<p align=\"justify\">As propriedades de fluorescência da 2,4-(1H,3H)-quinazolinediona, produto da reação entre o íon cianato e o ácido 2-aminobenzóico possibilitaram o desenvolvimento de um método simples, sensíveis, seletivo e reprodutível para a análise de íons cianato em meio aquo etanólico. O método foi aplicado a análises de íons cianato em diferentes frações do destilado de cana e os dados sugerem uma forte correlação entre a presença de ureia no vinho, e as concentrações de íons cianato e de carbamato de etila (CE) no destilado. A citrulina apresenta-se também como uma fonte de íons cianato, tendo como um de seus produtos o CE na presença do etanol. Acompanhando-se no destilado recém-obtido as variações nas concentrações de íons cianato e de carbamato de etila em função do tempo, observa-se que à medida que diminui a concentração de íons cianato há um aumento na concentração de carbamato de etila. Foram estudados os aspectos cinéticos e termodinâmicos da formação de CE por meio da reação entre íons cianato e o etanol. Os valores das constantes de velocidade para o consumo do íon cianato e para a de formação de CE são de (8&sbquo;0 &plusmn; 0&sbquo;4) &times; 10-5 e de (8&sbquo;90 &plusmn; 0&sbquo;4) &times; 10-5 s-1, respectivamente, a 25 &deg;C em solução etanólica 48% (v&frasl;v) com pH 4&sbquo;5. Nas condições experimentais, as constantes de velocidade são independentes das concentrações de etanol e dos íons cianato, porém são dependentes da acidez pH e apresentam os valores dos parâmetros de ativação de &Delta;H&#8225; &#61; 19&sbquo;4 &plusmn; 1 kcal&frasl;mol, &Delta;S&#8225; &#61; -12&sbquo;1 &plusmn; 1 cal&frasl;K e &Delta;G&#8225; &#61; 23&sbquo;0 &plusmn; 1 kcal&frasl;mol. Cálculos computacionais empregando-se teoria do funcional de densidade (DFT) sugerem que os valores calculados de &Delta;H&#8225;1 &Delta;S&#8225;1 e &Delta;G&#8225;1 estão de acordo com os obtidos experimentalmente e condizem com o mecanismo proposto. Observa-se que íons de Cu(II) catalisam a oxidação de íons cianeto à cianato promovendo a formação de CE. Além disso, íons de Cu(II) pode se coordenar com alguns precursores de CE. / <p align=\"justify\">Based on the fluorescence properties of 2,4-(1H,3H)-quinazolinedione, a product of the reaction between cyanate and 2-aminobenzoic acid, a simple, sensitive, selective, and reproducible method for the cyanate analysis in aqueous ethanolic media is proposed. The method was applied to cyanate analysis in different fractions of sugarcane distillate and the data strongly suggest a correlation between the presence of urea in wine, and cyanate and ethyl carbamate (EC) concentrations in the spirit. Citrulline also presents itself as a cyanate source, having EC as one of its products in the presence of ethanol. Monitoring changes in cyanate and EC concentrations as function of the time in freshly distilled sugar cane spirit, it was observed that as the cyanate concentration decreases, the EC concentration increases. Thermodynamic and kinetic aspects of EC formation through the reaction between cyanate and ethanol were investigated. The rate constant values for cyanate ion decay and EC formation are (8.0 &plusmn; 0.4) &times; 10-5 s-1 and (8.90 &plusmn; 0.4) &times; 10-5 s-1, respectively, at 25 &deg;C in 48% ethanolic solution at pH 4.5. Under the investigated experimental conditions, the rate constants are independent of the ethanol and cyanate concentrations but increase as the temperature increases &Delta;H&#8225; &#61; 19.4 &plusmn; 1 kcal&frasl;mol, &Delta;S&#8225; &#61; -12.1 &plusmn; 1 cal&frasl;K and &Delta;G&#8225; &#61; 23.0 &plusmn; 1 kcal&frasl;mol) and decrease as pH solution increases. According to molecular modeling (DFT) that was performed to analyze the reaction mechanism, Isocyanic acid is the active EC precursor. The calculated &Delta;H&#8225;1 &Delta;S&#8225;1 and &Delta;G&#8225;1 values are in very good agreement with the experimental ones. The copper effect on EC formation reaction was also studied. Copper acts on the cyanide oxidation reaction and could coordinate with some EC precursors.

