Study on the Effects of Composite Catalysts on the Curing Process and Pot Life of the HTPB/HDI‐Trimer Binder System

ABSTRACTHydroxyl‐terminated polybutadiene (HTPB), a linear liquid rubber with terminal hydroxyl groups, is a cornerstone binder in polymer‐bonded explosives (PBX) and composite propellants. Its cross‐linking with hexamethylene diisocyanate trimer (HDI‐trimer), a trifunctional isocyanate crosslinker, faces critical challenges in balancing pot life and curing rates for industrial scalability. Traditional single‐catalyst systems, such as dibutyl tin dilaurate (DBTDL) and tin octoate (TECH), exhibit high catalytic activity and a relatively short pot life, which limit the industrial application. This study aims to resolve these limitations by engineering blended catalyst systems to synergistically modulate cross‐linking kinetics and expand industrial adaptability. Five catalysts, namely TECH, FeAA (iron acetylacetonate), DABCO (1,4‐Diazabicyclo[2.2.2]octane), TPB (triphenyl bismuth), and nano‐ZnO, were blended pairwise at 0.05 w.t.% (1:1 functional group molar ratio) within HTPB/HDI‐trimer binder systems. Viscosity build‐up of the binder systems during the curing process was monitored via rotational viscometry at 45°C (rotor #29, 0.5 rpm), with Arrhenius modeling to quantify rheological reaction rates (kη) and pot life. Full curing at 45°C was achieved within 24 h, eliminating energy‐intensive thermal curing. This work pioneers a multi‐site catalytic strategy for HTPB systems, enabling energy‐efficient room‐temperature curing, which is a paradigm shift for PBX and solid composite propellant manufacturing. The composite catalysts significantly reduce energy consumption costs and provide tunable pot life to accommodate industrial processing requirements. Commercial applications span defense, aerospace, and automotive sectors, where rapid processing and material stability are paramount.