Polymeric Iodonium Salts to Trigger Free Radical Photopolymerization.

In a significant breakthrough from classical molecular (i.e., nonpolymeric) iodonium salts in light-induced photochemistry, the synthesis and use of new safer polymeric iodonium salts are reported here. They are shown to be involved in charge transfer complexes (CTCs) while in interaction with a safe amino acid derivative (N-phenylglycine). Also, this study demonstrates i) the formation of CTCs between the iodonium (acceptor) and an aryl/alkyl amine (donor) through UV-vis measurements of the monomer, ii) the formation of radicals in electron spin resonance spin trapping experiments when the CTCs are irradiated by visible light (405 nm), and iii) their efficiency as a photoinitiator to polymerize three different acrylic monomers under LED irradiation at 405 nm under air and their application to 3D resolved laser writing of thick samples (3 mm). High reactivity for polymeric iodonium salts comparable with molecular ones is exhibited with the advantage of potential lower migration. To the best of the authors' knowledge, this is the first reported instance of polymeric iodonium salts acting as polymerization initiators.

Use of biomass ash from different sources and processes in cement.

Substitution of cement clinker with suitable excess materials from other processes is an effective way to reduce CO2 emissions of cement production. Moreover, specific properties of the resulting mortar or concrete can be designed with different clinker replacement materials and their mixing ratios. In this study, bottom and fly ashes from six biomass power plants with different power scales and various flue-gas treatment strategies were admixed to mortars, whose properties (influence of water requirement and final compressive strength) were then assessed in the laboratory by following industrial standard procedures. Results reveal that fly ash from a cyclone of a medium-scale combustor burning Miscanthus straw amended with 2 wt % Ca(OH)2 (to prevent slagging during combustion) turned out to be well suited as a clinker replacement material, even boosting final compressive strength of the mortar. Wood-chip bottom ashes and fly ash from a cyclone exhibited acceptable results, whereas fly ash from electrostatic precipitators (ESPs) and baghouse filters lowered final compressive strength of the mortar when admixed. The scale of the power plant is positively correlated with final compressive strength in the case of ESPs. Cenospheres, typical fly ash particles present in cyclone ash, seem to have a positive effect on water-to-binder ratio and final compressive strength. In contrast, potassium salts, which are most abundant in ash from ESPs and baghouse filters, appear to have a negative influence on these properties. Grinding of the biomass ashes to a typical Portland cement fineness had a positive effect on mortar quality. All fly ashes had high contents of Cd, and baghouse filter ash contained As in amounts about four times the Swiss limit value for cement of 30 ppm; only bottom ash and cyclone ash from Miscanthus exhibited concentrations below respective limit values for all critical trace elements. To assess the immobilization potential of contaminating elements during the cement hardening process, blended mortars were crushed and subjected to multistep leaching, followed by subsequent analysis of the leachates by atomic absorption spectroscopy. Immobilization of Cd by the mortar was particularly effective. Our results indicate that fly ash from wood-chip combustion is most suitable as an amendment to cement when it was trapped by a cyclone rather than by the ESPs or baghouse filters.

Physicochemical and mineralogical characterization of biomass ash from different power plants in the Upper Rhine Region.

Bottom and fly ash samples from six biomass power plants with different power scales and various flue gas treatment strategies were collected and analyzed in regard to their mineralogical composition, and their bulk major and trace element contents, all of which are of concern for regulations on biomass ash for further utilization. Furthermore, individual ash particles were investigated by scanning electron microscopy to characterize their physicochemical microstructures. Thermal behavior of wood-pellet ash, i.e. decomposition processes and mineral transformations during combustion, was indicated by thermogravimetric analysis and X-ray diffraction. Results reveal extensive variation of physicochemical features across the different ash types: wood-chip fly ash from electrostatic precipitators mainly consisted of water-soluble salts, whereas wood-chip fly ash from cyclones contained predominantly cenospheres (hollow spherical fly ash particles) and higher heavy metal concentrations. In addition, the fuel type and admixture had influences on ash compositions; some fuels like Miscanthus straw require a liming agent such as calcium hydroxide to be admixed to prevent fouling, which is then predominantly found in the ash. Furthermore, boiler size had an influence on fly ash composition. Cadmium concentrations were elevated in some fly ash samples at levels of concern for further utilization, whereas concentrations of troublesome Cr(VI) were below the detection limit for all investigated ash samples. Other contaminating elements such as Ni, Pb and Zn were variable but below limit values. Results clearly show that the nature of biomass ash calls for careful analyses prior to further application as, e.g., cement clinker replacement material.

