Coal gangue-based polymer in-situ mineralization strong and tough type full-biomass seedling raising tray and preparation method thereof

Abstract

The present application belongs to the field of new agriculture, and particularly relates to a coal gangue-based polymer in-situ mineralization strong and tough type full-biomass seedling raising tray and a preparation method thereof. The preparation method first prepares a modified plant fiber suspension and a multi-stage activated coal gangue active slurry, realizes electrostatic self-assembly pre-bonding through mixing and standing, then makes silicon-aluminum sol penetrate into the fiber cell wall gap through negative pressure gradient dewatering, and finally triggers the polymerization reaction at low temperature of 95-110 DEG C through low-temperature molding, so as to realize self-sustaining curing by using reaction heat. The present application realizes the wet tensile strength of 4.5 MPa or more through the interface Si-O-C covalent bond construction, cancels the traditional drying process to reduce the unit product energy consumption by 62%, realizes permanent storage of heavy metals, full-cycle degradation and negative carbon emission, and the product can adapt to cold land, double-cropping rice, salt-tolerant and tropical rice and other multi-scene seedling raising requirements, and has the soil improvement and crop yield increasing benefits.

Description

Technical Field

[0001] This invention belongs to the field of new agriculture, specifically relating to a tough, in-situ mineralized all-biomass seedling tray for coal gangue base and its preparation method. Background Technology

[0002] Rice seedling trays are a core input in rice mechanized transplanting systems. Currently, mainstream seedling tray products and manufacturing technologies face several common industry challenges:

[0003] 1. Paper / biomass molded discs: These are made using a physical blend of plant fibers and fillers, relying on starch or resin adhesives. The fibers and inorganic phases are bound together solely by van der Waals forces, resulting in a wet tensile strength typically below 1.0 MPa. In the high-temperature and high-humidity environment of Southeast Asia, the interface rapidly fails after moisture absorption, leading to a machine-inserted disc failure rate as high as 30%-45%. Furthermore, existing processes require 8-12 hours of high-temperature drying, resulting in extremely high energy consumption.

[0004] 2. Plastic seedling trays are made of polypropylene, which is completely non-degradable. The amount of residual plastic fragments per acre of farmland can reach 12-18 kg per year, which has become an important source of agricultural non-point source pollution and has been listed as a key target for agricultural non-point source pollution control in the Asia-Pacific region.

[0005] 3. Traditional coal gangue-filled seedling trays only use unactivated coal gangue as a cheap filler, without exploring its silicon and aluminum chemical potential, and there is a risk of heavy metal leaching; some sintered coal gangue seedling trays need to be fired at temperatures above 1000℃, resulting in high carbon emission intensity, which does not meet global temperature control targets and low-carbon development requirements.

[0006] 4. Resin-bonded seedling trays require the addition of more than 20% urea-formaldehyde or phenolic resin, which leads to formaldehyde release during the seedling stage and can easily induce diseases, thus failing to meet the standards for green and organic agricultural inputs.

[0007] At the manufacturing process level, existing seedling tray production generally relies on a high-temperature drying process of 8-12 hours, which is energy-intensive, has a long production cycle, and cannot achieve chemical bonding between the inorganic and organic phases, making it difficult to balance material strength and degradation performance. Therefore, developing a low-energy, short-process method for preparing seedling trays that simultaneously achieves high strength, full degradation, and low environmental risk is a pressing technical problem to be solved in the field of green agricultural inputs. Summary of the Invention

[0008] To address the problems of high energy consumption, long production cycle, inability to achieve chemical bonding between inorganic and organic phases, and difficulty in balancing material strength and degradation performance in existing technologies, this invention provides a method for preparing a tough, all-biomass seedling tray using in-situ mineralization of polymers from coal gangue bases. This method constructs a chemical bonding interface between organic fibers and inorganic gels through low-temperature polymerization, combined with a short-process self-curing technology. This significantly reduces production energy consumption while simultaneously improving the wet strength of the seedling tray, stably sealing heavy metals, achieving full-cycle degradation, and providing soil improvement and negative carbon benefits, thus adapting to the rice seedling needs of different climatic zones.

[0009] The preparation method includes the following steps: (I) Raw material pretreatment (I-1) Pretreatment of plant fibers: Plant fibers are mixed with a eutectic solvent for pretreatment to obtain a suspension rich in cellulose nanofibers (CNFs); after treatment with a eutectic solvent (DESs), the three major components of cellulose, hemicellulose and lignin in the cell wall of the plant fibers are selectively separated, lignin and hemicellulose are directionally dissolved, and the cellulose component is retained and dissociates in situ to release a large number of cellulose nanofibers (CNFs), finally forming a dissolution slurry system with cellulose as the skeleton and high concentration of CNFs uniformly dispersed; (I-2) Pretreatment of coal gangue: The coal gangue is successively ground, thermally activated and ultrasonically activated to obtain coal gangue active slurry; (II) Electrostatic self-assembly pre-reaction The cellulose-rich nanofiber suspension is mixed with the coal gangue active slurry, and then a biomineralization regulator and functional biochar are added. The mixture is allowed to stand and self-assemble to obtain the mixed slurry. (III) Pre-dehydration during molding The mixed slurry is injected into a seedling tray mold, and free water is removed under reduced pressure to obtain a pre-dehydrated system; (IV) Low-temperature in-situ curing The pre-dehydration system is heated and pressurized to achieve pressure holding, degassing, and curing. After completion, it is demolded to obtain the finished seedling tray.

