Chain Scission Research Articles

Solvent-Free Chemical Recycling of Polyesters and Polycarbonates by Magnesium-Based Lewis Acid Catalyst.

Developing a simple and efficient catalyst system for closed-loop recycling of polymers to monomers is an essentially important but challenging task for the recycle of polymer wastes and preventing the downcycle of plastic products. Herein, we employ inexpensive, commercially available Lewis acids (LAs) to achieve closed-loop recycling in bulk through the catalytic depolymerization of aliphatic polyesters and polycarbonates. The scope of LAs is screened by thermogravimetric analysis experiments and distillation experiments. MgCl2 shows the best catalytic performance that can efficiently depolymerize eleven aliphatic polyesters and polycarbonates (i.e. poly(ϵ-caprolactone) and poly(trimethylene carbonate)), into monomers (up to 98 % yield) at temperatures significantly lower than the ceiling temperature. Moreover, this catalyst system exhibits high selectivity and compatibility towards the depolymerization of (co)polyesters as well as the blends of polyesters and polycarbonates in the presence of other commodity plastics, as well as excellent recycle and reuse catalyst performance. Mechanistic studies indicate that the closed-loop recycling of monomers is achieved through the random chain scission and terminal group cyclization.

Solvent‐Free Chemical Recycling of Polyesters and Polycarbonates by Magnesium‐based Lewis Acid Catalyst

Developing a simple and efficient catalyst system for closed‐loop recycling of polymers to monomers is an essentially important but challenging task for the recycle of polymer wastes and preventing the downcycle of plastic products. Herein, we employ inexpensive, commercially available Lewis acids (LAs) to achieve closed‐loop recycling in bulk through the catalytic depolymerization of aliphatic polyesters and polycarbonates. The scope of LAs is screened by thermogravimetric analysis experiments and distillation experiments. MgCl2 shows the best catalytic performance that can efficiently depolymerize eleven aliphatic polyesters and polycarbonates (i.e. poly(ε‐caprolactone) and poly(trimethylene carbonate)), into monomers (up to 98% yield) at temperatures significantly lower than the ceiling temperature. Moreover, this catalyst system exhibits high selectivity and compatibility towards the depolymerization of (co)polyesters as well as the blends of polyesters and polycarbonates in the presence of other commodity plastics, as well as excellent recycle and reuse catalyst performance. Mechanistic studies indicate that the closed‐loop recycling of monomers is achieved through the random chain scission and terminal group cyclization.

Water Ageing of Epoxies: Effect of Thermal Oxidation

ABSTRACTEpoxy samples obtained by curing bisphenol A diglycidyl ether with triethylenetetramine are thermally oxidized at 160°C under air. The impact on water sorption is investigated by water uptake recorded by Dynamic Vapor Sorption and the gravimetric method. Experimental data mainly showed that water solubility in epoxies increases due to oxidative degradation, meanwhile, the formation of clustering remains limited. In the investigated ageing conditions, water diffusion obeys Fick's law. Despite a significant chain scission process, water diffusivity in polymer remains constant, possibly in line with the fact that hydroxypropylethers are the driving force of water diffusion and are not degraded during thermal ageing.

Not Cutting Corners: Bioderived Triggers Driving Oxidative Main Chain Scission of Poly(ethylene terephthalate)

Not Cutting Corners: Bioderived Triggers Driving Oxidative Main Chain Scission of Poly(ethylene terephthalate)

Irradiation of hydrophilic acrylic intraocular lenses by a 365 nm UV lamp

Abstract Intraocular lenses (IOLs) based on a transparent hydrophilic acrylic polymer have been irradiated by a 365 nm UV lamp at a 200 mJ/cm2 fluence and at different exposure times, from 1 h up to 19 h, in air and at room temperature. The macromolecular modifications induced in the lens have been investigated by attenuated total reflectance coupled to Fourier transform infrared spectroscopy and optical spectroscopy. Particular attention was devoted to the study of chemical modifications of the IOL by UV irradiation, which induced chain scissions, radical formation, and cross-links in the more superficial polymer layers. The experimental results at long exposures demonstrate that the IOL transmission decreases in the UV and NIR ranges, remaining nearly constant in the visible range.

