Comparative Retanning Performance of Ecofriendly Melamine Resins Produced Using Different Condensing Agents

摘要

Formaldehyde has been a famous raw material for production of amino resins used in leather processing however; the proven carcinogenic hazards of formaldehyde contravene regulations are restricting the sale of leather goods with regard to human contact. In this study sulfonated melamine based resins were produced by using condensing agents other than formaldehyde, for example furfural, glyoxal, methylglyoxal and glutaraldehyde. Synthesised formaldehyde-free melamine resins were studied for determination of their molecular weights, thermal stability by TGA and spectroscopic studies using FTIR. Synthesised resins were used in leather retanning for investigation of their mechanical and organoleptic properties in comparison with leather samples based on a commercial resin. The effects of melamine resins on the fibrous structure of collagen were examined by SEM. Leather pieces were analysed for estimation of free formaldehyde contents and the pollution load of the retanning wastes was also investigated. The prepared resins conferred improved mechanical and organoleptic characteristics to the resulting leather compared to the control but the results produced by MGLSNA and MGSNA resins were more prominent. Leather produced from each resin sample was formaldehyde free.SEM images of the leather revealed the presence of fine grains with improved fibrous collagen structure especially for MGLSNA and MGSNA. Pollution load reduction efficiency of newly developed resins was improved in comparison with control indicating their better uptake and fixation in collagen fibres. Overall, all four novel resins produced formaldehyde-free leather with improved retanning and thermal properties but the results produced by MGLSNA and MGSNA resins were better due to introduction of more reactive sites and aromatic sulfonation agents.This work had successfully replaced the formaldehyde with four different condensing agents for making amino resins to produce formaldehyde-free leather with enhanced retannage properties. This research is a successful step towards a green approach in resin synthesis and leather production by addressing the environmental concerns of formaldehyde.