Determinaton of light fastness property of leathers tanned with different vegetable tannins and investigating the possibility of increasing the light fastness

Vegetable tannins are widely used for manufacturing tough, firm and durable leather types as sole leathers, saddlery leathers, shoe insole and shoe upper leathers. Vegetable tannins give leathers that have a natural handle and characterictic colour of tannins. As well as these favourable properties of the tannins, especially mimosa and quebracho tannins which belong to condensed tannin agents, have some undesirable properties, as fading or darkening by the influence of light. The change of colour in leather products especially shoes and bags, in the store or in customer usage, decreases the quality of products and affects the satisfaction and charm for customers. This research is aming to reduce the colour changing of leathers tanned with mimosa and quebracho tannins which is caused by exposure to light for prolonged times. For this aim some modifications, which include sulphitation, sulphomethilation and Novalac synthesis for mimosa and quebracho tannins have been applied. On the other hand, a UV stabilisator has been used for reducing the darkening effect in vegetable tanned leathers, including benzotriasol and Hindered Amine Light Stabilizer (HALS). Consequently, it has been confirmed that the modification of sulphomethylation of quebracho and mimosa tannins, is the best application for reducing color changing effect of vegetable tanned leathers. Application of bensotriasol and HALS, UV stabilisator, has been determined less efective on reducing the fading or darkening of vegetable tanned leathers than the modifications. Keywords: Vegetable tannins, UV, colour change, light fastness.