Preparation method and application of vinyl chloride soap-free emulsion grafted copolymer resin

Abstract

The invention relates to a preparation method and application of vinyl chloride soap-free emulsion grafted copolymer resin. According to the method, double reactive functional groups of acetoacetoxyethyl methacrylate are used as a bridging substance for connecting polyvinyl chloride and carboxymethyl chitosan, hydrophilic modification of a chitosan derivative on a comonomer is realized through free radical polymerization and condensation reaction, and then the functional monomer and vinyl chloride are used for in-situ chemical grafting modification; the film is directly formed based on the prepared copolymer without adding any modifier. The copolymer disclosed by the invention has long-term and effective hydrophilic and antifouling properties, the pure water flux, the retention rate, the flux recovery rate and other properties of the prepared ultrafiltration membrane are obviously enhanced, and the chitosan derivative unit is contained in the composition of the copolymer, so that the ultrafiltration membrane is endowed with excellent antibacterial properties.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and more specifically, to a preparation method of a vinyl chloride soap-free emulsion graft copolymer resin and its application in the field of ultrafiltration membranes. Background Art

[0002] Polyvinyl chloride (PVC), as a polymer material with low cost, excellent mechanical properties and various processing methods, shows great application potential in the field of ultrafiltration membranes. Ultrafiltration membranes have important separation and purification functions in the fields of water treatment, food industry and biomedicine. The PVC material, due to its good mechanical properties, chemical resistance, and the adjustable hydrophilicity and pore structure after modification, has become one of the ideal substrates for preparing ultrafiltration membranes. However, traditional PVC ultrafiltration membranes still have certain limitations in terms of anti-fouling performance, separation efficiency and functionality. Therefore, the present invention aims to introduce functional monomers into the PVC molecular chain through in-situ copolymerization modification technology to ultimately achieve precise control of the structure and properties of the membrane material.

[0003] Ethyl acetoacetoxyethyl methacrylate is a multifunctional monomer widely used in the fields of polymer modification and functional materials. The methacrylate group contained in its molecule can provide reactive sites and participate in free radical polymerization reactions. At the same time, the acetoacetoxyethyl group also has reactivity and can react with various functional groups (such as amino groups, hydroxyl groups, epoxy groups, etc.). Pan et al. (Chinese Patent: CN104292378B, July 31, 2018.) used the copolymer formed by copolymerizing ethyl acetoacetoxyethyl methacrylate and vinyl chloride monomer as seeds, and then added styrene as a secondary reaction monomer to copolymerize with the seeds. By utilizing the polarity difference of the polystyrene (PS) formed by the seeds and the secondary polymerization, phase separation occurred, and then non-spherical particles with different hydrophilicities (or polarity distributions) were prepared. Then, the particles were added to the blend of PS and PVC to improve the compatibility of the PS and PVC blend, thereby improving the mechanical properties and processing properties of the blend. However, ethyl acetoacetoxyethyl methacrylate is an oil-soluble monomer. Therefore, when the copolymer obtained by copolymerizing ethyl acetoacetoxyethyl methacrylate and vinyl chloride is used for the preparation of ultrafiltration membranes, the improvement effect of hydrophilicity brought by it is limited. Qiang et al. (Chinese Patent: CN103834037A, June 4, 2014.) utilized the reaction of amino groups with acetoacetate groups and prepared a novel functional acrylic resin composite coating by means of the room-temperature self-crosslinking of chitosan derivatives and acrylic resins. This preparation method utilizes the crosslinking reaction of chitosan derivatives and polyacrylate resins to improve the strength and compactness of the coating. Since the glass transition temperature of the polyacrylate copolymer resin used to manufacture the coating is low, the self-adhesion is strong, and the tensile strength is low, it is not suitable for manufacturing ultrafiltration membranes with multiple pores. Summary of the Invention

