Icephobicity of Flame-Sprayed Polymer Coatings

Abstract

Atmospheric ice accretes and accumulates outdoors on the surfaces of several engineering applications, representing a hazard for various industrial sectors, including power transmission, renewable energy, telecommunication and transportation (ground, sea and air). For instance, ice accumulation on power lines can compromise operational performance and mechanical stability, thus ultimately causing their collapse. Moreover, ice accretion on aircraft surfaces can alter aerodynamics, endangering flight operations and, most importantly, human life. Current methods to mitigate icing problems include manual operations, mechanical vibrations, compressed air, thermal heating and chemical fluids. However, these methods, known as active anti-icing and deicing methods, are not durable and cause additional costs, energy consumption and environmental pollution. Considering these drawbacks, passive methods, which can remove ice without external energy input, have been developed as more sustainable alternatives to active methods. These passive strategies mainly consist of coatings, which reduce ice adhesion and facilitate passive ice removal.

The work presented in this thesis aims at fabricating novel polymer composite coatings with icephobic properties using flame spray technology. Flame spraying allows the fast processing of materials, fed in powder form, heated to a melt or semi-molten state using a combustive flame, and accelerated towards a substrate to form a coating. As a result, coatings can be produced on large surfaces using a single fabrication step. The first stage of the research focused on fabricating plain low-density polyethylene (LDPE) coatings. The flame spraying parameters were varied to study their effect on the properties and icephobic behaviour of coatings. Coatings were characterised by measuring thickness, roughness, surface chemical composition, wetting behaviour and thermal properties. In addition, the icephobicity of coatings was evaluated by accreting ice using an icing wind tunnel and measuring ice adhesion using a centrifugal ice adhesion test. The results showed that the selected process parameters and resulting heat input transferred to the polymer significantly affected the icephobicity of coatings. In particular, the higher the heat input, the higher the oxidation produced in the polymer and the lower was the icephobic behaviour of coatings. The second stage of the research aimed at developing novel composite coatings, named lubricated icephobic coatings (LICs), by adding a solid lubricating additive to the LDPE material. To produce the composite coatings, the flame spray process was modified to feed the additive and simultaneously spray it with LDPE. The modified flame spray process was named flame spraying with hybrid feedstock injection. The results demonstrated that the addition of lubricating additives improved the icephobic behaviour of plain flame-sprayed LDPE coatings. The third stage of the research focused on assessing the durability of LICs under various environmental stresses, such as exposure to repeated icing/deicing cycles, different corrosive media and ultraviolet radiation on laboratory scale. The results showed that stable icephobic behaviour could be obtained for LICs over the icing/deicing cycles. Moreover, the lubricated coatings demonstrated good chemical resistance in the studied corrosive environments and limited photo-oxidation during exposure to ultraviolet radiation.

This research demonstrated the potential of lubricated icephobic coatings, which could be used as anti-icing solutions in the future. In addition, flame spraying allows the fast deposition of coatings on large surfaces, and these advantages are relevant to many industrial sectors facing icing problems. Therefore, further research is needed on the potential application of these coatings in various industrial sectors to limit the current inconveniences caused by ice formation.