Char to the Rescue: Processing and Transfer of Flame-Retardant Epoxy Resins, Adjusting the Fire Behavior and Post-Fire Structural Integrity of Glass Fiber Composites

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Sunder, Sruthi ; Jauregui Rozo, Maria ; Deshpande, Harshal ; Neyer, Alexia ; Papaiya, Vinay ; Meinel, Dietmar ; Schartel, Bernhard ; Ruckdäschel, Holger:
Char to the Rescue: Processing and Transfer of Flame-Retardant Epoxy Resins, Adjusting the Fire Behavior and Post-Fire Structural Integrity of Glass Fiber Composites.
In: Journal of Polymer Science. Bd. 63 (2025) Heft 20 . - S. 4295-4309.
ISSN 2642-4169
DOI: https://doi.org/10.1002/pol.20250692

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Abstract

Epoxy (EP) glass fiber reinforced composites (GFRCs) are extensively used in structural applications due to their excellent thermal and mechanical properties, but their inherent flammability limits fire-safe deployment. While numerous studies examine the flame retardancy of resins or individual composite systems, comprehensive studies evaluating simultaneous improvements in flame retardancy and post-fire mechanical integrity, specifically through prepreg processing, remain challenging. This study investigates the effectiveness and transferability of phosphorus-based flame retardant (FR) systems to diglycidyl ether of bisphenol A (DGEBA) and EP novolac resin matrices and their corresponding bidirectional glass fiber composites via prepregs. The FRs are chosen based on varying modes of action: ammonium polyphosphate with inorganic silicate (APP/InSi) primarily acts in the condensed phase (CP), and aluminum diethyl phosphinate with zinc hydroxystannate (AldietPO2/ZHS) is known to demonstrate both gas-phase (GP) and CP activity. Fire residues are tailored to compensate for structural defects from fire exposure. EP novolac, with higher aromaticity and cross-linking, possesses better inherent flame resistance compared to DGEBA. The novolac composites containing AldietPO2/ZHS simultaneously showed the highest retention of flexural properties after fire exposure and the best fire safety index. The experimental values of the post-fire flexural properties in the composites calibrated damage parameters in two theoretical models.