Thermal degradation of polyethylene

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

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). 

Z. Gao, 1. Amasaki and M. Nakada, A thermogravimetric stndy on thermal degradation of polyethylene. Journal of Analytical and Applied Pyrolysis, 67, 1-9 (2003). 

Investigations on thermal degradation of polyethylenes, linear and branched, have been carried out by a number of workers " . Both the linear and branched polyethylenes yield, on pyrolysis, less than 1% monomer. 

Hydrogen abstraction by the C from the or Q2 may also lead to the formation of these products. All of the aliphatic hydrocarbons formed according to eqs. (19) through (32) have been reported l to be the volatile products of thermal degradation of polyethylene. 

This reaction is known to occur during thermal degradation of polyethylene but proof of its contribution to the products formed during irradiation of polyethylenes in the solid state will have to await further evidence. 

Thermal degradation of polyethylene in vacuum leads to chain scission with the production of additional saturated and vinyl end groups and both short and long chain branches. 

To address the deactivation behavior in more detail, Uemichi et al. recently examined the change in activity of a silica-alumina catalyst with 13 wt% alumina as a function of time on stream. At a reaction temperature of 723 K, the SA catalyst accumulated over 12 wt% coke on the catalyst after 250 min time on stream. The liquid yield increased slightly from 60 wt"/o to approximately 70 wt% as the coke built up on the catalyst. The limited effect of the coke on the reaction was attributed to the inability of coke deposits to block completely the large pores (f/p,ave = 4.4 nm) of the amorphous catalyst. Although SA showed no activity toward cracking of -octane, the reactivity of polyethylene was substantially enhanced in the presence of the catalyst. This was attributed to the facile reaction on the catalyst of olefins which could be formed from thermal degradation of polyethylene at the temperatures used in this study. 

This was found by Benson [9] to describe more successfully the thermal degradation of polyethylene film. 

Figure 1.4 Temperature dependency plot of the low temperature thermal degradation of polyethylene in vacuum (1) up to 3% degradation, (2) from 3 to 15% degradation. Reproduced with permission from D.A. Anderson and E.S. Vrttman, Journal of Polymer Science, 1961, 54, 253, 1961, Wiley [2]...

Irgashi and Kambe [3] also studied the thermal degradation of polyethylene and used dynamic thermal analysis (DTA) as well as TGA techniques. The experiments were carried out in both air and nitrogen. The PE studied were, two low-density samples. By means of DTA, the crystallinities of the high-pressure samples were found to be 33% and 36% while those for the low-pressure samples were 64% and 77%, and the melting points of the latter samples were higher than those of the former. 

Table 3.6 Cyclic oligomers formed in the thermal degradation of polyethylene oxalate ...

Episulfide, thiophene, thiol-suhstituted thiophene and alkyl- and vinyl-substituted thiophenes were formed as the major products, which indicate that formation of cyclics is favonred during thermal degradation of polyethylene sulfide. The formation of thiophenes and alkyl-substituted thiophenes are due to the elimination of hydrogen sulfide cyclisation followed by a dehydrogenation reaction. The loss of hydrogen from 2,5-dihydrothiophene to form thiophene has been reported in the literature. Some of the product formations are illustrated in Equation 6.6. 

One early study of thermal degradation of polyethylene was carried out on low molecular weight polymers [453]. Later the work was repeated with high-density polyethylene [454]. The volatile products were identified by gas chromatogrq)hy. The biggest portiOTi of the volatiles was found to be propylene. 

Miskolczi N, Bartha L and Deak G (2006) Thermal degradation of polyethylene and polystyrene from the packaging industry over different catalysts into fuel-like feed stocks, Polym Degrad Stab 91 517-526. 

Gallet and co-workers [45] studied the oxidative thermal degradation of polyethylene oxide-ethylene oxide triblock copolymer. It was found by MALDI that degradation starts after 21 days at 80 °C. 

Talc causes thermal degradation of polyethylene [56-68,69], reduces thermal degradation of polyvinyl acetate [65,75, 76], and has no effect on the thermal stability of polymethyl methacrylate [66,68,69]. 

Besides MA, other monomers have been used for grafting. Crotonic acid (trans) grafting on oligomers obtained through thermal degradation of polyethylene is performed under similar conditions as for MA grafting. 

Figure 5.202 Thermal degradation of polyethylene terephthalate of different manufacturing routes at various temperatures DMT dimethyl terephthalate, EG ethylene glycol, TPA terephthalic acid...

Goodings, E. R Thermal Degradation of Polyethylene Terephthalate, Soc. Chem. Ind. Monograph No. 13 (1961)... 

---