the cellulose react with oxygen through oxidation, releasing a large amount of energy. Cotton fiber has a porous and loose structure, and has strong hygroscopicity, which creates favorable conditions for the breeding of bacteria, so it is easy to breed bacteria. Therefore, it is of great significance to modify cellulose for its flame retardant and antibacterial properties. Therefore, a method for modifying cellulose hydroxyl group while imparting flame retardant and antibacterial functions is needed.

[0003] Cellulose materials can achieve flame retardancy through impregnation, spraying, blending, coating and other finishing methods. The antibacterial ability of cellulose materials can be enhanced by adding active agents, including zinc oxide nanoparticles, quaternary ammonium compounds, silver nanoparticles and biological materials. However, there are many limitations in these cellulose finishing methods. The water resistance of added flame retardants and antibacterial agents is insufficient. According to the standardized washing test, the flame retardancy and water resistance of cellulose are significantly reduced, which cannot meet the long-term use requirements. In addition, if cellulose has both flame retardant and antibacterial properties, the processing technology is complex, the amount of additives is large, and the practicality of the prepared functional cellulose is poor. Therefore, it is of great significance to impart inherent flame retardant and antibacterial properties to cellulose materials. SUMMARY

[0004] The purpose of the present application is to solve the above-mentioned problems existing in the prior art, and to provide a preparation method of a modified cellulose membrane with flame retardant and antibacterial functions. It solves the problem that the flame retardant performance of the prior cellulose is poor in durability, and direct chemical flame retardant modification of cellulose will reduce the degree of polymerization of cellulose, greatly reducing the mechanical strength of the membrane material.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A preparation method of a modified cellulose membrane, comprising the following steps:

[0007] S1. 3-5 parts by weight of cellulose and 5-15 parts by weight of urea are added to 100-200 parts by weight of N,N-dimethylacetamide, stirred at 150-170℃ for 4-8h, filtered after reaction, and dried to obtain cellulose carbamate;

[0008] S2 adding 3-6 parts by weight of the cellulose carbamate in step S1 to a solution of 1-8 parts by weight of diammonium hydrogen phosphate, 5-20 parts by weight of urea and 50-100 parts by weight of water, uniformly mixing for 10-30 min, ultrasonic treatment for 5-15 min, drying, heating at 150-170℃ for 20-40 min, stirring to complete phosphatization, washing with hot and cold water alternately, and drying to obtain the phosphatized cellulose carbamate;

[0009] S3 adding 2-6 parts by weight of the phosphatized cellulose carbamate in step S2 to an alkaline solution, dissolving at -8 to -14℃ to obtain a phosphatized cellulose carbamate solution;

[0010] S4 after calendering the phosphatized cellulose carbamate solution in step S3 on a glass plate, placing it in a coagulation bath of 4-14 parts by weight of sulfuric acid and 50-150 parts by weight of water at room temperature for 1-10 min, soaking and washing to obtain the phosphatized cellulose carbamate film. Preferably, the coagulation bath temperature is 10-30℃.

[0011] Further, the preparation method of the flame-retardant modified cellulose film of the present application further comprises: S5 chlorinating the cellulose film in step S4 in a sodium hypochlorite solution with pH of 2-6 for 20-60 min, soaking and drying at room temperature to obtain the flame-retardant and antibacterial cellulose film. Preferably, the pH in S5 is 5-6.

[0012] The alkaline solution is a cellulose dissolving solution, which comprises 6-12 parts by weight of sodium hydroxide (or potassium hydroxide, lithium hydroxide), 8-16 parts by weight of urea (or thiourea) and water.

[0013] The present application also provides a flame-retardant and antibacterial multifunctional cellulose film prepared by the above method.

[0014] The cellulose film of the present application can be used as a packaging film and a filtering film. Its good flame-retardant and antibacterial properties, as well as the hydrophobic effect, make it particularly suitable for use as an active packaging film material.

