Towards the development of thermally latent novolac-based char formers for ABS resins

Abstract

Novel novolac-based char formers for ABS resins, [PN–PI], [PN–BPI], [CN–PI] and [CN–BPI], were prepared from phenol formaldehyde novolac (PN), cresol formaldehyde novolac (CN), phenyl isocyanate (PI), and 4-biphenyl isocyanate (BPI) via a simple urethane-forming reaction. The four compounds were used as thermally latent char formers for this study. Thus, a two component system employing novolac–isocyanate adduct as a char former, and tetra-2,6-dimethyl phenyl-resorcinol diphosphate (DMP-RDP) as a phosphorous-based flame retardant was blended with ABS, and the thermal degradation behaviour and flame retardancy were determined by thermogravimetric analysis (TGA) and LOI test. The mixtures show a synergistic effect between DMP-RDP and novolac–isocyanate adduct on the flame retardance enhancement of ABS. Those containing higher molar mass CN–BPI adduct are found to be most flame retardant, and a LOI value as high as 35 is obtained.