*Flame Retardant and Thermally Insulating Polymers*


of char yield are increased. The presence of hetero-cyclic pyridine core and silica (Si-O-Si) inherently provides to the higher thermal stability. The LOI value of pyridine core cardanol-based polybenzoxazine possesses a higher residual char (29.1%) than that of other cardanol based PBz's. The values of LOI were increased with increase in weight percentage content of bio-silica. Among the composites studied,

*Thermal and flame resistant (LOI and UL-94) properties of bio-based polybenzoxazine matrices and composites.*

*The proposed schematic representation for the formation of CBz/FRHA composites [34]. (Copyright 2020.*

**Samples Char(%) residue LOI UL-94 Reference** CBz 12.00 22.00 — [34] CBz/FRHA (1 wt%) 18.00 25.00 — [34] CBz/FRHA (5 wt%) 32.00 30.00 V-2 [34] CBz/FRHA (10 wt%) 36.00 32.00 V-2 [34] CBz/FRHA (15 wt%) 40.00 34.00 V-1 [34] CBz/FRHA (20 wt%) 47.00 36.00 V-1 [34]

**Samples Char(%) residue LOI Reference** BGF-FPbz 52.4 38.50 [51] BGF-SPbz 38.2 32.80 [51]

*Development of Halogen Free Sustainable Polybenzoxazine Matrices and Composites for Flame…*

*Thermal and flame resistant (LOI) properties of bio-based polybenzoxazine matrices and composites.*

**Table 2.**

*DOI: http://dx.doi.org/10.5772/intechopen.98470*

**Figure 8.**

**Table 3.**

**47**

*Reproduced with permission from Springer).*

10 wt% bio-silica reinforced composites indicated the LOI value of 32.7.

*Development of Halogen Free Sustainable Polybenzoxazine Matrices and Composites for Flame… DOI: http://dx.doi.org/10.5772/intechopen.98470*


### **Table 2.**

**Samples Char(%) residue LOI Reference** PBZ-C-F 11.11 21.94 [36] PBZ-C-F-S-1 35.32 31.63 [36] PBZ-C-F-S-2 41.51 34.10 [36] PBZ-C-F-S-3 42.96 34.68 [36] PBZ-C-F-S-4 43.77 35.01 [36] PBZ-C-F-S-5 48.63 36.95 [36] Poly(C-ida) 24.00 27.10 [73] Poly(C-ida) + 1 wt% SiO2 27.00 28.20 [73] Poly(C-ida) + 3 wt% SiO2 28.00 28.70 [73] Poly(C-ida) + 5 wt% SiO2 30.00 29.50 [73] Poly(C-ida) + 7 wt% SiO2 32.00 30.30 [73] Poly(C-ida) + 10 wt% SiO2 35.00 31.50 [73] Poly(C-pyta) 29.00 29.10 [73] Poly(C-pyta) + 1 wt% SiO2 30.00 29.50 [73] Poly(C-pyta) + 3 wt% SiO2 32.00 30.30 [73] Poly(C-pyta) + 5 wt% SiO2 33.00 30.70 [73] Poly(C-pyta) + 7 wt% SiO2 35.00 31.50 [73] Poly(C-pyta) + 10 wt% SiO2 38.00 32.70 [73] POSS-EPBz 24.00 24.00 [74] POSS-GPBz 38.00 38.00 [74] POSS-VPBz 36.00 36.00 [74] SBz 20.00 25.00 [37] SBz/FBS(1%) 21.00 26.0 [37] SBz/FBS(3%) 23.00 27.00 [37] SBz/FBS(5%) 25.00 28.00 [37] SBz/FBS(10%) 27.00 29.00 [37] FBz 46.00 36.00 [37] FBz/FBS(1%) 47.00 36.00 [37] FBz/FBS(3%) 48.00 37.00 [37] FBz/FBS(5%) 50.00 38.00 [37] FBz/FBS(10%) 53.00 39.00 [37] PBZ-E-F 41.32 34.03 [75] PBZ-E-F-S-1 53.64 38.96 [75] PBZ-E-F-S-2 55.43 39.67 [75] PBZ-E-F-S-3 62.78 42.61 [75] PBZ-E-F-S-4 65.16 43.56 [75] PBZ-E-F-S-5 67.54 44.52 [75] PE-fa 52.00 38.30 [76] PIE-fa 60.00 41.50 [76]

*Flame Retardant and Thermally Insulating Polymers*

**46**

*Thermal and flame resistant (LOI) properties of bio-based polybenzoxazine matrices and composites.*

#### **Figure 8.**

*The proposed schematic representation for the formation of CBz/FRHA composites [34]. (Copyright 2020. Reproduced with permission from Springer).*


**Table 3.**

*Thermal and flame resistant (LOI and UL-94) properties of bio-based polybenzoxazine matrices and composites.*

of char yield are increased. The presence of hetero-cyclic pyridine core and silica (Si-O-Si) inherently provides to the higher thermal stability. The LOI value of pyridine core cardanol-based polybenzoxazine possesses a higher residual char (29.1%) than that of other cardanol based PBz's. The values of LOI were increased with increase in weight percentage content of bio-silica. Among the composites studied, 10 wt% bio-silica reinforced composites indicated the LOI value of 32.7.

