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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Contribution à l'étude du vieillissement couplé thermo-hydro-mécanique de biocomposite PLA/lin / A contribution to the study of the coupled thermo-hydro-mechanical aging of PLA/flax biocomposites

Regazzi, Arnaud 12 December 2013 (has links)
L'utilisation croissante de composites biosourcés dans des applications de plus en plus techniques pose le problème de la prédiction de leur vieillissement dans des conditions réelles d'utilisation. En effet l'environnement dans lequel ils évoluent, conjugue généralement des sollicitations de nature thermique, hydrique et mécanique. Le comportement complexe de chaque constituant (fibre et matrice, et même leur interface) et donc du matériau composite dans sa globalité vis-à-vis de ces dégradations restent mal connu.L'objectif de ce travail est d'apporter des éléments de réponse à cette problématique en étudiant, de manière extit{ex situ} et extit{in situ}, le comportement de biocomposites poly(acide lactique) renforcés de fibre de lin soumis à un vieillissement couplé thermo-hydro-mécanique. Pour différents taux de renfort, l'influence de la présence d'eau à différentes températures couplée ou non à des contraintes de fluage a été évaluée.Dans un premier temps, la caractérisation de ces biocomposites dans un environnement thermo-hydrique a permis d'identifier les phénomènes mis en jeu. Plusieurs propriétés physiques, chimiques, thermiques et mécaniques ont été déterminées au cours de la diffusion. Par la suite, les conséquences irréversibles des phénomènes de vieillissement sur ces propriétés ont été évaluées. Dans un troisième temps, l'introduction de sollicitations mécaniques comme facteur supplémentaire de vieillissement a permis d'apprécier les effets du couplage thermo-hydro-mécanique. Enfin un modèle de calcul par éléments finis a été mis au point afin de pouvoir simuler le comportement physique et mécanique des biocomposites dans un environnement thermo-hydrique donné. / The growing demand for bio-based composites intended for high standard applications bring to light the specific problems of aging prediction in real life conditions. The various environment in which these products are likely to be used lead to different kinds of damage (hydric, thermal and mechanical). The complex behavior of each component (fiber, matrix, and even their interface), and thus the behavior of the composite material, are generally poorly understood.The objective of this work is to provide possible answers to these inter-related problems by studying, extit{ex situ} and extit{in situ}, the behavior of PLA/flax biocomposites subjected to a coupled thermo-hydro-mechanical aging. The influence of the presence or the absence of water at different temperatures coupled to a creep stress was assessed for different fiber contents.At first, the characterization of these biocomposites in a thermo-hydric environment allowed to identify the involved phenomena. Several physical, chemical and mechanical properties were determined during diffusion. Then, the irreversible consequences of thermo-hydric aging on these properties were assessed. Thirdly, the subjection of materials to additional mechanical loadings made possible the evaluation of the effects of thermo-hydro-mechanical couplings. Finally, a finite element model was established in order to simulate the physical and mechanical behavior of biocomposites in a given thermo-hydric environment.
32

Biobased carbon aerogels incorporated with zeolite nanoplates for carbon dioxide adsorption

Harila, Maria January 2021 (has links)
Over the last 100 years there has been an increase of greenhouse gases (CO2, CH4 and N2O) in the atmosphere. These gases cause several problems with the climate on Earth, such as increasing problems with extreme weather. One way to decrease the outlet of carbon dioxide is by adsorption and capture of CO2. Biobased aerogels are one way to adsorb CO2. In this project the goal is to increase the CO2 adsorption capacity of a biobased carbon aerogel with zeolite nanoplates. The biobased carbon aerogel is prepared via freeze-casting a suspension made of LignoBoost lignin and (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidized cellulose nanofibers, also called TEMPO-cellulose nanofibers (TOCNF). The freeze-casted structure is, after freeze-drying and carbonization, decorated with zeolite nanoplates. To find the optimal decorating method, three different decoration methods were tested. Thesemethods are called “decoration assisted by cationic polymer solution” (DC), “direct decoration” (DD) and “decoration incorporated directly in lignin suspension” (DS). The X-ray diffraction (XRD) together with Energy-dispersive X-ray spectroscopy (EDX), showed that the highest concentration of zeolite nanoplates in the samples, was achieved by the “decoration incorporated directly in lignin suspension” method. CO2 adsorption capacity test was performed at temperatures of 273.150K, 298.150K and 323.150K. The DS-sample did not perform better than the reference sample at low pressures (10kPa). At higher pressure (100kPa) the DS-sample had the highest adsorption capacity at test temperatures 273.150K and 323.150K.
33

