Interaction of Hindered Amine Light Stabilizers and Ultraviolet Absorbers

Abstract

The reason is discussed, why ultraviolet absorbers (UVA) having phenolic moiety show the synergism with HALS apparently, on the contrarily to phenolic antioxidants. A HALS nitrosonium is a substrate causing the useless oxidation of a phenol, and is formed from HALS more easily in the presence of a phenol. However, 2-hydroxybenzophenone (2-HBP) did not accelerate the formation of the nitrosonium so fast as 3,5-di-t-butyl-4-hydroxytoluene (BHT). A HALS nitrosonium, even if formed, did not oxidize 2-HBP so much as BHT. That is, 2-HBP can continue to work longer and more effi ciently in the presence of HALS. This fact suggests a weak antagonism of 2-HBP and a strong antagonism of BHT with HALS. On the other hand, quinones, derived from 2-HBP and BHT as result of peroxy radical-catching, were reduced to the corresponding hydroquinones by the action of HALS derivatives, such as HALS hydroxylamine. This reaction occurs strikingly faster and more easily for 2-HBP than for BHT. This fact shows a strong synergism of 2-HBP and a weak synergism of BHT with HALS. The above-mentioned results well explain the apparent synergism of UVA (2-HBP) with HALS, contrarily to the apparent antagonism of BHT with HALS.

Synergism between Hydrogen Bond-type Ultraviolet Absorbers and Hindered Amine Light Stabilizers

“…Bond-type UVA with HALS As described previously 5) , the antagonism of HALS with hydrogen bond-type UVA is directly related to HALS nitrosonium, the formation of which is promoted by a proton-donation of UVA, and which takes part in both a homolytic decomposition of hydroperoxides and a useless consumption of UVA.…”

“…functions of UVA and HALS based on the photoSuch interactions should be investigated from at least antioxidant ability, which is assessed by comparing the three approaches 5) . The first approach is to examine the antioxidant ability of a combination of HALS and UVA functions of HALS in the presence of UVA.…”

Search for Unified Action Mechanism of Hindered Amine Light Stabilizers

“…If such an interaction is evaluated semi-quantitatively by the kinetic approach, for instance, a benzophenone UVA promotes homolytic CHP decomposition by HALS, although the promotion degree is much lower than that of BHT. HALS nitrosonium forms in the presence of benzophenone similarly to BHT, but does not oxidize the benzophenone as much as BHT 42) . In addition, even if HALS nitrosonium oxidizes benzophenone to 2-benzoyl-p-quinone, this is promptly reduced to a new UVA by HALS NOH.…”

Analytical Methods in Uv Degradation and Stabilization Studies

“…40,41 NMR was instrumental in studies of interaction of UVA, antioxidant, and HAS. 42 The results helped in assessment of synergetic and antagonistic interactions of stabilizers. 42 In another study, NMR was used to understand the interaction between UVA and UVB filters in sunscreens.…”