We all know why we use fillers, especially carbon black, in our rubber compounds. Carbon black fillers enhance the ultimate performance of rubber products such as good wear resistance, damping behavior and the ability to undergo very large deformation with nearly no permanent deformation. They can affect not only the dynamic modulus, both viscous modulus and elastic modulus, but also their ratio, i.e., loss factor, which is related to the portion of the energy dissipated during dynamic deformation.

In practice, the energy loss in rubber products during dynamic strain is of great importance, for example, in vibration mounts and tires.  Energy loss acts as service performance predictors of these products. Specifically, energy loss is a predictor of heat generation and fatigue life for the vibration mounts, and rolling resistance, traction, and skid resistance for tires.  When rubber is deformed an energy input is involved which is released in part when the rubber returns to its original shape.  The part which is not returned as mechanical energy is dissipated as heat. 

Rubber products under dynamic conditions and subjected to repeated deformations with sufficient magnitude and frequency, will result in the generation of considerable heat (depending on the rate of heat dissipation) and significant rise in temperature.  The product’s temperature reaches steady state after running for a certain period, when the rate of heat generation equals with the rate of heat dissipation.  The extent of heat generation governs the change in viscoelastic properties of the product, which may lead to premature failure.  The process is more severe in thick rubber blocks and causes the interior part of the block to become so hot that the rubber explodes.  This is an important mode of failure in thick rubber products such as tire treads and tank track pads. 

Accurate, repeatable testing of rubber compounds to assess their heat build-up properties is essential for product manufacturers to safeguard the people using their products. Typically, tests for heat build-up characteristics involve multiple instruments such as those used in a this study.  Specifically:  

• • Rheometric properties were studied by using a Premier™ MDR (Alpha Technologies, USA) in line with ASTM D5289.  
  • Shore A hardness was determined on Multi Unit Hardness Tester in line with ASTM D2240.  
  • Stress strain and Hysteresis properties were ascertained by using Universal Testing Machine in line with ASTM D412 using a die C dumbbell.  
  • Density was carried out in line with ISO 2781.  
  • Rebound Resilience was tested in line with ISO 4662 at 100ºC.  
  • Heat buildup (HBU) test was carried out on a Goodrich Flexometer in line with ASTM D623.  
  • Dynamic Mechanical Analysis (DMA) of cured samples was carried out in line with ASTM D5992. 

Parallel testing was performed on identical samples on Alpha’s Premier RPA. 

The study was performed in two phases: phase 1 establishes that filler is the primary reason for HBU in the rubber compound; phase 2 studies the effect of carbon black particle size on HBU.