[0004] The problem to be solved by the present invention is to overcome the defect that the hydrophobicity of existing polyvinyl chloride resins cannot meet the antifouling requirements for the use of ultrafiltration membranes, and to provide a preparation method and application of a vinyl chloride soap-free emulsion graft copolymer resin. This method uses the dual-reactive functional groups of ethyl acetoacetoxy methacrylate as a bridge connecting polyvinyl chloride and carboxymethyl chitosan. Through free radical polymerization and condensation reactions, the hydrophilic modification of the comonomer by the chitosan derivative is achieved, and then the functional monomer is used for in-situ chemical graft modification with vinyl chloride. At the same time, in the reaction system, the amphiphilicity of the functional monomer is used as a stabilizer for the system without adding an emulsifier separately, thereby reducing the post-treatment process and avoiding pollution to the water environment. Based on the fact that the copolymer prepared does not require the addition of any modifiers to form a film directly, the structure of the ultrafiltration membrane prepared from the copolymer is controllable and has good repeatability. The copolymer of the present invention has a long-lasting and effective hydrophilic antifouling property, and the properties such as the pure water flux, rejection rate, and flux recovery rate of the ultrafiltration membrane prepared are significantly enhanced. Moreover, since the copolymer composition contains chitosan derivative units, the ultrafiltration membrane is endowed with excellent antibacterial properties.

[0005] The above object of the present invention is achieved by the following technical solutions:

[0006] A preparation method of a vinyl chloride soap-free emulsion graft copolymer resin, the method comprising the following steps:

[0007] (1) Under stirring, disperse and dissolve ethyl acetoacetoxy methacrylate and carboxymethyl chitosan in a mixed solution, and then react at 25 - 45 °C for 8 - 24 h to obtain a functionalized modified monomer;

[0008] Among them, the mass ratio of ethyl acetoacetoxy methacrylate, carboxymethyl chitosan, and the mixed solution is 10 : (3 - 9) : 100;

[0009] The stirring rate is 100 - 300 rpm;

[0010] The composition of the mixed solution is ethanol and water, and the mass ratio of the two is 1 - 3 : 7 - 9;

[0011] (2) Dissolve the functionalized modified monomer, initiator, and acid-base regulator in step (1) in deionized water, stir for 0.3 - 0.5 h, then transfer to an autoclave, add vinyl chloride monomer, continue to stir for 0.3 - 0.5 h, and then react at 55 - 65 °C for 3 - 10 h to obtain a copolymer resin;

[0012] Among them, the mass ratio of the functionalized modified monomer, initiator, acid-base regulator, deionized water, and vinyl chloride monomer is (10 - 30) : (3 - 6) : (0.5 - 1) : (600 - 800) : 300;

[0013] The stirring rate is 300 - 400 rpm;

[0014] The initiator described in step (2) is potassium persulfate or benzoyl peroxide;

[0015] The acid-base regulator is sodium bicarbonate, sodium dihydrogen phosphate or disodium hydrogen phosphate;

[0016] The application of the functionalized copolymer resin prepared by the method is used for preparing a copolymer ultrafiltration membrane. The specific steps are as follows:

[0017] S1. Mix the prepared copolymer uniformly with the solvent;

[0018] Among them, the ratio of the copolymer to the solvent is (10 - 20):(30 - 60);

[0019] S2. Use a four-sided spreader to uniformly scrape and coat the solution on a smooth glass plate into a liquid film with a thickness of 100 - 250 μm, and form a copolymer ultrafiltration membrane by the non-solvent induced phase separation method;

[0020] The solvent is a polar solvent or a non-polar solvent; the polar solvents include one or several mixtures of DMF, DMAc, THF or DMSO;

[0021] The non-solvent includes one or several mixtures of deionized water, ethanol or formaldehyde.

[0022] The essential feature of the present invention is:

[0023] In the present invention, through the condensation reaction of acetoacetate group and amino group, carboxymethyl chitosan is covalently connected with ethyl acetoacetoxy methacrylate, and β-ketoamide is generated by the reaction, functionalizing ethyl acetoacetoxy methacrylate, and further enhancing the hydrophilicity of the copolymer monomer; further using soap-free emulsion polymerization to in-situ modify polyvinyl chloride resin by a one-step method, combining the characteristics of low cost, good film-forming property and strong mechanical properties of polyvinyl chloride with the reactivity, hydrophilicity and antibacterial property of chitosan derivatives, enhancing its hydrophilicity and antibacterial property, and directly preparing a hydrophilic and antifouling ultrafiltration membrane from the copolymer resin by the non-solvent induced phase separation method.

