• polymer matrix composites
• Natural fibres
• morphology
• functionalization
• compatibilization

The present work is focused on the development of innovative and low environmental impact polymer composites with controlled structure and properties for potential applications in several advanced sectors (i.e.,food packaging, bio-engineering, electrical & electronics and automotive applications). In this thesis, the preparation, chemical modification and characterization of different types of thermoplastic polymers and their blends - such as poly(ε-caprolactone) (PCL), ethylene-co-vinyl acetate (EVA), poly(lactic acid) (PLA), Mater-Bi (MB) and polyolefins (PE, PP, PS) composites – containing various natural fibres (hemp, micro- and nano-fibrillated cellulose) have been reported.

Owing to the incompatibility of polymer matrices (hydrophobic) with cellulosic fibres (hydrophilic), either polymer or fibres have been functionalized, or a compatibilizer has been added during processing of composites. The functionalization was carried out by esterification or by grafting with bi-functional monomers - such as glycidyl methacrylate (GMA) and maleic anhydride (MA) - able to react with both polymer and fibres during melt mixing.
The composites were prepared by melt mixing in Brabeder Plasti-Corder and characterized by microscopic analyses (OM, SEM, TEM, AFM), diffractometry (WAXS), spectroscopy (FT-IR, NMR), calorimetry (DSC, TGA), tensile mechanical and rheological tests. Results demonstrated that morphology, phase behaviour, interfacial interactions, rheological and mechanical properties of composites were strictly affected by the component structure, composition and mixing processes.

For binary PCL/CF and EVA/CF composites the effect of functional modification of matrix (with GMA and MA) and fibres (with butanoic acid) on the final properties of materials was examined. Results obtained for composites with polymer blend matrix (PLA/EVA-GMA/CF) demonstrated that phase morphology and mechanical properties were influenced by the polymer-polymer miscibility, and properties varied with blend composition. In the case of ternary composites of biodegradable MB, polyolefins and hemp fibres (H), the crystallization behaviour, morphology and mechanical strenght of the composites were found to be markedly affected by the phase dispersion and compatibilizer type. A significant improvement of tensile modulus and strength was recorded for ternary MB/PE/H and MB/PS/H composites as compared to binary composites (MB/H). The results indicated that incorporation of polyolefins in the biodegradable matrix may have significant advantages in terms of properties, processability and cost.
Moreover, a novel approach to the preparation and functionalization of PLA bio-composites with nano-fibrillated cellulose (NC) has been reported. The effect of different processing strategies on the phase dispersion of NC, as well as on the thermal and mechanical properties of these systems has been analysed. To improve the dispersion of NC in PLA either functionalization of NC or PLA by GMA grafting, or inclusion of NC in poly(vinyl acetate) (PVAc) – which is miscible with PLA - were applied. Better dispersion of NC was observed for PLA nanocomposites containing functionalized components and/or NC included in PVAc. These systems – as compared to the unmodified PLA/NC composites - display a higher degree of fibre dispersion with improved tensile properties and thermal stability.