A comparative study of the cryogenic performance of CFRP composites with polyethersulfone/epoxy blends and electrospun polyethersulfone interleaves

Abstract

Thermoslastic-modifers have been widely utilized to enhance the fracture toughness of epoxy resins for cryogenic applications. Interleaving is an effective technique to incorporate thermoslastic-modifers without compromising the resin’s viscosity, making it feasible for large-scale manufacturing processes. This study presents a comparative analysis of the cryogenic performance of laminated fibre-reinforced composites, focusing on two different toughening approaches: utilizing electrospun polyethersulfone (PES) veils or epoxy/PES blends with varying PES loadings. The impact of PES loading on the developed phase morphology was examined using the single-edge-notch bending (SENB) tests. The particulate phase structure was formed in samples with PES content 2.5-10 phr, which transitioned to a co-continuous structure after exceeding 10 phr. At room temperature, the 15 phr epoxy/PES blend showed the most significant enhancements in the fracture toughness (Kic) and strain energy release rate (Gic) at 293 K were 72% and 168%, respectively. At cryogenic temperatures, the crack front tends to advance around, rather than through, the epoxy-rich domains in a co-continuous phase structure. Consequently, the 10 phr blend outperformed the 15 phr blend, with improvements in the order of 48% in Kic and 180% in Gic. Interleaving double cantilever beam (DCB) samples with a thin 5 µm electrospun PES veil have enhanced the Mode I critical strain energy release rate (Gic_ini) and the crack propagation energy (Gic_prop) by 76% and 33% at 293 K, respectively. The toughening effects were also present at 77 K, measuring improvements of 48% in Gic_ini and 24% in Gic_prop. The achieved toughening levels with interleaved laminates were comparable to those obtained with 7.5 phr PES-toughened laminates. The present results suggest that interleaving composite laminates offer great potential in enhancing the service lifetime of cryogenic fuel tanks.