JEC COMPOSITES MAGAZINE - Issue #107 - August/September 2016 - 61

Cure kinetics of a fast-cure epoxy with silica nanoparticles

Fig. 5: Modelled
glass transition
temperature gradient over the plate
thickness during
cure [5]

Fig. 6: Initial viscosity of the XB3585/
XB3458 epoxy resins
[3]

the glass transition temperature (Tg) distributions over the thickness,
as shown in Fig. 5. In the case of the unmodified epoxy, the difference
between the Tg at the edge and in the middle is 11°C. The addition
of 20 wt.% of silica nanoparticles results in a difference of only 5.5°C.
The temperature distribution over the thickness was not completely
dismissed with the addition of silica nanoparticles but significantly reduced, leading to more uniform properties over the thickness.
As, typically, the addition of particles can increase the viscosity, the
effect of particle concentration on the initial viscosity and cure cycle evolution was also studied. The effect of silica nanoparticles was
found to be relatively small for silica contents up to 20 wt.% (Fig. 6),
whereas a higher wt.% results in an exponential viscosity increase. The
influence of silica nanoparticles on the viscosity of the fast-cure resin
becomes negligible at about 10 Pas as the cure reaction kinetics dominate the evolution of the viscosity, explaining why no effect on the
gelation time was noticed.

Modelling
The temperature distribution during cure can be modelled by incor-

porating the cure kinetics into the heat transfer equation [3]. The prediction is shown in Fig. 3. Modelling the temperature makes it possible to calculate the viscosity, the degree of cure and the glass transition
temperature (more details are available in a previous study [3]). The
Tg gradient over the thickness of a 3 mm bulk epoxy plate without
and with 10 and 20 wt.% silica nanoparticles is shown in Fig. 5. These
models may be implemented into flow simulations to predict the flow
front during fibre impregnation in liquid composite moulding (LCM)
processes.

Conclusions
The addition of silica nanoparticles is a suitable method to reduce exothermic heat generation during cure without influencing the curing
reaction itself. This allows the use of fast cure cycles, makes the process more controllable and leads to more uniform properties over
the thickness of the part. Since the viscosity is only slightly increased
with contents up to 20 wt.%, the silica nanoparticles are well suited for
liquid composite moulding (LCM) processes. Modelling of the cure
kinetics, heat transfer and viscosity combined with flow simulations
may help to find the optimum process parameters during preform impregnation.
More information: www.fhnw.ch/ikt
Contact: andre.keller@fhnw.ch

References
[1] Kinloch, A. J., Masania, K., Taylor, A. C., Sprenger, S., & Egan, D.
(2008). The fracture of glass-fibre-reinforced epoxy composites using
nanoparticle-modified matrices. Journal of Materials Science, 43(3),
1151-1154.
[2] Hsieh, T. H., Kinloch, A. J., Masania, K., Sohn Lee, J., Taylor, A. C.,
& Sprenger, S. (2010). The toughness of epoxy polymers and fibre
composites modified with rubber microparticles and silica nanoparticles. Journal of Materials Science, 45(5), 1193-1210.
[3] Keller, A., Masania, K., Taylor, A. C., & Dransfeld, C. (2016).
Fast-curing epoxy polymers with silica nanoparticles: properties and
rheo-kinetic modelling. Journal of Materials Science, 51(1), 236-251.
[4] Studer, J., Dransfeld, C., & Masania, K. (2016). An analytical model
for B-stage joining and co-curing of carbon fibre epoxy composites.
Composites Part A: Applied Science and Manufacturing, 87, 282-289.
[5] Keller, A., Masania, K., Taylor, A. C., & Dransfeld, C. (2015). Modelling characterisation of a fast curing silica nanoparticle modified
epoxy. International Conference on Composite Materials (ICCM) 2016,
Copenhagen.

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Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #107 - August/September 2016