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Composite materials made of glass and carbon fibres have revolutionised many industries. Demand for composites is experiencing rapid growth and global demand is expected to double. As demand for composites grows it is clear that waste management will become an important issue for businesses. Technically composite materials evoke difficult recycling challenges due to the heterogeneity of their composition. As current waste management practices in composites are dominated by landfilling, governments and businesses themselves foresee that this will need to change in the future. The recycling of composites will play a vital role in the future especially for the aerospace, automotive, construction and marine sectors. These industries will require different recycling options for their products based on compliance with current legislation, the business model as well as cost effectiveness. In order to be able to evaluate waste management strategies for composites, a review of recycling technologies has been conducted based on technology readiness levels and waste management hierarchy. This paper analyses 56 research projects to identify growing trends in composite recycling technologies with pyrolysis, solvolysis and mechanical grinding as the most prominent technologies. These recycling technologies attained high scores on the waste management hierarchy (either recycling or reuse applications) suggesting potential development as future viable alternatives to composite landfilling. The research concluded that recycling as a waste management strategy is most popular exploration area. It was found mechanical grinding to be most mature for glass fibre applications while pyrolysis has been most mature in the context of carbon fibre. The paper also highlights the need to understand the use of reclaimed material as important assessment element of recycling efforts. This paper contributes to the widening and systematising knowledge on maturity and understanding composites recycling technologies.
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Technology readiness level assessment of composites recycling
technologies
Justyna Rybicka
a
,
*
, Ashutosh Tiwari
a
, Gary A. Leeke
b
a
Manufacturing and Materials Department, Craneld University, MK430AL, UK
b
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
article info
Article history:
Received 15 December 2014
Received in revised form
24 August 2015
Accepted 25 August 2015
Available online 3 September 2015
Keywords:
Technology readiness levels
Composites
Waste
Recycling
Waste hierarchy
Mapping
abstract
Composite materials made of glass and carbon bres have revolutionised many industries. Demand for
composites is experiencing rapid growth and global demand is expected to double. As demand for
composites grows it is clear that waste management will become an important issue for businesses.
Technically composite materials evoke difcult recycling challenges due to the heterogeneity of their
composition. As current waste management practices in composites are dominated by landlling, gov-
ernments and businesses themselves foresee that this will need to change in the future. The recycling of
composites will play a vital role in the future especially for the aerospace, automotive, construction and
marine sectors. These industries will require different recycling options for their products based on
compliance with current legislation, the business model as well as cost effectiveness. In order to be able
to evaluate waste management strategies for composites, a review of recycling technologies has been
conducted based on technology readiness levels and waste management hierarchy. This paper analyses
56 research projects to identify growing trends in composite recycling technologies with pyrolysis,
solvolysis and mechanical grinding as the most prominent technologies. These recycling technologies
attained high scores on the waste management hierarchy (either recycling or reuse applications) sug-
gesting potential development as future viable alternatives to composite landlling. The research
concluded that recycling as a waste management strategy is most popular exploration area. It was found
mechanical grinding to be most mature for glass bre applications while pyrolysis has been most mature
in the context of carbon bre. The paper also highlights the need to understand the use of reclaimed
material as important assessment element of recycling efforts. This paper contributes to the widening
and systematising knowledge on maturity and understanding composites recycling technologies.
©2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/).
1. Introduction
Composite materials have revolutionised many industries, pre-
dominately aerospace, marine, construction and automotive in-
dustries (Sims and Bishop, 2001; Jiang, et al., 2007; Bai, 2010). The
possibility of combining mechanical strength, design exibility,
reduced weight and low system cost, make composites the material
of choice in transportation allowing unique design and function-
alities in combination with high fuel efciency. For instance, Airbus
A350X Wide Body design is dominated by composites; by aircraft
weight, the A350 XWB will be 53% composites, 19% Al/AleLi, 14%
titanium and 6% steel.
The UK carbon bre composite production represents around
2130 tonnes (36% for aerospace and defence and 33% wind energy),
the rest being mostly in automotive, marine and sports goods
(Materials KTN, 2011). In comparison, the glass bre reinforced
plastics (GFRP) production represents 144,000 tonnes in UK and it
was estimated at approximately 1053 million tonnes in Europe in
2010 (Materials KTN, 2011). As composites materials in a form of
carbon bre-resin/glass bre-resin matrix are relatively new in
commercial use, the commercially available recycling processes of
these materials are still under development (Job, 2010). Waste
management of composites has started showing on the govern-
ment agenda (BIS, 2009). There are several European Directives and
regulations that impact polymer waste management, collection
and recycling, e.g. 99/31/EC on Landll of Waste; 2000/53/EC on
End-of-life vehicles; 2004/35/EC on Environmental Liability. Man-
ufacturers across Europe need to pay to dispose their production
Abbreviations: EPSRC, Engineering and Physical Sciences Research Council.
*Corresponding author. Tel.: þ44 1234 75 0111x5579.
E-mail address: j.e.rybicka@craneld.ac.uk (J. Rybicka).
