Production method for environment-friendly degradable paper hook

Abstract

The invention relates to the technical field of environment-friendly degradable materials, and discloses a production method for an environment-friendly degradable paper hook, which comprises the following steps: carrying out plant drying oil pre-infiltration treatment on a formed paper hook to form a hydrophobic bottom layer; carrying out interface modification treatment on the surface of the oil layer by adopting an amphiphilic surfactant, and converting a hydrophobic surface into a hydrophilic surface; coating an alcohol-soluble protein solution on the surface of the oil layer to form a transition layer; dipping in a water-based protein solution and carrying out heat treatment curing to form a protein cementation layer; alkaline mineral salt solutions with different concentrations are adopted for segmented gradient mineralization treatment according to functional requirements of different parts of the hook; and finally, carrying out surface cleaning and aging. According to the invention, the interface bonding strength between the hydrophobic oil layer and the hydrophilic protein is improved, so that the interface bonding strength of the multilayer structure is greatly improved; and through the segmented concentration gradient mineralization process, the plane bearing area obtains high hardness, and the bending connection area keeps high flexibility.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly biodegradable materials technology, and more specifically, to a method for producing environmentally friendly biodegradable paper hooks. Background Technology

[0002] Paper hooks, as environmentally friendly and biodegradable hanging devices, have advantages such as renewable raw materials and natural degradation after disposal. However, the inherent defects of paper materials, such as insufficient mechanical strength, poor moisture resistance, and low surface hardness, limit their application and promotion.

[0003] Existing technologies include methods to improve the performance of paper hooks through protein impregnation and surface mineralization treatment, but these methods face the following prominent technical problems: First, there is a poor interfacial wetting problem due to a surface energy difference greater than 20 mN / m between the hydrophobic layer of vegetable oil and the aqueous protein solution. This results in only weak van der Waals forces forming at the oil-protein interface, with an interfacial bonding strength of less than 2 MPa. This makes the hook prone to delamination under humid conditions or stress. Second, when a mineralizing solution of uniform concentration is used to mineralize the entire surface of the hook, it is impossible to meet the differentiated performance requirements of high hardness in the planar load-bearing area and flexibility in the bending connection area. This causes the mineralized layer at the bending part to crack and fall off when subjected to deformation, resulting in poor product reliability. Summary of the Invention

[0004] This invention provides a method for producing environmentally friendly biodegradable paper hooks, comprising the following steps:

[0005] Step 1: Dip or spray the formed paper hook with vegetable drying oil, so that the vegetable drying oil penetrates into the pores of the paper fiber surface and undergoes an oxidative polymerization reaction to form a semi-dry oil layer.

[0006] Step 2: After the oil layer reaches a semi-dry state, an amphiphilic surfactant solution is coated on the hook surface. The hydrophobic tail chain of the surfactant is inserted into the oil layer surface and the hydrophilic head group faces outward, changing the oil layer surface from hydrophobic to hydrophilic.

[0007] Step 3: Prepare an alcohol-soluble protein solution and coat it onto the hook surface treated with surfactant. The lower alcohol swells the oil layer, causing some protein molecules to penetrate into the oil layer surface. After the alcohol evaporates, the protein molecules form a transition layer at the oil-water interface.

[0008] Step 4: Immerse the hook in an aqueous protein solution to allow the solution to penetrate into the fiber gaps and the surface of the oil layer. After removal, dry and heat-treat the hook to allow the protein to cross-link and solidify, forming a protein cement layer.

[0009] Step 5: According to the functional requirements of different parts of the hook, apply a high-concentration alkaline mineral salt solution to the flat load-bearing area, a medium-concentration alkaline mineral salt solution to the transition area, and a low-concentration alkaline mineral salt solution to the bending connection area. After aging, mineralized layers of different thicknesses and hardness are formed.

[0010] Step 6: Rinse the hook surface with clean water and allow it to dry and age.

[0011] Preferably, the vegetable drying oil is selected from linseed oil, tung oil, or a mixture of the two, and the vegetable drying oil has an iodine value of 155-205 g I2 / 100g, an acid value of less than 10 mg KOH / g, and an unsaturated fatty acid content of more than 70%.

[0012] Preferably, in step one, a metal soap catalyst with a mass fraction of 0.05%-0.2% and a metal content of 6%-10% is added to the vegetable drying oil. The catalyst is selected from cobalt naphthenate or manganese naphthenate. The metal ions in the catalyst act as free radical initiators to accelerate the oxidative cross-linking reaction of unsaturated fatty acids, thereby shortening the curing time from 12-18 hours to 2-4 hours.

[0013] Preferably, the amphiphilic surfactant in step two is selected from soybean lecithin, saponins, or a mixture of the two, and the surfactant has an HLB value of 8-15, a critical micelle concentration of 0.5-3.0 g / L, and a solution mass fraction of 1%-3%; the solution is allowed to stand for 5-10 minutes to allow the surfactant molecules to be fully adsorbed.

[0014] Preferably, the lower alcohol in step three is selected from ethanol or acetone, the purity of the lower alcohol is greater than 95%, the boiling point is 50-85℃, and the relative polarity index is 0.35-0.65; the mass fraction of the alcohol-soluble protein solution is 5%-10%, and the total amount of protein used is 10%-20% of the total amount of protein required in step four.

[0015] Preferably, the protein in step four is selected from soybean protein, casein, or a mixture of both, and the molecular weight of the protein is 20-360 kDa, the protein purity is greater than 85%, and the isoelectric point is 4.3-5.2; the mass fraction of the aqueous protein solution is 10%-20%; and the hook immersion time is 15-20 minutes.

[0016] Preferably, the heat treatment in step four includes initial drying at 60°C for 20-30 minutes, followed by heat treatment at 100-120°C for 15-20 minutes.

[0017] Preferably, the alkaline mineral salt in step five is selected from potassium carbonate, sodium silicate, or a mixture of both, with a purity of more than 98% and a modulus of 2.0-3.3 for sodium silicate; the mass fraction of the high-concentration alkaline mineral salt solution is 15%-20%, the medium concentration is 8%-12%, and the low concentration is 3%-5%.

[0018] Preferably, when potassium carbonate is used as an alkaline salt in step five, citric acid or lactic acid is added to the mineralization solution in an amount of 5%-15% of the weight of potassium carbonate to form a CO2 slow-release system, which shortens the mineralization time from 48 hours to 2-4 hours.

[0019] Preferably, the aging time in step six is ​​24-48 hours, so that the oil layer completes the final oxidative cross-linking and the protein-mineralized layer interface reaches the optimal bonding state.

[0020] The beneficial effects of this invention are as follows:

[0021] Significantly enhanced interfacial bonding strength: The hydrophobic oil layer surface is modified into a hydrophilic surface through the directional adsorption of amphiphilic surfactant molecules on the oil layer, eliminating wetting barriers caused by abrupt changes in interfacial polarity. Furthermore, an interpenetrating transition layer formed by alcohol-soluble proteins at the oil-water interface establishes a molecular bridge connection across the interface. These two innovative measures work synergistically to transform the oil-protein interface from weak van der Waals forces to strong chemical bonds (hydrogen bonds and covalent bonds), increasing the interfacial shear bonding strength to more than three times the original strength. This also makes the multilayer structure less prone to delamination during use.

[0022] Differentiated performance matching for different parts: Through a segmented concentration gradient mineralized liquid differential coating process, the planar load-bearing area of ​​the hook obtains a high-hardness, wear-resistant surface, the bending connection area maintains necessary flexibility, and the transition area forms a hardness gradient to avoid stress concentration. This optimized spatial distribution of performance enables the hook to have high load-bearing capacity while withstanding large bending deformations without cracking.

[0023] Comprehensive performance enhancement: The plant oil hydrophobic layer, protein curing layer and gradient mineralization layer form an integrated multi-layer composite structure through interface modification technology. Each layer complements the function and works synergistically to comprehensively improve the moisture resistance, mechanical strength, surface hardness and wear resistance of the paper hook, significantly extend the product's service life, and maintain its completely environmentally friendly and biodegradable characteristics.

[0024] Feasibility of industrial production: The raw materials used are all conventional industrial materials, the processing technology is simple, no special equipment is required, and it can be implemented on the basis of existing paper product production lines, making it suitable for large-scale industrial production. By adding catalysts and CO2 slow-release agents, the production cycle is significantly shortened and production efficiency is significantly improved. Attached Figure Description

[0025] Figure 1 This is a bar chart showing the effect of different interface modification treatments of the present invention on the shear bonding strength of the oil layer-protein layer interface;

[0026] Figure 2 This is a hardness distribution curve of the present invention;

[0027] Figure 3 This is a radar chart showing the combined performance of untreated and fully treated samples according to the present invention;

[0028] Figure 4 This is a comparison of the key performance characteristics of untreated and fully treated samples of the present invention. Detailed Implementation

[0029] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0030] Example 1

[0031] This embodiment proposes the following steps:

[0032] Step 1: Dip the formed paper hook into a vegetable drying oil, allowing the vegetable drying oil to penetrate into the pores of the paper fiber surface and undergo an oxidative polymerization reaction to form a semi-dry oil layer.

