Zero-pollution synthetic leather based on hydrophilic microporous strong chain structure and its manufacturing method

Abstract

This invention discloses a zero-pollution synthetic leather based on a hydrophilic microporous strong-chain structure and its manufacturing method, belonging to the field of synthetic leather manufacturing technology. The manufacturing method uses GA-MA as a chain extender, reacting it with starch-based polyols, PTMG, PEG, and IPDI to obtain a self-catalytic bio-based waterborne polyurethane emulsion. It employs a single-material TPU system: the TPU base fabric is prepared by melt spinning, the impregnated layer is wet-coated to form hydrophilic micropores, the surface layer is dry-coated to form a water-resistant and breathable membrane, and heat-setting forms strong chain bonds. The product of this invention has a tensile strength of 142 N / cm and a moisture permeability of 6.2 mg / cm². 2 • h, DMF residue < 5 mg / kg, bio-based content 52-68%, melt recovery rate 96%, carbon emissions 0.85 kg CO2 / m (48.5% lower than traditional methods); achieving “0 carbon, 0 toxic, 0 waste” fully ecological manufacturing of synthetic leather.

Description

Technical Field

[0001] This invention relates to the field of synthetic leather manufacturing technology, and in particular to zero-pollution synthetic leather based on a hydrophilic microporous strong chain structure and its manufacturing method. Background Technology

[0002] The synthetic leather industry has a history of several decades in my country, and its products are widely used in clothing, footwear, bags, furniture, and automotive interiors. However, the traditional synthetic leather manufacturing industry has long faced three core problems: heavy pollution, toxic and harmful products, and enormous resource consumption, which severely restrict the industry's sustainable development.

[0003] Traditional synthetic leather typically employs a multi-layered composite structure: the surface layer uses polyurethane (PU) resin, the bonding layer uses PU adhesive, and the base fabric is made of cotton, polyester, nylon, or blended synthetic fibers. This multi-material system stems from the different performance requirements of each functional layer: the surface layer needs to be abrasion-resistant and weather-resistant, while the base fabric requires high strength and low cost. However, from a material compatibility perspective: although polyurethane (surface energy approximately 35-45 mN / m) and polyester (surface energy approximately 43 mN / m) have similar surface energies, their chemical structures differ significantly, making molecular-level mixing impossible. Furthermore, their melting points differ greatly (PU approximately 150-180℃, PET approximately 250-260℃), making co-melting for recycling impossible. After disposal, complex separation processes (density separation, solvent dissolution, etc.) are required, resulting in high costs and low efficiency. Therefore, this multi-material system makes effective separation and recycling of waste synthetic leather impossible, ultimately leading to landfill or incineration, creating a double environmental burden.

[0004] Traditional synthetic leather manufacturing uses a large amount of organic solvents. For example, in the wet process of polyurethane, DMF (dimethylformamide) is an excellent solvent for PU, with a solubility parameter δ=12.1 (cal / cm³). 3 ) (1 / 2) DMF is close to 10-13 in PU. It takes about 0.8-1.2 kg of DMF to produce 1 meter of synthetic leather. DMF is completely miscible with water. This property is used to achieve the coagulation of PU: when the DMF / PU solution enters the water bath, DMF diffuses into the aqueous phase, the solubility of PU decreases and it coagulates into a film.

[0005] Various organic solvents are toxic: DMF has reproductive toxicity: it is metabolized in the body to N-hydroxymethyl-N-methylformamide, which inhibits dihydrofolate reductase; toluene has neurotoxicity: it is highly lipid-soluble and can easily cross the blood-brain barrier, affecting neurotransmitter transmission; methyl ethyl ketone (MEK) has mucosal irritation: its oxidative metabolism produces 2,3-butanedione, which reacts with protein amino groups; the residual amount of DMF in traditional oily PU synthetic leather can reach 1000-3000 ppm, far exceeding the environmental protection standard (≤100 ppm).

[0006] In addition, thermoplastic polyurethane (TPU) is composed of soft segments (polyether / polyester) and hard segments (diisocyanate + chain extender). Its microphase separation structure gives it excellent mechanical properties, but it also brings the problem of insufficient hydrophilicity.

[0007] The surface energy of water is 72.8 mN / m, while that of TPU is approximately 22-35 mN / m, exhibiting hydrophobicity (water contact angle approximately 85-102°). This significantly impacts the performance of synthetic leather, such as weak interfacial bonding between TPU and water-based resins (only physical adsorption, no chemical bonding); poor moisture permeability and air permeability (water molecules cannot be adsorbed and diffused on the hydrophobic surface); and difficulty in forming an ideal hydrophilic microporous structure. Studies have shown that unmodified TPU can achieve a water contact angle of 102.3°, with a surface energy of only 22.935 mN / m.

[0008] The preparation of waterborne polyurethane (WPU) requires the use of hydrophilic chain extenders to introduce hydrophilic groups (-COOH, -SO3H, etc.) to achieve water dispersibility of the resin. However, traditional hydrophilic chain extenders have the following problems:

[0009] 1) Solvent residue problem in the DMPA / DMBA system: Dimethylolpropionic acid (DMPA) has a high melting point of 175-185℃ and extremely low solubility in polyether polyols; in order to carry out the reaction in a homogeneous phase, N-methylpyrrolidone (NMP) must be used as a solvent.

[0010] 2) NMP has a high boiling point (202℃) and will remain in the final product. The EU stipulates that formulations with an NMP mass fraction higher than 5% are classified as toxic and have reproductive toxicity.

[0011] 3) Use of organotin catalysts: Dibutyltin dilaurate (DBTDL) is a commonly used catalyst in WPU synthesis. Its catalytic mechanism is that tin atoms coordinate with oxygen atoms of isocyanate, activate carbonyl carbon, and promote reaction with hydroxyl groups. However, organotin is highly toxic and can leave residues in the dried WPU film, which can easily lead to contact poisoning.

[0012] In recent years, the leather industry has tried the following improvement solutions:

[0013] (a) Water-based PU replacement method: Using WPU to replace oil-based PU has poor water resistance (too many hydrophilic groups), insufficient mechanical properties (low molecular weight), and the base fabric is still a multi-material;

[0014] (b) Solvent-free technology: Using 100% solid PU reduces solvents, but the base fabric material is not standardized and cannot be recycled;

[0015] (c) Surface hydrophilic modification: such as using H2O2 etching or acrylic acid (AA) grafting, but only surface treatment is performed, without achieving overall hydrophilicity, and the treatment is uneven;

[0016] (d) Use biodegradable materials instead of TPU: such as polylactic acid (PLA) and polybutylene terephthalate (PBAT) are biodegradable materials, but they have poor mechanical properties, insufficient heat resistance and high cost. Summary of the Invention

[0017] This invention addresses the problems of existing synthetic leather material systems being mixed, leading to non-recyclability after disposal; the use of organic solvents causing environmental pollution and product toxicity residues; insufficient hydrophilicity of TPU materials resulting in weak interfacial bonding and poor moisture permeability; pollution problems from traditional hydrophilic chain extenders; and high energy consumption and high carbon emissions in the production process. This invention proposes a zero-pollution synthetic leather based on a hydrophilic microporous strong chain structure and its manufacturing method. It attempts to provide a single TPU material system and develop a solvent-free, catalyst-free bio-based WPU. It also attempts to design PEG copolymerization and GA-MA chain extenders for TPU molecular chains and synthesize a 100% bio-based GA-MA chain extender. The process employs a combination of low-temperature processing, bio-based raw materials, and solvent-free recovery.

