Thermally Activable Bistetrazoles for Elastomers Crosslinking

Abstract

Sulfur vulcanization is the most used method for curing of natural and synthetic rubbers. The crosslinking degree achieved is usually controlled by adding proper quantities of accelerants, activators, co-activators, retardants, and inhibitors, and influences the hardness, elasticity, hysteresis of elastomers and, consequently, the properties and behavior of the materials that incorporate them. Despite the fine tuning pursued over the years, sulfur crosslinking is still difficult to control both in terms of degree and homogeneity of cross-link. Addition of thermally activable bifunctional reagents able to crosslink the polymer matrix through covalent bonds could be a strategy to modulate and control finely the reticulation grade of elastomers. Tetrazoles can form highly reactive nitrilimines by thermal treatment at appropriate temperature, which can react with the vinyl double bonds present in the rubber. In this work a set of bis-tetrazoles were synthesized and those with the right activation temperatures were used for the curing of styrene-butadiene rubber, acting both as single crosslinkers and together with classic sulfur-based ones. The addition of bistetrazoles simplified and made more efficient the compounding process, allowing to prolong the mixing until optimum dispersion and homogeneity were obtained. Moreover, they led to an improvement in the hysteretic properties of the compound and to the reduction of the non-linearity of the dynamic behavior (Payne effect).

The Morphology, Mechanical and Dynamic Properties, Fire Hazard and Toxicity of Chloroprene and Butadiene Rubber Composites Cross-Linked with Zinc

“…A standard cross-linking system (with sulfur) is, however, not completely satisfactory as it is difficult to control the degree and homogeneity of cross-linking as well as the activation temperature. These latter aspects can lead to the undesirable scorching of the rubber composition due to early vulcanization and suboptimal sulfur dispersion, ending up with materials with poor hysteretic properties [ 14 , 15 ]. In addition, the use of a conventional curing system has disadvantages such as worse thermal resistance, low compression set, the migration of the curing agent or accelerators, the emission of toxic products of the accelerator decomposition (e.g., N-nitrosamines) and varied susceptibility of the elastomer to the pre-vulcanization and reversion [ 5 , 16 ].…”

Simultaneous Physical Cross-Linking and Mechanical Strengthening of Elastomers by Enantiomeric Interactions through Reactive Processing

“…One major challenge arises in the competitive trade-off between the strength and extensibility of the commercial elastomers. Despite the development of specific chemical agents − or reinforcing filler particles − to impart elastomers with desirable strength, the extensibility is always severely damaged. Furthermore, the long-term impacts of petroleum-based elastomers on the ecological environment are also acknowledged as a significant concern.…”