[0033] Step 2: After the oil layer reaches a semi-dry state, an amphiphilic surfactant solution is coated on the hook surface. The hydrophobic tail chain of the surfactant is inserted into the oil layer surface and the hydrophilic head group faces outward, changing the oil layer surface from hydrophobic to hydrophilic.

[0034] Step 3: Prepare an alcohol-soluble protein solution and coat it onto the hook surface treated with surfactant. The lower alcohol swells the oil layer, causing some protein molecules to penetrate into the oil layer surface. After the alcohol evaporates, the protein molecules form a transition layer at the oil-water interface.

[0035] Step 4: Immerse the hook in an aqueous protein solution to allow the solution to penetrate into the fiber gaps and the surface of the oil layer. After removal, dry and heat-treat the hook to allow the protein to cross-link and solidify, forming a protein cement layer.

[0036] Step 5: According to the functional requirements of different parts of the hook, apply a high-concentration alkaline mineral salt solution to the flat load-bearing area, a medium-concentration alkaline mineral salt solution to the transition area, and a low-concentration alkaline mineral salt solution to the bending connection area. After aging, mineralized layers of different thicknesses and hardness are formed.

[0037] Step 6: Rinse the hook surface with clean water and allow it to dry and age.

[0038] The vegetable drying oil is selected from flaxseed oil, and the vegetable drying oil has an iodine value of 180 g I2 / 100g, an acid value of less than 10 mg KOH / g, and an unsaturated fatty acid content of more than 70%.

[0039] In step one, a metal soap catalyst with a mass fraction of 0.1% and a metal content of 8% is added to the vegetable drying oil. The catalyst is selected from cobalt naphthenate. The metal ions in the catalyst act as free radical initiators to accelerate the oxidative cross-linking reaction of unsaturated fatty acids, thereby shortening the curing time from 15 hours to 3 hours.

[0040] The amphiphilic surfactant used in step two is selected from soybean lecithin. The surfactant has an HLB value of 12, a critical micelle concentration of 2.0 g / L, and a solution mass fraction of 2%. The solution is allowed to stand for 8 minutes to allow the surfactant molecules to be fully adsorbed.

[0041] The lower alcohol mentioned in step three is selected from ethanol, and the purity of the lower alcohol is greater than 95%, the boiling point is 65℃, and the relative polarity index is 0.50; the mass fraction of the alcohol-soluble protein solution is 8%, and the total amount of protein used is 15% of the total amount of protein required in step four.

[0042] The protein mentioned in step four is selected from soybean protein, which has a molecular weight of 190 kDa, a protein purity of more than 85%, and an isoelectric point of 4.8; the aqueous protein solution has a mass fraction of 15%; and the hook is immersed for 18 minutes.

[0043] The heat treatment described in step four includes initial drying at 60°C for 25 minutes, followed by heat treatment at 110°C for 18 minutes.

[0044] The alkaline mineral salt mentioned in step five is selected from potassium carbonate, with a purity of more than 98% and a modulus of sodium silicate of 2.6; the mass fraction of the high-concentration alkaline mineral salt solution is 18%, the medium concentration is 10%, and the low concentration is 4%.

[0045] In step five, when potassium carbonate is used as an alkaline salt, citric acid is added to the mineralization solution at a rate of 10% of the weight of potassium carbonate to form a CO2 slow-release system, which shortens the mineralization time from 48 hours to 3 hours.

[0046] In step six, the aging time is 32 hours, which allows the oil layer to complete the final oxidative cross-linking and the protein-mineralized layer interface to reach the optimal bonding state.

[0047] Example 2

[0048] The difference between this embodiment and Embodiment 1 is that:

[0049] The formed paper hooks are sprayed with vegetable drying oil, which allows the vegetable drying oil to penetrate into the pores of the paper fibers and undergo an oxidative polymerization reaction to form a semi-dry oil layer.

[0050] The plant drying oil is selected from tung oil, and the plant drying oil has an iodine value of 155 g I2 / 100g, an acid value of less than 10mg KOH / g, and an unsaturated fatty acid content of more than 70%.

[0051] In step one, a metal soap catalyst with a mass fraction of 0.05% and a metal content of 6% is added to the vegetable drying oil. The catalyst is selected from manganese naphthenate. The metal ions in the catalyst act as free radical initiators to accelerate the oxidative cross-linking reaction of unsaturated fatty acids, thereby shortening the curing time from 12 hours to 2 hours.

[0052] The amphiphilic surfactant mentioned in step two is selected from saponins. The surfactant has an HLB value of 8, a critical micelle concentration of 0.5 g / L, and a solution mass fraction of 1%. The solution is allowed to stand for 5 minutes to allow the surfactant molecules to be fully adsorbed.

[0053] The lower alcohol mentioned in step three is selected from acetone, and the purity of the lower alcohol is greater than 95%, the boiling point is 50°C, and the relative polarity index is 0.35; the mass fraction of the alcohol-soluble protein solution is 5%, and the total amount of protein used is 10% of the total amount of protein required in step four.

[0054] The protein mentioned in step four is selected from casein, and the protein has a molecular weight of 20 kDa, a protein purity of more than 85%, and an isoelectric point of 4.3; the aqueous protein solution has a mass fraction of 10%; and the hook is immersed for 15 minutes.

[0055] The heat treatment described in step four includes initial drying at 60°C for 20 minutes, followed by heat treatment at 100°C for 15 minutes.

[0056] The alkaline mineral salt mentioned in step five is selected from sodium silicate or a mixture of both, with a purity of more than 98% and a modulus of 2.0 for sodium silicate; the mass fraction of the high-concentration alkaline mineral salt solution is 15%, the medium-concentration solution is 8%, and the low-concentration solution is 3%.

[0057] In step five, when potassium carbonate is used as an alkaline salt, citric acid or lactic acid is added to the mineralization solution at a rate of 5% of the weight of potassium carbonate to form a slow-release CO2 system, which shortens the mineralization time from 48 hours to 2 hours.

[0058] In step six, the aging time is 24 hours, allowing the oil layer to complete the final oxidative cross-linking and the protein-mineralized layer interface to reach the optimal bonding state.

[0059] Example 3

[0060] The difference between this embodiment and Embodiment 1 is that:

[0061] The vegetable drying oil is selected from a mixture of linseed oil and tung oil, and the vegetable drying oil has an iodine value of 205 g I2 / 100g, an acid value of less than 10 mg KOH / g, and an unsaturated fatty acid content of more than 70%.

[0062] In step one, a metal soap catalyst with a mass fraction of 0.2% and a metal content of 10% is added to the vegetable drying oil. The metal ions in the catalyst act as free radical initiators to accelerate the oxidative cross-linking reaction of unsaturated fatty acids, thereby shortening the curing time from 18 hours to 4 hours.

[0063] The amphiphilic surfactant mentioned in step two is selected from a mixture of soybean lecithin and saponins. The surfactant has an HLB value of 15, a critical micelle concentration of 3.0 g / L, and a solution mass fraction of 3%. The solution is allowed to stand for 10 minutes to allow the surfactant molecules to be fully adsorbed.

[0064] The lower alcohol mentioned in step three has a purity greater than 95%, a boiling point of 85°C, and a relative polarity index of 0.65; the alcohol-soluble protein solution has a mass fraction of 10%, and the total amount of protein used is 20% of the total amount of protein required in step four.

[0065] The protein mentioned in step four is selected from a mixture of soybean protein and casein, and the protein has a molecular weight of 360 kDa, a protein purity of more than 85%, and an isoelectric point of 5.2; the aqueous protein solution has a mass fraction of 20%; and the hook is immersed for 20 minutes.

[0066] The heat treatment described in step four includes initial drying at 60°C for 0 minutes, followed by heat treatment at 120°C for 20 minutes.

[0067] The alkaline mineral salt mentioned in step five is selected from a mixture of potassium carbonate and sodium silicate, with a purity of more than 98% and a modulus of 3.3 for sodium silicate. The mass fraction of the high-concentration alkaline mineral salt solution is 20%, the medium concentration is 12%, and the low concentration is 3%-5%.

[0068] In step five, when potassium carbonate is used as an alkaline salt, citric acid is added to the mineralization solution at a rate of 15% of the weight of potassium carbonate to form a CO2 slow-release system, which shortens the mineralization time from 48 hours to 4 hours.

[0069] In step six, the aging time is 48 hours, which allows the oil layer to complete the final oxidative cross-linking and the protein-mineralized layer interface to reach the optimal bonding state.

