Review of polymer oxidation and its relationship with materials performance and lifetime prediction

Accelerated In Vitro Oxidative Degradation Testing of Ultra-High Molecular Weight Polyethylene (UHMWPE)

Nonabsorbable polymers used in biomedical applications are assumed to be permanently stable based on short-term testing, but some may be susceptible to oxidative degradation over several years of implantation. Traditional in vitro oxidative degradation screenings employ hydrogen peroxide (H2O2) solutions. However, the inherent instability of H2O2 can compromise the consistency of oxidative conditions, especially over extended periods and at elevated temperatures used for accelerated testing. In this study, an automated reactive accelerated aging (aRAA) system, which integrates an electrochemical detection method and a feedback loop, was utilized to ensure precise control of H2O2 concentrations during polymer oxidative degradation testing. The reproducibility of the aRAA system was evaluated by comparing four identical setups. Its efficacy as an oxidation challenge was demonstrated on (i) medical-grade vitamin E (VE) blended ultra-high molecular weight polyethylene (UHMWPE) and (ii) highly crosslinked (HXL) UHMWPE as model materials. The aRAA-aged VE-UHMWPE and HXL-UHMWPE samples were also compared against samples aged via an existing accelerated aging standard, ASTM F2003-02(2022). Samples were analyzed using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to calculate their oxidation index per ASTM F2102-17. We observed that the aRAA system was more effective in oxidizing VE-UHMWPE and HXL-UHMWPE than the traditional ASTM F2003-02(2022) method. By providing a standardized and reliable approach to assess polymer oxidative degradation, the aRAA system could enhance the accuracy of long-term stability predictions for nonresorbable polymers in medical devices.

Exploring micropollutants in polar environments based on non-target analysis using LC-HRMS

The routine use of chemicals in polar regions contributes to unexpected occurrence of micropollutants, with sewage discharge as a prominent pollution source. The aim of this study was to identify and quantify micropollutants in polar environments near potential point sources using non-target analysis (NTA) with liquid chromatography high-resolution mass spectrometry. Seawater samples were collected from Ny-Ålesund, Svalbard and Marian Cove, King George Island, in 2023. We tentatively identified 32 compounds with NTA, along with 105 homologous series substances. Of these, 18 substances were confirmed, and 13 were quantified using the internal standard method. Most quantified substances in the Ny-Ålesund, including caffeine, naproxen, and polyethylene glycols (PEGs), exhibited concentrations ranged from 0.9 to 770,000 ng/L. In Marian Cove, the analysis predominantly detected acetaminophen, with concentrations ranging from 13 to 35 ng/L. The findings underscore the presence and spatial distribution of emerging micropollutants resulting from wastewater discharge in polar regions.

Elaborating more realistic model microplastics by simulating polypropylene's environmental ageing

In this work, we propose a new protocol for producing model microplastics from an industrial polymer and compare it to a conventional method, cryomilling. Polypropylene industrial pellets were chosen due to their widespread production and frequent presence in the environment, making them a notable source of microplastics. Both protocols start with aging under Ultra-Violet light of the pellets but differ in the subsequent mechanical stress applied-strong vs. soft-to break down the photodegraded pellets into microplastics. All generated particles were fully characterized in terms of size, shape, oxidation rate, and stability in aqueous media. Microplastics produced via cryomilling exhibited significant size and oxidation heterogeneity and tended to aggregate in water. Although the new protocol involving soft mechanical stress required a longer preparation time, it simulated more accurately the environmental degradation of raw plastic. This method successfully produced oxidized microplastics with a controlled size distribution centered around 50 µm which remained stable in water without stabilizers.

Insights into the photoreactivity mechanisms of micro-sized rubber particles with different structure: The crucial role of reactive oxygen species and released dissolved organic matter

Micro-sized rubber particles (MRPs), as a significant component of tire wear particles (TWPs), increasingly garnered attention due to the potential ecological risks. However, the impact of photoaging of MRPs and the characteristics of the dissolved organic matter (DOM) derived from MRPs on the photoreactivity of co-existing pollutants is remain unclear. To bridge this knowledge gap, this study selected MRPs with different structure including butadiene rubber (BR), styrene butadiene rubber (SBR) and nitrile butadiene rubber (NBR) and took tetracycline (TC) as the target pollutant to firstly study potential effects of structural characteristics and active components of MRPs on TC photodegradation process under simulated sunlight irradiation. The results indicated that BR, NBR and SBR enhanced TC photodegradation to varying extents, with SBR having the most pronounced effect. This effect was attributed mainly to the high electron transport capacity and the generation of more triple excited DOM (3DOM*) of SBR, thereby producing more active species (•OH and 1O2) and significantly promoting TC photodegradation. Additionally, the unsaturated bonds and aromatic groups in MRPs-DOM was identified as another crucial factor influencing their photoreactivity. This study will provide a new perspective for understanding the potential ecological effects between MRPs and co-existing pollutants in the natural environment.

Constitutive Model for Thermal-Oxygen-Aged EPDM Rubber Based on the Arrhenius Law

Ethylene-propylene-diene monomer (EPDM) is a key engineering material; its mechanical characterization is important for the safe use of the material. In this paper, the coupled effects of thermal degradation temperature and time on the tensile mechanical behavior of EPDM rubber were investigated. The tensile stress-strain curves of the aged and unaged EPDM rubber show strong nonlinearity, demonstrating especially rapid stiffening as the strain increases under small deformation. The popular Mooney-Rivlin and Ogden (N = 3) models were chosen to fit the test data, and the results indicate that neither of the classical models can accurately describe the tensile mechanical behavior of this rubber. Six hyperelastic constitutive models, which are excellent for rubber with highly nonlinearity, were employed, and their abilities to reproduce the stress-strain curve of the unaged EPDM were assessed. Finally, the Davis-De-Thomas model was found to be an appropriate hyperelastic model for EPDM rubber. A Dakin-type kinetic relationship was employed to describe the relationships between the model parameters and aging temperature and time, and, combined with the Arrhenius law, a thermal aging constitutive model for EPDM rubber was established. The ability of the proposed model was checked by independent testing data. In the moderate strain range of 200%, the errors remained below 10%. The maximum errors of the prediction results at 85 °C for 4 days and 100 °C for 2 and 4 days were computed to be 17.06%, 17.51% and 19.77%, respectively. This work develops a theoretical approach to predicting the mechanical behavior of rubber material that has suffered thermal aging; this approach is helpful in determining the safe long-term use of the material.