[0024] The present invention has the following beneficial effects:

[0025] (1) In the present invention, ethyl acetoacetoxyethyl methacrylate has two reactive groups. The acetoacetate group can undergo condensation with the amino group of carboxymethyl chitosan, thereby realizing the functional modification of the ethyl acetoacetoxyethyl methacrylate monomer. At the same time, its methacrylate part can undergo free radical copolymerization with vinyl chloride monomer to achieve bonding with the PVC segment. Moreover, no additional synthetic aids are required during the polymerization of the copolymer. The functional monomer, while acting as a comonomer, utilizes its amphiphilicity to stabilize the polymerization system, realizing soap-free emulsion polymerization with the participation of a reactive monomer emulsifier.

[0026] (2) By changing the content of the functional monomer, the thermodynamic stability and solvent exchange kinetics of the polymer casting solution can be regulated to achieve the regulation of the membrane structure. In Example 1 (the water contact angle of the polymer is 64.4°), the hydrophilicity is significantly improved compared with Comparative Example 1 (the water contact angle of the polymer is 78.2°); by increasing the input amount of the functional monomer, the contact angle of the prepared copolymer is as low as 56.7°. In addition, the chitosan derivative endows the copolymer membrane with excellent antibacterial adhesion. In various examples, compared with Comparative Example 2, the bacterial removal rate exceeds 84%. Brief Description of the Drawings

[0027] Figure 1 is the FTIR spectrum of PVC and the copolymer; among them, Figure 1 a is the FTIR spectrum of the PVC resin, Figure 1 b is the FTIR spectrum of Example 1;

[0028] Figure 2 is the GPC curve of the molecular weight of the copolymers of Examples 1 to 3;

[0029] Figure 3 is the photo of the water contact angle of the polymers of Examples 1 to 3 and Comparative Examples 1 to 2;

[0030] Figure 4 is the photo of the water contact angle of the membranes of Examples 1 to 3 and Comparative Examples 1 to 2;

[0031] Figure 5 is the surface SEM photo of the membranes of Examples 1 to 3 and Comparative Examples 1 to 2;

[0032] Figure 6 is the cross-section SEM photo of the membranes of Examples 1 to 3 and Comparative Examples 1 to 2. Detailed Description of the Embodiments

[0033] The present invention will be further described below in conjunction with the embodiments and the drawings. The following embodiments are illustrative and not restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0034] Example 1

[0035] A preparation method of an amphiphilic PVC copolymer, the method comprising the following steps:

[0036] (1) Mix 60 g of ethanol, 140 g of deionized water, 20 g of acetylacetoxyethyl methacrylate and 6 g of carboxymethyl chitosan, and stir and react at 25 °C at 200 rpm for 24 hours;

[0037] (2) Subject the reaction solution obtained in step (1) to rotary evaporation to remove the solvent to obtain a functional monomer;

[0038] (3) Disperse 10 g of the functional monomer prepared in step (2) in 800 g of deionized water, add 5 g of potassium persulfate and 1 g of sodium bicarbonate, transfer to an autoclave and seal the reaction kettle, and stir at 300 rpm for 0.5 hour to obtain a homogeneous solution;

[0039] (4) Use an injection device to inject 300 g of vinyl chloride monomer into the sealed reaction kettle in step (3), stir at 350 rpm for 0.5 hour, and then raise the temperature to 65 °C and react for 6 hours to obtain the amphiphilic PVC copolymer.

[0040] A preparation method of a copolymer ultrafiltration membrane, the specific operation is as follows:

[0041] S1. Mix 15 g of the amphiphilic PVC copolymer described in step (4) with 60 g of DMF, stir at 60 °C for 10 hours, and let stand for 12 hours to obtain a casting solution;

[0042] S2. Use a four-sided preparation device to uniformly scrape and coat the solution prepared in step S1 into a liquid film with a thickness of 250 μm on a smooth glass plate, and then immerse it in a deionized water coagulation bath at 25 °C, and cure to obtain the ultrafiltration membrane.

