Hindered amine stabilizers aging

ESR Spectra of Nitroxides Derived from Hindered Amine Stabilizers in Aged... 

Lucarini and co-workers have determined the distribution of the nitroxide radicals in UV-irradiated PP containing a hindered amine stabilizer by one-dimensional (ID) ESRI. The spatial variation of nitroxide intensity in the thicker samples irradiated for longer times was explained by the diflnsion-limited oxidation (DLO) concept. The DLO regime and high oxidation rates lead to narrow penetration depth of oxygen. Recently, Marek et al. ° reported ID ESRI experiments on polystyrene and polypropylene plaques exposed to thermal aging and UV irradiation. 

ESR SPECTRA OF NITROXIDES DERIVED FROM HINDERED AMINE STABILIZERS IN AGED HETEROPHASIC POLYMERS... 

Haillant, O., Lemaire, J. Natural and artificial photo-aging of non-stabilized and pigmented, hindered-amine stabilized propylene-ethylene copolymers. Polym. Degrad. Stab. 91, 2748-2760 (2006)... 

In the past few decades, piperidine-based sterically hindered amine stabilizers (HA(L)S) gained attention as heat stabilizers for polyolefins at low and moderate temperatures below about 120 °C. It was ascertained that the degradation behavior of polymers, particularly of polyolefins stabilized with HA(L)S, differs significantly from that of phenol-stabilized polyolefins at aging temperatures ranging from T = 100 to 150 °C. 

Not all antioxidants respond to the OIT test in most cases the phenolic antioxidant concentration can be monitored by measuring the OIT, whereas phosphite antioxidants and hindered amine light stabilizers (HALS) in particular display little response. Because of this, the OIT test is a poor tool for polymer service life predictions as there is no real correlation between the OIT test results and the product s performance in the field. Additional test data such as heat oven aging are often required to supplement the OIT data in order to improve the accuracy of predicting long-term product performance. 

Light stabilizers based on sterically hindered amines do not act as radical interceptors at test temperatures of approx. 200 °C. However, in oven aging experiments, typically at 100°C, they contribute significantly to long-term stability. 

Stabilizers. Stabilizers are often added to slow down the rate of oxidation and uv aging. Heat stabilizers can be organic antioxidants (such as hindered phenols or aromatic amines), hydroperoxide decomposers, or metal salts. The latter are most commonly used in the form of copper halide mixtures. This system, which has the side effect of discoloring the nylon, acts as a regenerative free-radical suppressor. Above about 120°C, the copper halide system is by far the most effective... 

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