Production process of sintered hollow batten highly doped with straw

Abstract

The invention provides a production process of a high-straw-doped sintered hollow batten, which comprises the following steps: performing crushing, alkali treatment and biological enzyme treatment on crop straws to obtain modified straw fibers; then adding a cementing material and an exciting agent, performing dry mixing for 3-5 minutes, then adding the modified straw fibers and a toughening agent, and performing wet mixing to obtain a pretreated material; carrying out vibration extrusion molding on the pretreated material to obtain a pretreated mold; and then sintering the pretreated mold by adopting a two-stage sintering mode, and then carrying out surface strengthening treatment, thereby obtaining the product. According to the production technology, the technological production of the light high-strength hollow batten with the straw mixing amount as high as 40%-55% is achieved by optimizing the straw pretreatment, the gelation system design, the vibration forming and the segmented sintering technology.

Description

Technical Field

[0001] The invention belongs to the technical field of lightweight building materials, and in particular relates to a production process of sintered hollow slats with a high content of straw. Background Art

[0002] With the global construction industry's growing demand for sustainable development and green building materials, the resource utilization of agricultural waste has become a key research area in the field of building materials. Crop straw, an abundant and renewable biomass resource, produces over 3 billion tons annually worldwide. However, traditional disposal methods, such as incineration or landfill, not only waste resources but also pollute the environment. Converting straw into high-performance, lightweight building materials not only maximizes the value of agricultural waste but also promotes a green transformation in the construction industry, with significant economic and environmental benefits.

[0003] Currently, the application of straw in lightweight building materials faces three major technical bottlenecks: first, the poor interfacial compatibility between straw and inorganic cementitious materials results in insufficient mechanical properties of the composite materials; second, straw has poor thermal stability and easily decomposes and fails during traditional high-temperature sintering processes; and finally, existing straw building materials have a single function and cannot meet the multifunctional requirements of modern architecture. These problems have seriously restricted the industrial application and market promotion of straw building materials.

[0004] In existing technology, straw building materials are primarily produced using three process routes: First, straw boards are formed by hot-pressing with organic adhesives. While these materials offer a certain level of strength, they release formaldehyde and have poor weather resistance. Second, lightweight concrete is prepared by simply incorporating straw into cement-based materials. However, the strength decreases significantly when the straw content exceeds 20%. Third, straw-clay composites are sintered at high temperatures. However, excessive sintering temperatures can completely decompose the straw, rendering it useless as a reinforcement. None of these traditional methods effectively address the conflict between high straw content and material performance.

[0005] The construction industry has placed higher demands on lightweight building materials: not only does it need to achieve a high proportion of solid waste utilization (straw content >40%), but it also needs to meet performance indicators such as lightness, high strength, and low energy consumption. At the same time, it is best to have additional functions such as thermal insulation, sound insulation, and self-cleaning. However, existing technologies find it difficult to meet all these requirements at the same time, especially when it comes to the key issue of maintaining a high straw content while ensuring material strength. No effective solution has yet been found.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The first purpose of the present invention is to provide a production process for sintered hollow strips with a high straw content. By optimizing the platycodon pretreatment, gelling system design, vibration molding and segmented sintering process, the industrial production of lightweight and high-strength hollow strips with a straw content of up to 40-55% is achieved. At the same time, the straw is subjected to alkali-enzyme synergistic modification and nano-high-strength territorial reinforcement, thereby solving the problem of strength deterioration caused by high straw content.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0009] A production process for sintered hollow slats with a high straw content comprises the following steps:

[0010] The crop straw is crushed, alkali treated and bio-enzymed treated to obtain modified straw fiber;

[0011] Then, the gelling material and the activator are added and dry-mixed for 3-5 minutes, and then the modified straw fiber and the toughening agent are added and wet-mixed to obtain the pretreated material;

[0012] The pre-treated material is vibrated and extruded to obtain a pre-treated mold;

[0013] The pre-treated mold is then sintered in a two-stage sintering manner and then subjected to surface strengthening treatment to obtain the mold.

[0014] In the production process of sintered hollow strips with high straw content of the present invention, a complete process chain of "pretreatment-forming-sintering-post-processing" is constructed. Through the synergistic effect of four dimensions of raw material modification, interface optimization, structural regulation and function enhancement, it is achieved that the straw content can still maintain excellent mechanical properties at 40-55%. First, the straw is mechanically crushed, so that microcracks are generated in the straw fibers through shear force, thereby increasing the specific surface area and providing a reaction channel for subsequent treatment. Subsequently, the sheared straw is subjected to alkali treatment to penetrate the cell wall of the straw fiber, dissolve lignin and hemicellulose to expose cellulose microfibrils, and significantly enhance hydrophilicity. After the alkali treatment, the straw is subjected to composite enzyme treatment to directionally cut β-1,4 glycosidic bonds through the composite enzyme, oxidatively degrade residual lignin, and hydrolyze hemicellulose at the same time. The side chain is improved through the synergy of the complex enzyme, thereby improving the crystallinity of the straw fiber and further enhancing the tensile strength of the single fiber; then the present invention provides early strength while enhancing interface bonding through the gradient design of the gelling system; then in the raw material mixing stage, the present invention adopts a "dry mixing-wet mixing" two-step method, first dry mixing the gelling material and the activator for 3-5 minutes to ensure uniform dispersion of the powder, and then adding the modified straw and the toughening agent for wet mixing, controlling the solid-liquid ratio within the range of 0.25-0.35, and this process design of combining dry mixing and wet mixing enables the prepared pretreated material to avoid fiber agglomeration, and then vibration is used to realize extrusion molding of the pretreated material, thereby utilizing vibration energy to reduce the slurry viscosity and control the molding density deviation to be smaller, and then a two-stage sintering method is adopted to further enhance the interface strengthening mechanism of the pretreated material.

