Biomass-based degradable leather and preparation process thereof

Abstract

This invention relates to a biomass-based biodegradable leather and its preparation process, belonging to the field of environmentally friendly polymer composite materials technology. The leather composition includes: 30-60 parts biodegradable polyester, 15-30 parts surface-modified natural fibers, 5-15 parts castor oil-based silanized fatliquoring agent, 3-10 parts bio-based plasticizer, 5-20 parts biomass filler, 1-5 parts bio-based crosslinking agent, 0.5-3 parts foaming agent, 0.5-2 parts lubricant, and 0-3 parts functional additives. The key to this invention lies in: using a castor oil-based silanized fatliquoring agent with hydrolyzable siloxane groups at the ends to form covalent bonds with the fibers; utilizing a citric acid-polyol bio-based crosslinking agent to construct a three-dimensional network structure; and forming uniform micropores through a pressure-relief foaming process. The resulting product possesses excellent mechanical properties, a soft and breathable feel, and complete biodegradability, solving the problems of weak interfacial bonding and insufficient performance in existing bio-based leather materials.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly polymer composite materials technology, and in particular to a biomass-based biodegradable leather and its preparation process. Background Technology

[0002] With increasing global environmental awareness, the leather, textile, and polymer materials industries are facing immense pressure to reduce environmental pollution and resource consumption. Traditional animal leather production involves complex tanning processes that can generate heavy metals and organic pollutants; while widely used petroleum-based synthetic leathers such as polyurethane (PU) and polyvinyl chloride (PVC), due to their non-biodegradable nature, easily cause long-term "white pollution" after disposal. Therefore, developing leather materials based on renewable resources and capable of being environmentally decomposed harmlessly at the end of their service life has become an important development direction in this field.

[0003] Currently, using bio-based biodegradable polymers such as polylactic acid (PLA) and polybutylene succinate (PBS) as matrices and filling them with natural fibers such as bamboo powder, coffee grounds, and wood flour is one of the mainstream technical routes for preparing environmentally friendly leather materials. However, this technology still faces several key bottlenecks in practical applications: First, commonly used bio-based polymers such as PLA are inherently brittle and have poor toughness, resulting in insufficient flexibility in the final material, making it difficult to meet the requirements of leather products for a soft feel and wrinkle resistance. Second, the surface of natural fibers is rich in hydrophilic hydroxyl groups, which have poor interfacial compatibility with hydrophobic biodegradable polyesters, resulting in weak interfacial bonding. This not only leads to low stress transfer efficiency and limits the reinforcing effect of the fibers, but also makes the composite material prone to interfacial debonding under external forces, manifesting as low tear strength and poor durability.

[0004] To improve material flexibility, existing technologies often add plasticizers or attempt to use vegetable oil derivatives as fatliquoring agents. However, conventional plasticizers may have problems with migration or insufficient biodegradability, while many vegetable oil-based fatliquoring agents bind to the fiber matrix primarily through physical adsorption, resulting in weak binding forces, easy volatility, or migration. This leads to short-lasting fatliquoring effects, causing the material to harden and become brittle after use or storage. Furthermore, some existing fully bio-based leather materials often focus on biodegradability alone, while falling short in mimicking the unique microstructure, breathability, and overall mechanical properties of natural leather, thus limiting their application in high-value fields.

[0005] Therefore, there is an urgent need for an innovative solution that can synergistically optimize multiple aspects such as molecular design, composite material interface control, and molding process to develop a new type of leather alternative material that combines excellent mechanical properties, a soft and breathable feel, long-lasting performance, and complete biodegradability. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a biomass-based biodegradable leather and its preparation process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a biomass-based biodegradable leather, which, by weight, is made of the following components: 30-60 parts of biodegradable polyester, 15-30 parts of surface-modified natural fiber, 5-15 parts of castor oil-based silanized fatliquoring agent, 3-10 parts of bio-based plasticizer, 5-20 parts of biomass filler, 1-5 parts of bio-based crosslinking agent, 0.5-3 parts of foaming agent, 0.5-2 parts of lubricant, and 0-3 parts of functional additives. The biomass-based biodegradable leather is biodegradable under natural environment or industrial composting conditions.

[0009] Preferably, the biodegradable polyester is at least one of polylactic acid (PLA), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), and polybutylene adipate terephthalate (PBAT).

[0010] Preferably, the natural fiber is at least one of bamboo powder, wood powder, coffee grounds, and straw powder, with a particle size of 100-300 mesh. Before use, it needs to be surface modified with a silane coupling agent (such as KH-550) ethanol solution and fully dried to reduce its surface polarity and improve its compatibility with biodegradable polyester.

[0011] Preferably, the bio-based plasticizer is a citrate plasticizer, such as acetylated tributyl citrate (ATBC) or tributyl citrate (TBC), which can effectively reduce processing temperature, improve material brittleness, and is non-toxic and biodegradable.

[0012] Preferably, the biomass filler is at least one of microcrystalline cellulose, lignocellulose nanofibers, straw powder or cork powder, with a particle size of 100-400 mesh, and mainly serves to enhance strength, reduce cost, improve dimensional stability and provide fibrous texture.

