Amphoteric modified starch flocculant, its preparation method and application

Abstract

The application belongs to the technical field of water treatment, and provides an amphoteric modified starch flocculant, a preparation method and application thereof, the flocculant is formed by graft copolymerization of carboxymethyl starch sodium, acrylamide, methacryloyloxyethyl trimethyl ammonium chloride and sodium allyl sulfonate with a mass ratio of 10:2-4:8-12:0.8-2. The flocculant has good flocculation effect on microplastics in water and high removal rate.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and relates to an amphoteric modified starch flocculant, its preparation method, and its application. Background Technology

[0002] Microplastics, as a novel environmental pollutant, are widely present in environmental water bodies, posing a potential threat to ecosystems. Technologies for removing microplastics from wastewater mainly include filtration, flotation, membrane separation, adsorption, flocculation, and biodegradation. Among these methods, flocculation and sedimentation is the first stage in wastewater treatment, effectively removing colloids and impurities from the water and providing better water quality conditions for subsequent treatment stages. In wastewater, impurities have complex particle compositions; if flocculants with special properties are used at this stage, they can remove both conventional impurities and encapsulate microplastics, achieving a better flocculation effect.

[0003] Currently, there is limited research on the flocculation of microplastics. Qiu Fuguo et al. (Study on the removal performance and mechanism of microplastics by coagulation and sedimentation process, Environmental Science and Technology, 2024, 47(4): 54-61.) tested the removal rate of microplastics by three coagulants: aluminum chloride, ferric sulfate hydrate and aluminum sulfate octadecahydrate, and found that polyaluminum chloride had a removal rate of 49.07% for PVC.

[0004] Natural polymers such as starch, possessing certain flocculation properties, are carbohydrates formed by plants through photosynthesis. They are abundant, non-toxic, inexpensive, and readily biodegradable. Furthermore, starch has a unique chain structure and strong reactivity, characteristics that have led to its widespread research and development in non-food applications. However, starch also has drawbacks such as insolubility in cold water, poor shear resistance, and lack of melt flowability, making it difficult to use as a standalone polymer material. Modification is necessary to enhance certain functions or create new physicochemical properties. Starch molecules contain multiple hydroxyl groups, allowing for chemical modification through methods such as etherification, oxidation, esterification, and graft copolymerization. Among these, amphoteric natural polymers, compared to other modified natural polymers (such as non-grafted, anionic, and cationic polymers), not only exhibit significantly improved water solubility but also, due to their dual characteristics of anionic and cationic groups, are suitable for treating water bodies with different charges. Ding Yan et al. (Ding Yan, Hu Jiayue, Liu Ting. Synthesis and Flocculation Performance Study of Novel Amphoteric Starch-Based Polymer Flocculant [J]. Materials Reports, 2015, 29(S2): 388-392.) synthesized an amphoteric polymer St-g-AM-AMPS-DMDAAC using starch, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and dimethyl diallyl ammonium chloride (DMDAAC) as monomers, and investigated the flocculation performance of this flocculant on kaolin. The results showed that the optimal dosage was 40 mg / L, and the transmittance could reach over 90%. Yang Zhen et al. (YANG Zhen, YUAN Bo, LI Haijiang, et al. Amphoteric starch-based flocculants can flocculate different contaminants with even opposite surface charges from water through molecular structure control[J]. Colloids and Surface A: Physicochemical and Engineering Aspects, 2014, 455: 28-35.) synthesized an amphoteric modified starch flocculant CMS-CTA using 3-chloro-2-hydroxypropyltrimethylammonium chloride (CTA) as a cationic etherifying agent and chloroacetic acid as an anionic etherifying agent, and investigated its flocculation performance on kaolin and hematite powder. The results showed that CMS-CTA had good flocculation performance, and changing the pH value of the water sample could make the flocculant exhibit flocculation performance for suspended particles carrying different charges. This amphoteric modified starch introduced a single etherifying agent molecule into the molecular chain, without side chains, and had no entrapment effect. In addition, the performance of this modified starch was unstable, and the flocculation performance decreased after a long period of storage.Meanwhile, these studies are not flocculation studies on microplastics (polyvinyl chloride).

[0005] Therefore, improving flocculants to enhance microplastic removal efficiency has become a current research focus. Summary of the Invention

[0006] This invention proposes an amphoteric modified starch flocculant, its preparation method, and its application. This flocculant has a good flocculation effect and a high removal rate for microplastic polyvinyl chloride in water.

