Development of polyurethane-coated aluminum powder using solvent evaporation induced method

Abstract

The lack of shape and size uniformity and dispersibility of aluminum powder in a polymer binder has a compromising effect on the solid composite propellant's structure and performance. To tackle these issues, research aim to develop a coating system based on a polymer binder of polyurethane (PU) of Hydroxyl-Terminated Polybutadiene (HTPB) for aluminum powder was designed. The coating process was carried out using the solvent evaporation -induced coating using two variations of liquid and solid additions and two types of aluminum powders. Uncoated aluminum powder with high purity was coated using PU solution in ethyl acetate solvent. The solid-liquid mixture was then vigorously stirred to get a stable mixture. The solvent was removed from the mixture using a vacuum distillation system at 50°C. The solvent-free mixture was cured at 60°C for a week. SEM (Scanning Electron Microscopy) analysis of the PU-coated aluminum powder showed a higher shape factor of 0.861 and 0.900-0.907, a size reduction at 4.45-4.65 µm and 12.1 µm. The presence of the PU layer had been confirmed using FTIR (Fourier-Transform Infra-Red) spectroscopy and compared to the spectra of HTPB. The peak of 710 cm−1 (1,4-cis), 910 cm−1 (1,2-vinyl), and 970 cm−1 (1,4-trans) from the HTPB had been observed in the FTIR spectra of the PU-coated aluminum powders. The solvent -evaporation - induced coating method could produce highly spherical aluminum powder particles with a lesser size than the original uncoated powder particles, with a stable PU layer of coating suitable for solid composite propellant production.