Tannin antioxidant characteristics in leather versus leather light stability: Models

The variation of leather color as a function of aging time on prolonged irradiation with UV light of the leather produced by tanning with different polyflavonoid and hydrolyzable vegetable tannins is reported: A predictive model and two equations for the variation of leather color as a function of UV-irradiation time and as a function of the different vegetable tannins used was also established. This technique appears to describe well the overall phenomenon of oxidation and color change in situ observable in vegetable-tanned leathers. The variation of leather color as a function of aging time on prolonged irradiation with UV light of the leather produced based on different vegetable tannins was found to be composed of two main effects: The first one of these is the darkening reaction of the leather. This is due to the formation of quinones on the phenolic structure of the vegetable tannin. The second one is the leather-lightening reaction due to the photodegradation of the system. These two phases were equated and correlated with the radical uptake reaction and radical stabilization/decay reaction observed by ESR for UV-irradiation of pure tannin in the solid form and of the leather produced using the same. Thus, correlation among the antioxidant capability of tannins in the solid form, their antioxidant capability once included in the leather, and the color variation (darkening and lightening) of leather by colorimetry was established. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1030-1040, 2004.