Contents lists available at ScienceDirect
Journal of Cleaner Production
journal homepage: www.elsevier.com/locate/jclepro
http://dx.doi.org/10.1016/j.jclepro.2015.08.104
0959-6526/©2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Journal of Cleaner Production 112 (2016) 1001e1012
waste if it goes to landll, including a climate change levy. The
incineration of scrap is also restricted due to directive 2000/76/EC
that prevents air, water and soil pollution by limiting emission
levels. This has signicant cost and operational implication for the
future waste management of the composites in many industries
(Witik, 2013), but currently the most affected will be aerospace,
construction, marine and automotive industries (Sims and Bishop,
2001; Jiang et al., 2007; Bai, 2010). It is estimated that by 2015
end-of-life composite waste will reach 251,000 tonnes and pro-
duction waste will achieve 53,000 tonnes (Simth, 2009). Also, the
Lifting Off report (BIS, 2013) acknowledges that substantial growth
within the aerospace sector over the next 20 years will involve
step-change increases in aerospace production volumes.
In order to be able to respond to these changes, the industry
needs to understand its own waste management capabilities and
the recycling options available. Understanding the level of recycling
technologies and their potential legislation implications allow in-
dustry to identify opportunities for viable waste management so-
lution for composites. The aim of this research is to dene the
maturity and potential desirability of composites recycling tech-
nologies through using technology readiness level assessment and
waste management hierarchy frameworks for evaluation.
2. Related research
This section explores the research related to composites waste
management options.
The increased use of composites across different industries will
lead to creation of heterogeneous waste, either end-of-life or
manufacturing waste (Yang, 2012). As composite materials have
heterogeneous nature, the diversity of different production vari-
ables makes is very difcult to nd recycling routes (Yang, 2012).
Further, lack of infrastructure and market are the difculties in
funding commercial scale applications (Conory, 2006).
EU Waste Framework Directive denes the different types of
waste processing and provides a view on desirability of the
different strategies along with denitions of their meaning for in-
dustry (Conory, 2006; Council directive 2008/98/EC; Pickering,
2006). The framework has guided waste practice classication for
many industries and provides the scale of desirability in waste
management from the legislation perspective. EU Waste Frame-
work demonstrated in Fig. 1 outlines ve broad waste management
strategies, starting from most desirable to the least these are:
prevention, preparing for reuse, recycling, recovery and disposal.
Current waste management practices in composites are domi-
nated by landlling (WRAP, 2013), which still is a relatively cheap
option for industry in comparison to alternatives. However, it is the
least preferred option by legislation (Council directive 2008/98/EC).
It has also been recognised that landlling will become unviable for
industry mainly due to legislation-driven cost of disposal increases
(Pickering, 2006). From 1998 the standard landlling rate increased
from £7 per tonne to £64 per tonne in 2012 on average increasing £4
annually. From 2013 that annual increase has risen to £8, making
the 2014 landlling rate to be £80/tonne and in 2015 it is declared
to be 82,60/tonne (HM Revenue and Customs, 2015).
When considering waste management of composites the efforts
of researchers predominantly focus on the recycling technologies
that process the scrap material to a form which signicantly de-
creases the value of material (Correia, 2011; Chen, 2006; Turner,
2010). This falls mostly into recycling but sometimes covers re-
covery and reuse stages in the Waste Management Hierarchy.
There have been several classications of composites recycling
technologies. Yang (2012) recognises thermal, chemical and me-
chanical recycling for thermo-set matrix composites. Also, Job
(2010) has summarised research that has been done around recy-
cling efforts in glass bre reinforced- (GFR) and carbon bre rein-
forced (CFR) composites. The study describes ve recycling
processes: mechanical grinding, pyrolysis, cement kiln route, ui-
dised bed and solvolysis. Microwave heating is also discussed
(Lester, 2004). Pickering (2006) provides detailed review of recy-
cling technologies along with the graphical illustration of each
technology. Key recycling technologies are described below. Me-
chanical grinding is a process of using hammer mill or similar tools
where waste is milled to the level of powder (Job, 2010)orbrous
product that could have some reinforcement properties Correira
(2011). Pyrolysis is a thermal recycling process where composite
material is heated to a temperature between 450
Cto700
C in the
absence of oxygen (Lester, 2004). This process is mostly used for
carbon bre (CF) composites (Marsch, 2008) and produces bres of
reduced strength and llers (Pickering, 2006). Cement kiln is
identied as a method where the organic fraction is combusted to
generate energy and the inorganic fraction is incorporated into
cement (Job, 2010). Fluidised bed process is a thermal recycling
process that aims to recover high grade glass and carbon bre
reinforcement from scrap glass and carbon bre reinforced
Fig. 1. EU Waste Framework, source: DEFRA (2011) Government Review of Waste Policy in England 2011.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e1012100 2
composites (Marsh, 2008; Packering, 2000). The bre composites
are cut and fed into the silica sand bed and are treated with hot air
at temperatures between 450 and 550
C. Fibre-size and ller-size
are separated from each other to be used for different purposes
(Correia, 2011). Microwave heating is another thermal recycling
method where the bres are heated directly through the use of
microwaves to achieve bre separation. Lester (2004) has pub-
lished a technical feasibility study of this method; however there is
very limited research in this area. Solvolysis is a method of recycling
through various chemicals that decompose composites into
chemicals and fibres (Liu, 2012). Variable results have been ach-
ieved depending on the chemical selected and the experimental
conditions. All the above lead to reduced strength properties of
bres (Bai, 2010;Jiang et al., 2009;Pi~
nero-Hernanz, 2008; Xu, 2013;
Oliveux, 2013; Kao, 2012; Yuyan, 2009).
