AbstractIn this research, various concentrations of layered silicate based on vinyl ester nanocomposites were prepared and the effect of the incorporation of layered silicate into the polymer matrix on the different properties was investigated.
The characterisations of interlaminar structure of the nanocomposites by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectrometry and Transmission Electron Microscopy are undertaken. This study revealed that the incorporation of layered silicate into the polymer matrix formed uniformly distributed nanocomposites structure at low clay content (i.e. 1, 2, and 3 wt.%). At 4 wt.% clay loading, the partially intercalated / exfoliated nanocomposites system was observed as proved by the different characterisations' results. However, the addition of more clay such as 5 wt.% resulted in decreasing the overall intercalation level due to the existence of aggregation layers.
The addition of layered silicate into the vinyl ester matrix increased the environmental, mechanical and thermal properties, and the enhancements were correlated to the results of the characterisations' outputs. The mechanical properties such as flexural, tensile, nanoindentation, impact, and creep properties of neat samples were improved by the incorporation of layered silicate. The presence of layered silicate into the polymer matrix increased the tensile strength and modulus and flexural strength and modulus up to 4 wt.% clay content. The level of intercalation of nanocomposites played an important role in the improvements of the mechanical properties. So, the tensile and flexural properties were correlated to the characterisations' results. At 5 wt.% clay content, the modulus and strength of both tensile and flexural were reduced due to the effect of aggregation layers where the interfacial interaction between the layered silicate and the polymer is reduced.
The nanoindentation test showed that the addition of layered silicate increased the reduced modulus and hardness of the nanocomposites compared to the neat vinyl ester. The presence of only 1 wt.% clay loading increased the hardness and reduced modulus at up to 13% and 11% respectively compared to the pristine polymer. The improvement percentage of hardness and modulus at 2 wt.% were 31% and 19% respectively. The ultimate improvements were observed at 4 wt.% clay loading, where the enhancements in hardness and modulus were 56 and 50% respectively compared to the neat vinyl ester. Further addition of clay resulted in marginal reductions in these properties.
The impact properties of the neat vinyl ester and the nanocomposites were investigated using a low velocity impact testing. The addition of layered silicate into the polymer matrix showed that an optimum range of nanoclay reinforcement in the vinyl ester matrix can produce enhanced load bearing and energy absorption capability compared to the neat matrix.
Likewise, the influence of the clay addition into the neat polymer on the creep relaxation behaviour at 25°C and 60°C was studied. In both cases, the presence of the layered silicate remarkably improved the creep behaviour. The strain reduction is related to the clay concentration level. The neat polymer illustrated higher strain compared to the nanocomposites samples.
Moreover, the addition of layered silicate into the polymer matrix improved the thermal properties. Thermal Gravimetric Analysis (TGA) showed that the nanocomposites represent better stability compared to the neat polymer. The onset temperature of the nanocomposites was higher than the neat polymer. At 1, 2, 3, and 4, wt.% clay content, the improvements in onset temperature were 7 %, 4.2 %, 4 %, 2.5 % respectively compared to the virgin polymer. In addition, the incorporation of layered silicate into the polymer matrix increased the thermal conductivity. At 4 wt.% clay, the thermal conductivity was increased by 12% compared to the neat polymer. Differential Scanning Calorimetry (DSC) is also performed in order to study the effect of the addition of layered silicate into the polymer on the glass transition temperature. The level of intercalation is critical to the Tg values. The nanocomposites represented a marginal reduction in Tg, however at 4 wt.% clay loading the Tg was as same as the neat polymer which was traced to the well-dispersed structure.
Furthermore, the study of environmental measurements, which included the water absorption behaviour and its effect on the nanoindentation test, was investigated. The improvement of the water repellence behaviour was observed for the nanocomposites. The enhancements in barrier properties were related to the clay content. At 5 wt.% clay loading, the reduction of water uptake was about 1266% compared to the neat polymer. The hardness and elastic moduli after water absorption was reduced due to the effect of water molecules entering into the polymer chains. However, the higher amount of clay reinforcement led to less reduction in hardness due to the formation of the barrier properties by the layered silicate. The hardness of neat polymer after immersing in water was reduced by 30% whereas the hardness of 5 wt.% nanocomposites showed only a reduction by 10.3% compared to the dry sample.
|Date of Award||Jan 2014|
|Supervisor||Hom Dhakal (Supervisor), Zhong Yi Zhang (Supervisor) & Nick Bennett (Supervisor)|