Irradiation‐induced surface graft polymerization onto calcium carbonate nanoparticles and its toughening effects on polypropylene composites

Nano‐sized calcium carbonate was pretreated with silane coupling agent and then mixed with butyl acrylate that is of larger amount than the nanoparticles. Under γ‐irradiation, graft polymerization occurred on the nanoparticle surface, forming a nanocomposite structure consisting of grafted poly(butyl acrylate) (PBA), homopolymerized PBA, and the segregated nanoparticles. It was found that the silane pretreatment significantly promoted the graft reaction. When the grafted nano‐CaCO 3 particles were melt compounded with polypropylene (PP), an obvious synergistic effect, offered by (i) the chemical bonding between the elastomer type grafted PBA and nano‐CaCO 3 and (ii) the deliberately introduced thick interlayer mainly constructed by the homopolymerized PBA, led to a significant increase in notch impact strengths and elongation to break of PP at a rather low content of nano‐CaCO 3 . Meanwhile, the tensile stiffness of the composites was also slightly increased and the yielding strength of the composites was almost unchanged. The results are different from those with conventional rubber‐toughened plastics, in which the improvement of ductility is acquired at high additive fraction and a great expense of strength performance. POLYM. ENG. SCI., 45:529–538, 2005.