Thermal degradation of plasticizer

Thermal degradation of carboxylic ester stabilizers occurs according to the following mechanism  

Pyrolysis of 1 mol of DOP yielded 0.97 mol of 2-ethylhexene-l and 0.78 mol of 2-ethylhexanol. Pyrolysis of 1 mol of DOS yielded two mols of 2-ethylhexene-l. This seems to suggest that alcohol is produced as a side effect of anhydride formation because no alcohol was formed from DOS which does not form anhydride. Triaiyl phosphates have high boihng temperatures and are thermally stable but aryl alkyl phosphates are not. The 2-ethylhexyl diphenyl phosphate undergoes decomposition at 170°C  

barium stearate 1.5, calcium stearate 1.5. PG poly- PVC 100 phr, DOP 60 phr, acid 2 phr. Acids 1 - phos-ester based on thriethylene glycol. [Data from Barsh- phoric, 2 - phthalic, 3 - glutaric, 4 - adipic, 5 - hep- 

The exact kinetics of degradation of different plasticizers are not available. It would be convenient to know in future the compositions of degradation products of plasticizers 

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Thermal degradation of plastics can be classified as depolymerization, random decomposition and mid chain degradation [54, 55], In the process of depolymerization, the conjunction bonds between monomers are broken up, which leads to the forming of monomers. Depolymerization type plastics mainly include a-polymethyl styrene, polymethyl methacrylate and polytetrachloroethylene. In the random decomposition process, scission of carbon chains occurs randomly, and low-molecular hydrocarbons are produced. Random-decomposition-type plastics include PP, PVC and so on. In most cases, both decompositions take place. To be more specific, the degradation of polyolefins can be classified as the following three types ... 

This chapter presents the industrial applications and validations of certain detailed models which refer to the kinetics analysed earlier. The steam cracking process will be analysed first followed by visbreaking and delayed coking processes. Last of all, the method will be applied to the thermal degradation of plastic waste. 

The kinetic aspect common to all the topics discussed in this chapter is the pyrolysis reactions. The same kinetic approach and similar lumping techniques are conveniently applied moving from the simpler system of ethane dehydrogenation to produce ethylene, up to the coke formation in delayed coking processes or to soot formation in combustion environments. The principles of reliable kinetic models are then presented to simulate pyrolysis of hydrocarbon mixtures in gas and condensed phase. The thermal degradation of plastics is a further example of these kinetic schemes. Furthermore, mechanistic models are also available for the formation and progressive evolution of both carbon deposits in pyrolysis units and soot particles in diffusion flames. 

Thermal degradation of plastics and rubber proceeds through a radical mechanism, which may involve three different decomposition pathways ... 

This section reviews the different aspects of the thermal conversion of those polymers which are the main components of the plastic waste stream polyethylene, polypropylene, polystyrene, PVC and PET, although the thermal degradation of other polymers is also commented on. The discussion focuses on mechanistic and kinetic factors, as well as on the type of products derived from the thermal decomposition of each individual polymer. The thermal degradation of plastic mixtures, which reflects more accurately the phenomena taking place in the thermal conversion of plastic wastes, is analysed and discussed in the next section. 

Thermal degradation of plastic and rubber wastes in inert atmospheres has been extensively studied in the past. It is widely accepted that it takes place through radical mechanisms, two main pathways having been proposed depolymerization by end-chain cracking and random chain scission. In the first case, high concentrations of the starting monomer are obtained, but this mechanism is predominant only in the thermal degradation of a few polymers, such as PS and... 

The mechanism of thermal degradation of plastics proceeds through a radical chain reaction pathway with hydrogen transfer steps. In secondary reactions, branched products were only formed as a result of the interaction between two radicals without any rearrangement reactions [48]. As a consequence, thermal cracking of polyolefins leads toward a broad distribution of hydrocarbons up to waxy products. More than 500 °C temperatures are needed to receive more oily products. In contrast, catalytic cracking takes place at lower temperatures and leads to the formation of smaller branched hydrocarbons. This catalytic cracking can potentially lower the costs and increase the yields of valuable products. 

Many studies were carried out for the pyrolysis treatment of residues obtained from particular sectors, such as auto-motive " and electronic industries.Because pyrolysis involves the thermal degradation of plastic materials in the absence of air, it could yield valuable hydrocarbon products, while at the same time facihtating the recovery of the metal components. Pyrolysis would facihtate the recovery of both chemical hydrocarbons and metals embedded or mixed with... 

Gels Small round surface defects that resembles distorted plastic Poor mixing of plastic, thermal degradation of plastic at the barrel walls, un-melted plastic... 

Splay Mark Also called silver streak. Fan-like or streaking on the surface of fabricated plastic parts. Causes include moisture in the plastic material, thermal degradation of plastic material, relatively cold plastic on mold or die surface due to fast an operation (called jetting), injection mold gate restriction, foam molding, etc. 

Table 5.38 Data on thermal degradation of plastics temperatures at which a plastic loses...

Thermal degradation of plastics by any route should, though, be the method of last resort. They are too valuable to be burned. They should, if possible, be retained in their most useful state, in this case as structural materials. If, however, they are too badly contaminated for recovery and recycling in structures, thermal degradation for heat recovery and volume reduction is arguably better than landfill. 

Joints are weakened by incomplete softening, oxidation and thermal degradation of plastic material. Process variables are hot gas temperature, pressure (either from filler rod or fixtures) and speed of welding. 

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