Aramid Nanofiber Reinforced Polymer Nanocomposites via Amide-Amide Hydrogen Bonding

Polymer nanocomposites have received tremendous attention over the past several decades; however, they can be challenging to implement without establishing chemical interaction between the nanofillers and the matrix Poorly suited matrix materials can lead to agglomerations and poor interfacial stress transfer mechanisms, which limits the mechanical performance of the resulting polymer nanocomposites. Here, thermoplastic nanocomposites incorporating aramid nanofibers (ANFs) are studied, and it is shown that the performance of the nanocomposite is highly dependent on the similarity of the matrix with the ANF's chemical structure, indicating that amide-amide hydrogen bonding leads to improved mechanical properties. Aramid nanofibers are initially isolated and used to prepare polyamide (PA6), polyamide-imide (PAI), and polyimide (PI) nanocomposites. Solution-cast ANF reinforced PA6 nanocomposites displayed more than 62% and 27% increase in their tensile strength and elastic stiffness, respectively. Similarly, ANF reinforced PAI nanocomposites exhibited more than 25% and 40% increase in their tensile strength and elastic stiffness, respectively. However, solution-cast ANF reinforced PI exhibited negligible improvement in strength and stiffness. The contrast in the performance of ANFs as nano-reinforcements in these nanocomposites is attributed to the ability of the ANFs to establish amide-amide hydrogen bonding in a PAI and PA6 matrix, whereas such interactions are unavailable in PI. This work shows that the introduction of ANF nanofillers may offer a rapid approach free of preprocessing to improve the mechanical properties of polyamide-based nanocomposites through amide-amide hydrogen bonding, allowing for cost-effective and simplified production of stronger polymer materials.