Polymers coloring processes

Styrene-Acrylonitrile (SAN) Copolymers. SAN resins are random, amorphous copolymers whose properties vary with molecular weight and copolymer composition. An increase in molecular weight or in acrylonitrile content generally enhances the physical properties of the copolymer but at some loss in ease of processing and with a slight increase in polymer color. 

The level of technical service support provided for a given product generally tracks in large part where the suppHer considers thek product to be located within the spectmm of commodity to specialty chemicals. Technical service support levels for pure chemicals usually provided in large quantities for specific synthetic or processing needs, eg, ammonia (qv), sulfuric acid (see SuLFURic ACID AND SULFURTRIOXIDe), formaldehyde (qv), oxygen (qv), and so forth, are considerably less than for more complex materials or blends of materials provided for multistep downstream processes. Examples of the latter are many polymers, colorants, flocculants, impact modifiers, associative thickeners, etc. For the former materials, providing specifications of purity and physical properties often comprises the full extent of technical service requked or expected by customers. These materials are termed undifferentiated chemicals (9),... 

The stabilizer or stabilization system used depends on the heat and shear likely to be experienced by the polymer during processing, the end use application requirements, such as clarity or color, and the health concerns. A major health issue has been identified with the lead salts and soaps, because of their relative solubility and their corresponding potential to leach into water. For this reason, lead stabilizers currently find use only when other stabilizer systems do not provide the necessary stabilization or end use properties. Wire and cable sheathing is the only remaining application where the use of the lead stabilizer systems is widespread. Since most humans do not chew on wires (though mice, rats, and squirrels do) and lead-based stabilizers provide superior electrical properties, lead salts persist in this application. 

Individual size polymers may be used alone or in combination with one another and their performance may be further improved by the addition of other components such as waxes and lubricants. However, whilst sizing offers many benefits in the subsequent weaving of the yarns, it is anathema as far as wet processing is concerned. A typical sized yarn may contain as much as 34% of impurities, distributed as shown in Figure 10.15. These impurities can interfere with wetting-out and with bleaching. They may also affect coloration processes. Depending on the type of size and the dyes used, dye uptake may be increased or resisted ... 

The thermal requirements for pigments which are targeted for PETP melt extrusion are particularly severe. However, it is important to consider the individual conditions at the various stages of polymer coloration. Pigments, for instance, which are added during the so-called condensation process in a glycol dispersion prior to transesterification or condensation in the autoclave, are exposed to temperatures between 240 and 290°C for 5 to 6 hours [43]. These harsh conditions are only tolerated by very few polycyclic pigments, primarily by representatives of the quinacridone, copper phthalocyanine, naphthalenetetracarboxylic acid, and pery-lene tetracarboxylic acid series. 

Note 3 Examples of additives are antioxidants, plasticizers, flame retardants, processing aids, other polymers, colorants, UV absorbers, and extenders [7]. 

The high normal stress differences in comparison to the shear stress cause flow phenomena which may influence many technical processes. One example is the Weissenberg Effect (see Fig. 3.10), which arises when a shaft rotates within a viscoelastic fluid. The first normal stress difference leads to a pressure distribution which causes the fluid to climb up the stirrer shaft. This effect occurs when processing polymer color dispersions or mixing cake dough. 

Heat stability Indicates maximum processing temperature at typical loading for typical processing times. These values assume no reactivity with any compound ingredients. The nominal heat stability also depends on the ability of the pigment to mask any shifts in polymer color that occur at the upper end of its processing temperature range. 

A typical masterbatch for extrusion, injection, or blow molding would consist of an appropriate carrier resin for the polymer being processed, a fluorescent pigment, and a wax additive. The following example illustrates a 25% color concentrate formula for injection molding which should be let down at 4% to yield a final color loading of 1% ... 

Several factors are typically considered when selecting an antioxidant, including required concentration, compatibility with the substrate, stability, toxicity, ease of use and cost. Organophosphites are the most commonly used antioxidants. They are used to protect the color and molecular weight of the polymer during processing and have been shown to decompose peroxides, as well as chelate and react with metals. Other antioxidant groups include sterically-hindered phenols (BHT), thioesters and amines. 

To many people, color is at best a necessary evil. The coloring process amounts to adding a contaminant (the colorant) to a perfectly good polymer system to achieve a color while reducing all other properties This perception can be transformed into reality when color is an afterthought in the whole product development cycle. That cycle typically progresses as follows ... 

Uses Complex hosting guest molecules increases the sol. and bioavailability of other substances masks flavor, odor, or coloration stabilizes against light, oxidation, heat, and hydrolysis turns liqs. or volatiles into stable solid powds. for use in pharmaceuticals, cosmetics, toiletries, foods, tobacco, pesticides, textiles, paints, plastics, synthesis, polymers food processing aid Regulatory Japan approved not pemiitted in certain foods ManufJDistrib. Adept Sol ns. Aldrich Ashland Aventis Pharmaceuticals ... 

Uses Sulfur scavenger in lubricants improves antiwear and antifriction props. color/processing stabilizer for polymers ... 

In their simulations, Strickland et al ° employed discontinuous molecular dynamics to study the coloring process in macromolecular tethers made of various lengths. Specifically, they explored the effect of the grafting density of the parent polymer and the interplay between the solubilities of the unmodified and modified segments along the polymeric grafts on the comonomer distribution in designed copolymers. 

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