Antioxidants AO Processing Stabilizers

Ciba Specialty Chemicals Additives for Polyolefins Antioxidants (AO) Processing Stabilizers  

High molecular weight, phenolic AO with low volatility extends 

Phenolic AO for cross-linked or carbon black containing systems i.e. cable compounds) 

Highly compatible, low-color phenolic AO for PE available in preferred product forms. 

High performance, highly compatible AO for cross-linked PE i.e. high voltage power cable) 

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Classical antioxidants (AOs) like hindered phenols, Scheme 2, retard this transition metal promoted autoxidation process somewhat but give a very insufficient stabilization of powders or thin layers. However, by copolymerization with the so called "build-in" AOs, i.e. hindered phenols bearing 2-norbornene units like Ml - MS, the polymer stability could be improved. In addition, such compounds are very interesting AO s for the stabilization of other plastic substrates and rubbers [9]. AOs containing 2-norbornene units were also homo- and copolymerized to obtain polymeric stabilizers for plastics [10]. 

The use of phenolic and amino-based antioxidants (ie, thermal stabilizers) by this approach has been limited because they inhibit the free-radical polymerization process (polymerization inhibitor) leading to lower efficiency. One of the few commercial products produced is based on the polymerizable chain breaking antioxidant (AO 12b, Table 3), designed for NBR rubbers (Chemigum HR 665) that has been shown to offer superior antioxidant performance, especially imder aggressive (hot oil/high temperature) conditions, compared to low molecular mass conventional aromatic amine antioxidants (165). In spite of the successful synthesis and copoljmierization of a large number of reactive antioxidants, there is a lack of major commercial development and production of antioxidant systems... 

First, the granular resin was compounded into pellets along with commonly used stabilizing antioxidant (AO) additives. The pellets thus made were then used for the granular-pellet mixture experiments under the same process conditions used during the granular conversion step. The experiments were run in the order shown in Table 1. 

Transformation products of 16b contribute to some extent to the antioxidant effect. The dimer 103 is a weak AO in squalene [106] and in fish oil [98], The nitroxide 108 stabilizes fish oil, if present at a relatively high concentration (0.1%) [105], Its effect is not significant at lower concentrations. QI 105 was a weak retarder in oxidized fish oil [98] and decane [103]. It may be anticipated that other QI arising from 16 contribute similarly to the stabilization effect. A transient formation of the respective hydroxylamines is theoretically possible after hydrogen abstraction from a donor by 108 according to Eq. (8) or after thermolysis of the respective O-alkylhydroxylamine (an analogy to the process shown in Scheme 7). Their contribution to the stabilization effect is certainly not important, as revealed by a model study with NOH derived from 16b. It is very unstable and disproportionates to the parent 16b and nitroxide 108 [5,101]. 

The similarity between the CB AO mechanism of phenols and HAS was reported at 25 °C in radiation oxidation of 2,4-dimethylpentane performed in the dark [207]. It was concluded that the respective NOH formed from 28, R = H during the stabilization process was the species responsible for the antioxidant effect (Scheme 27). The NOH is considered to be formed via trapping H by lltNO . The authors declared that i NOR are not involved in the stabilization of the radiation-oxidation of hydrocarbons and have doubts about the importance of the involvement of NOR in the regenerative cycle in an oxygen containing environment. 

Recent developments in the field of AOs include improvements in effectiveness at higher temperatures, lower levels of volatility and extractability as well as improved handling and processing. The newer AOs are higher molecular and contain additional multifunctional groups that enhance the synergetic effect (antioxidants see also under stabilizers). 

Uses Color and m.w. stabilizer, antioxidant, melt flow aid for polymer processing (polyolefins, polyesters, elastomers, styrenics, engineering thermoplastics), adhesives, coatings antioxidant, UV stabilizer for polyolefins, food-grade polymers Regulatory FDA 21CFR 178.2010 Manuf./Distrib. Aldrich http //www.sigma-aidrich.com, GE Spec. http //www.ge.com/speciaitychemicais Trade Name Synonyms AO-2 f[Ciba Spec. Chems./Plastic Addit. http //www.cibasc.com]-, Doverphos S-680 [Dover http //www.doverchem.com]-, Doverphos S-686, S-687 t[Dover... 

The major transformations of phenolic antioxidants during melt processing, with both types of para-substitents (methyl and propionate types), consist of quinone-type products, C—C and C—O coupling product. Transformation products of antioxidants can greatly influence the extent of stabilization imparted to the polymer. Transformation products can exert anti- or pro-oxidant effects, hence synergizing or antagonizing the action of the parent antioxidant. For example, the formation of peroxydienones (PxD) (see Scheme 15, reaction b) from BHT (AO 1, Table 3) leads to pro-oxidant effects, whereas the C—C coupling products (DB) (eg Scheme 15, reaction c) and quinonoid products (SQ) (eg. Scheme 15, reactions d and f) exert antioxidant effects. 

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