Submitted to: International Union of Leather Technologists and Chemists Societies
Publication Type: Abstract only
Publication Acceptance Date: 3/1/2011
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Drying is an important mechanical operation in the leather making process. Leather acquires its final texture, consistency and flexibility in the drying operation. Vacuum drying offers fast water removal at a low temperature, which is particularly advantageous to heat-vulnerable chrome-free leather. Adding a toggle action during vacuum drying would significantly increase the area yield of the leather. We explored this composite drying method (vacuum + toggling) and investigated how drying variables affect the mechanical properties and area yield of chrome-free leather. The experimental material was bovine wet white, which was obtained from a major domestic tannery and was retanned with glutaraldehyde using the retanning and fatliquoring process previously reported for the preparation of our chrome-free samples. Using a statistical experimental design, we investigated how drying variables affect mechanical properties and area yield of chrome-free leather. Results showed that biaxially stretching the leather in two directions increases the tensile strength but has less of an effect on the toughness of leather. Our study also showed that tensile strength increases with apparent density and decreases with drying rate. Under an optimal drying condition, a significant increase in area yield with good properties can be achieved. Observation also showed that the Young’s modulus or stiffness of leather increases as the leather thickness decreases. The decrease in thickness is largely due to toggling (stretching) action during the vacuum drying operation. To examine the fibrous structure of the leather samples from various drying conditions, we used the field-emission environmental scanning electron microscope (ESEM) to examine the cross section of the leather samples. The highly stretched leather showed a more oriented fiber structure than that of the un-stretched leather sample. We also determined the viscous and elastic moduli for the drying study samples using a dynamic mechanical analyzer (DMA). Tests showed that drying conditions have a great effect on both the elastic modulus (E’) and viscous modulus (E”). For all the test frequencies, both E’ and E” increase significantly with drying temperature, drying time, and stretch %, particularly the drying temperature. We plan to scale-up the developed composite drying process using the optimal conditions estimated from the mathematical model.