Isolating the effect of polymer-filler interaction on polymer composite property enhancement: The example of polypropylene/halloysite hybrids

We prepare polypropylene (PP) composites with both pristine halloysite nanotubes (p-HNT) and PP grafted halloysite nanotubes (PP-g-HNT) using two processing techniques, solid-state shear pulverization (SSSP) and melt mixing. We address the role of isolated polymer-filler interaction effects on polymer nanocomposite property enhancement at similar, high levels of filler dispersion. As shown by microscopy and rheology, nanocomposites prepared by SSSP with p-HNT and PP-g-HNT fillers have very similar, well-dispersed states, eliminating differences in dispersion as a factor in property enhancements. The well-dispersed PP/PP-g-HNT nanocomposites exhibit a range of properties that are generally superior to those of the well-dispersed PP/p-HNT nanocomposites, including tensile strength, PP non-isothermal crystallization onset temperature, and isothermal PP crystallization half-time. However, the Young's modulus is the same regardless of filler modification. Superior filler dispersion achieved by SSSP relative to melt mixing contributes to Young's modulus enhancement in nanocomposites. For melt mixed samples with relatively poor dispersion, some properties are improved with PP-g-HNT filler relative to p-HNT filler but are nevertheless inferior to samples made by SSSP.