E-Book, Englisch, 312 Seiten
ISBN: 978-0-12-803610-5
Verlag: Elsevier Reference Monographs
Format: PDF
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Covers the chemistry and properties of lacquer, including synthesis of its various componentsProvides up-to-date analytical techniques for lacquer identification and characterizationDiscusses possible toxicity effectsOutlines new modification techniques for developing higher performance materialPresents the history of this versatile coating material that has evolved from its origins in Asian countries over thousands of years
Dr. Rong Lu is a senior researcher at Meiji University, Japan. He received his Master's degree from Wuhan University of China in 1995, specializing in organic chemistry and Ph.D. from Hokkaido University of Japan in 1999, specializing in polymer chemistry. His research interests in organic and polymer chemistry, including synthesis of low molecular weight of pharmaceutical intermediates, analysis and improvement of lacquer, and development of composite and functional coatings. He is a co-principal investigator in a project, led by Prof. Dr. Miyakoshi, Meiji University, and funded by the Ministry of Education, Culture, Sports, Science and Technology of Japan, to establish a scientific evaluation system of lacquer and investigation of lacquer culture.
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Chapter 2 History of lacquer chemistry
Abstract
This chapter introduces the brief research history of lacquer chemistry. It starts by presenting the research activities in several different countries and areas due to different lacquer tree resource allocations. It then describes chemical structure of urushiol, laccol, and thitsiol. Subsequently, the separation and compositions of lacquer sap were described. By the end of the chapter the emulsion structure of lacquer sap is discussed based on the photomicrograph observation results. Keywords Lacquer chemistry Brief history Urushiol Laccol Thitsiol Emulsion Lacquer chemistry, which is independent of oil and other fossil resources, uses only the natural cycles of plant materials to make various craft and industrial products. The polymerization of lacquer sap is catalyzed by the oxidation of lipid components (urushiol, laccol, and thitsiol) by laccase contained in the sap, followed by a coupling reaction as well as an autoxidation reaction on the long aliphatic unsaturated side chain. During the drying process, no organic solvent evaporates, only water. In recent years, new concepts of green and sustainable chemistry have been instituted and are considered in lacquer chemistry. Lacquer is a natural resource as long as lacquer trees are cultivated (Figure 2.1). Figure 2.1 Lacquer tree seedlings (a) and forest (b). 2.1 Brief History of Lacquer Chemistry
Like other disciplines, the study of lacquer chemistry has a long development and has been repeatedly revised, mainly in the following points: (1) The research has been carried out in several different countries and areas due to different lacquer resource allocations. Although the results from different laboratories exhibit certain differences, they could provide mutual correction and then gradually be unified. For example, in the latter half of the nineteenth century, T. vernicifluum lacquer sap was studied in Japan, and almost at the same time, France discovered this resource in its colony, Vietnam, and analyzed T. succedanea lacquer sap independently. Therefore, georelationships, production, and utilization are the power to promote the development of lacquer chemistry. (2) Lacquer chemistry developed along with the development of chemistry and biology as well as with the improvement of instrumentation and equipment technology. In the primary stage of lacquer chemistry research, in terms of studies of composition separation, structure analysis, and mechanisms, especially the catalytic mechanism of laccase, all reflected the phenomenon and qualitative research due to the basic theories of chemistry and biology. For example, the mechanism of active copper center of laccase gradually became clear after the development of spectroscopy technology. (3) The study of lacquer chemistry occurs more in the laboratory and less in the wilderness or plant due to limitations of lacquer resources. Because lacquer is a special Asian product not naturally available in Europe and America, European and/or American studies should only use extraction vacuum lacquer samples provided by Japan. However, because lacquer composition is easily changed (e.g., oxidized), some results of research on laccase are quite different from those of natural laccase, and thus the reliability of the results obtained is poor. For these reasons, fungal laccase instead of lacquer laccase has been used to study the catalytic mechanism. Although the results can be published and compared, they are distorted. Another example of the effect of the distribution of resources is the French loss of its Eastern colonies, making studies of lacquer chemistry in France increasingly rare. (4) Applied