Degradable waterproof and oil-proof disposable meal box and preparation method thereof

Abstract

The invention provides a degradable waterproof and oil-proof disposable meal box and a preparation method thereof, and belongs to the field of degradable meal boxes. The method comprises the following steps: respectively soaking, cooking, drying and crushing corn straws and wheat straws to obtain straw particles; dissolving the oxidized starch glue into paste by using hot water, and then reacting with citric acid at 90-110 DEG C for 20-40 minutes to obtain pre-esterified modified starch glue; mixing corn straw particles, wheat straw particles, pre-esterified modified starch glue, a liquid corn wax extract, functional composite microspheres and water, and pulping to obtain a mixed material; and carrying out hot press molding on the mixed material in a mold, which consists of a low-pressure permeation stage, a high-pressure shaping stage and a pressure relief cold quenching stage, and then demolding to obtain the disposable meal box. The water resistance, oil resistance, mechanical strength and surface stability of the straw-based meal box are synergistically improved, and meanwhile, the essential property of complete degradability of the straw-based meal box is strictly ensured.

Description

Technical Field

[0001] This application relates to the field of biodegradable lunch box technology, and in particular to a biodegradable, waterproof and oil-proof disposable lunch box and its preparation method. Background Technology

[0002] With the rapid development of the food delivery industry, the demand for disposable lunch boxes is enormous. Traditional petroleum-based plastic lunch boxes are difficult to degrade naturally, causing serious white pollution. At the same time, my country generates massive amounts of crop straw such as corn and wheat every year, and their improper disposal (burning or piling) leads to resource waste and environmental pollution. Utilizing these agricultural wastes to manufacture biodegradable lunch boxes is an ideal path to achieve resource recycling.

[0003] However, existing straw-based food container technologies have significant shortcomings: synthetic chemicals added to improve water and oil resistance can impair their biodegradability and safety; and methods relying solely on physical blending are ineffective at resisting oil penetration and generally suffer from poor mechanical properties, easy deformation, and breakage due to low bonding strength and insufficient fiber utilization. Therefore, how to fundamentally and synergistically improve the water resistance, oil resistance, mechanical strength, and surface stability of straw-based food containers while ensuring their complete biodegradability has become a core technical challenge that urgently needs to be overcome to achieve mature application of this technology. Summary of the Invention

[0004] This application provides a biodegradable, waterproof, and oil-resistant disposable lunch box and its preparation method to solve the following technical problem: how to fundamentally and synergistically improve the waterproofness, oil resistance, mechanical strength, and surface stability of straw-based lunch boxes, while ensuring their essential property of complete biodegradability.

[0005] In a first aspect, this application provides a method for preparing a biodegradable, waterproof, and oil-resistant disposable lunch box, the method comprising the following steps: S1. Soak, cook, dry and crush corn stalks and wheat stalks respectively to obtain corn stalk pellets and wheat stalk pellets; S2. Dissolve the oxidized starch gum into a paste using hot water, and then react it with citric acid at 90-110℃ for 20-40 minutes to obtain pre-esterified modified starch gum. S3. The corn stalk pellets, wheat stalk pellets, the pre-esterified modified starch adhesive, the liquid corn wax extract, the functional composite microspheres and water are mixed and pulped to obtain a mixture. S4. The mixture is hot-pressed in a mold, consisting of a low-pressure penetration stage, a high-pressure shaping stage, and a pressure relief and quenching stage, and then demolded to obtain a disposable lunch box. The functional composite microspheres are hollow mesoporous silica microspheres with fatty acid grafted on the surface and calcium malate loaded in the core. By weight, the corn stalk pellets are 25-30 parts, the wheat stalk pellets are 15-20 parts, the oxidized starch gum is 8-10 parts, the corn wax extract is 1-3 parts, and the functional composite microspheres are 0.5-3 parts.

[0006] Optionally, in step S1, the pretreatment of the corn stalks meets the following conditions: soaking in clean water for 5 to 6 hours, then steaming at a temperature of 100℃ to 110℃ and a pressure of 0.4MPa to 0.5MPa for 0.6 to 0.8 hours, then drying to a moisture content of 12% to 15%, and then crushing and screening to a particle size range of 0.3cm to 0.355cm; In step S1, the pretreatment of wheat straw meets the following conditions: soaking in clean water for 4 to 5 hours, then steaming at a temperature of 110°C to 120°C and a pressure of 0.5 MPa to 0.6 MPa for 0.5 to 0.7 hours, then drying to a moisture content of 12% to 15%, and then crushing and screening to a particle size range of 0.25 cm to 0.3 cm.

[0007] Optionally, in step S2, the mass of the citric acid is 5% to 15% of the dry basis mass of the oxidized starch gum.

[0008] Optionally, in step S3, the preparation method of the functional composite microspheres includes the following steps: S301. Hollow mesoporous silica microsphere carriers are immersed in calcium malate aqueous solution and dried to obtain intermediate microspheres loaded with calcium malate. S302. Under inert gas protection, the intermediate microspheres are reacted with fatty acids at 120℃~180℃ for 1h~3h, and the functional composite microspheres are obtained after cooling and washing.

[0009] Optionally, in step S301, the mass concentration of the calcium malate aqueous solution is 5% to 20%, and the soaking time is 2h to 6h. In step S302, the fatty acid is stearic acid, and the mass ratio of stearic acid to the intermediate microspheres is (0.1-0.5):1; the functional composite microspheres have a particle size of 0.5 μm-5 μm, a shell thickness of 50 nm-200 nm, and a specific surface area of ​​600 m². 2 / g~800m 2 / g.

[0010] Optionally, in step S3, the beating degree of the mixture is 28°SR to 32°SR.

[0011] Optionally, in step S4, the process conditions for the low-pressure permeation stage are: temperature of 140℃~150℃, pressure of 1MPa~2MPa, and holding time of 0.5min~1.5min.

[0012] Optionally, in step S4, the process conditions for the high-pressure setting stage are: temperature 150℃~155℃, pressure 5MPa~8MPa, and holding time 2min~4min.

[0013] Optionally, in step S4, the pressure relief and quenching stage meets the following conditions: the pressure is reduced to normal pressure within 1s to 3s, and a cooling medium of 10℃ to 25℃ is introduced at the same time, so that the mold temperature drops from above 150℃ to below 60℃ within 60s.

[0014] Secondly, this application provides a biodegradable, waterproof, and oil-resistant disposable lunch box prepared by the method described in any one of the first aspects, wherein the disposable lunch box comprises: A matrix formed by bonding corn stalk particles and wheat stalk particles through a cross-linked network; Functional composite microspheres dispersed in the matrix; Micron-nano composite rough structures distributed on the surface of the disposable lunch box; The micron-nano composite rough structure is formed by partially exposed functional composite microspheres and corn wax attached to the surface of the functional composite microspheres.

[0015] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing a biodegradable, waterproof, and oil-resistant disposable lunch box. Through an integrated scheme of intrinsic toughening, the waterproofness, oil resistance, mechanical strength, and surface stability of the straw-based lunch box are fundamentally and synergistically improved, while strictly ensuring its essential biodegradable properties. The synergistic improvement mechanism is reflected in three levels: molecular design of raw materials, construction of multi-scale structures, and precise triggering of the process.

