Modeling flow effects during polymer decomposition using percolation lattice statistics.

摘要

Foam encapsulants are commonly used in missile systems to increase the lifetime and reliability of the missile. The safety of the missile is greatly affected by the properties of the encapsulant. The pressure rises inside the missile as the foam degrades into smaller gaseous products, since the missile housing is essentially a closed container. If the pressure is high enough the housing may burst. The two foam encapsulants studied in this project are polyurethane foam and Removable Epoxy Foam. The ultimate goal of this project was to develop a computer model that can describe foam pyrolysis as a function of time, temperature, pressure, gas composition and confinement. The effect of pressure on foam decomposition was not well understood, with minimal of confinement effects. The effect of decomposition product flow was also not well understood. A previous model was able to empirically account for the pressure effects, but was not able to incorporate the confinement or flow effect into the foam decomposition.; Reliable pyrolysis data for both foams were obtained at atmospheric and high pressures, separate from confinement effects in this project. Buoyancy effects were found to be significant. The pyrolysis data showed that as the heating rate increased, the mass loss curves for the foam were shifted to higher reaction temperatures. A shift to higher reaction temperatures with increasing pressure and decreasing orifice size was observed. Furthermore, the decomposition product distribution shifted to produce less toluene diisocyanate and more carbon dioxide.; A model, called the MTPUF (Mass Transport PolyUrethane Model), was developed for the foam decomposition to include the capability for flow in and out of the cell. A population balance theory was the main idea that allowed for the capability of modeling the flow. Kinetic parameters were fit to the atmospheric pyrolysis data through an optimization technique. The parameters were tested against the high pressure and confinement data without being changed. The MTPUF modeling results correctly predicted the observed trend with heating rate, pressure and confinement and therefore, the MTPUF model seems capable of predicting these three effects on the polyurethane foam decomposition.