Measurement of the trapping and detrapping properties of polymers in relation with their microstructure

In the field of space charge physics, the role of electrical traps on space charge behaviour and therefore on the breakdown properties is well-established. However, the traps in polymers are very difficult to define compared to the case of ceramics for which a lot of studies have been performed. A new specific method for measuring the trapping and detrapping properties of dielectric materials has been developed. This method allows characterization of the electrostatic state of an insulating sample after irradiation by a high energy electron beam. We discuss the basis of the method and its general possibilities to measure breakdown relevant parameters such as the secondary electron yield for instance. Moreover, the method has been used on several polymers such as HDPE and LDPE. The difference of trapping properties between those materials can be explained by microstructure evolutions (crystallinity ratio) due to a difference of the branching rate. This difference of trapping and detrapping properties of these two polymers could be connected to the breakdown behaviour of the two materials which is known to be very different.