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Closing the loop for lightweight materials

From next-generation planes to electric vehicles and their already heavy batteries, every extra kilogramme matters when trying to achieve more sustainable transportation. Lightweight, high-performance materials have never been so successful, but their end-of-life remains a key...

From next-generation planes to electric vehicles and their already heavy batteries, every extra kilogramme matters when trying to achieve more sustainable transportation. Lightweight, high-performance materials have never been so successful, but their end-of-life remains a key concern. Every time a scientist or engineer comes to grips with the brain-teasing issue of greenhouse gas emissions and reduced fossil-fuel consumption, the weight element is central. Much of materials science now revolves around discovering or enhancing lighter materials, with better - or at least equal - performance, which explains the tremendous success of composite materials such as carbon-fibre reinforced polymers. However, there is another side to the coin. Composites still fall short of satisfactory second-life options, which is a real concern at a time when decision-makers increasingly think in terms of life-cycle assessments. Well aware of this issue and the urgency of solving it, the Institute of Chemistry and Technology of Polymers (ICTP) in Italy is investigating new waste-management processes with partners under the EU-funded SUSRAC project. Dr Mario Malinconico, who coordinates the project, told the research*eu results magazine about the consortium's achievements so far, their importance for the continued growth of the market and the remaining challenges before the end of the project. What are the main objectives of the project? Thermoplastic and thermoset composite materials are used in a wide range of applications, and about 1 million tonnes of composites are manufactured each year in Europe. This requires the setting up of specific strategies for composite-waste disposal, in particular for the recycling of this waste. Poor recyclability can be a barrier to the development - or even continued use - of composites in some markets. The purpose of this research, which is part of the EU-funded Joint Technology Initiative 'Clean Sky', is to develop recyclable thermoplastic composite materials capable of handling high weight loads. Those would be made from ground thermoplastic, thermoset aircraft-waste composites, such as 'carbon-fibre-reinforced polymers' (CFRPs), and recycled expanded polystyrene from loose-fill packaging. How important is it to solve this problem? Addressing sustainability issues related to plastic materials is one of the core activities at the Institute of Chemistry and Technology of Polymers. This is of utmost importance if you consider that the worldwide demand for carbon fibres (CFs) reached approximately 35 000 tonnes in 2008 and that this number is expected to double by 2014, representing a growth rate of over 12% per year. CFRPs are now used in a widening range of applications, with the aircraft industry being one of the most impressive examples: CFRP accounts for 50% of the weight of the new Boeing 787 and Airbus A350, and military aircraft are following a similar trend. The quick growth of the composite market raises the question of waste management, and it is only logical that recycling has become a high priority. At same time, plastic packaging materials account for almost 40% of all plastic consumption in the world, and loose-fill packaging materials are among the most difficult items to recycle due to their extreme lightness (on average one cubic metre of expanded polystyrene weighs only 30 kg). The idea to combine both materials to make a thermoplastic composite for building or furniture applications requires an innovative process, which is where SUSRAC comes in. What is new or innovative about the project and the way it is addressing these issues? Two compounding methodologies were explored, namely traditional melt mixing and innovative cold mixing. In the latter, a low-boiling-point industrial solvent was employed to dilute and guarantee the homogeneity of the thermoplastic matrix at the micro- and macroscopic levels. It is a purely physical approach, in a closed-loop strategy, which we have been studying since 2005. It was first applied to glass-fibre-reinforced thermosetting matrices resulting from the dismantling of boats. The results so far prove that the cold-mixing approach results in a material with mechanical properties up to four times higher than those obtained with a classical melt-mixing approach. What are some of the difficulties you have encountered and how did you solve them? The main difficulty appeared at the very beginning of the process, as we needed to obtain a controlled size reduction of thermosetting materials made of stiff resin and very hard carbon fibres while ensuring low energy input and safe operation. This has been achieved in cooperation with an Italian producer of grinders, who designed an effective industrial grinder for us. Another problem was the handling of the industrial solvent necessary for the emulsification. This solvent needs to be recycled internally to get a closed loop, and we are on the way to solving this problem. What are the concrete results from the research so far? One of the most concrete results is the fact that we can claim to have obtained, at a pre-industrial scale, highly-filled thermoplastic composites made from end-of-use materials. Those come with properties that make them comparable to composites made of virgin materials. Moreover, the resulting composites are thermoplastic, with the advantage that they can be recycled all over again at the end of their second life. When do you expect the project results to benefit the sector? At the moment, SUSRAC is in the third semester of a two-year project, and we have already started an industrialisation phase with an Italian company specialised in the design of industrial production plants. At the end of this industrialisation phase, planned for the middle of 2014, we will have a clear view of the investment costs, and we will be able to propose the results to interested companies. We hope to be ready by the middle of 2015. What are the next steps of the project, or next topics for your research? The next step is the realisation of demonstrators of a big-enough size for testing in a full-scale environment, such as the production of a specific element or aircraft part. This could be important, because it will allow the reuse of materials from dismantled aircraft in new aircraft production. In a similar way, in the automotive industry nowadays, car parts are made using materials originating from the dismantling of old cars. The SUSRAC project is coordinated by the Italian national research council (CNR). It also includes the Spanish research centre, Tecnalia, as a partner with a specific role in the validation of the fire resistance of the final material.For more information, please visit: SUSRAC Project factsheet