End-use stability

Mechanisms of Degradation Inhibitors. The degradation mechanisms described above have no little effect on end-use stability and processing stability of polypropylene. Indeed, without stabilizers and antioxidants to inhibit such degradation reactions, polypropylene would have limited usefulness as a structural plastic if any usefulness at all. 

End-use stability and performance are the net result of good design and colorant selection. In the case of colorants, end-use stability and performance most often refer to ability to resist attack by chemicals, solvents, heat, weather, and gases and aerosols found in the product environment. The resistance of a plastic product to attack by any of these in a laboratory can produce definitive results. In combination, these elements are difficult to quantify not only in the laboratory but also in actual exposure to them. Thus, testing throughout a project from start to finish is vital to the technical and commercial success of that plastic product. In this chapter the focus is on the role the colorants play in the success. 

BNX 1035 is a high molecular freight hindered phenolic antioxidant. It provides excellent processing and end use stability to a broad range of polymers. 

The basic type of stabilizer system selected is often dictated by end-use or regulatory constraints (NSF, PPI, FDA, and BGA). Subsequent choice of a specific stabilizer should be made with the major objective of achieving optimum cost-performance How much processing stability is available per dollar of stabilizer cost Or, conversely, what will be the lowest-cost choice to furnish the required processing stability for a particular process— including all safety factors such as regrind extmsion, power failures, and end-use stability needs A level of stability much beyond the necessary level can translate to significant unnecessary costs. Laboratory tests (Brabender, mill stability, and Metrastat oven stability) can furnish an indication of comparative cost-performance, but the final decision really should be based on... 

Nearly all polymeric materials require the addition of antioxidants to retain physical properties and to ensure an adequate service life. The selection of an antioxidant or system of antioxidants is dependent upon the polymer and the anticipated end use. A product that will not be exposed to the elements for a long period of time such as polyethylene grocery bags does not need a long term stabilizer polyethylenes used to iasulate communication cable must be stabilized for many years of service. 

Internal surfactants, i.e., surfactants that are incorporated into the backbone of the polymer, are commonly used in PUD s. These surfactants can be augmented by external surfactants, especially anionic and nonionic surfactants, which are commonly used in emulsion polymerization. Great attention should be paid to the amount and type of surfactant used to stabilize urethane dispersions. Internal or external surfactants for one-component PUD s are usually added at the minimum levels needed to get good stability of the dispersion. Additional amounts beyond this minimum can cause problems with the end use of the PUD adhesive. At best, additional surfactant can cause moisture sensitivity problems with the PUD adhesive, due to the hydrophilic nature of the surfactant. Problems can be caused by excess (or the wrong type of) surfactants in the interphase region of the adhesive, affecting the ability to bond. 

Water-soluble polymers eomprise a major elass of polymerie materials and are used in a wide variety of applieations. Synthetie water-soluble polymers inelude poly(vinyl aleohol), poly(aerylamide), poly(aerylie aeid), poly(ethylene oxide), poly(vinyl pyrrolidone), eellulosies, and many eopolymers of these types. Their end uses are quite varied and their applieations depend mainly on their viseosify-ing, rheologieal, and surfaee-aetive properties (1). For example, poly (vinyl aleohol) is used in adhesives, fibers, textile and paper sizing, paekaging, as a stabilizer for emulsion polymerization, and as a preeursor for the manufaeture of poly(vinyl butyral), whieh is used in automotive windshields. Poly(vinyl aleohol) is also the world s largest volume, eommodity, water-soluble polymer. 

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. 

For a given level of fuel at a given thickness with the same halogen content, most halogenated compounds show more or less the same flame retardancy. The key differences among these FR additives are effects on flow, melt stability, mechanical properties and long-term ageing of the FR-PBT blend. Different end-use requirements may call for the addition of different FR additives. 

End-use applications for naphthalate-based polyester resins depend on optimizing the balance of properties desired in a specific application. Usually this involves optimizing the orientation process (uni- or bi-axial) with its accompanying crystallinity development. Subsequent heat setting may be included when additional improvements in thermal stability are needed. 

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