Suppressing the Thermal and Ultraviolet Sensitivity of Kevlar by Infiltration and Hybridization with ZnO

Polyaramides, such as Kevlar, are of great technological importance for their extraordinary mechanical performance. As fibers, they are used in personal safety, for reinforcement of tires and ropes, and in further material composites that require extreme mechanical stability. However, the properties of the polymer depend on the environmental conditions. Specifically, elevated temperatures and/or irradiation with UV light seriously affect its toughness. Classical approaches to protect polyaramide fibers from these external factors rely on coatings with resins or metal oxides, which typically increase the weight and reduce the flexibility of the polymer. Here, we present a bioinspired approach to stabilize the mechanical properties of the polyaramide. With our solvent free vapor phase approach, zinc oxide is infiltrated into the polymer structure, resulting in intermolecular cross-linking of the polymer chains. The procedure results in an increased degradation temperature of the polyaramide, while at the same time it protects the fibers against UV-induced degradation. The chemical interaction between the zinc oxide and the polymer is theoretically modeled, and a chemical structure of the resulting organicinorganic hybrid material is proposed.