The need for sustainable development has raised interest in using natural fibres as reinforcement in polymer composites to replace synthetic fibres. Many studies have been performed on composites made of one kind of reinforcement, i.e. 100% plant fibres (jute, hemp, flax, sisal) or 100% mineral fibres (basalt). The results have shown that generally natural fibre composites do not fully attain the expected levels of mechanical performance due to poor fibre/matrix interfacial adhesion, an issue that demands an in-depth analysis and optimization of the interface quality at the micro-scale. A great deal of research over last fifteen years has been carried out into the interface between natural fibres and a huge range of polymer matrix materials, but most of the suggested treatments depend on the use of chemicals that lower the green character of such natural fibres along with their mechanical properties. In this framework, this research project aims to specifically design greener surface treatments based on peptides (poly(amino acids)) with tailored polarity to increase the compatibility of natural fibres with a range of polymer matrices without adversely affecting the mechanical properties of the pristine fibres. This study will involve the characterization of treated fibres in terms of their mechanical and thermal properties to assess the effects of surface treatment and optimize the related process parameters. The indirect evaluation of the influence of interfacial adhesion on the composite properties will be performed by mechanical testing of the conventional, macro-scaled composites.
Lightweight, high stiffness-to-weight ratio, consumer awareness regarding recyclable and biodegradable materials, are advantages of the use of natural fibre composites. Within the natural fibre composites market, the automotive segment is expected to remain the largest application by both value and volume. Increasing concern for passenger safety, government mandates for better fuel economy, and end-of-life vehicles directive are the major driving forces that spur growth for this segment. Europe is expected to remain the largest market due to higher acceptance level of environmentally sustainable composite materials by automotive OEMs, government directives, and growth in end use industries. Nonetheless, a higher acceptance rate of sustainable composites is to be expected only after successful implementation of new strategies to improve fibre/matrix adhesion. The management of natural resources and the reduction of the environmental impact of materials and manufacturing technologies is a key area of importance. The way society currently produces goods and services is unsustainable and contributes significantly towards many of today's environmental problems. It is here suggested that the present research project can assist the development of focused policies on the objective of reducing the carbon footprint and increasing the recyclability of materials used in several industrial sectors: this is likely to be a very long process due to the complexity of factors involved in these applications, but the project can offer a good drive towards this move. In this regard, the key and innovative aspect of the proposed synthetic route relies on the protection-deprotection strategy for the polar groups Z gathered in Scheme 1. In the case of acidic residues (Asp, Glu), suitable esters should yield the corresponding poly(amino acid)s, which incorporate carboxylic acids or their metallic salts via basic or acid hydrolysis. Poly(amino acids) incorporating amino or ammonium groups will be synthesized by means of a similar strategy. For example, the N-Phthalimido NCA prepared from N-phthalimido lysine can yield the corresponding polymer, from which the corresponding poly(lysine) derivative can be readily obtained by means of reaction with methylhydrazine. In order to get the best interactions between poly(amino acid)s and natural fibres, it is possible to alternate different monomers in the ROP processes. A detailed understanding of the factors influencing the microscale load-transfer mechanisms will be beneficial to tune the level of adhesion at the fibre/matrix interface through adjusting both the heterogeneity of surface morphology and chemical reactivity. This will potentially increase the overall load-bearing capacity of the resulting composites, thus broadening their exploitation at industrial level.