Effects of PAPP modified by silane coupling agent on the mechanical and flame-retardant properties of epoxy resin

A silane coupling agent containing DPOP functional group (DSCA) was hydrolyzed in the presence of piperazine pyrophosphate (PAPP), thereby preparing surface-modified PAPP, s-PAPP. The obtained s-PAPP was then incorporated into epoxy resin (EP) with the aim of enhancing both the flame retardancy and mechanical properties of EP. Investigations have revealed that when s-PAPP-7:3, prepared at a weight ratio of 7:3 for PAPP to DSCA, was added to EP, the resultant flame-retardant EP, EP7:3, exhibited superior flame retardancy and mechanical properties. Specifically, EP7:3 achieved a UL 94 V-0 rating, with a limiting oxygen index (LOI) value reaching up to 31.2%. In comparison with flame-retardant EP containing unmodified PAPP (EP10:0), the tensile strength and impact strength of EP7:3 was enhanced by 95.7% and 155.4%, respectively. The surface contact angle investigation on flame retardants and EP had revealed that the surface contact angles of s-PAPP-7:3 and EP were 57.3° and 73.6°, respectively. Such similarity in their polar characteristics elucidated the reason for which the resultant EP7:3 demonstrated notable flame retardancy and enhanced mechanical properties. Therefore, the incorporation of s-PAPP, a high-performance flame retardant, into EP not only endowed EP with desirable flame retardancy but also maintained the mechanical properties of EP.