Chemistry of Syntans and Their Influence on Leather Quality

Abstract

The first syntan, Neradol D, was a condensate of phenolsulfonic acid and formaldehyde. While this chemistry allowed more efficient use of vegetable tannins, it was not advantageous to be applied on leather alone and has to be considered an auxiliary. Incorporating urea into the phenolsulfonic acid - formaldehyde condensation established a second generation of syntans with significantly improved lightfastness. Replacement syntans weredeveloped to substitute vegetable tannins, giving rise to leathers of good softness and fullness. The formaldehyde condensation of dihydroxy diphenyl sulfone (sulfone) can be considered a further development of the replacement syntans with lower residual monomers. In order to compare these four generations of syntans, poly-condensates of a comparable molecular size had to be synthesized. These tested in hydrothermic denaturation of skin powder and applied in sole tanning and re tanning. The resulting leathers were compared in various aspects of performance including shrinkage temperature, softness, fullness, light fastness, and rest monomers.