Self-reinforced nanofibrillar polymer foams

A. Anstey, M.B. Mahmud, A. Tuccitto, C.B. Park, P.C. Lee
University of Toronto,
Canada

Keywords: nanofibrillar composites, foams

Summary:

In recent years, the concept of in-situ polymer fibrillation from melt processes has been heavily researched as a method for creating nanostructured composite materials via a facile, scalable process. In this process, an immiscible multi-phase polymer blend with sea-island morphology is rapidly drawn from the melt state, generating a fibre-in-fibre structure. Through this process, the dispersed polymer phase is transformed into extremely fine fibrils with diameters on the scale of 50-200 nm. By choosing a dispersed phase with a Tm significantly lower than that of the matrix phase, the composite can be reprocessed and reshaped into a desired shape while preserving this nanofibrillar structure. The presence of nanofibrils in a polymer melt has been shown to dramatically modify the rheological properties and crystallization kinetics of the melt; both of these aspects contribute to a dramatic enhancement in the foamability of polymers, particularly semicrystalline polymers. As is frequently the case in multi-phase polymer blends, interfacial tension remains a hindrance in nanofibrillated polymer composites, limiting both the dispersion of the secondary phase and stress transfer between phases in the solid state. In this research, we address this issue using the self-reinforced composite concept, in which the matrix and dispersed phase have a highly similar molecular structure. This minimizes the interfacial tension, facilitating the production of nanofibrillar composites with unprecedented thermomechanical properties and dramatically enhanced foamability. Self-reinforced blends were produced via a custom system consisting of a twin-screw extruder directly coupled to a spunbond fibrillation system. The morphology, mechanical performance, rheological properties, and crystallization kinetics of these self-reinforced blends were investigated and are presented in this research.