Polymer/clay nanocomposites consisting of an epoxy resin matrix filled with organoclays have been investigated. The main objective of this study was to determine which combination of components led to the greatest enhancement in properties of the epoxy resin. Exfoliation of the clay was desired, as exfoliated nanocomposites are known to exhibit great improvements in mechanical properties [1]. The epoxy resins studied were di-functional DGEBA and tetra-functional TGDDM. The epoxy resin was cured with three different hardeners, these included: the high functionality amine hardener, TETA, and two anhydride hardeners, accelerated MTHPA and pure HHPA. The three organoclays used, contained alkylammonium cations and were also compared to the unmodified clay. Morphology was investigated by XRD and TEM, and the flexural properties of the resulting nanocomposites were studied. The effect that the addition of an organoclay has on the cure of the epoxy resin was investigated using MDSC. Both the temperatures required to cure the resin with, and without, the clay, and any changes in the total heat flow that occurred were studied. The Tg++ of the cured nanocomposites was also measured using MDSC. The heat flow results indicated that the clays added to the epoxy resins act as a physical barrier, which prevents the resin from reaching full cure. In the higher functional resin, the addition of clay resulted in a significant decrease in the total heat flow, suggesting that a large amount of epoxy remains uncured, and, as a result, there should be a reduction in the amount of cross-linking. The lower cross-link density led to a significantly lower Tg and the mechanical properties were also poorer. The reactivity of the hardener towards the resin was found to have the greatest impact on the cured nanocomposite morphology. Intragallery polymerisation occurring at a faster rate than the extragallery polymerisation causes exfoliation. In order to achieve a balance that favours intragallery polymerisation, it was found that the curing reaction was required to be catalysed by the alkylammonium cation of the organoclay, and not catalysed by other means. The DGEBA cured with HHPA provided the largest layer expansion in the clay structure due to the alkylammonium cation catalysing the anhydride ring-opening reaction. The effect was not seen with TGDDM due to the tertiary amine in its structure. The accelerator within the MTHPA assisted extragallery polymerisation of the resin and the TETA cured readily without additional catalysis.

Melding is a novel process which offers a promising route to creating seamless bonds, by partially curing two laminates in a controlled manner using a Quickstep chamber and subsequently co-curing them. Previous research has focused on melding lap joints in the x-y plane of a composite, whereas this study investigates through-thickness melding, or melding in the z-plane of a composite. In this process, two composite stacks were exposed to heat from one side and actively cooled on the other through the z-axis. The two semi-cured parts were then co-cured creating a monolithic part with a seamless bond.The initial stage of the project developed the semi-curing process. After unsuccessful attempts to produce a semi-cured part in a general purpose Quickstep chamber, due to excessive heat transfer, the process was moved to a hot press with independently controlled platens. The hot press succeeded because the platens were separated from each other by the composite plate, unlike the Quickstep bladders which, as they are designed to conform to the part, came into contact allowing for heat transfer. Thermocouples were embedded every 15 plies to quantify the temperature profiles generated through the laminate stack.The next stage of the project developed a process of joining the semi-cured panels to form a through-thickness melded part. The final process involved constraining the sides of the panel with cork edge dams and inserting woven glass fabric at the corners to allow for gasses to escape. However, the outer parts of the fully melded panel exhibited excessive porosity which had an adverse effect on mechanical properties. For example, whereas tensile and flexural moduli measured for material from the edges of the panels were comparable to values reported in literature, the properties of samples from the middle of the panels deteriorated significantly due to the porosity. Mode I interlaminar fracture energy was approximately 10% lower than values measured for panels fabricated in an autoclave.The entire curing process, from semi-curing to a fully melded panel, was characterized extensively. Differential scanning calorimetry was used to determine the degree of cure and values of glass transition temperature (Tg). The degree of cure of the material exposed to the hot side was approximately 50%, the middle 25%, whereas the cold side was only 15% cured. A corresponding Tg profile through the curing process was developed in which the Tg varied from 0 degrees C for the uncured resin to 245 degrees C in highly cured samples. After melding the sample, the degree of cure was found to be in excess of 99%. Rheological studies were carried out to determine the effects of the semi-curing process on resin flow during the melding cycle.Results showed that there was a large transition zone between uncured plies and solid (cured) plies.This thesis demonstrated the broad feasibility of through-thickness melding as a process to create thick composite laminates. However, the complexity of the process gives rise to thermal and rheological phenomena which affect the structural and chemical properties of the fully melded part. The process must therefore be engineered with these factors in mind in order to create a high quality part.