Effect of Cyclic Stress while Being Dried on the Mechanical Properties and Thermostability of Leathers

Abstract

Various mechanical processes are usually applied in leather makingand using, which inevitably affect the structure and properties ofleathers, such as mechanical performance and hydrothermalstability. Cyclic stress is very common in leather making, which maycause different changes to leather, compared with constant stress.However, very few results have been reported regarding theinfluence of cyclic stress on leathers. In the present work, cyclicstresses were applied to leather in drying. The influences of cyclicstress on the mechanical properties, hydrothermal stability and dryheat resistance of leathers were investigated. Also, the cross sectionof leather was observed with SEM, and the changes of hydrogenbonds in collagen fibers were characterized and discussed with theresults of FT-IR. It was indicated that stress in drying leads toorientation of collagen fibers and increased mechanical strength. Abalance is set up between tensile strength and elongation at break ofleathers with the action cyclic stress. Longer stretching leads tohigher tensile strength and lower elongation at break. Meanwhile,stress in drying may prevent the formation of hydrogen bondsinside collagen fibers and change the weaving structure of collagenfibers, resulting in decreased hydrothermal stability of leathers.Cyclic stress may provide leathers with better dry heat resistancethan constant stress. Also, a simplified model of collagen fibersmovement was introduced, to establish a relationship betweenprocessing and properties of leathers from viewpoint of collagenfiber structure.