[0010] Preferably, in step (I-1), the plant fiber is mixed with a eutectic solvent, pretreated at 70-80°C for 4-5 hours, washed with water until neutral, and then pulped to obtain a cellulose-rich nanofiber suspension with a concentration of 3-3.5 wt%.

[0011] Preferably, in step (I-1), the eutectic solvent comprises choline chloride and a hydrogen bond donor, wherein the molar ratio of choline chloride to the hydrogen bond donor is 1:1 to 1:2; and the hydrogen bond donor is lactic acid, urea, or oxalic acid. And / or, the plant fiber is one of reed, bamboo, cotton stalk, or empty fruit clusters of oil palm; the pretreated cellulose-rich nanofibers have a diameter of 10-50 nm, a fiber crystallinity of over 78%, and a surface hydroxyl density ≥ 3.2 hydroxyl groups / nm. 2 It can serve as an organic reaction template for geopolymerization.

[0012] Preferably, in step (I-2), the coal gangue is ball-milled to D50≤3μm, then thermally activated at 300-350℃ for 2-3h to destroy the kaolinite crystal structure, and then ultrasonically activated with 1.5-2.0mol / L NaOH solution for 30-40min to obtain an active slurry (a silica-alumina sol slurry with high reactivity). And / or, the specific surface area of ​​the activated coal gangue is 300-500 m². 2 / g; After multi-stage activation, [SiO4] in coal gangue 4- [AlO4] 5- A large amount of active monomers are released, and the reactivity is increased by more than 17 times compared with unactivated coal gangue.

[0013] Preferably, in step (II), the cellulose-rich nanofiber suspension is mixed with the coal gangue active slurry, then a biomineralization regulator and functional biochar are added, deionized water is added, and an alkali regulator (NaOH or KOH) is added to adjust the pH of the system to 11.0-12.0. After stirring for 1-2 minutes until the system is homogeneous, it is allowed to stand for 5-15 minutes. The negative charge on the surface of the pretreated and modified fibers reacts with the Al released from the coal gangue. 3+ Electrostatic attraction is generated, spontaneously forming "fiber-Al" 3+ -The pre-bonded structure of silicon-oxygen tetrahedrons eliminates the need for additional crosslinking agents, and the resulting slurry is obtained after self-assembly.

[0014] Preferably, in step (II), the biomineralization regulator is a mixture of sodium alginate and xanthan gum, wherein the mass ratio of sodium alginate to xanthan gum is 2:1, and the carboxyl density in the biomineralization regulator is ≥4.8 mmol / g; it regulates the polymerization rate of silica-alumina monomers through steric hindrance effect, avoids interface defects caused by the rapid aggregation and precipitation of silica-alumina monomers, and guides NASH gel to form a continuous coating layer of uniform thickness on the fiber surface; And / or, the method for preparing the functional biochar is as follows: (i) The biochar raw material is pyrolyzed at 500-600℃ to obtain mesoporous biochar with a porosity ≥85%; (ii) The mesoporous biochar is loaded with potassium silicate and / or chelated zinc at a loading amount of 8-15 wt% of the mesoporous biochar to obtain functional biochar; it serves as a three-dimensional structural framework to improve the air permeability of the seedling tray, and can also serve as a slow-release micronutrient fertilizer source, while achieving permanent sequestration of biochar. And / or, in step (II), functional mineral powder is also added, wherein the functional mineral powder is serpentine powder or zeolite powder, and the functional mineral powder accounts for 1-5 wt% of the total solid content of the raw materials; the serpentine powder contains ≥35% MgO and has a particle size D50 ≤10 μm. Serpentine powder can release magnesium ions to activate rice silicon transporter genes and improve acidic soil; zeolite powder can adsorb salt and alkali ions, making it suitable for rice seedling cultivation in saline-alkali land.

[0015] Preferably, in step (III), the mixed slurry is injected into the seedling tray mold, and a vacuum of -0.08 to -0.1 MPa is applied to remove free water from the system under reduced pressure. At the same time, the silica-alumina sol penetrates into the intercellular spaces of the fiber cells under capillary force, with a penetration depth of up to 52±7 μm, to achieve cell-level two-phase composite, and a pre-dehydrated system is obtained after completion.

[0016] Preferably, in step (IV), the pre-dehydration system is placed in a molding equipment and molded and cured at 95-110°C for 10-15 minutes to trigger a polymerization reaction. The heat released by the reaction and the thermal field of the mold are used to maintain the temperature at the center of the mold at 100-120°C. After completion, the mold is removed to obtain the finished seedling tray.

[0017] Preferably, the raw materials include, by weight: 40-50 parts plant fiber, 35-42 parts coal gangue, 3-5 parts biomineralization regulator, and 8-12 parts functional biochar.

[0018] Based on the same technical concept, another aspect of the present invention is to provide a coal gangue-based polymer in-situ mineralized tough all-biomass seedling tray prepared by the above preparation method. The seedling tray matrix contains Si-OC covalent bonds, and the NASH gel coating thickness on the fiber surface is 40~120nm. The wet tensile strength after being placed at 35℃ and 90% relative humidity for 7 days is ≥4.5MPa, the soil humification rate is ≥94% within 90 days, and the heavy metal leaching concentration is less than 0.01μg / L.