[0018] To achieve the above objectives, the present invention adopts the following technical solution:

[0019] A method for manufacturing zero-pollution synthetic leather based on a hydrophilic microporous strong-chain structure includes the following steps:

[0020] Step 1: Thermoplastic polyurethane (TPU) melt spinning into fabric. Thermoplastic polyurethane particles are melt-spun into TPU fibers, which are then woven into a TPU base fabric using needle punching or hydroentangling processes. The TPU particles are polyethylene glycol (PEG) copolymerized TPU. The melt spinning temperature is 210-230℃, the stretch ratio is 2-4 times, and the heat setting temperature is 100-120℃. The core technology of this step is melt spinning and heat setting, which form a dense, hydrophobic skeletal structure.

[0021] Step 2: Synthesis of Bio-based Waterborne Polyurethane (WPU). Starch-based polyols and the bio-based hydrophilic chain extender GA-MA were used as raw materials, and a self-catalytic bio-based waterborne polyurethane emulsion was synthesized by reacting with diisocyanate. GA-MA is prepared by the monoesterification reaction of gallic acid and maleic anhydride, and possesses self-catalytic activity, requiring no external organotin catalyst. The core technology of this step is self-catalytic polymerization to prepare a hydrophilic impregnating material.

[0022] Step 3: Wet Impregnation and Coagulation. The TPU base fabric obtained in Step 1 is completely impregnated in the bio-based aqueous polyurethane emulsion obtained in Step 2, and then placed in a water coagulation bath. A non-solvent-induced phase separation process is used to form a foamed layer with a hydrophilic microporous structure inside and on the surface of the base fabric. The coagulation bath temperature is 25-40℃, and the coagulation time is 8-15 minutes. The core technology in this step is NIPS phase separation to form a hydrophilic microporous layer.

[0023] Step 4: Dry Coating. A surface layer is formed on the impregnated base fabric obtained in Step 3 using a dry coating process with a bio-based waterborne polyurethane emulsion. The coating thickness is 0.1-0.3 mm, the drying temperature is 110-130℃, and the drying time is 2-5 minutes. The core technology of this step is the hydrophilic moisture-permeable mechanism, forming a water-resistant and breathable layer.

[0024] Step 5: Heat setting. The semi-finished product obtained in Step 4 is subjected to heat setting treatment at a temperature of 100-130℃ for 2-5 minutes and a pressure of 0.1-0.5MPa. The core technology of this step is molecular chain diffusion, which forms strong interlayer chain bonds.

[0025] The core innovations of this invention are as follows: First, a single TPU material system, where the base fabric, impregnation layer, and top layer are all homologous thermoplastic polyurethane materials, achieving 100% recyclability; Second, the bio-based hydrophilic chain extender GA-MA, which has advantages such as 100% bio-based content, zero solvent use, no catalyst requirement, and self-catalytic activity; Third, a gradient structure design, where the dense hydrophobic fiber body provides strength, the hydrophilic micropores in the impregnation zone provide moisture permeability, and the water-proof and breathable top layer provides waterproofing; Fourth, self-catalytic polymerization, where the phenolic hydroxyl groups of gallic acid in GA-MA have catalytic activity, eliminating the need for external organotin catalysts.

[0026] It should be further explained that step 1 involves TPU molecular structure design and fiber preparation:

[0027] The design principle of TPU fiber body is based on the relationship between microphase separation structure and performance. The excellent performance of TPU comes from the microphase separation structure formed by the thermodynamic incompatibility of soft and hard segments. The soft segments are polyether or polyester with a glass transition temperature below -50°C, providing flexibility and elasticity; the hard segments are the reaction products of diisocyanate and chain extender, with a glass transition temperature above 50°C, forming physical crosslinking points, providing strength and heat resistance.

[0028] The specific requirements of this invention for the TPU fiber body are as follows: Regarding high strength, the tensile strength must reach above 35 MPa, achieved through high hard segment content and tensile orientation, with a hard segment content of 35-45%, increasing the physical cross-linking density of the hard segments; Regarding low water absorption, the water absorption rate must be below 5%, achieved through using polytetrahydrofuran glycol (PTMG) as the main soft segment and densification treatment. PTMG is hydrophobic, reducing the exposure of hydrophilic ether bonds; Regarding a dense skin layer, it must be pore-free, achieved through rapid cooling and heat setting to suppress crystallization defects; Regarding compatibility with the impregnated layer, it requires the use of TPU with the same chemical basis, allowing the molecular chains to diffuse into each other.

[0029] The design of TPU synthesis formulations is based on matching solubility parameters. The solubility parameters of each component should be similar to ensure homogeneous reaction. The solubility parameter of PTMG is 9.2-9.5 (cal / cm³). 3 ) (1 / 2) The PEG ratio is 9.8-10.2 (cal / cm³). 3 ) (1 / 2) IPDI is 10.0-10.5 (cal / cm²). 3 ) (1 / 2) The difference is less than 2, indicating good compatibility.

[0030] The specific components of the TPU synthesis formulation are as follows: The hydrophobic soft segment uses PTMG (molecular weight 2000, 70 parts, functionality 2), providing elasticity, hydrophobicity, and a low glass transition temperature; the hydrophilic soft segment uses PEG (molecular weight 1000, 20 parts, functionality 2), introducing ether-oxygen hydrophilic groups; the bio-based soft segment uses starch-based polyol (molecular weight approximately 500, 10 parts, functionality 3-4), providing a bio-based source and rigidity; the hard segment uses IPDI (molecular weight 222). The product is used in an amount of 85 parts, with a functionality of 2, to provide strength and weather resistance; the small molecule chain extender is BDO, with a molecular weight of 90, used in an amount of 12 parts, with a functionality of 2, for chain growth and hard segment formation; the hydrophilic chain extender is DMPA, with a molecular weight of 134, used in an amount of 6 parts, with a functionality of 2, to introduce carboxyl groups to achieve water dispersion; the catalyst is DBTDL, with a molecular weight of 631, used in an amount of 0.1 parts, for fiber preparation only; the neutralizing agent is triethylamine, with a molecular weight of 101, used in an amount of 4.5 parts, to neutralize carboxyl groups to form salts.

[0031] The TPU melt spinning process is as follows: TPU particles are dried and dehumidified, then melt-extruded, filtered through melt and extruded from the spinneret, cooled and solidified, stretched and oriented, and then heat-set and wound to obtain TPU fibers.

