Bio-based high polymer material and preparation method thereof

Abstract

One of the technical schemes of the invention is to provide a bio-based high polymer material which is prepared by compounding a base material, a functional modified monomer, a slow-release filler, a free radical initiator and a cross-linking agent according to a mass ratio of (40-60): (20-30): (10-15): (0.2-0.4): (5-8), the base material is hydroxylated cellulose; the functional modified monomer comprises a pH response type monomer and a temperature response type monomer, and the mass ratio of the pH response type monomer to the temperature response type monomer is 1: (1.2-1.5); the pH response type monomer is aminopropyltriethoxysilane or aminopropyltrimethoxysilane, the temperature response type monomer is N-isopropylacrylamide, the slow release filler is nanoscale potassium-based composite particles, potassium sulfate sodium alginate nano composite particles or potassium chloride chitosan nano composite particles, the free radical initiator is ammonium persulfate, and the pH response type monomer, the temperature response type monomer, the slow release filler and the free radical initiator are mixed uniformly. The cross-linking agent is polyethylene glycol diglycidyl ether. The technical problems that a traditional material is single in function, poor in synergism and insufficient in degradation are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of agriculture, in particular to a bio-based macromolecular material and a preparation method thereof. BACKGROUND

[0002] As an important bottleneck restricting the sustainable development of agriculture, the management of saline-alkali soil faces technical problems such as low desalination efficiency, repeated improvement effect, and poor water and fertilizer retention synergy. In the prior art, the saline-alkali soil improvement materials mostly focus on single desalination function, such as sodium ion replacement by biological materials or water locking by high molecular water retaining agent, but there are generally problems such as disconnection between desalination and water retention, insufficient nutrient supply, and mismatch between degradation rate and crop growth period.

[0003] Although traditional high molecular water retaining agents such as potassium polyacrylate materials have strong water absorption performance, they lack salt-alkali environment adaptability, and the water absorption capacity significantly decreases under high salt conditions, and they cannot realize sodium ion replacement and soil structure improvement; although the existing pH responsive improver can act on saline-alkali soil, it has insufficient water retention performance and cannot solve the core contradiction of drought and water shortage in saline-alkali soil. At the same time, some synthetic high molecular improvement materials have the problems of difficult degradation and easy secondary pollution, and natural biological materials generally have the defects of single function and short-acting effect. In addition, the existing technology is mostly separate application of the improver and the water retaining agent, which is complicated to operate and has poor synergy effect, and cannot meet the integrated needs of saline-alkali soil comprehensive management. SUMMARY

[0004] The present application provides a bio-based macromolecular material and a preparation method thereof, which solves the problems that traditional high molecular water retaining agents such as potassium polyacrylate materials have strong water absorption performance, but lack salt-alkali environment adaptability, and the water absorption capacity significantly decreases under high salt conditions, and they cannot realize sodium ion replacement and soil structure improvement; although the existing pH responsive improver can act on saline-alkali soil, it has insufficient water retention performance and cannot solve the core contradiction of drought and water shortage in saline-alkali soil. At the same time, some synthetic high molecular improvement materials have the problems of difficult degradation and easy secondary pollution, and natural biological materials generally have the defects of single function and short-acting effect. In addition, the existing technology is mostly separate application of the improver and the water retaining agent, which is complicated to operate and has poor synergy effect, and cannot meet the integrated needs of saline-alkali soil comprehensive management.

[0005] The biobased polymer material in the application takes modified cellulose derived from agricultural by-products as a base material, constructs a three-dimensional network structure by grafting pH-responsive amino monomers and temperature-responsive N-isopropyl acrylamide segments, and composites nano-sized potassium-based slow-release particles; has four functions of sodium ion replacement in saline-alkali soil, soil aggregate structure remodeling, long-term water locking, and intelligent nutrient release, and solves the technical pain points of traditional improvers, such as non-durability of desalination, disconnection of water and fertilizer conservation, and insufficient degradation. The material can realize efficient replacement of sodium ions triggered by pH in a saline-alkali environment, and complete on-demand release of water and potassium elements under day and night temperature changes, the desalination efficiency is 8-12 times higher than that of traditional materials, the water retention rate is 500-800 times of its own weight, and the material can be completely degraded into organic nutrients in the soil for 6-8 months. The preparation process uses a green solvent system and in-situ polymerization technology, which is environmentally friendly and cost controllable, and is suitable for ecological improvement and crop yield increase of various saline-alkali farmlands, and has significant agricultural application value and environmental benefits.

[0006] One of the technical solutions of the application is to provide a biobased polymer material, which is composed of a base material, a functional modified monomer, a slow-release filler, a free radical initiator and a crosslinking agent in a mass ratio of 40-60:20-30:10-15:0.2-0.4:5-8; the base material is hydroxylated cellulose; the functional modified monomer includes a pH-responsive monomer and a temperature-responsive monomer, the mass ratio of the pH-responsive monomer to the temperature-responsive monomer is 1:1.2-1.5; the pH-responsive monomer is aminopropyl triethoxysilane or aminopropyl trimethoxysilane, the temperature-responsive monomer is N-isopropyl acrylamide, the slow-release filler is a nano-sized potassium-based composite particle, a potassium sulfate sodium alginate nano-composite particle or a potassium chloride chitosan nano-composite particle, the free radical initiator is ammonium persulfate, and the crosslinking agent is polyethylene glycol diglycidyl ether.

[0007] The modified cellulose base material in the application is a basic carrier, and agricultural by-products such as corn stalks and wheat bran are used as raw materials, and after hydroxylation modification, abundant hydroxyl groups are obtained, which not only provide reaction sites for subsequent grafting of functional monomers, but also ensure good biocompatibility of the material.

[0008] The matching threshold of the base material and the crosslinking agent: 5-8 g of crosslinking agent can effectively crosslink 40-60 g of base material (crosslinking degree 70%-85%), ensuring stable structure and not blocking pores;

[0009] The effective concentration threshold of the functional monomer is 20-30 g of monomer corresponding to 40-60 g of base material, the grafting rate can be stabilized at 85%-92%, and the double-response function demand is met; the adaptation threshold of the filler and the network is that 10-15 g of nanofiller can be uniformly embedded in the network formed by 40-60 g of base material, agglomeration is avoided, and long-acting slow release is achieved. The base material is hydroxylated cellulose obtained by hydroxyl modification of cellulose extracted from agricultural by-products, and the agricultural by-products are at least one of corn stalks, wheat bran or cottonseed hulls.

[0010] In the application, the double-response monomer is adopted, the saline-alkali environment is adapted, the pH response type amino monomer (aminopropyl triethoxysilane) is used: in the high-alkali environment of the saline-alkali land with a pH of 8.5-10.5, the amino group is easily protonated to be positively charged, and efficient replacement with the negatively charged sodium ion in the soil occurs, the replacement rate is greater than or equal to 85%, and the problem of non-persistent desalination is solved.

[0011] The temperature response type N-isopropyl acrylamide segment: with the day and night temperature difference of 5-15 DEG C of the saline-alkali land, the segment undergoes swelling-shrinking transition, realizes the cycle of “locking-release” of water, and simultaneously regulates the on-demand release of potassium elements to match the growth rhythm of crops.