[0043] Performance testing:

[0044] A. Mechanical property testing: Use a tensile testing machine to measure the tensile strength when the ultrafiltration membrane sample tears, and evaluate its mechanical properties;

[0045] B. Hydrophilicity characterization: Use a hydraulic press to press the copolymer of Example 1 into a test sheet, and use a DSA30S contact angle tester from KRUSS, Germany to measure the static water contact angles of the polymer tablet and the ultrafiltration membrane respectively. At least 5 different positions of each sample are measured and averaged;

[0046] C. Permeation performance testing: At room temperature, use an ultrafiltration device to test the water flux of the ultrafiltration membrane (operating pressure 0.1 MPa, duration 0.5 h). The pure water flux (J w1 ) is calculated according to the formula J = V / (A×Δt), where: J - pure water flux (L / (m 2·ħ·bar), V - volume of permeated water (L), A - effective membrane area (m 2 ), Δt - test time (h);

[0047] D. Evaluation of anti - fouling performance:

[0048] (1) Use a 1000 ppm bovine serum albumin (BSA) solution to conduct a fouling test on the ultrafiltration membrane (0.1 MPa, 1 h), and record the permeation flux J during the fouling process p ;

[0049] (2) After the test, wash the membrane surface with deionized water for 5 minutes;

[0050] (3) Repeat the pure water flux test to obtain the flux J after cleaning w2 ;

[0051] (4) Evaluate the anti - fouling performance of the membrane through the flux recovery rate (FRR): FRR = (J w2 / J w1 ) × 100%;

[0052] E. Determination of rejection rate:

[0053] Collect the filtrate in the BSA filtration experiment; use an ultraviolet spectrophotometer to measure the BSA concentrations of the filtrate and the stock solution at a wavelength of 286 nm; calculate the rejection rate according to the formula r = (1 - C p / C f ) × 100%, where: r - rejection rate (%), C p - BSA concentration in the filtrate (mg / L), C f - BSA concentration in the stock solution (mg / L);

[0054] F. Test the anti - bacterial adhesion of the ultrafiltration membrane using the plate counting method. First, prepare ultrafiltration membrane samples and bacterial strains (Staphylococcus aureus or Escherichia coli), activate the strains and adjust them to a bacterial suspension of 10 7 CFU / mL. Cut the ultrafiltration membrane into circular pieces with a diameter of 4 cm, immerse them in the bacterial suspension and incubate for 1 - 2 hours, then wash with PBS buffer to remove non - adhered bacteria. Make the adhered bacteria fall off by ultrasonic treatment, perform gradient dilution on the bacterial solution and spread it on nutrient agar plates, and count the number of colonies after culturing at 37 °C for 24 hours to calculate the amount of bacteria adhesion per square centimeter of the membrane surface. Calculate the rejection rate of the ultrafiltration membrane through the formula E b = (1 - N t / N c ) × 100%; where E b (%) is the rejection rate of the membrane, N c and N t (number) are the colony counts of Comparative Example 2 and other membranes respectively.

[0055] Example 2

[0056] A preparation method of an amphiphilic PVC copolymer, the method comprising the following steps:

[0057] (1) Mix 40 g of ethanol, 160 g of deionized water, 20 g of acetylacetoxyethyl methacrylate and 12 g of carboxymethyl chitosan, and stir and react at 25 °C at 200 rpm for 24 hours;

[0058] (2) Subject the reaction solution obtained in step (1) to rotary evaporation to remove the solvent to obtain a functional monomer;

[0059] (3) Disperse 20 g of the functional monomer prepared in step (2) in 800 g of deionized water, add 3 g of benzoyl peroxide, 0.5 g of sodium dihydrogen phosphate and 0.5 g of disodium hydrogen phosphate, transfer to an autoclave and seal the reaction kettle, and stir at 300 rpm for 0.5 hour to obtain a homogeneous solution;

[0060] (4) Inject 300 g of vinyl chloride monomer into the sealed reaction kettle in step (3) using an injection device, stir at 300 rpm for 0.5 hour, and then raise the temperature to 58 °C and react for 10 hours to obtain the amphiphilic PVC copolymer.

