Preparation method of biodegradable superabsorbent resin

Abstract

This invention belongs to the field of polymer synthesis and application, specifically relating to a method for preparing a biodegradable superabsorbent resin. By introducing starch and titanium nitrile carbon nanomaterials into the polymerization system and adjusting various process conditions, this invention obtains a temperature- and salt-resistant, pressure-resistant, biodegradable superabsorbent resin. This improves upon the shortcomings of ordinary polyacrylamide series superabsorbent resins, which, although possessing high water absorption rates, exhibit poor temperature and salt resistance, low gel strength after water absorption, are non-degradable, and lack pressure resistance. The resin prepared by this invention is a biodegradable and environmentally friendly resin, suitable for applications such as oilfield water injection and leak sealing, environmental wastewater treatment, agricultural and forestry soil and water conservation, agricultural water storage, and sanitary materials.

Description

Technical Field

[0001] This invention belongs to the field of polymer synthesis and application, specifically relating to a method for preparing a biodegradable superabsorbent resin. Background Technology

[0002] Superabsorbent polymer (SAP) is a hydrophilic polymer compound with a network structure and low cross-linking degree. It is insoluble in water and organic solvents, but can absorb up to hundreds or even thousands of times its own weight in water. It absorbs water very quickly, does not easily lose water, and has a strong water retention capacity.

[0003] Since the establishment of Flory's theory in the 1950s and 60s, superabsorbent polymers (SAPs) have developed into a diverse, multi-purpose, high-volume, and theoretically in-depth discipline both domestically and internationally. The main products fall into five categories: nonionic, anionic, cationic, amphoteric, and various hydrophilic groups. These include sulfonic acid, carboxylic acid, phosphoric acid, tertiary amine, quaternary ammonium, amide, ether, starch, and combinations thereof. The highest absorbency can reach 5000 g / g. SAPs are widely used in agriculture, forestry, horticulture, pharmaceuticals, hygiene products, construction, fire protection materials, daily chemicals, papermaking, oilfield chemicals, and many other industries. The raw materials used in these five major series of SAPs are mainly acrylic acid, acrylamide, acrylonitrile, sodium acrylate, sulfonates, tertiary amine salts, quaternary ammonium salts, and starch. Different application areas have different requirements for SAPs. In sanitation, agriculture and forestry, soil and water conservation, and horticulture, high water absorption rate, fast water absorption speed, and biodegradability are emphasized. In engineering leak sealing, high compressive strength and toughness are required to prevent breakage and failure during use. In oilfield production, oilfield refining, and oil displacement plugging, especially in high-temperature and high-salt reservoir environments, the temperature and salt resistance of the hydrogel is crucial. Hydrogels prepared by multi-component copolymerization possess advantages such as temperature and pressure resistance, high water absorption rate, and fast water absorption speed due to the presence of carboxyl, sulfonate, phosphate, tertiary amine, quaternary ammonium, and starch groups. Acrylamide-based hydrogels, while having high water absorption rates, have lower temperature and pressure resistance, affecting their usability. Song Xuefeng's article, "Water Absorption and Anti-Fragmentation Properties of Modified Polyacrylamide Water Absorbent Resin," discusses that the high degree of fragmentation of this resin is due to its high water absorption rate. Therefore, water absorption rate and gel strength are two factors that must be considered. Simply pursuing a high water absorption rate is not advisable. The article also studies various methods to improve the compressive strength of the gel, mainly the grafting modification method, but this method is relatively cumbersome and the effect is generally average.

[0004] Especially in terms of temperature resistance, salt tolerance, and biodegradability, further improvements are urgently needed. Song Tianwen, in his paper "Synthesis and Water Absorption Properties of P(AA / AMPS) Salt-Tolerant Superabsorbent Resin," prepared a salt-resistant superabsorbent resin using a reverse-phase suspension method. However, this resin, synthesized from petroleum processing byproducts of acrylic acid, has non-renewable raw materials, and the product is not easily degradable and has poor environmental compatibility. The preparation of superabsorbent materials using natural and green materials is currently a hot topic. Li Kun, in his paper "Preparation and Characterization of AA / AMPS-Starch-OMMT-Composite Salt-Tolerant Superabsorbent Resin," obtained a resin with high salt absorption by grafting and copolymerizing montmorillonite with AA, AMPS, and starch. The paper emphasizes that the addition of starch and montmorillonite improved the gel strength of the resin after water absorption, but does not elaborate on its biodegradability. Zhang Teng, in his paper "Synthesis Study of Starch-Grafted Polyacrylamide Superabsorbent Resin," focuses on the process conditions for resin synthesis but does not conduct in-depth research on resin degradation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a biodegradable superabsorbent resin. The process is simple, and the prepared resin is biodegradable, has high water absorption, and also has good temperature resistance, salt resistance, and pressure resistance.

