Antioxidants blooming

Solubility. Another desirable property of a degradant is its high solubihty in mbber but poor solubihty in water and solvents that come in contact with mbber. Poor solubihty in the mbber means that only small quantities of antioxidants can be dissolved without producing a bloom. As an example, N,lSf-diphenyl- phenylenediamine (DPPD) has limited use because of its poor solubihty in mbber. On the other hand, phenohc and phosphite antioxidants have high solubihty and bloom is not a problem. 

Paraphenylene-diamine derivatives A/,N -Diphenyl-p-phenylenediamine (IV) /V,A/ -Di-p-naphthyl-p-phenylenediamine (V) Yes Yes Powerful antioxidants. Have been used in a variety of plastics materials. Tendency to bloom, bleed and stain mitigates against more extensive use. Compound (V) now withdrawn by some suppliers. 

Dithiocarbamates are polar in nature and thus will have a tendency to bloom when used in nonpolar rubbers. The worst bloom problems will be encountered with the dimethyl derivatives higher alkyl chain types have better solubility in non-polar rubbers. Some dithiocarbamates also confer antioxidant protection. 

Bisphenol derivatives show very good antioxidant activity and are the best materials for light coloured articles. Selected materials are FDA approved. These derivatives have low volatility and no effect on cure rate and do not give a bloom. A slight pink discoloration can occur after prolonged exposure to light in white or light coloured products. 

Diaryl-phenylenediamines have very good antioxidant activity with good to moderate antiozonant characteristics, with low volatility but will possibly bloom to the rubber surface. They give very good flex cracking resistance. 

Light. Ultraviolet (uv) light promotes free-radical oxidation at the mbber surface which produces discoloration and a brittle film of oxidized mbber (35). This skin cracks in random directions to form a pattern called crazing, which can be prevented by the addition of carbon black fillers or uv stabilizers. Black stocks are more resistant to uv light than are gum or light-colored stocks. Nonblack compounds require larger quantities of nonstaining antioxidants which should bloom to the surface as the surface uv stabilizers deplete. 

The most important chain transfer antioxidants are phenols and aromatic amines (B-81MI11502). They act by donating hydrogen to the peroxy radical with the formation of a stable free radical which does not take part in further chain reactions (equation 4). Two amine antioxidants, used in the rubber industry, are 6-dodecyl-l,2-dihydro-2,2,4-trimethylquinoline (1) and polymeric l,2-dihydro-2,2,4-trimethylquinoline (2). Because of its polymeric structure (2) is thermally stable, has low volatility and is non-blooming, i.e. it shows little tendency to migrate. 

This property can be improved by the addition of antioxidants. Higher zinc oxide loadings increase resistance to heat ageing. Paraffin wax offers surface protection by blooming to the surface during curing. Low sulphur or sulphurless cure improves heat ageing considerably. 

Bloom D, Dhakshinamoorthy S, Jaiswal AK. 2002. Site-directed mutagenesis of cysteine to serine in the DNA binding region of Nrf2 decreases its capacity to upregulate antioxidant response element-mediated expression and antioxidant induction of NAD(P)H quinone oxidoreductasel gene. Oncogene 21 2191-2200. 

MMBI is a rubber antioxidant that, in synergy with amine or phenolic antioxidants, protects against oxygen, heat, and metals (especially in thiuram and dithiocarbamate vulcanizates) at the cost of a retarding effect in the vulcanization process and the reduction of modulus. It also confers steam resistance to rubber compounds and has a brightening effect on transparent materials. It is non-staining/coloring and does not bloom. 

Bloom, D.A. and A.K. Jaiswal. Phosphorylation of Nrf2S40 by PKC in response to antioxidants leads to the release of Nrf2 from INrf2 but not required for Nrf2 stabilization/accumulation in the nucleus and transcriptional activation of ARE-mediated NQOl gene expression. J. Biol. Chem. 278 44675-44682, 2003. 

These are added to reduce the ageing effects of the rubber and include paraffin wax added to form a protective bloom and antioxidants such as phenolic compounds. These protecting agents are required for natural rubber and are not necessary for modem synthetic rubber formulations. 

Both yellowing and embrittlement of polypropylene are dose dependent but are significant at or around 25 kGy (the customary compendial dose for sterilizing medical devices). The extent of radiation-induced discoloration can be relieved by use of phosphite stabilizers. Stability against embrittlement may be improved by adding antioxidants, but these may in turn create problems such as surface blooms. ... 

A study of physiological effects in the green-lipped mussel (Perna viridis) to exposure to blooms of Nodularis spumigena reveals a complicated picture (Davies et al., 2005). As the bloom density increased and post-bloom lysis occurred, the activity of antioxidative, detoxification enzymes changed in opposite directions, and different organs of the mussel appear to come under toxic stress. 

Dhakshinamoorthy, S., Jain, A.K., Bloom, D.A., and Jaiswal, A.K. 2005. Bachl competes with Nrf2 leading to negative regulation of the antioxidant response element (ARE)-mediated NAD(P)H quinone oxidoreductase 1 gene expression and indnction in response to antioxidants.280, 16891-16900. 

Antioxidants need to be permanent. In the rubber industry, the problem of antioxidant loss by various mechanisms such as volatility and blooming has been coimtered by encapsulation in silica. The use of antioxidants in water pipes and other pipework raises the possibility of antioxidant loss by extraction or hydrolysis. Many pipes have a design lifetime of between 25 and 50 years, but their actual lifetime depends on antioxidant permanence. Underfloor heating and solar-powered hot water systems raise the temperature. 

Crompton has secured a number of additional stabiliser and antioxidant product lines through its recent deal with GE Specialty Chemicals, including Genox , Weston and Ultranox . Crompton s Naugard 900 antioxidant is claimed to be resistant to blooming. 

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