Oxidative Degradation Of Polymers Research Articles

Recent advances in oxidative degradation of plastics.

Oxidative degradation is a powerful method to degrade plastics into oligomers and small oxidized products. While thermal energy has been conventionally employed as an external stimulus, recent advances in photochemistry have enabled photocatalytic oxidative degradation of polymers under mild conditions. This tutorial review presents an overview of oxidative degradation, from its earliest examples to emerging strategies. This review briefly discusses the motivation and the development of thermal oxidative degradation of polymers with a focus on underlying mechanisms. Then, we will examine modern studies primarily relevant to catalytic thermal oxidative degradation and photocatalytic oxidative degradation. Lastly, we highlight some unique studies using unconventional approaches for oxidative polymer degradation, such as electrochemistry.

Selective Electrocatalytic Degradation of Ether‐Containing Polymers

AbstractLeveraging electrochemistry to degrade robust polymeric materials has the potential to impact society's growing issue of plastic waste. Herein, we develop an electrocatalytic oxidative degradation of polyethers and poly(vinyl ethers) via electrochemically mediated hydrogen atom transfer (HAT) followed by oxidative polymer degradation promoted by molecular oxygen. We investigated the selectivity and efficiency of this method, finding our conditions to be highly selective for polymers with hydridic, electron‐rich C−H bonds. We leveraged this reactivity to degrade polyethers and poly(vinyl ethers) in the presence of polymethacrylates and polyacrylates with complete selectivity. Furthermore, this method made polyacrylates degradable by incorporation of ether units into the polymer backbone. We quantified degradation products, identifying up to 36 mol % of defined oxidation products, including acetic acid, formic acid, and acetaldehyde, and we extended this method to degrade a polyether‐based polyurethane in a green solvent. This work demonstrates a facile, electrochemically‐driven route to degrade polymers containing ether functionalities.

Selective Electrocatalytic Degradation of Ether-Containing Polymers.

Leveraging electrochemistry to degrade robust polymeric materials has the potential to impact society's growing issue of plastic waste. Herein, we develop an electrocatalytic oxidative degradation of polyethers and poly(vinyl ethers) via electrochemically mediated hydrogen atom transfer (HAT) followed by oxidative polymer degradation promoted by molecular oxygen. We investigated the selectivity and efficiency of this method, finding our conditions to be highly selective for polymers with hydridic, electron-rich C-H bonds. We leveraged this reactivity to degrade polyethers and poly(vinyl ethers) in the presence of polymethacrylates and polyacrylates with complete selectivity. Furthermore, this method made polyacrylates degradable by incorporation of ether units into the polymer backbone. We quantified degradation products, identifying up to 36 mol % of defined oxidation products, including acetic acid, formic acid, and acetaldehyde, and we extended this method to degrade a polyether-based polyurethane in a green solvent. This work demonstrates a facile, electrochemically-driven route to degrade polymers containing ether functionalities.

Modification of polyvinyl alcohol by ozonated oxidation in an aqueous solution

Currently, the task of obtaining polyvinyl alcohol oligomers (PVA) is urgent to create functional materials of a new generation with specified properties. One of the methods of modification of PVS is ozonolysis, which has a number of advantages over other methods of oxidative degradation of polymers. The aim of the work is to evaluate the structural changes and physico–mechanical characteristics of film samples of PVS modified by ozonated oxidation. To carry out the oxidation process, a 5% aqueous solution of PVA brand 1799 was prepared. The ozone-oxygen mixture was obtained using an ozonizer of a known design. The oxidation of PVS was carried out in a glass thermostatically controlled flask at 70 ° C, blowing an ozone-oxygen mixture through an aqueous solution of PVS for 40 minutes. Sampling was carried out after 10, 20 and 40 minutes of oxidation. The films were obtained by irrigation followed by air drying, after which they were subjected to IR spectrometric analysis and strength indicators were determined. As a result of the study, it was found that the modification of PVA brand 1799 by ozonated oxidation in an aqueous medium is accompanied by the following change in IR spectrograms: in the region of 1400 - 1600 cm-1, a sharp decrease in the intensity of the peak corresponding to hydroxyl groups forming hydrogen bonds is observed for ozone-oxidized PVA, in the region of 1650 – 1700 cm-1, a pattern of decrease in intensity is noted the peak with an increase in the oxidation time of PVA with ozone, which indicates a decrease in the MM of the polymer as a result of oxidative degradation, in the region of 3400 – 3600 cm-1 marked a change in the nature of the spectrogram, which also indicates a change in the structure of hydrogen bonds in oxidized PVS; the physico-mechanical properties of film samples subjected to 40-minute ozonated oxidation of PVS change towards a decrease in both strength and elongation at break by an average of 4 times, the Young's modulus decreases by more than 3 times, and the stretching diagram changes character in the zone of highly elastic deformation (the intensity of stress growth decreases by 1.5-2 times as the film elongates during stretching) and the fracture zone (the diagram acquires a stepwise character without a sharp break), which is associated with a decrease in the molecular weight of the PVS, the acquisition of new functional groups, a change in the stereoregularity of the hydroxyl groups of the main polymer chains, an increase in amorphousness and a change in their relaxation time.

