UV-absorbing additives

Figures 13.4a and 13.4b compare chromatograms published by Heme et al. [23] and chromatograms calculated from the data formd in their paper, assuming Langmuir competitive isotherms (Eq. 13.3) and numerical values of the other parameters that permit the best approximation of the experimental results. In this experiment, a sample containing acetonitrile, N,N-dimethylformamide, ethyl formate, fso-butanol, ethyl acetate and 1-pentanol is eluted on a C18 chemically bonded silica phase (Nucleosil C18), using a water-methanol solution containing 0.00025 M salicylamide, the UV-absorbing additive. The agreement between experimental and calculated chromatograms is excellent. It demonstrates the validity of the theoretical approach. The system peaks associated with the first five components, those that are eluted before the additive system peak (peak 6), are...

C.M. Liauw, A. Quadir, N.S. Allen, M. Edge, and A. Wagner, Effect of hindered piperidine light stabilizer molecular structure and UV-absorber addition on the oxidation of HDPE. Part 1. Long-term thermal and photo-oxidation studies, J. Vinyl Add. Technol. 2004, 10, 79-87. 

We are now analysing the rejection behaviour of the atactic material along similar lines to those used for the uv absorbing additives to determine the mobility of the atactic fractions within the polymer. 

With all these additives, the outer surface layers of polyolefin films are degraded before the light can reach a conventional UV absorbing additive. Thin films are therefore more severely affected by light than thick ones, and the concentration of UV absorber has to be increased when the film is thin. 

Direct measurement of concentration can also be used for some UV absorbing additives by using thin films and a UV spectrophotometer. 

As it turns out, a matrix is not always necessary nor even desirable to obtain a mass spectrum of a sample. In fact, to rapidly determine if an UV absorbing additive is present in a paint sample by LDI-MS, it is not convenient to alter the sample to introduce a matrix. Instead, a paint chip can directly be analysed by laser desorption with a UV or other type of laser [212]. 

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