Predicting Long-Time-Scale Kinetics under Variable Experimental Conditions with Kinetica.jl

Predicting the degradation processes of molecules over long time scales is a key aspect of industrial materials design. However, it is made computationally challenging by the need to construct large networks of chemical reactions that are relevant to the experimental conditions that kinetic models must mirror, with every reaction requiring accurate kinetic data. Here, we showcase Kinetica.jl, a new software package for constructing large-scale chemical reaction networks in a fully automated fashion by exploring chemical reaction space with a kinetics-driven algorithm; coupled to efficient machine-learning models of activation energies for sampled elementary reactions, we show how this approach readily enables generation and kinetic characterization of networks containing ∼103 chemical species and ≃104-105 reactions. Symbolic-numeric modeling of the generated reaction networks is used to allow for flexible, efficient computation of kinetic profiles under experimentally realizable conditions such as continuously variable temperature regimes, enabling direct connection between bottom-up reaction networks and experimental observations. Highly efficient propagation of long-time-scale kinetic profiles is required for automated reaction network refinement and is enabled here by a new discrete kinetic approximation. The resulting Kinetica.jl simulation package therefore enables automated generation, characterization, and long-time-scale modeling of complex chemical reaction systems. We demonstrate this for hydrocarbon pyrolysis simulated over time scales of seconds, using transient temperature profiles representing those of tubular flow reactor experiments.

A review focusing on mechanisms and ecological risks of enrichment and propagation of antibiotic resistance genes and mobile genetic elements by microplastic biofilms

Microplastics (MPs) are emerging ubiquitous pollutants in aquatic environment and have received extensive global attention. In addition to the traditional studies related to the toxicity of MPs and their carrier effects, their unique surface-induced biofilm formation also increases the ecotoxicity potential of MPs from multiple perspectives. In this review, the ecological risks of MPs biofilms were summarized and assessed in detail from several aspects, including the formation and factors affecting the development of MPs biofilms, the selective enrichment and propagation mechanisms of current pollution status of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in MPs biofilms, the dominant bacterial communities in MPs biofilms, as well as the potential risks of ARGs and MGEs transferring from MPs biofilms to aquatic organisms. On this basis, this paper also put forward the inadequacy and prospects of the current research and revealed that the MGEs-mediated ARG propagation on MPs under actual environmental conditions and the ecological risk of the transmission of ARGs and MGEs to aquatic organisms and human beings are hot spots for future research. Relevant research from the perspective of MPs biofilm should be carried out as soon as possible to provide support for the ecological pollution prevention and control of MPs.

Variation of Young's modulus suggested the main active sites for four different aging plastics at an early age time

Precisely determining which bonds are more sensitive when plastic aging occurs is critical to better understand the mechanisms of toxic release and microplastics formation. However, the relationship between chemical bonds with the active aging sites changes and the aging behavior of plastics at an early age is still unclear. Herein, the mechanical behavior of four polymers with different substituents was characterized by the high-resolution AFM. Young's modulus (YM) changes suggested that the cleavage of C-Cl bonds in PVC, C-H bonds in PE and PP, and C-F bonds in PTFE are the main active aging sites for plastic aging. The aging degree of the plastics followed the order of PVC > PP > PE > PTFE. Two aging periods exhibited different YM change behavior, the free radical and cross-linking resulted in a minor increase in YM during the initiation period. Numerous free radicals formed and cross-linking reaction happened, causing a significant increase in YM during the propagation period. Raman spectroscopy verified the formation of microplastics. This research develops promising strategies to quantitatively evaluate the aging degrees using AFM and establish the relationship between chemical bonds and mechanical behavior, which would provide new method to predict plastic pollution in actual environments.

Influence of Polymeric Microparticle Size and Loading Concentration on 3D Printing Accuracy and Degradation Behavior of Composite Scaffolds

Successful employment of 3D printing for delivery of therapeutic biomolecules requires protection of their bioactivity on exposure to potentially inactivating conditions. Although intermediary encapsulation of the biomolecules in polymeric particulate delivery vehicles is a promising strategy for this objective, the inclusion of such particles in 3D printing formulations may critically impact the accuracy or precision of 3D printed scaffolds relative to their intended designed architectures, as well as the degradation behavior of both the scaffolds and the included particles. The present work aimed to elucidate the effect of poly(d,l-lactic-co-glycolic acid) particle size and loading concentration on material accuracy, machine precision, and degradation of 3D printed poly(ɛ-caprolactone)-based scaffolds. Using a main effects analysis, the sizes and loading concentrations of particle delivery vehicles investigated were found to have neither a beneficial nor disadvantageous influence on the metrics of printing quality such as material accuracy and machine precision. Meanwhile, particle loading concentration was determined to influence degradation rate, whereas printing temperature affected the trends in composite weight-average molecular weight. Neither of the two particle-related parameters (concentration nor diameter) was found to exhibit a significant effect on intra-fiber nor inter-fiber porosity. These findings evidence the capacity for controlled loading of particulate delivery vehicles in 3D printed scaffolds while preserving construct accuracy and precision, and with predictable dictation of composite degradation behavior for potential controlled release of encapsulated biomolecules.

