Ultra-violet absorbers

Unfortunately, the fluorescent effect is not directly proportional to the concentration of colorant present, since there is considerable quenching if quite low concentrations are exceeded. The light fastness of the fluorescent pigments is also less than that of many other organic pigments now available, but improvement can be achieved using overlayers containing ultra-violet absorbers. This is an area in which further research will clearly be needed. 

In laminates intended for use out-of-doors papers with superior colourfastness may be used and normally their construction includes an overlay sheet of ultra-violet absorbing thermoplastic film—which helps to reduce fading of the colour, and whitening. 

Table V. Ultraviolet Stability of Polypropylene Films with Various Ultra violet-Absorber Formulations...

Different methods have been used to follow crosslinking reactions. When polymers were irradiated by U. V. light in dilute THF solution above 200 nm (Method A) or 300 nm (Method B), the insolubilization reaction was followed by measuring the solution ultra violet absorbance versus time. Likewise the course of disappearance of cinnamic structure was measured on polymers films placed on quartz at 9cm of the lamp and irradiated above 200 nm (Method C). Lamp used for methods A and C was a PCQ 9 G-1 which emits in the U.V. region at 253.7 (2.5 W), 312.5, 365 nm, the other rays being in visible. A Pyrex filter was placed beetween 450 W Hanovia lamp and solution when only higher wave lenghts were expected. Lamps powers were controled before and after irradiation with a Black-Ray Ultra-Violet Intensity Meter. 

Ultra-violet absorbers on the basis of derivatives of 2 - oxybenzophenol specifically Benzon OA, where Rj =H and R 2 =C H-C g H, ... 

Interest in N, - diaryloxamides [67], as the class of non-toxic ultra-violet absorbers possessing light efficiency has raised lately ... 

According to the rule of ultra-violet absorbers selection the most effective stabilizers must absorb not only in the field of absorption of polymer itself, but in the field of its luminescence [24] that is the condition for realization of suppression mechanism of polymer excited state. 

From the series of highmolecular compounds the most interesting are polyconjugated azomethine compounds (PAC), stabilizing activity of which has been studied in the works [291, 292]. It is proved in these works that stabilizing effect is achieved at relatively small concentrations of azomethines. In the work [162] the author comes to a conclusion that at small concentrations azomethines work as inhibitors of radical processes, besides, they are ultra-violet absorbers. It should be noted that azomethines display light protective action both in vacuum and in the air. 

Scott, C. D., Analysis of urine for its ultra violet absorbing constituents by high-pressure anion-exchange chromatography. Clin. Chem. 14, 521-528 (1968). 

It is also conceivable that one may protect the plastic with a thin ultra-violet absorbing film. If this was a glass containing, say, Ce3+, Tl+ or Bi3+23) it might provide its own luminescence, utilizing the ultra-violet energy. However, it would seem more practical to use uranyl glass as the first layer in a multi-layer device as discussed in the next section. 

Turner, B.L., Bristow, A.W. and Haygarth, P.M. (2001) Rapid estimation of microbial biomass in grassland soils by ultra-violet absorbance. Soil Biology and Biochemistry 33, 91 3-91 9. 

Radiation such as ultra-violet light radiation may also promote reaction (1). This may be countered by the use of ultra-violet absorbers, light screens (which reflect ultra-violet) or quenching agents (which react with ultra-violet excited molecules to produce inert products). 

Fig. 5.4 shows a chromatogram of a mixture of antioxidants and ultra-violet absorbers. A reversed-phase system is again preferred because it can be washed clean with methanol but this time an isocratic solvent system is used. With the variable wavelength detector, the optimum wavelength can be set for the type of compounds being examined. 

Weishaar, J.L., Aiken, G.R., Bergamaschi, B.A.,Eram, M.S., andPujii, R. (2003). Evaluation of specific ultra-violet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon. Environ. Sci. Technol., 37,4702-4708. Westerhoff, R, Chem, W., and Esparza, M. (2001). Fluorescence analysis of a standard fulvic acid and tertiary treated wastewater. J. Environ. Qual., 30, 2037-2046. 

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