Hydroperoxide Decomposers Research Articles

Modifications of Polymers through the Addition of Ultraviolet Absorbers to Reduce the Aging Effect of Accelerated and Natural Irradiation.

The photooxidative degradation process of plastics caused by ultraviolet irradiation leads to bond breaking, crosslinking, the elimination of volatiles, formation of free radicals, and decreases in weight and molecular weight. Photodegradation deteriorates both the mechanical and physical properties of plastics and affects their predicted life use, in particular for applications in harsh environments. Plastics have many benefits, while on the other hand, they have numerous disadvantages, such as photodegradation and photooxidation in harsh environments and the release of toxic substances due to the leaching of some components, which have a negative effect on living organisms. Therefore, attention is paid to the design and use of safe, plastic, ultraviolet stabilizers that do not pose a danger to the environment if released. Plastic ultraviolet photostabilizers act as efficient light screeners (absorbers or pigments), excited-state deactivators (quenchers), hydroperoxide decomposers, and radical scavengers. Ultraviolet absorbers are cheap to produce, can be used in low concentrations, mix well with polymers to produce a homogenous matrix, and do not alter the color of polymers. Recently, polyphosphates, Schiff bases, and organometallic complexes were synthesized and used as potential ultraviolet absorbers for polymeric materials. They reduced the damage caused by accelerated and natural ultraviolet aging, which was confirmed by inspecting the surface morphology of irradiated polymeric films. For example, atomic force microscopy revealed that the roughness factor of polymers’ irradiated surfaces was improved significantly in the presence of ultraviolet absorbers. In addition, the investigation of the surface of irradiated polymers using scanning electron microscopy showed a high degree of homogeneity and the appearance of pores that were different in size and shape. The current work surveys for the first time the use of newly synthesized, ultraviolet absorbers as additives to enhance the photostability of polymeric materials and, in particular, polyvinyl chloride and polystyrene, based mainly on our own recent work in the field.

Tin Complexes Containing an Atenolol Moiety as Photostabilizers for Poly(Vinyl Chloride)

The lifetime of poly(vinyl chloride) (PVC) can be increased through the addition of additives to provide protection against irradiation. Therefore, several new tin complexes containing atenolol moieties were synthesized and their photostabilizing effect on PVC was investigated. Reacting atenolol with a number of tin reagents in boiling methanol provided high yields of tin complexes. PVC was then mixed with the tin complexes at a low concentration, producing polymeric thins films. The films were irradiated with ultraviolet light and the resulting damage was assessed using different analytical and surface morphology techniques. Infrared spectroscopy and weight loss determination indicated that the films incorporating tin complexes incurred less damage and less surface changes compared to the blank film. In particular, the triphenyltin complex was very effective in enhancing the photostability of PVC, and this is due to its high aromaticity (three phenyl rings) compared to other complexes. Such an additive acts as a hydrogen chloride scavenger, radical absorber, and hydroperoxide decomposer.

Long-term stabilization of organic solar cells using hydroperoxide decomposers as additives

Stability of organic solar cells (OPV) remains a big problem on the way to their commercialization. Different approaches are being investigated: development of intrinsically more photochemically stable materials, optimization of encapsulation, and implementation of getter and UV blocking layers. In this study, we investigate stabilization of OPV devices using hydroperoxide decomposers as stabilizing additives. A set of five commercially available additives of organophosphorus, organosulfur, Ni chelate, and blocked thiol type are compared, ternary blended into the active layer, under exposure to aging under ISOS-3 degradation conditions. Improvements in long-term performance of OPV devices were observed upon stabilization with Advapak NEO-1120, lifetime was prolonged by a factor of 1.7, and accumulated power generation increased by a factor of 1.4. The stabilizing mechanisms are discussed using spectroscopic and microscopic measurements.

