Preparation method of high-toughness bio-based synthetic leather

Abstract

The invention discloses a preparation method of high-toughness bio-based synthetic leather, which comprises the following steps: pre-treating base cloth, padding bio-based emulsion, and drying to obtain a polycaprolactone treated base cloth layer; coating the water-based bio-based polyurethane surface layer slurry on release paper, and drying to form a water-based bio-based polyurethane surface layer; coating the water-based bio-based polyurethane surface layer with solvent-free polycaprolactone-based polyurethane slurry, pre-drying the water-based bio-based polyurethane surface layer to a set dryness, immediately attaching the polycaprolactone-treated base cloth layer to the water-based bio-based polyurethane surface layer, and compacting the water-based bio-based polyurethane surface layer to obtain composite crust leather; and curing the composite crust leather, stripping the release paper, then spraying a surface treatment liquid on the surface, and drying to obtain a synthetic leather finished product which has the advantages of ultrahigh toughness, high strength, low VOC and high bio-based content.

Description

Technical Field

[0001] This invention belongs to the field of synthetic leather manufacturing technology, specifically relating to a method for preparing high-toughness bio-based synthetic leather for use in automotive interiors, high-end home furnishings and consumer products. Background Technology

[0002] With increasingly stringent environmental regulations and growing consumer awareness of environmental protection, the synthetic leather industry is accelerating its transformation from traditional petroleum-based and solvent-based processes to water-based and solvent-free green processes. However, current environmentally friendly synthetic leathers often face performance compromises while pursuing green production. Furthermore, the use of bio-based materials in synthetic leather has encountered three major problems: First, there is the issue of compatibility. Common bio-based materials (such as polylactic acid PLA) have significantly different chemical structures from polyurethane matrices, resulting in weak interfacial bonding between the two. Just like water and oil are difficult to mix, this causes synthetic leather to easily delaminate and peel during use.

[0003] Secondly, there is the issue of performance balance. Although many bio-based resins are environmentally friendly, the synthetic leather made from them tends to be hard and brittle, cracking easily when folded. It is difficult to achieve both softness and strength, making it hard to meet the dual demands of automotive interiors and high-end bags for a soft touch and high durability.

[0004] Third, the issue of reinforcing the base fabric. As the skeleton of synthetic leather, when the base fabric is treated with bio-based materials, it often results in either insufficient strength or being too stiff and not flexible, making it difficult to achieve both.

[0005] Therefore, developing a synthetic leather that can maintain a high bio-based content while surpassing traditional petroleum-based products in terms of flexibility, strength, and durability remains a pressing technical challenge for synthetic leather products. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing synthetic leather, this invention provides a method for preparing high-toughness bio-based synthetic leather with polycaprolactone polyol as the core, which combines ultra-high toughness, high strength, low VOC emissions, and high bio-based content.

[0007] To achieve the above objectives, the present invention provides a method for preparing high-toughness bio-based synthetic leather, comprising the following steps: S1: The base fabric is pretreated, then impregnated with a bio-based emulsion, and dried to obtain a polycaprolactone-treated base fabric layer; S2: Coat the release paper with a water-based bio-based polyurethane surface layer slurry and dry it to form a water-based bio-based polyurethane surface layer; S3: A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer. After pre-baking to a set dryness level, a polycaprolactone-treated base fabric layer is immediately bonded onto it and compacted to obtain a composite leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 80-95 parts of polycaprolactone polyol, 5-20 parts of polycarbonate diol, 59-63 parts of isocyanate, and 0.5-0.55 parts of compounded catalyst. S4: The composite leather is cured, the release paper is peeled off, and then a surface treatment liquid is sprayed on the surface. After drying, the finished synthetic leather product is obtained.

[0008] Furthermore, the polycaprolactone polyol is prepared by ring-opening polymerization of ε-caprolactone and 1,4-butanediol, with a number-average molecular weight of 2000±200 and a hydroxyl value of 56-60 mgKOH / g.

[0009] Furthermore, the isocyanate is an HDI trimer with an NCO content of 21±1%.

[0010] Furthermore, the composite catalyst is a mixture of an organozinc catalyst and an organozirconium catalyst, with a mass ratio of 1:(1-1.5).

[0011] Furthermore, in S1, the pretreatment is plasma treatment with a processing power of 450-550W and a processing time of 2-4s; the bio-based emulsion is a mixed emulsion of polycaprolactone emulsion and nanocellulose, wherein the solid content of the polycaprolactone emulsion is 12±1%, and the amount of nanocellulose added accounts for 1-2% of the total mass of the emulsion.