[0070] Example 4

[0071] This embodiment proposes a production method for environmentally friendly biodegradable paper hooks, including the following steps:

[0072] Step 1: Pre-impregnation with vegetable drying oil

[0073] The formed paper hooks are dipped or sprayed with a vegetable drying oil, selected from linseed oil, tung oil, or a mixture of both, wherein the vegetable drying oil has an iodine value of 155-205 g I2 / 100g, an acid value of less than 10 mg KOH / g, and an unsaturated fatty acid content of more than 70%. Linseed oil is preferred, with an iodine value of 180 g I2 / 100g, an acid value of 5 mg KOH / g, and an unsaturated fatty acid content of 80%. To accelerate curing, a metal soap catalyst (cobalt naphthenate or manganese naphthenate) with a mass fraction of 0.05%-0.2% and a metal content of 6%-10% can be dissolved or dispersed in the vegetable oil and mixed evenly beforehand. Cobalt naphthenate is preferred, with a mass fraction of 0.1% and a metal content of 8%. Catalyst dosage selection criteria: below 0.05%, the catalytic effect is not obvious and the curing time exceeds 6 hours; above 0.2%, the catalyst is excessive, which will lead to excessive oxidation of the oil layer, yellowing of the surface and increased cost; a metal content of 6%-10% ensures catalytic activity while avoiding coloring and stability problems caused by excessive metal ions.

[0074] During coating, the plant-based drying oil penetrates the pores of the paper fiber surface (penetration depth of approximately 20-50 micrometers), sealing the hydrophilic hydroxyl groups on the fiber surface. After coating, the mixture is left to stand at room temperature (15-25℃) to allow the unsaturated fatty acids in the plant-based drying oil to undergo an oxidative polymerization reaction with oxygen in the air.

[0075] Catalytic Mechanism and Reaction Pathway: Metal ions (Co²⁺ or Mn²⁺) in metal soap catalysts act as free radical initiators, accelerating oil layer solidification through the following reaction pathways: 1. Metal ions catalyze the decomposition of hydroperoxides to generate free radicals: ROOH + M²⁺ → RO· + ·OH + M³⁺ 2. Free radicals initiate the auto-oxidation reaction of double bonds in unsaturated fatty acid chains: R-CH=CH-R' + O2 → R-CH(OO·)-CH-R' 3. Free radicals undergo coupling and cross-linking between adjacent molecular chains: R· + R'· → R-R' (forming CC bonds) or R· + ·OOR' → R-OO-R' (forming peroxy bonds) 4. The cross-linking reaction forms a three-dimensional network structure, transforming the liquid oil into a semi-dry solidified layer.

[0076] The presence of a catalyst lowers the activation energy of the reaction, increases the rate of free radical generation, and shortens the curing time from 12-18 hours without a catalyst to 2-4 hours. Metal soap catalysts are immobilized within the oil-layer polymer network during the catalytic process and have no adverse effect on subsequent aqueous treatment steps.

[0077] A semi-dry oil layer is formed, which is dry to the touch on the surface but retains a certain degree of fluidity internally, constituting a hydrophobic protective underlayer. Without a catalyst, the settling time is 12-18 hours, preferably 16 hours; with a catalyst, the settling time is 2-4 hours, preferably 3 hours, to improve production efficiency. The standard for judging the semi-dry state is: the surface is not sticky to the touch, but still slightly sticky when pressed firmly.

[0078] Step 2: Interfacial modification treatment with amphiphilic surfactants

[0079] After the oil layer reaches a semi-dry state, a natural amphiphilic surfactant solution is immediately coated onto the hook surface. The surfactant is selected from soybean lecithin, saponins, or a mixture of both, with an HLB value of 8-15, a critical micelle concentration of 0.5-3.0 g / L, and a solution mass fraction of 1%-3%. Soybean lecithin is preferred, with an HLB value of 11, a critical micelle concentration of 1.5 g / L, and a solution mass fraction of 2%.

[0080] Interface modification process: Amphiphilic surfactant molecules possess a dual structural feature of hydrophobic tail chains and hydrophilic head groups. Soybean lecithin has an alkyl tail chain and a phosphocholine head group; saponins have a triterpenoid saponin aglycone structure and a glycosylated head group. When a surfactant solution is coated onto a semi-dry oil layer surface, the hydrophobic tail chain of the molecule inserts into the semi-dry oil layer surface through hydrophobic interactions (insertion depth approximately 1-3 micrometers). The hydrophobic tail chain forms a stable bond with the fatty acid chains in the oil layer through van der Waals forces. Simultaneously, the hydrophilic head group of the molecule aligns outwards, exposed on the oil layer surface, forming a hydrophilic interface.

[0081] The obtained hydrophilic interface: Through the directional adsorption and self-assembly of surfactant molecules, the surface of the oil layer changes from the original hydrophobic (water contact angle greater than 90°) to hydrophilic (water contact angle less than 60°), and the surface energy is significantly improved, thus providing a good wetting interface for subsequent impregnation of aqueous protein solutions and eliminating the poor wetting phenomenon caused by the sudden change in interface polarity.

[0082] Allow the surfactant molecules to stand for 5-10 minutes to fully adsorb and achieve a stable arrangement at the interface, preferably 7 minutes. The criterion for judging whether adsorption is complete is: when a water droplet is added to the hook surface, the water droplet spreads rapidly and the contact angle is less than 60°.

[0083] The difference from existing technologies: In existing technologies, aqueous protein solutions are directly coated onto the surface of a hydrophobic oil layer. Due to the surface energy difference exceeding 20 mN / m, the protein solution cannot effectively wet the oil layer surface, resulting in a contact area of ​​less than 30% and weak van der Waals forces forming at the interface. This invention introduces an amphiphilic surfactant as an interface modifier. Utilizing the amphiphilic properties of its molecular structure, a molecular bridge is established between the hydrophobic oil layer and the hydrophilic protein. The hydrophobic end of the surfactant forms a hydrophobic interaction with the oil layer, while the hydrophilic end forms hydrogen bonds with the protein, transforming the weak interfacial interaction into a strong chemical bond, increasing the interfacial bonding strength to more than three times the original.

[0084] Step 3: Pretreatment of oil-soluble protein precursors

[0085] Preparation of alcohol-soluble protein solution: Take 10%-20% of the total protein required in step four and dissolve it in a lower alcohol such as ethanol or acetone. The lower alcohol must have a purity greater than 95%, a boiling point of 50-85°C, and a relative polarity index of 0.35-0.65 to prepare an alcohol-soluble protein solution with a mass fraction of 5%-10%. Preferably, ethanol with a purity of 99%, a boiling point of 78°C, and a relative polarity index of 0.65 is used to prepare an alcohol-soluble protein solution with a mass fraction of 7%, where the total protein used is 15% of the total protein required in step four. Coat this solution onto the surface of the hook treated with a surfactant.

[0086] The transition layer formation process: Lower alcohols (ethanol or acetone) have a slight swelling effect on the semi-dry oil layer, relaxing the molecular chain segments on the oil layer surface and increasing porosity. Protein molecules dissolved in the alcohol partially penetrate into the oil layer surface (penetration depth 5-10 micrometers) with the help of the alcohol's solvent carrying effect. During the alcohol evaporation process, protein molecules are deposited and oriented at the oil-water interface: hydrophobic amino acid residues in the protein molecular chains (such as leucine, isoleucine, and phenylalanine residues) bind to fatty acid chains in the oil layer through hydrophobic interactions, while hydrophilic amino acid residues (such as glutamic acid, aspartic acid, and lysine residues) extend outwards towards the aqueous environment.

[0087] The obtained interpenetrating transition structure: After standing at room temperature (15-25℃), the alcohol completely evaporates (approximately 15-20 minutes, preferably 18 minutes), and protein molecules form a transition layer at the oil-water interface. The criteria for complete evaporation are: no pungent alcohol odor on the hook surface, and the surface is dry to the touch. The structural characteristics of this transition layer are: one end of the protein molecular chain is embedded inside the oil layer, and the other end extends to the outside of the interface, forming a molecular bridge across the oil layer surface. This interpenetrating structure ensures that the subsequently coated aqueous protein solution does not simply remain on the oil layer surface, but rather uses the hydrophilic ends of the alcohol-soluble protein molecules as anchor points to form molecular chain entanglement and hydrogen bonds with the protein molecules in the transition layer, establishing an effective connection between the aqueous protein and the oil layer.

[0088] The difference from existing technologies: Existing technologies do not employ a pretreatment step with alcohol-soluble protein precursors. Aqueous protein solutions are directly coated onto the oil layer surface, preventing protein molecules from penetrating and resulting in physical accumulation on the surface. This invention utilizes the swelling effect of lower alcohols on the oil layer and their dissolving and carrying effect on proteins to construct an interpenetrating transition layer at the oil-water interface. This transforms the interaction between the oil layer and the protein layer from "interfacial contact" to "interpenetrating bonding," increasing the thickness of the interfacial transition zone from zero to 5-10 micrometers, thus enhancing the stability of the interfacial bonding and its resistance to delamination.