Assessing the in vitro gastric stability and intestinal transport of selected natural molecules

Natural antioxidants in foods and plants play a major role in helping the body's defense system to fight the destruction caused by reactive oxygen species. They may act by decreasing oxygen concentration and as metal inactivators, hydroperoxide decomposers, oxygen scavengers and synergists (Shahidi, 1997). Several studies have indicated the possible beneficial effects of natural antioxidants in the human body, without considering the influence the gastrointestinal tract may have on the composition, activity and absorption of these compounds (Cao et al., 1998; Serrano et al., 2007). This study aimed at assessing the in vitro gastrointestinal stability and intestinal transport of orally ingested antioxidants in food and plants. Curcumin, epicatechin, ferulic acid, gallic acid, quercetin, resveratrol, rosmarinic acid, and rutin were selected. Compounds were incubated in simulated gastric fluid (SGF, pH 1.2) for 1 hour and in simulated intestinal fluid (SIF, pH6.8) for 3 hours. Concentrations were detected before and after incubation. The results indicated that all the compounds were stable in SGF, only epicatechin and rutin were unstable in SIF (with 6.27%, 5.16% degradation, respectively). The in vitro transport experiment was conducted across porcine intestinal tissue in the apical-to-basolateral direction in a Sweetana-Grass diffusion apparatus. Apparent permeability coefficient (Papp) was calculated. Ferulic acid gallic acid and rutin exhibited low transport with Papp value 8.57×10–7, 4.89×10–7 and 1.78×10–7, respectively. Epicatechin, rosmarinic acid, curcumin. quercetin and resveratrol showed poor transport.

Modelling of thermal oxidation of phosphite stabilized polyethylene

The thermal oxidation behaviour of polyethylene films stabilized by various weight ratios of organophosphites (Irgafos 168) has been studied at selected temperatures. The duration of the induction period was found to increase proportionally with the stabilizer concentration, even at temperatures as low as 80 °C. Particular attention was paid to the phosphite–phosphate conversion during the induction period. A kinetic model, involving volatile and partially soluble hydroperoxide decomposers, was developed in order to simulate these results. With the use of kinetic parameters that can be at least tentatively justified from theoretical considerations, this model gave simulations in reasonable agreement with the experimental observations for stabilizer depletion and carbonyl formation. Of particular note is the fact that, even for non-trivial results such as the shape of the phosphite versus phosphate concentration plots, or phosphate build-up, there was also a quite good agreement.

Kinetic modelling of stabilization coupled with stabilizer loss by evaporation. Case of dithioester stabilized polyethylene

The thermal oxidation of medium density polyethylene (PE) films stabilized by various weight ratios of DiLaurylThioPropionate (DLTP) or DiStearylThioPropionate (DSTP) has been studied in air at 110 and 120 °C. DSC was used for the measurement of an induction time at 190 °C (directly linked to the concentration of residual stabilizing species) and FTIR spectrophotometry for the measurement of the total concentration of ester groups originating from unreacted and reacted stabilizer molecules. The growth in PE carbonyl groups is also recorded and the induction periods at the exposure temperatures are determined. The results show that the physical loss of these hydroperoxide decomposers cannot be neglected, and also imply that simple evaporation-reaction models are inadequate to predict the kinetic behaviour of these systems. A new model is tentatively proposed. It assumes the coexistence of two stabilizer phases: the insoluble (dispersed) phase as the stabilizer excess relatively to the solubility threshold, and the soluble phase from which evaporative loss and the chemical stabilization can occur. Both phases are in equilibrium where the insoluble phase acts as a reservoir for the soluble one.

Stabilization of γ-sterilized biomedical polyolefins by synergistic mixtures of oligomeric stabilizers. Part II. Polypropylene matrix

In our previous study we have found the synergistic combinations of stabilizers which follow different mechanisms of stabilization and are approved for food contact and biomedical applications. The present attempt is to test the potentials of those systems in stabilizing γ-sterilized isotactic polypropylene (i-PP). Isotactic polypropylene was melt-mixed with hindered amine stabilizers (HAS), phenolic antioxidants and organo-phosphites (hydroperoxide decomposer) and sterilized with different doses of γ-radiation. Stabilization was monitored in terms of changes in the functional groups (oxidation products), tensile properties, yellowing and surface morphology by FTIR spectroscopy, Instron, colorimetry (reflectance) and scanning electron microscopy (SEM), respectively. The trend in stabilizing the efficiency of binary (1:1), ternary (1:1:1) and quaternary (1:1:1:1) additive systems was confirmed by comparing the stabilizing efficiency of mixtures with and without phenol system as well as with their counter parts of EP copolymer matrix. The binary system of secondary HAS and tertiary HAS, has shown antagonistic effect of stabilization whereas their combination with organo-phosphite has exhibited synergistic effect even at higher doses of γ-sterilization. Due to the oxidation of hindered phenol, phenol systems have shown discoloration and it was reduced by mixing with secondary HAS, tertiary HAS and organo-phosphite. The response of the stabilizer systems is better to ethylene–propylene (EP) copolymer than to i-PP in terms of stabilization.

