Studies on Phenolic Resins. IV. Physical and Chemical Properties of Coating Films of Japanese Lac (Urushi) (Rigidity Modulus-Temperature Relations Measured by Torsional Pendulum Method)

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As to Japanese lac some reports are found in literature concerning chemical identification of the lac component, or electrical insulation and resistance of the film to chemical reagents, but no physical and chemical properties related to internal polymer structure of the film had ever been investigated. In this paper the authors studied the physical and chemical properties of the film of Japanese lac by means of the torsional pendulum method. As the results of the experiment, the following characteristics of the films prepared by various processes from Japanese lac were revealed: 1. The films do not show sharp glass transition phenomenon and are durable as a protective coating over a wide range of temperature. 2. The films from sugurome-processed Japanese lac have ample flexibility and considerable rigidity, ideally combined. 3. During exposure to air, the films are oxidized with formation of polar group in polymer molecules. But cross-linking does not take place except in air-dried film of raw Japanese lac. The above mentioned physical and chemical properties of the film account for the characteristic, complicated three dimensional polymer structure caused by action of laccase and chemical structure of urushiol, and such excellent properties can not be found in any other films from synthetic resins. The results obtained are of practical use and they should be taken into consideration in the study of preparation of fillers or substitutes for Japanese lac. Catechol derivatives synthesized by the authors were confirmed to be fairly good fillers.
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Studies on Phenolic Resins. IV. Physical and Chemical Properties of Coating Films of Japanese Lac (Urushi) (Rigidity Modulus-Temperature Relations Measured by Torsional Pendulum Method)

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