Nanoparticles as curing and adhesive aid for biobased and petrobased polybenzoxazines

Abstract

Alumina nanoparticles were incorporated in blends of benzoxazine monomers synthesized from bio- and petrobased phenols, cardanol and bisphenol A, respectively, by way of a one-pot solventless methodology. The structures of the monomers were characterized by proton (1H) nuclear magnetic resonance and Fourier transform infrared spectroscopy. Thermal characterization was performed using differential scanning calorimetry and thermogravimetry. The size of bare alumina nanoparticles and those in the polymer nanocomposite was analyzed by powder X-ray diffraction. Blending of alumina particles resulted in lowering of curing temperature of benzoxazine monomer. The effect of nanoparticle incorporation was reflected in the curing behavior and adhesive properties. The adhesive strength is found to be dependent on whether solution or solventless processing is used and on the weight percent of the nanoparticles in the monomer blend. The replacement of 75% bisphenol A content with cardanol in the benzoxazine resulted in a copolymer which showed a better or comparable adhesive strength. The adhesion was found to improve further with the incorporation of alumina nanoparticles. The lower viscosity of cardanol-based benzoxazine allowed both solventless synthesis and application of monomers, which is a way forward toward greener chemistry and low volatile organic compound processing strategies.