No description available.

No description available.

In recent years, the use of stereolithography (SL) to produce end-use parts has increased rapidly. However, only limited applications have been considered as there are several problems that impede the conversion of stereolithography to be used as a mainstream manufacturing process. One of the major problems is the instability of the SL parts post-build when subjected to environmental factors. This research included long-term material testing to investigate the effects of ageing, humidity and temperature on the mechanical properties of the SL parts. This work was carried out at a temperature range of -40°C to +100°C over differing ageing and humidity conditions (dry (10%RH), controlled (50%RH) and wet (100%RH)). The results indicated that the main degradation factor was humidity. It was therefore selected for further investigation in this research. This is the most comprehensive analysis and characterisation of materials data yet compiled for additively manufactured materials. Stereolithography materials tested have been shown to significantly degrade over time when subjected to a high level of relative humidity. Therefore, it was the primary aim of this research to identify the mechanism of hygroscopic degradation of epoxy-based SL materials. This was achieved using various techniques including mechanical tests, Differential Scanning Calorimetry (DSC) and Attenuated Total Reflectance (ATR). Modelling of water penetration into SL epoxy-based parts was undertaken and the type of diffusion was found to be anomalous (non-Fickian). Therefore a dual-Fickian model was developed to identify the diffusion coefficients of the investigated materials. Additional equations were developed to model the profiles of moisture concentration and Young's Modulus within a specimen and to predict the stiffuess of an SL material at a certain age. The methodology that has been developed in this work can now be further used to predict the mechanical properties of any future epoxy-based SL material providing the diffusion coefficient(s) of the material are known.

Studies have been carried out on reaction-induced phase separation in epoxy networks, formed from a DGEBA-type epoxy resin prepolymer, DER332, and m-xylylene diamine, MXDA, containing as modifiers either (i) butyl laurate (B) or (ii) m-cardura (C), (synthesised from Cardura El0 and 2-ethyUiexanoic acid). The reactants and modifiers were characterised using end-group analysis, Fourier transform infra-red spectroscopy (FTIR), differential scanning calorimetry (DSC), nuclear magnetic resonance and viscometry.

Block copolymer modified epoxy resins have generated significant interest since it was demonstrated that the combination could lead to nanostructured thermosets through self-assembly. In this work, samples of epoxy resin - formed by reaction of bisphenol-A diglycidyl ether (BADGE) and diethyltoulenediamine (DETDA) - and containing a range of copolymers composed of poly(ethylene oxide) (E) and poly(butylene oxide) (B), were prepared and characterized. Samples contained EB, EBE and BEB copolymers over a range of concentrations. Copolymers of low molecular weight and low B content were found not to microphase separate. BEB copolymers with high molecular weight and high B content were found to macrophase separate prior to, or during, cure. FTIR spectroscopy during cure demonstrated that the reaction kinetics in these systems differ from those previously reported for similar systems. Over moderate to high copolymer concentration the systems behaved as expected of a block copolymer in a solvent selective for one block. As concentration increased, transitions from BCC-Hex-Gyr-Lam phases were observed by SAXS. At lower concentrations, in some systems, spherical micellar structures were formed, as demonstrated by TEM. SAXS analysis was performed on those systems producing sufficiently clear patterns. Some degree of reaction-induced microphase separation (RI/lPS) was observed in all cases. A linear increase in scattering intensity with extent of reaction was observed during RI/lPS. In some cases non-equilibrium structures were apparently observed, due to vitrification prior to completion of the RI/lPS process. The increase in the number of micelles as a function of concentration was analyzed and found to deviate from linearity as the system goes from a solution of copolymer in epoxy to swollen copolymer gel. The association number of the micelles was found to vary as a function of copolymer composition following a similar scaling law to that observed, by others, in aqueous solution. Reaction-induced macrophase separation was observed in some BEB systems at elevated temperature, but not in similar EBE systems. The process was characterised by SALS and found to fit to the Cahn-Hilliard linear theory of spinodal decomposition. The systems were seen to vitrify before phase separation is complete, producing cured products that were phase separated into interpenetrating networks on the micron scale. No significant improvement of mechanical properties of the resin was observed in those samples tested.

No description available.

