The thesis deals with the properties of epoxy resins, their reinforcing by thermoplastic modified epoxies, rubbers and cellulose fibers. The thesis also describes the production, properties and types of cellulose fibers. In the practical part of this thesis, there was executed reinforcement of epoxy matrix by different amounts of cellulose fibers. Mixing was performed in two ways – by a homogenizer or an ultrasonic homogenizer. There were also executed the tensile strength and shear strength tests to the manufactured conglomerates.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, May 2016 / In this study, hybrid multiscale epoxy composites were developed from woven glass fabrics and PAN nanofibers embedded with short ECNFs (diameters of ~200nm) produced via electrospinning. Unlike VGCNFs or CNTs which are prepared through bottom-up methods, ECNFs were produced through a top-down approach; hence, ECNFs are much more cost-effective than VGCNFs or CNTs. Impact absorption energy, tensile strength, and flexural strength of the hybrid multiscale reinforced GFRP composites were investigated. The control sample was the conventional GFRP composite prepared from the neat epoxy resin. With the increase of ECNFs fiber volume fraction up to 1.0%, the impact absorption energy, tensile strength, and flexural strength increased. The incorporation of ECNFs embedded in the PAN nanofibers resulted in improvements on impact absorption energy, tensile strength, and flexural properties (strength and modulus) of the GFPC. Compared to the PAN reinforced GRPC, the incorporation of 1.0% ECNFs resulted in the improvements of impact absorption energy by roughly 9%, tensile strength by 37% and flexural strength by 29%, respectively. Interfacial debonding of matrix from the fiber was shown to be the dominant mechanism for shear failure of composites without ECNFs. PAN/ECNFs networks acted as microcrack arresters enhancing the composites toughness through the bridging mechanism in matrix rich zones. More energy absorption of the laminate specimens subjected to shear failure was attributed to the fracture and fiber pull out of more ECNFs from the epoxy matrix. This study suggests that, the developed hybrid multiscale ECNF/PAN epoxy composite could replace conventional GRPC as low-cost and high-performance structural composites with improved out of plane as well as in plane mechanical properties. The strengthening/ toughening strategy formulated in this study indicates the feasibility of using the nano-scale reinforcements to further improve the mechanical properties of currently structured high-performance composites in the coming years. In addition, the present study will significantly stimulate the long-term development of high-strength high-toughness bulk structural nanocomposites for broad applications. / MT2016

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this investigation was to evaluate and compare microleakage of teeth obturated using either RealSeal/Resilon or RealSeal Self-Etch/Resilon systems. The goal was to determine whether a significant difference in microleakage exists between these two groups. To date, no study has been done comparing the microleakage of root canal systems obturated with using RealSeal/Resilon versus RealSeal SE/Resilon. Sixty-two human, single-rooted, anterior teeth were accessed and instrumented for non-surgical root canal therapy. Teeth were randomly assigned to two experimental groups of 27 teeth each. Group I consisted of teeth obturated with the RealSeal/Resilon system, whereas Group II consisted of teeth obturated with the RealSeal SE/Resilon system. In addition, two control groups containing four teeth each served as positive and negative controls, Group (+) and Group (-), respectively. The teeth were then evaluated for microleakage using a dual-chamber microleakage model. Visual turbidity in the lower chamber denoted microleakage within the experimental groups observed for 33 days. RealSeal SE Group II had a significantly higher proportion of samples than Real Seal Group I. Time to microleakage was also significantly lower in RealSeal SE Group II than in Real Seal Group I. No microleakage was observed in the negative control and microleakage was observed in all four samples in the positive control. To date, this is the first study comparing the microleakage of RealSeal/Resilon and RealSeal SE/Resilon systems. The higher microleakage associated with RealSeal SE is attributed to the higher pH of the self-etch (SE) sealer in comparison with the self-etch primer of RealSeal. The self-etching potential of the sealer system is particularly critical in areas inaccessible to calcium chelating agents such as EDTA in root canal systems. Further research needs to be done to corroborate the microleakage results from this study. The microbial leakage apparatus devised in this study, which used a selective growth medium with streptomycin, has also been validated by the results of the study. The bacterial leakage apparatus has been considered to be clinically relevant and acceptable by the Journal of Endodontics. Thus, the modified dual-chambered microleakage apparatus with a selective growth medium used in this research can be replicated easily in future microleakage studies.

