Stabilization to light and heat

Lakes are prepared by adsorption or precipitation of a soluble dye on an insoluble substrate (e.g., alumina). They are useful in fatty products that have insufficient moisture to dissolve dyes (coated tablets, cake mixes, hard candies, chewing gum). Lakes are insoluble in most solvents including water, have high opacity, are easily incorporated in dry media, and show higher stability to light and heat. They are effective colorants for candies, pills, fats, and oils. The main characteristics and differences between lakes and dyes are well documented. ... 

For preparing lakes, a solution of aluminium sulfate (or chloride) is mixed with sodium carbonate, forming fresh alumina Al(OH)3. The colorant is then added and adsorbed on the surface of alumina. Usually the content of colorant in the lake ranges from 10 to 40%." The product is filtered, washed with water, dried, and milled. The product is allowed to contain unreacted alumina but must not contain more than 0.5% HCl-insoluble matter and not more than 0.2 % ether-extractable matter. - Lakes are insoluble in most solvents used for pure dyes, and they have high opacity and better stability to light and heat. Lakes impart their color by dispersion of solid particles in the food. The coloring properties of lakes depend on particles, crystal structures, concentrations of dye, etc. 

C. I. Pigment Red 183 (214), which range in shades from yellow to bluish-red and brown and exhibit excellent fastness properties. Their good stability to light and heat and their insolubility is attributed to extensive intermolecular association as a result of hydrogen bonding and dipolar forces in the crystal structure, as illustrated in Figure 9.3. 

MisceUaneous.—The phosphorescence and fluorescence characteristics of solid camphorquinone have been reinterpreted. The remarkable stability to light and heat of (565), unlike the diketone or imino-ketone analogues, is attributed to the consumption of the considerable energy which is absorbed in geometrical isomerizations of the imine groups. ... 

A number of patents have emphasized acrylic elastomers as a method of rubber-toughening plastics.The latexes are crosslinked, in part, to impart mechanical stability during processing. Acrylic latexes have improved stability to light and heat over SBR or NBR, and thus offer an improvement to ABS materials. In general, saturated elastomers have proved superior to the diene types for outdoor use because of their superior weather resistance. 

Becker, M. A. "The Stabilization of Silk to Light and Heat." M.S. Thesis, North Carolina State University, Raleigh, NC, 1988. 

The water-soluble chlorophyllins (uncoppered and coppered sodium or potassium pheophorbide) have good stability toward light and heat and moderate stability to both acid and alkalis. Food color usage is in canned products, confectioneries, soups, and dairy products. 

PVC, a polymer that is widely used because of its low gas permeability and high fire retardancy, is sensitive to light and heat. The degradation leads to dehydrochlorination and color formation [Chapiro, 1962 Bradley, 1984 Thomas et al., 1986]. To process the resin it is necessary to add heat stabilizers. The most common additives include metal organic compounds, acid acceptors and alkalis, dioctyl phthalate, and dioctyl sebacate [Bradley, 1984]. PVC is only slightly crystalline. However, it has been used to produce heat-shrink products [Bradley, 1984]. 

Polymers in their raw state are usually technically unsatisfactory in one respect or another, such as their stability to light or heat, or their processability, or flammability, or colour, or opacity, or antistatic characteristics, etc., and they simply could not be used in commercial applications successfully without the incorporation of one or more additives [2] to modify behaviour. The additives are often present at very low concentrations (0.1-3 parts per hundred of resin, by weight) and are called stabilizers, UV absorbers, viscosity modifiers, lubricants, fire retardants, pigments, etc. Fillers may be present at 50 or even 150 parts per hundred of resin, by weight. Thermosetting resins tend to have fewer additives of the kind... 

The statement that polyene antibiotics exhibit poor stability to heat, UV radiation and extremes of pH is often made [34,79—81]. When pure dry antibiotic is stored in the dark at low temperature, potency will not be lost, even over long periods [82,83]. Stability to light and temperature decreases as the aze of the chromophore increases. 

Polyvinyl chloride (PVC) (1933) n. Poly (vinyl chloride), poly(l-chloro-ethylene). A vinyl polymer which is similar to polyethylene, but on every other carbon in the backbone chain, one of the hydrogen atoms is replaced with a chlorine atom. It is produced by the free radical polymerization of vinyl chloride. A white, water-insoluble, thermoplastic resin, derived by the polymerization of vinyl chloride. A hard and tough plastic solid. Stabilizers are necessary to prevent discoloration from exposure to light and heat. Used for plastics and coatings. Commonly known as vinyl. Abbreviation is PVC See image). 

Plastics usually contain stabilizers that must protect the polymer during melt processing. They also contribute to the service life time of the finished article upon exposure (especially for out-door applications) to light and heat. The stabilizers are partially consumed during the processing and exposure of the plastic parts, thus they must be replaced. The amount of required stabilizer depends on the reprocessing conditions as well as on the envisaged use of recycled polymers. It must be noted that the stabilizers transformation products remain in the plastics. 

PVC is imstable imder exposure to light and heat resulting in discoloration and embrittlement. In the early 1940s it was found that this degradation could be prevented by addition of certain organotin derivatives. Presently, about 70% of the commercial organotin compounds are employed as PVC stabilizers in the form of mono and dialkyltin derivatives. Today, many of these stabilizers are based on organotin polymers made by Carraher and coworkers. [63]... 

The modacrylic fibers exhibit excellent resistance to chemical agents. They exhibit good stability to light and biological agents. Modacrylic fibers melt at 190°-210°C with slight decomposition. SEF modacrylic fibers possess somewhat greater heat stability than the other modacrylics. 

Stability. In order to have maximum effectiveness over long periods of time, an antioxidant should be stable upon exposure to heat, light, oxygen, water, etc. Many antioxidants, especially in the presence of an impurity when exposed to light and oxygen, are subject to oxidation reactions with the development of colored species. Alkylated diphenyl amines are least susceptible and the -phenylenediamine derivatives the most susceptible to direct oxidation. 

On the other hand, not only initial colour but colour change (discolouration) of the resin under UV light and heat is important. Colour retention of a resin is related to the chemical stability and increases as the degree of non-aromatic conjugated unsaturation of the resin molecule decreases. Thus, for rosins a high level of abietic-type resin acids lead to relatively unstable resins. Hydrogenation and disproportionation as well as esterification provide improved stability and colour retention to rosins. 

The polymer degradation scheme discussed above and shown in Figure 1 is valid in polymers without any additives. However, most commercially available materials are doped with UV absorbers and with light and thermal stabilizers in order to extend their lifetime. The HAS rank among the most important additives used for light and heat stabilization of polymers [9,15,16]. Most commercially available HAS stabilizers are 4-substituted 2,2,6,6-tetramethylpiperidines, as shown below [17],... 

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