1
Paper number 20069, Text pages 1 to 30, Session 3B, on 2018 NDIA-IMEMTS, event number 8550, April 23-29,
2018, Portland Oregon, USA. http://www.ndia.org/events/2018/4/23/imem
Influence of concentration, type and particle size of fillers on the dy-
namic mechanical behaviour of elastomeric HTPB binder
Manfred A. Bohn
1
, Mauricio Ferrapontoff Lemos
2, 1
, Günter Mussbach
3, 1
1
Fraunhofer Institut für Chemische Technologie (ICT), Pfinztal, Germany
2
Brazilian Navy Research Institute, Rio de Janeiro, RJ, 21931-090, Brazil
3
Bayern-Chemie GmbH, D-84544 Aschau am Inn, Germany
Abstract
Recently, it was found that the second peak of the loss factor curve determined by DMA of
HTPB bonded composite propellants and high explosives can change significantly in intensity
and shape with composition. Composite propellants with AP, whereby the AP particles are
connected via bonding agents to the binder matrix, can show a pronounced second peak,
whereas HMX and RDX produce a weaker peak and with high contents of them, it can show
only as shoulder attached to the first peak. The second peak is much more sensitive to ageing
and to de-wetting. This means interactions between filler and matrix influence the appearance
of the peak. Therefore, a more detailed investigation was started to elucidate the influences of
fillers on the loss factor curve. Polyurethane binders made from polyol HTPB and isocyanate
IPDI were filled with 20, 40 and 60 mass-% of ammonium perchlorate (AP), aluminum (Al) or
RDX, using fine and coarse particles. For obtaining the cured composite, a special turning de-
vice constructed and manufactured at Fraunhofer ICT was installed inside the curing oven in
order to avoid sedimentation of the fillers during curing. The composites were characterized by
DMA in torsion mode from -100°C to +70°C, and the quality of distribution of fillers was evalu-
ated by X-ray micro-tomography, which showed homogenous distribution of the filler particles
in the samples. The part of loss factor tanδ at lower temperatures originates from the glass-
rubber transition of the binder parts, which are unrestricted in mobility. This is defined in this
way in comparison of the second broader peak at the high temperature side of the first peak,
which is caused by binder parts restricted in mobility. The temperatures at each maximum are
called Tg
unr
and Tg
res
, respectively. The results are: AP and RDX cause more changes in in-
tensity of the first main peak in tanδ than Al particles. The maximum temperature Tg
unr
is near-
ly not changed by any of the fillers. The changes in tanδ intensity determined from baseline
corrected loss factor curves and modelled by EMG (exponentially modified Gauss) distribu-
tions indicate that Al has a stronger interaction with HTPB binder than AP and RDX particles.
The particle sizes of AP and RDX and probably their shapes effect the viscoelastic properties.
Increasing content of AP and RDX increase the storage shear modulus G’ and somewhat the
loss shear modulus G’’, but as a whole tanδ intensity is lowered in the main peak.
Keywords: AP; aluminum; RDX; HTPB; filler effects on loss factor; DMA loss factor modelling
1. Introduction
In a series of investigations [1 to 14] it was found that the second peak in the DMA loss factor
curve of HTPB (hydroxyl terminated polybutadiene) bonded composite rocket propellants
(CRP) can change significantly with composition. AP (ammonium perchlorate) bonded with
bonding agents to the binder matrix causes a pronounced peak see Fig. 1, curve CRP1,
whereas HMX and RDX show only a small peak, see Fig.1 curve HX1, which changes to a
shoulder with high degree of filling, see Fig. 1, curve HX2. Up to now for HMX and RDX no
such bonding agents exist as for AP. Total intensity and position of the maxima is also deter-
