Photochemical fate of nonionic polyacrylamide induced by hydroxyl radicals in the natural water: Mineralization mechanism exploration and half-life time evaluation.

Water-soluble polyacrylamide (PAM) compounds have been used extensively in various sectors. The abundance of PAM in the environment raises concerns about its environmental impact. However, the mineralization of PAM in water under natural light irradiation remains insufficiently explored. This study utilizes nonionic PAM (nPAM) as a representative model to investigate both the mechanism and efficiency of nPAM degradation in water when exposed to ultraviolet (UV) light with hydrogen peroxide (H2O2) as the hydroxyl radical source. In the dark or with only UVA irradiation, negligible mineralization of nPAM occurred. In contrast, the presence of hydroxyl radicals (produced by the UVA/H2O2 system) produced 50 % nPAM mineralization over 7 days under our experimental conditions. The corresponding molecular weight (MW) of the nPAM was swiftly reduced from 1.58 ×106 Da to 1.59 ×103 Da in 3 days. Moreover, five carboxylic acids and nitrate ions were identified as the photodegradation intermediates of nPAM. The efficiencies of nPAM photodegradation by the UVA/H2O2 system in different natural waters and environmental conditions were assessed. The rate constant for the reaction between the hydroxyl radical and nPAM was 2.17 ×109 M-unit-1 s-1. The half-lives of nPAM in the sea and continental surface waters were determined to be several years and dozens of days, respectively. The application of UVB obviously accelerated the mineralization of nPAM in ultrapure water (71 % degradation in 7 days). Moreover, mineralization of concentrated nPAM (200 mg/L) in sea water was more efficient when both UVA- and UVB-activated H2O2 were used. Additionally, toxic acrylamide was not generated during nPAM photodegradation. Moreover, the photodegradation intermediates from nPAM were found to be neither acutely nor chronically toxic to aquatic organisms. This comprehensive study sheds light on the photochemical fate of nPAM in natural waters and provides essential insight for practical treatment of PAM in water systems.

Study of sequential abiotic and biotic degradation of styrene butadiene rubber.

Styrene butadiene rubber is one of the main constituents of tire tread. During tire life, the tread material undergoes different stresses that impact its structure and chemical composition. Wear particles are then released into the environment as weathered material. To understand their fate, it is important to start with a better characterization of abiotic and biotic degradation of the elastomer material. A multi-disciplinary approach was implemented to study the photo- and thermo- degradation of non-vulcanized SBR films containing 15 w% styrene as well as their potential biodegradation by Rhodoccocus ruber and Gordonia polyisoprenivorans bacterial strains. Each ageing process leads to crosslinking reactions, much surface oxidation of the films and the production of hundreds of short chain compounds. These degradation products present a high level of unsaturation and oxidation and can be released into water to become potential substrates for microorganisms. Both strains were able to degrade from 0.2 to 1.2 % (% ThOD) of the aged SBR film after 30-day incubation while no biodegradation was observed on the pristine material. A 25-75 % decrease in the signal intensity of water extractable compounds was observed, suggesting that biomass production was linked to the consumption of low-molecular-weight degradation products. These results evidence the positive impact of abiotic degradation on the biodegradation process of styrene butadiene rubber.

Radiolysis effect on Eu(III)-superplasticiser interactions in artificial cement and squeezed cement pore waters.

In the framework of the French deep geological repository for radioactive waste, cement-based materials are envisaged to immobilize radionuclides and/or provide protection from radiation to the environment. Superplasticisers (SPs) are added to these materials to increase their workability. SPs will undergo degradation by coupled radiolytic and hydrolytic effects in the pore solution leading to the formation of potentially complexing degradation products. The objective was to study the potential effect of radiolyzed superplasticizers contained in cement-based materials on radionuclide uptake. The Eu speciation and solubility with organic ligands resulting from the degradation of SPs were studied for the two solutions and the results were compared. Two different SPs were selected, a polycarboxylate ether and a polynapthalene sulfonate. Two different protocols were followed: direct irradiation of the solution containing the superplasticizer, and irradiation of the compacted cement sample followed by extraction of the pore water. Solubility enhancements observed in artificial cement waters are not representative of real cement pore water interactions, in agreement with other studies. Finally, the effects of alkaline hydrolysis and radiolysis of SPs on Eu solubility in pore water are limited.

Characteristics, fate, and impact of marine plastic debris exposed to sunlight: A review.

The increase of plastic production from the middle of the twentieth century was inevitably followed by an increase in the amount of plastic dumped in the natural environment. There, the plastic debris are exposed to sunlight, temperature, humidity, and physical stress. This can induce photo-oxidative and thermal degradation. This review discusses the mechanism of plastics UV weathering and its characteristics. Comparison of the photodegradation rate and physico-chemical properties are made according to the weathering mode (natural/accelerated) and medium (air/water). Since the photodegradation can lead to plastics fragmentation, this phenomenon is described along with the methodologies used in literature to evaluate the fragmentation. The impact of the photodegraded plastic debris on the marine environment is also presented in term of (i) photodegradation products and stabilizers leakage, (ii) organic pollutants accumulation, transfer, and leakage, and (iii) toxicity on marine organisms.