[0015] Preferably, as a further specific embodiment, in terms of mass percentage, the pretreated material comprises 40-55% of modified straw fiber, 30-45% of gelling material, 5-10% of activator and 2-5% of toughening agent.

[0016] The high-straw-added sintered hollow slat production process of the present invention has achieved the industrial production of lightweight and high-strength hollow slats with a straw content of up to 40-55% through multi-dimensional collaborative innovation. The core lies in the scientific design of the raw material ratio, especially the limited pretreatment materials including 40-55% modified straw fiber, 30-45% cementitious material, 5-10% activator and 2-5% toughening agent. This ratio range is not a simple numerical stacking, but a dynamic balance result based on multiple factors such as straw-cementitious material interface compatibility, fiber network continuity, and enhanced distribution uniformity. When the modified straw fiber addition amount is less than 40%, it is difficult for the fiber to form a three-dimensional continuous network structure, resulting in low stress transfer efficiency and poor straw toughening. When the content of activator is more than 55%, the wrapping ability of the cementitious material on the straw fiber is insufficient, microcracks and pore defects are easily formed at the interface, and the gas generated by the pyrolysis of the straw during the sintering process cannot be effectively adsorbed, which ultimately leads to a significant decrease in the compressive strength of the material. The design of adding 30-45% of cementitious material reflects the composite mechanism of "skeleton-filler". The addition range of 5-10% of activator ensures the dynamic matching of the hydration reaction of the cementitious system and the pyrolysis process of the straw. Through the synergistic effect of multiple substances, the cementitious phase can adapt to the shrinkage behavior of the straw fiber in different temperature ranges. The ratio of 2-5% of toughening agent avoids the stress concentration caused by fiber agglomeration and ensures the dispersion stability of the nanomaterial.

[0017] Preferably, as a further specific embodiment, the alkali treatment is performed by soaking in a NaOH solution with a mass concentration of 5-8% for 6-8 hours.

[0018] In the production process of the high-straw-doped sintered hollow strip board of the present invention, the alkali treatment process is also limited to soaking in a NaOH solution with a mass concentration of 5-8% for 6-8 hours. This process setting is a key step to ensure that the straw fiber and the cementitious material form a high-strength interface. This parameter range is not an empirical selection, but is optimized based on the microstructural characteristics of the straw fiber and its binding mechanism with the inorganic cementitious material. When the NaOH concentration is lower than 5%, it is difficult for the alkali solution to fully penetrate the cell wall structure of the straw fiber, and the dissolution of lignin and hemicellulose is not complete, resulting in insufficient exposure of the fiber surface active groups (such as hydroxyl and carboxyl groups), and the subsequent chemical bonding ability with the cementitious material is weak; and when the concentration exceeds 8%, although the detachment efficiency of lignin is improved, the excessive hydrolysis of the cellulose chain will destroy the crystalline region structure of the fiber, significantly reduce the mechanical properties of the single fiber, and even cause premature decomposition due to decreased thermal stability during the subsequent sintering process;

[0019] At the same time, the setting of the soaking time of 6-8 hours has also been strictly verified. When it is shorter than 6 hours, the alkali treatment is insufficient, and a hydrophobic lignin film layer still remains on the fiber surface, which hinders the interface bonding between the hydration products of the cementitious material and the fiber; and more than 8 hours will cause the fiber to swell excessively, the internal microfibril structure to be loose, and it is easy to break during the subsequent wet mixing and molding process, affecting the reinforcement effect of the fiber; therefore, for the present invention, the core role of the alkali treatment is to selectively dissolve the lignin and hemicellulose in the straw through the alkali solution, exposing the highly active surface of the cellulose microfibrils, wherein the 5-8% NaOH solution can effectively destroy the ether bonds and ester bonds of the lignin-carbohydrate complex in the straw cell wall, so that the fiber surface forms a porous structure, the specific surface area increases by 3-5 times, and provides sufficient reaction sites for subsequent bio-enzyme treatment. At the same time, the phenolic hydroxyl group and sodium carboxylate group generated during the alkali treatment can react with the Ca in the cementitious material. 2+ Through ionic bonds and coordination bonds, a stable "cellulose-calcium silicate hydrate (CSH)" transition layer is formed at the interface.

[0020] Preferably, as a further specific embodiment, the bio-enzyme treatment uses a composite enzyme, which includes cellulase, laccase and xylanase; the mass ratio of the cellulase, laccase and xylanase is 3:1:1.

