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 organic−inorganic hybrid material is proposed.

Abstract

In the present work, perfluoroalkylated laponite nanoparticles with a high degree of functionalization (60 wt %) have been prepared and a methodology to prepare transparent, antistatic, and omniphobic laponite-based films with holistic self-cleaning properties against liquids, solids and liquid-solid mixtures has been developed. The intrinsic electrical and ionic conductivities observed in unmodified laponite coatings are combined with perfluoroalkyl-modified laponite clays. As a result, films with improved self-cleaning functionality based on dust-repellency and omniphobic liquid-repellence (sheet resistance in the range of 10 Ω/□ and contact angles of 106° (HO) and 93° (oil)) were obtained. These unique films, being capable to repel dust and liquids, were applied to a variety of substrates (i.e., glass and plastics) and tested against solids and liquids of different nature with excellent performance. Bending tests of these holistic self-cleaning films deposited over flexible substrates showed better mechanical performance than unmodified laponite films.

The physical properties of polymers can be significantly altered by blending them with inorganic components. This can be done during the polymerization process, but also by post-processing of already shaped materials, for example through coating by atomic layer deposition (ALD) or hybridizing through vapor phase infiltration (VPI), both of which are beneficial in their own way. Here, a new processing strategy is presented, which allows distinct control of the coating and infiltration. The process is a hybrid VPI and ALD process, allowing separate control of infiltrated and coated components. This new simultaneous vapor phase coating and infiltration process (SCIP) enhances the degrees of freedom for optimizing the properties of polymers, as shown on the example of Kevlar 29 fibers. The SCIP treated fibers show an increase of 17% of their modulus of toughness (MOT) in comparison to native Kevlar, through the nanoscale coating with alumina. At the same time their intrinsic sensitivity to 24 hours UVirradiation was completely suppressed through another infiltrated material, zinc oxide, which absorbs the UV irradiation in the subsurface area of the fibers. Fig. 2 Mechanical properties comparison. Comparison of the mechanical properties of untreated Kevlar fibers and fibers after infiltration (I-Al 2 O 3 ) or coating (C-Al 2 O 3 ) with Al 2 O 3 and after infiltration with ZnO and simultaneous coating with Al 2 O 3 (SCIP). (A) Modulus of toughness before and after irradiation with UV light (all values are averaged from 7 samples and the error bars correspond to the standard error) C-ZnO and I-ZnO refer to sample processed in earlier work, 6 and (B) stress-strain curves before and after irradiation with UV light.This journal is