Sub-micron scale mechanical properties of polypropylene fibers exposed to ultraviolet and thermal degradation

Nanoindentation studies using atomic force microscopy (AFM) was conducted to investigate the effect of accelerated ultra violet (UV) and thermal degradation on mechanical properties of Polypropylene textile fibers. The Polypropylene fibers with initial stabilizers were exposed to UV degradation using Q-UV Panel Weatherometer. The effect of degradation on gradation of Young’s modulus values across fiber cross-section was investigated by doing progressive nanoindentation from the surface to the center of the fiber. It was identified that UV degradation initially increases the Young’s modulus values from center to surface of the fibers till 120 hours of exposure and the values show decreasing trend at 144 hours of exposure. The Youngs modulus values at 144 hours exposure are less than those of unexposed fibers. To investigate thermal degradation effect on Polypropylene fibers, the fibers were exposed to 125oC as a function of number of weeks in increments of one week for four weeks. Results indicate that the thermal exposure did not have much impact on variation of Young’s modulus values for the first three weeks and showed increase in Young’s modulus values at the surface when they are exposed to four weeks. The increase in Young’s modulus values of Polypropylene fibers exposed to UV will be correlated with oxidation chemistry and micro-structural changes using Wide Angle X-ray spectroscopy and infra red spectroscopy techniques.