Abstract
The mechanical and dielectric breakdown properties of polylactic acid (PLA), which is a biodegradable plastic, were examined, and a physicochemical analysis was performed. At room temperature, the tensile strength of PLA was about 100 MPa, almost the same as for PP, but at 100°C, even the value for LDPE decreased. The Young's modulus of PLA at room temperature was about 3.6 GPa, about 1.7 times the value for PP, and about 11 times the value for LDPE. The Young's modulus of PLA decreased slowly with a rise in temperature, and at high temperatures, 60°C and above, it decreased rapidly. The dielectric breakdown strength (EB) of PLA at room temperature was about 6.2 MV/cm, about 1.4 times the value for LDPE. The EB of PLA increased with an increase in temperature, and was about 6.9 MV/cm at 60°C (∂EB/∂T≥0). In this region, it is thought that a secondary effect due to space charge occurred, as well as an electron avalanche breakdown. However, the EB of PLA decreased at temperatures higher than 60°C in the high temperature region (∂EB/∂T<0). In this domain, it is thought that thermal breakdown occurred, and that electromechanical breakdown also occurred in the high temperature domain of 80°C and above.
