Modified cellulose membrane as well as preparation method and application thereof

Abstract

The invention discloses a modified cellulose membrane as well as a preparation method and application thereof, and belongs to the technical field of cellulose membrane preparation, the method comprises the following steps: preparation and phosphorylation of cellulose carbamate, contact forming of a solution containing phosphorylated cellulose carbamate and a coagulating bath, washing to obtain a regenerated cellulose membrane, and chlorination of the cellulose membrane; the solution containing phosphorylated carbamate contains 8 wt% of alkali and 12 wt% of urea; the coagulating bath is a 8wt% sulfuric acid aqueous solution; the contact conditions are as follows: the temperature is 0-25 DEG C; the chlorination condition is a sodium hypochlorite solution with the concentration of 8 wt% and the pH value of 5.5. The regenerated cellulose membrane prepared by the method disclosed by the invention has antibacterial, flame-retardant and hydrophobic properties.

Description

Technical Field

[0001] The invention relates to the technical field of natural polymers, and in particular to a modified cellulose film and a preparation method and application thereof. Background Art

[0002] Cellulose is an abundant renewable biological natural material with the advantages of biocompatibility, biodegradability and environmental friendliness, and has been widely used in membrane materials. Cellulose is mainly composed of three elements: carbon (C), hydrogen (H) and oxygen (O). It is flammable and easy to breed bacteria. During the chemical reaction of combustion, 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 strong hygroscopicity, which creates favorable conditions for the reproduction of bacteria and makes it easy to breed bacteria. Therefore, it is of great significance to modify cellulose in a targeted manner to change its flame retardant and antibacterial properties. Therefore, a method of modifying cellulose hydroxyl groups and giving it flame retardant and antibacterial functions is needed.

[0003] Cellulose materials can be made flame retardant by 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 biomaterials. However, these current cellulose finishing methods have many limitations. The added flame retardants and antibacterial agents are not water resistant enough. According to the standardized water washing test, the flame retardancy and water resistance of cellulose are significantly reduced and cannot meet the requirements of long-term use. In addition, if cellulose has both flame retardant and antibacterial properties, the processing technology is complicated, the amount of additives used is large, and the practicality of the prepared functional cellulose is poor. Therefore, it is of great significance to give cellulose materials inherent flame retardant and antibacterial effects. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems existing in the prior art and provide a method for preparing a modified cellulose film with flame retardant and antibacterial functions. The method solves the problem that the flame retardant durability of cellulose is poor, and the direct chemical flame retardant modification of cellulose will reduce the polymerization degree of cellulose and greatly reduce the mechanical strength of the film material.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a modified cellulose film comprises the following steps:

[0007] S1: weigh 3-5 parts by weight of cellulose and 5-15 parts by weight of urea, add them into 100-200 parts by weight of N,N-dimethylacetamide, stir at 150-170° C. for 4-8 hours, filter after the reaction is completed, and dry 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 minutes, ultrasonically treating for 5-15 minutes, drying, heating at 150-170° C. for 20-40 minutes, stirring to complete phosphorylation, washing with cold and hot water alternately, and drying to obtain phosphorylated cellulose carbamate;

[0009] S3: adding 2 to 6 parts by weight of the phosphorylated cellulose carbamate in step S2 into an alkaline solution and dissolving the solution at -8 to -14°C to obtain a phosphorylated cellulose carbamate solution;

[0010] S4: rolling the phosphorylated cellulose carbamate solution in step S3 on a glass plate and placing it in a coagulation bath containing 4-14 parts by weight of sulfuric acid and 50-150 parts by weight of water for coagulation at room temperature for 1-10 minutes, and then soaking and washing to obtain a phosphorylated cellulose carbamate film. Preferably, the coagulation bath temperature is 10-30°C.

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

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

[0013] The present invention also provides a flame-retardant, antibacterial multifunctional cellulose film, which is prepared by the above method.

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

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention grafts the ammonium phosphate group onto the surface of cellulose carbamate by covalent bonding, so that the cellulose film has an intrinsic flame retardant effect and improves the durability of the flame retardant effect;

[0017] (2) The present invention first performs a carbamate reaction and then a phosphorylation reaction, which can better balance the flame retardant properties and mechanical properties of the membrane material. In addition, the amino group in the carbamate can react with sodium hypochlorite again to obtain an N-haloamine structure, thereby achieving both flame retardant and antibacterial effects.

[0018] (3) After the cellulose of the present invention is grafted and modified, a large number of hydrophilic hydroxyl groups are bonded on the surface, thereby improving its hydrophobicity and expanding its application in the field of active packaging;

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

[0020] Figure 1 This is a test chart of the antibacterial activity of the cellulose films prepared in Comparative Example 1 and Example 3, wherein S represents Staphylococcus aureus and E represents Escherichia coli.