[0012] The two are synergized in a ratio of 1:1.2-1.5, which not only ensures the desalination efficiency, but also solves the synergistic problem of water retention and nutrient supply.

[0013] The core role of the polyethylene glycol diglycidyl ether is to act as a crosslinking agent, chemically react with other components (hydroxylated cellulose, double-response monomer grafted polymer, nanoscale potassium-based composite particles) in the system, and construct a dense and stable three-dimensional network structure, which is a key reagent for realizing the function synergy and performance stability of the material “improvement, water retention integration”.

[0014] Another embodiment provided in the application is that the hydroxyl substitution degree of the hydroxylated cellulose is 0.8-1.2.

[0015] In the application, the number of hydroxyl groups of the bio-based macromolecular material is significantly increased, sufficient reaction sites are provided, the hydrophilicity is greatly improved, the water retention basis is strengthened, the reaction activity is improved, the adaptation to the saline-alkali environment is optimized, structural failure is avoided, the biocompatibility is maintained, and the degradation rate is regulated.

[0016] The hydroxyl groups on the cellulose molecular chain are “activated and newly added” through chemical modification, and the substitution degree is controlled through process parameters.

[0017] Definition of degree of substitution (DS) of hydroxyl groups: Cellulose molecules are composed of repeating glucose units, each of which has 3 reactive hydroxyl groups (C2-OH, C3-OH, C6-OH). Degree of substitution (DS) refers to the average number of hydroxyl groups per glucose unit that are chemically modified (here, the introduction of new hydroxyl groups by etherification), with a theoretical maximum of 3. In the present invention, the degree of substitution of hydroxyl groups is 0.8-1.2, which is the key to balancing the "grafting requirements of subsequent functional monomers" and "stability of cellulose structure" - ensuring sufficient reaction sites while not damaging the backbone structure of cellulose.

[0018] Preparation of hydroxylated cellulose in two steps of "sodium hydroxide activation" and "epichlorohydrin etherification", i.e. first alkaline activation, then reaction with epichlorohydrin, both steps together determine the DS range:

[0019] First step: sodium hydroxide activation - exposing "potential reaction sites" and laying the foundation for etherification: Natural cellulose has high crystallinity (molecular chains are tightly arranged through hydrogen bonds), most of the hydroxyl groups are wrapped in the crystalline region and cannot participate in the reaction, only a small amount of surface hydroxyl groups are available, direct etherification will result in very low DS (far below 0.8). The effect of "1-2 mol / L sodium hydroxide solution 60-70°C activation for 2-3h" is: sodium hydroxide (strong base) will penetrate into the crystalline region of cellulose, break the intermolecular hydrogen bonds, and make the cellulose chains change from tight arrangement to loose state, exposing a large number of hydroxyl groups (C2-OH, C3-OH, C6-OH) that were originally hidden in the crystalline region; at the same time, sodium hydroxide will form a salt reaction with the surface hydroxyl groups of cellulose (generate cellulose sodium: Cell-OH + NaOH → Cell-ONa + H2O), the nucleophilicity (electron cloud density) of cellulose sodium is much higher than that of the original hydroxyl group, and it can react more efficiently with subsequent epichlorohydrin; the activation conditions (1-2 mol / L alkali concentration, 60-70°C temperature, 2-3h time) are precisely controlled: if the alkali concentration is too low / activation time is insufficient, the crystalline region is not sufficiently damaged, and the exposed hydroxyl groups are few, making it difficult to achieve a DS of 0.8; if the alkali concentration is too high / temperature is too high, it will cause the cellulose chains to break (degrade), thereby reducing the reactivity and damaging the backbone structure.

[0020] Second step: epichlorohydrin etherification - introducing "new hydroxyl groups" to directly increase DS: The activated cellulose (containing a large number of exposed hydroxyl groups / cellulose sodium) reacts with epichlorohydrin at 50-60°C for 4-6h, which is the key step to introduce new hydroxyl groups and achieve a DS of 0.8-1.2. The reaction mechanism is a nucleophilic ring-opening etherification reaction: the epichlorohydrin molecule contains a three-membered epoxy ring (large ring strain, easy to open) and a chloromethyl group (-CH2Cl), and the activated cellulose hydroxyl group (or the -O - Na +) as a nucleophile, will attack the carbon atom of the epoxy ring (a position with lower electron cloud density), causing the opening of the three-membered ring; after the opening, the epichlorohydrin molecule is connected to the cellulose chain through an ether bond (-O-), (forming Cell-O-CH2-CH(OH)-CH2Cl), and the hydroxyl group (-CH(OH)-) in the opening product becomes a "newly added hydroxyl group"; during the reaction, part of the chloromethyl group (-CH2Cl) will also further undergo a hydrolysis reaction (in an aqueous system) to generate an additional hydroxyl group (-CH2OH), further increasing the number of hydroxyl groups on each glucose unit; the etherification reaction conditions (temperature of 50-60 DEG C, time of 4-6 h) are also the key to the control of DS: if the temperature is too low / time is insufficient, the opening rate of the epoxy ring is slow, the etherification reaction is insufficient, and the DS will be lower than 0.8; if the temperature is too high / time is too long, it will cause the epichlorohydrin to be excessively polymerized (to form oligomers by itself), which will reduce the combination with cellulose, and may cause the cellulose to be excessively etherified (DS exceeding 1.2), destroying the biocompatibility and degradability of the cellulose.

[0021] The key to stabilizing the DS at 0.8-1.2 is to match the reaction conditions: the parameters of "activation-etherification" (alkali concentration, temperature, time) form a synergistic control, finally making the DS lock at 0.8-1.2: the number of exposed hydroxyl groups in the activation stage (1-2 mol / L NaOH, 60-70 DEG C, 2-3 h) is just enough to react with the epichlorohydrin in the subsequent etherification stage (50-60 DEG C, 4-6 h) to form a ratio of "1 glucose unit corresponding to 0.8-1.2 newly added hydroxyl groups";

[0022] The step of washing to neutral (after the reaction) can terminate the etherification reaction, avoid the residual alkali to continue to catalyze the excessive reaction, and ensure that the DS will not exceed the target range due to subsequent hydrolysis / etherification;

[0023] The drying process (without high-temperature destruction) retains the hydroxyl structure generated by the etherification reaction, and finally obtains the hydroxylated cellulose with a DS of 0.8-1.2.

[0024] Another embodiment provided in the application is that the particle size of the slow-release filler is 50-200 nm.

[0025] Another embodiment provided in the application is that the bio-based high molecular material is applied to the improvement of saline-alkali farmland, the application mode is to spread and then plough, and the application amount is 20-50 kg / mu. It is suitable for soil improvement for the planting of wheat, corn, cotton and salt-tolerant vegetables.

[0026] Another embodiment provided in the application is that the sodium ion replacement rate of the bio-based high molecular material is greater than or equal to 85% under the conditions of saline-alkali soil pH 8.5-10.5 and diurnal temperature difference 5-15℃, the soil aggregate structure content is increased by 40-60%, the water holding time is prolonged by 15-20 days compared with ordinary soil, and the potassium element release period is 30-45 days.