As the value of glass bre (GF) type composites is small, the
process of recycling needs to reect the potential prots that could
be achieved. So far mechanical grinding is considered a commer-
cially viable strategy although on a small scale (Filon publications).
Due to large volumes of GF scrap available, the demand for viable
recycling of GF is increasing. However, BIS (2009) reports that ever
increasing end-of-life composite waste does not have sufcient
infrastructure and facilities in place for recycling.
CF recycling is predominantly driven by tightening legislation
around its disposal. As the value of CF is much higher than GF, there
is opportunity for more expensive technologies to be applied in
recycling (Pickering, 2006). So far, pyrolysis (thermal recycling
process) has been developed to a commercial scale (Wood, 2006),
however it still is limited in capacity as the supply of waste is
discontinuous due to the small volumes available and lack of
infrastructure facilitating waste ows (Pickering, 2006). In the case
of CF, the issue of recycling is the devaluation of the material after
recycling.
For composites waste management it is important to establish
process or processes that could compete with the cost of disposal.
This is going to become more attractive as the landll tax increases
(Conory, 2006). Understanding the maturity of the recycling tech-
nologies will enable industry to assess the options available and
explore the capabilities required to facilitate composite recycling.
So far no context landscaping has been done for the composites
recycling industry although many efforts of classication of recy-
cling technologies have been proposed in the past (Conory, 2006;
Pickering, 2006; Correia, 2011). This is the rst attempt, however
to look at the maturity of composites recycling technologies with
the use of landscaping to build understanding of capabilities
requirements.
3. Methods
As the purpose of this research paper is to evaluate recycling
technologies, it is key to review the relevant and signicant
research and to evaluate recycling technologies in the new contexts
(Saunders, 2007). Therefore, this paper focuses on literature review
of recycling technologies available and its evaluation on two-
dimensional scale ematurity and sustainability as waste man-
agement option.
Inductive approach in the literature review is applied
(Saunders, 2007) to take into account the need for organising data
into the relevant context. The waste management hierarchy and
technical readiness level frameworks are used as assessment scales
for the technologies. The technologies are assessed on the scale
and cross-validated with several experts from materials and
recycling environments. Finally, the recycling technologies are
displayed in two-dimensional graphs to demonstrate its maturity
landscape. The graphical representation of the methods used is
presented in Fig. 2.
These methods allow coverage of the wide research scope
needs: understanding the state of current composites recycling
technologies as well as dening the requirements of industry and
academia to inform future research in developing commercial
composites recycling technologies and systems.
Fig. 2. Research methods.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e1012 100 3
3.1. Literature review
As this research look at the technical readiness level of tech-
nologies not only academia but industry sources had to be
considered in this study. State of the art in composites recycling in
industry has been investigated to understand the magnitude of
composites waste management impact on business. This work
supported understanding of what technologies are commercially
available today. Further, literature review of different processes of
composites waste management has been researched in order to
identify the types of recycling and processing available. In order to
understand the scale of composites recycling and identify arising
trends, reviews of journals, white papers and company publications
have been carried out. The journals search has been carried out in
SCOPUS database whereas the white papers have been identied
on the interest group networks (i.e. Materials KTN) and company
publications have been found directly on company websites. Fifty
six projects and publications on composites recycling processes
have been identied. The search key words were selected to ensure
consistency of themes covered in the context of waste management
strategies conveying: composite, CRFP, GFRP, reuse, recycling, re-
covery, disposal, and incineration. The investigation of the tech-
nologies focused on what type of waste management strategies are
explored in composites, whether there is a difference between
glass- and carbon-bre composites waste management, and what
recycling strategies have received most interest.
3.2. Context mapping
The 56 projects have been classied on the TRL and on the Hi-
erarchy of Waste Management frameworks in order to develop a
landscape of these technologies in the relevant context. TRL clas-
sication enabled identication of technological maturity of the
current developments and Waste Management hierarchy allowed
to understand the potential legislation-driven desirability of the
technologies.
3.2.1. TRL scale assessment
Technology Readiness Level (TRL) is a framework that has been
used in many variations across industries to provide a measure-
ment of technology maturity from idea generation (basic princi-
ples) to commercialisation (Nakamura, 2012). TRL can also be
adapted to support understanding of capabilities and resources
required to develop technologies at different stages of develop-
ment. Conrow (2011) provides description of the TRL stages in
terms of the development adopted in NASA. The TRL stages are
summarised in Table 1.
