THE VISCOELASTIC BEHAVIOR OF JAPANESE LACQUER FILM II - THE CHANGES OF VISCOELASTIC PROPERTIES DUE TO HEAT-TREATMENT

The storage modulus (E') of Japanese lacquer films rapidly increased w ith time at temperatures above 100 degrees C and remained unchanged at temperatures below 50 degrees C. The increasing rate of E' increased with increasing temperature in the early stage. The films shrunk remar kably at temperatures above 150 degrees C. The loss modulus (E '') of the films heated at various temperatures for 12 hours had two peaks in the temperature range of 100 degrees C to 200 degrees C and at about -140 degrees C, labeled alpha and gamma respectively. The alpha loss p eak was attributed to the micro-Brownian motions of lacquer molecules. The temperature location of the alpha loss peak had the largest value when the film was heated at 250 degrees C. Both the alpha peak value and the apparent activation energy of the alpha relaxation process sho wed the smallest values when the film was heated at 200 degrees C. The se results suggested that heating promoted the cross-linking formation of the lacquer molecules at temperatures below 200 degrees C and thei r remarkable degradation at temperatures above 250 degrees C.