[0021] In the biological enzyme treatment process of the present invention, a composite enzyme system composed of cellulase, laccase and xylanase in a mass ratio of 3:1:1 is used. The refined modification of straw fiber is achieved through the synergistic action of multiple enzymes, providing key technical support for the interface strengthening of high-dosage straw building materials. In traditional single enzyme treatment, only a certain component of straw (such as cellulose or hemicellulose) is often targeted, making it difficult to achieve comprehensive optimization of fiber performance. The composite enzyme system of the present invention achieves three key functions through precise proportioning: cellulase selectively hydrolyzes cellulose chains in amorphous regions, thereby improving the crystallinity of straw fibers; laccase oxidatively degrades residual lignin, eliminating interface binding barriers; and xylanase hydrolyzes hemicellulose side chains, promoting microfibril dissociation; and the mass ratio between the three is more important for the present invention. When the proportion of cellulase is less than 3, the degree of crystallization of straw fibers is insufficient, and the improvement of single fiber strength is limited; and the proportion of laccase exceeding 1 will lead to excessive oxidation, destroying the cellulose skeleton structure, and in this invention. Under the invented ratio, cellulase first opens the β-1,4 glycosidic bond of cellulose, exposing more lignin binding sites. Then laccase breaks the phenolic unit of lignin through free radical reaction. At the same time, xylanase synergistically decomposes the hemicellulose branch chain. The three form a "hydrolysis-oxidation-debranching" cascade reaction chain, which greatly improves the crystallinity of the treated straw fiber and further increases the tensile strength. Therefore, the present invention provides a macro channel for straw alkali treatment and enzyme treatment to achieve micro modification. The combination of the two enables the straw fiber to maintain structural strength and have excellent interfacial reaction activity. Ultimately, the pretreated material can still achieve a high compressive strength at a straw content of 55%, breaking through the performance bottleneck of traditional straw building materials.

[0022] Preferably, as a further specific embodiment, the straw fibers after the straw is crushed have a length of 2-5 mm and an aspect ratio of ≥50.

[0023] The present invention defines regular parameters of straw fibers, thereby achieving better mechanical properties and process adaptability of high-dosage straw hollow strips. When the fiber length is shorter than 2 mm, although the dispersion is good, the fiber reinforcement effect is significantly reduced, and it is difficult to form an effective stress transfer network; when the length exceeds 5 mm, it will cause fiber entanglement during the mixing process, resulting in local stress concentration in the molding stage, affecting the overall uniformity of the material; the design of an aspect ratio ≥ 50 ensures that the fibers can not only play a reinforcing role similar to steel bars, but also achieve directional arrangement during vibration molding.

[0024] Preferably, as a further specific embodiment, the cementitious material is a composite system of Portland cement, slag powder and nano-high-temperature territories;

[0025] The mass ratio of the silicate cement, slag micropowder and nano-high-temperature slag is 3:1:0.5-5:2:1.

[0026] The cementitious material system of the present invention adopts a composite system composed of silicate cement, slag powder and nano-metakaolin in a mass ratio of 3:1:0.5-5:2:1. This design successfully solves the key technical problem of insufficient cementitious phase strength development in high-content straw building materials through the synergistic effect of multiple components. The silicate cement serves as the main matrix to provide early strength, and its proportion range of 3-5 parts ensures sufficient hydration activity. Secondly, 1-2 parts of slag powder continuously consume calcium hydroxide through the pozzolanic effect to form a secondary CSH gel, which effectively fills the interface transition zone between the straw fiber and the matrix. Finally, the nano-sheet structure of 0.5-1 part of nano-metakaolin not only plays a physical reinforcement role, but also forms a stable hydrated calcium aluminate phase through the chemical reaction of its highly active aluminum phase with the cement hydration products, significantly improving the volume stability of the material during the high-temperature sintering stage.

[0027] Furthermore, the cementitious system plays a differentiated role in different stages of material preparation: in the wet mixing stage, the high specific surface area of ​​nano-metakaolin can absorb a large amount of free water, precisely controlling the solid-liquid ratio within the optimized range of 0.25-0.35; in the first stage of sintering, the glassy structure in the slag micropowder begins to depolymerize and reacts with the active siliceous components produced by the pyrolysis of straw to form a low-temperature ceramic phase; in the second stage of sintering, the nano-metakaolin forms active alumina through a dehydroxylation reaction, which reacts with the calcium components of silicate cement to form calcium aluminum feldspar. This high-temperature stable phase can effectively compensate for the volume shrinkage caused by the carbonization of straw.

[0028] Preferably, as a further specific embodiment, the activator is a mixture of sodium silicate, calcium hydroxide and potassium phosphate;

[0029] The mass ratio of the sodium silicate, calcium hydroxide and potassium phosphate is 2:1:0.5-3:1:1.

[0030] In the present invention, the activator system adopts a composite activator composed of sodium silicate, calcium hydroxide and potassium phosphate in a mass ratio of 2:1:0.5-3:1:1. This formula successfully solves the core technical problem of insufficient reaction activity of high-dosage straw-gelling system through a triple synergistic activation mechanism. The sodium silicate in the composite activator serves as an alkaline activator, which preferentially releases the vitreous structure of the polyslag powder at room temperature and accelerates the early hydration reaction; while the calcium hydroxide provides a stable alkaline environment, maintaining the pH value in the optimal range of 11.5-12.5, which not only promotes The hydration of the cementitious material is promoted while avoiding excessive corrosion of the straw fiber; potassium phosphate plays a key role in the high-temperature sintering stage, reacting with the straw pyrolysis products to form a calcium phosphate ceramic phase, significantly improving the high-temperature resistance of the interface transition zone. At the same time, the activator system can present precise time-sequential activation characteristics at each stage of material preparation. In the wet mixing stage, sodium silicate quickly dissociates into silicate ions, thereby forming an early CSH gel with calcium ions in cement, providing an initial wrapping layer for the straw fiber; and in the subsequent drying and curing stage, calcium hydroxide continuously releases OH - ions react with the active SiO2 in the slag powder to form secondary CSH gel, which gradually fills the pores at the fiber-matrix interface. During the high-temperature sintering stage, the potassium ions and phosphate ions produced by the decomposition of potassium phosphate react with the carbonized products of the straw to in situ generate nanostructured hydroxyapatite, which further improves the microhardness of the interface area.