[0021] Figure 2 The antibacterial test diagram of the cellulose membranes prepared in Comparative Example 1 and Example 2, wherein RPCCM is a phosphorylated cellulose carbamate membrane and RCCM is a cellulose carbamate membrane. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0023] Comparative Example 1

[0024] A method for preparing a cellulose film comprises the following steps:

[0025] S1 Weigh 5g of cellulose (the cellulose used in the present invention is cosmo pulp, with an α-cellulose content of >94%) and 15g of urea, add them to 150g of N,N-dimethylacetamide, react at 160°C for 6h, filter after the reaction, and dry at 80°C to obtain cellulose carbamate;

[0026] S2: adding 3.1 g of the cellulose carbamate prepared in step S1 to an alkaline urea system of 8 g of sodium hydroxide, 12 g of urea and 80 g of water, and dissolving the mixture at -12°C for 3 min to obtain a cellulose carbamate solution;

[0027] S3: The cellulose carbamate solution in step S2 is rolled onto a glass plate and then placed in a sulfuric acid coagulation bath (32 g sulfuric acid, 368 g water) for coagulation at room temperature for 5 min. The cellulose carbamate film is obtained after being soaked, washed, and air-dried.

[0028] Comparative Example 2

[0029] A method for preparing a flame retardant cellulose film comprises the following steps:

[0030] S1: Weigh 5g of cellulose (the cellulose used in the present invention is cosmo pulp, with an α-cellulose content of >94%) and add it to a solution of 5g of diammonium phosphate, 18g of urea and 70g of water, mix evenly for 20min and then ultrasonically treat for 10min. After drying, heat at 150°C for 35min, stir to complete phosphorylation, wash with cold and hot water alternately and dry to obtain phosphorylated cellulose;

[0031] S2: adding 3.1 g of the phosphorylated cellulose prepared in step S1 to an alkaline urea system of 8 g of sodium hydroxide, 12 g of urea and 80 g of water, and dissolving the mixture at -12°C for 3 min to obtain a phosphorylated cellulose solution;

[0032] S3: The phosphorylated cellulose solution in step S2 is rolled onto a glass plate and then placed in a sulfuric acid coagulation bath (32 g sulfuric acid, 368 g water) for coagulation at room temperature for 5 min. The phosphorylated cellulose membrane is obtained after being soaked, washed, and air-dried.

[0033] Example 1

[0034] A method for preparing a flame retardant cellulose film comprises the following steps:

[0035] S1: Weigh 5 g of cellulose and 15 g of urea, add them to 150 g of N,N-dimethylacetamide, stir at 160 °C for 6 h under a nitrogen atmosphere, filter after the reaction, and dry to obtain cellulose carbamate;

[0036] S2: 3.1 g of cellulose carbamate in step S1 is added to a solution of 5 g of diammonium phosphate, 18 g of urea and 70 g of water, and the mixture is uniformly mixed for 20 min and then ultrasonically treated for 10 min. After drying, the mixture is heated at 150°C for 35 min, stirred to complete phosphorylation, and washed with cold and hot water alternately and dried to obtain phosphorylated cellulose carbamate;

[0037] S3: adding 3.1 g of the phosphorylated cellulose carbamate prepared in step S2 into an alkaline urea system of 8 g of sodium hydroxide, 12 g of urea and 80 g of water, and dissolving the mixture at -12°C for 3 min to obtain a phosphorylated cellulose carbamate solution;

[0038] S4: rolling the phosphorylated cellulose carbamate solution in step S3 onto a glass plate and placing it in a coagulation bath of 32 g sulfuric acid and 368 g water to coagulate at room temperature for 5 min, soaking, washing, and air-drying to obtain a phosphorylated cellulose carbamate film.

[0039] Example 2

[0040] The method for preparing a flame-retardant cellulose film in this embodiment is the same as that in Embodiment 1 except for the amount of cellulose carbamate added in step S2 and the amount of phosphorylated cellulose carbamate added in step S3, specifically:

[0041] S2: 5 g of cellulose carbamate in step S1 is added to a solution of 5 g diammonium phosphate, 18 g urea (cosolvent) and 70 g water, mixed evenly for 20 min and then subjected to ultrasonic treatment for 10 min. After drying, the mixture is heated at 150°C for 35 min, stirred to complete phosphorylation, and washed with cold and hot water alternately and dried to obtain phosphorylated cellulose carbamate;

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

[0043] Example 3

[0044] This embodiment provides a method for preparing a flame-retardant, antibacterial multifunctional cellulose film. Except for step S5, the rest is the same as that of embodiment 2, specifically:

[0045] S5: placing the cellulose membrane in step S4 in a sodium hypochlorite solution with a pH of 5.5 for 30 minutes for chlorination, soaking and drying at room temperature to obtain a flame-retardant and antibacterial cellulose membrane.

[0046] Test Example 1

[0047] The polymerization degrees of cellulose carbamate prepared in Comparative Example 1, phosphorylated cellulose prepared in Comparative Example 2, and phosphorylated cellulose carbamate prepared in Example 1 were tested, as shown in the following table. It can be understood that directly phosphorylating cellulose greatly reduces the polymerization degree of the material. Although it can improve its solubility in alkaline solution and more phosphorylated groups have better flame retardant properties, the polymerization degree is reduced, and the strength and durability of the film material finally prepared are reduced, affecting the use of the film material. Therefore, in order to balance the relationship between the flame retardant properties, strength and durability of the film material, cellulose is first converted into cellulose carbamate and then phosphorylated.

