Heat stabilizers, additive coloring effects

The compatibility of a colorant is assessed not only on the basis of the ease with which it can be mixed with the base resin to form a homogeneous mass but also on the requirement that it neither degrades nor is degraded by the resin. In relation to product functional properties, incompatibihty of a colorant can affect mechanical properties, flame retardancy, weatherability, chemical and ultraviolet resistance, and heat stability of a resin through interaction of the colorant with the resin and its additives. Flame retardancy, for example, may impinge directly on the performance of a colorant. Pressure to produce materials with lower levels of toxic combustion products can involve organic fire retardant additives that interact with the colorant either to negate the effect of the additives or affect the color. 

As expected the period of induction decreases due to the thermomechanical treatment during processing, but a comparison of the unmodified and the modified PVC wastes indicates a considerable stabilizing effect of chalk. Also, the visual evaluation of the produced specimens indicates a better color quality of the modified samples. Especially PVC scrap with a low residual stability (material 2 and material 3) needs an additional stabilization if intended for a re-use. This is also impressively illustrated by the conversion-time-curve of material 2 (Figure 10). The chalk modified sample has a better heat stability than the original product in spite of one more processing cycle. 

The FS system developed by CIBA Additives seems to be a breakthrough for color-critical PO applications. These new systems do not contain phenolic antioxidants so they provide good color stability and gas fade resistance, long term thermal, and UV light stability. They improve the activity of the HAS. Doverphos HiPure 4, introduced by Dover Chem. Corp, is a high purity processing and heat stabilizer, cost effective, and FDA approved for food contact applications and medical devices. 

Plastics are compounds made up of resins (polymers) and additives. Additives, which are used to obtain specific effects in the plastic material during fabrication or use, expedite processing, heighten certain properties, provide color, and furnish the needed protection during fabrication and use. Some of the key additives used in thermoplastic piping are heat stabilizers, antioxidants, ultraviolet saeens, lubricants, pigments, property modifiers, and fillers. Table 2.1 lists some of the main additives used in plastic piping materials and their purpose. 

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. 

Compounded pellets are those that have been through an intermediate mixing extrusion to improve the properties of the first-generation polymer with additives such as colorants, stabilizers, and fillers. The compounding step gives these pellets an additional heat history, which should be considered as a potential effect on polymer degradation. 

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