Highly durable hydrophobic thin films for moisture prevention of composite structures for aerospace applications

Abstract

Advanced polymeric composites are widely used in aerospace industry because of the high strength-to-weight ratio, manufacturability and other distinctive advantages. These polymeric composites are usually subjected to wide ranges of environmental conditions where they can absorb a significant amount of moisture or solvents from the environment and reduce their mechanical, thermal, and other physical properties and service times. In the present work, four different hydrophobic thin barrier films were co-bonded to the surfaces of composite structures to investigate mechanical properties, moisture prevention and absorption characteristics, and other physical behaviors of these materials. These hydrophobic films include polyvinyl fluoride (PVF), polyether ether ketones (12.5 mμ and 25 mμ), polyimide, and polytetrafluoroethylene. Eight different tests were conducted on the coupons for comparison and evaluation purposes, which consisted of short beam shear, sandwich flexure, compression, paint tape test, moisture absorption and ingression, UV light and water contact angle, shrinkage, and bonding. In addition to these tests, finite element analysis (FEA) modeling was used to predict the stiffness of the conditioned coupons. Conditioning performed by fully immersing coupons in water at 22 ±2°C for 14 and 29 days, and in Skydrol for 7 days prior to the testings. The duration of the water exposure was determined based on the equilibrium time of the coupons which had no barrier film. The test results confirmed that using the barrier films as the outermost ply on the composite significantly increased the mechanical and physical properties of the composite coupons, which will be a drastic improvement for aerospace applications. Finally, the FEA model was developed to predict the mechanical behavior of the composites associated with barrier films. The test results of the FEA are closely related to the experimental results.