There were two allocation stages to the TRL framework. First
stage allocation was adopted from Yang (2012) where TRL 1e3were
dened as lab scale, TRL 4e6 as pilot scale and 7e9 as commercial
scale. This rst allocation was performed to identify the range
within the three scales. Following that the second run of allocation
was performed; the description of the processes used in each of the
56 research projects have been compared with the TRL level de-
scriptions from Williamson (2011). This activity provided specic
information that allowed allocation to one stage on the TRL level.
The whole process is demonstrated in Fig. 3.
3.2.2. Hierarchy of Waste Management
The assessment of technologies in terms of waste management
level has been performed on a basis of matching the technology
outputs to the denition in the Waste Management Hierarchy
(DEFRA, 2011). The mapping of these technologies is discussed
further in the Results section.
3.3. Validation
The maturity of the technologies has been evaluated through
expert evaluation sessions with 10 experts from the University of
Birmingham, University of Manchester, Exeter University, Craneld
University and the Materials KTN (Knowledge Transfer Network) in
the UK. The evaluation has been conducted by asking the experts to
allocate the recycling technologies to TRL levels represented by the
technology cards. The cards are presented in Fig. 4. The cards
characterised the technology application detailing: the process
description, specied material and its different forms that could be
treated through the process, process outputs, potential applica-
tions, and identication of organisations and projects that imple-
mented the process in their work/company. The experts were asked
to provide their view on the technology maturity. This ndings
were then compared to the original assessment.
3.4. Landscaping
The crosslinking between TRL levels and Waste Management
Hierarchy allocations were registered on two dimensional diagram.
These data were then analysed to gain an understanding based on
desirability of the Waste Management Hierarchy maturity of
technology. Fig. 5 demonstrates how the scatter diagram sections
are divided and their respective explanations.
The technologies that fall above the 0X axis are more desirable
to implement from the legislation perspective, whereas the pro-
jects below could have limited or negative impact on future waste
Table 1
Technology Readiness Level (TRL) framework. Adapted from Williamson (2011).
TRL Description
9 Actual system ight proventhrough successful mission operations
8 Actual system completed and ight qualiedthrough test and
demonstration (ground or space)
7 System prototype demonstration in a space environment
6 System/subsystem model or prototype demonstration in a relevant
environment (ground or space)
5 Component and/or breadboard validation in relevant environment
4 Component and/or breadboard validation in laboratory environment
3 Analytical and experimental critical function and/or characteristic
proof-of-concept
2 Technology concept and/or application formulated
1 Basic principles observed/reported
Fig. 3. TRL scale allocation to 56 research projects: Table AYang TRL scale allocation: L-
Lab; P- Pilot; C- Commercial.; Table B TRL level scale allocations stage two.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e1012100 4
management strategies. The low TRL scores (projects on the left
side of the 0Y axis) suggests that the amount of work required by
industry for adapting the technology to business needs requires
more effort than the technologies on the right (with high TRL
score). These require less effort and are therefore easier to uptake.
Fig. 5 provides four technology allocation categories: desired,high
innovation potential,re-thinking neededand not viable.
4. Results
The results form review of the papers is presented in this sec-
tion. The allocation of the composites recycling practices in a
context of Waste Management Hierarchy and TRLs is discussed and
it is followed with by material and by technology breakdowns.
4.1. Composites recycling practices in a context of waste
management hierarchy
Fig. 6 presents a summary of composites recycling processes
captured using the Waste Management Hierarchy framework.
Landlling falls under the disposalcategory, Incineration falls
under as recovery, as it allows burning for energy. Recycling
strategies are represented by waste processing technologies: sol-
volysis, microwave heating, pyrolysis, mechanical grinding Reuse
strategies focus either on options where change to the
manufacturing processes or supply chain is required; these are
rather bespoke to individual production lines. Finally, prevention
as a strategy is looking at a system approach and aims to minimise
the composite waste in the rst place. From a technology devel-
opment perspective, the areas of recycling and recovery allow the
trailing and testing of individual recycling technologies. When
looking at waste from manufacturing, reuseand recyclingcate-
gories are seen to spur research interest.
From the review of 56 papers on composites recycling and
allocation of these technologies in the Waste Management Hier-
archy, it was possible to detect what types of waste management
strategies have been researched in the past. Fig. 7 demonstrates
that recycling of composites (45%) followed by reuse of composites
(38%) are research areas that received most interest from re-
searchers accounting for 83% of the research undertaken in the area
Fig. 4. Technology cards developed for TRL evaluation.
Fig. 5. Explanation of the context-relevant technology analysis.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e1012 100 5
of composites waste management. Disposal of composites through
landlling has not been researched.
In terms of focus on types of materials researched in composites
recycling carbon bre (CF) is accounting for 53% and glass bre (GF)
for 34% of the research. This is outlined in Fig. 8. This however
might not be entirely representative as for 11% of research in
composites recycling it was not possible to identify the type of
composites material used.
In order to explore how composites recycling evolved in relation
to the type of material used the comparisons of glass- and carbon
bre recycling research has been compared with the time of its
publication. There is an increasing trend to publish composites
recycling. GF recycling has been published more than CF recycling
between 2000 and 2009, however only in the last three years of the
last decade carbon bre recycling has shown not only a 360% in-
crease from the last decade, but has also outgrown glass bre
research. This might be due to the increase in funding available for
research in materials recycling in the UK as well as building of
research expertise in the UK universities is leading to greater
publication development. Fig. 9 summarises this trend.
