Poly coloration

We shall find that a fundamental difference in behavior exists between the one- and poly-colored indicators. The former group will be considered first. 

AppHcation of an adhesion-promoting paint before metal spraying improves the coating. Color-coded paints, which indicate compatibiHty with specific plastics, can be appHed at 20 times the rate of grit blasting, typically at 0.025-mm dry film thickness. The main test and control method is cross-hatch adhesion. Among the most common plastics coated with such paints are polycarbonate, poly(phenylene ether), polystyrene, ABS, poly(vinyl chloride), polyethylene, polyester, and polyetherimide. 

Plastic Sheet. Poly(methyl methacrylate) plastic sheet is manufactured in a wide variety of types, including cleat and colored transparent, cleat and colored translucent, and colored semiopaque. Various surface textures ate also produced. Additionally, grades with improved weatherabiUty (added uv absorbers), mat resistance, crazing resistance, impact resistance, and flame resistance ate available. Selected physical properties of poly(methyl methacrylate) sheet ate Hsted in Table 12 (102). 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Vinyl Acetate—Ethylene Copolymers. In these random copolymers, the ratio of ethylene to vinyl acetate (EVA) is varied from 30—60%. As the vinyl acetate content increases, the oil and heat resistance increases. With higher ethylene content the physical strength, tensile, and tear increases. The polymers are cured with peroxide. The main properties of these elastomers include heat resistance, moderate oil and solvent resistance, low compression set, good weather resistance, high damping, exceUent o2one resistance, and they can be easily colored (see Vinyl polymers, poly(VINYL acetate)). 

Poly(vinyl acetate) emulsions are used to prime-coat fabrics to improve the adhesion of subsequent coatings or to make them adhere better to plastic film. Plasticized emulsions are appHed, generally by roUer-coating, to the backs of finished mgs and carpets to bind the tufts in place and to impart stiffness and hand. For upholstery fabrics woven from colored yams, PVAc emulsions may be used to bind the tufts of pile fabrics or to prevent sHppage of synthetic yams. 

Poly(vinyl alcohol) [9002-89-5] was discovered through the addition of alkaU to a clear alcohoHc solution of poly(vinyl acetate), which resulted in the ivory-colored poly(vinyl alcohol) (4). The same discovery has been made by studying the reversible transformation between poly(vinyl alcohol) and poly(vinyl acetate) via esterification and saponification (5). The first scientific reports on poly(vinyl alcohol) were pubUshed in 1927 (6,7). 

PuUy hydroly2ed poly(vinyl alcohol) and iodine form a complex that exhibits a characteristic blue color similar to that formed by iodine and starch (171—173). The color of the complex can be enhanced by the addition of boric acid to the solution consisting of iodine and potassium iodide. This affords a good calorimetric method for the deterrnination of poly(vinyl alcohol). Color intensity of the complex is effected by molecular weight, degree of... 

Drying of the poly(vinyl alcohol) is critical to both the color and solubiHty of the final product. Excessive drying temperatures result in high product color and an increase in the crystallinity, which in turn reduces the solubiHty of the product. Drying is initially subjected to a flash regime, where the solvent not contained within the particles is flashed off. This first phase is foUowed by a period where the rate is controUed by the diffusion rate of solvent from the poly(vinyl alcohol) particles. Because the diffusion rate falls as the material dries, complete drying is not practical. The polymer is therefore generally sold at a specification of 95% soHds. 

Plastics and Synthetic Products. To prevent degradation of plastics at elevated processing temperatures, it is necessary to use suitable heat stabilizers. Eor example, flexible poly(vinyl chloride) (PVC) manifests uncontroUed color development in the absence of stabilizers. Accordingly, cadmium salts of organic acids are typically used in a synergistic combination with corresponding barium salts, in about a 1 3 cadmium barium ratio, to provide a cost-competitive heat stabilizer for flexible PVC. 

The cadmium chalcogenide semiconductors (qv) have found numerous appHcations ranging from rectifiers to photoconductive detectors in smoke alarms. Many Cd compounds, eg, sulfide, tungstate, selenide, teUuride, and oxide, are used as phosphors in luminescent screens and scintiUation counters. Glass colored with cadmium sulfoselenides is used as a color filter in spectroscopy and has recently attracted attention as a third-order, nonlinear optical switching material (see Nonlinear optical materials). DiaLkylcadmium compounds are polymerization catalysts for production of poly(vinyl chloride) (PVC), poly(vinyl acetate) (PVA), and poly(methyl methacrylate) (PMMA). Mixed with TiCl, they catalyze the polymerization of ethylene and propylene. 

Poly(hydroxyethyl methacrylate)-dye copolymers —The color additives formed by reaction of one or more of the foUowiag reactive dyes with poly(hydroxyethyl methacrylate), so that the sulfate group (or groups) or chlorine substituent of the dye is replaced by an ether linkage to poly(hydroxyethyl methacrylate) (see Dyes, reactive). The dyes that may be used alone or ia combination are... 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

In general, the azo colors are useful for coloring polystyrene, phenoHcs, and rigid poly(vinyl chloride). Many are compatible with poly(methyl methacrylate), but in this case the weatherabiUty of the resin far exceeds the life of the dyes. Among the more widely used azo dyes (qv) are Solvent Yellows 14 and 72 Orange 7 and Reds 1, 24, and 26. 

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