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Sustainable recycling of aircrafts composites

Final Report Summary - SUSRAC (Sustainable recycling of aircrafts composites)

Executive Summary:
The working plan was divided in different tasks:
1 – Dimensional reduction of the composite, with investigation of the proper grinding system, in order to get particles not greater than 3 mm.
2 – Mixing the so obtained granules with fluidified polymer matrices, according to a proprietary process, aiming at producing a fluid composite containing at least 50% by weight of thermoset residue.
3 –Processing the obtained compounds into solid plates with different thickness that find application in outdoor furnishing (tiles, flooring, etc.), or polymer granules to be processed with conventional injection molding equipment to get tailor shaped manufacts. The latter should have properties comparable to those of virgin materials, but with lower cost.

WPs/tasks vs. DoW in % of completion:
WP1 - Selection of the machining technologies for CFRP cutting and grinding. It is completed at 100 % in all his Tasks

WP2 - Definition and execution of the recycling process for the manufacturing of recycled specimens. It is completed at 100% in all his Tasks

WP3 - Characterization of specimen morphology and analysis of the interfacial adhesion between the selected recycling matrix and CFRP fillers. It is completed at 100% in all his Tasks

WP4 - Characterization of thermal and mechanical properties of the recycled thermoplastic composites. It is completed at 100 % in all his Tasks

WP5 - Prototype manufacturing and testing. It is completed at 100 % in all his Tasks

WP6 - Dissemination. It is completed at 100 % in all his Tasks

WP7 - Final Report. It is completed at 100 % in all his Tasks

Main Resources used in the Project
Most of the resources were employed for the activation of a Research Contract. Some resources were allocated for the participation to conferences on sustainable materials and for the acquisition of consumables.

Project Context and Objectives:
The project aims at developing a sustainable, cost effective, purely physical approach to the recycling of thermosetting and thermoplastic carbon fibres reinforced composites typically obtained from the dismantling of End-of-Life Aircrafts.
The increasing use of carbon fibre reinforced polymers (CFRPs) has raised an environmental and economic awareness for the need to recycle the CFRP waste.
The world-wide demand for carbon fibres (CFs) reached approximately 35,000 t in 2008; this number is expected to double by 2014, representing a growth rate of over 12% per year. CFRP is now used in a widening range of applications, and in growing content in most of them; the aircraft industry is an impressive example, with the new Boeing 787 and Airbus A350 having up to 50% of their weight in CFRP, and military aircraft showing a similar trend.
Despite all the advantages associated with CFRPs, their increasing use generates also an increasing amount of CFRP waste. Common sources of waste include out-of-date pre-pregs, manufacturing cut-offs, testing materials, production tools and end-of-life (EoL) components; manufacturing waste is approximately 40% of all the CFRP waste generated, while woven trimmings contribute with more than 60% to this number.
Continuing with the aeronautics sector as example, happen to the new composite-generation aircraft (8500 commercial planes will be retired by 2025), with each vehicle representing more than 20 t of CFRP waste. Within a similar time frame, the wind industry will be another great source of CFRP waste.
Recycling composites is inherently difficult because of (i) their complex composition (fibres, matrix and fillers), (ii) the crosslinked nature of thermoset resins (which cannot be remoulded), (iii) the simultaneous presence of very high Tg thermoplastics (very difficult to be recycled as well) and (iv) the combination with other materials (metal fixings, honeycombs, hybrid composites, etc.).
Presently, most of the CFRP waste is landfilled; the airframe of EoL vehicles is usually disposed in desert graveyards, airports, or by landfilling.

However, these are unsatisfactory solutions for several reasons:
-Environmental impact: the increasing amount of CFRP produced raises concerns on waste disposal and consumption of non-renewable resources.
-Legislation: recent European legislation is enforcing a strict control of composite disposal; the responsibility of disposing EoL composites is now on the component’s manufacturer, legal landfilling of CFRP is limited, and for instance it is required that automotive vehicles disposed after 2015 are 85% recyclable (EU 1999/31/EC; EU 2000/53/EC).
-Production cost: CFs are expensive products, both in terms of energy consumed during manufacturing (up to 165 kWh=kg) and material price (up to 45 € per kg).
-Management of resources: demand of virgin (v-) CFs usually surpasses supply-capacity, so recycled (r-) CFs could be re-introduced in the market for non-critical applications.
-Economic opportunity: disposing of CFRP by landfilling, where not illegal, can cost approximately 0,30 €=kg; recycling would convert an expensive waste disposal into a profitable reusable material.
It is clear that turning CFRP waste into a valuable resource and closing the loop in the CFRP lifecycle is vital for the continued use of the material in some applications, e.g. the automotive industry. This need has driven not only a great amount of research on recycling processes for CFRPs over the last 15 years, but also the formation of several collaborative entities working on a more commercial or industrial level