Manufacturing induced shape distortions is a common problem for composite materials. Due to the non-isotropic nature of carbon fibre reinforced polymers (CFRP) unavoidable deformations occur during part production. During fabrication of polymer composites, the material obtains its final shape at elevated temperatures. The curing process involves a transition from the liquid state to the solid, glassy state, allowing bonding between fibres and matrix. As the material cools the mismatch in thermal expansion coefficients and cure shrinkage obtained during the matrix polymerization leads to residual stresses on the mechanical level within composite part. There is a great interest from the aircraft and automotive industries, to increase the ability to understand development of shape distortions and residual stresses during the cure, since these deformations often lead to dissatisfaction of tolerances and it is essential to predict the deformations beforehand in order to compensate time and cost.  In this context, a study of residual stresses during the curing process of thermosetting resin composites is presented. A methodology is proposed for predicting the formation and development of manufacturing- induced residual stresses. The present project reports on a comprehensive experimental study on the dependency of different short curing cycles on the build-up of residual stresses in a carbon fibre/fast-curing epoxy system and evaluate of post-curing methods through induction heating and oven post-curing with unidirectional [904] and unsymmetrical [9020] laminates. It includes characterization in thermo-elastic properties and degree-of-cure of the material by Thermal bending test, thermal expansion test, mechanical tensile test and Differential Scanning Calorimetry (DSC) in non-post-cured and post-cured laminates. The results showed slight variation in the thermal properties and not effect in the mechanical properties at different cure and post-curing conditions. Analytical data by Laminate Analysis program validated the experimental thermo-elastic data with analytical simulations. In addition, it is shown improvements in the temperature distributions in the post-curing by induction heating with different experimental set-ups, however, oven post-curing showed a more systematic system, higher heat efficient a low cure temperature, with more consistent mechanisms of shape distortions and residual stresses compared to induction heating. These findings are relevant for the future development of prediction methods for process induced deformations of Fast Curing Epoxy Resins (FCER).

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This thesis has focused on the synthesis and characterization of amino functional monomers, principally monomers containing aryl phosphine oxide units. Utilization of these monomers was demonstrated in various types of linear and network polymerizations. The diamines monomers included bis(3-aminophenyl) methyl phosphine oxide (DAMPO), bis(3-aminophenyl) phenyl phosphine oxide (DAPPO), bis(3-aminophenoxy phenyl) phenyl phosphine oxide (BAPPO) and bis(3-aminophenoxy phenyl) methyl Phosphine oxide (BAMPO). From these monomers high molecular weight poly(ether imides), polyurea-urethanes, poly(arylene ether ketones) poly(arylene ether sulfones) and poly(arylene ether phosphine oxides) were. Internal and external fire testing methodologies showed that the new polymers containing phosphine oxide units were fire resistant while maintaining the desirable physical characteristics of carefully selected control systems. In addition, suitable curing schedules for epoxy networks were determined by using dielectric monitoring techniques. The curing rates varied with the structure of the monomers and were slowest for the deactivated control (4,4'aminophenyl sulfone). Epoxy networks containing aryl phosphine oxide units had higher char yields in dynamic thermogravimetric analyses than control specimens. This correlated with their superior flame resistance. The brittle epoxy matrices were subsequently modified with reactive or non-reactive thermoplastic polymers in order to improve their fracture toughness. Poly(ether imides) and poly(ether sulfones) showed good phase separation behavior with tetrafunctional epoxy matrices during the curing reactions, as confirmed by scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). Mechanical tests showed that reactive thermoplastic modification of the epoxy networks improved the fracture toughness of the systems, without noticeable decreases in other characteristics such as flexural modulus. Reactive systems also maintained chemical resistance in contrast to non-reactive thermoplastic controls. / Ph. D.