[0012] Furthermore, in S2, the raw materials of the waterborne bio-based polyurethane surface slurry include, by weight, 78-83 parts of bio-based polyurethane, 3-6 parts of tackifier, 1.5-2 parts of defoamer, 2-4 parts of crosslinking agent, and 11-14 parts of color paste; the soft segment of the bio-based polyurethane is compounded from polycaprolactone polyol and linseed oil polyol at a weight ratio of (2.5-3.0):1.

[0013] Furthermore, in S3, the solvent-free polycaprolactone-based polyurethane slurry is dried to form a solvent-free polycaprolactone-based polyurethane bonding layer. The pre-drying temperature is 120-130℃, the pre-drying time is 2-3 minutes, and the dryness of the bonding layer after pre-drying is controlled at 63-67%.

[0014] Furthermore, in S4, a surface treatment layer is formed after spraying the surface treatment liquid. The raw materials of the surface treatment liquid include, by mass, 86-87 parts of castor oil-modified waterborne polyurethane, 7-8 parts of sulfonate-modified isocyanate crosslinking agent, and 4-6 parts of wear-resistant agent. The wear-resistant agent is a compound composed of graphene and boron nitride in a mass ratio of 1:2, and the wear-resistant agent is ultrasonically dispersed before use.

[0015] Furthermore, in S4, the curing process adopts segmented heating. The first curing temperature is 130-135℃ and the time is 0.5-1.5min; the second curing temperature is 135-140℃ and the time is 1-2min.

[0016] Furthermore, the base fabric is selected from 800-900μm polyester knitted fabric, with a warp tensile strength ≥300N / 5cm and a weft tensile strength ≥280N / 5cm.

[0017] This invention discloses a method for preparing high-toughness bio-based synthetic leather. It addresses the performance balance issue through the compounding of polycaprolactone polyol and polycarbonate diol, solves the base fabric reinforcement problem through plasma pretreatment and polycaprolactone / nanocellulose composite emulsion, achieves high bio-based content through multi-layer addition of bio-based raw materials, ensures interfacial bonding through precise control of drying degree, and enhances fatigue resistance through segmented curing. The final product is a synthetic leather possessing ultra-high toughness (elongation at break ≥2000%), high strength (peel strength ≥4.5N / mm), low VOC (≤8mg / m³), and high bio-based content (53%-56%). This method comprehensively overcomes the technical bottlenecks of existing bio-based synthetic leathers and possesses significant inventiveness and industrial applicability. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a method for preparing high-toughness bio-based synthetic leather, comprising the following steps: S1: The base fabric is pretreated, then impregnated with a bio-based emulsion, and dried to obtain a polycaprolactone-treated base fabric layer.

[0020] S2: Coat the release paper with a water-based bio-based polyurethane surface layer slurry and dry it to form a water-based bio-based polyurethane surface layer.

[0021] S3: Coat a solvent-free polycaprolactone-based polyurethane slurry onto an aqueous bio-based polyurethane surface layer, pre-bake to a set dryness level, and immediately attach a polycaprolactone-treated base fabric layer onto it and compact it to obtain a composite leather; the solvent-free polycaprolactone-based polyurethane slurry is composed of 80-95 parts of polycaprolactone polyol, 5-20 parts of polycarbonate diol, 59-63 parts of isocyanate, and 0.5-0.55 parts of compounded catalyst.

[0022] S4: The composite leather is cured, the release paper is peeled off, and then a surface treatment liquid is sprayed on the surface. After drying, the finished synthetic leather product is obtained.

[0023] The method for preparing high-toughness bio-based synthetic leather of the present invention has the following beneficial technical effects: 1. The pretreatment in step S1 (such as plasma treatment) synergistically with the polycaprolactone / nanocellulose composite emulsion impregnation significantly improves the strength of the base fabric and its interfacial bonding with the bonding layer. Step S1 uses a polycaprolactone-containing emulsion to treat the base fabric, giving the base fabric surface the same polycaprolactone chemical structure as the bonding layer in step S3, forming a similarly compatible chemically compatible interface, fundamentally improving the interlayer compatibility between the bio-based material and the polyurethane matrix; the aqueous surface layer in step S2 and the bonding layer in step S3 are bonded together by an adhesive to strengthen the interfacial bonding and prevent delamination.