[0027] The application further provides a method for preparing the bio-based high molecular material, which comprises the following steps: vacuum drying hydroxylated cellulose to obtain dried hydroxylated cellulose with water content less than or equal to 5%, adding the dried hydroxylated cellulose into deionized water, ultrasonic dispersion to form a suspension with mass fraction of 5-8%, sequentially adding pH responsive monomers and temperature responsive monomers into the suspension, removing oxygen by nitrogen blowing, adding ammonium persulfate for reaction to obtain modified cellulose polymer; adding nanoscale potassium-based composite particles into the modified cellulose polymer, stirring, adding a crosslinking agent, crosslinking reaction at 70-80℃, and granulating and drying after the reaction to obtain the bio-based high molecular material.

[0028] Specifically, (1) substrate pretreatment: preparing hydroxylated cellulose, vacuum drying to obtain dried hydroxylated cellulose with water content less than or equal to 5%, and reserving; (2) in-situ polymerization modification: adding the dried hydroxylated cellulose into deionized water, ultrasonic dispersion for 30-40 min to form a suspension with mass fraction of 5-8%, sequentially adding pH responsive monomers and temperature responsive monomers, removing oxygen by nitrogen blowing for 30 min, adding an initiator ammonium persulfate, and reacting at 65-75℃ for 6-8 h to obtain modified cellulose polymer; (3) composite molding: adding nanoscale potassium-based composite particles into the modified cellulose polymer, stirring at 40-50℃ for 2-3 h, adding a crosslinking agent, crosslinking reaction at 70-80℃ for 3-4 h, and granulating and drying after the reaction to obtain granular integrated material with particle size of 1-3 mm.

[0029] The power of ultrasonic dispersion in step (2) is 300-500 W, and the frequency is 20-40 kHz; the stirring rate in step (3) is 200-300 rpm, the drying temperature is 60-80℃, and the drying time is 8-10 h.

[0030] Another embodiment provided in the application is that the dosage of the free radical initiator is 0.8-1.2% of the total mass of the functional modified monomers, and the bio-based high molecular material is granular with particle size of 1-3 mm.

[0031] Another embodiment provided by the application is that the preparation of the hydroxylated cellulose comprises: crushing an agricultural byproduct to obtain cellulose powder with a size of 80-100 mesh; activating the cellulose powder in a 1-2 mol / L sodium hydroxide solution at 60-70 DEG C for 2-3 hours to obtain alkali-activated cellulose; adding epichlorohydrin to the alkali-activated cellulose and reacting at 50-60 DEG C for 4-6 hours; washing until neutral and drying to obtain the hydroxylated cellulose.

[0032] Another embodiment provided by the application is that the preparation of the nanoscale potassium-based composite particles comprises: mixing a potassium chloride aqueous solution with a 2-3 wt% sodium alginate solution at a volume ratio of 1:3, uniformly stirring, then adding a 0.1-0.2 mol / L calcium chloride solution dropwise, ultrasonic dispersing for 20-30 minutes, centrifugal separating, and freeze-drying to obtain the nanoscale potassium-based composite particles.

[0033] The nanoscale potassium-based slow-release particles in the application have the dual effects of nutrient supply and structure enhancement, have a nanoscale design with a particle size of 50-200 nm, increase the specific surface area, and are combined with a three-dimensional network to improve the material structure stability.

[0034] The nanoscale potassium-based slow-release particles are prepared by ionic crosslinking of potassium chloride and sodium alginate, realize long-acting slow release of potassium elements for 30-45 days, and avoid nutrient loss.

[0035] The natural hydrophilicity of sodium alginate further strengthens the water retention effect and forms a complement with the water retention function of the base material and the monomer.

[0036] The three-dimensional network structure is the core link of functional synergy, and the modified cellulose, the double-response monomer, and the nanoscale potassium-based particles are integrated into a dense network through the chemical bonding effect of the crosslinking agent polyethylene glycol diglycidyl ether.

[0037] The network structure can physically lock water, so that the water retention rate reaches 500-800 times of its own weight, and at the same time, promotes the formation of soil aggregate structure, and the improvement rate reaches 40-60%.

[0038] Compared with the prior art, the application has the following advantages:

[0039] 1) The application provides a saline-alkali soil adaptive double-response bio-based high molecular modification-water retention integrated material, which has the functions of efficient desalination, long-acting water retention, and nutrient slow release, is an integrated high molecular material that is environmentally friendly and adaptive to the special environment of saline-alkali soil, and solves the saline-alkali soil treatment problem.

[0040] 2) The application provides a bio-based saline-alkali soil modification material, which realizes the synergistic effect of saline-alkali soil desalination, soil improvement, water retention, and nutrient locking, has environmental responsiveness and biodegradability, and solves the technical pain points of single function, poor synergy, and insufficient degradation of traditional materials.

[0041] 3) Strong functional synergy: integrated sodium ion replacement, soil structure improvement, long-term water retention, and nutrient release, realizing comprehensive management of saline-alkali land, with desalination efficiency 8-12 times higher than traditional materials, water retention rate up to 500-800 times of its own weight, and significant improvement in soil aggregate structure content.

[0042] 4) Double-response intelligent adaptation: pH-responsive monomers efficiently replace sodium ions in high-pH environments of saline-alkali land, and temperature-responsive monomers release water and potassium elements on demand according to day-night temperature differences, adapting to the special environment of saline-alkali land and the growth needs of crops.

[0043] 5) Environmentally friendly and sustainable: using agricultural by-products as the base material, with excellent biodegradability, completely degradable into organic nutrients in 6-8 months without secondary pollution; the preparation process uses green solvents, meeting the requirements of low carbon and environmental protection.

[0044] 6) Wide application range: suitable for various types of saline-alkali land, meeting the planting needs of various crops such as wheat, corn, and cotton, with convenient application, significant synergistic effect, and broad agricultural application prospects. DETAILED DESCRIPTION

[0045] The following examples are used to further illustrate the present application, and the purpose is to illustrate the present application, but should not be interpreted as limiting the scope of the present application. The following uses weight parts and weight percentages unless otherwise specified.

[0046] The raw materials used in the present application, such as no special instructions, are conventional commercial products; the methods used in the present application, such as no special instructions, are conventional methods in the art.

[0047] The following embodiments of the present application are further illustrated in the following multiple examples.

[0048] It should be clear that the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope of protection of the present application.

[0049] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0050] The biobased polymer material in the application takes modified cellulose derived from agricultural by-products as a base material, constructs a three-dimensional network structure by grafting pH-responsive amino monomers and temperature-responsive N-isopropyl acrylamide segments, and composites nano-sized potassium-based slow-release particles; has four functions of saline-alkali soil sodium ion replacement, soil aggregate structure remodeling, long-term water locking and nutrient intelligent release, and solves the technical pain points of traditional improvers such as non-durability of desalination, disconnection of water and fertilizer conservation, and insufficient degradation. The material can realize efficient replacement of sodium ions triggered by pH in saline-alkali environment, and complete on-demand release of water and potassium elements under day and night temperature changes, with desalination efficiency increased by 8-12 times compared with traditional materials, water retention rate reaching 500-800 times of its own weight, and being completely degraded into organic nutrients in soil for 6-8 months. The preparation process uses green solvent system and in-situ polymerization technology, which is environmentally friendly and cost controllable, and is suitable for ecological improvement and crop yield increase of various saline-alkali lands, and has significant agricultural application value and environmental benefits.

