Poly(butylene terephthalate) fire retarded by 1,4-diisobutylene-2,3,5,6-tetraxydroxy-1, 4-diphosphine oxide. I. Combustion and thermal decomposition

1,4-Diisobutylene-2,3,5,6-tetraxydroxy-1,4-diphosphine oxide (Cyagard) provides good fire retardant performance for poly(butylene terephthalate) (PBT) as measured by the UL94 test whereas the combination of Cyagard with some co-additives helps to increase the limiting oxygen index (LOI). A correlation between the solid residue measured by thermogravimetry and LOI was observed. Kinetic analysis of the thermogravimetric data showed a strong increase in the activation energy of the thermal decomposition of PBT in the presence of Cyagard and ferric oxide.