Vegetal Polyphenol Extracts as Antioxidants for the Stabilization of PLA: Toward Fully Biobased Polymer Formulation

The use of natural antioxidants as substitutes for traditional synthetic stabilizers has been investigated for the stabilization of biobased and biodegradable polymers, with the aim of designing fully biobased plastic formulations. This study focused on the thermo- and photostabilization of poly(lactic acid) (PLA) using vegetal polyphenol extracts as biosourced antioxidants. The polyphenols were extracted by microwave-assisted extraction from the valorization of vegetal waste, and their potential as antioxidant additives was evaluated (e.g., polyphenol content, composition, and antioxidant activity). PLA was then formulated with 2 wt % of the extracts exhibiting the highest antioxidant activities: green tea residues, pomegranate peels, grape marc, bramble leaves, and yellow onion peel extracts. The efficiency of the natural additives as thermal stabilizers was evaluated and compared with a synthetic antioxidant using rheological and thermal analyses. The results demonstrated the capacity of grape marc extract and pomegranate peel extract to significantly improve PLA thermal stability during processing and thermo-oxidation. Finally, photorheology was conducted to evaluate the influence of the bioadditives on the biopolyester photodegradation. The different polyphenol extracts seemed to significantly hinder the photo-oxidation of PLA and constitute very promising natural UV stabilizers, combining UV absorbers and antioxidant functions.

From biomimetics to smart materials and 3D technology: Applications in orthodontic bonding, debonding, and appliance design or fabrication

This review covers aspects of orthodontic materials, appliance fabrication and bonding, crossing scientific fields and presenting recent advances in science and technology. Its purpose is to familiarize the reader with developments on these issues, indicate possible future applications of such pioneering approaches, and report the current status in orthodontics. The first section of this review covers shape-memory polymer wires, several misconceptions arising from the recent introduction of novel three-dimensional (3D)-printed aligners (mistakenly termed shape-memory polymers only because they present a certain degree of rebound capacity, as most non-stiff alloys or polymers do), frictionless surfaces enabling resistance-less sliding, self-healing materials for effective handling of fractured plastic/ceramic brackets, self-cleaning materials to minimize microbial attachment or plaque build-up on orthodontic appliances, elastomers with reduced force relaxation and extended stretching capacity to address the problem of inadequate force application during wire-engagement in the bracket slot, biomimetic (non-etching mediated) adhesive attachment to surfaces based on the model of the gecko and the mussel, and command-debond adhesives as options for an atraumatic debonding. This review's second section deals with the recent and largely unsubstantiated application of 3D-printed alloys and polymers in orthodontics and aspects of planning, material fabrication, and appliance design.

Asphaltenes from Heavy Crude Oil as Ultraviolet Stabilizers against Polypropylene Aging

The destruction of polymers under the influence of ultraviolet (UV) radiation is the cause of their aging and deterioration of strength properties. Asphaltenes are low-value waste products after the refining and deasphalting of heavy crude oil, which absorb UV radiation well. Asphaltenes require rational utilization, which suggests their use as UV stabilizing agents for polymers. In this work, asphaltenes were used to prevent UV aging of polypropylene (PP) by adding them in a mass fraction from 5% to 30% within an asphaltene/PP composite material. Rheometry, calorimetry, X-ray diffraction analysis, and tensile strength of PP films containing asphaltenes were performed before and after their intense UV irradiation for accelerated aging. Asphaltenes slightly reduce the viscosity, crystallinity, and mechanical strength of the initial PP due to their plasticizing effect. However, this deterioration in properties is more than compensated when studying UV-aged samples. Intense UV aging causes multiple catastrophic drops in the viscosity and strength of pure PP with the preservation of crystallinity due to the break of polymer chains and a decrease in molecular weight by approximately eight times. Asphaltenes suppress the destruction of PP, which is expressed in a significantly smaller decline in its viscosity and strength due to UV aging. The most optimal content of asphaltenes is 20%, which suppresses UV destruction by six times and best preserves the strength properties of PP.

Hazardous state lifetimes of biodegradable plastics in natural environments

Plastic pollution is a critical problem that has the potential for long-lasting impact. While all plastics eventually break down to at least some degree, they can remain in different transition states, such as microplastics and nanoplastics, for extended periods of time before reaching complete mineralisation to non-hazardous end products. Each of the transition states represents different types of hazards, so it is critical to understand the factors driving the lifetimes of plastics within these states. To do this, we propose a framework for assessing plastic lifetimes in natural environments based on the flow of material through potentially hazardous states: macroplastic and mesoplastic, microplastic, nanoplastic and soluble products. State changes within this framework are underpinned by three key processes: fragmentation, depolymerisation, and bioassimilation, with the pathways for generation of the different plastic states, and the lifetimes within these states, varying widely for individual materials in different environments due to their dependence on polymer material type, form and properties, and environmental factors. The critical factors driving these processes can therefore appear complex, but molecular weight, crystallinity, oxygen and water diffusivity, and inherent polymer chain reactivity (including to enzymes) are key to our understanding. By analysing currently available data that take factors such as these into consideration, we have generated information on the most likely states in which a range of plastics with different environmental degradation behaviour may exist over time in natural environments. Polyethylene (PE), for example, should be expected to fragment and accumulate in the environment as microplastic and nanoplastic. Interestingly, the state-profile for the biodegradable plastic polylactic acid (PLA) is similar, albeit over shorter timeframes. PLA also likely fragments, but then the relatively slow process of abiotic depolymerisation results in accumulation of microplastic and nanoplastic. By contrast, the state-profile for the biodegradable plastic polyhydroxyalkanoate (PHA) would be expected to be very different. The bulk material is less susceptible to embrittlement and fragmentation as a primary path to biodegradation, since the rapid enzyme catalysed depolymerisation of exposed surfaces proceeds in conjunction with bioassimilation.

