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Lacquer Chemistry and Applications explores the topic of lacquer, the only natural product polymerized by an enzyme that has been used for a coating material in Asian countries for thousands of years.
Although the human-lacquer-culture, including cultivation of the lacquer tree, harvesting, and the use of lacquer sap, has a long history of more than thousand years, there is very little information available on the modern scientific methods to study lacquer chemistry.
This book, based on the results of the authors' 30 years of research on lacquer chemistry, offers lacquer researchers a unique reference on the science and applications of this extremely important material.
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.
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).
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 . 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.
Compositions of lacquer sap (separated by Ishimatsu sadama)
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 . 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" . 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].
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.
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 . After that, polychrome formulas of lacquer , morphological and physiological bases of the lacquer tree , and lacquer toxicity  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...
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