Elastomer performance and processing can be customized through the choice of both the prepolymer and the curative. Specifically looking at curatives, MBOCA, the industry standard for TDI systems, provides good overall performance, processing and cost benefits. Alternative curatives or curative blends, on the other hand, allow for adjustments or optimizations of the elastomer system.
The curative usage level (percent stoichiometry) also affects elastomer performance. Since physical properties are sensitive to percent stoichiometry, particular properties can be enhanced by changing the percent stoichiometry. Typical curative levels are between 85 and 105% stoichiometry, with 95% being the standard recommended target level for most polyurethane elastomer systems. The following table outlines the elastomer physical property changes that can be expected by adjusting the percent stoichiometry.
Effect of Percent Stoichiometry on Elastomer Physical Properties
| Hardness |
Stable; minor change over the range of 85-100% |
| Modulus |
Stable; minor change over the range of 85-100%; decrease outside this range |
| Break Tensile |
Maximizes at 90-95%; slight decrease outside this range |
| Tear Strength |
Maximizes at 100-105%; significant decrease below this range |
| Elongation |
Maximizes at 100-105%; minor decrease below this range |
| Compression Set |
Low % stoichiometry results in low compression set |
| Abrasion Resistance |
High % stoichiometry favors good abrasion resistance; 100-105% is optimum range |
| Hysteresis, Dynamic Mechanical |
Low % stoichiometry is preferred; 90-95% is optimum |
| Flex Life |
High % stoichiometry favors good flex performance; 100-105% is optimum range |
| Resilience |
Maximizes at 85-90%; slight decrease above this range |
|
|