A preliminary investigation will be carried out to assess which are the suitable analytical techniques, aimed to the characterization of the material, both in terms of matrix and filler. This procedure, along with the information provided by the material’s data sheets, will also help to devise the best recycling and reutilization options. Potential application of the recycled compounds are automotive, interior and outdoor design, as well as nonstructural components in aircraft industry. Improvement of mechanical, thermal, and aging resistance properties of the recycled compounds will be obtained through the use of proper compatibilizing/emulsifying agents. As far as the thermoplastic components are concerned, they will be blended with suitable commodity thermoplastics and then characterized in terms of morphology and tensile, impact and dynamic-mechanical properties. The activity on thermosets will develop novel methods to recycle stabilized fiber-reinforced epoxy-based composites. The working plan is divided in different tasks:
1 – Dimensional reduction of the composite, with investigation of the proper grinding system, in order to get particles not greater than 1 mm.
2 – Mixing the so obtained granules with fluidified polymer matrices, according to a proprietary process, aiming at producing a fluid composite containing at least 50% by weight of thermoset residue.
3 –Processing the obtained compounds into solid plates with different thickness that find application in outdoor furnishing (tiles, flooring, etc.), or polymer granules to be processed with conventional injection molding equipment to get tailor shaped manufacts. The latter should have properties comparable to those of virgin materials, but with lower cost.

WPs/tasks vs. DoW in % of completion:
WP1 is completed at 100 % in all his Tasks
WP2 is completed at 100% in all his Tasks
WP3 is completed at 100% in all his Tasks
WP4 is completed at 100 % in all his Tasks
WP5 is completed at 100 % in all his Tasks
WP6 is completed at 100 % in all his Tasks
WP7 is completed at 100 % in all his Tasks

Main Resources used in the Project
Most of the resources were employed for the activation of a Research Contract. Some resources were allocated for the participation to conferences on sustainable materials and for the acquisition of consumables.

Project Results:
The first target of the activity has been the evaluation of suitable technologies and conditions for comminuting and stabilizing thermoplastic and thermoset carbon fiber reinforced aircraft composites (CFRP). Recycling techniques for various types of FRP are available. Generally the material are sorted, shredded and milled to fine powders which can be used as filler materials for thermoplastic polymers. Different equipments and milling technologies have been proposed. Milling of large amount of FRP usually requires a multistep procedure: firstly to size reduce the composite components in some primary shredding process, which is typically achieved with the use of a slow speed cutting or crushing mill. A second step consists of a reduction stage where the material is ground into a finer product. Based on the analysis of the state of the art and on the typology of the recycling CFRP, the suitable comminuting technology were selected and evaluated as a function of the maximum output, efficiency and reliability as well as the cost-effectiveness of the process.
In a second step, thermoset CFRP parts of end-of-life aircrafts provided by Alenia were used as CFRP waste.
The granules obtained by the mechanical recycling process were mixed with fluidified thermoplastic polymer matrices, according to a proprietary process, aiming at producing a fluid composite containing at least 50% by weight of thermoset residue.
The procedure has been described in the Technical Report I (Reporting period: March-July 2010), it is designed for the production of plastic compounds at very high filler content and, specifically, it is designed for the compounding of waste.The obtained compounded granules were pressed into sheets (thickness 3.5 mm) by using an hot press machine (Collin Laboratory Press) and were cut out for mechanical tests.
Thermoplastic CFRP parts of end-of-life aircrafts were also provided by Alenia. Grinding procedures by usiong the same milling apparatus of Thermosets was effective also for thermoplastics.

WP1 - Selection of the machining technologies for CFRP cutting and grinding
The aim of this Workpackage was the evaluation of suitable technologies and conditions for comminuting and stabilizing thermoplastic and thermoset carbon fiber reinforced aircraft composites (CFRP). Recycling techniques for various types of CFRP were found in literature and critically analysed.