Nouveaux matériaux photo-réparables à base d'huile végétale. / Titre en anglais non fourni

Geelhand de Merxem, Ludovic 04 April 2019 (has links)
Un revêtement photoréparable à base de 4 constituants, dont de l’huile de lin époxydée et du disulfure de 4,4’-diphényldiamine, a été élaboré via une réaction époxy/amine selon un procédé en deux étapes. Le caractère photoréparable est assuré par la présence de ponts disulfures qui, sous irradiation UV, peuvent être photolysés de manière réversible. Le revêtement obtenu renferme environ 46% en masse de composés biosourcés et 24% en masse de molécules photosensibles. Comparé à un matériau homologue sans pont disulfure, ce revêtement présente une densité de réticulation plus faible et un allongement à la rupture plus élevé. Une réparation significative d’un endommagement de 100 μm de profondeur a pu être réalisée. Un recouvrement de 42% de l’allongement à la rupture a ainsi été observé en seulement 3h d’irradiation UV a 100°C. / A biobased photohealing coating has been developed from 4 components, including epoxidized linseed oil and 4,4’- diphenyldiamine disulfide. The process has been carried out in two steps via an epoxy/amine reaction. The photohealing character is ensured by the presence of disulfide bridges which, under UV irradiation, can be photolyzed reversibly. The obtained coating contains about 46 wt-% of biobased compounds and 24 wt-% of photosensitive molecules. Compared to an analogous material without disulfide bond, the coating exhibits a lower crosslinking density and a higher fracture elongation.A significant repair of a 100 μm depth scratch has been occurred. An increase of 42% of tensile strength has been observed in only 3 hours of UV irradiation at 100°C.
34

Periodate oxidation of cellulose for internal plasticization and materials design / Plastification interne et design de matériaux par oxydation périodate de cellulose