Fig. 10a and b shows the waste management strategy break-
down for composites recycling of GF and CF, respectively. Recycling
seems to be a dominating area of research interest for both types of
materials accounting for over half of the research- 57% for GF and
51% for CF. Reuse is the second most popular area covering 33% for
GF and 32% for CF research. CF recovery (14%) seems to be handled
more than GF recovery (5%).
Fig. 6. Composites waste management strategies allocated on the Waste Management
Hierarchy.
Fig. 7. Number of research projects by type of composites waste management stra-
tegies (based on 56 projects identied from journals and white papers*).
*As some papers covered more than one strategy, the total number of identied entries
is 56.
Fig. 8. Waste management strategies by material (based on 56 projects identied from
journals and white papers).
Fig. 9. Composites recycling research uptake by material.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e1012100 6
Fig. 11 demonstrates the breakdown of recycling technologies
explored by research and industry. Solvolysis (24%), pyrolysis (31%)
and mechanical grinding (18%) stand out with the most uptake. 20%
are technologies dened as other. Fluidised bed has been allocated
to pyrolysis as they are closely related. In this area it was not
possible to identify the processes falling into one category, but
usually a combination of different techniques and activities were
identied.
Fig. 12 introduces the ndings from the literature review ana-
lysed through the TRL scale allocations combined with the expert
evaluation based on the technology card scoring. The scoring was
based on average and median scores for each recycling technology.
Incineration and landlling are assumed TRL 9 as a system
currently in place. Pyrolysis for carbon bre and mechanical
grinding for glass bre applications scored averages of 8.3 and 8.2
and a median of 8 which places it on a TRL 8. Pyrolysis for glass bre
and mechanical grinding for carbon bre has achieved average
scores 6.25 and 6.3 with a median of 7. Fluidised bed pyrolysis and
solvolysis process has achieved average scores of 4.2 and 2.24 and
median of 4. Finally, microwave heating had average of 3.2 and
median of 3.
Fig. 13 presents the waste management strategies allocation on
the TRL scale of individual projects researched in this study.
Research in recyclingof composites seems to cover the whole
Fig. 10. (a) Glass bre projects breakdown by waste management strategy (b) Carbon bre projects by waste management strategy.
Fig. 11. Composites recycling projects by recycling technique.
Fig. 12. Allocation of composites recycling technologies on TRL scale.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e1012 100 7
spectrum of TRL scale. This implies that research within composites
recycling is consistently developing. Reuseactivities cover TRLs 3
to 6 suggesting that the research in this area has consistently
evolved from lab to pilot scale. Recoveryand disposalcover lower
TRLs. This may reect the low interest in these areas from the new
product development and legislation perspective.
The TRL allocation was analysed for CF and GF allocation (shown
in Fig. 14a and b) and it is very clear that there is less research in GF
recycling, a trend that is consistent across the TRL spectrum,
whereas CF recycling is covered well from TRL 1 to 6 which suggest
a clear development trend towards commercialisation.
4.2. Recycling technology landscaping
The three main recycling technologies dened in this research e
pyrolysis, mechanical grinding, solyolysis have been plotted on
Figs. 15, 16 and 18 to evaluate their environmental impact and
technological readiness recognition. The diagrams show the
disposal to reuse stages of the Waste Management Hierarchy on the
Y axis and TRLs on the X axis. Projects that have used a composites
recycling technology have been positioned on the diagrams. The
denition of the Waste Management Hierarchy Stages meaning is
represented in the context of recycling technologies analysis.
Reusestage represents where the recycled material has found
reuse application in a new product; recyclingmeans that material
has been recycled but it is not been proven to reuse beyond its
reclamation value; recoveryfocus on recycled materials trailed to
be burnt for energy; and disposalintrudes project where
reclaimed material has been tested and disposed when considered
as invaluable. Fig. 15 shows the specication of materials types and
key symbols used in different projects.
4.2.1. Pyrolysis
Fig. 16 demonstrates how pyrolysis is plotted on the TRL/waste
management strategies matrix. Most of the pyrolysis processes are
used in CF research. This is a process that allows recycling of ma-
terial (although it downgrades its value and currently has limited
recyclate application), and ts in recycling and reuse sections
depending on the purpose of recyclate use after processing. In
terms of technological development, the projects in the laboratory
scale are well developed with a strong trend of moving into com-
mercial applications. The technology maturity suggests that there is
viable opportunity in developing this technology further.
Fig. 13. TRL of composites recycling projects categorised by waste management stra-
tegies (based on 56 projects identied from journals and white papers*).
* Some publications covered more than one strategy; therefore total number of waste
management strategies identied is 64.
Fig. 14. (a) Glass bre recycling by TRLs (b) Carbon bre recycling by TRLs.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e1012100 8
4.2.2. Solvolysis
For solvolysis there is a clear split between CF and GF research
projects in terms of technological maturity. This is presented in
Fig. 17. GF projects still reside in laboratory scale operations,
whereas CF projects are moving towards the pilot scale and dem-
onstrators. Both CF and GF solvolysis research covers a wide spec-
trum in terms of waste management strategies due to the different
use of the end product. The recovery projects cover incineration
after solvolysis processing whereas reuse projects describe the
reuse of the recyclate in different applications.