[0024] 2. Step S3 restricts the compounding of polycaprolactone polyol (80-95 parts) and polycarbonate diol (5-20 parts) to construct a micro-phase separation structure of flexible segments (polycaprolactone) + rigid segments (polycarbonate). Polycaprolactone provides ultra-high flexibility (elongation at break ≥2000%), while polycarbonate diol provides strength support (peel strength ≥4.5N / mm), breaking the limitation of traditional bio-based materials that are strong but brittle and tough but weak.

[0025] 3. By using bio-based raw materials throughout the entire process—from the top layer (bio-based polyurethane), the connecting layer (polycaprolactone polyol), the surface treatment layer (castor oil-modified waterborne polyurethane), and the base fabric treatment layer (polycaprolactone emulsion)—the finished product achieves a bio-based content of 53%-56%. Simultaneously, the entire process is solvent-free, with a VOC content ≤8mg / m³. 3 .

[0026] In S1, the base fabric is selected from 800-900μm polyester knitted fabric, with a warp tensile strength ≥300N / 5cm and a weft tensile strength ≥280N / 5cm. This specification of polyester knitted fabric balances support and softness: sufficient thickness and strength ensure that the base fabric can withstand the mechanical tension during processing, while providing a mechanical basis for the finished synthetic leather; the knitted structure gives the base fabric good extensibility, matching the high elongation at break of the synthetic leather, and preventing the base fabric from cracking before the coating during use.

[0027] In S1, the pretreatment is plasma treatment with a power of 450-550W and a treatment time of 2-4 seconds. The fiber is then fed into a two-dip, two-roll mill to impregnate it with polycaprolactone emulsion at 45±2℃ with a roll-in rate of 90±2%. It is then pre-dried at 85℃ for 4 minutes and dried at 115℃ for 6 minutes until the moisture content is ≤1.5%. After cooling, it is wound up for later use. Plasma treatment introduces polar groups (such as hydroxyl and carboxyl groups) onto the surface of the polyester fiber, significantly improving the wettability between the fiber and the treatment solution, allowing the polycaprolactone emulsion to spread evenly and form a continuous polymer film. Plasma treatment is like polishing and waxing the fiber surface, but instead of making it smooth, it introduces small hooks (polar groups) onto the surface, allowing the treatment solution to adhere better to the fiber and form a uniform and strong film.

[0028] In S1, the bio-based emulsion is a mixed emulsion of polycaprolactone emulsion and nanocellulose, wherein the solid content of the polycaprolactone emulsion is 12±1%, and the amount of nanocellulose added accounts for 1-2% of the total mass of the emulsion. The polycaprolactone emulsion can form a uniform film on the surface of the base fabric, significantly improving the toughness of the base fabric and the interfacial bonding force with the subsequent bonding layer. Nanocellulose fills the fiber gaps like micro-reinforcing bars, increasing the strength of the base fabric itself and improving the bonding force with the subsequent bonding layer by more than 30%, completely solving the problem of base fabric strength.

[0029] In S2, the raw materials of the water-based bio-based polyurethane topcoat slurry, by weight, include: 78-83 parts bio-based polyurethane, 3-6 parts tackifier, 1.5-2 parts defoamer, 2-4 parts crosslinking agent, and 11-14 parts color paste. The proportions of each component ensure the stability and film uniformity of the topcoat slurry, resulting in high surface smoothness and a color fastness to rubbing of ≥4 on the synthetic leather surface.

[0030] The soft segment of the bio-based polyurethane is composed of polycaprolactone polyol and linseed oil polyol in a mass ratio of (2.5-3.0):1. The polycaprolactone polyol is obtained by ring-opening polymerization of ε-caprolactone and 1,4-butanediol, with a number-average molecular weight of 2000±200 and an acid value ≤0.4mgKOH / g. Polycaprolactone provides flexibility, while linseed oil polyol increases the bio-based content and hydrophobicity, giving the surface layer both flexibility and environmental friendliness.

[0031] The tackifier is a polycaprolactone-grafted modified acrylate with a grafting rate of ≥18%, which enhances compatibility with the bonding layer. The addition of the tackifier strengthens the interfacial compatibility between the surface layer and the bonding layer, preventing delamination during use.

[0032] The defoamer used is BYK-024 silicone type.

[0033] The crosslinking agent is a sulfonate-modified isocyanate. The sulfonate-modified isocyanate crosslinking agent improves the crosslinking density and water resistance of the surface layer.

