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Ce travail porte sur l’étude des composites à base de polypropylène et de farine de bois. Seuls des composites à base d’une matrice polypropylène et de fibres végétales ont été mis en oeuvre sans aucun recours à quelque agent comptabilisant que ce soit. En premier lieu nous avons regardé l’influence de la viscosité initiale de la matrice polypropylène sur la processabilité des biocomposites en utilisant des polymères de grades variés. Puis nous avons étudié l’influence de la nature et de la concentration de la farine en utilisant des farines de pin (bois mou) et de chêne (bois dur). Enfin, une attention spécifique a été portée sur la possibilité de nucléation en phase Beta de la matrice polypropylène en présence de fibres végétales. Des polypropylènes β-Nucléés ainsi que des farines ayant subies des extractions par des solvants de leurs composés volatils ont été utilisées. Les mélanges obtenus ont été testés au moyen de la viscoélasticité à l’état fondu pour mettre en évidences les effets d’interaction charges-Matrices et par des mesures de diffraction aux rayons X ainsi que d’analyse thermique différentielle pour la caractérisation de leurs morphologies cristallines. / This doctoral thesis is focused on composites based on polypropylene and wood flour. Firstly, the experimental work deals with preparation of composites based on wood flour with various concentrations and isotactic polypropylene with various melt flow indexes. In terms of this study, one polypropylene, which can have also practical use, was chosen. Further, this polypropylene is investigated with various types and concentrations of wood flour. Also, the attention is devoted to the modification of polypropylene by a specific β-Nucleating agent. The differences are compared and described between the composites with neat and nucleated polypropylene. Further, the work is focused on solvent extraction of wood flour. The effect of extraction and solvent of wood flour is also examined in composites with neat and nucleated polypropylene. On prepared composites, the rheological, structural and thermal properties are studied. These properties differ depending on specific type of wood flour, its concentration and specific type of polypropylene. / Předložená doktorská práce je zaměřena na kompozity polypropylenu a dřevní moučky. V experimentální části práce jsou připraveny kompozity s různými koncentracemi plniva a izotaktických polypropylenů s různými indexy toku taveniny. Na základě této studie je vybrán jeden konkrétní polypropylen, který může mít v kombinaci s dřevní moučkou i praktické využití. Tento polypropylen je dále zkoumán s různými druhy a koncentracemi dřevní moučky. Pozornost je také kladena na úpravu vlastností izotaktického polypropylenu užitím specifického β-nukleačního činidla. Jsou porovnávány a popisovány rozdíly mezi kompozity s čistým a nukleovaným polypropylenem. Práce se dále zabývá extrakcí dřevní moučky v rozpouštědle. Je studován vliv extrakce a rozpouštědla dřevní moučky na vlastnosti připravených kompozitů. Byly studovány reologické, strukturální a tepelné vlastnosti, které se lišily v závislosti na zvoleném typu plniva, jeho koncentraci a typu polymerní matrice.

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This work is concerned with the prediction of short (SGF) and long glass fiber (LGF) orientation in a center-gated disk and end-gated plaque injection molding test geometry using a simulation method that has not been attempted previously. Previous work has used assumptions to simplify the fiber orientation geometry (assuming a thin cavity) or flow field (neglecting fountain flow and entry regions). LGF orientation is predicted in a center-gated disk injection molding geometry including the advancing front and simulating the sprue and gate region (SGM method) so that no assumption about fiber orientation at the mold entrance has to be made. Using a semi-flexible fiber model and orientation parameters obtained through rheology, increased agreement was found between predicted and experimentally obtained values of orientation using the SGM method and a semi-flexible fiber model than was found using a Hele-Shaw approximation. The SGM method was applied to the end-gated plaque to predict SGF orientation both along and away from the centerline using an objective (reduced strain closure model) and non-objective (strain reduction factor model) orientation model. The predicted values of the strain reduction factor model showed reasonable agreement with experimentally obtained values of orientation throughout the three-dimensional cavity when using orientation parameters fit to experimental orientation data. Furthermore it was found that the objective model predicted results very similar to the non-objective model suggesting that objectivity may not play a role in predicting orientation in more complex geometries such as an end-gated plaque. Finally, the SGM method was applied to the end-gated plaque geometry to predict LGF orientation using a rigid and semi-flexible fiber model. It was found that the SGM method and the semi-flexible fiber model provides orientation predictions that are similar to experimentally obtained values of orientation. / Ph. D.

