Protection of polymers

Protection of polymers against thermal and photo-oxidative degradation is achieved with appropriate stabilizers that ensure the desirable polymer properties throughout the entire service life of the polymer. Compatible and polymeric stabilizers usually give the best protection. In order to avoid migration and evaporation, polymeric stabilizers are used. 

Polymer-bound antioxidants must be molecularly dispersed (i.e. infinitely soluble) and cannot be physically lost from the substrate. High-MW phenolic AOs are preferred for applications requiring FDA approval, minimal discoloration, and long service life at high temperatures. Antioxidants are used for protection of polymers, plastics, elastomers, foods, fuels and lubricants. 

Besides these "physical aspects" of the light protection of polymers there are some hints that UV-stabilizers of the o-hydroxyphenyl-benzotriazole type are able to scavenge radicals ("chemical aspects") the production of which could not be suppressed completely by the methods described in this paper (23). 

H.J. Heller and H.R. Blathmann, Some aspects of light protection of polymers . Pure A Appl. Chem., 30, 1972, 145. 

Dioxathiolane. Y-oxidc, benzo-l,3,2-dioxathiolene. Y-oxidc, and other cyclic sulfites have been studied as secondary antioxidants <1997MI209>. They decompose hydroperoxides in a nonradical way at a faster rate than phosphites, and may be used for the protection of polymers against aging. 

Le Bras M, Bourbigot S, Siat C, Delobel R. Comprehensive study of protection of polymers by intumescence—application to ethylene vinyl acetat copolymer formulations. In Fire Retardancy of Polymers The Use of Intumescence. Le Bras M, Camino G, Bourbigot S, Delobel R, Eds. The Royal Chemical Society Cambridge, U.K., 1998 pp. 266-279. 

Some polymers show discoloration as well as reduction of the mechanical properties (e.g. aromatic polyesters, aromatic polyamides, polycarbonate, polyurethanes, poly (phenylene oxide, polysulphone), others show only a deterioration of the mechanical properties (polypropylene, cotton) or mainly yellowing (wool, poly(vinyl chloride)). This degradation may be less pronounced when an ultraviolet absorber is incorporated into the polymer. The role of the UV-absorbers (usually o-hydroxybenzophenones or o-hydroxyphenylbenzotriazoles) is to absorb the radiation in the 300-400 nm region and dissipate the energy in a manner harmless to the material to be protected. UV-protection of polymers can be well achieved by the use of additives (e.g. nickel chelates) that, by a transfer of excitation energy, are capable of quenching electronically excited states of impurities (e.g. carbonyl groups) present in the polymer (e.g. polypropylene). 

Y. Gudimenko, Z. Iskanderova, J. Kleiman, G. Cool, D. Morison and R. Tennyson, Erosion Protection of Polymer Materials in Spaice, 7th International Symposium on Materials in a Space Environment, held in Tolouse, France, 16-20 June 1997, ESA Special Publication 399, Ed. T. D. Guyenne (European Space Agency, Paris, Prance, 1997) pp. 403-410. 

As a conclusion, if it is possible to foresee if a compound can be a protective agent, only experimentation allows to know what polymers it can protect. Furthermore a compound can have opposite effects on two polymers, even if they have similar absorption properties. Protection of polymers is the result of several factors, at least in the case of orthohydroxylated benzophenones the screening effect is less important than compatibility and quenching effect. 

Another important field of the application of nitroxyl radicals and their precursors, hindered amines, is the protection of polymers and other organic compounds against the factors causing their thermo- and photo-destruction. In the present work, an attempt has been made to describe briefly the main achievements in this field. 

The protection of polymers against high doses (20 - 1000 kGy) requires efficient additives preventing and/or stopping chain reaction type oxidative degradation. Primary and secondary antioxidants work well here in synergy. Commercial raw materials are available for radiation-sterilizable medical devices made out of polyolefins and other thermoplastics. Similarly, polymer compounds of suitable formulae are offered commercially for high-dose applications of polymers in nuclear installations. 

H.J. Heller, Protection of polymers against light irradiation, Eur. Polym. J. Suppl. 1969, 105-132. 

To obtain an integral protection of polymers, HAS is also combined with other stabilizers, aromatic phosphites in particular [129], Blends HAS/phosphite impart excellent light and heat stability to PO, polyamides, PC or PVC [13,129], Multicomponent blends HAS/phenol/phosphite, combined moreover with UVA or FR were proposed for protection of PUR, PO or PC [268,269]. A complementary mechanism should be accepted for the combinations. 

Typical representatives of primary antioxidants are secondary aromatic amines and sterically hindered phenols both classes are widely used in the protection of polymers (Figs. 11.5 and 11.6). Aromatic amines act as H donors by forming aminyl radicals, followed by coupling reactions and/or nitroxide formation and further coupling reactions. 

Preservatives based on BIT may be used for the in-tank/in-can protection of polymer emulsions, latex paints, pigment and filler slurries, paper coatings, adhesives and other aqueous functional fluids. Because of the heat stability and non-volatility of BIT the preservatives can be incorporated in fluids which are still hot. BIT exhibits no headspace activity. It is compatible with non-ionic and anionic compounds and active in acid and alkaline media. 

Examples of appropriate microbicides for the in-tank protection of polymer emulsions are ... 

The blacks used for UV protection of polymers have very small primary particle sizes. The industry standard for UV protection is primary particle sizes of less than 20 nm. 

Biocides used for the protection of polymer dispersions have changed, as the user industry has demanded improved properties. For example, heavy metal based biocides such as those containing mercury have now... 

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