The Effect of Low Earth Orbit Atomic Oxygen Exposure on Phenylphosphine Oxide-Containing Polymers

Abstract

Thin films of phenylphosphine oxide-containing polymers were exposed to low Earth orbit aboard a space shuttle flight (STS-85) as part of flight experiment designated Evaluation of Space Environment and Effects on Materials (ESEM). This flight experiment was a cooperative effort between the NASA Langley Research Center (LaRC) and the National Space Development Agency of Japan (NASDA). The thin film samples described herein were part of an atomic oxygen exposure experiment (AOE) and were exposed to primarily atomic oxygen (~1 X 10 19 atoms/cm 2 ). The thin film samples consisted of three phosphine oxide containing polymers (arylene ether, benzimidazole and imide). Based on post-flight analyses using atomic force microscopy, X-ray photoelectron spectroscopy, and weight loss data, it was found that atomic oxygen exposure of these materials efficiently produces a phosphate layer at the surface of the samples. This layer provides a barrier towards further attack by AO. Consequently, these materials do not exhibit linear erosion rates which is in contrast with most organic polymers. Qualitatively, the results obtained from these analyses compare favorably with those obtained from samples exposed to atomic oxygen and or oxygen plasma in ground based exposure experiments. The results of the low Earth orbit atomic oxygen exposure on these materials will be compared with those of ground based exposure to AO.

Effect of LEO Exposure on Aromatic Polymers Containing Phenylphosphine Oxide Groups

“…Both films exhibited sufficient toughness such that they could be creased without visible damage, cracking, or fracture. In comparing these visual results with those from previous flight experiments [5,7,8], the previous samples were not visibly frosted and remained transparent, however the AO fluence was only in the range of 1-7 x 10 19 atoms/cm 2 . Figure 3.…”

“…In the second stage AO erosion is significantly lessened due to the reduced reactivity between the polyphosphate layer and AO. Evidence for this comes from the erosion rate, XPS, 31 P nuclear magnetic resonance (NMR) spectroscopy, and X-ray adsorption near edge spectroscopy (XANES) analyses [2][3][4][5][6][7][8]32]. …”

“…Thus it seems more valid to compare the results of this MISSE experiment with other space flight exposure experiments. In prior space flight exposure experiments involving aromatic polymers containing phenylphosphine oxide groups the samples were exposed to AO fluences of 7 x 10 19 atoms/cm 2 [5,7] and 1 x 10 19 atoms/cm 2 [8]. Based on these results, it was determined that aromatic polymers containing phenylphosphine oxide groups had a reaction efficiency of about 15 times less than that of Kapton ® HN.…”

Data on Specific Polymers

“…Aromatic polyimides [567][568][569][570][571][572][573][574][575][576][577][578][579][580][581][582][583][584][585][586] have attracted considerable interest due to their excellent mechanical properties, thermal and oxidative stability, and chemical resistance. Several groups of materials are involved:…”

“…Studies conducted aboard of space shuttle produced similar results. 580 Surface erosion is generally a nonlinear process.…”