[0034] In S3, the polycaprolactone polyol is prepared by ring-opening polymerization of ε-caprolactone and 1,4-butanediol under organotin catalysis, with a number-average molecular weight of 2000±200 and a hydroxyl value of 56-60 mgKOH / g. Too low a molecular weight leads to an incomplete cross-linking network and insufficient mechanical properties; too high a molecular weight results in decreased reactivity and processing difficulties. The hydroxyl value range ensures accurate functionality and a regular cross-linking network structure, laying the molecular foundation for the high peel strength and fatigue resistance of the finished product. Furthermore, the use of ring-opening polymerization of ε-caprolactone and 1,4-butanediol, with raw materials derived from bio-based sources, guarantees a high overall bio-based content.

[0035] In S3, the isocyanate is an HDI trimer with an NCO content of 21±1%. The HDI trimer is an aliphatic isocyanate, which imparts excellent resistance to yellowing and flexibility to synthetic leather, making it suitable for high-end applications such as automotive interiors where color stability and tactile feel are crucial. Precise control of the NCO content ensures a stoichiometric match with the polyol, resulting in a thorough and controllable crosslinking reaction, thus improving the mechanical properties and hydrolysis resistance of the bonding layer.

[0036] In S3, the composite catalyst is a mixture of organozinc catalyst and organozirconium catalyst, with a mass ratio of 1:(1-1.5). Organozinc promotes the main chain polymerization reaction, while organozirconium promotes side chain cross-linking, together forming a denser network structure, thus improving the product's hydrolysis resistance and fatigue resistance. Compared to traditional organobismuth / amine catalysts, this system is non-toxic and odorless, meeting the environmental requirements for low VOCs and low odors; simultaneously, the gelation time can be precisely controlled within 8-10 minutes, adapting to the rhythm of continuous industrial production.

[0037] In S3, the solvent-free polycaprolactone-based polyurethane slurry is dried to form a solvent-free polycaprolactone-based polyurethane bonding layer. The pre-drying temperature is 120-130℃, and the pre-drying time is 2-3 minutes. The dryness of the bonding layer after pre-drying is controlled at 63-67%. If the dryness is too high (>67%), the bonding layer loses its adhesiveness and cannot adhere well to the base fabric; if the dryness is too low (<63%), residual moisture or solvent will affect the subsequent crosslinking reaction, leading to a decrease in peel strength. Controlling the dryness at 63-67% ensures that the bonding layer is in an optimal viscous flow state at the moment of bonding, allowing it to penetrate into the fiber gaps of the base fabric to form an anchoring effect while maintaining a certain structural strength. This is the process guarantee for achieving high peel strength (≥4.5N / mm).

[0038] In step S4, the curing process employs segmented heating. The first stage of curing is at 130-135℃ for 0.5-1.5 minutes; the second stage is at 135-140℃ for 1-2 minutes. Segmented heating avoids the problem of excessively rapid surface curing and insufficient internal cross-linking caused by a single high temperature: the first stage, at a low temperature, initially cross-links to form a basic framework, while the second stage, at a high temperature, deepens the reaction and eliminates internal stress. This process ensures uniform overall performance of the synthetic leather, excellent fatigue resistance (stress retention rate >80% after 5000 cycles), and stable peel strength.

[0039] In step S4, a surface treatment layer is formed after spraying a surface treatment liquid. The raw materials of the surface treatment liquid, by weight, include: 86-87 parts castor oil-modified waterborne polyurethane, 7-8 parts sulfonate-modified isocyanate crosslinking agent, and 4-6 parts wear-resistant agent. The castor oil-modified waterborne polyurethane is a castor oil-modified type with a bio-based content ≥35% and a solid content of 30±2%. The surface treatment layer uses castor oil-modified waterborne polyurethane to further increase the bio-based content; the sulfonate-modified isocyanate crosslinking agent improves the crosslinking density and water resistance of the coating. The wear-resistant agent is a compound composed of graphene and boron nitride in a weight ratio of 1:2, and the wear-resistant agent is ultrasonically dispersed before use. The two form a layered synergistic lubrication mechanism: graphene provides conductivity and reinforcement, while boron nitride provides self-lubrication and thermal conductivity, significantly improving the surface wear resistance (Taber wear ≤4.0mg / 1000 cycles). Ultrasonic dispersion treatment ensures that the nanomaterials are uniformly dispersed in the coating, avoiding surface defects caused by agglomeration.