New insights into the mechanism of photodegradation of chitosan.

Chitosan films were subjected to accelerated artificial weathering at λ>300 nm and 60 °C in the presence of O2. The resulting variations in the chemical structure were characterized by IR spectroscopy and UV-vis spectroscopy, and a photooxidation mechanism was proposed based on the identified oxidation photoproducts. The formation of gluconolactone derivatives leading to chain scissions was shown. In addition, low molecular weight photoproducts, which accounted for chitosan deacetylation, were detected. Furthermore, crosslinking reactions occurred, as revealed by gel fraction characterization. Variations in the mechanical and surface properties were characterized by AFM, and the reduction in macroscopic properties was correlated with the structural changes observed at the molecular scale by a multiscale approach.

Optical calcium test for measurement of multiple permeation pathways in flexible organic optoelectronic encapsulation.

Organic photovoltaic (OPV) devices and other organic electronics have the promise to provide lightweight, flexible alternatives to traditional rigid semiconductor technologies. However, organic electronics often degrade rapidly upon exposure to oxygen, water, light, and combinations thereof, as well as upon exposure to elevated temperatures. This requires the use of high gas barrier packaging in order for devices to have operational lifetimes on the order of years. To meet the challenge of transparent high gas barrier materials which maintain the flexibility of organic optoelectronics, many different materials and encapsulation schemes have been developed including the lamination of devices between flexible multi-layer barrier films. Because of their excellent barrier properties, these materials often require specialized testing for permeation measurements which evaluate materials independently. In this work, we demonstrate the use of an optical calcium test, which uses a sample geometry that closely mimics an OPV device, to evaluate a complete encapsulation scheme and to elucidate the relative importance of different permeation pathways. Using an encapsulation scheme of laminating a device between two multi-layer barrier films using an adhesive, measurements were made for water vapor permeation through the barrier film, the bulk adhesive, and along the adhesive-to-barrier film interface. The results show that the combined lateral permeation, including through the bulk adhesive and along the adhesive-to-barrier film interface, can constitute over 50% of the total permeation for small devices (4.5 cm × 4.5 cm). The adhesive-to-barrier film interface was also found to be a very important pathway as it was deemed responsible for more permeation than the bulk adhesive. The technique was also used to evaluate encapsulation design variables such as the effects of adhesive thickness and surface treatments on the lateral water permeation. We demonstrate that decreasing the adhesive thickness leads to a decrease in the lateral water permeation.

Water as a morphological probe to study polymer-filler interfaces: an original application of thermoporosimetry.

This paper is devoted to the characterization of polymer-filler interfaces by thermoporosimetry using water as a probe. Composites of EVA filled with aluminium hydroxide with high filler content for the required fire retardant properties have been studied. After water sorption at 90 °C, the composites have been analyzed by thermoporosimetry using water as a morphological probe. This technique first allowed studying the influence of the filler content and the specific surface area on the water uptake. The study with drying steps and two molecular probes (water and cyclohexane) has highlighted that water is confined at the interface and thus thermoporosimetry is a powerful tool to characterize interfaces in EVA-ATH composites.

Photooxidation of cellulose nitrate: new insights into degradation mechanisms.

Cellulose nitrate (or nitrocellulose) has received considerable interest due to its uses in various applications, such as paints, photographic films and propellants. However, it is considered as one of the primary pollutants in the energetic material industries because it can be degraded to form polluting chemical species. In this work, the UV light degradation of cellulose nitrate films was studied under conditions of artificially accelerated photooxidation. To eliminate the reactivity of nitro groups, the degradation of ethylcellulose was also investigated. Infrared spectroscopy analyses of the chemical modifications caused by the photooxidation of cellulose nitrate films and the resulting formation of volatile products revealed the occurrence of de-nitration and the formation of oxidation photoproducts exhibiting lactone and anhydride functions. The impact of these chemical modifications on the mechanical and thermal properties of cellulose nitrate films includes embrittlement and lower temperatures of ignition when used as a propellant.

Investigation on combustion derived BaMgAl10O17:Eu2+ phosphor powder and its corresponding PVP/BaMgAl10O17:Eu2+ nanocomposite.

This work focuses on the study of BaMgAl10O17:Eu(2+) (BAM:Eu) nanophosphors prepared by a microwave-assisted combustion procedure and more especially on the polymer/BAM:Eu nanocomposite film suitable for optical devices such as solid-state-lighting. Powder presented a specific nanomorphology, highly friable and thus easily ground into fine particles. They were then homogeneously dispersed into a polymer solution (poly(N-vinylpyrrolidone) or PVP) to elaborate a polymer phosphor nanocomposite. The structural, morphological and optical features of the nanocomposite film have been studied and compared to those of a pristine PVP film and BAM:Eu powder. All the characterizations (XRD, SEM, SAXS, etc.) proved that the blue phosphor nanoparticles are well incorporated into the polymer nanocomposite film which exhibited the characteristic blue emission of Eu(2+) under UV light excitation. Furthermore, the photostability of the polymer/phosphor nanocomposite film has been studied after exposure to accelerated artificial photoageing at wavelengths above 300 nm.

