Effects of glass transition on the dielectric breakdown and electrical conduction in several biodegradable polymers

Results of the conductivity and breakdown strength measured for several biodegradable polymers are reported. At room temperature, poly-L-lactic acid (PLLA) and polyethylene terephthalate succinate (PETS) have relatively low conductivity values that are comparable to low density polyethylene (LDPE). However, when the fact that PLLA and PETS are in the glass state is taken into consideration, the conductivity values of PLLA and PETS should be considered to be relatively high. Moreover, PLLA and PETS show rapid increase in the conduction current around their glass transition temperatures. The other three biodegradable polymers that are in the rubber state at room temperature, namely ε-polycaprolactone butylene succinate (PCL-BS), polybutylene succinate (PBS), and polybutylene succinate adipate (PBSA), have much higher conductivities. Although the impulse breakdown strength is relatively similar in all the samples, PLLA and PETS have higher breakdown strengths in temperature regions around their glass transition temperatures. This apparently anomalous behavior is explainable by assuming that part of the energy supplied by the applied impulse voltage was consumed due to the glass transition. As for DC or AC breakdown strength at room temperature, PLLA and PETS show a relatively higher strength than PCL-BS and PBS.