An improved model to estimate trapping parameters in polymeric materials and its application on normal and aged low-density polyethylenes

Abstract

Trapping parameters can be considered as one of the important attributes to describe polymeric materials. In the present paper, a more accurate charge dynamics model has been developed, which takes account of charge dynamics in both volts-on and off stage into simulation. By fitting with measured charge data with the highest R-square value, trapping parameters together with injection barrier of both normal and aged low-density polyethylene (LDPE) samples were estimated using the improved model. The results show that, after long-term ageing process, the injection barriers of both electrons and holes is lowered, overall trap depth is shallower and trap density becomes much greater. Additionally, the changes in parameters for electrons are more sensitive than those of holes after ageing.

Trapping parameters estimation of fresh and thermally-aged low-density polyethylene by using an improved trapping/detrapping model

“…The calculation of (or ) will not be shown in the present paper due to the limit of pages, and details can be found in our paper [4]. The second negative term on right side of Eq.…”

“…(13) Details of derivation for equation (13) can be found in [4]. With an averaged drift velocity v , the momentum p of the particle moving between two trap sites can be found as:…”

“…The model was initially proposed in our previous paper [4]. It will be briefly described so the extracted trapping parameters can be understood.…”

“…Moreover, in the depolarization stage, charge carriers should move under the field produced by local space charges. For the mobile carriers, the direction of movement should be dependent on the direction of local space charge field, new expression of has to be derived for volts-off condition, see details in our previous paper [4]. derivations of the averaged electric fields at both volts-on and volts-off conditions in either charge region can be found in [4].…”

“…At every moment, mobile holes of shall flow from the positive charge region to the other side of bulk meanwhile mobile electrons will flow from the negative region towards the positive charge region with amount of . Detailed calculations of , can be referred to [4]. For the changing rate of positive trapped charge density , it should consist of three parts, i.e.…”