[0032] The process parameters and mechanisms are as follows: Drying process: temperature 100-110℃, preferably 105℃, time 4-8 hours, preferably 6 hours, moisture content controlled below 80ppm to prevent hydrolysis and degradation; Melt extrusion process: temperature 210-230℃, preferably 220℃, 150-180℃ above the melting point and 250℃ below the decomposition temperature; screw speed 30-50rpm, preferably 40rpm, to control the melt delivery rate; Spinning process: die temperature 220-240℃, preferably 230℃, to reduce melt viscosity; spinneret diameter is... 0.2-0.5mm, preferably 0.3mm, to control the fineness of the nascent fibers; Cooling process: air cooling is used, and the cooling distance is 5-15cm, preferably 10cm, to rapidly cool and form a dense skin layer; Stretching process: the stretching ratio is 2-4 times, preferably 3 times, to orient the molecular chains and improve strength; the stretching temperature is 60-100℃, preferably 80℃, which is higher than the glass transition temperature and is conducive to chain segment movement; Heat setting process: the temperature is 100-120℃, preferably 110℃, and the time is 30-60 seconds, preferably 45 seconds, to eliminate internal stress and stabilize the structure.

[0033] The densification mechanism is as follows: after the melt is extruded from the spinneret, the surface cools rapidly to form a dense skin layer. The skin layer inhibits the formation of internal micropores, reduces water absorption, and heat setting further arranges the molecular chains in a more regular manner, thereby increasing the crystallinity.

[0034] The weaving parameters for TPU nonwoven fabric are as follows: fiber fineness is 1.5-3.0D, preferably 2.0D, which affects specific surface area and porosity; the weaving method is needle punching or hydroentangling, preferably needle punching, which mechanically entangles without chemical adhesives; the base fabric weight is 80-150 g / m². 2 120g / m 2 It influences the mechanical properties and moisture permeability balance; the base fabric thickness is 0.5-1.2mm, preferably 0.8mm, to ensure impregnation space; the porosity is 70-85%, preferably 78%, to provide channels for impregnation.

[0035] TPU fiber properties: Fiber diameter: 0.3mm spinneret, stretched 3 times; Tensile strength: 38.2MPa, molecular chain orientation and hard segment physical cross-linking, higher than the 30-35MPa of traditional polyester fiber, test standard is GB / T 14344; Elongation at break: 245%, test standard is GB / T 14344, soft segments provide elastic recovery; Water contact angle: 88.5°, close to the hydrophobic boundary (greater than 90° is hydrophobic), meeting the low water absorption requirement, test method is seat drop method, PTMG as the main soft segment has hydrophobicity; Water absorption rate (24h): 4.2%, far lower than the hydrophilic modified control sample (greater than 15%), test method is immersion method, dense skin layer plus hydrophobic soft segment; Thermal decomposition temperature: 312℃, test method is TGA, hard segment decomposition temperature is relatively high.

[0036] It should be further noted that step 2 involves the synthesis of the bio-based hydrophilic chain extender GA-MA:

[0037] The molecular design of GA-MA is based on renewable resources. Gallic acid (GA) is a polyphenol extracted from fruits, nuts, and flowers. Each molecule contains three hydroxyl groups and one carboxyl group, possessing natural antioxidant properties. Maleic anhydride (MA) is the third largest source of anhydrides. It is chemically reactive, hydrolyzing to produce two carboxyl groups, exhibiting strong hydrophilicity.

[0038] The reaction mechanism is a monoesterification reaction: the anhydride ring of maleic anhydride undergoes ring-opening under acid catalysis, and esterifies with the phenolic hydroxyl or carboxyl group of gallic acid to generate a GA-MA monoester containing a carboxyl group and a double bond. The molecular structure is HOOC-CH=CH-COO-C6H2(OH)2-COOH.

[0039] The GA-MA synthesis formula is as follows: Gallic acid (GA): 100 parts, molar ratio 1.0, molecular weight 170, providing the polyphenol structure and three hydroxyl groups. Maleic anhydride (MA): 65 parts, molar ratio 1.2, molecular weight 98, providing the anhydride and hydrophilic groups. p-Toluenesulfonic acid: 2 parts, molar ratio 0.02, molecular weight 172, serving as an acid catalyst to accelerate esterification. Acetone: 250 parts, molecular weight 58, used as a solvent to dissolve the raw materials. The molar ratio is designed based on GA:MA = 1:1.2, with a slight excess of MA to ensure complete reaction of GA. Excess MA can be recovered in subsequent vacuum distillation.

[0040] The synthesis process of GA-MA is as follows: Step 1: Feeding: Add all raw materials to the reactor at room temperature. Step 2: Dissolve: Dissolve GA and MA in acetone by stirring at 40℃ for 30 minutes. Step 3: Esterification: React at 60-80℃ for 4-8 hours to achieve anhydride ring-opening esterification. Step 4: Solvent recovery: Recover acetone by vacuum distillation at 50℃ for 1 hour. Step 5: Drying: Dry at 60℃ for 2 hours to remove residual solvent.

[0041] Reaction kinetics analysis indicates that the esterification reaction is reversible, requiring timely removal of the generated water; the catalytic mechanism of p-toluenesulfonic acid involves protonation of the carbonyl oxygen of the acid anhydride, enhancing its electrophilicity; at a reaction temperature of 80℃, the reaction rate constant k is approximately 0.15 h⁻¹. -1 The conversion rate is greater than 95% within 4 hours.

[0042] GA-MA properties: pale yellow powder; melting point: 145-150℃, the melting point is lower than GA's 250℃ after the introduction of MA; acid value: 380-420mg KOH / g, containing gallic acid carboxyl and maleic acid carboxyl groups, tested by titration; hydroxyl value: 280-320mg KOH / g, the phenolic hydroxyl group of gallic acid is retained, tested by acetylation; purity: ≥95%, tested by HPLC, is the monoesterification main product; bio-based content: 100%.

[0043] The following is a comparison of GA-MA with traditional chain extenders: **Bio-based content:** GA-MA is 100%, DMPA is 0%, DMBA is 0%, and GA-MA is plant-derived. **Catalyst requirements:** GA-MA requires no catalyst, while DMPA and DMBA require organotin catalysts. The phenolic hydroxyl groups in GA-MA exhibit autocatalytic activity. **Organic solvents:** GA-MA uses acetone, which is recyclable. DMPA and DMBA use NMP, which leaves residues. DMPA requires NMP for solubilization. **VOC emissions:** GA-MA is close to zero, while DMPA and DMBA are moderately high. NMP has a high boiling point and is difficult to remove. **Autocatalytic activity:** GA-MA exhibits autocatalytic activity, while DMPA and DMBA do not. The phenolic hydroxyl groups in GA-MA demonstrate catalytic activity.

[0044] It should be further noted that step 2 also involves the synthesis of bio-based waterborne polyurethane:

[0045] The autocatalytic mechanism is based on the catalytic effect of the phenolic hydroxyl group. The catalytic cycle is as follows: First, the phenolic hydroxyl group Ar-OH forms a hydrogen-bonded complex with the isocyanate R-NCO; second, the carbonyl carbon of the isocyanate in the complex is activated, and its electrophilicity is enhanced; third, the alcoholic hydroxyl group R'-OH attacks the activated carbonyl carbon; fourth, urethane is generated, and the phenolic hydroxyl group is regenerated.

[0046] The kinetic comparison shows that the reaction rate constant k is 0.015 L·mol⁻¹ without a catalyst. -1 ·s -1 The activation energy Ea is 68.5 kJ / mol; the activation energy k is 0.095 L·mol⁻¹ for organotin DBTDL catalyst. -1 ·s -1 Ea is 52.3 kJ / mol; k is 0.082 L·mol⁻¹ during GA-MA autocatalysis. -1 ·s -1 The Ea is 55.8 kJ / mol. GA-MA exhibits autocatalytic activity close to that of organotin catalysts, but is completely non-toxic.