Leguy, Julien 30 March 2018 (has links)
La cellulose, abondante et renouvelable, offre une alternative biosourcée intéressante pour remplacer les thermoplastiques pétrosourcés très présents dans la vie courante. Cependant, elle ne peut être utilisée dans les procédés de thermoformage de l’industrie de la plasturgie car sa température de fusion est supérieure à sa température de dégradation. Des dérivés comme l’acétate de cellulose montrent un caractère thermoplastique plus affirmé, avec des températures de transition vitreuse et de fusion plus basses que celles de la cellulose, mais nécessitent néanmoins l’usage de plastifiants externes pour être mis en forme. Ces plastifiants peuvent à terme migrer en dehors des matériaux, provoquant une dégradation des propriétés et des problèmes environnementaux si ces molécules sont dangereuses.Le travail présenté ici propose de remplacer la plastification externe par une plastification interne qui consiste à greffer les plastifiants sur les macromolécules, évitant ainsi toute migration. Pour cela, une modification en deux étapes de la cellulose a été imaginée : une oxydation au périodate pour augmenter la flexibilité du squelette cellulosique et introduire des groupements aldéhyde donnant lieu à la dialdéhyde cellulose (DAC), suivie d’un greffage des molécules plastifiantes sur ces aldéhydes.Une étude complète de l’oxydation de la cellulose au périodate a d’abord été réalisée en faisant varier de nombreux paramètres tels que la quantité d’oxydant, le temps de réaction ou la température. Elle a permis de préciser les conditions optimales de contrôle du degré d’oxydation (DO) qui est un paramètre clé dans la compréhension des relations structure-propriétés au sein des matériaux réalisés à partir de DAC. En particulier, une méthode de caractérisation fiable et précise du DO par résonance magnétique nucléaire du solide (13C CP-MAS RMN) a été développée et comparée aux méthodes de la littérature. Une réduction de la DAC a ensuite permis de générer des nanobâtonnets colloïdaux chevelus, non chargés mais stables en suspension aqueuse, qui ont été caractérisés par une combinaison de techniques (diffusion de rayonnement, microscopie électronique en transmission et turbidimétrie). Par ailleurs, le séchage de ces suspensions produit des films thermoplastiques avec une structuration nanocomposite de type cœur-écorce. Enfin, grâce à des réactions d’amination réductrice avec différentes amines, de nouveaux matériaux thermoplastiques ont été obtenus. Les propriétés ultrastructurales et thermomécaniques de ces différents matériaux ont été caractérisées par des méthodes telles que la RMN, l’analyse mécanique dynamique, la calorimétrie différentielle à balayage ou l’analyse thermogravimétrique (ATG). Ces résultats montrent que les matériaux issus de ces modifications possèdent une Tg inversement proportionnelle au DO, comprise entre 122 et 65 °C selon le DO et le type de modification. Notre stratégie est donc prometteuse pour la fabrication de matériaux thermoplastiques transformables élaborés à partir de cellulose. / Cellulose, an abundant and renewable polymer, offers an interesting biosourced alternative to replace petrosourced thermoplastics commonly used in our everyday life. However, cellulose cannot be used in industrial thermoforming processes since its melting temperature is higher than its degradation temperature. Derivatives such as cellulose acetate show glass transition and melting temperatures below the thermal decomposition but still require the addition of external plasticizers to be processable. These plasticizers can exude over time, making the materials brittle and causing environmental issues due to the release of potentially toxic molecules.The present work proposes to introduce internal plasticization of cellulose, by increasing both the flexibility of the chains and the free volume using a grafting strategy, thus preventing exudation. To achieve this goal, a two-steps strategy was followed: first, a periodate oxidation was performed to cleave the glucose ring and generate aldehyde groups, resulting in dialdehyde cellulose (DAC). Second, the highly reactive aldehyde groups were used to graft plasticizing agents.The periodate oxidation of cellulose was first studied by varying parameters such as the amount of oxidant, the reaction time or the temperature, in order to precisely map the reaction conditions leading to a controlled degree of oxidation. To characterize DAC samples, an accurate and reliable quantification method based on solid-state nuclear magnetic resonance (13C CP-MAS NMR) has been developed and compared to other methods from the literature. The reduction of DAC led to colloidally stable hairy neutral nanorods suspensions, which were characterized by a combination of structural investigation techniques (light and X-ray scattering, transmission electron microscopy and turbidimetry). Casting of the suspensions led to thermoplastic films with a core-shell nanocomposite structure. Reductive amination of DAC with different amines also led to thermoplastic materials. The thermo-mechanical properties of all these materials were studied by solid-state NMR, dynamic mechanical analysis, differential scanning calorimetry and thermogravimetric analysis. Results show that materials produced from this strategy have a Tg inversely proportional to DO, between 122 and 65 °C, depending on the DO and the modification. This strategy is promising for the synthesis of processable thermoplastic materials from cellulose.
35

Experimentell studie av egenskaperna av protein-baserat plast / Experimental study on the properties of protein-based plastics