[0013] Preferably, the bio-based crosslinking agent is composed of a polycarboxylic acid and a polyol in a molar ratio of 1:0.8-1.2, wherein the polycarboxylic acid is citric acid and the polyol is glycerol or sorbitol. At high temperatures during processing, the carboxyl groups of citric acid and the hydroxyl groups of the polyol undergo an esterification condensation reaction, which can form a crosslinking network between polymer molecular chains. This crosslinking network can significantly improve the strength, heat resistance and water resistance of the material, and all components are biodegradable.

[0014] Preferably, the foaming agent is sodium bicarbonate, which decomposes to produce carbon dioxide gas when heated during processing, forming a uniform microporous structure inside the material, giving the finished product lightweight, soft, and breathable and moisture-permeable properties.

[0015] Preferably, the lubricant is epoxidized soybean oil, used to improve processing fluidity.

[0016] Preferably, the functional additives include at least one of the following: hydrolysis-resistant stabilizers (such as carbodiimides), antioxidants (such as hindered phenolic antioxidant 1010), light stabilizers (such as nano titanium dioxide), and antibacterial and antifungal agents (such as vanillin and nano zinc oxide).

[0017] Preferably, the castor oil-based silanized fatliquoring agent is synthesized from castor oil through a three-step reaction: First, castor oil is esterified with maleic anhydride to generate maleic anhydride-modified castor oil (MACO) intermediate; second, MACO reacts with malic acid to introduce additional carboxyl groups into the molecular chain, generating functionalized castor oil ester; finally, the functionalized castor oil ester undergoes a grafting reaction with a silane coupling agent (such as KH-550) to obtain a castor oil-based silanized fatliquoring agent with hydrolyzable siloxane groups at the end.

[0018] The method for preparing the castor oil-based silanized fatliquoring agent is as follows:

[0019] Step 1. Dehydrate castor oil under reduced pressure at 100-105°C for 1.5-2.5 hours until no bubbles are generated. Cool to 50-60°C for later use. Dry malic acid and KH-550 in 4A molecular sieve for one day. Add castor oil and toluene to a three-necked flask (castor oil to toluene ratio 1g:1-2ml). Heat to 75-85°C at 400-600 rpm. Add maleic anhydride to the flask all at once, add catalyst, and slowly raise the temperature to 110-115°C. Stir and react at this temperature for 4-5 hours. During the reaction, remove water using a water separator. After the reaction is complete, lower the system temperature to 60-70°C and recover toluene by vacuum distillation to obtain the MACO intermediate. The reaction process is as follows:

[0020] ;

[0021] The secondary hydroxyl group on castor oil serves as a key reaction site. Under the action of the catalyst stannous octoate, the tin ion coordinates with a carbonyl oxygen of maleic anhydride, thereby significantly polarizing and activating the anhydride group. Subsequently, the secondary hydroxyl group on castor oil acts as a nucleophile, attacking the activated maleic anhydride carbonyl carbon with a partial positive charge, forming a new CO bond and causing the five-membered ring of the anhydride to open. The intermediate formed after ring opening undergoes proton transfer, and its carboxylate structure is transformed into a free carboxyl group, ultimately generating maleic acid monoesterified castor oil. This product successfully introduces a new ester bond, a reactive carbon-carbon double bond, and a highly polar carboxyl group into the castor oil skeleton.

[0022] Step 2. Add malic acid, catalyst, and toluene to the MACO intermediate obtained in Step 1. Heat to 90-95°C at 400-600 rpm and stir for 3-4 hours. During the reaction, remove water using a water separator. After the reaction, cool to 60-70°C and recover toluene by vacuum distillation. Then wash 1-2 times with 50-60°C warm water to remove residual catalyst and unreacted malic acid. Finally, dehydrate under vacuum at 100-110°C for 1-2 hours to obtain functionalized castor oil ester (F-CO-MA). The reaction process is as follows:

[0023] ;

[0024] The free carboxyl group of the terminal maleyl group of the first-step product MACO acts as an electrophilic center and undergoes a classic acid-alcohol esterification reaction with the secondary hydroxyl group of malic acid. Under the action of a catalyst (p-toluenesulfonic acid), the terminal carboxyl group introduced in the first step in the MACO molecule is activated, which enhances the positive charge of its carbonyl carbon atom. At the same time, the secondary hydroxyl group in the malic acid molecule acts as a nucleophile and attacks the activated carbonyl carbon. Under the conditions of heating and toluene azeotropic dehydration, intermolecular dehydration occurs, removing one molecule of water and forming a stable new ester bond. This covalently links the malic acid structural unit to the MACO skeleton. Finally, this reaction introduces two additional strongly polar carboxyl groups into the MACO molecule, giving the product (F-CO-MA) significantly enhanced hydrophilicity and ion-binding ability. At the same time, due to its compact molecular structure, it also brings excellent penetration potential to the final fatliquoring agent.

