Effects of Polyethylene Glycol on Cryogenic Tensile Strength, Impact Toughness, and Gas Barrier Properties of Epoxy Resins: Mechanism and Experiment

ABSTRACT Carbon fiber‐reinforced polymer composites offer significant potential for linerless liquid hydrogen (LH 2 ) tanks due to their high specific strength and low density. However, the inherent brittleness of the epoxy matrix under cryogenic conditions limits practical application. This study addresses this limitation by incorporating thermoplastic polyethylene glycol (PEG‐600) to simultaneously enhance the cryogenic toughness and strength of epoxy resin. Molecular dynamics simulations and experimental characterization reveal PEG's dual mechanism: it increases free volume and reduces crosslinking density to improve toughness, while promoting hydrogen bond formation and molecular‐level densification to enhance strength. At 7 wt% PEG content, the modified epoxy exhibits a 111% increase in cryogenic impact strength (35.75 kJ/m 2 ) and a 13% improvement in tensile strength (90.2 MPa) compared to pure epoxy. However, at room temperature, the tensile strength decreases significantly due to the reduction in crosslink density induced by PEG incorporation. These findings demonstrate that PEG modification enables a temperature‐dependent synergistic enhancement of strength and toughness specifically under cryogenic conditions. These findings demonstrate that PEG modification effectively enables a synergistic enhancement of both cryogenic toughness and strength in epoxy resins.