Several problems must be solved in the construction, design, and operation of a nuclear fusion reactor. One of the chief problems in the manufacture of high-powered copper/polymer composite magnets is the difficulty to precisely control the fiber volume fraction. In this thesis, the effect of variations in fiber volume fraction on thermal stresses in copper/cyanate ester composite cylinders is investigated. The cylinder is a composite that uses copper wires that run longitudinally in a cyanate ester resin specifically developed by Composite Technology Development, Inc. This composite cylinder design is commonly used in magnets for nuclear fusion reactors. The application of this research is for magnets that use cylindrical coil geometry such as the Mega Amp Spherical Tokamak (MAST) in the UK. However, most stellarator magnet designs use complex geometries including the National Compact Stellarator Experiment (NCSX), and the Quasi-Poloidal Stellarator (QPS). Even though the actual stresses calculated for the cylindrical geometry may not be directly applicable to these projects, the relationship between fiber volume fraction and stresses will be useful for any geometry. The effect of fiber volume fraction on stresses produced by mechanical, thermal and magnetic loads on cylindrical magnet coils is studied using micromechanics with laminate plate theory (LPT) and finite element analysis (FEA). Based on the findings of this research, variations in volume fraction do significantly affect the stress experienced by the composite cylinder. Over a range of volume fractions from 0.3 to 0.5, the LPT results demonstrate that thermally induced stresses vary approximately 30% while stresses due to pressure vary negligibly. The FEA shows that magnetic stresses vary much less at around only 5%. FEA results seem to confirm the LPT model. It was also concluded that the stress in the insulation layers due to all types of loadings is significant and must be considered when using this system in fusion applications.

Several problems must be solved in the construction, design, and operation of a nuclear fusion reactor. One of the chief problems in the manufacture of high-powered copper/polymer composite magnets is the difficulty to precisely control the fiber volume fraction. In this thesis, the effect of variations in fiber volume fraction on thermal stresses in copper/cyanate ester composite cylinders is investigated. The cylinder is a composite that uses copper wires that run longitudinally in a cyanate ester resin specifically developed by Composite Technology Development, Inc. This composite cylinder design is commonly used in magnets for nuclear fusion reactors. The application of this research is for magnets that use cylindrical coil geometry such as the Mega Amp Spherical Tokamak (MAST) in the UK. However, most stellarator magnet designs use complex geometries including the National Compact Stellarator Experiment (NCSX), and the Quasi-Poloidal Stellarator (QPS). Even though the actual stresses calculated for the cylindrical geometry may not be directly applicable to these projects, the relationship between fiber volume fraction and stresses will be useful for any geometry. The effect of fiber volume fraction on stresses produced by mechanical, thermal and magnetic loads on cylindrical magnet coils is studied using micromechanics with laminate plate theory (LPT) and finite element analysis (FEA).Based on the findings of this research, variations in volume fraction do significantly affect the stress experienced by the composite cylinder. Over a range of volume fractions from 0.3 to 0.5, the LPT results demonstrate that thermally induced stresses vary approximately 30% while stresses due to pressure vary negligibly. The FEA shows that magnetic stresses vary much less at around only 5%. FEA results seem to confirm the LPT model. It was also concluded that the stress in the insulation layers due to all types of loadings is significant and must be considered when using this system in fusion applications.

