Increasing attention is being paid to the environmental fate and impact of plastics and their additives under sunlight exposure. We evaluated the photodegradation of polystyrene (PS) films (∼100 μm) ...containing brominated flame retardants (BFRs): decabromodiphenylether (BDE-209), tetrabromobisphenol A (TBBPA), and tetrabromobisphenol A-bis (2.3-dibromopropylether) (TBBPA-DBPE). Irradiations were performed in a solar simulator and outdoors. Infrared (IR) analyses indicated an acceleration of the photooxidation rate of fire-retarded PS films compared to pure PS with an enhancement factor of 7 for TBBPA-DBPE and TBBPA, and 10 for BDE-209. The accelerating effect was found to be correlated with the quantum yield for BFR photodegradation and its absorbance in the PS films. The presence of BFRs also modified the PS photooxidation mechanism and resulted in the formation of 14 brominated photoproducts via bromination and oxidation of PS. Furthermore, a drastic increase in chain scissions and loss of molecular weight was revealed by size exclusion chromatography. This enhanced degradation of PS led to significant leaching (15%) of oxidation products from PS films after immersion in water, and to the gas-phase emission of several volatile brominated products. Our findings suggest that fire-retarded plastics may be a source of potentially hazardous contaminants when exposed to sunlight.
We have investigated the impact of residual additives such as diiodooctane (DIO) and octanedithiol (ODT) on the photostability of state of the art P3HT:PCBM active layers. A series of active layers ...prepared with and without additives as well as neat additives were submitted to light irradiation in ambient air and analyzed by UV–vis and IR spectroscopy. We show not only that residues are sensitive to the combined action of light and oxygen but also that their presence can dramatically impact the polymer blend stability. DIO molecules are highly sensitive to light and can directly saturate the polymer conjugated backbone or be trapped by the fullerene moieties. ODT molecules can be photooxidized and may accelerate the intrinsic photooxidation of the active layer. Another important result is that the additives’ impact is directly linked to the presence of a top layer above the active layer. The confinement makes that additives react within the active layer, and thus accelerate its photodegradation, rather than decomposing in the gas phase (irradiation without top layer). Thus, a light-soaking step before top layer deposition could allow a clean removing of additives without affecting the optimized morphology and polymer blend stability. This process would be easily adaptable to industrial scale production.
Poly(3-hexylthiophene) (P3HT) has been the focus of great interest as it is widely used in organic solar cells. However, P3HT has relatively poor photochemical and thermal stability under ambient ...atmosphere, which leads to a reduced lifetime of the solar cells. It was therefore necessary to study the photo- and thermooxidation of P3HT. Thin P3HT films were exposed to UV–visible light irradiation and thermal ageing, both in the presence of air. Changes in the infrared spectra of the aged samples were recorded, and the oxidation products were identified. A degradation mechanism that accounted for the modifications in the infrared spectra was then developed. This mechanism confirmed that singlet oxygen plays no decisive role, as previously reported. Oxidation was shown to involve the radical oxidation of the
n-hexyl side-chains and the subsequent degradation of the thiophene rings. The breaking of the macromolecular backbone resulted in a loss of π-conjugation, provoking the bleaching of the sample.
Brominated flame retardants (BFRs) are widely used as additives in plastics, textiles and electronics materials. Here, we investigated the photodegradation of four BFRs including ...decabromobiphenylether (BDE-209), tetrabromobipsphenol A (TBBPA), tetrabromobisphenol A-bis(2,3-dibromopropylether) (TBBPA-DBPE) and tetrabromobisphenol A bis (allyl) ether (TBBPA-BAE). Experiments were carried out in polystyrene (PS) films using monochromatic and polychromatic irradiations. For comparison, irradiations were also carried in a solvent (tetrahydrofuran: THF). Monitoring of BFR degradation was performed using bulk and surface infrared (IR) measurements, as well as by extraction and HPLC-UV. Photoproducts were characterized using HPLC-high resolution electrospray ionization mass spectrometry (HPLC-ESI-Orbitrap-MS).
All four BFRs underwent photochemical transformation in THF at 290 nm with a quantum yield (Φ) ranging from 0.05 for TBBPA to 0.27 for BDE-209, indicating an increase of photoreactivity with the number of Br atoms in BFRs. On the other hand, no major difference in the Φ values was observed when BFRs were embedded in PS films (Φ: 0.82–0.89). The higher photoreactivity in PS appears to be associated with a fast oxidation of PS as revealed by infrared (IR) analysis and yellowing of the films. Interestingly, the faster the yellowing occurred, the faster the BFR degradation was inhibited due to light screening effect. Several major photoproducts were identified for TBBPA and TBBPA-DBPE. Additional photoproducts possibly arising from PS oxidation and bromination by Br● were observed for the first time. This work provides a better understanding of the reactivity and fate of BFRs in polymers allowing for a better assessment of their environmental impacts.
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•Quantum yields of four BFRs were measured in tetrahydrofuran and polystyrene.•Higher photoreactivity of BFRs was observed in polystyrene.•Photodegradation of BFRs induced oxidation and yellowing of polystyrene.•The less absorbing BFR was found to be further degraded during irradiation.•C7-brominated photoproducts of polystyrene oxidation were detected for the first time.
