Recombination Of Free Radicals Research Articles

Fast Recombination of Free Radicals in Solution and Microviscosity

Fast Recombination of Free Radicals in Solution and Microviscosity

Mechanisms of Action in FLASH Radiotherapy: A Comprehensive Review of Physicochemical and Biological Processes on Cancerous and Normal Cells.

The advent of FLASH radiotherapy (FLASH-RT) has brought forth a paradigm shift in cancer treatment, showcasing remarkable normal cell sparing effects with ultra-high dose rates (>40 Gy/s). This review delves into the multifaceted mechanisms underpinning the efficacy of FLASH effect, examining both physicochemical and biological hypotheses in cell biophysics. The physicochemical process encompasses oxygen depletion, reactive oxygen species, and free radical recombination. In parallel, the biological process explores the FLASH effect on the immune system and on blood vessels in treatment sites such as the brain, lung, gastrointestinal tract, skin, and subcutaneous tissue. This review investigated the selective targeting of cancer cells and the modulation of the tumor microenvironment through FLASH-RT. Examining these mechanisms, we explore the implications and challenges of integrating FLASH-RT into cancer treatment. The potential to spare normal cells, boost the immune response, and modify the tumor vasculature offers new therapeutic strategies. Despite progress in understanding FLASH-RT, this review highlights knowledge gaps, emphasizing the need for further research to optimize its clinical applications. The synthesis of physicochemical and biological insights serves as a comprehensive resource for cell biology, molecular biology, and biophysics researchers and clinicians navigating the evolution of FLASH-RT in cancer therapy.

Thermochemical conversion of guaiacol with supercritical CO2: Experimental insights

The excessive CO2 in the environment resulting from the combustion of fossil fuels has posed a significant challenge in terms of its conversion and utilization. In this work, the thermochemical conversion of guaiacol under supercritical CO2 (scCO2) was proposed, which not only enabled the consumption of CO2 but also facilitated the conversion of biomass into valuable products. It was concluded that the carbon gasification efficiency (CE) and hydrogen gasification efficiency (HE) were 37.10 % and 51.77 %, respectively, when the CO reached the maximum of 8.72 ± 0.28 mol/kg at 700 °C for 20 min. The addition of catalyst promoted the production of H2 and increased CE, the H2 yield of guaiacol gasification under different catalysts was ordered as Al2O3 > KOH > without catalyst > KCl. As the reaction temperature increased, the unreacted guaiacol and phenol decreased and were gradually converted to liquid products such as pyrene and benzo[c]phenanthrene. With the increase in reaction temperature, the more fully guaiacol was reacted, the easier it was to carbonize and form more carbon microspheres. In addition, reaction pathways for free radicals were proposed, including cleavage of free radicals, isomerization of free radicals, secondary cleavage of free radicals and recombination of free radicals. In short, degrading guaiacol using scCO2 is a feasible approach, which provides a new direction for the disposal and energy recovery of biomass in the future.

Stable and selective multi-porous nickel nanoparticles catalysts for hydrocracking of dibenzyl ether supported by DFT studies

Preparation of clean fuel from biomass has a crucial significance on the development and utilization of renewable clean energy. In this study, a multi-stage porous mordenite supported nickel nanoparticles catalyst (Nix%/HMOR) was prepared, which showed that its acid content, acidity, porosity, specific surface area and metal dispersion were significantly improved while the crystallization strength was basically the same compared with microporous mordenite. In order to study the conversion mechanism of biomass energy, dibenzyl ether was selected as a typical lignin model compound. Under the condition of Ni10%/HMOR in n-hexane at 160 °C for 2 h under 5 MPa of initial hydrogen pressure, the conversion of dibenzyl ether was 100 % and the selectivity of methyl cyclohexane was 84.4 %, which manifested that Ni10%/HMOR had good activity in the selective hydrocracking process under mild conditions. Furthermore, density functional theory (DFT) was selected to study the activation energies of different reaction sites on dibenzyl ether bridge bonds and the recombination process of free radicals in the reaction process. It comes to a conclusion that the O atom on the C-O bridge bond is easier to be attacked by H*, and the C-O bond of the unsaturated aromatic ring is easier to break. During the recombination of free radicals, the two C-O bond breaking energy barriers of OMD are different, and H free radicals are more likely to attack the O atom in cyclohexane-methanol. It is conducive to the formation of stable compound 1 - (cyclohexylmethyl) − 1-methylcyclohexane and its isomers.