High Efficiency Electroplating (220)-Orientation Nano-Twinned Copper in Methanesulfonic Acid System and Mechanism Analysis

Nano-twinned copper, distinguished by intricately arranged twin boundaries within each grain, manifests superior mechanical properties compared to commercial copper foil. The cohesive twin structure effectively impedes dislocation motion through intricate interactions between twin boundaries and slip bands. Consequently, copper endowed with a twinned structure achieves an ultrahigh tensile strength of approximately 1 GPa, surpassing the performance of coarse-grained polycrystalline copper, which attains only around 200 MPa under equivalent testing conditions. Furthermore, the resistivity of coherent twin boundaries is approximately half that of stacking faults and grain boundaries. This characteristic allows twinned copper to attain heightened tensile strength without significant compromises in conductivity. In the context of resistance to electromigration, the twinned structure significantly hampers copper's atomic diffusion by an order of magnitude at the triple points where twin and grain boundaries intersect, compared to commercial copper. Moreover, in certain instances, nano-twinned copper demonstrates exceptional thermal stability, maintaining elevated hardness levels even subsequent to annealing at 800 °C, in contrast to nanocrystalline copper. In a distinct scenario, annealing at 250 °C for a duration of 3 hours results in only a marginal reduction in tensile strength, stabilizing at approximately 700 MPa.Given the exemplary performance demonstrated by nano-twinned structures, the imperative is to devise efficient methodologies for the production of high-density nano-twinned copper films. High-speed electroplating emerges as a viable approach to achieve this objective, attributed to its one-step process and facile control.Mainly because the high current density induces the higher copper nucleation rate, making interfacial energy larger, so that copper films would easier to proceed twin formation reaction to lower the residual stress. Numerous scholarly works underscore the application of high-speed electroplating in producing nano-twinned copper films, particularly through the pulse electrodeposition mode. This mode, characterized by a clear nucleation mechanism and well-defined performance metrics, facilitates the systematic creation of nano-twinned structures. However, the incorporation of a pulse-off period resulted in a reduction of the average current density, which was suboptimal from an efficiency standpoint. Consequently, specific scholarly works explore the electroplating of a twin-crystal structure through DC electroplating, aiming for enhanced efficiency with higher average current density. Presently, the literature reports instances of achieving elevated current densities, reaching up to 40 ASD, to produce nano-twinned copper with a (111) orientation and an average twin spacing of approximately 100 nm. Nevertheless, the solubility of cupric ions serves as a limiting factor for the overall electroplating reaction rate efficiency. Consequently, an inherent upper limit to efficiency exists within the copper sulfate system, posing a challenging constraint to ameliorate through adjustments to temperature or additives.However, existing literature indicates that the cupric ions' solubility in copper sulfate is 1.35 M, while copper methanesulfonate demonstrates an impressive solubility of up to 2 M, as confirmed through vacuum filtration. The heightened ion solubility provides the opportunity to increase current density without inducing deleterious powdery deposition issues, thereby maintaining a uniformly conductive surface. Also, the higher current density would conduct better twin formation condition. Thus, the metal methanesulfonate solution, constituting an organic acid system designed to enhance the solubility of metal ions, involves the substitution of metal sulfate with metal methanesulfonate and the replacement of sulfuric acid with methanesulfonic acid, can be considered as a feasible optimization for efficiency issue and twin formation.In the copper sulfonate system, the induction of a nano-twinned structure involves adding organic additives to form an ionic complex with Cu+ in remediation and chloride ions, subsequently altering the deposition route and nucleating copper crystals through a stress relaxation process. Conversely, in the copper methanesulfonate system, chloride ions exhibit an antagonistic effect with organic additives. Moreover, the use of organic additives is associated with potential challenges related to aging, chain scission and cracking issues, potentially transforming the system into a batch manufacturing paradigm. Therefore, investigating the possibility of directly improving the electrochemical mechanism on the negative surface through chloride ions in this organic system to plate nano-twin crystals is a question worth exploring in order to create a sustainable electroplating process for commercial nano-twinned copper manufacture.Here presents a novel approach to the production of (220) orientation nano-twinned copper films, achieved through the incorporation of chloride ions as additives in a high-concentration methanesulfonate copper solution. The primary objective is to leverage chloride ions for the induction of numerous twin boundaries on the copper surface, enabling meticulous control of the average twin spacing at the nanoscale.The investigation herein provides a comprehensive analysis of the nuanced role played by chloride ion distribution in the formation of nano-twinned copper. Figure 1

