JEC COMPOSITES MAGAZINE - Issue #141 - July/August 2021 - 57

Rapid-cure epoxy formulations for next-generation composite manufacturing
Fig. 2: Rheological profiles of epoxy
curing with rapid-cure additives
(Hameed et al. ACS Appl. Polym.
Mater. 2020, 2, 7, 2651-2657)
On the other hand, there are no major scientific breakthroughs reported
in rapid curing of epoxies other than a few new compositions with a
cycle time of 10 minutes. In an established industry, the promotion of
new processes that require capital expenditure and re-training of people
is frowned upon, thus it is always best to develop innovative materials
that will not significantly disrupt the existing manufacturing processes
to support high-rate production speeds.
The main requirements for the mass production of component parts are
short production cycles and consistent quality. Fundamentally, disruptions
to the current manufacturing process should also be kept to a minimum.
To address these concerns, a team of researchers from Swinburne
University of Technology and Deakin University (Australia) recently
discovered novel epoxy formulations using an ionic liquid chemistry
that significantly decreases thermoset curing time and temperature.
Recent breakthroughs
According to a recently published journal article, the new rapid-curing
resin formulation was obtained from a mixture of an ionic liquid with
commercially-available epoxy resin and hardener. This type of ionic liquid
is termed as solvate ionic liquid (SIL) (Figure 1). In specific compositions,
this resin system cures 72x faster than a standard epoxy/hardener
combination on its own, making it the most advanced rapid-cure resin.
In addition, the thermoset material was shown to exhibit thermoformability
where it can be moulded or stamped into a desired shape. This
discovery of a novel rapidly-curing polymer network has the potential to
address the key issues in rapid processing and become an ideal choice for
composite automation, thus revolutionizing manufacturing.
The SIL is added either into the epoxy resin or the hardener prior to mixing
all the components together. In this way, the resin viscosity can be
maintained for a sufficiently long time. On mixing, the resin has a good
thermal latency, and the curing reaction is activated at above ambient
temperature, depending on the amount and type of additive used. This
latency is critical for carbon fibre impregnation at specific temperatures
and short time cycles, accompanied by rapid curing of the resin when
the specific temperature is reached. In specific compositions, up to 50%
reduction in curing temperature compared to neat epoxy resin was also
observed (Figure 2). This significant lowering in cure temperature provides
energy savings and consequently lowers the cost of curing these
polymers.
Future plans
The new resin systems are currently undergoing a range of material testing
and modelling to investigate their reaction mechanisms, curing-induced
imperfections and a range of material characteristics. The resins
will be primarily used to create 3D-printed structures using a variety of
printing methods including stereolithographic techniques. Additionally,
these resins will be optimised for infusion processes for fibre-reinforced
composite manufacturing.
Solvate ionic liquids possess immense potential as rapid-cure additives
in high-technology and high-volume (low-cost) composite manufacturing
due to the way they induce the rapid curing of epoxy resin. With ionic
liquids as drop-in additives in epoxy formulation, rapid-cure systems
with acceptable allowance for glass transition temperature change from
the neat epoxy precursor may be obtained with small amounts of ionic
liquid.
More information:
https://pubs.acs.org/doi/abs/10.1021/acsapm.0c00257
https://www.swinburne.edu.au/research/our-research/access-our-research/find-a-researcher-or-supervisor/researcher-profile/?id=nisharhameed
N°141
July - August 2021 / jec composites magazine
57

https://pubs.acs.org/doi/abs/10.1021/acsapm.0c00257 https://www.swinburne.edu.au/research/our-research/access-our-research/find-a-researcher-or-supervisor/researcher-profile/?id=nisharhameed

JEC COMPOSITES MAGAZINE - Issue #141 - July/August 2021

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