**3. Eugenol based polybenzoxazines for flame resistant applications**

Among renewable phenolic alternatives to substitute the conventional phenolic, eugenol appears as most imminent raw-materials for the sustainable PBz's production owing to their abundance availability and low cast production. Eugenol is obtained from several bio-sources including, clove, tulsi, cinnamon, pepper, turmeric, and thyme. The eugenol structure is very exciting as allyl functional group permits additional cross-linking with numerous functional groups. In addition, the phenolic group offers numerous chemical reactions and formation of products including esterification, cyanogenation, alkylation, and novalac, epoxy and BZs, etc.

Sarojadevi Muthusamy research group reported [74] the successful synthesis of the polyhedral oligomeric silsesquioxane (POSS) tethered PBz nano-composites using renewable bio-phenols (eugenol, guaiacol, vanillin), POSS-octaamine with paraformaldehyde through Mannich reaction. The developed POSS-PBz nanocomposites (**Figure 11**) from sustainable bio-sources have a great potential application as high-performance materials owing to its excellent thermal and flame resistant properties. Thermal and flame resistant properties of POSS-PBz nanocomposites were determined using TGA under nitrogen atmosphere. The char yield percent and LOI values (**Table 2**) are found to be 24, 38, 36 and 27.1, 32.7, 31.9 respectively for POSS-EPBz, POSS-GPBz, and POSS-VPBz. Among the nanocomposites developed POSS-GPBz nanocomposites shows better thermal and flame resistant properties over other two POSS-PBz systems.

Alagar group have also reported [37] the new type of bio-based PBz's synthesized using eugenol and furfurylamine/stearylamine through greener synthetic

approach (**Figure 12**). The synthesized benzoxazine monomers were further reinforced with varying weight percentage content (0, 1, 3, 5, and 10 wt%) of biosilica obtained from rice-husk to fabricate PBz hybrid composites (**Figure 13**). The TGA results obtained inferred that the developed bio-silica reinforced PBz composites possess the higher thermal and improved flame resistant properties. The furfuryl amine based PBz (FBz), the char yield value was increased to 53% from 46%. In case of stearyl amine based PBz (SBz), the char yield value was increased to 27% from 20%. The value of char yield of SBz is lower than that of FBz because of the presence of long aliphatic chain. In common, the polymeric materials with LOI values more than 26 are considered as flame-retardant materials, it was found that the bio-silica reinforced bio-based PBz's composites possess the LOI values of 25 to 39 (**Table 2**), signifying an enhanced flame resistant nature of the developed

*The schematic representation for the formation of FBS/FBz and FBS/SBz [37] composites.*

bio-based PBz composites.

**Figure 12.**

**Figure 13.**

**51**

*Synthesis of eugenol based benzoxazine monomers using different amines.*

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

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

**Figure 11.** *Synthesis POSS based renewable benzoxazine monomers.*

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

**Figure 12.** *Synthesis of eugenol based benzoxazine monomers using different amines.*

**Figure 13.** *The schematic representation for the formation of FBS/FBz and FBS/SBz [37] composites.*

approach (**Figure 12**). The synthesized benzoxazine monomers were further reinforced with varying weight percentage content (0, 1, 3, 5, and 10 wt%) of biosilica obtained from rice-husk to fabricate PBz hybrid composites (**Figure 13**). The TGA results obtained inferred that the developed bio-silica reinforced PBz composites possess the higher thermal and improved flame resistant properties. The furfuryl amine based PBz (FBz), the char yield value was increased to 53% from 46%. In case of stearyl amine based PBz (SBz), the char yield value was increased to 27% from 20%. The value of char yield of SBz is lower than that of FBz because of the presence of long aliphatic chain. In common, the polymeric materials with LOI values more than 26 are considered as flame-retardant materials, it was found that the bio-silica reinforced bio-based PBz's composites possess the LOI values of 25 to 39 (**Table 2**), signifying an enhanced flame resistant nature of the developed bio-based PBz composites.

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

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

**3. Eugenol based polybenzoxazines for flame resistant applications**

Among renewable phenolic alternatives to substitute the conventional phenolic, eugenol appears as most imminent raw-materials for the sustainable PBz's production owing to their abundance availability and low cast production. Eugenol is obtained from several bio-sources including, clove, tulsi, cinnamon, pepper, turmeric, and thyme. The eugenol structure is very exciting as allyl functional group permits additional cross-linking with numerous functional groups. In addition, the phenolic group offers numerous chemical reactions and formation of products including esterifica-