[0025] Step 3. Cool the functionalized castor oil ester obtained in Step 2 to 60-70℃. At 400-600 rpm, slowly add the silane coupling agent dropwise into the reaction system through a constant-pressure dropping funnel, controlling the dropwise addition time to approximately 25-30 minutes. After the addition is complete, raise the temperature to 80-90℃ and continue the reaction for 2.5-3.5 hours. After the reaction is complete, vacuum the product at 110-120℃ for 1-2 hours, cool it to 80-90℃, add antioxidant 1010, and stir at 400-600 rpm for 20-30 minutes to obtain the castor oil-based silanized fatliquoring agent. Transfer it to a sealed, light-protected container for storage. The reaction process is as follows:

[0026] ;

[0027] Under heating conditions, the abundant carboxyl groups on the F-CO-MA molecular chain undergo an amidation condensation reaction with the amino groups at the ends of KH-550, removing one molecule of water and forming a stable covalent amide bond. This firmly grafts KH-550 onto the product backbone. The grafted KH-550 still retains its three terminal ethoxy groups. These groups can hydrolyze in the aqueous environment of subsequent fatliquoring applications to generate highly active silanol groups. The generated silanol groups can condense with each other to form a flexible siloxane network, or they can undergo dehydration condensation with active groups such as hydroxyl and amino groups on the surface of leather collagen fibers to form strong Si-OC or Si-O-Si covalent bonds. This step, by constructing a covalent "molecular bridge" from the fatliquoring agent molecule to the leather fiber, ultimately endows the product with excellent binding strength and long-lasting fatliquoring effect.

[0028] Preferably, the molar ratio of castor oil to maleic anhydride in step 1 is 1:1.2-1.5; the catalyst is stannous octoate, and its amount is 0.1-0.5% of the mass of castor oil.

[0029] Preferably, in step 2, the molar ratio of malic acid to maleic anhydride is 1:1.0-1.1; the catalyst is p-toluenesulfonic acid, and its amount is 0.5-1.0% of the mass of malic acid; the amount ratio of toluene to functionalized castor oil ester is 1-2 ml:1 g.

[0030] Preferably, the silane coupling agent in step 3 is 3-aminopropyltriethoxysilane (KH-550), and its addition amount is 8-15% of the mass of the functionalized castor oil ester used; the addition amount of antioxidant 1010 is 0.2-0.5% of the total mass of the S3 product.

[0031] This invention provides a process for preparing the above-mentioned biomass-based biodegradable leather, comprising the following steps:

[0032] S1. Surface modification of natural fibers: Dry the natural fibers in an oven at 100-110℃ for 3.5-4.5h to completely remove moisture. Take the dried natural fibers and mix them with 1-2wt% of silane coupling agent KH-550 ethanol solution at a solid-liquid ratio of 1:8-12 (g / mL). Place the mixture in a three-necked flask equipped with a stirring and reflux condenser. Stir the mixture at 200-300rpm for 1-2h at a water bath temperature of 50-60℃. After the reaction is complete, filter to separate the solid. Wash the filter cake 2-3 times with anhydrous ethanol to remove unreacted coupling agent. Finally, dry the modified natural fibers in a forced-air drying oven at 60-70℃ for 6-8h. After pulverizing, pass the mixture through a 200-mesh sieve and seal for storage.

[0033] S2. Premix: First, add the biodegradable polyester, bio-based plasticizer, castor oil-based silanized fatliquoring agent, and lubricant to a high-speed mixer and mix at a low speed of 200-400 rpm for 2 minutes to allow the liquid additives to initially wet the polymer particles. Then, add the biomass filler, bio-based crosslinking agent, functional additives, and foaming agent in sequence. Raise the mixer temperature to 45-55℃, adjust the speed to 800-1000 rpm, and mix for 8-10 minutes until the materials are evenly mixed to obtain the premix.

[0034] S3. Melt Blending and Plasticization: The premixed material and surface-modified natural fibers are melt-blended in a twin-screw extruder. The temperature of each section of the twin-screw extruder needs to be strictly controlled. The temperature range from the feed port to the die head is set as follows: Zone 1 115-125℃, Zone 2 125-135℃, Zone 3 135-140℃, Zone 4 135-140℃, Zone 5 135-140℃, and Die head 135-140℃. The screw speed is set to 150-200 rpm. The material is fully melted, mixed, and plasticized. After extrusion at the die head, water cooling, and pelletizing, uniform compound granules are obtained.

[0035] S4. Open Milling and Molding Foaming: The above granules are preheated and thin-passed on an open mill. The front roller temperature is set to 115-125℃, the rear roller temperature is set to 110-120℃, and the initial roller gap is set to 1.5-2.5mm. After the granules wrap around the rollers, the roller gap is adjusted to 0.8-1.0mm. The thin-passing is repeated 3-4 times to obtain a sheet blank with uniform texture and smooth surface. Then, according to the size of the mold cavity, an appropriate amount of blank is weighed and placed into a flat vulcanizing mold preheated to 140-150℃ (the mold surface can be pre-made with leather texture). After the mold is closed, the first step (preheating and plasticizing and mold filling): Under a pressure of 10-15MPa, pressure is maintained for 4-5 minutes to ensure that the material completely fills the cavity and is further homogenized. The second step... Step (Pressure Relief Foaming and Crosslinking): Quickly reduce the pressure to 0.5-1.0 MPa (the pressure relief process is completed within 2-3 seconds). This pressure relief action induces the gas dissolved in the melt (from the initial trace decomposition of sodium bicarbonate) and the subsequent continuous decomposition of CO2 to form bubble nuclei and expand, forming micropores inside the material. Under this low pressure, continue to maintain the mold temperature at 140-150℃ and keep it at the temperature and pressure for 10-12 minutes. This stage is the key crosslinking and curing period: the bio-based crosslinking agent (citric acid and glycerol) undergoes esterification condensation reaction in a high temperature and acidic environment (provided by citric acid) to form a three-dimensional crosslinking network. This network can effectively stabilize and fix the microporous structure formed by foaming, preventing the bubbles from merging or collapsing.