Carbonyl Identification and Quantification Uncertainties for Oxidative Polymer Degradation

The most revealing indicator for oxidative processes or state of degraded plastics is usually carbonyl formation, a key step in materials degradation as part of the carbon cycle for man-made materials. Hence, the identification and quantification of carbonyl species with infrared spectroscopy have been the method of choice for generations, thanks to their strong absorbance and being an essential intermediate in carbon oxidation pathways. Despite their importance, precise identification and quantification can be challenging and rigorous fully traceable data are surprisingly rare in the existing literature. An overview of the complexity of carbonyl quantification is presented by the screening of reference compounds in solution with transmission and polymer films with ATR IR spectroscopy, and systematic data analyses. Significant variances in existing data and their past use have been recognized. Guidance is offered how better measurements and data reporting could be accomplished. Experimental variances depend on the combination of uncertainty in exact carbonyl species, extinction coefficient, contributions from neighboring convoluting peaks, matrix interaction phenomena and instrumental variations in primary IR spectral acquisition (refractive index and penetration depth for ATR measurements). In addition, diverging sources for relevant extinction coefficients may exist, based on original spectral acquisition. For common polymer degradation challenges, a relative comparison of carbonyl yields for a material is easily accessible, but quantification for other purposes, such as degradation rates and spatially dependent interpretation, requires thorough experimental validation. All variables highlighted in this overview demonstrate the significant error margins in carbonyl quantification, with exact carbonyl species and extinction coefficients already being major contributors on their own.

Novel High Molecular Weight Synthetic Phenolic Antioxidants in Indoor Dust in Toronto, Canada

Synthetic phenolic antioxidants (SPAs) are additives that are used to retard oxidative degradation in polymers, extending their lifespans. Previous studies have mainly focused on the pollution and ...

CoFe2O4 Nano-particles for Radical Oxidative Degradation of High Molecular Weight Polybutadiene

Polymer waste production increased dramatically in the last decades, and has reached to 380 million tons (Mt.) in 2015. Due to their long-term stability, these materials impose a serious environmental challenge. Currently, recycling of polymer waste focuses on re-use of actual products, mechanical processing, chemical recycling, and bio-degradation into environmentally friendly materials. In our previous work, we proposed a new approach for radical-initiated oxidative degradation of polymers using cobalt ferrite (CoFe2O4) nanoparticles. In our current work, we focus on the use of CoFe2O4 nanoparticles as catalysts for radical degradation of high molecular weight polybutadiene. Cobalt ferrite nanoparticles were embedded into the polybutadiene polymeric matrix, with the aim of studying degradation in polymeric products that can be manufactured with catalytic nanoparticles. The polymer degradation process was characterized using gel permeation and size exclusion chromatography measurements, thermogravimetric analysis, FTIR, NMR, and mass spectroscopy. Based on the results from these diverse measurements, we propose a mechanism for the degradation process. Overall, our results show that the radical processes within the polybutadiene polymer lead to two parallel processes: polymer crosslinking and polymer scission. Moreover, we show that the ratio between crosslinking and degradation can be controlled by the reaction duration and catalyst concentration.

Radical Degradation Processes Initiated by Catalytic Nanoparticles of CoFe2O4 Towards Polymer Waste Application