[0031] Preferably, as a further specific embodiment, the toughening agent is a mixture of polyvinyl alcohol fibers and carbon nanotubes, wherein the mass ratio of the polyvinyl alcohol fibers to the carbon nanotubes is (10-12):1.

[0032] In the present invention, a composite toughening material composed of polyvinyl alcohol fibers and carbon nanotubes in a mass ratio of (10-12):1 is used as a toughening agent to construct a multi-scale synergistic toughening network, effectively solving the key technical bottleneck of high-dosage straw building materials, such as high brittleness and poor impact resistance. The polyvinyl alcohol fibers serve as a macroscopic toughening phase, inhibiting the propagation of millimeter-scale cracks through crack bridging and fiber pull-out effects; while the carbon nanotubes serve as nanoscale reinforcements, strengthening the fiber-matrix interface at the microscale through their extremely high specific surface area and excellent mechanical properties. When the mass ratio of polyvinyl alcohol fibers to carbon nanotubes is lower than 10:1, the agglomeration effect of the nanotubes will lead to stress concentration; while when the mass ratio is higher than 12:1, the nano-reinforcement effect cannot be fully exerted.

[0033] In addition, the hydrophilic properties of polyvinyl alcohol fibers can form a good bond with straw fibers and cement matrices, solving the problem of poor interfacial bonding of traditional polypropylene fibers. Secondly, carbon nanotubes can form a permeable network at low dosages, significantly reducing costs while ensuring the reinforcement effect. Finally, the system has excellent compatibility with vibration molding processes. At a vibration frequency of 80-120Hz, the fiber orientation is extremely high, and the pretreated material can also obtain controllable anisotropic properties. This toughening design also produces a synergistic effect with enzyme-treated straw fibers. The cellulose hydroxyl groups exposed by the enzyme treatment form hydrogen bonds with the polyvinyl alcohol fibers, while the carbon nanotubes can be embedded in the nanogrooves on the fiber surface, forming a "mechanical-chemical" dual bonding interface.

[0034] Preferably, as a further specific embodiment, in the staged sintering process:

[0035] In the first stage, a mixture of 10-15% CO2 and 3-5% silane coupling agent vapor is introduced and the temperature is raised to 200-250°C at 5-8°C / min and kept at this temperature for 1-2 hours;

[0036] The second stage adopts oxygen-enriched combustion, in which the oxygen concentration is 25-30% and the temperature is increased to 600-650℃ at 3-5℃ / min and kept at this temperature for 0.5-1h.

[0037] In the present invention, a staged sintering process is adopted to achieve structural optimization and performance improvement of high-straw hollow strips during the sintering process. In the first stage, a mixed gas of 10-15% CO2 and 3-5% silane coupling agent vapor is introduced, and in the second stage, an oxygen-rich environment with an oxygen concentration of 25-30% is used for sintering. This staged gas control strategy effectively solves the compatibility problem of straw pyrolysis and ceramic sintering. In the first stage, the introduction of CO2 has a dual role: on the one hand, it reacts with Ca(OH)2 in the cementitious material to generate a CaCO3 reinforcing phase, thereby improving the initial strength of the green body; on the other hand, it forms a weakly oxidizing environment to control the slow pyrolysis of straw fibers and avoid pore defects caused by sudden decomposition. Simultaneously, the silane coupling agent vapor reacts with the hydroxyl groups on the straw surface under thermal conditions, forming an organic-inorganic transition layer and significantly enhancing the interfacial bonding strength. The second stage of oxygen-enriched combustion embodies precise oxidation control: an oxygen concentration of 25-30% ensures complete combustion of the straw carbonization products while preventing over-oxidation that could lead to failure of the fiber reinforcement phase. Below 25% oxygen concentration results in incomplete combustion, leaving residual organic matter that affects the material's durability. Above 30% oxygen concentration leads to over-oxidation of the fiber-carbon skeleton, resulting in loss of its reinforcing properties. During this stage, the oxygen-rich environment promotes a chemical reaction between the straw carbonization products and the mineral phase in the cementitious material, causing the biochar to react with CaCO₃ to form the CaC₂ reinforcement phase. Meanwhile, the pyrolysis product of the silane coupling agent, SiO₂, reacts with Al₂O₃ to form mullite whiskers. The decomposition of potassium phosphate acts as a flux to promote sintering of the ceramic phase. These reactions together create a "fiber-ceramic" composite reinforcement structure, enabling the pretreated material to maintain excellent mechanical properties even after high-temperature treatment.

[0038] Preferably, as a further specific embodiment, the surface strengthening treatment uses a water-based epoxy resin system modified with nano-SiO2, the vacuum degree is maintained at -0.08 to -0.1 MPa, and the immersion time is 30-60 minutes.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention provides a production process for sintered hollow strips with a high straw content. By optimizing the platycodon pretreatment, gelling system design, vibration molding and segmented sintering process, the industrial production of lightweight and high-strength hollow strips with a straw content of up to 40-55% is achieved. At the same time, the straw is subjected to alkali-enzyme synergistic modification and nano-high-strength terrestrial reinforcement, thereby solving the problem of strength degradation caused by high straw content and improving the compressive strength. DETAILED DESCRIPTION

[0041] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the embodiments described below are part of the embodiments of the present invention, not all of them, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] In order to more clearly illustrate the technical solutions of the present invention, specific embodiments are provided below for illustration.

