Thermal degradation, various polyethylenes

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

Polyethylene (PE) waxes, i.e lov/ molecular weight poly-ethylenes, are useful materials in various applications PE waxes available on the market are usually polymers of 1000 to 10000 molecular weight obtained by telomerization, i e the polymerization of ethylene mder conditions able to assure only the formation of low-molecular-wei t polymers Some of these waxes are obtained by the thermal degradation of the usual-molecular-weight polyethylenes No information seems to be available about the use of waxes resulting as by-products in high-density polyethylene (HDPE) plants ... 

Brack and co-workers [15] discussed the effect of the degree of fluorination, irradiation and grafting with PS on the crystallinity and thermal degradation of some radiation grafted films and membranes fabricated in PVDF, polyethylene-iafe-tetrafluoroethylene and PTFE-co-hexafluoropropylene.The variation of the chain lengths of the grafted PS chains is a primary factor responsible for the influence of these various parameters on the degradation process. 

Thermal degradation can be avoided by instant heating of the biomolecule of interest using laser desorption. Laser desorption in combination with supersonic expansion has been widely used to bring intact biomolecules into the gas phase [27]. The non-volatile molecules are deposited on a sample bar made of a material that is believed to assist the desorption process. Various matrices, such as activated carbon, fritted glass [28, 29], polyethylene [30] or graphite [31-35], have been used, although matrix-free desorption (bare molecules) has been performed as well... 

When polyesters are processed, thermal degradation is caused by ester bond cleavage here, polyethylene terephthalate is more stable than polybutylene ter-ephthalate. Ester cleavage is influenced to various degrees by different trans-esterification and polycondensation catalysts. This is less significant in the thermai degradation of polybutylene terephthalate compared to polyethylene terephthalate. 

Figure 5.203 Increase in number of carboxyl groups during thermal-oxidative degradation of polyethylene terephthalate (2 mm thick) with various diethylene glycol contents and catalysts at 160 °C in air DMT dimethyl terephthalate, DEG diethylene glycol, TPPat triphenyl phosphate...

Recently the pyrolysis of polymer mixtures has become a focus of interest due to the increasing role of plastics recycling. Many researchers have investigated the thermal decomposition of various polymers in the presence of PVC. Kniimann and Bockhom [25] have studied the decomposition of common polymers and concluded that a separation of plastic mixtures by temperature-controlled pyrolysis in recycling processes is possible. Czegfny et al. [31] observed that the dehydrochlorination of PVC is promoted by the presence of polyamides and polyacrylonitrile however, other vinyl polymers or polyolefins have no effect on the dehydrochlorination. PVC generally affects the decomposition of other polymers due to the catalytic effect of HCI released. Even a few per cent PVC has an effect on the decomposition of polyethylene (PE) [32], HCI appears to promote the initial chain scission of PE. Day et al. [33] reported that PVC can influence the extent of degradation and the pyrolysis product distribution of plastics used in the... 

Gugumus F. Re-examination of the thermal oxidation reactions of polymers 3. Various reactions in polyethylene and polypropylene. Polym Degrad Stab 2002 77(1) 147-55. 

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