[0040] The beneficial technical effects of the preparation method of the present invention will be described below through several examples and comparative examples. Unless otherwise specified, all raw materials used in the following examples are commercially available industrial products. Polycaprolactone polyol, number average molecular weight 2000±200, hydroxyl value 56-60 mgKOH / g; polycarbonate diol, number average molecular weight 2000±200; organozinc catalyst: zinc octanoate; organozirconium catalyst: zirconate ester compound. Example 1

[0041] S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and subjected to plasma pretreatment (power 500W, time 3s). The treated base fabric was then fed into a two-dip, two-nip apparatus to be impregnated with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The nip temperature was 45℃, and the nip rate was 90%. After nip, the base fabric was pre-dried at 85℃ for 4 min, then dried at 115℃ for 6 min, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0042] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0043] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 88 parts polycaprolactone polyol, 12 parts polycarbonate diol, 61 parts isocyanate (HDI trimer, NCO content 21%), and 0.52 parts compounded catalyst (0.26 parts organic zinc, 0.26 parts organic zirconium).

[0044] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product. Example 2

[0045] S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and subjected to plasma pretreatment (power 500W, time 3s). The treated base fabric was then fed into a two-dip, two-nip apparatus to be impregnated with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The nip temperature was 45℃, and the nip rate was 90%. After nip, the base fabric was pre-dried at 85℃ for 4 min, then dried at 115℃ for 6 min, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0046] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0047] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately bonded onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 95 parts polycaprolactone polyol, 5 parts polycarbonate diol, 61 parts isocyanate (HDI trimer, NCO content 21%), and 0.52 parts compounded catalyst (0.26 parts organic zinc, 0.26 parts organic zirconium).

[0048] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product. Example 3

[0049] S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and subjected to plasma pretreatment (power 500W, time 3s). The treated base fabric was then fed into a two-dip, two-nip apparatus to be impregnated with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The nip temperature was 45℃, and the nip rate was 90%. After nip, the base fabric was pre-dried at 85℃ for 4 min, then dried at 115℃ for 6 min, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0050] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0051] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 80 parts of polycaprolactone polyol, 20 parts of polycarbonate diol, 61 parts of isocyanate (HDI trimer, NCO content 21%), and 0.52 parts of a compounded catalyst (0.26 parts of organic zinc and 0.26 parts of organic zirconium).

[0052] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product. Example 4

[0053] S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and subjected to plasma pretreatment (power 500W, time 3s). The treated base fabric was then fed into a two-dip, two-nip apparatus to be impregnated with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The nip temperature was 45℃, and the nip rate was 90%. After nip, the base fabric was pre-dried at 85℃ for 4 min, then dried at 115℃ for 6 min, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0054] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0055] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 88 parts polycaprolactone polyol, 12 parts polycarbonate diol, 61 parts isocyanate (HDI trimer, NCO content 21%), and 0.52 parts compounded catalyst (0.31 parts organic zinc, 0.21 parts organic zirconium).

[0056] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product. Example 5

[0057] S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and subjected to plasma pretreatment (power 480W, time 3.5s). The treated base fabric was then fed into a two-dip, two-nip apparatus to be impregnated with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The nip temperature was 45℃, and the nip rate was 90%. After nip, the base fabric was pre-dried at 85℃ for 4 min, then dried at 115℃ for 6 min, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0058] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0059] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 88 parts polycaprolactone polyol, 12 parts polycarbonate diol, 61 parts isocyanate (HDI trimer, NCO content 21%), and 0.52 parts compounded catalyst (0.26 parts organic zinc, 0.26 parts organic zirconium).

[0060] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product.

[0061] Comparative Example 1 S1: Base Fabric Treatment. The base fabric is an 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm), which is fed into a two-dip, two-padding machine to be impregnated with polylactic acid emulsion (solid content 12%). After padding, the base fabric is pre-dried at 85℃ for 4 min, dried at 115℃ for 6 min, and the moisture content is controlled to be ≤1.5%. It is then cooled and wound up for later use.

[0062] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0063] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 100 parts of polylactic acid-based polyol (number average molecular weight 2000), 61 parts of isocyanate (HDI trimer, NCO content 21%), and 0.52 parts of a compounded catalyst (0.18 parts of organic bismuth catalyst and 0.34 parts of triethanolamine).

[0064] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product.

[0065] Comparative Example 2 S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and subjected to plasma pretreatment (power 500W, time 3s). The treated base fabric was then fed into a two-dip, two-nip apparatus to be impregnated with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The nip temperature was 45℃, and the nip rate was 90%. After nip, the base fabric was pre-dried at 85℃ for 4 min, then dried at 115℃ for 6 min, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0066] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0067] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 100 parts of polycaprolactone polyol, 61 parts of isocyanate (HDI trimer, NCO content 21%), and 0.52 parts of a compounded catalyst (0.26 parts of organic zinc and 0.26 parts of organic zirconium).