Later, epoxy (EP)-C-dopo composites was developed by thermally activated polymerization. To addition, to improve the flame resistant efficacy, BG nano-sheets was introduced in to EP-C-dopo systems. The influence of cardanol based benzoxazine and BG nano-sheet on thermal, and flame retardant properties of EP resin was studied. The flame retardant properties of cured EP and EP/C-dopo composites were studied using LOI and UL-94 vertical burning performance, as presented in **Table 4**. Neat epoxy has a LOI value of 25%, and burns aggressively with no UL-94 classification. The introduction of flame retardant C-dopo prompts a remarkable increment in the LOI values and UL-94 rating. 10 wt% C-dopo introduced EP/Cdopo-1 system shows the LOI value of 31% and V-1 rating in UL-94 test. Further, increasing the C-dopo amount marginally increase the LOI values and achieved as V-0 rating from UL-94. In contrast, in combination of 8 wt% C-dopo and 2 wt% borondoped graphene (BG), the EP/C-dopo/BG-1 system passed V-0 rating from UL-94 test, signifying the presence of BG effectively depresses the ignition ability of the EP composites. Further, the EP/C-dopo/BG-2 and EP/C-dopo/BG-3 systems exhibit

*Development of Halogen Free Sustainable Polybenzoxazine Matrices and Composites for Flame…*

The flammability behavior of cured EP and EP/C-dopo composites was further analyzed with cone calorimeter. **Table 4** shows the total heat release (THR) and heat release rate (HRR) values of EP and EP/C-dopo composites. Numerous significant flame related parameters including time to PHRR (TPHRR), time to ignition (TTI), peak heat release rate (PHRR), THR, smoke produce rate (SPR) and fire growth rate index (FIGRA) are presented in **Table 4**. From the MCC data, neat EP

tent leads to further reduction in PHRR values to 920 and 962 kW/m<sup>2</sup>

**%**

**UL-94**

*Formulations and flame retardant properties of neat EP, EP/CBz and EP/CBz/BG composites.*

**TTI (s)**

EP 100 0 0 25 NR 53 110 1262 84.7 0.40 11.5 EP/C-dopo-1 90 10 0 31 V-1 49 92 1119 80.5 0.39 12.2 EP/C-dopo-2 85 15 0 32 V-0 50 95 920 79.4 0.40 9.7 EP/C-dopo-3 80 20 0 33 V-0 50 100 962 77.2 0.38 9.6 EP/C-dopo/BG-1 90 8 2 30 V-0 49 89 870 75.9 0.29 9.8 EP/C-dopo/BG-2 85 13 2 33 V-0 52 120 650 74.4 0.29 5.4 EP/C-dopo/BG-3 80 18 2 33 V-0 56 120 716 78.7 0.31 6.0

**TPHRR (s)**

**s) EP CBz BG**

**PHRR (kW/m<sup>2</sup> )**

**THR (MJ/m<sup>2</sup> ) SPR m<sup>2</sup> /s**

Further introduction of BG nano-sheet in to EP/C-dopo composites leading to the

dopo/BG-1, EP/C-dopo/BG-2 and EP/C-dopo/BG-3, respectively. The most substantial PHRR reduction is perceived in case of EP/C-dopo/BG-2. THR of neat EP indicates the speedy heat release and reached the value of 84.7 MJ/m<sup>2</sup> at the end of combustion. In contrary, both of EP/C-dopo and EP/C-dopo/BG composites observed as lower heat release to certain amount, suggesting that the introduction of C-dopo and BG into EP possibly will trigger to reduce the combustible volatile product. The incorporation of C-dopo leads to a marginal reduction in TTI. Further, the introduction of BG into EP/C-dopo increases the TTI, owing to the "tortuous path" influence of BG that retards the volatilization of combustible degradation products. Neat EP, EP/C-dopo systems reveal no changes in the value of SPR, while

, 650 kW/m<sup>2</sup>

. While, the PHRR of the 10 wt% EP/C-

. Subsequent increasing of C-dopo con-

, and 716 kW/m<sup>2</sup> for EP/C-

, respectively.

