Abstract

Sulfonated amino resins are an important class of polymers which are used as retanning agents in the leather industry. There is challenge for such resins to be synthesised without formaldehyde to satisfy the strict regulation in leather goods. In this work, formaldehyde-free melamine based retanning agents have been synthesised by acid catalysed process using furfural as condensing agent and sodium metabisulfite as the sulfonating agent. Sulfonated melamine furfural (SMFr) resins were synthesised using different molar ratio of melamine, sodium metabisulfite and furfural. Stable and water-soluble resins were produced without etherification.

The sodium metabisulfite to melamine ratio (SMB/M) was changed from 0.5-2.0 and furfural to melamine mole ratio (Fr/M) was varied from 2-6. The viscosity behaviour of the produced resins was evaluated with the increasing trend of sulfonation and increasing mole ratio of furfural to melamine. Functional group analysis and conversion of reactants into product was elucidated by FTIR.

Synthesised formaldehyde-free resins (SMFr) were comparatively evaluated as retanning agents on goatskin wet-blue against a commercially available sulfonated melamine formaldehyde (SMF) resin. The retanning performance of synthesised resins was studied and found better than that of the commercial SMF resin.