Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2005
Publication Date: 9/1/2006
Citation: Liu, C., Latona, N.P., Cooke, P.H. 2006. Effects of stretching and drying rate on the mechanical properties of chrome-free leather. Journal of American Leather Chemists Association. 101(9):330-335.
Interpretive Summary: Drying, by which leather acquires its final texture, consistency and flexibility, is one of the most important and expensive operations in leather manufacturing. The objective for this research is to obtain an improved drying method, merging toggling and vacuum drying together. This is because vacuum drying offers fast speed and low temperature drying, which is particularly advantageous to heat-vulnerable chrome-free leathers, because they are often have a lower denaturizing temperature. On the other hand, adding a toggle action, such as stretching during vacuum drying, can potentially increase the area yield. However, this research indicated that stretching should not be overdone; otherwise the resultant leather will have mechanical properties that are not acceptable for most leather products. This research also formulated a mathematical model to estimate the drying rate for chrome-free leather. The drying constant indicates and showed that chrome-free leather dries faster than chrome-tanned leather. The model presented for the drying rate may benefit the leather industry in estimating the right drying parameters to dry leather.
Technical Abstract: Stretching leather during vacuum drying may possibly be the best drying method, because the resultant leather has an improved area yield with a lower drying temperature, resulting in better mechanical properties. We explored this composite drying method and investigated how drying variables affect the drying rate and mechanical properties of chrome-free leather that was tanned with glutaraldehyde. Using a statistical experimental design, a second order polynomial equation was derived to quantitatively describe the relationship between the drying rate and three major independent variables: drying temperature, stretch %, and drying time. Drying rate models derived from this investigation provide a clear understanding of the drying process for chrome-free leather. The drying constant indicates that chrome-free leather dries faster than chrome-tanned leather. These models will help the leather industry estimate the proper drying parameters. Our studies showed that stretch % during vacuum drying is the most significant variable affecting the stiffness and area retention of leather. This research indicated that stretching should not be overdone and the preferable length increase should not be greater than 10%; otherwise poor leather properties may result, such as an elongation less than 40% and toughness index less than 1.