[0015] Compared with the prior art, the present application has the following advantages:

[0016] (1) The ammonium phosphate group in the present application is grafted on the surface of the cellulose carbamate by covalent bonding, so that the cellulose film has intrinsic flame-retardant effect and improves the durability of the flame-retardant effect;

[0017] (2) The present application first performs a carbamate reaction, and then performs a phosphatization reaction, which can better balance the flame-retardant property and mechanical property of the film material, and the amino group in the carbamate can react with sodium hypochlorite again to obtain N-haloamine structure, so that it obtains double effects of flame-retardant and antibacterial;

[0018] (3) After the cellulose is subjected to graft modification, a large number of hydrophilic hydroxyl groups on the surface are combined, and the hydrophobicity is improved, so that the application of the cellulose in the field of active packaging is expanded;

[0019] (4) The preparation method of the flame-retardant and antibacterial multifunctional cellulose film is simple, the prepared flame-retardant and antibacterial multifunctional cellulose film has high thickness uniformity, the film surface is flat, the light transmittance is high (about 90%), and the film has high mechanical properties. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The figure is an antibacterial property test diagram of the cellulose films prepared in Comparative Example 1 and Example 3, in which S is Staphylococcus aureus, and E is Escherichia coli.

[0021] Figure 2 The figure is an antibacterial property test diagram of the cellulose films prepared in Comparative Example 1 and Example 2, in which RPCCM is a phosphorylated cellulose carbamate film, and RCCM is a cellulose carbamate film. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application are further described below in combination with the drawings and technical solutions.

[0023] Comparative Example 1

[0024] A preparation method of a cellulose film, comprising the following steps:

[0025] S1 5 g of cellulose (the cellulose used in the present application is cosmo pulp, and the alpha cellulose content is > 94%) and 15 g of urea are weighed and added to 150 g of N,N-dimethylacetamide, and the mixture is reacted at 160 DEG C for 6 h. After the reaction is completed, filtration is performed, and the cellulose carbamate is obtained by drying at 80 DEG C;

[0026] S2 3.1 g of the cellulose carbamate in step S1 is added to an alkali urea system of 8 g of sodium hydroxide, 12 g of urea and 80 g of water, and is dissolved at -12 DEG C for 3 min to obtain a cellulose carbamate solution;

[0027] S3 The cellulose carbamate solution in step S2 is calendered on a glass plate, and then is placed in a sulfuric acid coagulation bath (32 g of sulfuric acid and 368 g of water) at room temperature for coagulation for 5 min. After immersion and washing, the cellulose carbamate film is obtained by air drying.

[0028] Comparative Example 2

[0029] A preparation method of a flame-retardant cellulose film, comprising the following steps:

[0030] S1 take 5 g of cellulose (cellulose used in the invention is cosmo pulp, alpha cellulose content > 94%) into a solution of diammonium phosphate 5 g, urea 18 g and water 70 g, uniformly mix for 20 min and then ultrasonic treatment for 10 min. After drying, heat at 150℃ for 35 min, complete phosphonation by stirring, and then wash with cold and hot water alternately and dry to obtain phosphonated cellulose;

[0031] S2 add 3.1 g of phosphonated cellulose in step S1 into an alkali urea system of sodium hydroxide 8 g, urea 12 g and water 80 g, and dissolve at -12℃ for 3 min to obtain a phosphonated cellulose solution;

[0032] S3 after calendering the phosphonated cellulose solution in step S2 on a glass plate, place it in a sulfuric acid coagulation bath (sulfuric acid 32 g, water 368 g) for coagulation at room temperature for 5 min, and then soak, wash and dry to obtain a phosphonated cellulose membrane.

[0033] Example 1

[0034] A preparation method of a flame-retardant cellulose membrane, comprising the following steps:

[0035] S1 take 5 g of cellulose, 15 g of urea and add into 150 g of N,N-dimethylacetamide, stir at 160℃ under nitrogen atmosphere for 6 h, filter after the reaction is completed, and dry to obtain cellulose carbamate;

[0036] S2 take 3.1 g of cellulose carbamate in step S1 and add into a solution of diammonium phosphate 5 g, urea 18 g and water 70 g, uniformly mix for 20 min and then ultrasonic treatment for 10 min. After drying, heat at 150℃ for 35 min, complete phosphonation by stirring, and then wash with cold and hot water alternately and dry to obtain phosphonated cellulose carbamate;

[0037] S3 add 3.1 g of phosphonated cellulose carbamate in step S2 into an alkali urea system of sodium hydroxide 8 g, urea 12 g and water 80 g, and dissolve at -12℃ for 3 min to obtain a phosphonated cellulose carbamate solution;

[0038] S4 after calendering the phosphonated cellulose carbamate solution in step S3 on a glass plate, place it in a coagulation bath of sulfuric acid 32 g and water 368 g for coagulation at room temperature for 5 min, and then soak, wash and dry to obtain a phosphonated cellulose carbamate membrane.

