Dyestuffs and formaldehyde content in split leather treated with formaldehyde resins

The highest reduction ability of basic dyes corresponded to the dye that has the greatest amount of amino residues amenable to reaction with formaldehyde (Basic Orange 2). Basic Orange 2 dye exhibited higher reduction ability (90% of reduction in leathers treated with resin of high formaldehyde content after 90 days of leather processing) than the Acid Black 234 dye (approximately 20%), both containing similar amount of free amino residues. Thin layer chromatography analysis revealed that the Basic Orange 2 dye is mainly a single major component, while the Acid Black dye 234 is a mixture of components that can have a reduced reactivity with formaldehyde. Further experiments are required to investigate if the surface leather dyeing (Basic Orange 2 dye) have a higher influence on formaldehyde content reduction than the through-dyeing (Acid Black 234 dye).