Nanocellulosics, often found in the form of cellulose nanocrystals (CNCs) and nanofibrillated cellulose (NFCs), provide promise as rheological modifiers and reinforcement fillers for composite materials. The biological origin of CNCs promises a bio-renewable resource with the potential to expedite degradation times compared to synthetic polymer species. Additionally, the surface functional groups provide a route for both hydrogen bonding and further chemical modification. While much research is currently investigating the possible uses of these materials, they offer limited aid if their use is not scalable to industrial processing techniques. Common processing techniques such as injection molding subject materials to high temperatures and strain rates upwards of 100000 s-1. Thermal stability is a known challenge that can be increased via chemical modifications, but little is known about the effects of high or extended shear stresses typical of those experienced during typical polymer processing. High shear rates, which proportionally result in high shear stresses, have the potential to influence the alignment, degradation, and overall usability of these materials when employed in consumer applications. In this work, we investigate the rheology and processing of aqueous CNC suspensions at concentrations up to 12.1 wt% and of aqueous NFC suspensions at concentrations up to 20 wt% under capillary shear stresses. Traditional capillary rheology corrections, including the Weissenberg-Rabinowitsch-Mooney (WRM) correction for non-Newtonian fluids, and the Bagley correction for entrance pressure effects, have been applied to determine the true rheological behaviors of these suspensions. Additional analysis using atomic force microscopy (AFM), wide-angle x-ray scattering (WAXS), and conductometric titration assist identification of morphological and chemical changes that affect the CNMs after they have been subjected to industry-relevant shear rates. These studies demonstrate that processing conditions can significantly affect the size and shape of the post-processed nanomaterials by fracturing the CNCs and unwinding the larger bundles of the NFCs. Given the importance of the final aspect ratio of filler and reinforcement materials, the impact of this discovery will substantially influence how these materials are used and processed to create consumer products. / Doctor of Philosophy / As the world struggles with the problem of plastic waste and climate change, it is important to develop biologically friendly solutions to combat these issues. Filler materials such as carbon fibers and glass fibers can help create lightweight materials for cars and transportation containers. However, carbon fibers can be hazardous and expensive to obtain. Glass fibers offer a more cost-effective option, but they often break during processing and are heavy in comparison to carbon fibers. Cellulose nanomaterials (CNMs) can provide a lightweight and more bio-friendly alternative to these fillers. These CNMs can come from a wide variety of sources, such as hardwood trees, bacteria, or tunicates (a type of marine animal). This makes them abundantly available, relatively cheap to produce, and easy for the environment to break down fully. Using these as fillers instead of glass fibers, carbon fibers or other materials could help reduce much of our waste, but we need to be able to process them in the same ways we currently handle other composite materials. This work focuses on characterizing the effect of high-speed flows and the forces those flows put on the cellulose nanomaterials. The following document will show that the smaller, more rigid, cellulose nanocrystals (CNCs) often break under these stresses, while the longer nanofibrillated cellulose (NFCs) unwind and disperse.

The objective of this project was to evaluate and model the effects of moisture, temperature, and combined hygrothermal aging on the durability of a graphite/epoxy woven composite material system. Imposed environmental and aging conditions were considered to be representative of service conditions for the engine of an advanced subsonic aircraft for which the composite system is a candidate material. The study was designed such that the results could be used in a residual strength based life prediction approach that accounted for both the mechanical fatigue and environmental conditions. Damage mechanisms and failure modes were determined through fatigue testing, residual strength testing, and nondestructive evaluation. The experimental data generally revealed little effect of environment on strength degradation during fatigue despite notable differences in damage accumulation processes. Modeling efforts were concentrated on initial stiffness, moisture uptake, and residual strength prediction, where the results from the first two efforts were intended to generate inputs for the life prediction. The Ishikawa and Chou fiber undulation and bridging model [22] was shown to provide an accurate stiffness prediction and was subsequently used in parametric studies to determine the effect of weave architecture and geometry. A moisture uptake model developed by Roy [16] for laminates containing single direction cracks was extended to predict moisture uptake in laminates containing cracks in directions parallel and transverse to the loading direction. The life prediction approach was based on ideas developed by Reifsnider and colleagues [36,37,43]. The intention in this case was to use the critical element paradigm to predict the combined effects of alternating environmental (temperature and moisture) conditions imposed during fatigue. Since experimental results indicated that temperature and moisture did not significantly affect the strength and life of the material, a successful life prediction analysis was performed as a function of only fatigue stress level and cycles. / Master of Science

