Effect of cyclic stress while being dried on the mechanical properties and thermostability of leathers

Authors: HUANG, JINBOA - Zhengzhou University; LIU, JIE - Zhengzhou University; TANG, KEYONG - Zhengzhou University; YANG, PENGYUAN - Zhengzhou University; FAN, XIALIAN - Zhengzhou University; WANG, FANG - Zhengzhou University; DU, JING - Zhengzhou University; Liu, Cheng Kung

Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2018
Publication Date: 11/1/2018
Citation: Huang, J., Liu, J., Tang, K., Yang, P., Fan, X., Wang, F., Du, J., Liu, C. 2018. Effect of cyclic stress while being dried on the mechanical properties and thermostability of leathers. Journal of American Leather Chemists Association. 113(11):318-325.

Interpretive Summary: A research was conducted to understand the effects of the various mechanical operations applied in leather making processes on the structure and properties of leathers, such as physical performance and hydrothermal stability. Cyclic stress is very common in leather making, which may cause different changes to leather, compared with constant stress. In the present work, cyclic stresses were applied on leather in drying process. The influences of cyclic stress on the mechanical properties, hydrothermal stability and dry heat resistance of leathers were investigated. Observation showed that stress in drying process led to orientation of leather (collagen) fibers, thereby increasing mechanical strength of leather. Results also showed longer stretching led to higher mechanical strength and lower stretch-ability of leather. Furthermore, research showed cyclic stress may provide leathers with better dry heat resistance than constant stress. More importantly, this study provides the useful knowledge to the leather industry regarding the relationship between mechanical operations and properties of leathers from viewpoint of collagen fiber structure.

Technical Abstract: Various mechanical processes are usually applied in leather making and using, which inevitably affect the structure and properties of leathers, such as mechanical performance and hydrothermal stability. Cyclic stress is very common in leather making, which may cause different changes to leather, compared with constant stress. However, very few reports have been reported regarding the influence of cyclic stress on leathers. In the present work, cyclic stresses were applied on leather in drying. The influences of cyclic stress on the mechanical properties, hydrothermal stability and dry heat resistance of leathers were investigated. Besides, the cross section of leather was observed with SEM, and the changes of hydrogen bonds in collagen fibers were characterized and discussed with the results of FT-IR. It was indicated that stress in drying leads to orientation of collagen fibers, thereby increasing mechanical strength. A balance is set up between tensile strength and elongation at break of leathers with the action cyclic stress. Longer stretching leads to higher tensile strength and lower elongation at break. Meanwhile, stress in drying may prevent the formation of hydrogen bonds inside collagen fibers and change the weaving structure of collagen fibers, resulting in decreased hydrothermal stability of leathers. Cyclic stress may provide leathers with better dry heat resistance than constant stress. Besides, a simplified model of collagen fibers movement was introduced, to establish a relationship between processing and properties of leathers from viewpoint of collagen fiber structure.