[0051] Specifically, the application provides a saline-alkali soil adaptive dual-responsive biobased polymer improvement-water retention integrated material, which is composed of a base material, a functional modified monomer, a slow-release filler and a crosslinking agent in a specific proportion. The base material is hydroxylated cellulose derived from agricultural by-products, which realizes resource utilization of agricultural waste and has good biocompatibility and degradability; the functional modified monomer triggers sodium ion replacement in saline-alkali soil high-pH environment through the synergistic effect of pH-responsive amino monomers and temperature-responsive N-isopropyl acrylamide, and regulates the release of water and nutrients under day and night temperature changes; the nano-sized potassium-based composite particles serve as slow-release fillers, providing potassium nutrients and enhancing the stability of the three-dimensional network structure of the material; and the crosslinking agent constructs a dense water-retention-slow-release network through chemical bonding, improving the structural strength and functional durability of the material.

[0052] The preparation method includes three steps of base material pretreatment, in-situ polymerization modification and composite molding, uses green solvent system and in-situ polymerization technology, avoids the pollution problem of organic solvents in traditional processes, ensures the firm combination of functional monomers and base materials, and improves the comprehensive performance of the material. The preparation process is simple, cost controllable, and suitable for large-scale production.

[0053] The application forms a dense and intelligent three-dimensional network structure through the compounding of "hydroxylated cellulose base material (skeleton) + pH / temperature dual-responsive monomer (environment adaptation) + nano potassium-based particles (nutrient / structure enhancement) + polyethylene glycol diglycidyl ether (crosslinking stabilization)". The network is a "carrier" of four functions, which ensures uniform distribution and continuous action of each functional component, and avoids the problems of traditional materials such as "dispersion loss of functional components and disconnection of effects" (background technical pain points).

[0054] Sodium ion replacement function: "Environment-triggered ion exchange" of pH-responsive monomers Protonation activation: the amino group (-NH2) in the amino propyl triethoxysilane molecule will react with H + Combine (protonate) to generate a positively charged -NH3 + group (H + in basic environment) to replace Na + : The soil colloids in saline-alkali soil adsorb a large amount of Na + , which makes them negatively charged (the surface of soil colloids is usually negatively charged), and the positively charged -NH3 + group will compete with the Na + on the surface of soil colloids through electrostatic attraction - because the adsorption energy of -NH3 + (hydrogen bonding + electrostatic interaction) is much higher than that of Na + (electrostatic interaction), it can "replace" Na + from the surface of colloids; Na + migration and removal: the replaced Na + enters the soil solution and can be removed from the soil through natural leaching (rainfall / irrigation) or crop root absorption, achieving desalination.

[0055] The key to 8-12 times efficiency improvement: traditional desalination materials (such as single gypsum, biochar) have two major defects: ① the functional components (such as Ca 2+ ) are easily lost with rainwater, and the desalination is not durable; ② the components are not evenly distributed, and the contact area with soil colloids is small. This material grafts pH-responsive monomers onto a three-dimensional network through in-situ polymerization: ① the monomers form chemical bonds with the substrate and do not lose, continuously providing -NH3 + ; ② the network pore structure allows the monomers to be evenly distributed, increasing the contact area with soil colloids by more than 10 times compared to traditional dispersed materials, thus greatly improving the desalination efficiency.

[0056] Soil structure improvement function: "skeleton-bridging synergy" of substrate and nanoparticles: substrate bonding and pore construction: after modification, the hydroxylated cellulose retains a fibrous structure and the surface is rich in hydroxyl groups (-OH) - hydroxyl groups can bond with small soil particles (sand particles, silt particles) through hydrogen bonding, agglomerating small particles into large aggregates; at the same time, the three-dimensional network of cellulose swells in the soil, opening up soil pores (aeration pores, capillary pores), reducing compaction; nanoparticle "bridging" enhancement: nano-potassium particles have extremely small particle size and can fill between the cellulose network and soil particles, forming a three-dimensional bridging structure of "cellulose-nanoparticle-soil particle" - which not only enhances the mechanical stability of the aggregate (avoiding the collapse of the aggregate when it encounters water), but also further refines the pore structure, improving the soil's water and fertilizer retention capacity;

[0057] Structure locking of crosslinking agent: polyethylene glycol diglycidyl ether crosslinks cellulose, double-responsive monomer, and nanoparticles into a dense network through ether bonds, avoiding the collapse of the substrate structure in high-salt / temperature difference environments, and ensuring long-term stability of the granular structure.

[0058] Reason for significant improvement in granular structure: Traditional soil improvement materials (such as straw return) rely solely on physical bonding to form granules, which are loose and easily broken; this material, through the triple action of "fiber skeleton + nano bridging + chemical crosslinking", significantly improves the stability and quantity of the granular structure, with a 40-60% increase in granular structure content (performance test table).

[0059] Long-term water retention function: "smart water locking-release cycle" of temperature-responsive monomer and three-dimensional network: temperature-responsive "swelling-shrinking" regulation: NIPAM has a low critical solution temperature (LCST, about 32°C) — ① Night temperature is lower than LCST (e.g. 15-20°C at night in saline-alkali soil): NIPAM segments are in a swollen state, absorbing a large amount of water from the soil solution and storing it in the three-dimensional network pores; ② Daytime temperature close to / higher than LCST (e.g. 25-30°C during the day in saline-alkali soil): NIPAM segments shrink, slowly squeezing and releasing the stored water for crop root absorption.

[0060] Long-term water locking of substrate and network: a large number of hydroxyl groups in hydroxylated cellulose absorb water through "hydration" (hydrophilicity is much higher than that of unmodified cellulose); at the same time, the dense structure of the crosslinked network can physically block water evaporation (reduce surface water loss) and leakage (avoid rapid water infiltration to deep soil), prolonging water retention time.

[0061] Key to water retention rate of 500-800 times: Traditional water-retaining agents (such as potassium polyacrylate, see Comparative Example 2) have two major drawbacks: ① High salt environment causes a sharp drop in water absorption due to "salting-out effect"; ② No intelligent release function, water is easily evaporated. This material: ① Three-dimensional network can resist the inhibition of high salt environment on water absorption (network pores reduce the competitive adsorption of salt ions on water molecules); ② Temperature-responsive "water locking-release" cycle avoids water waste, so the water retention rate is much higher than that of traditional materials, and the water retention time is 15-20 days longer than that of ordinary soil.

[0062] Nutrient release function: "gel wrapping-environment triggered release" of nano-potassium-based composite particles: gel wrapping of sodium alginate: nano-potassium-based particles are made from potassium chloride and sodium alginate through ionic crosslinking (calcium chloride as crosslinking agent) — the carboxyl groups (-COO-) of sodium alginate and Ca 2+ Form a gel structure, wrap potassium chloride inside the gel, form a "nutrient core-gel shell" structure, avoid rapid dissolution and loss of potassium chloride;

[0063] Environment triggered slow release: ①Temperature response: during the day, NIPAM segments shrink, squeezing the gel shell and prompting a small amount of K + release; at night, the segments swell, and the gel absorbs water and swells, K + slowly diffuses into the soil solution; ②Biodegradation: sodium alginate is slowly degraded by soil microorganisms (completely degraded in 6-8 months, abstract), and as the gel shell gradually decomposes, K + is continuously released, achieving a release period of 30-45 days.

