Functionalized Aramid Nanofibers for the Reinforcement of Thermosets and Rubber Nanocomposites

Abstract

Polymer nanocomposites have received attention for a wide range of applications over the past few decades due to their high mechanical properties. With the introduction of a relatively low weight fraction of nanofillers, polymer nanocomposites have shown superior properties to composites reinforced with macro- or micro-sized fillers. The properties and performance of polymer nanocomposites are affected by the morphology and dimensions of the nanofillers and the interfacial interactions between polymer matrices and nanofillers. Recently, aramid nanofibers (ANFs) have been obtained through the dissolution and deprotonation process of macroscale aramid fibers in a solution with dimethyl sulfoxide and potassium hydroxide. ANFs have shown great potential as a reinforcing filler for polymer nanocomposites due to their excellent mechanical properties, high aspect ratio, and large surface area. In addition to these unique characteristics, there are rich functionalities on the surface of ANFs that can be used to introduce surface modification agents or multifunctional nanomaterials on the ANFs. Therefore, the properties of polymer nanocomposites can be further increased through the introduction of functionalized ANFs that enhance their chemical and mechanical interaction. In this work, ANFs are modified using various silane coupling agents to reinforce rubber nanocomposites for tire tread and epoxy nanocomposites. The silane coupling agent treatment improves the dispersion of ANFs in polymer matrices and chemical interfacial interaction between the matrices and ANFs through covalent linkages between them. The functionalization of ANFs is investigated using characterization techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Rubber nanocomposites reinforced with functionalized ANFs exhibit improved mechanical properties and tire performance metrics, including an 11.3% increase in abrasion resistance and 14.7% improvement in fuel efficiency, without decreasing wet grip performance. As shown from the results of rubber nanocomposites, functionalized ANF reinforced epoxy nanocomposites also show enhanced tensile strength, elastic modulus, fracture toughness, and dynamic mechanical properties due to the improved interfacial interaction. In addition, this work also considers the hybridization of ANFs using other strong nanomaterials such as graphene oxides (GOs) and cellulose nanocrystals (CNCs) for the reinforcement of tire tread rubber nanocomposites and epoxy nanocomposites. The novel hybrid materials based on ANFs are expected to contribute to improved chemical and mechanical interaction within nanocomposites through the extensive branching and network structure of the hybrid fillers and covalent bonding between the polymer matrix and fillers. The hybrid filler reinforced rubber nanocomposites and epoxy nanocomposites exhibit a synergetic effect of nanofillers on increasing mechanical properties and performance compared to the nanocomposites reinforced with ANFs or GOs or CNCs alone. Especially, the ANF/GO hybrid filler reinforced rubber compounds show an 18.2% improvement in abrasion resistance and 21.8% improvement in rolling resistance. Thus, the research presented in this dissertation provides novel reinforcement methods to improve the overall performance of tire tread rubber nanocomposites, including abrasion resistance and fuel efficiency, which can help overcome energy and environmental challenges. In addition, thermosetting polymers using functionalized ANFs are expected to have an impact in the field of structural polymer composites with improved properties.