Application of multi-channel in situ infrared spectroscopy: the case of PVB thermal aging

Thermal kinetic parameters are important for establishing the relationship between the aging process, time, and temperature, which would help predict the thermal aging lifetime and stability in the application of polymer materials. We developed a multi-channel in situ detecting device, which provided an efficient method for IR spectrum measurement. The thermal aging process of polyvinyl butyral (PVB) at several constant temperatures (100 °C, 110 °C, 120 °C, 135 °C, and 150 °C) had been studied by the multi-channel in situ infrared reaction device. The kinetic parameters (Eα) were calculated from the absorbance intensity of -C-O-, -C[double bond, length as m-dash]O, -CH3, and -OH. The -OH proved to be the active site of PVB during thermal aging, and a possible thermal aging mechanism of PVB was proposed. We proved the method using a combination of a multi-channel in situ reaction device and FTIR was suitable to study the aging mechanism and kinetics of polymers.

Improved Dual Network Model for Aging of Rubber Composites under Set Strains

A new model is presented to predict rubber behavior during chemical aging at fixed strains. The model is validated using a carbon black-filled nitrile butadiene rubber aged in air at 125 °C. The model improves upon Tobolsky's dual network theory, designed for unfilled elastomers undergoing conventional aging but which has also often been used in rubber composites undergoing more complex aging scenarios. This work explores the shortcomings of the original model and demonstrates how the new model overcomes them. The model was validated using uniaxial tensile samples aged at 125 °C for 24-72 h at strains from 0-30%. The permanent set was measured, and the samples were tested on an Instron uniaxial test machine after aging. The cross-link density was estimated by equilibrium swelling. Results show that the new model more accurately models the stress-strain behavior to higher strains and provides more reliable estimates of chain scission and cross-linking after aging.

Antiradical and Antioxidant Activity of Compounds Containing 1,3-Dicarbonyl Moiety: An Overview

Free radicals and oxidants may cause various damages both to the lifeworld and different products. A typical solution for the prophylaxis of oxidation-caused conditions is the usage of various antioxidants. Among them, various classes are found-polyphenols, conjugated polyalkenes, and some sulfur and nitrogen derivatives. Regarding the active site in the molecules, a widely discussed group of compounds are 1,3-dicarbonyl compounds. Among them are natural (e.g., curcumin and pulvinic acids) and synthetic (e.g., 4-hydroxy coumarins, substituted Meldrum's acids) compounds. Herein, information about various compounds containing the 1,3-dicarbonyl moiety is covered, and their antiradical and antioxidant activity, depending on the structure, is discussed.

Exploring into a light-avoided environment: Mechanical-thermal coupled conditions responsible for the aging behavior of plastic waste in landfills

Plastics in landfills undergo a unique micronization process due to multi-factor and light-avoided conditions, but their aging process in such a typical environment remains unexplored. This study investigated the aging behavior of polyethylene plastics, representative of landfills, under simulated dynamic mechanical forces and high temperature-two prevalent environmental factors in landfills. The study explored the individual and combined contributions of these factors to the aging process. Results indicated that high temperature played a primary role in aging plastics by depolymerization and degradation through ·OH production, while mechanical forces contributed mainly to surface structure breakdown. The combined effect leads to more serious surface damage, creating holes, cracks, and scratches that provide access for free radical reactions to plastic bulk, thereby accelerating the aging and micronization process. The resulting microplastics were found to be 14.25 ± 0.53 μg L-1. Aged plastics exhibit a rapid aging rate of depolymerization and oxidation compared to virgin plastics due to their weak properties, suggesting a higher potential risk of microplastic generation. This study fills a knowledge gap regarding the aging behavior of plastics under complex and light-avoided landfill conditions, emphasizing the need for increased attention to the evolution process of microplastics from aged plastic waste in landfills.

Arrhenius-model-based degradable oligourethane hydrogels for controlled growth factor release

Biodegradable hydrogels are growing in demand to enable the delivery of biomolecules (e.g. growth factors) for regenerative medicine. This research investigated the resorption of an oligourethane/polyacrylic acid hydrogel, a biodegradable hydrogel which supports tissue regeneration. The Arrhenius model was used to characterize the resorption of the polymeric gels in relevant in vitro conditions, and the Flory-Rehner equation was used to correlate the volumetric swelling ratio with the extent of degradation. The study found that the swelling rate of the hydrogel follows the Arrhenius model at elevated temperatures, estimating degradation time in saline solution at 37°C to be between 5 and 13 months, serving as a preliminary approximation of degradation in vivo. The degradation products had low cytotoxicity towards endothelial cells, and the hydrogel supported stromal cell proliferation. Additionally, the hydrogels were able to release growth factors and maintain the biomolecules' bioactivity towards cell proliferation. The study of the vascular endothelial growth factor (VEGF) release from the hydrogel used a diffusion process model, showing that the electrostatic attraction between VEGF and the anionic hydrogel allowed for controlled and sustained VEGF release over three weeks. In a rat subcutaneous implant model, a selected hydrogel with desired degradation rates exhibited minimal foreign body response and supported M2a macrophage phenotype, and vascularization. The low M1 and high M2a macrophage phenotypes within the implants were associated with tissue integration. This research supports the use of oligourethane/polyacrylic acid hydrogels as a promising material for delivering growth factors and supporting tissue regeneration. STATEMENT OF SIGNIFICANCE: There is a need for degradable elastomeric hydrogels that can support the formation of soft tissues and minimize long-term foreign body responses. An Arrhenius model was used to estimate the relative breakdown of hydrogels, in-vitro. The results demonstrate that hydrogels made from a combination of poly(acrylic acid) and oligo-urethane diacrylates can be designed to resorb over defined periods ranging from months to years depending on the chemical formulation prescribed by the model. The hydrogel formulations also provided for different release profiles of growth factors, relevant to tissue regeneration. In-vivo, these hydrogels had minimal inflammatory effects and showed evidence of integration into the surrounding tissue. The hydrogel approach can help the field design a broader range of biomaterials for tissue regeneration.