[0064] Reasons for nutrient disconnection: traditional fertilization (such as spreading potassium chloride) is prone to leaching and volatilization loss, and nutrient supply is not long-lasting; this material uses "gel wrapping + environmental regulation" to match the release rate of K + with the crop growth demand (more fertilizer needed during the day, less fertilizer needed at night), avoiding "excessive fertilizer supply" or "insufficient fertilizer supply".

[0065] The core feature of temperature-responsive monomer N-isopropyl acrylamide (NIPAM for short) is the low critical solution temperature (LCST, about 32℃). When the environmental temperature is lower than LCST, the NIPAM segment is in "swelling state"; when it is higher than LCST, it is in "shrinking state". In this invention, the diurnal temperature difference of saline-alkali soil (5-15℃) is exactly in the "adaptation window" with NIPAM's LCST (night temperature is usually 10-15℃, which is lower than LCST; daytime temperature is usually 25-30℃, which is close to LCST), and its regulation process relies on the synergistic effect of segment morphology change and three-dimensional network:

[0066] First step: low temperature at night (lower than LCST), segment swelling, locking water and potassium elements; water locking: at night, the temperature is low (such as 10-15℃ < 32℃), the NIPAM segment is in swelling state due to intermolecular hydrogen bonding (forming hydrogen bonds with water molecules), the segment stretches and expands the three-dimensional network of hydroxylated cellulose, the network pore becomes larger, and it can absorb water in the soil (including rainfall / irrigation water, soil capillary water) like a "sponge", at the same time, through the physical barrier effect of the network, it reduces the evaporation of water at night (although the temperature is low at night in saline-alkali soil, the wind is strong, and the evaporation is still significant); potassium element storage: nano-sized potassium-based composite particles (slow-release filler, claim 3) are embedded in the three-dimensional network, and the swollen segments will "wrap" the potassium-based particles, slowing down their degradation rate (the degradation of the sodium alginate shell requires the action of microorganisms, and the swollen network can reduce the contact efficiency of microorganisms), avoiding the excessive release of potassium elements at night (when crops need less fertilizer).

[0067] Second step: high temperature (close to LCST) segment contraction, release of moisture and potassium elements; moisture release: as the temperature rises during the day (such as 25-30°C close to 32°C), the intermolecular hydrogen bonds of NIPAM segment break, the segment changes from relaxed to contracted state, and the three-dimensional network pores are squeezed out, the water absorbed by the network is "squeezed" out and released into the soil, which is used for the crops' photosynthesis (peak water demand) during the day; potassium release: the contracted segment will produce physical extrusion to the embedded potassium particles, accelerate the degradation of the sodium alginate shell (after the shell is damaged, the internal potassium chloride is more easily dissolved), at the same time, the network pores become smaller, and the dissolved potassium ions (K + ) will diffuse to the crop root zone with the release of water, meeting the peak demand for fertilizer for crop growth during the day (such as wheat jointing stage, corn filling stage, high potassium demand).

[0068] The principle and key groups / chemical bonds of the pH-responsive monomer (aminopropyl triethoxysilane) for efficient replacement of sodium ions: the essence of the core effect: high pH environment triggers protonation, electrostatic adsorption, and ion exchange chain reaction; the core feature of the saline-alkali soil in the present application is high pH value 8.5-10.5, which provides the "triggering condition" for the aminopropyl triethoxysilane to work, and the process of replacing sodium ions can be divided into three steps, and each step depends on the chemical properties of the specific groups of the monomer:

[0069] First step: high pH environment activates the protonation of the monomer amino group (-NH2):

[0070] The aminopropyl triethoxysilane molecule contains an amino group (-NH2, strong alkaline group), which will combine with the trace amount of H - in the soil solution under the high pH environment of the saline-alkali soil (high concentration of OH + , low concentration of H + but still exists in trace amount), and undergoes protonation reaction: -NH2+ H + →-NH3 + The generated positively charged amino group (-NH3 + ) is the "functional core" for subsequent replacement of sodium ions. The Ca 2+ of the traditional single desalination material (such as gypsum) is easily lost with rainwater, while the -NH3 + formed by the protonation of the amino group in the present material does not flow away and can continuously work due to the chemical bond with the hydroxylated cellulose.

[0071] Second step: electrostatic adsorption of soil colloids, -NH3 + attracts the force of the negative charge of the soil:

[0072] The core problem of the saline-alkali soil is that the soil colloids adsorb a large amount of sodium ions (Na +):soil colloids (such as clay particles, organic matter) are usually negatively charged due to the breakage of siloxane bonds or the dissociation of carboxyl groups, and need to maintain electrical neutrality by adsorbing cations (such as Na + , Ca 2+ ). After protonation, -NH3 + is positively charged and will combine with the negative charge on the surface of the soil colloids through strong electrostatic attraction. This binding force (hydrogen bond + electrostatic interaction) is much stronger than the binding force of Na + to soil colloids (only electrostatic interaction), so -NH3 + will "compete for adsorption" of the adsorption sites on the surface of the soil colloids, "displacing" Na + from the surface of the colloids.

[0073] Third step: ion exchange to achieve desalination:

[0074] Na + displaced from the soil colloids by -NH3 + will enter the soil solution, and can subsequently be removed from the soil in two ways: natural leaching: when it rains or irrigates, Na + in the solution will percolate with the water to the deep soil (non-crop root zone); crop uptake: the crop roots will absorb Na + in the soil solution (partially salt-tolerant crops can absorb it moderately);

[0075] Finally, the soil is desalted, and because -NH3 + continuously provides adsorption sites, the desalination efficiency is 8-12 times higher than that of traditional materials.

[0076] The key to ensuring the durability of the effect is the grafting chemical bond of the alkyl group (-OC2H5): the amino propyl triethoxysilane molecule also contains three alkyl groups (-OC2H5), which are the "bridges" that bind the monomers to the hydroxylated cellulose: during in-situ polymerization, the alkyl group will undergo condensation with the hydroxyl group (-OH) on the surface of the hydroxylated cellulose to form a stable ether bond (-O-): Cell-OH + CH3CH2O-Si- → Cell-O-Si- + CH3CH2OH Through the ether bond, the pH-responsive monomers are "permanently grafted" onto the three-dimensional network of the hydroxylated cellulose, avoiding the problem of loss of functional components (such as Ca 2+ , single amino compounds) due to the lack of chemical bonds, ensuring the durability of the sodium ion replacement effect.

[0077] Comparative Example 1: Single pH-responsive material

[0078] Substrate preparation: wheat bran was crushed to 90 mesh, activated with 1.5 mol / L sodium hydroxide at 65°C for 2.5 h, reacted with epichlorohydrin at 55°C for 5 h, and hydroxylated cellulose with a hydroxyl substitution degree of 1.0.

[0079] Preparation of nanoscale potassium-based composite particles: A potassium chloride aqueous solution was mixed with a 2.5 wt% sodium alginate solution at a volume ratio of 1:3, and then 0.15 mol / L calcium chloride solution was added dropwise after uniform stirring. The mixture was ultrasonically dispersed at 400 W and 30 kHz for 25 min, and then freeze-dried after centrifugal separation to obtain potassium-based composite particles with a particle size of 100-150 nm.