Impact of weak electromagnetic fields on the properties of coal substance

Purpose. To establish the regularities of the influence of magnetic fields on the peculiarities of changing the chemical and structural characteristics of the coal substance according to the size of microparticles enriched with vitrinite. To formulate a new system of views on the mechanisms of structural and functional transformations of coal substance under the influence of weak external fields. Methodology. The authors used an electric furnace heating up to 320 K that creates a pulsation magnetic field with a strength of up to 4,000 A/m to process dispersed samples of hard coal with a weak magnetic field. The methods of infrared spectroscopy and electron paramagnetic resonance were used in the research. Findings. Experimental works were carried out to estimate the impact of weak fields on the state and properties of coal substance. It is shown that weak energy fields, and the electromagnetic one in particular, are able to reduce the energy barriers of reactions in coal substance due to spin-spin interaction, which leads to the activation of processes at the atomic-molecular level and interfacial interaction. Originality.It is experimentallyestablished that for coal micro-particles with sizes from 0.16 to 0.1 m, enriched with vitrinite, the coupling coefficient decreases after exposure to an external magnetic field, and for micro-particles with sizes less than 0.63 m, this indicator increases. Such changes are caused by the redistribution of hydrogen between aromatic and aliphatic components during free-radical reactions. Changes in the spectrum on vitrinite (0.160.10 mm), are more significant than on inertinite (0.063<0.05 mm). At the same time, the external action of the electromagnetic field has caused the opposite consequences. It is shownthat magnetically stimulated chemical reactions occurring in the coal substance are aimed at the recombination of free radicals with active surface states of the organic mass of coal into stable gas molecules. The results of laboratory studies using the methods of electron magnetic resonance and infrared spectroscopy and infrared spectroscopy allow assuming that the changes in structural characteristics recorded during experiments with low-energy impacts can be considered as intermediatorsfor the matter transformation or changes in the state of coal in preparation for structural and functional transformations.For example, to the sorption interaction or destructive processes with methane generation. Practical values.The magnetic field effect can be used to develop new research methods for the study on elementary processes by electron spin resonance; control spin-dependent phase transitions. The use of magnetic resonance methods allows the usage of magnetically field effects in the form of basic tools for the research on structural defects. The results obtained will be a scientific ground for the development of methods for estimating the parameters of electromagnetic processes in coal to develop new technologies for the extraction and processing of hydrocarbon energy carriers.

Direct Hydrogen Production from Extra-Heavy Crude Oil under Supercritical Water Conditions Using a Catalytic (Ni-Co/Al2O3) Upgrading Process

