Abstract

The reduction in the use of salt in pickling due to the application of different chemicals with non-swelling capacity – polyacrylic acid, naphthol 3-6-disulphonic acid, p-hydroxydiphenyl sulphonic acid and a blend of naphthalene and naphthol sulphonic acids- has been studied in previous papers. These chemicals were applied in the pickling process either alone or with small amount of salt.

In Part I, it was confirmed that the blend of naphthalene and naphthol sulphonic acids at an offer of 3% (on pelt weight) and at a salinity of 2°Bé could be a valid alternative since it adequately prevented the swelling of hides. Tanning treatments with conventional chromium salts yielded the correct shrinkage temperatures.

In Part II it was observed that the conventional tanning process of hides pickled with sulphuric acid and 3% (on pelt weight) of the blend of naphthalene and naphthol sulphonic acids at a salinity of 2°Bé yielded leathers that could be acceptable as far as physical properties and handle were concerned. However; these leathers showed an irregular stratigraphic distribution of Cr2O3 and a marked colour difference between grain and flesh sides. Optimization of the tanning process of these hides confirmed that the best results were obtained with a strongly masked chromium salt with a very low basicity.

In Part III, the possible application of chemicals with non-swelling capacity to reduce the use of salt in the pickling process of sheepskins was studied. In this case, the use of a strongly masked chromium salt with a very low basicity in the tanning process was not necessary since conventional tanning salts were adequate. The best results in terms of non-swelling capacity, shrinkage temperature of the tanned hides, conductivity and Chemical Oxygen Demand of the residual baths were achieved under the following conditions: 2% p-hydroxydiphenyl sulphonic acid (salinity 2°Bé); 2% naphthol 3-6-disulphonic acid (salinity 2°Bé) and 4% polyacrylic acid (salinity 2°Bé.)