Additives light stabilisers

Kawaguchi et al [839] have reviewed the application of ESR for studies of reaction mechanisms of polymer additives (light stabilisers, antioxidants, carbon-black/rubber coupling agent), and of molecular motions of polymers. More recently, more general ESR applications have been reviewed [840]. Various books deal with applications of ESR [841], in particular also in relation to polymer research [842]. 

Polymer formulations usually include one or more compounds such as antioxidants, secondary antioxidants, antistatic additives, light stabilisers, lubricants, plasticisers, stabilisers, slip and antiblock agents. In addition, the polymer and hence the extractant liquid might contain other substances not deliberately added such as unreacted monomers, residual polymerisation solvents and catalysts. The result is that practical extractants from such plastics can contain very low concentrations of several very different types of substances which may or may not mutually interfere with each other during these subsequent analyses and one or more of which it may be necessary to determine. 

Obviously, use of such databases often fails in case of interaction between additives. As an example we mention additive/antistat interaction in PP, as observed by Dieckmann et al. [166], In this case analysis and performance data demonstrate chemical interaction between glycerol esters and acid neutralisers. This phenomenon is pronounced when the additive is a strong base, like synthetic hydrotalcite, or a metal carboxylate. Similar problems may arise after ageing of a polymer. A common request in a technical support analytical laboratory is to analyse the additives in a sample that has prematurely failed in an exposure test, when at best an unexposed control sample is available. Under some circumstances, heat or light exposure may have transformed the additive into other products. Reaction product identification then usually requires a general library of their spectroscopic or mass spectrometric profiles. For example, Bell et al. [167] have focused attention on the degradation of light stabilisers and antioxidants... 

Oligomeric hindered amine light stabilisers, such as Tinuvin 622 and Chimassorb 944, resist satisfactory analysis by conventional HPLC and have required direct UV spectroscopic analysis of a polyolefin extract [596], PyGC of an extract [618,648], or SEC of an extract [649]. Freitag et al. [616] determined Tinuvin 622 in LDPE, HDPE and PP by saponification of the polymer dissolution in hot toluene via addition of an... 

David et al. [184] have shown that cool on-column injection and the use of deactivated thermally stable columns in CGC-FID and CGC-F1D-MS for quantitative determination of additives (antistatics, antifogging agents, UV and light stabilisers, antioxidants, etc.) in mixtures prevents thermal degradation of high-MW compounds. Perkins et al. [101] have reported development of an analysis method for 100 ppm polymer additives in a 500 p,L SEC fraction in DCM by means of at-column GC (total elution time 27 min repeatability 3-7 %). Requirements for the method were (i) on-line (ii) use of whole fraction (LVI) and (iii) determination of high-MW compounds (1200 Da) at low concentrations. Difficult matrix introduction (DMI) and selective extraction can be used for GC analysis of silicone oil contamination in paints and other complex analytical problems. 

Oligomeric additives with broad MWD tend to be a problem in conventional HPLC conditions. In cases where no interest exists in the oligomer distribution it is common practice to solve the problem by creating a uniform structural unit useful for analysis. For example, isocratic (or gradient) LC-UV was used for the determination of the polymeric light stabiliser Tinuvin 622 in polyolefins using dissolution (toluene)/derivatisation (TBAH)-precipitation (alcohol) the diol formed was quantitatively determined by NPLC [653]. 

An excellent and comprehensive review has covered HPLC analysis of AOs and light stabilisers up to 1990 [576]. Normal vs. reversed-phase and isocratic vs. gradient-elution HPLC separation of synthetic mixtures of additives and of solvent extracts from polymers were discussed. 

NMR spectroscopy is most effective in qualitative analysis when the samples examinated are substantially pure compounds and has been used to confirm the theoretically predicted low-energy conformations of the Af-acylated hindered amine light stabiliser Tinuvin 440 [210]. Trace amounts of PDMS (quantification limit 0.1 ppm) in plastic additives, dyes and pigments were determined by 111 NMR after Soxhlet extraction [211]. ll NMR was also used for the detection of octadecanol, an impurity in Irganox PS 802 (3,3 -dioctadecyl thiodipropionate). NMR has identified the nature of a supposedly UV stabiliser of empirical formula C17H18N3CIO [44] (Scheme 5.2). 

Bromoacetone is only slightly soluble in water, but very soluble in alcohol, ether, acetone and other organic solvents. It is not very stable, even in the pure state. It polymerises in time, especially under the influence of light and heat, though this process may be impeded by the addition of stabilising substances. During the war a small quantity of magnesium oxide was added to bromoacetone and this checked the polymerisation for several months (Meyer). 

E Gugumus and H. Zweifel (Ed.), Light Stabilisers in Plastic Additives Handbook, 5th edition, Hanser Publisher, Munich, 2001, pp. 141 125. 

F. Gugumus, Light Stabiliser, in R. Gachter and H. Muller (Eds.), Plastic Additives Handbook, 3th edition, Hanser Publisher, Munich, pp. 129-270. 

An alternative mechanism by which additives may protect polymers from photo-oxidation is radical trapping. Additives which operate by this mechanism are strictly light stabilisers... 

Photo/light stabilisers are anti-ageing additives. It is commonly known that PVC plastic windows can develop yellowish-brownish spots with time, mainly caused by sunlight... 

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