JEC COMPOSITES MAGAZINE - Issue #136 - September/October 2020 - 48

FEATURE
matrix

Novel thermoset composites for more
competitive and sustainable industries

Dr. Alaitz Rekondo,
Head of Polymers and composite
Dr. Gemma Vara,
Technical Marketing Head
Cidetec Surface Engineering

particularly useful approach to
generate reprocessable and recyclable
thermosets is the introduction of
reversible or exchangeable bonds into the
polymer network. The idea behind this is to
be able to reconnect the chemical crosslinks
that are broken when a material fractures,
restoring the material's integrity. The dynamic hardener used to formulate 3R epoxy
resins contains a reversible chemical bond
(aromatic disulphide) that can be rearranged
under a determined external stimulus such
as temperature or the exposure to a specific
chemical agent after its complete cure. This
rearrangement capacity of the aromatic disulphide bond enables the reprocessing, repairing and recycling of 3R Composites. 3R
resins and composites are easily formulated
from readily-available commercial products.
When produced for the first time, 3R
Composites can be processed just like
traditional composites, as the resin viscosity
and curing temperatures can be adjusted to

Being aware that the thermoset composite materials sector
needs processes that allow higher production rates and a recycling solution, CIDETEC Surface Engineering started studying
dynamic covalent chemistries in 2013, resulting in the development and patenting of a thermo-mechanically reprocessable
epoxy resin and its composites that preserve all the advantages
of conventional thermosets while showing unprecedented features such as re-processability, repairability and recyclability.
The new material was named 3R Composite.

the process requirements. Thus, the 3R resin
has already been adapted for use in RTM,
infusion and pultrusion technologies.
Reprocessability
Once 3R Composites are cured, reshuffling
of the dynamic crosslinks can be promoted
at high temperatures (typically 200-220°C).
This permits innovative processes to be
carried out, such as thermoforming of
fully-cured laminates, using conventional
thermoplastic compression moulding and
thermoforming processes. As a result, 3R
Composites allow faster and more automated production rates when compared to
conventional methods.
Repairability
Similarly, easy repair of resin/fibre delaminations and resin micro-cracks is possible
by simply applying heat and pressure to the
damaged part. Repairing parts delaminated
either during the manufacturing process or
in service, which are currently rejected due
to high costs, is also possible.

jec composites magazine / N°136 September - October 2020

3R-thermoforming

Recyclability
Two different routes can be considered for
recycling 3R Composites. The first one is
the chemical route. The dynamic network
can be completely disrupted by exposure
to a specific chemical reagent, which exchanges bonds with the dynamic network,
the resin being totally dissolved without
affecting the reinforcement. The clean fibres
remain continuous as they are not degraded
by the reagent used to dissolve the resin. In
addition, the resin can also be recovered and
re-used. It should be noted that the 3R resin
shows the same good chemical resistance
as conventional thermoset composites to

JEC COMPOSITES MAGAZINE - Issue #136 - September/October 2020

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