The Effect of Vulcanization Temperature on the Network Structure and Properties of TBAF-Functionalized BR/VMQ Blends for Mars Environment Applications

Rubber compounds intended for Mars exploration missions must remain elastic at extremely low temperatures while being manufactured in a reliable and energy-efficient manner. In this study, the effect of vulcanization temperature (100–160 °C) on the network structure and properties of butadiene/silicone rubber (BR/VMQ) blends was investigated, comparing a conventional sulfur curing system (REF) with the same system activated by fluoride anion obtained from tetra-n-butylammonium fluoride (TBAF). The fluoride anion acts as an in situ activator of elemental sulfur, through the opening of the S8 ring, facilitating the crosslinking process at significantly lower temperatures. Fluoride enabled rapid vulcanization at 100–120 °C, shortening the optimum cure time from 129.1 min to 61.4 min at 100 °C and from 36.7 min to 16.9 min at 120 °C. Equilibrium swelling and thiol-amine analysis revealed opposite structural responses to lowered curing temperature: the crosslink density of the reference compounds increased (from 1.25 × 10−4 to 1.56 × 10−4 mol/cm3 between 160 °C and 120 °C), whereas that of the TBAF-containing compounds decreased (from 1.32 × 10−4 to 0.60 × 10−4 mol/cm3 between 160 °C and 100 °C), yielding networks dominated by elastic polysulfidic crosslinks (up to 97.2%). We attribute this to a suppressed crosslink maturation under conditions of reduced thermal energy and shortened curing time. Low-temperature curing also suppressed the crystallization of the VMQ phase (melting enthalpy decreasing from 1.23 J/g to 0.21 J/g for TBAF compounds), which we hypothesize results from insufficient energy for phase separation and regular chain packing in this strongly immiscible blend. TBAF-cured compounds exhibited lower tanδ peaks, a stable tanδ plateau between approximately −60 °C and +20 °C, a tanδ-peak shift towards lower temperatures with decreasing curing temperature, and higher elongation at break and tensile strength at −40 °C. The results show that low-temperature, fluoride-activated vulcanization is a promising route for tailoring BR/VMQ networks towards stable dynamic performance across the Martian daily temperature range.