JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 69

prepreg

Elevating aerospace prepreg
performance
Henkel has developed and brought to market the Loctite
Benzo¬xazine (BZ) composites family that includes prepregs,
infusion resins, film adhesives and tooling materials. Developed
spe¬cifically for the aerospace industry, Loctite BZ products
offer a comprehensive solution over commonly used epoxies,
phenolics and BMIs, in areas such as product performance, storage, processing, and health and safety.

ualifications for benzoxazine prepregs
are currently in progress for both the
Airbus A380 and COMC C919, with
the material fully tested according
to major OEM specifications and design
requirements. Benzoxazines can compete
in all ranges of service temperatures and
tough¬ness for both primary and secondary
struc¬ture applications.

Room temperature stability
The fact that Loctite Benzoxazine (BZ) is a
ring-opening mole¬cule means it has latency
at ambient temperature. It can be stored at
room temperature with minimal advancement of the resin, removing the need for
refrigerated shipping and storage. The prepreg systems have been shown to be stable at
room temperature for more than six months,
retaining good shop handling characteristics,
such as tack, drape and flow, over this time.
This is confirmed by thermal analysis such
as differential scanning calorimetry (DSC)
which shows minimal changes in reactivity
after long-term, room temperature storage.
Resin dominated mechanical properties
also show very little change after extended
ambient storage of the prepregs before cure,

for example the cured Tg, compression
after impact (CAI) and interlaminar shear
properties. The storage life of BZ prepregs
can be extended considerably by cold storage. Current studies show no change to the
prepregs after 2-years of refrigerated storage,
and these long-term evaluations of storage
life are continuing.

Superior qualities
over comparable technologies
BZ prepregs demonstrate a unique combination of properties including high service
temperature, high toughness and flammability resistance. Three prepreg grades have
been commercialized with Tgs ranging up
to 230°C. While BMI does hold a small
advantage over BZ in terms of absolute
service temperature, BZ holds a significant
advantage with regards to cost and processing, demonstrating a total autoclave cure
cycle of just 6 hours.
BZ's main advantage over primary and
secondary structure epoxy applications is its
excellent performance in terms of CAI and
open-hole compression (OHC). The moisture uptake of BZs during hot-wet exposure
is significantly lower than that of epoxy or
bismaleimide (BMI) resins, and hence BZs
have better retention of properties in the
moisture conditioned state. In every grade of

By
David Leach, Global Composites
Segment Manager - Aerospace,
Henkel Adhesive Technologies

the material, it is possible to push the hot-wet
compression further while maintaining good
toughness. OHC shows good retention
of properties from room temperature up
to 213°C wet, as well as very good CAI.
Shear performance is linear up to 204°C.
The materials also meet aerospace in-plane
shear fluid resistance requirements, showing
over 90% retention in both modulus and
strength after exposure to a wide range of
aircraft fluids. Cured Loctite BZ resin also
has superb resistance to UV light exposure
compared to a typical epoxy, showing no
discolouration, chalking or degradation after
95 days in outdoor exposure. Benzoaxzine
resins have inherent resistance to fire and

Specifically developed for the aerospace industry

No97 May - June 2015 / jec

composites magazine 69

JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015