[0016] At the raw material and molecular design level, the solution abandons exogenous synthetic chemicals and uses only natural biodegradable components, ensuring environmental friendliness from the source. Through the pre-esterification reaction of citric acid and oxidized starch, hydrophobic segments are grafted onto the starch molecular chain, creating an amphiphilic bio-based adhesive. This adhesive can bind to the hydroxyl groups of straw fibers through its hydrophilic portion and is compatible with corn wax through its hydrophobic portion, thus achieving efficient bridging between the hydrophilic fiber and the hydrophobic wax phase at the interface, laying the chemical foundation for the overall material's densification and waterproof / oil-resistant properties. The introduced functional composite microspheres are the key intelligent unit for synergistic enhancement. The calcium malate loaded in their core decomposes under high temperature and hot pressing, releasing calcium ions that can form a uniformly distributed ionic crosslinking network with the carboxyl groups in straw fibers and oxidized starch. This is a dynamic crosslinking that can gradually dissociate in the natural environment, significantly enhancing the mechanical strength of the matrix without sacrificing degradability. The fatty acids grafted onto the microsphere surface give it excellent affinity for corn wax, ensuring its uniform dispersion and firm anchoring in the matrix.

[0017] At the level of multi-scale structural construction and performance integration, the unique dynamic hot pressing process, especially the pressure relief and quenching stage, plays a decisive role. The low-pressure infiltration stage allows molten wax and modified starch adhesive to fully encapsulate the fibers. The high-pressure setting stage completes material densification and solidifies the cross-linked network under high temperature and pressure, jointly constructing a dense and tough internal matrix, directly improving the material's bulk strength and water and oil barrier properties. The subsequent pressure relief and quenching stage triggers a dual physical effect through the instantaneous and dramatic changes in pressure and temperature: the sudden pressure drop causes residual moisture to flash-evaporate, leaving micron-scale structures on the surface; the sudden temperature drop forces the molten wax to rapidly nucleate heterogeneously on the surface of the microspheres and these newly formed micron-scale structures, epitaxially growing nanoscale wax crystals. This in-situ forms a surface rough structure combining micron and nanoscale elements. This structure is not an external coating, but rather grows from the material itself, making it extremely stable. Its micro-nano binary characteristics greatly reduce the actual contact between the liquid and the solid surface by trapping air, thereby transforming the hydrophobicity of the material itself into surface-stable superhydrophobic properties. This achieves efficient repulsion of water and high surface tension liquids, greatly enhancing its oil and grease resistance.

[0018] In summary, this method, through interfacial bridging with bio-based adhesives, enhancement and triggering cross-linking with smart microspheres, and precise construction of the bulk structure and surface morphology via dynamic hot pressing, forms a complete system with internal strength, robust interfaces, and functionalized surfaces. Each step and component is interdependent and synergistic, constructing degradable strong interactions at the molecular scale and building stable biomimetic structures at the micro-nano scale. This simultaneously achieves a series of performance goals that are difficult to achieve simultaneously in traditional technologies, including waterproofing, oil resistance, strength, surface stability, and full degradability, thus completing the high-performance conversion of agricultural waste. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic flowchart illustrating a method for preparing a biodegradable, waterproof, and oil-resistant disposable lunch box provided in this application embodiment; Figure 2 A physical image of the mixture obtained in step S3 of Embodiment 1 of this application; Figure 3 This is a physical image of the hot pressing process in step S4 of Embodiment 1 of this application; Figure 4 This is a physical image of the disposable lunch box provided in Embodiment 1 of this application; Figure 5 SEM image of the surface of the disposable lunch box provided in Embodiment 1 of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0024] Figure 1 This is a schematic flowchart illustrating a method for preparing a biodegradable, waterproof, and oil-resistant disposable lunch box, as provided in an embodiment of this application.

[0025] like Figure 1 As shown, this application provides a method for preparing a biodegradable, waterproof, and oil-resistant disposable lunch box, which includes the following steps: S1. Soak, cook, dry and crush corn stalks and wheat stalks respectively to obtain corn stalk pellets and wheat stalk pellets; S2. Dissolve the oxidized starch gum into a paste using hot water, and then react it with citric acid at 90-110℃ for 20-40 minutes to obtain pre-esterified modified starch gum. S3. Mix corn stalk pellets, wheat stalk pellets, pre-esterified modified starch gum, liquid corn wax extract, functional composite microspheres and water, and then pulp to obtain a mixture. S4. The mixture is hot-pressed in a mold, consisting of a low-pressure penetration stage, a high-pressure shaping stage, and a pressure relief and quenching stage, and then demolded to obtain a disposable lunch box. Among them, the functional composite microspheres are hollow mesoporous silica microspheres with fatty acid grafted on the surface and calcium malate loaded in the core. By weight, the amount of corn stalk pellets is 25-30 parts, wheat stalk pellets are 15-20 parts, oxidized starch gum is 8-10 parts, corn wax extract is 1-3 parts, and functional composite microspheres are 0.5-3 parts.

[0026] This preparation method is a systematic engineering project that involves precise design and control at the molecular and microscale. Its high performance stems from the deep and targeted control of the physicochemical changes of components such as straw fiber, starch glue, and functional microspheres during processing, ultimately transforming agricultural waste into advanced sustainable materials with high barrier properties, high strength, and superhydrophobic properties.

[0027] First, differentiated cooking pretreatment was used to break down the robust lignin-carbohydrate complex (LCC) network in the straw cell walls. Under high temperature and high pressure hydrothermal conditions, water dissociation produced hydrated hydrogen ions (H3O). + As a catalyst, it attacks and breaks the ester and ether bonds (such as ferulic acid ester bonds and β-O-4 ether bonds) between lignin and hemicellulose, while simultaneously promoting the hydrolysis of hemicellulose glycosidic bonds. This "self-hydrolysis" process selectively dissociates LCC, exposing the abundant primary and secondary hydroxyl groups on the surface of the internal cellulose microfibrils. These newly exposed hydroxyl groups are not only sites for subsequent hydrogen bonding but also active centers for esterification reactions with carboxyl groups during the hot-pressing stage, thus realizing the transformation of the fiber from an "inert filler" to an "active reactant."

[0028] Secondly, the starch adhesive underwent pre-esterification functional modification to construct an amphiphilic molecular structure. Under acidic and heating conditions, the hydroxyl groups on the starch chain (especially the primary hydroxyl group at C6) undergo an acid-catalyzed esterification reaction with the carboxyl groups of citric acid, covalently grafting citrate groups onto them. This molecular design endows the modified starch adhesive with a distinct "comb-like" amphiphilic structure: the hydrophilic starch backbone and residual carboxyl groups ensure its water dispersibility and hydrogen bonding with fibers; while the hydrophobic citric acid side chains exhibit excellent thermodynamic compatibility with the subsequently added corn wax, enabling it to play a key role as an "emulsifier" and "interfacial compatibility agent" in the system, significantly reducing the interfacial energy between the hydrophobic wax phase and the hydrophilic fiber / starch phase, laying the foundation for achieving uniform composite.