WP2 - Definition and execution of the recycling process for the manufacturing of recycled specimens.
The aim of this task was the set up of a cost effective emulsion technology aimed to the recycling of carbon fibres reinforced composites (CFRP) deriving from the dismantling of end-of-life aircrafts with the final target at realizing new high loaded thermoplastic based composites.
Previous researches carried out at ICTP showed the feasibility of an emulsion technology to prepare recycled thermoplastic composites containing large amount of filler of various size and nature (organic and inorganic). According to it, carbon or glass fibre reinforced resins, after grinding to small sizes, are emulsified in a thermoplastic matrix in order to obtain sheets or granules. The emulsification process is carried out at room temperature (hence, cost effective) using as thermoplastic matrix expanded Polystyrene (EPS) previously made in form of a physical gel by the help of volatile organic solvent. Postconsumer EPS is made widely available as result of its use as loose fill packaging for fragile goods. Moreover, its lightness (30 kg per cubic meter, on average) makes its disposal highly difficult. Combining these two streams of End-of-Waste (EoW) materials, we aim to obtain good performing composites and, at same time, low cost. The realization of good performances is expected on the basis of the effective incorporation of grinded CRFP into the EPS gel. In fact, EPS in the form of gel is able to combine a fluid state with the elasticity of the physical network. The gel is a kind of gage, in which the filler particles will be accommodate in high amounts without loss of continuity. When the gel is condensed in dry state, the plastic gage will shrink around the particles, firmly entrapping them in a tri-dimensional network. Hopefully, such network will be stable during subsequent machining operations, hence assuring good mechanical properties to the obtained composites.

WP3 - Characterization of specimen morphology and analysis of the interfacial adhesion between the selected recycling matrix and CFRP fillers.
The main objective of this Workpackage was the definition and execution of tests for a complete evaluation of the chemical and physical characteristics of the obtained recycled materials. In particular, it was required to evaluate inner morphology of obtained materials and mode and state of interfacial adhesion between the thermoplastic matrix and CFRP fillers.

Scanning electron microscopy (SEM)
Morphological analysis was carried out using a FEI Quanta 200 FEG environmental scanning electron microscope (ESEM) (Eindhoven, The Netherlands) in high vacuum mode, using a Large Field Detector (LFD) and an accelerating voltage ranging between 10 and 20 kV. SEM analysis was performed on 0.25 and 1 mm sized CFRP powders and on fractured surface of high charged composites. Before the analysis, samples were mounted on aluminium stubs and coated with Au/Pd alloy by means of a sputtering device Baltec Med 020.The SEM images of the fracture surfaces of the composites show that carbon fibres are embedded into a soft polystyrene matrix revealing a ductile crack surface, as confirmed by the presence of the pronounced local plastic deformation, which is the accompanying phenomenon during ductile fracture. This result suggests that the emulsion-based process carried out for composite preparation guarantees the homogeneity at microscopic level allowing a good surface interaction between matrix and CFRP particles.
For comparison, EPS/CFRP composites were prepared by using a classical melt mixing approach, i.e. CFRP and EPS powders were added in the chosen composition (70/30, 60/40 and 50/50) in the mixing chamber of a Haake Brabender and processed at 200 °C for 10 min, increasing progressively the mixing speed from 16 to 64 rpm.It is concluded from the morphological analysis that the cold processing technology allows a more intimate dispersion of the CFRP material into the EPS thermoplastic matrix and the interfacial adhesion of the filler to the matrix is enhanced with respect to a material prepared through a melt mixing approach.

WP4 - Characterization of thermal and mechanical properties of the recycled
thermoplastic composites
Objectives: Evaluation of the recycled composites performances by tests able to define their service behaviour in selected environmental conditions (combined moisture/temperature atmosphere).

