Hier finden Sie wissenschaftliche Publikationen aus den Fraunhofer-Instituten.

Evaluation of concentration, type and particle size of fillers on the dynamic mechanical behaviour of elastomeric HTPB binder

: Bohn, Manfred A.; Lemos, Mauricio Ferrapontoff; Mußbach, Günter

Pachman, J. ; University of Pardubice, Faculty of Chemical Technology:
20th Seminar on New Trends in Research of Energetic Materials, NTREM 2017. Proceedings. Pt.1 : April 26-28, 2017, Pardubice, Czech Republic
Pardubice: University of Pardubice, 2017
ISBN: 978-80-7560-056-1 (Print)
ISBN: 978-80-7560-057-8 (CD-ROM)
Seminar on New Trends in Research of Energetic Materials (NTREM) <20, 2017, Pardubice>
Fraunhofer ICT ()

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 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 content, it can show only as shoulder attached to the first peak at lower temperatures. The second peak is also much more sensitive to ageing and to de-wetting. This means interaction 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 elastomer, a special turning device constructed and manufactured at Fraunhofer ICT was installed inside the curing oven in order to avoid sedimentation of the fillers during curing. The cured composites were characterized by DMA in torsion mode from -100°C to +70°C, and the quality of distribution of fillers was evaluated 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, defined so as comparison for the second broader peak at the high temperature side, which is caused by binder parts restricted in mobility. The temperatures at each maximum are called Tgunr and Tgres, respectively. The results are: AP and RDX cause more changes in intensity of the first main peak in tanδ than Al particles. The maximum temperature Tgunr is nearly 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) distributions indicate that Al has a stronger interaction with HTPB binder than AP and RDX particles. The particle sizes of AP and RDX and their shapes effect the viscoelastic properties. Increasing content of AP and RDX increase the storage modulus G’ and somewhat the loss modulus G’’, but as a whole tanδ intensity is lowered in the main peak.