The generation of hydrogen from unconventional oil is expected to increase significantly during the next decade. It is commonly known that hydrogen is an environmentally friendly alternative fuel, and its production would partially cover the gap in energy market requirements. However, developing new cheap catalysts for its production from crude oil is still a challenging area in the field of petroleum and the petrochemical industry. This study presents a new approach to synthesizing and applying promising catalysts based on Ni, Co, and Ni-Co alloys that are supported by aluminum oxide Al2O3 in the production of hydrogen from extra-heavy crude oil in the Tahe Oil Field (China), in the presence of supercritical water (SCW). The obtained catalysts were characterized via scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, transmission electron microscopy (TEM), and, X-ray diffraction analysis (XRD). The obtained XRD data showed 3.22% of Co2+ in the Co/Al2O4 catalyst, 10.89% of Ni2+ in the Ni/Al2O4 catalyst, and 1.51% of Co2+ and 2.42% of Ni2+ in the Ni-CoAl2O3 bimetallic catalyst. The BET measurements of the obtained catalysts showed a surface area ranging from 3.04 to 162 m2/g, an average particle size ranging from 0.037 to 0.944 µm, and micropore volumes ranging from 0.000377 to 0.004882 cm3/g. The thermal, SCW, and catalytic upgrading processes of the studied samples were conducted in a discontinuous autoclave reactor for 2 h at a temperature of 420 °C. The obtained results revealed that thermal upgrading yielded 1.059 mol.% of H2, and SCW led to 6.132 mol.% of H2; meanwhile, the presence of Ni-CoAl2O3 provided the maximal rate of hydrogen generation with 11.783 mol.%. Moreover, Ni-CoAl2O3 and NiAl2O3 catalysts have been found to possess good affinity and selectivity toward H2 (11.783 mol.%) and methane CH4 (40.541 mol.%). According to our results, the presence of SCW increases the yield of upgraded oil (from 34.68 wt.% to 58.83 wt.%) while decreasing the amount of coke (from 51.02 wt.% to 33.64 wt.%) due to the significant amount of hydrogen generation in the reaction zone, which reduces free-radical recombination, and thus, improves oil recovery. Moreover, the combination of SCW and the synthetized catalysts resulted in a significant decrease in asphaltene content in the upgraded oil, from 28% to 2%, as a result of the good redistribution of hydrogen over carbons (H/C) during the upgrading processes, where it increased from 1.39 to 1.41 in the presence of SCW and reached 1.63 in the presence of the Ni-CoAl2O3 catalyst. According to the XRD results of the transformed form of catalysts (CoNi3S4), after thermal processing, heteroatom removal from extra-heavy crude oil via oxidative and adsorptive desulfurization processes is promoted. These findings contribute to the expanding body of knowledge on hydrogen production from in situ unconventional oil upgrading.

Influence of impulse magnetic fields of extremely low frequencies on H2O2- and Fe2+-induced free radical lipid oxidation in liposomal suspensions

Background: For a long time, special attention in experimental biology and medicine is paid to free radical processes involving reactive oxygen species. In electromagnetic biology, the interest in free radical oxidation in biological membranes has increased significantly due to the discovery of spin mechanisms of magnetic fields on free radical processes. In the present day, these mechanisms are considered to be key in the processes of magnetoreception in living organisms. Liposomes, as the simplest models of biological membranes, are often used to study the primary mechanisms of action of different factors on the structural and functional properties of membranes. However, the influence of ecological significant extremely low-frequency magnetic fields on free radical oxidation in liposomal suspensions has not been studied enough. Objectives: The elucidation of the peculiarities of the influence of the extremely low frequency pulsed magnetic fields (ELF PMF) on H2O2- and Fe2+-induced peroxidation of natural phospholipids in liposomal suspensions. Materials and methods: The liposomal suspensions in phosphate buffer pH=7.4 were used. According to the literature and own results on light scattering the average diameter of liposomes was about 500Å. Ultra-weak chemiluminescence of liposomal suspensions was recorded using a device that operated in the mode of single photons counting. It consisted of a light-insulated cuvette unit where the test samples were placed, as well as a temperature sensor and a solenoid, which was used to create the PMF. Optical contact of the test samples with the photoelectron multiplier was carried out using a light guide. The recording system consisted of a broadband photomultiplier tube detector — FEU-130, which was at a temperature of –20°C. The pulse analyzer AI-256 was used to separate the useful signal that corresponded to the registration of single chemiluminescence light quanta. The voltage on the photomultiplier tube detector was applied in the range of current-voltage characteristics of this detector, in which a random voltage fluctuation had a minimal effect on the measurement of the useful signal. The number of light quanta that were recorded for defined time intervals characterized the overall intensity of the process of free radical oxidation of lipids in the experimental samples. The pulsed magnetic field was created using a solenoid coil located in the cuvette part. PMF was created using a serial generator G6-28. The magnetic field pulses were rectangular in shape with variable polarity for a period of oscillations. The induction of PMF was monitored using microteslameter G-79. The series of extremely low frequencies (5–80 Hz) and induction (5–500 μT) of PMF was chosen due to their environmental and physiological significance. Results: PMF of different frequencies with induction of 5 and 50 μT did not affect (p>0.05) H2O2- and Fe2+-induced lipid oxidation in liposomal suspensions. Statistically significant changes (p<0.05) were revealed only when liposomal suspensions were exposed to PMF with induction of 500 μT. It was found that the action of PMF with the frequency of 8 Hz 500 μT significantly inhibited H2O2-induced and enhanced Fe2+-induced chemiluminescence. This effect is associated with inhibition of the decomposition and with the accumulation of phospholipid hydroperoxides, which decompose and recombine in the presence of Fe2+ ions, which is accompanied by stronger chemiluminescence. The study of the dependence of the dynamics of the chemiluminescence intensity on the frequency of the PMF indicates the presence of a certain dependence of the effects in the range of up to 30 Hz. However, the inhibitory effect of PMF for the H2O2-induced oxidation phase is not always accompanied by a statistically significant increase in the amplitude of Fe2+-dependent light flash of chemiluminescence that indicates the general inhibitory effect of PMF at a certain frequency. Conclusions: PMF of extremely low frequencies statistically significantly affects the free radical oxidation in liposomal suspensions only at inductions exceeding several hundred microteslas. This indicates the effect of PMF on free radical processes for the conditions of the selected membrane model is realized mainly through spin interactions that determine the recombination of free radicals. The decrease of induction by one or two orders of magnitude, as well as increasing in frequency of the PMF above 50 Hz, leads to a decrease in the effectiveness of the influence of this physical factor on the intensity of lipid-free radical oxidation in liposomal suspensions. The most sensitive to the influence of ELF PMF is the phase of H2O2-induced free radical oxidation of lipids.

