Light stabilizer, additive mechanisms

Quenchers are light-stabilizing additives able to take over the energy of photons already absorbed by a suitable chromophore (Chr) of the polymer (see Scheme 9). Carbonyl groups, hydroperoxides, and singlet molecular oxygen (or its precursors) are chromophores commonly believed to be involved in the photodegradative mechanisms for numerous hydrocarbon polymers. ... 

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. 

Before its conversion into plastic products the resulting resin is almost always compounded with various additives of different nature and constitution, meant to improve processing, stability, or mechanical specifications as a function of a given application (outdoors, i.e. UV-light exposed, oxidation, high-temperature processing). Such additives are regularly used as ... 

Exposure to solar irradiation (sunlight) may alter their chemical integrity and in due course some physical properties such as mechanical strength (e.g. brittleness) or color (e.g. fading) as well. Additives like industrial ultra violet (UV)-absorbers, hindered amine light stabilizers, radical scavengers and antioxidants are incorporated or applied in these products to effectively reduce or delay such radiation induced deteriorations. 

Interest to this problem is proved by a great number of scientific publications in our country and abroad [1, 2, 8, 10, 42]. However, it is impossible to make systematic analysis of stabilizers efficiency, mechanism of their action, to form scientific approach to the synthesis and use of additives in different and specific cases according to literature surveys [44, 45] and patent information [46, 47], where many classes of compounds are presented as light stabilizers. Interaction of stabilizing efficiency of die additive with its structure is not... 

In order to elicit the light stabilizing mechanism of the examined additions, modified CDA- films were dissolved in acetonitrile before and after being radiated. The obtained solutions were spectrographed in Ultra-violet (Figure 2.28-2.30). 

Studying ultra-violet spectrums of indan derivatives let us make a supposition about their "shield" mechanism, which causes light stabilizing effect, as indan sulphuryl amide additions (as carbazolsulphonamides) absorb radiation in the same wave length interval as cellulose diacetate. 

Before hand testing of light stabilizing activity of DTIU while introducing it into a polymer as mechanical additive was carried out. Data of Table 24 show that DTIU possesses photostabilizing activity that gives the reason to consider the fact that its condensation with CDA will improve light fastness of the latter. 

Oxidative addition see Oxidative Addition) of H-C, H-Si, H-Sn, Cl-C, and other <7-bonded atom pairs have been used to add group 14 donor ligands to metal clusters. Additions of H-C, H-Si, and H-Sn bonds require an unsaturated metal center. A number of studies of the mechanism are consistent with a mechanism involving addition at a single metal atom through a three-center, synchronous process, the same as commonly occurs for monometallic complexes. Some examples of H-Si addition to unsaturated (equation 10) and lightly stabilized (equation 11) Osg clusters are shown. Oxidative additions of unactivated C-H bonds are rarer. Preferential addition of terminal C-H bonds to... 

Commercial polyolefins often contain additives such as colorants, flame retardants, antioxidants, light stabilizers, nucleating agents, antistatic agents, lubricants (microcrystalline waxes, hydrocarbon waxes, stearic acid, and metal stearates), and so on. These additives aid the processing and fabrication of products from polyolefins. Detailed treatments about specific polyolefins, polymerization systems/ mechanism/processes, structures, properties, processing, and applications may be found in References 2-9. 

In the following part, the most important classes of additives (antioxidants, PVC heat stabilizers, light stabilizers, and flame retardants) are presented, as well as general information on chemical structures and mechanisms, on testing methods, and on use examples in selected polymer... 

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