JEC COMPOSITES MAGAZINE - Issue #107 - August/September 2016 - 59

Software

Structural health of polymer composites:
non-destructive diagnosis using a hybrid NDT approach

TECHNOLOGY

Reaction kinetics

Cure kinetics of a fast-cure epoxy
with silica nanoparticles

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62

reaction kinetics TECHNOLOGY

Cure kinetics of a fast-cure epoxy
with silica nanoparticles
This article describes how the strong exothermic reaction of
a fast-cure epoxy can be better controlled with the addition of
non-reactive silica nanoparticles, further enhancing the benefits
of a fast process, the toughness and the ability to understand the
properties of thicker composite parts.
Andre Keller, Research Assistant,
Prof. Clemens drAnsfeld, Head of Institute of Polymer
Engineering, Institute of Polymer Engineering, FHNW
University of Applied Sciences and Arts Northwestern
Switzerland,
dr Ambrose C. TAylor, Reader in Materials Engineering, Department of Mechanical Engineering, Imperial
College London,
dr.dr.-Ing. sTePhAn sPrenger, Senior Market Development
Manager Composites & Lightweight Construction
Evonik Hanse GmbH
KlAus rITTer, Head Centre of Excellence Composites
Huntsman Advanced Materials
dr KunAl mAsAnIA, Senior Scientist
Complex Materials Group, Department of Materials,
ETH Zürich

ast-cure epoxy systems are used for the mass production of
composite parts with cycle times in the minute range. However, the use of fast-cure resins results in new challenges regarding
the understanding of their properties and processing behaviour. One
of the major difficulties with fast-cure resins is their strong exothermic reaction during cure, which may result in a significant temperature overshoot and large temperature (and therefore Tg, shrinkage
and residual stress) gradients over the thickness. Further, the resin
viscosity evolution strongly affects the impregnation process.

Cure cycle optimisation through modelling of heat transfer and
flow helps to find more suitable process parameters to reduce the
exothermic reaction. However, in some cases it is also necessary to
reduce the cure temperature with a negative influence on the cycle
time. A possible approach is to reduce the exothermic mass of the
resin itself, which can be achieved by adding non-reactive particles
to the resin. In composite manufacturing, any such particles must
be small enough that they are not filtered out during infusion processes, for example silica nanoparticles with a diameter of 20 nm [1].
The addition of silica nanoparticles up to 20 wt.% has been shown
to increase stiffness and fracture energy [2] without having a strong
influence on the viscosity of the epoxy matrix [3].
This article focuses on a fast-cure resin for automotive applications,
XB3585/XB3458, supplied by Huntsman, Switzerland. This epoxy
has a cure time of 5 min at 100°C. The results are compared to HexFlow RTM6, a commonly used RTM epoxy. Nanopox F400 from
Evonik Hanse, Germany, was supplied as a masterbatch containing
40 wt.% of silica nanoparticles predispersed in a diglycidyl ether
of bisphenol A (DGEBA) epoxy resin. These particles were then
mixed with the XB3585 resin and the masterbatch resin in order
to produce formulations including 10 wt.% and 20 wt.% of silica
nanoparticles.

No107 August - September 2016

/ jec composites magazine

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