Thermally resettable laser transmission induced transparency in polymer waveguides at 635 nm.

Laser transmission induced transparency (LTIT) has been observed in a polymer waveguide using commercial perfluorinated acrylate-based materials when a continuous-wave laser at 635 nm is injected. The transmitted optical power increases continuously and follows a non-linear curve with respect to the laser injection time. Loss reduction over 13 dB is observed within 60 min at a moderate laser power of 5 mW. While higher injection power leads to a quicker change of the waveguide transparency, this loss reduction tends to saturate at a level irrelevant to the injection power. Further experiments demonstrate that a laser injection at 635 nm can also slightly improve the transparency at near-infrared wavelengths from 1500 nm to 1600 nm which is also the target wavelength range for this material. The state after a certain laser injection dose of 635 nm proves to be stable and the transmission characteristics of the polymer waveguide can be maintained and will continue after being stored at room temperature over a long period of time. By baking the waveguide at 200 °C for 20 min, the transparency property can be reset and the waveguide will return to the original high-loss state of 635 nm. These unique properties can be attributed to the photo-induced generation and thermally induced recombination of free radicals in the organic material. Our discovery may trigger interesting applications of polymer waveguides in the development of optical memory, clock, and encryption devices, beyond their target applications in optical communication.

Application of TiO2-ceramic/UVA photocatalyst for the photodegradation of sulfamethoxazole

Sulfamethoxazole (SMX) is one of the most antibiotic compounds detected in the aquatic environment. The potential concentration of SMX could raise the ecotoxicological effects on microbial. The photocatalyst based on TiO2 has been demonstrated as the effective material for the elimination of SMX in water. However, due to the non-selected attack of hydroxyl radical derived from photocatalysis to S–N, C–N bond, –NH2 group, or isoxazole ring, therefore SMX could be transferred to different intermediate products. In this study, SMX at 5 mg L−1 has been removed up to 84.7% after 7 h of irradiation by TiO2-ceramic photocatalyst. The highest removal efficiency could maintain at pH (5–6) where SMX existed in neutral form and the TiO2 reached to point of zero charge (PZC). On the other hand, environmental parameters such as bicarbonate ions and the dissolved organic matter (DOM), which are generally existing in ambient water, have negative effects on the elimination of SMX. Therefore, we investigated the effect of these factors on SMX photocatalyst removal. The efficiency of TiO2-ceramic was stable for 15 cycles of the experiment. In addition, the intermediate products were identified by UPLC-MS/MS and the degradation pathways were proposed. There were 11 intermediates detected with a molecular mass higher than 254. The result suggested that there was the recombination of free radicals to form new compounds. Therefore, although TiO2-ceramic is a promising photocatalyst for SMX removal an ecotoxicity test still needs to be evaluated for a deeper understanding of transformation products.

