Studies on thermal, mechanical, electrical, and morphological behavior of organoclay-reinforced polybenzoxazine–epoxy nanocomposites

Abstract

Organoclay-reinforced polybenzoxazine–epoxy nanocomposites were prepared via in situ polymerization and thermal, thermomechanical, mechanical, electrical, and morphological properties were characterized by standard methods. Two types of skeletal-modified benzoxazines namely 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane benzoxazine and bis(4-maleimidophenyl) benzoxazine were synthesized by reacting paraformaldehyde and 4,4′-diaminodiphenylmethane with 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane and N-(4-hydroxyphenyl)maleimide, respectively. Diglycidyl ether bisphenol A epoxy resin was modified with 5, 10, and 15 wt% of benzoxazines and were cured using 4,4′-diaminodiphenylmethane at appropriate conditions. The occurrence of chemical reaction between benzoxazines and epoxy resin was ascertained by Fourier transform infrared spectra. Epoxy and benzoxazines-modified epoxy systems were further reinforced with 1, 3 and 5 wt% of organically modified montmorillonite (OMMT). Thermal behavior of matrices was characterized by differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. Mechanical properties were studied as per ASTM standards. The organoclay (OMMT)-reinforced polybenzoxazine–epoxy nanocomposites exhibited lower values of glass transition temperature and dielectric constant/dielectric loss with enhanced values of thermal stability, char yield, impact strength, and storage modulus than those of neat matrix. The morphology of organoclay-reinforced benzoxazine-modified epoxy matrix was studied by scanning electron microscopy, x-ray diffraction, and transmission electron microscopy analyses.