Biodegradable Polyesters Blends for biomedical applications. A Comprehensive Study on the Preparation and Characterization of Poly(lactide)/Poly(ε-caprolactone) Physical and Reactive Blends

This PhD work has been intended first of all to find a new suitable class of materials to employ in the biomedical and environmental field. Starting from literature reviews and the acknowledgment of the state of art in the field of biodegradable polyester blends, the attention was put on the reactive blending process, to obtain miscibility among two polymers of high commercial and academic interest for their specific and complementary properties, the Poly(lactide) (PLA) and the Poly(ε-caprolactone) (PCL). PLA/PCL physical and reactive blends, with Ethyl Ester L-Lysine Triisocyanate as reactive agent, have been manufactured and analysed by means of several characterization methods. It has been found that the reactive mixing conducted during the thermo-mechanical processing of blends, resulted for low LTI concentrations, into properly miscible systems, despite the evident immiscibility of the pure components in the molten state, confirmed by the large amount of literature in this regard. High LTI concentration mixtures, showed a transition from a proper ductile thermoplastic, to a solid-like elastic dominant material, as shown by moduli build-up and frequency response rheological curves. Furthermore, mechanical tests have shown how, at all LTI concentrations, the polymer ductility was maintained and, at the same time, a great increase in tensile resistance characteristics was noticed. These effects are apparently proportional with the reactive agent content. Electronic microscopy, together with rheological analysis, underlined the appearing of a proper third phase, a densely cross-linked part resulting from the co-polyesterurethane structures, obtained by reactive mixing. As a preliminary study, to underline the differences between a physical and a chemical method of emulsification, diblock PCL-b-PLA copolymers were also synthesised, used as additives and their effects evaluated. The work has been conducted at the University of Messina, at the Department of Engineering, regarding the blends preparation and the mechanical, thermal, and surface characterization on processed samples. Jointly, at the Department of Materials of Loughborough University, have been instead studied the Rheological, morphological and chemical properties of the blends.