Morphology and thermal degradation studies of melt-mixed poly(hydroxybutyrate-co-valerate) (PHBV)/poly(ε-caprolactone) (PCL) biodegradable polymer blend nanocomposites with TiO₂ as filler

The morphology, thermal stability and thermal degradation kinetics of melt-mixed poly(hydroxybutyrate-co-valerate) (PHBV)/poly(ε-caprolactone) (PCL) blends filled with small amounts of titanium(IV)oxide (TiO₂) nanoparticles were investigated. The nanoparticles were mostly well dispersed in both phases of the PHBV/PCL blend, which showed a co-continuous morphology at a 50/50 w/w ratio, but some large agglomerates were also observed. The equal dispersion of the TiO₂ nanoparticles in both polymers was attributed to the polymers having the same surface properties, polarities and viscosities. The thermal stability of PHBV was improved when blended with the more thermally stable PCL, but the PCL became less thermally stable when blended with PHBV. The introduction of only 1 wt% of TiO₂ nanoparticles seems to have observably improved the thermal stabilities of both polymers in the blend, but the nanoparticles probably retarded the evolution of the degradation products through their interaction with these products. Further improvement in thermal stability at higher nanoparticle contents was insignificant because of the nanoparticles’ agglomeration which reduced their effectiveness. Changes in the activation energies of degradation, determined through the Flynn–Wall–Ozawa model from thermogravimetric analysis mass loss data, and differences between the Fourier-transform infrared spectra of the degradation volatiles obtained during the degradation process, to a large extent support the other observations.