UV-light Stabilizers

The second type of UV stabilizer is hindered amine light stabilizers (HALS) that are an extremely efficient stabilizer against the photodegradation process. They are compounds that do not absorb UV radiation, but act to inhibit degradation. Relatively high levels of stabilization are achieved with relatively low levels of concentration because the HALS are not consumed during the stabilization process (unlike primary and secondary antioxidants). 

The addition of inorganic compounds to polyethylene is carried out for a variety of reasons. Fillers are sometimes only low-cost particulate materials used to extend the polyethylene and, therefore, lower the cost of the fabricated item. However, fillers usually affect some other aspect of the finished product such as the stiffness (modulus) or the processability of the polyethylene to increase rates of fabrication. Fillers may also reduce mold shrinkage and the thermal expansion coefficient Filler such as mica may increase heat resistance. Some examples of these compounds are discussed below. 

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Uv-curable polymers Uv devices Uvilon Uvithane 893 Uv light stabilizers... 

Diazo Coupling Reactions. Alkylphenols undergo a coupling reaction with dia2onium salts which is the basis for the preparation of a class of uv light stabilizers for polymers. The interaction of orxv i -nitrobenzenediazonium chloride with 2,4-di-/ r2 -butylphenol results in an azo-coupled product (30). Reduction of the nitro group followed by m situ cyclization affords the benzottiazole (31) (19). 

As a pharmaceutical, methyl salicylate is used in liniments and ointments for the relief of pain and for rheumatic conditions. As a flavor and fragrance agent, it is used in confectioneries, dentifrices, cosmetics, and perfumes. Other commercial applications for methyl salicylate are as a dye carrier, as a uv-light stabilizer in acrylic resins, and as a chemical intermediate. The May 1996 price was 5.50/kg (18). 

Any plastic constituent in addition to the function it serves must have heat stability, UV light stability, weather resistance, low solubility in terms of extraction, compatibility with other constituents and good dispensability. Where plastics have to be sterilised by irradiation, certain constituents may be degraded, or even continue to degrade after irradiation. Certain antioxidants are degraded by gamma irradiation. 

To mention some examples, benzoylation of xylenes was particularly studied because of the use of dimethylbenzophenones as UV-light stabilizers in plastics. Moreover, 2-acetyl-6-methoxynaphthalene represents the precursor to the antirheumatic Naproxen.i ortho- and para-Hydroxy-acetophenones are widely used for the synthesis of aspirin and paracetamol (4-acetamidophenol), respectively. orf/zo-Hydroxyacetophenone is also a key intermediate in the production of 4-hydroxycoumarin and warfarin, both used as anticoagulant drugs in the therapy of thrombotic diseases, and it is also employed in the synthesis of flavonones. ... 

Carstab . [Morton huT.] Benzophe-nones and thiodipropionates uv light stabilizer, antioxidant for PP, HDPE, LDPE, EVA, PVC, PC, acetals, epoxies, some cellulosics, in cosmetics, protective coatings, food use. 

Significantly improved UV light stability is found with polymeric substrates stabilized with bis(2,2,6,6-tetramethyl-piperidinyl-4) sebacate, an example of hindered-amine class light stabilizers, compared with those stabilized with conventional light stabilizers. Application areas covered include polyolefin fibers, films and molded sections, polyurethane, and styrenics. Synergistic performance with o-hydroxyphenyl benzotriazoles in these polymers is apparent. 

Triazoles, such as phenylbenzotriazole, naphthylbenzotriazole, and related compounds, such as benzophenone are UV absorbers. A particularly well-known group of ultraviolet stabilizers are hydroxyphenylbenzo-triazole-based compounds. However, UV light stabilizers of this type are often lost from the product into which they are incorporated by leaching or hy evaporation. To overcome these difficulties, efforts have been directed towards chemically incorporating the ultraviolet light stabilizer into the polymeric backbone of the material to be protected. ... 

With the exception of UV light stability, thermoset polymers resist weathering, being resistant to normal atmospheric pollutants. Refer to Table 3.3 for the atmospheric resistance of fiberglass reinforced thermoset polymers. 

Polypropylene in comparison with polyethylene is more sensitive to UV light. Stabilizers including benzotriazoles together with HALS can be used to provide... 

Saytex BT-93W can be used to flame retard PBT compounds for use in electrical connector applications. It is EBTBP, also called EBT for short, which is ethylene bis(tetrabromophthalimide). It is the only EBT on the market. It is compounded with antimony trioxide and provides excellent impact strength, tensile elongation and UV light stability. Typically an 11% loading is accompanied by 5% Sb203 to achieve UL94 V-0 rating. 

Ultraviolet Light Stabilization. UV light stabilization is produced by fillers that reflect UV, particularly aluminum flake and Ti02, and by fillers that absorb UV radiation and reduce it to harmless wavelengths, particularly carbon black and zinc oxide (Sec. 5.1.4). 

Hindered amine light stabilizers (HALS). Hindered amine light stabilizers are the newest type of UV light stabilizer. They were introduced in 1975 by Ciba and Sankyo. HALS do not screen ultraviolet light, but stabilize the resin via free-radical termination. HALS are used at lower levels than benzophenones and benzotriazoles, and are widely used in polyolefins for their cost-effectiveness and performance. The successful growth of HALS has been directly related to their substitution for benzophenones and benzotriazoles in many applications as well as their blending with benzophenones. 

Outstanding properties good color maintenance and long-term thermal and UV light stabilization ... 

Cyagard, Antioxidants, antistatics, UV light stabilizers, UV absorbers, Cytec Industries Inc. 

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