Abstract

Details of the Modified Standard Process (MSP) for the controlled experimental production of side upper leather have been recorded in Part 3 (J. Soc. Leather Technol. Chem., 1984, 68, 125). The present part of the investigation examines the drying stage of the experimental procedure. MSP leather is dried, in the standard operation, using free hanging for the first drying and toggle drying for the second stage. The consequences of using different air temperatures and humidities for each of the two stages have been investigated. Leather produced using higher air temperatures for both drying stages was shown to differ from MSP leather in some properties. In particular, the leather has a tighter break but a firmer temper. Much more marked changes resulted from the use of paste drying, toggle drying or vacuum drying in place of free hanging for the first stage of drying. These first stage drying techniques were combined with the use of vacuum drying for the second stage. The leather dried initially either by paste drying or by toggle drying showed a coarser break, firmer temper, poorer grain quality and lower cutting value than the leathers dried initially by free hanging or vacuum drying. The differences were further shown in the physical tests, where the lastometer distension at grain crack was unacceptably low for the paste and toggle dried leathers and was reduced (to some degree) even for the vacuum dried leather, in comparison with free hanging. A limited study was made of the effect of the slicking direction, before paste drying, on the resulting leather properties. Only a small effect was noticed, the statistical significance of which could not be fully established. The study of how to improve the adversely affected properties of the paste dried leathers is described in Part 5, J. Soc. Leather Technol. Chem, (awaiting publication).