Dielectric properties of ion-exchanged electrotechnical insulation papers : A study on the properties of novel papers

Sammanfattning: Electrical insulation papers are a widely used group of papers in insulation applications and has been used for more than 100 years. Common applications include use as the dielectric medium in capacitors and insulation material in cables, bushings and transformers. As new advances in the study of the electrical properties of paper are made, the prospects of future applications grow. One interesting prospect is the use of paper as a substrate in sensing devices, biodegradable, printed and flexible electronics. Paper is a renewable and recyclable material and it would therefor be desirable to replace non-renewables materials such as plastics with paper as e.g., substrate in printed electronics. For this to be feasible the paper must be able to meet the electric and dielectric requirements of the intended application, among which low dielectric losses is a key parameter. One way to alter and control the electric and dielectric properties of a paper sample is through the selection of different ions in the ion-exchange step of the paper making process. In a collaboration between KTH Royal Institute of Technology and RISE - Research Institutes of Sweden AB working within a greater Digital Cellulose Center (DCC) project, this thesis aims to measure and characterise the dielectric response of a set of novel ion-exchanged paper samples together with a set of reference papers currently used in electrical applications. The greater goal of RISE work is to understand and map the influence of ion choice in order to better understand and control the dielectric properties of paper. The samples were measured using an impedance spectroscopy method from which capacitance and permittivity can be calculated. A parallel plate Kelvin guard-ring capacitor consisting of two electrodes and a guard ring placed in a custom made climate controlled chamber was used to measure the samples in different environmental conditions. The results show that the choice of ion used in the ion-exchanged papers heavily influence the samples dielectric response, both its dielectric constant and dielectric losses. Further, the choice of ion valence appears correlated with the change in responses; monovalent ions had much greater influence than bivalent ions. This effect appears to stem from monovalent ions having a greater mobility within the bulk material, more research is however needed for a definite answer.