[0006] This invention is achieved through the following technical solution:

[0007] The method for preparing the biodegradable superabsorbent resin of the present invention includes the following steps:

[0008] (1) Dispersion of carbon nanomaterials: Mix carbon nanomaterials with deionized water and disperse by ultrasonication until no flocs are formed;

[0009] (2) Starch gelatinization: Add starch to the solution obtained in step (1), stir evenly, heat and gelatinize to obtain carbon nanomaterial starch solution;

[0010] (3) Aqueous solution polymerization: Acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), hydrolysant, crosslinking agent and carbon nanomaterial starch solution obtained in step (2) are added into a closed polymerizer. After deoxygenation of the polymerizer, an initiator dissolved in deionized water is added into the polymerizer to carry out the polymerization reaction and obtain polymerized colloidal product.

[0011] (4) Colloidal post-treatment: The polymerized colloidal product is granulated, dried and crushed to obtain the final product, namely the biodegradable superabsorbent resin.

[0012] Preferably, the carbon nanomaterial is titanium nitrile (TiCN), and the size of the nanoparticles is 20~40 nanometers.

[0013] In step (1), the ultrasonic frequency is 25000~30000Hz and the ultrasonic time is 25~35 minutes.

[0014] In step (2), the gelatinization temperature is 65~75℃ and the gelatinization time is 25~35 minutes.

[0015] In step (3), the deoxygenation of the polymerizer is carried out by nitrogen gas to make the oxygen content of the polymerization system less than 0.2 ppm;

[0016] At the start of the polymerization reaction, the polymerizer temperature is 10~40℃, and as the polymerization reaction proceeds, the material temperature reaches 90~100℃, with a reaction time of 4~6 hours.

[0017] In the preparation process of the biodegradable superabsorbent resin, the required raw materials are in the following amounts by weight: 0.0003 parts carbon nanomaterials, 73.6 parts deionized water, 2 parts starch, 15 parts acrylamide, 5 parts 2-acrylamido-2-methylpropanesulfonic acid, 4.4 parts hydrolysate, 0.03 parts crosslinking agent, and 0.048 parts initiator.

[0018] In step (1), the amount of deionized water used is 70 parts, and in step (3), the amount of deionized water used is 3.6 parts.

[0019] The hydrolysing agent is sodium hydroxide, sodium carbonate, or sodium bicarbonate, with sodium bicarbonate being preferred.

[0020] The crosslinking agent is N,N-methylenebisacrylamide (MBA).

[0021] The initiator is a combination of an oxidant and a reducing agent in a 1:1 mass ratio. The oxidant is one or more of ammonium persulfate, potassium persulfate, or sodium persulfate, and the reducing agent is one or two of sodium bisulfite and sodium sulfite.

[0022] In step (4), the drying temperature is 60~90℃ and the solid content is 96%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention uses an aqueous solution polymerization process, which is stable and simple. By introducing starch and titanium nitrile carbon nanomaterials into the polymerization system and adjusting various process conditions, a degradable water-absorbing resin that is heat-resistant, salt-resistant, and pressure-resistant is obtained. This improves the defects of ordinary polyacrylamide series water-absorbing resins, which have high water absorption rate but poor temperature and salt resistance, low gel strength after water absorption, are non-degradable, and are not pressure-resistant.

[0025] 2. The resin prepared by this invention is a biodegradable and environmentally friendly resin, which can be used for oilfield water injection and leak plugging, environmental sewage treatment, agricultural and forestry soil and water conservation, agricultural water storage and sanitary materials (such as diapers). Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments.

[0027] It should be noted that, unless otherwise specified, all raw materials used in the examples and comparative examples were commercially available. The acrylamide and 2-acrylamido-2-methylpropanesulfonic acid monomers used in the experiments were of polymerization grade, the conductivity of deionized water was ≤5μs / cm, the crosslinking agent and initiator were all analytical grade reagents, and the nitrogen gas was high-purity nitrogen.