[0061] A preparation method of a copolymer ultrafiltration membrane, the specific operation is as follows:

[0062] S1. Mix 15 g of the amphiphilic PVC copolymer described in step (4) with 30 g of DMF and 30 g of DMAc, stir at 60 °C for 10 hours, and let stand for 12 hours to obtain a casting solution;

[0063] S2. Use a four-sided applicator to evenly scrape and coat the solution into a liquid film with a thickness of 250 μm on a smooth glass plate, and then immerse it in a deionized water coagulation bath at 25 °C. After curing, the ultrafiltration membrane is obtained. The relevant performance testing methods are the same as those in Example 1.

[0064] Example 3

[0065] (1) Mix 20 g of ethanol, 180 g of deionized water, 20 g of acetylacetoxyethyl methacrylate and 18 g of carboxymethyl chitosan, and stir and react at 25 °C at 200 rpm for 24 hours;

[0066] (2) Subject the reaction solution obtained in step (1) to rotary evaporation to remove the solvent to obtain a functional monomer;

[0067] (3) Disperse 20 g of the functional monomer prepared in step (2) in 800 g of deionized water, add 5 g of benzoyl peroxide, 0.5 g of sodium dihydrogen phosphate and 0.5 g of disodium hydrogen phosphate, transfer to an autoclave and seal the reaction kettle, stir at 300 rpm for 0.5 hour to obtain a homogeneous solution;

[0068] (4) Use an injection device to inject 300 g of vinyl chloride monomer into the sealed reaction kettle in step (3), stir at 350 rpm for 0.5 hour, then heat to 60 °C and react for 8 hours to obtain the amphiphilic PVC copolymer.

[0069] A preparation method of a copolymer ultrafiltration membrane is as follows:

[0070] S1. Mix 15 g of the amphiphilic PVC copolymer described in step (4) with 10 g of DMF and 50 g of DMAc, stir at 60 °C for 10 hours, and let stand for 12 hours to obtain a casting solution;

[0071] S2. Use a four-sided coater to uniformly scrape and coat the solution on a smooth glass plate to form a liquid film with a thickness of 200 μm, and then immerse it in a deionized water coagulation bath at 25 °C. After curing, the ultrafiltration membrane is obtained. The relevant performance test methods are the same as those in Example 1.

[0072] The relevant performance test methods are the same as those in Example 1.

[0073] Comparative Example 1

[0074] This comparative example provides a preparation method of PVC, and the method includes the following steps:

[0075] Dissolve 10 g of acetoacetyloxyethyl methacrylate in 800 g of deionized water, mix 4 g of potassium persulfate and 0.8 g of sodium bicarbonate, transfer to an autoclave and seal the reaction kettle, stir in the reaction kettle at 350 rpm for 0.5 h to obtain a homogeneous solution, use an injection device to inject 300 g of vinyl chloride monomer into the sealed reaction kettle, stir at 300 rpm for 0.3 h, and then react at 60 °C for 6 h to obtain Comparative Example 1;

[0076] The ultrafiltration membrane preparation method is the same as that in Example 1.

[0077] The relevant performance test methods are the same as those in Example 1.

[0078] Comparative Example 2

[0079] This comparative example provides a preparation method of PVC, and the method includes the following steps:

[0080] Dissolve 3 g of sodium dodecyl sulfate in 800 g of deionized water, mix 4 g of potassium persulfate and 0.8 g of sodium bicarbonate, transfer to an autoclave and seal the reaction kettle. Stir in the reaction kettle at 300 rpm for 0.3 h to obtain a homogeneous solution. Inject 300 g of vinyl chloride monomer into the sealed reaction kettle using an injection device, stir at 300 rpm for 0.3 h, and then react at 60 °C for 6 h to obtain Comparative Example 2;

[0081] The preparation method of the PVC ultrafiltration membrane is the same as that in Example 1.

[0082] The relevant performance testing method is the same as that in Example 1.

[0083] Results and Analysis

[0084] The test results of the above specific examples and comparative examples are shown in Table 1.

