Rubber Compounding
Rubbers are materials that are elastic in nature (therefore often called elastomerics) ,meaning (in laymen’s terms) they have the ability to go back to their original shape and size after having been stretched.
There is natural rubber (latex from a rubber-tree) and synthetic rubbers, EPDM probably the most common one.
Rubbers are polymeric materials and depending on the backbone will exhibit different additional preferred properties beyond the ability to reform after stretching.
These preferred properties can be further achieved through rubber compounding: mixing the rubber-polymers with other materials like, minerals, curing agents and additives (manufacturing the rubber compound). This is generally done on a 2-,or 3 roll mill:
The final article is actually produced when the rubber compound is vulcanised (formation of links between one polymer-molecule to another) and shaped in mold or thru extrusion (e.g. profiles). There are different mechanisms by which this vulcanisation can take place.
Properly formulated and vulcanised compounds can fulfill the requirements of the article or application they are used for. This can be for seals, tires, matts.
Incorporation of Sibelco’s mineral fillers in 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)
- Chemically inert/ pH neutral (Silica, Cristobalite, Barite, Nepheline Syenite)
- High density/ sound deadening (Barite)
In 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 in 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). Only Sibelco’s Wollastonite based products be used as reinforcing fillers.
