Approaches to Polymer Stabilization

Organosulfur compounds hindered amines oigano-phosphates, etc. Thermal stabilizers Thermal stabilizers are antioxidants that protect polymers during thermal treatments. For example, oiganosuUiir compounds are efficient hydroperoxide decomposers, which thermally stabilize the polymers, while hindered amines efficiently scavenge radicals which are produced by heat 

Paraffin waxes ethylene diurea (EDU) p-phenylenedi-amines, etc. Antiozonants Antiozonants prevent or slow down the degradation of material caused by ozone gas in the air. For example, paraffin waxes form a surface barrier for ozone 

Oxanilides (for polyamides) benzophenones (for PVC) benzotriazoles and hydroxyphenyltriazines (for polycarbonate) TiO, etc. UV absorbers The UV absorbers dissipate the absoibed light energy from UV rays as heat by reversible intramolecular proton transfer. This reduces the absorption of UV rays by polymer matrix and hence reduces the rate of weathering 

Hindered amine Light stabilizers Hindered amine scavenges radictils which are produced by light. This effect may be expltiined by the formation of nitroxyl radictils 

Nickel compounds (for polyolefins) Quenchers A quencher induces harmless dissipation of the energy of photoexcited states 

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There are also other approaches to polymer stabilization (Aldiss 1989). For example, it was found that the formation of composites of two conducting polymers, one of which is air stable, improves the stability of polymer materials. Experiments carried out with pyrrole/polyacetylene and polyaniline/ polyacetylene composites have shown that the composites appeared to be more stable than doped polyacetylene and possessed mechanical properties similar to polyacetylene. Stabilization can also be achieved chemically by copolymerization. In particular, it was found that copolymerization of acetylene with other monomers such as styrene, isoprene, ethylene, or butadiene was accompanied by the increase of improvement of polymer stability (Aldiss 1989). Crispin et al. (2003) established that... 

The approaches to polymer-stabilized copper nanomaterials can be divided into three main classes (i) the so-called polyol process (ii) soft-template processes in which the polymer is employed (either as such or in combination with other capping agents), aiming exclusively at stabilization of the Cu phases and (iii) dendrimer-encapsulation. 

Within the last decade, there have been new approaches to polymer stabilization. One new stabilizer chemistry is based on the hydroxylamine functionality that can serve as a very powerful hydrogen atom donor and free radical scavenger as shown in Figure 15(a) and hydroperoxide decomposer as shown in Figure 15(b). 

Another approach to safer stabilization is to use a biological antioxidant such as vitamin E (a-tocopherol is the active form of vitamin E, AO-9, Table la). It is essentially a hindered phenol which acts as an effective chain breaking donor antioxidant, donating a hydrogen to ROO to yield a very stable tocopheroxyl radical, a-Tocopherol is a very effective melt stabilizer in polyolefins that offers high protection to the polymer at very low concentration [41], (Table 2). 

Now we turn our attention to the water and the solids that compose the myriad of fresh and processed foods we consume. When a component is added to water (or coexists with water, as in a fresh food), the overall mobility of the water decreases, compared to that of pure water. The magnitude of the decrease depends on the number, amount, and nature of the component(s) added, as well as the effect of any processing methods used. In the past, researchers focused their attention on the relationship between water (activity, availability, mobility) and food stability. Based on the introduction of the polymer science approach to food stability by Slade and Levine (1985, 1988, 1991), the focus has shifted to the relationship... 

Hunter, R. J., Foundations of Colloid Science, Vol. 2, Clarendon Press, Oxford, England, 1989. (Undergraduate and graduate levels. Along with Volume 1, these two volumes cover almost all the topics covered in the present chapter at a more advanced level. Volume 1 discusses DLVO theory and thermodynamic approaches to polymer-induced stability or instability and is at the undergraduate level. Volume 2 presents advanced topics (e.g., statistical mechanics of concentrated dispersions, rheology of dispersions, etc.).)... 

Approaches to photoanode stabilization based on polymer films containing redox functionalities have been reviewed elsewhere, e.g., Refs. [6, 373j. 