Carbazole-based compounds as photoinitiators for free radical and cationic polymerization upon near visible light illumination.

Six new carbazole based compounds (Ca1-Ca6) are synthesized and proposed as high performance photoinitiators with iodonium salt (iod) and/or an amine (EDB) for both the free radical polymerization (FRP) of acrylates and the cationic polymerization (CP) of epoxides upon near UV and visible light exposure using light emitting diodes (LEDs) @385 nm and @405 nm. Excellent polymerization initiating abilities are found and high final reactive function conversions are acquired. A full picture of the involved photochemical mechanisms is given.

Charge-Transfer Complexes as New Inhibitors/Photoinitiators for On-Demand Amine/Peroxide Redox Polymerization.

Redox free-radical polymerizations have widespread applications but still clearly suffer from poor time control of the reaction. Currently, the workability (delay of the gel time) in redox polymerization after mixing is possible thanks to two main types of inhibitors (radical scavengers): phenols and nitroxides. Out of this trend, we propose in this work an alternative strategy for time delaying of the redox polymerization, which is based on charge-transfer complexes (CTCs). Thanks to iodonium salt complexation, the amine (here 4-N,N-trimethylaniline) is proposed to be stored in a CTC equilibrium and is slowly released over a period of time (as a result of the consumption of free amines by peroxides). This alternative strategy allowed us to double the gel time (e.g., from 60 to 120 s) while maintaining a high polymerization efficiency (performance comparable to reference nitroxides). More interestingly, the CTCs involved in this retarding strategy are photoresponsive under visible LED@405 nm and can be used on demand as photoinitiators, allowing (i) spectacular increases in polymerization efficiencies (from 50 °C without light to 120 °C under mild irradiation conditions); (ii) drastic reduction of the oxygen-inhibited layer (already 45% C=C conversion at a 2 µm distance from the top surface) compared to the nonirradiated sample (thick inhibited layer of more than 45 µm); and (iii) external control of the redox polymerization gel time due to the possible light activation.

New Synthetic Route to an Highly Efficient Photoredox Catalyst by Mechanosynthesis.

Photoredox catalysis based on the [Cu(neo)(DPEphos)]BF4 copper complex allowed getting a significant improvement of the polymerization performances (e.g., thick samples, coatings...) compared to that obtained with other benchmarked photoinitiators in both cationic (CP) and free radical polymerizations (FRP). Nevertheless, as for other copper complexes classically used as photoinitiators in polymer science, the synthesis of these complexes is carried out in a solvent; this fact remains an obstacle to their widespread use because of the cost associated with the use of a solvent and the complex synthesis procedure. In the present study, on the contrary, an outstanding efficient mechanosynthesis of [Cu(neo)(DPEphos)]BF4-purity ≥95% outranking the previous Cu(I) mechanosynthesis-allowed (i) to divide the synthesis time by 170-fold (as only 5 min is necessary to get the complex), (ii) to lower the environmental impact and cut the synthetic costs associated with solvent usage, and (iii) to access a new Cu(I) complex with a counteranion that is impossible to introduce under the traditional chemistry methods (e.g., I-). Reactivities of the mechanosynthesized copper complexes in resins (FRP and CP) confirmed the very high purity of the obtained copper complex by 1H nuclear magnetic resonance spectroscopy and high-resolution electrospray ionization mass spectrometry.