[0036] S5. Post-processing: After cross-linking and foaming, cooling water is passed through to reduce the mold temperature to below 60°C. Then the mold is opened and the product is demolded to obtain biomass-based biodegradable leather.

[0037] Compared with the prior art, the beneficial effects of the present invention are:

[0038] 1. Excellent environmental protection and sustainability: The raw materials of the product are mainly derived from renewable biomass resources (such as PLA, natural fibers, and bio-based additives), and all components are biodegradable. The final product can be completely degraded under natural environment or industrial composting conditions, avoiding the "white pollution" problem of traditional synthetic leather.

[0039] 2. Significantly Improved Overall Performance: Surface modification of natural fibers enhances compatibility with the matrix; a unique bio-based crosslinking agent (citric acid-polyol system) forms a three-dimensional network during processing, significantly improving the material's strength, heat resistance, and water resistance; the "pressure relief foaming" process, combined with sodium bicarbonate foaming agent, creates uniform micropores within the material, resulting in a finished product that is lightweight, soft, and has excellent breathability and moisture permeability, more closely resembling the performance of natural leather; the castor oil-based silanized fatliquoring agent has hydrolyzable siloxane groups at its end, which can form covalent bonds with the fibers, giving the product excellent fatliquoring effect and lasting softness, and preventing migration and exudation.

[0040] 3. Process Innovation and Synergy: The preparation process organically combines melt blending, compression molding foaming, and online cross-linking and shaping. The cross-linking network can stabilize the foam structure and prevent cell collapse. The one-step molding simplifies the process. The synthesis path of the castor oil-based silanized fatliquoring agent is precisely designed, and key functional groups are gradually introduced, ultimately achieving efficient bonding with the substrate.

[0041] 4. Cost and Texture Advantages: The extensive use of natural fibers such as bamboo powder and straw powder, as well as biomass fillers, effectively reduces raw material costs while ensuring performance. The addition of natural fibers also gives the product a unique fibrous texture and appearance. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating the preparation process of biomass-based biodegradable leather proposed in this invention. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0044] Preparation Example 1: The specific preparation method of castor oil-based silanized fatliquoring agent is as follows:

[0045] Step 1. Add 100.0g of refined castor oil that has been dehydrated under reduced pressure and 150ml of toluene to a three-necked flask. Heat to 80°C with stirring at 400rpm. Add 18.5g of maleic anhydride and 0.3g of stannous octoate catalyst at once. Slowly raise the temperature to 115°C and stir the reaction at this temperature for 4.5h. Separate the generated water using a water separator. After the reaction is complete, cool to 65°C and recover the toluene by vacuum distillation to obtain the MACO intermediate.

[0046] Step 2. Add 13.6 g malic acid, 0.11 g p-toluenesulfonic acid and 150 ml toluene to the MACO intermediate obtained in the previous step, heat to 95 °C, stir at 400 rpm for 3.5 h, continue to separate water, after the reaction is completed, cool to 65 °C, recover toluene by vacuum distillation, wash the product twice with 55 °C warm water, and then dehydrate under vacuum at 105 °C for 1.5 h to obtain functionalized castor oil ester (F-CO-MA);

[0047] Step 3. Cool F-CO-MA to 65℃, and slowly add 12.0g KH-550 dropwise over 30min using a constant pressure dropping funnel while stirring at 500rpm. After the addition is complete, raise the temperature to 85℃ and continue the reaction for 3h. After the reaction is complete, vacuum at 115℃ for 1.5h to remove low-boiling substances, cool to 85℃, add 0.34h of antioxidant 1010, and stir for 25min until completely dissolved to obtain castor oil-based silanized fatliquoring agent. Store in a sealed container away from light.

[0048] Preparation Example 2: The specific preparation method of castor oil-based silanized fatliquoring agent is as follows:

[0049] The preparation method is the same as in Preparation Example 1. In step 3, the amount of KH-550 added is 10% of the mass of F-CO-MA.

[0050] Preparation Example 3: The specific preparation method of castor oil-based silanized fatliquoring agent is as follows:

[0051] The preparation method is the same as in Preparation Example 1. In step 3, the amount of KH-550 added is 15% of the mass of F-CO-MA.

[0052] Preparation Example 4: The specific preparation method for surface modification of natural fibers is as follows:

[0053] 20g of 200-mesh bamboo powder was dried in an oven at 105℃ for 4 hours. A 1.5% KH-550 ethanol solution (3g KH-550 dissolved in 197ml anhydrous ethanol) was prepared. The dried bamboo powder was added to the solution and stirred and refluxed in a water bath at 60℃ for 2 hours. The mixture was then filtered, washed twice with anhydrous ethanol, and finally dried in a vacuum oven at 65℃ for 7 hours to obtain surface-modified bamboo powder. The powder was then pulverized and passed through a 200-mesh sieve and sealed for later use.

