Synthetic Na-zeolites (NaA, NaX, NaAX) were investigated as tanning agents in leather production from sheepskin and calfskin pelts. It was found in laboratory scale testing that the combined use of zeolite and chrome sulphate results in both higher float exhaustion and higher shrinkage temperatures in shorter time than in conventional chrome tannage. The best results were obtained with zeolite NaA. The operating conditions were optimized with respect to chrome and zeolite concentration, tanning bath pH and pelt weight/bath volume ratio. The analysed Si/Al ratio in the leather is about 1.1, similar to that of NaA zeolite. The promoting effect of zeolite A in chrome tanning has been confirmed on pilot scale: higher tanning rate as well as higher float exhaustion were found. Mechanical properties of the finished leathers, such as tensile strength, elongation, tearing strength and ball bursting are similar or better when compared with chrome usually tanned leather.
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