Mahmutovic, Muhamed January 2020 (has links)
På grund av ökad användning av plast har biobaserade polymerer som förpackningsmaterialfått stor uppmärksamhet de senaste åren på grund av miljöhänsyn. Flera proteinmaterial, t.ex.vetegluten har varit i fokus för betydande forskning kring ny biobaserad plast och resultatenär lovande. Det idag stora intresset för biobaserad och miljövänlig plast beror påväxthuseffekten från konventionell petroleumbaserad plast. Ett proteinmaterial från undersöktes här för dess plastmaterialegenskaper. Proteinrenheten varca. 65%. Filmerna skapades genom att först mala proteinflingorna till ett fint pulver ochblanda det med glycerol. Glycerolhalten var 30 %. Därefter varmpressades materialet. För atttesta plasten användes flera tekniker och metoder. TGA, DSC, FT-IR, WVTR, OTR ochdragprovning. I allmänhet var materialet relativt svagt. Liksom de flesta proteinplaster hadedet också dåliga vattenbarriäregenskaper, men hade relativt goda syrebarriäregenskaper. Sammanfattningsvis är det ett material som kan ha en ljus framtid eftersom det är tillverkat avbiomassa istället för petroleum, vilket innebär att det är mer miljövänligt. Med modifieringkan det bli en bra plast för flera ändamål. / Due to increase use of plastics, bio-based polymers as packaging materials have garneredmuch attention in recent years due to environmental concerns. Several protein materials, e.g.wheat gluten, have been in focus for significant research towards new biobased plastics andresults are promising. Bio-based and environmentally friendly plastics gather much interestand attention today due to the green-house generating effects of conventional petroleum-basedplastics. A protein material was investigated here for its plastic material properties. The protein puritywas ca. 65 %. The films were created by first grinding the protein flakes to a fine powder andmixing it with glycerol. The glycerol content was 30 %. The material was subsequently hotpressed.To test the plastic, multiple techniques and methods were used. TGA, DSC, FT-IR, WVTR,OTR and tensile testing. In general, the material was relatively weak. As most protein plasticsit had also poor water barrier properties, however it had relatively good oxygen-barrierproperties. In conclusion it is a material that could have a bright future as it is made from biomass insteadof petroleum, which means that it is more environmentally friendly. With modification andimprovement, it can be a good plastic for several applications in future.
36

Structure-Property Relationships of Alicyclic Polyesters

Thompson, Tiffany Nikia 27 July 2023 (has links)
Polyesters are an important class of polymers in many applications ranging from common-use objects—such as packaging containers, clothing, and upholstery—to more advanced applications, such as lightweight strength materials in construction, electronics, and automotive parts. Poly(ethylene terephthalate) (PET), a semicrystalline aromatic polyester, is commercially the most common and widely used polyester. However, the inability to reuse polyesters such as PET over multiple reprocessing cycles in the same application remains a challenge due to the susceptibility of the polymer to thermal, hydrolytic, and oxidative degradation during melt processing. The various degradation modes result in a drop in molecular weight, loss of key physical properties, and release of volatile compounds. Furthermore, the vast issue of plastic accumulation and pollution in diverse ecosystems, landfills, and waste streams underscores the burgeoning need to create a closed loop—responsible materials management from the cradle to the grave—through these materials' continual reuse and recycling. Additionally, most feedstock monomers used in polyester synthesis primarily come from fossil fuels. Fossil fuel extraction processes release gases and particulate matter that adversely affect health, climate, and the environment, so finding alternative sources for polyester monomers is paramount. This dissertation addresses key polyester challenges by designing and synthesizing alicyclic polyesters. First, we synthesized a series of alicyclic polyesters using various ratios of two regioisomers of a previously unexplored alicyclic monomer, bicyclohexyldimethanol (BCD). We learned from this alicyclic polyester series that we could tailor properties such as morphology and elongation while raising the glass transition temperatures (Tg) and lower melting temperatures (Tm) of the polymers based on the regioisomer composition. Furthermore, the regioisomer that led to polymers with semicrystalline morphologies inspired us to apply it to PET as a copolymer, with the goal of increasing PET's stability under melt processing conditions by lowering Tm. Next, we synthesized a series of alicyclic copolyesters with different BCD compositions in the polymer. The results showed that the presence of the alicyclic rings of BCD lowers the melting temperature and enhances the stability of the polymer in the melt compared to PET. These results directed us toward synergistically combining the benefits of alicyclic monomers with sustainable biobased monomers to enhance polyester properties, thereby decoupling fossil fuels from polymer feedstock production. Accordingly, we explored naturally ubiquitous, structurally diverse, and chemically modifiable terpenes present in the resin exudate of conifers. Specifically, we derived alicyclic diacid and diol monomers from the terpene verbenone and used them to synthesize a series of biobased alicyclic polyesters. The polymer series exhibited a range of morphologies, Tg's, as well as enhanced stabilities. The semicrystalline composition exhibited higher Tg and slightly lower Tm than PET while possessing exceptional stability in the melt over PET. / Doctor of Philosophy / Polyesters are important materials widely used today. They are very large molecules composed of a basic chemical unit linked together in a repeating fashion to make a long chain. The nature of the links between the basic units is referred to as an ester link, and materials are described as polyester when the number of these links is large. The applications of polyesters range from common-use objects—such as packaging containers, clothing, and upholstery—to more advanced applications in construction, transportation, and defense—such as body armor, seat belts, and lightweight strength materials and coatings in construction. The properties of its basic structural unit enable the wide breadth of applications of polyesters. A significant challenge that faces polyesters is the inability to reuse the material in the same application multiple times. The material must be reprocessed by melting at high temperatures to be reused. This melting breaks down the polyester chain, weakening the material and rendering it unsuitable for continued use. The need to reuse polyesters is an important area of concern because of the growing problem of plastic accumulation and pollution in diverse ecosystems and landfills. If these materials are continually reused, they will not accumulate as environmental waste. Furthermore, the basic starting unit that makes up polyesters largely comes from fossil fuels. Fossil fuel extraction processes release gases and particulate matter that adversely affect health, climate, and the environment. The issues of polyester breakdown in the melt and fossil fuel use to make the polyester can be addressed in two ways. First, reinforcing the polyester through changes to the basic structural unit can prevent the breakdown of the material when melted, thereby enabling its reuse over multiple cycles. Second, reducing the dependence on fossil fuels to make the basic structural unit of the polyester can be accomplished by using more renewable biobased sources instead. This dissertation seeks to address these two challenges. In the first approach, we investigate the effect of using a special cyclic structure in the polyester make-up to reinforce its stability when melted and enable its reuse. Next, we use plant materials to derive these unique structures to reduce the dependence on fossil fuels and mitigate the environmental, climate, and health effects of fossil fuel use.
37