Characterization and in vitro biological effects of ambient air PM10 from a rural, an industrial and an urban site in Sulaimani City, Iraq.

High urban atmospheric pollution is caused by economic and industrial growth, especially in developing countries. The objective of this study was to assess possible relationships between in vitro effects on human alveolar epithelial cells of source-related dust types collected at Sulaimani City (Iraq), and to determine their mineralogical and chemical composition. A passive sampler was used to collect dust particles at a rural, an industrial and an urban sampling site during July and August 2014. The samples were size-fractionated by a low-pressure impactor to obtain respirable dust with aerodynamic diameters of less than 10 µm. The dust was mainly composed of quartz and calcite. Chrysotile fibres (white asbestos) were also found at the urban site. Dust from the industrial and urban sites triggered cytotoxic and genotoxic effects in the cells, whereas only minor effects were observed for the sample from the rural site.

Novel Carbazole Skeleton-Based Photoinitiators for LED Polymerization and LED Projector 3D Printing.

Radical chemistry is a very convenient way to produce polymer materials. Here, an application of a particular photoinduced radical chemistry is illustrated. Seven new carbazole derivatives Cd1-Cd7 are incorporated and proposed as high performance near-UV photoinitiators for both the free radical polymerization (FRP) of (meth)acrylates and the cationic polymerization (CP) of epoxides utilizing Light Emitting Diodes LEDs @405 nm. Excellent polymerization-initiating abilities are found and high final reactive function conversions are obtained. Interestingly, these new derivatives display much better near-UV polymerization-initiating abilities compared to a reference UV absorbing carbazole (CARET 9H-carbazole-9-ethanol) demonstrating that the new substituents have good ability to red shift the absorption of the proposed photoinitiators. All the more strikingly, in combination with iodonium salt, Cd1-Cd7 are likewise preferred as cationic photoinitiators over the notable photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) for mild irradiation conditions featuring their remarkable reactivity. In particular their utilization in the preparation of new cationic resins for LED projector 3D printing is envisioned. A full picture of the included photochemical mechanisms is given.

Cytotoxic and genotoxic responses of human lung cells to combustion smoke particles of Miscanthus straw, softwood and beech wood chips.

Inhalation of particulate matter (PM) from residential biomass combustion is epidemiologically associated with cardiovascular and pulmonary diseases. This study investigates PM0.4-1 emissions from combustion of commercial Miscanthus straw (MS), softwood chips (SWC) and beech wood chips (BWC) in a domestic-scale boiler (40 kW). The PM0.4-1 emitted during combustion of the MS, SWC and BWC were characterized by ICP-MS/OES, XRD, SEM, TEM, and DLS. Cytotoxicity and genotoxicity in human alveolar epithelial A549 and human bronchial epithelial BEAS-2B cells were assessed by the WST-1 assay and the DNA-Alkaline Unwinding Assay (DAUA). PM0.4-1 uptake/translocation in cells was investigated with a new method developed using a confocal reflection microscope. SWC and BWC had a inherently higher residual water content than MS. The PM0.4-1 emitted during combustion of SWC and BWC exhibited higher levels of Polycyclic Aromatic Hydrocarbons (PAHs), a greater variety of mineral species and a higher heavy metal content than PM0.4-1 from MS combustion. Exposure to PM0.4-1 from combustion of SWC and BWC induced cytotoxic and genotoxic effects in human alveolar and bronchial cells, whereby the strongest effect was observed for BWC and was comparable to that caused by diesel PM (SRM 2 975), In contrast, PM0.4-1 from MS combustion did not induce cellular responses in the studied lung cells. A high PAH content in PM emissions seems to be a reliable chemical marker of both combustion efficiency and particle toxicity. Residual biomass water content strongly affects particulate emissions and their toxic potential. Therefore, to minimize the harmful effects of fine PM on health, improvement of combustion efficiency (aiming to reduce the presence of incomplete combustion products bound to PM) and application of fly ash capture technology, as well as use of novel biomass fuels like Miscanthus straw is recommended.