[0028] Example 1

[0029] (1) Dispersion of carbon nanomaterials: Add 0.0003g of nano-titanium nitrile and 70g of deionized water into a beaker, place it in a 25000 Hz ultrasonic cleaner and ultrasonically disperse for 30 minutes until no flocs are visible to the naked eye.

[0030] (2) Starch gelatinization: Add 2g of starch to the solution obtained in step (1), stir evenly, heat to 70℃, gelatinize for 30 minutes to obtain carbon nanomaterial starch solution;

[0031] (3) Aqueous solution polymerization: 15g acrylamide, 5g 2-acrylamido-2-methylpropanesulfonic acid, 4.4g sodium bicarbonate, 0.03g N,N-methylenebisacrylamide and the carbon nanomaterial starch solution obtained in step (2) were added to a closed polymerizer. Nitrogen gas was passed through the polymerizer to remove oxygen, so that the oxygen content of the system was less than 0.2ppm. The temperature of the polymerization system in the polymerizer was adjusted to 40℃. Then, 0.024g ammonium persulfate and 0.024g sodium bisulfite dissolved in 3.6g deionized water were added to the polymerizer to carry out the polymerization reaction. The viscosity of the system increased significantly. At this time, the nitrogen gas was stopped and the polymerization was allowed to stand for 5 hours to obtain a polymerized colloidal product with rubber elasticity.

[0032] (4) Post-processing of colloid: The polymerized colloid product is cut into small pieces and fed into a granulator for granulation. It is dried at 70°C until the solid content reaches 96%. Then it is crushed and sieved. The final product is 80-100 mesh, which is the biodegradable superabsorbent resin.

[0033] Examples 2-3

[0034] Referring to Example 1, the only difference is that the polymerizer temperature at the start of the polymerization reaction was 10°C (Example 2) and 30°C (Example 3).

[0035] Examples 4-5

[0036] Referring to Example 1, the only difference is that the polymerization reaction time is 4 hours (Example 4) and 6 hours (Example 5).

[0037] Comparative Example 1

[0038] Referring to Example 1, the only difference is that no carbon nanomaterials were added; instead, 2g of starch was directly added to 70g of deionized water for gelatinization.

[0039] Comparative Example 2

[0040] Refer to Example 1, the only difference being that 2-acrylamido-2-methylpropanesulfonic acid was not added.

[0041] Comparative Example 3

[0042] Referring to Example 1, the only difference is that no starch was added. 0.0003g of nano-titanium nitrile and 72g of deionized water were added to a beaker and ultrasonically dispersed.

[0043] Comparative Example 4

[0044] Referring to Example 1, the only difference is that nano-montmorillonite is used instead of nano-titanium nitrile.

[0045] Comparative Example 5

[0046] Referring to Example 1, the only difference is that carbon nanotubes are used instead of nano-nitrile titanium.

[0047] Comparative Example 6

[0048] Referring to Example 1, the only difference is that graphene is used instead of nano-nitrile titanium.

[0049] Comparative Example 7

[0050] Referring to Example 1, the only difference is that the nano-titanium nitrile is not ultrasonically dispersed but directly added to the polymerization system. 0.0003g of nano-titanium nitrile, 70g of deionized water, and 2g of starch are mixed, stirred evenly, gelatinized, and then polymerized.

[0051] Comparative Example 8

[0052] The copolymerization of acrylamide and starch, without the addition of titanium nitrile and AMPS, is carried out through the following steps:

[0053] (1) Starch gelatinization: Mix 2g starch and 70g deionized water, stir evenly, heat to 70℃, gelatinize for 30 minutes to obtain starch solution;

[0054] (2) Aqueous solution polymerization: 15g acrylamide, 4.4g sodium bicarbonate, 0.03g N,N-methylenebisacrylamide and the starch solution obtained in step (2) were added to a closed polymerizer. Nitrogen gas was passed through the polymerizer to remove oxygen, so that the oxygen content of the system was less than 0.2ppm. The polymerization system temperature in the polymerizer was adjusted to 40℃. Then, 0.024g ammonium persulfate and 0.024g sodium bisulfite dissolved in 3.6g deionized water were added to the polymerizer to carry out the polymerization reaction. The viscosity of the system increased significantly. At this time, the nitrogen gas was stopped and the polymerization was allowed to stand for 5 hours to obtain the polymerized colloidal product.

[0055] (4) Post-processing of colloids: The polymerized colloid product is cut into small pieces and fed into a granulator for granulation. It is dried at 70°C until the solid content reaches 96%. Then it is crushed and sieved, and 80-100 mesh is taken as the final product.

