Bismuth-Catalyzed Multifunctional Polydimethylsiloxane (PDMS) Composites with Tunable Thermomechanical Properties for Scalable Manufacturing

Abstract

Bismuth-catalyzed silicone systems have recently emerged as promising eco-friendly alternatives to conventional tin- and platinum-based catalysts; however, their behavior in highly filled, scalable composite formulations remains insufficiently understood. In this work, multifunctional polydimethylsiloxane (PDMS) composites were developed using a bismuth carboxylate catalyst and two structurally distinct inorganic fillers, perlite and hollow glass microspheres (GMBs), to systematically investigate structure–processing–property relationships and enable tunable thermomechanical performance. Rheological analysis revealed that filler incorporation significantly alters curing behavior, with gelation temperatures increasing from ∼105 °C for neat PDMS to ∼155 °C (+50 °C) for 40 wt % perlite and ∼162 °C (+57 °C) for 40 wt % GMBs, enabling extended processing windows critical for scalable manufacturing. Thermomechanical characterization demonstrated that filler type, through its morphology, intrinsic density, and resulting volume fraction, governs property evolution. Perlite enhanced through-thickness thermal conductivity by up to 42% (0.193 to 0.274 W·m–1·K–1), whereas GMBs reduced thermal conductivity by 47% (to 0.102 W·m–1·K–1), enabling bidirectional thermal transport tuning within a single material platform. Significant reductions in coefficient of thermal expansion (CTE) were achieved, reaching 43% (perlite) and 74% (GMBs), while density decreased to <0.65 g·cm–3 for GMB-filled systems, highlighting lightweighting potential. Mechanical performance was substantially improved, with compressive modulus increasing by 339% for perlite-filled composites and up to 1889% for GMB-filled systems, alongside a ∼255% (∼3.6×) higher compressive strength than the perlite-filled composite at the highest filler content. Importantly, the bismuth-catalyzed PDMS formulations exhibited robust scalability, demonstrated through successful sheet molding compound (SMC) processing and compression molding of kilogram-scale, fiber-reinforced composite structures with excellent dimensional stability and flame resistance. These results establish bismuth-catalyzed PDMS composites as a versatile, environmentally benign materials platform with tailorable properties. The findings provide critical insights into filler–matrix–cure interactions and offer a pathway toward the design of next-generation silicone composites for thermal management, lightweight structures, building materials, and large-scale industrial manufacturing.