[0029] One of the core innovations lies in the introduction of functional composite microspheres loaded with calcium malate, which constitute a "chelation-slow-release" intelligent cross-linking system. During the room-temperature mixing stage, the malate anion, with its two carboxyl groups and one hydroxyl group as coordination sites, forms stable five- or six-membered cyclic chelates with calcium ions. This strong chelation "locks in" the calcium ions and achieves uniform dispersion at the molecular level, completely avoiding the material embrittlement problem caused by premature local cross-linking of conventional calcium salts. During the high-temperature stage of hot pressing (150–155°C), thermal energy overcomes the chelation bond energy, and calcium malate decomposes in a controlled manner. At this time, the malate group acts as a "slow-release carrier," ensuring that calcium ions are released primarily at the optimal time when the material has fully melted and flowed. The released calcium ions rapidly combine with the carboxyl groups on the surface of oxidized starch and fibers, forming a uniform and strong "ion bridge" cross-linking network (-COO). - …Ca 2+ … - OOC-). In addition, malic acid itself is a multifunctional small molecule. The hydroxyl and carboxyl groups remaining after its release can further optimize the multiphase interface such as fiber-wax-starch through hydrogen bonding or weak coordination, thereby enhancing the coherence and stability of the overall network.

[0030] Finally, a unique "dynamic hot pressing-cold quenching" process is used to integrate all components and finalize the structure. During the high-pressure setting period, high temperature and pressure cause the corn wax to completely melt and the starch to fully gelatinize. The fatty acids grafted on the surface of the functional microspheres diffuse with the wax to form a strong interfacial bond. At the same time, the aforementioned esterification crosslinking and ionic crosslinking reactions deepen simultaneously, building a stable matrix with multi-level bonding. The subsequent pressure relief and cold quenching is a key innovation: the pressure drops sharply within 1 to 3 seconds, causing the superheated trace moisture in the material to flash evaporate, tearing out micron-sized cavities in the near-surface layer; the almost simultaneous rapid cooling puts the system into a deep supercooled state, causing the molten wax to rapidly form a large number of nano-sized fine crystals on the heterogeneous nucleation points, mainly on the surface of the microspheres and the walls of the flashed cavities. Thus, a biomimetic hierarchical rough structure of "micron-sized cavities / protrusions + nano-sized wax crystals" is constructed in situ on the surface of the lunch box. This structure traps air, allowing water droplets to contact only the raised wax crystal tips. Based on the Cassie-Baxter model, it achieves a superhydrophobic state with a contact angle greater than 150° and a roll-off angle less than 10°, giving the product excellent waterproof, stain-resistant, and self-cleaning capabilities.

[0031] In summary, the innovation of this method lies in the synergistic and proactive regulation of multi-scale physicochemical processes in biomass conversion: from fiber activation and amphiphilic design of adhesives to intelligent ionic crosslinking based on the malate "chelation-slow release" mechanism, and finally locking the biomimetic structure through a flash evaporation-cold quenching physical process. Each step is interconnected, generating a strong synergistic effect and achieving integrated innovation from molecular crosslinking and interfacial fusion to macroscopic morphology construction.

[0032] Meanwhile, this application rationally designs the raw materials for disposable lunch boxes, constructing a multi-level, functionally complementary collaborative system.

[0033] Corn and wheat straw serve as the matrix framework, with cellulose, hemicellulose, and lignin as their core molecular components. The dense hydroxyl groups on the long chains of cellulose provide abundant polar reaction sites and hydrogen bonding points for the entire system, forming the molecular basis of the material's strength. The differences in fiber size and lignin content between the two types of straw result in a physical structure that is both rigid and flexible, with a balanced density.

[0034] Pre-esterified modified starch gum is a key amphiphilic interface molecule. Its molecular structure is the core of its innovation: the hydrophilic starch backbone is tightly bound to straw cellulose via hydrogen bonds, while the citric acid hydrophobic segments grafted through esterification (the carboxyl-containing hydrophobic branches introduced after citric acid grafting) exhibit thermodynamic affinity with the subsequent hydrophobic components. This molecular design makes it a bridge connecting the hydrophilic fibrous phase and the hydrophobic functional phase, fundamentally solving the common phase separation problem in biomass composites.

[0035] The main molecular components of corn wax extract are long-chain alkanes (C26-C32), fatty acids, and fatty alcohols. These molecules have long, nonpolar hydrocarbon chains, which are the essential source of their hydrophobic and oleophobic properties. The alkane chains interact with the hydrophobic segments of pre-esterified starch and the modified layer on the surface of the functional microspheres primarily through van der Waals forces, achieving uniform dispersion and binding at the molecular level, rather than simple physical encapsulation.

[0036] Functional composite microspheres are multifunctional molecular assemblies. The calcium malate core decomposes upon heating, releasing calcium ions that act as powerful ionic crosslinking agents. These ions form ionic bonds with the carboxyl groups on the surfaces of straw fibers and oxidized starch. These ionic bonds are much stronger than hydrogen bonds, significantly enhancing the rigidity of the entire network. The fatty acids grafted onto the surface (such as C18 stearic acid), with their long alkyl chains similar in structure to corn wax molecules, are bound together by strong intermolecular forces (inductive and dispersion forces), making the microspheres preferred nucleation sites and strong anchoring points for wax crystallization, guiding the wax molecules to oriented alignment.

[0037] The ultimate manifestation of molecular synergy lies in the following: the hydroxyl groups of straw fibers and the carboxyl / hydroxyl groups of starch gum construct the main network through hydrogen bonds and covalent bonds; the hydrophobic segments of starch gum, the alkane chains of corn wax, and the surface modification layer of microspheres achieve mutual solubility and interfacial reinforcement through van der Waals forces; and the calcium ions released from the core of the microspheres form ionic bonds with the carboxyl groups in the network, constituting key reinforcing nodes. This molecular network, woven by covalent / ionic bonds (strong interactions) and hydrogen bonds / van der Waals forces (weak interactions), with a gradient transition from polar to nonpolar, is the fundamental reason why the material simultaneously achieves high strength, high barrier properties, and structural stability.

[0038] In some embodiments, in step S1, the pretreatment of corn stalks meets the following conditions: soaking in clean water for 5 to 6 hours, then steaming at a temperature of 100°C to 110°C and a pressure of 0.4 MPa to 0.5 MPa for 0.6 to 0.8 hours, then drying to a moisture content of 12% to 15%, and then crushing and screening to a particle size range of 0.3 cm to 0.355 cm; In step S1, the pretreatment of wheat straw meets the following conditions: soaking in clean water for 4 to 5 hours, then steaming at a temperature of 110℃ to 120℃ and a pressure of 0.5MPa to 0.6MPa for 0.5 to 0.7 hours, then drying to a moisture content of 12% to 15%, and then crushing and screening to a particle size range of 0.25cm to 0.3cm.