[0080] In-situ polymerization modification: 50 g of hydroxylated cellulose was added to deionized water, ultrasonically dispersed for 35 min to form a 6% suspension, and only 12 g of pH-responsive monomer (aminopropyl triethoxysilane, no temperature-responsive monomer) was added. The mixture was deoxygenated by nitrogen for 30 min, 0.14 g of ammonium persulfate (initiator dosage was 1.2% of the mass of the single monomer) was added, and the mixture was reacted at 70°C for 7 h to obtain a modified cellulose polymer.

[0081] Composite molding: 12 g of nanoscale potassium-based composite particles were added, stirred at 45°C and 250 rpm for 2.5 h, 6 g of polyethylene glycol diglycidyl ether was added, and crosslinking reaction was carried out at 75°C for 3.5 h. After granulation, the mixture was dried at 70°C for 9 h to obtain a granular material (particle size 1-3 mm).

[0082] Purpose of implementation: To verify the key role of temperature-responsive monomers in water retention performance and nutrient on-demand release of the material.

[0083] Comparative Example 2: Traditional synthetic substrate material (polyacrylic acid instead of bio-based cellulose)

[0084] Substrate preparation: Commercially available polyacrylic acid (molecular weight 50000) was used as the substrate without hydroxylation modification. 50 g of polyacrylic acid was directly taken for use (without the participation of agricultural by-products).

[0085] Preparation of nanoscale potassium-based composite particles: A potassium chloride aqueous solution was mixed with a 2.5 wt% sodium alginate solution at a volume ratio of 1:3, and then 0.15 mol / L calcium chloride solution was added dropwise after uniform stirring. The mixture was ultrasonically dispersed at 400 W and 30 kHz for 25 min, and then freeze-dried after centrifugal separation to obtain potassium-based composite particles with a particle size of 100-150 nm.

[0086] In-situ polymerization modification: 50 g of polyacrylic acid was added to deionized water, ultrasonically dispersed for 35 min to form a 6% suspension, and 12 g of aminopropyl triethoxysilane and 18 g of N-isopropyl acrylamide were added. The mixture was deoxygenated by nitrogen for 30 min, 0.36 g of ammonium persulfate was added, and the mixture was reacted at 70°C for 7 h to obtain a modified polymer.

[0087] Composite molding: Same as Example 2 of the present application (12 g of potassium-based particles, 6 g of crosslinking agent, crosslinking at 75°C for 3.5 h, drying at 70°C for 9 h, particle size 1-3 mm).

[0088] Implementation purpose: to compare the differences between bio-based cellulose and traditional synthetic materials in terms of salt-alkali land adaptability and environmental friendliness.

[0089] Example 1

[0090] 1. Preparation of substrate: Corn straw was crushed to 80 mesh, activated with 1 mol / L sodium hydroxide solution at 60°C for 2h, and then 50°C for 4h with the addition of epoxy chloropropane. After washing to neutral and drying, hydroxylated cellulose with a hydroxyl substitution degree of 0.8 was obtained. (The hydroxyl group (-OH) of corn straw cellulose is not replaced by a single atom or simple group, but is replaced by an etherification group with the structure of -O-CH2-CH(OH)-CH2Cl through nucleophilic ring-opening etherification reaction of epoxy chloropropane. The essence is that the hydroxyl group of cellulose reacts with epoxy chloropropane to form a stable ether bond (-O-), while a new hydroxyl group (-CH(OH)-) is retained in the new group.)

[0091] 2. Preparation of nano-sized potassium-based composite particles: Mix the potassium chloride aqueous solution with 2wt% sodium alginate solution at a volume ratio of 1:3, stir uniformly, then add 0.1 mol / L calcium chloride solution, and ultrasonically disperse at 300W and 20kHz for 20min. After centrifugal separation and freeze-drying, potassium-based composite particles with a particle size of 50-100nm are obtained.

[0092] 3. In-situ polymerization modification: Add 40g of hydroxylated cellulose to deionized water, ultrasonically disperse for 30min to form a 5% suspension, add 10g of aminopropyl triethoxysilane and 12g of N-isopropyl acrylamide, deoxygenate under nitrogen for 30min, add 0.22g of ammonium persulfate, and react at 65°C for 6h to obtain a modified cellulose polymer.

[0093] 4. Composite molding: Add 10g of nano-sized potassium-based composite particles, stir at 40°C and 200rpm for 2h, add 5g of polyethylene glycol diglycidyl ether, and crosslink at 70°C for 3h. After granulation, dry at 60°C for 8h to obtain granular integrated material.

[0094] The core role of ammonium persulfate is as a free radical initiator; the core role of polyethylene glycol diglycidyl ether is as a crosslinking agent, which chemically reacts with other components in the system (hydroxylated cellulose, double-responsive monomer grafted polymer, nano-sized potassium-based composite particles) to build a dense and stable three-dimensional network structure, which is the key reagent to realize the function synergy and performance stability of material "improvement and water retention integration".

[0095] Example 2

[0096] 1. Substrate preparation: wheat bran was crushed to 90 mesh, activated with 1.5 mol / L sodium hydroxide solution at 65°C for 2.5 h, and reacted with epichlorohydrin at 55°C for 5 h. After washing to neutral and drying, hydroxylated cellulose was obtained with a hydroxyl substitution degree of 1.0. (The core purpose of hydroxylation modification is to solve two major problems of natural cellulose: ① High crystallinity, molecular chains are arranged tightly through hydrogen bonds, and most of the hydroxyl groups are wrapped in the crystalline region, which cannot be combined with the subsequent double-responsive monomers (aminopropyl triethoxysilane, N-isopropyl acrylamide); ② Insufficient hydrophilicity and reactivity, which is difficult to adapt to the high pH environment and water retention demand of saline-alkali soil.

[0097] The essence of hydroxylation modification (NaOH activation + epichlorohydrin etherification) is to destroy the crystalline structure of cellulose and introduce new hydroxyl groups, and "hydroxyl substitution degree (DS)" is an index that quantifies the average number of hydroxyl groups per glucose unit that are chemically modified (etherification introduces new hydroxyl groups) (natural cellulose contains 3 reactive hydroxyl groups per glucose unit, and the theoretical maximum value of DS is 3).

[0098] DS = 1.0 means that on average, one hydroxyl group per glucose unit of wheat bran cellulose is replaced by an "-O-CH2-CH(OH)-CH2Cl" etherification group through epichlorohydrin etherification reaction (while retaining the original unsubstituted hydroxyl group)

[0099] "Modification success" is not only based on DS = 1.0, but also needs to meet the comprehensive conditions of "DS standard, process adaptation, and subsequent functional support", which can be verified by the following three dimensions:

[0100] 1. Direct standard: hydroxyl substitution degree falls within the "effective range" defined in the present application

[0101] The hydroxyl substitution degree of the hydroxylated cellulose in the present application needs to be "0.8-1.2", and the DS of Example 2 is 1.0, which is exactly within this range;

[0102] The modified substrate needs to support the integrated material to achieve the "saline-alkali soil treatment function", which is the ultimate goal of successful modification:

[0103] 2. Preparation of nano-sized potassium-based composite particles: mix the potassium chloride aqueous solution with 2.5 wt% sodium alginate solution at a volume ratio of 1:3, stir uniformly, then add 0.15 mol / L calcium chloride solution, and ultrasonically disperse at 400W, 30kHz for 25 min. After centrifugal separation, freeze-drying is performed to obtain potassium-based composite particles with a particle size of 100-150 nm.

