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Thanks to their lower weights, composites typically lead to lower

CO2 emissions. Despite advances in industries such as aerospace

and automotive, another sustainability aspect is putting the material

to the test: two materials joined together form an inherently strong

and tough entity that is almost impossible to separate again. This

results in substantial consequences for the material complexity

of waste fl ows on product disposal. Because of this complexity, a

closed recycling loop can only be achieved by deploying energy-

intensive separation processes.

The following processing routes for recycling composites are

normally suggested: mechanical milling, thermal processing (e.g.

pyrolysis and processing in the cement industry) and solvolysis

(the chemical route). Although these technologies can be applied

to both carbon and glass composites, a shift has taken place in

practice. Glass fi bre composites are mostly processed using

mechanical shredding and end up in the cement industry, while for

carbon fi bre composites either pyrolysis or solvolysis is often used.

This white paper discusses recycling both types of materials

individually:

1. Recycling composites: hopeful developments for the

Belgian circular economy (introduction)

2. Recycling carbon fi bre composites: high quality recyclate

in response to ambitious legislation

3. Recycling glass fi bre composites: what is the cheapest

way of disposing of this enormous waste mountain?

RECYCLING COMPOSITES

WHITE PAPER

The use of lightweight components

stands or falls on the choice

of materials. Product value,

product costs, production costs,

development costs and risks are

however diffi cult to estimate when

talking about less known materials

such as composites. Moreover,

the wide range of materials and

processes makes selection even

more diffi cult.

This is why the SLC-Lab, the

Sustainability Department at

Sirris and their partners in the

CompositeBoost project, want

to pass on essential tools and

methodologies to help designers

and OEMs make the right choices.

In providing support, we want

to give more clarity with the

publication of various white papers

dealing with current issues. The

fi rst white paper introduced the

issue of sustainability, the second

white paper goes deeper into

‘recycling composites’.

SirrisLeuven-GentCompositesApplication Lab

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1. RECYCLING COMPOSITES: PROMISING DEVELOPMENTS FOR THE BELGIAN CIRCULAR ECONOMY

The quality of separated materials is very important in the recycling

process. The properties should be as near to the original quality

as possible so that both materials can be directly integrated into a

new production cycle. However in practice, the materials cycle of

composites is not closed. After milling the waste material, normally

just the fibres can be recovered for recycling. This means relatively

short fibres (up to 150 mm) that can only be used in low-performing

applications such as injection moulding applications or SMC/BMC.

Currently, the industry is giving a lot of attention to the development

of higher quality applications in answer to the rapidly growing

composites waste mountain, and it is also searching for cheaper

raw materials. Using recycled carbon fibres could offer significant

cost reductions.

About 6,000 tons of composite waste material is created each year

in Belgium. On top of that, there is another 4,000 tons of production

waste, mainly from glass fibre composites. The waste from carbon

fibre composites is a fraction of this. The greatest part of the

waste is currently sent to landfill, although from the large, pure,

homogeneous flows of glass fibre composite, a substantial part of

this is currently processed by way of co-processing in the cement

sector. The glass fibre acts as a replacement raw material and the

polymer provides energy thanks to its calorific value. Although all

the composite components are usefully processed this way, the

reinforcing properties of the fibres are not put to use. This has

resulted in increasing global interest in finding alternative, high

quality methods of recycling composites. As there are substantial

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differences in these new developments between the carbon fibre

and glass fibre sectors, the latest recycling technologies and the

individual applications are dealt with separately in this paper.

It can be estimated that around twenty companies are involved

in composite recycling around the world. This number includes

companies who carry out their own recycling, as well as companies

who take in this waste for recycling. These companies are currently

overcoming obstacles such as collecting consistent flows and

upscaling and optimising technologies. A lot of attention is also

being paid to outlets for these new materials, which is done by

gaining the trust of their customers for example. This requires very

detailed technical supporting information about the properties of

the materials created from recyclate.

Glass fibre reinforced composite waste being shredded to be used in the cement industry [1]

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The arrival of composite recycling companies goes hand in hand

with increasing interest from the academic world. Still at different

levels of maturity, various technologies have already been developed

for separating the fibre and plastic materials from each other while

retaining the original properties. Some have already upscaled to

industrial levels and are commercially active, others are still at the

development stages.

Recycling therefore puts a halt to landfilling composites, which

complies with a landfill ban that operates in some countries, or is

mandatory according to product legislation, but that’s not all. It also

lowers the environmental impact of new products by limiting

energy-intensive fibre production. It has been estimated for example

that if 50 percent of the current glass fibre production was replaced

by recycled fibres, the annual level of CO2 emissions would be at

least two million tons less. Recycling significantly lowers the cost

of reinforcement fibres. [3] Recycled carbon fibre with a decrease

in mechanical properties would be 20 to 40 percent cheaper than

the primary material. Thanks to these advantageous economic

conditions, the recycling option is actually cheaper than landfilling,

certainly where carbon is concerned.