[0043] Example 1

[0044] 1. Raw Materials Preparation

[0045] Wheat straw was selected, crushed by hammer mill and sieved to control the fiber length to 2mm and the aspect ratio to 52-55;

[0046] Take 4 kg of crushed straw, place it in a 5% NaOH solution (solid-liquid ratio 1:10), and soak it at room temperature for 6 hours;

[0047] After soaking, the straw was washed with water until neutral, and then transferred into a complex enzyme solution (cellulase: laccase: xylanase = 3:1:1, with the total enzyme dosage being 2% of the dry weight of the straw) and treated at pH = 6.0 and 50°C for 4 hours;

[0048] Finally, rinse with deionized water and dry at 60℃ until the moisture content is ≤3%;

[0049] 2. Preparation of cementitious materials:

[0050] 3kg of Portland cement;

[0051] Slag powder (specific surface area 420m 2 / kg)1kg;

[0052] Nanometakaolin (d50 = 150 nm) 0.5 kg;

[0053] Mechanically mix until homogeneous;

[0054] 3. Preparation of stimulant:

[0055] Sodium silicate 0.57kg;

[0056] Calcium hydroxide 0.28kg;

[0057] Potassium phosphate 0.15kg;

[0058] Dry mix evenly;

[0059] 4. Toughening agent preparation:

[0060] Polyvinyl alcohol fiber (length 6 mm, diameter 20 μm) 0.45 kg;

[0061] Carboxylated multi-walled carbon nanotubes (OD 8-15 nm) 0.05 kg;

[0062] Pre-disperse and then mix (mass ratio 10:1).

[0063] 5. Preparation Process

[0064] 5.1 Mixing process:

[0065] First, add the gelling material and activator into the forced mixer and dry mix for 3 minutes;

[0066] Add modified straw fiber (total amount 4 kg, accounting for 40% of the dry material mass) and toughening agent, control the solid-liquid ratio to 0.25, and wet mix for 8 minutes to obtain the pretreated material;

[0067] 5.2 Molding process:

[0068] The pretreated material was injected into a 300×600×100 mm mold;

[0069] Use hydraulic vibration table (frequency 80Hz, pressure 8MPa) for vibration molding, and maintain pressure for 3 minutes;

[0070] 5.3 Segmented sintering:

[0071] After demolding, the first stage of sintering was carried out: the temperature was raised to 200°C at 5°C / min, 10% CO2 + 3% silane coupling agent (the rest was N2) was introduced, and the temperature was kept for 1 hour;

[0072] The second stage: heating to 600℃ at 3℃ / min, switching to 25% O2 (the rest is N2), and keeping warm for 0.5h;

[0073] Cool naturally to room temperature;

[0074] 5.4 Surface strengthening:

[0075] Preparation of nano-SiO2 modified waterborne epoxy resin (SiO2 content 8%);

[0076] Immerse for 30 minutes at a vacuum of -0.08 MPa;

[0077] Curing at 80℃ for 2 hours.

[0078] Example 2

[0079] 1. Raw Materials Preparation

[0080] Wheat straw was selected, crushed by hammer mill and sieved to control the fiber length to 5mm and the aspect ratio to 52-55;

[0081] Take 5.5 kg of crushed straw, place it in 8% NaOH solution (solid-liquid ratio 1:10), and soak it at room temperature for 6 hours;

[0082] After soaking, the straw was washed with water until neutral, and then transferred into a complex enzyme solution (cellulase: laccase: xylanase = 3:1:1, with the total enzyme dosage being 2% of the dry weight of the straw) and treated at pH = 6.0 and 50°C for 4 hours;

[0083] Finally, rinse with deionized water and dry at 60℃ until the moisture content is ≤3%;

[0084] 2. Preparation of cementitious materials:

[0085] Portland cement 2.375 kg;

[0086] Slag powder (specific surface area 420m 2 / kg)0.95kg;

[0087] Nanometakaolin (d50 = 150 nm) 0.475 kg;

[0088] Mechanically mix until homogeneous;

[0089] 3. Preparation of stimulant:

[0090] Sodium silicate 0.3kg;

[0091] Calcium hydroxide 0.1kg;

[0092] Potassium phosphate 0.1kg;

[0093] Dry mix evenly;

[0094] 4. Preparation of toughening agent:

[0095] Polyvinyl alcohol fiber (length 6 mm, diameter 20 μm) 0.18 kg;

[0096] Carboxylated multi-walled carbon nanotubes (OD 8-15 nm) 0.02 kg;

[0097] Pre-disperse and then mix (mass ratio 12:1).