Simulation of in-Situ Chemical Membrane Degradation in the Presence of Fe and Ce Cations in Reinforced Fuel Cell Membranes

A PEM fuel cell’s durability and lifetime are affected by various degradation phenomena, among which chemical degradation of PEM material exerts the most damage. Chemical degradation of PEM occurs when reactive radicals such as hydroxyl (·OH) and hydroperoxyl (·OOH) are generated from the decomposition of hydrogen peroxide. The radicals chemically attack the main and side chains of the perfluorosulfonic acid-based PEM and change its internal chemical structure. This leads to excessive membrane thinning and pinhole formation that causes higher gas crossover and electrode shorting inside the PEM fuel cell1. The generation of harmful radicals accelerates in the presence of Fenton’s metal, such as iron (Fe)2. Evaluation of PEM fuel cell chemical degradation durability is performed using long-term pure chemical accelerated stress test (AST) under high temperature (T), low relative humidity (RH), and open circuit voltage (OCV) conditions3. Physical characterization of a membrane sample used in a fuel cell can help to visualize and assess damage incurred during an AST. These results, however, fail to encompass the formation rate of radicals and intermediate degradation products generated during the AST3. To overcome these issues, computational fluid dynamics models are developed that simulate the evolution of degraded products and predict the lifetime of PEM fuel cells4,5.The present work aims to develop an in-situ one-dimensional (1-D) transient chemical degradation model that describes reaction-transport phenomena within the membrane electrode assembly (MEA) in the presence of Fe and Ce cations. This work considers mechanically reinforced GORE-SELECT® 15 µm baseline (MemA) and chemically and mechanically reinforced 12 µm (MemB-Ce) membranes. The developed in-situ model simulates pure chemical AST operating conditions with variable Fe ion loading and follows the computational algorithms originally presented by Wong and Kjeang4. The model successfully predicted that side chain scission is followed by main chain unzipping, as reported in the literature6. The evaluation of the change in ionomer structure by chemical degradation was done by computing the temporal concentration profile of intermediate degraded ionomer species, hydrogen peroxide, and membrane thickness reduction. The 1-D model also encapsulates the concentration profile of Fe2+ and Fe3+ ions across the PEM and predicts their temporal distribution throughout the simulated AST duration under OCV conditions. It was observed that the MemA thickness decreased rapidly in the presence of Fe ions, as shown in Figure 1. The computational parameters and results were calibrated and validated using in-house AST results for MEAs with embedded Fe metallic particles, which were shown to completely dissolve during conditioning and hence treated as uniformly distributed Fe cations with an initial concentration of 900 ppm at the beginning-of-life7. The model identified a limiting Fe ion concentration limit of 100 ppm that accentuates the chemical attack. Experimentally, a low Fe concentration of 10 ppm was determined in the baseline MemA, which also reduced the membrane thickness within 1125 h of operation, as shown in Figure 1. It is known that cerium (Ce) ions can scavenge harmful radicals and increase the lifetime of PEM fuel cells8. The model, therefore, simulates the effectiveness of Ce ions in the MemB-Ce membrane and the temporal distribution of Ce3+/Ce4+ ions and shows a lower rate of membrane thickness reduction, as shown in Figure 1. The modelling framework was, therefore, able to predict PEM fuel cell lifetime in conjunction with the transport behaviour of both harmful and beneficial cations as well as their interactions during the chemical degradation process at OCV conditions. Keywords: PEM fuel cell, fuel cell durability, chemical degradation model, in-situ modelling, iron, cerium Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. It was also undertaken in part thanks to funding from the Canada Research Chairs program. References J. Healy et al., Fuel Cells, 5, 302–308 (2005).S. Kundu, L. C. Simon, and M. W. Fowler, Polym. Degrad. Stab., 93, 214–224 (2008).Y. Singh, F. P. Orfino, M. Dutta, and E. Kjeang, J. Electrochem. Soc., 164, F1331–F1341 (2017).K. H. Wong and E. Kjeang, J. Electrochem. Soc., 161, F823–F832 (2014).R. B. Ferreira, D. S. Falcão, and A. M. F. R. Pinto, Int. J. Hydrogen Energy, 46, 1106–1120 (2021).L. Ghassemzadeh, K. D. Kreuer, J. Maier, and K. Müller, J. Phys. Chem. C, 114, 14635–14645 (2010).N. Kumar et al., ECS Meet. Abstr., MA2023-02, 1919–1919 (2023).S. M. Stewart, D. Spernjak, R. Borup, A. Datye, and F. Garzon, ECS Electrochem. Lett., 3, F19–F22 (2014). Figure 1

