The flame retardancy and rheological properties of PA6/MCA modified by DOPO-based chain extender

Thermal degradation of polyamide-6 (PA6) readily takes place during the high temperature melt processing, particularly when highly hydrophilic additives are present in the system, consequently inducing the deterioration in viscosity and mechanical properties. To solve such problems, 9,10-dihydro-9-oxa-10-phosphenanthrene- 10-oxide (DOPO)-based diepoxide compound (DEP) was synthesized and employed to realize the chain extension of the PA6 macromolecule and to concurrently ameliorate the flame retardancy of PA6/melamine cyanurate (MCA). The addition of 2 wt% DEP successfully assisted the PA6/ MCA system (10 wt% of MCA) to pass the UL-94 V-0 rating. The flame-retarding mechanism was studied in-depth by cone calorimeter test and characterization of the charred residue and evolved gas. The rheological data showed that the complex viscosity, storage and loss moduli increased following the chain extension and the chain-extended samples became more sensitive to shear. The tensile and flexural strengths of PA6/MCA/DEP were superior to those of PA6/MCA.