[0007] The technical solution of this invention is implemented as follows:

[0008] Technical Topic 1

[0009] An amphoteric modified starch flocculant is composed of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride and sodium allyl sulfonate graft copolymerized in a mass ratio of 10:2-4:8-12:0.8-2.

[0010] Preferably, the mass ratio of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate is 10:3:10:1.

[0011] Technical Theme Two

[0012] The present invention also provides a method for preparing an amphoteric modified starch flocculant as described in Technical Subject 1, comprising the following steps: mixing sodium carboxymethyl starch with deionized water, boiling, lowering the temperature to 60~75℃, then placing it in an inert atmosphere, adding an initiator, initiating for 8~12 min, then adding a grafted monomer solution, reacting at a constant temperature for 3.5~4.5 h, and after post-treatment of the product, obtaining the flocculant;

[0013] The grafting monomer solution is a mixed aqueous solution of acrylamide, methacryloyloxyethyltrimethylammonium chloride and sodium allyl sulfonate.

[0014] Preferably, the ratio of acrylamide to water in the grafted monomer solution is 2~4g:45~55mL.

[0015] Preferably, the ratio of sodium carboxymethyl starch to deionized water is 10g: 140~160mL.

[0016] Preferably, the grafting monomer is added at a rate of 0.8~1.2 mL / min.

[0017] Preferably, the initiator is an aqueous solution of ammonium persulfate, wherein the ratio of ammonium persulfate to water in the aqueous solution is 0.6g:8~12mL.

[0018] Preferably, the amount of the initiator added is 3.75-5% of the total mass of acrylamide, methacryloyloxyethyltrimethylammonium chloride and sodium allyl sulfonate.

[0019] Preferably, the amount of the initiator added is 4.3% of the total mass of acrylamide, methacryloyloxyethyltrimethylammonium chloride and sodium allyl sulfonate.

[0020] Preferably, the post-processing includes: precipitating and washing the product with ethanol, and then drying it.

[0021] Preferably, the drying specifically includes vacuum drying at 60°C.

[0022] Technical Theme 3

[0023] This invention also provides the application of the amphoteric modified starch flocculant as described in Technical Subject 1 in the removal of microplastics from water.

[0024] Preferably, the microplastic is polyvinyl chloride.

[0025] Preferably, the microplastic particle size is 100~300μm.

[0026] The beneficial effects of the present invention using the above technical solution are as follows:

[0027] This invention provides a flocculant made from sodium carboxymethyl starch, a starch derivative, through graft copolymerization of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate. This invention introduces positively charged quaternary ammonium groups, negatively charged carboxyl groups, and sulfonic acid groups onto the starch molecular chain. Experimental verification shows that this flocculant can achieve a removal rate of over 70% for microplastics (polyvinyl chloride, PVC) in water, exhibiting good flocculation effect, high removal rate, and stable flocculation performance even after prolonged storage. Attached Figure Description

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 The infrared spectrum is shown for the product prepared in Example 1 of this invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Unless otherwise specified, the experimental or testing methods involved in the embodiments of this invention are conventional methods in the prior art, and their names and / or abbreviations are conventional names in the art, clearly defined within their respective fields of application. Those skilled in the art can understand the conventional process steps and apply the corresponding equipment based on these names, implementing them according to conventional conditions or conditions recommended by the manufacturer. The various instruments, equipment, raw materials, or reagents used in the embodiments of this invention are not subject to any special restrictions on their source; they are all conventional products that can be purchased through legitimate commercial channels and can be prepared according to conventional methods well known to those skilled in the art.

[0032] The substances used in the following examples and comparative examples, along with their sources of purchase, are described below:

[0033] Sodium carboxymethyl starch was purchased from Aladdin Reagent Company. It was of analytical grade, batch number C105665-500g, CAS number 9063-38-1, and the measured degree of substitution was 0.52.

[0034] Example 1

[0035] An amphoteric modified starch flocculant is prepared by graft copolymerization of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate in a mass ratio of 10:3:10:1. Specifically, the process includes the following steps:

[0036] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0037] Weigh out 3.0 g of acrylamide (AM), 10 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 1.0 g of sodium allyl sulfonate (SAS), and dissolve them in 50 mL of water to prepare a grafting monomer solution.

[0038] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain a light yellow solution product;

[0039] S3. The product is precipitated and washed with ethanol, and then dried under vacuum at 60°C. The resulting white powder is the flocculant.