Studying the Effect of Carbonous Fillers on the Properties of Conductive Polymer Composites As Flow Field Plates in Redox Flow Batteries

Redox flow batteries (RFBs) are large-scale stationary energy storage technologies that are integrated with solar and wind power plants. Flow field plates guide the electrolyte inside the RFB and conduct electrons from the electrodes to the current collector; hence, designing thin, durable, and electrically conductive flow field plate benefits RFB performance.Bipolar graphite plates (BGPs) are traditionally used in RFBs due to their high electrical conductivity. However, BGPs are brittle, difficult to machine, and have high contact resistance with electrodes1-4. Hence, conductive polymer composites (CPCs) were proposed as alternatives. the CPCs are composed of one (or multiple) carbonous filler(s) and a durable polymer; the former provides the electrical conductivity, and the latter ensures mechanical flexibility and durability. Although many articles have explored this area1-12, a comprehensive study on the effect of size and shape of the carbonous fillers (majority and minority ones) is absent from the literature.Many methodologies to produce CPCs are proposed; however, most lead to polymer chain scission or non-homogeneous mixing of components. Solution blending of all components, casting the solution, drying, and hot pressing it afterwards (to ensure compactness) is one of the methodologies that avoids mentioned complications. Preliminary results with natural graphite flakes and PVDF-co-HFP utilizing this method showed very low conductivity (<0.1 S/cm). This result is attributed to the formation of a superficial polymer-rich layer, as shown in Fig. 1. Hence, producing CPCs either without hot pressing or utilizing surface treatments to remove the polymer-rich region are studied here. Additionally, this study focuses on understanding the effect of shape and size of the carbonous filler(s) within CPCs as flow field plates for RFBs.Fig. 1. SEM images of PVDF-co-HFP and graphite (50/50% wt/wt) distribution in CPCs produced by solution blend method. Before hot pressing the composites, the polymer was homogeneously blend with the graphite. However, an insulating polymer-rich layer was formed on the surface of the CPCs after hot pressing.