[0039] Example 2

[0040] A preparation method of a flame-retardant cellulose membrane, except that the addition amount of cellulose carbamate in step S2 and the addition amount of phosphonated cellulose carbamate in step S3 are different from those in example 1, and other steps are the same as those in example 1, which are as follows:

[0041] S2 cellulose carbamate 5g in step S1 is added to a solution of diammonium hydrogen phosphate 5g, urea (co-solvent) 18g, water 70g, and uniformly mixed for 20 min and then ultrasonically treated for 10 min. After drying, phosphorization is completed by heating at 150°C for 35 min with stirring, and after washing with hot and cold water alternately, phosphorized cellulose carbamate is obtained;

[0042] S3 phosphorized cellulose carbamate 6.4g in step S2 is added to a sodium hydroxide 8g, urea 12g, water 80g alkali urea system, and dissolved at -12°C for 3 min to obtain a phosphorized cellulose carbamate solution.

[0043] Example 3

[0044] The preparation method of the flame-retardant, antibacterial multifunctional cellulose film in this example is the same as that in Example 2 except for step S5, and specifically:

[0045] S5 cellulose film in step S4 is chlorinated in a sodium hypochlorite solution with pH = 5.5 for 30 min, and then soaked and dried at room temperature to obtain a flame-retardant, antibacterial cellulose film.

[0046] Test Example 1

[0047] The degree of polymerization of cellulose carbamate prepared in Test Comparative Example 1, phosphorized cellulose prepared in Test Comparative Example 2, and phosphorized cellulose carbamate prepared in Example 1 is shown in the following table. It can be understood that direct phosphorization modification of cellulose greatly reduces the degree of polymerization of the material, although it can improve the solubility in alkaline solution, the more phosphorized groups, the better the flame retardant performance, but the degree of polymerization is reduced, and the strength and durability of the finally prepared film material are reduced, which affects the use of the film material. Therefore, in order to balance the relationship between the flame retardant performance, strength and durability of the film material, cellulose is first converted into cellulose carbamate, and then phosphorized.

[0048] Table 1

[0049]

[0050] The mechanical properties of the film are measured at room temperature according to the ASTM standard method. The rectangular cellulose film (10x100mm2) is fixed on the tensile carrier of the instrument; the initial tension interval is set to 50mm, the tensile speed is 5mm / min, and each sample is repeated at least 5 times. The specific test results are shown in Table 2.

[0051] Table 2 Test results of tensile strength of flame-retardant, antibacterial multifunctional cellulose film

[0052] Experimental protocol Tensile stress / MPa Tensile strain / % Comparative example 1 88.40 5.30 Example 1 100.48 1.73 Example 2 123.83 14.06

[0053] Comparative Example 1 and Example 1 have the same cellulose concentration when dissolved, and Example 1 has a higher tensile stress, but the tensile strain is only 32.6% of that of Comparative Example 1. Overall, the mechanical strength of Comparative Example 1 is better, which also corresponds to the degree of polymerization in Table 1. Comparative Example 1 and Example 2 have approximately the same solution viscosity after being dissolved, and Example 2 achieves a higher tensile stress and tensile strain. The cellulose in Example 2 is more easily dissolved in the alkali urea system due to the destruction of hydrogen bonds in the chemical modification, and the obtained solution is more uniform and stable, so the mechanical strength is improved to a certain extent.

[0054] Test Example 2

[0055] The antibacterial activity of chlorinated samples was evaluated using the test method of GB / T 20944.3-2008 “Evaluation of antibacterial properties of textiles (Part 3): oscillation method (GB / T 20944.3-2008)”. Cellulose membranes were contacted with E. coli (ATCC 25922) and S. aureus (ATCC 6538). The specific operation is as follows: cut the membrane into small pieces (1 x 1 cm 2 ), then add 5 ml of E. coli and S. aureus suspensions with a concentration of 105 CFU / ml into a conical flask containing 70 ml, seal, and place in a shaking bed at 25°C and shake for 18-24 h. Record the concentration of 105, 104, 103, 102 in a counterclockwise manner on a nutrient agar plate, and incubate at 37°C for 24 h. The specific test results are shown in Table 2. Figure 1 .

[0056] As shown in the figure, the bacteriostatic rate of Example 3 for S. aureus and E. coli reached 99.99%. The bacteriostatic property of the cellulose membrane in Example 3 is attributed to the N-Cl structure generated during the chlorination process. After contacting with microorganisms, these halogenated amine compounds can penetrate the cell wall and interact with biological molecules (proteins, nucleic acids, etc.) inside the cell. Therefore, they destroy the physiological structure and function of microorganisms, effectively achieving the antibacterial goal.

