Influence de l'utilisation d'une matrice recyclée sur le comportement et les performances d'un composite lin/polypropylène lors de sa mise en oeuvre et de son vieillissement hydrothermique.

To respond to the growing interest in ecology, the development of eco-responsible materials has become preponderant in areas such as transportation and mobility. One potential solution is to replace synthetic fibers by natural ones and virgin polymers by recycled ones. Indeed, these materials present similar specific properties and a lesser environmental footprint. However, natural fibers are very hydrophilic, which can be a problem in long-term outdoor use. As for the polymers, they undergo modifications during recycling that can affect their compatibility with fibers. This thesis' aim is to investigate how the use of a recycled matrix affects the properties of polypropylene/flax composites and their behavior under hydrothermal and cyclic ageing. First, the influence of processing parameters (compatibilizing agent's percentage, consolidation time, temperature and pressure, cooling rate and exit temperature) on the mechanical properties of virgin matrix composites was studied in order to obtain a reference material. Then, the impact of the use of recycled matrices on the properties of the composite was studied. Finally, hydrothermal and cyclic ageing (immersion, freezing and drying) were applied to all composites (with virgin and recycled matrices). A multiscale analysis combining physicochemical, structural and mechanical characterizations was carried out during ageing to better understand the influence of the matrix on the behavior of the composites over time.Afin de répondre à l'intérêt grandissant autour de l'écologie, le développement de matériaux éco-responsables est devenu prépondérant dans des domaines tels que les transports et la mobilité. Le remplacement des fibres synthétiques par des fibres naturelles et des polymères vierges par des recyclés sont des solutions potentiellement intéressantes. En effet, ces matériaux présentent des propriétés mécaniques spécifiques similaires et une empreinte environnementale plus faible. Néanmoins, les fibres naturelles présentent une forte hydrophilie, ce qui peut poser problème lors d'une utilisation à long terme en extérieur. Les polymères quant à eux subissent des modifications lors de leur recyclage qui peuvent affecter leur compatibilité avec les fibres. L'objectif de cette thèse est d'étudier comment l'utilisation d'une matrice recyclée influe sur les propriétés d'usage de composites polypropylène/lin et sur leur comportement lors de vieillissements hydrothermiques et cycliques. Dans un premier temps, l'influence des paramètres de mise en œuvre (pourcentage d'agent compatibilisant, temps, température et pression de consolidation, vitesse de refroidissement et température de sortie du moule) sur les propriétés mécaniques des composites à matrice vierge a été étudiée afin d'obtenir un matériau de référence. Ensuite, l'impact de l'utilisation de matrices recyclées sur les propriétés du composite a été étudiée. Enfin, des vieillissements hydrothermiques et cycliques (immersion, gel, séchage) ont été appliqués aux différents composites (matrices vierges et recyclées). Une analyse multi-échelle conjuguant caractérisations physico-chimiques, structurales et mécaniques a été réalisée au cours du vieillissement afin de mieux comprendre l'effet de matrices recyclées sur le comportement dans le temps des composites

Potential benefits of load flexibility: A focus on the future Belgian distribution system

