Amine Antioxidants Research Articles

The Screening of Antioxidants for Furfural

Solvent refining is the main process of refining lubricant oil and furfural is often used as a solvent. One of the methods of avoiding the oxidation of furfural is by addition of antioxidants to it. The antioxidants not only heighten the antioxidation characteristics but also enhance the yield and quality of oil. In this paper, some phenolic and amine antioxidants are investigated for furfural oxidation at 90°C and at room temperature. These antioxidants are 2,6-di-tert-butyl-phenol (T501); 2,2′-Methylene bis(2,6-Di-t-Butylphenol) (MB26); 4,4′-Furfurylidene bis(2,6-Di-t-Butylphenol) (FB26); 2,2′-Methylene bis(4,6-di-t-butylphenol) (MB46); N,N′-Di-sec-butyl-p-phenylenediamine (DBPDA); and N,N′-diethylhydroxylamine (DEHA). The antioxidation performance of DBPDA for furfural is much better than that of phenolic inhibitors at room temperature, so it is set at 90°C. When the 100 ppm inhibitor is used, the effect of FB26 is as good as that of DEHA. When the 500 ppm inhibitor is used, the effect of antioxidation of FB26 is better than that of DEHA and as good as that of DBPDA. Therefore, it is proposed that FB26 should be used as an antioxidant at normal temperature and DBPDA should be used as an antioxidant at higher temperature.

Addition of an Aminic Antioxidant to a Hindered Ester-Based Heat Resisting Oil to Improve Lubrication for Press Forming of Magnesium Alloy Sheets

High heat resistance is required for the lubricant used during the mass production of press formed magnesium parts using a warm press forming process. The heat resistance of a hindered ester has previously been found to be high, but insufficient at temperatures around 573 K. Therefore, further improvement of hindered ester-based heat resisting lubricants is required. This paper describes the influence on lubricity of adding aminic antioxidants to hindered esters. The results showed that excellent heat resistance was obtained by adding 5 to 20% styrenated diphenylamine. While a 5% addition improved heat resistance and inhibited lubricant degradation, addition of 10 or 20% additive resulted in decreased lubricity. Furthermore, the best lubricity was obtained when DLC-coated carbide was used as the die material in combination with the lubricant containing aminic antioxidant.

On increasing the efficiency of amine antioxidant

AbstractThe amine antioxidant, Neozon D, was treated to increase its effectiveness in suppressing oxidation of polyethylene in contact with copper. It was found that this antioxidant becomes more efficient after interaction with a copper substrate. These experimental results show that the role of substrate is to catalyze oxidation transformations in the antioxidant. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 401–406, 2005

Benefits of antioxidants in lubricants and greases assessed by pressurised differential scanning calorimetry

The long-term thermo-oxidative stability of lubricants and greases is a prerequisite to meet today's ‘stay in grade’ and extended drain interval requirements. To achieve this goal, there is a need for a better understanding of thermo-oxidative lubricant degradation and of how antioxidants can affect this process. In this paper a two-stage degradation model is discussed. Primary degradation leads to the formation of very reactive species such as radicals and peroxides. These are the precursors for generating secondary degradation products, such as oligomers, sludge, or deposits. By applying the theory of reaction kinetics and the Arrhenius law, quantitative correlations may be derived between oxidation induction time (OIT) and temperature, and between OIT and antioxidant treat level. Pressurised differential scanning calorimetry (PDSC) data confirm these theoretical findings and demonstrate the benefit of the addition of aminic antioxidants in comparison with high-molecular-weight hindered phenolic antioxidants.

Thermal Oxidation of Polyethylene Films Containing Dispersed Copper and Amine Antioxidant

Thermal oxidation of polyethylene filled with dispersed copper and containing an amine antioxidant was studied. The concentration ranges in which the catalytic effect of the metal on the polymer oxidation or the stabilizing effect of the antioxidant prevails were determined. Under certain conditions, dispersed copper enhances the stabilizing effect of the antioxidant.