Sarojadevi Muthusamy research group reported [74] the successful synthesis of the polyhedral oligomeric silsesquioxane (POSS) tethered PBz nano-composites using renewable bio-phenols (eugenol, guaiacol, vanillin), POSS-octaamine with paraformaldehyde through Mannich reaction. The developed POSS-PBz nanocomposites (**Figure 11**) from sustainable bio-sources have a great potential application as high-performance materials owing to its excellent thermal and flame resistant properties. Thermal and flame resistant properties of POSS-PBz nano-

composites were determined using TGA under nitrogen atmosphere. The char yield percent and LOI values (**Table 2**) are found to be 24, 38, 36 and 27.1, 32.7, 31.9 respectively for POSS-EPBz, POSS-GPBz, and POSS-VPBz. Among the nanocomposites developed POSS-GPBz nanocomposites shows better thermal and flame

Alagar group have also reported [37] the new type of bio-based PBz's synthesized using eugenol and furfurylamine/stearylamine through greener synthetic

s). In comparison,

s)), suggesting the consider-

burning method. The FIGRA of the neat EP is 11.5 kW/(m<sup>2</sup>

tion, cyanogenation, alkylation, and novalac, epoxy and BZs, etc.

resistant properties over other two POSS-PBz systems.

is perceived in case of EP/C-dopo/BG-2 (5.4 kW/(m<sup>2</sup>

*Flame Retardant and Thermally Insulating Polymers*

ably inhibited fire hazards.

**Figure 11.**

**50**

*Synthesis POSS based renewable benzoxazine monomers.*

**Figure 14.** *Schematic representation for the preparation of renewable PBZ–E–F– silica hybrids [75].*

**4. Guaiacol based polybenzoxazine for flame resistant applications**

*Synthesis of fully bio-based mono and tri-furan functional mono and bis-benzoxazine resin.*

39.9 and 42.3 respectively. Both PBz's possess better LOI values in the selfextinguishing region (LOI > 28). Also MCC analysis was utilized further to assess the flammability performance of poly(GU-fa) and poly(FBP-fa). From the MCC characterization of poly(GU-fa) and poly (FBP-fa) display HRC values of 79.6 and

*Formulations and flame retardant properties of bio-based polybenzoxazines.*

**Sample Char residue (%) LOI % HRC (J/gK) THR (KJ/g) Reference** Poly(GU-fa) 56 39.9 70.6 6.5 [78] Poly(FBP-fa) 62 42.3 30.4 5.8 [78] Poly(RES-a) 55 79.7 15.9 [45] Poly(RES-ac) 74 30.7 6.0 [45] Poly(RES-ch) 59 73.4 14.2 [45] Poly(RES-fa) 64 54.0 9.3 [48] Poly(API-fa)-1 63 42.7 22.5 11.2 [79] Poly(API-fa)-1 66 43.9 20.2 9.4 [79] Poly(NAR-fa) 64 31.9 6.6 [80]

30.4 J/gK, respectively (**Table 5**).

**Figure 16.**

**Table 5.**

**53**

Kan Zhang research group have developed [78] the fully bio-based tri-furan functional bis-benzoxazine resin (**Figure 16**) and was synthesized using furfural, guaiacol, furfurylamine and paraformaldehyde via a two-step reaction approach. In the first step, bio-based bis-phenol containing furan ring was synthesized using furfural and guaiacol via base mediated condensation reaction. Then the bio-based sustainable tri-furan functional bis-benzoxazine (FBP-fa) was synthesized using bio-based bis-phenol, furfurylamine and paraformaldehyde through greener approach. The flammability behaviour of poly(GU-fa) and poly(FBP-fa) was assessed using LOI. As a result, poly(GU-fa) and poly(FBP-fa) show LOI values of

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

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

**Figure 15.** *Synthesis of renewable bio-based isomeric benzoxazine E-fa and IE-fa.*

In addition, the same group have further reported [75] the high thermal and flame resistant PBz-silica hybrid materials were synthesized using eugenol and furfurylamine via sol–gel-techniques (**Figure 14**). An inorganic component of TEOS was introduced into eugenol- benzoxazine (BZ–E–F) with the help of MPTMS as a coupling agent viz. thiol-ene click approach. The thermal studies indicate that the char yield increases to 67.54 from 41.32 (neat PBz) and LOI increased to 44.52 for PBZ–E–F silica hybrid from 34.03 for neat PBz (**Table 2**).

Bimlesh Lochab research group have reported [76] the synthesis of sustainable biobased benzoxazine monomers (**Figure 15**) using isomeric phenols, eugenol (E) and iso-eugenol (IE), and furfurylamine (fa) to form E-fa and IE-fa monomer, respectively. The monomers differ in the position of the double bond in the p-substituted propylene unit forming non-conjugated Vs. conjugated alkylene chain with the benzene ring containing benzoxazine in E-fa and IE-fa respectively. In comparison to other bio-based PBz's, both PE-fa and PIE-fa exhibited the higher thermal stability and high flame resistant properties. The char residue values of PE-fa and PIE-fa are 52 and 60 respectively and the LOI values observed are 38.3 and 41.5 respectively (**Table 2**).

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

**Figure 16.** *Synthesis of fully bio-based mono and tri-furan functional mono and bis-benzoxazine resin.*