[0098] 5. Preparation Process

[0099] 5.1 Mixing process:

[0100] First, add the gelling material and activator into the forced mixer and dry mix for 5 minutes;

[0101] Add modified straw fiber (total amount 5.5 kg, accounting for 55% of the dry material mass) and toughening agent, control the solid-liquid ratio to 0.35, and wet mix for 8 minutes to obtain the pretreated material;

[0102] 5.2 Molding process:

[0103] The pretreated material was injected into a 300×600×100 mm mold;

[0104] Use hydraulic vibration table (frequency 120Hz, pressure 12MPa) for vibration molding, and maintain pressure for 3 minutes;

[0105] 5.3 Segmented sintering:

[0106] After demolding, the first stage of sintering was carried out: the temperature was raised to 250°C at 8°C / min, 15% CO2 + 5% silane coupling agent (the rest was N2) was introduced, and the temperature was kept for 2 hours;

[0107] The second stage: heating to 650℃ at 5℃ / min, switching to 30% O2 (the rest is N2), and keeping warm for 1h;

[0108] Cool naturally to room temperature;

[0109] 5.4 Surface strengthening:

[0110] Preparation of nano-SiO2 modified waterborne epoxy resin (SiO2 content 8%);

[0111] Immerse for 60 minutes at -0.1 MPa vacuum;

[0112] Curing at 80℃ for 2 hours.

[0113] Example 3

[0114] 1. Raw Materials Preparation

[0115] Wheat straw was selected, crushed by hammer mill and sieved to control the fiber length to 4mm and the aspect ratio to 52-55;

[0116] Take 4 kg of crushed straw, place it in a 6% NaOH solution (solid-liquid ratio 1:10), and soak it at room temperature for 6 hours;

[0117] After soaking, the straw was washed with water until neutral, and then transferred into a complex enzyme solution (cellulase: laccase: xylanase = 3:1:1, with the total enzyme dosage being 2% of the dry weight of the straw) and treated at pH = 6.0 and 50°C for 4 hours;

[0118] Finally, rinse with deionized water and dry at 60℃ until the moisture content is ≤3%;

[0119] 2. Preparation of cementitious materials:

[0120] 2.7 kg of Portland cement;

[0121] Slag powder (specific surface area 420m 2 / kg)0.9kg;

[0122] Nanometakaolin (d50 = 150 nm) 0.9 kg;

[0123] Mechanically mix until homogeneous;

[0124] 3. Preparation of stimulant:

[0125] Sodium silicate 0.6kg;

[0126] Calcium hydroxide 0.2kg;

[0127] Potassium phosphate 0.2 kg;

[0128] Dry mix evenly;

[0129] 4. Toughening agent preparation:

[0130] Polyvinyl alcohol fiber (length 6 mm, diameter 20 μm) 0.46 kg;

[0131] Carboxylated multi-walled carbon nanotubes (OD 8-15 nm) 0.04 kg;

[0132] Pre-disperse and then mix (mass ratio 11:1).

[0133] 5. Preparation Process

[0134] 5.1 Mixing process:

[0135] First, add the gelling material and activator into the forced mixer and dry mix for 4 minutes;

[0136] Add modified straw fiber (total amount 4 kg, accounting for 40% of the dry material mass) and toughening agent, control the solid-liquid ratio to 0.3, and wet mix for 8 minutes to obtain the pretreated material;

[0137] 5.2 Molding process:

[0138] The pretreated material was injected into a 300×600×100 mm mold;

[0139] Use a hydraulic vibration table (frequency 100Hz, pressure 12MPa) for vibration molding and maintain pressure for 3 minutes;

[0140] 5.3 Segmented sintering:

[0141] After demolding, the first stage of sintering was carried out: the temperature was raised to 220°C at 8°C / min, 12% CO2 + 4% silane coupling agent (the rest was N2) was introduced, and the temperature was kept for 2 hours;

[0142] The second stage: heating to 630°C at 4°C / min, switching to 25% O2 (the rest is N2), and keeping warm for 1 hour;

[0143] Cool naturally to room temperature;

[0144] 5.4 Surface strengthening:

[0145] Preparation of nano-SiO2 modified waterborne epoxy resin (SiO2 content 8%);

[0146] Immerse for 60 minutes at -0.1 MPa vacuum;

[0147] Curing at 80℃ for 2 hours.

[0148] Example 4

[0149] The specific implementation steps are the same as those in Example 3, except that the mass concentration of the NaOH solution in Example 3 is adjusted to 1%.

[0150] Example 5

[0151] The specific implementation steps are the same as those in Example 3, except that the mass concentration of the NaOH solution in Example 3 is adjusted to 15%.

[0152] Example 6

[0153] The specific implementation steps are the same as those in Example 3, except that the mass ratio of cellulase, laccase and xylanase in Example 3 is adjusted to 1:1:1.

[0154] Example 7

[0155] The specific implementation steps are consistent with those in Example 3, except that the mass ratio of cellulase, laccase and xylanase in Example 3 is adjusted to 5:2:1.

[0156] Example 8

[0157] The specific implementation steps are consistent with those in Example 3, except that the mass ratio of Portland cement, slag powder and nano-high-temperature slag in Example 3 is adjusted to 1:1:0.5.

[0158] Example 9

[0159] The specific implementation steps are consistent with those in Example 3, except that the mass ratio of Portland cement, slag powder and nano-high-temperature slag in Example 3 is adjusted to 10:1:0.5.

[0160] Example 10

[0161] The specific implementation steps are consistent with those in Example 3, except that the mass ratio of sodium silicate, calcium hydroxide and potassium phosphate in Example 3 is adjusted to 1:1:1.

[0162] Example 11

[0163] The specific implementation steps are consistent with those in Example 3, except that the mass ratio of sodium silicate, calcium hydroxide and potassium phosphate in Example 3 is adjusted to 5:2:1.

