Rapid evaluation of UV and thermal aging of boiled tung oil by micro-UV/Py-GC/MS system

Abstract

Boiled tung oil is the commonly used drying oil in Chinese cultural relics, and light radiation, temperature are the important factors leading to its aging. In order to investigate the photo and thermal aging behavior of boiled tung oil and determine the characteristic parameters to evaluate its aging degree, micro-UV/Py-GC/MS system has been applied in the present work to monitor the volatile aging products released by boiled tung oil film, to obtain high aging degree boiled tung oil film in short time and to investigate its composition change in different aging degree.Research results showed that volatile products released by boiled tung oil film during UV irradiation and 60 ℃ were mainly series of aldehydes, ketones, carboxylic acids and hydrocarbons with small molecule. With increase of aging time, the type of volatile products remain unchanged, but their amount gradually decreases until cannot be detected. Pyrolytical products of unaged and aged boiled tung oil is the same, but with the increase of aging degree, relative content of glycerol, dicarboxylic acids and azelaic acid in boiled tung oil film gradually increased, while the relative content of oleic, linoleic and eleostearic acid, as well as the content ratio of mono-carboxylic acids to di-carboxylic acids gradually decreased.Changes of volatile and pyrolytical products during aging process were summarized to evaluate the aging degree of boiled tung oil used in cultural relics. Boiled tung oil used in two lacquerware samples collected from the same carved lacquer panel from Fuwang Ge in the Forbidden City, and two polychrome samples separately collected from the inner and outer eave of Yanxi Tang in the Forbidden City were investigated, the aging degree evaluation results of boiled tung oil in historical samples have further confirm the reliability of summarized parameters. Research results of the present work can provide scientific support for the conservation and restoration of related cultural relics, and also lay a foundation for the in-depth study of the photo and thermal aging mechanism of boiled tung oil.