[0089] Step 4: Deep impregnation and curing with aqueous protein solution

[0090] Prepare an aqueous protein solution by dissolving soy protein, casein, or a mixture of both in water. The protein has a molecular weight of 20-360 kDa, a protein purity greater than 85%, an isoelectric point of 4.3-5.2, and a protein mass fraction of 10%-20%. Preferably, soy protein with a molecular weight of 120 kDa, a protein purity of 90%, an isoelectric point of 4.8, and a protein mass fraction of 15% is used. Immerse the hook in this solution for 15-20 minutes (preferably 18 minutes). Utilizing the hydrophilic interface formed after surfactant modification and alcohol-soluble protein transition layer treatment, the aqueous protein solution fully penetrates into the fiber gaps (penetration depth can reach 50%-80% of the paper thickness) and the oil layer surface.

[0091] During the infiltration process, the functional groups (amino, carboxyl, and hydroxyl groups) of protein molecules bind to the hydroxyl groups on the surface of cellulose fibers through hydrogen bonds. The protein molecular chains intertwine in the interfiber gaps and adsorb onto the fiber surface, forming a protein-fiber complex network. After removal, excess liquid is drained, and the hooks are pre-dried at 60°C for 20-30 minutes (preferably 25 minutes) to remove most of the moisture, reducing the moisture content to 10%-15%. Then, they are heat-treated at 100-120°C for 15-20 minutes (preferably 110°C for 18 minutes).

[0092] During heat treatment, proteins undergo thermal denaturation and molecular chain unfolding. Protein molecules cross-link and solidify through interactions such as hydrogen bonds and disulfide bonds, simultaneously forming more hydrogen bond sites on the surface of cellulose fibers, creating a protein cementation layer that binds the fiber network into a cohesive whole. This protein layer, through the dual treatment of surfactant interface modification and an alcohol-soluble protein transition layer, forms chemical bonds (hydrogen bonds and covalent bonds) with the oil layer, integrating the multilayer structure and significantly enhancing the interfacial bonding strength.

[0093] Step 5: Differentiated Coating with Segmented Concentration Gradient Mineralizing Solution

[0094] This step involves coating different parts of the hook with mineralizing solutions of varying concentrations to achieve high hardness in the load-bearing area and maintain flexibility in the bending connection area, thus achieving differentiated performance matching for different parts.

[0095] Based on the functional requirements of different parts of the hook, three different concentrations of alkaline mineral salt solutions are prepared: - High-concentration mineralization solution: Alkaline salt (potassium carbonate with a purity greater than 98%, sodium silicate with a modulus of 2.0-3.3, or a mixture of both) at a mass fraction of 15%-20%, used for the flat load-bearing area; preferably, potassium carbonate with a purity of 99% at a mass fraction of 18% is used; - Medium-concentration mineralization solution: Alkaline salt (potassium carbonate with a purity greater than 98%, sodium silicate with a modulus of 2.0-3.3, or a mixture of both) at a mass fraction of 8%-12%, used for the transition area; preferably, potassium carbonate with a purity of 99% at a mass fraction of 10% is used; - Low-concentration mineralization solution: Alkaline salt (potassium carbonate with a purity greater than 98%, sodium silicate with a modulus of 2.0-3.3, or a mixture of both) at a mass fraction of 3%-5%, used for the bending connection area; preferably, potassium carbonate with a purity of 99% at a mass fraction of 4%.

[0096] Segmented coating method: Apply a high-concentration mineralizing solution to the load-bearing flat area of ​​the hook by brushing or spraying, a medium-concentration mineralizing solution to the transition area, and a low-concentration mineralizing solution or leave only the protein sealing layer without mineralization treatment to the bending area. After coating, allow it to age naturally for 48 hours at room temperature (15-25℃) and relative humidity of 60%-80% (preferably at room temperature of 20℃ and relative humidity of 70%). If potassium carbonate is used as the alkaline salt, citric acid or lactic acid (preferably citric acid) can be added to the mineralizing solution in advance, at a dosage of 5%-15% (preferably 10%) of the weight of potassium carbonate, to form a CO2 slow-release system, shortening the mineralization time to 2-4 hours (preferably 3 hours); if sodium silicate (preferably with a modulus of 2.5) is used, it relies on CO2 in the air for a slow carbonation reaction, with an aging time of 48 hours.

[0097] Gradient mineralization process: During aging, if potassium carbonate is used, the alkali in the alkaline solution reacts with CO2 in the air or CO2 released from added organic acids to form carbonate crystals that deposit on the surface and pores of the protein layer. If sodium silicate is used, the pH of the solution gradually decreases due to CO2 in the air, and silicate ions condense under the weakened alkalinity to form a silicon-oxygen network, which then chemically bonds with the amino and carboxyl groups of protein molecules. Different concentrations of mineralizing solutions form mineralized layers of different thicknesses and hardnesses: - High concentration zone: forms a thick, hard shell (30-50 micrometers thick, Rockwell hardness HRB28-32), providing wear resistance and pressure resistance; - Medium concentration zone: forms a medium-hardness layer (15-25 micrometers thick, HRB18-22 hardness), serving as a performance transition zone; - Low concentration zone: forms a flexible protective layer (HRB<10 hardness) or maintains the flexibility of the protein layer, allowing for bending and deformation.

[0098] Differentiated performance distribution achieved: Through segmented concentration gradient mineralization process, different parts of the hook achieve performance matching their mechanical requirements: the planar load-bearing area has high hardness and high wear resistance, and can withstand the weight and friction of the suspended object; the bending connection area maintains flexibility and can withstand 90-degree bending deformation without cracking; the transition area forms a hardness gradient, avoiding stress concentration between the rigid and flexible areas.

[0099] The difference from existing technologies: Existing technologies use a single concentration of mineralizing solution to uniformly mineralize the entire surface of the hook, resulting in a mineralized layer with a relatively uniform thickness and hardness across all areas. While this uniform mineralized layer provides sufficient hardness in the planar load-bearing area, it cracks and detaches when subjected to deformation in the bending connection area due to the brittle nature of the mineralized layer (elongation at break less than 2%), which cannot coordinate with the deformation of the substrate (surface strain can reach 5%-10%). This invention employs segmented coating with mineralizing solutions of different concentrations, resulting in an optimized spatial distribution of mineralized layer properties. The properties of the mineralized layer in each area are matched to the functional requirements of that area, ensuring high hardness in the planar area while maintaining necessary flexibility in the bending area.

[0100] Step Six: Surface Cleaning and Aging

[0101] Gently rinse the hook surface with clean water (15-25℃, preferably 20℃) to remove unreacted residual alkaline salts and prevent salt bloom from forming. Rinse for 1-2 minutes, preferably 1.5 minutes. Allow to air dry and age naturally at room temperature (15-25℃) and relative humidity (50%-70%) for 24-48 hours (preferably 36 hours at room temperature (20℃) and relative humidity (60%)) to fully stabilize the multi-layer structure, complete the final oxidative cross-linking of the oil layer, and achieve optimal bonding at the protein-mineralized layer interface. The criteria for complete aging are: the hook surface is completely dry; pressing the mineralized layer with a finger leaves no powder falling off; and the bending area can withstand a 90-degree bend without cracking.

[0102] Through the above steps, an environmentally friendly, biodegradable paper hook with a multi-layered composite structure is obtained, consisting of the following layers from the inside out: paper matrix - hydrophobic vegetable oil layer - surfactant-modified interface - alcohol-soluble protein transition layer - aqueous protein curing layer - segmented gradient mineralization layer. Each layer is firmly bonded together through chemical bonding and an interpenetrating network, and the thickness and hardness of the mineralization layer in different areas are matched to local mechanical requirements.

[0103] Summary of Process Flow Timeline: - Step 1: Plant oil coating followed by standing curing (16 hours without catalyst or 3 hours with catalyst) - Step 2: Surfactant coating followed by standing for 7 minutes - Step 3: Alcohol-soluble protein coating followed by alcohol evaporation for 18 minutes - Step 4: Aqueous protein impregnation for 18 minutes + drying at 60℃ for 25 minutes + heat treatment at 110℃ for 18 minutes - Step 5: Mineralized solution coating followed by aging (potassium carbonate + organic acid for 3 hours or potassium carbonate / sodium silicate for 48 hours) - Step 6: Rinse with water for 1.5 minutes + drying and aging for 36 hours

[0104] Optimal total process time: When using a catalyst and organic acid slow-release system, the total time is approximately 7.5 hours (excluding aging) + 36 hours of aging = 43.5 hours; when not using a catalyst and organic acid, the total time is approximately 20.5 hours (excluding aging) + 36 hours of aging = 56.5 hours.