[0047] The synthetic formulation is as follows: The bio-based soft segment uses 24 parts of the starch-based polyol Ecotrion, with a molecular weight of approximately 500 and a functionality of 3-4, providing a bio-based source and rigidity. The polyether diol uses 36 parts of PTMG with a molecular weight of 2000 and a functionality of 2, providing elasticity and hydrophobicity. The hydrophilic diol uses 20 parts of PEG with a molecular weight of 1000 and a functionality of 2, providing hydrophilicity and moisture permeability. The hard segment uses 43.5 parts of IPDI with a molecular weight of 222 and a functionality of 2, providing strength and weather resistance. The small molecule chain extender uses 11 parts of BDO with a molecular weight of 90 and a functionality of 2, for chain growth. The hydrophilic chain extender uses 6.5 parts of GA-MA with a molecular weight of approximately 268 and a functionality greater than 2, providing hydrophilicity and autocatalytic activity. The end-capping monomer uses 11 parts of HEA with a molecular weight of 116 and a functionality of 1, introducing double bonds. The neutralizing agent used was triethylamine, 5 parts, with a molecular weight of 101, to neutralize carboxyl groups. The dispersion medium was deionized water, 180 parts, with a molecular weight of 18, as the continuous phase.

[0048] The NCO / OH equivalence ratio is calculated as follows: the total number of NCO moles is 43.5, which is equal to 0.392 moles, because IPDI is bifunctional; the total number of OH moles is 24, which is approximately equal to 0.35 moles; the NCO / OH ratio is approximately 1.12, with excess NCO used for end capping.

[0049] The synthesis process steps are as follows: Step 1: Dehydrate the polyol and GA-MA under vacuum at 100-110℃ for 2 hours to remove moisture and prevent side reactions. Step 2: Add IPDI and prepolymerize at 80-90℃ for 2 hours, where NCO reacts with OH to form a prepolymer. Step 3: Add BDO and extend the chain at 85℃ for 1 hour to increase the molecular weight. Step 4: Add HEA and cap the ends at 80℃ for 1 hour to introduce double bonds and control the molecular weight. Step 5: Cool to 40℃ for 15 minutes to reach the neutralization temperature. Step 6: Add triethylamine and neutralize at 40℃ for 15 minutes, where the carboxyl groups form salts to achieve hydrophilicity. Step 7: Add deionized water and emulsify at high speed at 40℃ for 30 minutes to induce a phase inversion emulsification. Step 8: Desolventize under reduced pressure at 50℃ for 1 hour to remove acetone.

[0050] The prepolymerization kinetics are as follows: at a temperature of 85℃, the reaction rate constant k is approximately 0.025 L·mol⁻¹. -1 ·s -1 The conversion rate is greater than 95% in 2 hours, and the NCO residue is about 2-3%.

[0051] The properties of the bio-based WPU emulsion are as follows: Solid content: 42% (tested by gravimetric method); pH value: 7.5-8.5 (tested by pH meter); Viscosity at 25℃: 350 mPa·s (tested by rotational viscometer, suitable for impregnation); Average particle size: 85 nm (tested by DLS, sufficient hydrophilic groups); Storage stability: greater than 6 months (tested by static observation, no sedimentation or stratification); Bio-based content: 52%, derived from starch and GA-MA; VOC content: less than 10 g / L (tested by GC-MS, free of NMP and organotin).

[0052] The properties of the bio-based WPU membrane are as follows: tensile strength: 24.5 MPa, tested according to GB / T 1040, with physical cross-linking of the hard segment; elongation at break: 685%, tested according to GB / T 1040, with flexibility of the soft segment; water contact angle: 72.5°, tested by the seat drop method, with PEG and GA-MA providing hydrophilicity; water absorption rate 24h: 12.8%, tested by the immersion method, moderately absorbent but not permeable; thermal decomposition temperature: 418℃, tested by TGA, with good thermal stability of the hard segment.

[0053] It should be further explained that step 3 involves wet impregnation and gradient structure construction:

[0054] The core challenge of gradient structure design is achieving the difference between the dense, hydrophobic fibers and the hydrophilic micropores in the impregnation zone. The solution is selective impregnation: the TPU fiber body has a dense structure that prevents water-based TPU from penetrating; the impregnating material has an appropriate viscosity, spreading and filling the voids only on the fiber surface; during solidification, phase separation occurs only in the voids without damaging the fiber.

[0055] The performance division of the three-layer gradient structure is as follows: The main function of the TPU fiber body is skeletal support, with low hydrophilicity (contact angle greater than 85°), dense and non-porous pore structure, and water absorption rate less than 5%; the main function of the impregnated zone is moisture-permeable buffering, with high hydrophilicity (contact angle less than 70°), micropore structure of 1-10μm, and water absorption rate of 15-30%; the main function of the surface layer is waterproof and breathable, with medium hydrophilicity (contact angle 60-80°), dense pore structure containing molecular channels, and water absorption rate of 8-15%.

[0056] The impregnation slurry formulation is as follows: The matrix uses a bio-based WPU emulsion, 100 parts, for film formation, with hydrophilic groups providing moisture permeability; the crosslinking agent uses aziridine, 2.5 parts, to enhance water resistance and react with carboxyl groups to form crosslinks; the foaming agent uses a microsphere foaming agent, 6 parts, to form micropores, with thermal expansion generating bubbles; the leveling agent uses polyether-modified silicone, 0.5 parts, for leveling and reducing surface tension; the thickener uses a polyurethane associative type, 0.6 parts, for viscosity adjustment and hydrophobic association thickening; the functional filler uses leather ultrafine powder, 10 parts, to enhance moisture permeability, with collagen providing hydrophilic pores.

[0057] The wet coagulation mechanism is solvent-inducing phase separation. The thermodynamic analysis of the phase separation process is divided into five stages. Stage 1: The base fabric is impregnated, and aqueous TPU fills the voids. The water concentration is 50%, and the TPU concentration is 50%, resulting in a continuous liquid structure. Stage 2: Upon entering the coagulation bath, water diffuses in, increasing the water concentration to 60% and decreasing the TPU concentration to 40%, initiating phase separation. Stage 3: Reaching the critical concentration, phase separation occurs at 65% water concentration and 35% TPU concentration, separating the TPU-rich phase from the TPU-poor phase. Stage 4: The TPU-rich phase solidifies to form a framework, with a water concentration of 70% and a TPU concentration of 30%, forming a microporous framework. Stage 5: The TPU-poor phase forms micropores, with a water concentration of 80% and a TPU concentration of 20%, forming interconnected micropores.

[0058] The impregnation process parameters are as follows: Impregnation time: 1-3 minutes, preferably 2 minutes, to fully penetrate the pores; Liquid carryover rate: 150-250%, preferably 200%, to control the impregnation amount; Coagulation bath temperature: 25-40℃, preferably 32℃, to affect the phase separation rate; Coagulation time: 8-15 minutes, preferably 10 minutes, to ensure complete coagulation; Water washing temperature: 30-50℃, preferably 40℃, to remove residual substances; Drying temperature: 80-100℃, preferably 90℃, to remove moisture.

