Effect of HMX distribution and plasticizer content variations on the DMA loss factor of HTPB-IPDI binder

It is known that different content of solid fillers in HTPB-IPDI elastomer binder have a significant influence on shape and intensity of the loss factor tand (=ratio of loss modulus to storage modulus). The loss factor is determined with forced periodical deformation of the sample, best obtained with DMA (dynamic mechanical analysis). To analyse such changes, the methodology of EMG (exponentially modified Gauss) distribution is used. Therewith very precise description and modelling and consequently evaluation of the loss factor curves is possible regarding binder parts of different molecular mobility. Some years ago, around 2011, the idea came up to augment the binder energetically by very fine energetic particles. One objective was to get a more homogenous distribution of the high explosive filler to improve the detonation front. Other aspects are: higher solid filler content, to increase density and therefore detonation velocity and eventually also a reduction in shock sensitivity. At the Fraunhofer ICT the idea of enriched binder was further followed. Techniques were developed to manufacture energetically augmented binders, whereby the fine energetic particles were created inside the binder itself. Besides a lot of aspects with regard to detonation front, shock sensitivity and reduced sensitivity of the energetic formulations, the mechanical behavior of such binders is important. An energetic particle augmented HTPB binder was used to manufacture cured formulations. The energetic material was HMX. The achieved mean particle size was 1.37 mm. The amount of very fine HMX in HTPB alone was 10 mass-%, which yielded in the high explosive formulation 0.75 mass-%. Total HMX content was 85 mass-%, bimodal and formally trimodal with the very fine particles. For comparison a normal binder was used to get a formulation with the same total HMX content, using the bimodal filling with HMX. A second set of formulations were made with another HMX quality. One formulation was bimodal the other contained only the fine material, but in higher concentration as usual. Torsion-DMA measurements were performed. The evaluation revealed clear differences in the loss factor shapes between all formulations. The differences can be explained and are discussed.