Simulated Low Earth Orbit Environment Interaction with Different Types of Polyethylene

The present study investigated the interactions of four different types of polyethylene (PE) surfaces with RF oxygen plasma components, simulating the low Earth orbit (LEO) environment. The samples were exposed in the plasma afterglow, with and without the plasma-generated vacuum UV (VUV) radiation. The polymers studied were low-density polyethylene (LDPE), ultra high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), and a composite of highly-oriented fibres of ultra-high molecular weight polyethylene (PolyEitan) having crystalline-to-amorphous phases ratio of 65, 74, 87 and 92%, respectively. Erosion of the LDPE, UHMWPE, and HDPE samples under atomic oxygen (AO) irradiation showed an etching rate dependence on the degree of crystallinity - the higher the crystallinity level the lower the erosion rate. The addition of VUV radiation to the AO flux resulted in a significant increase of the etching rate. An increase of the crystallinity level resulted in a decrease of the total oxygen uptake and an increase of the surface roughness. The composite polyethylene, although highly crystalline, revealed similar erosion rate and chemical composition changes as highly amorphous LDPE. The erosion mechanism of the different PE samples under AO or AO+VUV is discussed in terms of the initial internal structure.