[0068] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product.

[0069] Comparative Example 3 S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and fed into a two-dip, two-paste equipment to impregnate the fabric with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The padding temperature was 45℃, and the padding rate was 90%. After padding, the base fabric was pre-dried at 85℃ for 4 minutes, then dried at 115℃ for 6 minutes, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0070] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0071] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 88 parts polycaprolactone polyol, 12 parts polycarbonate diol, 61 parts isocyanate (HDI trimer, NCO content 21%), and 0.52 parts compounded catalyst (0.26 parts organic zinc, 0.26 parts organic zirconium).

[0072] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product.

[0073] Comparative Example 4 S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and subjected to plasma pretreatment (power 500W, time 3s). The treated base fabric was then fed into a two-dip, two-nip apparatus to be impregnated with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The nip temperature was 45℃, and the nip rate was 90%. After nip, the base fabric was pre-dried at 85℃ for 4 min, then dried at 115℃ for 6 min, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0074] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0075] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 2.5 min, and after controlling the dryness to 65%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 88 parts polycaprolactone polyol, 12 parts polycarbonate diol, 61 parts isocyanate (HDI trimer, NCO content 21%), and 0.52 parts compounded catalyst (0.26 parts organic zinc, 0.26 parts organic zirconium).

[0076] S4: The composite raw leather is baked in stages at 132℃ for 1 minute and 136℃ for 1.5 minutes. After cooling, the release paper is peeled off, and the leather is dried at 120℃ for 3 minutes. After inspection and slitting, the finished product is obtained.

[0077] Comparative Example 5 S1: Base Fabric Treatment. 850μm polyester knitted fabric (warp breaking strength 320N / 5cm, weft breaking strength 290N / 5cm) was selected and subjected to plasma pretreatment (power 500W, time 3s). The treated base fabric was then fed into a two-dip, two-nip apparatus to be impregnated with a bio-based emulsion. The bio-based emulsion was a mixture of polycaprolactone emulsion (solid content 12%, viscosity 500cps) and nanocellulose, with the nanocellulose content accounting for 1.5% of the total emulsion mass. The nip temperature was 45℃, and the nip rate was 90%. After nip, the base fabric was pre-dried at 85℃ for 4 min, then dried at 115℃ for 6 min, controlling the moisture content to ≤1.5%, and then cooled and wound up for later use.

[0078] S2: Preparation of waterborne bio-based polyurethane surface layer. Raw materials were weighed according to the following proportions by weight: 80 parts of bio-based polyurethane (the soft segment is a blend of polycaprolactone polyol and linseed oil polyol in a 2.8:1 ratio), 4.5 parts of polycaprolactone grafted modified acrylate tackifier, 1.8 parts of BYK-024 silicone defoamer, 3.2 parts of sulfonate modified isocyanate crosslinking agent, and 12.5 parts of color paste. The raw materials were added to a double planetary mixer and stirred at 400 rpm and 28°C for 55 min under nitrogen protection to obtain a surface layer slurry with a viscosity of 4000 cps. This slurry was coated onto preheated release paper to a thickness of 0.15 mm and dried at 120°C for 4.5 min to form the waterborne bio-based polyurethane surface layer.

[0079] S3: Preparation and lamination of solvent-free polycaprolactone-based polyurethane connecting layer. A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer, pre-baked at 125℃ for 4 minutes, and after controlling the dryness to 75%, a polycaprolactone-treated base fabric layer is immediately laminated onto it and compacted under a pressure of 0.4 MPa to obtain the composite pre-fabricated leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 88 parts of polycaprolactone polyol, 12 parts of polycarbonate diol, 61 parts of isocyanate (HDI trimer, NCO content 21%), and 0.52 parts of a compounded catalyst (0.26 parts of organic zinc and 0.26 parts of organic zirconium).

[0080] S4: The composite raw leather is sequentially baked at 132℃ for 1 min and then at 136℃ for 1.5 min for segmented curing. After cooling, the release paper is peeled off, and a surface treatment liquid is sprayed on. The surface treatment liquid consists of 86.5 parts of castor oil-modified waterborne polyurethane, 7.8 parts of sulfonate-modified isocyanate crosslinking agent, and 5.2 parts of abrasion-resistant agent (graphene:boron nitride = 1:2, ultrasonically dispersed at 300W for 20 min before use). After spraying, it is dried at 120℃ for 3 min, inspected, and slit to obtain the finished product.

[0081] Table 1. Performance parameters of synthetic leather products obtained in each embodiment and comparative example.