An example of production waste incurred by cutting fibre mats to size at BMW [2]

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2. RECYCLING CARBON FIBRE COMPOSITES: HIGH QUALITY RECYCLATE IN RESPONSE TO AMBITIOUS LEGISLATION

In most European countries landfilling is the most common practice

for end of life-cycle plastics. There is currently a landfill ban post-

consumer plastics in nine European countries. So in Flanders for

example, this means that composites collected separately may no

longer be landfilled. [4] The automotive industry has also set its

limits: it has said that it must be possible to reuse or recycle 85

percent, and to reuse, recycle or recover 95 percent of the weight

of a vehicle. (“Recover” includes burning for energy recovery in

compliance with the End-of-life Vehicles Directive, ELV.)

The need to comply with such legislation is reinforced by the sharply

growing volume of carbon fibre composites. The automotive

industry together with the aerospace industry represents more than

50 percent of the global demand for carbon fibre composites. It is

anticipated that this demand will triple by 2020 when compared

with 2010. [5] Moreover, by that year the global demand will exceed

supply. Therefore economically feasible answers must be found in

the short-term for the end-of-life stage of this growing volume of

carbon composites. This will involve recycling technologies, but

also new logistical chains for the waste flows, as well as new end-

use applications.

Two typical processes for dealing with carbon composites are

pyrolysis and solvolysis.

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Pyrolysis

The most advanced is the thermal process: pyrolysis with or without

oxygen. Waste in the form of prepregs, dry fibres or hardened

laminates are processed in temperatures between 450 and 700 °C.

The waste is converted into fibres, oils and gases. For example

pyrolysis applied to SMC glass fibres results in 75 percent solid fibre,

14 percent oil and the remainder gas by weight. [4] The oil contains

monomers that in principle can be reused in new resin. However,

extraction of monomers is not carried out in practice because of the

economic reasons. After milling the recyclate, it typically consists of

fibres (up to 150 mm) that can be used in the compounding industry

as milled powder, or as non-wovens. The figure below shows some

commercially available semi-finished products.

The pyrolysis process is the most commercially used process. The

process is currently at an optimisation phase in which the parameters

are gradually being altered and fine-tuned. For example, leading UK

company ELG, managed to lower processing energy consumption in

2015 by 35 percent. There are also thermal processes (e.g. fluidised

bed technology and microwave technology) that are currently being

developed, yet with limited applications.

Prepreg

Compounds [7]

Short fibres [9]

Non-wovens, with or without TP binder [8]

Milled carbon [9]

Dry fibres/fabrics

Laminates

POSSIBLE TYPES OF WASTE [7] COMMERCIAL SEMI-FINISHED PRODUCTS

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A kayak made from fibres recovered from the aerospace industry [10]

Solvolysis

Solvolysis is a recycling technology in which a solvent dissolves

composite resin at lower temperatures. The process gives

good results at laboratory level, whether or not in combination

with pyrolysis. Commercial applications currently remain limited.

Although it appears to be a very promising route making it possible

to retain the fibre structure, as well as the plastic monomers. The

process also avoids the formation of carbonized materials, which

following pyrolysis contaminates the fibre surface and as such

prevents good fibre matrix adhesion. The kayak below for example

is a demonstrator made from fibres recovered from the aerospace

industry.

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Search for high quality recyclate

Recycled fibres are usually milled shorter than the primary ones so

that a uniform level of quality can be achieved. The properties of

the shorter fibres are the same as those of the primary fibres.

Companies state that after recycling by pyrolysis, recycling the

modulus remains virtually unchanged and the tensile strength can

be about 10 to 20 percent lower. There is also a potential cost

reduction of 20 to 30 percent in comparison with primary carbon

fibre. [6] The recycled fibres recovered from the pyrolysis process

are best used in the manufacture of non-wovens, either with or

without a thermoplastic binder. The photograph below shows the

roof of a BMW i3 made from secondary carbon fibre.

In addition to the individual fibre properties, the textile structure

is also very important. The non-woven properties are still low

when compared with their primary unidirectional or textile-based

composites. This is only because of the orientation potential of the

primary fibres. For this reason, primary carbon fibres are used for

guaranteeing rigidity where this plays a crucial role. Therefore the

orientation of short, recycled fibres is an important study subject

found in literature. Studies are carried out using air flows in the

production of yarn for example. The results will definitely make a

difference where fibres are concerned and will widen the design

opportunities of the recycled material. The latest step in the search

for high quality recyclate.