Operando Fluorescence Spectroscopy Setup for Radical Detection during Proton Exchange Membrane Water Electrolysis Operation

In a world with an ever-increasing energy demand, efficient and durable energy conversion devices for renewable energy sources are of great importance. Proton exchange membrane water electrolyzers (PEMWEs) are among the industry-established systems for converting electricity into hydrogen as a chemical energy carrier. In these systems, the proton exchange membrane (PEM) has to separate the two evolved gases (H2 and O2). The degradation of this membrane during operation, e.g., membrane thinning, can lead to system failure due to electrical shorts or dangerous explosive gas mixtures of H2 in O2 [1]. Therefore, it is important to gain a detailed understanding of the membrane degradation mechanisms in order to develop suitable mitigation strategies and extend the device lifetime. One possible cause of ionomer degradation is the evolution of reactive oxygen species (ROS), namely hydroxyl and hydroperoxyl radicals, during WE operation, causing main chain scission and leading to membrane thinning [2]. Due to the very short lifetime of these highly reactive species, direct detection within the PEM is challenging.However, there is an indirect detection method possible that has already been applied to PEM fuel cells [3]: The membrane is infused with a radical-sensitive fluorescent dye and an optical probe is embedded within this dyed membrane [Fig.1]. This way, a fluorescence signal can be measured upon excitation with a suitable light source. With the membrane being exposed to ROS, the radicals attack the membrane as well as the dye molecules, which can be measured by a change in fluorescence intensity. This setup was adapted for the application in PEMWEs to measure the effect of various operating conditions of the cell on ROS production and, hence, to detect stressors for membrane degradation.

Disclosing the UV aging mechanisms of polyamide 66 industrial fiber on the base of the multi-scale structural evolutions

This study investigated the changes in the properties of polyamide 66 (PA66) industrial fibers during UV aging and explored the underlying UV aging mechanisms through structural data analysis across varying length scales. The findings reveal a three-stage progression in the deterioration of mechanical properties due to UV aging. Initially, in the pre-aging stage (t ≤ 1 day), both mechanical properties and microscopic structural parameters remain stable, showing no significant changes. Following this, UV-induced degradation and concurrent recrystallization in the amorphous region result in a decline in mechanical parameters as the aging process continues, albeit with varying magnitudes across the stages. A notable decrease in tenacity and elongation at break is observed in the mid-aging stage (1 day < t ≤ 49 days). While the formation of low-melting-point microcrystals enhances crystallinity and crystalline size, the predominant effect of molecular chain scission due to UV exposure leads to a significant increase in carbonyl group content and a marked decrease in intrinsic viscosity. Furthermore, the formation of microcrystals hinders oxygen diffusion, resulting in the gradual stabilization of intrinsic viscosity and carbonyl content in the late-aging stage (t > 49 days), which significantly slows the deterioration of mechanical properties. These results indicate that UV-induced molecular degradation is the primary driver of changes in break elongation, while the development of new crystalline structures within the fibers contributes to the preservation of mechanical properties.

Poroelastic fracture of polyacrylamide hydrogels: Enhanced crack tip swelling driven by chain scission

The deformation of hydrogels is accompanied by water migration, a process that plays a crucial role in their fracture behaviors. Previous investigations primarily focus on how the water migration between the environment and hydrogel affects the fracture of hydrogels. Herein, a novel mechanism of the rate-dependent fracture of hydrogels induced by interior water migration is uncovered. Notched polyacrylamide (PAAm) hydrogels are stretched at various stretch rates in both oil and deionized (DI) water environments. Notably, the critical stretches to crack propagation are positively correlated with the stretch rates in both the two environments. This rate-dependent fracture is attributed to the crack tip swelling of PAAm hydrogels. Delayed fracture tests conducted in oil further verify the co-existence of delayed fracture and rate-dependent fracture resulted from interior water migration in PAAm hydrogels. The experimental findings are interpreted by considering the imperfection of a real polymer network, in which the scission of short chains in the region neighboring the crack tip reduces the average crosslinking density locally, thereby greatly amplifying the degree of crack tip swelling and its influence on the fracture of hydrogels. A constitutive model coupling the evolution of polymer network and the diffusion of water molecules is proposed, which can predict the crack tip swelling of notched PAAm hydrogels through the finite element method. Assuming that the decrease in fracture toughness is positively related to the swelling along the crack propagation surface, the predicted normalized fracture toughness matches the experimental results of PAAm hydrogels stretched in water well, and satisfies those in oil environment qualitatively. This work highlights the significant influence of interior water migration on the fracture of hydrogels and provides insights that may guide the design of hydrogels with enhanced fracture resistance.

