Introduction to peroxide crosslinking
Crosslinking of polymers changes thermoplastic materials into thermoset materials and elastomers into rubber materials. This change in molecular structure provides the following benefits:
- Improvement of thermal resistance, heat aging properties and low temperature impact
- Improvement of tensile strenght, modulus, abrasion resistance, creep resistance
- Improvement of chemical resistance and stress crack resistance
- Improvement of heat distortion properties and hot set behavior
The two mainly used crosslinking systems in the rubber industry are vulcanization with sulfur and crosslinking by peroxides. Peroxide crosslinking provides materials with much higher heat stability due to the higher bonding strenght of C-C-bonds versus C-Sulfur and Sulfur-Sulfur-bonds. Another advantage of peroxide crosslinking is the lower compression set. Therefore, this technology is used for rubber materials in all applications where high heat stability is required as e.g. “under hood” applications in the automotive industry and for applications where a high resilience of the material is necessary as e.g. in sealings and gaskets.
In the plastic industry the main crosslinking technologies are peroxide crosslinking and crosslinking by electron beams. With the peroxide technology the crosslinking process can be combined with the shaping process, but it needs elevated temperatures. Electron beam crosslinking is a separate process step, which needs special equipment and a separated area with special safety requirements.
With addition of the coagents TAC and TAICROS® to the peroxide formulation the crosslinking efficiency can be significantly improved. This is advanatgeous in two directions. On one hand TAC or TAICROS® can be added on top of the regaular peroxide concentration to increase the crosslinking density and improve all properties aligned with this. On the other hand, a part of the peroxide can be replaced by TAC or TAICROS® to reduce the disadvantages associated with the peroxide like volatile or toxic byproducts or blooming without a reduction of crosslinking degree. In cases where more expensive peroxides are required TAC and TAICROS® also help to reduce cost.