Effect of crystallinity on the partial discharge resistance of poly-L-lactide

We have changed the crystallinity of biodegradable poly-L-lactide (PLLA) by drawing or by annealing thermally, and have examined its effect on the partial discharge (PD) resistance. Although the depth eroded by a fixed period of PD degradation becomes shallower when the sample was crystallized by the drawing or by the heat treatment, its reduction ratio is almost equal to the reduction ratio of PD activities due to the decrease in permittivity. Therefore, it is hard to assume that crystallization of PLLA improves its PD resistance to a unit amount of charge.