[0040] like Figure 1 The infrared spectrum of the product prepared in Example 1 of this invention is shown at 3343 cm⁻¹.-1 and 3186 cm -1 The absorption peak at 1658 cm⁻¹ is a double peak for primary amines. -1 The absorption peak is for the asymmetric stretching vibration of the carboxyl group; 1450 cm⁻¹ -1 The peak at 1560 cm⁻¹ is formed by the superposition of the absorption peak of the symmetric stretching vibration of the carboxyl group and the absorption peak of the stretching vibration of the methyl group in the quaternary ammonium group; -1 The absorption peak is due to the bending vibration of the NH bond in the amide group; 1402 cm⁻¹ -1 The peak at 1158 cm⁻¹ represents the absorption peak of the CH bending vibration connecting the broken double bond to the double bond in DMC. -1 and 1080cm -1 The characteristic absorption peak for sulfonic acid groups is located at 1015 cm⁻¹. -1 The peaks at this point represent the stretching vibrations of the CO bonds in the polysaccharide ring. The presence of these peaks indicates the presence of amide, carboxyl, quaternary ammonium, and sulfonic acid groups in the product structure.

[0041] Example 2

[0042] An amphoteric modified starch flocculant is prepared by graft copolymerization of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate in a mass ratio of 10:3:8:1. Specifically, the process includes the following steps:

[0043] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0044] Weigh out 3.0 g of acrylamide (AM), 8 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 1.0 g of sodium allyl sulfonate (SAS), and dissolve them in 50 mL of water to prepare the grafting monomer solution.

[0045] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain a light yellow solution product;

[0046] S3. The product is precipitated and washed with ethanol, and then dried under vacuum at 60°C. The resulting white powder is the flocculant.

[0047] Example 3

[0048] An amphoteric modified starch flocculant is prepared by graft copolymerization of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate in a mass ratio of 10:4:10:2. Specifically, the process includes the following steps:

[0049] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0050] Weigh out 4.0 g of acrylamide (AM), 10 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 2.0 g of sodium allyl sulfonate (SAS), and dissolve them in 50 mL of water to prepare the grafting monomer solution.

[0051] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain a light yellow solution product;

[0052] S3. The product is precipitated and washed with ethanol, and then dried under vacuum at 60°C. The resulting white powder is the flocculant.

[0053] Example 4

[0054] An amphoteric modified starch flocculant is prepared by graft copolymerization of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate in a mass ratio of 10:3:10:1. Specifically, the process includes the following steps:

[0055] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0056] Weigh out 3.0 g of acrylamide (AM), 10 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 1.0 g of sodium allyl sulfonate (SAS), and dissolve them in 50 mL of water to prepare a grafting monomer solution.

[0057] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 60℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain a light yellow solution product;

[0058] S3. The product is precipitated and washed with ethanol, and then dried under vacuum at 60°C. The resulting white powder is the flocculant.

[0059] Example 5

[0060] An amphoteric modified starch flocculant is prepared by graft copolymerization of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate in a mass ratio of 10:4:8:0.8. Specifically, the process includes the following steps:

[0061] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 8mL of water to prepare an initiator solution;

[0062] Weigh out 4.0 g of acrylamide (AM), 8 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 0.8 g of sodium allyl sulfonate (SAS), and dissolve them in 45 mL of water to prepare the grafting monomer solution.

[0063] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 140mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 12min; inject the grafted monomer into the flask using a syringe at an injection rate of 1.2mL / min; react at a constant temperature for 3.5h to obtain a light yellow solution product;

[0064] S3. The product is precipitated and washed with ethanol, and then dried under vacuum at 60°C. The resulting white powder is the flocculant.

[0065] Example 6

[0066] An amphoteric modified starch flocculant is prepared by graft copolymerization of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate in a mass ratio of 10:2:12:1.5. Specifically, the process includes the following steps:

[0067] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 12mL of water to prepare an initiator solution;

[0068] Weigh out 2.0 g of acrylamide (AM), 12 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 1.5 g of sodium allyl sulfonate (SAS), and dissolve them in 55 mL of water to prepare the grafting monomer solution.

[0069] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 160mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 75℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 8min; inject the grafted monomer into the flask using a syringe at an injection rate of 0.8mL / min; react at a constant temperature for 4.5h to obtain a light yellow solution product;

[0070] S3. The product is precipitated and washed with ethanol, and then dried under vacuum at 60°C. The resulting white powder is the flocculant.

[0071] Comparative Example 1

[0072] Compared to Example 1, the only difference is that sodium carboxymethyl starch is replaced with an equal mass of corn starch. Specifically:

[0073] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0074] Weigh out 3.0 g of acrylamide (AM), 10 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 1.0 g of sodium allyl sulfonate (SAS), and dissolve them in 50 mL of water to prepare a grafting monomer solution.