Stabilization of γ-sterilized biomedical polyolefins by synergistic mixtures of oligomeric stabilizers

The stabilization of polyolefins against γ-sterilization has been studied with single or binary additive system. The present attempt is to utilize synergistic mixtures of stabilizers which are approved for food contact applications. Ethylene–propylene (EP) copolymer has been melt-mixed with hindered amine stabilizers (HAS), phenolic antioxidants and organo-phosphites (hydroperoxide decomposer). Samples were sterilized with different doses of γ-radiation. Stabilization was characterized in terms of changes in the functional groups (oxidation products), tensile properties, yellowing and surface morphology by FTIR spectroscopy, Instron, colorimetry (reflectance) and scanning electron microscopy (SEM), respectively. Results were discussed by comparing the stabilizing efficiency of mixtures with and without phenol system. Among phenol containing systems, where we mostly observe discoloration due to the oxidation of hindered phenol and the combination of secondary HAS, tertiary HAS, organo-phosphite and hindered phenol exhibited improved stabilization efficiency than single or binary additive systems. The mixture of secondary HAS and tertiary HAS, has shown antagonistic effect of stabilization whereas their combination with organo-phosphite has exhibited synergistic effect of stabilization even at higher doses of γ-sterilization. The effects have been explained through the interaction between the stabilizers.

Organic Phosphites as Polymer Stabilizers

AbstractThe antioxidative action of phosphonites and phosphites depends on their structure, the nature of the polymer to be stabilized and the aging conditions. Phosphorus compounds can act in different ways: as hydroperoxide decomposers (secondary antioxidants), as free‐radical scavengers (primary antioxidants), as well as metal‐complex forming agents. The stabilizing action of phosphites and phosphonites is due to three basic mechanisms: oxidation by hydroperoxides, substitution by alkoxyl radicals and hydrolysis to acidic phosphorus compounds and phenols. Modification of phosphites with additional functional groups such as hindered amine moieties leads to new stabilizing properties. An intramolecular synergistic effect is observed.

Effect of hydroperoxide decomposer and slipping agent on recycling of polypropylene

Polypropylene (PP) recycling has always been challenging because the polymer is highly susceptible to thermooxidative degradation during extrusion. Recycled (degraded) PP is normally blended with virgin PP to achieve reasonable mechanical properties after reprocessing operations. However, impurities present in recycled PP tend to degrade even the virgin PP in this process. In this study, standard recycled PP was produced in a laboratory by repeated extrusion and pelletization operations of virgin PP. This material was blended with virgin PP in a ratio from 3 : 7 to 7 : 3. An attempt was made to stabilize the recycled blend by adding a peroxide decomposer (triphenylphosphite, TPP) and a slipping agent (zinc stearate) in contrast to radical scavengers normally used in reprocessing. It was found that by using 0.3–0.5 wt % of TPP and 2 wt % of zinc stearate, this degradation could be effectively attested. Compared to the tensile strength retention of 68% (based on strength of pure virgin PP) of a 60 : 40 (recycled : virgin) PP blend without any stabilizer, a value of 77% was obtained for the same blend with the above-mentioned stabilizers. This stabilization effect was attributed to decomposition of unstable hydroperoxides to stable compounds in the recycled materials by TPP, and lower generation of new radicals in the presence of zinc stearate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3247–3251, 2004

Stabilization and mechanical properties of biodegradable aliphatic polyesteramide and its filled composites

The stabilization of polyesteramide (PEA) was studied by TGA, melt index and intrinsic viscosity. Primary antioxidant A1010 (0.6 wt.%) combined with 0.2 wt.% of hydroperoxide decomposer A168 is effective in stabilizing PEA; but the holding life of PEA in the extruder barrel is only 30 min, and the antioxidants are completely consumed when it is extruded four times. Fillers including heavy calcium carbonate (HCC), tricalcium phosphate (TCP) and talc affect both the thermal stability and mechanical properties of the resultant composites, which are discussed in detail. The Turcsanyi model can best describe the composition dependence of tensile strength of the HCC and talc filled PEA, and the Sato-Furukawa can best predict the Young's modulus of HCC filled PEA, but is poor for the talc-filled material