**FIGRA kW/ m<sup>2</sup>**

higher LOI values and UL-94 V-0 rating performance.

shows a high PHRR value of 1262 kW/m<sup>2</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.98470*

dopo composites decreases to 1119 kW/m2

further reduction in PHRR to 870 kW/m<sup>2</sup>

**Sample Formulations LOI**

**Table 4.**

**49**

**Figure 9.**

*Preparation of bio-silica reinforced, (A) C-ida polybenzoxazine and (B) C-pyta polybenzoxazine composites [73]. (Copyright 2020, Reproduced permission from Society of Plastics Engineers).*

#### **Figure 10.**

*Synthetic routes of BA-DOPO and cardanol based benzoxazine monomer (C-dopo).*

Xin Wang and Yuan Hu research group have reported [77] the phosphoruscontaining cardanol based benzoxazine (C-dopo) monomer (**Figure 10**) and was synthesized using cardanol, DOPO-based diamine (BA-DOPO) and formaldehyde. *Development of Halogen Free Sustainable Polybenzoxazine Matrices and Composites for Flame… DOI: http://dx.doi.org/10.5772/intechopen.98470*

Later, epoxy (EP)-C-dopo composites was developed by thermally activated polymerization. To addition, to improve the flame resistant efficacy, BG nano-sheets was introduced in to EP-C-dopo systems. The influence of cardanol based benzoxazine and BG nano-sheet on thermal, and flame retardant properties of EP resin was studied. The flame retardant properties of cured EP and EP/C-dopo composites were studied using LOI and UL-94 vertical burning performance, as presented in **Table 4**. Neat epoxy has a LOI value of 25%, and burns aggressively with no UL-94 classification. The introduction of flame retardant C-dopo prompts a remarkable increment in the LOI values and UL-94 rating. 10 wt% C-dopo introduced EP/Cdopo-1 system shows the LOI value of 31% and V-1 rating in UL-94 test. Further, increasing the C-dopo amount marginally increase the LOI values and achieved as V-0 rating from UL-94. In contrast, in combination of 8 wt% C-dopo and 2 wt% borondoped graphene (BG), the EP/C-dopo/BG-1 system passed V-0 rating from UL-94 test, signifying the presence of BG effectively depresses the ignition ability of the EP composites. Further, the EP/C-dopo/BG-2 and EP/C-dopo/BG-3 systems exhibit higher LOI values and UL-94 V-0 rating performance.

The flammability behavior of cured EP and EP/C-dopo composites was further analyzed with cone calorimeter. **Table 4** shows the total heat release (THR) and heat release rate (HRR) values of EP and EP/C-dopo composites. Numerous significant flame related parameters including time to PHRR (TPHRR), time to ignition (TTI), peak heat release rate (PHRR), THR, smoke produce rate (SPR) and fire growth rate index (FIGRA) are presented in **Table 4**. From the MCC data, neat EP shows a high PHRR value of 1262 kW/m<sup>2</sup> . While, the PHRR of the 10 wt% EP/Cdopo composites decreases to 1119 kW/m2 . Subsequent increasing of C-dopo content leads to further reduction in PHRR values to 920 and 962 kW/m<sup>2</sup> , respectively. Further introduction of BG nano-sheet in to EP/C-dopo composites leading to the further reduction in PHRR to 870 kW/m<sup>2</sup> , 650 kW/m<sup>2</sup> , and 716 kW/m<sup>2</sup> for EP/Cdopo/BG-1, EP/C-dopo/BG-2 and EP/C-dopo/BG-3, respectively. The most substantial PHRR reduction is perceived in case of EP/C-dopo/BG-2. THR of neat EP indicates the speedy heat release and reached the value of 84.7 MJ/m<sup>2</sup> at the end of combustion. In contrary, both of EP/C-dopo and EP/C-dopo/BG composites observed as lower heat release to certain amount, suggesting that the introduction of C-dopo and BG into EP possibly will trigger to reduce the combustible volatile product. The incorporation of C-dopo leads to a marginal reduction in TTI. Further, the introduction of BG into EP/C-dopo increases the TTI, owing to the "tortuous path" influence of BG that retards the volatilization of combustible degradation products. Neat EP, EP/C-dopo systems reveal no changes in the value of SPR, while


**Table 4.**

*Formulations and flame retardant properties of neat EP, EP/CBz and EP/CBz/BG composites.*

Xin Wang and Yuan Hu research group have reported [77] the phosphoruscontaining cardanol based benzoxazine (C-dopo) monomer (**Figure 10**) and was synthesized using cardanol, DOPO-based diamine (BA-DOPO) and formaldehyde.

*Synthetic routes of BA-DOPO and cardanol based benzoxazine monomer (C-dopo).*

*Preparation of bio-silica reinforced, (A) C-ida polybenzoxazine and (B) C-pyta polybenzoxazine composites*

*[73]. (Copyright 2020, Reproduced permission from Society of Plastics Engineers).*

*Flame Retardant and Thermally Insulating Polymers*

**Figure 9.**

**Figure 10.**

**48**

the EP/C-dopo/BG system indicate the lower value of SPR, designating that BG nano-sheet with proficient barricade effect can help as suppressant of smoke in the burning method. The FIGRA of the neat EP is 11.5 kW/(m<sup>2</sup> s). In comparison, excluding that the EP/C-dopo-1 system displays a marginally improved value of FIGRA, all other systems display lower value of FIGRA. The most noticeable result is perceived in case of EP/C-dopo/BG-2 (5.4 kW/(m<sup>2</sup> s)), suggesting the considerably inhibited fire hazards.