The state of cure of epoxies is an important issue in the manufacture of graphite epoxy composites used in aerospace structures. Variations in the initial state and process used to cure the epoxy resin in a composite material lead to variations in the mechanical properties of the part manufactured from the composite._[12] Control of these variation can be accomplished by monitoring the bulk and shear moduli of the epoxy resin as it cures. The moduli properties of the resin determine the acoustic properties of the epoxy._{[12],[13],[14]} Hence measurement of the acoustic longitudinal velocity and attenuation of the epoxy during its cure cycle provides a good indicator of the state of cure. Optical fiber waveguides can be embedded within a host material and used to detect longitudinal acoustic waves._[15],[16] Herein, the mechanisms allowing the detection of ultrasound with optical fiber are presented. An analysis of optical fiber waveguides and optical fiber based interferometric detection methods is performed in detail. The interaction of radial strain fields, induced by longitudinal acoustic waves, with singlemode optical fibers is described. Experimental results obtained in epoxy cure monitoring, using an optical fiber based method for acoustic detection, are compared with results obtained using conventional piezoelectric based acoustic detection methods. / Master of Science

Ce travail de thèse examine trois voies de valorisation de l'huile de pépins de raisin au travers de l'élaboration de matériaux polymères auto-associatifs, réticulés ou hybrides. L'huile végétale ou un modèle lipidique (l'oléate de méthyle) sont d'abord fonctionnalisés grâce à leurs insaturations menant à des huiles hydroxylées, aminées, ou phosphorées.Dans une première étude, l'huile et l'oléate de méthyle ont été hydroxylés par réaction thiol-ène. Les alcools gras sont ensuite transformés en macroamorceurs capables d'amorcer la polymérisation cationique par ouverture de cycle de la 2-méthyl-2-oxazoline. Les lipopolymères (LipoPOx) amphiphiles ainsi synthétisés sont capables de s'auto-associer et de former des nanoparticules monodisperses observées par DLS. Dans une deuxième étude, l'huile et certains de ses dérivés amide ont été modifiés sous UV par addition radicalaire du chlorure de cystéamine, conduisant à une diamine linéaire et à une polyamine ramifiée. Ces dernières ont été utilisées comme durcisseurs d'huile époxydée permettant la réticulation de résines époxy à fort taux de carbone biogénique. L'étude thermomécanique par analyse rhéologique montre que ces matériaux thermodurcissables ont des Tg comprises entre -38 et -9°C.Dans une troisième étude, les lipides ont été fonctionnalisés par addition radicalaire de diméthylphosphite par voie photochimique ou thermique. La transformation ultérieure des esters phosphonés en fonctions silylées a rendu ces composés réactifs vis-à-vis du titane et de ses oxydes. L'ancrage de lipides sur des particules de TiO2 ou des feuilles de Titane influe sur leurs propriétés de surface. / This Ph-D work deals with the valorization of grapeseed oil for the preparation of novel and various bio-based polymers. Three pathways are developed starting from lipids and leading to polymeric materials such as self-assembled polymers, thermosets and hybride polymers. First, the vegetable oil and methyloleate were modified using radical addition on their double bonds. Following, hydroxylated, aminated and phosphonated lipids were synthesized.In a first study, the oil was hydroxylated via thiol-ene coupling reaction. The fatty alcohol was then converted into initiator for the cationic ring-opening polymerization of 2-methyl-2-oxazoline. These Lipopolymers so-called LipoPOx exhibit hydrophilic POx block and fatty block. Their amphiphilic nature confer them a self-organization ability in water. A monomodal and narrow distribution of nanoparticles was observed by DLS and AFM.In a second study, the oil and some fatty amides were also functionalized by UV-induced radical addition using cysteamine hydrochloride. A linear diamine and a branched polyamine were synthesized and used as hardeners of epoxidized vegetable oil leading to thermosets with high level of bio-carbone. The investigation on thermo-mechanical properties showed a Tg between -38 and -9°C.In a last study, the lipids were modified by radical addition of dimethylphosphite using thermal or photochemical process. Then, the phosphonate esters were converted into silylated moieties making them reactive toward titanium. The anchoring of lipids onto titanium based materials induced a modification of their surface properties.