[0054] Preparation Example 5: The specific preparation method for surface modification of natural fibers is as follows:

[0055] 200g of 150-mesh wood flour was dried in an oven at 105℃ for 4 hours. A 1.5% KH-550 ethanol solution (3g KH-550 dissolved in 197ml anhydrous ethanol) was prepared. The dried straw powder was added to the solution and stirred and refluxed in a water bath at 60℃ for 2 hours. The mixture was then filtered, washed twice with anhydrous ethanol, and finally dried in a vacuum oven at 65℃ for 7 hours to obtain surface-modified wood flour. The flour was then pulverized and passed through a 200-mesh sieve and sealed for later use.

[0056] Preparation Example 6: The specific preparation method for surface modification of natural fibers is as follows:

[0057] 200g of 250-mesh straw powder was dried in an oven at 105℃ for 4 hours. A 1.5% KH-550 ethanol solution (3g KH-550 dissolved in 197ml anhydrous ethanol) was prepared. The dried bamboo powder was added to the solution and stirred and refluxed in a water bath at 60℃ for 2 hours. The mixture was then filtered, washed twice with anhydrous ethanol, and finally dried in a vacuum oven at 65℃ for 7 hours to obtain surface-modified straw powder. The powder was then pulverized and passed through a 200-mesh sieve and sealed for later use.

[0058] Example 1: A process for preparing biomass-based biodegradable leather, comprising the following steps:

[0059] S1. Surface modification of natural fibers: using surface-modified bamboo powder prepared in Preparation Example 4;

[0060] S2. Premixing: 460.0g PLA, 80.0g ATBC, 100.0g castor oil-based silanized fatliquoring agent prepared in Preparation Example 1, and 10.0g epoxidized soybean oil were added to a high-speed mixer and mixed at 300 rpm for 2 min. Then, 100.0g 200-mesh microcrystalline cellulose, 30.0g bio-based crosslinking agent (20.3g citric acid and 9.7g glycerol), 5.0g nano zinc oxide, and 15.0g sodium bicarbonate were added sequentially. The mixer temperature was set to 50℃, the speed was increased to 900 rpm, and the mixture was mixed for 9 min to obtain a uniform premix.

[0061] S3. Melt blending and plasticizing: The premixed material and 200.0g of surface-modified bamboo powder were added to a co-rotating twin-screw extruder (screw diameter 35mm, L / D=40). The temperatures of each section were set as follows: Zone 1 120℃, Zone 2 130℃, Zone 3 135℃, Zone 4 138℃, Zone 5 135℃, and Die head 135℃. The screw speed was 180rpm. After melt blending, the material was extruded through the die head, water-cooled, and pelletized to obtain uniform composite material granules.

[0062] S4. Open Milling and Compression Foaming: The granules are preheated and thin-passed on an open mill. The front roller temperature is set to 120℃, the rear roller temperature is set to 115℃, and the initial roller gap is set to 2mm. After the material wraps around the rollers, the roller gap is adjusted to 0.9mm. The thin-passing is repeated 3 times to obtain a sheet blank with a smooth surface and uniform texture. According to the mold cavity volume (20cm×20cm×2mm), about 220g of blank is weighed and placed into a flat vulcanizing mold (the mold surface is pre-made with cowhide texture) that has been preheated to 150℃. After the mold is closed, the first step is to apply a pressure of 12MPa and hold the pressure for 4.5min to fully plasticize the material and fill the cavity. The second step is to quickly release the pressure to 0.8MPa within 2s and continue to hold the temperature and pressure at 150℃ and 0.8MPa for 11min to complete the foaming and cross-linking reaction.

[0063] S5. Post-processing: Cooling water is introduced into the mold of the flat vulcanizing machine to reduce the mold temperature to below 50°C. The mold is then opened, and the product is removed to obtain biomass-based biodegradable leather sheet.

[0064] Example 2: A process for preparing biomass-based biodegradable leather, comprising the following steps:

[0065] S1. Surface modification of natural fibers: using the surface-modified wood flour prepared in Preparation Example 5;

[0066] S2. Premixing: 250g PBAT, 250g PBS, 60g TBC, 80g castor oil-based silanized fatliquoring agent prepared in Example 2, and 15.0g epoxidized soybean oil were added to a high-speed mixer and mixed at 300 rpm for 2 minutes. Then, 115.0g 300-mesh straw powder, 25.0g bio-based crosslinking agent (13.5g citric acid and 11.5g sorbitol), 5.0g nano titanium dioxide, and 20.0g sodium bicarbonate were added sequentially. The mixer temperature was set to 50℃, the speed was increased to 900 rpm, and the mixture was mixed for 10 minutes to obtain a uniform premix.

[0067] S3. Melt blending and plasticizing: The premixed material and 180.0g of surface-modified wood powder were added to a co-rotating twin-screw extruder (screw diameter 35mm, L / D=40). The temperatures of each section were set as follows: Zone 1 125℃, Zone 2 135℃, Zone 3 135℃, Zone 4 138℃, Zone 5 135℃, and Die head 135℃. The screw speed was 180rpm. After melt blending, the material was extruded through the die head, water-cooled, and pelletized to obtain uniform composite material pellets.

