Investigating filler-rubber interactions and amplification effect in reinforced elastomers

ABSTRACT Rubber represents one of the most important classes of polymers in modern industry due to its unique elastic properties. To satisfy the demanding technical requirements of industrial applications, solid (nano-)particles are often incorporated into the rubber matrix, leading to a reinforcement effect that enhances the mechanical performance of these materials. Rubber reinforcement theories establish quantitative relationships between the macroscopic mechanical properties and the molecular parameters that define the structure of rubber compounds. Nevertheless, quantification of all the structural parameters that define the reinforcement mechanism in rubber materials is still a complex challenge due to the number of parameters and their interrelation in the measurable physical properties. In this work, a new methodology based on the combination of uniaxial mechanical testing under quasi-static conditions and solid-state proton multiple-quantum nuclear magnetic resonance ( 1 H MQ-NMR) is proposed to quantify all molecular parameters involved in the rubber reinforcement phenomenon. The achievement of this goal requires an extension of the current theory, to establish a common physical framework between the experimental approaches and to develop a novel combined analysis protocol. Finally, independent experiments based on strain sweep test (Payne effect) and selective cleavage of sulfur cross-links using chemical probes, have been employed to validate the proposed methodology, demonstrating strong agreement and internal consistency among all results. This study highlights the critical importance of including the amplification effects (strain and stress) on the reinforcement theory, which has been shown to play a decisive role in determining key molecular parameters, including the number of crosslinks, entanglements and filler–rubber interactions.