Properties and Semicrystalline Structure Evolution of Polypropylene/ Montmorillonite Nanocomposites under Mechanical Load

Small-angle X-ray scattering (SAXS) monitors tensileand load-cycling tests of metallocene isotactic polypropylene (PP), ablend of PP and montmorillonite (MMT), and two block copolymercompatibilized PP/MMT nanocomposites. Mechanical properties of thematerials are similar, but the semicrystalline nanostructure of the PPdiffers. This is explained by a nucleation effect of the MMT. Competitivecrystal growth diminishes crystallite sizes. The reinforcing effect ofthe MMT filler appears consumed by weakening the PP matrix. Decaysof mechanical and nanostructure response in dynamic load cyclingindicate materials fatigue. Lifetimes describe the reinforcing and weakening effects. Addition of 3% MMT halves the fortifyingeffect of the PP nanostructure. A net gain of reinforcement (11%) is observed with the highly compatibilized composite in whichthe strength of the semicrystalline PP is reduced to 25%. Other results concern the evolution of Strobl’s block structure and voidformation during tensile loading.