Σκοπός της παρούσας πτυχιακής εργασίας ήταν η μελέτη της περιβαλλοντικής γήρανσης ινωδών συνθέτων υλικών με κυανεστερική μήτρα σε ακραίες θερμοοξειδωτικές ή/και υγροθερμικές συνθήκες. Επίσης, ο θερμομηχανικός χαρακτηρισμός και η αρχική μελέτη των μηχανισμών υποβάθμισης. Για το σκοπό αυτό παρασκευάστηκαν πέντε τύποι πολύστρωτων πλακών οι τρείς εκ των οποίων έφεραν ως ενίσχυση οχτώ στρώσεις προεμποτισμένου πανιού ινών γυαλιού (GFRPs) τριών διαφορετικών κυανεστερικών μητρών (PN901-G201-45{GRT},HTM143,MTM110) και πλέξης 2*2 twill. Η παρασκευή των τριών αυτών πλακών έγινε με τη μέθοδο του κενού σακούλας (Hand Lay Up Vacuum Bag).Όσον αφορά στις δυο άλλες πλάκες οι οποίες προέκυψαν μέσω της διαδικασίας χύτευσης με μεταφορά ρητίνης RTM σε γνωστό ερευνητικό ινστιτούτο της Ισπανίας (Tecnalia), δύο διαφορετικοί τύποι κυανεστέρα (DT-4000,PT-30) χρησιμοποιήθηκαν ως μήτρα για τον εμποτισμό πανιού άνθρακα (CFRPs) τύπου πλέξης 5H Satin. Από την παραπάνω διαδικασία προέκυψαν πλάκες πέντε στρώσεων. Οι πλάκες ελέγχθηκαν ποιοτικά αρχικά, με τη μέθοδο υπερήχων C-Scan όπου διαπιστώθηκε η ομοιογένεια τους και έπειτα με χρήση της μεθόδου Διαφορικής Θερμιδομετρίας Σάρωσης DSC μέσω της οποίας ελέγχθηκε και επιβεβαιώθηκε το ποσοστό πολυμερισμού τους. Στην παρούσα εργασία ορίστηκαν τρεις διαδικασίες γήρανσης:(α) τοποθέτηση των δοκιμίων σε λουτρό απιονισμένου νερού στους 200C έως το σημείο ισορροπίας (AP2),(β) τοποθέτηση των δοκιμίων σε φούρνο στους 2300C για 30 μέρες (AP3) και (γ) τοποθέτηση των δοκιμίων σε φούρνο στους 2300C για 16h και σε λουτρό απιονισμένου νερού στους 200C για 16h με διάρκεια δέκα κύκλων. Αρχικά, και προ της γήρανσης τους, τα υλικά χαρακτηρίστηκαν ως προς την διαστρωματική τους αντοχή σε διάτμηση μέσω της διεξαγωγής πειραμάτων κάμψης τριών σημείων SBS (Short Beam Strength) με βάση το στάνταρντ ASTM D2344(M) και ως προς τη θερμομηχανική τους απόκριση με χρήση της πειραματικής διάταξης Δυναμικής-Μηχανικής Ανάλυσης DMA (Dynamic Mechanical Analysis). Στη συνέχεια, ακολούθησε ο χαρακτηρισμός των δοκιμίων που υποβλήθηκαν στις παραπάνω διαδικασίες γήρανσης ως προς την διαστρωματική αντοχή τους σε διάτμηση και τις θερμομηχανικές τους ιδιότητες. Επίσης, πραγματοποιήθηκε μικροσκοπικός χαρακτηρισμός των δοκιμίων μέσω της ηλεκτρονικής μικροσκοπίας σάρωσης SEM (Scanning Electron Microscopy). Συγκρίνοντας τη συμπεριφορά, μεταξύ των δοκιμίων αναφοράς και των δοκιμίων που είχαν υποβληθεί σε κάποια από τις διαδικασίες γήρανσης, στην περίπτωση του θερμοοξειδωτικού και του συνδυασμένου περιβάλλοντος γήρανσης παρατηρήθηκε υποβάθμιση των ιδιοτήτων και μεγάλη αλλαγή/απώλεια στη μάζα των υλικών. Στην περίπτωση του υγροθερμικού περιβάλλοντος παρατηρήθηκε υψηλή απορρόφηση υγρασίας σε όλα τα δοκίμια ενώ όσον αφορά τις ιδιότητές τους άλλα τις διατήρησαν και άλλα υπέστησαν πολύ μικρές μεταβολές σε σύγκριση με τις αρχικές τους. Από την παραπάνω διαδικασία προέκυψε συζήτηση και αρχικά συμπεράσματα για τους μηχανισμούς που πιθανώς έδρασαν σε κάθε διαδικασία γήρανσης. / The aim of the current investigation was to study the environmental aging of fiber reinforced polymer composites with cyanate ester resin at extreme thermooxidative, hydrothermal and combined environmental conditions. During the ageing mechanical, thermo-mechanical as well as optical characterization was performed aiming at an initial study of the active degradation mechanisms under the defined environmental conditions. For this purpose five laminated plates were developed three of which bore a reinforcement of eight layers of glass fiber preimpregnated 2 * 2 twill woven cloth (GFRPs) with three different cyanate ester matrices (PN901-G201-45 {GRT}, HTM143, MTM110). The aforementioned three plates were manufactured by the Hand Lay Up Vacuum Bag method. Regarding the two other plates which arose by following the resin transfer molding RTM technique in a known institute of research located in Spain (Tecnalia), two different types of cyanate ester resin (DT-4000, PT-30) were used as matrices for impregnation of a 5H Satin woven carbon cloth (CFRPs). The above procedure leaded to two plates of five layers. The plates were initially