[0039] In step S1, the straw pretreatment process uses differentiated parameters for corn straw and wheat straw, based on the inherent differences in their fiber structure and chemical composition. Corn straw is soaked for 5–6 hours and then steamed at 100–110℃ and 0.4–0.5 MPa for 0.6–0.8 hours; while wheat straw is soaked for 4–5 hours and steamed at 110–120℃ and 0.5–0.6 MPa for 0.5–0.7 hours. This differentiated energy input more effectively disrupts the lignin-carbohydrate complex in the cell walls of their respective fibers, achieving full dissociation and softening of the fiber bundles, thereby maximizing the exposure of the active hydroxyl groups on the cellulose surface. Both are dried to a moisture content of 12%–15%, which is beneficial for uniform dispersion and re-swelling during subsequent pulping. After crushing, the corn stalks are controlled to a relatively long particle size of 0.3cm to 0.355cm, aiming to utilize their coarse and long fibers as a mechanical skeleton; the wheat stalks are controlled to a relatively short particle size of 0.25cm to 0.3cm, aiming to utilize their fine and short fibers to fill the gaps. The combination of the two lays the foundation for forming a high-density and high-strength fiber network.

[0040] In some embodiments, in step S2, the mass of citric acid is 5% to 15% of the dry basis mass of the oxidized starch gum.

[0041] In the pre-esterification modification step S2, the amount of citric acid is controlled to be 5%–15% of the dry weight of the oxidized starch gum. This ratio range ensures that the starch molecular chains can undergo moderate rather than excessive esterification grafting under reaction conditions of 90–110°C. This successfully introduces sufficient hydrophobic segments of citric acid into the starch molecules, giving them significant amphiphilicity to be compatible with the subsequent corn wax phase; on the other hand, it retains a sufficient number of free carboxyl and hydroxyl groups, reserving ample active sites for further esterification crosslinking and ionic crosslinking with straw fibers during the hot pressing stage.

[0042] In some embodiments, step S3, the method for preparing functional composite microspheres includes the following steps: S301. Hollow mesoporous silica microsphere carriers are immersed in calcium malate aqueous solution and dried to obtain intermediate microspheres loaded with calcium malate. S302. Under inert gas protection, the intermediate microspheres are reacted with fatty acids at 120℃~180℃ for 1h~3h, and the functional composite microspheres are obtained after cooling and washing.

[0043] In some embodiments, in step S301, the mass concentration of the calcium malate aqueous solution is 5% to 20%, and the soaking time is 2 hours to 6 hours. In step S302, the fatty acid is stearic acid, and the mass ratio of stearic acid to the intermediate microspheres is (0.1–0.5):1; the particle size of the functional composite microspheres is 0.5 μm–5 μm, the shell thickness is 50 nm–200 nm, and the specific surface area is 600 m². 2 / g~800m 2 / g.

[0044] In some embodiments, in step S3, the beating degree of the mixture is 28°SR to 32°SR.

[0045] In step S3, the preparation of the functional composite microspheres focuses on achieving their "smart carrier" function. Hollow mesoporous silica microsphere carriers are impregnated with a 5%–20% (w / w) calcium malate aqueous solution for 2–6 hours. This combination of concentration and time allows for effective loading of calcium malate onto the large mesoporous cavities and surface of the microspheres through capillary action and physical adsorption. Subsequently, under inert gas protection, the loaded intermediate microspheres are reacted with stearic acid at a mass ratio of (0.1–0.5):1 at 120–180°C for 1–3 hours. These conditions ensure that stearic acid molecules are firmly grafted onto the microsphere surface through esterification, forming a stable hydrophobic monolayer. The resulting functional composite microspheres have a particle size of 0.5 μm–5 μm, a shell thickness of 50 nm–200 nm, and a high specific surface area of ​​600 m² / g–800 m² / g. This structure allows it to disperse uniformly in the matrix while possessing excellent load-bearing capacity, structural strength, and good interfacial compatibility with the hydrophobic matrix (corn wax). Controlling the beating degree of the mixture within the range of 28°SR to 32°SR is crucial for ensuring suitable water permeability and fiber suspension, enabling rapid dehydration and shaping during subsequent molding while ensuring uniform distribution of all solid components, thereby obtaining a dense preform.

[0046] In some embodiments, the process conditions for the low-pressure permeation stage in step S4 are: temperature of 140°C to 150°C, pressure of 1 MPa to 2 MPa, and holding time of 0.5 min to 1.5 min.

[0047] In some embodiments, the process conditions for the high-pressure setting stage in step S4 are: temperature 150℃~155℃, pressure 5MPa~8MPa, and holding time 2min~4min.

[0048] In some implementations, the pressure relief and quenching stage in step S4 meets the following conditions: the pressure is reduced to normal pressure within 1s to 3s, and a cooling medium of 10°C to 25°C is introduced at the same time, so that the mold temperature drops from above 150°C to below 60°C within 60s.

[0049] In the dynamic hot pressing molding process of step S4, the parameters of the three-stage process precisely control the formation of the final structure and the locking of its properties. The main function of the low-pressure penetration stage (140℃~150℃, 1MPa~2MPa, 0.5min~1.5min) is to allow the molten corn wax and gelatinized starch adhesive to fully penetrate into every pore and surface of the straw fiber network at a lower pressure, achieving initial wetting and bonding. The subsequent high-pressure setting stage (150℃~155℃, 5MPa~8MPa, 2min~4min) is the core of material densification and the deepening of chemical reactions. The higher temperature provides the activation energy required to trigger the decomposition of calcium malate and deepen esterification crosslinking; the high pressure of 5MPa~8MPa forcefully removes residual moisture and air, compressing the fibers, starch, wax, and microspheres to an extremely dense state, greatly improving the macroscopic mechanical strength of the material. The final pressure relief and cold quenching stage is a key innovation in constructing the superhydrophobic surface micro / nano structure: the pressure is released to atmospheric pressure within 1 to 3 seconds, causing the trace amounts of superheated moisture inside the material to flash evaporate instantly, forming the prototype of micron-sized pores; at the same time, a cooling medium of 10℃ to 25℃ is introduced to rapidly cool the mold from above 150℃ to below 60℃ within 60 seconds. This drastic temperature change (cold quenching) greatly inhibits the slow and orderly crystallization of corn wax molecules, forcing them to rapidly nucleate heterogeneously on the pore walls and the surface of functional microspheres formed by flash evaporation, growing dense nano-sized wax crystals, thus ultimately freezing and locking the biomimetic multi-level rough structure composed of micron-sized pores / protrusions and nano-sized wax crystals, giving the product excellent superhydrophobic properties.

[0050] Based on a general inventive concept, this application provides a biodegradable, waterproof, and oil-resistant disposable lunch box prepared by any of the methods described above. The disposable lunch box includes the following structure: A matrix formed by bonding corn stalk particles and wheat stalk particles through a cross-linked network; Functional composite microspheres dispersed in a matrix; Micron-nano composite rough structures distributed on the surface of disposable lunch boxes; The micron-nano composite rough structure is formed by partially exposed functional composite microspheres and corn wax attached to the surface of the functional composite microspheres.

