Abstract
Atomic oxygen (AO) in low earth orbit environment causes significant physical sputtering and/or chemical changes in most materials particularly in polymeric systems. In this review, five major techniques utilized to date to protect AO attacks in polymeric substances have been described. Surface coatings, compounding, compositing, use of novel homopolymers or copolymers, and polymer blending are discussed. AO protection by surface coatings is predominantly used in current space industry due to its ease of fabrication with minor modification to the existing polymers. Durability and uniformity of the coating surface as well as substantial adhesion between the core and the coating skin are critical for the success or failure of this technique. The modifications of polymeric systems by compounding or compositing yield marginal improvement in AO protection depending mainly upon types of fillers used whereas the syntheses of novel AO resistant polymers based on stable atoms such as fluorine, silicon, or phosphorus are actively pursued and proposed with some reported commercial success. In addition, AOR Kapton manufactured by DuPont is one example of utilizing miscible polymer blend systems for AO protection in polymers. The utilization of phase-separated polymer blends to yield protective skin layers which are Si-rich or P-rich may render another prospective way for AO protection in extensively space-utilized polyimide systems. By controlling the discrepancy in the blend-pair affinity, layered phase separation may be induced. Overall properties of core polyimide are expected to remain unchanged due to the relatively low quantity of the skin layer material used i.e. in the range of few percent by weight.