Example of carbon fibre recycling by the SGL Group in Germany: on the left is the non-woven produced with secondary carbon fibre - on the right the roof of the BMW i3 [2]

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3. RECYCLING GLASS FIBRE COMPOSITES: WHAT IS THE CHEAPEST WAY OF DISPOSING OF THIS ENORMOUS WASTE MOUNTAIN?

The composites market is heavily dominated by glass fibre

composites (more than 90 percent). The largest volume of composite

waste comes from glass fibre composites based on thermosets.

In Belgium alone that is around 10,000 tons of waste annually.

These flows of waste originate principally from the transport

and construction sectors. Although the largest part of fibre glass

composite production is for export, a lot of composites are imported.

A recent study instigated by OVAM, concluded that the greatest

challenge lies in the analysis of all the various material flows.

Companies are often not particularly clear about either their

production or associated waste figures. Apart from that, many

manufacturers have no idea of what happens at the end of life-cycle

stage of their products. It is also difficult to make estimates about

the imports.

Though it is clear that the volumes being released are growing rapidly.

For example the operational wind turbine capacity in Belgium is

currently approximately 2,300 MW, which is roughly equivalent to

about 28,000 tons of composite material. Taking account of the annual

increase in generation capacity, this could mean that from 2030 on,

3,000 tons of wind turbine blades are released each year. Polyester

boats are being released in great numbers too. Old boats in Belgian

harbours and marinas are already creating a problem, particularly as

some neglected boats and yachts start sinking after a while and the

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harbour authorities are unable to take the initiative to remove them.

In addition, there are several thousand tons of composite water

sports equipment stored in gardens, sheds and garages that are fast

approaching the end of life-cycle stage. According to a Dutch study,

about 4,000 tons of composite material will be released annually

over the next 15 years. These figures demonstrate that wind turbine

blades and boats are ideal candidates for recycling, particularly as

they produce relatively pure waste flows. Other waste flows such as

swimming pools and printed circuit boards are usually smaller and

often more contaminated.

The ambiguous volumes and quality of these waste flows makes

it difficult to provide suitable collection channels. A reasonable

number of recycling centres for separately collecting glass fibre

waste could be the solution here. However transporting lightweight,

voluminous glass fibre composites is expensive and processing

(i.e. removing contaminates, chopping up, etc.) is an intensive task.

Nonetheless, because of current legislation, landfilling and burning

will no longer be a feasible option.

Boats, wind turbine blades and pultrusion sections: examples of pure glass fibre waste flows for which the first recy-cling options exist. [12a,b,c]

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Pyrolysis

Although pyrolysis is the most convenient processing method for

carbon, it is actually more difficult to apply to glass. The figure below

[3] shows just how much glass fibres lose their strength during

thermal processing. The high temperatures degrade the sizing of

the glass fibre and the glass fibre structure.

The ReCoVeR research project, which ended in 2015, claimed to be

able to recover 80 percent of the strength of thermally treated glass

using an economically feasible recovery process. The recyclate

can be used in existing process chains for glass fibre products that

include injection moulding applications and GMT. This patented

process is currently one of the few recycling routes that retains

so much added value from the fibre and therefore has a lot of

commercial potential.

Typical results from the litterature on residual fibre strength after heat conditioning. [3]

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Cement industry

Studies show that the current and most efficient way of valorising

glass fibre composites is by processing them in cement ovens.

Milled material is mixed with other raw materials in which 30 percent

of the composite is used as the source of energy and 70 percent

as the raw material. Processing 1,000 tons of pultrusion profiles for

example saves 450 tons of coal, 200 tons of lime, 200 tons of sand

and 150 tons of aluminium oxide. [1] This recognised and developed

process is however not so economically attractive in countries

where landfilling is still permitted.

Glass fibre composite waste to be milled for the cement industry at the Fiberline company [1]

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Mechanical milling

Mechanical milling technologies are commercially available, but

only on a small scale. The price of primary glass fibre is very low

and recyclate is generally of low quality.

There are examples of companies that have made technologies

available that produce mechanically functional fibres. But

contamination of these fibres along with the remaining resin

sometimes prevents proper fibre resin matrix adhesion in the new

composite. Deploying this type of recyclate fibre is going to demand

intensive testing and quality control.

Composites can be finely milled into filler, however standard

fillers are currently cheaper. Despite these setbacks, a number of

companies are actively working on this, as can be seen from the

examples below.

AB-VAL (France) processes production waste (left) by way of compressing a mixture of recyclate and thermoplastic materials (right). [13]

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CONCLUSION

The development and implementation of recycling technologies is

rapidly growing at both research and commercial levels. Important

motivation includes a ban on landfilling composites, a lowering of

the environmental impact and dropping cost prices. The latter is

currently giving the recycling of carbon fibre composites a substantial

boost in commercial applications.