Analysing the Content of Antioxidants in PP Materials

The effective stabilisation of polypropylene (PP) plastics for durable applications is often achieved by compounding with a combination of hindered phenolic (SHPh) and amine (HAS) antioxidants. Hence, to assess the lifetime of these materials it is useful and often necessary to test the status of each type of stabiliser used during or after exposure. In this paper, we discuss the measurement of the steady-state rate of post-induction oxygen consumption during the model reaction of initiated cumene oxidation. This is in order to determine antioxidants of the HAS type derived from 2,2.6,6-tetramethylpiperidine. As already published, the measurement of the induction period can be used for the simultaneous determination of the SHPh content. The rate of the post-induction oxidation reaction depends linearly on the reciprocal square root of the concentration of this HAS-antioxidant type, for a sufficiently wide concentration range. The presence of sterically hindered phenolic stabilizers (SHPh) and organophosphites usually of the kind used has no influence on this post-induction phase. Thus the dependence established offers a remarkable possibility of determining simultaneously the effective stabiliser concentrations of the HAS and SHPh antioxidants by means of one model reaction. We present the results of the successful determination of a HAS and an SHPh antioxidant in PP granules. They have to be ground down to particles with mean dimensions smaller than 250 μm. We found perfect coincidence with the data given by the granule producer. Thus the model reaction of initiated cumene oxidation is a useful method for the simultaneous quantitative study of SHPh and 2,2.6,6-tetramethylpiperidine derived HAS-antioxidants, even in the presence of organophospites in PP, and possibly other plastics.

Antioxidants as Sources of Plastics Discoloration: Structural Effects

Sacrificial transformation (consumption) of antioxidants is an inevitable consequence of their active role in the protection of plastics from oxidation. The process results in various new products with conjugated double bonds, some of them being responsible for plastics discoloration. Structures of principal colorants arising from phenolic and aromatic amine antioxidants and phenolic UV absorbers are outlined.

Study on aging of clay-rubber masterbatch from modified clay

Clay was modified by using a polymeric coating agent, a silicane coupling agent, and a titanate coupling agent together with the antioxidant for preparing the clay–rubber masterbatch. After the thermooxidative, photooxidative, and ozone aging, the properties of the masterbatch were also determined. The results indicate that, under the synergistic actions of the polymeric coating agent, antioxidant, and coupling agent, the thermooxidative and photooxidative aging resistances of the masterbatch were greatly improved. The properties of ozone aging resistance of the masterbatch can be increased by 50% under the combined action of a new kind of amine antioxidant with a titanate coupling agent. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 338–342, 2001

Thermo-oxidative degradation of linear low density poly(ethylene) in the presence of carbon black: a kinetic approach

The mechanistim of carbon black (CB) effects on the thermo-oxidative degradation of linear low density polyethylene (LLDPE) was studied. Quantitative measurement, in both the kinetic and diffusion mode, of the kinetics of LLDPE's thermo-oxidative degradation was done in four ways as follows: (i) in the absence of both CB and a stabilizer; (ii) in the absence of a stabilizer but in the presence of CB (Black Pearl 3700) (2), (iii) without CB but in the presence of an amine stabilizer (AI) (iv) with both CB and AI. The stabilizer chosen for this study was polymerized 1,2-dihydro-2,2,4-trimethylquinoline (Trademark: Naugard Super Q). Measurements were done at 180° C, the AI concentration being (1.1–9.8)×10 −2 mol/kg, based upon a molecular mass of 0.874 kg/mol for the monomer unit. CB concentration was 5% by weight while oxygen pressure pO 2=(50–300) mm Hg. Quantitative parameters for the thermo-oxidative degradation of LLDPE were established for kinetic and diffusion conditions. The kinetics of the inhibited thermo-oxidative degradation of LLDPE, in the presence of an amine antioxidant such as Naugard Super Q, was found to be essentially no different than the degradation kinetics in the presence of hindered phenolic antioxidants. It was shown that CB may act as an inhibitor albeit a rather weak one. However, during inhibition of the thermo-oxidative degradation of LLDPE with AI, CB shows itself to be an effective synergist, especially over the AI concentration range of from (2 to 6) × 10 −2 mol/kg (0.4–1.2% by weight). The most probable explanation for this synergy lies in the adsorption of stabilizer radical In onto the surface of the CB particles and a resultant decrease in the value of the rate constant k 10 of the chain transfer reaction between a polymer molecule RH and Inhibitor radical In .

Action mechanism of oil‐soluble potassium‐containing antioxidant synergists: evidence for micellar inhibition

One of the most promising synergistic compositions for use in high‐temperature lubricants comprises aromatic amine and an oil‐soluble alkali metal compound although action mechanism of this synergism is still questionable. The greatest efficiency of this additive pair is demonstrated for PEE based compositions using thin‐layer oxidation test at 250°C. Addition of potassium‐containing additive to aromatic amine antioxidant results in decreasing of formation of strongly‐oxidized substances. Determination of electrophysical parameters (dielectric constant and specific conductivity) for tested samples indicates formation of reversed micelles at the potassium content of about 0.6⋅10‐2 mol/l, and the latter corresponds to the potassium content that provides the highest antioxidant efficiency. A novel method of inhibiting oxidation is proposed: micellar inhibition that suggests novel possibilities for protection of lubricants against oxidative degradation.