Polymer waste presents a modern environmental challenge due to the long-term stability of these materials. Elastomer-based polymers (e.g., tires, pipelines and shoes) are unique in comprising numerous double bonds, which are typically sensitive to radical-initiated oxidative degradation leading to the scission of polymer chains. In this paper, we propose a new approach for radical-initiated oxidative degradation of polymers using cobalt ferrite (CoFe2O4) nanoparticles (NPs). We show that magnetic CoFe2O4 NPs can effectively catalyze the oxidative degradation of polybutadiene (PB), offering easy magnetic recycling and reuse without affecting their catalytic efficiency. The CoFe2O4 NPs were synthesized via a facile surfactant-free method based on a sonochemical reaction. We used methyl ethyl ketone peroxide (MEKP), a model system, to study the rate of radical decomposition catalyzed by the NPs. The radical decomposition rates were determined by following the discoloration of methylene blue (MB) using ultraviolet–visible (UV/Vis) spectroscopy; electron paramagnetic resonance (EPR) measurements were used to study radical formation. The radical-initiated oxidative degradation of PB was studied by thermogravimetric analysis with mass spectrometry detection (TGA–MS). Our results show that cobalt ferrite NPs lead to formation of polymers with low molecular weight fragments and crosslinking, indicating that these NPs are very effective catalysts for the radical degradation of PB. CoFe2O4 NPs are potentially suitable for other polymers, hence this approach may provide a novel route for the chemical (tertiary) recycling of polymers.

Effect of Dissolved Iron and Oxygen on Stability of Hydrolyzed Polyacrylamide Polymers

Summary This paper describes an experimental study of the stability of a hydrolyzed polyacrylamide (HPAM) polymer and an HPAM-2-acrylamido-tertbutylsulfonic acid (ATBS) terpolymer in the presence of varying initial levels of dissolved oxygen (0 to 8,000 ppb), Fe2+ (0 to 220 ppm), and Fe3+ (0 to 172 ppm). A special method was developed to attain and confirm dissolved-oxygen levels. Stability studies were performed at 23 and 90°C. For Fe2+ concentrations between 0 and 30 ppm, viscosity losses were insignificant after 1 week when the initial dissolved oxygen concentration was 200 ppb or less. Above this level, significant viscosity losses were seen, especially if iron was present. If the temperature is high, a greater need arises to strive for very low dissolved-oxygen content. For samples stored for 1 week at 90°C with only 10-ppb initial dissolved oxygen, contact with steel caused HPAM-ATBS solution viscosity losses greater than 30%. In contrast at 23°C, contact with steel caused no significant degradation when the dissolved O2 concentration was 1,000 ppb or less. Several different methods are discussed to control oxidative degradation of polymers during field applications. We advocate physical means of excluding oxygen (e.g., stopping leaks, better design of fluid transfer, gas-blanketing, gas-stripping) rather than chemical means. Addition of Fe3+ to polymer solutions caused immediate crosslinking. Because crosslinked polymers were never observed during our studies with Fe2+, we conclude that free Fe3+ was not generated in sufficient quantities to form a visible gel.

Effects of sterically hindered N-alkoxyamines on photooxidative stability of reinforced polypropylene

AbstractIn the present paper the influence of Flamestab® NORTM 116 (abbrev. FNOR), a sterically hindered N-alkoxyamine stabilizer, on the photo-oxidative stability of calcium carbonate reinforced polypropylene (abbrev. CCPP) used for production of plastic collars has been investigated. The samples, prepared by melt compounding, were exposed to artificial accelerated photo-ageing carried out at λ>300 nm and 45 °C in air. FT-IR and UV-VIS analysis revealed that the deterioration of neat CCPP takes place very rapidly in comparison with the composites containing FNOR. Hydroperoxides and various carbonyl species are formed as the main degradation products during the photo-oxidation process. Moreover, the intensity of the absorption bands grows with increasing of UV exposure time indicating that the material suffers a photo-oxidative degradation process. Indeed, addition of only 0.1 wt.-% FNOR did not significantly modify the length of the induction period of neat CCPP, but a strong efficiency was obtained by increasing the amount of FNOR (0.5 wt.-%) which shows an increase of eight times more as compared with neat CCPP. Therefore, it may be supposed that OIT is linked to the level of concentration of the stabilizer. This remarkable increase in composite stability demonstrated by a lengthening of OIT is typical for sterically hindered N-alkoxyamine stabilizers since they are very efficient at scavenging freeradicals formed as the polymer degrades. In other words, these UV stabilizers are converted to nitroxide radicals (see Scheme 1) which readily trap the polymer degradation species to produce alkoxyamines. Then, the formed alkoxyamines do subsequently react with peroxy radicals to regenerate the active nitroxide radical, thereby this process (called Denisov cycle) proceed in a regenerative cycle, thus retarding oxidative polymer degradation. The increase of absorbance in the carbonyl region as a function of irradiation time was used to determinate the photooxidation rate. It was found out that the photooxidation rate measured from the slope of linear part of the curves is significantly decreased for the CCPP/FNOR 0.5 composite compared to neat CCPP. In the light of the above mentioned findings, FNOR could be taken into consideration as an UV stabilizer for CCPP.

