Relating polymer architecture to water absorption properties in a waterborne coating

Abstract

In this thesis, the relationship between the polymer architecture and the water absorption properties of a commercially available waterborne anticorrosion coating are investigated with the purpose of improving the barrier properties. \\
To explore this relationship, the polymer architecture had to first be characterized. This is because waterborne polymers present a particular structure that is not well understood. These coatings are made from a suspension of polymer particles in water. This means that a heterogeneous structure is expected to arise despite the homogenization processes happening after the drying process. The main hypothesis of the thesis is that such chemical and physical heterogeneities can explain the relationship between polymer architecture and water absorption.
To characterize these heterogeneities, positron annihilation spectroscopy experiments and the deconvolution of the continuous relaxation spectrum were used.
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The deconvolution of the relaxation spectrum allowed probing of the relaxation mechanism present in the material. An intermediate relaxation mechanism with a characteristic time in between the main chain relaxation and the terminal flow was observed. The analysis of the dependence of this mechanism on structural parameters such as the particle size and the annealing process allowed establishing it as the interdiffusion phase for smaller particles and the hydrophilic interface for bigger particle sizes. This confirms that a chemically and physically heterogeneous area
exists in the material and characterizes its dependence on structural parameters.
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The Positron Annihilation Spectroscopy experiments allowed probing the physical structure of the material by studying its defect density and free volume. Two main results were obtained from this technique. \\
Firstly, the characterization of the bulk of the material confirmed the results of the thermomechanical experiments, confirming the technique can be applied to this complex polymer. Despite the good agreement between the different techniques, however, the results were not sufficiently accurate to study the effect of water diffusion through the material, suggesting more efforts are necessary to improve the technique. \\
A second interesting result was the observation of a physically heterogeneous structure along the thickness of the coatings, which was hypothesized to be related to the drying process. More experimental evidence could help not only improve the understanding of this structure, but also shed light on the incredibly important drying process.
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Relating the polymer architecture to water absorption revealed how the physical heterogeneities and the free volume present at the interdiffusion phase are not influencing the water absorption. Rather, it is the polar interface that is a leftover of the drying process to control the water absorption. \\
This can be exploited to improve current anticorrosion waterborne coatings by reducing the particle size to increase the coherence of the film while at the same maintaining the polar character of the interface.