Photo-oxidation of Polypropylene Fibers Exposed to Short Wavelength UV Radiations

Polypropylene fibers were exposed to short wavelength radiations (lambda=253.7 nm). The samples were analyzed by microscopy, staining, FTIR spectroscopy, tensile testing, and X-ray diffraction. The short-wavelength UV irradiation produces much more reactive radicals such as peroxy and alkoxy groups, which speeds up the photo-oxidation process. The products were identified by FTIR spectroscopy to be alcohols, peroxides, ketones, aldehydes, carboxylic acids, and anhydrides. Comparison of the amount of functional groups leads to an estimation of the mechanism of photo-oxidation. The short-range order increases during the photo-oxidation and the long-range order or crystalline fraction remains intact. Transverse cracks appeared on the surface of fibers after a long period of exposure to the radiation. A proposed mechanism for crack formation is the removal of the photo-oxidation products and the restructuring of the residuals. Similar to the thermal oxidation, mass loss and density increase are the main reasons for the crack formation in photo-oxidation.