Influence of power ultrasound on leather processing. Part II: fatliquoring

Power ultrasound (38 kHz, 1.36 W cm^-2) was applied to the preparation of fatliquor emulsion as well as the fatliquoring process. It was found that fatliquor emulsions prepared with ultrasound have their particle size reduced by more than 15%. Use of this finer emulsion in a conventional fatliquoring process can markedly increase the fat content by up to 36% and improve both penetration of fat and evenness of the fat distribution. Increases of the fat content mainly locate in the mid- and grain strata. Ultrasound per se was found less effective than mechanical agitation in enhancing the fatliquoring process but a combination of ultrasound and mechanical agitation can produce a synergistic effect, increasing fat content by 20-40% and improving fat penetration as well as the evenness of the fat distribution. It was shown that ultrasound is better applied in the later stages of a fatliquoring process for a shorter period of time rather than continuously for the whole length of the process, and there is an optimal temperature for maximum ultrasonic effect. Also analysis of fat distribution showed that ultrasonic fatliquoring is particularly useful for increasing the fat content in the flesh side. The results suggested that ultrasound is effective in enhancing the fatliquoring process when the particle size is relatively small compared to the pathway available.