Activity performed
The properties of carbon fibre reinforced plastics (CFRP) differ so much from that of their matrix material, that a relationship is barely discernible any more. CFRP materials are distinguished by their extremely high strength and rigidity. Good interfacial bonding (or adhesion), to ensure load transfer from matrix to reinforcement, is a primary requirement for effective use of reinforcement properties. Thus, a fundamental understanding of interfacial properties and a quantitative characterization of interfacial adhesion strength can help in evaluating the mechanical behaviour and capabilities of composite materials. In this frame, the engineering applications of composite materials require adequate assessment of their response under severe conditions like impact loading and high strain rates. In the present Work Package we investigated the relevant mechanical properties of the obtained materials, at low and high deformation rate, and their thermal behaviour in selected environmental conditions, including tests for fire properties.
The obtained results in terms of mechanical properties clearly prove that the achieved mechanical performance are satisfactory for the composites obtained through the emulsification process, while are clearly inferior when a classical process of melt compounding is applied. From the above, we can say that the targets of realizing a material innovative and mechanically performing were achieved.
On the other side, the thermal properties also are satisfactory, thermal degradation starts well above 280 °C meaning that the service temperature of the composites can be sufficient for many commodity as well as specialty applications.
Less positive are the results of the fire resistance of the materials.The results of the Cone calorimetry tests have classified the composites as E, which is a not satisfactory classification for many applications.
Rather low classification. This could be ascribed to the removal of smoke suppressants during the emulsification process.
On this respect, in the following actions (manufacturing of prototypes, WP5) the addition of proper fillers able to improve the classification of the material was performed.

WP5 - Prototype manufacturing and testing
Objectives: Definition of proper pilot process for manufacturing composites prototypes based on recycled CFRP and TPC and manufacturing of and test on a reference part to use as demonstrator of the technology (a proper demonstrator should have dimension of at least 30 cm width and 50 cm length)

Activity performed
Here it is described the procedure for obtaining references samples of big size to use as demonstrators of the emulsion technology.
Samples of different compositions and of dimensions equal to 40x40x0.4 cm were prepared through emulsion technology.
In particular, two formulations were realized that differ by the nature and proportion of filler (CFRP thermosetting (ths) alone or in a 50/50 blend with CFRP thermoplastic (thp)) loaded in the thermoplastic matrix (EPS).

Basically, the prototype machine realised at ICTP partner location consists of a mixing chamber, an extruder chamber and a “flat exit head” equipped with a moving roll for setting the thickness of the slabs; at the end of the exit head, conveyors rollers are used to transport the slabs.
From the obtained results of mechanical tests, carried out according to ASTM standards typical of fiber reinforced plastics (ASTM D3039 for tensile and fracture tests, ASTM D695 standard for compression tests, ASTM D 5961 standard open hole bearing testing) we can deduce that:
The blends containing a mixture of thermoplastic and thermosetting carbon reinforced composites as filler have tensile and impact properties about 15 % lower that those obtained with a filler made of purely thermosetting carbon fiber reinforced composite. This finding may be due to the different chemical nature of the resins in the filler, but also to a slightly different granulometry of the fillers. Anyway, it is to be underlined that still the obtained values are in the range of good performing techno-composites.
The ultimate strength obtained in the ASTM D695 and ASTM D 5961 tests is very satisfactory, the values are very close to those reported for highly filled composites, such as Corian by DuPont. They compare also very positively with the data obtained in tensile.
We are then in the presence of materials that can be used for indoor and outdoor application for furniture in substitution of virgin materials. Moreover, they come from recycled materials, and can be recycled many times, being now of thermoplastic nature.
In order to verify if the fire classification of the material could be improved, 2 prototypes were obtained with an overall composition of 40/60, with ABS and EPS as thermoplastic matrices, and with the addition of a fire retardant, such as a powder of Mg(OH)2 which is a well know fire retardant additive. The results of the tests, carried out at Tecnalia, proved that, compared to the not modified composites, the fire response of the composites has substantially improved.

Concluding Remarks

The Project activities have proceeded smoothly, with an excellent cooperation between the Coordinator ICTP and the Beneficiary Tecnalia. Progress reports were provided and Technical Meetings were regularly held internally and between the partners, also by using internet conference calls, whenever needed.
The results are very promising for the effective industrial exploitation. As matter of facts, ICTP has applied and succeeded to get a further support in another Clean Sky project (IRECE) to design the industrial process to bring the prototype process developed in SUSRAC to an industrial level.

Potential Impact:
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. owever, 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.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. he 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. 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. 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.
At the moment, SUSRAC is at the end 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.

List of Websites:

www.susracproject.com