Modification of polyolefins utilizing C–H insertion of azides: Azidoformate end-functionalized polystyrene for modifying polypropylene

Polyolefins dominate the global plastics industry, constituting roughly 60% of all commercial plastics. However, their limited chemical functionality restricts their applicability in adhesion, printability, and compatibility-dependent applications. To overcome these limitations, this study investigated metal-free, melt-process, post-polymerization modification of polypropylene (PP) via C-H insertion of azidoformate (AF) groups. Specifically, we investigated grafting of AF end-functionalized polystyrene (PS) onto PP and demonstrated the successful preparation of novel PP hybrids with interesting properties, including enhanced compatibility between PP and PS components due to grafting, smaller PP crystallite size, high Young's modulus, and elastic rheological behavior, likely attributable to the presence of PS branches. Importantly, the presented approach avoids chain scission of PP and undesirable coloration of the product, offering a promising pathway for industrial transformations of conventional polyolefins. This research paves the way for developing polyolefin-based hybrid materials with enhanced properties and potential environmental benefits.

Fungal Chitin Nanofibrils Improve Mechanical Performance and UV-Light Resistance in Carboxymethylcellulose and Polyvinylpyrrolidone Films.

Materials from renewable carbon feedstock can limit our dependence on fossil carbon and facilitate the transition from linear carbon-intensive economies to sustainable, circular economies. Chitin nanofibrils (ChNFs) isolated from white mushrooms offer remarkable environmental benefits over conventional crustacean-derived nanochitin. Herein, ChNFs are utilized to reinforce polymers of natural and fossil origin, carboxymethyl cellulose (CMC) and polyvinylpyrrolidone (PVP), respectively. Incorporation of 5 wt % ChNFs increases the Young's modulus from 1217 ± 11 to 1509 ± 22 MPa for PVP and from 1979 ± 48 to 2216 ± 102 MPa for CMC. ChNFs increase surface hydrophobicity and retard the scission of the C-H bond as a result of UV-light irradiation in both polymers under investigation. The yellowing from chain scission is reduced, while long-lasting retention of ductility is ensured. Given these results, we propose the utilization of ChNFs in sustainable polymeric materials from renewable carbon with competitive performance against fossil-based benchmark plastics.

Fracture of polymer-like networks with hybrid bond strengths

The design and functionality of polymeric materials hinge on failure resistance. While molecular-level details drive crack evolution in polymer networks, the connection between individual chain scission and bulk failure remains unclear and difficult to probe. In this work, we systematically study the fracture mechanics of polymer-like networks with hybrid bond strengths. We reveal that varying the ratio of strong and weak strands within otherwise identical networks gives a non-monotonic relationship between intrinsic fracture energy and strong strand fraction. Networks with some weak strands can counterintuitively outperform those with exclusively strong strands. Experiments on poly(ethylene glycol) gels and architected polymer-like lattices together with simulations unveil these properties. We show through computational visualization that strand type concentrations impact crack growth patterns and fracture energy trends. Cracks propagate through weak layers at low strong strand fractions. Aggregate clusters deflect or pin cracks at similar concentrations of strong and weak strands. Cracks blunt due to dispersed weak strand failure at high strong strand fractions. The sacrificial weak strands can notably deconcentrate stress near the crack tip, which toughens by delaying crack advancement. The interplay between concentration and clustering of strand types in networks with hybrid bond strengths, combined with crack growth phenomena and nonlocal energy release, provides insights into unusual fracture characteristics. Results shed light on fracture in polymer networks and percolated lattices.

