Pyrolysis and Oxidative Pyrolysis of Polypropylene

Abstract

Amorphous and semi-crystalline polypropylene samples were pyrolyzed in He from 388°-438°C and in air from 240°-289°C. A novel interfaced pyrolysis gas chromato graphic peak identification system was used to analyze the products on-the-fly; the chemical structures of the produ were determined also by mass spectrometry. Pyrolysis of polypropylene in He has activation energies of 5-1-56 kcal mol -1 and a first-order rate constant of 10 -3 sec -1 at 414°C. The olefinic products observed can be rationalized by a mechanism involving intramolecular chain transfer processes of primary and secondary alkyl radicals, the latter being of greater importance. Oxidative pyrolysis of polypropylene has an activation energy of about 16 kcal mol -1 ; the first -order rate constant is about 5 X 10 -3 sec -1 at 264°C. The main products aside from CO 2 , H 2 O, acetaldehyde, and hydrocarbons are ketones. A simple mechanistic scheme ha been proposed involving C-C scissions of tertiary alkoxy radical accompanied by Η transfer, which can account for most of the observed products. Similar processes for sec ondary alkoxy radicals seem to lead mainly to formaldehyde Differences in pyrolysis product distributions reported here and by other workers may be attributed to the rapid re moval of the products by the carrier gas in our experiments sphere has been surprisingly little fundamental work reported on the chemistry of the process involved in the burning of polymers and its inhibition, despite the great technological and socio-economical impor tance of the subject. In our laboratories we have undertaken a funda-0-8412-0381-4/78/33-169-175$05.75/l

The Involvement Of Oxygen In The Primary Decomposition Stage Of Polymer Combustion

“…For example, with polypropylene, oxygen decreases the reaction temperature by some 200 0 and reduces the activation energy by about 150 kJ mol (19,20); and similar behaviour is found with poly-(vinylidene fluoride), where oxygen, in addition to causing a dramatic lowering of the activation energy and the pre-exponential factor, changes a normally second-order reaction to one of zero order (21).…”

Kinetic Phenomena in Mechanochemical Depolymerization of Poly(styrene)

“…During pyrolysis reactions, O 2 can attach to a carbon-centered radical chain end to form a peroxyl radical . The peroxy radical then abstracts a hydrogen atom, and subsequent elimination of the hydroxy radical leaves a chain-end oxy radical, which is the site of depropagation.…”

“…During pyrolysis reactions, O 2 can attach to a carbon-centered radical chain end to form a peroxyl radical. 77 The peroxy radical then abstracts a hydrogen atom, and subsequent elimination of the hydroxy radical leaves a chain-end oxy radical, which is the site of depropagation. Thus, we propose an O 2 -initiated pathway via a peroxy radical intermediate at the metal grinding surfaces as an alternative for depolymerization under mechanochemical conditions.…”

Degradation of synthetic polymers: Microbial approach

“…7 Microorganisms that are capable of degrading the polyolefins (Polyethylene, Polystyrene, and Polypropylene) polyvinyl chloride, polyethylene terephthalate are isolated from the open environment, the soil of plastic dumpsite, sewage sludge, landfills, marine water, and the plastic-eating worm. 8…”