Scheutjens and Fleer (1982) have developed a theory for depletion stabilization and depletion flocculation based upon their statistical thermodynamic approach to polymer adsorption and steric stabilization. This theory is cast in terms of the most primitive model for a polymer molecule, the random flight chain. This weakens the theory in so far as providing quaintitative predictions at the fundamental level for real systems is concerned. The theory does, however, offer qualitative results over a wide range of conditions, being especially powerful in establishing the various trends involved. 

Introduces the quantum decoherence theory approach to polymer conformational stability and transitions... 

Tremendous research works have been performed on the synthesis of conducting polymer nanomaterials using dispersion polymerization method [181-188]. There are two categories of dispersion polymerization in order to fabricate the conducting polymer colloids. The first approach forms polymer stabilizer coated conducting polymer nanoparticles. In this case, the monomer and oxidant are dissolved in a stabilized liquid mediiun and the formation of insoluble conducting polymer nanoparticles occurs as the polymerization proceeds. 

Huang, Y, Yang, K., and Dong, J.-Y. 2007. An in situ matrix functionalization approach to structure stability enhancement in pKjlyethylene/montmorillonite nanocomposites prepared by intercalative polymerization. Polymer 48 4005-4014. 

Another approach to the stability of the metal-polymer interface proves useful as well. Here, the energy of all individual atomic constituents is subtracted from the total energy of the metal-polymer complex. This is referred to as the cluster assembly energy (CAE) and is representative of total stability. The CAE serves as an indicator of stability when substantial charge transfer occurs affecting states... 

Garti, N. (1998) A new approach to improved stability and controlled release in double emulsions, by the use of graft-comb polymeric amphiphiles. Acta Polymer., 49,606-616. 

The comparison of the results obtained in this study for the LCP degradation imder processing temperatures with the peculiarities of some thermally stable polyheteroaiylenes degradation [14] brings to light some common features carbonization of the structure, H2 evolution, improvement in thermo-oxidative stability with transition metal compoimds. That is why we took into accoimt the stabilization of polysulfones, aiyl-aliphatic polyimides, polyamides etc. The approach to such stabilization is based on the following proposals on the mechanisms of the above said polymer degradation ... 

In a novel approach to enzyme stabilization, chymotrypsin, trypsin and subtilisin have been separately coupled reductive amination (NaBHjCN) to polymers prepared from N-methacrylamido-sugar monomers, themselves synthesized from 2-,3- or especially 6-aroinodeoxy-D-glucose. About 3 lysines residues per enzyme molecule are conjugated, and the conjugates are more stable than the native en mes. ... 

Commercially feasible approaches to complex stabilization of polymer blends are required. 

One common form of deterioration results from exposure to light [in particular, ultraviolet (UV) radiation]. Ultraviolet radiation interacts with and causes a severance of some of the covalent bonds along the molecular chains, which may also result in some crosslinking. There are two primary approaches to UV stabilization. The first is to add a UV-absorbent material, often as a thin layer at the surface. This essentially acts as a sunscreen and blocks out the UV radiation before it can penetrate into and damage the polymer. The second approach is to add materials that react with the bonds broken by UV radiation before they can participate in other reactions that lead to additional polymer damage. 

In the 1990s this approach became more common in order to ensure sufficient compressive strength with the trend to lower bulk densities. Furthermore the proportion of SAN to polyol has been increased to about 40%. This may lead to serious stability problems and care must be taken to control the size and distribution of the particles and prevent agglomeration. Polymer polyols using polystyrene as the polymer component have recently become available (Postech-Shell) and are claimed to exhibit good stability, low viscosity and less discolouration as well as providing price advantages. 

Photostabilizers, regardless of their mechanism of action, have been added as low molecular weight materials at some point in processing. Subsequently, these stabilizers are often lost in further processing due to their volatility or else later migrate to the surface and evaporate. One method which avoids this modifies the polymer to include the quencher as an additional monomer in the polymerization. This paper will describe some recent efforts in our laboratory to pursue this latter approach in the stabilization of poly(ethylene terephthalate). 

A very fast testing of polymer stability is based on non-isothermal experiments (DSC, chemiluminescence) where the whole plot of the parameter followed may be visualized over a large temperature interval. The transfer of non-isothermal data to isothermal induction times involves a variety of more or less sophisticated approaches such as published in Ref. [8] or discussed later. 

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