Abstract
Examination of thermal degradation of natural and synthetic lacquer films by pyrolysis-gas chromatography with mass spectrometry (Py-GC/MS) is reviewed. Due to the instantaneous heating decomposition, side reactions of internal or intermediate samples hardly occur, and the pyrolysis products can be retrieved without any change. Py-GC/MS has been used to analyze the composition of insoluble polymers and investigate degradation of resin materials. Lacquer film is a cross-linked polymer that is insoluble in any solvent. The aim of this review is to describe the application of Py-GC/MS to the analysis of lacquer, including natural lacquer saps, synthetic lacquer derivatives, and their films. After analyzing the chemical structures of the specific pyrolysis products by mass spectrometry, the lacquer tree species and growing region can be determined. These results have great significance for the protection and restoration of lacquer-coated cultural treasures.
Highlights
The Asian lacquer known as Shengqi, in China, and Urushi, in Japan, is sap collected fromRhus vernicifera lacquer trees, and the main lipid component is urushiol
Frade et al analyzed two lacquer shields exported to Portugal from Asia in the 16th century; the results showed that the sample in the Soares dos Reis National Museum was coated with Rhus succedanea lacquer sap and that oil was used as the binding medium, and another sample in a private collection showed characteristic pyrolysis products of Melanorrhoea (Gluta) usitata [49]
The results showed that both lacquer wares are coated with lacquer sap tapped from Rhus vernicifera lacquer trees, and linseed oil was found to be the binding medium for drying
Summary
The Asian lacquer known as Shengqi, in China, and Urushi, in Japan, is sap collected from. All three lipid components are composed mainly of substituted catechols in the 3- or 4-position that have long unsaturated side chains with 1–3 olefins These saps have been utilized for coating materials because of their particular beauty and high durability. After doing a full literature review, we believe that the first successful use of pyrolysis-gas chromatography with mass spectrometry (Py-GC/MS) to analyze lacquer films was reported by Niimura et al in 1995 [4]. They used urushiol, plant gum, and glycoproteins isolated from the same lacquer sap as a control to study the pyrolytic behavior of lacquer film. Setting the temperature of the oven high enough and using a heat-resistant column are important because urushiol is undetectable at temperatures lower than 280 °C
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