Objective This study aims to address the critical bottleneck of insufficient air and moisture permeability in conventional microfiber synthetic leather caused by dense polyurethane coatings. It focuses on the development of a high-performance composite microfiber synthetic leather with balanced air permeability, moisture permeability, and mechanical properties by regulating key process parameters, and the verification of the effectiveness of multi-scale porous structure design in enhancing material functionality.

Methods Using a PE/PA6 irregular islands-in-the-sea fiber needle-punched nonwoven as the substrate, the "sea" phase PE was selectively dissolved by toluene to achieve fiber splitting, thereby constructing a three-dimensional network leather substrate mimicking natural leather collagen fibers. Electrospun thermoplastic polyurethane (TPU) nanofiber membranes with mass fractions of 10%, 15%, and 20%, respectively, were prepared using N,N-dimethylformamide (DMF) as the solvent. Foamed waterborne polyurethane (WPU) adhesives with foaming ratios of 150%, 200%, and 300%, respectively, were formulated by adding foaming agents, foam stabilizers, thickeners, and leveling agents. The composite microfiber synthetic leather was fabricated by compounding the leather substrate, TPU nanofiber membrane, and foamed WPU adhesive through blade coating (with coating thicknesses of 150 μm, 200 μm, and 300 μm, respectively), followed by drying and curing. The material’s morphology, thickness, softness, air permeability, moisture vapor transmission rate (MVTR), and mechanical properties were systematically tested using a scanning electron microscope (SEM), a thickness gauge, a leather softness tester, an air permeability tester, moisture permeability test equipment, and a universal testing machine, respectively.

Results The mass fraction of TPU solution significantly influenced fiber structure and performance. Specifically, as the mass fraction increased from 10% to 20%, the average fiber diameter increased from 100 nm to 1450 nm, and the MVTR of the synthetic leather increased by 30.9% (from 932.86 to 1221.36 g/(m²·24 h)), while the air permeability was slightly improved from 15.11 to 15.38 L/(m²·s), and the longitudinal and transverse breaking strengths increased from 868.41 to 886.32 N and 1061.23 to 1065.32 N, respectively, realizing the synergistic enhancement of moisture permeability and mechanical properties. Coating thickness had a prominent impact on moisture transmission. At a foaming ratio of 200%, the 150 μm thin coating yielded a MVTR of 2120.14 g/(m²·24 h) and a softness of 7.54 mN·m; when the thickness increased to 300 μm, the MVTR decreased to 1399.29 g/(m²·24 h) due to the extended diffusion paths, despite slight improvements in breaking strength. When the foaming ratio was elevated from 150% to 300%, both porosity and pore connectivity were enhanced, leading to a 45% increase in MVTR (from 1356.89 to 1992.93 g/(m²·24 h)) and a 5% increase in air permeability (from 16.58 to 17.42 L/(m²·s)), with softness improving from 7.40 to 7.62 mN·m and mechanical properties remaining stable.

Conclusions The optimal process parameters for high-performance microfiber synthetic leather were determined as follows: TPU solution mass fraction of 15%, coating thickness of 150 μm, and foaming ratio of 300%. Under these conditions, the material achieved an optimal balance among air permeability (>17 L/(m²·s)), MVTR (significantly higher than conventional polyurethane laminated leather, which is typically below 800 g/(m²·24 h)), structural biomimicry, and mechanical integrity (longitudinal/transverse breaking strengths exceeding 870 N and 1070 N, respectively). This study demonstrates that regulating TPU nanofiber structure and foamed layer parameters could effectively construct interconnected multi-scale pores, reconciling the "strength-moisture permeability" contradiction. The developed synthetic leather exhibits broad application prospects in footwear, high-end apparel, and automotive interiors, while providing key technical references for the design and optimization of high-comfort bionic synthetic leather.