Ultrasound-aided leather dyeing: a preliminary investigation on process parameters influencing ultrasonic technology for large-scale production

Abstract

The application of ultrasound to leather processing has a significant role for more efficient and advanced manufacturing techniques for leather production. The effect of important process parameters for scale-up such as mechanical agitation, float, and concentration of dye bath has been experimentally examined. The results indicate that float level and dye bath concentration has significant effect on exhaustion of dye. There is no appreciable improvement due to mechanical agitation over the effect of ultrasound in leather dyeing. Dyeing of chrome-tanned wet-blue leather has been carried out directly in the ultrasonic tank with larger area of sample for scale-up possibility. The results indicate notable improvement (1.6-fold) in dye exhaustion as compared to dyeing in process vessel immersed in the ultrasound tank. This is also equivalent to 4.3-fold increase due to ultrasound as compared to control process without ultrasound at static condition. Ultrasound-aided dyeing of vegetable-tanned (EI) leather shows sixfold improvement as compared to control process. Acoustic cavitation energy in the ultrasonic tank, another important parameter for the scale-up, has been measured and the results indicate that ~60% acoustic energy is absorbed by leather in the process. Influence of ultrasound on dye aggregate size, an important parameter for diffusion, was also studied and found to be beneficial. Different ultrasonic equipments such as ultrasonic tank or ultrasonic probe have been tested and compared for their efficacy. Mass balance for ultrasonic leather dyeing process was performed and compared with control processes. Preliminary techno economic cost benefit analysis indicates positive trend for ultrasonic dyeing as compared to conventional drumming process. Savings in dye due to the use of ultrasound yield significant profit taking into account of ultrasonic energy cost, with a payback period for ultrasonic equipment cost. Therefore, the use of ultrasound in leather processing is a potential viable option for tanners in near future as advanced technology.