Abstract

A series of formaldehyde-free melamine-methylglyoxal resins has been produced at various mole ratios of reactants. The methylglyoxal to melamine mole ratio (MG/M) was varied from 3 to 6 and the sodium metabisulfite to melamine mole ratio (SMB/M) was varied from 0.05 to 0.2. Viscosity trend of resins within the series was examined. The prepared resins were used as retanning agents and their improved mechanical and organoleptic properties were noticed in comparison with a commercial melamine-formaldehyde resin. The morphology of grain surface and fibre structure of the leathers was investigated by scanning electron microscopy (SEM). Thermal stability of the optimal resin was assessed and observed to show an improvement over the commercial melamine-formaldehyde resin. Molecular weight and FTIR study of optimal resin was also pursued. Determination of free formaldehyde confirmed that the resulting leather was free from formaldehyde. A pollution load study of retanning effluent showed a significant reduction in chemical oxygen demand, total suspended solids and total dissolved solids for the optimal resin reflecting its improved exhaustion due to optimised molecular size and ability to undergo in situ polymerisation in collagen fibres. The results have shown that the melamine resins of this novel work are suitable for producing formaldehyde-free leather with improved retanning properties and reduced pollution load of the wastewater. Methylglyoxal has been proved as a successful alternate of formaldehyde in resin synthesis to control air emissions and carcinogenic effects while producing sustainable leather.