tested qualitatively through the ultrasonic C-Scan method from which the homogeneity of the plates was confirmed. Moreover the curing percentage was checked by using the Differential Scanning Calorimetry DSC method. For the environmental ageing of the aforementioned plates three aging processes were specified as following: (a) control of hydrothermal degradation by immersing the samples in a bath of deionized water at 200C until the equilibrium point (AP2), (b) control of thermo-oxidative degradation by placing the samples in an oven at 2300C for 30 days (AP3), and finally (c) control of materials degradation in cycled environmental conditions that combine both thermo-oxidative and hydrothermal atmosphere by keeping the samples at 2300C for 16h that is followed by their immersion in deionized water bath at 200C for 16h with duration ten cycles. Initially, and prior to aging, the materials were characterized towards their unaged response by conducting three point bending SBS (Short Beam Strength) experiments under the standard ASTM D2344 (M) as well as thermomechanical measurements by performing Dynamic Mechanical Analysis DMA (Dynamic Mechanical Analysis) measurements. This was followed by the characterization of the samples after the aforementioned aging processes towards the interlaminar shear strength and thermo-mechanical properties. In parallel with the above microscopic characterization of samples by scanning electron microscopy SEM (Scanning Electron Microscopy) was take place, too. Comparing the behavior between reference specimens and the aged specimens subjected to environmental ageing under thermooxidative atmosphere the oxidation seemed to be the main degradation mechanism in all material systems without excluding the synergistic effect of rest of the possible active degradation mechanism (e.g. further crosslinking, chain scission etch.). As for the hydrothermal environment the analysis of the results allowed to say that the plasticization is mainly activated under the specific conditions. Finally as far as the response of the materials under the cycled and combined environmental conditions is concerned, no certain conclusion for the main degradation mechanisms could be derived as the phonomemenon is too complicated.

No description available.

Molecules in the ‘X-C≡N’ chemical family serve as markers for chemical processes happening in various regions of space and are members of the prebiotic molecular pool, which makes them important in astrochemistry and astrobiology. Although these kinds of molecules have been identified in the interstellar medium, cometary comae, plumes of Enceladus, meteorites, and around young stellar objects, it is not clear which mechanisms are responsible for their formation. However, it has been suggested that they may serve as precursors to prebiotically important compounds, such as amino acids and nucleobases. In this work, a theoretical computational study was conducted using quantum mechanical approaches to predict properties of sixteen astrochemically relevant ‘X-C≡N’ molecules. To perform this study, General Atomic and Molecular Electronic Structure System (GAMESS(US)) and AutoGAMESS software were used to calculate optimized geometries, harmonic vibrational frequencies, infrared intensities, and Raman activities of each molecule using density functional theory (BLYP, B3LYP, PBE, and PBE0) and second order Møller-Plesset perturbation theory (MP2, SCS-MP2) paired with several basis sets (6-311++G(d,p), def2QZVPD, Sadlej-pVTZ, and aug-cc-pVQZ). Geometries and frequencies were additionally calculated using coupled cluster approaches (CCSD, CCSD(T), and CCSD(2)T) to help assess accuracy and reliability of the other calculations. For many of these species, experimentally and computationally determined Raman activities have not been reported in the literature. We assess the reliability of our calculations in comparison to previous works and discuss how the implementation of both Raman and infrared spectroscopy can offer new insights into potential reaction mechanisms linking these prebiotically relevant compounds.

