Effect of novolac phenol and oligomeric aryl phosphate mixtures on flame retardance enhancement of ABS

Tetra-2,6-dimethyl phenyl resorcinol diphosphate (DMP-RDP), which is one of the phosphorus flame retardants exhibiting higher evaporation temperature, and novolac phenol resin (NP) were employed to investigate whether the synergistic effect of using them together could be observed on the flame retardance of ABS. For this purpose, various NPs were incorporated into DMP-RDP as co-flame retardants and a series of ABS/DMP-RDP/NP compounds were manufactured and their flame retardancies were evaluated by measuring the limiting oxygen index (LOI) values and UL-94V classes. The results showed that the incorporation of DMP-RDP/NP mixture is very effective in enhancing the thermal stability of ABS and that the LOI value as high as 53 is obtained for a certain formulation. The reason for this finding was believed to be originated from the crosslinking reaction between –OH of NP and –OH generated from the combustion of DMP-RDP. Some direct evidences from FTIR experiments were presented. Moreover, optical microscopy analysis showed the formation of intumescent chars that were very dense. The effect of molecular weight of NP on the flame retardancies of the compounds is also discussed.