Core–shell nanoparticle–plasticizers for design of high-performance polymeric materials with improved stiffness and toughness

Core–shell nanoparticle–plasticizers were synthesized and blended with PVC in an attempt to simultaneously improve the toughness and stiffness of the resulting materials. Halloysite, kaolin and silicon dioxide nanofillers, representing acicular, layered and spherical morphologies, were surface-grafted with poly(butylene adipate) (PBA). The surface-grafting was confirmed by FTIR and the amount of PBA grafted on the surface was determined by TGA. In the case of halloysite and silicon dioxide nanoparticles their dispersion and miscibility in the PVC matrix were remarkably improved by the surface-grafting as shown by SEM, tensile testing and DMA. The tensile stress at break for the PVC films containing 5 wt% surface-treated halloysite nanoparticles increased 15%, modulus by 65% and the strain at break was 30 times higher compared to PVC containing 5 wt% untreated halloysite nanoparticles. The PVC films containing 5 wt% surface-treated silicon dioxide nanoparticles exhibited remarkably higher strain at break values compared to plain PVC/silicon dioxide composites, but also somewhat lower stress at break values probably due to the considerably higher amount of PBA grafted on the silicon dioxide surfaces. The higher storage modulus for PVC with surface modified silicon dioxide, however, still indicates higher stiffness for the material containing surface treated nanoparticles. Altogether the results show that the nanoparticle–plasticizer concept could be applied to simultaneously improve the toughness and stiffness of the materials and further improvements could be achieved after optimization of the number of PBA chains and their molecular weight.