In view of an increasing number of reports describing epoxy resinthermoplastic blends, it is clearly important to identify the effects of the thermoplastic on the blend properties. In this work difunctional epoxy resin monomer (Epikote 828) cured with diaminodiphenylsulphone (DDS) or dicyandiamide (DICY) are the model systems used. The thermoplastic is a polyethersulphone (PES) with either hydroxyl terminations (Victrex 5003P, ICI) capable of reaction with epoxy monomer or chlorine terminated (Ultrason E2010, BASF) which is incapable of reaction. The glass transition characteristics of the PES materials are very similar but the Ultrason E2010 is of lower average molecular weight and can be expected to contain more chain ends. Epoxy-DDS-PES systems were prepared with 20phr and 30phr of PES. The effects of the PES on crosslinking and isothermal physical ageing behaviour were examined. Enthalpy relaxation data were curve fitted using a Kohlrausch function. Mechanical and dielectric spectroscopy data were analysed using W-L-F and power law methods. Despite a tendency for the PES to reduce the crosslink density of the network, the blends had glass transition temperatures almost identical to the unmodified resin. The reduction in crosslink density improved Glc compared to the unmodified resin but promoted faster physical ageing and more rapid embrittlement when the blends were aged at the same temperature as the neat resin. The epoxy-DICY-PES system was studied at one composition of 30phr PES. The system was two phase but fast curing led to premature arrest of the phase separation process. Annealing at various temperatures from below the glass transition of the low temperature phase to just below the glass transition of the high temperature phase resulted in what is believed to be microscopic morphological changes detectable only barely by DSC and quite clearly from dynamic mechanical analysis. These changes were not manifest in the morphology of fracture surfaces. Annealing was found to decrease G1c.

The non-hydrolytic sol-gel process has been used for the synthesis of ORganically- MOdified SILicas (ORMOSILs). The effect on morphology of the ormosil particles has been investigated using different solvents, types of stirring, and additives such as surfactants or polystyrene. Dimethyl sulfoxide has been used as a novel oxygen donor for the catalyst-free formation of colourless silsesquioxanes. The products are organic- inorganic hybrid (nano)composite materials where the organic modifications (methyl, ethyl, hexyl or phenyl groups) are covalently attached to silicon. Spherical particles of ca. 1 mum diameter were obtained in the non-hydrolytic sol-gel synthesis of methyl-modified silicate particles under certain conditions such as using BrijRTM 52 as surfactant and using DMSO as oxygen donor. Product yields were generally high, and the products were characterised by Fourier transform infra-red (FT-IR) spectroscopy, 29Si nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM) and elemental analysis (EA). Selected ormosils were used as additives to an epoxy resin system (XLVR16-2) .as toughening agents. Compatibility of the hybrid with the epoxy was varied by changing the nature of the organic group in the hybrid. The ormosil additives were uniformly dispersed throughout the resin matrix. The fracture toughness of the resin was improved using 5 parts per hundred of the resin of ethyl-modified silicate (50 % greater than that of the unmodified resin) maintaining the excellent thermal properties of the system. Epoxy resin systems were characterised by SEM, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and fracture toughness testing. Emulsion polymerisation of polyhedral oligomeric silsesquioxanes (POSS) with methacrylate functionalities covalently attached to them was also investigated. Two types of polymerisation were carried out: homopolymerisation of POSS monomers, and copolymerisation of POSS monomers with methyl methacrylate (MMA) at different molar ratios, which lead to spherical nanoparticles ranging from ca. 5 to 15 mm in diameter.

This study combines cure kinetics modelling and thermal and ultrasonic cure monitoring to characterize the cure state of a complex commercial modified epoxy thermosetting system of industrial importance containing two epoxies, diethylene triamine hardener, external catalyst, aliphatic reactive diluent, and mica. Both catalyst and reactive diluent in the formulation of two epoxy resin mixture keep this complex system odd from others and to some extent a new one to report cure kinetics to the best of our knowledge. The cure was monitored using differential scanning calorimetry (DSC) and broadband ultrasonic techniques over a group of isothermal cure temperatures within corresponding acceptable time scales. The sensitivities of both techniques to the chemical, physical, and mechanical changes associated with each part of the cure was discussed comprehensively and critically together with an inspection of the similarities between them coupled with qualitative and quantitative correlations. An in depth details analysis of the chemical cure kinetics of the investigated system was presented utilizing the model free iso-conversional method coupled with the light of physics of advanced kinetics research. The modelling of the calorimetric cure kinetics of the epoxy system under study was developed utilizing the empirical approach of fitting of the experimental data to various kinetic models. The best fit model which best possibly describe the non-typical autocatalytic cure behaviour of the resin system and predicts the reaction course was evaluated and analyzed in details. Utilization of the maximum attained conversion at a specific curing temperature enables this model to most closely simulate the curing reaction under both chemical controlled and diffusion controlled conditions with almost a reasonable degree of satisfaction over the entire range of conversion and temperature studied without the a priori need of a glass transition temperature model. The non-conventional autocatalytic effect and prediction of the trimolecular catalysis mechanism of the curing reaction was found to be manifested in temperature dependence of reaction orders, which was elucidated and justified. In comparison to other epoxy resins without reactive diluents, the analysis of our data shows that most possibly, the reactive diluent increased the maximum value of calorimetric conversion and reaction rate, reduced the viscosity, while the values of activation energy and process parameters remained within the typical values of epoxy formulations and the crosslink density was unaffected. The performance of each particular model tested was discussed along with their comparisons. Implementing diffusion factor in conventional models some useful information associated with the diffusion controlled kinetics related to our data were explored. The cure kinetics was also analyzed from both kinetic and thermodynamic viewpoint in the context of Horie model. This approach we employed, is, to some extent uncommon, can contribute towards a new way of characterization and the critical understanding of the cure reaction from the microkinetic standpoint providing information of the effect of reactive diluent on kinetics, regarding reaction pathways, kinetic homogeneity I inhomogeneity associated with reaction phase and the properties of the end product which are important to monitor and ultimately control the cure to attain desired properties in the end material. A TTT diagram of the cure process of this system was also constructed. The ultrasonic compression wave velocity was demonstrated to be the most interesting and potential parameter for monitoring and characterizing the cure process at all stages which provided with the information of degree of mechanical property development and can detect gelation and vitrification that occur during cure. Therefore, ultrasonic velocity measurement could be exploited for non-destructive on-line process control in an industrial environment. It was demonstrated that ultrasonic compression wave velocity can be used as a predictor of calorimetric conversion measurements and thus can be used to track chemical reaction online which is of potential importance for cure monitoring. Though system specific, the methodology we utilized, at least in part, constitutes a novel way of quantifying the degree of cure of a commercial epoxy thermoset network from ultrasonic longitudinal velocity measurements which is interesting and promising. It was found that the DSC is much more sensitive to changes occurring at the early stages of the cure but is relatively insensitive to the changes occurring at the latter stage. Ultrasonic compression wave velocity shows a better sensitivity at the end of the cure. It was also demonstrated that ultrasonic compression wave attenuation, real and imaginary parts of compression modulus, ultrasonic loss tangent and associated central relaxation time, also provided information of the material state and the cure process as well. The end of cure ultrasonic data, in general, provide a convenient assessment of final product quality.

