Antioxidant effect polyamide

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

For quality control reasons, rapid screening methods are needed to identify the volatiles in polymeric materials collected for recycling. HS-SPME-GC-MS was shown to be a fast and sensitive method to screen for brominated flame retardants in recycled polyamide materials [78]. HS-SPME effectively extracted several brominated compounds, all possible degradation products from the common flame-retardant Tetrabromobisphenol A from recycled polyamide 6.6. Furthermore, the high extraction capacity of the PDMS/DVB stationary phase towards aromatic compounds was demonstrated, as the HS-SPME-GC-MS method allowed the extraction and iden-tiflcation of brominated benzenes, from a complex matrix only containing trace amounts of analytes. In addition, degradation products from an antioxidant, a hindered phenol, were extracted. Figure 14 shows a typical chro-... 

In contrast to polyamides in polystyrene phenolic antioxidants are not able to reduce the decrease in tensile strength during UV irradiation [141]. UVAs as well as HALS stabilizers are effective in polystyrene (PS). The best protection can be reached by using combinations of a UVA and a HALS. According to Gugumus [133,134] the synergism between UVA and HALS is distinct when the time until a AYI = 5 is taken as failure criterion (see Table 17.12). However, when as criterion the yellowness index after 1600 h in a Weather-Ometer is taken, the synergism between a UVA and a HALS is much smaller (see Fig. 17.14). 

The largest volumes of phenjienediamines are used for the production of polymers, primarily polyurethanes, where the diisocyanates of toluenediamines (meta isomer) are used. For the manufacture of polyamides both meta and para isomers are used. Another significant use for -phenylenediamines is as antioxidants and antiozonants for elastomers, plastics, and petroleum products. The /V-alkyl-/V-aryl- -phenylenediamines are by far the most commonly used and represent the bulk of the volume of the iV-substituted -phenylenediamines reported in Table 3. Some iV iV-dialkyl compounds ate also stiU used as antiozonants, but they oxidize more rapidly and lose activity sooner. The iV,iV-diaryl-/)-phenylenediamines ate used primarily as antioxidants, especially where copper and other harmful metals might be present. -Dinaphthalenyl- -phenylenediamine is especially effective in this application. The... 

Porter, L.W., Black, D.E., and Drolet, M.A., Use of polyamide oxidative fluorescence test on hpid emulsions Contrast in relative effectiveness of antioxidants in bulk versus dispersed systems, J. Agric. Food Chem., 37, 615, 1989. 

All the brands of polyamides studied, in conjunction with an antioxidant, manifest considerable effectiveness in the stabilization of polyformaldehyde. ... 

Experiments we conducted have shown that the addition of a polyamide alone or an inhibitor alone is relatively ineffective, somewhat reducing the gas evolution in the oxidation of polyformaldehyde. Only the joint introduction of a polyamide and an inhibitor proves far more effective than the introduction of the polyamide and antioxidant individually (Fig. 76). The effectiveness of the inhibitor was evaluated in [22] according to the amount and rate of gas evolution in the thermooxidative destruction of polyformaldehyde [18] on a static setup. 

The optimum ratio of the polyamide and antioxidant can be considered to be 0.6 0,4. However, within a broad interval of ratios (0.4-0.8 with respect to polyamide), deviation from the optimum has almost no effect. An analogous picture is also observed in the establishment of the optimum ratios of polyamide and antioxidant according to the loss in weight in the oxidation of polyformaldehyde (Fig, 81),... 

Protection from photoaging can be accomplished by the introduction of antioxidants that suppress the processes of photosensitized oxidation. For example, effective stabilizers of polyamide film are the 2,6-di-tert-butyl-4-methylphenyl ester of pyrocatecholphosphorous acid, 2,6-di-tert-butylhydroquinone, and a mixture of potassium iodide with copper naphthenate. All these additives exhibit considerable protective action in the thermal oxidation of polyamides as weU [92]. 

By far the most important stabilisers are the hindered phenols, which are used in a wide range of polymers including the polyolefins, (e.g., PE and PP), polyamides, polycarbonate and PET. These stabilisers are effective both during processing at high temperature and for long-term use under ambient conditions. For increased effectiveness, they are usually combined with other stabilisers to attain an optimised combination of stabilisation and other properties such as discoloration. Often, the antioxidant is physically lost, primarily by extraction or volatilisation, rather than by chemical consumption [145]. The trend is therefore to use higher molecular mass antioxidants [132,139, 146]. 

Introduction of additives is a well-known method for the mechanism of the chemical reaction investigation. The experience has shown effectiveness of triple stabilizing formulations (Cu-containing compound + phenolic antioxidant + phosphite) for aryl-aliphatic polyamides, polyphthtalamides and other thermally stable polymers. The conception of such formulation is based on the mechanisms of the stabilizing action of the components ... 

Naugard A la a cost effective amine based antioxidant finding use in polyamides and carbon black filled olefin formulations for use in geomembranes, wire and cable jacketing, and irrigation piping. 

However, efficient grafting and dispersion was found to reduce the short-term thermally induced morphological changes. Use of efficient heat stabilizers and antioxidants are, of course, necessary to suppress the long term, thermo-oxidative effects of embrittlement in rubber toughened polyamides. 

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