[0051] The disposable lunch box prepared in this application has a unique tertiary structure consisting of a stable fiber matrix, uniformly dispersed functional microspheres, and a biomimetic micro-nano rough surface. This structure is not a product of simple mixing, but rather the inevitable result of the orderly superposition and synergistic effect of a series of precisely controlled physical and chemical reactions in the preparation method.

[0052] The formation of the matrix structure begins with the differentiated pretreatment of straw and the introduction of pre-esterified starch adhesive. Corn and wheat straw particles, after being cooked and crushed according to specific parameters, expose a large number of activated hydroxyl groups on their surfaces. During the hot-pressing stage, these active sites, along with the excess carboxyl and hydroxyl groups on the pre-esterified modified starch adhesive molecular chains, undergo esterification condensation reactions under high temperature and the catalysis of residual citric acid, forming covalent cross-links. Simultaneously, calcium ions released in a controlled manner from the functional composite microspheres rapidly form ionic cross-linking bridges with the carboxyl groups on the straw and starch. This synergistic effect of covalent and ionic bonds tightly weaves the originally loose straw particles into a continuous, strong, and stable three-dimensional network framework, thus forming the matrix of the lunchbox.

[0053] The uniform dispersion and positioning of functional composite microspheres in the matrix are determined by both their surface properties and the mixing process. The long fatty acid chains grafted onto the microsphere surface give them excellent thermodynamic compatibility with molten corn wax. During the low-pressure infiltration stage of pulping and subsequent hot pressing, the hydrophobically modified microspheres spontaneously tend to and anchor themselves in the hydrophobic wax phase. Because the corn wax is uniformly coated on the fiber surface under the compatibility effect of the starch adhesive, the microspheres loaded with calcium malate are also uniformly dispersed throughout the matrix and firmly locked in place by the cross-linked network formed during subsequent curing.

[0054] The in-situ construction of the surface micron-nano composite rough structure is entirely driven by a dynamic process of pressure relief and cold quenching. At the end of the high-pressure setting stage, the material is under high temperature and pressure with moisture forcibly trapped. When the pressure drops rapidly in a very short time, the superheated water evaporates instantly, tearing countless micron-sized pores or protrusions into the surface of the food container close to the mold. Almost simultaneously, rapid cooling causes a precipitous drop in the system temperature, and the molten corn wax enters a deep supercooled state. At this point, the pre-uniformly dispersed functional composite microspheres, due to their inherent hydrophobicity and high specific surface area, become the most effective heterogeneous nucleation sites; simultaneously, the newly formed micron-sized pores or protrusions also possess extremely high surface energy. Under the combined guidance of these two factors, wax molecules cannot slowly grow into large crystals, but can only instantly form dense and fine nanoscale lamellar or needle-like crystals on their surface. Thus, the microspheres themselves act as first-level micron-sized protrusions, their surfaces covered with nano-wax crystals; the flash-evaporated pores, as another level of micron-sized structure, are also covered with nano-wax crystals on their inner walls. The two intertwine and merge, ultimately locking onto the surface of the lunchbox as a multi-level composite rough structure composed of micron-level protrusions or pores and nano-level wax crystals.

[0055] In summary, the hierarchical structure of this lunchbox is an external manifestation of the underlying mechanism of the method. Molecular-level cross-linking design constructs a robust matrix, interfacial compatibility design ensures the uniform distribution and anchoring of functional microspheres, and the extreme thermodynamic process of pressure relief quenching stimulates the synergistic self-assembly of the microspheres and the wax phase, thereby growing a biomimetic surface structure in situ. Each process step creates the necessary conditions for subsequent steps, ultimately achieving precise and controllable preparation of a high-performance product with a high-strength matrix and a superhydrophobic surface from straw waste.

[0056] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0057] Example 1 This embodiment provides a biodegradable, waterproof, and oil-resistant disposable lunch box, the specific steps of which are as follows: S1. Differentiated pretreatment of straw raw materials Take dry corn stalks and dry wheat stalks with a moisture content of ≤12%.

[0058] The dried corn stalks were soaked in clean water for 5.5 hours, stirring regularly to remove impurities. Then, they were placed in a high-pressure cooking device and cooked at 105℃ and 0.45MPa for 0.7 hours. After cooking, the corn stalks were dried under ventilation until the moisture content was 13%, then crushed and screened through a 0.32cm mesh screen to obtain corn stalk particles with a particle size range of 0.3–0.355cm.

[0059] The dry wheat straw was soaked in clean water for 4.5 hours, stirring regularly during the process. Then, it was cooked at 115℃ and 0.55MPa for 0.6 hours. After cooking, it was dried to a moisture content of 13%, crushed, and then sieved through a 0.28cm mesh to obtain wheat straw particles with a particle size range of 0.25–0.3cm.

[0060] S2. Preparation of pre-esterified modified starch adhesive Weigh 10 parts by weight of oxidized starch gum (carboxyl content 1.0%, CAS No. 65996-62-5, purchased from Wuhan Lingjia Yi Chemical Co., Ltd.). Dissolve it in hot water at 80℃ with stirring until a uniform, particle-free paste is formed. Add citric acid (CAS No. 5949-29-1) to this paste, the amount of citric acid added being 10% of the dry basis weight of the oxidized starch gum used. React the mixture at 105℃ for 30 minutes to obtain pre-esterified modified starch gum.

[0061] S3, Multifunctional Mixture Preparation By weight, accurately weigh 28 parts of corn stalk pellets and 18 parts of wheat stalk pellets obtained in step S1, 10 parts of pre-esterified modified starch gum obtained in step S2 (based on the dry basis of the added oxidized starch gum), and 2 parts of corn wax extract (purity 92%, corn wax is prepared by acetone extraction using corn wax paste as raw material, see article: Preparation of corn wax by acetone extraction)

[0062] Heat the corn wax extract to 60°C until it is completely melted into a liquid for later use.

[0063] Preparation of functional composite microspheres: Hollow mesoporous silica microspheres (average particle size of 2 μm, specific surface area of ​​700 m²) were prepared. 2 / g (purchased from Zhongke Keyou) was impregnated in a 12% (w / w) aqueous solution of calcium malate (CAS No. 17482-42-7) for 4 hours, then dried to obtain intermediate microspheres loaded with calcium malate. Under nitrogen protection, these intermediate microspheres were mixed with stearic acid at a mass ratio of 1:0.3 and reacted at 150℃ for 2 hours. After cooling and washing, functional composite microspheres with stearic acid grafted on the surface and calcium malate loaded in the core were obtained. 1.5 parts by weight of these functional composite microspheres were used for later use.

[0064] Corn stalk pellets and wheat stalk pellets were poured into a mixer and dry-mixed at 300 rpm for 10 minutes. Then, the pre-esterified modified starch gum, liquid corn wax extract, and functional composite microspheres were added, along with an appropriate amount of water, to bring the solid content of the mixture to 32% by mass. The mixer speed was increased to 400 rpm, and mixing continued for 22 minutes. A freeness meter was used to check and adjust the mixture until the final freeness reached 30°SR.