research needs to continue and improve. Our lab is continuously engaged in the reforms and improvements of lacquer, such as blends, hybrids, and microdispersion. Of course, synthesis of lacquer sap also needs to continue. It is also necessary to do interdisciplinary and international research in lacquer chemistry. The systematic study of lacquer has long been carried out in Japan. In 1878, the Japanese researcher Ishimatsu Sadama, a student at the University of Tokyo, tried to separate lacquer sap with ethanol [1]. He added anhydrous ethanol to the lacquer sap, then mixed and filtered it. The filtrate was evaporated, and an “alcohol-soluble” residue was obtained. The residue was treated with hot water, stirred, and filtered, the filtrate was evaporated to obtain a “gum” and the matter insoluble in hot water was considered the residue. The residue included bark, cellulose, and a mud-like matter (glycoprotein), and the “gum” was like an ordinary gum (gum Arabic) according to element analysis. The alcohol-soluble portion was the main component of lacquer sap that had a brown color and was rather viscous. Although Ishimatsu attempted to determine the molecular formula of the alcohol-soluble residue by elemental analysis, the results were not satisfactory. The results of Ishimatsu are summarized in Table 2.1. Table 2.1 Compositions of lacquer sap (separated by Ishimatsu sadama) Alcohol soluble 58.24 Gum (alcohol insoluble, water soluble) 6.34 Residue (both alcohol-, water insoluble) 2.24 Moisture and other volatile matters 33.18 Total 100 Five year later, urushiol, the main component of lacquer, was investigated by Yoshida, who was one generation younger than Ishimatsu, in the same laboratory at the University of Tokyo [2]. He used acetone as the separation solvent to instead of anhydrous alcohol. Because the acetone-soluble portion has a –COOH group according to a Litmus test, Yoshida named the acetone-soluble portion “urushi acid” and gave it the molecular formula of C14H18O2 from element analysis results. He also pointed out that the part insoluble in ethanol contained tree gum and an enzyme that made the lacquer self-drying, and found that the enzyme is not stable, but subject to thermal decomposition. Almost at the same time, in 1890, a French researcher, Gabriel Bertrand, studied Vietnamese lacquer and suggested that the acetone-soluble component was a kind of polyphenol and named it “laccol.” The alcohol-insoluble water-soluble material was a “gum” containing a small amount of nitrogen. It was not clear whether this nitrogen belonged to an enzyme protein or not, but because it can catalyze laccol to dry and solidify, he named it “laccase” [3–6]. In fact, the acidic property of lacquer is due to the phenolic hydroxyl group, which was later confirmed by Miyama, and the main lipid component of lacquer was named “urushiol” [7]. In 1907, Majima found that the urushiol from T. vernicifluum tree grown in Japan is a hydroxyl compound with a divalent benzene nucleus due to the O-dihydroxy benzol reaction. He found that urushiol is not composed of a single substance, but a mixture having the basic chemical structure shown in Scheme 2.1. The side chain is a straight 15-carbon chain mixture with saturated and unsaturated monoenes, dienes, and trienes in the carbohydrate structures [8–12]. Scheme 2.1 Urushiol structure (Majima). Lacquer saps from T. succedanea and G. usitata trees were also studied by Majima. He concluded that laccol has 17-carbon side chain combination on the 3-position of a catechol ring mixture with saturated and unsaturated monoenes, dienes, and trienes. On the other hand, thitsiol has a 17-carbon side chain combination on the 4-position of a catechol ring mixture with saturated and unsaturated monoenes, dienes, and trienes, as shown in Scheme 2.2. Scheme 2.2 Laccol and thitsiol structures (Majima). Majima and his coworkers published many research papers on lacquer chemistry. They revealed a part of the urushiol structure by carbonization, nitric acid oxidation, methylation, acetylation, potassium permanganate oxidation, and ozone oxidation methods. They also successfully synthesized the hydrogenation of urushiol. In China, Xu Shanxiang was the first to study lacquer chemistry in 1926. He reported physical and chemical properties, use, and drying behaviors of lacquer [13]. After that, polychrome formulas of lacquer [14], morphological and physiological bases of the lacquer tree [15], and lacquer toxicity [16] were reported. It is worth mentioning here that Bertrand and Brooks studied the main component of lacquer sap from Gluta laccifera trees grown in Cambodia and Thailand, and named it “moreacol.” However, due to insufficient research, it is considered to be the same structure as the thitsiol described by Majima. About 30 years later, in 1954, Dawson et al. examined the numbers and positions of the double bonds in the side chains of urushiol by an ozonolysis method and ultraviolet spectroscopy [17–19]. They compared the structure of poison ivy and lacquer urushiol, analysis of -ene...