Since the last United Nations Climate Change Conference in 2015 in Paris (the COP 21), world leaders acknowledged climate change. There is no need any more to justify the switch from fossil fuel-based to renewable energy sources. Nevertheless, this transition is far from being straightforward. Besides technologies that are not yet mature -- or at least not always financially viable in today's economy -- the power grid is currently not ready for a rapid and massive integration of renewable energy sources. A main challenge for the power grid is the inadequacy between electric production and consumption that will rise along with the integration of such sources. Indeed, due to their dependence on weather, renewable energy sources are intermittent and difficult to forecast with today's tools. As a commodity, electricity is a quite distinct good for which there must be perfect adequacy of production and consumption at all time and characterized by a very inelastic demand. High shares of renewable energy sources lead to high price volatility and a higher risk to jeopardize the security of supply. Additionally, the switch to renewable energy sources will lead to an electrification of loads and transportation, and thus the emergence of new higher-consumption loads such as electric vehicles and heat pumps. These new and higher-consumption loads, combined with the population growth, will cause over-rated power load increases with less predictable load patterns in the future.This work focuses on issues specific to the distribution power grid in the context of the current energy transition. Traditional low-voltage grids are perhaps the most passive circuits in power grids. Indeed, they are designed primarily using a fit and forget approach where power flows go from the distribution transformer to the consumers and no element has to be operated or regularly managed. In fact, low-voltage networks completely lack observability due to very low monitoring. The distribution grid will especially undergo drastic changes from this energy transition. Distributed sources and new high-consumption -- and uncoordinated -- loads result in new power flow patterns, as well as exacerbated evening peaks for which it is not designed. The consequences are power overloads and voltage imbalances that deteriorate grid components, such as a main asset like the medium-to-low voltage transformer. Additionally, the distribution grid is characterized by end-users that pay a price for electricity that does not reflect the grid situation -- that is, mostly constant over a year -- and allow little to no actions on their consumption.These issues have motivated authorities to propose a global approach to ensure security of electricity supply at short and medium-term. The latter requires, among others, the development of demand response programs that encourage users to take advantage of load flexibility. First, we propose adequate electricity pricing structures that will allow users to unlock the potential of such demand response programs; namely, dynamic pricings combined with a prosumer structure. Second, we propose a fast and robust two-level optimization, formulated as a mixed-integer linear program, that coordinates flexible loads. We focus on two types of loads; electric vehicles and heat pumps, in an environment with solar PV panels. The lower level aims at minimizing individual electricity bills while, at the second level, we optimize the power load curve, either to maximize self-consumption, or to smoothen the total power load of the transformer. We propose a parametric study on the trade-off between only minimizing the individual bills versus only optimizing power load curves, which have proven to be antagonist objectives. Additionally, we assess the impact of the rising share of flexible loads and renewable energy sources for scenarios from today until 2050. A macro-analysis of the results allows us to assess the benefits of load flexibility for every actor of the distribution grid, and depending on the choice of a pricing structure. Our optimization has proved to prevent evening peaks, which increases the lifetime of the distribution transformer by up to 200%, while individual earnings up to 25% can be made using adequate pricings. Consequently, the optimization significantly increases the power demand elasticity and increases the overall welfare by 10%, allowing the high shares of renewable energy sources that are foreseen.Doctorat en Sciences de l'ingénieur et technologieinfo:eu-repo/semantics/nonPublishe

Assessing the benefits for the distribution system of a scheduling of flexible residential loads

The integration of distributed renewable energy sources (RES) and the electrification of devices raise new challenges for the distribution system operator (DSO). This paper assesses the benefits for the distribution system of scheduling flexible residential loads and focuses on electric vehicles (EV). We propose an extensive load model and formulate a bilevel Mixed-Integer Linear Programming (MILP) optimization problem. At the lower level, we minimize individual household electricity bills using dynamic pricings. At the upper level, we aim to smooththe power load curve of a typical Brussels MV/LV transformer. Harnessing load flexibility incentivizes load aggregators to participate in power grid balancing or the ancillary services market. It also allows the DSO to manage the transformer load to avoid grid congestion.info:eu-repo/semantics/publishe

Optimal bilevel scheduling of electric vehicles in distribution system using dynamic pricing

The integration of distributed renewable energy sources (RES) and the electrification of devices raise new challenges for the distribution system operator (DSO). This paper assesses PAR versus cost tradeoff when scheduling an electric vehicle (EV) fleet. We formulate a bilevel Mixed-Integer Linear Programming optimization problem. At the lower level, we minimize individual household electricity bills using dynamic pricings. At the upper level, we aim to smooth the power load curve of a typical Brussels MV/LV transformer. We show that a small deviation from cost-only optimization can reduce significantly the Peak-to-Average Ratio of the power load curve of a transformer. Harnessing load flexibility from EV allows the DSO to manage the transformer load to avoid grid congestion and also incentivizes load aggregators to participate in the ancillary services market.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Influence of processing and matrix parameters on the manufacturing of unidirectional flax/polypropylene composites

International audienceThe manufacturing by thermocompression of flax fiber composites requires a good understanding of process parameters. This work focuses on the influence of key parameters in the manufacture of quality unidirectional flax/polypropylene composites by thermocompression. To this effect, a number of matrix and process parameters have been studied and ranked according to their influence on composite morphology and tensile properties. Among tested parameters, process time and temperature tend to decrease tensile strength as they increased from 3 to 11 min and from 180 to 200 °C. As a result, decrease of cooling speed from 15 to 5 °C min−1 also decreased tensile strength. Temperature of 180 °C also led to composites with no dispersion of fibers. Using a compatibilized agent, maleic anhydride grafted polypropylene (PP), also increased tensile strength of composites. Increasing its percentage from 3 to 5% increased tensile properties in the 90° direction. Pressure had no significant effect on mechanical properties, though lower pressures increase fiber dispersion

How does the use of a recycled polypropylene matrix influence the performance of flax/polypropylene composites compared to a virgin matrix?