[0065] S4, Dynamic Hot Pressing and Demolding The above mixture is evenly filled into the lunchbox molding mold, filling it to approximately 95% of the mold's volume. The inner wall of the mold has been pre-coated with a layer of liquid corn wax.

[0066] The mold is placed in a hot pressing machine and hot-pressed in the following three stages: 1) Low-pressure penetration stage: holding pressure at 145℃ and 1.5MPa for 1.0min; 2) High-pressure setting stage: raising the temperature to 150℃ and the pressure to 5MPa, holding pressure for 3.0min; 3) Pressure relief and quenching stage: releasing the pressure from 5MPa to normal pressure within 2 seconds, and immediately introducing 15℃ cooling water into the mold circulation pipeline, so that the mold temperature rapidly drops from above 150℃ to below 55℃ within 45 seconds. After hot pressing and cooling are completed, the mold is opened and the molded product is demolded, thus obtaining a biodegradable, waterproof, and oil-proof disposable lunch box.

[0067] Example 2 This embodiment provides a biodegradable, waterproof, and oil-resistant disposable lunch box, the specific steps of which are as follows: S1. Differentiated pretreatment of straw raw materials Take dry corn stalks and dry wheat stalks with a moisture content of ≤12%.

[0068] Soak dried corn stalks in clean water for 6 hours, stirring periodically. Then, place them in a high-pressure cooking device and cook at 110℃ and 0.5MPa for 0.8 hours. After cooking, dry the corn stalks to a moisture content of 15%, then crush them and sieve them through a 0.32cm mesh screen to obtain corn stalk particles with a particle size range of 0.3–0.355cm.

[0069] The dried wheat straw was soaked in clean water for 5 hours, stirring regularly during the process. Then, it was cooked at 120℃ and 0.6MPa for 0.7 hours. After cooking, it was dried to a moisture content of 15%, crushed, and then sieved through a 0.28cm mesh to obtain wheat straw particles with a particle size range of 0.25–0.3cm.

[0070] S2. Preparation of pre-esterified modified starch adhesive Weigh 10 parts by weight of oxidized starch gum (carboxyl content 1.2%). Dissolve it in hot water at 80℃ with stirring to form a uniform paste. Add citric acid to this paste, the amount of citric acid added being 12% of the dry basis weight of the oxidized starch gum used. React the mixture at 110℃ for 25 minutes to obtain pre-esterified modified starch gum.

[0071] S3, Multifunctional Mixture Preparation Accurately weigh 30 parts by weight of corn stalk pellets obtained in step S1, 20 parts by weight of wheat stalk pellets, 10 parts by weight of pre-esterified modified starch gum obtained in step S2 (based on the dry basis of the added oxidized starch gum), and 3 parts by weight of corn wax extract (90% purity).

[0072] Heat the corn wax extract to 60°C until it is completely melted into a liquid for later use.

[0073] Preparation of functional composite microspheres: The preparation method is the same as in Example 1. Take 2.5 parts by weight of the functional composite microspheres for later use.

[0074] Corn stalk pellets and wheat stalk pellets were poured into a mixer and dry-mixed at 300 rpm for 10 minutes. Then, the pre-esterified modified starch gum, liquid corn wax extract, and functional composite microspheres were added, along with an appropriate amount of water, to ensure the solid content of the mixture reached 35% by mass. The mixer speed was increased to 400 rpm, and mixing continued for 25 minutes. A freeness meter was used to measure and adjust the mixture until the final freeness reached 32°SR.

[0075] S4, Dynamic Hot Pressing and Demolding The above mixture is evenly filled into the lunchbox molding mold, filling it to approximately 96% of the mold's volume. The inner wall of the mold has been pre-coated with a layer of liquid corn wax.

[0076] The mold is placed in a hot pressing machine and hot-pressed in the following three stages: 1) Low-pressure penetration stage: holding pressure at 150℃ and 2.0MPa for 0.8min; 2) High-pressure setting stage: raising the temperature to 155℃ and the pressure to 8MPa, holding pressure for 2.5min; 3) Pressure relief and quenching stage: releasing the pressure from 8MPa to atmospheric pressure within 1 second, and immediately introducing 10℃ cooling water into the mold circulation pipeline, causing the mold temperature to rapidly drop from above 155℃ to below 58℃ within 50 seconds. After hot pressing and cooling are completed, the mold is opened and the molded product is demolded, thus obtaining a biodegradable, waterproof, and oil-proof disposable lunch box.

[0077] Example 3 This embodiment provides a biodegradable, waterproof, and oil-resistant disposable lunch box, the specific steps of which are as follows: S1. Differentiated pretreatment of straw raw materials Take dry corn stalks and dry wheat stalks with a moisture content of ≤12%.

[0078] Soak dried corn stalks in clean water for 5 hours, stirring periodically. Then, place them in a high-pressure cooking device and cook at 100℃ and 0.4MPa for 0.6 hours. After cooking, dry the corn stalks to a moisture content of 12%, then crush them and sieve them through a 0.32cm mesh screen to obtain corn stalk particles with a particle size range of 0.3–0.355cm.

[0079] The dried wheat straw was soaked in clean water for 4 hours, stirring regularly during the process. Then, it was cooked at 110℃ and 0.5MPa for 0.5 hours. After cooking, it was dried to a moisture content of 12%, crushed, and then sieved through a 0.28cm mesh to obtain wheat straw particles with a particle size range of 0.25–0.3cm.

[0080] S2. Preparation of pre-esterified modified starch adhesive Weigh 8 parts by weight of oxidized starch gum (carboxyl content 0.8%). Dissolve it in hot water at 80℃ with stirring to form a homogeneous paste. Add citric acid to this paste, the amount of citric acid added being 8% of the dry basis weight of the oxidized starch gum used. React the mixture at 95℃ for 35 minutes to obtain pre-esterified modified starch gum.

[0081] S3, Multifunctional Mixture Preparation By weight, accurately weigh 25 parts of corn stalk pellets, 15 parts of wheat stalk pellets obtained in step S1, 8 parts of pre-esterified modified starch gum obtained in step S2 (based on the dry basis of the added oxidized starch gum), and 1 part of corn wax extract (purity 95%).

[0082] Heat the corn wax extract to 60°C until it is completely melted into a liquid for later use.

[0083] Preparation of functional composite microspheres: The preparation method is the same as in Example 1. Take 0.8 parts by weight of the functional composite microspheres for later use.

[0084] Corn stalk pellets and wheat stalk pellets were poured into a mixer and dry-mixed at 300 rpm for 10 minutes. Then, the pre-esterified modified starch gum, liquid corn wax extract, and functional composite microspheres were added, along with an appropriate amount of water, to ensure the solid content of the mixture reached 30% by mass. The mixer speed was increased to 400 rpm, and mixing continued for 20 minutes. A freeness meter was used to measure and adjust the mixture until the final freeness reached 28°SR.

[0085] S4, Dynamic Hot Pressing and Demolding The above mixture is evenly filled into the lunchbox molding mold, filling it to approximately 93% of the mold's volume. The inner wall of the mold has been pre-coated with a layer of liquid corn wax.

