Combusition of polymers and the effect of fore retardant additives : a mechanistic approach.

Abstract

CHAPTER 1 This chapter constitutes a general description of the combustion of polymers and the various processes involved. Processes like gas‑phase reactions, surface reactions and solid‑phase reactions are discussed in detail. Combustion of hydrocarbons, mechanism of smoke formation, cool flames etc. are considered under gas‑phase reactions. The controversy regarding polymer degradation at the surface during burning — whether the degradation is oxidative or thermal — and the evidences for both are presented. A brief account of the smouldering combustion is given. The discussion of solid‑phase reactions considers thermal and oxidative degradation of polymers in general and polystyrene in particular. The last section gives a short account of combustion models. CHAPTER 2 In this chapter, the available fire retardants and the mechanisms of fire retardancy are reviewed. Various types of fire retardants — reactive as well as additive — particularly phosphorus and halogen compounds are discussed, considering few specific systems also. The char‑forming action of phosphorus fire retardants and the flame‑inhibition effects of halogen fire retardants are illustrated in various systems. CHAPTER 3 The first part of this chapter gives a review of the literature of polymer ignition including theories of ignition, effect of additives, self‑ignition phenomena etc. The second part describes the experimental techniques employed in the present study on polymer ignition. The procedures for the preparation of the polymer samples, the measurement of ignition temperature, ignition delay and weight‑loss before ignition are described in this section. The third part of the chapter presents the various results and the interpretation obtained from the ignition experiments on PS samples containing different additives. A correlation between various parameters of ignition was attempted. The effect of char formation on ignition was analysed and a semi‑quantitative treatment was done, applying the solid‑phase thermal model of ignition. A comparative study of the effects of ammonium phosphates, ammonium halides and organic bromine compounds on the ignition of PS was made. Further, an analysis of the weight‑loss and the rate of weight‑loss for these samples at ignition has been conducted. The final section presents the results of a kinetics study of ignition. CHAPTER 4 The effects of various additives on the regression rates during burning of PS are discussed in this chapter. The details of the experimentation form the first part. The later sections describe the results of this study. The influence of sample diameter, dripping and flow rate of the oxidizer on the regression rate was investigated. The results of the degradative studies on samples containing ammonium phosphates, ammonium halides etc. are also given in this chapter. The mechanism of char formation in samples containing phosphate additives and its significance are explained. The proposed mechanism has been substantiated with various analytical results. The effect of HCl and HBr has been studied on the degradation and combustion of PS. The influence of condensed‑phase degradation on steady‑state combustion has been examined in PS + phosphates and PS + halides systems. CHAPTER 5 This chapter discusses the salient features of the extinction of polymer flames. A review of the available literature on this aspect has been given in the beginning of this chapter. Subsequently, the details of the experimental technique employed in the present investigation and the results obtained on the quenching of polymer flames are discussed. The dependence of the flame quenching on the nature of flames, char formation etc. were examined. CHAPTER 6 This chapter presents a general treatment on polymer gasification processes. The first part constitutes an introduction to this aspect of polymer combustion, which includes a description of the methods for determining the heats of gasification for polymers, the chemistry and kinetics of gasification etc. Following sections deal with the development of a new term — the Mean Fragment Size (M.F.S.) — which is important in polymer pyrolysis and its evaluation from heats of gasification (Qg) data. A convenient experimental technique has been designed to determine Qg of polymers at different temperatures and the M.F.S. values were calculated for several polymers. The usefulness of this parameter is also discussed. The reliability of the calculated M.F.S. data was checked by directly determining M.F.S. from the actual composition of pyrolysis products. Pyrolysis gas chromatography was resorted to for the analysis of the products of pyrolysis and the results are presented in the final sections of the chapter. CHAPTER 7 The essential features and findings of the present investigation are summarised in this chapter. CHAPTER 8 This chapter constitutes 4 appendices. Appendix I gives a brief discussion on mass transfer number, B, and its calculation from the Q data. Appendix II considers the effects of diammonium phosphate on wood and wood‑polymer composites. Appendix III and IV describe the application of a new parameter — termed as the Flammability Index — in polymers and other combustible materials.