[0068] S4. Open Milling and Compression Foaming: The granules are preheated and thin-passed on an open mill. The front roller temperature is set to 120℃, the rear roller temperature is set to 115℃, and the initial roller gap is set to 2mm. After the material wraps around the rollers, the roller gap is adjusted to 0.9mm. The thin-passing is repeated 3 times to obtain a sheet blank with a smooth surface and uniform texture. According to the mold cavity volume (20cm×20cm×2mm), about 220g of blank is weighed and placed into a flat vulcanizing mold (the mold surface is pre-made with cowhide texture) that has been preheated to 145℃. After the mold is closed, the first step is to apply a pressure of 13MPa and hold the pressure for 5min to fully plasticize the material and fill the cavity. The second step is to quickly release the pressure to 1.0MPa within 2s and continue to hold the temperature and pressure at 145℃ and 1.0MPa for 10min to complete the foaming and cross-linking reaction.

[0069] S5. Post-processing: Cooling water is introduced into the mold of the flat vulcanizing machine to reduce the mold temperature to below 50°C. The mold is then opened, and the product is removed to obtain biomass-based biodegradable leather sheet.

[0070] Example 3: A process for preparing biomass-based biodegradable leather, comprising the following steps:

[0071] S1. Surface modification of natural fibers: using surface-modified straw powder prepared in Preparation Example 6;

[0072] S2. Premixing: 400.0g PHA, 50.0g ATBC, 120.0g castor oil-based silanized fatliquoring agent prepared in Preparation Example 3, and 8.0g epoxidized soybean oil were added to a high-speed mixer and mixed at 300rpm for 2min. Then, 120.0g lignocellulose nanofibers, 40.0g bio-based crosslinking agent (26.2g citric acid and 13.8g glycerol), 7.0g vanillin and 10.0g sodium bicarbonate were added sequentially. The mixer temperature was set to 50℃, the speed was increased to 900rpm, and the mixture was mixed for 8min to obtain a uniform premix.

[0073] S3. Melt blending and plasticizing: The premixed material and 245.0g of surface-modified straw powder were added to a co-rotating twin-screw extruder (screw diameter 35mm, L / D=40). The temperatures of each section were set as follows: Zone 1 115℃, Zone 2 125℃, Zone 3 135℃, Zone 4 138℃, Zone 5 135℃, and Die head 135℃. The screw speed was 180rpm. After melt blending, the material was extruded through the die head, water-cooled, and pelletized to obtain uniform composite material granules.

[0074] S4. Open Milling and Compression Foaming: The granules are preheated and thin-passed on an open mill. The front roller temperature is set to 120℃, the rear roller temperature is set to 115℃, and the initial roller gap is set to 2mm. After the material wraps around the rollers, the roller gap is adjusted to 1.0mm. The thin-passing is repeated 3 times to obtain a sheet blank with a smooth surface and uniform texture. According to the mold cavity volume (20cm×20cm×2mm), about 220g of blank is weighed and placed into a flat vulcanizing mold (the mold surface is pre-made with cowhide texture) that has been preheated to 140℃. After the mold is closed, the first step is to apply a pressure of 10MPa and hold the pressure for 5min to fully plasticize the material and fill the cavity. The second step is to quickly release the pressure to 0.5MPa within 3s and continue to hold the temperature and pressure at 140℃ and 0.5MPa for 12min to complete the foaming and cross-linking reaction.

[0075] S5. Post-processing: Cooling water is introduced into the mold of the flat vulcanizing machine to reduce the mold temperature to below 50°C. The mold is then opened, and the product is removed to obtain biomass-based biodegradable leather sheet.

[0076] Comparative Example 1: Based on Example 1, the difference is that the castor oil-based silanized fatliquoring agent prepared in this invention is replaced with an equal mass of ordinary castor oil, and the rest is the same as in Example 1.

[0077] Comparative Example 2: Based on Example 1, the difference is that no bio-based crosslinking agent (citric acid and glycerol) was used, otherwise it was the same as Example 1.

[0078] Comparative Example 3: Based on Example 1, the difference is that the bamboo powder used was not surface modified by silane coupling agent (KH-550), and the rest was the same as Example 1.

[0079] Comparative Example 4: Based on Example 1, the difference is that the bio-based plasticizer acetylthiol tributyl citrate (ATBC) was replaced with an equal part by mass of dioctyl phthalate (DOP), otherwise it was the same as Example 1.

[0080] Comparative Example 5: Based on Example 1, the difference is that no fatliquoring agent is added, and the rest is the same as Example 1.

[0081] Comparative Example 6: Based on Example 1, the difference is that the polycarboxylic acid in the bio-based crosslinking agent is replaced with adipic acid instead of citric acid, and the rest is the same as in Example 1.

[0082] Comparative Example 7: Based on Example 1, the difference is that: the biodegradable polyester is replaced with 40 parts of polyvinyl chloride (PVC), the plasticizer is 15 parts of diisononyl phthalate (DINP), the lubricant is 1 part of calcium stearate, the castor oil-based silanizing fatliquoring agent, bio-based crosslinking agent, biomass filler and foaming agent are not added, 20 parts of calcium carbonate filler are added, the preparation process adopts the conventional PVC calendering process, and the rest is the same as Example 1.

[0083] Comparative Example 8: Based on Example 1, the difference is that the "pressure relief foaming" process is not used in preparation process S4. Instead, it is directly molded at 150°C for 15 minutes under a constant pressure of 10MPa. The rest is the same as in Example 1.

