Development, characterisation and validation of functionalised polymer-based materials for smart applications

Abstract

The understanding of new materials and methodologies have led to an exponential progress of polymer science. Recent advances in polymer modification and processing techniques have endorsed amazing functionalities to cover the features required in specific applications. The aim of this thesis was to develop appropriate research strategies of functionalisation of polymers based on a multi-stage scheme, involving the design, processing, characterisation, and validation to meet the requisites of specific durability and service life. This methodology was applied to provide alternative solutions that respond to service requirements in several applications, such as photo-stabilisation of polyolefins for outdoor applications, polyelectrolyte membranes for fuel cells, and scaffolds for tissue engineering. The functionalisation of polymers was performed by macromolecular modification, blending, and combination with micro and nanoparticles. Processing techniques such as solvent-casting, hot-melt extrusion, compression moulding and electrospinning permitted to obtain specific physico-chemical features, which were determined by spectroscopy, chromatography, microscopy and thermal analysis. In addition, a validation procedure was performed by means of real or simulated service conditions, which helped assess the suitability of the functionalised polymer-based materials. In the field of the photo-stabilisation of polyolefins, polydisperse silicon particles provided high stability to raw non-additivated polypropylene (PP) against sunlight irradiation in terms of appearance, thermal stability and mechanical properties. In order to design polyelectrolytes for fuel cells, the cross-linking and sulfonation of poly(vinyl alcohol) (PVA) with sulfosuccinic acid (SSA) was considered. The combination with graphene oxide (GO) and chitosan (CS) was also explored. The new functionalised films or nanofibrous polyelectrolytes, offered dimensional and thermal stability under service conditions, were electric insulators, and revealed promising performance in terms of proton conductivity. Functionalised blended scaffolds of polycaprolactone (PCL) and gelatin (Ge) were obtained for tissue engineering. The control of the dissolution time into a formic/acetic acid hydrolytic solvent prior to electrospinning permitted to obtain tailored scaffolds, in terms of nanofibrous morphology, physico-chemical performance and biocompatibility. The scaffolds with balanced ratios of PCL/Ge promoted in vitro cell adhesion and proliferation, as well as suited appropriate durability under in vitro conditions and during the in vivo implantation.