THE ANALYSIS OF WEATHERING TESTS ON INDUSTRIAL HELMETS MOLDED FROM COLORED POLYETHYLENE

The effects of accelerated weathering and outdoor exposure on polyethy lene shells of industrial helmets are compared. Outdoor levels of WB a nd the surface temperature of the plastic were measured as a function of time. The molecular weight profile through the thickness of helmet shells differed for outdoor and accelerated tests. The attenuation of the radiation by the HDPE was measured and used in a computer model to predict the molecular weight profile in the polymer as a function of the UVB exposure. Accelerated exposure depletes the oxygen concentrati on to zero for depths greater than 0.5 mm from the surface, while the slower outdoor photo-oxidation continues deep into the plastic. Fading of the red organic colorant played a major part in allowing the penet ration of the UVB. The outdoor weathered shells are more likely to sha tter in an impact than those subjected to accelerated tests. The draft European standard for industrial safety helmets includes an accelerat ed UV exposure before impact testing, and the validity of such acceler ated tests is discussed.