The Effect of Polymer Matrix Carbonization Processes on the Durability and Residual Strength of GFRP under Fire Conditions Using Epoxidized Dinaphthols

This study investigates the strength degradation processes of structural glass-fiber reinforced plastics (GFRP) under transient heating, simulating standard fire conditions. A comparative analysis of the thermomechanical behavior of composites based on a traditional bromine-containing epoxyphenolic binder and a modified system based on epoxidized dinaphthol was conducted. It is established that at temperatures exceeding the glass transition temperature of the polymer matrix, the classic Zhurkov thermofluctuational equation becomes inapplicable due to complex phase and structural transformations in the material. It is proven that the use of oligomers with conjugated aromatic rings allows for significantly slowing down the degradation process and retaining up to 60% of the initial strength of the GFRP due to intensive pyrolytic transformations and the formation of a carbonized protective layer. Additionally, the effect of the free cooling stage on the residual load-bearing capacity of the materials is evaluated. It is shown that GFRPs based on epoxidized dinaphthols retain from 20 to 45% of their residual strength (depending on the type of loading) after the cessation of heat exposure in the fire regime and the free cooling of the material.