With respect to glass fibre, developments are taking longer, because

the economic value of it tends to be limited for now. Nonetheless,

various studies indicate a substantially strong recycling potential.

Reprocover (which applied for bankruptcy earlier this year) converts BMC for example from the automotive indus-try (left) into cable channel covers (right). [14]

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SOURCES

[1] Fiberline, fiberline.com[2] BMW[3] Thomason, J.; Jenkins, P.; Yang, L. Glass Fibre Strength—A Review with Relation

to Composite Recycling. Fibers 2016, 4, 18.[4] OVAM[5] AVK Market research[6] Current status of recycling of fibre reinforced polymers; University of

Birmingham; 2015[7] ELG CF[8] SGL Group[9] Procotex[10] Cranfield University, Nick Rawle Photography[11] Composites World: Recycled koolstof fiber: Comparing cost and properties, 2014[12a] © Ssuaphoto | Dreamstime.com[12b] © Gary Parker | Dreamstime.com[12c] © Alexander Sorokopud | Dreamstime.com[13] AB-VAL, France[14] ReprocoverComposites recycling: where are we now?, CompositesUK, 2016OVAM; market research into the reuse of high quality recycling for fibre reinforced thermosets, 2016

AUTHORSLinde De Vriese (Sirris)

Thomas Vandenhaute (Sirris)

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‘Eco-compliance as a competitive weapon’, a collaborative

project with Sirris and Agoria, gives active support to companies

including manufacturing companies, where the impact lies on

production or production design in order to take advantage

of innovation opportunities presented by eco-compliance:

cost savings, improved market access, extended production

life-cycles, lower total costs of ownership and the design of

new ecological products. This acts as leverage for sustainable

innovation by adopting a proactive approach towards changing

environmental legislation and standards, and market demands.

This is how the barriers to innovation are lowered and the

technology choices for participating companies become clearer.

Thomas Vandenhaute (Sirris) is project leader for sustainability

and engaged in the areas of sustainable material management and

ecological production. He is also co-author of the book, ‘Innoveren

met materialen’ [innovating with materials] and an approved

OVAM SIS Toolkit coach. He also contributed to the TWOL study

for OVAM (http://www.ovam.be/kunststofcomposieten), which

involved visiting and interviewing many companies. Together

with Agoria he supports companies wanting to make the move

towards the circular economy with activities such as setting

up learning networks, as well as providing support in bringing

together partners for specific materials or material flows.

ECO-COMPLIANCE AS A COMPETITIVE WEAPON

This white paper was written within the scope

of two projects: ‘CompositeBoost’ and

‘Eco-compliance as a competitive weapon’.

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‘CompositeBoost’ is a collaborative project involving the Sirris

SLC-Lab, UGent and KU Leuven. Based on these six highly

relevant issues, the project partners want to use these essential

tools and methodologies to allow designers and OEMs to make

the right choices. The masterclasses, demonstrations and

exploratory case studies will help transform the composites

processor into a reliable production company and partner. This

will mean that our companies will retain their competitiveness over

foreign competitors.

COMPOSITEBOOST

Markus Kaufmann, PhD (Sirris)

is the program manager of the composites division of Sirris and head

of the SLC-Lab since April 2012. Before that he acquired experience

in design and cost estimation of composite structures. Markus is

responsible for coordinating CompositeBoost.

Linde De Vriese (Sirris)

is the team member specialising in material characterisation, press

forming of thermoplastic composites, and bio-composites. Linde re-

ceived her Master’s in Materials Engineering at KU Leuven in 2010,

specialising in polymers and composite materials.

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Bart Waeyenbergh (Sirris)

works at SLC-Lab on prototyping, product development, mould

design and processing of thermoset composites. He graduated

with a Master’s in industrial sciences at Group T in Leuven in 2008,

specialising in advanced manufacturing.

Tom Martens (Sirris)

is the senior technician at SLC-Lab, with 18 years of experience

in the plastics industry. He is responsible for the production

of prototypes and demonstrators in both thermoplastics and

thermoset composites.

Katleen Vallons, PhD (KU Leuven)

is a post-doctoral researcher at SLC-Lab. She has worked with the

Composite Materials Group at KU Leuven since 2005, mostly on

projects in collaboration with industrial partners. Her expertise is in

the material behaviour of composites.

Geert Luyckx, PhD (UGent)

is a post-doctoral researcher at SLC-Lab. He has worked at

UGent, Mechanics of Materials and Structures, since 2003 and is

involved in the experimental validation of new optical measuring

technologies for measuring shape distortion in composite

components.

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PARTNERS

SIRRIS LEUVEN-GENT COMPOSITES APPLICATION LABCelestijnenlaan 300C3001 Heverlee+32 498 91 94 91www.sirris.beinfo@sirris.beblog.sirris.be

SirrisLeuven-GentCompositesApplication Lab