The effect of thermal-cycling-induced microcracking in fiber-reinforced polymer matrix composites is studied. Specific attention is focused on microcrack density as a function of the number of thermal cycles, and the effect of microcracking on the dimensional stability of composite materials. Changes in laminate coefficient of thermal expansion (CTE) and laminate stiffness are of primary concern. Included in the study are materials containing four different Thornel fiber types: a PAN-based T50 fiber and three pitch-based fibers, P55, P75, and P120. The fiber stiffnesses range from 55 Msi to 120 Msi. The fiber CTE's range from -0.50x10⁻⁶/°F to -0.80x10⁻⁶/°F. Also included are three matrix types: Fiberite's 934 epoxy, Amoco's ERL1962 toughened epoxy, and YLA's RS3 cyanate ester. The lamination sequences of the materials considered include a cross-ply configuration, [0/90]2s, and two quasi-isotropic configurations, [0/+45/-45/90]s and [0/+45/90/-45]s. The layer thickness of the materials range from a nominal 0.001 in. to 0.005 in. In addition to the variety of materials considered, three different thermal cycling temperature ranges are considered. These temperature ranges are ±250°F, ±150°F, and ±50°F. The combination of these material and geometric parameters and temperature ranges, combined with thermal cycling to thousands of cycles, makes this one of the most comprehensive studies of thermal-cycling-induced microcracking to date. Experimental comparisons are presented by examining the effect of layer thickness, fiber type, matrix type, and thermal cycling temperature range on microcracking and its influence on the laminates. Results regarding layer thickness effects indicate that thin-layer laminates microcrack more severely than identical laminates with thick layers. For some specimens in this study, the number of microcracks in thin-layer specimens exceeds that in thick-layer specimens by more than a factor of two. Despite the higher number of microcracks in the thin-layer specimens, small changes in CTE after thousands of cycles indicate that the thin-layer specimens are relatively unaffected by the presence of these cracks compared to the thick-layer specimens. Results regarding fiber type indicate that the number of microcracks and the change in CTE after thousands of cycles in the specimens containing PAN-based fibers are less than in the specimens containing comparable stiffness pitch-based fibers. Results for specimens containing the different pitch-based fibers indicate that after thousands of cycles, the number of microcracks in the specimens does not depend on the modulus or CTE of the fiber. The change in laminate CTE does, however, depend highly on the stiffness and CTE of the fiber. Fibers with higher stiffness and more negative CTE exhibit the lowest change in laminate CTE as a result of thermal cycling. The overall CTE of these specimens is, however, more negative as a result of the more negative CTE of the fiber. Results regarding matrix type based on the ±250°F temperature range indicate that the RS3 cyanate ester resin system exhibits the greatest resistance to microcracking and the least change in CTE, particularly for cycles numbering 3000 and less. Extrapolations to higher numbers of cycles indicate, however, that the margin of increased performance is expected to decrease with additional thermal cycling. Results regarding thermal cycling temperature range depend on the matrix type considered and the layer thickness of the specimens. For the ERL1962 resin system, microcrack saturation is expected to occur in all specimens, regardless of the temperature range to which the specimens are exposed. By contrast, the RS3 resin system demonstrates a threshold effect such that cycled to less severe temperature ranges, microcracking does not occur. For the RS3 specimens with 0.005 in. layer thickness, no microcracking or changes in CTE are observed in specimens cycled between between ±150°F or ±50°F. For the RS3 specimens with 0.002 in. layer thickness, no microcracking or changes in CTE are observed in specimens cycled between ±50°F.. Results regarding laminate stiffness indicate negligible change in laminate stiffness due to thermal cycling for the materials and geometries considered in this investigation. The study includes X-ray examination of the specimens, showing that cracks observed at the edge of the specimens penetrate the entire width of the specimen. Glass transition temperatures of the specimens are measured, showing that resin chemistry is not altered as a result of thermal cycling. Results are also presented based on a one-dimensional shear lag analysis developed in the literature. The analysis requires material property information that is difficult to obtain experimentally. Using limited data from the present investigation, material properties associated with the analysis are modified to obtain reasonable agreement with measured microcrack densities. Based on these derived material properties, the analysis generally overpredicts the change in laminate CTE. Predicted changes in laminate stiffness show reasonable correlation with experimentally measured values. / Ph. D.

