Abstract: In the traditional intumescent flame retardant system, the poor interfacial compatibility between ammonium polyphosphate (APP), as the acid source, and epoxy resin (EP) is a common problem, resulting in the need for a higher additive amount to achieve a good flame retardant effect. In order to solve this kind of problem, this paper synthesized a core-shell structural material APP@CS with APP as the core and chitosan (CS) as the shell to improve its compatibility with EP, and at the same time synthesized an aminophenol-formaldehyde resin (APS), which has better compatibility with EP matrix, as the carbon source of intumescent flame-retardant system. Thermal analysis results show that EP/8%APP@CS/APS has a significant increase in residual carbon of about 173% compared to EP. In terms of flame retardancy, EP/8%APP@CS/APS passed UL 94 V-1 rating with an ultimate oxygen index of 31.6%. The peak heat release rate, total heat release rate, total smoke emission, and smoke release rate of the EP/8% APP@CS/APS composite were reduced by 78.0%, 55.1%, 54.5%, and 58.3%, respectively, compared to pure EP. The above results show that APP@CS and APS have synergistic effects in improving the thermal and flame retardant properties of EP.

Key words: core-shell structure, ammonium polyphosphate, chitosan, amino-phenolic resin, flame retardant performance