Ultraviolet absorbers, polymeric material

Paints are complex formulations of polymeric binders with additives including anti-corrosion pigments, colors, plasticizers, ultraviolet absorbers, flame-retardant chemicals, etc. Almost all binders are organic materials such as resins based on epoxy, polyurethanes, alkyds, esters, chlorinated rubber and acrylics. The common inorganic binder is the silicate used in inorganic zinc silicate primer for steel. Specific formulations are available for application to aluminum and for galvanized steel substrates. 

Polymerizable ultraviolet absorbers are highly compatible with plastics in which they can be easily incorporated. The absorbers, can be chemically bound to polymeric materials either by copolymerization techniques, grafting techniques or during processing of the pol5uner. Thus, the ultraviolet absorber becomes an integral part of the polymer chain. 

A simple and convenient method of polymer modification is to introduce an additive. This method is most effectively utilized in the modification of nylon fibers. For antistatic and conductive properties, hygroscopic polymeric materials and conductive materials such as carbon and metal powders are incorporated, respectively. For flame retardant properties, antimony trioxide is added. To impart ultraviolet shielding properties, ultraviolet absorbents are included and inoiganic particles of metal such as silver and zeolite containing metal ions are used for antibacterial and odor preventing properties. 

The shift in activation spectrum with thickness of an aromatic polymer exposed to solar radiation demonstrates the importance of testing these materials in the form in which they will be used in practice. The type of ultraviolet absorber required to screen the harmful wavelengths and its effectiveness will differ with the thickness of the aromatic-type polymeric tested. Due to differences among different types of polymeric materials in the effect of thickness on their wavelength sensitivities, the form in which they are tested can change their stability ranking. 

Ultraviolet and visible light spectroscopy makes use of the quantized nature of the electronic structure of molecules. One example that is commonly observed by eye is the yellow color of polymeric materials that have been slightly degraded by heat or oxidation. Frequently this is due to the appearance of conjugated double bonds (5). For example, the 10-polyene conjugated structure absorbs light at 473 nm in the blue region. 

The art of compounding (110) rises to the fore in the development of polymeric materials. Thus, fillers can be either reinforcing or inert and low price, or serve as pigments. Plasticizers and lubricants need to be added on occasion. Antioxidants and ultraviolet light absorbers lengthen the life of many polymers. Curatives such as sulfur for vulcanization or peroxides reduce flow, producing cross-linking. 

The main component of stabilizing systems of polymeric materials for outdoor applications is a light stabilizer, which absorbs the ultraviolet part of solar radiation, which ranges in wavelength from 100 to 380 nm. This slows the process of aging. 

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. ... 

The cost of solar collectors can be reduced by using polymeric glazing and absorber materials, but the durability of their optical and mechanical properties must be demonstrated. Polycarbonate glazings with ultraviolet screening layers have been shown to survive accelerated light intensity for an equivalent 20 years outdoor exposure in Miami, FL. The mechanical properties of two candidate absorber materials— metallocene-based multi-density polyethylene and polypropylene— have been measured as a function of wet and dry thermal exposure. 

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