More Efficient Chemical Recycling of Poly(Ethylene Terephthalate) by Intercepting Intermediates.

The research presented in this paper offers insight into the availability of intermediates in the depolymerization of polyethylene terephthalate (PET) to be used as feedstock to create value-added products. Monitoring the dispersity, molecular weight, end groups, and crystallinity of reaction intermediates during the heterogeneous depolymerization of PET offers insight into the mechanism by which the polymer chains evolve during the reaction. Our results show dispersity decreases and crystallinity increases while the yield of insoluble PET remains high early in the reaction. Our interpretation of this data depicts a mechanism where chain scission targets amorphous tie chains between crystalline phases. Targeting the tie-chains lowers the Mn of the polymer without changing the amount of recovered polymer flake. Chain scission of tie-chains and isolating highly crystalline PET lowers the dispersity (Đ) of the polymer chains, as the size of the crystalline lamellae guides the molecular weight of the depolymerized oligomers. When sufficient end groups of PET chains are converted to alcohol groups, the PET flakes break apart into highly crystalline and less disperse polymer. Our results also demonstrate that the oligomeric depolymerization intermediates are readily repolymerized, offering new opportunities to chemically recycle PET more effectively and efficiently, from both an energy and purification standpoint.

Study on the aging behavior and mechanism of nitrile rubber composites in combined radiation-thermal environments

This contribution investigates the aging property changes and mechanism of nitrile rubber (NBR) under the combined radiation-thermal environments in the N2 atmosphere. Aging resulted in a decrease in elongation at break from 309.01 % to 64.74 %, an increase in modulus of elasticity from 3.84 MPa to 9.09 MPa, and a slight increase in thermal stability. The crosslink density increases and the mass loss of the sample is reduced, while the chemical structure of the sample surface is almost intact. By gas-phase infrared spectroscopy, the irradiation aging-induced gases from NBR were also analyzed, including CO2, CO, and alkanes (CH4, C2H6, C3H8). This indicates that chain scission and pendant group removal also take place, whereas chain breaking primarily occurs at the macromolecular chain end. The above degradation reactions and the decomposed additives account for the generated trace amount of small molecule gas products. These findings suggest that the primary aging mechanisms of NBR are the cross-linking of macromolecular chains and additive loss. Furthermore, radiation and thermal have a synergistic effect on NBR aging, and this effect has a threshold temperature that is clearly between 50 °C and 70 °C. The synergistic effect of additive cleavage is only apparent at temperatures above 65 °C under radiation-thermal conditions.

Mechanical characterization and structural analysis of elastodontic appliances under intraoral and artificial aging conditions

BackgroundThis study focused on the aging mechanism and degradation of mechanical and structural features of elastodontic appliances (EA) under artificial and intraoral aging to achieve oral myofunctional therapy with particular removable silicone elastomer devices.Materials and methodsEAs artificially aged in saliva with different pH values were investigated through cyclic compression testing along with characterization techniques (Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy), and characterization analysis was also performed on clinically retrieved EAs.ResultsArtificial aging was found to have minimal effect on the structural properties of EAs, and intraorally aged samples showed perceptible micro-morphology. The Mullins index and peak stress decreased (P<0.01), while the compression set increased with prolonged aging time. Samples in alkaline saliva showed the largest Mullins effect (P<0.05).ConclusionsThe aging mechanism of the elastomer was found to be the crosslinking of main chains and scission of side chains. The presence of OH- enhanced the rupture degree of side bonds. The decline in viscoelastic properties was shown to be more severe with longer service durations.Clinical relevanceResearch on how the salivary environment and pH affect the aging characteristics of EAs is vital for guiding clinical applications and future modifications to extend their clinical lifetime.

