Improving flame retardancy and mechanical properties of polyamide 6 induced by multiple reactions among flame retardants and matrix

A bio-based flame retardant TFD was synthesized using tyrosine (Tyr), furfural and 9,10-Dihydro-9-oxa-10-phos-phaphenanthrene 10-oxide (DOPO) which was used in polyamide 6 (PA6) to modify its flame retardancy. A bio-based chain extender EDPDO which was obtained by epoxidation of the reaction product between phenyl-phosphonic dichloride and magnolol, was used to regulate the mechanical properties of PA6. TFD endows PA6 with a UL-94 V0 rating at the content of 12 wt%. If TFD and EDPDO were premixed and incorporated into PA6, 8 wt% TFD and 1 wt% EDPDO are needed for PA6 to display a UL-94 V0 rating. Moreover, the mechanical properties were improved. The tensile strength of PA6 containing 8 wt% TFD and 2 wt% EDPDO is 97 MPa which is 21 MPa higher than that of PA6. The TFD reduces the molecular weight of PA6, while the chain extension reactions increase the molecular weight to a certain extent. In addition, the adhesion among the char particles is so poor that some small char particles volatilize into the gas phase to form smoke. The improved flame retardancy in UL-94 test is mainly caused by the melting-away effect.