International audienceWhen manufacturing unidirectional flax/thermoplastic composites by thermocompression, the intrinsic characteristics of the matrix can potentially influence the properties of the composite. The objective of this study is to determine the impact of recycled matrix on the performance of flax/MAPP/PP composite. In this work, three PP matrices, one virgin and two recycled, were used in the manufacture of flax/MAPP/PP composites. By a multi‐scale analysis of the three PP matrices, their characteristics influencing the quality of the composite could be identified. It appears that the length of the polymer chains changes the quality of the interface as a short chain length leads to poor entanglement of PP with MAPP. Additionally, high viscosity lowered dispersion of fiber bundles, however it could be corrected by modifying the process pressure. Finally, the presence of a small amount of PE, as is common in recycled PP, has no significant effect on the mechanical properties of composites

Impact of Ionic Liquids on the (bio)degradability of Poly(butylene succinate)/Poly(lactic acid) blends

International audienceBio-based and (bio)degradable polymers constitute an important material innovation because they reduce the amount of waste materials inducing persistent microplastics and can offer similar benefits to conventional polymer materials. Poly(butylene succinate) and poly(lactic acid) blends exhibit interesting properties and can be possible alternatives to some traditional polymers. Some of their properties can be tailored by adding small proportions of ionic liquids (IL) that can act as interfacial agents between PBS and PLA. In our study, samples formulated with ionic liquids display a broader morphology with thermal properties close to the PBS/PLA reference, whereas Young’s modulus is lowered in the presence of one of the IL studied. Nevertheless, the blends have a rather different ability to (bio)degrade. Indeed, disintegration experiments show that PBS/PLA/IL exhibit higher weight losses and faster fragmentation. DSC thermograms display an important decrease of PLA melting temperature after composting experiment, indicating that PLA phases are affected the most by degradation at 58°C. Our study shows that elaborating polymer materials, for which degradation processes are preferentially located in a “predegraded” dispersed phase, can be considered as a way to speed up macroscopic (bio)degradation. In the present work, morphologies, mechanical properties as well as (bio)degradability can be tailored by adding a small amount of ionic liquids

Tailoring Biodegradability of Poly(Butylene Succinate)/Poly(Lactic Acid) Blends With a Deep Eutectic Solvent

International audienceBiodegradable polymers concern an important topic for innovation in materials, as they are supposed to contribute to the reduction in the amount of waste materials, which lead to microplastics with similar properties as conventional polymer materials. Poly(butylene succinate) and poly(lactic acid) blends are polymers with interesting properties offering possible alternatives to some conventional petrochemical-sourced polymers. Some of the physical properties of such blends can be tailored from the addition of small amounts of deep eutectic solvents (DESs) that can act as compatibilizers, i.e., interfacial agents between poly(butylene succinate) (PBS) and poly(lactic acid) (PLA). In our study, materials formulated with a DES having a coarse morphology according to the dispersed particle sizes display thermal and mechanical properties rather close to the non-compatibilized PBS/PLA blends but a higher ability to biodegrade. In comparison with PBS/PLA blend, biodegradation experiments show that PBS/PLA/DES blend exhibits higher weight losses and faster fragmentation under conventional conditions. A significant decrease in PLA melting temperature under composting conditions, i.e., at 58 • C, is observed indicating that PLA phase is the component mainly concerned. As a conclusion, this work demonstrates that morphologies as well as the biodegradability process can be tailored by adding a small amount of a DES in such biosourced polymer blends. Indeed, designing polymer materials, for which degradation processes are targeted in the dispersed phase, i.e., in multiple locations of the material, can be an efficient route to "predegrade" phases in a polymer matrix to accelerate macroscopic biodegradation

Hydrothermal Ageing and Its Effect on Fracture Load of Zirconia Dental Implants

International audienceDue to growing demand for metal-free dental restorations, dental ceramics, especially dental zirconia, represent an increasing share of the dental implants market. They may offer mechanical performances of the same range as titanium ones. However, their use is still restricted by a lack of confidence in their durability and, in particular, in their ability to resist hydrothermal ageing. In the present study, the ageing kinetics of commercial zirconia dental implants are characterized by X-ray diffraction after accelerated ageing in an autoclave at different temperatures, enabling their extrapolation to body temperature. Measurements of the fracture loads show no effect of hydrothermal ageing even after ageing treatments simulated a 90-year implantation