Liquid-phase methane bubble plasma discharge for heavy oil processing: Insights into free radicals-induced hydrogenation

Hydrogenation, an alternative to conventional cracking, is poised to revolutionize heavy oil upgrading by raising the hydrogen-to-carbon ratio at lower process pressures and temperatures. The emerging low-temperature plasma-enabled hydrogenation is an effective, fast, and environment-friendly process; however, the conversion rate and energy efficiency are still insufficient. To address these limitations, here we propose an innovative bubble-assisted methane plasma-liquid process for heavy oil processing (using ethylbenzene as a model compound) and offer new insights into radical-assisted hydrogenation. Results from the plasma kinetics modeling and density functional theory calculations indicate that ·H and ·CH3 radicals generated by CH4 plasma are two main drivers for ethylbenzene hydrogenation, and their chemical reaction rates with ethylbenzene molecules strongly depend on their spatial distribution in bubbles, which further govern the reaction direction towards ethylbenzene hydrogenation or free radical recombination. Moreover, it is found that by controlling the bubble numbers and plasma parameters, the H density can increase by an order of magnitude from 1.4 × 1020 to 3.88 × 1021 m−3, while the number of hydrogenated aromatic rings increases by ∼ 58%, which further confirms the excellences of the proposed plasma-bubble technology in chemical regulation and feasible processing. In addition, the feasibility of the plasma-enabled hydrogenation has been verified by the experiment, which highlighted the competition between the radical recombination and radical-aromatic ring interactions. Overall, the revealed interaction mechanisms between the plasma-generated radicals and ethylbenzene provide new insights and guiding principles for the future upgrading of heavy oils and other industrial hydrocarbon products.

Ultrafine-Mn2O3@N-doped porous carbon hybrids derived from Mn-MOFs: Dual-reaction centre catalyst with singlet oxygen-dominant oxidation process

Ultrafine-Mn2O3@N-doped porous carbon hybrids [Mn2O3@NC] derived from Mn-MOFs was constructed with 1O2 and O2−• as main Reactive oxygen species (ROS). Cation-π bonds and N-Mn complexation induced the formation of electron-rich Mn centre which provided electron for peroxymonosulfate activation to produce radicals, accompanying with generation of 1O2 via chain reaction. Notably, the porous structure of N-doped carbon shell could not only facilitate free radical recombination for generation of 1O2 but also provide adsorption sites for organics. On the other hand, as electron-poor centre, N-doped carbon shell could improve the electrons transfer from organic intermediate radicals to electron-rich Mn centre via π -π reaction, C-O-Mn and C-N-Mn bonds, which promote the redox of Mn to avoid peroxymonosulfate invalid decomposition. Being attributed to synergistic effects of dual-reaction centres and strong oxidation ability of 1O2, Mn2O3@NC achieved high mineralization of BPA at low-dose peroxymonosulfate (0.033 g/L).

How do dissolved gases affect the sonochemical process of hydrogen production? An overview of thermodynamic and mechanistic effects – On the “hot spot theory”

Although most of researchers agree on the elementary reactions behind the sonolytic formation of molecular hydrogen (H2) from water, namely the radical attack of H2O and H2O2 and the free radicals recombination, several recent papers ignore the intervention of the dissolved gas molecules in the kinetic pathways of free radicals, and hence may wrongly assess the effect of dissolved gases on the sonochemical production of hydrogen. One may fairly ask to which extent is it acceptable to ignore the role of the dissolved gas and its eventual decomposition inside the acoustic cavitation bubble? The present opinion paper discusses numerically the ways in which the nature of dissolved gas, i.e., N2, O2, Ar and air, may influence the kinetics of sonochemical hydrogen formation. The model evaluates the extent of direct physical effects, i.e., dynamics of bubble oscillation and collapse events if any, against indirect chemical effects, i.e., the chemical reactions of free radicals formation and consequently hydrogen emergence, it demonstrates the improvement in the sonochemical hydrogen production under argon and sheds light on several misinterpretations reported in earlier works, due to wrong assumptions mainly related to initial conditions. The paper also highlights the role of dissolved gases in the nature of created cavitation and hence the eventual bubble population phenomena that may prevent the achievement of the sonochemical activity. This is particularly demonstrated experimentally using a 20 kHz Sinaptec transducer and a Photron SA 5 high speed camera, in the case of CO2-saturated water where degassing bubbles are formed instead of transient cavitation.