Mammalian heme peroxidases are fascinating due to their unique peculiarity of oxidizing (pseudo)halides under physiologically relevant conditions. These proteins are able either to incorporate oxidized halides into substrates adjacent to the active site or to generate different oxidized (pseudo)halogenated species, which can take part in multiple (pseudo)halogenation and oxidation reactions with cell and tissue constituents. The present article reviews basic biochemical and redox mechanisms of (pseudo)halogenation activity as well as the physiological role of heme peroxidases. Thyroid peroxidase and peroxidasin are key enzymes for thyroid hormone synthesis and the formation of functional cross-links in collagen IV during basement membrane formation. Special attention is directed to the properties, enzymatic mechanisms, and resulting (pseudo)halogenated products of the immunologically relevant proteins such as myeloperoxidase, eosinophil peroxidase, and lactoperoxidase. The potential role of the (pseudo)halogenated products (hypochlorous acid, hypobromous acid, hypothiocyanite, and cyanate) of these three heme peroxidases is further discussed

This investigation explored the feasibility of recently developed toughened cyanate ester networks as candidate materials for high performance composite matrix applications. The resin investigated was a Bisphenol-A cyanate ester toughened with hydroxy functionalized phenolphthalein based amorphous poly(arylene ether sulfone). The thermoplastic modified toughened networks exhibited improvement in the fracture toughness over the base cyanate ester networks without significant reductions in mechanical properties or glass transition temperature. Void free, unidirectional carbon fiber prepreg was successfully manufactured with the toughened cyanate resin using a solventless hot-melt technique. The resin mass fraction of the prepregs was between 31 and 35%. The carbon fiber, toughened cyanate ester prepreg was fabricated into composite panels for mechanical and physical testing. The cure cycle used to manufacture the composite laminates was developed with the aid of a process simulation model developed by Loos and Springer. In order to accurately simulate the resin curing and flow processes, the cure reaction kinetics and melt viscosity was characterized as a function of temperature and degree of cure and input into the simulation model. The model generated cure cycle was used in the manufacture 8-ply unidirectional and 16-ply quasi-isotropic composite laminates. The manufactured laminates were well consolidated to the specified fiber volume fraction between 59 and 60%. Photomicrographs showed that the laminates are void free, the fiber and resin distribution is uniform and fiber wet-out is very good. Mechanical tests were performed to measure the impact damage resistance and shear properties of the toughened cyanate ester resin composites. The results show improvements in impact damage resistance compared with the commonly used hot-melt epoxy resin composites. The influence of processing on performance was observed from the results of shear tests. Carbon fabric composite panels were manufactured by liquid molding processes (resin transfer molding and resin film infusion), with a series of four toughened cyanate ester resins generated by varying the concentration and the molecular weight of the toughener. The panels were subjected to physical, damage tolerance, and fracture toughness tests. The results of physical testing indicate consistently uniform quality, and the void content was found to be less than 2%. The toughened cyanate ester composites exhibited significantly improved impact damage resistance and tolerance compared with hot-melt epoxy systems. Marked increase in the mode II fracture toughness were observed with an increase in the concentration and the molecular weight of the toughener. / Ph. D.

