Objective Thorough dispersion of collagen fibers is crucial for improving the physical properties of leather. While silane coupling agent (SCA) offers excellent hydrophobicity and reactivity, its application in current dehydration−hydrophobic modification technologies for leather is limited by the high consumption of ethanol. This study proposed a low-solvent hydrophobic modification method based on physical treatments. A "vacuum drying + milling" process was used to control the moisture content and dispersion degree of collagen fibers. This approach obviously reduced ethanol usage while ensuring uniform penetration and effective binding of SCA within the leather. Furthermore, the hydrophobic modification effect of SCA promoted efficient fiber dispersion, comprehensively enhancing the overall performance of the leather.

Methods Chrome-tanned leather was pretreated using the "vacuum drying + milling" physical treatments. First, vacuum drying was conducted at 50 ℃ and 100 kPa for 0-4 minutes. The moisture content was measured, and fiber morphology was observed. This was followed by 30 minutes of milling, and changes in pore structure were analyzed. Ethanol dehydration experiments were conducted to investigate the effect of the physical treatment on dehydration rate and equilibrium moisture content, with kinetic fitting performed. The physically treated leather was then dehydrated with 120% anhydrous ethanol for 60 minutes, followed by hydrophobic modification with 6% SCA, resulting in physically treated and silane-modified leather (P−SCA). The penetration, distribution, chemical bonding behavior, and hydrophobic properties of SCA within the leather were characterized using scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The performance of P−SCA leather was compared with conventional chrome-tanned leather (CL) and leather treated with SCA after multiple ethanol dehydration steps (E-SCA).

Results Combined vacuum drying of 2 minutes and milling treatment reduced the moisture content of the chrome-tanned leather to 42.0%. The fibers showed good dispersion degree, and the porosity was maintained at 44.7%. This physical treatment remarkably improved ethanol dehydration efficiency: the dehydration rate constant increased by 3.8 times; the equilibrium moisture content decreased to 22.4%; ethanol usage was reduced by 66.7%; and dehydration time was shortened by 77.8%. FT-IR and XPS analyses indicated that hydrolyzed SCA formed covalent bonds (Si-O-C and Si-N bonds) with -OH and -NH₂ groups on the collagen fibers and were uniformly distributed within the leather. The P−SCA leather achieved a contact angle of 154.5°. After 2025 cycles in a dynamic water resistance test, the water absorption rate was only 3.3%. Mechanical property tests showed that P−SCA leather exhibited superior tensile strength (25.9 MPa), tear strength (102.7 N/mm), bursting strength (557.1 N/mm), and elongation at break (54.2%) compared to both CL and E-SCA leathers. Its softness reached 8.6 mm, and it demonstrated better compression and resilience properties.

Conclusions A "vacuum drying + milling" physical treatment technology was established, effectively controlling the moisture content and fiber dispersion of chrome-tanned leather. This method overcomes the reliance on large amounts of ethanol in conventional dehydration−hydrophobic modification processes. It obviously reduces solvent consumption while promoting the uniform penetration of SCA within the three-dimensional network structure of leather and its covalent binding with collagen. This endows the leather with excellent hydrophobicity and physical properties. The prepared P−SCA leather outperforms products from traditional processes in key indicators such as mechanical strength, softness, and resilience. This study provides an innovative concept and practical pathway for developing efficient and eco-friendly functional modification technologies for leather.