Hierarchical Glass Fiber Superstructures with Supramolecular Nanofibers for the Nucleation of Isotactic Polypropylene

Abstract

Supramolecular additives are an established class of nucleating agents to modify and control the solid-state morphology of semi-crystalline polymers, in particular isotactic polypropylene (iPP). A widely used reinforcement material for iPP is glass fibers (GFs), which significantly improve the mechanical properties. Here, these two types of materials are combined by creating defined hierarchical superstructures composed of glass microfiber nonwovens and supramolecular nanofibers based on selected 1,3,5-benzetrisamides (BTA). The supramolecular nanofibers are prepared by physical vapor deposition (PVD), a straightforward solvent-free process. By systematically varying PVD process parameters, it is shown that supramolecular BTA nanofibers can be reproducibly prepared on flat substrates. The morphology of the supramolecular nanofibers can be controlled by substrate temperature, evaporation time, and evaporation rate. The use of GF nonwovens enables the fabrication of hierarchical superstructures with a bottlebrush morphology comprising supramolecular nanofibers of defined length. These hierarchical superstructures are capable of nucleating iPP and thus promote transcrystallization of the iPP from the decorated GFs surface, which ultimately improves the adhesion between the GFs and the iPP. Laminating decorated GF nonwovens between two iPP films clearly increases the mechanical properties of the composites in contrast to composites without nucleating agents.