Braun et al. [87] studied the FR activities of epoxy resins containing phosphorus
oxides of different oxidations states; the order of FR is as follows: EPC (epoxy resin
composite)-Ar 3 PO > EPC-Ar 2 PO 2 > EPC-ArPO 3 > EPC-PO 4 . Therefore, on the
basis of bond strength, EPC-Ar 3 PO shows better FR activity than EPC-PO 4 .
Phosphorus atoms are released faster from EPC-Ar 3 PO compared to EPC-PO 4 ;
further, EPC-Ar 3 PO exhibits gas-phase FR activity. However, the researchers did
not consider the effect of aromaticity or crosslinking on the FR activity. They also
studied the FR activity of 4,4′-diaminodiphenyl sulfone-containing epoxy resins
(EPC-DDS). The LOI of EPC-PO 4 is lower than that of EPC-DDS due to the
presence of –SO 2 groups, which accelerate decomposition in the condensed phase
and dilute the fuel available in the flame zone. Cheng et al. [88] prepared epoxy
resins with glycidyloxy diphenylphosphine oxide (GDPPO) as the phosphoruscontaining chain extender. As the GDPPO content increased in the epoxy resins,
their thermal stability and FR activity decreased, even though the phosphorus
content in the resins increased. Owing to a high gel fraction and less crosslinking,
Fig. 4.1 A schematic of the intumescent flame-retardant mechanism of PP/DP7/A10H. Reproduced with permission from [80]. Copyright 20177, Elsevier Science Ltd. PVFA, polyvinylformal
acetal; DOPO, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide; HBPA, hyperbranched
polyamide
4.3 Phosphorus-Based FRs
27
oxides of different oxidations states; the order of FR is as follows: EPC (epoxy resin
composite)-Ar 3 PO > EPC-Ar 2 PO 2 > EPC-ArPO 3 > EPC-PO 4 . Therefore, on the
basis of bond strength, EPC-Ar 3 PO shows better FR activity than EPC-PO 4 .
Phosphorus atoms are released faster from EPC-Ar 3 PO compared to EPC-PO 4 ;
further, EPC-Ar 3 PO exhibits gas-phase FR activity. However, the researchers did
not consider the effect of aromaticity or crosslinking on the FR activity. They also
studied the FR activity of 4,4′-diaminodiphenyl sulfone-containing epoxy resins
(EPC-DDS). The LOI of EPC-PO 4 is lower than that of EPC-DDS due to the
presence of –SO 2 groups, which accelerate decomposition in the condensed phase
and dilute the fuel available in the flame zone. Cheng et al. [88] prepared epoxy
resins with glycidyloxy diphenylphosphine oxide (GDPPO) as the phosphoruscontaining chain extender. As the GDPPO content increased in the epoxy resins,
their thermal stability and FR activity decreased, even though the phosphorus
content in the resins increased. Owing to a high gel fraction and less crosslinking,
Fig. 4.1 A schematic of the intumescent flame-retardant mechanism of PP/DP7/A10H. Reproduced with permission from [80]. Copyright 20177, Elsevier Science Ltd. PVFA, polyvinylformal
acetal; DOPO, 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide; HBPA, hyperbranched
polyamide
4.3 Phosphorus-Based FRs
27