The effect of flame retardant additives on the flammability and smoke formation of glass-reinforced plastics based on epoxy resins

Abstract

The paper presents the results of the studies of flammability and smoke formation of reinforced materials based on glass fiber Т-15(P)-76(92) and ED-22 epoxy resin without additives of flame retardants and with the addition of phosphorus-containing flame retardants DOPO-THPO (9,10-dihydro-9-oxy-10-phosphaphenanthrene-10-oxide-trihydroxy-methyl-phosphine oxide) DOPO-DDM (6,6′-((methylenebis(4,1-phenylene))bis(azanedyl))bis(6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide))), graphene and their combinations in concentrations from 2 to 9.98 %. The mass fraction of a binder in GFRER was 31±1 wt.% and 50±1 wt.%. To assess the flammability of the samples, the Limiting Oxygen Index, UL-94 HB, Vertical Bunsen Burner (VBB), Cone Calorimeter tests, and the Controlled atmosphere pyrolysis apparatus with a gas analyzer were used. The sample with the addition of 4 % graphene demonstrated the lowest rate of thermal decomposition, while the sample with the addition of 4 % DOPO-THPO had the lowest total heat release during combustion in a cone calorimeter. The addition of a mixture of graphene and DOPO-THPO resulted in a synergistic effect of these additives on the fire resistance of glass-reinforced composites. In contrast, all flame retardant additions led to an increase in the amount of smoke produced. For 2 % and 4 % graphene addition, as well as for 2 % DOPO-THPO addition, the increase in the smoke formation was 8-9 %, and for other compositions it was much greater. Thus, the results of the flammability tests and the smoke formation do not correlate with each other. Additions of the studied flame retardants lead to incomplete combustion, which is characterized by an increase in the amount of carbon monoxide (II) released during the combustion relative to the final combustion product CO2, that is, an increase in the smoke toxicity. It is found that DOPO-THPO as a flame retardant acts in both the gas and condensed phases however, it also leads to an increase in the formation of smoke and carbon monoxide. The addition of graphene leads to the strengthening of the carbon residue, but has a lesser effect on the toxicity of combustion products.