Carbonization of biomass is a type of pyrolysis that allows for the formation of byproducts that have applications in many other industries [1]. In the field of materials science concerned with environmental impact intersecting with desirable material properties and performance, the process of carbonization in particular with commonplace biomass such as food waste is of great interest. In this thesis, pistachio shell was used as the organic biomass of choice for carbonization, and reinforcement was provided by titanium powder. These two materials were milled together at two different compositions and milling times. Experimental conditions consisted of replicates of three bulk samples made from uniaxially pressed powder mixtures heat treated from 800 °C up to 1200 °C in increments of 100 °C. Heat treatment occurred in a tube furnace with a heating rate of 5 °C/min up to the heat treatment temperature, holding the temperature for 1 hour, then ramping back down to room temperature, all in an inert atmosphere. XRD was performed on heat treated samples before polishing, while optical microscopy and SEM were performed after mounting and polishing. TGA was performed on the milled powders, while hardness was performed on the heat treated bulk samples after mounting and polishing. Results obtained suggested that increasing heat treatment temperature and milling time decreased carbon matrix porosity. In addition, greater amounts of titanium seemed to result in increased porosity. However, at increased temperature, more surface cracking was observed, leading to the conclusion that an excessively high temperature is detrimental to mechanical properties. Finally, rutile TiO2 was formed as a result of the heat treatment process. In considering environmental impact, cost, and mechanical properties, a balance must be maintained between higher temperature processing, duration, milling time, and porosity present due to these factors. Future work includes further investigations into processing parameters and characterization such as XPS and abrasion testing. / Master of Science / Carbonization of organic materials such as wood or nut shells can be explained in short as a decomposition that occurs when those materials are heated up without allowing them access to oxygen as in a normal combustion like a fire. Because of that, carbonization can produce useful products and materials of interest to many. Adding titanium to pistachio shell powder, performing compaction and carbonization, then further heating up those samples, resulted in composite materials consisting of mostly carbon char and particles inside that improve the properties. After testing multiple experimental conditions and analyzing them using equipment such as X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA), optical microscopes, Scanning Electron Microscopy (SEM)/Energy Dispersive Spectroscopy (EDS), and a hardness tester, some trends in properties and structure were observed. Generally, increasing heat treatment temperature and milling time will reduce porosity in the matrix. On the other hand, decreasing amount of Ti powder added seems to reduce porosity. However, too high of a heat treatment temperature seems to have a detrimental effect on the part manufactured (i.e. surface cracking). In addition, considering processing costs and time costs could discourage one from using a very high temperature to heat treat these samples. Therefore, it is important to balance amount of energy used to heat treat, time spent, and resulting porosity of the final product for its applications. Future work should be done to further determine the effects of processing parameters by making more samples to test the properties of. Other characterization techniques like X-Ray Photoelectron Spectroscopy (XPS) and abrasion testing could be good to determine the exact makeup of the particles in the composite as well as see the sample's performance in its intended application (i.e. brake pads).

Experimental methods were developed and used to quantify the behavior of composite materials during heating to support development of heat and mass transfer pyrolysis models. Methods were developed to measure specific heat capacity, kinetic parameters, microstructure changes, porosity, and permeability. Specific heat and gravimetric data for kinetic parameters were measured with a simultaneous differential scanning calorimeter (DSC) / thermogravimetric analyzer (TGA). Experimental techniques were developed for quantitative specific heat measurement based on ASTM standards with modifications for accurate measurements of decomposing materials. An environmental scanning electron microscope (ESEM) was used in conjunction with a heating platform to record real-time video of microstructural changes of materials during decomposition and cooling following decomposition. A gas infusion technique was devised to measure porosity, in which nitrogen was infused into the pores of permeable material samples and used to determine the open-pore porosity of the material. Permeability was measured using a standard pressure differential gas flow technique with improvements over past sealing techniques and modifications to allow for potential high temperature use. Experimental techniques were used to measure the properties of composite construction materials commonly used in naval applications: E-glass vinyl ester laminates and end-grain balsa wood core. The simultaneous DSC/TGA was used to measure the apparent specific heat required to heat the decomposing sample. ESEM experiments captured microstructural changes during decomposition for both E-glass vinyl ester laminate and balsa wood samples. Permeability and porosity changes during decomposition appeared to depend on microstructural changes in addition to mass fraction. / Master of Science

