Fracture behaviour of polymers toughened with CaCO₃ nanoparticles

The objective of this PhD thesis is to develop new tough and rigid nanocomposites based on polypropylene (PP) and polystyrene (PS) which are two of the polymers with the highest demand and growth rates worldwide. Recently, attempts have been made to improve the mechanical properties and processability of PP and PS through several procedures. Nowadays the market of fillers for polyolefines is dominated by calcium carbonate which is one of the most widely used particulate fillers for polymer applications due to it’s low cost, ready availability and useful properties. However, even if CaCO₃ enhances the Young’s modulus it is often reported that decreases impact strength. Thus, researchers are studying to improve the mechanical properties of polymers toughened with CaCO₃ nanoparticles so they are expected to be very desirable materials. In fact, previous results from our work in collaboration with Solvay Advanced Functional Minerals have shown that a dry-coated PCC substantially enhances impact in both homopolymer and copolymer iPP and so this result encourage us to continue these studies and to extend its use on both PP and PS. So we studied the possibility to tough some polyolefines mixed with different type of CaCO₃ nanoparticles (PCC) and the mechanism that explains their mechanical deformation. In this way we tested the effect of the different characteristics of the powders on the final properties of the nanocomposites, as the various particles differ for shape, granulometric size, surfactant agent and kind of process utilized to prepare them. This work is divided into three main parts: the first regards the fracture behaviour of polyproylene filled with different kinds of CaCO₃ powders, the second the development of a new alternative procedure to produce nanocomposites (based on PP and PS matrices) with the relative comparison with the extrusion method and the third the interface characterization with various techniques.