Collection of substantial amount of fine and ultrafine particles during the combustion of miscanthus and forest residues in small and medium scale boilers for morphological and chemical characterizations

Renewable energies are destined to play a very important role in the future world energy balance. Among these energies, biomass production and utilization is growing considerably since it offers the possibility to provide partial substitution of fossil fuels. If health impacts of fine particles (PM2.5) from diesel combustion are well documented (Gangwar et al., 2012), those from biomass combustion need substantial information and improvements. Size fractionations of PM2.5 have to be performed in order to both determine morphological and chemical characteristics, these properties being essential for biological effects. Particulate matter was sampled during combustion of miscanthus and forest residues in medium and small scale biomass boilers (400 kW from Köb Pyrot and 40 kW from REKA). Fly ashes from medium scale boiler were sampled with a cyclone device and their granulometry was studied with both optical microscope and Malvern laser granulometer. PM2.5 (sized in the range of 0.4 μm to 2.07 μm) from low scale boiler were sampled using a DEKATI DGI impactor modified for substantial PM collection. A quick overview of setup modifications for manual impactor will be developed. Particles were observed using fluorescence microscopy. A semi-quantitative method to compare fly ashes fluorescence was developped using ImageJ (Schneider et al., 2012). Speciation of organic compounds Polycyclic Aromatic Hydrocarbon (PAH) and Humic Like Substances (HULIS) was determined on PM2.5 and fly ashes. A correlation between observed fluorescence and concentration was attempted

New highly efficient amine-free and peroxide-free redox system for free radical polymerization under air with possible light activation

International audienceEfficient redox initiating systems for radical polymerizations under air usually show some severe drawbacks such as handling and toxicity of the oxidizing agent (peroxides, persulfates, peroxidiphosphates, disulfides, etc.), toxicity of the reducing agent (aromatic amines such as 4-N,N-trimethylaniline), and more generally a low top surface conversion due to high oxygen inhibition. The originality of the proposed paper relies on the development of new redox initiating systems for the polymerization of (meth)acrylate monomers that does not contain any hazardous compound (no peroxide) and is amine-free (low toxicology issues). And these new systems that possess the advantages of redox-initiated polymerization (possibility to cure thick samples) can also be photoactivated in order to have a faster and better curing of the surface of the sample (advantages of the photopolymerization to overcome the oxygen inhibition). The light activations presented in this work have been done with light-emitting diodes (LEDs) as they have a low energy consumption and are safer to the user than UV light. Two wavelengths have been used: 405 nm (in the blue range of the spectrum) and 780 nm (in the near-infrared) showing the versatility of these new photo/redox initiating systems. In particular, the reactivity in the near-IR (not related to any heating of the sample) is a very original result. In addition with the presentation of the performance of the new systems in polymerization and photoactivated polymerization, a full analysis of the chemical mechanisms and species involved has been performed. Remarkably, the new proposed Cu(acac)2/2dppba system is also able to overcome the oxygen inhibition for free radical redox (photo)polymerization

Flavones as Natural Photoinitiators for Light Mediated Free-Radical Polymerization via Light Emitting Diodes

International audienceIn this work, we propose the use of flavones that can be derived from natural products as versatile high performance visible light photoinitiators initially with amino acid and later with iodonium salt and phosphino benzoic acid combinations for free‐radical polymerization acrylates of thin specimen (25 μm) and methacrylates thick specimen (1.4 mm) upon illumination with near ultraviolet light or visible light utilizing light emitting diodes (LED)@385 nm and LED@405 nm. High polymerization initiating capabilities are found with different hydroxyflavones and high final conversions of the reactive function are obtained. Their application as materials for three‐dimensional (3D) printing patterns is especially carried out for 1 mm thick 3D printed photopolymers. A full description of the comprised photochemical mechanisms is additionally given

Photopolymerization processes of thick films and in shadow areas: a review for the access to composites

International audienceThe photopolymerization processes are currently associated with thin samples for which the light penetration is good enough to activate the photoinitiator or the photoinitiating system for the entre sample's thickness. The photopolymerization of very thick films and in shadow areas where the light penetration is inhibited (e.g. in filled, pigmented, and dispersed samples) remains a huge challenge (e.g. for the access to composites). In the present paper, an overview of the different strategies for the photopolymerization of thick samples is reported. First, strategies based on the optimization of the photonic (light intensity, excitation wavelength, etc.) or chemical (efficiency/reactivity/bleaching of the photoinitiating systems, etc.) parameters are presented that result in a full temporal and spatial control. Then, the main strategies based on propagation/diffusion mechanisms of latent species for the curing beyond the irradiated areas are given (partial loss of spatial resolution and access to shadow areas). Also, dual systems (thermal/ photochemical or photochemical/redox) are described. The state of the art for the access to thick samples by photopolymerization processes as well as some perspectives are provided

Redox two-component initiated free radical and cationic polymerizations: Concepts, reactions and applications

WOS:000474332100002International audienceRedox polymerizations are of huge importance throughout academic and industrial polymer science. Many authors propose the reaction of reducing (Red) and oxidizing (Ox) agents to accelerate/initiate radical or cationic polymerizations. As a result of activation energies typically below 80 kJ/mol, such reactions can occur under mild conditions, e.g., at room temperature, with reduced energy consumptions and robust in applications, such as the fabrication of composites. However, a clear definition of redox polymerization can only be found in reviews dealing with redox free radical polymerizations (FRP) published twenty years ago (or more). Therefore, a fresh and broader update is provided here for more recent work. The concepts involved when the Redand Oxagents (constituting the redox initiating system) are mixed under mild conditions are presented, followed by a discussion of the redox FRP initiating systems in bulk. Initiating systems dealing with the redox cationic polymerization (CP) are reviewed, and parallels between conventional FRP/CP and controlled polymerizations, in which redox systems are used, is provided. Many redox agents are useful in both modes. Finally, dual-cure (redox/photochemical; redox dual FRP/CP) systems is presented and selected applications are reviewed. Altogether, the state of the art for redox two-component polymerizations is provided, along with some perspectives. (C) 2019 Elsevier B.V. All rights reserved

Charge Transfer Complexes as Dual Thermal and Photochemical Polymerization Initiators for 3D Printing and Composites Synthesis

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Copper-Based (Photo)redox Initiating Systems Systems for Interpenetrating Polymer Network as Highly Efficient Preparation

WOS:000425473600004Simultaneous redox free radical polymerization (FRP) and redox cationic polymerization (CP) are combined for the synthesis of methacrylate/diepoxide interpenetrating polymer networks (IPN). At first, the Cu(acac)(2)/phosphine/iodonium salt operates according to the principles of free radical promoted cationic polymerization (FRPCP). A photoactivation of the reaction for that system was necessary to enhance the mild methacrylate and diepoxide conversions. Second and at least, two complementary copper catalytic cycles are used simultaneously: the recently developed Cu(II)/reducing agent/peroxide FRP system combined with the older Cu(II)/reducing agent/iodonium salt redox CP system. For this latter hybrid system, outstanding efficiency was observed with more than 90% of epoxy functions conversion for the cationic difunctional monomers and 78% conversion for the vinylic functions conversion for difunctional monomers. The radical and cation generations are discus sed in order to fill the interrogations raised by the experimental results. The relevance of dual FRP/CP in IPN synthesis is fully demonstrated. The performance of the hybrid copper catalytic system is remarkable to overcome the oxygen inhibition; i.e., almost no oxygen inhibited layers are observed compared to the \textgreater60 mu m inhibited layer obtained with a reference redox FRP such as amine/BPO