COMPREHENSIVE ANALYSIS OF INGREDIENT PROPERTIES AND THEIR IMPACT ON THE MECHANICAL PROPERTIES OF COMPOSITE SOLID PROPELLANTS

Composite solid propellants (CSP) consist of ammonium perchlorate (AP), aluminum powder, polymer binder, and various additives. Anomalous behavior in the modulus of CSP during segment processing prompted an extensive investigation into the test parameters affecting mechanical properties. This included examining the moisture and volatile content of all ingredients, acid value of dioctyl adipate (DOA) and hydroxyl terminated polybutadiene (HTPB), 2-ethyl hexanol (raw material of DOA) content in DOA, and total moisture content of AP and HTPB microstructure. Despite meeting ingredient property qualifications, modulus variance persisted. Sample processing trials at a 3.5 kg scale contrasted with final processing involving 2.5 tons per batch, up to 32.5 tons per segment. Significant dispersion in mechanical properties was observed within production programs. Although sample trials used the same raw materials, multiple lots of AP ranging from 17 to 22 tons were required per production program due to AP's significant role in CSP. This led to a focused examination of AP particle morphology beyond particle-size distribution (PSD) as AP's substantial proportion directly affects processing and mechanical properties. Microscope analysis indicated that smooth, round particles resulted in a Young's modulus under 3.92 MPa, irregular particles in the 3.92-5.88 MPa range, and agglomerated particles exceeding 5.88 MPa. A particle-size and shape analyzer further evaluated sphericity, symmetry, and aspect ratio, revealing a decrease in these values as modulus increased (from 3.14 to 8.04 MPa). These findings, aligned with microscopy study conclusions, contribute to a deeper understanding of CSP mechanical properties relative to AP particle shape.