Synergistic effects of atomic oxygen and thermal cycling in low earth orbit on polymer-matrixed space material

Polymer-matrixed materials are widely used in the spacecrafts' structures. However, crafts located in the LEO（Low Earth Orbit） would suffer from hazardous environment factors when orbiting in the space. It has been reported that the space environment factors' integral effect (which represents the factual detriment in space) is not equivalent to the simple summation of each individual. Hence, atomic oxygen and thermal cycling were selected as the starting point for studying the typical LEO synergistic effects on polymer-matrixed space material. In this work, methods such as surface morphology observation, surface components analyzation and inter-laminar-shear strength test were embraced to gather the basic information for the study of degradation. As a result, focusing on the composites selected in this work, synergistic effects do exist between the two factors (AO&TC, representing for atomic oxygen and thermal cycling combined). Besides, a quantified index was proposed to represent synergistic characteristics，so as to lay the foundation for the scientific evolution of material characterization.

Biofilm-Colonized versus Virgin Black Microplastics to Accelerate the Photodegradation of Tetracycline in Aquatic Environments: Analysis of Underneath Mechanisms

Tire wear particles (TWPs) exposed to the aquatic environment are rapidly colonized by microorganisms and provide unique substrates for biofilm formation, which potentially serve as vectors for tetracycline (TC) to influence their behaviors and potential risks. To date, the photodegradation capacity of TWPs on contaminants due to biofilm formation has not been quantified. To accomplish this, we examined the ability of virgin TWPs (V-TWPs) and biofilm-developed TWPs (Bio-TWPs) to photodegrade TC when exposed to simulated sunlight irradiation. V-TWPs and Bio-TWPs accelerated the photodegradation of TC, with rates (k_obs) of 0.0232 ± 0.0014 and 0.0152 ± 0.0010 h^-1, respectively (k_obs increased by 2.5-3.7 times compared to that for only TC solution). An important factor of increased TC photodegradation behavior was identified and linked to the changed reactive oxygen species (ROS) of different TWPs. The V-TWPs were exposed to light for 48 h, resulting in more ROS for attacking TC, with hydroxyl radicals (^•OH) and superoxide anions (O₂^•-) playing a dominant role in TC photodegradation measured using scavenger/probe chemicals. This was primarily due to the greater photosensitization effects and higher electron-transfer capacity of V-TWPs in comparison to Bio-TWPs. In addition, this study first sheds light on the unique effect and intrinsic mechanism of the crucial role of Bio-TWPs in TC photodegradation, enhancing our holistic understanding of the environmental behavior of TWPs and the associated contaminants.

Characterization Techniques of Polymer Aging: From Beginning to End

Polymers have been widely applied in various fields in the daily routines and the manufacturing. Despite the awareness of the aggressive and inevitable aging for the polymers, it still remains a challenge to choose an appropriate characterization strategy for evaluating the aging behaviors. The difficulties lie in the fact that the polymer features from the different aging stages require different characterization methods. In this review, we present an overview of the characterization strategies preferable for the initial, accelerated, and late stages during polymer aging. The optimum strategies have been discussed to characterize the generation of radicals, variation of functional groups, substantial chain scission, formation of low-molecular products, and deterioration in the polymers' macro-performances. In view of the advantages and the limitations of these characterization techniques, their utilization in a strategic approach is considered. In addition, we highlight the structure-property relationship for the aged polymers and provide available guidance for lifetime prediction. This review could allow the readers to be knowledgeable of the features for the polymers in the different aging stages and provide access to choose the optimum characterization techniques. We believe that this review will attract the communities dedicated to materials science and chemistry.

A Physical Basis for Kinetic Compensation

Kinetic compensation is a strong, positive correlation between the Arrhenius activation energy E and the frequency factor A for a reaction between the same reactants under similar experimental conditions or similar reactants under the same conditions, even though these parameters are supposed to be independent. The kinetic compensation effect (KCE) is demonstrated by a linear relationship between ln[A] and E/R in the eponymous Constable plot and has been the subject of more than 50 000 publications over the past 100 years, with no consensus opinion about the cause of this effect. In this paper, it is suggested that the linear relationship between ln[A] and E is the result of a real or spurious path dependence of the reaction history between the initial state of the pure reactant(s) and the final state of the pure product(s) having standard enthalpy and entropy differences, ΔH° and ΔS°, respectively. The single-step rate law approximation of a reversible reaction leads to T₀ = H°/ΔS° as the dynamic thermal (thermodynamic) equilibrium temperature and 1/T₀ = (ln[A̅/k₀])/(E̅/R) as the slope of a Constable/KCE plot or the crossover temperature of Arrhenius lines in an isokinetic relationship (IKR), where A̅ and E̅ are mean values for the ensemble of compensating {E_i, A_i} pairs and k₀ is a constant that accounts for the path dependence of the reaction history and reconciles the KCE with the IKR. This proposed physical basis for the KCE and IKR is supported by qualitative agreement between ΔH° and ΔS° calculated from the statistics of compensating {E_i, A_i} pairs in the literature, and the difference in the standard enthalpies and entropies of formation of the products and reactants for thermal decomposition of organic peroxides, calcium carbonate, and poly(methyl methacrylate).

Prevalence and implications of microplastics in potable water system: An update

Synthetic plastics, which are lightweight, durable, elastic, mouldable, cheap, and hydrophobic, were originally invented for human convenience. However, their non-biodegradability and continuous accumulation at an alarming rate as well as subsequent conversion into micro/nano plastic scale structures via mechanical and physio-chemical degradation pose significant threats to living beings, organisms, and the environment. Various minuscule forms of plastics detected in water, soil, and air are making their passage into living cells. High temperature and ambient humidity increase the degradation potential of plastic polymers photo-catalytically under sunlight or UV-B radiations. Microplastics (MPs) of polyethylene terephthalate, polyethylene, polystyrene, polypropylene, and polyvinyl chloride have been detected in bottled water. These microplastics are entering into the food chain cycle, causing serious harm to all living organisms. MPs entering into the food chain are usually inert in nature, possessing different sizes and shapes. Once they enter a cell or tissue, it causes mechanical damage, induces inflammation, disturbs metabolism, and even lead to necrosis. Various generation routes, types, impacts, identification, and treatment of microplastics entering the water bodies and getting associated with various pollutants are discussed in this review. It emphasizes potential detection techniques like pyrolysis, gas chromatography-mass spectrometry (GC-MS), micro-Raman spectroscopy, and fourier transform infrared spectroscopy (FT IR) spectroscopy for microplastics from water samples.