[0086] The mold is placed in a hot pressing machine and hot-pressed in the following three stages: 1) Low-pressure penetration stage: holding pressure at 140℃ and 1.0MPa for 1.5 minutes; 2) High-pressure setting stage: raising the temperature to 150℃ and the pressure to 5MPa, holding pressure for 4.0 minutes; 3) Pressure relief and quenching stage: releasing the pressure from 5MPa to normal pressure within 3 seconds, and immediately introducing 20℃ cooling water into the mold circulation pipeline, so that the mold temperature rapidly drops from above 150℃ to below 60℃ within 60 seconds. After hot pressing and cooling are completed, the mold is opened and the molded product is demolded, thus obtaining a biodegradable, waterproof, and oil-proof disposable lunch box.

[0087] Comparative Example 1 This comparative example is modified from the one disclosed in Example 1 as follows: In step S3, no functional composite microspheres are added, and the remaining raw materials and all preparation steps are exactly the same as in Example 1.

[0088] Comparative Example 2 This comparative example is modified from the one disclosed in Example 1 as follows: In step S2, citric acid is not used for the pre-esterification reaction. Instead, the oxidized starch gum is directly dissolved into a paste using hot water at 80°C and then used directly for mixing in step S3. That is, unmodified oxidized starch gum is used instead of pre-esterified modified starch gum, and all other raw materials and preparation steps are exactly the same as in Example 1.

[0089] Comparative Example 3 This comparative example is modified from the one disclosed in Example 1 as follows: The "pressure relief and quenching stage" in step S4 is cancelled. Specifically, after the "high-pressure shaping stage" is completed, the heat source is turned off, and the material is allowed to cool naturally to below 60°C while maintaining constant pressure. Then, the pressure is released and the material is demolded. That is, the traditional "pressure holding and cooling" method is used instead of "pressure relief and quenching," and all other raw materials and preparation steps are exactly the same as in Example 1.

[0090] Comparative Example 4 This comparative example is modified from the one disclosed in Example 1 as follows: In step S3, an equal amount of hollow mesoporous silica microspheres (loaded only with calcium malate) without surface grafting fatty acid modification are used to replace the functional composite microspheres, and the remaining raw materials and all preparation steps are exactly the same as in Example 1.

[0091] Comparative Example 5 This comparative example is modified from the one disclosed in Example 1 as follows: In the preparation of the functional composite microspheres (step S3), calcium chloride was used instead of calcium malate for loading, to prepare "calcium chloride-loaded, surface-grafted fatty acid hollow silica microspheres", which replaced the original functional composite microspheres in the same amount. All other raw materials and preparation steps were exactly the same as in Example 1.

[0092] The disposable lunch boxes obtained in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests, and the results are shown in Table 1. The performance test methods are as follows: Degradability: Samples were cut and buried in simulated soil with specific humidity and temperature. They were periodically removed, cleaned, dried, and weighed to calculate the mass loss rate. The data in the table are the test results on day 28 and day 90, used to compare degradation rates.

[0093] Water resistance (water absorption rate): After weighing the dried sample, immerse it in distilled water at (23±1)℃ for 24 hours, remove it, wipe off the surface moisture, weigh it immediately, and calculate the water absorption rate.

[0094] Oil resistance (oil absorption rate): After weighing the dried sample, immerse it in edible soybean oil at (23±1)℃ for 30 minutes, remove it, drain it until no oil drips, weigh it, and calculate the oil absorption rate.

[0095] Mechanical strength (bending strength): Three-point bending test is performed using a universal testing machine until the sample breaks, and the bending strength is calculated.

[0096] Surface hydrophobicity (water contact angle): Using a contact angle meter, ultrapure water (approximately 5 μL) was dropped at different locations on the sample surface, and the static contact angle was measured and averaged. ≥150° is generally considered the superhydrophobic threshold.

[0097] Table 1. Performance of disposable lunch boxes from Examples 1-3 and Comparative Examples 1-5

[0098] As shown in Table 1, the disposable lunch boxes prepared using the method of the present invention in Examples 1 to 3 exhibit excellent and stable comprehensive performance, with all key indicators within the ideal range: the weight loss rates of the lunch boxes after 28 days and 90 days of soil landfill degradation are 30.8%–32.1% and 81.1%–83.8%, respectively, demonstrating highly efficient and thorough biodegradability; their water absorption rate and oil absorption rate are as low as 6.9%–7.4% and 4.2%–4.8%, respectively, showing excellent waterproof and oil-proof barrier properties; their mechanical bending strength reaches 16.8–19.5 MPa, indicating a robust structure; and most notably, their surface water contact angle is as high as 149.5–152.5°, achieving a stable superhydrophobic state.

[0099] Comparative Example 1, lacking the functional composite microspheres, exhibited the most severe performance defects. Its oil absorption rate (8.3%) was significantly higher than all other examples, resulting in the worst oil resistance. This was due to the absence of the uniform ionic cross-linking network constructed by the microsphere-loaded calcium malate, and the lack of the guiding effect of stearic acid grafted onto the microsphere surface on corn wax crystallization. This led to poor wax phase distribution and bonding, reducing its ability to block oils. Simultaneously, its flexural strength (12.1 MPa) was the lowest, significantly weakening its mechanical properties and directly demonstrating the crucial reinforcing role of the microspheres as "nano-reinforcing units" and providing cross-linking through calcium ion release. Its surface water contact angle was only 108.2°, completely losing its superhydrophobicity. This was because the microspheres, as the core "template" for forming the surface micro-nano rough structure and the heterogeneous nucleation sites, no longer existed.

[0100] Comparative Example 2, without pre-esterification modification, lacked amphiphilicity in its starch adhesive, resulting in poor compatibility between the hydrophilic starch and the hydrophobic corn wax. The direct consequence was a water absorption rate as high as 12.5%, far inferior to the example (<7.4%), severely reducing its waterproof performance. Simultaneously, the poor interfacial bonding also led to a low flexural strength (14.5 MPa). Although the surface water contact angle (130.5°) improved (due to the presence of wax), it could not reach superhydrophobic levels, demonstrating the indispensability of pre-esterification modification for constructing a dense, homogeneous matrix to achieve high performance.

[0101] Comparative Example 3, using conventional pressure-holding cooling, showed a sharp drop in the surface water contact angle to 102.0°, with the superhydrophobicity completely disappearing. This definitively proves that the "pressure-relief quenching" process is the only key step in constructing the micron-nano graded rough surface structure. Traditional slow cooling processes cause corn wax to slowly form large-sized crystals, failing to achieve the biomimetic structure of nano-wax crystals and micron-sized pores. Although its water absorption, oil absorption, and mechanical properties are similar to the examples, the loss of surface properties means its antifouling, self-cleaning, and dynamic liquid-repellent capabilities are severely insufficient. The superhydrophobic surface obtained in this application can effectively resist water droplets and common water-based stains. For oils with even lower surface tension, the material mainly defends against grease through the bulk barrier effect of corn wax and the increased oleophobic pathways of the micro-nano structure; therefore, the oil absorption rate remains at an extremely low level (<5%).