[0019] The beneficial effects of this invention are as follows: 1. Significant improvement in wet tensile strength achieved through interfacial chemical bonding: Si-OC covalent bonds are formed between plant fibers and inorganic phases through low-temperature polymerization reaction, constructing a "brick-and-mortar interlocking" structure similar to the nacreous layer of a seashell. NASH gel forms a continuous coating layer of 40-120nm on the fiber surface. After being placed in a high-temperature and high-humidity environment of 35℃ and 90% relative humidity for 7 days, the wet tensile strength of the product can reach more than 4.5MPa, and the machine transplanting tray breakage rate is less than 0.2%, which is far superior to traditional paper seedling trays.

[0020] 2. Short process significantly reduces energy consumption: This invention has developed an “electrostatic self-assembly-negative pressure dehydration-self-heating curing” process, which completely eliminates the traditional 8-12h drying process. It utilizes the exothermic reaction of the geopolymerization reaction and the coupling with the external heat field to achieve self-sustaining curing. The curing time is only 10-15 minutes, and the energy consumption per unit product is reduced by 62% compared with the traditional process, significantly reducing the production cycle and carbon emissions.

[0021] 3. Permanent sequestration of heavy metals eliminates ecological risks: The NASH gel formed by alkali activation has a cage-like structure, which can encapsulate heavy metals such as Pb, Cd, and As associated with coal gangue within the structure through coordination complexation, forming stable MO-Si bonds; the heavy metal leaching concentration of the product is less than 0.01 μg / L in acidic environment, and the sequestration efficiency is greater than 99.5%, which fully meets the environmental safety requirements of agricultural land soil.

[0022] 4. Dual benefits of complete degradation and soil improvement: The seedling tray can be directly transplanted into the soil along with the seedlings. The humification rate can reach more than 94% within 90 days, and the degradation products are transformed into soil organic matter. At the same time, the functional biochar and mineral components can slowly release nutrients such as silicon, zinc and magnesium, regulate soil pH, increase the available silicon content in the soil, and reduce the amount of chemical fertilizers and soil conditioners used.

[0023] 5. Strong negative carbon attributes and regional adaptability: Through the disposal of coal gangue solid waste and biomass carbon sequestration, the product achieves negative carbon emissions throughout its entire life cycle, meeting the green process standard of "treating waste with waste". The carbon sink of a single tray can reach 0.23kg CO2-eq. By adjusting the fiber raw materials, functional components and process parameters, it can be adapted to different planting scenarios such as cold-region japonica rice, double-cropping rice, salt-alkali tolerant rice and tropical rice. The raw materials can be obtained locally and are suitable for major rice planting areas around the world. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] This invention provides a method for preparing a robust, in-situ mineralized polymer seedling tray from a coal gangue base, the method comprising the following steps: (I) Raw material pretreatment (I-1) Pretreatment of plant fibers: Plant fibers are mixed with a eutectic solvent and pretreated at 70-80℃ for 4-5 hours. After washing with water until neutral, the mixture is pulped to obtain a cellulose nanofiber suspension with a concentration of 3-3.5 wt%. The eutectic solvent comprises choline chloride and a hydrogen bond donor, with a molar ratio of choline chloride to the hydrogen bond donor of 1:1-1:2. The hydrogen bond donor is lactic acid, urea, or oxalic acid. The plant fiber is one of reed, bamboo, cotton stalks, or empty fruit bunches of oil palm. The cellulose-rich nanofibers obtained after pretreatment have a diameter of 10-50 nm and a surface hydroxyl density ≥ 3.2 hydroxyl groups / nm. 2 ; (I-2) Pretreatment of coal gangue: The coal gangue was ball-milled to D50≤3μm, then thermally activated at 300-350℃ for 2-3h to destroy the crystal structure. Subsequently, it was ultrasonically activated with 1.5-2.0mol / L NaOH solution for 30-40min to obtain an activated slurry. The specific surface area of ​​the activated coal gangue was 300-500m². 2 / g; (II) Electrostatic self-assembly pre-reaction The cellulose-rich nanofiber suspension was mixed with the coal gangue active slurry, and then a biomineralization regulator and functional biochar were added. The mixture was stirred for 1-2 minutes until homogeneous, and then allowed to stand for 5-15 minutes for self-assembly, resulting in a mixed slurry. Wherein: The biomineralization regulator is a mixture of sodium alginate and xanthan gum, wherein the mass ratio of sodium alginate to xanthan gum is 2:1, and the carboxyl density in the biomineralization regulator is ≥4.8 mmol / g. And / or, the method for preparing the functional biochar is as follows: (i) The biochar raw material is pyrolyzed at 500-600℃ to obtain mesoporous biochar with a porosity ≥85%; (ii) The mesoporous biochar is loaded with potassium silicate and / or chelated zinc at a loading amount of 8-15 wt% of the mesoporous biochar to obtain functional biochar. And / or, in step (II), functional mineral powder is also added, wherein the functional mineral powder is serpentine powder or zeolite powder, and the functional mineral powder accounts for 1-5 wt% of the total solid content of the raw material; the serpentine powder contains ≥35% MgO and the particle size D50 of the serpentine powder is ≤10 μm.

[0026] (III) Pre-dehydration during molding The mixed slurry is injected into the seedling tray mold, and free water is removed under reduced pressure by applying a vacuum of -0.08 to -0.1 MPa to obtain a pre-dehydrated system.