Antioxidant Selection for Peroxide Cure Elastomer Applications

Abstract For applications demanding the best high temperature aging performance with lowest compression set, polymers are crosslinked with peroxides. The carbon-carbon bonds that are formed are more thermally stable than crosslinks containing sulfur atoms generated by conventional vulcanization by sulfur- and sulfur based cure systems. However, peroxide crosslinking requires special attention to the selection of compounding ingredients. Materials such as plasticizers, oils, and acidic materials such as silicas and air-floated clays detract from crosslinking efficiency by competing with the polymer for the free radicals produced by peroxides. Antioxidants, as a class, are free-radical scavengers and inhibit peroxide crosslinking. This paper discusses selecting the best antioxidant systems for peroxide cured elastomers by comparing various classes of antidegradants: peroxy and alkoxy radical traps (amines and hindered phenols), hydroperoxide decomposers, and synergists. Among the most effective include: 1) a quinoline polymerized 1,2-dihydro-2,2,4-trimethylquinoline 2) an amine, p-dicumyl-diphenylamine, 3) a hindered phenol, tetrakis (metylene (3,5-di-t-butyl-4-hydroxy-hydrocinnamate)) methane, and 4) a dithiocarbamate, nickel dimethyl-dithiocarbamate. For optimum performance, these are used in combination with the synergist, zinc-2-mercaptotoluimidazole. Also presented is an antioxidant system optimization study using a statistically designed experiment.

Synergism between polymer antioxidants—kinetic modelling

A classical kinetic model, without the stationary state hypothesis, has been developed to simulate the behaviour of a hydrocarbon polymer of polypropylene type, stabilised by a mixture of a chain breaking antioxidant of hindered phenol type with a hydroperoxide decomposer of the organic sulphide or phosphite type. From a numerical solution of the system of differential equations representing the rate variations of the reactive species, one obtains kinetic curves of hydroperoxide build-up from which induction time can be determined. The variations of the induction time (at 140 °C in O 2 excess) have been studied with the composition of the stabiliser mixture, the nature of the hydroperoxide decomposition process (unimolecular or bimolecular), the reactivity of the chain breaking antioxidant, and the rate of an “extrinsic” initiation process added to the POOH decomposition. Two main results were obtained: (i) The chosen model is able to simulate strong synergistic effects only due to action of both stabilisers at distinct levels of the radical chain (initiation for hydroperoxide decomposer and termination for the chain breaking antioxidant). (ii) The high stabilising efficiency of these systems is strongly linked to the “closed loop” character of oxidation, i.e. to the fact that the radical chain process generates its own initiator (POOH). When an “extrinsic” initiation process is added, this stabilising efficiency and the magnitude of synergistic effects decrease sharply.

Some features of phenolic inhibitor consumption in oxidized polypropylene in the presence of synergists–hydroperoxide decomposers

AbstractThe influence of sulfur and phosphors containing substances, hydroperoxide decomposers, on the kinetics of the consumption of two phenolic antioxidants in polypropylene (PP) was studied. The induction periods of PP autoxidation at 130°C were measured in the presence of inhibiting compositions that consisted of phenolic inhibitors and decomposers of hydroperoxide. The obtained results indicated that the influence of the hydroperoxide decomposer became significant when the concentration of the phenolic antioxidant became close to a critical value. It was shown also that the influence of the hydroperoxide decomposer significantly depended on the mechanism of the phenolic inhibitor transformation: first of all, on the nature of its transformation products. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2226–2229, 2003

Influence of synergists: The influence of hydroperoxide decomposers on phenolic inhibitors consumption in oxidized polypropylene

AbstractThe influence of sulphur‐ and phosphorum‐containing substances (hydroperoxide decomposers) on the kinetics of the consumption of two phenolic antioxidants in polypropylene (PP) was studied. The induction periods of PP autoxidation at 130°C were measured in the presence of inhibiting compositions that consisted of phenolic inhibitors and decomposers of hydroperoxide. Obtained results indicated that the influence of the hydroperoxide decomposer became significant when the concentration of the phenolic antioxidant became close to critical value. It also was shown that the efficiency of the hydroperoxide decomposer significantly depended on the mechanism of the transformation of the phenolic inhibitor; and first of all on the nature of its transformation products. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2239–2243, 2002

Polymer Weathering: Photo-Oxidation

As the polymer industry evolved, considerable effort was made to understand the degradation processes of high polymers during weathering and ways were found to inhibit or at least retard their chemical modification and loss of their physical and mechanical properties. Weathering is particularly severe for polymers because it combines the photophysical and photochemical effects of ultraviolet radiation with oxidative and hydrolytic effects of the outdoor environment. This article discusses photo-oxidation degradation (the behavior of polymers as a result of outdoor factors) and mainly concentrates on the photo-oxidative degradation of polyolefins and poly(vinyl) chloride. Polymer photostabilization with ultraviolet screeners, quenchers, hydroperoxide decomposers, and radical scavengers is also described.