[0059] The parameter-structure-performance relationship for microporous structure regulation is as follows: As the solid content increases, the pore size decreases and the porosity decreases. At high solid content, phase separation is limited, and the volume fraction of the polymer-rich phase is high, with an optimization range of 35-45%. As the solidification temperature increases, the pore size first increases and then decreases. Increased temperature increases the water diffusion rate and accelerates phase separation, but excessively high temperatures cause TPU to solidify too quickly, leading to micropore coarsening, with an optimization range of 25-40℃. Extended solidification time increases porosity, resulting in more complete phase separation and an increase in the volume of the lean phase, with an optimization range of 8-12 minutes. Increased foaming agent dosage increases both pore size and porosity, with chemical foaming generating additional gas pores that overlap with the phase separation pores, with an optimization range of 4-8 parts.

[0060] Characteristics of the obtained hydrophilic microporous foamed layer: Average pore size: target value 1-10μm, measured value 3.8μm, dual mechanism of phase separation and foaming; Porosity: target value 40-60%, measured value 52%, tested by density method, volume calculation; Connectivity: target value greater than 80%, measured value 86%, tested by bubble point method, open-cell structure; Pore wall thickness: target value 0.5-2μm, measured value 1.2μm, pore wall thickness is TPU-rich phase.

[0061] It should be further noted that step 4 involves dry topcoat application:

[0062] The core mechanism of the topcoat formulation design is hydrophilic permeability. This mechanism includes three key points: First, macroscopic non-porous, meaning the topcoat is dense and liquid water cannot pass through, thus achieving waterproofing; second, molecular hydrophilic channels, meaning the ether oxygen groups of the PEG segments form hydrogen bonds with water molecules; and third, gradient transfer, meaning water molecules are adsorbed on the high humidity side, diffuse along the hydrophilic segments to the low humidity side, and desorb on the low humidity side.

[0063] The water molecule transport pathway is as follows: sweat reaches the outer surface of the surface layer in liquid form, is adsorbed by hydrophilic groups, is transferred along the molecular chain through hydrogen bonds, and desorbs into water vapor on the inner surface.

[0064] The relationship between the diffusion coefficient and the density of hydrophilic groups follows Fick's first law: J = -D·(dc / dx). As the density of hydrophilic groups increases, the adsorption capacity of water molecules strengthens, and the diffusion coefficient D increases. However, an excessive number of hydrophilic groups can lead to membrane swelling, resulting in a decrease in strength.

[0065] The surface coating formulation is as follows: The matrix uses a bio-based WPU emulsion, 100 parts, for film formation; the hydrophilic groups provide moisture permeability channels. The crosslinking agent uses aziridine, 3.0 parts, to control swelling and inhibit excessive water absorption through crosslinking. The hand-feel agent uses a composite hand-feel agent, 4 parts, for a soft and smooth feel and reduced coefficient of friction. The defoamer uses polyether-modified silicone, 0.3 parts, to eliminate bubbles and reduce surface tension. The leveling agent uses polyacrylate, 0.4 parts, for a smooth surface and improved wettability.

[0066] The coating process parameters are as follows: Coating method: scraper coating or roller coating, scraper coating is preferred, and the thickness is uniform and controllable; Coating thickness: 0.1-0.3mm, preferably 0.18mm, to ensure waterproofness; Pre-drying temperature: 60-80℃, preferably 70℃, to slowly evaporate moisture; Main drying temperature: 110-130℃, preferably 120℃, to form a complete film; Drying time: 2-5 minutes, preferably 3 minutes, to ensure full cross-linking.

[0067] Analysis of the drying process: During the pre-drying stage, the temperature is 60-80℃, and the moisture evaporates slowly to prevent the formation of bubbles; during the main drying stage, the temperature is above 100℃, and the moisture evaporates rapidly, allowing the cross-linking reaction to proceed; the aziridine cross-linking reaction is activated at a temperature above 100℃.

[0068] The surface layer performance is as follows: Film thickness: target value 0.1-0.3mm, measured value 0.18mm, tested using a thickness gauge, coating amount controlled; Hydrostatic pressure resistance: target value greater than 50kPa, measured value 62kPa, tested according to GB / T 4744, dense film blocks liquid water; Water contact angle: target value 60-80°, measured value 72°, tested using the seat drop method, moderately hydrophilic; Moisture permeability: target value greater than 2000g / m³ 2 • 24h, measured value 2350g / m 2 • 24h, test standard is GB / T 12704, hydrophilic gate effect; surface hardness: target value H-2H, measured value H, test method is pencil hardness, cross-linked network; abrasion resistance: target value greater than 1000 times, measured value 1250 times, test method is Talbot method, dense surface.

[0069] It should be further explained that step 5 involves heat setting and the formation of a strong chain structure:

[0070] The formation mechanism of strong chain structures includes a triple strong chain mechanism:

[0071] Mechanism 1 involves molecular chain diffusion. The heat treatment temperature is 120℃, higher than the glass transition temperature of TPU, with the soft segment at approximately -50℃ and the hard segment at approximately 50-80℃. The molecular chains gain sufficient energy to diffuse into each other at the interface, with a diffusion depth of approximately 5-10 nm, forming a molecular-level interpenetrating network.

[0072] Mechanism 2 involves chemical bonding. The aziridine crosslinking agent reacts with the carboxyl groups in the impregnation layer and surface layer to form covalent bonds, significantly improving the interfacial bonding strength. The crosslinking reaction proceeds fully at temperatures above 100°C.

[0073] Mechanism 3 is physical anchoring. The impregnated layer penetrates into the fiber gaps, forming a mechanical interlock. After curing, it forms anchor points that resist interfacial peeling.

[0074] The heat setting process parameters are as follows: Setting temperature: 100-130℃, preferably 120℃, which is higher than the glass transition temperature so that the molecular chains can move; Setting time: 2-5 minutes, preferably 3 minutes, to allow for sufficient diffusion and cross-linking; Pressure: 0.1-0.5MPa, preferably 0.3MPa, to promote interlayer contact.

[0075] The interface bonding strength comparison is as follows: the peel strength of the traditional PU and polyester interface is 8-12 N / cm, which is only physical adhesion; the peel strength of the present invention before heat setting is 12-15 N / cm, which is reinforced by impregnation anchoring; the peel strength of the present invention after heat setting is 18-25 N / cm, which is 80-100% higher than that before heat setting, due to molecular chain diffusion and chemical cross-linking.

[0076] The method for manufacturing zero-pollution synthetic leather based on a hydrophilic microporous strong-chain structure proposed in this invention refers to... Figure 1 The specific process parameters are shown in Table 1 below:

[0077] Table 1. Summary of process parameters for zero-pollution synthetic leather manufacturing methods

[0078]

[0079] Compared with the prior art, the present invention has the following significant advantages.

