Abstract

In recent years, there has been a growing focus on amphoteric retanning materials due to their crucial role in enhancing the electropositivity of retanned leather and improving the absorption of anionic dyes and fatliquors. This paper introduces a novel design and successful preparation of amphoteric retanning agents. Initially, a series of poly(N-vinylformamide-co-acrylic acid) copolymers were synthesized through a free radical copolymerization reaction initiated by azodiisobutyamidine hydrochloride. Subsequently, these polymers were hydrolyzed to produce an amphoteric retanning agent (A-PVAm) with a solid content of 15%(Wt). Their structures were characterized using FT-IR, and their isoelectric points were determined through a zeta potential analyzer. Following this, a fluorescent tracer (FA-PVAm) was synthesized by reacting fluorescein 5-isothiocyanate with A-PVAm. This tracer was utilized to monitor the real-time penetration and mass transfer of A-PVAm during the retanning process as a signaling agent. The mass transfer of A-PVAm was observed concerning dosage and running time. It was observed that within 60 minutes, A-PVAm could evenly distribute throughout the leather. In instances where the retanning agent dosage was inadequate, the inner part of the crust showed minimal presence of the retanning agent. However, at dosages exceeding 20%, the retanning agent exhibited uniform distribution within the leather. The utilization of the fluorescent tracing technique proved effective in creating a tracer to monitor the penetration of the amphoteric acrylic resin retanning agent in leather. This approach can assist in optimizing the molecule structure of the polyacrylate retanning agent and analyzing its mechanism of action.