Properties of bio-based thermosetting composites synthesized from epoxidized soybean oil and azo-cardanol benzoxazine

In this study, a new type of bio-based azobenzene-containing benzoxazine (Bza) was synthesized using p-aminoazobenzene, paraformaldehyde, and cardanol the raw materials, and the resulting Bza was mixed with bio-based epoxy soybean oil (ESO) in different composition ratios in the presence of adipic acid as a reaction curing agent, affording a bio-based thermosetting composite thermosets. The chemical structure of the synthesized Bza was characterized by Fourier transform infrared spectroscopy and H-1 nuclear magnetic resonance spectroscopy. The thermal curing behavior in the absence of any catalyst was investigated by differential scanning calorimetry, indicating that the synthesized Bza exhibits certain liquid crystalline characteristics during heating. The existence of liquid crystal state was further confirmed by the polarizing microscope studies. The mechanical and thermal properties of the composite thermosets with different proportions of Bza were studied. The results show that the addition of increasing amount of Bza to ESO improved its performance to a certain extent; however, further addition beyond a certain range deteriorated the performance. Attributing to excellent processability and high performance of soybean oil-based thermosetting materials and photochromism of azobenzene compounds, the resulting composite materials endowing the characteristics of their components will have a wide range of applications in many fields.