The impact of inorganic fillers in unsaturated polyester resins

Recently, concern has been expressed as to the effects fillers have on the long-term performance of a resin utilizing inorganic filler. The author examines four different inorganic fillers, focusing on various performance properties as well as the practical aspects of using a resin containing inorganic filler. The fillers are silica, slate flour, talc, and a silica and hydrated alumina mixture. An assessment is made of the advantages and disadvantages of utilizing inorganic fillers in electrical insulating resins. From the data presented it is seen that inorganic fillers affect such liquid properties as viscosity and thixotropic index. They may also affect the pot life as measured by the gel time. The thermal and mechanical properties may be affected as well. However, the data seem to show minimal effects on the thermal and mechanical performance. In general, inorganic fillers seem to enhance the various performance properties of the unsaturated polyester resins tested. However, there are possible disadvantages, such as settling or an increase of viscosity to an undesirable level