BREAKTHROUGH CHEMISTRY FOR PROCESSING STABILIZATION OF POLYPROPYLENE

Traditional stabilization systems for polypropylene are typically based on a binary combination of a phenolic antioxidant and a phosphorus based melt processing stabilizer. The phenolic antioxidant provides melt processing stability as a hydrogen atom donor and free radical scavenger; it also provides the polymer with some desired level of short-term or long-term thermal stability, simply for storage or throughout the lifetime of the final article. The phosphorus based melt processing stabilizer, usually a phosphite or phosphonite, functions as a hydroperoxide decomposer above the melting point of the polymer, during melt compounding and processing. Both chemistries work together synergistically to help maintain the original molecular architecture of the polymer. Recently, a new class of additives, 3-aryl-benzofuranones (lactones) has been introduced and adopted commercially. Lactones are highly efficient at scavenging both carbon and oxygen centered radicals during melt processing of polyolefins. Investigations have been underway to examine the impact of low concentrations of lactone in regard to enhancing the performance of traditional stabilization systems. The presumed stabilization mechanism of a lactone and the optimum composition of ternary stabilizer blends for polypropylene are discussed.

Inhibition of Jet Fuel Oxidation by Addition of Hydroperoxide-Decomposing Species

We have explored the use of hydroperoxide decomposing species for inhibiting oxidation in jet fuel. We find that hydroperoxide decomposing species, such as alkyl sulfides, do not slow or delay oxidation in hydrocarbon solvents at 140 °C. However, when phenolic species are also present, such as those naturally occurring in fuel or by addition of hindered phenols, substantial delays in oxidation are observed. We used a pseudo-detailed chemical kinetic mechanism to provide insight into the oxidation process. The combination of hydroperoxide decomposer and hindered phenol can substantially inhibit oxidation of fuel under the conditions studied here.

Oxidative Degradation of Mineral Oil under Tribocontact and Ineffectiveness of Inhibitors

Oxidative degradation of mineral oil under tribocontact is investigated in comparison with static oxidation. A rolling four-ball apparatus lubricated with a small amount of sample oil (approximately 10 mg) was selected as the method for degrading oil samples. Applications of very small amounts of sample oils made it possible to detect small amounts of degradation product after friction tests. An FTIR analysis and gel permeation chromatography were used to characterize the degraded oils. It was found that mineral oil oxidatively degraded during tribo-operation at nominally moderate temperatures. The effect of oxidation inhibitors on the tribodegradation of mineral oil was investigated. A hindered phenol inhibitor, which acts as a radical scavenger, and a sulfur compound inhibitor, which acts as a hydroperoxide decomposer, were used. No inhibition was observed in the tribodegradation of mineral oils with either of two inhibitors, though they were effective for the static oxidation. It was also found that the sulfur compound inhibitor deteriorated triboconditions by forming considerable amounts of wear debris even under the wiling contacts. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, October 26–28, 1998

Pseudo-Detailed Chemical Kinetic Modeling of Antioxidant Chemistry for Jet Fuel Applications

Chemical kinetic modeling was used to simulate the autoxidation of jet fuel including the chemistry of peroxy radical inhibiting antioxidants and hydroperoxide decomposing species. Recent experimental measurements of oxygen concentration during autoxidation of model hydrocarbon solvents were used to “calibrate” the rate parameters of the mechanism. The model showed good agreement with oxygen profiles of static measurements at 140 °C. At this temperature, the model predicts large increases in oxidation rate upon peroxy radical inhibiting antioxidant consumption to below 1 × 10-5 M. At 185 °C we have shown that peroxy radical inhibiting antioxidants and hydroperoxide decomposers both slow and/or delay oxidation, but the resulting oxygen profiles display different characteristics. We have shown that comparison of these profiles with fuel blending and fuel dilution measurements has the potential to differentiate between the two types of oxidation-slowing species. The modeling predicts that the presence of both types of species in a fuel results in a synergistic behavior.