An innovative organocatalyst for the recycling of commodity polymers

El contenido del capítulo 3 está sujeto a confidencialidad 252 p.Polymat, Warwick University, IB

Laser beam shaping for enhanced Zero-Group Velocity Lamb modes generation

Optimization of Lamb modes induced by laser can be achieved by adjusting the spatial source distribution to the mode wavelength ($\lambda$). The excitability of Zero-Group Velocity (ZGV) resonances in isotropic plates is investigated both theoretically and experimentally for axially symmetric sources. Optimal parameters and amplitude gains are derived analytically for spot and annular sources of either Gaussian or rectangular energy profiles. For a Gaussian spot source, the optimal radius is found to be $\lambda_{ZGV}/\pi$. Annular sources increase the amplitude by at least a factor of 3 compared to the optimal Gaussian source. Rectangular energy profiles provide higher gain than Gaussian ones. These predictions are confirmed by semi-analytical simulation of the thermoelastic generation of Lamb waves, including the effect of material attenuation. Experimentally, Gaussian ring sources of controlled width and radius are produced with an axicon-lens system. Measured optimal geometric parameters obtained for Gaussian and annular beams are in good agreement with theoretical predictions. A ZGV resonance amplification factor of 2.1 is obtained with the Gaussian ring. Such source should facilitate the inspection of highly attenuating plates made of low ablation threshold materials like composites.Comment: 11 pages, 12 figure

STRUCTURAL, ELECTRONIC AND MAGNETIC PROPERTIES OF THE LINEAR CHAIN COMPOUNDS CsMI3(M = V, Cr, Mn) FROM 129I MÖSSBAUER SPECTROSCOPY

The coordination symmetry of the M2+ ion in the compounds CsMI3 (M = V, Cr, Mn) is deduced from 129I Mössbauer spectroscopy. For CsCrI3, a crystal phase transition is observed at 165 K. Magnetic transitions are observed for CsCrI3 and CsMnI3. The hyperfine interactions parameters are interpreted for the charge and spin densities in the iodine valence orbitals. An antiferromagnetic alignement of the spins along the chain axis is suggested for CsMnI3

Search for the Tunguska event in the Antarctic snow

The Tunguska explosion in 1908 is supposed to have been produced by the impact of a small celestial body. The absence of any identifiable crater together with the huge energy released by the event suggest that the impactor exploded in midair and that its material was widely spread over the Earth. The short term contribution of such exceptional events to the total accretion rate of extraterrestrial material by the Earth could be significant. Samples were chosen in a core electromechanically drilled in 1984 near South Pole Station. There, the low temperatures, preventing melting all year long, and the nearly regular snow fall rate provide good conditions for a reliable continuous record of any infalling material. In many samples Ir was below the detection limit of the instrumentation. The iridium infall averaged over 45 samples is given. In a few samples the iridium content is significantly higher than the average: the frequency and amplitude of such fluctuations can be explained by the presence on some filters of finite size cosmic particles. No significant systematic increase above the average level is observed in the part of the core corresponding to the Tunguska event. The two major results of this study are: (1) The presence of Tunguska explosion debris in the Antarctic snow is not confirmed; and (2) The estimate of the average iridium infall, is an order of magnitude lower than the Ganapathy's background but is close to the values measured in Antarctic snow and atmospheric samples by Takahashi et al. The results are also consistent with the flux of micrometeoroids deduced from optical and radar observations or derived from the study of Greenland cosmic dust collection but are lower than the flux at mid-latitude measured in paleocene-oligocene sediments from the central part of the Pacific Ocean

Automatic System For Carpooling Proof Computation And Delivery

This document aims at providing a solution to edit a carpooling proof. The proposed solution aims at providing a fully integrated solution avoiding at maximum any manual action and the use of GPS interface which is power consuming and may not be accurate enough in case of low battery or non-synchronization with satellites

Fast Luminosity Monitoring using Diamond Sensors for the Super Flavor Factory SuperKEKB

ISBN 978-3-95450-132-8 - http://accelconf.web.cern.ch/AccelConf/IPAC2014/papers/thpme090.pdfInternational audienceSuper luminous flavor factories, as SuperKEKB in Japan, aim to achieve very high luminosity thanks to a newly employed concept, the nano-beam scheme, where ultra-low emittance beams collide at very large crossing angle. Luminosity optimisation and dynamic imperfections require fast luminosity measurements. The aimed precision, 10−3 in 10 ms, can be achieved thanks to the very large cross-section of the radiative Bhabha process at zero-photon scattering angle. As a result of huge particle fluxes, diamond sensors are chosen to be placed just outside the beam-pipe, downstream of the interaction point, at locations with event rates consistent with the aimed precision and small enough contamination by backgrounds from single-beam particle losses. We will present the results concerning the investigation of the optimal positioning of our diamond sensors, taking into account the rate of Bhabha particles as well as their interactions with the beam pipe material

Self-Attention in Colors: Another Take on Encoding Graph Structure in Transformers