Organic matter in interstellar dust lost at the approach to the heliosphere

Aims. We tackle the conundrums of organic materials missing from interstellar dust when measured inside the Solar System, while undoubtedly existing in the local interstellar cloud (LIC), which surrounds the Solar System. Methods. We present a theoretical argument that organic compounds sublimate almost instantaneously by exothermic reactions, when solar insolation triggers the recombination of free radicals or the rearrangement of carbon bonds in the compounds. Results. It turns out that the triggering temperature lies in the range of 20–50 K by considering that sublimation of organic materials takes place beyond the so-called filtration region of interstellar neutral atoms. We find that in-situ measurements of LIC dust in the Solar System result in an overestimate for the gas-to-dust mass ratio of the LIC, unless the sublimation of organic materials is taken into account. We also find that previous measurements of interstellar pickup ions have determined the total elemental abundances of gas and organic materials, instead of interstellar gas alone. Conclusions. We conclude that LIC organic matter suffers from sublimation en route to the heliosphere, implying that our understanding of LIC dust from space missions is incomplete. Since space missions inside the orbit of Saturn cannot give any information on the organic substances of LIC dust, one must await a future exploration mission to the inner edge of the Oort cloud for a thorough understanding of organic substances in the LIC. Once our model for the sublimation of interstellar organic matter by exothermic chemical reactions of free radicals is confirmed, the hypothesis of panspermia from the diffuse interstellar medium is ruled out.

Analysis of the viscosity reduction of crude oil with nano-Ni catalyst by acoustic cavitation

The present study discusses ultrasound wave and heterogeneous catalysts act synergistically on viscosity reduction of crude oil. The reasons for the possible viscosity reduction were analyzed from the structural changes of asphaltene. This paper presents a systematic and unified approach to analyzing asphaltene clusters structure based on FTIR spectra and XRD patterns. The results reveal that the cavitation effect can be intensified by the addition of metallic nickel particles. The cavitation effect destroys the spatial network structure formed by resin, asphaltene and wax crystals, so that the viscosity of the treated oil sample tends to be stable. With the addition of metallic nickel particles which has a synergistic effect on cavitation, the asphaltene molecules have undergone a cracking reaction and decomposed into small molecular hydrocarbon compounds, contributing to viscosity reduction. However, when added a certain amount of metallic nickel particles, the degree of surface cavitation leads to increasing number of cavitation bubbles, free radicals recombination, and aromatic hydrocarbons polymerizing to form secondary asphaltenes. This leads to a slight rise in viscosity.

On the mechanism of conductivity enhancement in PEDOT:PSS/PVA blend fiber induced by UV-light irradiation

In this paper, a simple method of UV-light irradiation treatment was employed to enhance electrical performance of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/poly(vinyl alcohol) blend fiber. It could be seen that fiber conductivity had significant increase after exposure to UV light (λ = 255 nm) under vacuum. Mechanism of UV-light irradiation on the improvement of electrical performance of blend fiber was investigated by FT-IR, Raman, XPS, and ESR spectroscopies. FT-IR spectroscopy revealed that UV irradiation decomposed chemical bonds of PSS chains, leading to cross-linking of PSS chains via recombination of free radicals. Raman results showed that PEDOT polymer chain transformed from benzoid structure to quinoid structure improving planarity of PEDOT polymer chains. ESR spectroscopy proved that fibers treated by UV-light irradiation had higher degree of charge delocalization across conjugated PEDOT backbone. Cross-linking of PSS chains formed multiple paths for better charge transportation among PEDOT-rich grains, which was responsible for conductivity enhancement in blend fiber. Our results demonstrated that UV-light irradiation could effectively improve the conductivity of PEDOT:PSS/PVA blend fiber by decomposition and cross-linking of PSS chains. Decomposition of PSS chains is favorable for better inter-connection between adjacent PEDOT chains, and cross-linking of PSS chains will provide higher degree of barrier-free path for charge transportation through π-conjugated PEDOT chains. Conductivity enhancement induced by UV-light irradiation is independent of fiber formation process thus allowing them to be candidate for broader applications.