A reação entre resinas epóxi e polialquileno glicóis gera um aduto de elevado peso molecular que pode ter aplicações em diferentes segmentos, tais como polímeros usados na composição base de fluidos de têmpera, viscosificantes para lubrificantes e desemulsificantes de petróleo. As condições envolvendo a formação destes adutos possuem referências limitadas na literatura aberta e basicamente envolvem um polialquileno glicol com diferentes funcionalidades, tipicamente duas hidroxilas reagindo com os grupos epóxi presentes na resina epóxi que tipicamente possui funcionalidade igual a dois, a uma temperatura ao redor de 120°C na presença de catalisador de hidróxido de potássio (KOH). O presente trabalho avaliou a formação destes adutos considerando um delineamento experimental de resolução III onde as variáveis de controle foram temperatura, velocidade de agitação do meio reacional, velocidade de adição de resina epóxi, concentração de catalisador e relação molar entre a resina epóxi e o polialquileno glicol. Ao total onze experimentos foram realizados de acordo com o planejamento experimental e incluindo triplicata para avaliação do erro experimental. Diferenças significativas nas características físico químicas dos produtos obtidos tais como viscosidade, teor de epóxi residual e de performance de desemulsificação foram encontradas. Dois produtos apresentaram gelificação. Com um bom nível de confiabilidade estatística pode-se dizer que o peso molecular ponderal médio é influenciado principalmente pelo teor de catalisador seguido da temperatura e proporção molar entre resina epóxi e polialquileno glicol nesta ordem de importância. Com menor nível de significância a conversão é influenciada positivamente com respeito ao incremento do teor de catalisador e da temperatura e pela redução na proporção molar entre resina epóxi e polialquileno glicol. Apesar de terem sido atingidos elevados níveis de conversão de resina epóxi na maioria dos experimentos, pelas analises de GPC foi observado uma grande proporção de polialquileno glicol livre residual nos produtos. Pode-se observar também uma fraca correlação estatística positiva entre a qualidade da separação petróleo-água com respeito à conversão e ao peso molecular numérico médio dos produtos. / The reaction between epoxy resins and polyalkylene glycols generates an adduct of high molecular weight that may have applications in several sectors such as polymers for metal quenchant fluids, demulsifiers and viscosifiers for lubricating oil. The conditions involving the formation of these adducts have limited references in the open literature and basically it involves a polyalkylene glycol having different functionalities, typically two hydroxyl groups reacting with the epoxy groups present in the epoxy resin with typical functionality equal to two at a temperature around 120°C and in the presence of catalyst, potassium hydroxide (KOH). This study evaluated the formation of these adducts considering a resolution III experiment design where the controllable variables were temperature, stirring speed of the reaction medium, rate of addition of epoxy resin, catalyst concentration and molar ratio between the epoxy resin and polyalkylene glycol . In total eleven experiments were carried out according to the experimental design, including three replications at the center point to evaluate the experimental error. Significant differences in chemical and physical characteristics such as viscosity, residual epoxy content and performance of demulsification were found between the synthesized materials. Two products showed gelation. With a good level of statistical reliability it can be considered that the weight average molecular weight is mainly influenced by the amount of catalyst followed by temperature and mole ratio of epoxy resin to polyalkylene glycol in this order of importance. With lower significance level conversion is influenced positively with respect to the increment of the catalyst amount and temperature and by the decrease in molar ratio of epoxy resin and polyalkylene glycol. Despite achieving high levels of conversion of epoxy resin in most of the experiments, by GPC analysis it was observed a large proportion of free residual polyalkylene glycol in the products. It can be observed also a slight positive statistical correlation between the quality of oil-water separation with respect to conversion and number average molecular weight of the products.