A “Taiji-Bagua” inspired multi-functional amphoteric polymer for ecological chromium-free organic tanned leather production: Integration of retanning and fatliquoring

Comprehensive promotion of chrome-free organic tanning system has become an inevitable trend for cleaner production in leather manufacturing industry. However, the imbalance of interface charge between conventional anionic wet finishing material and organic tanned leather leads to poor quality of finished leather. Herein, a novel amphoteric polymer P (AA-AM-C12DM) as retanning and fatliquoring dual-functional wet finishing material was prepared by free radical polymerization using acrylic acid (AA), acrylamide (AM), and (2-methacryloyloxyethyl) dodecyl ammonium bromide (C12DM) as raw materials in an aqueous system and further applied in TWS organic tanned leather. Comprehensive structural and performance characterization of P (AA-AM-C12DM) confirmed the presence of amphoteric groups and hydrophobic long chains in its structure. Number average molecular weight and isoelectric point were determined to be 6396 g mol−1 and 5.16, respectively. The physical and mechanical properties, morphology of the P (AA-AM-C12DM)-treated leather, and their reactivities to anionic dye were investigated. The effect of hydrogen bond and ionic bond, which resulted from reactions between the carboxyl groups, amide groups, cation N+ in P (AA-AM-C12DM), and the pendant amino groups, hydroxyl groups, carboxyl groups from collagen fibers, benefitted in enhancing the physical and mechanical properties of crust leather and their reactivity to anionic dye. Moreover, P (AA-AM-C12DM) showed remarkable environmental benefits compared to the commercial fatliquor, by significantly promoting dye absorption as high as 96.57%. These findings provide a potential application of P (AA-AM-C12DM) to coordinate well with an ecological chrome-free organic tanning system, significantly promoting the cleaner production in the leather industry.