Additives hindered amine light stabilisers

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... 

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). 

Polymer is degraded by heat, energy, UV or residues of catalyst and generates alkyl radicals. This alkyl radical reacts with oxygen and form peroxy radicals. These peroxy radicals abstract hydrogen from other polymer and forms alkyl radicals and hydroperoxide. The decomposition of hydroperoxide to alkoxy and hydroxyl radicals induces additional decomposition of the polymer chain. In order to stop the radical chain reaction of degradation, stabilisers such as phenolic antioxidant, phosphites, thioether and hindered amine light stabilisers (HALS) are added. 

Hindered amine light stabilisers (HALS) are the main stabiliser type (as a scavenger to inhibit free radical chain propagation) in addition to organo-nickel compounds (as a quencher to prevent initiation of polymer degradation) are used for UV stabilisation. 

Combinations of stabilisers, (e.g., a hindered phenolic primary antioxidant, a phosphite secondary antioxidant and a hindered amine light stabiliser) are frequently used. Knowledge of the adsorption activity of a filler towards such additives can indicate what additives can be avoided or how the filler surface may be modified, for example with an epoxy resin or fatty acid, so that it no longer adsorbs the additive [15]. 

Hindered amine light stabilisers function as free radical scavengers and can double as thermal antioxidants. They are, though costly, effective at very low concentrations. Hindered amines can interact with other additives (e.g., phenolic antioxidants, titanium dioxide) in the PP to produce yellowishness. Halogenated flame retardants can react with hindered amine light stabilisers and render them ineffective. 

Additionally, all four basic materials were stabilised with Hostavin N 30 and Hostanox 0 10, in different amounts. Oligomeric HALS (hindered amine light stabiliser) N 30 was added in three different quantities (0.02 %, 0.06 %, 0.1 %). 

Acrylic urethanes are used widely in the coating of plastic components, primarily as a clear or pigmented topcoat for basecoated or primed plastics. Clearcoats are formulated with aliphatic polyisocyanates. The addition of a UV absorber and a hindered amine light stabiliser further improve the photostability. Catalysts for the reaction fall into two categories, namely metallic salts and tertiary amines. 

An alternative mechanism by which additives may protect polymers from photo-oxidation is radical trapping. Additives which operate by this mechanism are strictly light stabilizers rather than antioxidants. The most common materials in this class are the hindered amines, which are the usual additives for the protection of poly (ethylene) and poly (propylene). The action of these stabilisers is outlined in Reactions 8.3-8.5. 

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