Polymer stabilization processing stability

As discussed in Chapter 10, a wide variety of additives is used in the polymer industry. Stabilizers, waxes, and processing aids reduce degradation of the polymer during processing and use. Dyes and pigments provide the many hues that we observe in synthetic fabrics and molded articles, such as household containers and toys. Functional additives, such as glass fibers, carbon black, and metakaolins can improve dimensional stability, modulus, conductivity, or electrical resistivity of the polymer. Fillers can reduce the cost of the final part by replacing expensive resins with inexpensive materials such as wood flour and calcium carbonate. The additives chosen will depend on the properties desired. 

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. 

Polymer structure and formulation. As an example, Woo et al. [7] measured OIT values for series of commercial PVC resins and polyester thermoplastic elastomers (TPEs). The researchers used the ASTM D3895-80 procedure, but substituted air as the oxidising gas instead of pure oxygen. A dependency on thermal processing history of the TPE film samples appeared to influence the measured OIT in the PVC study, chemically different chain ends affected polymer stability and hence OIT values. 

The generation of acetaldehyde (AA) as a decomposition product in PET processing plays an important role in bottle manufacturing. This depends on the vicious circle of the polymer stability, the AA content of the chips prior to processing, and the processing conditions. The basis of stability is a qualified polymer produced under appropriate conditions. This argument also includes the SSP process which can drastically reduce the AA content of the chips, as shown in Figure 13.21. 

Alkene polymers such as poly(methyl methacrylate) and polyacrylonitrile are easily formed via anionic polymerization because the intermediate anions are resonance stabilized by the additional functional group, the ester or the nitrile. The process is initiated by a suitable anionic species, a nucleophile that can add to the monomer through conjugate addition in Michael fashion. The intermediate resonance-stabilized addition anion can then act as a nucleophile in further conjugate addition processes, eventually giving a polymer. The process will terminate by proton abstraction, probably from solvent. 

Synthetic polymers stabilize metal colloids as important catalysts for multi-electron reactions. Polynuclear metal complexes are also efficient catalysts for multielectron processes allowing water photolysis. 

Polymer-stabilized Au NPs have been the object of intense research in recent years because, apart from their intrinsic synthetic interest, these hybrid materials have interesting properties and potential applications. There are also several advantages in the use of polymers as stabilizers enhancement of long-term stability adjustment of solubility or amphiphilicity of nanoparticles, tuning of the properties of Au NPs, and the promotion of compatibility and processability. 

Chemical Stability. Chemical stability is just as important as the physical stability just discussed. In general, chemical deterioration of the polymers is no problem, and they can be stored at room temperature for years. However, the polymeric surfaces are subjected to an extreme variety of chemicals during the accumulation process. Some of these may react with the polymer. For example, reactions of styrene-divinylbenzene polymers and Tenax with the components of air and stack gases have been documented (336, 344, 540). The uptake of residual chlorine from water solutions has also been observed in my laboratory and elsewhere (110, 271, 287). Although the homogeneous nature of synthetic polymers should tend to reduce the number of these reactions relative to those that occur on heterogeneous surfaces of activated carbons, the chemical reaction possibility is real. In the development of methods for specific chemicals, the polymer stability should always be checked. On occasion, these checks may lead to... 

Hyperbranched PEI or functionalized PEIs with glycidol (PEI-GLY), glu-conolactone (PEI-GLU) or lactobionic acid (PEI-LAC) have been used as support materials for metal nanoparticles in water. Polymer-stabilized metal nanoparticles were prepared in a two-step process. After complexation of the metal ions with the respective polymer in a first step, a chemical reduction with sodium borohydride was performed in a second step to obtain the metal... 

Relevance of Polymer Stabilization to Flame-Retardant Processes.34... 

RELEVANCE OF POLYMER STABILIZATION TO FLAME-RETARDANT PROCESSES... 

Plastics have to be stabilized to withstand chemical and physical stresses during different phases of their lifetime. Stabilizers protecting plastics against particular degradation processes were developed and commercialized by various companies. According to their principal activity mechanisms, polymer stabilizers are conventionally classified as antioxidants, photoantioxidants, photostabilizers, heat stabilizers and... 

Spivack J D, Pastor S D, Patel A and Steihuebel L D (1985) Bis- and trisphosphites having dioxapho-sphepin and dioxaphosphocin rings as polyolefin processing stabilizers, In Polymer stabilization and degradation, Klemchuk P (Ed), ACS Symp Ser 280 247-257. 

Kissi NE and Piau J-M, "Stability Phenomena During Polymer Melt Extrusion" in Piau J-M and Agassant J-F (Eds), "Rheology for Polymer Melt Processing", Rheology Series, Vol. 5, Elsevier, Amsterdam, 1996, pp 389-420. Langelaan HC and Gotsis AD, J Rheol 40 (1996) 107. 

Traces of formaldehyde, present in neat end-capped polymer or produced by processing polymer under abusive conditions, detract from polymer stability. Commercial resins typically contain formaldehyde scavengers. Nitrogen compounds, especially amines and amides, epoxies, and polyhydroxy compounds, are particularly efficacious scavengers. 

Shifting the site of nucleation to the droplets greatly enhances the robustness of the nucleation process to recipe variations, inhibition levels, and changes in operating procedure (initiation rate and/or agitation rate). As a result of droplet nucleation, polymer-stabilized miniemulsion polymerizations are far less sen-... 

An enhanced robustness can benefit a process in a number of ways. Since the polymer-stabilized miniemulsions are less susceptible to disturbances, their polymerization is less hkely to be affected by operator error, fluctuations in feed stream concentrations and residual contaminants in the reaction vessel. Many monomers contain species that can act as inhibitors or retarders as a result of monomer production, storage, or processing. These contaminants also cause batch-to-batch variability in particle number in macroemulsions. Therefore, miniemulsion polymerization may be an alternative to seeded polymerization as a way of maintaining robust control of particle number. 

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