Structural, thermal and rheological studies of nanocalcium–strontium hexaferrite/polyacrylic acid composites

Polyacrylic acid and its composites with nanocalcium–strontium hexaferrites (PAA, PAA1, PAA2, PAA3) were prepared by in situ chemical polymerization. The synthesized composites were characterized by wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetry (TG). The rheological characteristics of the synthesized compounds were also investigated. The WAXD patterns indicated the successful incorporation of nanoferrites into the polymer matrix, hence affecting its crystallinity. The thermal stability and degradation pattern of the synthesized polymers were studied by TGA. The kinetic triplet [activation energy, pre-exponential factor and g(α) model] of the composites was evaluated by Coats Redfern calculation procedure. The TG data of polymer degradation depicted chemical reaction as the rate controlling step. The rheological characteristics of the samples were explored by flow curve and frequency sweep test at 20–40 °C. The flow curves of all the samples at this range of temperature showed a shear thinning trend to establish their pseudo-plastic nature. Frequency sweep test showed direct dependence of dynamic moduli (G′ and G″) and inverse dependence of complex viscosity on angular frequency. Relaxation time increased with nanoferrite loading, revealing the increased entanglement between the nanoferrite and polymer matrix.