Monday  |  Milwaukee  |  04:40 PM–05:00 PM

#19266, Investigating the Interphase in Hydroxyl-Terminated Polybutadiene (HTPB) Composites via Dynamic Mechanical Analysis and Atomic Force Microscopy

State of the art explosive and propellant systems typically consist of energetic particles and a binder system. Specialized systems may contain additional components to meet application requirements, but in general these systems can be classified as highly filled polymer composite materials. The most extensively used binder systems across the energetics community are hydroxyl-terminated polybutadienes (HTPB). The HTPB binder functions to hold the particulates together into a consolidated structural media. It is well established that HTPB binders can significantly influence mechanical behavior, but much of the understanding of the fundamental mechanisms at play is lacking. Specifically, there exists a knowledge gap for the role of the interphase between the particles and the binder (i.e. the transition zone between pure binder and a particulate).
Dynamic mechanical analysis (DMA) is a technique that may shed light on the quality of the particle-binder interphase. Many polymer composites exhibit what appear to be two independent relaxation mechanisms via DMA experiments. There is general agreement that the first relaxation mechanism correlates to the glass transition temperature of the bulk polymer, however there is debate of the cause of the second relaxation mechanism. One prominent suggestion is that the secondary relaxation mechanism is attributed to the significant presence of an interphase region.
In this work we systematically investigate the effects of an effective interphase region on the presence of the loss factor peaks as exhibited through DMA experimentation. Specifically, we vary glass bead filler content of a HTPB-based composite and compare the loss factor to the measured effective volume of the interphase via atomic force microscopy (AFM). This approach may prove useful to understand the interphase mechanisms at play in energetic systems which will lead to the ability to create materials with tailored bulk mechanical properties and mitigate mechanical failures.

Jarred Tramell   Air Force Research Laboratory
Emily Hockey   Air Force Research Laboratory
Marcel Hatter   University of Dayton Research Insitute
Jesus Mares   Air Force Research Laboratory