Aerospace & Defense Technology - December 2023 - 30

Tech Briefs
Towards Sustainable Recycling of Epoxy-Based Polymers:
Approaches and Challenges of Epoxy Biodegradation
Composites are especially important for the development and implementation of sustainable technologies
such as wind power, energy-efficient aircrafts, and electric cars. Despite their advantages, their
non-biodegradability raises challenges for the recycling of polymer and composites in particular.
University of Hamburg, Hamburg, Germany
E
poxy polymers are widely used in various
industries, e.g., as coatings, adhesives,
and for lightweight construction due
to their unique properties such as high
strength, chemical resistance, and adhesion
to various surfaces. Therefore, one of
the most prominent applications is their
use as matrix material in fiber-reinforced
composites, which are heavily employed in
the aerospace sector. However, the disposal
of epoxy polymers and composites thereof
has become a significant concern due to
their recalcitrant nature and the adverse
environmental effects caused by traditional
recycling methods.
In this context, the overall production of
plastic waste is projected to double within
the next 20 years, with only 18 percent currently
being recycled, leading to the deposition
of around 12,000 Mt of plastic waste
in landfills and the environment by 2050
(see figure 1). Even though epoxy polymers
only accounted for a rather small share of
the global plastic production volume of
around 7.1 percent in 2021, the demand for
fiber-reinforced polymers is steadily
increasing. This is closely linked to emerging
sustainable technologies such as off
and on-shore wind power plants or electric
vehicles that rely on lightweight construction
materials for increased efficiency. To
Recycled plastics
8.3%
Fossil-based thermosets
7.1%
Other fossil-based
thermoplastics
7.1%
PS
5.3%
Production
PUR
5.5%
PP
PET
6.2%
PVC
12.9%
Recycling
Incineration Landfilling
Figure 1: Production volume (status 2021) and end-of-life fate of plastics (status 2017) [7,11]; LD/HD-PE-
Low-density/High-density polyethylene, PP-Polypropylene, PVC-Polyvinyl chloride, PET-Polyethylene
terephthalate, PUR-Polyurethane, PS-Polystyrene.
30
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19.3%
End-of-life fate
18 %58 %
24 %
Bio-based plastic
1.5%
LD/HD-PE
26.9%
cover the resource demand of the composite
industry and to reduce the environmental
impact of accumulated epoxy waste,
there is an urgent need for the development
of sustainable recycling methods.
Conventional recycling methods for
epoxy polymers, such as solvolysis, pyrolysis,
or nitric acid treatment, involve harsh
chemicals and the application of high temperatures
and pressures. Not only does this
lead to the emission of large quantities of
CO2 and other pollutants, but it also generally
results in a reduction of the material
properties. Particularly with regard to composites,
the fibers often suffer from the
extreme reaction conditions, resulting in a
reduction in their quality.
As a result, plastic-degrading biocatalysts
have attracted growing attention due to
their advantageous properties such as milder
process conditions, high substrate specificity,
and overall reduced environmental
impact. Enzymatic PET (polyethylene terephthalate)
depolymerization is one example
of the significant progress that has been
made within the last decade in the field of
plastic degradation. However, the development
of biodegradation approaches for
recalcitrant plastics such as epoxy polymers
has been less comprehensive and is still limited
to a few studies undertaking this challenge.
In this regard, the exploitation of
biodiversity resources, especially in combination
with metagenome mining and
environmental screenings, represents a
promising approach towards the development
of novel biocatalysts for plastic degradation.
This approach has been successful
in identifying enzymes that can degrade
plastics such as PET and can potentially be
used to develop biocatalysts for the degradation
and recycling of epoxy polymers.
There are a variety of existing approaches
taken towards the development of biochemical
degradation methods for epoxy
and epoxy-based fiber-reinforced composites.
As the development of bio-based recycling
technologies also requires comprehensive
analysis of the underlying
processes, an overview of available analytical
approaches is given.
The recycling of epoxy resins with biobased
methods is an important area of
research, as it offers a sustainable and environmentally
friendly alternative to conventional
methods. While challenges exist
in terms of recalcitrant epoxy degradation
and the need for robust biocatalysts,
advancements in metagenome mining,
directed evolution, and utilization of oxidative
enzymes provide avenues for overcoming
these hurdles. Additionally, research on
bio-degradable epoxy and bio-reinforced
materials contributes to a holistic approach
towards a more sustainable epoxy industry.
Continued interdisciplinary efforts in
exploring and optimizing bio-based epoxy
recycling methods will pave the way for a
greener future and a circular economy.
This work was performed by Leon
Klose, Neele Meyer-Heydecke, Sasipa
Wongwattanarat and Jennifer Chow for
the University of Hamburg and the
Office of Naval Research Global. For
more information, download the Technical
Support Package (free white paper)
at mobilityengineeringtech.com/tsp
under the Materials category.
Aerospace & Defense Technology, December 2023
http://mobilityengineeringtech.com/tsp http://mobilityengineeringtech.com
Aerospace & Defense Technology - December 2023

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