Photostabilizing process

A novel photostabilization process of anchoring ligands onto a polystyrene support which would eliminate the possibility of leaching the metal moieties by the coordinating solvent is due to Cais et al. [24]. A typical system is the... 

It is well known that HALS compounds (sterically hindered amine light stabilizers) exert excellent photostabilizing effect on polyolefins (1-3). Most of the authors agree that N-oxyl radicals formed from HALS compounds play an important role in the photostabilizing process (4-6). 

Photostabilization processes have not received much attention in the last year other than a multitude of review and specialist industrial articles. These include stabilization of polypropylene fibres, new stabilizer developments, sorting of stabilizers for polyethylene, trends in UV absorbers, hindered piperidines (hindered amine stabilizers (HAS)) for polyacrylics and urethanes, new stabilizers for polyolefins, enhanced service life applications, stabilizer mas-terbatches for polyester, stabilizers for UV cured acrylic overcoats for PVC, ° stabilization of clearcoats and various commercial packages. ... 

Additives such as antioxidants and photostabilizers of low-molecular weight face two major problems (1) they may evaporate during high temperature moulding and extrusion process or (2) they may migrate to the surface of the plastic and get extracted. There are, in general, three ways of overcoming these problems. 

When the photostabilization of a polymer material is to be obtained through such a surface treatment process, it is all important to make sure that the protective effect will last throughout the service life and therefore to ensure a long-term adhesion of the coating onto the substrate. This can be best achieved by promoting a grafting reaction between the two elements (20). For that purpose, the photoinitiator was partly incorporated in the top layer of the PVC plate by a surface treatment with an acetone solution. Upon UV-irradiation of the resin-coated sample, the following reactions are expected to occur ... 

Laser flash photolysis techniques offer the possibility of examining in detail the transient processes responsible for the photostabilizing effect discussed above. The triplet lifetimes are frequently too short, even for this technique however, they can still be estimated using as a probe the quenching by 1-methyl-naphthalene, which leads to the formation of its easily detectable triplet. The optical absorbance due to the 1-methylnaphthalene triplet (Aft) produced as a result of energy transfer is related to the Stern-Volmer slope by equation 5, where N stands for... 

Photostabilizers, regardless of their mechanism of action, have been added as low molecular weight materials at some point in processing. Subsequently, these stabilizers are often lost in further processing due to their volatility or else later migrate to the surface and evaporate. One method which avoids this modifies the polymer to include the quencher as an additional monomer in the polymerization. This paper will describe some recent efforts in our laboratory to pursue this latter approach in the stabilization of poly(ethylene terephthalate). 

Plastics have to be stabilized to withstand chemical and physical stresses during different phases of their lifetime. Stabilizers protecting plastics against particular degradation processes were developed and commercialized by various companies. According to their principal activity mechanisms, polymer stabilizers are conventionally classified as antioxidants, photoantioxidants, photostabilizers, heat stabilizers and... 

Principally, the photostabilization of modem paper involves the retardation or elimination of the various photophysical and photochemical processes that take place during photoinduced discoloration. This goal may be accomplished by the following three stabilizing systems. 

It is easier to dissolve a stabilizer than to evaporate it [27]. The physical loss of stabilizers due to the leaching from polymer surfa< layers into liquids which come into contact is therefore more serious than volatilization. Problems arise mainly in systems where the degradation process has been concentrated at the surface layer and therefore an efficient surface protection of a polymer is mandatory. This phenomenon takes place mainly in photostabilization of plastics or antiozonant protection of rubbers. The surface loss of stabilizers is extremely serious in very thin profiles or products having a very high surface/mass ratio. 

For infusion liquids, no completely UV-VIS photon impermeable immediate package can be used. These products require dilution and the inspection for particulates before use both processes hindered by such packaging. To guarantee safe application/dosing additional photostabilizing packaging is applied for extremely photosensitive drug preparations. 

The timescale for these processes to occur is dependent on the type of polymer, the content of added materials, plasticizers and additives such as antioxidants, photostabilizers, thermostabilizers, etc), filling and reinforcing materials such as particles and fibers, etc. 

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