Polylactic acid (PLA), a biodegradable plastic, has excellent electrical insulation properties at temperatures ranging from room temperature to around 70 °C. At temperatures higher than 70 °C, however, the insulation performance of PLA deteriorates due to its poor heat resistance. In this study, PLA was heat‐treated at 100 °C to endow it with greater heat resistance, and the effects of this heat treatment on the electrical properties of PLA were investigated. Before being subjected to heat treatment, the crystallinity (xc) of PLA was about 6%. After the heat treatment was begun, xc increased in proportion to the heat treatment time, such that measurements revealed that xc had increased to about 42% by 15 minutes after the start of the heat treatment. The temperature dependence of the insulation breakdown strength (EB) of heat‐treated PLA was investigated, and it was found that EB of heat‐treated PLA (PLA‐A) decreases at a more moderate rate at temperatures above 60 °C. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(1): 1–8, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21272

-crystalline chitin was added to polylactic acid (PLA), and this PLA was then heat-treated at for one minute. The crystallinity of the heat-treated PLA increased to more than 40%, and its crystallization speed also increased significantly. The temperature dependency of these materials’ relative permittivity () and relative dielectric loss factor () was also examined. The dielectric absorption peak value in curve of the PLA to which chitin was added and was smaller than that of PLA without chitin. Additionally, the Havriliak-Negami relaxation function was used to produce approximation curves for the frequency dependency of and of chitin with PLA added at . As a result, the relaxation strength of the chitin with PLA added was smaller than that of the PLA without chitin, and the relaxation time of the chitin with PLA added was approximately 2.5 times larger than that of the PLA without chitin.

Poly-lactic acid (PLA), a biodegradable plastic, has excellent electrical insulation properties at temperatures ranging from room temperature to around 70°C. At temperatures higher than 70°C, however, the insulation performance of PLA deteriorates due to its poor heat resistance. In this study, PLA was heat-treated at 100°C to endow it with greater heat resistance, and the effects that this heat treatment had on the electrical properties of PLA were investigated. Before being subjected to heat treatment, crystallinity (x c ) of PLA was about 6%. After the heat treatment was begun, x c increased in proportion to the heat treatment time, such that measurements revealed that x c had increased to about 42% by the time 15 minutes had passed since the start of the heat treatment. The temperature dependence of the insulation breakdown strength (E B ) of heat-treated PLA was investigated, and it was found that E B of heat-treated PLA (PLA-A) decreases at a more moderate rate at temperatures higher than 60°C.

We examined the electrical properties of polylactic acid (PLA) with a nucleating agent added. The PLA with added nucleating agent was then heat-treated at 100 °C for 30 seconds. The crystallinity of the PLA with added nucleating agent increased to more than 40%, and its crystallization speed also increased significantly. The temperature dependence of the conductivity (σ) was investigated; at temperatures higher than 60 °C, σ of PLA to which the nucleating agent had been added showed a tendency to become lower than σ of PLA to which no nucleating agent had been added. The temperature dependence of the dielectric breakdown strength (E B ) was investigated. E B of the PLA with added nucleating agent was about 5.0 MV/cm at 25 °C. Of particular note was the fact that the E B of PLA with added nucleating agent was about 4.7 MV/cm at 100°C, which is about 3 times the E B value for PLA with no added nucleating agent. The temperature dependence of the relative dielectric constant (ε r g ) and the relative dielectric loss factor (ε r gg ) was investigated. The peak dielectric absorption value of ε r gg for the PLA to which nucleating agent had been added showed a tendency to be lower than that of the PLA to which no nucleating agent had been added.

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β‐Crystalline chitin was added to polylactic acid (PLA), and this PLA was then heat treated at 100 °C for 1 min. The crystallinity of the heat‐treated PLA increased to more than 40%, and its crystallization speed also increased significantly. Furthermore, the temperature dependence of the dielectric breakdown strength (EB) was checked, and it was found that at a temperature of 80 °C, the EB value of the PLA with chitin was around 1.8 times greater than that of the PLA without chitin. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.