Synthesis of high‐performance bio‐based benzoxazine for flame retardant application

• Published in: Polymers for advanced technologies 2022-05, Vol.33 (5), p.1481-1495
• Main Authors: Naiker, Vidhukrishnan E., Patil, Dhananjay A., More, Aarti P., Mhaske, Shashank T.
• Format: Article
• Language: English
• Subjects: Benzoxazine; Benzoxazines; bio‐based; Chemical synthesis; Diamines; Flame retardants; flame‐retardant; Fourier transforms; Infrared spectroscopy; Mechanical properties; Molecular structure; NMR spectroscopy; paraformaldehyde; Phenyl phosphonate; Polybenzoxazines; Polymerization; Ring opening polymerization; Spectrum analysis; Stability tests; Thermal stability; Thermodynamic properties; Thermogravimetric analysis; Vanillin
• ISSN: 1042-7147; 1099-1581
• DOI: 10.1002/pat.5615

In this study, a phosphorous‐containing benzoxazine was synthesized using a bio‐based primary amine, vanillin diamine true sample 2 (VDTS2, IUPAC name: 4‐(([3‐aminopropyl] imino) methyl)‐2‐methoxyphenyl(4‐(([3‐aminopropyl] imino) methyl)‐2‐methoxyphenyl) phenylphosphonate), paraformaldehyde and vanillin and tested for its use as a flame‐retardant. The molecular structure of the synthesized benzoxazines was characterized by FTIR spectroscopy and 1H NMR spectroscopy. Polybenzoxazine was obtained through the ring‐opening polymerization of the benzoxazine monomer, and the formation of the same was confirmed through FTIR spectroscopy. The polymerization mechanism of the benzoxazine was investigated using thermogravimetric analysis (TGA). The thermal properties of the benzoxazine were studied using differential scanning calorimetry and TGA. The flame‐retardant properties of the polybenzoxazine films obtained were investigated by the LOI. Due to the highly brittle nature of the polybenzoxazine, the synthesized polybenzoxazine was further crushed and incorporated into an epoxy system to investigate its use as a flame‐retardant additive. The thermal property and flame‐retardant property of the epoxy films were then studied. The flame‐retardant and thermal stability test results of the epoxy‐pbz films showed that the epoxy‐pbz films showed improved thermal stability and achieved a UL‐94 V‐0 rating and an LOI of 28% at 15% by weight of the polybenzoxazine concentration. SEM analysis was also conducted to study the surface morphology of the polybenzoxazine and epoxy‐pbz films pre and post the flame test. FTIR analysis was carried out to study the flame retardant mechanism of the polybenzoxazine and the epoxy‐pbz film. The respective films' mechanical properties were also investigated to study the film‐forming capability of the films.