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Certification and Characterization of Photovoltaic Packaging
Published in Michelle Poliskie, Solar Module Packaging, 2016
Hindered amine light stabilizers (HALS) are a special class of organic compounds called free radical scavengers. They are formulated to terminate free radicals that occur during photolytic degradation [76]. All HALS are organic compounds that contain a secondary amine group constrained within a hydrocarbon ring. There are a number of proposed chemical mechanisms to describe HALS stabilization, but most proposed theories involve a HALS reaction with the polymeric free radicals generated during photodeg-radation [77]. This prevents the free radical from creating further polymeric breakdown. The presence of HALS is denoted in the polymer’s UV-Vis spectrum as a double absorption. Peak maxima usually occur at 300 and 350 nm, but the exact wavelength is dependent on the commercial grade of HALS in the polymer (Figure 2.38). Those absorbed wavelengths will not reach the underlying PV cells and therefore cannot be harnessed for electricity generation.
Automotive Plastic Coatings in Europe
Published in Rose A. Ryntz, Philip V. Yaneff, Coatings Of Polymers And Plastics, 2003
Hans Christian Gruner, Klaus-Werner Reinhart
In terms of resin chemistry, the clearcoats are based on a hydroxy-func-tional polyester and acrylic-resin blend. The polyester is responsible for providing the high flexibility at low temperature. The hardener is based on hexamethy-lene diisocyanate (HDI) trimer. Ultraviolet absorbers (UVA), and hindered amine light stabilizers (HALS) are additives added to absorb UV light, protect the basecoat pigments and to quench free radicals that could deteriorate and decompose the backbone resins.
Plastic Additives
Published in Kathleen Hess-Kosa, Building Materials, 2017
Free radical “scavengers,” as opposed to UV absorbers, stabilize polymers. These scavengers, referred to as hindered-amine light stabilizers (HALS), are almost exclusive derivatives of 2,2,6,6-tetramethylpiperidine (Figure 9.3). Due to their volatility, HALS may contribute to polymer emissions and poor indoor air quality. Although unregulated, HALS may cause serious eye irritation, skin, and respiratory tract irritation.
UV resistance graft modification of poly(p-phenylene-l,3,4-oxadiazole) fiber with polyhedral oligomeric silsesquioxane
Published in The Journal of The Textile Institute, 2018
Yahong Mao, Qingshuang Song, Yu Guan
Aromatic poly(1,3,4-oxadiazole) (POD), whose chemical structure is showed in Scheme 1, is a kind of conjugated polymer with excellent photoelectric properties, which is similar to polythiophene (PTh), poly-p-phenylene benzobisthiazole (PBO), and poly(phenylene vinylene) (PPV).(Zhou et al., 2013) POD, as a class of heterocyclic polymers, has excellent thermal stability, good chemical stability, high glass transition temperature, low dielectric constant, and tough mechanical properties, which had been extensively studied for a long time.(Frazer, Sweeny, & Wallenberger, 1964; Frazer & Wallenberger, 1964; Varma, Sambandam, & Varma, 1973) However, like other aromatic heterocyclic polymers, POD is also sensitive to the ultraviolet, which will deteriorate the mechanical properties and structures of POD. Generally, there are two frequently used methods to improve the UV resistance of fibers. The coating covers the fibers or fabrics with UV protecting additives such as carbon black or anti-UV agent UV326. Yang selected poly(vinyl alcohol) 1799, cellulose acetate, and sodium carboxymethylcellulose as anti-UV agents to coat the p-POD film(Yang, 2011),whose anti-UV effect was not obvious. The second method is blending the light stabilizers into the fibers that are common used. Benzotriazole UV absorbers, hindered amine light stabilizers and many other conventional light stabilizers were used to enhance the UV resistance of conjugated polymers. But POD is generally dissolved in concentrated sulfuric acid and polyphosphoric acid during spinning, which will destroy the structure of the light stabilizers, many of those light stabilizers used for POD performed poorly.