Abstract

In Part 4 (J. Soc. Leather Technol. Chem., 1984, 68, 159) the effect of the main techniques of leather drying, free hanging, toggling, paste drying and vacuum drying, on the properties of side upper leather was studied. The leather was prepared by the Modified Standard Process (MSP) as described in Part 3 (J. Soc. Leather Technol. Chem., 1984, 68, 125), except for the drying variants. The leathers that had been dried by processes involving stretching (especially toggling and paste drying) were adversely affected as regards break and were also modified in temper. They showed substantially reduced distension to grain crack (lastometer) and elongation to rupture. The present investigation examined how far retannage and modified fatliquoring can restore the leather properties to the generally satisfactory standards of MSP leather itself. Preliminary experiments resulted in the selection of a combination retannage made up of Tanigan OS, Retingan R7 and mimosa extract. This retannage was used together with normal and enhanced levels of fatliquoring. The combined action of retanning and increased fatliquoring appeared, from the first trials, to be effective in improving the break characteristics and giving a softer leather. It failed, however, to achieve a satisfactory distension to grain crack in the lastometer test. A trial was carried out on retannage and modified fatliquoring, using the full range of subjective and physical tests that were employed in previous parts of this work. The results fully confirmed the previous tentative conclusions that the subjective properties could be adjusted to match standard MSP leathers. Retannage had no significant effect on the grain brittleness arising from paste drying but the extra fatliquoring reduced somewhat the grain brittleness, in comparison with MSP leather, as assessed by the distension to grain crack (lastometer). The final sections of the paper describe studies on the weight, area and thickness of the sides, using data from the various packs studied in Parts 3, 4 and 5. The paper concludes with a summary of findings collected from the entire investigation (Parts 1-5).