[0082] Performance testing methods: Bio-based content: determined according to ASTM D6866 standard.

[0083] Peel strength: Measured in accordance with GB / T 8808 standard.

[0084] Elongation at break: determined according to GB / T 1040.3 standard.

[0085] VOC content: determined using the 1m³ chamber method, in accordance with GB / T 27630 standard.

[0086] Abrasion resistance: Refer to GB / T 1768 standard (Taber abrasion tester, load 1000g, grinding wheel CS-10).

[0087] Hydrolysis resistance: The peel strength retention rate was tested by placing the sample in an environment of 50℃ and 95% relative humidity for 72 hours.

[0088] Fatigue resistance: The sample was subjected to 5000 reciprocating bends at room temperature, and the stress retention rate was tested.

[0089] Surface hardness: Measured according to GB / T 2411 standard.

[0090] According to Table 1, we can see that: 1. Polycarbonate diol is key. Comparing Examples 1-3 (with polycarbonate diol) and Comparative Example 2 (without polycarbonate diol), we can see that the elongation at break increased dramatically from 1200% to 2100%-2800%, equivalent to going from barely bendable to being virtually indestructible; the peel strength also increased from 4.2 N / mm to 4.8-5.5 N / mm, like glue going from sticky to unbreakable. This demonstrates that polycaprolactone and polycarbonate work together very well, one providing softness and the other strength, perfectly solving the defects of bio-based materials that are either strong but brittle or tough but weak.

[0091] 2. Comparative Example 1 simulated existing polylactic acid-based bio-based synthetic leather technology, with an elongation at break of only 150% and a peel strength of 2.8 N / mm, far lower than the embodiments of this invention (elongation at break ≥ 2000%, peel strength ≥ 4.5 N / mm). Furthermore, Comparative Example 1 had a VOC content as high as 25 mg / m³ and a bio-based content of only 42%, while the VOC content of this invention is ≤ 8 mg / m³ and the bio-based content is 53%-56%. This demonstrates that the compound system of this invention, with polycaprolactone polyol as its core, represents a significant improvement over existing technologies in terms of flexibility, interfacial bonding strength, and environmental performance.

[0092] 3. Comparative Example 1 and Comparative Example 3: After omitting plasma treatment, the peel strength decreased from 5.2 N / mm to 3.5 N / mm (a decrease of 32.7%), proving that plasma treatment introduces polar groups on the fiber surface, significantly improving the interfacial bonding force between the base fabric and the connecting layer, and is a key technology for solving the problem of base fabric reinforcement.

[0093] Comparing Example 1 and Comparative Example 5: When the dryness exceeds the range (75%), the peel strength drops sharply from 5.2 N / mm to 3.2 N / mm (a decrease of 38.5%), which illustrates the critical importance of controlling the dryness at 63-67%. This range ensures that the bonding layer is in the optimal viscous flow state at the moment of bonding, which can both penetrate the base fabric and maintain strength, and is a process guarantee for achieving high peel strength.

[0094] Comparative Example 1 and Comparative Example 4: After omitting the surface treatment layer, the wear resistance deteriorated from 3.5 mg / 1000 cycles to 8.9 mg / 1000 cycles (a decrease of 154%), proving that the layered lubricating protective film formed by the graphene / boron nitride composite wear-resistant agent significantly improves surface durability.

[0095] Comparing Example 1 and Example 4, Example 1, which uses a compound of organozinc and organozinc (mass ratio 1:1), showed slightly better hydrolysis resistance (95%) and fatigue resistance (88%) than Example 4 (94% and 86%, respectively). This indicates that the compound catalyst has a synergistic advantage in building a more stable cross-linked network structure, which helps to improve the physical properties and long-term durability of the product.

[0096] 4. The VOC content of all embodiments is ≤7mg / m³, which is far superior to the 25mg / m³ of Comparative Example 1, and also superior to the most stringent standard in the automotive interior industry (GB / T 27630, ≤50mg / m³). The bio-based content is consistently between 53% and 56%, meeting the European bio-based material certification standard. This is due to the synergistic effect of using bio-based raw materials in the surface layer, connecting layer, surface treatment layer, and base fabric treatment layer.

