Influence of β irradiation on carbon nanotube reinforced polypropylene

Abstract

Single walled carbon nanotubes (SWNT) have been incorporated into a polypropylene (PP) matrix in different concentrations ranged 0.25-2.5 wt %, by an extrusion process. The nanotubes were blended with PP particles (approximately 500 μm in size) before mixing in the extruder. Finally, rectangular plates were obtained by compression moulding. In order to improve the mechanical properties, these PP-SWNT composites were gamma irradiated at different doses, 10 and 20 kGy, to promote crosslinking in the matrix and to enhance the interaction between nanotubes and PP. Uniaxial tensile tests and dynamic mechanical thermal analysis (DMTA) were performed to assess the mechanical behaviour depending on the different nanotubes concentrations and irradiation doses. Besides, differential scanning calorimetry (DSC) measurements and thermogravimetrical analysis (TG) were carried out to characterize thermal properties. The values of elastic modulus confirmed the reinforcement of the polypropylene matrix with increasing SWNT concentrations, although stiffness saturation was observed at the highest concentration. Loss tangent DMTA curves showed three transitions for raw polypropylene, and there were no significant variations in the non-irradiated nanocomposites at the different nanotube concentrations. Gamma irradiated samples exhibited an increase in β transition temperature, associated with changes in glass transition due to polypropylene crosslinking. This effect is less pronounced at the highest nanotube concentration. Finally, DSC thermograms pointed out that an increase in degree of crystallinity with increasing nanotube concentration exists.