Design and synthesis of novel benzoxazines to replace traditional reinforcing resins in rubber compounds

The mechanical performance of tires is controlled by many of the ingredients used in their production. Among them, novolac-type phenolic resins (PR) are petroleum-based materials commonly employed to reinforce rubber compounds. Even though overall performance is efficient, there is a growing societal need to develop alternatives to these resins as they are challenged by REACH regulations. Benzoxazine resins (Bz) are a new generation of materials that can be suitable for this purpose; they hold potential for improvement of both the mechanical properties and the sustainability of the rubber compounds. However, while PR have been extensively used and their interactions with tire compounds are well known, the use of benzoxazines in rubber compounds requires extensive studies and in-detail investigations.
This thesis aims at filling this gap and designing benzoxazine resins that could be relevant alternatives to PR. For this purpose, novel sulfur containing dibenzoxazines were successfully synthesized and their interactions with rubber compounds were methodically investigated. Diphenolic compounds with either disulfide bonds (S‒S), or monosulfide bonds (‒S‒) were reacted with monoamines such as furfurylamine, a bio-based amine produced from agricultural byproducts. These partially bio-based original precursors, which were never reported before, exhibited polymerization behaviors that greatly fit the required conditions for rubber vulcanization. Indeed, the curing of these novel benzoxazine monomers occurred during rubber vulcanization, allowing the elaboration of reinforced materials at the molecular scale without detrimental side-reactions with the curing package. A fine investigation of the mechanical and thermal properties of the resulting rubber compounds indicated the reinforcing effect of these new resins at the macroscale. Therefore, the potential of each benzoxazine to act as a reinforcing resin was tested in real tire parts confirming the potential of Bz to be used as alternatives to PR resins in carbon-black filled compounds.
In conclusion, the outcome of this thesis emphasizes that structural features of benzoxazines are a major parameter to be considered for their use in rubber reinforcement. Thanks to the knowledge generated, it was possible to develop novel benzoxazine resins capable of reinforcing rubber compounds in place of traditional phenolic resins. This study also paves the way to replace petroleum based resins by partially bio-based precursors, improving the sustainability of tire compounds.