[0164] Example 12

[0165] The specific implementation steps are consistent with those in Example 3, except that the mass ratio of the polyvinyl alcohol fibers to the carbon nanotubes in Example 3 is adjusted to 1:1.

[0166] Example 13

[0167] The specific implementation steps are consistent with those in Example 3, except that the mass ratio of the polyvinyl alcohol fibers to the carbon nanotubes in Example 3 is adjusted to 20:1.

[0168] Comparative Example 1

[0169] The specific implementation steps are the same as those in Example 3, except that only cellulase is used to enzymatically treat the straw.

[0170] Comparative Example 2

[0171] The specific implementation steps are the same as those in Example 3, except that only slag powder is used as the cementitious material.

[0172] Comparative Example 3

[0173] The specific implementation steps are consistent with those of Example 3, except that only calcium hydroxide is used as the activator.

[0174] Comparative Example 4

[0175] The specific implementation steps are the same as those in Example 3, except that only polyvinyl alcohol fiber is used as the toughening agent.

[0176] Comparative Example 5

[0177] The specific implementation steps are the same as those in Example 3, except that the crop straw is not modified.

[0178] Experimental Example 1 Performance Test of Hollow Strip Board

[0179] 1. Sample Preparation

[0180] The sintered hollow slabs with high straw content prepared in Examples 1-13 and Comparative Examples 1-5 were taken as samples and subjected to performance tests after curing at room temperature for 7 days.

[0181] 2. Test items and standards

[0182] The compressive strength is tested according to the standard of GB / T23451-2009;

[0183] Thermal conductivity is tested according to GB / T10294-2008 standard;

[0184] The water absorption rate is tested according to the standard of GB / T5486-2008;

[0185] The bulk density is tested in accordance with the standard of GB / T5486-2008;

[0186] The final test results are shown in Table 1 below.

[0187] Table 1 Test results

[0188]

[0189] From the above experimental data, it can be seen that Examples 1-3, as the optimal process group, show the best comprehensive performance, among which Example 3 performs the best, with a compressive strength of 14.6 MPa, a thermal conductivity of 0.136 W / (m·K), a water absorption rate of only 7.8%, and a volume density of 1010 kg / m 3 , the overall performance is significantly better than that of other groups. This is because the hollow strips prepared by the synergistic effect of alkali-enzyme pretreatment and composite gelling system have excellent performance. The alkali treatment effectively dissolves lignin and hemicellulose, exposing the active surface of cellulose; the composite enzyme further optimizes the fiber crystallinity and interface bonding, and the composite system of silicate cement, slag powder and nano-metakaolin in the gelling material provides a multi-scale reinforcement network, while the vibration molding and staged sintering process further ensure the material density and interface stability. The synergistic effect of these technologies allows the straw content to reach 40-55% while still maintaining excellent mechanical properties and durability.

[0190] By comparing Examples 4 and 5, it can be seen that the key influence of NaOH concentration on material properties is verified by adjusting the alkali treatment concentration. When a mass concentration of 1% NaOH is used in Example 4, the compressive strength drops to 9.2 MPa and the water absorption rate rises to 12.4%, indicating that the low-concentration alkali solution cannot fully dissolve lignin, resulting in a weakened interface between the fiber and the cementitious material. When a high-concentration alkali solution is used in Example 5, the performance of the hollow strip is further deteriorated, indicating that excessively high concentrations of alkali solution destroy the cellulose crystal structure and weaken the fiber's own strength. These two sets of data highlight the necessity of a 5-8% NaOH concentration: below 5%, the interface modification is insufficient, and above 8%, the fiber is damaged, both of which will reduce the mechanical properties and water resistance of the material.

[0191] By comparing Examples 6-7, it can be seen that Examples 6-7 explore the effect of the ratio of the complex enzyme on the performance of the hollow strips finally prepared. When the ratio of the complex enzyme in Example 6 is 1:1:1, the compressive strength is 10.3 MPa, which is significantly lower than the compressive strength in Example 3, indicating that when the proportion of cellulase is insufficient, the improvement of fiber crystallinity is limited, and the excessive action of laccase and xylanase may destroy the fiber structure; and when the ratio of the complex enzyme in Example 7 is 5:2:1, although the performance of the hollow strips prepared is improved, it is still not optimal, indicating that too high a ratio of cellulase may lead to excessive hydrolysis of the fiber, and the relative deficiency of laccase and xylanase causes lignin and hemicellulose to remain. In contrast, the 3:1:1 ratio of Example 3 achieves a balance between cellulose crystallization, lignin degradation and hemicellulose hydrolysis, thereby optimizing interfacial bonding while improving fiber strength;

[0192] By comparing Examples 8-9, it can be seen that Examples 8-9 reveal the influence of the proportion of cementitious materials on material properties by adjusting the ratio of cementitious materials. When the mass ratio of cement: slag: nano-metakaolin in Example 8 is 1:1:0.5, the compressive strength is only 7.9 MPa, indicating that too little cement leads to insufficient early strength, and the high proportion of slag delays the hydration reaction; when the mass ratio in Example 9 is 10:1:0.5, the performance is slightly better, but the insufficient proportion of nano-metakaolin weakens the stability of the high-temperature sintering stage. In contrast, the ratio of Example 3 provides early strength through cement, fills the interface pores with slag, and enhances the sintering stability with nano-metakaolin, forming a multi-stage reinforcement mechanism.