Study on the aging of three typical rubber materials under high- and low-temperature cyclic environment

As the key components of sealing applications, rubber seals are subject to complicated environmental conditions during the service lifetime. In this study, the aging of three typical rubber materials, ethylene–propylene–diene monomer rubber, liquid silicone rubber, and fluorine rubber, was tested under different high- and low-temperature cycle aging environments. The experimental results confirm that the reciprocating temperature cycle causes a type of fatigue failure, which could result in an increase in the rubber compression set. In addition, a novel accelerated aging test method was proposed based on the dominant damage mechanism of rubber material caused by the temperature cycle treatments. Based on this method, the long-term aging test results of rubber samples under high- and low-temperature cycle conditions can be predicted. This method could significantly shorten the aging test time and reduce the test cost.

Influence of aged and pristine polyethylene microplastics on bioavailability of three heavy metals in soil: Toxic effects to earthworms (Eisenia fetida)

Virgin microplastics (MPs) would undergo aging process when entering environment, the adsorption capability of pollutants onto MPs may change during the aging process. To better understand the influence of aged polyethylene microplastics (PE-MP) on the bioavailability of three heavy metals (Zn, Pb, and Cd) in soil, hydrogen peroxide exposure (3% H₂O₂) and ultraviolet irradiation methods were employed to simulate the aging process. After aging process, different amount (0.1%, 1%, 10%) of PE-MP (pristine or aged) was added into soil to assess the ability of soil (containing PE-MP) adsorbing heavy metal. Moreover, different amount (0.01%, 0.1%, 1%) of PE-MP (pristine or aged) was added into soil to cultivate the earthworms to assess the impact of PE-MP on bioavailability of three heavy metals. Results indicated that the aged and virgin PE-MP had similar capability to adsorb heavy metal, the adsorption ability of Zn²⁺, Pb²⁺, and Cd²⁺ to pristine PE-MP were 2.42, 7.47, and 7.76 mg/g, respectively. The concentration of Zn or Pb in earthworms in treatments of metal +1% PE-MP was slightly higher than that in single metal (Zn or Pb) treatment, moreover, the concentration of Cd in earthworms in treatment of Cd + 1% PE-MP was significantly (p < 0.05) higher than that in single Cd treatment, exhibiting that 1% of PE-MP enhanced the bioavailability of heavy metals in soil. However, heavy metal concentrations in earthworms in treatments of metal + pristine PE-MP showed insignificant (p > 0.05) difference with those in treatments of metal + aged PE-MP, indicating that the aging process in this study did not change the environmental influence of PE-MP on heavy metals bioavailability. Superoxide dismutase activity, reactive oxygen species level, malondialdehyde content, and related gene expression in earthworms showed that PE-MP and heavy metals would bring toxic synergy to earthworms, therefore, the influence of MPs should be comprehensively considered when determining the environmental risk of heavy metals in soil.

Effect of Water-Induced and Physical Aging on Mechanical Properties of 3D Printed Elastomeric Polyurethane

In this study, the effect of moisture on the elastic and failure properties of elastomeric polyurethane (EPU 40) 3D printed via Vat Photopolymerization was investigated. EPU 40 samples were printed, and uniaxial tensile tests were performed on Dry-fresh, Dry-aged (eight months aged), and after various times of being immersed in water (0−8 months). Elastic response, initial stiffness, failure strength, and failure elongation were analyzed. Besides, gravimetric analysis was performed to determine the increase in weight and thickness after water immersion. The elastic response was fitted by the Arruda-Boyce constitutive model. Results show that initial stiffness decreased after immersion (mean 6.8 MPa dry vs. 6.3 MPa immersed p-value 0.002). Contrary, the initial stiffness increased due to physical aging under a dry state from a mean 6.3 MPa to 6.9 MPa (p = 0.006). The same effect was observed for stiffness parameter G of the constitutive model, while the limit stretch parameter λL was not affected by either aging. The 95% confidence intervals for strength and failure stretch were 5.27−9.48 MPa and 2.18−2.86, respectively, and were not affected either by immersion time or by physical aging. The median diffusion coefficient was 3.8·10−12 m^2/s. The immersion time has a significant effect only on stiffness, while oxidative aging has an inverse effect on the mechanical properties compared to water immersion. The transition process is completed within 24 h after immersion.

Polymer aging affects the bioavailability of microplastics-associated contaminants in sea urchin embryos

Microplastics (MPs) in the marine environment undergo complex weathering factors that can affect their ability to interact with different coexisting environmental contaminants (termed here co-contaminants). In this study, the influence of artificially aging using UV on the sorption of a complex mixture of co-contaminants onto MPs was investigated in order to provide meaningful hypotheses on their individual and combined toxicities on sea urchin embryos. A mixture of artificially aged MPs (PS particles and PA microfibers) combined with 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), or Cd or Cu, both alone and in a mix, were used to expose embryos of Paracentrotus lividus. The effects of polymer aging on co-contaminants bioavailability were assessed by measuring changes in the transcriptional profile of genes involved in oxidative-stress response and skeletogenic and endo-mesodermal specification. Changes in the sorption ability of MPs to co-contaminants in the aqueous phase highlighted that aging did not affect the sorption of BDE-47 and Cd on MPs, although a certain influence on Cu sorption was found. Despite no morphological effects in embryos at the gastrula stage after MPs/contaminants combinatorial exposure emerged, the greatest influence of the aging process was mainly found for combined exposures which included BDE-47. Finally, the exposure to multiple contaminants generated transcriptional profiles poorly related to those activated by single contaminant, at times suggesting a mixture-dependent different aging influence. These results open new scenarios on the controversial role of vector of co-contaminants for MPs, especially when complex and different types of mixtures were considered.