4.2.3. Mechanical grinding
From summary of mechanical grinding technologies in Fig. 18 it
is clear that mechanical grinding processing is primarily used for GF
recycling applications. This might be due to the low cost of pro-
cessing in comparison to the more expensive solyolysis and
pyrolysis routes. The mechanical grinding process allows for reuse
of the material in different ways, and is therefore positioned high
on the waste management strategy hierarchy. It is also clear that
there are two areas of development for GF recycling through me-
chanical grinding: there are recycling projects moving towards
pilot scale development; and mature technologies that are reaching
commercial scale. This suggests mechanical grinding can provide a
viable option for recycling. CF recycling through mechanical
grinding does not seem to get similar attention, only one project
that uses GF as material has been identied. Two reasons for that
were mentioned in literature and by experts: CF material is difcult
to grind and was often leading to failure of grinding equipment;
and value of CF recycled through mechanical grinding becomes too
low for the process to be viable.
5. Discussion
As established by the results in Fig. 7 composites recycling
research demonstrates a growing trend. This reects the view that
the industry recognises the changing conditions of composites
waste management.
In terms of specic material recycling, CF research seems to span
to a variety of technologies and processing options due to the
material value reclaiming potential. On the other hand, GFresearch
predominantly focuses on recycling options where volume is a
more signicant factor than retaining value of the bres. As sug-
gested in the literature, the main UK composites production ca-
pabilities lie in CF for aerospace industry and in GF structural
applications for the automotive and construction industries. This
suggests that recycled bres, in order to be reused will require
respective similar bre qualities. This is currently not achievable
with the recycling technologies available. It can be concluded that
currently reclaimed bres will need to be used in applications that
use lower value bres and have less quality requirements. The
potential for bre reuse requires understanding of composites
supply chain that is beyond the scope of this paper. From com-
parisons between glass and carbon bre research, it is evident that
CF research has increased within the last decade. This might be due
to the change in focus of funding for research into composites. A
Fig. 15. Landscaping activity legend.
Fig. 16. Landscaping of pyrolysis process in the context of Waste Management Hierarchy index and technology readiness level.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e1012 100 9
change that may be driven by the increase in composites demand
and tightening of legislation around waste management.
The landscaping activity aims to provide an understanding of
current state of composites recycling in the context of legislation
and technological development. Waste Management Hierarchy
(WMH) has been chosen as a framework to allocate different
recycling projects. The framework allowed the demonstration of
technologies' future desirability from the legislative and business
model perspective. It was identied that the majority of composites
waste management effort addresses recyclingand reusestages of
WMH.
Technology Readiness Level (TRL) framework allows to under-
stand the advancement of technologies. The TRL allocation, pre-
formed on the 56 projects in composites recycling, showed that TRL
level 3e4 is the most common stage of research. This suggests that
the research still requires further development and investment for
commercialisation.
Three composites recycling technologies cover 75% of the total
research activity: pyrolysis (31%) and solvolysis (22%) and me-
chanical grinding (18%). These three technologies dominate the
picture of recycling, however in many instances combining me-
chanical grinding with another technology took place. Also, 20% of
technologies were identied as othersuggesting that there is a
host of niche technologies unexplored in this paper: recycling with
use of injection moulding, chemical recycling with use of phenol
and potassium hydroxide.
The landscaping activity demonstrated that GF recycling is
dominated by mechanical grinding and it appears to reach high TRL
levels; an observation also conrmed in the literature (Job, 2010).
Currently, the Resource Efciency Action Plan (REAP) study focuses
on GF recycling due to the increasing volume of production. This
may lead to new recycling opportunities.
For CF recycling, pyrolysis and solvolysis research are on the
different stages of development. The most mature technology
seems to be pyrolysis. Pyrolysis is dened high on the Waste
Management Hierarchy and is a well-developed technology. Py-
rolysis as a process can be developed in different congurations and
it is reected by diversication of projects on different develop-
ment stages. This variety of recycling options in pyrolysis creates a
variety of development opportunities for organisations as it is still
relatively a new area of research, but proves to be commercially
viable. There is one company ofcially registered to recycle CF by
pyrolysis and has bases in the UK and Germany.
As a recycling process, solvolysis can be performed with di-
versity of chemicals and in a variety of conditions. This provides
many options for recycling solutions and hence many applications
are dened around TRL 3. For solvolysis, there is a clear diversi-
cation of technological maturity between GF and CF applications. It
seems that CF research is focussed at the laboratory scale, whereas
GF research is closer to proof-of-concept. However, there are iso-
lated projects where the TRL stages are higher than the trend, for
both GF and CF, which suggests that applications for commerciali-
sation are possible.
Mechanical grinding as a recycling method predominantly is
used in GF recycling. This method of composites recycling has
Fig. 17. Landscaping of solvolysis process in the context of Waste Management Hierarchy index and technology readiness level.