Thèse ou mémoire avec insertion d'articles. / Ce mémoire de maitrise présente les résultats de la diffusivité thermique de matériaux composites et le calcul de la température pyrométrique d'une plaque d'acier et d'un matériau composite. L'introduction donne les enjeux et objectifs du travail ainsi qu'un bref survol du corps du mémoire. Le chapitre 2 présente le premier article scientifique intitulé "Thermal Diffusivity Measurements With Flash Method at Different Depths In a Burned Composite Material". On mesure dans ce chapitre la diffusivité thermique à la température de la pièce de matériaux composites avant et après attaque d'une flamme d'un brûleur au propane. Les diffusivités thermiques obtenues varient entre 1.23e-07 m²/s à 3.14e-07 m²/s pour le premier échantillon de composite et entre 2.10e-07 m²/s et 3.14e-07 m²/s pour d'autres échantillons. On y présente également dans l'annexe A la diffusivité thermique en fonction de la profondeur d'un échantillon de composite brûlé pendant 15 secondes. Dans la partie brûlée de l'échantillon, on observe une convergence de la diffusivité thermique vers sa valeur initiale de 4.25 e-07 m²/s, lorsque non brûlée. Cette convergence en fonction de la profondeur suit une tendance polynomiale d'ordre 2. Le chapitre 3 présente le deuxième article scientifique intitulé "Temperature Calculation of a Steel Plate under Kerosene Flame Attack Using Two-Color Pyrometry". On mesure la température d'une plaque d'acier à l'aide d'une caméra infrarouge contenant deux filtres "transparents à la flamme" à 3 800 nm et 3 950 nm. Ces mesures avec la caméra infrarouge sont non-intrusives. Les températures pyrométriques calculées atteignent 600°C en régime permanent et sont en concordance avec des thermocouples préalablement incrustés dans la plaque. L'annexe B donne la température pyrométrique pour un échantillon de composite. La conclusion générale revient sur les points saillants des différents chapitres et donne une perspective pour de futurs travaux. / This master's thesis presents the results of the thermal diffusivity of composite materials and the calculation of the pyrometric temperature of a steel plate and a composite material. The introduction gives the challenges and objectives of the work as well as a brief overview of the body of the dissertation. Chapter 2 presents the first scientific article entitled "Thermal Diffusivity Measurements With Flash Method at Different Depths In a Burned Composite Material". In this chapter, we measure the thermal diffusivity at room temperature of composite materials before and after attack by a flame from a propane burner. The thermal diffusivities obtained vary between 1.23e-07 m²/s to 3.14e-07m²/s for the first sample of composite and between 2.10e-07 m²/s and 3.14e-07 m²/s for other samples. The Annex A also presents the thermal diffusivity as a function of the depth of a sample of composite burnt for 15 seconds. In the burnt part of the sample, we observe a convergence of thermal diffusivity towards its initial value of 4.25 e-07 m²/s when unburned. This convergence as a function of depth follows a polynomial trend of order 2. Chapter 3 presents the second scientific article entitled "Temperature Calculation of a Steel Plate under Kerosene Flame Attack Using Two-Color Pyrometry". The temperature of a steel plate is measured without touching the material using an infrared camera containing two "flame-transparent" filters at 3 800 nm and 3 950 nm. The calculated pyrometric temperatures reach 600°C in steady state and agree with thermocouples previously embedded in the plate. Annex B gives the pyrometric temperature for a composite sample. The conclusion returns to the salient points of the different chapters and gives a perspective for future work.

Composites have been developed with great success by the use of fiber reinforcements in metallic materials. Fiber reinforced metal matrices possess great potential to be the next generation of advanced composites offering many advantages compared to fiber reinforced polymers. Specific advantages include high temperature capability, superior environmental stability, better transverse modulus, shear and fatigue properties. Although many Metal Matrix Composites (MMCs) are attractive for use in different industrial applications, Aluminium Matrix Composites (AMCs) are the most used in advanced applications because they combine acceptable strength, low density, durability, machinability, availability, effectiveness and cost. The present study focuses on the fabrication of aluminium matrix composite plates by squeeze casting using plain weave carbon fiber preform (AS4 Hexcel) as reinforcement and a matrix of wrought aluminium alloy 1235-H19. The objective is to investigate the process feasibility and resulting materials properties such as hardness at macro- and micro-scale, impact and bend strength. The properties obtained are compared with those of 6061/1235-H19 aluminium plates that were manufactured under the same fabrication conditions. The effect of fiber volume fraction on the properties is also investigated. Furthermore, the characterization of the microstructure is done using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) in order to establish relationships between the quality of the fiber/aluminium interface bond and mechanical properties of the composites. In conclusion, aluminium matrix composite laminate plates were successfully produced. The composites show a good chemical bond between the fiber and the aluminium matrix. This bond resulted from heterogeneous precipitation of aluminium carbides (Al4C3) at the interface between aluminium matrix and carbon fiber. The hardness at macro- and micro-scale of the composites increases by over 50% and the flexural modulus increases by about 55%. The toughness of the composite decreases due to the presence of brittle phases which can be improved by better oxidation prevention. Also, an optimal carbon volume fraction was observed that provides optimal properties including peak hardness, peak stiffness and peak toughness.