The evaluation of an inorganic-organic poly(carborane-siloxane-arylacetylene) hybrid resin system

The realization of aerospace vehicle technologies demanding extreme service conditions is facilitated by the development of materials with greater oxidative stability at high temperatures. Thermal performance of polymer composites can be increased by incorporating a hybrid (organic-inorganic) resin as a thermal barrier coating. One such resin system, meta-poly (carborane-siloxane-arylacetylene) ( m-PCSAA), developed by the U.S. Naval Research Laboratory, shows potential for such application and is further investigated in this work. The resin has a low viscosity (0.1 Pa s) with large processing window (2.5 h) from 100°C to 230°C. These processing characteristics are advantageous for infusion processes or the inclusion of fillers for coating applications. Curing was accomplished in two stages, corresponding to two exothermic reactions. After the first curing stage, the resin exhibits elastomeric behavior, and after the second curing stage is rigid with a high glass transition temperature (∼330°C). The materials exhibited high char yields (89%) in air at 1000°C and may be useful in space or for attritable technology. No cracks were observed during long-term service at 288°C, but significant degradation and cracking were observed after aging at 316°C. The materials exhibited high coefficients of thermal expansion; 186.9 and 168.6 μm/(m∙°C) after first and second curing stage respectively. Similar to epoxies and polyimides, the resin acquired up to 3% moisture at 70°C and 85% relative humidity.

Investigation on Some Algal Extracts as Appropriate Stabilizers for Radiation-Processed Polymers

This study presents the appropriate solution, algal extracts, for the improvement of polymer durability when the material is subjected to acute oxidation damage. The investigated support, styrene-isoprene-styrene (SIS), is modified by three algal extracts: Chlorella vulgaris, Spirulina platensis, and Ascophyllum nodosum (Kelp) with a low concentration (1 wt%). The presence of polyhedral oligomeric silsesquioxane (POSS) ensures the growth of stability with respect to the pristine polymer. The thermal performances of the host polymer, indicated by chemiluminescence, reveal the essential contribution of an additive to the improvement in oxidation strength. The stability of the polymer adjusted by algal extracts is proved by the activation energy values, which increase from 49 kJ mol^-1 to 89 kJ mol^-1 for the same polymer modified with Ascophyllum nodosum. This main important characteristic is the consequence of the highly efficient activity of the polyphenol components of algal extracts and the effect of the three natural additives on the favorably changed kinetic parameters (oxidation induction time and onset oxidation temperature). The exposure of the polymer matrix to the damaging action of γ-rays does not affect the proper contributions to the fast delay in material ageing. The irradiation of 100 kGy, a usual technological dose, may be successfully applied in the radiation processing of a polymer stabilized with algal extracts due to the efficient protection of the additive as the chain-breaking agents.

Exhaustive Baeyer-Villiger oxidation: a tailor-made post-polymerization modification to access challenging poly(vinyl acetate) copolymers

The discovery of exhaustive (nearly quantitative) post-polymerization modifications (PPM) relies heavily on the efficiency of their corresponding small-molecule protocols. However, the direct translation of existing small-molecule protocols into PPM methods has never been guaranteed due to the intrinsic differences between small-molecule substrates and polymers. Herein, we introduce the direct optimization on polymers (DOP) as a complementary approach to developing exhaustive PPM reactions. As proof of the DOP concept, we present an exhaustive Baeyer-Villiger (BV) post-modification which cannot be accessed by conventional approaches. This user-friendly methodology provides general access to synthetically challenging copolymers of vinyl acetate and more activated monomers (MAMs) including both statistical and narrow-dispersed block copolymers. Furthermore, a scalable one-pot copolymerization/exhaustive BV post-modification procedure was developed to produce such materials showing improved performance over regular PVAc.

Radical Composition and Radical Reaction Kinetics in the Probe-Irradiated XLPE Samples as a Potential Source of Information on Their Aging Degree

Polyethylene is a model polyolefin, and a widely used material for the manufacture of many products, including cable sheaths. Understanding degradation mechanisms at the atomic scale leading to oxidation during aging is crucial for many long-term applications. The concentrations of radicals derived from oxidation and chain scission during radio-oxidation, as well as their ratio, are important parameters controlling the predominance of chain scission or crosslinking of the polymer. In this work, we propose a cryogenic EPR technique for measuring oxidation- and fragmentation-derived radicals as a less-destructive method for the evaluation of cable insulation aging and performance capability. We investigate the effect of the low-dose and high-dose radiation aging on the formation of free radicals in the polymer matrix that are both unprotected and protected by antioxidants. The stability of radicals after aging is a determinant of macroscopic processes and structural changes during aging. Under the conditions of the higher dose rate, the peroxy radical buildup is lower per dose. Peroxy radical buildup is followed by decay during aging, in accordance with POOH content. Our results allow the prediction of the capability of the antioxidant to protect the XLPE material in the function of dose and time.

Aging of biodegradable blended plastic generates microplastics and attached bacterial communities in air and aqueous environments

The use of biodegradable plastics (BPs) has been widely promoted in recent years, but before their complete degradation, the phase of microplastics (MPs) is inevitable. However, little information concerning the production of MPs from blended polymers is available. This study aimed to explore the characteristics of MPs produced from blended plastics and the development of biofilms on plastic surfaces under long-term aging. Here, three blended materials (i.e., PBAT (53%)+PLA (10%)+Starch (20%), PBAT (80%)+Starch (20%), HDPE (60%)+CaCO₃ (40%)) were aged for 90 days in air, deionized (DI) water and seawater. The results showed massive production of MPs (9653 ± 3920-20,348 ± 5857 items/g) from blended plastics accompanied by a large quantity of flocculent substances during 90 days aging period. Furthermore, the richness of bacteria communities on hydrophobic plastics (i.e., PBAT (53%)+PLA (10%)+Starch (20%), PBAT (80%)+Starch (20%)) was higher than hydrophilic plastics (i.e., HDPE (60%)+CaCO₃ (40%)), and bacterial communities attached to blended plastics exhibited significantly variation with aging times. Overall, promoting the marketable application of blended plastics is risky if their environmental behavior is not effectively addressed.

