Comparative Study of Retanning Properties of Melamine-Glyoxal Resins Produced by Different Sulfonating Agents

Amino resins have many applications including leather retanning. Being condensation products of formaldehyde, amino resins are one of the sources of free formaldehyde in leather. In this work novel glyoxylated melamine resins were produced to make formaldehyde-free leather. The optimised process of synthesis was used to produce stable resins which were able to polymerise further in situ at retanning pH conditions. Water solubility of the resins was achieved by using various aromatic sulfonating agents including, orthanilic acid (ONA), metanilic acid (MNA), sulfanilic acid (SNA) and aniline 2,5-disulfonic acid (ADS). Synthesised resins were used in leather retanning to evaluate their comparative mechanical properties, organoleptic properties, free formaldehyde content and SEM analysis. The effluent of each retanning bath was also analysed for pollution load studies. All the resins showed improvements in mechanical and organoleptic properties in comparison with a commercial melamine resin but, the novel resin MGSNA exhibited remarkable results. Estimation of free formaldehyde content showed absence of free formaldehyde content in leather and retanning effluent of all the novel resins. Determination of COD, TDS and TSS of effluent confirmed a significant reduction in pollution load due to improved exhaustion of resins attributed to their in-situ polymerisation in collagen fibres to enhance their fixation. SEM analysis of leather confirmed improvements in retanning results due to formation of more orderly arranged networks of collagen fibres. Moreover, the introduction of an aromatic ring in the resin structure resulted in improved thermal stability of the resins. The results indicate that this development is remarkable for production of formaldehyde-free leather with improved retanning properties along with reduction in water pollution. This work also addresses the carcinogenic effects of formaldehyde.