A rapid and cleaner chrome tanning technology based on ultrasound and microwave

Abstract At present, chrome tanning had irreplaceable advantages and was still the dominant tanning method in leather making, thus more and more attention should be paid to minimizing chrome-containing effluent discharging during tanning with some new techniques. In this work, a rapid and clean chrome tanning method based on wringing, ultrasound and microwave was developed for cleaner chrome tanning. In the new method, chrome tanning agent could penetrate into leather within 6 min because of the synergistic effect of capillary generated by wringing and cavitation resulted from ultrasound, and the tanning could finish without basification by using microwave irradiating well-penetrated leather for 5 min. The total time for one complete tanning was only 11 min, while it takes 8–12 h or longer to finish this process with traditional method. On aspects of the leather properties tanned by the new method, the chrome content, thermal stability and chrome distribution uniformity of the wet blue were slight poorer than traditional, but the mechanical properties, organoleptic properties and collagen fiber inter-woven structure were comparable. Moreover, the leather properties kept stable during continuous tanning for 10 times. Since there was no additional substance added into the system, the tanning liquor in the method might be recycled by replenishing corresponding materials according to analysis. In sum, since the innovative tanning method has an outstanding features of rapid tanning with almost zero chrome-containing wastewater discharging, it would be a new potential routine for cleaner chrome tanning in future.