Soysomes and Other Functional Biomaterials from Sucrose Soyate Derivatives

Wright, Ruvimbo Pearl January 2019 (has links)
Biomaterials serve as interventional tools in medicine to treat, improve or replace diseased tissues, organs or function of the body. Although several polymeric biomaterials already exist, they often present challenges, at material level, such as non-biodegradability, degradation into acidic by-products or tissue incompatibility, or at functional level such as failure to sustain prolonged release of therapeutic payload for a desired period. Research has been focused on investigating new polymeric candidates to address these problems of current systems. The use of renewable resources to generate smart polymers for biomedical and pharmaceutical purposes presents a new and exciting avenue for biomaterials. As part of these efforts, a new set of biomaterials were developed from plant-derived high molecular weight (~3.0 kDa) compounds. The advantages of biobased materials include availability for large-scale synthesis, facile post-synthetic modification, biocompatibility, improvement of functional properties and affordability. In this project we used sucrose soyates, i.e. octa-esters obtained from conjugation of sucrose molecules and multiple soybean oil fatty acid chains, to prepare three groups of functional biomaterials namely: a). self-assembled soy-based nano-constructs, b). blended soy-based free-standing films and c). three-dimensional cross-linked soy-based soft matrices. Here, we will discuss the fabrication and physical, chemical and mechanical characterization of these biomaterials prepared from soy-based compounds, as well as, the assessment of their functional performance in biological environment. / National Science Foundation ND EPSCoR Grant No. IIA1355466 through Center of Sustainable Materials Science
38

