Evaluation of the protective performance of hydrophobic coatings applied on carbon-fibre epoxy composites

Abstract

Carbon–fibre epoxy composites are widely used for high-performance structural applications, where they are often exposed to harsh environments. The result of moisture ingress has been extensively studied, causing significant deterioration in the mechanical properties of these composites. This study evaluates the performance of five commercial hydrophobic coatings as protective layers, to inhibit moisture ingress into the composite. The coatings evaluated were NeverWet, HydroBead, SHC, Aculon and LiquidGlass. These coatings were characterised and compared in terms of hydrophobicity, surface energy, roughness and chemical composition. This study also evaluated two atmospheric plasma pre-treatments as a means of enhancing the adhesion performance of these coatings. The pre-treatments involved the use of an air plasma for the activation of the epoxy, as well as the plasma deposition of a nanometre thick SiOx interlayer coating. The durability and protective performance of the coatings, with and without the pre-treatments were then compared using an abrasion test as well as a water immersion study. The use of both plasma pre-treatments was found to enhance the adhesion and the abrasion performance of four out of the five coatings. Of the coatings and pre-treatments investigated, the LiquidGlass in conjunction with a SiOx-coating interlayer was found to exhibit the highest abrasion resistance. This was followed by the composite, which was plasma activated prior to the application of the Aculon coating. Only minor differences were observed when comparing the total moisture ingress (M%) of the epoxy, coated with the different hydrophobic layers. The composite coated with the Aculon and SiOx interlayer exhibited the least amount of moisture ingress, at 0.90%, compared to 1.08% of the uncoated specimen. The shear strength of epoxy composite, coated with the LiquidGlass, NeverWet and the activated Aculon combination, were within the range of the uncoated specimens, therefore the moisture ingress was reversible upon heating and no permanent damage to the epoxy–fibre interface was observed. It is concluded that, of the five coatings investigated, both the Aculon coating and LiquidGlass in combination with a SiOx interlayer coating, exhibit the greatest potential as protective layers for carbon fibre epoxy composites.

Effect of homologous molecular crosslinking on the tribological properties of PTFE composites

“…With the addition of MP1100, the water contact angle of the composite material does not change significantly for the following reasons: first, another component of the composite material, short carbon fiber (SCFs), is hydrophobic, which affects the water contact angle on the surface of the composite material. A similar conclusion was also found in literature 53 . Second, the effective free radical concentration of COOH on the composite surface containing MP1100 is low, and its ability to change the surface contact angle is limited.…”

“…A similar conclusion was also found in literature. 53 Second, the effective free radical concentration of COOH on the composite surface containing MP1100 is low, and its ability to change the surface contact angle is limited. In general, the influence of SCFs and h-BN on the water contact angle of the composite surface is greater than that of MP1100, resulting in little change in the water contact angle of the composite surface containing MP1100.…”

Advance in Using Plasma Technology for Modification or Fabrication of Carbon‐Based Materials and Their Applications in Environmental, Material, and Energy Fields

“…Compared to oxygen plasmas, the air plasma required mid to high powers (150 W) and short exposure times (60 s) to obtain improved mechanical performance. Similarly, O'Connor and Dowling [ 118 ] tested the improvement of adhesion of CF/epoxy composites after atmospheric air plasma pretreatment and concluded that air plasmas could activate the epoxy and thus improve abrasion resistance by increasing the surface energy of the composite substrate.…”

High-Temperature Tribological Behavior of HDPE Composites Reinforced by Short Carbon Fiber under Water-Lubricated Conditions

“…However, different from hardness variation trends, the HDPE composites exhibit the maximum contact angle of 95.2 • when the content of SCFs is 20 wt %, which exhibits the hydrophobicity; the contact angle decreased to 93.5 while the content of SCFs continued increasing. The SCFs have a lower surface energy compared to the HDPE matrix and, thus, cause an increase in contact angle of HDPE composites [36]; nevertheless, the SCFs are prone to agglomeration when the concentration reaches 25 wt %, which might reduce the specific surface area of HDPE composites. As a result, the contact angle decreased.…”