1 AN EXPERIMENTAL AND THEORETICAL INVESTIGATION INTO BURNING CHARACTERISTICS OF PPS-GLASS FIBER COMPOSITES

In this study experiments are conducted on thick PPS-fiberglass composites instrumented with thermocouples. These samples are especially manufactured from prepreg with installed in-depth thermocouples. The samples were exposed to various external radiant heat fluxes (2-7 W/cm2) in air and nitrogen atmospheres, and mass loss and in-depth temperatures were measured as a function of time. It was observed that the composite goes through two transformations: (1) Physical transformation from crystalline to molten PPS at about 545 K and (2) Chemical decomposition of molten PPS at about 813 K. At high heat fluxes it spontaneously ignites in air. From these experiments, a melting front and a decomposition front inside the composite were identified and two models were developed and solved numerically. The first model was a simple two front (moving boundaries) model that gave excellent results for low heat fluxes i.e. prior to the onset of thermal decomposition. This model allowed us to determine the properties of the PPS-fiberglass composite prior to melting. The second model included both the melting front and the decomposition front, simulated by one-step Arrhenius decomposition kinetics. This model works satisfactorily for both low and high heat fluxes. Comparison with experiments resulted in an excellent match with in-depth temperatures and volatile mass flux rates. It was found that the properties of the composite change substantially with temperature and density. It was also determined that melting of PPS could be treated as a sudden change in density but not decomposition of PPS