Transformation of lignin into biobased thermoset

Cederholm, Linnea January 2018 (has links)
Combined microwave assisted extraction/degradation of technical lignin in green solvents was successfully employed to generate polyphenolic oligomers with lower Mw than the starting material. For Lignoboost, the highest liquid yield (65 %) was obtained in 20 min at 160 °C using ethanol as solvent. This is an increase in ethanol soluble yield with 38 % compared to solvent extraction. The highest yield for Lignosulfonate was obtained with methanol as solvent, at 160 °C for 20 min. Obtained liquid fractions were analysed by SEC, FT-IR, DSC, TGA, 31P-NMR and 2D-HSQC NMR in order to explain the mechanism of the increased yield, and to study the structural changes after microwave extraction/degradation. 2D-NMR indicates cleavage of β-O-4 inter-unit linkages, but also that some modification around the bond could take place. Lignin based thermosets were synthesised employing the polyesterification between lignin, citric acid and poly(ethylene glycol) (PEG). It was concluded that introduction of PEG into the system was crucial for a homogenous thermoset synthesis with a high gel content. From TGA analysis it could be concluded that the thermoset based on original Lignoboost had a lower thermal stability than the counterparts prepared from lower molecular weight fractions. This implies that the esterification reaction between original Lignoboost and the other co-monomers is obstruct by sterically hindrance, which means that pre-conditioning is positive for the final material properties. / I denna studie utnyttjades en mikrovågsbaserad teknik, för att framgångsrikt extrahera och bryta ner lignin till polyfunktionella oligomerer med lägre molekylvikt än ursprungsmaterialet. Både lignin extraherat genom sulfat- och sulfitprocessen, d.v.s. kraft lignin (Lignoboost) och lignosulfonat, undersöktes. Det högsta lösliga utbytet för Lignoboost (67 %) kunde uppnås efter 20 min vid 160 °C genom att använda etanol som lösningsmedel, vilket är en ökning med 38 % jämfört med enbart extraktion i etanol. Under samma förhållanden uppnåddes även det högsta lösliga utbytet för Lignosulfonat, fast genom att använda metanol som lösningsmedel. De erhållna lösliga fraktionerna analyserades med hjälp av SEC, FT-IR, DSC, TGA, 31P-NMR samt 2D-HSQC NMR, med syftet att förklara ökning i lösligt utbyte samt studera eventuella strukturella förändringar efter bearbetning i mikrovågsugnen. Resultat från 2D-NMR indikerar på nedbrytning av β-O-4 bindningar, men även på att modifikationer kring bindningen kan ha uppkommit. Tvärbundna, ligninbaserade material syntetiserades genom att nyttja polykondensationsreaktionen mellan lignin, citronsyra och polyetylenglykol (PEG), vilket resulterade i esterbindningar. Det var möjligt att dra slutsatsen att introducering av PEG in i systemet var avgörande för att nå homogena material med hög andel tvärbindningar. Genom TGA analyser kunde det fastslås att tvärbundna material baserade obehandlad Lignoboost hade lägre termisk stabilitet än dess motsvarigheter baserade på fraktioner med lägre molekylvikt. Detta tyder på att esterreaktionen mellan obearbetad Lignoboost och de två andra monomererna försvåras genom steriskhindring, vilket innebär att bearbetning av ligninet medför positiva effekter på egenskaperna hos det slutgiltiga materialet.
39

Fiber based biocomposite material with water and grease barrier properties / Fiberbaserat biokompositmaterial med vatten-och fettbarriäregenskaper

Martinsdotter, Linnea January 2021 (has links)
Syftet med denna studie var att utveckla en biokomposit med både fett-och vattenbarriär. Material med dessa egenskaper innehåller idag ofta PFAS-molekyler (per- och polyfluorerade alkylsubstanser). Det är av stor betydelse att byta ut dessa mot ett biobaserat alternativ då de är giftiga och ackumuleras i naturen. Biokompositen utvecklades genom att kombinera icke-trä pappersmassa (75%) och trä pappersmassa (25%) som matris. Därefter tillsattes olika biobaserade additiv i våtände för att påverka materialets egenskaper. Proverna testades på deras dragstyrka, vattenavvisning och fettavvisning. Den stora utmaningen var att lyckas med fettavisningen. 1% Polysackarid 1 tillsammans med 0.5% sizing komponent var det provet som gav bäst resultat. För att utvärdera denna metod gjordes en jämförelse med ytbehandling. Det gjordes genom att stryka på några av de tidigare använda additiven på ytan av matrisen. Ytbehandlingen visade sig ha en större påverkan på fettavvisningen men med liknande eller sämre påverkan på vattenavvisningen. Nackdelen med denna metod är att den kräver ett flertal extra steg i produktionen. / The aim of this thesis work was to develop a pulp-based biocomposite material with good water and grease barrier properties. It is important to achieve such properties to able to replace PFAS (poly- and perfluoroalkyl substances) molecules due to their toxicity and accumulation. Different types of pulp were evaluated as the matrix and the optimal matrix was based on non-wood pulp (75%) with wood pulp 1 (25%).  This was also combined with several different additives in the wet-end. The samples were tested for their tensile strength, water resistance and grease resistance. The biggest challenge was to achieve adequate grease resistance. 1% Polysaccharide 1 together with 0.5% sizing agent was one of the better samples. It was clear the additives affected each other when used in combination with each other which indicates that wet end chemistry is complex. For a comparison, some additives were also tested as coatings. This technique resulted in better grease resistance but requires several extra steps in the production.
40