[0057] Test Example 3

[0058] The cellulose membranes prepared in the control example and the examples were tested for hydrophobicity, and the surface hydrophobicity of the cellulose membranes was determined by the water contact angle, which was measured by a contact angle tester. Three parallel tests were performed for each group, and the average value was calculated. The hydrophilicity and wettability of the samples were studied by measuring the water contact angle of the membrane samples in each group, and the specific test results are shown in Table 3.

[0059] Table 3 Test results of hydrophobicity of cellulose membranes

[0060] Experimental protocol Water contact angle / ° Comparative example 1 40.5 Example 1 68.0 Example 2 78.2

[0061] The water contact angle of Comparative Example 1 was 40.5°, which was due to the presence of a large amount of hydrophilic hydroxyl groups, thereby showing high hydrophilicity. After chemical modification, the hydroxyl groups on the cellulose molecules were largely consumed, so the water contact angle of the film was improved, and the hydrophobicity of the film was improved.

[0062] Test Example 4

[0063] The flame retardant properties of the cellulose film were evaluated using the MCC (micro calorimetry) method using ASTM D7309. The sample weight was 5 mg, and the sample was tested in a mixed atmosphere of oxygen (20 vol%) and nitrogen (80 vol%), at a temperature range of 100°C to 700°C, at a temperature increase rate of 1°C / S, and the specific test results are shown in Table 3.

[0064] Table 3 MCC test table of cellulose film

[0065] Experimental protocol HRR (heat release rate) / (W / g) Comparative example 1 197.67 Example 2 46.97

[0066] As shown in Figure 2 , after phosphorylation modification, the HRR value of the cellulose film was reduced from 197.67 W / g of Comparative Example 1 to 46.97 W / g of Example 2. This was due to the introduction of anionic phosphate groups, which consumed heat through decomposition during combustion, reduced the temperature of the burning material and the speed of flame propagation, thereby achieving a flame retardant effect.

Claims

1. A method for preparing a modified cellulose membrane, characterized in that, Includes the following steps: S1 Weigh 3-5 parts by weight of cellulose and 5-15 parts by weight of urea and add them to 100-200 parts by weight of N,N-dimethylacetamide. Stir at 150-170°C for 4-8 hours. After the reaction is complete, filter and dry to obtain cellulose carbamate. S2 Take 3-6 parts by weight of cellulose carbamate from step S1 and add it to a solution of 1-8 parts by weight of diammonium hydrogen phosphate, 5-20 parts by weight of urea and 50-100 parts by weight of water. Mix evenly for 10-30 minutes, then sonicate for 5-15 minutes. After drying, heat at 150-170℃ for 20-40 minutes and stir to complete phosphorylation. After washing with alternating hot and cold water and drying, obtain phosphorylated cellulose carbamate. S3. Add 2-6 parts by weight of the phosphorylated cellulose carbamate from step S2 to an alkaline solution and dissolve it at -8 to -14°C to obtain a phosphorylated cellulose carbamate solution. S4. The phosphorylated cellulose carbamate solution from step S3 is rolled on a glass plate and then placed in a coagulation bath containing 4-14 parts by weight of sulfuric acid and 50-150 parts by weight of water to coagulate at room temperature for 1-10 minutes. After soaking and washing, a phosphorylated cellulose carbamate membrane is obtained.

2. The method for preparing the modified cellulose membrane according to claim 1, characterized in that, S5. The cellulose membrane from step S4 is placed in a sodium hypochlorite solution with a pH of 2-6 for 20-60 minutes for chlorination, and then soaked and dried at room temperature to obtain a flame-retardant and antibacterial cellulose membrane.

3. The method for preparing the modified cellulose membrane according to claim 2, characterized in that, The pH in S5 is 5-6.

4. The method for preparing the modified cellulose membrane according to claim 1, characterized in that, The alkaline solution is a cellulose-dissolving solution, comprising 6-12 parts by weight of sodium hydroxide, 8-16 parts by weight of urea, and water.

5. A modified cellulose membrane prepared by the method according to any one of claims 1-4.

6. The use of the modified cellulose membrane according to claim 5 as a packaging film.

7. An application of a modified cellulose membrane prepared according to the method of claim 2 or 3, characterized in that, Application of modified cellulose membranes as active packaging films.

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