[0027] (IV) Low-temperature in-situ curing The pre-dehydrated system is placed in a molding equipment and molded at 95-110℃ for 10-15 minutes to trigger a polymerization reaction. The heat released by the reaction and the thermal field of the mold are used to maintain the temperature at the center of the mold at 100-120℃. After completion, the mold is removed to obtain the finished seedling tray.

[0028] The raw materials used, by weight, include: 40-50 parts plant fiber, 35-42 parts coal gangue, 3-5 parts biomineralization regulator, and 8-12 parts functional biochar.

[0029] Example 1 This embodiment provides a method for preparing a tough, all-biomass seedling tray (a special seedling tray for cold-region japonica rice in Northeast China) using in-situ mineralized polymers from coal gangue bases. It is suitable for early spring seedling raising in temperatures ranging from -5 to 15℃. The specific preparation steps are as follows: (1) Raw material preparation and eutectic solvent preparation: Weigh 45 kg of reed fiber, 38 kg of coal gangue, 3 kg of sodium alginate / xanthan gum compound regulator (sodium alginate to xanthan gum mass ratio 2:1), 12 kg of functional corn straw biochar, and 120 kg of deionized water according to the ratio; separately take NaOH solid for later use to adjust the pH of the system.

[0030] Preparation of choline chloride / lactic acid eutectic solvent: Add choline chloride and lactic acid to the reaction vessel at a molar ratio of 1:2, stir at 150 r / min at 70℃ until the system is a homogeneous, clear and transparent liquid, and keep it at this temperature for later use.

[0031] Reed fiber pretreatment: The reed fiber is crushed to a length of 2-5mm using a shearing and crushing machine, and then screened to remove impurities before use.

[0032] (2) Preparation of modified reed fiber suspension: The crushed reed fiber was added to the above-mentioned eutectic solvent at a solid-liquid mass ratio of 1:10, heated to 80℃, and stirred at 200 r / min for 4 h; after treatment, the solvent was discharged, and the fiber was repeatedly washed with deionized water until the pH of the filtrate was neutral. Then it was transferred to a high-shear pulper and pulped at 3000 r / min for 20 min to obtain a cellulose-rich nanofiber suspension with a mass concentration of 3 wt%; the obtained fiber diameter was 10~50 nm and the surface hydroxyl density was about 3.2 hydroxyl groups / nm. 2 The fiber crystallinity is 79.2%.

[0033] (3) Preparation of multi-stage activated coal gangue slurry: After coarse crushing, the coal gangue was transferred to a planetary ball mill with zirconia balls as the grinding medium. The ball-to-material mass ratio was 10:1, the rotation speed was set at 450 r / min, and the ball milling was carried out alternately in both directions for 2 hours until the median diameter of the powder D50 was 2.8 μm and the specific surface area was measured to be 385 m². 2 / g; The ball-milled coal gangue powder was transferred to a muffle furnace and heated to 300℃ at a heating rate of 5℃ / min. It was then held at this temperature for 2 hours to activate the kaolinite crystal structure. After natural cooling, the powder was removed and a 1.5mol / L NaOH solution was added. The solid-liquid mass ratio was 1:8. The powder was then transferred to an ultrasonic disperser and activated by ultrasonication at 250W power for 30 minutes to obtain an activated coal gangue slurry.

[0034] (4) Electrostatic self-assembly pre-reaction: The cellulose-rich nanofiber suspension and coal gangue active slurry were fed into a mixing vessel, and sodium alginate / xanthan gum compound regulator and functional corn straw biochar were added. Deionized water was added until the total mass of the system met the ratio. NaOH solid was added to adjust the pH of the system to 11.5. The system was stirred at 300 r / min for 1.5 min until it was homogeneous. Then the stirring was stopped and the system was allowed to stand for 10 min. The reaction was carried out by the negative charge on the fiber surface and the Al released from the coal gangue. 3+ Electrostatic attraction is generated, spontaneously forming "fiber-Al" 3+ -The silicon-oxygen tetrahedral pre-bonded structure completes electrostatic self-assembly to obtain a mixed slurry.

[0035] (5) Negative pressure molding pre-dehydration: The mixed slurry is injected at a constant speed into a seedling tray molding mold with a size of 600mm×300mm. The vacuum system is turned on and a vacuum degree of -0.09MPa is applied for filtration for 15s to remove most of the free water in the system. During the process, the silica-alumina sol penetrates into the intercellular space of the fiber cells under the action of capillary force to obtain the pre-dehydration system.

[0036] (6) Low-temperature molding in-situ curing: The mold with the pre-dehydration system is transferred to the flat vulcanizing machine, the molding pressure is set to 6MPa, the heating temperature is 100℃, and the molding curing is 12min; the polymerization reaction is triggered during the molding process, and the reaction exothermic coupling with the mold thermal field is used to maintain the mold center temperature at 105~115℃ to achieve self-sustaining curing; after curing, the pressure is released and the mold is demolded, and the seedling tray is placed in a room temperature and relative humidity environment of 50% for 24h to balance, and the finished product is obtained.

[0037] Performance testing: The wet tensile strength of the product in this embodiment is 4.85 MPa, the field degradation rate is 94% after 45 days, and the leaching concentration of heavy metal Pb is <0.005 μg / L; field seedling raising trials show that the incidence of damping-off disease after seedling transplanting is reduced by 19.2% compared with the control plastic tray, and the yield of rice per mu is increased by 42 kg.