[0193] By comparing Examples 10-11, it can be seen that Examples 10-11 studied the effect of the activator ratio on the performance of the hollow strips finally prepared. When the ratio of sodium silicate: calcium hydroxide: potassium phosphate in Example 10 is 1:1:1, the compressive strength of the hollow strips is 8.4 MPa, indicating that the slag powder is not sufficiently excited when sodium silicate is insufficient, and excessive potassium phosphate may interfere with the low-temperature reaction; and when the mass ratio in Example 11 is 5:2:1, the performance is improved to 10.6 MPa, but the high proportion of sodium silicate leads to excessive alkalinity, which may corrode the straw fiber, while the 2:1:0.5-3:1:1 ratio of Example 3 achieves triple synergy: sodium silicate activates the slag activity, calcium hydroxide maintains pH stability, and potassium phosphate optimizes high-temperature ceramicization;

[0194] By comparing Examples 12-13, it can be seen that Examples 12-13 investigate the effect of the toughening agent ratio on the performance of the hollow strips finally prepared. When the polyvinyl alcohol fiber: carbon nanotube = 1:1 in Example 12, the compressive strength of the hollow strips is 9.1 MPa. Excessive carbon nanotubes lead to agglomeration and increased stress concentration. When the mass ratio in Example 13 is 20:1, although the performance is slightly better, the nano-enhancement effect is not fully exerted. The 10-12:1 ratio in Example 3 constructs a multi-scale toughening network: polyvinyl alcohol fiber suppresses macro cracks, and carbon nanotubes strengthen micro interfaces.

[0195] Comparative Examples 1-5 verify the importance of each key technology in the present invention through single variable missing experiments. In Comparative Example 1, the straw is only enzymatically hydrolyzed by cellulase. At this time, the compressive strength of the material after enzymatic hydrolysis is only 6.3MPa, indicating that the synergistic effect of the composite enzyme is irreplaceable; in Comparative Example 2, only slag powder is used as a gelling material, resulting in the worst performance of the prepared hollow strip, indicating the necessity of a cement-based gelling system. In Comparative Example 3, when only calcium hydroxide is used as an activator, the compressive strength is significantly reduced, thereby highlighting the temporal activation advantage of the composite activator. In Comparative Example 4, only polyvinyl alcohol fiber is used as a toughening agent, resulting in a lower strength of the prepared hollow strip, indicating that nano-reinforcement of carbon nanotubes is indispensable. In Comparative Example 5, the straw is not modified. At this time, the performance of the prepared material can be fully degraded, directly proving the core value of the pretreatment process.

[0196] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A production process for sintered hollow lath with high straw content, characterized in that: The following steps are involved: The crop straw is crushed, alkali treated and bio-enzymed treated to obtain modified straw fiber; Then, the gelling material and the activator are added and dry-mixed for 3-5 minutes, and then the modified straw fiber and the toughening agent are added and wet-mixed to obtain the pretreated material; The pre-treated material is vibrated and extruded to obtain a pre-treated mold; The pre-treated mold is then sintered in a two-stage sintering manner and then subjected to surface strengthening treatment to obtain the mold.

2. The generation process according to claim 1, characterized in that Calculated by mass percentage, the pre-treated material comprises 40-55% of modified straw fiber, 30-45% of gelling material, 5-10% of activator and 2-5% of toughening agent.

3. The production process according to claim 1, characterized in that During the alkali treatment, a NaOH solution with a mass concentration of 5-8% is used for soaking for 6-8 hours.

4. The production process according to claim 1, characterized in that The bio-enzyme treatment uses a composite enzyme, which includes cellulase, laccase and xylanase; the mass ratio of the cellulase, laccase and xylanase is 3:1:

1.

5. The generation process according to claim 1, characterized in that After the straw is crushed, the length of the straw fiber is 2-5 mm, and the aspect ratio is ≥50.

6. The production process according to claim 1, characterized in that: The cementitious material is a composite system of silicate cement, slag micropowder and nano-high-temperature terrestrial particles; The mass ratio of the silicate cement, slag micropowder and nano-high-temperature slag is 3:1:0.5-5:2:

1.

7. The production process according to claim 1, characterized in that: The activator is a mixture of sodium silicate, calcium hydroxide and potassium phosphate; The mass ratio of the sodium silicate, calcium hydroxide and potassium phosphate is 2:1:0.5-3:1:

1.

8. The production process according to claim 1, characterized in that: The toughening agent is a mixture of polyvinyl alcohol fibers and carbon nanotubes, wherein the mass ratio of the polyvinyl alcohol fibers to the carbon nanotubes is (10-12):

1.

9. The production process according to claim 1, characterized in that: In the staged sintering process: In the first stage, a mixture of 10-15% CO2 and 3-5% silane coupling agent vapor is introduced and the temperature is raised to 200-250°C at 5-8°C / min and kept at this temperature for 1-2 hours; The second stage adopts oxygen-enriched combustion, in which the oxygen concentration is 25-30% and the temperature is increased to 600-650℃ at 3-5℃ / min and kept at this temperature for 0.5-1h.

10. The production process according to claim 1, characterized in that: The surface strengthening treatment adopts a water-based epoxy resin system modified with nano-SiO2, the vacuum degree is maintained at -0.08 to -0.1 MPa, and the immersion time is 30 to 60 minutes.

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