Polypropylene thermal degradation

Keywords charring diffusion flammability kinetics nanocomposite polypropylene thermal degradation... 

Ranzi EM, Dente M, Faravelli T, Bozzano G, Fabini S, Nava R, Cozzani V, Tognotti L (1997) Kinetic modeling of polyethylene and polypropylene thermal degradation. J Anal Appl Pyrolysis 40-41 305-319... 

The thermal degradation of mixtures of the common automotive plastics polypropylene, ABS, PVC, and polyurethane can produce low molecular weight chemicals (57). Composition of the blend affected reaction rates. Sequential thermolysis and gasification of commingled plastics found in other waste streams to produce a syngas containing primarily carbon monoxide and hydrogen has been reported (58). 

This comprehensive article supplies details of a new catalytic process for the degradation of municipal waste plastics in a glass reactor. The degradation of plastics was carried out at atmospheric pressure and 410 degrees C in batch and continuous feed operation. The waste plastics and simulated mixed plastics are composed of polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene, and polyethylene terephthalate. In the study, the degradation rate and yield of fuel oil recovery promoted by the use of silica alumina catalysts are compared with the non-catalytic thermal degradation. 9 refs. lAPAN... 

The dithiocarbamates have the pentacoordinate binuclear structure (44). The diamyl- and diethyl-dithiocarbamate complexes have been found to inhibit the hardening of asphalt, but the effect appears too weak to be useful.127 The latter complex is an effective antioxidant for polyethylene,128 polypropylene,129 polystyrene,130 poly(methyl methacrylate)130 and an isoprene-styrene copolymer.131 The di-n-butyldithiocarbamate complex is important in the vulcanization and injection moulding of rubber,132 as a stabilizer against photolytic and thermal degradation. 

For both polyethylene and its many copolymeric variants and polypropylene, the main thermal degradative routes follow initial random chain scission. These reactions are only slightly affected by the differences in the physical structure such as crystallinity, but are influenced by the presence of impurities. However, it is largely true that while these may influence the proces-sibility and long-term stability of respective polyolefins, they may have little or no effect on the flammability. 

R. Bernstein, S.M. Thornberg, R.A. Assink, A.N. Irwin, J.M. Hochrein, J.R. Brown, D.K. Derzon, S.B. Klamo, and R.L. Clough, The origins of volatile oxidation products in the thermal degradation of polypropylene, identified by selective isotopic labeling. Polym. Degrad. Stab., 92, 2076-2094 (2007). 

Camino, G. Costa, L. Trossarelli, L. Thermal degradation of polymer-fire retardant mixtures Part III— Degradation products of polypropylene-chlorinated paraffin mixtures, Polymer Degradation and Stability, 1982,4(2), 133-144. 

Costa, L. Camino, G. Luda, M. P. Mechanism of condensed phase action in fire retardant bismuth compound-chloroparaffin-polypropylene mixtures Part II—The thermal degradation behavior, Polymer Degradation and Stability, 1986, 14(2), 165-177. 

Li, B. and Xu, M. 2006. Effect of a novel charring-foaming agent on flame retardancy and thermal degradation of intumescent flame retardant polypropylene. Polym. Deg. Stab. 91 1380-1386. 

Bockhorn, H., Homung, A., Homung, U., and Schwaller, D. Kinetic study on the thermal degradation of polypropylene and polyethylene. Journal of Analytical and Applied Pyrolysis 1999 48 17. 

R. C. Mordi, R. Fields, and J. Dwyer, Gasoline range chemicals from zeolite-catalysed thermal degradation of polypropylene, J. Chem. Soc., Chem. Commun. 374 (1992). 

G. Audiso, A. Silvani, P. L. Beltrame and P. Camiti, Catalytic thermal degradation of polymers degradation of polypropylene, J. Anal. Appl. Pyrolysis 1, 83-90 (1984). 

J. H. Chan and S. T. BaUce, The thermal degradation kinetics of polypropylene Part 111. Thermogravimetric analyses. Polymer Degradation and Stability, 57, 135-149 (1997). 

R. Navarro, L. Torre, J. M. Kenny and A. Jimenez, Thermal degradation of recycled polypropylene toughened with elastomers. Polymer Degradation and Stability, 82, 279-290 (2003). 

While condensation polymers such as PET and polyamides can be broken down into their monomer nnits by thermal depolymerization processes, vinyl (addition) polymers snch as polyethylene and polypropylene are very difficnlt to decompose to monomers. This is becanse of random scission of the carbon-carbon bonds of the polymer chains during thermal degradation, which prodnces a broad prodnct range. 

Polypropylene (PP). Pyrolysis of PP is favored by the branched structure of the polymer the thermal degradation also proceeds in this case via a random-chain scission, but the influence of the temperature on the product spectrum is more pronounced than in the case of PE [43, 31], At temperatures as low as 515°C, Predel and Kaminsky [26] found that PP pyrolysis leads to the production of 6.8% of gases, 36.7% of oils, 21.6% of hght waxes and 34.6% of heavy waxes. At these low temperatures the main compounds in the gas fraction are propene and butenes (about 51 and 17% in [26]), but at higher temperatures these products are converted into others [43]. Ponte et al. [31] found a remarkable... 

The volatile products of thermal degradation of polypropylene (PP) under vacuum in the temperature range 300-360°C comprise a complex mixture of saturated and unsaturated hydrocarbons. Under u.v. radiation at these temperatures (photothermal degradation), the general pattern of products is similar but the rate is Increased, ehtylene appears as a minor product and the relative amount of methane is very much greater, especially as the temperature Is decreased below 300°C. Energies of activation of the thermal, photothermal and photoreactions are 50.1, 33.9 and 11.7 k cal mole" respectively. 

Tsuchlya and Suml (6) have thermally degraded polypropylene in the temperature range ShO-AOO C and have made a detailed analysis of all products with 1-12 carbon atoms. On this basis, a decomposition mechanism has been proposed. Initiation occurs by random scission of the main chain. The radicals thus formed undergo transfer reactions most readily at tertiary carbon atoms but the distribution of products indicates that intramolecular transfer to both third and fourth carbon atoms is particularly important. 

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