[0038] Example 2 This embodiment provides a method for preparing a tough, in-situ mineralized polymer seedling tray (a special seedling tray for regeneration of double-cropping rice in southern China) from a coal gangue base. It is suitable for multiple seedling raising cycles and high-humidity environments. The specific preparation steps are as follows: (1) Raw material preparation and preparation of eutectic solvent: Weigh 50 kg of bamboo fiber, 35 kg of coal gangue, 4 kg of sodium alginate / xanthan gum compound regulator (sodium alginate to xanthan gum mass ratio 2:1), 8 kg of functional camellia shell biochar (biochar loaded with potassium silicate, loading amount 15wt%), and 110 kg of deionized water according to the ratio; take KOH solid for later use to adjust the pH of the system.

[0039] Preparation of choline chloride / urea eutectic solvent: Add choline chloride and urea to the reaction vessel at a molar ratio of 1:1.5, stir at 75°C until clear and transparent, and keep warm for later use.

[0040] Bamboo pretreatment: Cut the bamboo into 1-2cm long strips and sieve to remove debris and impurities.

[0041] (2) Preparation of modified bamboo fiber suspension: bamboo chips were fed into a steam explosion device, the steam pressure was set to 1.5 MPa, and the pressure was maintained for 5 min before instantaneous depressurization was completed to complete the explosion; the exploded bamboo fibers were put into the above-mentioned eutectic solvent with a solid-liquid mass ratio of 1:12, the temperature was raised to 70℃, and the mixture was stirred at 180 r / min for 5 h; after the treatment was completed, the solvent was recovered, the fibers were washed with deionized water until neutral, and then transferred to a high shear pulper and pulped at 3200 r / min for 18 min to obtain a cellulose-rich nanofiber suspension with a mass concentration of 3 wt%.

[0042] (3) Preparation of multi-stage activated coal gangue slurry: The activation process of coal gangue is the same as in Example 1: planetary ball milling to D50=2.8μm, thermal activation at 300℃ for 2h, adding 1.5mol / L NaOH solution and ultrasonic activation at 250W for 30min to obtain activated slurry.

[0043] (4) Electrostatic self-assembly pre-reaction: The cellulose-rich nanofiber suspension is mixed with the coal gangue active slurry, compound regulator and functional camellia shell biochar are added, deionized water is added to the set total amount, KOH solid is added to adjust the pH of the system to 11.0, and the mixture is stirred at 280 r / min for 1 min until homogeneous. After standing for 10 min, the electrostatic self-assembly is completed and the mixed slurry is obtained.

[0044] (5) Negative pressure molding pre-dehydration: The mixed slurry is injected into a seedling tray mold of the same specification, and a vacuum of -0.09MPa is applied for filtration for 15s to remove free water and obtain a pre-dehydration system.

[0045] (6) Low temperature molding in situ curing: Transfer the mold to a flat vulcanizing machine, set the molding pressure to 7MPa, the heating temperature to 105℃, and mold for 10min; use the exothermic polymerization reaction to maintain the temperature of the mold center. After curing, release the pressure and demold, and allow the mold to equilibrate at room temperature for 24h to obtain the finished product.

[0046] Performance testing: The wet tensile strength of the product in this embodiment is 5.02 MPa, the strength retention rate is 87% after two repeated seedling raisings, and the humification rate is 96% after 90 days; field trials show that the effective silicon content in the soil increases by 18.7%, the yield of the first season of ratooning rice increases by 51 kg per mu, and the yield of the ratooning season increases by 37 kg per mu.

[0047] Example 3 This embodiment provides a method for preparing a robust, all-biomass seedling tray (salt-tolerant rice seedling tray for arid regions in Northwest China) using in-situ mineralized polymers from coal gangue bases. This tray is suitable for seedling cultivation in saline-alkali soils and meets the requirements for stress resistance. The specific preparation steps are as follows: (1) Raw material preparation: Weigh 40 kg of cotton stalk fiber, 42 kg of coal gangue, 5 kg of sodium alginate / xanthan gum compound regulator (sodium alginate to xanthan gum mass ratio 2:1), 10 kg of functional reed biochar, 3 kg of clinoptilolite powder (functional mineral powder, accounting for 3wt% of the total solid content of raw materials), and 130 kg of deionized water; separately prepare NaOH solid for later use.

[0048] Cotton stalk pretreatment: Crush the cotton stalks to a length of 3-6mm, remove dust and impurities, and set aside for use.

[0049] (2) Preparation of modified cotton stalk fiber suspension: The crushed cotton stalks were put into a 5 wt% NaOH solution with a solid-liquid mass ratio of 1:10, heated to 60℃, and stirred at 150 r / min for 3 h; after treatment, the stalks were washed with water until neutral, and then put into a pulping machine for pulping for 25 min to obtain a modified CNFs-rich suspension.

[0050] (3) Preparation of multi-stage activated coal gangue and mineral blend slurry: The activation process of coal gangue is the same as in Example 1: planetary ball milling to D50≤3μm, thermal activation at 300℃ for 2h, ultrasonic activation in 1.5mol / L NaOH solution for 30min; after activation, clinoptilolite powder is added to the activated slurry and ultrasonically dispersed at 200W for 10min until the powder is uniformly dispersed to obtain the blended activated slurry.

[0051] (4) Electrostatic self-assembly pre-reaction: The modified CNFs-rich suspension and the blended active slurry were introduced into the mixing tank, the compound regulator and functional reed biochar were added, deionized water was added to the total amount, NaOH was added to adjust the pH of the system to 12.0, and the mixture was stirred at 300 r / min for 2 min until homogeneous. After standing for 12 min, the electrostatic self-assembly was completed and the mixed slurry was obtained.