The search and research for high performance materials for aerospace applications is a continuous evolving process. Among several fibre reinforced polymers, carbon fibre reinforced polymer (CFRP) is well known for its high specific stiffness and strength. Though high modulus and high strength carbon fibre with structural resin systems have currently been established reasonably well and are catering to a wide variety of aerospace structural applications, these properties are generally directional with very high properties along the fibre direction dominated by fibres and low in other directions depending mainly on the resin properties. Thus, there is a need to enhance the mechanical properties of the resin systems for better load transfer and to improve the resin dominated properties like shear strength and properties in directions other than along the fibre. Use of carbon nanotubes (CNTs) with their extraordinary specific stiffness and strength apparently has great potential as an additional reinforcement in resin for development of CNT-CFRP nanocomposites. However, there are several issues that need to be addressed such as compatibility of a particular resin with CNTs, amount of CNTs that can be added, uniform dispersion of these nanotubes, surface treatment and curing process etc., for optimal enhancement of the required properties. Epoxy and cyanate ester resin systems are finding applications in aerospace structures owing to their desirable set of properties. Of these, bisphenol E cyanate ester (BECy) resin of low viscosity with its low moisture absorption, better dimensional stability, and superior mechanical properties can establish itself as potential structural resin system for these applications. BECy in particular has the advantage of being more suitable for out of autoclave manufacturing process such as Vacuum Assisted Resin Transfer Molding (VARTM). Literature shows that, significant work has been carried out by various researchers reporting improvements using CNTs in epoxy resins along with various associated problems. However, studies on effects of addition of CNTs /fCNTs to BECy-CFRP composite system are not well reported. Thus, objective of this work is to study the effects of adding pristine and functionalized CNTs to low viscosity cyanate ester as well as epoxy resin systems. Further, to study the effects on mechanical properties of nanocomposites with carbon fibre reinforcement in these CNT dispersed resin system through a combination of experimental and computational approaches. Multiwall carbon nanotubes (CNTs) without and with different chemical functionalization are chosen to be added to epoxy and BECy resins. The quantity of these CNTs /fCNTs is varied in steps up to 1% by weight. Different methods of mixing such as shear mixing, ultrasonication and combined mixing cycles are implemented to achieve uniform dispersion of these nanotubes in the resin system. Standard test samples are prepared from these mixtures of nanotubes in resin systems to study the variation in mechanical properties. Further, these nanotubes added resin systems are used in fabricating CFRP laminates by VARTM process. Both uni-directional and bi-directional laminates are made with the above modified resin systems with CNTs/fCNTs. Series of experimental investigations are carried out to study various aspects involved in making of nanocomposites and the effects of the same on different mechanical properties of the nanocomposites. Standard specimens are cut out from these laminates to evaluate them for tension, compression, flexure, shear and interlaminar shear strength. The main parameters investigated are the effects of varied quantity of CNTs and functionalized CNTs in the resin mix and in CFRP nanocomposites, effect of different mixing / curing cycles etc. on the mechanical properties of the nanocomposites. The investigations have yielded very interesting and encouraging results to arrive at optimum quantity of CNTs to be added and also the effects of functionalization to achieve enhanced mechanical properties. In addition, correlation of mechanical property enhancements with failure mechanisms, dispersion behaviour and participation of CNTs / fCNTs in load transfer are explained with the aid of scanning electron microscope images. Computational studies are carried out through atomistic models using computational tools to estimate the mechanical properties, understand and validate the effects of various parameters studied through series of experimental investigations. An atomistic model is built taking into consideration the nanoscale effects of the single wall carbon nanotubes (SWCNTs) and its reinforcement in the BECy resin. Using these atomistic models, mechanical properties of individual SWCNT, BECy polymer resin, polymer with different quantities of added SWCNT, and the CFRP laminates with improved resin are computed. As the interaction of CNT with the polymer is only at the outermost layer and the mechanical properties of either MWCNTs or SWCNTs are too high compared to resin systems, it is not expected to have any difference in the final outcome whether it is MWCNT or SWCNT. Hence, only SWCNTs are considered in computational studies as it helps in reducing the complexity of atomistic models and computational time when coupled with polymer resin. This is valid even for functionalized CNT as functionalization is also a surface phenomenon. To start with, the mechanical behaviour of SWCNT is studied using molecular mechanics approach. Molecular