Invariant kinetic parameters of polymer thermolysis. III. The influence of a fire‐retardant additive on polypropylene thermolysis

Abstract

SYNOPSISThe present paper analyzes the thermolysis gross-kinetics of polypropylene ( P P ) and a PP-based fire-resistant composition containing 10% of hexabrominecyclododecane ( HBCD ) as the fire-retardant additive. The kinetic parameters of thermolysis of an individual PP are calculated by the isoconversion method. The increasing dependence of the effective activation energy on the transformation degree has been established. This dependence is attributed to the competitive character of the processes of thermodestruction initiated by oxidation and to the PP pyrolysis. Thermolysis in the helium atmosphere leads to oxidation suppression and increases the effective activation energy at the initial stage of thermolysis. A similar effect can be attained by introducing HBCD into PP, which permits considering the ability of inhibiting the oxidation process proceeding in the condensed phase as one of the reasons of the fire-retardant activity of this additive. JTRODl CTlONThis paper is a sequel to our previous Since then, we have carried out investigations aimed at elucidating the methods of calculation that permit obtaining reliable values of the kinetic parameters ( K P ) of a process. In particular, it has been found3 that besides the method4 of invariant K P (IKP), reliable information about KP can also be obtained by other methods that do not use the discrimination of formal models in solving the inverse kinetic problem. In this case, the KP obtained by the nondiscrimination methods, like the parameters calculated by the IKP method, display the property of invariance with respect to the choice of the process model. This fact makes it possible to dissociate the concept "invariant KP" from a concrete method of calculation, thus giving it a broader sense, namely: parameters calculated without any assumptions about the concrete form of the process model.Besides, it has been found5 that the application of the IKP method is limited by the gross-single-* To whom correspondence should be addressed. stage processes (i.e., by processes whose kinetics can be described by one rate constant). To obtain information about complex processes, a special approach was proposed previ~usly,~ which is based on the analysis of the shape of the transformation-degree dependence of the effective activation energy calculated by the isoconversion method. The isoconversion methods permit finding the values of K P that are not associated with the choice of the process model or, in other words, display the property of being invariant. Therefore, in this paper, which aims to study the kinetic features of thermolysis of pure polypropylene (PP) and a PP-based fire-resistant composition containing hexabrominecyclododecane (HBCD ) , all the kinetic information has been obtained from the viewpoint of the above-mentioned approach relying on one of the isoconversion methods.6The urgency of our investigation is due to the necessity of elaborating theoretically substantiated approaches to the solution of the practically important problem of increasing the ...

Thermal and fire degradation of recycled and polluted polypropylene‐based materials

“…Reactions 2 and 4 can be assigned to char oxidation reactions. The values of activation energies found for the reactions are similar to other studies 32, 33…”

Properties and thermal degradation kinetics of polystyrene/organoclay nanocomposites synthesized by solvent blending method: Effect of processing conditions and organoclay loading

“…21 21 and also the effect of hexabromocyclododecane as a fire-retardant additive on polypropylene (PP) thermal degradation. 22 Wang and coworkers [23][24][25] systematically investigated the thermal oxidative degradation behavior of poly(ethylene terephthalate) and its blend with MMT nanocomposite. Very few studies on the thermal or thermo-oxidative degradation kinetics of the flameretarded PP with intumescent flame-retardants (IFRs), e.g., Neininger et al 26 used a mathematical model, i.e., simplified kinetic scheme, to predict the global kinetics of the thermal degradation of IFRs added in textile-reinforced composite.…”

“…Many researchers have investigated the thermal degradation kinetics of the nanocomposite material 21–25. Lesnikovich et al examined the kinetics of oxidative degradation of flame‐retardant polyesters [poly(ethylene terephthalate)]21 and also the effect of hexabromocyclododecane as a fire‐retardant additive on polypropylene (PP) thermal degradation 22. Wang and coworkers23–25 systematically investigated the thermal oxidative degradation behavior of poly(ethylene terephthalate) and its blend with MMT nanocomposite.…”

Invariant kinetic parameters of polymer thermolysis. IV. Influence of fire‐retardant additives on polypropylene thermolysis

“…Dependencies ( 1) and ( 2 ) were obtained in our previous work.' It is seen from Figure 1 that unlike the monotonically increasing dependencies ( 1) and (2) characteristic parallel reactions, dependence (3 ) goes through the minimum in the region of transformation degree near 0.2. As mentioned above, the increasing character of dependencies ( 1 ) and ( 2 ) is attributed to the competition of two main processes proceeding at PP thermolysis: the oxidation-initiated destruction and pyrolysis.…”

“…It is seen from Figure 1 that unlike the monotonically increasing dependencies ( 1) and (2) characteristic parallel reactions, dependence (3 ) goes through the minimum in the region of transformation degree near 0.2. As mentioned above, the increasing character of dependencies ( 1 ) and ( 2 ) is attributed to the competition of two main processes proceeding at PP thermolysis: the oxidation-initiated destruction and pyrolysis. Likewise, we can, perhaps, explain the character of dependence ( 3 ) in the range of transformation degrees 0.2-0.9, where it is similar in shape and position (taking into account the uncertainty in activation energy calculating; see The difference in shape of the above dependencies is a source of useful information on the mechanism of the action of fire-retardant additives on the kinetics of PP thermolysis.…”