Abstract
This PhD dissertation details the synthesis and characterisation of a new family of biobased thermoplastic polyurethanes based on 2,5-furandicarboxylic acid polyesters to generate materials with a reduced carbon footprint. Moreover, their petrochemical isophthalate analogous were developed to compare and assess the differences in reactivity and properties induced by the two different aromatic diacids. The synthesis of the polyesters was carried out with two different diols, 1,3-propanediol and 1,6-hexanediol, and a variety of different molecular weights, in the range of 1000-2000 g/mol. These polyesters were then introduced into a large number of polyurethane formulations, consisting of two different diisocyanates, methylene diphenyl diisocyanate and hexamethylene diisocyanate and hard segment contents (10, 30 and 50% molar fraction). This large formulation domain has enabled us to gain a deep insight into the effect that the aromatic polyesters have on the morphology and mechanical properties of these new thermoplastic polyurethanes. To gather the information about how the different diacids affect the morphology of the polyurethanes, and how that impacts their mechanical properties, a large array of different techniques was employed. Differential scanning calorimetry, small angle X-ray scattering and wide-angle X-ray scattering were selected to gain an insight into the chain mobility, phase segregation and crystallinity of the materials. Moreover, the hardness, tensile strength and shape memory properties of the studied materials were measured and correlated with the variations in morphology between the different polyurethane formulations. The materials synthesised in this work exhibit exceptional mechanical properties, achieving polymers with high hardness at low diisocyanate contents and shape memory polymers with outstanding actuation strength, overcoming those of the current state-of-the-art. Overall, the properties of the studied polyurethanes depend on just one factor, the supramolecular interactions present in the materials. These supramolecular interactions govern all of their characteristics, from their microphase morphology and chain mobility to their mechanical and shape memory properties. These supramolecular interactions can be divided into two groups, the cohesion forces within each of the domains, hard segment and soft segment, and the interactions between them. As a general trend, strong cohesion forces result in polymers with a high segregation and crystallisation capability, while strong interactions between the phases inhibit the segregation process, limiting the crystallinity of the materials. The degree of phase segregation of the materials is responsible for many of their mechanical properties and therefore, the factors that reduce this phase segregation produce materials with the worst mechanical properties. Accordingly, the low interaction of the aliphatic hexamethylene diisocyanate moieties from the hard segment, with the highly aromatic soft segment domains, results in materials with a high phase segregation and therefore, excellent mechanical properties, namely, tensile strength, and actuation strength. Likewise, the high cohesion forces of the soft segment containing 2,5-furandicarboxylate moieties induce the segregation of the polymers, resulting in polymers with outstanding mechanical properties.
Originalsprog | Engelsk |
---|---|
Bevilgende institution |
|
Vejledere/rådgivere |
|
Dato for forsvar | 27. okt. 2022 |
Udgiver | |
Status | Udgivet - 27. okt. 2022 |
Udgivet eksternt | Ja |