New Insights into the Mechanism of Amine/Nitroxide Cycling during the Hindered Amine Light Stabilizer Inhibited Oxidative Degradation of Polymers

High-level ab initio molecular orbital theory calculations are used to identify the origin of the remarkably high inhibition stoichiometric factors exhibited by dialkylamine-based radical-trapping antioxidants. We have calculated the free energy barriers and reaction energies at 25, 80, and 260 °C in the gas phase and in aqueous solution for a broad range of reactions that might, potentially, be involved in amine/nitroxide cycling, as well as several novel pathways proposed as part of the present work, including that of N-alkyl hindered amine light stabilizer activation. We find that most of the literature nitroxide regeneration cycles should be discarded on either kinetic or thermodynamic grounds; some are even inconsistent with existing experimental observations. We therefore propose a new mechanistic cycle that relies on abstraction of a β-hydrogen atom from an alkoxyamine (R(1)R(2)NOCHR(3)R(4)). Our results suggest that this cycle is energetically feasible for a range of substrates and provides an explanation for previously misinterpreted or unexplained experimental results. We also explore alternative mechanisms for amine/nitroxide cycling for cases where the alkoxyamines do not possess an abstractable β-hydrogen.

Calix[4]pyrogallolarenes as novel high temperature inhibitors of oxidative degradation of polymers

Oxidative stability of high density polyethylene containing C-alkylcalix[4]pyrogallolarenes was studied by Differential Scanning Calorimetry. The kinetic parameters of non-isothermal oxidation indicate that pyrogallolarenes are effective antioxidants at temperatures above 150 °C.

The Effect of Redox Potential and Metal Solubility on Oxidative Polymer Degradation

Summary Oxidative degradation of polymers is a serious concern in their field application for enhanced oil recovery (EOR). This study is an attempt to resolve some of the discrepancies in the literature regarding the occurrence and extent of this degradation, as well as to present a coherent framework for discussing the multitude of possible radical reactions. Sodium carbonate and bicarbonate are demonstrated to play a key role in stabilizing polymer against multiple reported sources of degradation, and it seems likely that this is caused by their effect on iron solubility. Brines containing iron in the reduced state are often obtained from aquifers for use in polymer hydration. These brines are shown to be prone to causing immediate degradation if exposed to air during or after polymer hydration because of the oxidation of soluble iron. If this cannot be avoided, preaeration may be a feasible strategy to minimize degradation during hydration. However, care must be taken to ensure subsequent degradation is not caused by the injection of a polymer solution containing oxygen into a formation containing iron. For instance, sodium dithionite can be added downstream of the last exposure to oxygen. The use of sodium carbonate may also mitigate degradation caused by the oxidation of iron (II) during polymer hydration.

Development of new pyrolysis–GC/MS system incorporated with on-line micro-ultraviolet irradiation for rapid evaluation of photo, thermal, and oxidative degradation of polymers

A new pyrolysis–GC/MS system incorporating with on-line micro-ultraviolet (UV) irradiation was developed to make rapid evaluation of the synergistic material deterioration during UV irradiation under thermal and oxidative atmospheres. The basic effectiveness of the system was demonstrated by polystyrene, polypropylene and polycarbonate as the test samples. The volatile products evolved during deterioration of the polymers were analyzed on-line by thermal desorption GC/MS, and then the residual degraded polymers were analyzed by evolved gas analysis (EGA) and/or Py–GC/MS to obtain specific thermograms and pyrograms. Based on these results, the deterioration mechanism of the polymeric materials during irradiation under thermal and oxidative atmosphere can be evaluated using a sub-milligram polymer sample within a relatively short period of time.

Measurement of the heat of smoldering combustion in straws and stalks by means of simultaneous thermal analysis

Abstract In order to investigate reaction heat of agro-stalks smoldering, wheat straw, corn stalk, cotton stalk, millet straw, sorghum stalk and sweet potato rattan powder were smoldered and pyrolyzed in a simultaneous thermal analyzer (STA). The samples were placed in a platinum crucible (∅5 mm×5 mm) with a lid (with a ∅1 mm hole) on a high-accuracy differential scanning calorimetry–heat capacity (DSC-cp) holder in the furnace of an STA and heated from 303 to 1073 K at a heating rate of 10 K min−1. Sweeping gas with a flow rate of 25 ml min−1 was air and nitrogen during smoldering and pyrolysis, respectively. Results showed that the heat emission characteristic of the smoldering process differed remarkably from the pyrolysis process. Based on the analysis of the DSC curves, oxidative polymer degradation heat and char oxidation heat were obtained from experimental data. It showed that the oxidative polymer degradation heat of the agro-stalks is more than 6.92 MJ kg−1 consumed matter, higher than that of cellulose paper. And char oxidation heat is around 23 MJ kg−1 consumed matter, similar to that of cellulose paper, but higher than that of cigarette. Total net heat emission of smoldering in STA was also obtained. These data can be used as reference data in analyzing smoldering of agro-stalks under similar conditions.

