Competing Effects of Plasticization and Miscibility on the Structure and Dynamics of Natural Rubber: A Comparative Study on Bio and Commercial Plasticizers

Plasticizers are essential for improving the processability and flexibility of rubber compounds by reducing viscosity, aiding filler dispersion, and softening the rubber matrix. Traditionally, petroleum-based phthalate esters like dioctyl phthalate (DOP) and dibutyl phthalate (DBP) have been widely used for these purposes. However, these plasticizers pose significant challenges, including migration from the rubber over time, which can lower performance and raise environmental and health concerns. This study investigates the competing effects of plasticization and miscibility on the structure and dynamics of natural rubber (NR) and epoxidized natural rubber (ENR) when plasticized with glycerol trilevulinate (GT), a biobased plasticizer, and tris-(2-ethylhexyl) trimellitate (TOTM), a petroleum-derived plasticizer. Results show that GT accelerates vulcanization and reduces reversion risks, promoting faster curing and greater flexibility in the rubber network. In contrast, TOTM delays vulcanization and increases reversion, while forming a more rigid cross-linked network. Structurally, GT promotes longer sulfur bridges and strain-induced crystallization in NR, while TOTM favors the formation of shorter sulfur bonds and a more homogeneous network structure. In terms of miscibility, GT is fully miscible with ENR, improving segmental mobility, but shows partial miscibility in NR, restricting chain dynamics as evidenced by Broadband Dielectric Spectroscopy. These findings highlight GT as a potential sustainable alternative to petroleum-derived commercial plasticizers, offering promising advantages for high-performance, biobased rubber applications.