2. OBJECTIVES OF THE WORK
The increasing efforts in the development of bio-based polymeric materials in recent years are motivated by the basic concept of meeting the sustainability criteria for industrial development in the third millennium and independence from fossil feedstock. Within this framework, our research group is currently involved in assessing the potentiality of some agro-industrial overproduction and by-products in the formulation of eco-compatible bio-based polymeric materials displaying, among the other, the propensity to biodegrade under controlled environment conditions. In this view, the present PhD thesis was focused on the development of new formulations and composites based on the fully biodegradable microbial poly(3-hydroxybutyrate) (PHB), and the evaluation of the environmental impact related to the production and application of some representative PHB based composites.
Up to now, the application of this microbial polyester on an industrial scale has been hampered by several factors, such as:
o The secondary crystallization, which occurs after the crystallization from the melt with consequent formation of new lamellae in the amorphous phase and loss of plasticity.
o The slow nucleation rate, which leads to the attainment of large and fractured spherulites and affects negatively the final properties of the products.
o The narrow processability window, due to the high thermal degradation rate during melt processing.
o The high cost, due to the relatively limited productivity by the microbial-driven process.
Therefore, three different experimental tasks were developed within the PhD work.
PHB stabilization with commercial additives. Aiming to the reduction of PHB thermal
degradation during melt processing, the polymer was melt processed in a torque rheometer in presence of commercial stabilizing additives. A mixture of phenolic and organophosphitic antioxidants and a carbodiimide-based antihydrolysis compounds were tested. The mixtures were then characterized regarding their chemical structure, molecular weight, thermal and mechanical properties.
PHB – Natural fibres composites. PHB based composites containing sugar cane bagasse
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considered as a waste in the industrial production of sugar from cane, the application of SCB for this purpose could increase the positive environmental value of these formulations, along with a reduction of weight and price. Prior to processing, natural fibres were treated by esterification and alkalization reactions, in order to improve dispersion and adhesion with the continuous PHB matrix. PHB based composites were melt processed in a torque rheometer and then characterized regarding their morphological and structural behaviour, molecular weight, thermal properties, mechanical and dynamic mechanical properties.
PHB – Organophilic montmorillonite composites. Composites based on PHB reinforced
with organophilic montmorillonite (OMMT) modified with various surfactants were prepared by solution casting and melt processing techniques. OMMTs are very appreciated as polymeric fillers, as they are able to enhance, even at low concentration, polymer matrix properties such as thermal stability, mechanical prformance, and barrier to gas permeation. Composites were characterized regarding their morphological and structural behaviour, molecular weight, thermal properties, mechanical and dynamic mechanical properties, and oxygen permeability. Particular attention was focused in the characterization of melt processed composites containing silane modified OMMT, due to the high potential showed by this type of materials.
Finally, a cradle-to-grave environmental LCA of some representative PHB based composites, containing both SCB and OMMT, was performed with the purpose of assessing the potential environmental benefits that might have been reached with the application of these new biodegradable materials instead of petrochemical polymers. Commercial products investigated were cathode ray tube (CRT) monitor housing (conventionally made of high impact polystyrene, HIPS) and the internal panels of an average car (conventionally made of glass fibers filled polypropylene, PP-GF). This evaluation was performed considering two key environmental parameters, i.e. non-renewable energy use (NREU) and global warming potential over a 100 year time horizon (GWP100).