[0056] Comparative Example 9

[0057] Referring to Example 1, the only difference is that the starch is not gelatinized by heating.

[0058] Comparative Example 10

[0059] Referring to Example 1, the only difference is that the polymerizer temperature is 70°C at the start of the polymerization reaction.

[0060] The resins prepared in Examples 1-5 and Comparative Examples 1-10 were subjected to performance tests. The test indicators included water absorption rate, water absorption rate after pressure, and residual amount after degradation. The results are shown in Table 1.

[0061] Table 1. Water absorption rate and residual amount of resin in pure water and salt water under heating and pressurization.

[0062]

[0063] As shown in Table 1, compared with the examples, Comparative Example 1, without the addition of titanium nitrile, showed a decrease in the compressive strength of the water-absorbing resin; Comparative Example 2, without the addition of AMPS, exhibited poor temperature and salt resistance; Comparative Example 3, without the addition of starch, showed only 0.05% degradation after 6 months of water absorption; Comparative Example 4, using nano-montmorillonite instead of nano-titanium nitrile, showed the largest decrease in compressive strength; Comparative Examples 5 and 6 also showed significant decreases in compressive strength; Comparative Examples 7 and 9, respectively, showed decreases in both compressive strength and degradation performance due to the lack of ultrasonic dispersion of nano-titanium nitrile and the lack of starch gelatinization, indicating that the nano-titanium nitrile and starch were not uniformly dispersed in the solution; and Comparative Example 8, prepared from pure acrylamide, showed the lowest temperature, salt, and compressive strength resistance. Examples 1-3 and Comparative Example 10 demonstrate that a lower initial polymerization temperature is beneficial for improving water absorption.

Claims

1. A method for preparing a biodegradable superabsorbent resin, characterized in that: Includes the following steps: (1) Dispersion of carbon nanomaterials: Mix carbon nanomaterials with deionized water and disperse by ultrasonication until no flocs are formed; (2) Starch gelatinization: Add starch to the solution obtained in step (1), stir evenly, heat and gelatinize to obtain carbon nanomaterial starch solution; (3) aqueous solution polymerization: acrylamide (AM), 2 acrylamide 2 Methyl propyl sulfonic acid (AMPS), hydrolysis agent, crosslinking agent and carbon nanomaterial starch solution obtained in step (2) are added into a closed polymerizer, deoxygenation is performed on the polymerizer, an initiator dissolved in deionized water is added into the polymerizer, and polymerization reaction is performed to obtain a polymerization colloid product; (4) Colloidal post-treatment: The polymerized colloidal product is granulated, dried and pulverized to obtain the final product, namely the biodegradable superabsorbent resin. The carbon nanomaterial is titanium nitrile (TiCN).

2. The method of claim 1, wherein the method is characterized by: The polymerizer temperature is 10~40℃ at the start of the polymerization reaction, and the reaction time is 4~6 hours.

3. The method for preparing the biodegradable superabsorbent resin according to claim 1 or 2, characterized in that: The required raw material dosage in the preparation process is 0.0003 parts of carbon nanomaterial, 73.6 parts of deionized water, 2 parts of starch, 15 parts of acrylamide, 2 Acrylamide group 2 Methylpropanesulfonic acid 5 parts, hydrolysis agent 4.4 parts, crosslinking agent 0.03 parts, initiator 0.048 parts.

4. The method for preparing the biodegradable superabsorbent resin according to claim 3, characterized in that: In step (1), the amount of deionized water used is 70 parts, and in step (3), the amount of deionized water used is 3.6 parts.

5. The method for preparing the biodegradable superabsorbent resin according to claim 3, characterized in that: The hydrolysing agent is sodium hydroxide, sodium carbonate, or sodium bicarbonate.

6. The method for preparing the biodegradable superabsorbent resin according to claim 3, characterized in that: The crosslinking agent is N,N Methylenebisacrylamide.

7. The method for preparing the biodegradable superabsorbent resin according to claim 3, characterized in that: The initiator is a combination of an oxidant and a reducing agent in a 1:1 mass ratio.

8. The method for preparing the biodegradable superabsorbent resin according to claim 7, characterized in that: The oxidizing agent is one or more of ammonium persulfate, potassium persulfate, or sodium persulfate.

9. The method for preparing the biodegradable superabsorbent resin according to claim 7, characterized in that: The reducing agent is one or both of sodium bisulfite and sodium sulfite.

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