Photochemical behavior of polylactide/ZnO nanocomposite films.

This study reports the effect of light on PLA/ZnO nanocomposites films produced by melt-extrusion. The attention focused on the discrimination between the photocatalytic degradation of PLA provoked by ZnO and the UV screening effect of the ZnO nanoparticles. The chemical modifications of PLA induced by UV light irradiation were analyzed using infrared spectroscopy and completed through the analysis of the low-molecular-weight photoproducts using IC and SPME and the characterization of chain scissions with SEC. A comprehensive mechanism for the photooxidation of PLA was then proposed. The results indicated that the photocatalytic activity of ZnO nanoparticles induces the oxidation of PLA. Because ZnO limits the penetration of light inside the samples, this effect mainly concerns the first micrometers at the surface of the exposed samples. Cross-sectional analysis using micro-IR and ATR-IR spectroscopies was performed to highlight the degradation profile in the PLA/ZnO nanocomposites.

Effect of ZnO nanofillers treated with triethoxy caprylylsilane on the isothermal and non-isothermal crystallization of poly(lactic acid).

The crystallization of PLA-silane surface-treated ZnO nanocomposites was investigated by DSC and compared to that of neat PLA. Several modes of crystallization were considered: isothermal and non-isothermal cold crystallization and also isothermal and non-isothermal melt crystallization. The kinetics of cold crystallization were studied using different methods, namely the Avrami and Ozawa-Flynn-Wall models, to calculate activation energies and kinetic constants. In contrast to what is typically observed when the foreign particles are added in a polymer matrix, the silane surface-treated ZnO delayed the crystallization of PLA and made it more difficult to start. The nucleation activity of the ZnO nanoparticles, ϕ, was calculated and found to be greater than 1 (ϕ = 1.7). This indicated that ZnO played an anti-nucleating role in the crystallization of PLA nanocomposites. This effect has been linked mainly to the interactions between the silane groups onto the surface of nanoparticles and PLA macromolecules. These interactions which reduce the mobility of polymer chains have been evidenced by rheological experiments.

Luminescent nanocomposites made of finely dispersed Y3Ga5O12:Tb powder in a polymer matrix: promising candidates for optical devices.

This paper reports the initial results of an original and simple method to elaborate flexible, self-standing, and thick luminescent films suitable for optical devices. PVP/Y(3)Ga(5)O(12):Tb(3+) nanocomposite films have been successfully achieved from a sol-gel derived Y(3)Ga(5)O(12):Tb(3+) powder and an alcoholic solution of poly-N-vinylpyrrolidone (PVP). The structural, morphological, and optical properties of these nanocomposite films have been studied and compared to those of a pristine PVP film and Y(3)Ga(5)O(12):Tb(3+) powder. The nanocomposite films were characterized by infrared and Raman spectroscopies as well as scanning and transmission electron microscopies (SEM and TEM) and demonstrated good dispersion of the phosphor particles within the polymer matrix via an alveolar mesostructure. The optical properties of these nanocomposites were fully characterized, and both their excitation and emission spectra and decay curves were recorded. Furthermore, photostability of the nanocomposite films and of the luminescent raw powder has been studied after exposure to an accelerated artificial photoageing at wavelengths higher than 300 nm. The elaboration process used is both tunable and applicable to a large variety of powders and polymers because it does not require any additive to form homogeneous and easily shapeable phosphor/polymer nanocomposites applicable in a large variety of optical devices such as solid-state-lighting.

Multiscale investigation of the poly(N-vinylcarbazole) photoageing mechanism.

During the past decade, the development of polymeric solar cells has received a great deal of attention from both academic and industrial laboratories. In order to enhance the device performances both in terms of power conversion efficiency stability in use conditions, Polycarbazole copolymers have attracted increasing attention. In this paper, the photodegradation of poly(N-vinylcarbazole) (PVK) was investigated from the molecular scale to the nanomechanical properties. It was shown irradiation provoked chain scissions, homolysis of the C-N bond and formation of new covalent bonds between the macromolecular chains. To fully understand the mechanism of the degradation of PVK provoked by exposure to UV radiation, mechanical analyses were performed. The consequences of the cross-linking reactions on the surface modifications were analyzed. Roughness and stiffness measurements were obtained through surface analysis and nanoindentation by atomic force microscopy (AFM), and depth-profiling experiments were also performed. The surface modifications and the shape of the profiles of the degradation photoproducts were explained in light of the chemical modifications of the PVK structure. Quantitative correlations were successfully obtained between the main relevant criteria of degradation, from the chemical structure to the mechanical properties. It was found that cross-linking reactions were prevalent.