[0102] In Comparative Example 4, the microspheres were not grafted with stearic acid, resulting in poor compatibility between the hydrophilic silica microspheres and the hydrophobic corn wax matrix, leading to easy aggregation. This was directly manifested in higher oil absorption (5.9%) and water absorption (7.5%) compared to the example, decreased barrier properties, and lower flexural strength (15.3 MPa), indicating that microsphere aggregation affected the reinforcing effect and crosslinking uniformity. The surface water contact angle (121.4°) did not reach superhydrophobicity, proving that surface hydrophobicity of the microspheres is a prerequisite for their effective dispersion and structural guiding role.

[0103] Comparative Example 5, which used calcium chloride instead of calcium malate, revealed the core advantages of calcium malate as a "smart, sustained-release" crosslinking agent. Its degradation rates at 28 days and 90 days (29.4% and 78.1%, respectively) were the lowest, indicating that the premature and rapid crosslinking of calcium chloride may have formed an overly dense network or one unfriendly to microbial activity, slightly impairing its final degradability. Simultaneously, its flexural strength (15.9 MPa) was also lower than that of the example, indicating that this premature and uncontrollable crosslinking method is unlikely to form a uniform network with optimal mechanical properties.

[0104] Figure 2 A physical image of the mixture obtained in step S3 of Embodiment 1 of this application; Figure 3 This is a physical image of the hot pressing process in step S4 of Embodiment 1 of this application; Figure 4 This is a physical image of the disposable lunch box provided in Embodiment 1 of this application.

[0105] Depend on Figures 2-4 As can be seen, the disposable lunch box in Example 1 uses a molding process based on corn stalks and wheat stalks, and the surface exhibits the rough texture of natural fibers.

[0106] Figure 5 SEM image of the surface of the disposable lunch box provided in Embodiment 1 of this application.

[0107] Depend on Figure 5 It is evident that the surface of the disposable lunch box exhibits a dense, interwoven network structure of straw fibers, with tight interlocking and low porosity. The microstructure reveals a uniformly distributed binder phase and spherical particles, corresponding to the pre-esterified modified starch adhesive and functional composite microspheres. The overall structure is dense and uniform, highly compatible with the three-stage hot-pressing molding process and the straw-based composite formulation.

[0108] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0109] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0110] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a biodegradable, waterproof, and oil-proof disposable lunch box, characterized in that, The method includes the following steps: S1. Soak, cook, dry and crush corn stalks and wheat stalks respectively to obtain corn stalk pellets and wheat stalk pellets; S2. Dissolve the oxidized starch gum into a paste using hot water, and then react it with citric acid at 90-110℃ for 20-40 minutes to obtain pre-esterified modified starch gum. S3. The corn stalk pellets, wheat stalk pellets, pre-esterified modified starch adhesive, liquid corn wax extract, functional composite microspheres and water are mixed and pulped to obtain a mixture. S4. The mixture is hot-pressed in a mold, consisting of a low-pressure penetration stage, a high-pressure shaping stage, and a pressure relief and quenching stage, and then demolded to obtain a disposable lunch box. The functional composite microspheres are hollow mesoporous silica microspheres with fatty acid grafted on the surface and calcium malate loaded in the core. By weight, the corn stalk pellets are 25-30 parts, the wheat stalk pellets are 15-20 parts, the oxidized starch gum is 8-10 parts, the corn wax extract is 1-3 parts, and the functional composite microspheres are 0.5-3 parts.

2. The method for preparing the biodegradable, waterproof, and oil-proof disposable lunch box according to claim 1, characterized in that, In step S1, the pretreatment of the corn stalks meets the following conditions: soaking in clean water for 5h to 6h, then steaming at a temperature of 100℃ to 110℃ and a pressure of 0.4MPa to 0.5MPa for 0.6h to 0.8h, then drying to a moisture content of 12% to 15%, and then crushing and screening to a particle size range of 0.3cm to 0.355cm; In step S1, the pretreatment of wheat straw meets the following conditions: soaking in clean water for 4 to 5 hours, then steaming at a temperature of 110°C to 120°C and a pressure of 0.5 MPa to 0.6 MPa for 0.5 to 0.7 hours, then drying to a moisture content of 12% to 15%, and then crushing and screening to a particle size range of 0.25 cm to 0.3 cm.

3. The method for preparing the biodegradable, waterproof, and oil-proof disposable lunch box according to claim 1, characterized in that, In step S2, the mass of the citric acid is 5% to 15% of the dry basis mass of the oxidized starch gum.

4. The method for preparing the biodegradable, waterproof, and oil-proof disposable lunch box according to claim 1, characterized in that, In step S3, the preparation method of the functional composite microspheres includes the following steps: S301. Hollow mesoporous silica microsphere carriers are immersed in calcium malate aqueous solution and dried to obtain intermediate microspheres loaded with calcium malate. S302. Under inert gas protection, the intermediate microspheres are reacted with fatty acids at 120℃~180℃ for 1h~3h, and the functional composite microspheres are obtained after cooling and washing.

5. The method for preparing the biodegradable, waterproof, and oil-proof disposable lunch box according to claim 4, characterized in that, In step S301, the mass concentration of the calcium malate aqueous solution is 5% to 20%, and the soaking time is 2 hours to 6 hours. In step S302, the fatty acid is stearic acid, and the mass ratio of stearic acid to the intermediate microspheres is (0.1-0.5):1; the functional composite microspheres have a particle size of 0.5 μm-5 μm, a shell thickness of 50 nm-200 nm, and a specific surface area of ​​600 m². 2 / g~800m 2 / g.

6. The method for preparing the biodegradable, waterproof, and oil-proof disposable lunch box according to claim 1, characterized in that, In step S3, the beating degree of the mixture is 28°SR to 32°SR.

7. The method for preparing the biodegradable, waterproof, and oil-proof disposable lunch box according to claim 1, characterized in that, In step S4, the process conditions for the low-pressure permeation stage are: temperature of 140℃~150℃, pressure of 1MPa~2MPa, and holding time of 0.5min~1.5min.

8. The method for preparing the biodegradable, waterproof, and oil-proof disposable lunch box according to claim 1, characterized in that, In step S4, the process conditions for the high-pressure setting stage are: temperature 150℃~155℃, pressure 5MPa~8MPa, and holding time 2min~4min.

9. The method for preparing the biodegradable, waterproof, and oil-proof disposable lunch box according to claim 1, characterized in that, In step S4, the pressure relief and quenching stage meets the following conditions: the pressure is reduced to normal pressure within 1s to 3s, and a cooling medium of 10℃ to 25℃ is introduced at the same time, so that the mold temperature drops from above 150℃ to below 60℃ within 60s.

10. A biodegradable, waterproof, and oil-resistant disposable lunch box prepared by the method according to any one of claims 1 to 9, characterized in that, The disposable lunch box has the following structure: A matrix formed by bonding corn stalk particles and wheat stalk particles through a cross-linked network; Functional composite microspheres dispersed in the matrix; Micron-nano composite rough structures distributed on the surface of the disposable lunch box; The micron-nano composite rough structure is formed by partially exposed functional composite microspheres and corn wax attached to the surface of the functional composite microspheres.

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