[0075] S2. Weigh 10g of corn starch, add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and carry out the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain the product;

[0076] S3. The product is precipitated and washed with ethanol, and then vacuum dried at 60°C to obtain the flocculant.

[0077] Comparative Example 2

[0078] Compared to Example 1, the only difference is that sodium allyl sulfonate is replaced with an equimolar amount of 2-acrylamido-2-methylpropanesulfonic acid. Specifically:

[0079] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0080] Weigh out 3.0 g of acrylamide (AM), 10 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 1.4 g of 2-acrylamide-2-methylpropanesulfonic acid, and dissolve them in 50 mL of water to prepare a grafting monomer solution.

[0081] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain the product;

[0082] S3. The product is precipitated and washed with ethanol, and then vacuum dried at 60°C to obtain the flocculant.

[0083] Comparative Example 3

[0084] Compared to Example 1, the only difference is that methacryloyloxyethyltrimethylammonium chloride (DMC) is omitted, and an equimolar amount of sodium allyl sulfonate is added. Specifically:

[0085] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0086] Weigh out 3.0 g of acrylamide (AM) and 7.9 g of sodium allyl sulfonate (SAS), and dissolve them in 50 mL of water to prepare the grafting monomer solution;

[0087] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain the product;

[0088] S3. The product is precipitated and washed with ethanol, and then vacuum dried at 60°C to obtain the flocculant.

[0089] Comparative Example 4

[0090] Compared to Example 1, the only difference is that sodium allyl sulfonate is omitted, and an equimolar amount of methacryloyloxyethyltrimethylammonium chloride (DMC) is added. Specifically:

[0091] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0092] Weigh out 3.0 g of acrylamide (AM) and 11.4 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and dissolve them in 50 mL of water to prepare the grafting monomer solution;

[0093] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain the product;

[0094] S3. The product is precipitated and washed with ethanol, and then vacuum dried at 60°C to obtain the flocculant.

[0095] Comparative Example 5

[0096] Compared to Example 1, the only difference is that it is a graft copolymer of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate in a mass ratio of 10:3:15:1. Specifically:

[0097] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0098] Weigh out 3.0 g of acrylamide (AM), 15 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 1.0 g of sodium allyl sulfonate (SAS), and dissolve them in 50 mL of water to prepare a grafting monomer solution.

[0099] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain the product;

[0100] S3. The product is precipitated and washed with ethanol, and then vacuum dried at 60°C to obtain the flocculant.

[0101] Comparative Example 6

[0102] Compared to Example 1, the only difference is that it is a graft copolymer of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate in a mass ratio of 10:3:5:1. Specifically:

[0103] S1. Weigh 0.6g of ammonium persulfate (APS) and dissolve it in 10mL of water to prepare an initiator solution;

[0104] Weigh out 3.0 g of acrylamide (AM), 5 g of methacryloyloxyethyltrimethylammonium chloride (DMC), and 1.0 g of sodium allyl sulfonate (SAS), and dissolve them in 50 mL of water to prepare the grafting monomer solution.

[0105] S2. Weigh 10g of sodium carboxymethyl starch (CMS), add it to 150mL of deionized water, heat to boiling for 5min, and pour into a four-necked flask; place the four-necked flask in a 70℃ water bath, purge with nitrogen, and proceed with the subsequent reaction under nitrogen protection; pour the initiator solution into the flask and initiate for 10min; inject the grafted monomer into the flask using a syringe at an injection rate of 1mL / min; react at a constant temperature for 4h to obtain the product;

[0106] S3. The product is precipitated and washed with ethanol, and then vacuum dried at 60°C to obtain the flocculant.

[0107] Example of effect

[0108] The performance of the flocculants obtained in Examples 1-6 and Comparative Examples 1-6 was compared. The specific experimental methods are as follows:

[0109] 1. Preparation of microplastic suspensions

[0110] Accurately weigh 0.1000 g (using an analytical balance, accuracy 0.00001 g) of PVC microplastics (100 μm, purchased from Topmiao Biotechnology (Shanghai) Co., Ltd.) and place them in 1 L of deionized water. Disperse the mixture by sonication at 100 W for 30 minutes to ensure uniform suspension of the particles. The suspension concentration was 100 mg / L, and the pH was adjusted to 7.0. The suspension was used immediately after preparation to avoid particle sedimentation or aggregation.