[0104] 3. In-situ polymerization modification: 50 g of hydroxylated cellulose was added to deionized water and ultrasonically dispersed for 35 min to form a 6% suspension, 12 g of aminopropyl triethoxysilane and 18 g of N-isopropyl acrylamide were added, deoxygenated for 30 min under nitrogen, 0.36 g of ammonium persulfate was added, and the reaction was carried out at 70°C for 7 h to obtain a modified cellulose polymer.

[0105] 4. Composite molding: 12 g of nano-sized potassium-based composite particles were added, stirred at 45°C and 250 rpm for 2.5 h, 6 g of polyethylene glycol diglycidyl ether was added, the temperature was raised to 75°C for crosslinking reaction for 3.5 h, and after granulation, drying was carried out at 70°C for 9 h to obtain granular integrated material.

[0106] Example 3

[0107] 1. Substrate preparation: cottonseed hulls were crushed to 100 mesh, activated with 2 mol / L sodium hydroxide solution at 70°C for 3 h, and then reacted with epichlorohydrin at 60°C for 6 h. After washing to neutral, drying was carried out to obtain hydroxylated cellulose with a hydroxyl substitution degree of 1.2.

[0108] 2. Preparation of nano-sized potassium-based composite particles: a potassium chloride aqueous solution was mixed with a 3 wt% sodium alginate solution at a volume ratio of 1:3, uniformly stirred, and then 0.2 mol / L calcium chloride solution was added dropwise, ultrasonically dispersed at 500 W and 40 kHz for 30 min, centrifuged, and then freeze-dried to obtain potassium-based composite particles with a particle size of 150-200 nm.

[0109] 3. In-situ polymerization modification: 60 g of hydroxylated cellulose was added to deionized water and ultrasonically dispersed for 40 min to form an 8% suspension, 15 g of aminopropyl triethoxysilane and 22.5 g of N-isopropyl acrylamide were added, deoxygenated for 30 min under nitrogen, 0.45 g of ammonium persulfate was added, and the reaction was carried out at 75°C for 8 h to obtain a modified cellulose polymer.

[0110] 4. Composite molding: 15 g of nano-sized potassium-based composite particles were added, stirred at 50°C and 300 rpm for 3 h, 8 g of polyethylene glycol diglycidyl ether was added, the temperature was raised to 80°C for crosslinking reaction for 4 h, and after granulation, drying was carried out at 80°C for 10 h to obtain granular integrated material.

[0111] Example 4: Rice straw-based material (widening the source of substrates)

[0112] Substrate preparation: rice straw (large yield and wide source) was crushed to 90 mesh, activated with 1.5 mol / L sodium hydroxide solution at 65°C for 2.5 h, and then reacted with epichlorohydrin at 55°C for 5 h. After washing to neutral, drying was carried out to obtain hydroxylated cellulose with a hydroxyl substitution degree of 1.0.

[0113] Nano-sized potassium-based composite particle preparation: same as Example 2 of the present invention (potassium chloride + 2.5 wt% sodium alginate, 0.15 mol / L calcium chloride, 400 W ultrasonic for 25 min, particle size 100-150 nm).

[0114] In-situ polymerization modification: 50 g of hydroxylated cellulose was added to deionized water and ultrasonically dispersed for 35 min to form a 6% suspension, 12 g of aminopropyl triethoxysilane and 18 g of N-isopropyl acrylamide were added, oxygen was removed by nitrogen for 30 min, 0.36 g of ammonium persulfate was added, and the reaction was carried out at 70°C for 7 h to obtain a modified cellulose polymer.

[0115] Composite molding: 12 g of nano-sized potassium-based composite particles were added, stirred at 45°C and 250 rpm for 2.5 h, 6 g of polyethylene glycol diglycidyl ether was added, the temperature was raised to 75°C for crosslinking reaction for 3.5 h, and after granulation, it was dried at 70°C for 9 h to obtain a granular material (particle size 1-3 mm).

[0116] Purpose of implementation: to broaden the source of agricultural by-product substrates, use rice straw (the highest yield of global crop by-products) to reduce raw material costs, and maintain the core function of the material.

[0117] Example 5: composite substrate material (corn straw + peanut shell)

[0118] Substrate preparation: corn straw (60%) + peanut shell (40%) were mixed and crushed to 90 mesh, activated with 1.5 mol / L sodium hydroxide solution at 65°C for 2.5 h, and reacted with epichlorohydrin at 55°C for 5 h, washed and dried to obtain hydroxylated cellulose (mixed substrate improves structural stability), with a hydroxyl substitution degree of 1.1.

[0119] Nano-sized potassium-based composite particle preparation: same as Example 2 of the present invention (particle size 100-150 nm).

[0120] In-situ polymerization modification: 50 g of mixed hydroxylated cellulose was added to deionized water and ultrasonically dispersed for 35 min to form a 6% suspension, 13 g of aminopropyl triethoxysilane and 19.5 g of N-isopropyl acrylamide (monomer ratio 1:1.5) were added, oxygen was removed by nitrogen for 30 min, 0.39 g of ammonium persulfate was added, and the reaction was carried out at 70°C for 7 h.

[0121] Composite molding: 13 g of nano-sized potassium-based composite particles were added, stirred at 45°C and 250 rpm for 2.5 h, 6 g of polyethylene glycol diglycidyl ether was added, crosslinked at 75°C for 3.5 h, and dried at 70°C for 9 h, with a particle size of 1-3 mm.

[0122] Purpose of implementation: by combining two agricultural by-products, the substrate structure is optimized, and the water retention stability and soil improvement effect of the material are improved.

[0123] Example 6: Low pH saline-alkali land adaptation material (adjusting the ratio of dual-responsive monomers)

[0124] Substrate preparation: same as Example 2 of the present invention (wheat bran, hydroxyl substitution degree 1.0).

[0125] Nanoscale potassium-based composite particle preparation: same as Example 2 of the present invention.

[0126] In-situ polymerization modification: 50 g of hydroxylated cellulose was added to deionized water and ultrasonically dispersed for 35 min to form a 6% suspension, 15 g of aminopropyl triethoxysilane (pH-responsive monomer) and 15 g of N-isopropyl acrylamide (temperature-responsive monomer, ratio 1:1) were added, deoxygenated for 30 min under nitrogen, 0.36 g of ammonium persulfate was added, and reacted at 70°C for 7 h.

[0127] Composite molding: 12 g of nanoscale potassium-based composite particles were added, stirred at 45°C and 250 rpm for 2.5 h, 6 g of polyethylene glycol diglycidyl ether was added, crosslinked at 75°C for 3.5 h, dried at 70°C for 9 h, and the particle size was 1-3 mm.

[0128] Purpose of implementation: adjust the ratio of dual-responsive monomers, adapt to mild saline-alkali land (pH 7.5-8.5), and solve the limitation of the present invention that it only adapts to moderate saline-alkali land (pH 8.5-10.5).