mechanics based finite element analysis is adopted to evaluate the mechanical properties of armchair, zigzag and chiral SWCNT of different diameters. Three different types of atomic bonds, i.e., carbon-carbon covalent bond and two types of carbon-carbon van der Waals bonds are considered in the carbon nanotube system. The stiffness values of these bonds are calculated using the molecular potentials, namely Morse potential function and Lennard-Jones interaction potential function respectively and these stiffness values are assigned to spring elements in the finite element model of the SWCNT. The importance of inclusion of Lennard-Jones interactions is highlighted in this study. Effect of these non-bonded interactions is studied by making the numerical stiffness of these bonds to negligible levels and found that they significantly reduce the mechanical properties. The effect of non-bonded Lennard-Jones atomic interactions (van der Waal interactions) considered here is a novelty in this work which has not been considered in previous research works. The finite element model of the SWCNT is constructed, appropriate boundary conditions are applied and the behaviour of mechanical properties of SWCNT is studied. It is found that the longitudinal tensile strength and maximum tensile strain of armchair SWCNTs is greater than that of zigzag and chiral SWCNTs and its value increases with increasing SWCNT diameter. The estimated values of the mechanical properties obtained agree well with the published literature data determined using other techniques. As the systems become more complicated with the inclusion of polymers, molecular dynamics (MD) method using well established codes is more adoptable to study the effect of SWCNTs on BECy. Hence, it is used to model and solve the nanosystems to generate their stress-strain behavior. Further, MD approach followed here can effectively include interfacial interaction between polymer and the CNTs as well. Mechanical properties of SWCNT functionalized SWCNT (fSWCNT), pure BECy resin and that of the CNT nanocomposite consisting of specific quantity of SWCNT / fSWCNT in BECy are estimated using MD method. Atomistic models of SWCNT, fSWCNT, BECy, BECy with specific quantities of CNT / fSWCNT are constructed. A monomer of BECy is modelled and stabilized before its usage as a building block for modelling of BECy resin and to compute its properties. A cell of specific size containing monomers of BECy and another cell of same size with SWCNT at centre surrounded by BECy monomer molecules are built. The appropriate quantity of SWCNT in resin is modelled. This model captures the required density of the composite resin. The models so constructed are subjected to geometric optimization satisfying the convergence criteria and equilibrated through molecular dynamics to obtain a stable structure. The minimized structure is subjected to small strain in different directions to calculate the Young’s modulus and other moduli of the CNT-BECy resin composite. The process is repeated for different quantities of SWCNT in BECy resin to obtain their moduli. Further, tensile and shear strengths of CNT-BECy are obtained by subjecting the equilibrated structure to a series of applied strains from 0 to 10% in steps of 1%. The stress values corresponding to each strain are obtained and a stress – strain curve is plotted. From the stress- strain curve, the strengths of the CNT -BECy which is the stress corresponding to the modulus after which the material starts to soften are determined. Effects of functionalization on mechanical properties of SWCNT are observed. Further, effects of functionalization of SWCNT are studied with a specific quantity of fSWCNT on different moduli and strengths of BECy are investigated. The properties of enhanced CNT–BECy nanocomposite resin with different quantities of added CNT obtained through MD are used to estimate the mechanical properties of the CNT-BECy-CFRP nanocomposite using micromechanics model. Further, validation with experimental results is attempted comparing the trends in enhancement of properties of the CNT-BECy resin and CNT-BECy-CFRP nanocomposite system. The outcome of this research work has been significantly positive in terms of i) Development of an appropriate process establishing different parameters for dispersing CNTs in the resin system, mixing, curing cycle for making of nanocomposites demonstrating significant and consistent enhancement of mechanical properties of BECy based resin system and CFRP nanocomposites using optimum quantity of CNTs /fCNTs through a series of well planned and executed experimental investigations. Evaluation of mechanical properties for each of the cases has been carried out experimentally. ii) Establishing a computational methodology involving intricate atomistic modelling and molecular dynamics of nanosystems for estimation of mechanical properties of BECy polymer resin and to study the effects by addition of SWCNT / functionalized SWCNT on the properties. Results obtained through series of experimental investigations have been validated through this computational study. This could be an important step towards realising the potential of this resin system for high performance aerospace applications. Thus, in brief, detailed experimental work combined with computational studies performed as presented in this thesis resulted in achieving structurally efficient cyanate ester based nanocomposites which is unique and not reported in open literature.