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Sustainable Surface Technology for Multifunctional materials

Final Report Summary - SURFACET (Sustainable Surface Technology for Multifunctional materials)

The main goal of SURFACET project was the development of an innovative supercritical carbon dioxide (SCCO2) surface technology, applicable to existing and new high performance functional products. SURFACET project was covering the topics proposed by the European Commission in the Priority 3 'Nanotechnologies and nano-sciences, knowledge-based multifunctional materials and new production processes and devices' in the VI FP (2004), and, specifically the project was covering the topics of the call 'Materials processing by radically innovative technologies'. It was expected that by developing this technology, breakthroughs to come not only from the new method but also from the new obtained products, since surface control is very important for production of new high performance functional products. In this respect, the development of SCCO2 technology has allowed to break some classical boundaries between types of materials related to processing methods, since a similar technology can be applied to both inorganic and organic matrixes or even to hybrid composites.

This lead to the last very important point proposed in SURFACET project: to show that SCCO2 technology is a crosscutting technology serving multisectorial applications by developing general SCCO2 procedures that enable the creation of complex surface structures and at the same time, enabling the production of unique product characteristics in relation to composition, purity, and effectiveness. The main goal of SURFACET has been achieved using an end-product driven approach (retroprocessing) by developing generic SCCO2 procedures integrated with advanced reaction-engineering concepts, that enable the creation of complex-shaped structures with controlled size, morphology and surface or interface:
(i) Study case systems: A+A ? A (or A') and A+B ? C. Because of the additional degree of freedom on reaction control related to the density of SCCO2, single step processes have been designed. Process and reactions have been carried out homogeneously in the solution bulk and heterogeneously on specific surfaces or confined into microreactors (microemulsions and zeolites).
(ii) SCCO2 technology has been used for the production of existing and new high performance products with unique characteristics in regard to composition (purity, sterilisation), size (micro ornanoscale) and architecture (fibres, foams). Materials with a large surface to volume ratio are generally extremely reactive since they have a high number of surface atoms with a low coordination number. It has been demonstrated that SCCO2 is a non-aggressive solvent technology adequate to manipulate these kinds of materials without damage.

The choice of solvent must be done in an early stage of chemical industrial development and is usually not questioned unless dramatic problems are encountered during up-scaling. Hence, environmentally friendly solvents must be considered in the used synthetic pathway already at a lab-scale. The organic solvents and additives presently used for the manufacturing of most products have well-known disadvantages like toxicity, flammability and environmental concerns. Furthermore, with increasing complexity and size reduction to nanoscale in new materials, classical solvent approaches are destructive because the used liquids destroy the functional surfaces they are helping to create.

This is due to viscosity and surface tensions. On top of this, obtaining end-products free of residual solvents becomes more and more important for several clinical (and non-clinical) applications. In general, there are two alternatives for the use of organic solvents. The first is to use no solvent at all. This involves physical techniques such as vapour-condensation, freeze drying and heat treatment, which are difficult to apply to the chemical synthesis of thermally labile organics. The second option is to replace the organic solvent by intrinsic benign solvents. Only water, carbon dioxide and nitrogen can be considered environmentally benign in all aspects. Technology based on SCCO2 is an alternative to overcome the problems associated with the use of traditional organic solvents. SCCO2 has a number of characteristics that allows processing a broad range of materials:
- low critical temperature (31 degrees Celsius) which allows the processing of thermally unstable compounds;
- large quadruple moment which confers large solubility to organic reagents.
- high selectivity between reagents and products.
- tunability of its solvent power through simple pressure changes;
- high diffusivity which enhances mass transfer and reaction kinetics;
- low viscosity and surface tension. SCCO2 is a non aggressive solvent adequate to manipulate complex functional materials and nanostructures;
- low cost, no flammability and negligible toxicity. A reduction of the use of toxic products in the industry is foreseen, since the SCCO2 based chemical technology avoids the production of organic waste with a net reduction of the released amount of CO2 to the atmosphere;
- gaseous at ambient conditions. Products are simply isolated by depressurisation, resulting in dry compounds and reducing reaction / post-processing steps. This eliminates the cost of filtration (especially complicated for nanoparticulated matter) and the energy-intensive drying procedure.

The SURFACET project results are expected to accelerate transition towards a more efficient knowledge based economy, since it addressed important environmental issues: towards a less intensive solvent-use industry. SCCO2 used as a solvent for chemical processes or else as a reagent, may greatly expand in the short term to higher levels if several possible approaches to its use are implemented.

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