AbstractIn the present paper the influence of Flamestab® NORTM 116 (abbrev. FNOR), a sterically hindered N-alkoxyamine stabilizer, on the photo-oxidative stability of calcium carbonate reinforced polypropylene (abbrev. CCPP) used for production of plastic collars has been investigated. The samples, prepared by melt compounding, were exposed to artificial accelerated photo-ageing carried out at λ>300 nm and 45 °C in air. FT-IR and UV-VIS analysis revealed that the deterioration of neat CCPP takes place very rapidly in comparison with the composites containing FNOR. Hydroperoxides and various carbonyl species are formed as the main degradation products during the photo-oxidation process. Moreover, the intensity of the absorption bands grows with increasing of UV exposure time indicating that the material suffers a photo-oxidative degradation process. Indeed, addition of only 0.1 wt.-% FNOR did not significantly modify the length of the induction period of neat CCPP, but a strong efficiency was obtained by increasing the amount of FNOR (0.5 wt.-%) which shows an increase of eight times more as compared with neat CCPP. Therefore, it may be supposed that OIT is linked to the level of concentration of the stabilizer. This remarkable increase in composite stability demonstrated by a lengthening of OIT is typical for sterically hindered N-alkoxyamine stabilizers since they are very efficient at scavenging freeradicals formed as the polymer degrades. In other words, these UV stabilizers are converted to nitroxide radicals (see Scheme 1) which readily trap the polymer degradation species to produce alkoxyamines. Then, the formed alkoxyamines do subsequently react with peroxy radicals to regenerate the active nitroxide radical, thereby this process (called Denisov cycle) proceed in a regenerative cycle, thus retarding oxidative polymer degradation. The increase of absorbance in the carbonyl region as a function of irradiation time was used to determinate the photooxidation rate. It was found out that the photooxidation rate measured from the slope of linear part of the curves is significantly decreased for the CCPP/FNOR 0.5 composite compared to neat CCPP. In the light of the above mentioned findings, FNOR could be taken into consideration as an UV stabilizer for CCPP.
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