Abstract

The manufacture of footwear with greasy leathers can be estimated at about 25% of the total production with bovine leathers present. This type of leather causes problems in upper—sole bonding during footwear manufacturing. Therefore, the objective of this work is to study the composition of the greasy leathers that have previously been selected as particularly problematic for bonding. An attempt is made to determine what factors (distribution and/or type of grease) most negatively influence the adhesion capability of these materials, as well as to look for alternative ways to modify these factors during manufacture of the leather. In accordance with the results obtained in the characterization, modifications will be proposed to the tanner in terms of procedure, with the aim of achieving a better distribution of the greasy matter throughout the thickness of the leather, and in terms of the products which must be used. The experimental controls and procedures used were the following:

1) Quantitative determination of the greasy extract according to standard ISO 4048
2) Analysis of the greasy extract

• Determination of unsaponifiable fraction (paraffin waxes and mineral oils)
• Thin layer chromatography (TLC) • High pressure liquid chromatography (HPLC)
• Gas chromatography—Mass spectrometry (GC.-MS)

3) Determination of the bonding capacity of the greasy leather according to standards ISO 11644 and BS-5131 Sec. 1.1.2.

Leathers that contain extractable greasy matter below 15% of the dry weight of the material, do not present bonding problems, independently of the composition of the greasy extract. If the leathers contain more than 15% of extractable greasy matter they can be problematic for bonding depending on the composition of the greasy extract. Analysis and subsequent tests have shown that wax or mineral oils of high molecular weight are more detrimental for bonding. It is possible to improve the bonding results of the difficult greasy leathers by modifying the composition of the grease, e.g. replacing paraffin waxes of high molecular weight with others of low molecular weight.

Our main conclusions were:

1) Leathers with greasy extract levels above 15% can be difficult in bonding.
2) Paraffin waxes and mineral oils with a high molecular weight are the most detrimental components for bonding. Both products are easy to detect by thin layer chromatography applied to the extract.
3) Alternative grease products have been proposed.