[0097] In summary, the preparation method of this invention solves the performance balance problem by compounding polycaprolactone polyol and polycarbonate diol, solves the base fabric reinforcement problem by plasma pretreatment and polycaprolactone / nanocellulose composite emulsion, achieves high bio-based content by adding multiple layers of bio-based raw materials, ensures interfacial bonding by precise control of drying degree, and improves fatigue resistance by segmented curing. Finally, it produces synthetic leather with ultra-high toughness (elongation at break ≥2000%), high strength (peel strength ≥4.5N / mm), low VOC (≤8mg / m³), and high bio-based content (53%-56%), which comprehensively overcomes the technical bottlenecks of existing bio-based synthetic leather and has significant inventiveness and industrial applicability.

[0098] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-toughness bio-based synthetic leather, characterized in that: Includes the following steps: S1: The base fabric is pretreated, then impregnated with a bio-based emulsion, and dried to obtain a polycaprolactone-treated base fabric layer; S2: Coat the release paper with a water-based bio-based polyurethane surface layer slurry and dry it to form a water-based bio-based polyurethane surface layer; S3: A solvent-free polycaprolactone-based polyurethane slurry is coated onto an aqueous bio-based polyurethane surface layer. After pre-baking to a set dryness level, a polycaprolactone-treated base fabric layer is immediately bonded onto it and compacted to obtain a composite leather. The solvent-free polycaprolactone-based polyurethane slurry is composed of 80-95 parts of polycaprolactone polyol, 5-20 parts of polycarbonate diol, 59-63 parts of isocyanate, and 0.5-0.55 parts of compounded catalyst. S4: The composite leather is cured, the release paper is peeled off, and then a surface treatment liquid is sprayed on the surface. After drying, the finished synthetic leather product is obtained.

2. The method for preparing high-toughness bio-based synthetic leather according to claim 1, characterized in that: The polycaprolactone polyol is prepared by ring-opening polymerization of ε-caprolactone and 1,4-butanediol, with a number-average molecular weight of 2000±200 and a hydroxyl value of 56-60 mgKOH / g.

3. The method for preparing high-toughness bio-based synthetic leather according to claim 2, characterized in that: The isocyanate is an HDI trimer with an NCO content of 21±1%.

4. The method for preparing high-toughness bio-based synthetic leather according to claim 3, characterized in that: The composite catalyst is a mixture of organozinc catalyst and organozirconium catalyst, with a mass ratio of 1:(1-1.5).

5. The method for preparing high-toughness bio-based synthetic leather according to claim 4, characterized in that: In S1, the pretreatment is plasma treatment with a power of 450-550W and a treatment time of 2-4s; the bio-based emulsion is a mixed emulsion of polycaprolactone emulsion and nanocellulose, wherein the solid content of the polycaprolactone emulsion is 12±1%, and the amount of nanocellulose added accounts for 1-2% of the total mass of the emulsion.

6. The method for preparing high-toughness bio-based synthetic leather according to claim 5, characterized in that: In S2, the raw materials of the waterborne bio-based polyurethane surface slurry include, by weight, 78-83 parts bio-based polyurethane, 3-6 parts tackifier, 1.5-2 parts defoamer, 2-4 parts crosslinking agent, and 11-14 parts color paste. The soft segment of the bio-based polyurethane is compounded from polycaprolactone polyol and linseed oil polyol in a mass ratio of (2.5-3.0):

1.

7. The method for preparing high-toughness bio-based synthetic leather according to claim 1, characterized in that: In S3, the solvent-free polycaprolactone-based polyurethane slurry is dried to form a solvent-free polycaprolactone-based polyurethane bonding layer. The pre-drying temperature is 120-130℃, the pre-drying time is 2-3 minutes, and the dryness of the bonding layer after pre-drying is controlled at 63-67%.

8. The method for preparing high-toughness bio-based synthetic leather according to claim 1, characterized in that: In S4, a surface treatment layer is formed after spraying the surface treatment liquid. The raw materials of the surface treatment liquid include, by mass, 86-87 parts of castor oil modified waterborne polyurethane, 7-8 parts of sulfonate modified isocyanate crosslinking agent, and 4-6 parts of wear-resistant agent. The wear-resistant agent is a compound composed of graphene and boron nitride in a mass ratio of 1:2, and the wear-resistant agent is ultrasonically dispersed before use.

9. The method for preparing high-toughness bio-based synthetic leather according to claim 8, characterized in that: In S4, the curing process adopts segmented heating. The first curing temperature is 130-135℃ and the time is 0.5-1.5min; the second curing temperature is 135-140℃ and the time is 1-2min.

10. The method for preparing high-toughness bio-based synthetic leather according to claim 1, characterized in that: The base fabric is made of 800-900μm polyester knitted fabric with a warp breaking strength ≥300N / 5cm and a weft breaking strength ≥280N / 5cm.

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