[0129] Example 7: Zinc-containing composite nutrient material (supplementing trace elements)

[0130] Substrate preparation: same as Example 2 of the present invention (wheat bran, hydroxyl substitution degree 1.0).

[0131] Nanoscale potassium-zinc composite particle preparation: potassium chloride (95%) + nanometer zinc powder (5%) were mixed, mixed with 2.5 wt% sodium alginate solution at a volume ratio of 1:3, uniformly stirred, then 0.15 mol / L calcium chloride solution was added dropwise, ultrasonically dispersed at 400 W and 30 kHz for 25 min, centrifuged and freeze-dried to obtain potassium-zinc composite particles with a particle size of 100-150 nm (containing 0.4 wt% zinc).

[0132] In-situ polymerization modification: same as Example 2 of the present invention (50 g of substrate + 12 g of pH monomer + 18 g of temperature monomer).

[0133] Composite molding: 12 g of nanoscale potassium-zinc composite particles were added, stirred at 45°C and 250 rpm for 2.5 h, 6 g of polyethylene glycol diglycidyl ether was added, crosslinked at 75°C for 3.5 h, dried at 70°C for 9 h, and the particle size was 1-3 mm.

[0134] Purpose of implementation: supplement the essential trace element zinc for crops, solve the problem of single nutrient in traditional materials, and improve the stress resistance of crops (such as salt-alkali resistance and disease resistance).

[0135] Example 8: Low energy consumption process optimization material (reduce ultrasonic power)

[0136] Substrate preparation: same as Example 2 of the present application (wheat bran, degree of hydroxyl substitution 1.0).

[0137] Nanoscale potassium-based composite particle preparation: mix the potassium chloride aqueous solution with 2.5wt% sodium alginate solution at a volume ratio of 1:3, stir uniformly, then add 0.15mol / L calcium chloride solution, 300W, 30kHz ultrasonic dispersion for 30min (reduce ultrasonic power, extend time), centrifugal separation, then freeze-drying, particle size 100-150nm.

[0138] In-situ polymerization modification: add 50g hydroxylated cellulose to deionized water, 300W ultrasonic dispersion for 40min (reduce power, extend time) to form a 6% suspension, add 12g aminopropyl triethoxysilane and 18g N-isopropyl acrylamide, deoxygenate under nitrogen for 30min, add 0.36g ammonium persulfate, react at 70℃ for 7h.

[0139] Composite molding: add 12g nanoscale potassium-based composite particles, stir at 45℃, 250rpm for 2.5h, add 6g polyethylene glycol diglycidyl ether, crosslink at 75℃ for 3.5h, dry at 75℃ for 8h (increase drying temperature, shorten time), particle size 1-3mm.

[0140] Purpose of implementation: optimize process parameters (reduce ultrasonic power, adjust drying conditions), reduce production energy consumption, improve industrialization economy.

[0141] Performance test

[0142] The integrated materials prepared in Examples 1-8 were tested for performance, and the results are as follows:

[0143]

[0144]

[0145] The test results show that the integrated material prepared by the present application has excellent sodium ion replacement capacity, water retention performance and nutrient release effect in saline-alkali environment, and good degradation performance, fully meeting the integrated needs of saline-alkali soil improvement.

[0146] The above examples illustrate the structure, features and effects of the present application. The above description is only the preferred embodiment of the present application. Any changes or modifications made in accordance with the concept of the present application, or equivalent embodiments with equivalent changes, shall be within the scope of the present application.

[0147] Although the embodiments of the present application have been disclosed for illustrative purposes, those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present application and the appended claims, and thus the scope of the present application is not limited to the disclosed embodiments.

Claims

1. A bio-based polymeric material, characterized in that, The base material, functional modification monomer, slow-release filler, free radical initiator and crosslinking agent are compounded in a mass ratio of 40-60:20-30:10-15:0.2-0.4:5-8; the base material is hydroxylated cellulose; the functional modification monomer comprises a pH-responsive monomer and a temperature-responsive monomer, and the mass ratio of the pH-responsive monomer to the temperature-responsive monomer is 1:1.2-1.5; the pH-responsive monomer is aminopropyl triethoxysilane or aminopropyl trimethoxysilane, and the temperature-responsive monomer is N-isopropyl acrylamide; the slow-release filler is a nano-sized potassium-based composite particle, a potassium sulfate sodium alginate nano-composite particle or a potassium chloride chitosan nano-composite particle; the free radical initiator is ammonium persulfate; and the crosslinking agent is polyethylene glycol diglycidyl ether.

2. The bio-based polymeric material according to claim 1, characterized in that, The hydroxyl group substitution degree of the hydroxylated cellulose is 0.8-1.

2.

3. The bio-based polymeric material according to claim 2, c h a r a c t e r i z e d in that, The particle size of the slow-release filler is 50-200 nm.

4. The bio-based polymeric material according to any one of claims 1 to 3, c h a r a c t e r i z e d in that, The bio-based high molecular material is applied to the improvement of saline-alkali farmland, and the application mode is spreading and ploughing, and the application amount is 20-50 kg per mu.

5. The bio-based polymeric material according to claim 4, wherein Under the conditions of soil pH 8.5-10.5 and diurnal temperature difference 5-15℃, the sodium ion replacement rate of the bio-based high molecular material is ≥85%, the soil aggregate structure content is increased by 40-60%, the water holding time is prolonged by 15-20 days compared with ordinary soil, and the potassium element release period is 30-45 days.

6. A method of producing the bio-based polymeric material according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: vacuum drying hydroxylated cellulose to obtain dried hydroxylated cellulose with a water content of ≤5%, adding the dried hydroxylated cellulose into deionized water, ultrasonic dispersion to form a suspension, sequentially adding a pH-responsive monomer and a temperature-responsive monomer into the suspension, removing oxygen by nitrogen blowing, adding ammonium persulfate to obtain a modified cellulose polymer; adding a nano-sized potassium-based composite particle into the modified cellulose polymer, stirring, adding a crosslinking agent, crosslinking reaction at 70-80℃, and granulating and drying after the reaction to obtain a bio-based high molecular material.

7. The method of claim 6, wherein, The free radical initiator is used in an amount of 0.8-1.2% of the total mass of the functional modification monomers, and the bio-based high molecular material is in the form of a granular particle with a particle size of 1-3 mm.

8. The method of claim 7, wherein, The preparation of the hydroxylated cellulose comprises the following steps: crushing an agricultural byproduct to 80-100 mesh to obtain cellulose powder, activating the cellulose powder in 1-2 mol / L sodium hydroxide solution at 60-70℃ for 2-3 h to obtain alkali-activated cellulose, adding epichlorohydrin to the alkali-activated cellulose and reacting at 50-60℃ for 4-6 h, washing to neutral and drying to obtain the hydroxylated cellulose.

9. The method of claim 8, wherein, The preparation of the nano-sized potassium-based composite particle comprises the following steps: mixing a potassium chloride aqueous solution and a 2-3 wt% sodium alginate solution in a volume ratio of 1:3, uniformly stirring, adding a 0.1-0.2 mol / L calcium chloride solution dropwise, ultrasonic dispersion for 20-30 min, centrifugal separation and freeze-drying to obtain the nano-sized potassium-based composite particle.

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