JEC COMPOSITES MAGAZINE - Issue #125 - November/December 2018 - 46

FEATURE
sandwich structure

Material shift in wind energy

Philipp Angst,
Global Product Director AIREX®
Roman Gaetzi,
Director Global Business Development
3A Composites Core Materials

F

irst-generation PET foam cores
were introduced over 10 years
ago and quickly adopted as
a cost-efficient core in wind rotor
blades. Continuous improvement and
some radical innovations have made
PET the material of choice for wind
rotor blades.
Such radical innovations include improved damage tolerance and specific
mechanical properties, resin-saving
surface coatings (e.g. AIREX® SealX),
and direct extrusion technology (as
opposed to welded blocks/sheets)
with improved directional properties
and foam homogeneity (e.g. AIREX®
T10).

The dominant design of today's wind rotor blades consists of sandwich
structures both in the blade shells and in their shear webs. The core
materials in these sandwiches are rigid foam and structural balsa cores.
While SAN- and PVC-based foams have been predominantly used as
foam cores for blades in the past, today the more recent PET-based
foam cores have taken over a leading role that continues to gather
momentum. PVC and PU foams are widely used for nacelle covers, and
PET foams are also increasingly chosen.
lation - polyethylene terephthalate:
-- Foam production process: Contrary to
batch-produced PVC, SAN, or PU foams,
PET is produced in a fully-automatic, continuous extrusion process. Advantages are
very consistent properties, well-controlled
quality, and a high degree of automation.
-- Thermoplastics/recyclability: PET foam
cores are pure thermoplastics. This has
advantages in processing but also allows
for the simple and cost-efficient recyclability of the material so that a modern,
professional PET foam core production
has a yield of close to 100%.
-- Raw material cost base: PET is one of the
most widely used polymers across the

PET foam core - the rising star
These major innovations increased the
cost efficiency of PET and therefore
further fuelled its growth. In addition to
the high mechanical properties required
in core materials, PET foam cores excel
with their unparalleled fatigue resistance, very high temperature resistance
and their recyclability. Moreover,
second-generation, directly-extruded
PET cores (e.g. AIREX® T10) feature
unrivalled directional properties and
cell homogeneity (figure1).
Base polymer and raw material
costs favour PET foam cores
PET foam cores have several advantages that stem from their polymer formu-

46

jec composites magazine / N°125 November - December 2018

world, also thanks to its use as beverage
bottles. Raw material prices for PET resin
are among the lowest (see Figure 2) and
- more importantly - historic data shows
that they are quite stable while others - e.g.
polyurethanes, which are also needed to
produce PVC foams - have seen dramatic
price hikes in the past.
The following graph illustrates selected raw material prices and their relative
evolution. It shows a remarkable price
increase in MDI, which is an important raw material for both PVC and PU
foams. It also shows the cost-efficient
and stable pricing of PET raw materials (figure2).

Fig. 1: Fatigue resistance of different core
materials. The Wöhler
curve of PET (AIREX®
T92 and T10) is much
flatter than the steep
PVC curves. PET cores
can sustain repeated
load cycles much longer/at higher load

Fig. 2: Price evolution
of polymer raw materials used for the most
important foam cores;
PU raw materials (MDI)
experienced a steep
increase while PET
raw material prices
remained quite stable
(Source KI - Kunststoff
Information,
www.kiweb.de)
http://www.kiweb.de
Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #125 - November/December 2018