[0052] (5) Negative pressure molding pre-dehydration: The mixed slurry is injected into the seedling tray mold, and a vacuum of -0.09MPa is applied for filtration for 18s to remove free water and obtain a pre-dehydration system.

[0053] (6) Low temperature molding in situ curing: Transfer the mold to a flat vulcanizing machine, set the molding pressure to 5MPa, the heating temperature to 98℃, and the molding curing to 15min; use the exothermic reaction to maintain the temperature stability of the mold center, demold after curing, and equilibrate at room temperature for 24h to obtain the finished product.

[0054] Performance testing: The wet tensile strength of the product in this embodiment is 4.68 MPa; the salt-alkali stress seedling raising test shows that the seedling survival rate increased to 92% (compared to 76% for the control plastic tray), the soil pH value decreased by 0.4 units compared to the control, and the yield of salt-alkali tolerant rice increased by 63 kg per mu.

[0055] Example 4 This embodiment provides a method for preparing a robust, in-situ mineralized polymer seedling tray (a seedling tray specifically designed for tropical rice-growing areas in Southeast Asia) from a coal gangue-based polymer base. It is suitable for high-temperature and high-humidity environments, acidic soils, and scenarios with a high incidence of rice blast. The specific preparation steps are as follows: (1) Raw material preparation and eutectic solvent preparation: Weigh 48 kg of oil palm hollow fruit bunch fiber, 36 kg of coal gangue, 4 kg of sodium alginate / xanthan gum compound regulator (sodium alginate to xanthan gum mass ratio 2:1), 10 kg of functional coconut shell biochar, 2 kg of serpentine powder (functional mineral powder, accounting for 2wt% of the total solid content of raw materials), and 115 kg of deionized water according to the ratio; take KOH solid for later use.

[0056] Among them, the functional coconut shell biochar is loaded with potassium silicate and chelated zinc, with potassium silicate loading of 12wt% and chelated zinc loading of 3wt%; the serpentine powder contains 38% MgO and has a particle size D50 of 5μm.

[0057] Preparation of choline chloride / oxalic acid eutectic solvent: Add choline chloride and oxalic acid to the reaction vessel in a molar ratio of 1:1, stir at 70°C until homogeneous and clear, and keep warm for later use.

[0058] Pretreatment of empty fruit bunches of oil palm: Crush the empty fruit bunches of oil palm to a particle size of 2~5mm, and sieve to remove dust and impurities.

[0059] (2) Preparation of modified oil palm hollow fruit bunch fiber suspension: The crushed oil palm hollow fruit bunch fiber was put into a eutectic solvent with a solid-liquid mass ratio of 1:10, heated to 75℃, and stirred at 200 r / min for 5 h; after treatment, the solvent was recovered, and the fiber was repeatedly washed with deionized water until the filtrate was neutral. It was then transferred to a high-shear homogenizer and homogenized at 3500 r / min for 20 min to obtain a cellulose-rich nanofiber suspension with a mass concentration of 3.5 wt%; the hydroxyl density on the fiber surface was found to be 3.5 hydroxyl groups / nm. 2 .

[0060] (3) Preparation of multi-stage activated coal gangue and mineral blend slurry: The activation process of coal gangue is the same as in Example 1: planetary ball milling to D50≤3μm, thermal activation at 300℃ for 2h, adding 1.5mol / L NaOH solution, ultrasonic activation at 250W for 30min; after activation, serpentine powder is added, and ball milling is performed together for 10min until uniformly dispersed to obtain blended activated slurry.

[0061] (4) Electrostatic self-assembly pre-reaction: The cellulose-rich nanofiber suspension was mixed with the blended active slurry, compound regulator and functional coconut shell biochar were added, deionized water was added to the set total amount, KOH solid was added to adjust the pH of the system to 11.2, and the mixture was stirred at 300 r / min for 1.5 min until the system was homogeneous. After standing for 10 min, the electrostatic self-assembly was completed and the mixed slurry was obtained.

[0062] (5) Negative pressure molding pre-dehydration: The mixed slurry is injected into the seedling tray mold, and a vacuum of -0.09MPa is applied for filtration for 15s to remove free water and obtain a pre-dehydration system.

[0063] (6) Low temperature molding in situ curing: Transfer the mold to a flat vulcanizing machine, set the molding pressure to 6MPa, the heating temperature to 95℃, and the molding curing time to 12min; use the exothermic reaction of the geopolymerization reaction and the thermal field of the mold to maintain the stability of the curing temperature of the system. After curing, release the pressure and demold, and equilibrate at room temperature for 24h to obtain the finished product.

[0064] Comparative Example 1 This comparative example provides a method for preparing a traditional physically blended paper seedling tray, using a commercially available mainstream process. The preparation steps are as follows: (1) Raw material preparation: Weigh 60 kg of unmodified rice straw fiber, 30 kg of ordinary unactivated coal gangue powder, 10 kg of talc powder, 5 kg of starch adhesive, and an appropriate amount of deionized water.

