Modular design of vegetable polyphenols enables covalent bonding with collagen for eco-leather

Natural renewable materials have been engineered to synthesize functional products because of their wide availability and excellent biodegradability. Particularly, vegetable polyphenols have been regarded as sustainable tanning agents in the leather industry. However, the non-covalent binding nature and high consumption of polyphenols in the leather matrix have limited its potential for replacing chrome tannage. In this work, we developed a series of new polyphenol derivatives by selectively conjugating cyanuric chloride (CC) with phenolic group, and therefore introduced covalent binding moieties in polyphenol for the tanning process. Specifically, polyphenols with different molecular sizes, i.e., tannic acid (TA), ellagic acid (EA), and gallic acid (GA), were modified and evaluated in a comparative study. The obtained triazine-conjugated polyphenol derivatives (i.e., GACC, EACC, and TACC) exhibited appropriate molecular weight (460−1130 Da) and superior stability in the tanning bath (pH ∼8.0), which can effectively penetrate collagen networks. We further investigated the tanning performance of GACC, EACC, TACC, and a commercial triazine tanning agent (i.e., SACC). These polyphenol derivatives exhibited covalent and non-covalent synergistic interaction with collagen, endowing leather with excellent fiber dispersion and overall performance (i.e., thermal stability, organoleptic and physical properties). Of note, the tanning system effectively reduced the dosage of polyphenols and organic carbon emission and improved the biodegradability of wastewater. Together with these outstanding results, we envision that this work will pave the promising way for eco-leather manufacturing.