Texas A&M University,
Keywords: Scalable Manufacturing, Thermoplastic Composites, Tailored Microstructure
Summary:High-performance thermoplastic composites are emerging in industries to replace metals as these composites offer lightweighting, outstanding mechanical properties, chemical stability, and manufacturability within few minutes (e.g. via additive manufacturing or thermoforming). However, in fast-rate processes with high cooling rates, there is no sufficient time for the polymer to form long chain orders (crystals) that in turn reduces the crystallinity level leading to loss in the strength. Achieving simultaneous high strength and high interlaminar fracture toughness in thermoplastic composites is challenging because higher crystallinity improves strength but reduces fracture toughness. Yet, high fracture toughness needs strong interfacial adhesion, i.e. high crystallinity. To overcome this paradox, we use a novel processing and manufacturing approach, in which cellulose nanocrystals (CNCs) are attached to graphene nanoplatelets (GNPs) to create a planar-branched nanomaterial system with unique spatial geometry to locally control the nucleation, growth, preferential orientation, and size distribution of crystals during the processing of carbon fiber reinforced thermoplastic composites. Our results show that in hybrid composites, CNC-GNPs promote the oriented formation of crystals and enhance interfacial adhesion at molecular level and simultaneously increase macroscopic flexural/interlaminar strength and fracture toughness. The new method will enable new capabilities in harnessing the formation of crystals and tailoring the microstructure and performance at multiple length scales in fast-rate manufacturing of composites.