JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 49

New products for longer blades help to cut cost

Tab. 1: Properties of AIRSTONE™ 870 bonding paste

Conditions

Unit

Value

Density

23°C, cured

g cm-3

1.16

Tensile strength

23°C

MPa

57.6

Tensile elongation

23°C

%

4.7

Single lap shear strength

23°C, GFRP substrate

MPa

Crack resistance k1c

23°C, CT

MPa m

2.5

Impact resistance

-40°C

kJ m

22.2

Open time

40°C

min

120

30
-1/2

-2

Fig. 1: Single lap shear strength of AIRSTONE™ 870 vs. open time (28°C, 70%RH)

The adhesive curing time directly
influences mould occupation time, and
therefore the blade production cycle
time. Despite the long open time, this
bonding paste is designed for fast cure
cycles. As an example, 95% conversion
and 78°C Tg midpoint are already
reached after 4 hours of cure of at 70°C.
This is a good basis for cure cycle optimization to enable high productivity.
With global environmental, health
and safety regulations becoming more
stringent, end users are putting pressure
on their suppliers to refrain from using
highly hazardous materials in their
formulations. Although regulations
tend to be moving targets, the paste

has been designed to neither require
a toxic label nor contain substances of
very high concern (SVHC).
Infusion resin
Vacuum infusion is basically a simple
process, but in practice, there are a
number of challenges, including the
critical need to reproducibly generate
high quality under changing workshop
conditions. The move towards longer
blades tends to increase the potential
cost of nonconformities. In particular,
increased laminate thickness can lead
to higher exotherm, while the desire
to use carbon fibre to reduce weight
is difficult to achieve with standard
infusion resins.

By developing the AIRSTONE™ 880
infusion resin system and AIRSTONE™
870 bonding paste for wind turbine
blades, Olin Epoxy has shown not only
its dedication to the wind market, but
also its ability to listen to customer
requirements, translate these into a
well-defined set of product properties,
and finally deliver innovative products
that meet customer requirements.
More information:
www.olinepoxy.com

Tab. 2: Viscosity and pot life of AIRSTONE™ 880 infusion system

AIRSTONE™880E Epoxy Resin with Hardener

882H

886H

Viscosity @ 25 °C (mPa s), ASTM D-445
Pot Life @ 24 °C (min), Gel Timer

250
124

235
705

N°116 October 2017

/ jec composites magazine

Feature Wind energy

machine. As a side effect, the density
is decreased by ~10%, thereby reducing the blade weight. As a result, the
mechanical load on all turbine components is reduced, increasing fatigue life
and, therefore, reliability.

To better serve customers having
challenging process conditions, Olin
has developed an improved infusion
resin system, AIRSTONE™ 880. The
most striking feature of this material
is a significantly lower mix viscosity
(see Table 2), compared with standard
infusion systems. The low viscosity
provides good flow properties. This
will make infusion faster, directly
reducing processing time. Customer
feedback has proven the additional
benefits of using this material: it has
been stated that the material has bestin-class degassing behaviour and fibre
wetting properties, leading to lower
defect rates, higher first-pass quality,
and less re-work.
All these properties make this infusion
resin the first choice for carbon fibre
infusion, not only for building windblade spar caps but also for other
non-wind applications. Currently,
carbon fibre is often infused using
semi-latent systems, because these
have very long open times. Trials have
shown that AIRSTONE 880™ can
infuse carbon fibre at the same speed
and quality, while avoiding the thermal
problems normally encountered with
latent systems due to the higher kick-in
temperature of the reaction and the
internal stresses generated at the high
gelation temperature.

49
http://www.olinepoxy.com
Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #116 - October 2017
