Abstract

In the last ten years, the use of various types of aromatic sulphonic acids in the pickling process to prevent swelling has been suggested by many authors.

In previous papers, we studied the capacity of four commercial products to prevent acid swelling of hides during pickling: polyacrylic acid, naphthol 3-6-disulphonic acid, p-hydroxydiphenyl sulphonic acid and a blend of naphthalene and naphthol sulphonic acids.

It was found that the best results were obtained using the blend of naphthalene and naphthol sulphonic acids. This process yielded leathers that could be acceptable as far as physical properties and handle are concerned. However; this process, which also reduced the chloride content and conductivity of the residual bath when compared with a standard pickling process, presented some disadvantages such as an irregular stratigraphic distribution of chromium and a marked difference of colour between the dyed grain and flesh layers after shaving, when using a conventional chromium tanning salt. This was due to the thickness of the hides (3.0 mm) which caused problems of penetration of the chemicals. In order to solve these disadvantages, the joint use of a mixture of a blend of naphthalene and naphthol sulphonic acids with a chromium salt of low basicity and high masking capacity was recommended.

Aim of the work

In the present work, the behaviour of the four commercial products with non-swelling capacity in the pickling/tanning processes of sheepskins is studied. The successful application of these products to thinner skins would allow us to reduce salinity and, hence, the conductivity of waste waters. The results obtained by using these products are compared with those achieved by applying a conventional pickling/tanning process.