Alginic acid derivatives/DOPO modified epoxy resins: Excellent flame retardancy, mechanical properties, chemical resistance

An alginic acid derivative AA@MEL with flame retardant effect in both gas and condensed phases was synthesized by the neutralization reaction of alginic acid (AA) and melamine (MEL). Modified EP obtained the UL-94 V-0 rating and limiting oxygen index (LOI) of 33.8% when the total addition of AA@MEL and 9,10-dihydro-9-oxa-10-phosphophenanthrene-10-oxide (DOPO) in the epoxy resin was only 4 wt% and the phosphorus content was only 0.29%. Compared with pure EP, the total heat release (THR) and total smoke production (TSP) of flame-retardant EP were reduced by 42% and 60%, respectively, and the quality of the char residue was improved by forming higher graphitization layer. The flame retardancy mechanism was proposed through the pyrolysis products analyses and the characterization of the condensed phase. Meanwhile, the appropriate amount of AA@MEL/DOPO can enhance the tensile property, flexural property and impact strength of EP materials. It was closely related to the -COOH/-OH in AA@MEL and the P-H bond and rigid structure of DOPO. In addition, the modified EP has good chemical resistance, which ensures long-lasting flame retardant and mechanical properties. The AA@MEL/DOPO system exhibits low cost, low loading, high flame-retardant efficiency and environmental friendliness for industrial needs, which is promising for industrial applications.