[0080] 1. Achieving "Zero Carbon" Emissions. This invention employs a fully aqueous system, eliminating the use of any organic solvents and completely eliminating solvent recovery energy consumption (approximately 0.6 kWh per meter of synthetic leather). The drying temperature of the aqueous system is 80-140℃, approximately 40℃ lower than the 130-180℃ of the oil-based system, resulting in a 29% reduction in drying energy consumption. Bio-based raw materials (starch-based polyols, GA-MA) replace petroleum-based raw materials, reducing the carbon footprint by approximately 40%. The synergistic effect of these three factors reduces carbon emissions per meter of synthetic leather from 1.65 kg CO2 in traditional processes to 0.85 kg CO2, a reduction of 48.5%. The mechanism lies in: the aqueous system eliminates the phase change energy consumption of solvent distillation, the low temperature reduces heat loss, and the bio-based system utilizes carbon fixation through plant photosynthesis.

[0081] 2. Achieving "zero toxicity" and environmental friendliness. This invention does not use any organic solvents such as DMF, toluene, or NMP. DMF residue in the product is <5 mg / kg, and toluene and methyl ethyl ketone were not detected. GA-MA exhibits autocatalytic activity (reaction rate constant 0.082 L·mol⁻¹). -1 ·s -1 The GA-MA catalyst (with an activation energy of 55.8 kJ / mol) replaced the toxic organotin catalyst, resulting in zero organotin residue in the product. Precise control of the NCO / OH equivalent ratio (1.12) ensured that free isocyanate residue was <0.5 mg / kg. The mechanism lies in the fact that the phenolic hydroxyl groups of GA-MA form hydrogen-bonded complexes with isocyanates, lowering the reaction activation energy and achieving catalyst-free polymerization. The all-aqueous system eliminates the introduction of toxic substances at the source.

[0082] 3. Achieving "Zero Waste" Recycling. This invention employs a single TPU material system, with the base fabric, impregnated layer, and top layer all made of homologous TPU. After disposal, it can be directly crushed, melted, granulated, and reprocessed, achieving a melt recovery rate of 96% and retaining 85-92% of its tensile strength after recycling. The mechanism lies in the fact that the TPU molecular chain has a linear structure, and the urethane bonds in the hard segments can reversibly break and recombine at high temperatures, giving the material thermoplastic reprocessing capabilities; the homologous materials ensure compatibility during the melting process.

[0083] 4. Significantly improved overall performance. The strong-chain structure, through a triple mechanism (molecular chain diffusion depth of 5-10 nm, chemical cross-linking density of 0.05-0.10 mol / kg, and physical anchoring interlocking), increases the interfacial peel strength from 8-12 N / cm to 22 N / cm, an improvement of 120%. Hydrophilic micropores (pore size 3.8 μm, porosity 52%, connectivity 86%) combined with a hydrophilic moisture permeability mechanism increase the moisture permeability from 2.5 mg / cm³. 2 • h increased to 6.2 mg / cm 2 •h, improved by 148%. The dense surface film (resistant to hydrostatic pressure of 62kPa) achieves water resistance and breathability. The product has a tensile strength of 142N / cm, a tear strength of 58N, an elongation at break of 285%, and an abrasion resistance of 1250 cycles, with overall performance surpassing traditional oil-based PU synthetic leather. Attached Figure Description

[0084] Figure 1 This is a flowchart of the manufacturing method for zero-pollution synthetic leather based on a hydrophilic microporous strong chain structure proposed in this invention. Detailed Implementation

[0085] 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.

[0086] Example 1. Standard Formulation (Optimal Combination):

[0087] A method for manufacturing zero-pollution synthetic leather based on a hydrophilic microporous strong-chain structure includes the following steps:

[0088] Step 1: Thermoplastic polyurethane (TPU) melt spinning into fabric. Thermoplastic polyurethane particles are melt-spun into TPU fibers, which are then woven into a TPU base fabric using needle punching or hydroentangling processes. The TPU particles are polyethylene glycol (PEG) copolymerized TPU, with a melt spinning temperature of 210-230℃, a stretch ratio of 2-4 times, and a heat setting temperature of 100-120℃.

[0089] Step 2: Synthesis of bio-based waterborne polyurethane (WPU). A self-catalytic bio-based waterborne polyurethane emulsion was synthesized by reacting starch-based polyols and the bio-based hydrophilic chain extender GA-MA with diisocyanate. GA-MA is prepared by the monoesterification reaction of gallic acid and maleic anhydride, exhibiting self-catalytic activity and requiring no external organotin catalyst.

[0090] Step 3: Wet Impregnation and Coagulation. The TPU base fabric obtained in Step 1 is completely impregnated in the bio-based aqueous polyurethane emulsion obtained in Step 2, and then placed in a water coagulation bath. A non-solvent-induced phase separation process is used to form a foamed layer with a hydrophilic microporous structure inside and on the surface of the base fabric. The coagulation bath temperature is 25-40℃, and the coagulation time is 8-15 minutes. The core technology in this step is NIPS phase separation to form a hydrophilic microporous layer.

[0091] Step 4: Dry Coating. A surface layer is formed on the impregnated base fabric obtained in Step 3 using a dry coating process with a bio-based waterborne polyurethane emulsion. The coating thickness is 0.1-0.3 mm, the drying temperature is 110-130℃, and the drying time is 2-5 minutes. The core technology of this step is the hydrophilic moisture-permeable mechanism, forming a water-resistant and breathable layer.

[0092] Step 5: Heat setting. The semi-finished product obtained in Step 4 is subjected to heat setting treatment at a temperature of 100-130℃ for 2-5 minutes and a pressure of 0.1-0.5MPa. The core technology of this step is molecular chain diffusion, which forms strong interlayer chain bonds.

[0093] The specific components of the TPU synthesis formulation are as follows: The hydrophobic soft segment uses PTMG (molecular weight 2000, 70 parts, functionality 2); the hydrophilic soft segment uses PEG (molecular weight 1000, 20 parts, functionality 2); the bio-based soft segment uses starch-based polyol (molecular weight approximately 500, 10 parts, functionality 3-4); the hard segment uses IPDI (molecular weight 222, 85 parts, functionality 2); the small molecule chain extender uses BDO (molecular weight 90, 12 parts, functionality 2); the hydrophilic chain extender uses DMPA (molecular weight 134, 6 parts, functionality 2); the catalyst uses DBTDL (molecular weight 631, 0.1 parts, used only for fiber preparation); and the neutralizing agent uses triethylamine (molecular weight 101, 4.5 parts, used to neutralize carboxyl groups to form salts).

[0094] The GA-MA synthesis formula is as follows: Gallic acid (GA): 100 parts, molar ratio 1.0, molecular weight 170; Maleic anhydride (MA): 65 parts, molar ratio 1.2, molecular weight 98; p-Toluenesulfonic acid: 2 parts, molar ratio 0.02, molecular weight 172; Acetone: 250 parts, molecular weight 58. The molar ratio is designed based on GA:MA = 1:1.2, with a slight excess of MA to ensure complete reaction of GA. Excess MA can be recovered in subsequent vacuum distillation.

[0095] The bio-based waterborne polyurethane synthesis formulation is as follows: The bio-based soft segment uses 24 parts of starch-based polyol Ecotrion, with a molecular weight of approximately 500 and a functionality of 3-4; the polyether diol uses 36 parts of PTMG with a molecular weight of 2000 and a functionality of 2; the hydrophilic diol uses PEG with a molecular weight of 1000, with a functionality of 2; the hard segment uses IPDI, with a molecular weight of 222 and a functionality of 2; the small molecule chain extender uses BDO, with a molecular weight of 90 and a functionality of 2; the hydrophilic chain extender uses GA-MA, with a molecular weight of approximately 268 and a functionality greater than 2; the end-capping monomer uses HEA, with a molecular weight of 116 and a functionality of 1; the neutralizing agent uses triethylamine, with a molecular weight of 101; and the dispersion medium uses deionized water, with a molecular weight of 18.

