What's in a rubber compound?

Posted by LMI Custom Mixing on Nov 6, 2017 10:30:00 AM

When creating a rubber compound, the custom rubber mixer starts with a compound “recipe.” Recipes are developed to enhance or add to an elastomer’s inherent physical and chemical characteristics, then the recipe is mixed using precise weighments and advanced internal batch mixing technology into the final rubber compound.

There are several main components in a typical compound recipe: the polymer base, carbon black, mineral filler, oil, activators, processing aids, antidegradants and curing agents.

What does each ingredient do?

Each ingredient in the recipe serves a specific function during the mixing or curing process.

Polymers 4.jpgThe rubber or polymer base is the basic building block of the compound. Any number of elastomers can be used depending on the end-use application and in-service conditions.

Carbon black acts as a reinforcing agent and helps build the structure of the compound. Carbon black also provides tensile strength, elongation and tear properties.

Mineral fillers such as clay or talc reinforce or alter physical properties of a compound, help facilitate final processing and help to reduce cost. 

Oils make a compound mixable and help develop proper hardness levels. Oils can be used to promote elasticity and increase tack, or the “stickiness” of the compound.

Process aids are often added to modify the compound during mixing and promote processing during extrusion or molding.

Curing agents like sulfur and peroxide help crosslink the polymer chains together during the curing process. Activators and accelerators help speed up the curing process and in many cases also improve the final product’s physical properties.

A03 50X.jpgFor sponge compounds, a blowing agent system is required. Blowing agents generate gases during the curing process that creates cell structure, making the compound softer and lighter.

Learn more about rubber compounding and elastomeric materials design in our Custom Rubber Mixing eBook.

Download Custom Rubber Mixing eBook

Download our Custom Rubber Mixing eBook