Medium effects on the antioxidant activity of dipyridamole

Very strong medium effects have been observed when testing the antioxidant activity of dipyridamole (DP) in different media such as benzene, tert-butanol, methanol solutions and egg yolk lecithin unilamellar and multilamellar vesicles. Actually, dipyridamole behaves as a very poor antioxidant in benzene while its ability to inhibit the lipid peroxidation reaction increases with increasing solvent polarity, being the highest in lipid vesicles. This behavior can not be rationalized on the basis of the classical chain breaking mechanism which operates in the case of phenolic and amine antioxidants and involving the transfer of a hydrogen atom to peroxyl radicals. An explanation is instead given in terms of an electron transfer reaction which leads to the oxidation of DP by the chain carrying peroxyl radical to give the dipyridamole cation radical, DP + •, and the peroxyl anion LOO −, and whose rate constant is expected to increase in strongly polar media. EPR and electrochemical data supporting this interpretation have been collected.

Microhardness testing of plated coatings

The aims of the research work are: Achieving maximum reduction in the exhaust emissions of the diesel engine and investigate the potentiality of a higher ratio of biodiesel blended with suitable additives as an alternative for diesel fuel. Herein, a coated engine (CE) was produced by the application of bond coating NiCrAlY on the cylinder head and liner substrate, further it was coated with 8 mol.% Yttria-stabilized zirconia (8-YSZ) ceramic. The YSZ restrict the in-cylinder combustion heat loss to the coolant and combustion chamber components due to its low thermal conductivity. The CE was coupled with an exhaust gas recirculation (EGR) system at an optimal constant rate of 10% by vol. to reduce the formation of NOx emissions. Fuel blends with different combinations of microalgae (Chlorella protothecoides) oil-based biodiesel (MB) and additives diethyl ether (DEE), amine antioxidant N, N′-diphenyl-1,4-phenylenediamine (DPPD) were synthesized and tested. The experiment was carried out by scrutinizing the emissions and performance of CE fuelled by blends with a comparison to the uncoated engine (UE) with diesel at different load conditions. The results had shown that the additives enhanced the oxidation stability, cetane number while decreasing the viscosity of the biodiesel. The EGR coupled CE displayed improvement in all the investigated parameters with optimum of particulate emissions by 45.5%, un-burnt hydrocarbons by 51%, NOx by 18.5, CO emissions by 47%, peak brake thermal efficiency by about 6% and brake specific fuel consumption by 8.5% found for the blend MB85DEE15DPPD 1000 ppm (microalgae biodiesel 85%+ diethyl ether 15%+DPPD 1000 ppm) at 80% load. This work made a substantial approach to an economic contribution by simultaneously addressing global issues like air-pollution and fossil fuel crisis.

Gamma radiation effects on an amine antioxidant added in an ethylene-propylene copolymer

The aim of this work was to compare the gamma radiation induced effects on samples of an ethylene-propylene copolymer antioxidant free with samples loaded with an antioxidant characterised by the presence of an -NH functional group. The employed techniques were Electron Spin Resonance spectroscopy (ESR) and High Performance Liquid Chromatography (HPLC). Stable radicals RNO° due to the interaction of free radicals produced in the irradiated polymer with the antioxidant have been observed by ESR at room temperature. The time evolution of the ESR signals following the irradiation was examined at different doses. The amount of antioxidant not involved in the oxidation reactions has been determined using HPLC.

Critical antioxidant concentrations in polymer oxidation—III. Application to lifetime prediction ∗

Lifetime predictions based on the ‘critical antioxidant concentration’ are misleading. This results not only from the fact that there is no ‘critical antioxidant concentration’ for fundamental reasons. The basic assumption used in numerous publications over the past 35 years, i.e. first-order decrease of the antioxidant concentration with aging time, has even more drawbacks. An improved version, which assumes the existence of a minimal effect or no-effect antioxidant concentration, can explain the results with phenolic antioxidants stabilized polyolefins. A completely independent lifetime prediction method based on the polymer oxidation level is much more broadly applicable. It is not only valid with phenolic and aromatic amine antioxidants but also accounts for the effect of Hindered Amine Stabilizers on thermal oxidative aging. Furthermore, the oxidation level is useful for the prediction of lifetime under photo-oxidative conditions.