Novel biobased epoxy networks derived from renewable resources : Structure-property relationships / Novel biobased epoxy networks derived from renewable resources : Structure-property relationships

Chrysanthos, Marie 21 June 2012 (has links)
Récemment, les polymères obtenus à partir de ressources renouvelables ont connus un véritable engouement pour le remplacement de matériaux obtenus à partir de ressources pétrolières. L'objectif de notre étude a été de développer de nouveaux systèmes bio-sourcés réactifs, plus précisément des systèmes époxy, pour des applications dans le domaine des matériaux composites. Le monomère le plus souvent utilisé pour formuler des réseaux époxy est le diglycidyl éther de bisphenol A, DGEBA, obtenu à partir du bisphenol A et de l’épichlorhydrine. L’intérêt pour le remplacement du bisphénol A par un précurseur bio-sourcé est accentué par la toxicité de ce dernier. Dans cette étude, nous avons étudié différents systèmes obtenus à partir de prépolymères époxy bio-sourcés et les avons comparés à un système classique à base de DGEBA en utilisant l'isophorone diamine (IPD) comme agent durcisseur. Parmi les différents prépolymères époxy bio-sourcés étudiés, certains ont été obtenus à partir de dérivés polysaccharides tels que le sorbitol et l'isosorbide. Le sorbitol polyglycidyl éther est disponible commercialement, tandis que le diglycidyl éther d'isosorbide a été synthétisé soit par une voie classique faisant intervenir l’épichlorhydrine soit par l'intermédiaire du diallyle isosorbide. Un autre prépolymère époxy dérivé du cardanol a été étudié et est aussi un produit commercial. Les structures chimiques de ces prépolymères époxy bio-sourcés ont été analysées. Les phénomènes de gélification et de réticulation des systèmes obtenus à partir de ces prépolymères et de l’IPD ont été étudiés. L’influence de la structure du prépolymère bio-sourcé et de l'agent de réticulation (classique ou dérivé de ressources renouvelables) sur les propriétés des réseaux ainsi que l'absorption d'eau par ces réseaux ont également été discutés. / In recent years, bio-based polymers derived from renewable resources have become increasingly important as sustainable and eco-efficient products which can replace the products based on petrochemical-derived stocks. The objective of our work was to develop novel bio-based reactive systems suitable for high performance composite materials especially epoxy systems. The most commonly used starting monomer to formulate epoxy networks is the diglycidyl ether of bisphenol A, DGEBA, derived from bisphenol A and epichlorohydrin. Bio-based epichlorohydrin is commercially available. So the challenge to obtain a fully bio-based epoxy prepolymer is to replace bisphenol A by a bio-based precursor. Another interest for replacing bisphenol A by a bio-based precursor is that bisphenol A has been known to have estrogenic properties. In this study, we studied different bio-based epoxy systems and compared them to a classical DGEBA based system using, in a first step, isophorone diamine (IPD) as conventional curing agent. Bio-based epoxy prepolymers were derived from natural sugars, sorbitol and isosorbide respectively. Sorbitol polyglycidyl ether is available commercially, while isosorbide diglycidyl ether was synthesized either via conventional epoxidation (i.e. using epichlorohydrin) or via the diallyl isosorbide intermediate. Another bio-based epoxy prepolymer was derived from cardanol and is also a commercial product. Chemical structure of the bio-based epoxy prepolymers were analyzed by different analytical methods, gelation and crosslinking reactions were studied using rheological measurements and differential scanning calorimetry, respectively. Properties of the cured networks were evaluated using dynamic mechanical analysis and thermo gravimetric analysis. Influence of the bio-based epoxy prepolymer structure on the system properties as well as the influence of the crosslinking agent structure (either derived from renewable resources or bio-based ones) was discussed. Water absorption of the bio-based networks was also studied.

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