[0111] 2. Filter membrane pretreatment

[0112] Use a glass fiber filter membrane with a pore size of 0.45 μm. Before use, dry the filter membrane in an oven at 105°C for 1 hour, transfer it to a desiccator to cool to room temperature, and weigh it using an analytical balance (record as W0, unit mg) with an accuracy of at least 0.1 mg. Avoid contamination of the filter membrane and store it in a desiccator for later use.

[0113] 3. Flocculation performance test

[0114] Water sampling: Take 100 mL of PVC suspension into a 150 mL beaker.

[0115] Experimental group: According to the dosage of 10 mg / L, flocculant was added to 100 mL of water sample. The stirring was started immediately after the addition. The stirring program was: 500 rpm for 1 minute, 150 rpm for 15 minutes. After stirring, the mixture was left to stand for 1 hour (avoid vibration during the standing period).

[0116] Blank control group: A blank group without flocculant was set up (only PVC suspension was added) to evaluate the natural sedimentation effect. The same stirring procedure was performed as the experimental group. After stirring, the mixture was left to stand for 1 hour.

[0117] Sampling of supernatant from each group: After standing, carefully aspirate 10 mL of the supernatant from the top of the beaker with a pipette (avoid disturbing the sediment) and transfer it to the vacuum filtration device.

[0118] 4. Filtration and Weighing

[0119] Filter 10 mL of supernatant through a pre-weighed filter membrane (W0). Wash the inner wall of the filter cup with a small amount of deionized water to ensure that all particles are captured. After filtration, carefully remove the filter membrane with tweezers, place it in a glass petri dish and store it in the dark. After it dries naturally, weigh it (record as W1, unit: mg).

[0120] Perform at least three parallel experiments on each sample and take the average value.

[0121] 5. Removal rate calculation

[0122] Calculate the mass of PVC in 10 mL of the experimental group supernatant: m1 = W1 - W0, where m1 is the mass (mg) of PVC in 10 mL of the experimental group supernatant.

[0123] Removal rate (%) = (m0-m1) / m0×100%; where m0 is the mass of PVC in 10mL blank test solution, and its calculation method is the same as the calculation method of PVC mass in the supernatant of the experimental group. The results are shown in Table 1.

[0124] Table 1

[0125]

[0126] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An amphoteric modified starch flocculant for removing microplastics from water, characterized in that, It is a graft copolymer of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride and sodium allyl sulfonate in a mass ratio of 10:2~4:8~12:0.8~2; The degree of substitution of the sodium carboxymethyl starch is 0.

52.

2. The amphoteric modified starch flocculant for removing microplastics from water according to claim 1, characterized in that, The mass ratio of sodium carboxymethyl starch, acrylamide, methacryloyloxyethyltrimethylammonium chloride, and sodium allyl sulfonate is 10:3:10:

1.

3. A method for preparing an amphoteric modified starch flocculant for removing microplastics from water as described in claim 1 or 2, characterized in that, The process includes the following steps: mixing sodium carboxymethyl starch with deionized water, boiling, lowering the temperature to 60-75°C, then placing it in an inert atmosphere, adding an initiator, initiating for 8-12 minutes, then adding the grafted monomer solution, reacting at a constant temperature for 3.5-4.5 hours, and then post-processing the product to obtain a flocculant. The grafting monomer solution is a mixed aqueous solution of acrylamide, methacryloyloxyethyltrimethylammonium chloride and sodium allyl sulfonate.

4. A method for preparing an amphoteric modified starch flocculant for removing microplastics from water according to claim 3, characterized in that, The ratio of acrylamide to water in the grafted monomer solution is 2-4 g: 45-55 mL; the ratio of sodium carboxymethyl starch to deionized water is 10 g: 140-160 mL.

5. The preparation method of the amphoteric modified starch flocculant for removing microplastics from water according to claim 3, characterized in that, The grafting monomer is added at a rate of 0.8~1.2 mL / min.

6. The preparation method of the amphoteric modified starch flocculant for removing microplastics from water according to claim 3, characterized in that, The initiator is an aqueous solution of ammonium persulfate, and the ratio of ammonium persulfate to water in the aqueous solution is 0.6g:8~12mL.

7. The preparation method of the amphoteric modified starch flocculant for removing microplastics from water according to claim 3, characterized in that, The amount of the initiator added is 3.75-5% of the total mass of acrylamide, methacryloyloxyethyltrimethylammonium chloride and sodium allyl sulfonate.

8. The application of the amphoteric modified starch flocculant for removing microplastics from water as described in any one of claims 1-2.

9. The application according to claim 8, wherein the microplastic is polyvinyl chloride.

10. The application according to claim 8, wherein the microplastic particle size is 100~300μm.

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