Redox targeting of LY231617, an antioxidant with potential use in the treatment of brain damage

Several brain-targeting chemical delivery systems (CDS) based on a dihydropyridine ⇌ pyridinium salt-type targetor were synthesized and evaluated for LY231617 (1), a di-tert-butylated phenolic amine antioxidant with potential use in the treatment of brain injuries. The dihydropyridine moiety was chemically attached to the amine (by either amide or various substituted carbamate linkages) or to the phenolic hydroxyl (by carboxylic ester linkage) functionalities of LY231617. In vitro stability and in vivo tissue distribution studies (in the rat) were performed with the novel derivatives. The results indicated that a simple amide-type CDS demonstrated efficient delivery of LY231617-targetor conjugate to the CNS. This derivative which contains the intact pharmacophore might possess intrinsic pharmacological antioxidant activity. Favorable in vitro properties suggested that a substituted carbamate-type CDS might be a better delivery modality for LY231617.

Effects of environment and composition on degradation of guayule rubber

Bales of antioxidant-stabilized guayule rubber underwent significant losses in bulk viscosity when stored under ambient conditions at an Arizona processing facility. Previous work implicated the unsaturated fatty acid esters present in entrained resin as promoters of such degradation. Aging studies as functions of storage temperature and unsaturated acid ester content were carried out on both bulk rubber and rubber-resin solution (miscella) for cultivar AZ-101. The rate of thermooxidative degradation, determined as a function of Mooney viscosity, was increased by the addition of unsaturated ester. Anaerobic degradation was not affected in this way. The activation energy of chain thermolysis was found to be 116 ± 6 kJ/mol (28 ± 1 kcal/mol). At temperatures above 60°C, chain recombination successfully competed with chain scission in lower viscosity rubber. The rate of thermoox-idative degradation was substantially higher in a typical process miscella. A hindered amine antioxidant significantly reduces chain scission under these conditions. © 1996 John Wiley & Sons, Inc.

Cyclic voltametry and differential scanning calorimetry of lubricating oils: amine antioxidants

The use of cyclic voltametry for the determination of dioctyldiphenylamine in three different types of lubricating oils has been investigated. The electrochemical measurements were made using a three-electrode configuration with the oils dissolved in a mixture of methylene chloride and tetrabutylammonium perchlorate. The analytical results are obtained from the experimental data using a convolution procedure in which the concentration of the antioxidant is determined from the limiting value of the convoluted current. The results are compared with those obtained from differential scanning calorimetry where the overall oxidative stability is measured.

Effect of antioxidants and metal deactivator on the oxidation of transformer oil

Comparative experimental data on the effectiveness of selected antioxidants and a metal deactivator in inhibiting the accelerated oxidation of reclaimed transformer oil are generated using the bomb oxidation apparatus. Energy of activation involved in the oxidation of uninhibited and inhibited oils deduced from the analysis of data are reported. Estimated lives of uninhibited and inhibited oils at the operating temperatures of transformers are also reported. Due to the difference in activation energies of inhibited oils, comparative assessment of inhibitors at a single temperature in the bomb oxidation apparatus as per standard appears to be insufficient. Among the range of antioxidants, i.e. monomeric and polymeric phenolic and aminic antioxidants chosen for study, the grading of only monomeric phenolic antioxidants seems to be consistent with temperature. >

The Processes Running during the Induction Period of Inhibiting Oxidation of Polyethylene

Abstract Oxygen absorption in the induction period of polyethylene oxidation inhibited by a strong amine antioxidant N-phenyl-N-cyclohexyl-p-phenylenediamine (PCHA) in the temperature range of from 200°C to 230°C is investigated. It is found that the rate of O2 absorption during the induction period in the presence of antioxidant varies in the range of from 2 × 10−6 to 2 × 10−5 mol/kg (210°C). It is also stated that the main method of antioxidant consumption during the induction period consists of its direct oxidizing by molecular oxygen. The rapid oxidation of the polymer is shown to begin after the current antioxidant concentration reduction to the critical value. Kinetic parameters of the oxidation reaction in a wide range of initial antioxidant concentration are determined.

Chemical sensing of amine antioxidants in turbine lubricants

A chemically modified microelectrode has been developed for the determination of amine antioxidants in turbine lubricants. The electrochemical probe is coated with a thin film of conducting poly(ethylene oxide), which, when placed into a lubricant environment, results in the extraction of the electroactive species into the polymer. Cyclic voltammetric experiments have been performed and an ability to measure the phenyl-α-napthylamine additive quantitatively has been demonstrated.