Analytical and Numerical Modeling of Degradation and Pyrolysis of Polyethylene: Measuring Aging with Thermogravimetry

Aging reactions due to heat and radiation cause chain scissions and cross-linking in cross-linked polyethylene (XLPE). We have developed theoretical and numerical graph models to study the evolution of the gel fraction and network properties during aging as well as the mass loss during thermogravimetric analysis (TGA). Our analytical and kinetic Monte Carlo (KMC) based models that combine degradation reactions and a simple vaporization model can quantitatively predict TGA curves for aged XLPE. Fitting the model to experimental TGA data yields the number of scission reactions, showing that thermogravimetry combined with our models can present a nondestructive aging characterization tool for lifetime prediction.

Degradation of low-density polyethylene to nanoplastic particles by accelerated weathering

When plastics enter the environment, they are exposed to abiotic and biotic impacts, resulting in degradation and the formation of micro- and nanoplastic. Microplastic is ubiquitous in every environmental compartment. Nevertheless, the underlying degradation processes are not yet fully understood. Here, we studied the abiotic degradation of commonly used semi-crystalline, low-density polyethylene (LDPE) in a long-term accelerated weathering experiment combining several macro- and microscopic methods. Based on our observations, the degradation of LDPE proceeds in three stages. Initially, LDPE objects are prone to abrasion, followed by a period of surface cracking. A large number of secondary particles with a high degree of crystallinity are formed, with sizes down to the nanometer scale. These particles consist of highly polar oligomers leading to agglomeration in the final stage. We therefore suppose that weathered microplastic and nanoplastic particles will attach to colloidal environmental matter. This offers an explanation for the absence of free nanoplastic particles in natural samples.

Adsorption properties and influencing factors of Cu(II) on polystyrene and polyethylene terephthalate microplastics in seawater

As an emerging contamination in the ocean, microplastics can act as effective vectors of pollutants, the ecological risks caused by the combined pollution of microplastics and other pollutants have attracted growing attention. In this work, Copper (Cu(II)) was chosen as the classic pollutant, polystyrene (PS) and polyethylene terephthalate (PET) pellets were used as the typical marine microplastics, the adsorption performance of Cu(II) on PS and PET beads was investigated by adsorption kinetics and isotherm experiments, and other influencing conditions, such as pH, salinity, coexisting heavy metals ions and aging treatment, were evaluated. The results indicated that the adsorption behavior of Cu(II) on PS and PET was spontaneous and endothermic in the simulated seawater environment, and the batch experimental data can be effectively described by pseudo-second-order model and Freundlich isothermal model. Besides, the adsorption capacity of microplastics for Cu(II) was the best at pH 7, the change of salinity had no obvious effect on the adsorption in the natural marine environment. Moreover, co-existence of lead (Pb(II)) exhibited evident impacts on Cu(II) sorption onto PS and PET, which confirmed the adsorption competition effect between them. Additionally, high temperature aging treatment of microplastics in different environments for different duration time could obviously affect the properties of microplastics. It was found that the microplastics after being exposed to high temperature environment in the air for 168 h showed relatively stronger adsorption amount for Cu(II). In summary, these findings suggested that electrostatic interaction and distributed diffusion mechanisms may be the main mechanisms of adsorption, while no new functional groups were generated after the adsorption, indicating that physisorption may dominate the adsorption performance of PS and PET pellets for Cu(II). This study provides supplementary insights into the role of microplastics as carriers of heavy metals in the marine environment.

Plasma generated ozone and reactive oxygen species for point of use PPE decontamination system

This paper reports a plasma reactive oxygen species (ROS) method for decontamination of PPE (N95 respirators and gowns) using a surface DBD source to meet the increased need of PPE due to the COVID-19 pandemic. A system is presented consisting of a mobile trailer (35 m3) along with several Dielectric barrier discharge sources installed for generating a plasma ROS level to achieve viral decontamination. The plasma ROS treated respirators were evaluated at the CDC NPPTL, and additional PPE specimens and material functionality testing were performed at Texas A&M. The effects of decontamination on the performance of respirators were tested using a modified version of the NIOSH Standard Test Procedure TEB-APR-STP-0059 to determine particulate filtration efficiency. The treated Prestige Ameritech and BYD brand N95 respirators show filtration efficiencies greater than 95% and maintain their integrity. The overall mechanical and functionality tests for plasma ROS treated PPE show no significant variations.

Dielectric Spectroscopy as a Condition Monitoring Technique for Low-Voltage Cables: Onsite Aging Assessment and Sensitivity Analyses

This work presents the development, validation, and sensitivity analyses of a portable device capable of performing high-frequency dielectric spectroscopy tests on site. After a brief introduction on the operation principle and the description of the impact of frequency on dielectric spectroscopy, the article presents the results of tests on reference samples confirming good agreement with expected values. The frequency region in which the device operates, 1–200 kHz, was chosen because of its correlation with oxidative species of polymeric compound. The sensitivity analyses were performed measuring the dielectric response of low voltage cables with different aged lengths. The outcome of these tests is twofold. On the one hand, they confirm the suitability of the technique for aging evaluation, and, on the other hand, they allow the assessment of the minimum aged length (damage ratio) which causes appreciable variations on the obtained dielectric spectrum. This quantity was found to be ~35% of the total cable length.