Polypropylene thermal destruction

Boric acid esters provide for thermal stabilization of low-pressure polyethylene to a variable degree (Table 7). The difference in efficiency derives from the nature of polyester. Boric acid esters of aliphatic diols and triols are less efficient than the aromatic ones. Among polyesters of aromatic diols and triols, polyesters of boric acid and pyrocatechol exhibit the highest efficiency. Boric acid polyesters provide inhibition of polyethylene thermal destruction following the radical-chain mechanism, are unsuitable for inhibition of polystyrene depolymerization following the molecular pattern and have little effect as inhibitors of polypropylene thermal destruction following the hydrogen-transfer mechanism. 

Upon thermal destruction of polyethylene the chain transfer reactions are predominant, but depolymerization proceeds to a much lesser extent. As a result, the products of destruction represent the polymeric chain fragments of different length, and monomeric ethylene is formed to the extent of 1-3% by mass of polyethylene. C—C bonds in polypropylene are less strong than in polyethylene because of the fact that each second carbon atom in the main chain is the tertiary one. 

Experimental and theoretical studies are presented from a laboratory-scale thermal destruction facility on the destructive behavior of surrogate plastic and nonplastic solid wastes. The nonplastic waste was cellulosic while the plastic waste contained compounds such as polyethylene, polyvinyl chloride, polystyrene, polypropylene, nylon, rubber, and polyurethane or any of their desired mixtures. A series of combustion tests was performed with samples containing varying composition of plastic and nonplastic. Experimental results are presented on combustion parameters (CO, excess air, residence time) and toxic emissions (dioxin, furan, metals). 

THERMAL DESTRUCTION OF POLYPROPYLENE, POLYSTYRENE, POLYETHYLENE, AND POLYVINYL CHLORIDE... 

Isomerization of the radicals formed is also possible. Thus, it has been shown in a number of studies [14, 15] that isomerization of the polymer radicals formed occurs in the thermal destruction of polypropylene and polyethylene oxide. 

During processing polypropylene melts under the action of transverse strain there occur strain-chemical conversions which can result in both decrease and increase in their molecular masses the mechanical effect on the rapidity and level of the occurring processes is considerably more prominent than the mere contribution of thermal and thermal-oxidative breakdown. These data necessitate studying the process of polymer destruction. For this purpose it would be most effective to apply the criterion of assessment of the intensity with which destructive processes happen in polymer melts. 

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