We introduce a novel self-attention mechanism, which we call CSA (Chromatic Self-Attention), which extends the notion of attention scores to attention _filters_, independently modulating the feature channels. We showcase CSA in a fully-attentional graph Transformer CGT (Chromatic Graph Transformer) which integrates both graph structural information and edge features, completely bypassing the need for local message-passing components. Our method flexibly encodes graph structure through node-node interactions, by enriching the original edge features with a relative positional encoding scheme. We propose a new scheme based on random walks that encodes both structural and positional information, and show how to incorporate higher-order topological information, such as rings in molecular graphs. Our approach achieves state-of-the-art results on the ZINC benchmark dataset, while providing a flexible framework for encoding graph structure and incorporating higher-order topology

An innovative organocatalyst for the chemical recycling of commodity polymers

Over the past century, synthetic plastics have become ubiquitous in our daily life, occupying an ever-expanding range of uses. Their global production has exponentially increased in the past half-century, from 15 to 311 million tons between 1964 and 2014, and is expected to double again by 2035. Many of those materials have extremely short lifetimes and the direct consequence is the tremendous quantities of plastic wastes accumulating in the environment for years. Produce, buy, use and dispose, this linear way of consuming more and more plastics is nowadays raising concerns, not only from governments, interstate institutions and companies but also by citizens themselves. The treatment of plastic wastes is a global problem which requires innovative solutions to collect, sort, degrade, and re-process these materials. Thus, recycling is a crucial matter from an environmental point of view but also taking into account the plastic production and the tremendous income recycling could be for the global economy. Currently, most of the recycled plastics are by means of mechanical methods that involve grinding and re-processing of the material into lower value plastic products. The structural deteriorations lead to recycled product which does not share the same properties as the virgin polymer and also rapidly ends up as waste. Another approach relies on their direct conversion into high calorific value fuels through pyrolysis, but this thermal deterioration only postpones their unsustainable end-of-life since the resulting combustible will typically be burnt releasing mainly green-house gases such as CO2 and potentially affecting to the global warming. In comparison, chemical recycling involves the depolymerisation of polymers into monomers or oligomeric fragments that can then be subsequently polymerised to yield recycled materials, it represents an attractive long-term strategy to create a sustainable polymer supply chain. Recently, the chemical recycling of polymers has attracted a lot of attention among the scientific community, mainly driven by the current public awareness of the plastic pollution problem. However, as a consequence of the high stability of most polymers, depolymerisation processes are generally conducted in very harsh conditions and in the presence of catalysts, principally organometallics, which can present several drawbacks: possible presence of metal in the final product, low monomer yields or challenging purification procedures. Organocatalysts are promising “green” substitutes to classic organometallic catalysts. Although they are currently widely investigated for various polymerisation techniques, they have been much less explored in depolymerisation processes. One of the main reason behind this is that typically organic catalysts show poor thermal stability at temperatures that would be practical for recycling reactions. Thus, the partial or full degradation of the catalyst hinders the perspective of reusing it for several reactions and entails colouration of the final products, low conversion or undesirable side-reactions. In Chapter 1, an innovative series of acid and base mixtures have been explored as catalyst for depolymerisation reactions. Not only these acid-base mixtures displayed unique thermal stability, a tremendous advantage compared to most of organocatalysts which usually degrade at relatively low temperatures, but also reveals very good abilities for the depolymerisation of commodity polymers. Indeed, both poly(ethylene terepthalate) (PET) and Bisphenol A-based polycarbonate (BPA-PC) have been depolymerised using an equimolar mixture of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and methanesulfonic acid (MSA) as catalyst in a solvent-free procedure. The comparison with already reported procedures have demonstrated the superior control of the reaction employing the present organocatalyst. Chapter 2 has explored the influence of different parameters on the PET glycolysis catalysed by TBD:MSA (1:1). Using the adequate amount of reagent and catalyst, over 90% of Bis(hydroxyethyl)terephtalate (BHET) is obtained and easily recovered. Kinetics have emphasised the high selectivity of the reaction to form the desired monomer compared to well-known organocatalyst. Both the reagent and the catalyst can be easily recycled, demonstrating no loss of catalytic activity even after 6 cycles. Finally, it was demonstrated that this catalyst could even be used in the self-condensation of BHET to obtain recycled PET exhibiting good thermal and physical properties, closing the polymer to monomer to polymer loop. In a similar way, Chapter 3 has investigated the same procedure for the depolymerisation of BPA-PC into both Bisphenol A (BPA), its industrial monomer, and valuable building blocks. By wisely choosing the starting reagent and tuning the reaction conditions, 5- and 6-membered cyclic carbonates were obtained in reasonable to excellent yields (up to 97 %), constituting a phosgene-free, 100% atom economy procedure for the ringclosing of valuable carbonates widely reported for the synthesis of highperformance materials. Similarly, innovative linear carbonates and ureas were obtained. Density functional theory (DFT) methodology was employed for determining the mechanisms involved for both reactions – with PET and with BPA-PC. The obtained pathways exhibited similar chemical interactions but with a large energetic difference, inspiring the possibility for these two polymers to be recycled selectively. Thus, in Chapter 4, using different reagents and different reaction conditions investigated in the previous chapters, the simultaneous depolymerisation of BPA-PC and PET was explored using different reagents and in the presence of other plastics (i.e. polyolefins)

Log-normal distributions of suspended particles in the open ocean

A scanning electron microscope-electron microprobe technique was used to chemically distinguish and size particles as fine as 0.2/µm on GEOSECS suspended matter filters from the open ocean…