Oxidation stability aromatics, effect

Physical properties of carbon black-filled EPR and EPDM elastomers have been found to be comparable with the suUur-cured analogues [372]. Aromatic oils increase the optimum dose requirement for these compounds due to the reaction of the transient intermediates formed during radiolysis of the polymer with the oil as well as energy transfer which is particularly effective when the oil contains aromatic groups. The performance and oxidative stability of unfilled EPDM as well as its blend with PE [373], and the thermal stabdity and radiation-initiated oxidation of EPR compounds are reported by a number of workers [374,375]. 

Nadimide- and V-CAP type PMR resins use aliphatic endcaps (multiple carbon-carbon double bonds) to affect crosslinking. Such aliphatic moieties adversely effect the thermal oxidative stability of the cured system. Effort is therefore directed towards PMR resins which use reactive aromatic endgroups to obtain cured polymers free of aliphatic chain- or crosslinking segments. 

The stability of the products from coal-derived syncrudes must be examined carefully. Many unique compounds are present in these syncrudes peri-condensed aromatics and naphthenes, oxygen compounds, and asphaltene-like hydrocabons. Traces of these compounds may remain in the hydrotreated product and their effect on jet, thermal, and oxidation stabilities cannot be predicted from the behavior of petroleum products. 

Environmental demands and are as follows (a) improved fuel economy (reduced viscosities, reduced friction, special viscosity improvers), (b) reduced oil consumption (unconventional base oils, improved seal compatibility), (c) extended oil life (improved thermo-oxidative stability), (d) extended engine life (improved detergents and antiwear additives), (e) beneficial effects on emission/after treatment hardware (new additives), (f) technological and environmental sensitivity (no halogens, limited metal types/concentrations, new organic compounds), (g) recyclability (limitations the polycyclic aromatic hydrocarbons content and high chlorine levels (Havet et al., 2001 Waara et al., 2001). 

Recently, the X-ray analysis of 3,4-bis(methylthio)-l,2,5-thiadiazole 1-oxide demonstrated that the oxidized form of the ring is essentially non-aromatic and shows a pyramidal sulfoxide structure. Interaction between the sulfur lone pair of electrons and the diene is small, the C(3)—C(4) bond length lying closer to that of cyclopentadiene than of thiophene or (3). Theoretical calculations indicate that aromaticity effects lower the inversion barrier nearly equally in the thiophene and thiadiazole 1-oxides by stabilizing the planar transition state and destabilizing the pyramidal structure (82JA1375). 

The formation of a dinitrone - in contrast to the ozonation of DOPPD - is inhibited most probably just by the stabilizing effect of the N-phenyl group. The same structural moiety stabilizes aromatic nitro and nitroso compounds formed via the amine oxide pathway no Bandrowski bases were detected in the ozonation product of HPPD. The authors (40) favor the N-alkyl side reactivity in HPPD also in the interpretation of the formation of N-phenyl-N -acyl-l,4-PD, i.e. in the condensation with aliphatic aldehydes. 

Clay treating has a marked effect on the oxidation stability of oil 7 (Table 5.4), described as a moderately aromatic residual-type base stock of intermediate VI. 

Von Fuchs and Diamond (Shell Oil) pursued these results further by examining the effects of increasing the content of the aromatics on base stock oxidation rates.15 They undertook this study because of the increasing realization that while solvent extraction technology improved lubricant performance, overextraction of the base stock could make it less resistant to oxidation because of removal of the autoretardant components. Since extraction removed aromatics and nitrogen and sulfur compounds, a relationship between these levels and oxidation stability seemed likely. 

The oxidative stability of the fractions and some blends (no antioxidants or accelerators present) were measured from induction times at 170°C and 190°C using DSC.5 These times, in Table 5.14, show that for the saturates alone, oxidative stability at 170°C decreases with increasing complexity (more naphthenes, fewer isoparaffins) that is, polycyclic naphthenes do not have good oxidation resistance, as we have seen already. Polynuclear aromatic fractions added to the saturates at 16% stabilize the blends (induction times increase), with the more polynuclear and more thiophenic fractions having the greatest effect. Monoaromatics had no effect or actually decreased the stability of the more isoparaffinic fractions. We have seen this effect before, where naphthalenes and higher polycyclic aromatics due to sulfur... 

R.A. Dine-Hart, W.W. Wright, Effect of structural variations on the thermo-oxidative stability of aromatic polyimides, Makromol. Chem. 153 (1)(1972) 237-254. 

Thermooxidative degradation, which is more of a problem with polyether polyurethanes, can be inhibited by the addition of antioxidants. Mathur et al. have studied the effectiveness of several commercial antioxidants for stabilizing polyether polyurethanes against UV and thermally induced oxidation. Stabilizers against thermooxidation include hindered phenols, aromatic amines, and phosphites. Commercially available antioxidants have recently been reviewed by Allbee. Replacement of some, or all, of the ether linkages in polyether polyurethanes by silicone has led to a marked improvement in the thermooxidative stability of the resulting polymer. " ... 

It was described earlier that the interaction between radical anions and ketones in a partially oxidized, PCB contaminated oil, produces alcohols. It would therefore be expected that the formation of aromatic alcohols in particular would give rise to natural oxidation inhibitors. It is very likely that the effectiveness of the inhibitors formed in this way is small, relative to DBPC but, in any case, the oil should not be deleteriously affected by the treatment provided that the reclaimed oil has DBPC added to it. The oxidation stability of the processed oil should then be as good as, or possibly better than, new oil. Experimental data have shown that the oxidation stability of oils treated by the MOP system are the same as new oil by ASTM D2112. 

Extraction is typically the second process although this is not always the case. The primary goal of extraction is to remove aromatics and polar molecules. This is accomplished through solvent extraction of the distillate using NMP, furfural, or phenol. By removing aromatics, the VI is raised. Secondary effects of extraction include reduction in the refractive index, reduction in density, reduction in Conradson carbon and improvement in color, color stability and oxidative stability. 

Several stabilizers are useful in minimizing oxidative degradation during thermoplastic processing or in the bulk soHd. Phenothiazine, hindered phenohc antioxidants such as butylated hydroxytoluene, butylatedhydroxyanisole, and secondary aromatic amines in concentrations of 0.01—0.5% based on the weight of polymer, are effective. 

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