Hindered phenolic antioxidants, as the most important free radical traps, convert peroxyl radicals into hydroperoxides, and the resulting phenoxy radicals continue to react with peroxyl radicals in different ways to form non-free radical products (as shown in the figure). However, phenoxy radicals can also be formed to snatch a hydrogen atom from the polymer and start a new oxidation cycle in this way. But most phenolic antioxidants are in 2,6-There are two tert-butyl groups that shield the phenoxy radicals formed (steric hindrance) and prevent the formation of new oxidation cycles, however the introduction of steric hindrance also leads to a decrease in the efficiency of free radical trapping. Decreasing steric hindrance can increase the activity of hindered phenolic antioxidants, but it can also increase the activity of phenoxy radicals, which can trigger a new oxidation cycle of polymers. The ratio between the rate of free radical capture and the rate of initiation of oxidation determines the efficiency of the antioxidant.
As can be seen from the above figure, each functional group can scavenge at least two (alkyloxy) radicals in the hindered phenolic antioxidant reaction, but the benzoquinone (chromogenic ) produced by the reaction is still reactive, and can undergo a variety of side reactions and develop color (diphenylquinone).
For acrylate-type phenolic antioxidants (e.g., 1010 1076 1098), benzoquinone can undergo a rearrangement reaction to reduce to a hindered phenolic structure, suggesting that this class of hindered phenol groups can be cleared at least4(alkoxy) radicals.
The benzoquinone series products formed after free removal by hindered phenolic antioxidants develop color (yellowing) and have relatively low yellowing for hindered phenolic antioxidants grafted with isocyanurate rings (e.g., 3114 1790) due to the fact that this structure can reduce the formation of diphenylquinones. In addition, the reaction of nitrogen oxide NOx in the air with it will also cause color change, the so-called gas-fading, and the reaction mechanism is as follows.
However, for special applications such as films and fibers, the phenol yellow problem is difficult to solve (semi-hindered phenols such as GA80 are slightly improved, but they will still be yellowed), but non-phenolic antioxidants (hydroxylamines, benzofurans) products can completely avoid the phenol yellow problem and capture free radicals to effectively protect heat aging.
Sarex Chemical's Grade 0 antioxidants are non-phenolic antioxidants
l Hydroxylamine SARANOX 021 and 042 effectively solve the problem of NOX gas yellowing, of which SARANOX 042 is benchmarked against BASF's IRGASTAB FS 042, which is widely used in upstream petrochemical plant polyolefin and irradiation-resistant yellowing modified products.
Product Recommendation - NOx Resistant RadiationResistantOptimal Color ProtectionAntioxidant SARANOX® 042 (FS 042).
l Benzofuranone SARANOX 036 056 066, which has high structural activity, can effectively capture carbon free radicals and protect polymer processing stability, and has a wide range of applications, including general plastics PP, PE, engineering plastics PA, PC, PET, etc., as well as polyurethane series products (TPU, PU Foam, CPU, etc.).