[0085] Table 1 Performance of samples in examples and comparative examples

[0086]

[0087] From the appendix Figure 1 It can be concluded that the copolymerization reaction of the functionalized modified monomer and vinyl chloride monomer is successful; from Figure 2 it can be estimated that the number-average molecular weight of the copolymers in the three examples is about 3.8×10 4 ~5.1×10 4 g / mol; from Table 1 and appendix Figure 3 and appendix Figure 4 it can be seen that compared with the two comparative examples, the polymer water contact angles of the three different examples have decreased to varying degrees, proving that the hydrophilic modification of the copolymers in the examples is effective; at the same time, the copolymer membranes in the examples are more hydrophilic than the comparative examples. Appendix Figure 5 and appendix Figure 6 show SEM photos of the surfaces and cross-sections of various example and comparative example membranes. It can be found that the surface porosity of all examples has increased significantly, and at the same time, the cross-sectional structure has also changed significantly, indicating that the thermodynamic state of the casting solution of the polymers in the examples is different from that of the comparative examples. In addition, due to the introduction of the 2-acetoacetoxyethyl methacrylate chain segment in the polymer chain of Comparative Example 1, the long strip-shaped finger holes inside the membrane are shorter than those in Comparative Example 2. From the experimental results of the pure water flux, rejection rate, total flux decline ratio, and flux recovery rate in Table 1, it can be concluded that the filtration performance and antifouling performance of the copolymer membranes in the examples can be effectively enhanced. In addition, due to the introduction of carboxymethyl chitosan, the ultrafiltration membranes in the examples can effectively resist bacterial adhesion.

[0088] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

[0089] Matters not covered by the present invention are well-known technologies.

Claims

1. A preparation method of a vinyl chloride soap-free emulsion graft copolymer resin, characterized in that, The method comprises the following steps: (1) Under stirring, acetyl acetoacetoxyethyl methacrylate and carboxymethyl chitosan are dispersed and dissolved in a mixed solution, and then reacted at 25 - 45 °C for 8 - 24 h to obtain a functionalized modified monomer; Among them, the mass ratio of acetyl acetoacetoxyethyl methacrylate, carboxymethyl chitosan, and the mixed solution is 10:(3 - 9):100; The mixed solution is composed of ethanol and water, and the mass ratio of the two is 1 - 3:7 - 9; (2) The functionalized modified monomer, initiator, and acid-base regulator in step (1) are dissolved in deionized water, stirred for 0.3 - 0.5 h, then transferred to an autoclave, vinyl chloride monomer is added, and stirring is continued for 0.3 - 0.5 h, and then reacted at 55 - 65 °C for 3 - 10 h to obtain a copolymer resin; Among them, the mass ratio of the functionalized modified monomer, initiator, acid-base regulator, deionized water, and vinyl chloride monomer is (10 - 30):(3 - 6):(0.5 - 1):(600 - 800):

300.

2. The preparation method of the vinyl chloride soap-free emulsion graft copolymer resin according to claim 1, characterized in that, The stirring rate in step (1) is 100 - 300 rpm; the stirring rate in step (2) is 300 - 400 rpm.

3. The preparation method of the vinyl chloride soap-free emulsion graft copolymer resin according to claim 1, characterized in that, The initiator in step (2) is potassium persulfate or benzoyl peroxide.

4. The preparation method of the vinyl chloride soap-free emulsion graft copolymer resin according to claim 1, characterized in that, The acid-base regulator is sodium bicarbonate, sodium dihydrogen phosphate, or disodium hydrogen phosphate.

5. The application of the functionalized copolymer resin prepared by the method according to claim 1, characterized in that it is used for preparing a copolymer ultrafiltration membrane.

6. The application according to claim 5, characterized in that, It includes the following steps: S1. Mix the prepared copolymer uniformly with a solvent; Among them, the ratio of the copolymer to the solvent is (10 - 20):(30 - 60); S2. Uniformly scrape-coat the solution into a liquid film with a thickness of 100 - 250 μm on a glass plate, and make a copolymer ultrafiltration membrane by the non-solvent induced phase separation method; The solvent is a polar solvent or a non-polar solvent; the polar solvent includes one or several mixtures of DMF, DMAc, THF, or DMSO; The non-solvent includes one or several mixtures of deionized water, ethanol, or formaldehyde.

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