Pignatiello, Gioacchino (2025) Multiscale analysis on the miscibility of bio-derived compounds for tires: impact on microstructure and performance. [Tesi di dottorato]

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Abstract

In the tire industry, while past efforts predominantly focused on enhancing safety and performance, there is now a growing interest in environmental sustainability. One notable trend is the growing use of bio-based ingredients to substitute traditional petroleum-derived materials. However, incorporating these components into complex elastomeric mixtures poses considerable challenges due to the intricate physical and chemical interactions between the many constituents of a typical tire compound. In this PhD work we explore the potential of different techniques and theories to predict and investigate the miscibility and degree of interaction between the various additives and the rubber matrix, which are crucial for achieving the desired set of performance. A series of model tread compounds, both unfilled and silica-filled, containing different bio-based components, was investigated, using traditional petroleum-based formulations as a reference. Hansen solubility parameters (HSP) theory was used to predict the compatibility of the additives with the rest of the rubber compound. For the analyzed materials, the solubility parameters – atomic dispersive interactions, permanent dipole molecular interactions, and molecular hydrogen bonding interactions – were determined through an evaluation of the affinity between the test material and a series of solvents with known HSP values. Knowing these parameters for the components in the formulation, the "distance" between them in the Hansen space can be calculated, and the miscibility among the components can be assessed. In addition, since the miscibility of materials affects their dielectric relaxations, broadband dielectric spectroscopy was conducted to investigate the impact of additive compatibility on the compound. Differential scanning calorimetry was also employed to analyze the thermal transitions of the compounds, with particular focus on the glass transition temperature (Tg). The experimental Tg values were compared with predictions obtained using the Fox and Gordon-Taylor equations, providing further insights into the degree of miscibility between additives and elastomer matrix. To gain a deeper understanding of the morphology and the reinforcement mechanisms, transmission electron microscopy and complementary electron microscopy techniques were employed to assess filler dispersion and the distribution of additives within the elastomer matrix. Furthermore, dynamic-mechanical analysis and mechanical characterization provided insights into the viscoelastic response and macroscopic properties, enabling a comprehensive validation of the results obtained from the other techniques.

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