[0065] (2) Pulp preparation: Rice straw fiber is put into a hydraulic pulper and pulped for 30 minutes. After pulping, it is beaten to a freeness of 35°SR to obtain a pulp suspension. Ordinary coal gangue powder and talc powder are added to the pulp and stirred for 10 minutes to disperse evenly. Starch adhesive is gelatinized with 90°C hot water for 20 minutes and then added to the pulp. Stirring is continued for 5 minutes to obtain a mixed pulp. The pulp mass fraction is adjusted to 1.2wt%.

[0066] (3) Forming the mixed slurry into a rotary paper machine to form a wet paper roll for seedling trays, controlling the wet paper roll quantity to be 650g / m².

[0067] (4) Drying and shaping: The wet blanks are sent into a tunnel oven and dried with hot air at 80°C for 8 hours until the product moisture content is ≤10%. After cutting the edges and punching, the traditional paper seedling tray is obtained.

[0068] Test results: wet tensile strength 0.72 MPa, machine-insulated disc breakage rate 31%; only surface cracking after 45 days, internal filler not fully degraded; heavy metal Pb leaching concentration reached 0.12 μg / L.

[0069] Comparative Example 2 This comparative example provides a method for preparing high-temperature sintered coal gangue seedling trays, which are prepared using a high-temperature sintering process. The preparation steps are as follows: (1) Raw material preparation: Weigh 80 kg of coal gangue powder, 20 kg of bentonite, and an appropriate amount of deionized water.

[0070] (2) Mixing and molding: Coal gangue powder and bentonite are put into a ball mill and dry-milled for 1 hour until the powder is uniformly mixed and D50≤10μm; Add an appropriate amount of deionized water to the mixed powder and stir until it becomes a plastic mud. Then, send it into a molding machine and press it into seedling tray blanks under a pressure of 10MPa. Let it air dry naturally for 24 hours.

[0071] (3) High-temperature sintering: After the green body is dried, it is transferred into a shuttle kiln and heated to 1200℃ at a heating rate of 5℃ / min. It is then kept at the temperature for 2 hours for sintering. After sintering, it is cooled to room temperature with the furnace and then taken out and inspected to obtain the finished high-temperature sintered coal gangue seedling tray.

[0072] Performance testing: Carbon emissions per tray reach 0.92 kg CO2-eq, and it is not biodegradable; it is brittle and easily damaged, and the incidence of seedling damping-off disease reaches 27%.

[0073] Verification Example 1 The seedling trays obtained in Example 4 were compared with commercially available paper trays and commercially available plastic trays in terms of performance, and the results are shown in Table 1.

[0074] Table 1

[0075] As shown in Table 1: 1. Wet Mechanical Properties: Under test conditions of 35℃ and 90%RH high temperature and high humidity for 7 days, the wet tensile strength of the product in Example 4 reached 4.72MPa, which is 8.1 times that of commercially available paper trays in Southeast Asia (0.58MPa) and superior to commercially available plastic trays (4.1MPa). This solution uses a "brick-mud interlocking" interface constructed by Si-OC covalent bonding and continuous coating with geopolymer gel, which can resist strength decay under high temperature and high humidity conditions, completely solving the problem of high tray breakage rate in traditional paper tray machines, and its mechanical performance exceeds that of non-degradable plastic seedling trays.

[0076] 2. Disease control performance: The incidence of rice blast in seedlings raised using the product in Example 4 was only 6.3%, far lower than that of commercially available paper trays (28.7%) and commercially available plastic trays (24.5%). Its core mechanism is that the chelated zinc loaded on functional biochar can slowly release zinc ions, enhancing the seedlings' own disease resistance; simultaneously, the porous structure of the geopolymer gel and biochar can regulate the rhizosphere microecology, inhibiting pathogen growth and significantly reducing the risk of rice blast in tropical high-humidity environments.

[0077] 3. Soil Improvement Effect: After using the product in Example 4 for seedling cultivation, the pH value of acidic soil increased from 4.8 to 5.6, and the available silicon content increased by 26.3%. In contrast, commercially available paper and plastic trays had no effect on soil pH improvement, and the available silicon content decreased due to seedling absorption and consumption. After complete degradation, the serpentine powder and silicon-based components of this product release trace elements such as magnesium and silicon, neutralizing acidic soil and transforming the seedling input into a soil conditioner, while also providing added value for improving soil fertility.

[0078] 4. Carbon Reduction and Carbon Sequestration Benefits: The total life-cycle carbon emissions of the product in Example 4 are -0.23 kg CO2-eq / tray, meaning each seedling tray can achieve a carbon sequestration of 0.23 kg of carbon dioxide equivalent. In contrast, commercially available paper trays emit +0.14 kg CO2-eq / tray, and commercially available plastic trays emit as much as +0.37 kg CO2-eq / tray. This product achieves negative carbon emissions through coal gangue solid waste disposal, permanent biomass carbon sequestration, and a short-process, low-energy-consumption technology, aligning with the global trend of low-carbon agricultural development.

[0079] 5. Yield and Quality Performance: After transplanting rice seedlings using the product in Example 4, the yield per mu (667 square meters) was 582 kg, which was superior to the yield per mu of commercially available paper and plastic trays. The increased yield and improved quality are attributed to the product's root-strengthening and growth-promoting effects, the slow-release effect of micronutrients, and the healthy rhizosphere microenvironment.

[0080] Verification Example 2 The cost of the seedling trays obtained in Example 4 was compared with that of commercially available plastic trays (in US dollars), and the results are shown in Table 2.

[0081] Table 2

[0082] Objective: To demonstrate the economic feasibility of large-scale application of the technology.