[0084] Comparative Example 9: Based on Example 1, the difference is that the thin-pass step is omitted in the preparation process S4, and only molding foaming is performed. Under a pressure of 12MPa, the pressure is maintained at 150℃ for 4.5min, and the pressure is rapidly released to 0.8MPa within 2s. The pressure is then maintained at 150℃ and 0.8MPa for 11min. The rest is the same as in Example 1.

[0085] Performance testing:

[0086] 1. Mechanical properties: Tensile strength and elongation at break shall be tested according to GB / T 1040.3-2006, and tear strength shall be tested according to QB / T 2710-2005.

[0087] 2. Hardness: Shore A hardness was tested according to GB / T 531.1-2008.

[0088] 3. Softness (feel): Based on industry feel assessment, it is blind-rated by 5 experienced personnel (1-10 points, the higher the score, the softer).

[0089] 4. Air permeability and moisture permeability: Air permeability is tested according to GB / T 5453-1997, and moisture permeability is tested according to GB / T 12704.2-2009.

[0090] 5. Thermal stability: The heat distortion temperature (HDT) test is adopted, and the thermal stability is tested according to GB / T 1634.2-2004.

[0091] 6. Water absorption rate: Test the water absorption rate for 24 hours according to GB / T 1034-2008.

[0092] 7. Biodegradability: Tested according to GB / T 19277.1-2011, and the biodegradation rate was determined after 58 days.

[0093] Table: Performance tests were conducted on a biomass-based biodegradable leather from Examples 1-3 and Comparative Examples 1-9.

[0094] Table 1. Results of Mechanical Properties and Hardness Tests

[0095]

[0096] Table 2. Results of tests on performance, durability, and degradability.

[0097]

[0098] Data Analysis:

[0099] 1. The influence of core components on material properties

[0100] The key role of castor oil-based silanized fatliquoring agent: Compared with Comparative Example 1 (ordinary castor oil) and Comparative Example 5 (no fatliquoring agent), Example 1 showed a 65% and 146% improvement in softness score, respectively, and a 49% and 118% improvement in elongation at break, respectively, with significantly optimized air permeability and moisture permeability. This is because the silane-grafted castor oil fatliquoring agent synthesized in this invention can form covalent bonds with fibers, rather than through physical adsorption. This solves the problems of easy migration and deterioration of hand feel associated with conventional fatliquoring agents, while simultaneously improving interfacial compatibility and balancing softness and mechanical strength.

[0101] The optimization effect of bio-based crosslinking agents: Compared with Comparative Example 2 (no crosslinking agent) and Comparative Example 6 (adipic acid instead of citric acid), Example 1 showed an increase in tensile strength of 49% and 21%, an increase in heat distortion temperature of 29% and 18%, and a decrease in 24-hour water absorption of 55% and 42%. The citric acid-glycerol crosslinking system can form a three-dimensional esterified crosslinking network during processing, effectively binding polymer chains and improving the material's heat resistance, water resistance, and structural stability, while preventing cell collapse. In contrast, adipic acid has low crosslinking activity, poor crosslinking network density, and limited performance improvement.

[0102] The necessity of surface modification of natural fibers: Comparative Example 3 used unmodified bamboo powder, and its tensile strength and tear strength decreased by 27% and 38% respectively compared with Example 1, while its water absorption doubled and its softness decreased significantly. The unmodified bamboo powder has strong polar hydroxyl groups on its surface, resulting in poor interfacial compatibility with the hydrophobic PLA matrix, which easily leads to interfacial debonding and hinders stress transmission. However, after modification with KH-550, the polarity of the fiber surface is reduced, achieving efficient bonding between the fiber and the matrix and fully leveraging the fiber's reinforcing effect.

[0103] Environmental friendliness of plasticizers and matrix: Comparative Example 4 used petroleum-based DOP plasticizer, with a biodegradability of only 42.3%, far lower than the 91.2% of Example 1. Furthermore, DOP poses a migration risk, failing to meet environmental requirements. The citrate ester plasticizer selected in this invention is completely degradable, with a mild plasticizing effect, balancing processability and degradability. Comparative Example 7 used petroleum-based PVC material, which had acceptable mechanical properties and flexibility, but its 58-day biodegradability was only 3.6%, making it non-degradable and causing white pollution, contradicting the environmental protection concept of this invention.

[0104] 2. The Influence of Preparation Process on Material Properties

[0105] The core value of pressure-relief foaming technology: Comparative Example 8 did not use pressure-relief foaming; its material lacked a uniform microporous structure, resulting in an air permeability of only 3.4 mm / s and a moisture permeability of only 860 g / (m³). 2 •24h), the feel is too hard, and the softness score is only 5.8 points, which does not meet the performance of leather for wearing at all; the rapid pressure relief foaming process of this invention can form uniform and interconnected micropores, taking into account lightness, softness and breathability, and conforming to the wearing characteristics of natural leather.

[0106] The importance of the open mixing and thin-passing step: In Comparative Example 9, the open mixing and thin-passing step was omitted, and the granules were directly molded. The material was not mixed evenly, and there were many defects in the cell structure. The mechanical properties and feel were greatly reduced. The open mixing and thin-passing step can further plasticize and homogenize the composite granules, eliminate internal stress, ensure that the cells are uniform and the texture is dense after molding and foaming, and improve the overall performance of the finished product.

