Thermal synergism

Synergism can also arise from cooperative effects between mechanistically different classes of antioxidants, e.g., the chain breaking antioxidants and peroxide decomposers (heterosynergism) [42]. For example, the synergism between hindered phenols (CB—D) and phosphites or sulphides (PD) is particularly important in thermal oxidation (Table 2). Similarly, effective synergism is achieved between metal dithiolates (PD) and UV-ab-sorbers (e.g., UV 531), as well as between HALS and UV-absorbers, (Table 3). 

Modesti, M. Lorenzetti, A. Besco, S. Hrelja, D. Semenzato, S. Bertani, R. Michelin, R.A.. Synergism between flame retardant and modified layered silicate on thermal stability and fire behaviour of polyurethane nanocomposite foams. Polym. Degrad. Stab. 2008, 93, 2166-2171. 

C. Breen, M. Last Philip, S. Taylor and P. Komadel, Synergic chemical analysis - the coupling of TG with FTIR, MS and GC-MS 2. Catalytic transformation of the gases evolved during the thermal decomposition of HDPE using acid-activated clays, Thermochimica Acta, 363, 93-104 (2000). 

All antioxidants have points of strengths and weaknesses. Therefore, certain points, such as thermal stability, effective concentration, and synergism, should be taken into consideration when selecting antioxidants for use in particular foods. Regulatory status is another factor that cannot be ignored, especially for some antioxidants that have been reported to show potential adverse health effects. Synthetic antioxidants have been tested for safety and approval for use in food at low concentrations on the basis of complex toxicity studies (10). Allowable limits for use of antioxidants vary greatly from country to country, and depend on the food product under consideration (11). 

HALS exhibit a complex behavior when present in combination with other antioxidants and stabilizers. Effective synergism in both melt and thermal stabilization has been achieved when secondary and tertiary HALS were used in combination with both aromatic and aliphatic phosphites the synergistic optimum depends on the structure of the phosphite. HALS also synergize the action of UV-absorbers, e.g., benzo-triazoles, in different polymers such as polypropylene, polystyrene, and ABS. " ... 

Removal of the latter in the cyclic regeneration mechanism of piperidine stabilisers by reaction with hindered phenol radical intermediates is also believed to be important in antagonism. During thermal oxidation the interactions were more favourable and synergism prevailed due here to the complementary behaviour of nitroxyl free radicals and antioxidant radicals in free radical scavenging processes. 

Cannabinoids induce a site-specific topical antinociception to thermal stimulation (Dogrul et al. 2003 Johanek and Simone 2004 Ko and Woods 1999 Yesilyurt et al. 2003). This local antinociceptive effect synergizes with spinal cannabinoid antinociception, as reflected by a 15-fold leftward shift in the dose-response curve (Dogrul et al. 2003), and also synergizes with topical morphine antinociception (Yesilyurt et al. 2003). The latter effects were blocked by a CBIR antagonist (Yesilyurt et al. 2003). 

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