[0083] Calculation benchmark: A production line with an annual output of 10 million seedling trays serves 50,000 mu of paddy fields.

[0084] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a tough, in-situ mineralized all-biomass seedling tray made from coal gangue aggregate, characterized in that, The preparation method includes the following steps: (I) Raw material pretreatment (I-1) Pretreatment of plant fibers: Plant fibers are mixed with a low eutectic solvent for pretreatment to obtain a suspension rich in cellulose nanofibers; (I-2) Pretreatment of coal gangue: The coal gangue is successively ground, thermally activated and ultrasonically activated to obtain coal gangue active slurry; (II) Electrostatic self-assembly pre-reaction The cellulose-rich nanofiber suspension is mixed with the coal gangue active slurry, and then a biomineralization regulator and functional biochar are added. The mixture is allowed to stand and self-assemble to obtain the mixed slurry. (III) Pre-dehydration during molding The mixed slurry is injected into a seedling tray mold, and free water is removed under reduced pressure to obtain a pre-dehydrated system; (IV) Low-temperature in-situ curing The pre-dehydration system is heated, pressurized, and solidified. After completion, it is demolded to obtain the finished seedling tray.

2. The method for preparing the in-situ mineralization and toughening all-biomass seedling tray based on coal gangue base polymer according to claim 1, characterized in that, In step (I-1), plant fibers are mixed with a eutectic solvent and pretreated at 70-80℃ for 4-5 hours. After washing with water until neutral, the mixture is pulped to obtain a cellulose nanofiber suspension with a concentration of 3-3.5wt%.

3. The method for preparing the in-situ mineralization and toughening all-biomass seedling tray based on coal gangue base polymer according to claim 1, characterized in that, In step (I-1), the eutectic solvent includes choline chloride and a hydrogen bond donor, and the molar ratio of choline chloride to the hydrogen bond donor is 1:1 to 1:2; the hydrogen bond donor is lactic acid, urea, or oxalic acid. And / or, the plant fiber is one of reed, bamboo, cotton stalk, or empty fruit clusters of oil palm; the cellulose-rich nanofibers obtained after pretreatment have a diameter of 10-50 nm and a surface hydroxyl density ≥ 3.2 hydroxyl groups / nm. 2 .

4. The method for preparing the in-situ mineralization and toughening all-biomass seedling tray based on coal gangue base polymer according to claim 1, characterized in that, In step (I-2), coal gangue is ball-milled to D50≤3μm, then thermally activated at 300-350℃ for 2-3h to destroy the crystal structure, and then ultrasonically activated with 1.5-2.0mol / L NaOH solution for 30-40min to obtain an active slurry; And / or, the specific surface area of ​​the activated coal gangue is 300-500 m². 2 / g.

5. The method for preparing the in-situ mineralization and toughening all-biomass seedling tray based on coal gangue base polymer according to claim 1, characterized in that, In step (II), the cellulose-rich nanofiber suspension is mixed with the coal gangue active slurry, and then a biomineralization regulator and functional biochar are added. After stirring for 1-2 minutes until the system is homogeneous, it is allowed to stand for 5-15 minutes for self-assembly, and the mixed slurry is obtained after completion.

6. The method for preparing the in-situ mineralization and toughening all-biomass seedling tray based on coal gangue base polymer according to claim 1, characterized in that, In step (II), the biomineralization regulator is a mixture of sodium alginate and xanthan gum, the mass ratio of sodium alginate to xanthan gum is 2:1, and the carboxyl density in the biomineralization regulator is ≥4.8 mmol / g; And / or, the method for preparing the functional biochar is as follows: (i) The biochar raw material is pyrolyzed at 500-600℃ to obtain mesoporous biochar with a porosity ≥85%; (ii) The mesoporous biochar is loaded with potassium silicate and / or chelated zinc at a loading amount of 8-15 wt% of the mesoporous biochar to obtain functional biochar. And / or, in step (II), functional mineral powder is also added, wherein the functional mineral powder is serpentine powder or zeolite powder, and the functional mineral powder accounts for 1-5 wt% of the total solid content of the raw material; the serpentine powder contains ≥35% MgO and the particle size D50 of the serpentine powder is ≤10 μm.

7. The method for preparing the in-situ mineralization and toughening all-biomass seedling tray based on coal gangue base polymer according to claim 1, characterized in that, In step (III), the mixed slurry is injected into the seedling tray mold, and a vacuum of -0.08 to -0.1 MPa is applied to remove free water under reduced pressure to obtain a pre-dehydrated system.

8. The method for preparing the in-situ mineralization and toughening all-biomass seedling tray based on coal gangue base polymer according to claim 1, characterized in that, In step (IV), the pre-dehydrated system is placed in a molding equipment and molded at 95-110℃ for 10-15 minutes to trigger the polymerization reaction. The heat released by the reaction and the heat field of the mold are used to maintain the temperature of the mold center at 100-120℃. After completion, the mold is demolded to obtain the finished seedling tray.

9. The method for preparing the in-situ mineralization and toughening all-biomass seedling tray based on coal gangue base polymer according to claim 1, characterized in that, The raw materials, by weight, include: 40-50 parts plant fiber, 35-42 parts coal gangue, 3-5 parts biomineralization regulator, and 8-12 parts functional biochar.

10. The in-situ mineralization and toughening all-biomass seedling tray of coal gangue base polymer obtained by the preparation method according to any one of claims 1-9.

Images