Investigation Of Pyrolysis, Flame Spread And Toxicity Of Acrylonitrile Butadiene Styrene Copolymer And Its Nanocomposites

Acrylonitrile butadiene styrene coplolymer (ABS) is a kind of widely used thermoplastic polymeric material, due to high strength, good toughness, drug resistance, eaze of processing and high price-to-performance ratio. It is a terpolymer of acylontrile, butadiene and styrene. It has been extensively employed in traffic and transportation, electronics and construction. However, ABS exihibits low thermal resistanceand high fire risk. Nano-additives have been used to improve the flame retardancy of ABS. However, the investigation into the influence of nanoclays on pyrolysis process, flame spread characteristics and fire toxicity is rarely reported. In this dissertation, those factors related to fire hazards of ABS and its nano composites were investigated, which was meaningful for fire risk evaluation of polymer materials. The main research work was as follows:1. The thermal degradation of ABS, ABS/CNT and ABS/MMT nanocomposites were investigated by thermogravimetric analysis (TGA) at different heating rate. With the increase of heating rate, TG and DTG curves moved to high temperature. The peak value of DTG was reduced with increasing the heating rate. The activation energies were calculated based on Kissinger and OFW methods. The results indicated that the activation energies of these three kinds of materials were similar, impling the negligible influence of nano-addtives on the decomposition process.2. The early fire characteristic test of ABS and ABS/MMT were conducted in this study. The influence of heat flux and addtives on mass loss rate were discussed. Both those experiments and the pyrolysis process of polypropylene (PP), PP/MMT composites, ABS and ABS/GNS/MHR composites in a cone calorimeter test were simulated with a numerical codes ThermaKin. The heat release rate (HRR) and the surface temperature as a function of time were compared with experiment data. With reasonable input parameters, the pyrolysis behaviors were predicted reasonably. Subsequently, the influence of properties of char residue on the HRR was discussed. The char residue of ABS/MMT and PP/nano-clay acted as a heat transfer barrier, while the char layer of ABS/MHR/GNS played as a mass transfer barrier. Finally, the sensitivity of the residue characteristic parameters to the model output were studied.3. In order to determine the effect of additives effect on the flammability of ABS, a series of comparative experiments of flame spread have been conducted. For flame spread experiment, both the addition of nanofillers and the dimension and package level of sample were also considered. Without sidewall, widths and heights increased with W; With sidewall, widths were essentially constant, and heights increased. Without sidewall, the addition of MMT increased the flame width and decreased the flame height; With sidewall, MMT increased the flame width. The flame height had no obvious change. The addition of MMT could reduce the flame spread rate by forming the char layer to delay the release of flammable gas. Consequently the flame feedback reduce, thus the spread rate also decreased. The reduction effects of MMT were more obviously for samples with side walls. The flame spread rates of samples with sidewall increased with increasing sample width while the spread rates of samples without sidewall had a turning-point. The crucial factor influencing the variation tendency with width was the relative magnitudes of enlargement part from the radiation heat flux and the diminishing part from the convection heat and side burning.4. The yields of toxic products of ABS nanocomposites have then been measured under different ventilation and temperature conditions by the steady state tube furnace (SSTF). Under well-ventilated condition, the yield of CO was lower, and the yield of CO2 and O2 consumption were higherthan under-ventilated condition due to a higher combustion efficiency. Under well-ventilated condition at 625℃, MMT and CNT reduced the smoke toxicity. On other conditions, the effect of nanoclay was not obvious. The presence of flame retardants and the incorporation of nano-clay reduced flammability, but this work showed that there was no systematic increase in fire toxicity through the use of these additives, particularly under the most lethal under-ventilated fire conditions. A fire simulation using CFD techniques has been conducted to investigate the tube furnace environment for well ventilated conditions. The simulation predictions have been compared with the corresponding measurements taken from experiments of the tube furnace and a good agreement between the computation and the measurement was obtained.5. On the basis of cone calorimeter, flame spread and SSTF results, analytic hierarchy process (AHP) method was used to evaluate the fire hazards of ABS and its nanocomposites. The results indicated the sequence of fire hazard was as follows: ABS>ABS/CNT>ABS/MMT.