Mechanical properties and area retention of leather dried with biaxial stretching under vacuum

The conversion of animal hides to leather involves many complicated chemical and mechanical operations. Drying is one of the mechanical operations, and plays a key role in determining the physical properties of leather. It is where leather acquires its final texture, consistency, and flexibility. We have investigated a drying method using a combination of vacuum and biaxial stretching. Total area loss often accompanies drying of leather; however, by adding a stretching action during vacuum drying one may significantly increase the area retention and dimensional stability. Moreover, this method is particularly advantageous to heat-vulnerable organic tanned leathers because vacuum drying offers fast moisture removal at a low temperature. We investigated this dual functional drying method and observed how drying variables affected the mechanical properties and area retention of chrome-free leather. We used a central composite experimental design to formulate the relationship between drying variables and resultant leather properties into second-order polynomial equations. Results showed that the stretching applied in a drying operation significantly affects mechanical properties, area retention, and thickness of leather. Moreover, studies showed that biaxial stretching increased the tensile strength but had less effect on fracture energy. A significant area increase of 16% can be achieved by using this combined drying (vacuum plus stretching) method compared to the regular vacuum dried leather without stretching.