Viscoelasticity Studies for Chrome-Free Leather

Authors: Liu, Cheng Kung; Latona, Nicholas - Nick; Dimaio, Gary; Cooke, Peter

Submitted to: Journal of Materials Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2007
Publication Date: 7/1/2007
Citation: Liu, C., Latona, N.P., Dimaio, G.L., Cooke, P.H. 2007. Viscoelasticity Studies for Chrome-Free Leather. Journal of Materials Science. 42:8509-8516.

Interpretive Summary: Due to concerns over the use and disposal of chrome-tanned leather, the leather industry is now facing increased scrutiny over its use of chrome as a tanning agent. Organic non-chrome tannages have gradually become pre-eminent to producing leather, particularly in the European automotive leather markets. Many tanneries have started to provide chrome-free leather to meet their customers' demands for leather in such items as children's and health care leather products. In some respects, however, the quality of current chrome-free leather, such as glutaraldehyde-tanned leather, is inferior to that of chrome-tanned leather -- for example, lower resiliency, UV resistance, and hydrothermal stability. We have designed a test method to gain insight into the structural differences between chrome-tanned and chrome-free leather. By understanding these fundamental differences, tanners would be able to properly adjust the leather-making processes to improve its properties to match that of chrome-tanned leather. Observations revealed that the chrome-free leather structure is not as elastic as the chrome-tanned leather in terms of recovery from deformation. Observation also showed chrome-free leather is relatively stiffer than chrome-tanned leather. The results from this investigation indicate that when making chrome-free leather, more lubricants may be needed in the fibers. For improving elasticity, filler may be added to the chrome-free leather to improve its density.

Technical Abstract: Chrome-free leather such as glutaraldehyde-tanned leather behaves very differently from chrome-tanned leather. Information regarding its viscoelasticity has not been reported. Hysteresis and stress relaxation are two essential properties associated with viscoelasticity. We have designed a cyclic tensile test to measure these properties to gain insight into the structural difference between chrome-free and chrome-tanned leather. Observations revealed that chrome-free leather tanned with glutaraldehyde has a higher hysteresis than chrome-tanned leather. Stress relaxation experiments, on the other hand, showed chrome-free leather has a longer relaxation time. We also designed a linear stress rate model to predict the time-dependence of stress relaxation; the new model fits the data better than the traditional Maxwell model. Moreover, observations showed the viscoelasticity of leather was affected significantly by its fatliquor content. A decrease of loading energy in a cyclic stress-strain experiment resulted from a higher fatliquor content in leather.