Possible Mechanism of Thermal Reduction of Graphite Oxide

A mechanism for the thermal reduction of graphite oxide is proposed. The process begins with the homolysis of the C–C bond in the basal plane of graphite oxide with subsequent reactions of isomerization of the formed radicals. The formation of both CO and a significant amount of CO2 was explained to occur via the cleavage of 1,3-dioxetane, which forms by the disproportionation and recombination of free radicals.

Flame‐retarded polyethylene terephthalate with carbon microspheres/magnesium hydroxide compound flame retardant

SummaryA novel compound flame retardant (carbon microspheres/magnesium hydroxide, abbreviated as CMSs/MH) was used to improve the fire performance of polyethylene terephthalate (PET). LOI, UL94, and Cone test results showed that CMSs/MH/PET composites obtained the best fire performance at the mass ratio of CMSs to MH, which was 5:5, where the CMSs/MH content was 1.0 wt. % of PET. The Py‐CS‐MS, TGA‐DSC results, and morphology of char residue revealed the flame‐retardant mechanism. CMSs/MH increased the thermal stability of PET by increasing the activation energy at the initial combustion stage. At the second stage of combustion, CMSs/MH increased the chance of recombination of free radicals and slowed the combustion. Additionally, CMSs/MH promoted the cross‐linking of pyrolysis products and further improved the continuity of the char layer. Thus, a dense and continuous char layer of CMSs/MH/PET composites was produced; this char layer reduced the heat release rate and increased the amount of char residue.

Observation of dose-rate dependence in a Fricke dosimeter irradiated at low dose rates with monoenergetic X-rays

Absolute measurements of the radiolytic yield of Fe3+ in a ferrous sulphate dosimeter formulation (6 mM Fe2+), with a 20 keV x-ray monoenergetic beam, are reported. Dose-rate suppression of the radiolytic yield was observed at dose rates lower than and different in nature to those previously reported with x-rays. We present evidence that this effect is most likely to be due to recombination of free radicals radiolytically produced from water. The method used to make these measurements is also new and it provides radiolytic yields which are directly traceable to the SI standards system. The data presented provides new and exacting tests of radiation chemistry codes.

Analysis of the effects of chemical ageing of ethylene-propylene diene monomer by chemical, spectroscopic, and thermal means

Ethylene-propylene diene monomer (EPDM) failures due to material degradation poses a major risk in the biopharmaceutical industry, which can result in long periods of production downtime. It is suspected that a key cause of this EPDM degradation is due to the chemical solutions used in equipment cleaning processes, resulting in crosslinking of the EPDM polymer bulk. However, the mechanisms responsible for crosslink formation, and whether other degradation sources are also present, has never been investigated in the public domain. Twenty four virgin samples were utilised for testing, twelve of which were subject to common chemical cleaning solutions used in the biopharmaceutical sector. The chemical solutions under investigation were aqueous solutions of NaOH, NaClO, H3PO4, and the interaction between 100 °C H2O and NaClO. The characterisation of the degradation process was conducted via chemical, spectroscopic and thermal means. The results show that degradation of the polymer bulk proceeds predominantly via crosslinking for all exposure types, due to oxidative damage and the formation and recombination of free radicals. Loss of plasticiser in the polymer matrix and thermo-oxidative damage are contributory degradation mechanisms. NaOH and H3PO4 exposure results in an accelerated rate of crosslinking compared to NaClO in the early stages of exposure.

Benzophenone as a photoprobe of polymer films

The review article is devoted to kinetics of fast reactions following photoexcitation of benzophenone in polymer films. We observed three processes by ns laser flash photolysis in elastomers: (i) decay of a triple state of benzophenone with hydrogen abstraction from polymer matrix, (ii) formation and decay of geminate radical pairs, (iii) cross-termination of the formed radicals in the polymer bulk. Application of external magnetic field (MF) of B=0.2T essentially affects recombination of geminate (G-) and a bimolecular recombination of free radicals, which escaped polymer cage (F-pairs). Theoretical calculation of MF effects on G- and F-pairs is in agreement with corresponding experimental data. Elongation of elastomer leads to an unexpected observation: recombination in the bulk becomes slower. An explanation of this phenomenon based on elastomer free volume Vf approach was suggested.