The development of high-performance, multifunctional post-tanning materials is crucial for advancing metal-free tanning technologies toward a sustainable leather industry. However, metal-free leathers often suffer from poor hydrophobicity, a stiff handle, and low uptake of conventional anionic post-tanning chemicals. Herein, a series of silicone-containing cationic amphiphilic copolymers (PSDV) was synthesized, and the influence of organosilicon content on their aggregation behavior in an aqueous solution, penetration within the leather matrix, and subsequent application performance was systematically investigated. Dynamic light scattering revealed an intriguing aggregation behavior: while all silicone-containing PSDV predominantly formed small aggregates with a number-average diameter of ∼ 10 nm, a minor population of larger aggregates driven by strong hydrophobic interactions was also present, as evidenced by the intensity-average diameter analysis. The size and fraction of these larger aggregates increased substantially with higher organosilicon content, with the intensity-averaged diameter increasing from 106.0 nm for PSDV1 to 475.4 nm for PSDV5 at a concentration of 10 g/L. This unique distribution critically governed the penetration behavior─optimal silicon content enabled uniform fibril-level penetration dominated by small aggregates─whereas excessive silicon led to larger aggregates that hindered deep penetration into the fibrous network. When applied to TWS-tanned leather, the cationic PSDV achieved an outstanding uptake rate of 96% and effectively increased the leather’s isoelectric point, enhancing compatibility with subsequent anionic auxiliaries. The penetrated PSDV formed a durable, low-surface-energy film on collagen fibrils, dramatically enhancing hydrophobicity. Concurrently, the flexible siloxane chains provided excellent fiber lubrication, increasing the softness from 4.5 mm to above 6.3 mm. Furthermore, PSDV-treated leather exhibited significantly enhanced dye exhaustion, with residual dye concentration decreasing from 156.8 to 16.8 mg/L. This work elucidates the intrinsic relationships among molecular design, multiscale aggregation behavior, and application performance of amphiphilic copolymers. PSDV successfully integrates retanning, fatliquoring, hydrophobization, and dye-promoting functions into a single treatment, offering an effective chemical strategy for producing high-performance, eco-friendly, metal-free leather.
Yi et al. (Wed,) studied this question.