As mentioned in the application “Compounding Rubber”, a rubber compound consists of a polymer, fillers, curing agents and additives. The same applies for silicone rubber and the only difference that sets this type of rubber apart from the rest is the type of polymer being used: siloxane polymers. Depending on the type of the polymer different vulcanisation mechanisms are possible: e.g when very highly viscous polymersystems (gums) are being used to make the compounds (produced on a 2,- or 3 roll mill) it almost always means that the compound be vulcanised through a radical peroxide mechanism (heat-cure)
Silicone rubbers are often the material of choice for applications where service temperatures are extremely low (up to -50dC) . Furthermore they are the materials of choice when good heat-stability, electrical insulation, oxidative resistance and UV degradation are critical performance requirements.
Incorporation of Sibelco’s mineral fillers in silicone rubber compounds allows the skilled formulator to cost-effectively address the needs for the application of the compound when it comes to:.
- Flame retardancy (ATH, Hydro magnesite)
- Thermal conductivity (Silica, Spherical Alumina)
- Electrical insulating (Silica, ATH)
- Mechanical properties (Wollastonite)
- Chemical rersistance (Silica, Cristobalite, Barite, Nepheline Seynite)
In silicone rubber compounding as in any other formulation the interaction between all the constituents is critical to the behaviour of the material during processing and to the performance final the final application. Thus also the interaction between fillers and polymers is very important. From a filler perspective this means that beyond the intrinsic properties of the mineral-type itself, particles-size (distribution), surface area, porosity, particle morphology and surface chemistry all are relevant parameters in selecting the proper grade for a balance of properties (compression set, oil-resistance, thermal conductivity, sound deadening).