Daniel Van Dommelen

Expansion of polystyrene using water as the blowing agent

Heating of polystyrene beads containing pentane isomers as the blowing agent traditionally produces polystyrene foam. Undesirable emissions of the blowing agent and its high flammability are the complications of this process. A new process for the production of expandable polystyrene has been developed, using water as the blowing agent. Water is trapped inside the polystyrene matrix through the use of starch that is introduced as a separate phase during the suspension polymerization. The problems created by the incompatibility of starch with the organic phase can be partially overcome by “compatibilization” with maleic anhydride. The type of starch can influence the foam morphology of the pre-expanded beads, while the density is changed only in the range of the experimental error. The density of the pre-expanded beads is influenced by the blowing technique used (hot air or high frequency electric field). The use of these different blowing techniques does not influence significantly the foam morphology.

Design and Application of a Field Mill as a High-Voltage DC Meter

Field mill instruments are often employed for the measurement of electric fields, electric charges, voltage potentials and atmospheric effects. This paper discusses in more detail the application of a field mill for measuring DC voltages in high-voltage laboratories. Some specific problems, arising when voltages in the kV or MV range have to be measured, are emphasized. Safety, signal transmission and electrode design are dealt with. Field meter theory is summarized and generalized in function of this application. The design of a practical, field mill based electrostatic voltmeter is described along with some useful enhancements. Finally, test results of the voltmeter are presented