Investigation the structural and surface characteristics of irradiated flexible polymeric nanocomposites films

This study is to investigate the surface and structural characteristics of the pure and irradiated novel PEO/NiO composite by subjecting the films to argon ions with different ion beam fluencies. The structural characteristics were studied by the EDX and FTIR techniques, while the surface was investigated by SEM technique. The FTIR showed a notable decrease in the peak intensity for the bombarded composite, due to the functional groups with hydrophilic characteristics and the occurrence of chain scission processes. The PEO/NiO composite demonstrates a consistent structure without any nanoparticle clusters, as depicted in the SEM image of PEO/NiO. Moreover, the electrical conductivity for the pure and the irradiated samples were determined. Exposing the composite PEO/NiO to a fluence of 15×1016 ions.cm-2, increasing the conductivity from 7.5×10–8 S/cm to 8.4×10–7 S/cm. By increasing ion fluence from 5×1016 to 15×1016 ions.cm-2. The contact angle is decreased from 81.15o to 72.22o for water, while is decreased from 74.32o to 62.20o for diiodomethane. Moreover, the surface wettability and the adhesion force were determined from the data of the contact angle. The work of adhesion of water increases from 84.37 to 94.16 mJ/m2 and for dioodomethane from 64.52 to 74.49 mJ/m2 , respectively, by increasing ion fluence from 5×1016 to 15×1016 ions.cm-2. This suggests that, in comparison to a unirradiated surface, the increase in 𝑊𝑊𝑎𝑎 is the result of surface cleanliness following radiationThe results of this study show the opportunities for utilizing these irradiated materials in the fields of coating and printing applications.

Quantum Simulations of Radiation Damage in a Molecular Polyethylene Analog.

An atomic-level understanding of radiation-induced damage in simple polymers like polyethylene is essential for determining how these chemical changes can alter the physical and mechanical properties of important technological materials such as plastics. Ensembles of quantum simulations of radiation damage in a polyethylene analog are performed using the Density Functional Tight Binding method to help bind its radiolysis and subsequent degradation as a function of radiation dose. Chemical degradation products are categorized with a graph theory approach, and occurrence rates of unsaturated carbon bond formation, crosslinking, cycle formation, chain scission reactions, and out-gassing products are computed. Statistical correlations between product pairs show significant correlations between chain scission reactions, unsaturated carbon bond formation, and out-gassing products, though these correlations decrease with increasing atom recoil energy. The results present relatively simple chemical descriptors as possible indications of network rearrangements in the middle range of excitation energies. Ultimately, the work provides a computational framework for determining the coupling between nonequilibrium chemistry in polymers and potential changes to macro-scale properties that can aid in the interpretation of future radiation damage experiments on plasticmaterials.

A review on rheological approaches as a perfect tool to monitor thermal degradation of biodegradable polymers

AbstractThis review provides an in-depth analysis of the thermal degradation of biodegradable polymers through rheological methods. Focusing on key techniques such as time sweep tests, frequency sweep tests, and nonlinear rheological analyses gained at higher shear tests, the review highlights how these approaches offer critical insights into polymer stability and degradation kinetics. It entails an understanding of how molecular weight reduction, a common degradation mechanism, significantly impacts the performance of biodegradable polymers, and how the use of appropriate fillers can enhance thermal stability by mitigating chain scission. The review also discusses the application of the Arrhenius equation in modelling thermal degradation, helping predict degradation rates and optimize processing conditions. Time sweep tests are particularly emphasized for their ability to monitor polymer stability under various environmental conditions, while frequency sweep tests provide insights into the effects of processing/thermal history on material degradation. Tests at higher shear rates, which simulate real-world processing conditions such as extrusion and injection moulding, are explored for their role in understanding how processing-induced shear forces accelerate polymer degradation. Various biodegradable polymers are considered in this review, with polylactic acid (PLA) being the dominant polymer studied across most research, providing a clear picture of its degradation behaviour and strategies for enhancing its thermal stability. Therefore, it is expected that this review will be a comprehensive guide for researchers and engineers looking to optimize the thermal stability and performance of biodegradable polymers in various industrial applications. Graphical abstract