Effect of H2O and H2O2 on the Mechanical Properties and Microstructure of Selected Natural and Synthetic Polymer Structures

Abstract

Modern transportation systems may be subjected to unintentional contamination from infected passengers as well as deliberate contamination from terrorism. Hydrogen peroxide has been used for years as a disinfectant in the medical community and is under consideration in the dilute vapor form as a decontaminant/disinfectant/sterilant for transportation vehicles like aircraft, buses, subway trains, ambulances, etc. Although the biological efficacy of STERIS Corporation’s Vaporized Hydrogen Peroxide (VHP®) technology has been demonstrated elsewhere, the compatibility of the process with typical aircraft materials has not been rigorously established. The present thesis documents a two-part investigation involving (i) a materials compatibility evaluation involving the effects of moisture and hydrogen peroxide exposures on the physical, mechanical and chemical properties of synthetic and natural airliner cabin polymeric fabric materials and (ii) a detailed investigation of the effects of moisture on the relatively unstudied north American porcupine quill – a natural keratin material. Physical changes induced by the sorption of moisture had an effect on the mechanical properties of all of the fabric materials (synthetic and natural) examined. However, only hydrogen peroxide chemically attacked the natural, keratin-based wool fabric and this had (along with moisture sorption) a significant deleterious effect on the mechanical properties of wool. To more fully understand the relationship between mechanical behavior and moisture sorption of keratin materials, a less-studied but larger keratin-based material was used for additional detailed investigation. Porcupine quills belong to one of the alpha-keratin families and their macrostructure is composed of a cylindrical outer shell with a reinforcing inner foam core. As expected, increasing the water content decreased the tensile stiffness and strength and increased the ductility of the porcupine quills. The shell of the porcupine quill, in contrast to the inner foam structure, carried the majority of the axial tensile loads. In addition, the quill shells’ axial tensile properties and resistance to nanoindentation were generally higher than similar mechanical properties measured in the circumferential direction of the shells due to the axial orientation of the keratin fibers. Infrared spectroscopy of quill shells showed that the content of α-type keratin decreased while β-type keratin increased as the strain increased to 15% - consistent with literature results for wool fibers. Scanning electron microscopy of the fracture surfaces of porcupine quill shells reveal 2 - 3 distinct layers with different fracture characteristics in the shells. The outer layer of the porcupine shell appears to resist the plasticizing effects of moisture, due to the presence of hydrophobic lipids in the outer layer.