[0096] The impregnation slurry formulation is as follows: the matrix is ​​a bio-based WPU emulsion, with a dosage of 100 parts; the crosslinking agent is aziridine, with a dosage of 2.5 parts; the foaming agent is a microsphere foaming agent, with a dosage of 6 parts; the leveling agent is a polyether-modified silicone, with a dosage of 0.5 parts; the thickener is a polyurethane associative type, with a dosage of 0.6 parts; and the functional filler is leather ultrafine powder, with a dosage of 10 parts.

[0097] The surface layer slurry formulation is as follows: the matrix is ​​bio-based WPU emulsion, with a dosage of 100 parts; the crosslinking agent is aziridine, with a dosage of 3.0 parts; the hand feel agent is a composite hand feel agent, with a dosage of 4 parts; the defoamer is polyether-modified silicone, with a dosage of 0.3 parts; and the leveling agent is polyacrylate, with a dosage of 0.4 parts.

[0098] The parameters are set as follows in this embodiment:

[0099] In the bio-based WPU emulsion: 6.5 parts GA-MA;

[0100] Hydrophilic microporous foamed layer: coagulation bath 32℃, foaming agent 6 parts;

[0101] Top layer: 3 parts crosslinking agent, heat set at 120℃, 10 parts leather powder.

[0102] The test results are shown in Table 2 below:

[0103] Table 2. Performance of the synthetic leather product from the reference example 1

[0104]

[0105] To further verify the technical effects of the present invention, and based on the formulation and process parameters of Example 1, the following experimental series was designed as shown in Table 3:

[0106] Table 3. Single-factor experimental design

[0107]

[0108] Example A series:

[0109] The experimental design for optimizing the amount of GA-MA added in bio-based WPU emulsion was as follows: other parameters of Example 1 were kept constant, but the amount of GA-MA added was 0, 2, 4, 6, 8, 10, and 12 parts respectively;

[0110] Table 4. Single-factor experiments on GA-MA addition levels

[0111]

[0112] As shown in Table 4, when GA-MA increases from 0 to 6 parts, the particle size decreases by 50%, the contact angle decreases by 15%, and the water absorption rate decreases by 31%, indicating that the increase in hydrophilic groups improves emulsification efficiency. When GA-MA increases from 6 to 12 parts, the particle size decreases by 22%, the contact angle decreases by 9%, and the water absorption rate decreases by 23%, indicating a diminishing marginal effect. This indicates that >8 parts reaches the critical micelle concentration, therefore the optimal range is 6-8 parts of GA-MA.

[0113] Example B series:

[0114] Experimental design for optimizing the coagulation bath temperature of hydrophilic microporous foamed layer: other parameters of Example 1 are fixed, but the coagulation bath temperatures are 15, 20, 25, 30, 35, 40, 45, and 50°C respectively;

[0115] Table 5. Single-factor experiments on coagulation bath temperature

[0116]

[0117] Table 5 shows that as the temperature increases from 15°C to 40°C, the pore size increases by 375%, the porosity increases by 69%, the moisture permeability increases by 93%, and the strength decreases by 9%, indicating a faster water diffusion rate and more complete phase separation. However, as the temperature increases from 40°C to 50°C, the pore size only increases by 18%, but the porosity decreases by 2%, the moisture permeability also decreases by 2%, and the strength decreases by 13%, indicating that the temperature is too high, the TPU solidifies too quickly, and structural defects occur. Therefore, the optimal range is a coagulation bath temperature of 30-40°C.

[0118] Example C series:

[0119] Experimental design for optimizing the amount of foaming agent added in hydrophilic microporous foamed layer: The amount of microsphere foaming agent added was 0, 2, 4, 6, 8, 10, 12, and 14 parts respectively;

[0120] Table 6. Single-factor experiments on foaming agent addition amount

[0121]

[0122] As shown in Table 6, increasing the foaming agent from 0 to 6 parts increases porosity by 63%, moisture permeability by 63%, strength by 9%, and hand feel score by 44%, indicating increased micropores, improved moisture permeability, and a slight decrease in strength. Increasing the foaming agent from 6 to 10 parts increases porosity by 21%, moisture permeability by 19%, strength by 13%, and hand feel score by 2%, indicating diminishing marginal effects. When the foaming agent content is greater than 10 parts, porosity increases by 11%, moisture permeability increases by 8%, strength decreases by 22%, and hand feel score decreases by 6%, indicating over-foaming and a significant decrease in strength. Therefore, the optimal range is 6-8 parts of foaming agent.

[0123] Example D series:

[0124] Experimental design for optimizing the amount of surface crosslinking agent added: The amount of aziridine crosslinking agent added was 0, 1, 2, 3, 4, 5, and 6 parts respectively;

[0125] Table 7. Single-factor experiments on the amount of surface crosslinking agent added.

[0126]

[0127] As shown in Table 7, increasing the crosslinking agent from 0 to 3 parts increases hydrostatic pressure resistance by 77%, decreases moisture permeability by 13%, and reduces strength by 3%, indicating that a crosslinking network is formed, water resistance is improved, and moisture permeability is slightly reduced; increasing the crosslinking agent from 3 to 6 parts only increases hydrostatic pressure resistance by 21%, decreases moisture permeability by 19%, and reduces strength by 9%, indicating excessive crosslinking and restricted molecular chain movement; the optimal range is 2-4 parts of crosslinking agent.

[0128] Example E series:

[0129] Experimental design for optimizing the heat setting temperature of the surface layer: heat setting temperatures are 80, 90, 100, 110, 120, 130, and 140℃;

[0130] Table 8. Single-factor experiments on heat setting temperature

[0131]

[0132] Table 8 shows that as the heat setting temperature increases from 80°C to 120°C, the interlayer peel strength increases by 76%, the overall strength increases by 6%, and the moisture permeability decreases by 7%, indicating enhanced molecular chain diffusion and cross-linking reaction. However, as the heat setting temperature increases from 120°C to 140°C, the interlayer peel strength only increases by 9%, the overall strength decreases by 6%, and the moisture permeability decreases by 9%, indicating that the temperature is approaching the decomposition temperature and partial degradation may occur. Therefore, the optimal range for heat setting temperature is 110-130°C. The heat setting temperature of the TPU base fabric should also be adapted to this range, or slightly lower, such as 110-120°C.

[0133] Example F series:

[0134] Experimental design for optimizing the addition amount of leather powder in impregnation slurry: The addition amounts of modified leather ultrafine powder were 0, 5, 10, 15, 20, 25, and 30 parts;

[0135] Table 9. Single-factor experiments on the addition amount of leather powder

[0136]

[0137] As shown in Table 9, increasing the amount of leather powder added from 0 to 15 parts increases moisture permeability by 27%, decreases strength by 6%, and reduces cost by 8%, indicating that collagen is hydrophilic and porous, thus improving moisture permeability. In contrast, increasing the amount of leather powder added from 15 to 30 parts only increases moisture permeability by 14%, decreases strength by 18%, and reduces cost by 15%, indicating that excessive filler disrupts continuity. The optimal range is 10-20 parts of leather powder added.

