Cyanate esters (CEs) are an important class of materials among high-temperature-performance thermosets. They are used in aerospace launch vehicles, heat sinks, booms, trusses of satellites, etc., due to their high glass transition temperatures (>220 °C), excellent thermal stability, and low flammability. Current approaches to improve the thermal stability of CEs include incorporation of siloxanes or phosphorus-based flame retardants. In this work, we have explored boron-based hydroxy (PD)-and epoxy (EP)functionalized carborane additives to improve the thermal properties of CEs. Carborane fillers were solvent-blended at various mass loadings in the resin and cured to study their effect on thermal properties. PD and EP carboranes react with CEs to form iminocarbonates and oxazolidinone linkages, respectively. Cure kinetic studies at different wt % loadings explained that carboranes catalyze the curing reaction by reducing the curing activation energy by about 54 and 26% for 10 wt % loadings of PD and EP carboranes, respectively. In addition, carborane-filled CE nanocomposites demonstrate an exceptionally high thermal stability as compared to the pristine resin in air and inert environments. Our thermogravimetric analysis (TGA) experiments show that the ultimate char yield of the resin can be increased from 0% to as high as 76 and 82% with 30 wt % PD and EP carborane loadings, respectively, at 1000 °C in air. The initial degradation temperature T d,5 of the composites decreased with increasing carborane loadings in both air and argon. For instance, T d,5 values for CE were 465 and 471.6 °C in argon and air, while those for P20 were 437.4 and 452.1 °C, respectively. Modulated TGA studies gave evidence of the effect of carboranes on degradation mechanism and kinetics in air and inert environments. The effect of bonding between carboranes and CEs at various loadings on the thermal expansion of the matrix was also studied using a thermomechanical analyzer. PD carborane reduced the T g for P20 to about 225 °C, while CE had T g > 350 °C.

Fiber-reinforced thermoset composites are a class of materials that address the arising needs from the aerospace and hypersonic industries for high specific strength, temperature-resistant structural materials. Among the high-temperature resistant thermoset categories, phenolic triazine (PT) cyanate esters stand out thanks to their inherent high degradation temperature, glass transition temperature, and mechanical strength. Despite the outstanding properties of these thermosets, the performance of carbon fiber composites using PT cyanate esters as matrices has not been thoroughly characterized. This work evaluated PT and carbon fiber composites’ compressive properties and failure mechanisms with different fiber arrangements. A PT resin with both plain weave (PW) and non-crimped unidirectional (UD) carbon fiber mats was analyzed in this research. Highly loaded thermoset composites were obtained using process temperatures not exceeding 260 °C, and the composites proved to retain compressive strength at temperatures beyond 300 °C. Compressive testing revealed that PT composites retained compressive strength values of 50.4% of room temperature for UD composites and 61.4% for PW composites. Post-compressive failure observations of the gage section revealed that the mechanisms for failure evolved with temperature from brittle, delamination-dominant failure to shear-like failure promoted by the plastic failure of the matrix. This study demonstrated that PT composites are a good candidate for structural applications in harsh environments.

The curing of Lonza Primaset PT-30 novolac cyanate ester resin and EPON 826 bisphenol-A diglycidyl ether were investigated using convective thermal heating and variable frequency microwave (VFM) heating. The addition of 1 part per hundred reduced graphene oxide (r-GO) to PT-30 novolac cyanate ester increased the VFM cure rate compared to thermal heating. Curing it at 160 C for 240 min with VFM heating resulted in a 55% degree of cure compared to a 26% degree of cure with thermal heating. This observed VFM rate enhancement is due to selective microwave heating of the r-GO particles in the resin resulting in increased r-GO catalytic activity toward cyanate ester curing. It is both a thermal and catalytic effect, the latter of which is absent when r-GO is added to a bisphenol-A diglycidyl ether resin with ophenylenediamine hardener. Impurities present in the PT-30 matrix do not appear to contribute to its overall cure kinetics, nor do they participate in the observed VFM rate enhancement.

In this study, we investigate the molecular mechanisms of the microwave-driven selective heating process by performing molecular dynamics simulations for three different systems such as pure water, pure polyethylene oxide...