Comparative study of the effect of different nanoparticles on the mechanical properties and thermal degradation mechanism of in situ prepared poly(ε-caprolactone) nanocomposites

Various poly(ε-caprolactone) nanocomposites were prepared in situ by the ring-opening polymerization of ε-caprolactone. Four different nanoparticles were used. Two layered silicates, such as montmorillonite (Cloisite Na+ and Cloisite 20A), one in the form of spherical nanoparticles (fumed silica SiO2) and multi-walled carbon nanotubes (MWNT). Thermal degradation under dynamic conditions as well as mechanical properties under tension of the prepared materials were comparatively examined. All nanoparticles, despite resulting in a small molecular weight (Mv) decrease, induced a substantial enhancement of Young’s modulus and tensile strength compared to neat PCL. From TGA analysis it was concluded that modified montmorillonite and fumed silica accelerate the decomposition of PCL due to respective aminolysis and hydrolytic reactions that the reactive groups on the surface of these materials can induce. On the other hand, carbon nanotubes and unmodified montmorillonite can decelerate the thermal degradation of PCL due to a shielding effect. The activation energies of all the prepared samples were estimated using the Ozawa, Flynn and Wall (OFW) and Friedman methods. Thermal degradation of PCL and its nanocomposites was found to be satisfactorily represented by two mechanisms having different activation energies. The first corresponds to a small mass loss, while the second, attributed to the main decomposition mechanism, corresponds to the substantial mass loss that takes place. The nanoparticles do not affect the decomposition mechanism but only the activation energies.