Aspects of segregation phenomena in polyester resin blends.

Abstract

The concept of phase separation offers one route of applying a primer and top-coat in a single coat. In such systems, two incompatible resin materials are blended in a common solvent, which then phase separates as two coating layers upon solvent evaporation. The goal of this thesis is to provide an insight into the phase separation phenomena based on two commercial, incompatible, resins Dynapol and Synoalc which are both polyesters. To accomplish this, two complementary areas of study were undertaken: surface analysis of the constituents that compose the system and interfacial analysis of the phase-separated coating. In this study, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) have been utilised. Ultra-low-angle microtomy (ULAM) has been used for the exposure of the buried interfacial layers. Principal component analysis (PCA) and non-negative matrix factorization (NMF), were used for the development of data analysis pre-processing procedures for interpreting the ToF-SIMS spectra and imaging datasets. Due to the complex nature of the commercial resins, containing similar monomer constituents, six model polyesters were synthesised specifically for the structural characterisation of the commercial systems. The model resins were synthesised under a systematic manner i.e. by precisely designing their chemical structure in relation to the monomer composition of the commercial systems. These spectra permitted the determination of the molecular composition of Dynapol and Synoalc accurately. The use of PCA in combination with the model resins permitted the discrimination of Dynapol and Synoalc on the basis of glycol monomer, with the identification of key diagnostic ions necessary for ToF-SIMS imaging. Using ToF-SIMS-NMF image analysis, the identification, differentiation and visualisation of the phase separated constituents throughout the bulk was achieved. The parameters influencing the phase segregation process were identified and the dominant driving forces of layer formation were attributed to: i) minimisation of the surface energy of the whole system, ii) the influence of polarity difference between the phase separating layers and iii) the presence of pigmentation that supports and inhibits the mobility of the phase separated resin layers in favour of layer formation.