Synthesis and characterization of 1,1-bis(3-methyl-4-hydroxy phenyl)cyclohexane polybenzoxazine–organoclay hybrid nanocomposites

Typical high-performance polybenzoxazines were prepared from benzoxazines based on 1,1-bis(3-methyl-4-hydroxy phenyl) cyclohexane, paraformaldehyde and three distinctive aromatic diamines, namely 4,4’-diaminodiphenylmethane, 4,4’-diaminodiphenylether and 4,4’-diaminodiphenylsulfone, through ring-opening self-polymerization upon heating. The formation of benzoxazines was confirmed by Fourier transform infrared, ¹H and ¹³C nuclear magnetic resonance spectra. Polybenzoxazine–clay hybrid nanocomposites were prepared by a solvent method using polybenzoxazine precursors and organoclay (OMMT) (up to 5 wt.%). The hybrid mixture was subjected to ultrasonication for effective blending. The thermal properties of the resulting polybenzoxazine–clay nanocomposites were studied using differential scanning calorimetry and thermogravimetric analysis. The dispersion of OMMT in the polybenzoxazine and nanostructure of the composites was confirmed by X-ray diffraction analysis. The d spacing of the organoclay interlayers was found to be increased from 1.69 to 2.10 nm. Thermal decomposition temperatures of the nanocomposites were in the range 294–637 °C. These nanocomposites exhibited a high char yield relative to unfilled polybenzoxazines depicting interfacial interactions between the organic and inorganic phases. The homogeneous morphological behavior was studied by scanning electron microscopy.     

Thermo mechanical behaviour of unsaturated polyester toughened epoxy–clay hybrid nanocomposites

The intercrosslinked networks of unsaturated polyester (UP) toughened epoxy–clay hybrid nanocomposites have been developed. Epoxy resin (DGEBA) was toughened with 5, 10 and 15% (by wt) of unsaturated polyester using benzoyl peroxide as radical initiator and 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. The chemical reaction of unsaturated polyester with the epoxy resin was carried out thermally in presence of benzoyl peroxide-radical initiator and the resulting product was analyzed by FT-IR spectra. Epoxy and unsaturated polyester toughened epoxy systems were further modified with 1, 3 and 5% (by wt) of organophilic montmorillonite (MMT) clay. Clay filled hybrid UP-epoxy matrices, developed in the form of castings were characterized for their thermal and mechanical properties. Thermal behaviour of the matrices was characterized by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Mechanical properties were studied as per ASTM standards. Data resulted from mechanical and thermal studies indicated that the introduction of unsaturated polyester into epoxy resin improved the thermal stability and impact strength to an appreciable extent. The impact strength of 3% clay filled epoxy system was increased by 19.2% compared to that of unmodified epoxy resin system. However, the introduction of both UP and organophilic MMT clay into epoxy resin enhanced the values of mechanical properties and thermal stability according to their percentage content. The impact strength of 3% clay filled 10% UP toughened epoxy system was increased by 26.3% compared to that of unmodified epoxy system. The intercalated nanocomposites exhibited higher dynamic modulus (from 3,072 to 3,820 MPa) than unmodified epoxy resin. From the X-ray diffraction (XRD) analysis, it was observed that the presence of d ₀₀₁ reflections of the organophilic MMT clay in the cured product indicated the development of intercalated clay structure which in turn confirmed the formation of intercalated nanocomposites. The homogeneous morphologies of the UP toughened epoxy and UP toughened epoxy–clay hybrid systems were ascertained from scanning electron microscope (SEM).     

Influence of Multiwalled Carbon Nanotubes on Mechanical,Thermal and Electrical Behavior of Polybenzoxazine-Epoxy Nanocomposites

Multiwalled carbon nanotubes (MWCNT)-reinforced polybenzoxazine-epoxy nanocomposites were prepared via the solvent method and were investigated for their thermal, thermo-mechanical, mechanical, electrical and morphological properties. Epoxy resin (DGEBA) was modified with 5, 10 and 15 wt.% of benzoxazines using 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. Epoxy and benzoxazines-modified epoxy systems were further reinforced with 0.25, 0.50 and 0.75 wt.% of surface-modified MWCNT. MWCNT-reinforced polybenzoxazine-epoxy nanocomposites exhibited better thermal, mechanical and dielectric properties. Dispersion of MWCNT in benzoxazine-epoxy resins and nanostructure of the composites was confirmed by transmission electron microscopy analysis.