We report on the photochemical behaviour of the active layer of polymer solar cells when exposed to UV–visible light and temperature in the absence of oxygen. The paper focuses on the effects of ...UV–visible light irradiations on pristine poly(3-hexylthiophene) (P3HT) and subsequent blend with 6,6-phenyl C
61 butyric acid methyl ester (PCBM), both deposited on an inert substrate (KBr). The modifications of the chemical structure of the materials were monitored by UV–visible and infrared spectroscopies. We first observed a slow photochemical evolution of P3HT upon exposure to artificial accelerated photoageing. We observed that the process was considerably slowed down when P3HT was blended with PCBM. The comparison with the behaviour of MDMO-PPV-based active layers irradiated in similar conditions demonstrated that P3HT is much more stable. Finally, the extrapolation of the data obtained in conditions of artificial accelerated ageing to natural ageing suggested that the P3HT:PCBM blend would be chemically stable for at least three years under use conditions if well protected from oxygen.
In drinking water production plants, the use of oxidants such as sodium hypochlorite during in-place cleanings may impair the membrane integrity and radically impact the ultrafiltration process ...efficiency, leading to potential contamination of the permeate water with pathogens. This study investigates the effects of hypochlorite exposure on the properties of a commercially available UF hollow fiber. Mechanical performances and water permeability appeared to be greatly affected by the contact with hypochlorite. Monitoring the molecular changes by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy (ATR-IR), size exclusion chromatography (SEC) and VITA-mode atomic force microscopy (VITA-AFM) revealed high stability of the main polymer constituting the membrane (i.e. polyethersulfone (PES)) and very high reactivity of the additive (i.e. poly(N-vinyl pyrrolidone) (PVP)) towards immersion in aqueous sodium hypochlorite solution with maximal reaction rate for neutral to slightly basic pH. Correlation of those results unexpectedly leads to the conclusion that the overall membrane properties changes are governed by the additive fate.
•Hypochlorite exposure does not induce chain scission of PES.•Hypochlorite exposure induces radical degradation of PVP additive leading to chain scissions.•The maximal PVP degradation rate is reached for pH values between 7 and 8.•Hypochlorite exposure induces PES oxidation (without chain scissions) only in the areas where PVP is present.•PVP degradation and release from the membrane material are directly correlated to the membrane embrittlement.
Polymer-based organic solar cells are known to offer a poor stability in real use conditions, and the photodegradation of the active organic layer plays an important role in the reduced lifetime of ...the devices. This paper focuses on the photodegradation of two conjugated polymers used in organic solar cells, namely poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (MDMO-PPV) and poly(3-hexyylthiophene) (P3HT), and their blends with 60PCBM (methano-fullerene6,6-phenyl C61-butyric acid methyl ester), a fullerene derivative. MDMO-PPV and P3HT thin films were submitted to photoageing (
λ > 300 nm) in the presence and in the absence of oxygen. The mechanisms by which these polymers degrade were elucidated. P3HT, pristine and blended with PCBM, was shown to be much more stable under illumination than MDMO-PPV. The results showed that, if deposited on an inert substrate and well protected from oxygen with a convenient encapsulation, P3HT:PCBM based active layer should be intrinsically stable for several years in use conditions.
The impact of side-chain variations on the photothermal stability of solar cells containing poly(benzodithiophene-diketopyrrolopyrrole) polymers are investigated in the absence of oxygen. Four ...different side-chains of benzodithiophene (BDT) are synthesized and copolymerized with diketopyrrolopyrrole (DPP) by Stille polymerization. The photothermal stability is measured as active layer blends with phenyl-C61-butyric acid methyl ester (PCBM) in encapsulated inverted photovoltaic cell architecture with zinc oxide and
PSS as transport layers (ITO/ZnO/active layer/
PSS/Ag). Device degradation is correlated to the morphological behavior of the polymer:blend upon AM1.5 illumination (UV-visible light, 50 °C) and have been investigated by AFM, XRD, and UV-Vis. Once exposed to the light and to the temperature the BHJ stability is governed by two processes (i) PCBM crystallization and (ii) PCBM dimerization. Dimerization results in a rapid initial performance decrease followed by a more gradual decrease caused by a slower thermally activated crystallization. Depending on the blend morphology, dictated by the polymer's alkyl chain, the two processes occur to different extents thereby modulating the BHJ stability. Thus, of the polymer side-chains explored, linear alkyl side-chains stabilized the bulk heterojunction most effectively followed by no side-chain, alkoxy and branched side-chains. Lowering the concentration of fullerene in the active layer also reduces the rate of degradation across the polymers tested. This is a result of both the rate of crystallization and dimerization of fullerene being dependent on its concentration and the nature of the polymer side-chains. This approach appears to be a general strategy to increase the polymer:PCBM stability.
We studied the role that singlet oxygen plays in the solid‐state photochemistry of poly(3‐hexylthiophene) (P3HT). The photosensitized formation of singlet oxygen by solid‐state P3HT and its ...subsequent reactivity on the polymer were investigated. Using a fluorescent probe, it was found that singlet oxygen (1O2) could be produced by irradiation of P3HT by photosensitization, with no oxidation of the polymer. In addition, 1O2 was directly formed on P3HT via a chemical reaction, again with no oxidation of the polymer. These results give strong evidence that 1O2 is not the principal photo‐oxidative degradation intermediate of P3HT, which conflicts with previous reports.
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