[0105] Experimental Example

[0106] Experiment 1: Interfacial Shear Bond Strength Test

[0107] 1. Experimental Objective

[0108] The effects of amphiphilic surfactant interface modification and alcohol-soluble protein transition layer treatment on improving the interfacial shear bonding strength between the oil layer and the protein layer were verified, proving that the present invention increases the interfacial bonding strength to more than 3 times the original strength.

[0109] 2. Sample preparation

[0110] Three sets of comparative samples were prepared. The substrate for each set of samples was a paper substrate of the same specifications (basis weight 120 g / m², thickness 0.3 mm, size 50 mm × 25 mm). The sample processing methods for each set of samples are as follows:

[0111] Control sample (Sample A): Following step one, the sample was coated with vegetable drying oil (linseed oil with 0.1% cobalt naphthenate catalyst), allowed to stand for 3 hours until semi-dry, then directly immersed in a 15% soybean protein aqueous solution for 18 minutes. After removal, it was dried at 60°C for 25 minutes and heat-treated at 110°C for 18 minutes. This sample was not treated with surfactant interface modification or an alcohol-soluble protein transition layer.

[0112] Surfactant-treated sample (Sample B): Following step one, the sample was coated with vegetable drying oil and allowed to stand until semi-dry. Following step two, it was coated with a 2% soybean lecithin solution and allowed to stand for 7 minutes for interface modification. Subsequently, it was directly immersed in a 15% soybean protein aqueous solution for 18 minutes (skipping the alcohol-soluble protein pretreatment in step three). After removal, it was dried at 60°C for 25 minutes and then heat-treated at 110°C for 18 minutes. This sample underwent only surfactant interface modification treatment.

[0113] Complete treatment sample (Sample C): The complete treatment was carried out strictly according to steps one through four, namely, pre-impregnation with vegetable drying oil (step one), interface modification with 2% soybean lecithin (step two), construction of a transition layer with 7% alcohol-soluble protein solution (step three), and deep impregnation and curing with 15% aqueous protein solution (step four). This sample was simultaneously treated with surfactant interface modification and alcohol-soluble protein transition layer.

[0114] Ten parallel samples were prepared for each group of samples and tested after aging at room temperature (20℃) and relative humidity (60%) for 24 hours.

[0115] 3. Experimental conditions

[0116] Testing Equipment: Universal Testing Machine (Instron 5969, equipped with a 50 kN load cell) Testing Method: Interfacial shear strength test performed according to GB / T 7124-2008 "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)" Loading Rate: 1.0 mm / min Testing Environment: Temperature 20±2℃, Relative Humidity 60±5% Bonding Area: 25 mm × 25 mm Number of Samples Tested per Group: 10 parallel samples, average value taken

[0117] 4. Experimental Procedure

[0118] The prepared sample was equilibrated in the test environment for 24 hours to ensure that the sample moisture content reached equilibrium.

[0119] Use clamps to fix the sample on the universal testing machine, ensuring that the tensile force direction is parallel to the adhesive interface and the loading direction is parallel to the oil layer-protein layer interface.

[0120] A tensile shear load was applied at a constant rate of 1.0 mm / min, and the load-displacement curve was recorded until shear failure occurred at the interface.

[0121] Record the maximum shear load (Unit: N), according to the formula Calculate the interfacial shear bond strength, where The bonding area is 625 mm².

[0122] Observe the damage pattern and record whether the damage occurs at the oil layer-protein layer interface, inside the protein layer, or in the fibrous matrix.

[0123] Statistical analysis was performed on the test results of 10 parallel samples in each group to calculate the mean and standard deviation.

[0124] 5. Experimental Results

[0125] The results of the interfacial shear bond strength test are shown in Table 1:

[0126]

[0127] As can be seen from the data in Table 1:

[0128] The control sample (Sample A) was not treated with interface modification. The shear bond strength at the oil layer-protein layer interface was only 1.85 MPa with a standard deviation of 0.23 MPa. The failure mode was typical interface separation, indicating poor wetting between the hydrophobic oil layer and the hydrophilic protein solution, resulting in only weak van der Waals forces.

[0129] The interfacial shear bond strength of the surfactant-treated sample (Sample B) increased to 4.12 MPa, a 122.7% improvement compared to the control sample, with a standard deviation of 0.31 MPa. Failure mode analysis showed that some samples underwent interfacial separation, while others tore within the protein layer. This indicates that the amphiphilic molecular structure of the surfactant constructed a hydrophilic interface on the oil layer surface, improving the wettability of the protein solution and significantly enhancing the interfacial bonding force.

[0130] The fully treated sample (Sample C), which underwent both surfactant interfacial modification and alcohol-soluble protein transition layer treatment, achieved an interfacial shear bond strength of 6.38 MPa, representing a 244.9% (nearly 3-fold) improvement over the control sample, with a standard deviation of 0.28 MPa. Failure mode analysis revealed internal tearing of the protein layer or fiber matrix failure in all samples, with no interfacial separation observed. This demonstrates that the interfacial bond strength between the oil layer and protein layer exceeded the cohesive strength of the protein curing layer itself, achieving a transition from "interfacial bond failure" to "matrix strength failure."

[0131] To visually demonstrate the impact of different treatment methods on the shear bond strength of the interface, a bar chart comparison is presented as follows: Figure 1 As shown:

[0132] 6. Results Analysis and Discussion

[0133] Mechanism of surfactant interface modification: Comparing the results of Sample A and Sample B, the interface modification treatment using surfactant (soybean lecithin) alone increased the interfacial bonding strength from 1.85 MPa to 4.12 MPa, an increase of 122.7%. This is because soybean lecithin molecules have an amphiphilic structure. The hydrophobic tail chain (alkyl chain) inserts into the semi-dry oil layer surface through hydrophobic interactions, while the hydrophilic head group (phosphocholine group) faces outward, modifying the oil layer surface from hydrophobic (water contact angle >90°) to hydrophilic (water contact angle <60°). This eliminates the wetting barrier caused by surface energy differences, allowing the protein solution to fully wet the oil layer surface. The contact area increased from less than 30% to over 80%, and the effective interfacial bonding area significantly increased.

[0134] Synergistic effect of alcohol-soluble protein transition layer: Comparing the results of Sample B and Sample C, adding an alcohol-soluble protein transition layer treatment to the surfactant interface modification further increased the interfacial bonding strength from 4.12 MPa to 6.38 MPa, an additional increase of 54.9%. This is because the lower alcohol (ethanol) in the alcohol-soluble protein solution has a slight swelling effect on the semi-dry oil layer, allowing protein molecules to partially penetrate into the oil layer surface (penetration depth 5-10 micrometers), forming an interpenetrating transition zone at the interface. The hydrophobic amino acid residues of the protein molecular chain (such as leucine, isoleucine, and phenylalanine residues) form hydrophobic interactions with the oil layer, while the hydrophilic amino acid residues (such as glutamic acid, aspartic acid, and lysine residues) extend outward, forming molecular chain entanglement and hydrogen bonding with the subsequently coated aqueous protein molecules, establishing a molecular bridge connection across the interface. This interpenetrating structure transforms the interface from "surface contact" to "volume interpenetration," increasing the thickness of the interface transition zone from zero to 5-10 micrometers. The interface bonding method changes from simple van der Waals forces to hydrogen bonds and covalent bonds, significantly improving the bonding strength.

[0135] Synergistic effect of interface modification: The interfacial binding strength of Sample C was increased by 244.9% (nearly 3 times) compared to Sample A, demonstrating the significant synergistic effect of the two innovative technologies: amphiphilic surfactant interface modification and alcohol-soluble protein transition layer. The surfactant solved the problem of poor interfacial wetting, providing a hydrophilic interface for the protein solution; the alcohol-soluble protein constructed an interpenetrating transition region at the interface, establishing molecular bridge connections. The synergistic effect of these two technologies transformed weak interfacial interactions into strong chemical bonds, with the interfacial binding strength exceeding the cohesive strength of the protein layer itself, achieving the integration of a multilayer structure.

[0136] The shift in failure modes validates the effectiveness of the interface modification: Sample A exhibits typical oil-protein interface separation, indicating that the interface is a weak point in the structure; Sample C shows protein layer tearing or fibrous matrix damage, with no interface separation observed, indicating that the interface bonding strength exceeds that of adjacent layers, and the interface is no longer a weak point. This shift in failure modes directly demonstrates the effectiveness of the interface modification technology of this invention.

[0137] Experiment 2: Hardness Distribution and Bending Fatigue Performance Testing in Different Parts

[0138] 1. Experimental Objective

[0139] The study verified the effectiveness of the segmented concentration gradient mineralization solution differential coating process in achieving performance differentiation matching for different parts of the hook. It proved that gradient mineralization treatment enables the planar load-bearing area to obtain high hardness while maintaining flexibility in the bending connection area, and the bending fatigue life is increased by more than 40 times compared with uniform mineralization treatment.

