Hindered amine stabilizers films

Table III shows results obtained when three UV stabilizers, alone or in combination, were used in 5- and 12-mil films for protecting the blue wool fabrics. The hindered-amine stabilizer (UV-3) was not tested because it was ineffective in 8-mil films (Table II). In 5-mil-thick films, the trends in AE values for the hydroxybenzotriazole (UV-1B), hydroxy-benzophenone (UV-2), and the zinc acetate (UV- 1) stabilizers were the same as they were when these stabilizers were incorporated into 8-mil-thick films. However, after maximum exposure time, the AE values were somewhat higher than those observed with 8-mil films. Similar trends were observed with films of 12-mil thickness. Only the hydroxy-benzophenone (UV-2) had AE values less than 1.0 after 550 kj/m2 exposure. The relative effectiveness of a hydroxybenzotriazole (UV-1B), a hydroxybenzophenone (UV-2), and combinations of each of these stabilizers as a function of film thickness are shown in Figure 3. All films, even those containing no stabilizers, were most effective in protecting the wool fabrics from color change when they were 8-mil thick. Again, no advantage was observed in using combinations of stabilizers instead of a single stabilizer in the film.

Zaharescu T, Kaci M, Hebal G, Setnescu R, Setnescu T, Khima R, et al. Thermal stability of gamma irradiated low density polyethylene films containing hindered amine stabilizers. Macromol Mater Eng 2004 289(6) 524-30. 

UV absorbers have been found to be quite effective for stabilization of polymers and are very much in demand. They function by the absorption and harmless dissipation of the sunlight or UV-rich artificial radiation, which would have otherwise initiated degradation of a polymer material. Meyer and Geurhart reported, for the first time in 1945 [10], the use of UV absorber in a polymer. They found that the outdoor life of cellulose acetate film was greatly prolonged by adding phenyl salicylate (salol) [10]. After that, resorcinol monobenzoate, a much more effective absorber, was introduced in 1951 [11] for stabilization of PP, but salol continued to be the only important commercial stabilizer for several years. The 2,4-dihydroxybenzophenone was marketed in 1953, followed shortly by 2-hydroxy-4-methoxybenzophenone and other derivatives. Of the more commonly known UV absorbers, the 2-hydroxybenzophenones, 2-hy-droxy-phenyl-triazines, derivatives of phenol salicylates, its metal chelates, and hindered amine light stabilizers (HALS) are widely used in the polymer industry. 

Ultraviolet Stabilizers. Four commercial UV stabilizers and zinc acetate dihydrate (U.S.P. grade) were added to various films during their preparation. Two were of the hydroxybenzotriazole type, one a hydroxybenzophenone, and another a hindered-amine type (Table I). 

The other commercial stabilizer (UV-3), a hindered-amine type, is presumed to afford photochemical protection by functioning primarily as a free radical and/or oxygen scavenger (13). Thus protection should only occur in the primary substrate, the cellulose acetate film, and not in a secondary substrate such as the blue wool fabric. The results shown in Table II verified this assumption the AE values obtained, irrespective of the concentration of UV-3 used in the film, were within experimental error of those observed with the unprotected fabric. 

Significantly improved UV light stability is found with polymeric substrates stabilized with bis(2,2,6,6-tetramethyl-piperidinyl-4) sebacate, an example of hindered-amine class light stabilizers, compared with those stabilized with conventional light stabilizers. Application areas covered include polyolefin fibers, films and molded sections, polyurethane, and styrenics. Synergistic performance with o-hydroxyphenyl benzotriazoles in these polymers is apparent. 

As alluded to above, a second class of light stabilizers, the hindered amine light stabilizers (HALSs), provide additional stability to polymers and can function even in thin film or in sample surfaces. The chemistry of HALSs is based on the 2,2,6,6-tetramethylpiperidine derivatives (Fig. 5). Unlike UVAs, HALSs have no significant UV absorption and... 

UV stabilizers (particularly the hydroxybenzophenones and the hydroxybenzotriazoles). Also, blend ABS with PVC or cap the ABS part with a stable film like acrylic. Some hindered amines are also being used especially in blends with absorber systems Absorbers, quenchers and HALS are used, but only absorbers are recommended for protecting whatever is underneath an acrylic substrate Aryl esters (resorcinol monobenzoate). Also salicylates, hindered amines, then benzophenones, and the benzotriazoles... 

Improvement in the performance of hindered amine light stabilizers [2] (see the two articles on these stabilizers later in this book) as well as their resistance to pesticides (important for greenhouse films) can be achieved by acid scavengers as well. 

Sterically hindered amine light stabilizers (HALS) constitute another class of light stabilizers that efficiently reduce UV-induced degradation. They are compounds that intercept chemically highly reactive radicals formed hy photochemical reactions and transform them into harmless reaction products. Fig. 3.8. Their effectiveness is not based on a competing physical absorption effect, therefore no minimum layer thickness is required for HALS effectiveness, unlike for the UV absorbers. That makes them suitable for applications such as films and fibers (527). In particular, they provide surface protection, which plays a special role in visible automotive parts. Another essential difference to UV absorbers is the fact that photooxidation is not prevented, but after initial damage its propagation is either reduced or suppressed [510],... 

Yellowing in thermoplastic polyurethanes can be retarded by adding UV-stabilizers, antioxidants and/or reduction agents. Proven stabilizers are the combinations of a phenolic antioxidant with an absorber of the hydroxybenzophenone or the hydroxy-benzotriazole type, and the three-fold combination phenolic antioxidanf/UV absorber/sterically hindered amine. This has allowed significant improvements in the light resistance of thin cast films made from aromatic polyester urethane [86]. 

It is particularly recommended for light stabilization of TPO in applications where food approval is mandatory. In some instances, the combination with other light stabilizers such as UV absorbers is advisable. For LDPE agricultural films, it is advantageously combined with other polymerie sterieally hindered amines. 

Based on the findings of accelerated weathering by xenon tests and natural (outdoor) weathering for films of LLDPE and LDPE resins, it was concluded that PE films containing additives, particularly hindered amine stabilisers (HAS), have a UV stability four times higher than the corresponding pure films [43]. 

Christensen, P.A., Egerton, T.A., Fernando, S.S., White, J.R. Photogeneration of caibon dioxide from pol)q)ropylene film stabilized by hindered amines. Polym. Degrad. Stabil. 94, 1999-2003 (2009)... 

Kaci, M., Hebal, G., Benhamida, A., Boukerrou, A., Djidjelli, H., Sadoun, T. Kinetic study of hindered amine light stabilizer photografting in low density polyethylene films under natural weathering conditions. J. Appl. Polym. Sci. 84, 1524-1532 (2002)... 

The solvent-borne clearcoat is spray-applied over the basecoat at a dry film thickness of 1.8 to 2.0 mils. The clearcoat, responsible for UV protection, chemical resistance, chip resistance, and so on, is most often composed of a hydroxy functional acrylic binder together with a melamine or an isocyanate cross-linker. Ultraviolet light absorbers and hindered amine light stabilizers also are added to achieve better free-radical oxidative degrada-... 

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