Investigation of Flame Spread, Pyrolysis and Toxicity Characteristics of Acrylonitrile Butadiene Styrene and its Nanocomposites

丙烯腈-丁二烯-苯乙烯及其納米材料的火蔓延、熱解特性及毒性研究

Student thesis: Doctoral Thesis

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Award date26 Jan 2017

Abstract

Acrylonitrile butadiene styrene co-polymer (ABS) is a kind of widely used thermoplastic polymeric material, due to high strength, good toughness, drug resistance, easy of processing and high price-to-performance ratio. It is a ter-polymer of acrylonitrile, butadiene and styrene. It has been extensively employed in traffic and transportation, electronics and construction. However, ABS exhibits low thermal resistance and high fire risk. Nano-additives have been used to improve the flame retardancy of ABS. However, the investigation into the influence of nano-clays 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 nanocomposites are investigated, which is meaningful for fire risk evaluation of polymer materials. The main research work is as follows:

1. The thermal degradation of ABS, ABS/CNT and ABS/MMT nanocomposites are investigated by thermogravimetric analysis (TGA) at different heating rate. With the increase of heating rate, TG and DTG curves move to high temperature. The peak value of DTG is reduced with increasing the heating rate. The activation energies are calculated based on Kissinger and OFW methods. The results indicated that the activation energies of these three kinds of materials are similar, implying the negligible influence of nano-additives on the decomposition reaction. The early fire characteristic test of ABS and ABS/MMT are carried out in this study. The influence of heat flux and additives on mass loss rate are 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 are simulated with a numerical codes ThermaKin. The heat release rates (HRR) and the surface temperatures as a function of time are compared with experiment data. With reasonable input parameters, pyrolysis behaviors can be predicted reasonably. Subsequently, the influence of properties of char residue on the HRR is discussed. The char residue of ABS/MMT and PP/nano-clay act as a heat transfer barrier, while the char layer of ABS/MHR/GNS plays as a mass transfer barrier. Finally, the sensitivity of the residue characteristic parameters to the model output are studied.

2. 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, addition of nano-fillers, the dimensions and side walls are all considered. Without sidewall, flame widths and heights increase with sample widths. With sidewall, flame widths are essentially constant, and heights increase. Without sidewall, the addition of MMT increase the flame width and decreased the flame height. With sidewall, MMT increase the flame width. The flame height has 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 decrease. The reduction effects of MMT for flame speed are more obviously for samples with side walls. Flame spread rates of samples with sidewall increased with increasing sample width while the spread rates of samples without sidewall has a turning-point. The crucial factor influencing the variation tendency with sample widths is the relative magnitudes of enlargement part from the radiation heat flux and the diminishing part from the convection heat and side burning.

3. 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 is lower, and the yield of CO2 and oxygen consumption are higher than under-ventilated condition due to a higher combustion efficiency. Under well-ventilated condition at 625 °C, MMT and CNT reduce the smoke toxicity. On other conditions, the effect of nano-clay is not obvious. The presence of flame retardants and the incorporation of nano-clay reduce flammability, but this work shows that there is 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 is obtained.

    Research areas

  • Acrylonitrile-butadiene-styrene, Montmorillonite, Carbon nanotube, Pyrolysis, Flame spread rate, Toxicity, CFD simulations, fire risk