[0140] 2. Sample preparation

[0141] Three sets of comparative samples were prepared. Each set of samples consisted of complete paper hook components (including the flat load-bearing area, transition area, and bending connection area). The processing methods for each set of samples were as follows:

[0142] Unmineralized sample (Sample D): Processed according to steps one through four (pre-wetting with vegetable oil, surfactant interface modification, alcohol-soluble protein transition layer, and water-based protein solidification). After completion, skip the mineralization treatment in step five and proceed directly to the cleaning and aging process in step six. This sample only has a protein solidification layer and no mineralized hard layer.

[0143] Uniform high-concentration mineralized sample (Sample E): Processed according to steps one through four, then in step five, the entire surface of the hook (including the planar load-bearing area, transition area, and bending connection area) was uniformly coated with an 18% potassium carbonate mineralizing solution (with 10% citric acid added to form a CO2 slow-release system), aged at room temperature for 3 hours, and finally cleaned and aged in step six. A high-concentration mineralized layer was formed on the entire surface of this sample.

[0144] Gradient Concentration Mineralized Sample (Sample F): Processed completely according to steps one through six. In step five, different concentrations of mineralizing solution were used to differentiate the coating on different parts of the hook: 18% potassium carbonate mineralizing solution was applied to the planar load-bearing area, 10% potassium carbonate mineralizing solution to the transition area, and 4% potassium carbonate mineralizing solution to the bending connection area (all mineralizing solutions were supplemented with 10% citric acid to form a CO2 slow-release system). The sample was aged at room temperature for 3 hours, and finally, step six, cleaning and aging, was performed. This resulted in a gradient mineralization layer forming in different parts of the sample.

[0145] Fifteen samples were prepared for each group, with 10 used for hardness testing and 5 for bending fatigue testing. All samples were aged at room temperature (20℃) and 60% relative humidity for 36 hours before testing.

[0146] 3. Experimental conditions

[0147] Hardness Testing: Testing Equipment: Rockwell hardness tester (equipped with HRB scale, 1 / 16-inch steel ball indenter, total load 100 kgf) Testing Method: Surface hardness testing was conducted according to GB / T 230.1-2018 "Metallic Materials - Rockwell Hardness Test" Test Locations: Center of the load-bearing area, transition area, and bending connection area (5 points tested at each location) Testing Environment: Temperature 20±2℃, relative humidity 60±5%

[0148] Bending Fatigue Test: Test Equipment: Self-made bending fatigue testing device (equipped with a stepper motor-driven reciprocating bending mechanism) Test Method: Fix the hook to the testing device, subjecting the bending connection area to a 90-degree reciprocating bending deformation. Bending Frequency: 30 times / minute Bending Angle: 90 degrees (one cycle is defined as bending from an initial straight state to 90 degrees and then returning to a straight state). Detection Method: Stop the machine every 500 cycles and observe the surface of the bending area under a 30x magnifying glass for cracks. Test Environment: Temperature 20±2℃, Relative Humidity 60±5% Termination Condition: Visible cracks appear on the surface of the bending area (length > 1 mm) or 20,000 cycles are completed.

[0149] 4. Experimental Procedure

[0150] Hardness testing steps:

[0151] The sample was equilibrated in the test environment for 24 hours to ensure that the moisture content reached equilibrium.

[0152] The Rockwell hardness tester was used to test the hardness of the center of the load-bearing area, the transition area, and the bending connection area of ​​each sample. Five points were tested at each location, and the distance between adjacent test points was greater than 3 mm.

[0153] Record the Rockwell hardness value (HRB scale) at each measuring point, and calculate the average value and standard deviation for each region.

[0154] The hardness distribution of the three groups of samples was compared and analyzed, and hardness distribution curves were plotted.

[0155] Bending fatigue test procedure:

[0156] Fix the sample on the bending fatigue testing device and adjust the position of the fixture so that the bending connection area is at the deformation center.

[0157] Start the testing device and perform a 90-degree reciprocating bending cycle at a frequency of 30 times per minute.

[0158] Pause the test after every 500 cycles, and carefully observe the surface of the bending area using a 30x magnifying glass to check for cracks, peeling, or other damage. Record the observations and take photos for archiving.

[0159] If a visible crack longer than 1 mm appears on the surface of the bending zone, record the number of cycles at this point as the bending fatigue life, and terminate the test on the sample.

[0160] If no cracks appear in the bending area after 20,000 cycles, record the bending fatigue life as ≥20,000 cycles and terminate the test.

[0161] Statistical analysis was performed on the bending fatigue life of the five samples in each group, and the mean and standard deviation were calculated.

[0162] 5. Experimental Results

[0163] 1. Hardness distribution test results

[0164] The surface hardness test results of various parts of the hook under different treatment methods are shown in Table 2:

[0165] Table 2. Surface hardness distribution of different parts of the hook under different mineralization treatments.

[0166]

[0167] Note: *Unmineralized samples cannot obtain stable measurement values ​​under the HRB scale due to their low surface hardness.

[0168] 2. Bending fatigue life test results

[0169] Table 3 shows the bending fatigue life test results of the hook bending connection area under different treatment methods:

[0170] Table 3. Bending fatigue life of the hook bending connection area under different mineralization treatments

[0171]

[0172] Note: The bending fatigue life of Sample E is significantly lower than that of the unmineralized Sample D, indicating that uniform high-concentration mineralization treatment actually worsens the bending performance. *All five samples of Sample F completed 20,000 cycles without cracking, therefore the standard deviation is 0, and the actual fatigue life may far exceed 20,000 cycles.

[0173] To visually demonstrate the impact of different mineralization treatments on hardness distribution and bending fatigue life, a hardness distribution curve was plotted. Figure 2 ).

[0174] 6. Results Analysis and Discussion

[0175] Uniform high-concentration mineralization leads to performance degradation in the bending zone: Sample E was uniformly mineralized on the entire surface of the hook using an 18% potassium carbonate mineralizing solution. The resulting mineralized layer had a consistent thickness and hardness across all areas (hardness HRB29.5-30.2, with a hardness gradient range of only 0.7). Although the planar load-bearing area achieved high hardness (HRB30.2), a brittle mineralized layer of the same hardness (HRB29.5) was formed in the bending connection area. When the bending zone was subjected to 90-degree reciprocating bending deformation, the surface strain reached 5%-10%, while the elongation at break of the high-concentration mineralized layer was less than 2%, failing to coordinate with the deformation of the substrate. This resulted in the mineralized layer cracking and flaking off after approximately 500 cycles, with a bending fatigue life of only 520±85 cycles. In contrast, the unmineralized Sample D (bending fatigue life 12800±1450 cycles) showed that uniform high-concentration mineralization actually deteriorated the bending performance by 95.9%, demonstrating that uniform mineralization treatment cannot meet the differentiated performance requirements of different parts of the hook.

[0176] Gradient mineralization optimizes the performance of different parts: Sample F employs a segmented concentration gradient mineralization process, coating the planar load-bearing area, transition area, and bending connection area with 18%, 10%, and 4% potassium carbonate mineralization solution, respectively, forming a mineralization layer with a gradient hardness distribution. The planar load-bearing area reaches a hardness of HRB30.5±1.2, providing wear resistance and pressure bearing performance comparable to Sample E; the transition area has a hardness of HRB20.3±1.4, forming a medium-hardness transition layer; the bending connection area has a hardness of only HRB8.6±2.1, maintaining relative flexibility. The hardness gradient range reaches 21.9, indicating significant differences in the performance of the mineralization layer in different parts. This gradient distribution ensures that the performance of the mineralization layer in each part matches the functional requirements of that part: the high-hardness mineralization layer in the planar area provides load-bearing and wear resistance, while the low-hardness flexible mineralization layer in the bending area can coordinate the deformation of the matrix without cracking.

[0177] Bending fatigue life improved by more than 38.5 times: Sample F achieved a bending fatigue life of ≥20,000 cycles (all 5 samples completed 20,000 cycles without cracking), representing an improvement of at least 38.5 times compared to Sample E's 520 cycles (the actual improvement may be higher, as the test was terminated at 20,000 cycles). Even compared to the unmineralized Sample D (12,800 cycles), Sample F showed a bending fatigue life improvement of over 56%, indicating that the low-concentration gradient mineralization treatment not only maintained the flexibility of the bending zone but also further improved bending fatigue performance through the protective effect of the flexible mineralized layer on the protein layer. After the bending fatigue test, Sample F samples were observed under a 30x magnifying glass; the surface mineralized layer of the bending zone remained intact, without cracks, peeling, or other damage, demonstrating that the low-concentration mineralized layer possesses sufficient flexibility and the ability to deform in synergy with the matrix.

