Polyethylene thermal degradation

Keywords Catalysis intercalation polymerization kinetics layered clay nanocomposite oxidation polyethylene thermal degradation... 

There is much evidence that weak links are present in the chains of most polymer species. These weak points may be at a terminal position and arise from the specific mechanism of chain termination or may be non-terminal and arise from a momentary aberration in the modus operandi of the polymerisation reaction. Because of these weak points it is found that polyethylene, polytetrafluoroethylene and poly(vinyl chloride), to take just three well-known examples, have a much lower resistance to thermal degradation than low molecular weight analogues. For similar reasons polyacrylonitrile and natural rubber may degrade whilst being dissolved in suitable solvents. 

ACS polymers, developed primarily in Japan, are grafts of acrylonitrile and styrene onto elastomeric chlorinated polyethylene. Although the polymer has good weathering properties it is somewhat susceptible to thermal degradation during processing and to date these polymers have been of limited interest. 

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. 

The manufacture of packaging materials is often conducted under conditions of high temperatures. A burnt polyethylene odor has been experienced in the paper/foil/ polyethylene laminate field. These conditions can easily induce thermal degradation with the formation of volatile compounds in packaging materials (8-131. 

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. 

Costa, L. Camino, G. Thermal degradation of polymer-fire retardant mixtures Part V—Polyethylene-chloroparaffin mixtures, Polymer Degradation and Stability, 1985, 12(2), 105-116. 

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. 

McNeill, I.C. and Mohammed, M.H., A comparison of the thermal degradation behaviour of ethylene-ethyl acrylate copolymer, low density polyethylene and poly(ethyl acrylate), Polym. Deg. Stab., 1995,48, 175-187. 

M 2 Marshall, J. and A. Todd The thermal degradation of polyethylene tere-phthalate. Trans. Faraday Soc. 49, 67 (1953). 

Thermal degradation does not occur until the temperature is so high that primary chemical bonds are separated. It begins typically at temperatures around 150-200 °C and the rate of degradation increases as the temperature increases. Pioneering work in this field was done by Madorsky and Straus (1954-1961), who found that some polymers (poly (methyl methacrylate), poly(oc-methylstyrene) and poly (tetrafluoroethylene)) mainly form back their monomers upon heating, while others (like polyethylene) yield a great many decomposition products. 

Zitting A, Savolainen H. 1979. Neurotoxic effects of the oxidative thermal degradation products from low density polyethylene. Fire Mater 3 80-83. 

Figure 3.11 Bench-scale fixed-bed reactor used for the catalytic reforming of products coming from the thermal degradation of polyethylene [75]. (Reproduced with permission from Elsevier)...

Y. Sakata, M. A. Uddin, K. Koizumia and K. Muratab Thermal degradation of polyethylene mixed with poly(vinyl chloride) and poly(ethyleneterephthalate), Polym. Degrad. Stab., 53, 111-117 (1996). 

S. Karagoz, J. Yanik, S. Ugar, M. Sa-lam and C. Song. Catalytic and thermal degradation of high-density polyethylene in vacuum gas oil over non-acidic and acidic catalysts. Applied Catalysis A General, 242, 51-62 (2003). 

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