[0048] Table 1

[0049]

[0050] The mechanical properties of the membrane were measured at room temperature according to the ASTM standard method. A rectangular cellulose membrane (10×100 mm2) was fixed on the tensile carrier of the instrument; the initial tensile interval was set to 50 mm, the tensile speed was 5 mm / min, and each sample was repeated at least 5 times. The specific test results are shown in Table 2.

[0051] Table 2 Flame retardant and antibacterial multifunctional cellulose film tensile strength test results

[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] The cellulose concentrations of Comparative Example 1 and Example 1 are the same when dissolved, and Example 1 has a higher tensile stress, but the tensile strain is only 32.6% of that of the comparative example. Overall, the mechanical strength of Comparative Example 1 is better, which is also corresponding to the degree of polymerization in Table 1; the viscosity of the solution obtained after the dissolution of Comparative Example 1 and Example 2 is roughly the same, and Example 2 obtains higher tensile stress and tensile strain. The cellulose in Example 2 is more soluble in the alkaline urea system because the hydrogen bonds are destroyed during 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 antimicrobial activity of chlorinated samples was evaluated using the GB / T 20944.3-2008 "Evaluation of antimicrobial properties of textiles (Part 3): Oscillation method (GB / T20944.3-2008)" test method. The cellulose membrane was exposed to Escherichia coli (ATCC25922) and Staphylococcus aureus (ATCC 6538). The specific operation was as follows: the membrane was cut into small pieces (1×1 cm 2 ), then add 5 ml of Escherichia coli and Staphylococcus aureus suspension with a concentration of 105 CFU / ml to 70 ml conical flasks, seal them, and place them in a shaker at 25°C for 18 to 24 hours. Record the concentrations of 105, 104, 103, and 102 on the nutrient agar plate in a counterclockwise manner, and culture them at 37°C for 24 hours. For specific test results, see Figure 1 .

[0056] As shown in the figure, the antibacterial rate of Example 3 for Staphylococcus aureus and Escherichia coli reached 99.99%. The antibacterial property of the cellulose film 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 the biological molecules (proteins, nucleic acids, etc.) in the cells. Therefore, they destroy the physiological structure and function of microorganisms and effectively achieve the antibacterial goal.

[0057] Test Example 3

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

[0059] Table 3 Hydrophobicity test results of cellulose membrane

[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 is 40.5°, which is because it also contains a large number of hydrophilic hydroxyl groups, thus showing a higher hydrophilicity. After chemical modification, the hydroxyl groups on the cellulose molecules are consumed in large quantities, so the water contact angle of the membrane is increased, and the hydrophobic property of the membrane is improved.

[0062] Test Example 4

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

[0064] Table 3 MCC test results of cellulose membrane

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

[0066] like Figure 2 As shown, after phosphorylation modification, the HRR value of the cellulose film is reduced from 197.67 W / g in Comparative Example 1 to 46.97 W / g in Example 2. This is because the anionic phosphate group is introduced, which consumes heat through decomposition reaction during the combustion process, reduces 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 film, characterized in that: The steps include: S1: weigh 3-5 parts by weight of cellulose and 5-15 parts by weight of urea, add them into 100-200 parts by weight of N,N-dimethylacetamide, stir at 150-170° C. for 4-8 hours, filter after the reaction is completed, and dry to obtain cellulose carbamate; 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 minutes, ultrasonically treating for 5-15 minutes, drying, heating at 150-170° C. for 20-40 minutes, stirring to complete phosphorylation, washing with cold and hot water alternately, and drying to obtain phosphorylated cellulose carbamate; S3: adding 2 to 6 parts by weight of the phosphorylated cellulose carbamate in step S2 into an alkaline solution and dissolving the solution at -8 to -14°C to obtain a phosphorylated cellulose carbamate solution; S4: rolling the phosphorylated cellulose carbamate solution in step S3 on a glass plate and placing it in a coagulation bath containing 4-14 parts by weight of sulfuric acid and 50-150 parts by weight of water for coagulation at room temperature for 1-10 minutes, and then soaking and washing to obtain a phosphorylated cellulose carbamate film. Preferably, the coagulation bath temperature is 10-30°C.

2. The method for preparing a modified cellulose film according to claim 1, characterized in that: S5: placing the cellulose membrane in step S4 in a sodium hypochlorite solution with a pH of 2 to 6 for 20 to 60 minutes for chlorination, and soaking and drying at room temperature to obtain a flame-retardant and antibacterial cellulose membrane.

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

4. The method for preparing a modified cellulose film according to claim 1, characterized in that: The alkaline solution is a cellulose dissolving solution, which includes 6 to 12 parts by weight of sodium hydroxide (or potassium hydroxide, lithium hydroxide), 8 to 16 parts by weight of urea (or thiourea) and water.

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

6. Use of the modified cellulose film according to claim 5 as a packaging film or a filtration membrane.

7. The use according to claim 6, characterized in that: Application of modified cellulose film as active packaging film.

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