A Novel Profluorescent Dinitroxide for Imaging Polypropylene Degradation

Free-radical processes underpin the thermo-oxidative degradation of polyolefins. Thus, to extend the lifetime of these polymers, stabilizers are generally added during processing to scavenge the free radicals formed as the polymer degrades. Nitroxide radical precursors, such as hindered amine stabilizers (HAS),1,2 are common polypropylene additives as the nitroxide moiety is a potent scavenger of polymer alkyl radicals (R¥). Oxidation of HAS by radicals formed during polypropylene degradation yields nitroxide radicals (RRNO¥), which rapidly trap the polymer degradation species to produce alkoxyamines, thus retarding oxidative polymer degradation. This increase in polymer stability is demonstrated by a lengthening of the “induction period” of the polymer (the time prior to a sharp rise in the oxidation of the polymer). Instrumental techniques such as chemiluminescence or infrared spectroscopy are somewhat limited in detecting changes in the polymer during the initial stages of degradation. Therefore, other methods for observing polymer degradation have been sought as the useful life of a polymer does not extend far beyond its “induction period”

Heterogeneous degradation of chitosan with H 2O 2 catalysed by phosphotungstate

Phosphotungstate (PTA), an insoluble catalyst synthesized with phosphotungstic acid (PWA) and chitosan in acidic reaction system by electrostatic attraction. The catalyst was characterized by DRS and FTIR spectra. Under the catalysis of PTA, the heterogeneous degradation of chitosan with H 2O 2 was achieved. The effect of volume of H 2O 2, dosage of catalyst, reaction temperature and time on the degradation was discussed by orthogonal tests. The experimental results show that chitosan can be effectively degradated with H 2O 2 under the catalysis of PTA. The catalyst, PTA, may have a promising application in oxidative degradation of polymer.

The effect of thermal oxidative degradation of polymers on their viscoelastic response

A model is developed for thermal oxidative degradation of polymer melts and its effect on their viscoelastic response. Based on the theory of temporary heterogeneous networks, stress–strain relations are derived for the time-dependent behavior of a polymer melt at arbitrary three-dimensional deformations with small strains. Within the fragmentation–annihilation concept, kinetic equation is proposed for the distribution of strands with various lengths in a network, and its explicit solution is obtained. Material parameters in the constitutive equations are found by fitting experimental data in shear oscillation tests on a polypropylene melt annealed at elevated temperatures for various times. Good agreement is demonstrated between the observations and the results of numerical simulation.

Study on fluorimetric properties of 1,2-dihydro-2,2,4-trimethylquinoline

The title compound, 1,2-dihydro-2,2,4-trimethylquinoline (TMQ), is a quinoline family member and is among others used to prevent the oxidative degradation of polymers. TMQ has been characterized by its fluorescence emission. In this work the effects of solvent, acidity, continuous irradiation and the influence of some interferents upon the fluorescence intensity of TMQ were investigated. Under the selected conditions (in propan-1-ol solution at λexcitation/λemission = 334 nm/412 nm), the fluorescence intensity is proportional to the concentration of TMQ over the range 0.05–5 μg ml−1 with a correlation coefficient of 0.9963. The proposed method was applied to the determination of TMQ in synthetic mixtures of polymer additives and specific rubber samples.

Oxidation of ultra high molecular weight polyethylene (UHMWPE) part 3: Decomposition of hydroperoxides with SO 2 and its effect on the chemiluminescence signal

Samples of slightly oxidised UHMWPE were treated with SO 2 to decompose hydroperoxides prior to chemiluminescence measurements. It was found that the effect was quite substantial, but it was not just due to the elimination of hydroperoxides; a stabilising effect was also manifested. This effect increased with an increasing concentration of hydroperoxides in the samples. The stabilising effect could not be seen in fresh samples or when the hydroperoxides were decomposed by heating the sample in nitrogen. In addition, a stabilising effect was also observed for samples in which the hydroperoxides were reduced by DMS. It was concluded that the stabilisation was due to the formation of H 2SO 4 in the case of SO 2 and DMSO in the case of DMS. Both these substances can act as stabilisers against oxidative degradation of polymers and were evenly distributed in the sample films after the reaction with the hydroperoxides.