Le but de ce travail de thèse est d’obtenir une compréhension des mécanisme d’action des revêtements intumescents à base d’époxy afin de fournir des perspectives pour le développement de nouveaux systèmes de protection contre le feu. La formulation intumescente est un système très complexe. Ce travail se concentre en particulier sur les composants clés dont la compréhension des mécanismes d’action était absente. Tout d’abord, les mécanismes d’action des borates ont été étudiés en incluant des modifications chimiques et thermo-physiques; la combinaison des résultats obtenus sous différents aspects permet de comprendre son mode d’action. D’un côté, les borates en particulier l’acide borique ont été mentionnés comme Cancérogènes, Mutagènes, Reprotoxiques (CMR); la substitution de ces composants est nécessaire. Les résultats soulignent le rôle important et la réactivité élevée du zinc (de borate de zinc), ce qui suggère le développement de nouveaux systèmes en incorporant un composé à base de zinc au lieu du borate du zinc. Deuxièmement, l’effet du CaCO3 sur les propriétés de protection contre le feu et son mécanisme d’action dans le revêtement intumescent ont été examinés. L’ajout de CaCO3 améliore les propriétés de protection au feu et d’adhérence/cohérence du revêtement et son mécanisme d’action était justifié. De plus, plusieurs carbonates (MgCO3, ZnCO3, Na2CO3, K2CO3) en tant qu’ingrédient intumescent ont également été examinés. L’utilisation de MgCO3 comme ingrédient intumescent est favorable pour les propriétés de protection contre le feu du revêtement ainsi que pour l’utilisation de CaCO3. Dans ce travail, les mécanismes d’action des borates et des carbonates ont été étudies. Les résultats suggèrent le développement de nouveaux systèmes utilisant des ingrédients alternatifs tels que le composé à base de zinc ou MgCO3. / The goal of this PhD work is to get an insight into the mechanisms of action of epoxy based intumescent coating to be able to provide the outlooks for the development of novel systems of higher protection against fire. The intumescent formulation is highly complex system. This work focuses particularly on the key components of which the understanding of the mechanisms of action is still lacking. Firstly, the mechanisms of action of borates were investigated in both chemical and thermo-physical modifications; the combination of the results obtained from different aspects allows drawing its mode of action. On the one hand, borates in particular boric acid have been mentioned to be Carcinogenic, Mutagenic, Reprotoxic (CMR); the substitution of these important intumescent components are necessary. The results point out the important role and high reactivity of zinc (i.e. from zinc borate), this suggests the development of novel systems by incorporating zinc based compound instead of zinc borate. Secondly, the effect of CaCO3 on fire protective properties and its mechanism of action in intumescent coating were examined. The addition of CaCO3 improves the fire protective properties and adhesion/cohesion of the coating and its mechanism of action was fully justified. Additionally, various carbonates (i.e. MgCO3, ZnCO3, Na2CO3, K2CO3) as intumescent ingredient were also examined. The use of MgCO3 as intumescent ingredient is beneficial for the fire protective properties of the coating as well as the use of CaCO3. In this work, the mechanisms of action of borates and carbonates were fully examined. The results suggest the development of novel systems with using the alternative ingredients such as zinc-based compound or MgCO3.