Fig. 18. Landscaping of mechanical grinding process in the context of Waste Man-
agement Hierarchy index and technology readiness level.
J. Rybicka et al. / Journal of Cleaner Production 112 (2016) 1001e10121010
reached high TRL level. This suggests that GF recycling is potentially
viable in the current market. Also, mechanical grinding has been
identied for use in CF recycling in conjunction with an additional
technology to size the material.
This research was based on a database search, and it only covers
the work that has been published, either as a journal or a white
paper publication. The commercial work that has been done in this
area is not included due to commercial sensitivity and lack of
availability. This means that non-academic research or commercial
applications of recycling technologies may not be captured, and
therefore the landscaping activities might not represent the full
picture of composites recycling research.
6. Conclusions
The manufacturers and users of composites need to take into
account waste management as the legislation is increasingly
impacting on this industry. The recycling of composites will play a
vital role in the future for sectors like aerospace, automotive, con-
struction and marine. These industries will require different recy-
cling options for their products that will be complaint with current
legislation and support their business models.
This paper details the research trends in the research on com-
posites waste management options as well as provides context-
mapping to landscape of the recycling technologies based on
technological readiness levels. Fifty six research articles were used
to identify growing trends in composites recycling technologies,
and showed that pyrolysis, solvolysis and mechanical grinding as
the most uptaken recycling practices.
In terms of opportunity development, individual technologies
were analysed based on technology readiness level and Waste
Management Hierarchy to establish current maturity status and
potential opportunities for the development of viable strategies for
the future. The aforementioned recycling technologies have been
identied to have high Waste Management Hierarchy positioning
(either recycling or reuse applications) suggesting potential for
future development as a viable alternative to composites land-
lling. These technologies reached different TRLs of which me-
chanical grinding for glass bre application was considered as the
most advanced and pyrolysis most advanced for carbon bre
application.
The landscaping activity has also led to conclusion that not only
process used for recycling but the reclaimed material use has sig-
nicant impact on its identication on the waste hierarchy.
Although pyrolysis seems to be the most advanced technology for
CF and mechanical grinding is most mature for GF, it is important to
further evaluate the value and impact of applying these waste
management strategies in the context of the recovered materials
use. This suggests that it is required to consider a wider perspective
when selecting recycling technologies, taking into account design
the system to accommodate the materials reuse.
This paper contributes to the widening and systematising of
knowledge on maturity and understanding composites recycling
technologies. This research hopes to inform industry and research
organisations on current recycling technology landscape to support
decision making for industry-led recycling technology develop-
ment. The ndings from this research are applicable as guidance on
potential waste management options to the industries relying on
composites material currently and in the future in hope to make
informed and sustainable decisions.
For the future research a full LCA (attributional, consequential
and impact assessment) could be carried out to reinforce this pa-
pers conclusions. It is also important to note the advancements in
zero waste research programmes that are cannibalising the area of
composite materials recycling by diverting the waste as valuable
materials. Therefore widening of scope into considering system
level transformation could be additional research consideration
and landscaping not only technologies but strategies could be
assessed.
Acknowledgements
The authors of this paper would like to thank the EPSRC for
funding this research as part of the Efcient X-sector use of het-
erogeneous materials in manufacturinge(EXHUME) Project,
running from March 2013 to February 2016. Grant number: EP/
K026348/1/.
Enquiries for access to the data referred to in this article should
be directed to researchdata@craneld.ac.uk
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Carbon fiber recycling is driven by government research incentives, and by the desire for manufacturers to have green manufacturing processes and products. Airbus and its PAMELA (Process for Advanced Management of End-of-Life of Aircraft) consortium used pyrolysis to extract carbon from an A380 airframe. The project was dismantling of an A300 airframe, and applying it to the much larger A380 in an effort to scale-up the process and determine best practices for recovering advanced materials, including 55,000 lb of composites per plane. Adherent Technologies Inc. plans to open a facility capable of processing 1,000 metric tons of recyclate annually. Firebird Advanced Materials Inc. has developed a proprietary continuous microwave recycling method and plans to begin its commercialization in 2010. Boeing worked with RCF Ltd., MIT, the University of Nottingham (U.K.) and Adherent Technologies to produce a proof-of-concept molded armrest using carbon fiber reclaimed from pre-production Boeing 787 parts.
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The environmental benefits of recycling are assessed against other end-of-life (EOL) treatments for Carbon Fibre Reinforced Plastic (CFRP) waste. Recycling via pyrolysis, incineration with energy recovery, and disposal via landfilling are compared. To account for physical changes to materials from use and recycling, equivalence between recycled and virgin materials is calculated based on the ability to produce a short fibre composite beam of equivalent stiffness. Secondary effects of using Recycled Carbon Fibre (RCF) in a hypothetical automotive application are also analysed. Results underline the ecological constraints towards recycling CFRPs and demonstrate that benefits from recycling are strongly linked to the impacts of the selected recovery process, the materials replaced by RCF in a secondary application, and also to the type of secondary application in which they are used.
