Abstract

A new pretanning agent (HTPA) for high exhaustion chrome tannage 2,4-di-(1-hydroxymethyl-1, 2, 4-triazole-5- thione)-1,5-phthalic acid and 2,5-di-(1-hydroxymethyl-1, 2, 4-triazole-5-thione) -1,4-phthalic acid, has been synthesized from pyromellitic dianhydride and thiosemicarbazide. Its reaction with pelts and its effect on chrome uptake have been studied by applying it to delimed sheepskins and goatskins. The results show that HTPA reacts mainly with the amino groups in collagen to form crosslinks and that the reaction depends on the pH, temperature, time and amount of HTPA. Pelt pretanned with HTPA possesses a higher shrinkage temperature than control pelts. Subsequent chrome tanning results in a significant increase in chromium uptake, thus the chrome offer in conventional chrome tanning can be reduced significantly. The handle and the physical properties of pretanned crust leather are not too different from those of control crust leather.