[0138] Example 2. High moisture permeability type:

[0139] While maintaining other parameters of Example 1, the surface layer consisted of 20 parts leather powder and 8 parts foaming agent, with the following product specifications: moisture permeability: 7.8 mg / cm². 2 • h, an increase of 25.8% compared to Example 1; tensile strength: 128 N / cm, a decrease of 9.9% compared to Example 1.

[0140] Example 3. High wear-resistant type:

[0141] While keeping other parameters of Example 1 constant, the surface layer consists of 4 parts crosslinking agent and 5 parts of nano-SiO2. The product specifications are as follows: abrasion resistance is 1800 cycles, which is 44% higher than that of Example 1; tensile strength is 148 N / cm, which is 4.2% higher than that of Example 1; but moisture permeability is reduced by 25%.

[0142] Example 4. High bio-based type:

[0143] While maintaining other parameters of Example 1, the bio-based WPU emulsion contained: 50 parts starch-based polyol and 8 parts GA-MA; product specifications: bio-based content of 68%, tensile strength of 125 N / cm, and moisture permeability of 5.8 mg / cm. 2 ·h.

[0144] Example 5. Fully recyclable type:

[0145] Other parameters of Example 1 were kept constant, but the TPU base fabric used 30% recycled TPU and the impregnation slurry used 20% recycled polyol; product indicators: melt recovery rate of 96%, tensile strength of 138 N / cm, and tensile property retention rate of 92% in anti-aging test.

[0146] Comparative Example 1: A simulated product prepared using the process described in Chinese Patent Publication No. CN109252386 A, "A Dry-Foamed Synthetic Leather of PU and its Preparation Method," has the following specifications: tensile strength of only 95 N / cm and moisture permeability of only 2.5 mg / cm². 2 The residual DMF was 1850 mg / kg, and the melt recovery rate was <5%.

[0147] Comparative Example 2: A polyester base fabric was used instead of the TPU base fabric in Example 1. The resulting product specifications were: tensile strength of only 85 N / cm and moisture permeability of 4.2 mg / cm². 2 •h, the melt recovery rate of the base fabric is <5%.

[0148] Comparative Example 3: The surface layer of Example 1 was removed, and the structure was without gradient (including impregnation of fibers). Its product indicators were: fiber tensile strength was 22 MPa, which was 42% lower than that of Example 1; the overall tensile strength of the synthetic leather was 95 N / cm, which was 33% lower than that of Example 1.

[0149] Comparative Example 4: In the synthesis of the bio-based WPU emulsion in Example 1, GA-MA was not used, but a combination of DMPA and NMP was used. The product specifications were: NMP residue of 85 ppm; bio-based content of 18%, which is 68% lower than that in Example 1.

[0150] 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 method for manufacturing zero-pollution synthetic leather based on a hydrophilic microporous strong-chain structure, characterized in that, Includes the following steps: (1) Thermoplastic polyurethane is melt-spun to produce TPU fibers, which are then woven into TPU base fabric. The melt spinning temperature of the TPU fibers is 210-230℃, the stretching ratio is 2-4 times, and the heat setting temperature is 100-120℃. (2) Using starch-based polyol and bio-based hydrophilic chain extender GA-MA as raw materials, a bio-based waterborne polyurethane emulsion is synthesized. The GA-MA is prepared by gallic acid and maleic anhydride through a monoesterification reaction. (3) The TPU base fabric prepared in (1) is immersed in the bio-based waterborne polyurethane emulsion prepared in step (2), and a hydrophilic microporous foam layer is formed inside and on the surface of the TPU base fabric by wet coagulation process. The coagulation temperature is 25-40℃ and the coagulation time is 8-15 minutes. (4) On the surface of the impregnated base fabric prepared in (3), a surface layer is formed by dry coating process using bio-based waterborne polyurethane emulsion, with a coating thickness of 0.1-0.3 mm and a drying temperature of 110-130℃. (5) The semi-finished product obtained in (4) is subjected to heat setting treatment at a temperature of 100-130℃ for 2-5 minutes to form a strong chain structure. The TPU base fabric, hydrophilic microporous foam layer, and surface material used throughout the manufacturing process are all thermoplastic polyurethane materials.

2. The manufacturing method according to claim 1, characterized in that, The preparation method of the bio-based hydrophilic chain extender GA-MA is as follows: gallic acid and maleic anhydride are mixed in acetone solvent at a molar ratio of 1:1.1-1.3, and monoesterification reaction is carried out under the catalysis of p-toluenesulfonic acid at a reaction temperature of 60-80℃ for 4-8 hours.

3. The manufacturing method according to claim 1, characterized in that, The raw materials of the bio-based waterborne polyurethane emulsion in (2) include, by weight: 22-26 parts starch-based polyol, 30-40 parts PTMG, 15-25 parts PEG, 40-46 parts IPDI, 10-12 parts BDO, 5-8 parts GA-MA, and 10-12 parts HEA.

4. The manufacturing method according to claim 1, characterized in that, The solid content of the bio-based waterborne polyurethane emulsion in (2) is 35-45%, the average particle size is 80-120nm, and the bio-based content is ≥50%.

5. The manufacturing method according to claim 1, characterized in that, In the wet coagulation process of (3), the impregnating slurry includes, by weight, 100 parts of bio-based WPU emulsion, 2-4 parts of crosslinking agent, 4-8 parts of foaming agent, 0.3-0.8 parts of leveling agent, 0.5-1.0 parts of thickener, and 5-20 parts of functional filler; the average pore size of the hydrophilic microporous foam layer formed by (3) is 1-10 μm, the porosity is 40-60%, and the connectivity is ≥80%.

6. The manufacturing method according to claim 5, characterized in that, The crosslinking agent is aziridine, the foaming agent is a microsphere foaming agent, and the functional filler is modified leather ultrafine powder.

7. The manufacturing method according to claim 1, characterized in that, The dry surface layer slurry of (4) comprises, by weight: 100 parts of bio-based WPU emulsion, 2-4 parts of crosslinking agent, 3-5 parts of hand feel agent, 0.2-0.5 parts of defoamer, and 0.3-0.6 parts of leveling agent; the surface layer formed by (4) has a hydrostatic pressure resistance ≥50kPa, a water contact angle of 60-80°, and a moisture permeability ≥2000g / m². 2 ·24h.

8. The manufacturing method according to claim 1, characterized in that, After heat setting (5), the interfacial peel strength of the TPU base fabric, hydrophilic microporous foam layer and surface layer is 18-25 N / cm.

9. A zero-pollution synthetic leather based on a hydrophilic microporous strong-chain structure, manufactured by the method according to any one of claims 1-8, characterized in that, The zero-pollution synthetic leather is a single polyurethane material system, which can be 100% melted and recycled after disposal.

10. The zero-pollution synthetic leather according to claim 9, characterized in that, Its tensile strength is ≥130 N / cm, and its moisture permeability is ≥5.5 mg / (cm³). 2 •h), water contact angle 60-80°, DMF residue <5mg / kg, bio-based content ≥50%.

Images