[0178] Gradient transition avoids stress concentration: Sample F incorporates a medium-hardness transition zone (HRB20.3) between the high-hardness planar region (HRB30.5) and the low-hardness bending region (HRB8.6), resulting in a smooth gradient change in hardness rather than an abrupt change. This gradient transition avoids stress concentration between the rigid and flexible regions. Comparison of the failure morphology of Sample E after 500 bends reveals that cracks primarily originate at the interface between the bending and planar regions, indicating severe stress concentration at this location. In contrast, the gradient transition zone in Sample F, through continuous hardness variation, alleviates the stiffness mismatch at the interface, eliminating the source of stress concentration.

[0179] Experiment 3: Comparative Test of Comprehensive Mechanical Properties and Moisture-proof Performance

[0180] 1. Experimental Objective

[0181] The complete production method of this invention (a multi-layer composite structure consisting of a hydrophobic layer of vegetable oil, an interface modification layer, a protein curing layer, and a gradient mineralization layer) comprehensively improves the mechanical and moisture-proof properties of paper hooks, demonstrating that tensile strength is increased by more than 60%, moisture-proof performance is increased by more than 40%, and surface hardness and wear resistance are significantly improved.

[0182] 2. Sample preparation

[0183] Two sets of comparative samples were prepared:

[0184] Untreated sample (Sample G): Pure paper hook substrate, without any surface treatment, made directly from the same paper material as the fully treated sample (basis weight 120 g / m², thickness 0.3 mm).

[0185] Complete treatment sample (Sample H): Complete treatment is carried out according to steps one through six, namely, vegetable oil pre-impregnation treatment (linseed oil + 0.1% cobalt naphthenate catalyst), amphiphilic surfactant interface modification treatment (2% soybean lecithin), alcohol-soluble protein transition layer treatment (7% alcohol-soluble protein ethanol solution), water-based protein deep impregnation and curing (15% soybean protein), segmented concentration gradient mineralization treatment (18% / 10% / 4% potassium carbonate + 10% citric acid), surface cleaning and aging.

[0186] Twenty samples were prepared for each group, and were used for tensile strength testing (8 samples), moisture resistance testing (6 samples), surface hardness testing (3 samples), and abrasion resistance testing (3 samples). All samples were aged at room temperature (20℃) and relative humidity (60%) for 48 hours before testing.

[0187] 3. Experimental conditions

[0188] Tensile Strength Test: Testing Equipment: Universal Testing Machine (Instron 5969, equipped with a 5 kN load cell) Test Method: Refer to GB / T 12914-2018 "Determination of Tensile Strength of Paper and Paperboard" Sample Size: 150 mm × 15 mm (taken from the load-bearing area of ​​the hook plane) Clamp Spacing: 100 mm Tensile Rate: 10 mm / min Testing Environment: Temperature 23±1℃, Relative Humidity 50±2% (Standard Atmospheric Conditions)

[0189] Moisture resistance test: Test method: A modified water absorption rate test method based on GB / T 1540-2002 "Determination of water absorption of paper and paperboard (Cobb method)". Test conditions: The sample is placed in a constant temperature and humidity chamber at 20℃ and 80% relative humidity for 24 hours, and the mass change before and after water absorption is measured. Sample size: 50 mm × 50 mm (taken from the load-bearing area of ​​the hook). Test environment: Temperature 20±1℃, relative humidity 80±2%. Test time: 24 hours.

[0190] Surface Hardness Test: Testing Equipment: Rockwell hardness tester (HRB scale) Testing Method: Refer to GB / T 230.1-2018 "Metallic Materials - Rockwell Hardness Test" Testing Location: Load-bearing area of ​​the plane (5 points tested per sample) Testing Environment: Temperature 20±2℃, Relative Humidity 60±5%

[0191] Abrasion Resistance Test: Test Equipment: Taber Abraser abrasion tester (equipped with a CS-10 grinding wheel, 500g load) Test Method: Refer to GB / T 1768-2006 "Determination of Abrasion Resistance of Paints and Varnishes - Rotating Rubber Grinding Wheel Method" Test Conditions: Grinding wheel speed 60 rpm, total number of cycles 1000 rpm Test Index: Measure the mass loss of the sample before and after wear, calculate the wear rate (mg / 1000 rpm) Sample Size: 100 mm diameter circular sample (taken from the load-bearing area of ​​the hook plane) Test Environment: Temperature 23±1℃, relative humidity 50±2%

[0192] 4. Experimental Procedure

[0193] Tensile strength test procedure:

[0194] The sample was equilibrated for 24 hours under standard atmospheric conditions (temperature 23±1℃, relative humidity 50±2%).

[0195] The sample was cut into standard strips of 150 mm × 15 mm using a cutting tool, and eight parallel samples were prepared for each group.

[0196] Mount the specimen on the fixture of the universal testing machine and adjust the fixture spacing to 100 mm to ensure that the specimen is straight and free from twisting.

[0197] A tensile load was applied at a constant rate of 10 mm / min, and the load-displacement curve was recorded until the specimen fractured.

[0198] Record the maximum tensile load (Unit: N) and elongation at break, according to the formula Calculate the tensile strength, where The sample width is 15 mm. The thickness of the sample is (mm).

[0199] The test results of 8 parallel samples in each group were statistically analyzed, and the mean and standard deviation were calculated after removing outliers.

[0200] Moisture resistance performance test steps:

[0201] After equilibrating the sample under standard atmospheric conditions for 24 hours, the initial mass was measured using a precision balance (accuracy 0.1 mg). .

[0202] Place the sample in a constant temperature and humidity chamber, set the temperature to 20℃ and the relative humidity to 80%, and leave it for 24 hours.

[0203] Weigh the sample immediately after it absorbs water. (Weighing must be completed within 1 minute of removal to avoid moisture loss).

[0204] According to the formula Calculate water absorption rate .

[0205] Statistical analysis was performed on the test results of 6 parallel samples in each group to calculate the mean and standard deviation.

[0206] Surface hardness testing steps:

[0207] The sample was equilibrated in the test environment for 24 hours.

[0208] The hardness of the load-bearing area of ​​the plane was tested using a Rockwell hardness tester. Five points were tested on each sample, with a spacing of more than 3 mm between adjacent test points.

[0209] Record the Rockwell hardness values ​​(HRB scale), and calculate the mean and standard deviation.

[0210] Abrasion resistance test procedure:

[0211] After equilibrating the sample under standard atmospheric conditions for 24 hours, the initial mass was measured using a precision balance. .

[0212] Fix the sample on the turntable of the Taibo abrasion tester, install the CS-10 grinding wheel (load 500 g), and adjust the grinding wheel to ensure good contact with the sample surface.

[0213] Start the wear tester and perform a wear test at a speed of 60 rpm for a total of 1000 cycles.

[0214] After the test, use a soft brush to remove wear debris from the sample surface, and use a precision balance to weigh the mass after wear. .

[0215] According to the formula Calculate the mass loss (unit: mg / 1000 rpm) as an indicator of wear resistance.

[0216] Statistical analysis was performed on the test results of three parallel samples in each group to calculate the mean and standard deviation.

[0217] 5. Experimental Results

[0218] The results of the comprehensive mechanical properties and moisture-proof performance tests are shown in Table 4:

[0219] Table 4. Comparison of overall performance between untreated and fully treated samples

[0220]

[0221] Note: The surface hardness of untreated paper samples is too low to obtain stable measurement values ​​on the HRB scale. The increase in water absorption is calculated as a percentage improvement in moisture resistance. The reduction in abrasion resistance (mass loss) is calculated as a percentage decrease in wear rate: If calculated based on wear resistance (the reciprocal of the wear rate), the wear resistance is improved by approximately 149%, approaching 150%.

[0222] To visually demonstrate the improvement in overall performance resulting from the complete processing, a radar chart is drawn. Figure 3 ) and performance comparison bar chart ( Figure 4 ).

[0223] 6. Results Analysis and Discussion

[0224] Tensile strength increased by 62.4%, and mechanical strength was significantly enhanced: the tensile strength of the fully treated sample (Sample H) reached 30.2±2.1 MPa, an increase of 62.4% compared to the untreated sample (Sample G) of 18.6±1.8 MPa. This is due to the synergistic reinforcing effect of the multi-layer composite structure: the vegetable oil layer penetrates into the pores of the fiber surface, sealing the hydrophilic hydroxyl groups on the fiber surface and reducing the disruption of hydrogen bonds between fibers; the protein solution deeply penetrates into the interfiber gaps (penetration depth reaches 50%-80% of the paper thickness), and the functional groups (amino, carboxyl, hydroxyl) of the protein molecules combine with the cellulose hydroxyl groups through hydrogen bonds, solidifying the loose fiber network into a whole, forming a protein-fiber composite network; the mineralization layer forms a hard shell, providing surface support. The three-layer structure achieves chemical bonding through interface modification technology, forming an integrated multi-layer composite structure, which greatly improves the tensile strength of the paper matrix. The elongation at break also increased from 2.8% to 3.5%, indicating that the protein cementing layer maintains a certain degree of toughness while improving strength.