[0107] 3. Overall Performance Summary of the Implementation Examples

[0108] The biomass-based biodegradable leather prepared in Examples 1-3 of this invention exhibits a tensile strength consistently between 19.8-23.2 MPa, an elongation at break of 176-212%, and a tear strength of 65.7-71.4 N / mm, meeting the durability requirements for leather products. Its Shore A hardness is 49-54, its softness score is 8.4-8.8, and its hand feel is close to that of natural leather. Its air permeability is 11.9-13.5 mm / s, and its moisture permeability is 2740-3020 g / (m³). 2• 24h), excellent comfort when used; biodegradability rate of over 90% after 58 days, can be completely degraded by industrial composting, with no environmental hazards; at the same time, heat resistance and water resistance meet the standards, suitable for various leather product processing and usage scenarios.

[0109] In summary, this invention, through the synergistic effect of component optimization, interface modification, and process innovation, solves the technical bottlenecks of existing bio-based leathers, such as high brittleness, poor hand feel, weak interfacial compatibility, and difficulty in balancing degradability and mechanical properties. It produces an environmentally friendly leather material that combines high mechanical properties, a soft hand feel, good breathability and moisture permeability, and complete degradability, which meets the dual carbon goals and the development needs of the environmental protection industry.

[0110] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A biomass-based biodegradable leather, characterized in that, The product comprises the following components by weight: 30-60 parts biodegradable polyester, 15-30 parts surface-modified natural fiber, 5-15 parts castor oil-based silanized fatliquoring agent, 3-10 parts bio-based plasticizer, 5-20 parts biomass filler, 1-5 parts bio-based crosslinking agent, 0.5-3 parts foaming agent, 0.5-2 parts lubricant, and 0-3 parts functional additives; the biomass-based biodegradable leather is biodegradable under natural environmental or industrial composting conditions; the biodegradable polyester is at least one of polylactic acid, polybutylene succinate, polyhydroxyalkanoates, and polybutylene adipate terephthalate. The castor oil-based silanized fatliquoring agent is prepared by the following steps: Step 1. Dehydrated castor oil and maleic anhydride are reacted at 110-115℃ for 4-5 hours under the action of a catalyst to generate maleic anhydride-modified castor oil intermediate; Step 2. The intermediate obtained in Step 1 is reacted with malic acid at 90-95℃ for 3-4 hours under the action of a catalyst to obtain functionalized castor oil ester; Step 3. The functionalized castor oil ester obtained in Step 2 is reacted with silane coupling agent KH-550 at 80-90℃ for 2.5-3.5h to obtain the castor oil-based silanized fatliquoring agent.

2. The biomass-based biodegradable leather according to claim 1, characterized in that, The surface-modified natural fiber is a natural fiber that has undergone surface modification treatment with a silane coupling agent ethanol solution; the natural fiber is at least one of bamboo powder, wood powder, coffee grounds, and straw powder, and its particle size is 100-300 mesh.

3. The biomass-based biodegradable leather according to claim 1, characterized in that, The bio-based crosslinking agent is composed of a polycarboxylic acid and a polyol in a molar ratio of 1:0.8-1.2, wherein the polycarboxylic acid is citric acid and the polyol is glycerol or sorbitol.

4. The biomass-based biodegradable leather according to claim 1, characterized in that, The foaming agent is sodium bicarbonate.

5. The biomass-based biodegradable leather according to claim 1, characterized in that, In step 1, the molar ratio of castor oil to maleic anhydride is 1:1.2-1.5; the catalyst is stannous octoate, and its amount is 0.1-0.5% of the mass of castor oil.

6. The biomass-based biodegradable leather according to claim 1, characterized in that, In step 2, the molar ratio of malic acid to maleic anhydride is 1:1.0-1.1; the catalyst is p-toluenesulfonic acid, and its amount is 0.5-1.0% of the mass of malic acid.

7. The biomass-based biodegradable leather according to claim 1, characterized in that, In step 3, the amount of silane coupling agent KH-550 added is 8-15% of the mass of the functionalized castor oil ester used.

8. A process for preparing a biomass-based biodegradable leather as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Surface modification treatment of natural fibers; S2. Premix: Biodegradable polyester, bio-based plasticizer, castor oil-based silanized fatliquoring agent, and lubricant are mixed together, and then biomass filler, bio-based crosslinking agent, functional additives and foaming agent are added. The mixture is heated and mixed at high speed to obtain a premix. S3. Melt blending and plasticizing: The premixed material and surface-modified natural fibers are melt blended and extruded into granules in a twin-screw extruder to obtain composite material granules; S4. Open milling and molding foaming: The composite material granules are thinly passed through an open mill to obtain sheet blanks. The blanks are then placed into a preheated mold, preheated at 10-15MPa pressure for 4-5 minutes, and then quickly depressurized to 0.5-1.0MPa. The mold is then held at 140-150℃ for 10-12 minutes to complete the foaming and cross-linking shaping. S5. Post-processing: Cooling and demolding to obtain the biomass-based biodegradable leather.

9. The preparation process of a biomass-based biodegradable leather according to claim 8, characterized in that, The pressure relief process described in S4 is completed within 2-3 seconds.

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