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The study reports mechanical performance of the recycled glass fibres produced from a water-based solvolysis technology, known as the hydrolysis process. The chemical reaction was carried out using sub-critical water to dissolve polyester resin and recover the glass fibres from composites. The effect of temperatures, times, catalyst and water amount on mechanical properties of the recovered glass fibres were investigated. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and time-of flight secondary ion mass spectroscopy (ToF-SIMS) analyses were also employed to examine the fibre surface associated with the polyester resin eliminated level after the hydrolysis reaction. The results revealed that by carefully adjusting the hydrolysis parameters the tensile strength and failure strain of the recycled fibres decrease by approximately 40–70% in comparison with virgin fibres while Young’s moduli remain similar. The relationship between the hydrolysis conditions, recovered fibres and mechanical performance was discussed in this study.
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A two-step method to recycle high-quality carbon fibres (CFs) from carbon fibre/epoxy (CF/EP) composites in high yield under mild conditions was reported in this paper. Firstly, the composites were pretreated in acetic acid to be expanded and be layered to get larger surface area. Secondly, a synergistic oxidative degradation system is supposed to recover CF, which is a mixed solution of peroxide hydrogen (H2O2) and N,N-dimethylformamide (DMF) in a hermetic reactor. The structure and properties of recovered CFs were investigated. The results showed that clean CFs can be successfully recycled after the pretreated composites was treated at 90 °C for 30 min in a solution of H2O2/DMF (1:1, v/v). The decomposition ratio (Dr) of EP in composites was more than 90%. The surface of the CFs was smooth with few residues of EP observed by scanning electron microscope (SEM). The degree of graphitization of recovered CFs was decreased slightly tested by using Raman and X-ray diffraction (XRD) spectrum. The tensile strength of the recovered CFs was more than 95% of the virgin ones’ according to the single fibre tensile test.
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Composite materials are used in a wide range of applications such as automotive, aerospace and renewable energy industries. But they have not been properly recycled, due to their inherent nature of heterogeneity, in particular for the thermoset-based polymer composites. The current and future waste management and environmental legislations require all engineering materials to be properly recovered and recycled, from end-of-life (EOL) products such as automobiles, wind turbines and aircrafts. Recycling will ultimately lead to resource and energy saving. Various technologies, mostly focusing on reinforcement fibres and yet to be commercialized, have been developed: mechanical recycling, thermal recycling, and chemical recycling. However, lack of adequate markets, high recycling cost, and lower quality of the recyclates are the major commercialization barriers. To promote composites recycling, extensive R&D efforts are still needed on development of ground-breaking better recyclable composites and much more efficient separation technologies. It is believed that through the joint efforts from design, manufacturing, and end-of-life management, new separation and recycling technologies for the composite materials recycling will be available and more easily recyclable composite materials will be developed in the future.
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Fibre reinforced polymer (FRP) materials are being increasingly used in several applications, but especially in the construction and transportation industries. The composites industry is now producing a wide range of FRP products that include strengthening strips and sheets, reinforcing bars, structural profiles, sandwich panels, moulded planks and piping. The waste management of FRP materials, in particular those made with thermosetting resins, is a critical issue for the composites industry because these materials cannot be reprocessed. Therefore, most thermosetting FRP waste is presently sent to landfill, in spite of the significant environmental impact caused by disposing of it in this way. Because more and more waste is being produced throughout the life cycle of FRPs, innovative solutions are needed to manage it. This paper first presents a state-of-the-art review of the present alternatives available to manage FRP waste. It then describes an experimental study conducted on the technical feasibility of incorporating the fine waste generated during the manufacturing of glass fibre reinforced polymer (GFRP) composites in concrete mixtures. Tests were carried out to evaluate the fresh-state and hardened-state properties of concrete mixes in which between 0% and 20% of sand was replaced by GFRP fine waste. Although the incorporation of high proportions of GFRP waste was found to worsen concrete performance in terms of both mechanical and durability-related properties, it seems feasible to incorporate low proportions and reuse GFRP fine waste in concrete, particularly in non-structural applications such as architectural concrete or pavement slabs, where good mechanical properties are less important.
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In this paper, a method of chemical recycling of thermosetting epoxy composite was discussed. Water was used to be reaction medium and the decomposition of carbon fibre reinforced epoxy composites was studied. Experiments were devised in order to identify the significant process parameters that affect fibre reinforced composite recovery potential including temperature, time, catalyst, feedstock, and pressure. Experiments were performed in a batch-type reactor without stirring. Under the condition that the temperature was 260°C and the ratio of resin and water was 1:5g/mL, the decomposition rate could reach 100wt.% and the carbon fibres were obtained. The results from the Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM) measurements showed that the fibres were clean and no cracks or defects were found. The average tensile strength of the reclaimed fibres was about 98.2% than that of the virgin fibres.
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Today, end of life composites are generally shredded and sent to landfill or incinerated. A number of organisations are trying to develop viable alternatives, especially for carbon, which could have residual value and might pose an environmental hazard if disposed of inappropriately. Reinforced Plastics correspondent George Marsh has been to see Milled Carbon Ltd, a key player in a putative supply chain that could one day be disposing of thousands of tonnes of used carbon composite.