Weatherability of polypropylene monofilaments. Effects of fiber production conditions

From a comparison of the photo-and γ-irradiation-initiated oxidations of monofilaments and films, polypropylene oxidation rates and product ratios were found to be independent of sample morphology and orientation. Filament sensitivity to photo-oxidation was, however, drastically affected by extrusion and draw conditions, photosensitivity increasing with increasing draw speed and decreasing draw temperature. Draw effects were minimized by the exclusion of oxygen, indicating that free radicals produced by backbone cleavage during draw react with oxygen to give chromophoric oxidation products. The most important product detectable after drawing was probably the polypropylene hydroperoxide. A phenolic antioxidant reduced hydroperoxide formation, although sufficient hydroperoxide was still produced to accelerate photodegradation as compared with a similarly stabilized undrawn filament. Melt oxidation within the extruder was concluded to be much more important than thermal oxidation of the extruded filament as it cooled on the spinline