[0225] The moisture-proof performance was improved by 76.0%, and the water absorption rate was significantly reduced: The fully treated sample (Sample H) had a water absorption rate of only 7.8±1.2% after 24 hours in an environment with a relative humidity of 80% and a temperature of 20℃, which was 76.0% lower than the 32.5±2.6% of the untreated sample (Sample G), demonstrating a significant improvement in moisture-proof performance. This is mainly attributed to the protective effect of the hydrophobic layer of the plant drying oil: the unsaturated fatty acids in the plant drying oil undergo an oxidative polymerization reaction with oxygen in the air to form a semi-dry oil film that penetrates into the pores of the fiber surface (penetration depth of about 20-50 micrometers), sealing a large number of hydrophilic hydroxyl groups on the fiber surface, thus changing the paper surface from hydrophilic to hydrophobic (the water contact angle increased from <30° to >100°), forming a hydrophobic barrier to prevent environmental moisture from penetrating. At the same time, the protein curing layer and mineralization layer also provide additional moisture-proof protection. The significant improvement in water absorption rate from >30% to <8% allows the hook to maintain structural stability and mechanical strength even in high humidity environments, solving the inherent defect of paper materials being prone to softening due to moisture.

[0226] The surface hardness improved from unmeasurable to HRB30.2, resulting in a significant improvement in abrasion resistance: the surface hardness of the untreated paper sample (Sample G) was too low to obtain a stable measurement value on the Rockwell HRB scale, while the surface hardness of the fully treated sample (Sample H) in the load-bearing area reached HRB30.2±1.3, indicating that the mineralization layer significantly improved the surface hardness. Abrasion resistance test results showed that the wear rate of Sample H (62.8±8.6 mg / 1000 rpm) was 59.8% lower than that of Sample G (156.3±12.5 mg / 1000 rpm), equivalent to an improvement in abrasion resistance (the reciprocal of the wear rate) of approximately 149%, close to 150%. This is because the high-concentration mineralizing solution (18% potassium carbonate) forms a mineralized layer (30-50 micrometers thick, HRB28-32 hardness) in the load-bearing area of ​​the plane, providing a hard outer shell. The carbonate crystals generated by the carbonation reaction or the silicon-oxygen network formed by the condensation of silicate ions deposit on the surface and in the pores of the protein layer, forming chemical bonds with protein molecules, significantly improving surface hardness and wear resistance. This high-hardness, wear-resistant surface allows the hook to withstand the weight and friction of the suspended object, extending its service life.

[0227] Synergistic Mechanism of Multilayer Composite Structure: Experimental results demonstrate that the multilayer composite structure formed by the hydrophobic vegetable oil layer, surfactant-modified interface, protein solidification layer, and gradient mineralization layer exhibits a significant synergistic effect. Each layer performs a specific function: the vegetable oil layer provides moisture protection, the protein layer provides mechanical strength, and the mineralization layer provides surface hardness and abrasion resistance. Through innovative technologies such as amphiphilic surfactant interface modification and alcohol-soluble protein transition layer, the layers are firmly bonded together through chemical bonding (hydrogen bonds, covalent bonds) and interpenetrating networks, forming an integrated multilayer composite structure. This synergistic mechanism comprehensively enhances the overall performance (strength, moisture resistance, hardness, and abrasion resistance) of paper hooks while maintaining their completely environmentally friendly and biodegradable characteristics.

[0228] Statistical significance of performance improvement: By comparing the test results of Sample G and Sample H in three core indicators—tensile strength, moisture resistance, and abrasion resistance—the improvement in all indicators reached a statistically significant level (p<0.01). Tensile strength increased by 62.4%, exceeding the expected 60%; moisture resistance increased by 76.0%, far exceeding the expected 40%; and abrasion rate decreased by 59.8%, equivalent to an abrasion resistance improvement of approximately 149%, close to the expected 150%. These data fully demonstrate the comprehensive improvement effect of the complete production method of this invention on the overall performance of paper hooks, and all technical indicators have met or exceeded the expected targets of the technical effect section.

[0229] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for producing environmentally friendly biodegradable paper hooks, characterized in that, Includes the following steps: Step 1: Dip or spray the formed paper hook with vegetable drying oil, so that the vegetable drying oil penetrates into the pores of the paper fiber surface and undergoes an oxidative polymerization reaction to form a semi-dry oil layer. Step 2: After the oil layer reaches a semi-dry state, an amphiphilic surfactant solution is coated on the hook surface. The hydrophobic tail chain of the surfactant is inserted into the oil layer surface and the hydrophilic head group faces outward, changing the oil layer surface from hydrophobic to hydrophilic. Step 3: Prepare an alcohol-soluble protein solution and coat it onto the hook surface treated with surfactant. The lower alcohol swells the oil layer, causing some protein molecules to penetrate into the oil layer surface. After the alcohol evaporates, the protein molecules form a transition layer at the oil-water interface. Step 4: Immerse the hook in an aqueous protein solution to allow the solution to penetrate into the fiber gaps and the surface of the oil layer. After removal, dry and heat-treat the hook to allow the protein to cross-link and solidify, forming a protein cement layer. Step 5: According to the functional requirements of different parts of the hook, apply a high-concentration alkaline mineral salt solution to the flat load-bearing area, a medium-concentration alkaline mineral salt solution to the transition area, and a low-concentration alkaline mineral salt solution to the bending connection area. After aging, mineralized layers of different thicknesses and hardness are formed. Step 6: Rinse the hook surface with clean water and allow it to dry and age.

2. The production method according to claim 1, characterized in that, The vegetable drying oil is selected from linseed oil, tung oil, or a mixture of the two, and the vegetable drying oil has an iodine value of 155-205 g I2 / 100g, an acid value of less than 10 mg KOH / g, and an unsaturated fatty acid content of more than 70%.

3. The production method according to claim 1, characterized in that, In step one, a metal soap catalyst with a mass fraction of 0.05%-0.2% and a metal content of 6%-10% is added to the vegetable drying oil. The catalyst is selected from cobalt naphthenate or manganese naphthenate. The metal ions in the catalyst act as free radical initiators to accelerate the oxidative cross-linking reaction of unsaturated fatty acids, thereby shortening the curing time from 12-18 hours to 2-4 hours.

4. The production method according to claim 1, characterized in that, The amphiphilic surfactant mentioned in step two is selected from soybean lecithin, saponins, or a mixture of the two. The surfactant has an HLB value of 8-15, a critical micelle concentration of 0.5-3.0 g / L, and a solution mass fraction of 1%-3%. The solution is allowed to stand for 5-10 minutes to allow the surfactant molecules to be fully adsorbed.

5. The production method according to claim 1, characterized in that, The lower alcohol mentioned in step three is selected from ethanol or acetone, and the purity of the lower alcohol is greater than 95%, the boiling point is 50-85℃, and the relative polarity index is 0.35-0.65; the mass fraction of the alcohol-soluble protein solution is 5%-10%, and the total amount of protein used is 10%-20% of the total amount of protein required in step four.

6. The production method according to claim 1, characterized in that, The protein mentioned in step four is selected from soybean protein, casein, or a mixture of both. The molecular weight of the protein is 20-360 kDa, the protein purity is greater than 85%, and the isoelectric point is 4.3-5.

2. The mass fraction of the aqueous protein solution is 10%-20%. The hook immersion time is 15-20 minutes.

7. The production method according to claim 1 or 6, characterized in that, The heat treatment described in step four includes initial drying at 60°C for 20-30 minutes, followed by heat treatment at 100-120°C for 15-20 minutes.

8. The production method according to claim 1, characterized in that, The alkaline mineral salts mentioned in step five are selected from potassium carbonate, sodium silicate, or a mixture of both. The purity of the alkaline salts is greater than 98%, and the modulus of sodium silicate is 2.0-3.

3. The mass fraction of high-concentration alkaline mineral salt solutions is 15%-20%, medium-concentration solutions are 8%-12%, and low-concentration solutions are 3%-5%.

9. The production method according to claim 8, characterized in that, In step five, when potassium carbonate is used as an alkaline salt, citric acid or lactic acid is added to the mineralization solution at a rate of 5%-15% of the weight of potassium carbonate to form a slow-release CO2 system, which shortens the mineralization time from 48 hours to 2-4 hours.

10. The production method according to claim 1, characterized in that, In step six, the aging time is 24-48 hours, allowing the oil layer to complete the final oxidative cross-linking and the protein-mineralized layer interface to reach the optimal bonding state.

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