Investigations on Phthalonitrile – Cyanate ester blends and their light weight composites; Synthesis, thermal, mechanical and ablative characteristics

Abstract

Newer high performing polymer matrix resins are highly demanded given the rapid development trend in aero-space exploration sector. The present work focuses on synthesis and performance evaluation of Phthalonitrile- Cyanate ester blend as matrix resin for ablative composite applications. Incorporation of Cyanate ester facilitated early cure initiation (by about 35 °C) of Phthalonitriles without comprising thermal stability, a novel strategy that improves the sluggish cure profile of phthalonitriles. Low density (0.5g/cc) syntactic foam composites prepared from the blend exhibited low Coefficient of Thermal Expansion (CTE) (1.3 × 10−5 – 1.7 × 10−5/°C), high specific heat (0.32–0.38 J/g/°C at 80 °C) and low thermal conductivity (0.11–0.13 W/mK at 80 °C). Exposure of the composites to moderate re-entry heat flux conditions using radiant heating facility (∼55W/cm2, 1200s) and Plasma Arc jet (70&125 W/cm2, 50s) resulted in excellent surface uniformity with minimal of mass loss (4.77–5.77%) and excellent heat of ablation (8000–12000 cal/g) with reduced back-wall temperature (230–260 °C). The composites possessed very good mechanical properties such as Flexural strength of 5–6.5 MPa and compressive strength of 5–9 MPa. 1:1 combination of pyrolyzed system possessed high degree of graphitization. The promising results confirm that the new matrix blend can be a potential replacement for conventionally used phenolics as ablative Thermal Protection System (TPS) matrix.